Section 1. What is hidden under the foundation?
When choosing a plot for construction, most people pay attention to the location, transport accessibility, utilities and land value. However, there is a factor that cannot be assessed visually, but it largely determines the reliability and durability of the future building. This factor is the soil base.
It is widely believed that the ground is only a layer of earth on which it is enough to install the foundation. In practice, this idea is far from reality. Under the surface of the site there may be dozens of meters of soils of different composition and properties: dense sands, soft-plastic loams, rocks, просадочныеsubsident loess soils, peatlands, man-made embankments and other geological formations. Each of them reacts differently to the load, changes in humidity, seasonal freezing and environmental impact.
That is why two almost identical buildings built according to the same project can behave completely differently. One retains its geometry and performance characteristics for decades, while the other is covered with cracks, receives uneven precipitation, structural distortions, and requires expensive reinforcement within a few years.
The reason for such differences is most often not in the quality of building materials or installation errors, but much deeper – in the base of the building.
Modern engineering geology considers the soil as a complex natural system with its own mechanical, physical and hydrogeological characteristics. The engineer evaluates not only the strength of the soil, but also its ability to deform, take long-term loads, change properties when saturated with water, freezing, dynamic effects and long-term operation.
Today, the cost of engineering and geological surveys is usually less than 1-3 % of the construction budget. At the same time, it is the results of surveys that allow you to avoid errors, the elimination of which may later require costs comparable to the cost of the building itself.
Therefore, the foundation is always designed not by itself, but as a single “building-foundation-foundation” system, where all elements work together. Ignoring the properties of at least one of them inevitably affects the reliability of the entire structure.
Section 2. Where can I build? Limits of the possible
Modern construction technologies allow you to build structures in almost any natural environment. Humanity has been building for more than ten thousand years, and during this time, engineers have learned to build structures in almost any natural environment. Today, there are technologies for building on permafrost, swamps, sand dunes, sea shelves, mountain slopes, and even on floating bases. However, despite the impressive progress of construction science, most buildings in the world are still built on natural soil foundations.
The reason is simple: it is the soil that is the most reliable, economical and durable natural base, capable of handling huge loads without complex engineering systems. With proper design, the ground becomes an almost eternal foundation for the structure.
The history of construction clearly shows that the success of any large-scale project began with an understanding of the properties of the foundation.
Even the ancient Egyptian pyramid builders chose exceptionally strong limestone plateaus. It is thanks to the well-chosen base that the Great Pyramid of Cheops, weighing about 6 million tons, has remained stable for more than 4,500 years. Modern research shows that uneven precipitation at the base of the pyramid was only a few centimeters-an outstanding result even by modern engineering standards.
Ancient Roman engineers also understood the significance of the foundation perfectly. Before building bridges and aqueducts, they manually removed weak soils before reaching dense layers, and if necessary, arranged massive stone pillows. Many Roman bridges have been in operation for almost two thousand years.
On the other hand, history knows many examples when underestimation of soils led to serious consequences. One of the most famous is the Leaning Tower of Pisa. Its construction began in 1173 on weak water-saturated alluvial soils. Already after the construction of the third tier, uneven precipitation appeared, which caused the famous slope. Engineers of the following centuries repeatedly tried to correct the situation, and large-scale work to stabilize the foundation continues today.
Such examples confirm a simple engineering truth: mistakes in choosing the base can survive the construction itself and accompany the structure throughout its entire operation.
2.1. Traditional foundations: earth, rock and bulk soils
For most capital construction projects, natural soil remains the most rational foundation option.
Depending on the geological structure of the site, buildings may rely on:
- rock massifs.
- coarse-grained soils;
- sandy soils.
- clay soils.
- artificially compacted bases;
- man-made embankments.
Each of these options has its own advantages and limitations.
The most favorable are considered to be rocky bases. Their strength is so great that the pressure from most civil buildings is only a small fraction of their load-bearing capacity.
Dense sands are also an excellent foundation due to their high load-bearing capacity and ability to drain water quickly.
Clay soils require a more careful approach. They are capable of handling heavy loads for a long time, but their behavior significantly depends on humidity, temperature and duration of operation.
Modern engineering methods allow you to successfully build on almost any ground, but the cost of preparing the base can vary several times.
For example, the construction of a production complex on dense sands often requires only the installation of conventional tape or slab foundations. If peat bogs or weak silts lie under the site, the cost of preparing the foundation sometimes reaches 20-40 % of the total construction cost, and in some cases exceeds the cost of erecting the building itself.
2.2. Alternative solutions
Despite the fact that ground foundations are the most common, engineering is constantly looking for ways to build where the use of natural foundations is impossible or economically impractical.
Construction on the water
One of the most interesting areas is construction on floating bases.
The first floating settlements appeared several millennia ago. The Uros, who live on Lake Titicaca in South America, still build islands out of totorareeds that can support dozens of residential buildings.
Today, technology has become much more complex.
Modern floating structures include:
- offshore oil and gas platforms;
- floating liquefied natural gas terminals;
- floating power plants;
- hotels.
- residential areas.
- artificial islands.
One of the most impressive projects is the Palm Jumeirah complex in Dubai, an artificial island covering more than 560 hectares, created by alluvium of about 100 million cubic meters of sand.
An even larger example is the Kansai International Airport (Japan), built entirely on an artificial island. When designing, the engineers understood that the base would gradually sink under its own weight and the weight of the structures. The structure was pre-installed with adjustable supports to compensate for long-term precipitation.
These examples show that even construction “on the water” is ultimately reduced to working with the ground — only already marine.
Underwater construction
Construction under water is considered one of the most complex branches of engineering.
Back in the XIX century, caisson technologies were widely used. The workers were located inside sealed chambers with high air pressure, which made it possible to develop the soil below the water level.
Many famous bridges across the Thames, Mississippi and Neva Rivers were built in this way.
Modern underwater construction includes:
- tunnels.
- metro stations.
- underwater pipelines;
- sea terminals;
- deep-water bridge foundations.
An interesting example is the tunnel under the English Channel with a length of more than 50 kilometers, a significant part of which passes under the sea floor. Its construction required a detailed study of the geological structure over tens of kilometers of the route.
Construction in permafrost conditions
A special category includes buildings in the Far North.
Here, the main task is not to strengthen the soil, but to preserve its natural frozen state.
If permafrost soil begins to thaw under the influence of the building’s heat, its load-bearing capacity may decrease several times.
Therefore, in the northern regions, the following are widely used:
- pile foundations;
- ventilated underground areas.
- thermal stabilizers of soils;
- cooling devices that operate without electricity due to the natural circulation of the refrigerant.
It is thanks to these technologies that the cities of Norilsk, Novy Urengoy, Yakutsk and many other localities are successfully operated today in permafrost conditions.
Construction in the marshes
Swampy areas are traditionally considered extremely unfavorable for construction.
However, engineering practice knows many successful examples.
The historical center of St. Petersburg was built on the marshy grounds of the Neva Delta. Wooden piles were widely used for the construction of foundations, many of which have retained their load-bearing capacity for more than three hundred years. Paradoxically, the constant presence of wood below the water table protects it from rotting due to the lack of oxygen.
Modern technologies allow the use of drillбуроинъекционные-driven, drill-injection and driven piles, which transfer the load to stronger soil layers.
Aerial structures
At first glance, it seems that some structures do not need a foundation at all.
These items include:
- suspension bridges.
- cable-stayed bridges.
- cable cars.
- magnetic levitation systems;
- experimental hovercraft facilities.
However, this is only an illusion.
Each suspended structure transmits huge forces through pylons and anchoring devices to the ground.
For example, the force in the anchor blocks of large cable-stayed bridges reaches tens of thousands of tons. Therefore, the reliability of such structures is still determined by the quality of the ground base.
2.3. Why does the soil remain the “gold standard”?
For thousands of years, engineers have sought to find an alternative to natural foundations, but to date, no technology has been able to completely replace the ground.
The reasons are obvious.
A natural foundation has a number of unique advantages:
- virtually unlimited service life;
- no operating costs.
- high reliability.
- ability to take huge loads;
- resistant to climatic influences;
- easily accessible on almost any construction site.
Even the most modern engineering solutions-pile fields, artificial islands, deep caissons, floating platforms or underwater structures-ultimately interact with the ground. The only difference is in the way the load is transmitted.
