Topic: Hydrogeology as a Science. Water in nature.

1. Hydrogeology. Stages of development of hydrogeology.

Let us recall the definition of the science of hydrogeology. Hydrogeology - the science of groundwater, which studies their origin, conditions of occurrence and distribution, laws of motion, interaction with water-bearing rocks, formation of chemical composition, etc.

Let us consider briefly the history of the development of this science.

1.1 Stages of development of hydrogeology

In the history of the study of groundwater in the USSR, there are 2 periods:

1) pre-revolutionary;

2) post-revolutionary.

In the pre-revolutionary period, 3 stages of the study of groundwater can be distinguished:

1.accumulation of experience in the use of groundwater (X - XVII centuries)

2.the first scientific generalized information about groundwater (XVII - mid-XIX century)

3.the formation of hydrogeology as a science (second half of the 19th century and the beginning of the 20th century)

In 1914, the first department of hydrogeology in Russia was organized at the engineering faculty of the Moscow Agricultural Institute (now the Moscow Hydrometeorological Institute).

The post-revolutionary period can be divided into 2 stages:

1.pre-war (1917-1941)

2.post-war

In 1920, a hydrogeological specialty was established at the Moscow Mining Academy to train hydrogeological engineers: a little later it was introduced at other institutes and universities. The most prominent scientists, hydrogeologists F.P. Savarensky, N.F. Pogrebov, A.N. Semikhatov, B.C. Ilyin and others.

By the beginning of the first five-year plan (1928), as well as during the subsequent five-year plans, hydrogeological studies were carried out in the Donbass, in the Eastern Transcaucasia, in Central Asia, in the north of Ukraine, in Kazakhstan, Turkmenistan and in many other regions of the country.

For the further development of hydrogeology, the First All-Union Hydrogeological Congress, held in 1931, was of great importance. in Leningrad.

In the 30s, for the first time, consolidated maps (hydrogeological, mineral waters, hydrogeological zoning) were compiled, which were of great importance for planning further hydrogeological studies. At the same time, edited by N.I. Tolstikhin, the volumes "Hydrogeology of the USSR" began to be published. To Veliko Patriotic War 12 issues of this multivolume work were published.

The post-war stage is characterized by the accumulation of materials on deep-lying waters.

For a deeper scientific analysis and wide regional generalization of materials on groundwater, it was decided to prepare 45 volumes of "Hydrogeology of the USSR" for publication, and, in addition, to compile 5 consolidated volumes.

2. Water in nature. The water cycle in nature.

On the globe, water is found in the atmosphere, on the earth's surface and in the earth's crust. In the atmosphere water is in its lower layer - the troposphere - in various states:

1. vaporous;

2. drop-liquid;

3. solid.

Superficial water is in liquid and solid state. In the earth's crust water is found in vapor, liquid, solid, and also in the form of hygroscopic and film water. Taken together, surface and ground waters make up the water envelope - hydrosphere.

The underground hydrosphere is bounded from above by the surface of the earth; its lower boundary has not been reliably studied.

Distinguish between large, internal and small cycles. With a large cycle, moisture evaporating from the surface of the oceans is carried in the form of water vapor by air currents to land, falls here on the surface as precipitation, and then returns to the seas and oceans by surface and underground runoff.

With a small cycle, moisture evaporating from the surfaces of the oceans and seas. Here it falls in the form of precipitation.

The process of circulation in nature in quantitative terms is characterized by water balance, the equation of which the share of a closed river basin has the form for a long-term period:

X \u003d y + Z-W (according to Velikanov),

where x - precipitation per catchment area, mm

y - river flow, mm

Z - evaporation minus condensation, mm

W - mean long-term recharge of deep aquifers due to precipitation or groundwater inflow to the surface within the river basin.

The internal circulation is provided by that part of the water that evaporates within the continents - from the water surface of rivers and lakes, from land and vegetation, and falls there in the form of precipitation.

3. Types of water in minerals and rocks.

One of the earliest classifications of water types in rutted rocks was proposed in 1936 by A.F. Lebedev. In subsequent years, a number of other classifications have been proposed. Based on Lebedev's classification, most scientists distinguish the following types of water:

1. Vaporous water

It is in the form of water vapor in the air present in the pores and cracks of rocks and in the soil, moves along with air currents. Under certain conditions, by condensation, it can pass into a liquid form.

Vaporous water is the only species capable of moving in pores with little moisture.

2. Bound water

It is present mainly in clay rocks, is held on the surface of particles by forces that significantly exceed gravity.

