Longitudinal plowing of steep slopes. Design of the transverse profile of the dam. Justification for choosing the site and type of earth dam

Introduction

River banks are subject to erosion (undermining and collapse). Water flows rush in the direction of the channel slope, are pushed away from it with sediment and wash away the banks from below. The washed away, overhanging blocks of soil are not held by adhesion forces and collapse into the riverbed. The banks are most intensively destroyed during floods or floods, when the entire channel slope is flooded and saturated with water.

The degree of channel erosion depends on the geomorphology of the bank, its protection by vegetation and the angle of approach of the water flow to the eroded bank.

The erosion and collapse of banks cause significant damage to fertile floodplain lands, as well as roads, water intakes, populated areas, navigation and other riverine structures. In addition, during high water, erosion occurs in the riverbed floodplain in areas adjacent to concave, eroded banks.

Water erosion causes the loss of fertile soil layer, the growth of ravines and a sharp decrease in agricultural yields in these areas. Typically, soil destruction begins when there is a slope of more than 1-2 0. Floodplain lands on which irrational cultivation is carried out are especially susceptible to erosion processes. economic activity. Longitudinal plowing of the slopes of a river valley, cutting down of riverbed vegetation, and grazing of livestock in the water protection zone lead to intensive erosion of both floodplain lands and river banks.

In this regard, to retain surface water flow, it is necessary to use hydraulic techniques to combat erosion. One of the effective measures to combat erosion processes is the construction of anti-erosion ponds.

For this purpose, a dam is built from soil materials. When designing a dam, engineering-geological, topographical, hydrological, biological and other environmental conditions are taken into account, as well as specifications systems, including information about water consumption.

The designs and dimensions of structures must provide a favorable hydraulic flow regime when passing normal and maximum design flow rates of water, the required maneuverability in changing levels and flow rates.

It is also necessary to provide for engineering protection or relocation of residential and industrial facilities, historical and architectural monuments.

During the design process, the possibility of combining the functions performed by individual structures, their water measurement, their construction and commissioning in queues, and the unification of individual elements, units and structures as a whole is considered.

Justification for choosing the site and type of earth dam

The dam site, as a rule, is located in the narrowest part of the watercourse, usually normal to the horizontal, which ensures a minimum amount of work. Topographic conditions determine the length and height of the dam. It is advisable to select the dam site simultaneously with the routing of the spillway. When choosing a site, they also take into account the method of passing construction costs, the availability and possibility of constructing a road network, and laying power lines.

During the survey process, several sections are identified. The site of the future dam is selected from them taking into account the listed factors and based on the results of a technical and economic comparison of options.

For the accepted alignment, a longitudinal profile is made with fixation of ground surface marks at pickets and intermediate points. At the site, boreholes are being dug or drilled to illuminate the engineering-geological structure of the dam’s base.

When designing dams, the shape of river valleys is also taken into account, in which two characteristic sections are observed: the channel section, where water flows during low-water periods, and the floodplain section, which is flooded during floods.

In reservoirs created with the help of earth dams, there are three levels of the water surface: forced retaining water (FRU), normal retaining water (NRU) and dead volume (ULV). The marks of these levels are established using water management calculations.

Design of the dam cross section

2.1 Determination of dam crest width

One of the main issues in designing a dam from soil materials is determining its stable and economically viable profile. The dimensions of the cross profile depend on the type of dam, its height, the characteristics of the soil of the dam body and its foundation, as well as construction and operating conditions.

The dam crest is designed based on the conditions of work and operation of the dam. First of all, it is necessary to ensure the passage of transport. Therefore, the width of the ridge is taken depending on the category of the road, but not less than 4.5 m. For this work we accept: road category – IV; carriageway width (A) 6.0 m; shoulder width (B) 2.0 m; the width of the roadbed is 10 m.

In the transverse direction, the road is given a two-way slope, taking it equal to 1.5% for asphalt concrete pavement, and 3% for cobblestone or dirt pavement. Roadsides are usually given a slightly greater slope. Within the boundaries of the roadsides, in accordance with GOST 23457-79, fences are installed in the form of ridges, low walls or parapets.

If the dam crest is made of clay soils, then in order to prevent it from heaving during frosts, a protective layer of sandy or gravel soil (crushed stone) is provided. The thickness of the protective layer, including the thickness of the road surface, should be no less than the depth of seasonal freezing in the given area.

The elevation of the crest is determined by a method based on the condition of preventing water from overflowing over the crest of the dam.