In fact, the task of an engineer has remained unchanged for thousands of years: to find or create a reliable foundation that can safely take the loads from the structure.
That is why engineering and geological surveys are the starting point of any project. They allow you to determine which soils are hidden under the future building, what are their properties and what design solutions will ensure reliable and long-term operation of the object.
The history of construction convincingly proves that technologies are changing, materials are improving, architectural forms are becoming bolder, but one rule remains unchanged — the reliability of any structure begins with understanding the ground on which it will stand.
Section 3. Soil diversity: types, classes and their nature
The surface of the Earth seems rather monotonous. To a human, most sites simply look like land covered with grass, sand, or clay. However, for a geological engineer, the ground is a complex natural system that has been formed over thousands, millions, and sometimes billions of years.
Each layer of soil is a kind of “chronicle” of the geological history of the territory. Some rocks were formed during the destruction of ancient mountain ranges, others were brought by glaciers, others were formed at the bottom of disappeared seas and lakes, others appeared as a result of the activity of rivers, wind or man himself.
That is why two sites located just a few dozen meters from each other can significantly differ in their engineering characteristics. Under one building there may be dense sand, and under the neighboring one — weak water-saturated loam or man-made embankments.
Modern engineering geology considers the soil as a multicomponent system consisting of four interrelated elements:
- solid mineral skeleton.
- water;
- air supply.
- organic inclusions.
The ratio of these components determines almost all the properties of the substrate: strength, deformability, water permeability, frost resistance, resistance to dynamic loads and durability.
That is why externally similar soils can behave completely differently during construction.
It is interesting to note that the first attempts to classify soils were made in Ancient China and Ancient Rome. Even then, the builders understood that dense sand is much more reliable than swampy soil, and the rock is practically not deformed under load. However, scientific engineering classification appeared only in the XIX-XX centuries, when the development of industrial construction required a quantitative assessment of soil properties.
Today, geotechnical classification is based not only on the origin of the soil, but also on its composition, structure, particle size, humidity, density, plasticity, strength, and many other characteristics.
3.1. Classification by origin (genesis)
The origin of the soil is one of the most important factors determining its engineering properties. Knowing how a particular layer was formed, a specialist can already assume its behavior under load at the stage of preliminary analysis.
Rocky grounds
Rocky soils represent the most ancient formations of the Earth’s crust.
Some granites and gneisses are more than 2-3 billion years old, meaning that they were formed long before the first multicellular organisms appeared.
This group includes:
- granites;
- basalts;
- diabases.
- quartzites;
- gneisses.
- limestones.
- dolomites;
- sandstones.
It is these rocks that form the mountain ranges on which many cities of the world are located.
For an engineer, rocky ground is an almost ideal foundation due to the following properties:
- extremely high strength;
- almost complete lack of compressibility;
- high frost resistance;
- durability;
- water resistance.
For example, dense granites are able to accept pressures of tens or hundreds of megapascals, whereas the pressure from most multi-storey buildings is only a small fraction of this value.
That is why many of the world’s largest dams are built exclusively on a rock foundation.
However, even rock formations are not always safe.
Under the influence of time, they contain:
- cracks.
- weathering zones.
- karst voids;
- tectonic disturbances.
Therefore, the engineer examines not only the type of rock, but also the condition of the entire massif.
Clastic soils
Clastic soils are a product of natural destruction of rocks.
For millions of years, water, wind, temperature changes and glaciers have crushed massive rocks, turning them first into boulders, then into rubble, gravel and sand.
Depending on the particle size, there are:
- boulders;
- shingle fields.
- crushed stone;
- gravel soils.
Interestingly, many large boulders of central Russia were brought here by ancient glaciers from Scandinavia about 15-20 thousand years ago.
During the last glaciation, giant ice masses more than a kilometer thick moved at a rate of several meters per day, gradually transferring millions of tons of rocks.
After the melting of glaciers, they formed a significant part of the modern engineering and geological conditions of the north-west of Russia.
Coarse-grained soils have a number of advantages:
- high load-bearing capacity;
- good drainage;
- low compressibility.
- resistant to frost heaving.
Therefore, they are considered one of the best natural bases.
Sandy soils
Sand is one of the most common building materials.
Each grain of sand is a small fragment of mineral about 0.05 to 2 mm in size..
Most often, sand consists of quartz — one of the most stable minerals in the Earth’s crust.
By origin, the sands are:
- river routes.
- sea;
- ozernye;
- glacial areas.
- Aeolian (formed by wind).
Interestingly, the famous sand dunes of the Sahara Desert are practically unsuitable for making concrete.
The reason is the shape of the grains of sand.
Under the influence of wind, they acquire an almost perfectly rounded surface, which is why they do not adhere well to cement stone.
Therefore, for the production of construction concrete, river or quarry sand is usually used, the particles of which have a more angular shape.
For an engineer, sandy soil is valuable because:
- passes water quickly.
- practically does not change the volume when freezing;
- compacts well.
- it has a fairly high load-bearing capacity.
However, the properties of sands strongly depend on their density.
Loose sand can be a much less reliable foundation than dense loam.
Clay soils
If sand consists of relatively large mineral grains, then clays are formed from the smallest particles less than 0.005 mm in size..
These particles are so small that they have a huge specific surface area.
That is why clay soils are able to retain a large amount of water.
Hence their main properties arise:
- plasticity;
- swelling.
- shrinkage;
- frost heaving;
- slow consolidation.
An interesting fact is that clay was used by humans as a building material long before the appearance of bricks.
The first adobe houses were built more than 9,000 years ago.
Even today, about a billion people in the world live in buildings where the walls are completely or partially made of clay.
However, as a base, clay soils require special attention.
When the humidity changes, their strength can change significantly.
Organic soils
A special category consists of soils containing a large amount of organic substances.
These include:
- peat;
- sapropel;
- il.
- frozen ground.
These formations occur in swamps, lakes, and river floodplains.
From an engineering point of view, they are extremely unfavorable grounds.
The reason is simple.
The organic mass resembles a sponge.
Under load, it gradually shrinks, displacing water.
This process can last for decades.
That is why construction on peat bogs almost always requires special engineering measures.
Technogenic soils
Technogenic soils are a relatively young category.
They are created by humans during the construction process.
These include:
- road embankments.
- ground dumps.
- backfill operations.
- reclaimed territories;
- construction waste;
- territories of former industrial sites.
In large cities, the thickness of man-made soils sometimes reaches 10-20 meters.
For example, a significant part of the historical center of St. Petersburg, Amsterdam and Venice is actually built on artificially formed soils.
A modern engineer always considers man-made soils as a potentially heterogeneous environment that requires a mandatory survey.
3.2. Engineering and geological classification of soils
If the origin of the soil helps to understand the history of its formation, then the engineering classification answers the main practical question:
How will this soil behave under load?
In Russian practice, the classification of soils is carried out in accordance with GOST 25100 ” Soils. Classification”, which establishes common approaches to the separation of soils by origin, granulometric composition, structure, condition, and physical and mechanical properties. This approach provides a common understanding of geotechnical characteristics between surveyors, designers, experts, and builders.
Coarse-grained soils
These are soils where particles larger than 2 mm predominate:
- boulders.
- pebbles.
- crushed stone.
- gravel.
Their strength is mainly determined by the strength of the stone particles themselves and the degree of their compaction.
With a dense composition, such soils have a high load-bearing capacity and low compressibility.
Sandy soils
Sands are classified according to grain size and compositional density.
Distinguish between:
- gravelly areas.
- large ones.
- medium size;
- small ones.
- dusty ones.
Even a small change in the particle size distribution can significantly affect the load-bearing capacity and water permeability of the soil.
Clay soils
Clay deposits include:
- sandy loam.
- loam;
- clay.
Their key feature is plasticity due to the presence of clay minerals. In engineering practice, plasticity and fluidity indicators are of great importance, which allow us to assess the consistency of the soil and predict its behavior when humidity changes.
Loess soils
Loess soils have a special macroporous structure. In the dry state, they are quite strong, but when soaked, they can dramatically lose their load-bearing capacity and give significant drawdowns. That is why the areas of loess distribution require particularly thorough engineering and geological surveys.
Organic soils
Organic soils are characterized by a high content of plant residues. Their main feature is very high compressibility and long-term deformations under load. In most cases, construction on such grounds without special measures is not allowed.
3.3. Why does the same soil behave differently?
One of the most frequent questions from customers is: “If it is clay (or sand), why are the test results so different in neighboring areas?”