Distinguish between firmly and loosely bound water.

and) tightly bound water (hydroscapic) it is in the form of molecules in an absorbed state, is held on the surface of particles by molecular and electrostatic forces. It has a high density, viscosity and elasticity, characteristic of finely dispersed rocks, is not able to dissolve salts, and is not available for plants.

b) loosely bound (film) is located above strongly bound water, is held by molecular forces, is more mobile, the density is close to that of free water, is able to move from particles to particles under the influence of sorption forces, the ability to dissolve salts is reduced.

3. Capillary water

It is located in the capillary pores of rocks, where it is held and moved under the influence of capillary (meniscus) forces acting on the boundary between water and air in the pores. It is divided into 3 types:

and) capillary water proper is located in the pores in the form of moisture in the capillary floodplain above the GWL. The thickness of the capillary floodplain depends on the grain size distribution. It varies from zero in pebbles to 4-5 m in clayey rocks. Capillary water itself is available to plants.

b) suspended capillary water is located mainly in the upper horizon of the rock or in the soil and is not in direct connection with the GWL. With an increase in the moisture content of the rock above the lowest moisture capacity, water flows into the underlying layers. This water is available to plants.

in) pore corners water held by capillary forces in the pores of sandy and clayey rocks in the places of contact of their particles. This water is not used by plants; with an increase in humidity, it can pass into suspended water or into the capillary itself.

4. Gravity water

Submits to gravity. The movement of water occurs under the influence of this force and transfers the hydrostatic head. It is divided into 2 types:

and) oozing - free gravitational water in a state of downward movement in the form of separate streams in the aeration zone. The movement of water occurs under the influence of gravity.

b) aquifer moisture, which saturates the aquifers up to PV. Moisture is retained due to the waterproofness of the waterproof layer (further discussion refers to the topic "Gravity water").

5. Crystallization water

It is part of the crystal lattice of a mineral, such as gypsum (CaS0 4 2H 2 O), retains its molecular form.

6. Solid water in the form of ice

In addition to the above six types, there are chemically bound water, which participates in the structure of the crystal lattice of minerals in the form of ions H +, OH ", ie does not retain its molecular form.

4. The concept of duty cycle and porosity.

One of the most important hydrogeological indicators of rocks is their porosity. In sandy rocks, steam porosity, and in strong - fissure.

Groundwater fills pores and cracks in rocks. The volume of all voids in the rock is called duty cycle. Naturally, the greater the duty cycle, the more water the rock can hold.

The dimensions of the voids are of great importance for the movement of groundwater in rocks. In small pores and cracks, the area of \u200b\u200bcontact of water with the walls of the voids is greater. These walls provide significant resistance to the movement of water, so its movement in fine sands, even with significant pressures, is difficult.

Distinguish the duty cycle of rocks: capillary (porosity) and non-capillary.

To capillary duty cycle include small voids, where water moves mainly under the influence of surface tension forces and electrical forces.

To non-capillary duty cycle include large voids devoid of capillary properties, in which water moves only under the influence of gravity and the difference in pressure.

Small voids in rocks are called porosity.

There are 3 types of porosity:

2.open

3.dynamic

Total porosity quantitatively determined by the ratio of the volume of all small voids (including those not communicating with each other) to the entire volume of the sample. Expressed in fractions of a unit or as a percentage.

Or

where V n is the pore volume in a rock sample

V - sample volume

Total porosity is characterized by the coefficient of porosity e.

Porosity coefficient e expressed by the ratio of the volume of all pores in the rock to the volume of the solid part of the rock (skeleton) V c, expressed in fractions of a unit.

This coefficient is widely used especially in research

clayey soils. This is due to the fact that clayey soils swell when moistened. Therefore, it is preferable to express the porosity of clays in terms of e.

The porosity coefficient can be expressed as follows

dividing the numerator and denominator by V c we get

The total porosity is always less than 1 (100%), and the value e can be equal to 1 or be greater than 1. In plastic clays e ranges from 0.4 to 16.

The porosity depends on the nature of the addition of particles (grains).

Non-capillary porosity includes large pores in coarse-grained rocks, cracks, channels, caves and other large voids. Cracks and pores can communicate with each other or be torn.

Open porosity characterized by the ratio of the volume of communicating open pores to the entire volume of the sample.

For granular unconsolidated rocks, the open porosity is close to the total one.

Dynamic porosity is expressed as the ratio to the entire sample volume of only that part of the pore volume through which liquid (water) can move.

Studies have shown that water does not move through the entire volume of open pores. Part of the open pores (especially at the junction of particles) is often occupied by a thin film of water, which is firmly held by capillary and molecular forces and does not participate in movement.