The slopes of the dam must be stable during its construction and operation under the influence of static and dynamic loads, filtration, capillary pressure, waves, etc. The slope coefficients are pre-assigned according to recommendations, as well as experience in the construction and operation of analogue dams; then their stability is checked using a special calculation.

When the height of embankment dams is from 10 to 15 m, the coefficient of foundation of the upstream slope is taken to be 3.0, and for the downstream slope - 2.5. If a screen is constructed on the upstream slope of a dam made of a material that has lower values ​​of the angle of internal friction and adhesion coefficient than the soil of the main body of the dam, the placement of the upstream slope should be determined taking into account not only the collapse of the slope as a whole, but also the shift of the screen along the surface of the slope, and also shifting the protective layer over the surface of the screen..

On high slopes, if necessary, berms are installed approximately every 10 m, the dimensions of which are determined by the conditions of work, operational passage, collection and drainage of storm water on the lower slope. On an upslope, the berm can be placed at the end of the fastening to create the necessary support. Berm width earth dams are prescribed within 1 ... 3 m, and for dams made of stone materials - at least 3 m. If it is necessary to drive along a berm, its width is determined according to road design standards. In all cases, the installation of berms should not lead to a general slope position compared to the design one.

Ravine - a steeply sloped valley, often highly branched, formed by temporary water flows. The geological process that determines their development is called gully formation.

The main driving force behind the emergence and development of ravines is water erosion, that is, the erosion and destruction of the earth's surface by flowing water. In contrast to planar washout (erosion), when flowing water washes away the entire surface layer on a slope, during gully formation, mainly linear water erosion acts, i.e., erosion and destruction occur along the line of maximum slope of the slope surface.

Stages of ravine development: erosion furrow - pothole(depth up to 1 m, length 5-20 m) - ravine - ravine.

The length of ravines can reach several kilometers, depth - up to 40-50 m (in the loess layer up to 80-100 m), and width 150-300 m. The rate of development of a ravine is determined by the erosion of rocks and can range from 0.3-0.8 m up to 10-20 m/year.

Gully formation is extremely widespread in the steppe and forest-steppe zones of our country (Central Russian, Upper Volga, Volga, Azov uplands, steppe regions of Altai and Eastern Siberia, etc.).

The ravines complicate the construction development of the territory. By dismembering the terrain, they pose a great threat to populated areas, roads and other engineering structures. In a number of regions of the Central Black Earth region of the European part of Russia, almost a quarter of the total land area is occupied by waste lands occupied by active ravines. Gully erosion is a typical process leading to local loss of resource in geological space with all the ensuing consequences (V.T. Trofimov and D.G. Ziling, 2002).

The main conditions for the development of ravines: 1) the presence of easily eroded rocks (sandy loam, loam, especially loess, to a lesser extent - silty sand, clay, chalk deposits, etc.); 2) rainfall, rapid spring snowmelt, unorganized discharge of technogenic and irrigation waters; 3) slope steepness is more than 4-8°.

The depth of the ravine is limited by the position erosion basis, i.e., the level mark of the reservoir into which the ravine flows. A decrease in the base of erosion causes increased growth of the ravine and its deepening, which can create a significant threat to already built structures.

The ravine grows with its top up the slope up to the watershed line. At the same time, it deepens and expands due to the erosion of the slopes of the ravine and the appearance of side holes. When the ravine reaches the watershed line, and the mouth reaches the base of erosion, the development of the ravine fades. Its bottom is leveling out, the slopes are covered with vegetation. The ravine completely loses its eroding activity and turns into bulk y, a negative form of relief with a flat bottom and gentle turfed slopes.

It is clear that the real danger during construction and other economic development of the territory is represented by existing or growing ravines. Signs of growing ravines are steep exposed slopes, sharply defined edges, a V-shaped transverse profile, side openings, etc.

Measures to combat gully formation are complex in nature and are divided into preventive and active (engineering).

Preventive actions are aimed at preventing the development of gully formation processes. Deforestation, longitudinal plowing of slopes, excessive grazing of livestock, excavation work on slopes, etc. are prohibited.

TO engineering activities refers to the device of protozoa hydraulic structures to intercept and drain surface water flow: upland ditches, water-retaining shafts, runoff sprayers, reinforced concrete drainage trays, etc. A system of dams is erected along the bottom of ravines to dampen the energy of the eroding flow. Areas of active erosion are covered with soil and strengthened with rock fill, concrete slabs, etc., followed by paving with stone.

Design of foundations during construction on frozen soils should be carried out in accordance with SNiP 2.02.04-88 based on the results of special engineering and geocryological surveys taking into account constructive and technological features designed structures.