The answer is that the name of the soil reflects only its general type. Real engineering properties are determined by a combination of factors:
- humidity level.
- the density of addition.
- porosity.
- mineral composition.
- degree of weathering. выветрелости;
- depth of occurrence.
- temperature;
- ground water level;
- the formation history.
For example, two sandy soils of the same size may differ in bearing capacity several times only because of the different density of addition. Similarly, two clays with the same granulometric composition may behave quite differently when humidity changes due to differences in mineral composition.
Soil properties are also affected by temperature. In areas of permafrost, the same ground in the frozen state is able to take significant loads, and after thawing — sharply lose strength. Therefore, designing in the northern regions requires taking into account the thermal regime of the base.
It is for this reason that engineering and geological surveys are not limited to determining the type of soil. Specialists determine its physical and mechanical characteristics, which are then used in calculations of foundations and foundations. Only a comprehensive analysis allows you to objectively assess the behavior of the soil under specific construction conditions and choose the most reliable design solution.
Section 4. Danger and reliability: Who is the leader, who is the outsider?
One of the first questions that customers ask after completing geological engineering surveys is very simple:
“Do I have good soil?”
At first glance, it seems that the answer should be unambiguous. However, in engineering practice, everything is much more complicated.
There are no absolutely “good” or absolutely “bad” soils. Any soil has its own advantages and limitations. Moreover, the ground that is ideally suited for the construction of a single-story residential building may be completely unsuitable for the construction of a high-rise building or an industrial complex with heavy equipment.
Engineers evaluate the foundation based on several dozen characteristics at once:
- load-bearing capacity;
- deformability.
- shear strength;
- frost resistance;
- water permeability;
- tendency to swell;
- probability of drawdown.
- dynamic stability.
- aggressiveness of the environment.
- durability.
It is the combination of these factors that determines the suitability of the site for construction.
It is interesting that the first engineering ratings of soils appeared long before modern science.
Even the ancient Roman architect and engineer Marcus Vitruvius Pollio, who lived in the I century BC, in the famous treatise “Ten Books on Architecture” recommended carefully exploring the ground before construction, avoiding wetlands and, if possible, arranging foundations on dense natural rocks.
More than two thousand years have passed, but these recommendations are almost completely consistent with modern engineering practice.
4.1. The most stable and secure bases
In almost all countries of the world, there are soils that engineers consider the most reliable. It is on them that they try to place the most important structures.
Rocky soils — the foundation of civilization
The undisputed leader is rock formations.
They were formed as a result of complex geological processes hundreds of millions or even billions of years ago and are monolithic massifs of high strength.
These include:
- granites;
- basalts;
- quartzites;
- gneisses.
- dense limestones.
- diabases.
- dolomites.
Such bases have a number of unique properties:
- they are practically not compressed.
- they are not subject to frost heaving.
- resistant to water;
- they can withstand huge loads.
- they practically do not change their properties over time.
The bearing capacity of dense granites is so great that the pressure from a modern multi-storey building is often less than one percent of the tensile strength of the rock itself.
That is why most of the largest hydraulic structures in the world are located on a rock base.
For example, during the construction of the Aswan dam in Egypt, engineers carefully selected the site according to its geological structure. Before construction began, hundreds of exploration wells were drilled, which allowed us to confirm the presence of a powerful granite massif.
The largest hydroelectric power stations in Russia — Sayano-Shushenskaya, Krasnoyarsk, and Bratskaya-were designed in the same way. For such facilities, the reliability of the foundation is crucial, since the mass of the dam reaches millions of tons.
Interesting fact
The most ancient “building material”, which is also an ideal base, is considered granite.
Some granite massifs in Karelia are more than 3 billion years old, meaning they are older than most known life forms on Earth.
Coarse-grained soils
The next place is occupied by boulder, pebble and gravel soils.
They were formed due to the destruction of rocks by glaciers and rivers.
Their advantages are obvious:
- high density.
- excellent water permeability;
- no water accumulation;
- low compressibility;
- almost complete absence of frost heaving.
That is why the construction of bridge supports, transport interchanges and industrial buildings on such soils is usually considered very favorable.
In many regions of Siberia and Northwestern Russia, such foundations were formed after the last ice age about 12-15 thousand years ago.
Dense sands
Dense large and medium sands are traditionally considered one of the best foundations for construction.
Despite its apparent simplicity, sandy soils have an interesting feature.
Under the action of the load, individual grains of sand are redistributed in such a way that the compression resistance increases.
That is why well-compacted sand is able to take very significant loads.
In addition:
- water passes freely through the sand.
- pressure in the pores practically does not accumulate;
- there is no long-term consolidation.
- reduces the risk of frost heaving.
It is no coincidence that most artificial foundations under buildings are made of compacted sand.
Why aren’t skyscrapers always built on rocks?
It may seem strange, but many of the tallest buildings in the world are not located on granite massifs at all.
For example, the BurjKhalifa in Dubai is built on relatively weak carbonate soils.
The solution turned out to be different — the load was transferred to deeply located strong layers using almost two hundred bored piles about 50 meters long.
This example perfectly shows the main idea of modern geotechnics:
The engineer doesn’t choose the perfect ground — he creates a system that can work safely in these conditions.
4.2. Risk group: the most unstable and dangerous soils
Some types of soils are able to maintain stability for years, and then almost instantly change their properties after moistening, vibration or increasing the load.
They are the cause of most serious deformations of buildings.
Bulk soils
One of the most unpredictable are artificial mounds of unknown origin.
They may include:
- construction debris;
- broken brick.
- wood;
- metal;
- household waste;
- different types of soils.
The main problem is heterogeneity.
Under load, different sections of the embankment are compacted differently.
Even if the average draught is only a few centimeters, the difference between adjacent foundations can cause serious damage to the building.
That is why engineering and geological surveys are of particular importance before construction on former industrial territories.
Historical example
After the Second World War, many European cities were rebuilt in areas covered with construction debris.
In the first decades of operation of new buildings, many cases of uneven precipitation were recorded precisely because of insufficient compaction of man-made soils.
Today, such territories must undergo a complex of engineering studies.
Dusty sands and quicksand
The most insidious variety of sandy soils are powdery sands.
In a water-saturated state, they can almost completely lose stability.
This is how the phenomenon known as ground liquefaction occurs.
During strong earthquakes, dense sand can literally turn into a fluid mass.
Similar processes were observed:
- in Japan.
- New Zealand;
- Chile;
- USA.
During Ниигатеthe 1964 Niigata earthquake in Japan, several high-rise buildings tilted almost without structural damage.
The reason was precisely the liquefaction of the sandy base.
It is interesting that some buildings remained almost intact after the earthquake stopped, but they stood at a significant angle.
Highly plastic clays
Clays are one of the most difficult soils for an engineer.
The reason lies in their ability to actively interact with water.
When moistened, they:
- they swell up.
- lose their strength.
- they become plastic.
When drying:
- decrease in volume.
- they crack.
- create additional stresses in the base.
Frost heaving is particularly dangerous.
When frozen, the water contained in the ground turns into ice, increasing in volume by about 9 %.
However, the actual increase in soil volume is often much greater due to the migration of moisture to the freezing front.
The resulting forces can reach hundreds of kilopascals.
This is quite enough to lift even massive foundations.
Interesting fact
In many northern regions of Russia in the spring, you can see how small buildings literally “breathe”.
During the winter, the foundation rises by several centimeters, and in the summer it gradually returns to its original position.
That is why modern standards require taking into account frost heaving even at the design stage.
Subsidence loess soils
Loess is considered one of the most unusual natural soils.
When dry, it has high strength.
However, after soaking, its structure begins to collapse.
Imagine a house of cards.
As long as it is dry, it is stable.
If the cards get wet, the structure instantly loses its rigidity.
Loess behaves in much the same way.
Therefore, even a small water pipe failure can cause significant additional precipitation of the building.
It is for this reason that construction in areas where loess soils are distributed is always accompanied by particularly thorough engineering surveys.
Peat and organic soils
Organic soils are considered to be the weakest natural bases.
They contain a large amount of undecomposed plant residues.
Such soils:
- they have very high porosity.
- they contain a large amount of water.
- they have low strength.
- they are compacted for a long time under load.
The consolidation of peatlands can last for decades.
Therefore, construction directly on such foundations almost always requires the use of pile foundations or a complete replacement of weak soil.