Dynamic porosity, in contrast to open porosity, does not take into account the pore volume occupied by capillary-bound water. Typically, the largest dynamic porosity is less than open.

Thus, the fundamental difference between the described types of porosity is (quantitatively) in the fact that in cemented rocks the total porosity is more open, and open - more dynamic.

Test questions:

1. What does the science of hydrogeology study?

2. How is the water cycle carried out in nature?

3. Name the types of water found in minerals and rocks.

4. What is called porosity? What are its types? How is porosity determined?

5. What do I mean by duty cycle? Name and describe its types.

Modern concepts of geoecological science define the hydrosphere as one of the main life-supporting geospheres; the hydrosphere is an integral part of the natural environment, inextricably linked with the lithosphere, atmosphere and biosphere, and indirectly - with human activity, his life.

Waters located in the upper part of the earth's crust are called underground. The science of groundwater, its origin, bedding conditions, laws of motion, physical and chemical properties, connections with atmospheric and surface waters are called hydrogeology.

For builders, groundwater in some cases serves as a source of water supply, while in others it acts as a factor hindering construction. It is especially difficult to carry out excavation and mining operations in conditions of an influx of groundwater that floods pits, quarries, trenches, underground mine workings: mines, adits, tunnels, galleries, etc. Groundwater worsens the mechanical properties of loose and clayey rocks, can act as an aggressive environment in relation to building materials, cause the dissolution of many rocks (gypsum, limestone, etc.) with the formation of voids, etc.

Builders must study underground waters and use them for production purposes, be able to resist their negative impact during the construction and operation of buildings and structures.

Water in the conditions of the earth's surface is in constant motion. Evaporation from the surface of the seas, oceans and land, it enters the atmosphere in a vaporous state. Under appropriate conditions, vapors condense and in the form of atmospheric precipitation

kov (rain, snow) return to the surface of the Earth - to sea basins and to land. There is a water cycle in nature.

The water cycle in nature.Distinguish between large, small and internal (local) water cycle. When great circulation The moisture evaporating from the surface of the World Ocean is transferred to land, where it falls in the form of precipitation, which again returns to the ocean in the form of surface and underground runoff. Small cycle characterized by the evaporation of moisture from the ocean surface and its fallout in the form of precipitation on the same water surface. During internal circulation moisture evaporated from the surface of the land falls back onto the land in the form atmospheric precipitation.

Intensity of groundwater exchange. In the process of the water cycle in nature, there is a constant renewal of natural waters, including underground ones. The process of replacing initially accumulated water by incoming water is again called water exchange. It is estimated that more than 500 thousand km 3 of water annually participate in the water cycle on Earth. River waters are most actively renewed.

The intensity of groundwater exchange is different and depends on the depth of their occurrence. The following vertical zones are distinguished in the upper part of the earth's crust:

• intensive water exchange (mostly fresh water); located in the uppermost part of the earth's crust to a depth of 300-400 m, less often more; groundwater in this zone is drained by rivers; on a geological time scale, these are young waters; water exchange takes tens and thousands of years;
• slow water exchange (brackish and salty waters); occupies an intermediate position and is located up to a depth of 600-2000 m; the renewal of waters in the process of circulation takes place over hundreds of thousands of years;
• very slow water exchange (water like brines); confined to deep zones of the earth's crust and completely isolated from surface waters and atmospheric precipitation; water exchange - over hundreds of millions of years.

Groundwater circulating in the zone of intensive water exchange is of the greatest importance for water supply. Constantly replenished with atmospheric precipitation and surface water, they usually have significant reserves and high quality. The waters of the two lower zones, located to a depth of 10-15 km, are practically not renewed during the cycle, their reserves are not replenished.

Quantification of the water cycle. The water cycle in nature is quantitatively described by the water balance equation

where 0a.o is the number of ATMOSPHERIC SEDGE;0 PO dz - underground runoff; ? 2 P0V - surface runoff; 0 And - evaporation.

Main consumables (0 PO dz, (? Pov AND(? and) and income (@ ao) items of the water balance depend on natural conditions, mainly on the climate, relief and geological structure of the area.

Study of the water balance of individual regions or the globe in general, it is necessary for the purposeful transformation of the water cycle, in particular for increasing the reserves of fresh groundwater used for water supply.

The origin of groundwater.Groundwater in the upper crust is formed by infiltration. Atmospheric precipitation, river and other waters under the influence of gravity seep through large pores and cracks in rocks. At depths, they encounter waterproof rock layers. Water retains and fills the voids in the rocks. This is how the groundwater horizons are created. The amount of water infiltrating from the surface is determined by the action of many factors: the nature of the relief, the composition and filtering capacity of rocks, climate, vegetation cover, human activities, etc.