4.11. Gravity processes on slopes and in pits.

They appear when the adhesion forces between particles, i.e., the strength of the rock, are disrupted in the slope soil mass or in the layered strata. This usually happens when rocks are moistened during or after heavy rainfall. The moving force here is gravitational and the movement of the detached mass of soil goes to the base (level) of erosion (to the base of the slope).

There are screes, rockfalls and landslides.

Loess rocks are characterized by anisotropy of filtration properties. Vertically, it is 5-10 times greater than the horizontal water permeability value. The natural humidity of loess rocks is 10-14%.

The fine fraction of loess rocks is represented by hydromicas, quartz, calcite, and montmorillonite. The remaining clay minerals are of secondary importance.

The main distinguishing property of many loess rocks is their ability to sag when soaked.

Subsidence soil- soil that, under the influence of external load and its own weight (I type of subsidence) or only from its own weight (P type of subsidence) when soaked with water or other liquid, undergoes vertical deformation (subsidence) and has a relative deformation  s 1 > 0.01. The greatest subsidence is confined to horizons lying directly under modern and buried soils. Subsidence increases in the zone of seasonal freezing and thawing of soils and decreases towards the base of the loess rock layer.

The problem of the genesis of loess has not yet been completely resolved. “Obviously loess rocks, like sandy and clayey rocks, can be of different genesis; they are polygenetic” (E.M. Sergeev).

There are a number of hypotheses and theories of the origin of loess rocks. The most famous are aeolian, proluvial, alluvial, etc. In the geological history of the formation of loess rocks, two main stages are distinguished:

1. 
   Accumulation of precipitation.
2. 
   Their transformation during lithification into loess rocks.

When designing and constructing buildings and structures on loess subsidence soils, according to SNiP, measures must be taken to eliminate the dangerous influence of possible subsidence on their stability, as well as external monitoring of the condition design position objects.

5. Engineering-geological surveys.

5.1. Goals and objectives of the research.

Conducted:

• 
  To ensure design various types construction engineering-geological characteristics of construction sites.
• 
  During exploration and exploitation of deposits of building materials.
• 
  To provide data on engineering and geological conditions during reconstruction and other types of construction work in built-up areas.

• 
  Study of geomorphological, geological, hydrogeological conditions and modern geological processes.
• 
  Determination of strength and deformation properties of soils for calculations of rational types of foundations and structures.
• 
  Determination of the distribution of conditions of occurrence, genesis, age, thickness, engineering-geological properties of rocks in the massif and the properties of groundwater associated with them, as well as all types of modern geological and engineering-geological processes and phenomena.

• 
  Engineering-geological report with an assessment of the geological conditions of construction.
• 
  Maps, sections, tables of results of laboratory and field studies of soils - graphs, diagrams, tables, photographs.

Industrial and civil engineering (IGC).

Roads and railways.

Urban planning is carried out in all natural zones in diverse and, often, complex engineering and geological conditions. Underestimation of one of these factors leads to a reduction in the service life of objects and an increase in the cost of their reconstruction or restoration, and to increased pollution of the geological environment.

Features of engineering geology and urban geoecology include:

Multi-branch construction: civil, industrial, hydraulic, mining, municipal, transport, above-ground, in-depth, underground, i.e. different types impact on the geological environment.

A wide variety of types of structures by weight, size, configuration, structures, operating mode, loads (static, dynamic, variable mode).

Large areas of urban areas where new construction is underway are subject to the complete demolition of old structures or the existing facilities are reconstructed (a new foundation is laid, floors are added, the internal layout, type of roofing, etc. are changed). In this case, the foundation rocks experience not only an increase in loads, but sometimes also a series of cycles of loading and unloading. IN as a result occurs compaction of the soil in the zone of influence of the structure, some physical and mechanical properties of the soil change.

In existing cities, the atmosphere, hydrosphere, relief, vegetation and soil cover (embankments, pruning, planning, etc.) are subject to technogenic changes; and with what ancient city, the more significant these processes are. Under the influence of dynamic influences from moving vehicles under the roadways, soil compaction occurs to a depth of 1.5-2.0 meters. When water leaks from utility networks, technogenic aquifers are formed.

In many cities (St. Petersburg, Kyiv, Omsk, etc.) construction is carried out on alluvial soils.

With the expansion of urban areas in the city limits turn out to be old landfills, cemeteries, exhausted and still active quarries, agricultural lands, which complicates the geo-ecological situation of the urban area.