Is it possible to build on “bad” soils?
Modern engineering practice gives an unambiguous answer-yes.
Today, the following projects are being successfully built:
- skyscrapers on weak marine sediments;
- bridges over deep estuaries.
- airports on artificial islands.
- industrial enterprises on the territories of former swamps;
- residential complexes in permafrost areas.
However, such projects become possible only thanks to detailed engineering and geological surveys, numerical modeling, state-of-the-art foundation reinforcement technologies, and constant geotechnical monitoring.
That is why the main conclusion of the engineer sounds a little different than many customers expect:
It is not the weak ground itself that is dangerous. The lack of reliable information about its properties and the wrong choice of design solution are dangerous.
Section Results
Over the millennia of construction development, engineers have learned to work with almost any ground conditions. Today, the reliability of a structure is determined not so much by the natural features of the site, but by the quality of engineering and geological surveys, the accuracy of calculations and the literacy of design decisions. That is why modern engineering geology does not divide soils into “good” and “bad” — it determines their real properties, predicts behavior under load, and helps to choose the optimal construction strategy.
This approach allows you to safely implement projects of almost any complexity-from individual residential buildings to high-rise complexes, bridges, hydraulic structures and industrial infrastructure.
Section 5. Territory diagnostics: Why do we need geological engineering surveys?
Imagine that a doctor prescribes a complex operation without even measuring the patient’s blood pressure or performing an examination. Obviously, such an approach would look absurd. Nevertheless, in construction, many still perceive engineering and geological surveys as an optional formality or an unnecessary expense item.
In fact, it is engineering surveys that are the” health diagnostics ” of the construction site. They allow you to determine what is hidden under the surface of the earth, assess the ability of soils to perceive loads, identify potentially dangerous processes and provide designers with objective initial data for calculating foundations.
Construction practice shows that most serious accidents are not related to errors in materials or construction technologies, but rather to insufficient study of engineering and geological conditions. According to various estimates, problems caused by foundation deformations account for a significant proportion of all defects in capital buildings and structures. That is why modern building codes require mandatory implementation of engineering and geological surveys for almost any capital construction object.
However, this was not always the case.
How did the engineering survey come about?
For thousands of years, people have built almost blindly.
The construction site was selected based on external characteristics:
- how hard is the ground under your feet?
- whether the site is swamped.
- does the river wash it away?
- have there been any landslides here?
Such experience was gradually accumulated, but the scientific approach did not yet exist.
Even ancient Egyptian builders chose places for pyramids exclusively on dense limestone plateaus. They could not determine the modulus of deformation or the angle of internal friction of the ground, but they were well aware that a heavy structure should rest on the strongest possible foundation.
Ancient Roman engineers manually excavated the ground before building bridges, checking the depth of dense rocks. Some historians consider these works to be the first engineering and geological studies in the history of mankind.
Real engineering geology as an independent science began to form only in the second half of the XIX century.
The development of railways, the construction of the first skyscrapers, large bridges and dams required an accurate understanding of the behavior of soils under huge loads. It was then that the first drilling rigs, laboratories for testing soils and scientific methods for determining their characteristics appeared.
Today, engineering and geological surveys are a complex complex of field, laboratory and cameral studies, without which it is impossible to imagine modern design.
5.1. Objectives of geological engineering surveys
The main task of engineering surveys is to study the geological structure of the site in as much detail as possible and predict the behavior of the foundation throughout the entire life of the building.
In practice, experts answer several key questions at once.
What is under the surface of the earth?
Even if the plot looks completely flat from above, the following items may be located below it:
- peski;
- loam;
- peat bogs;
- ancient riverbeds;
- karst cavities;
- construction embankments.
- remnants of old foundations.
Sometimes, within a single construction spot, the thickness of individual layers varies by several meters.
Will the ground support the projected structure?
After determining the physical and mechanical characteristics, engineers evaluate:
- load-bearing capacity of the base.
- the amount of expected precipitation.
- probability of developing rolls.
- risk of uneven deformations.
For heavy industrial buildings, these calculations are particularly important.
How will the ground change in 10, 50 or 100 years?
Current research allows us to predict the impact of:
- changes in the ground water level;
- frost heaving;
- flooding;
- base seals;
- consolidation of weak soils;
- technogenic impact.
In fact, engineers try to predict in advance the behavior of the foundation throughout the entire life cycle of the building.
Interesting fact
The longest engineering and geological observations in the world have been conducted for more than a hundred years.
In many European countries and the United States, there are pilot sites where scientists annually measure the precipitation of buildings, changes in the water table and soil properties. These data are used to improve building codes and calculation methods.
5.2. Field research: how do engineers “see” underground?
The most interesting part of engineering surveys is fieldwork.
It is here that specialists receive information that cannot be determined from satellite images or topographic maps.
Modern methods allow you to literally “look” tens of meters below the surface of the earth.
Drilling of engineering and geological wells
Drilling remains the main method.
Depending on the complexity of the object, the depth of wells can be:
- several meters — for individual residential buildings.
- tens of meters — for multi-storey buildings.
- more than one hundred meters — for bridges, hydraulic structures and high-rise complexes.
During drilling, the engineer records:
- soil sequence;
- power of each layer.
- availability of ground water;
- depth of occurrence of rocks;
- common inclusions.
Soil samples are taken from each characteristic depth.
Of particular value are monoliths of undisturbed composition, which allow preserving the natural structure of the soil for laboratory tests.
Interesting fact
During the construction of the world’s tallest building, the BurjKhalifa, engineering and geological wells reached a depth of more than 140 meters.
This was necessary to study weak carbonate rocks and choose the optimal pile length.
Pits
If the drill hole allows you to get information only on a small diameter, then the hole allows you to directly see the soil and foundation.
Pits are widely used:
- when examining existing buildings.
- during reconstruction;
- when strengthening foundations.
- when determining the actual construction of the base.
In addition to soils, specialists get the opportunity to evaluate:
- state of waterproofing;
- foundation material.
- depth of laying;
- presence of defects.
That is why pits are a mandatory element of most surveys of existing buildings.
Static and dynamic sensing
These methods allow you to study the soil almost continuously in depth.
During the test, a metal cone is submerged in the ground.
The immersion resistance is determined by:
- sand density.
- consistency of clays;
- depth of weak layers.
- heterogeneity of the array.
Modern digital installations automatically record data every few centimeters.
In fact, the engineer receives a kind of “cardiogram” of the ground.
Geophysical methods
Sometimes drilling isn’t enough.
For example, when building large industrial facilities, it is necessary to understand the structure of the massif between wells.
To do this, use:
- seismic survey;
- geo-radiolocation.
- electrotomography;
- electrical profiling;
- magnetometry.
These methods allow you to detect:
- karst voids;
- decompression zones.
- old underground structures.
- ancient riverbeds;
- soil heterogeneities.
Historical example
During the construction of the Channel tunnel, engineers performed thousands of geophysical surveys of the sea floor. Thanks to this, it was possible to detect several potentially dangerous areas even before the start of tunneling.
5.3. Laboratory tests: where the soil passes the “exam”
After the fieldwork is completed, the most important part of the engineering survey begins.
Each soil sample is sent to a specialized laboratory.
This is where the parameters are defined, which are then used in foundation calculations.
The number of tests can run into dozens.
Determination of physical properties
At the first stage, the following parameters are defined:
- humidity;
- density.
- particle density.
- porosity coefficient.
- degree of water saturation;
- granulometric composition.
These indicators allow you to pre-evaluate the behavior of the soil.
Shear tests
The next step is to determine the strength characteristics.
During the tests, the following parameters are set:
- internal friction angle.
- specific adhesion.
These parameters are used for calculating stability:
- slopes.
- ditches;
- retaining walls.
- foundations.
Compression testing
To assess the sediment content, the soil is subjected to sequential loading.
Engineers define:
- modulus of deformation.
- compressibility coefficients.
- consolidation properties.
The data obtained allows you to predict the building’s draft even before construction begins.
Interesting fact
Some compression tests last several weeks or even months.
This is necessary to assess the long-term consolidation of weak clay soils.
Chemical research
Chemical tests are equally important.
Experts determine:
- aggressiveness of ground water;
- content of sulfates;
- acidity of the medium.
- the presence of soluble salts.
These indicators are necessary for choosing the brand of concrete, waterproofing and protective coatings.