To determine the value of infiltration nutrition (? Un, it is necessary to know the intensity of infiltration of atmospheric precipitation @ inf and evaporation 0 And:

bi.p Q ^^ nf 2-

In some cases, the infiltration theory is unable to explain the appearance of groundwater. For example, in dry deserts, where the amount of precipitation is insignificant, aquifers arise near the surface. It has been proven that the formation of groundwater is also involved condensation water vapor that penetrates the pores of rocks from the atmosphere. This path of formation of groundwater is well traced in loose rocks, which serve as the basis for structures. Due to the fact that these rocks have a temperature lower than the surrounding rocks, vapor condensation occurs in them under the foundations of buildings.

The waters of the earth's crust are constantly replenished over a long geological time juvenile watersthat arise in the depths of the earth due to oxygen and hydrogen released by magma. Juvenile waters in the form of vapors and hot springs have a direct outlet to the earth's surface during volcanic activity.

In zones of slow and very slow water exchange, mineralized (salty) waters of the so-called sedimentary origin. These waters arose after the formation (sedimentation) of ancient marine sediments at the beginning of the geological history of the earth's crust.

Groundwater is found in the upper part of the earth's crust (lithosphere). The science of groundwater is called hydrogeology. She studies the distribution, origin, physical and chemical properties, the laws of movement of groundwater. Precipitation falling on land is divided into three parts: 1) evaporation, 2) runoff, and 3) seepage (infiltration) into the soil.

The formation of groundwater is possible in four ways:

1) due to the infiltration of sediments into the lithosphere, the bulk of groundwater is formed (including the mineral waters of the KMV),

2) due to condensation of vapors in the pores of the soil (underground dew at night in deserts),

3) sedimentation water simultaneously with the deposition of marine sediments (for example, the remainder of seawater in the clay strata of the Sarmat and Maikop of Stavropol),

4) the so-called juvenile waters released by magma.

Classification of groundwater according to the conditions of occurrence. In the geological section, according to the conditions of occurrence, the following groundwater can be distinguished:

1) soil water located in the soil layer,

2) upper water is formed above the local aquiclude in the spring or due to technogenic water leakage,

3) groundwater at the first aquiclude from the surface, unpressurized, can be polluted,

4) interstratal (non-pressure and pressure-artesian) waters.

Types of groundwater. Depending on the state of the soil, the following types of water are distinguished:

1) Vaporous water - water vapor in the pores of the soil with a relative humidity of W \u003d 100%, the movement occurs in the direction of the temperature drop. In this way, moisture can accumulate underground in summer.

2) Strongly bound (adsorbed, hygroscopic) water. This is a layer of up to 10-15 H2O molecules with a thickness of 0.1 micron, covering soil (clay) particles, does not dissolve salts, is not electrically conductive, does not freeze at 0оС, and at negative temperatures of about minus 100оС, has a high viscosity, is removed at Т≥105о. The content of tightly bound water depends mainly on the amount of clay particles: in sands - 1-2%, in loams - 5-10%, in clays - 10-25%, in highly dispersed montmorillonite clays - up to 30%.

3) Loosely bound (film) water is held by electric forces up to P \u003d 70,000g, has a density \u003d 1.0, freezing point minus 1-3-5оС, weakly dissolves salts, flows from thick to thin films.

4) Free water - capillary and gravitational. Capillary water is held in the pores by capillary forces, moves due to the difference in capillary pressures, dissolves salts, freezes at temperatures below 0 ° C. The height of the capillary rise in clays reaches 3-4 m, in sands - several dm.

Gravitational water moves under the action of gravity (pressure difference).

5) Water in a solid state (ice), free water first freezes, and then all other types of water sequentially.

6) Crystallization water is involved in the construction of the crystal lattice of minerals (gypsum CaSO4 ∙ 2H2O). Chemically bound water is a part of minerals (limonite Fe2O3 nH2O, opal SiO2 ∙ H2O, hydroxide CaO H2O). These forms of moisture are removed at T\u003e 100 ° C.

Chemical composition. Dissolved salts and gases are present in groundwater. Basic salts are chlorides and sulfates Na, K, Ca, Mg. Gases are dissolved in water - О2, Н2, СО2. It is these ions that determine many of the properties of water: hardness, alkalinity, salinity, aggressiveness. By the size of the dry residue, waters are distinguished: 1) fresh -<1 г/л, 2) соленые – 1-30 г/л, 3) рассолы - >30g / l.

Hydrogeology (from ancient Greek. ὕδωρ "water" + geology) - a science that studies the origin, conditions of occurrence, composition and patterns of movements of groundwater. The interaction of groundwater with rocks, surface waters and the atmosphere is also being studied.