The main urban planning document is the city master plan, on the basis of which detailed development plans and layouts of individual residential complexes, industrial hubs, transport and utilities are developed. IN master plan the peculiarities of the geological structure of the territory, hydrogeological conditions, engineering-geological and geoecological zoning must be taken into account, taking into account the types and characteristics of man-made load on the geological environment.

6. Applications.

6.1. Literature.

1. 
   Ananyev V.P., Potapov A.D. Engineering geology - M.: Higher
   school, 2000
2. 
   Goldshein M. N. Mechanical properties soils. - M.: Stroyizdat, 1979
3. 
   Geological reference book. In 2 volumes - M., 1973.
4. 
   GOST 25100-95. Soils. Classification. - M., 1995
5. 
   Druzhinin M.K. Fundamentals of engineering geology. - M.: Nedra. 1978.
6. 
   Ivanov M.F. General geology. - M.: graduate School. 1974.
7. 
   Lomtadze V.D. Engineering geology, engineering geodynamics - Leningrad, 1977.
8. 
   Maslov N. N. Fundamentals of engineering geologists and soil mechanics. -
   M.: Higher School, 1982.
9. 
   Maslin N. N., Kotov M. F. Engineering geology. - M.: Stroyizdat, 1971.
10. 
    Peshkovsky L. M., Pereskokova T. M. Engineering geology. - M.: Higher School, 1982.
11. 
    Sergeev I.M. Engineering geology - M.: Moscow State University Publishing House, 1979.
12. 
    SNNP II - 02 - 96. Engineering surveys for construction. Basic provisions. - M., 1996.
13. 
    Handbook of Engineering Geology. - M.: Nedra, 1968.
14. 
    Handbook of engineering surveys for construction M., 1963.
15. 
    Chernyshev S. N., Chumachenko A. N., Revels I. L. Problems and exercises in engineering geology. - M.: Higher School, 2001.
16. 
    Shvenov G.I. Engineering geology - M: Higher School, 1997.
17. 
    Gorbunova T. A., Kamaev S. G. Elements of soil science and geodynamic processes. Tutorial. – Barnaul: From AltGTU, 2004.

1. 
   Describe the mutual influence of engineering structures and the geological environment.
2. 
   Name the main branches of engineering geology.
3. 
   Give brief description geosphere
4. 
   For what purposes is age determined? rocks what methods exist.
5. 
   What are minerals and rocks called?
6. 
   How rocks are divided by genesis.
7. 
   Formation and occurrence patterns of igneous rocks, their fracturing and structural properties.
8. 
   Formation and conditions of occurrence of sedimentary rocks, their classification, application in construction.
9. 
   Metamorphic rocks. Main factors of metamorphism, application in construction.
10. 
    Basics of soil science.
11. 
    Processes of the Earth's internal dynamics. Types of tectonic movements.
12. 
    Types of dislocations, their influence on engineering and geological conditions during construction.
13. 
    Seismic phenomena, Types of seismic waves and the nature of earthquakes.
14. 
    Lithospheric plates of the upper shell of the Earth and types of their contacts.
15. 
    What does hydrogeology study?
16. 
    Types of water in rocks.
17. 
    Classification of groundwater.
18. 
    What does the hydroisohypsum map characterize?
19. 
    Types of water intakes. Darcy's law.
20. 
    Name the processes of the external dynamics of the Earth and their influence on the geological environment.
21. 
    Weathering processes and weathering products. Eluvium.
22. 
    Geological activity of wind: deflation, correction, transportation and accumulation.
23. 
    Planar and deep erosion. Gully formation. Elements of a ravine.
24. 
    Geological activity of the river. Elements of the valley, types of terraces, engineering and geological features during construction.
25. 
    Describe hazardous geological processes, such as:

• 
  Suffusion;
• 
  Karst;
• 
  Quicksand;

1. 
   Geological activity of lakes and swamps, features of construction in these conditions.
2. 
   Types of glaciers. Features of construction on moraine deposits.
3. 
   Mudflows. Areas of occurrence and measures to preserve slopes.
4. 
   Types of permafrost. Occurrence conditions, hydrogeology and construction features.
5. 
   Gravitational processes on slopes and pits: screes, collapses, landslides. Origin, movement mechanism, classification, control measures.
6. 
   Engineering-geological features of loess rocks.
7. 
   Goals and objectives of engineering-geological surveys.
8. 
   Research by types of construction.
9. 
   What are the engineering-geological and geo-ecological problems of cities?

6.3. Geochronological table.

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