5.4. What does the customer receive?
The final stage of engineering and geological surveys is the preparation of a technical report.
However, this is not a set of tables and laboratory protocols.
In fact, the report is an engineering model of the construction site.
It includes:
- engineering and geological sections.
- well placement plans;
- description of all soils.
- results of laboratory tests;
- characteristics of ground water;
- forecast of changes in engineering and geological conditions.
- recommendations for choosing foundations;
- conclusions about the site’s suitability for construction.
For the designer, the following design characteristics are most important:
- design resistance of the base;
- modulus of deformation.
- internal friction angle.
- specific adhesion;
- porosity coefficients.
- plasticity indicators.
- ground water level;
- seasonal freezing depth.
- information about dangerous geological processes.
These parameters become the initial data for calculating foundations, foundations, and underground structures.
How much do errors cost?
At first glance, geological engineering surveys may seem like an additional expense item. However, practice shows the opposite.
The cost of surveys for most sites is only a small fraction of the total construction budget, while eliminating the consequences of errors associated with incorrect assessment of soil conditions may require many times more costs. Correction of uneven deposits, strengthening of foundations, installation буроинъекционныхof drill-injection piles or injection fixing of the base often cost an amount comparable to the cost of new construction.
Therefore, experienced customers consider geological engineering surveys not as a formal requirement of regulatory documents, but as a risk management tool. They allow you to make informed design decisions, avoid unexpected expenses and ensure safe operation of the facility throughout its entire service life.
That is why any professional construction begins not with the development of architectural solutions and not with the release of construction equipment on the site, but with a comprehensive study of what is hidden under the future foundation. It is here that the foundation for the reliability of any structure is laid — from a small private house to a unique industrial or infrastructure facility.
Section 6. Soil dynamics: How do they live and change?
There is a common misconception that after construction is completed, the foundation begins to rest on “fixed ground”, which remains unchanged for decades. In fact, this is far from the case. The foundation of a building is a living dynamic system that continuously responds to changes in the environment and the impact of the structure itself.
Geotechnical engineers often say that the ground is never completely at rest. Even if the surface of the earth looks absolutely motionless, complex processes are constantly occurring inside the massif: stresses are redistributed, humidity changes, ground water moves, minerals dissolve, and micro-deformations occur.
That is why modern construction considers the foundation not as a separate structure, but as part of a single “building — foundation — foundation” system, where changing any element inevitably affects the rest.
Interestingly, the ancient Roman architect and engineer Marcus Vitruvius Pollio, who lived in the I century BC, wrote in his treatise “Ten Books on Architecture” about the need to carefully study the soil before building temples and public buildings. Even then, the builders understood that the reliability of the structure is determined not only by the strength of the stone, but also by the properties of the land on which it stands.
6.1. Natural factors
Throughout the entire life of the building, the ground is continuously exposed to natural processes. Some changes occur daily, while others take decades or even centuries.
The most significant impact is exerted by:
- seasonal freezing and subsequent thawing;
- changes in the ground water level;
- prolonged atmospheric precipitation;
- dry periods.
- seismic impacts;
- karst processes;
- erosion and suffusion.
- changing the temperature regime of the surface.
- growth and death of root systems of large trees.
Frost heaving
One of the most well-known natural processes is frost heaving.
When freezing, water increases in volume by about 9 %. However, the main danger is not the expansion of water itself, but the formation of so-called ice lenses. Moisture from the underlying horizons begins to migrate to the freezing front, gradually forming ice layers that can significantly increase in size.
As a result, frost heaving forces can reach tens of tons per square meter, which is enough to lift light buildings, road surfaces and utilities.
That is why in the Nordic countries the depth of foundation laying is determined not only by the load from the building, but also by the estimated depth of seasonal freezing.
Ground water
An equally important role is played by changes in the ground water level.
Spring snowmelt, heavy rains, construction of reservoirs, or changes in the city’s drainage system can significantly change the water saturation of the base.
When humidity increases, many clay soils become less strong, while sandy soils may partially lose their load-bearing capacity due to the erosion of small particles.
Sometimes changes in the water table occur decades after construction, when the original engineering conditions have already changed significantly.
Drought
At first glance, it may seem that only excess water is dangerous. However, long dry periods can also cause serious problems.
Drying out, some varieties of clays decrease in volume, forming shrinkage cracks. If such processes occur unevenly, the foundation begins to experience additional deformations.
This is especially noticeable in regions with hot climates, where large trees actively absorb moisture from the ground. The root system of an adult oak or poplar can extract hundreds of liters of water daily, causing local drying of the base.
Karst processes
One of the most dangerous natural phenomena is karst processes.
If soluble rocks — limestone, gypsum, or rock salt-lie underground, the circulating groundwater gradually erodes them, forming voids.
Sometimes such cavities exist unnoticed for hundreds of years, and then suddenly the roof collapses, accompanied by the formation of a karst funnel.
Similar processes are known in many regions of the world and pose a serious threat to urban development.
Seismic impacts
During earthquakes, the ground ceases to be a fixed support and begins to behave as a complex oscillatory medium.
Especially dangerous are loose water-saturated sands, in which the phenomenon of soil liquefaction can occur. Under the influence of vibrations, the water pressure in the pores increases sharply, the particles lose their mutual adhesion, and the soil temporarily begins to behave like a thick liquid.
This effect was one of the causes of large-scale damage to buildings during earthquakes in Japan, New Zealand and Alaska.
6.2. Technogenic impact
In many cases, human activity changes engineering and geological conditions much faster than natural processes.
The most common reasons include:
- leaks from water and sewer networks;
- changing the scheme of surface water disposal;
- construction of new pits near the building;
- construction of underground structures;
- heavy traffic;
- operation of industrial equipment;
- vibration effects;
- additional development of the adjacent territory;
- artificial change of terrain.
- prolonged lowering of the ground water level.
Even a relatively small leak from a damaged pipeline, lasting several months, can change the humidity of the base so much that additional precipitation begins to develop.
The construction of neighboring facilities has an equally serious impact.
When developing a deep pit, the stress state of the soil mass changes. If the project does not provide for protective measures, neighboring buildings may receive additional precipitation, despite the fact that their foundations themselves remain unchanged.
That is why in modern cities the construction of large facilities is almost always accompanied by constant geotechnical monitoring.
Vibration
Constant vibrations can also gradually change the properties of the substrate.
Sources can include:
- railway tracks.
- metro lines.
- heavy industrial equipment;
- piling installations;
- heavy car traffic.
Under the influence of repeated vibrations, a gradual compaction of sandy soils occurs, or, conversely, a decrease in the strength of some water-saturated bases.
6.3. How does the ground react to the load?
After the load is transferred from the building, deformation processes of various nature begin to develop in the base.
Initially, elastic deformations occur, which appear almost immediately after the load is applied. They are relatively small and largely reversible.
Then a much slower process begins — consolidation.
It is associated with the gradual displacement of water from the soil pores under the influence of building pressure. This process develops especially slowly in clay soils, where the pore sizes are very small.
For this reason, the final precipitation of some structures can last for many years after completion of construction.
Of particular interest is the fact that the first scientific models of consolidation were developed by the American engineer Carl Terzaghi, who is now called the founder of modern soil mechanics. It was his research in the first half of the 20th century that made it possible to explain why many buildings continue to slowly settle even years after they were commissioned.
If the load exceeds the capacity of the base or the soil properties change due to moisture, freezing or other factors, plastic deformations begin to develop.
Such changes do not disappear after the load is removed and can gradually accumulate.
Особую опасность представляет Uneven precipitation is particularly dangerous.
Even if the average draft of the entire building is only a few centimeters, the difference in draft between individual parts can cause significant internal stresses in the load-bearing structures.
That is why engineers pay more attention not to the absolute amount of precipitation, but to its uniformity.
6.4. When does the ground cause an accident?
Most damage to buildings develops gradually.
The first signs may remain almost invisible for months or even several years.
The most characteristic manifestations of base deformation are:
- appearance of inclined and vertical cracks in load-bearing walls;
- opening of seams between structural elements;
- skewed door and window openings.
- failure of engineering communications;
- deformation of floors and floors;
- rolls of individual parts of the building.
- loss of stability of retaining walls and slopes;
- local drawdowns occur around the building.
It is important to understand that a small crack in itself does not always indicate an emergency condition of the building. However, changes in its width, the appearance of new cracks or their systematic development are a serious signal for conducting an engineering survey.