The field of this science includes such issues as dynamics of groundwater, hydrogeochemistry, prospecting and exploration of groundwater, as well as meliorative and regional hydrogeology. Hydrogeology is closely related to hydrology and geology, including engineering geology, meteorology, geochemistry, geophysics, and other earth sciences. She relies on the data of mathematics, physics, chemistry and widely uses their research methods.

Hydrogeological data are used, in particular, to address issues of water supply, land reclamation and exploitation of deposits.

The groundwater.

All waters of the earth's crust that are below the surface of the Earth in rocks in gaseous, liquid and solid states are considered underground. Groundwater is part of the hydrosphere - the water shell of the globe. The reserves of fresh water in the bowels of the Earth are up to 1/3 of the waters of the World Ocean. In Russia, about 3367 groundwater deposits are known, of which less than 50% are exploited. Sometimes underground waters cause landslides, waterlogging of territories, sedimentation of the soil, they complicate the conduct of mining operations in mines, to reduce the inflow of groundwater, they drain deposits and construct drainage systems.

History of hydrogeology

The accumulation of knowledge about groundwater, which began in ancient times, accelerated with the emergence of cities and irrigated agriculture. In particular, the construction of dug wells, built in 2-3 thousand BC, made its contribution. e. in Egypt, Central Asia, China and India and reached depths of several tens of meters. Around the same period, treatment with mineral waters appeared.

The first ideas about the properties and origin of natural waters, the conditions of their accumulation and the water cycle on Earth were described in the works of the ancient Greek scientists Thales and Aristotle, as well as the ancient Roman Titus Lucretius Kara and Vitruvius. The study of groundwater was facilitated by the expansion of water supply work in Egypt, Israel, Greece and the Roman Empire. The concept of non-pressure, pressure and self-flowing waters arose. The latter received in the 12th century AD. e. the name of the artesian - from the name of the province of Artois ( ancient name - Artesia) in France.

In Russia, the first scientific ideas about groundwater as natural solutions, their formation by infiltration of atmospheric precipitation and the geological activity of groundwater were expressed by MV Lomonosov in his essay "On the layers of the earth" (1763). Until the middle of the 19th century, the study of groundwater developed as an integral part of geology, after which it became a separate discipline.

Distribution of groundwater in the earth's crust

Groundwater in the earth's crust is distributed over two floors. The lower floor, composed of dense igneous and metamorphic rocks, contains a limited amount of water. Most of the water is in the upper layer of sedimentary rocks. Three zones are distinguished in it - the upper zone of free water exchange, the middle zone of water exchange and the lower zone of delayed water exchange.

The waters of the upper zone are usually fresh and serve for drinking, household and industrial water supply. In the middle zone there are mineral waters of various compositions. In the lower zone, there are highly mineralized brines. Bromine, iodine and other substances are extracted from them.

The surface of the groundwater table is called the "groundwater table". The distance from the groundwater table to the water-resistant layer is called the "thickness of the water-resistant layer".

Formation of groundwater

Groundwater is generated in a variety of ways. One of the main ways of groundwater formation is percolation, or infiltration, of precipitation and surface water. Escaping water reaches the waterproof layer and accumulates on it, saturating the rocks of a porous and porous-fractured nature. This is how aquifers or underground water horizons arise. In addition, groundwater is formed by condensation of water vapor. Juvenile groundwater is also distinguished.

The two main ways of groundwater formation - by infiltration and by condensation of atmospheric water vapor in rocks - are the main ways of groundwater accumulation. Infiltration and condensation waters are called vandose waters (Latin vadare - to walk, to move). These waters are formed from atmospheric moisture and participate in the general water cycle in nature.

Infiltration

Groundwater is formed from the waters of atmospheric precipitation that fall on the earth's surface and seep into the ground at a certain depth, as well as from the waters of swamps, rivers, lakes and reservoirs, which also seep into the ground. The amount of moisture that gets into the soil in this way is 15-20% of the total amount of precipitation.

The penetration of water into soils depends on the physical properties of these soils. With regard to water permeability, soils are divided into three main groups - permeable, semi-permeable and waterproof or waterproof. Permeable rocks include coarse-grained rocks, pebbles, gravel, sands and fractured rocks. Impervious rocks are dense igneous and metamorphic rocks such as granite and marble, as well as clays. Semi-permeable rocks include clayey sands, loess, loose sandstones, and loose marls.

The amount of water seeped into the soil depends not only on its physical properties, but also on the amount of precipitation, the slope of the terrain and the vegetation cover. At the same time, prolonged drizzling rain creates better conditions for seepage than a heavy downpour.