The history of construction knows many cases when the cause of serious accidents was precisely a change in the condition of the soil.
One of the most famous examples is the Leaning Towerof Pisa. Its construction began in 1173, but after the construction of several tiers, uneven sediment of the base, composed of soft water-saturated soils, appeared. It is thanks to this draft that the tower acquired the famous slope, which today exceeds 3° after the stabilization work.
Another well — known example is MexicoCity, much of which is built on the ancient dried-up Lake Texcoco. Thick layers of weak water-saturated clays continue to slowly condense under the load of urban development. In some areas, the total surface precipitation over the past hundred years has exceeded several meters, which has become one of the most difficult geotechnical problems of our time.
Modern technologies allow timely detection of such processes. Geodetic monitoring, satellite interferometry (InSAR), automated sediment sensors, inclinometers, piezometers and remote monitoring systems are used for this purpose.
Practice shows that timely engineering and geological surveys, regular monitoring of the condition of the foundation and inspection of the building when the first signs of deformations appear allow you to identify the problem at an early stage. In most cases, preventive measures are several times cheaper than capital strengthening of foundations, restoration of damaged load-bearing structures, or elimination of the consequences of an accident.
Thus, the ground cannot be considered as a fixed base. This is a complex natural system that continuously interacts with the climate, water, engineering infrastructure and the building itself. Understanding these processes is one of the key tasks of modern geotechnics and the basis for safe construction.
Section 7. Engineering strategy: What to do if the ground is bad?
The detection of weak, просадочныхsubsident or waterlogged soils does not mean that construction on the site is impossible. Modern geotechnics has a wide range of technologies that can significantly increase the load-bearing capacity of the foundation, reduce deformations and ensure safe operation of the building.
The main rule of engineering practice is that any decision should be made after analyzing the results of engineering and geological surveys and calculating the “base-foundation-structure” system. There is no universal method of reinforcement: the technology is selected based on the properties of the soil, the structural scheme of the building, the construction conditions and economic feasibility.
7.1. On-the-fly diagnostics: how do I know if the base is already deformed?
A hundred years ago, the discovery of weak, swampy or subsident soils often meant one thing-construction will have to be moved to another location. Today, the situation has changed dramatically. Modern geotechnics allow you to build buildings where it was previously considered almost impossible: in swamps, artificially washed territories, loose sands, peat bogs, and even in permafrost areas.
The main principle of modern engineering is not to find the “perfect” ground, but to be able to adapt the foundation to the future structure. To do this, engineers use dozens of technologies for soil reinforcement, groundwater management, and load redistribution.
At the same time, any decision begins not with the construction site, but with the analysis of the results of engineering and geological surveys. The designer considers the building, foundation, and ground as a single system. Only after evaluating their joint work can you choose the optimal construction method.
There is no universal amplification method. The decision depends on many factors:
- geological structure of the site.
- physical and mechanical properties of soils;
- depth of weak layers.
- ground water level;
- mass and purpose of the building.
- surrounding buildings.
- construction costs and deadlines.
It is interesting that modern engineering methods allow not only to correct the mistakes of nature, but also to compensate for the consequences of human activity — for example, subsidence of soil after prolonged operation of underground utilities or changes in the water table.
Crack control
The easiest way to observe remains the installation of control beacons.
Despite the development of digital technologies, this method has been used for more than a hundred years and is still considered one of the most reliable.
Previously, lighthouses were made of plaster or alabaster. If the crack continued to open, the plaster plate collapsed.
Modern lighthouses can be made of transparent plastic with a measurement scale or equipped with electronic sensors.
They allow you to define:
- whether the crack is still being opened.
- the rate of deformation development.
- direction of displacement of structures;
- the moment of process stabilization.
At particularly critical facilities, information can be transmitted automatically to the dispatch center, where the software continuously analyzes changes in the condition of the structure.
Geodetic monitoring
If there is a possibility of precipitation, high-precision geodetic leveling is applied.
Today, modern electronic total stations and satellite technologies allow you to record vertical movements of less than one millimeter.
Observations allow you to determine:
- the absolute amount of precipitation.
- the speed of its development.
- uneven deformations.
- rolls of individual structures;
- changing the spatial position of the building.
Satellite radar interferometry (InSAR) technology has become particularly interesting.
It allows you to use satellite images to detect precipitation on the earth’s surface with an accuracy of several millimeters on the territory of entire cities at once.
Today, such systems are used to monitor skyscrapers, dams, bridges, subways, and historical monuments.
7.2. Methods for improving soil properties
When engineering and geological surveys show insufficient load-bearing capacity of the foundation, it is not necessary to change the construction site.
Modern geotechnics offers dozens of ways to change the properties of the soil directly on the construction site.
The choice of technology depends on the depth of the weak layer, its composition, the degree of water saturation, the requirements for the structure and economic efficiency.
Replacing weak soil
This is one of the most understandable and ancient methods.
Even the builders of Ancient Rome removed the soft soil under the roads and replaced it with layers of stone of various sizes. Thanks to this approach, many Roman roads have been preserved for more than two thousand years.
Modern technology has hardly changed its idea.
Weak soil is removed and replaced:
- coarse sand.
- sand and gravel mixture.
- crushed stone.
- compacted mineral soils.
After layer-by-layer compaction, a new artificial base is formed with predictable characteristics.
The method is widely used in the construction of cottages, industrial sites, highways and railway embankments.
Deep compaction
If a weak layer is too strong, removing it becomes economically impractical.
In this case, the soil is compacted directly in its natural occurrence.
Used for:
- heavy rammers;
- vibration compaction;
- vibroflotation;
- dynamic compaction.
- deep vibrators.
During processing, the soil particles are denser, the pore volume decreases, and the mass density increases.
After compaction, the bearing capacity of the base is significantly increased and the probability of uneven precipitation is reduced.
An interesting fact: during dynamic compaction, metal loads weighing up to several tens of tons are repeatedly dropped on the surface from a height of more than 20 meters. The shock waves propagate to the depth and compact the ground for several meters.
Chemical binding
Sometimes it is necessary to strengthen the ground without large-scale earthworks.
Various injection technologies are used for this purpose.
The most common ones are:
- cementation;
- silikatization;
- smolization;
- струйная цементация (Jet Grouting.
Under high pressure, special solutions are pumped into the soil thickness.
Filling the pores, they bind individual particles together and form a strong artificial array.
Особенно впечатляет технология Jet Grouting technology is particularly impressive Grouting.
Through a small well, the cement solution is fed at a pressure of up to 400-600 atmospheres. The jet destroys the surrounding soil and simultaneously mixes it with the cement mortar.
As a result, strong soil-cement columns with a diameter of up to several meters are formed.
This technology is widely used in the construction of subways, tunnels and underground parking lots, as well as in strengthening the foundations of historical buildings without stopping their operation.
Ground reinforcement
Sometimes the soil is reinforced not chemically, but mechanically.
Special synthetic materials are used for this purpose:
- geotextiles.
- geogrids.
- geogrids.
- three-dimensional geocells.
Working together with the ground, they redistribute loads, reduce deformations and increase the stability of the base.
The principle of their operation is very similar to reinforced concrete reinforcement.
Concrete works well in compression, and rebar accepts tensile forces.
Similarly, geosynthetics helps the ground to take loads much more efficiently.
Today, such materials are used in almost all major infrastructure projects-from highways to airports and high-speed railways.
7.3. Features of reconstruction of existing buildings
Working with existing structures is much more difficult than new construction.
An engineer has to solve several tasks at once:
- keep the building functional.
- ensure the safety of people;
- prevent the development of existing deformities.
- perform reinforcement without completely stopping operation.
Especially difficult are the works in the historical centers of cities, where each building is of cultural value.
In such conditions, many operations have to be performed literally manually, controlling the movement of structures with an accuracy of millimeters.
Strengthening foundations
If the existing foundation is no longer able to handle the increased loads, it can be reinforced.
The most common methods are:
- increasing the width of the sole;
- installation of reinforced concrete clips;
- combining individual foundations.
- reinforcement with metal elements;
- installation of additional foundation beams.
By expanding the sole, engineers reduce the pressure on the ground, which reduces the likelihood of further precipitation.
Drilling injection piles
One of the most effective methods of reinforcement is the device буроинъекционныхof drill-injection piles.
Small wells are drilled through or near the existing foundation.
After the reinforcement is installed, they are filled with cement mortar.
When concrete gains strength, a significant part of the load begins to be transferred to deeper and denser layers of soil.
This method allows you to strengthen buildings almost without stopping their operation.
It is thanks to such technologies that today it is possible to preserve many architectural monuments of Europe, built several centuries ago.
Drainage and drainage system
In many cases, the cause of deformations is not weak soil at all, but an incorrect water regime.
Even the most durable soil can lose some of its properties during prolonged waterlogging.
To protect the base, apply:
- ring drainage;
- reservoir drainage;
- storm sewer system;
- waterproofing of underground structures;
- ground water level lowering systems;
- anti-filtration screens.
Properly organized drainage can significantly increase the service life of a building.
No wonder engineers often say:
“Water is the best friend of the soil, as long as it is where it should be.”
If the movement of water becomes uncontrolled, it is most often the main enemy of the foundation.
Engineering of the XXI century: soil as an object of management
Modern geotechnics is gradually moving from the principle of “fix the problem” to the principle of “prevent its occurrence”.
Before starting construction, engineers create digital models of the ground mass, predict its behavior under load, and model the impact of climate factors, neighboring buildings, and underground utilities.
During construction, the foundation can be continuously monitored using automatic sensors, and after the building is put into operation, monitoring continues for many years.
This approach allows you to detect changes long before they become visible visually.
That is why modern skyscrapers, bridges, hydraulic structures and underground complexes can be safely operated for decades, even in the most difficult engineering and geological conditions.
The construction history convincingly shows: there are no ” bad ” soils — there are only soils whose properties need to be properly understood and taken into account. The deeper the engineer studies the foundation of the future structure, the more reliable and durable the building built on it will be.
Section 8. Design solution: How does physics turn into a blueprint?
Geotechnical surveys can be compared to a medical examination of a patient. They allow you to establish a” diagnosis ” of a construction site, determine its features and possible risks. However, the research results themselves do not yet create a reliable structure.
The next stage is design, where hundreds of numerical values obtained in laboratories and field tests are turned into real engineering solutions. This is where ground physics becomes mathematics, and then drawings, specifications, and building structures.
The designer answers not only the question “will the ground hold the building?”, but also dozens of others:
- what should be the foundation;
- how deep it needs to be laid.
- whether precipitation will occur.
- how evenly they will develop.
- whether the base will need to be reinforced.
- how the structure will behave in 10, 50, or 100 years.
Modern design has long ceased to be a selection of ready-made solutions. Each object represents a unique engineering challenge.
Interestingly, back in the 19th century, most foundations were designed mainly based on the experience of previous construction projects. The engineers used rules of thumb: if the neighboring building is standing securely, then a similar foundation will work here. This approach often led to errors.
A real revolution took place in the first half of the 20th century due to the development of soil mechanics. The work of the Austrian engineer Karl Terzaghi, who is called the “father of modern geotechnics”, for the first time allowed calculating the interaction of buildings and foundations with scientific accuracy. His ideas have formed the basis of most modern building codes.
Today, the engineer works not only with tables and calculation formulas. It uses three-dimensional computer models that allow you to literally “see” how the ground will react to construction.
8.1. Estimated ground resistance
One of the most important parameters of engineering calculations is the estimated ground resistance.
Simply put, it is a value that shows how much pressure the base is able to safely perceive without loss of stability and excessive deformations.
If you think of the foundation as the sole of a person, then the calculated resistance can be compared with the ability of the surface to withstand weight. On hard asphalt, a person walks confidently, and on loose sand, his feet begin to sink. The principle of operation of foundations is similar, only instead of the mass of a person, thousands of tons of load act.
The calculated resistance depends on:
- dimensions of the foundation sole;
- depth of its foundation;
- selecting the base type.
- the need to use piles;
- cost-effectiveness of the entire project.
The higher the design resistance of the ground, the smaller the area required for the foundation to transfer the same load.
For example, if a solid rock ground is able to withstand pressure that is many times higher than the capabilities of soft clays, the size of foundations may differ several times.
However, the engineer never fully exploits the ultimate capabilities of the ground.
In all calculations, a margin of reliability is applied, which allows taking into account possible changes in the properties of the substrate, inaccuracies in determining characteristics, and the influence of unfavorable factors.
It is thanks to such coefficients that modern buildings have high operational reliability even after many decades.
8.2. Deformation modulus
If the calculated resistance answers the question ” will the ground withstand the load?”, then the strain modulus allows you to understand“how much it will shrink”.
This characteristic reflects the ability of the soil to resist deformation under pressure.
The higher the modulus of deformation, the stiffer the base and the lower the future precipitation.
This indicator is used for calculating:
- total draft of the building.
- uneven precipitation.
- additional deformations during reconstruction;
- collaboration of several foundations;
- interaction of the building with the surrounding area.
Even if the load-bearing capacity fully meets the project requirements, excessive compressibility of the substrate can lead to cracks, warps, and other damage.
Special attention is paid to uneven precipitation.
If the entire building descends 20 to 30 millimeters evenly, residents will probably not even notice.
A completely different situation occurs when one part of the building settles significantly faster than the other. It is these differences that cause internal stresses and structural damage.
For this reason, engineers say:
It is not so much the amount of precipitation that is dangerous for the building, but its unevenness.
8.3. Internal friction angle and specific coupling
Any soil is able to resist shear.
This ability is defined by two interrelated characteristics:
- internal friction angle.
- specific adhesion.
They determine the stability of the soil mass.
To imagine the effect of these parameters, it is enough to recall the usual sand embankment.
Dry sand can maintain a certain slope angle due to the friction between individual grains of sand. If the angle becomes too large, the particles begin to slide relative to each other, and the slope is destroyed.
Clays behave differently.
In addition to internal friction, they have additional cohesion between particles due to the very small size of minerals and the action of molecular forces.
That is why wet clay is able to maintain an almost vertical cut for some time, while dry sand immediately crumbles.
These characteristics are necessary for calculating:
- retaining walls.
- slopes.
- ditches;
- anti-landslide structures;
- foundations with horizontal loads.
- tunnels.
- coastal fortifications.
Without determining these parameters, it is impossible to assess the probability of landslides, the stability of slopes, or the safety of deep pits.
History knows many examples when underestimating the resistance of soils to shear led to large-scale accidents during the construction of canals, railways and dams.
Today, such risks are significantly reduced thanks to modern laboratory tests and computer modeling.
8.4. Turnover rate
For clay soils, one of the most important characteristics is the flow rate.
It reflects the degree of moisture and allows you to determine the current state of the soil.
Depending on its value, soils are distinguished:
- solid;
- semi-solid ones.
- refractorymaterials.
- soft-plastic ones.
- flowablematerials.
- fluid ones.
As humidity increases, the strength of the clay gradually decreases.
If dry clay is difficult to break even with a hammer blow, then waterlogged clay can slowly flow under its own weight.
That is why clays of the same mineral composition can behave completely differently depending on the water content.
The flow rate affects:
- deformability of the base.
- frost heaving;
- slope stability;
- possibility of developing ditches;
- selection of construction equipment;
- foundation construction technology.
It is especially important to take this parameter into account during spring construction, when seasonal waterlogging significantly changes the properties of soils.
In many cases, engineering solutions that are safe in summer require additional measures during the snowmelt period.
Computer simulates the future
A modern engineer is almost never limited to manual calculations.
Today, specialized software packages based on the finite element method are widely used.
They allow you to create a digital model of the construction site and track how the stresses inside the ground will change after the construction of the building.
The computer can display:
- stress distribution;
- future precipitation.
- load concentration zones.
- probability of loss of stability.
- influence of neighboring buildings.
- impact of ditches;
- changes in the ground water level.
In fact, the engineer gets the opportunity to “look into the future” and evaluate the behavior of the structure even before construction begins.
That is why many potential problems can be eliminated at the project stage, when the design change takes several hours of the designer’s work, rather than months of expensive construction work.
Engineering calculation-the basis for safe construction
None of these parameters are used independently.
The designer always analyzes them together, since the properties of soils are closely interrelated.
Even the toughest soil can be too compressible.
Conversely, a very rigid base may have insufficient stability under horizontal loads.
In addition to the characteristics of the soil are taken into account:
- climatic conditions.
- seasonal freezing depth.
- ground water level;
- weight of the structure.
- structural diagram of the building.