Steep terrain slopes increase surface runoff and reduce the seepage of precipitation into the ground, while gentle slopes, on the contrary, increase seepage. The vegetation cover increases the evaporation of precipitated moisture, but at the same time delays surface runoff, which contributes to moisture seepage into the ground.

For many parts of the world, infiltration is the main method for the formation of groundwater.

Groundwater can also be generated by artificial hydraulic structures, such as irrigation canals.

Condensation of water vapor

The second way of groundwater formation is the condensation of water vapor in rocks.

Juvenile waters

Juvenile waters are another form of groundwater formation. Such waters are released during the differentiation of the magma chamber and are "primary". Under natural conditions, pure juvenile water does not exist: groundwater, which has arisen in different ways, mixes with each other.

Groundwater classification

Three types of groundwater are distinguished: upper water, groundwater and pressure (artesian). Depending on the degree of mineralization, fresh underground waters, salty, brackish and brines are emitted, according to temperature they are divided into supercooled, cold and thermal, and depending on the quality of underground water, it is divided into technical and drinking.

Verhovodka

Verkhovodka - underground waters occurring near the earth's surface and characterized by inconsistent distribution and flow rate. Verkhovodka is confined to the first water-resistant layer from the earth's surface and occupies limited territories. The upper water exists during the period of sufficient moisture, and disappears during dry times. In cases where the water-resistant layer lies close to the surface or comes out to the surface, waterlogging develops. Soil waters, or waters of the soil layer, represented by almost bound water, where droplet-liquid water is present only during the period of excessive moisture, are also often referred to as upper water.

The waters of the upper water are usually fresh, slightly mineralized, but they are often contaminated with organic substances and contain increased amounts of iron and silicic acid. As a rule, the top water supply is not a good source of water supply. However, if necessary, measures are taken to artificially preserve this type of water: they arrange ponds, outlets from rivers that provide constant power to the exploited wells, plantations of vegetation or delay snow melting.

Ground water

Ground waters are waters that occur on the first impervious horizon below the upper water. They are characterized by a more or less constant flow rate. Groundwater can accumulate both in loose porous rocks and in solid fractured reservoirs. The groundwater level is subject to constant fluctuations, it is influenced by the amount and quality of precipitation, climate, relief, the presence of vegetation and human economic activity. Groundwater is one of the sources of water supply; groundwater outlets to the surface are called springs, or springs.

Artesian waters

Pressurized (artesian) waters - waters that are in an aquifer enclosed between water-resistant layers, and experience hydrostatic pressure due to the difference in levels at the place of water supply and outlet to the surface. They are characterized by constant production rate. The recharge area of \u200b\u200bartesian waters, whose basins sometimes reach thousands of kilometers, usually lies above the area of \u200b\u200bwater flow and above the outlet of pressure waters to the Earth's surface. The recharge areas of artesian basins are sometimes significantly removed from the places of water extraction - in particular, in some oases of the Sahara, they receive water that fell in the form of precipitation over Europe.

Artesian waters (from Artesium, the Latin name for the French province of Artois, where these waters have long been used) are pressurized groundwater trapped in aquifers of rocks between water-resistant layers. They are usually found within certain geological structures (depressions, troughs, flexures, etc.), forming artesian basins. When opened, they rise above the top of the aquifer, sometimes gushing.

The science of groundwater, their origin, conditions of occurrence, laws of motion, physical and chemical properties, connections with atmospheric and surface waters are called hydrogeology.

For builders, groundwater in some cases serves as a source of water supply, while in others it acts as a factor hindering construction. It is especially difficult to carry out excavation and mining operations in the conditions of an inflow of underground waters that flood pits, quarries, trenches, underground mine workings: mines, adits, tunnels, galleries, etc. Groundwater deteriorates the mechanical properties of loose and clayey rocks, can act as an aggressive environment in relation to building materials, cause the dissolution of many mountain pores (gypsum, limestone, etc.) with the formation of voids, etc.

Builders must study underground waters and use them for production purposes, be able to resist their negative impact during the construction and operation of buildings.

Water properties of rocks

Rocks in relation to water are characterized by the following indicators: moisture capacity, water loss and water permeability. Indicators of these properties are used in various hydrogeological calculations.

Moisture capacity -the ability of the breed to contain and retain water. In the case when all the pores are filled with water, the rock will be in a state of complete saturation. The moisture corresponding to this condition is called the total moisture capacity. W n ... B:

wfi.b \u003d L / Rec,

where p -porosity; p ck is the density of the rock skeleton.