- construction sequence.
- impact of neighboring buildings.
- possible changes in operating conditions.
That is why two adjacent plots, which are almost identical in appearance, often require completely different design solutions.
Modern design is a combination of fundamental physics, structural mechanics, mathematical modeling and practical engineering experience. Each figure in the geotechnical survey report goes a long way: from a soil sample extracted from a depth of several meters, through laboratory tests and complex calculations-to a specific line in the drawing of the future foundation.
We can say that the reliability of any building begins not with the first cubic meter of concrete, but with the correct interpretation of the properties of the land on which it will stand. This is precisely the main task of a design engineer — to turn the laws of physics into a design that will serve people safely for many decades.
Section 9. Conclusion: Security algorithm
Over the millennia of construction history, materials, technologies and tools have changed, but one principle has remained unchanged: the strength of any structure begins with the reliability of the base.
You can build walls from the most durable concrete, usehigh-strength steel, modern composite materials and the latest installation technologies. But if the foundation is based on insufficiently studied or incorrectly evaluated soil, even the most perfect building can eventually face serious problems.
It is no coincidence that engineers say:
“Errors above ground can be seen immediately. Errors under the ground appear later — and are much more expensive.”
This idea is confirmed by the entire history of construction.
The ancient Egyptians carefully chose the sites for the pyramids, preferring the exits of strong limestone rocks. Thanks to this, many of these structures have been preserved for more than four thousand years.
The ancient Romans, creating roads, aqueducts and bridges, paid great attention to the preparation of the foundation. Some sections of the famous Roman roads continue to be used after almost two thousand years, and many stone bridges still remain operational.
In the Middle Ages, builders were often forced to learn from their own mistakes. The leaning of the Leaning Tower of Pisa was caused by uneven precipitation of a weak foundation, and construction had to be repeatedly stopped. Interestingly, it was the long breaks between construction stages that lasted for decades that allowed the ground to partially compact and, possibly, saved the tower from complete collapse.
Modern engineering science allows us to predict such processes in advance. But the main principle remains the same: nature cannot be forced to obey the project — the project must take into account the laws of nature.
That is why the foundation of a building should not be considered as a layer of earth hidden under the foundation, but as a full-fledged structural element of the entire construction system.
Why are there problems?
Practice shows that most serious defects are not associated with” bad ” soils.
The most common cause is:
- insufficient amount of engineering surveys;
- use of outdated or incomplete data.
- an attempt to save money on the site survey;
- incorrect interpretation of test results.
- changes in hydrogeological conditions after construction;
- failure to comply with design decisions in the course of work;
- lack of control during the construction process.
Engineering practice knows many cases when expensive strengthening of foundations, reconstruction of buildings or elimination of accidents cost tens of times more than the initial engineering surveys.
Therefore, today geotechnical research is considered not as a formal requirement of regulatory documents, but as one of the most effective ways to manage construction risks.
In fact, this is an investment that allows you to make technically and economically sound decisions even before the start of construction.
Practical algorithm for the customer
Regardless of the scale of the project — whether it is an individual residential building, an industrial complex, a public building or the reconstruction of an existing facility-the sequence of actions remains almost the same.
1. Engineering and geological surveys
The first stage is to get reliable information about the construction site.
Drilling operations, field tests, laboratory studies and analysis of hydrogeological conditions are performed.
The result is an objective view of the structure of the soil, the depth of solid layers, the water table and the physical characteristics of the base.
This stage determines the quality of all subsequent design decisions.
2. Comprehensive engineering analysis
The obtained data are considered not in isolation, but in interrelation.
Engineers evaluate:
- load-bearing capacity of the base.
- деформативностьsoil deformability;
- probability of drawdowns.
- frost heaving;
- influence of underground water;
- possibility of developing landslide or karst processes;
- features of construction in specific conditions.
If necessary, additional numerical modeling of the behavior of the base — foundation — structure system is performed.
3. Choosing a rational foundation type
Based on engineering calculations, the most effective design solution is determined.
Depending on the conditions, the following may apply:
- tape foundations.
- columnar columns.
- plitnye;
- pile structures.
- combined systems.
A rational project is not the most massive foundation, but one that provides the required reliability at the optimal cost of materials and labor.
Sometimes an additional study of the site allows you to abandon excessively expensive solutions, and in other cases, on the contrary, it timely identifies the need to strengthen the foundation.
4. Improving the properties of the substrate
If the natural properties of the ground are not sufficient for the safe operation of the building, this does not mean that construction is impossible.
Modern geotechnics has a wide range of technologies:
- replacement of weak soils;
- deep compaction;
- jet cementation;
- injection fixing;
- reinforcement with geosynthetic materials;
- installation of drainage systems;
- strengthening existing foundations.
The main task of an engineer is to choose a solution that is both reliable, technologically advanced and economically feasible.
5. Control during construction
Even the most high-quality project requires competent implementation.
During construction, specialists monitor:
- compliance of actual soils with survey results;
- quality of pit development;
- compliance with the foundation construction technology;
- quality of foundation concreting;
- implementation of water disposal measures;
- compliance of works with project documentation.
It is at this stage that many potential problems can be resolved without serious financial consequences.
6. In-service monitoring
The work of engineers does not always end after the delivery of the object.
For responsible structures, monitoring of the condition of the foundation and structures is organized.
It may include:
- geodetic observations;
- sediment control;
- crack monitoring;
- monitoring of the ground water level;
- instrumental control of deformations.
Such systems are now used in the operation of skyscrapers, bridges, tunnels, hydraulic structures, industrial enterprises and cultural heritage sites.
Regular monitoring allows you to detect changes long before serious damage occurs.
Engineering is about teamwork
Modern construction is impossible to imagine without close cooperation of specialists in various fields.
The reliability of an object is formed by working together:
- geological engineers.
- geotechnicalspecialists;
- designers.
- ad designers.
- building survey specialists;
- surveyors;
- builders.
- construction control experts.
Each of them sees the object from its own side, and combining this knowledge allows you to make the most balanced technical decisions.
That is why successful projects are rarely the result of the work of a single specialist — they become the result of a well-coordinated work of a professional team.
When is it especially important to contact specialists?
Practice shows that professional engineering support is most in demand when:
- construction of a new facility is planned.
- a plot of land is being purchased for construction purposes.
- the building is being reconstructed.
- the purpose of the structure changes or loads increase.
- cracks, distortions, or signs of uneven precipitation appear.
- it is necessary to assess the technical condition of the foundation and foundations.
- it is necessary to choose a rational solution for strengthening structures.
The earlier specialists join the project, the more opportunities there are to find the best solution and avoid unnecessary costs at subsequent stages.
A comprehensive approach is the key to reliable results
Working with foundations does not require separate services, but a consistent engineering process-from studying the site to supporting the object in operation.
That is why the most effective approach is an integrated approach, in which the results of engineering surveys, surveys, calculations and design are considered as parts of a single system.
EUCLID team performs a full cycle of engineering work: engineering and geological surveys, survey of buildings and structures, geotechnical calculations, design of bases and foundations, development of solutions for strengthening structures, as well as engineering support for projects of various complexity.
The use of modern equipment, specialized software, current regulatory documents and practical experience allows you to make decisions based not on assumptions, but on objective data and engineering calculations.
For the customer, this means not only receiving project documentation, but also the opportunity to discuss technical solutions with a single team of specialists who understand the entire life cycle of the object — from the first survey to the operation of the building.
Instead of an afterword
Each construction starts long before the construction equipment arrives on the site.
It begins with an understanding of what exactly he has to standon.
No concrete, rebar, or complex engineering solutions can be seen underground. But it is here that the fundamental basis for the reliability of any building is hidden.
A well-studied ground doesn’t make a project more visible — it makes it more predictable. And predictability in engineering means security, durability, and smart use of resources.
We can say that engineering and geological surveys are the first dialogue between a person and the territory of future construction. The more attentive this “conversation” is, the fewer surprises will arise in the future.
That is why professional engineering surveys and competent design should not be considered as an additional expense item, but as one of the most important stages in creating any object — whether it is a small private house, an industrial enterprise, a bridge, tunnel or high-rise building.
Ultimately, the foundation of a building is not just concrete and soil. This is the knowledge, experience and responsibility of people who make decisions even before the first stone is laid. And the more accurate these solutions are, the longer the structure will serve its purpose, preserving safety for all who will use it years or even decades later.
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