Highest value W a B is the same as the porosity of the rock. According to the degree of moisture content, rocks are divided into very water-consuming(peat, loam, clay), poorly hydrated(marl, chalk, loose sandstone, fine sand, loess) and non-drainable,not retaining water (pebble, gravel, sand).

Water lossW e - the ability of rocks saturated with water to release gravitational water in the form of free runoff. At the same time, it is believed that physically bound water does not flow out of the pores of the rock, therefore, W z = W n .„ - W MMB .

The amount of fluid loss can be expressed as the percentage of the volume of water freely flowing out of the rock to the volume of the rock or the amount of water flowing out of 1 m 3 of the rock (specific fluid loss). Coarse-clastic rocks, as well as sands and sandy loams, in which the value W B ranges from 25 to 43%. These rocks, under the influence of gravity, are able to give up almost all the iodine present in their pores. In clays, fluid loss is close to zero.

Water permeability -the ability of rocks to pass gravity water through pores (loose rocks) and cracks (tight rocks). The larger the pore size or the larger the fractures, the higher the water permeability of the rocks. Not every rock, which is characterized by porosity, is capable of passing water, for example, clay ff: with a porosity of 50-60%, water practically does not pass.

Water permeability of rocks (or their filtration properties) is characterized by filtration coefficientk$ (cm / s, m / h or m / day), which is the groundwater velocity at a hydraulic gradient equal to 1.

The largest kphrocks are divided into three groups: 1) permeable - & f\u003e 1 m / day (pebbles, gravel, sand, fractured rocks); 2) semi-permeable - k li > = 1 ... 0.001 m / day (clay sands, loess, peat, loose varieties of sandstones, less often porous limestones, marls); 3) impenetrable - & f< 0,001 м/сут (мас­сивные породы, глины). Непроницаемые породы принято назы­вать waterproofing,and semi-permeable and permeable - by the single term permeable, or aquifers, horizons

§ 3. Chemical composition of groundwater.

Water as an aggressive natural environment for building structures

All underground waters contain a certain amount of salts, gases, and organic compounds in a dissolved state.

Gases dissolved in water (O, CO 2, CH4, H2S, etc.) determine the degree of suitability of water for drinking and technical purposes. The amount of dissolved salts should not exceed 1 g / l. The content of chemical elements harmful to human health (uranium, arsenic, etc.) and pathogenic bacteria is not allowed.

Chlorides, sulfates and carbonates are the most widespread in groundwater. Groundwater is divided into insipid(up to 1 g / ldissolved salts), brackish(from 1 to 10 g / l), salty(10-35 g / l) and brines(more than 35 g / l). The amount and composition of salts is established by chemical analysis in milligrams per liter (mg / l) or in millimoles per liter (mmol / l).

The presence of salts gives water such properties as hardness and aggressiveness.

Rigidity groundwater is determined by the amount of Ca 2+ and Mg 2+ ions dissolved in water and is expressed in millimoles per liter. Distinguish

1. overall hardness, caused by the content of all calcium and magnesium salts in water: Ca (HCO 3) 2; Mg (HCO 3) 2, CaSO4, MgSO 4, CaCl 2, MgCl 2;

2. carbonate, or temporarydue to the content of calcium and magnesium bicarbonates, removed by boiling (precipitate in the ° cage in the form of carbonates);

3... non-carbonate, or permanentremaining in water after removal of bicarbonates. According to the total hardness, natural waters are divided into 5 groups:

Water rating Hardness, mmol / l

Very soft up to 1.5

Soft 1.5-3.0

Moderately soft 3-6

Hard 6-9

Very hard above 9

Hard water forms scale in boilers, soap scum is poorly formed in them, etc.

Aggressiveness groundwater is expressed in the destructive effect of salts dissolved in water on building materials, in particular on Portland cement. In the existing norms that assess the degree of aggressiveness of water in relation to concrete, in addition to the chemical composition of water, the filtration coefficient of rocks is taken into account.

1. Aggressiveness by the content of bicarbonate alkalinity(aggressiveness of leaching) is determined by the value of carbonate hardness. Groundwater is aggressive to concrete at a carbonate hardness of 4-2.14 mmol / l (depending on the type of cement in the concrete composition), and at higher values \u200b\u200bthe water becomes non-aggressive.

2. Aggressiveness by hydrogen index(general acid aggressiveness) is estimated by the pH value. In formations with high permeability, it is aggressive at pH \u003d 6.7-7.0, and in low-permeability at pH \u003d 5

3. Aggressiveness by the content of free carbon dioxide(CO 2) (coal aggressiveness) is determined by the content of carbon dioxide Distinguish between free, bound and aggressive carbon dioxide.

Agrnonsensecarbon dioxide is determined experimentally and by calculation, water is considered aggressive when the carbon dioxide content is\u003e 15 mmol / l in well-permeable soils and\u003e 55 mmol / l for poorly permeable soils.

4. Aggressiveness by the content of magnesian saltsis determined by the content of the Mg 2+ ion. In weakly filtering soils, the waters are aggressive with a magnesium content\u003e 2000 mg / l, and in other soils > 1000mg / l.

5. Aggressiveness by the content of caustic alkalisestimated by the amount of K + and Na + ions. Waters are aggressive to concrete when the content of these ions is\u003e 80 g / l in well-permeable and\u003e 50 g / l in low-permeable soils.

6. Sulfate aggressiveness.This type of aggressiveness is determined by the content of SO 4 2- ions. In highly permeable soils, it depends on the content of the C1 - ion. When the content of sulfate ions is less than 250-300 mg / l in all soils, the water is non-aggressive, in all other cases it is aggressive, even to special cements.

Aggressiveness in the content of chlorides, sulfates, nitrates and other salts and caustic alkalis is usually associated with artificial sources of groundwater pollution with a total content (aggressive ions\u003e 10 g / l.

The aggressiveness of groundwater is established by comparing the data of chemical analyzes of water with the requirements of SNiP 2.02.11-85. To combat it, special cements are used, the underground parts of buildings and structures are waterproofed, the level of groundwater is lowered by means of drainages, etc.

4. Classification and characteristics of typesgroundwater

Groundwater is classified by gi hydraulic characteristic- gravity and pressure, and conditionsoccurrencein the earth's crust there is a perch, groundwater, interstratal waters (Fig. 50). In addition to these main types, there are a number of groundwaters, such as fissure, karst, mineral, etc.

Verkhovodka.Verkhovodkaare called temporary accumulations of water in the aeration zone, which are located above the groundwater horizon, where part of the pores of the soil is occupied by air. The upper waterway is formed over small aquicludes such as a lens of clay and loam in the sand, over layers of denser rocks, etc. (Fig. 50), during water infiltration during periods of heavy snowmelt and rains. The rest of the time, the water of the upper water evaporates and seeps into the following groundwater.

In general, the verkhovodka is characterized by: a temporary, more often seasonal nature, a small area of \u200b\u200bdistribution, low power and pressurelessness. Lying within the underground parts of buildings and structures (basements, boiler rooms, etc.), it can cause their flooding, if drainage or waterproofing measures were not provided in advance.

During engineering and geological surveys, carried out in the dry season, upper water is not always detected. Therefore, its appearance for builders may be unexpected.

Groundwater.Unpavedare called constant in time and significant in the area of \u200b\u200bdistribution of underground water horizons occurring on the first aquiclude from the surface.

1. Groundwater unpressurizedhave a free surface called mirror(or level).The position of the mirror corresponds to some extent to the relief of the area. The depth of the level from the surface is different - from 1 to 50 m and more. The confining layer on which the aquifer lies is called waterproof bed,and the distance from it to

groundwater level poweraquifer (Fig. 51).

2. Nutritiongroundwater is due to precipitation,

reservoirs and rivers. Food area matcheswith the area of \u200b\u200bdistribution of groundwater. Groundwater is open to

pollution with various harmful impurities.

3. Groundwater forms streams that are directed towards the slope of the aquiclude (Fig. 51).

4. The quantity, quality and depth of groundwater depends

geology of the area and climatic factors.

In construction practice, most often it is necessary to meet

groundwater. They create great difficulties in production

construction work (fill pits, trenches, etc.) and interfere

normally operate buildings and structures.

Interstratal waters called aquifers located between aquicludes. They are non-pressure and pressure, the latter are otherwise called artesian.

Interstratal non-pressurewaters are relatively rare,

the aquifers are only partially filled with water (Fig. 51).

Pressure(artesian) waters are associated with the occurrence of aquifers

layers oblique to the horizon or in the form of a bend (fold) (Fig. 50

and 52). The area of \u200b\u200bdistribution of confined aquifers is called an artesian basin.

Separate parts of the aquifers lie at different altitudes

marks. This creates the pressure of groundwater. Power area like

as a rule, it does not coincide with the area of \u200b\u200bdistribution of interstratal waters.

The water pressure is characterized by the piezometric level. He can

be above the surface of the earth or be below it. In the first case, leaving

through boreholes, water gushes, in the second - rises

only to the piezometric level.

Many artesian basins, for example the Dono-Donetsk depression, occupy vast areas, contain a number of aquifers and are an important source of drinking water.