Determination of the angle of repose of soils. Angles of repose of soils and the ratio of slope height to foundation Determining the angle of repose of sandy soils

Encyclopedia of Plants 20.06.2020
Encyclopedia of Plants

Angle of repose

Angle of repose

Angle of repose- the angle formed by the free surface of loose rock mass or other bulk material with a horizontal plane. Sometimes the term "angle of internal friction" may be used.

Particles of material located on the free surface of the embankment experience a state of critical (limiting) equilibrium. The angle of repose is related to the coefficient of friction and depends on the roughness of the grains, the degree of their moisture, particle size distribution and shape, as well as the specific gravity of the material.

According to the angles of repose, the maximum allowable angles of slopes of ledges and sides of quarries, embankments, dumps and piles are determined. angle of repose of various materials

List of various materials and their angle of repose. The data is approximate.

Material (conditions) Angle of repose(degrees)
Ash 40°
Asphalt (crushed) 30-45°
Bark (wood waste) 45°
Bran 30-45°
Chalk 45°
Clay (dry piece) 25-40°
Clay (wet excavation) 15°
clover seeds 28°
Coconut (shredded) 45°
Coffee beans (fresh) 35-45°
Earth 30-45°
Flour (wheat) 45°
Granite 35-40°
Gravel (bulk) 30-45°
Gravel (natural with sand) 25-30°
Malt 30-45°
Sand (raw) 34°
Sand (with water) 15-30°
Sand (wet) 45°
dry wheat 28°
dry corn 27°


see also

Notes


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See what the "Angle of repose" is in other dictionaries:

    angle of repose- The limiting angle formed by the free slope of loose soil with a horizontal plane, at which there is no violation of the stable state [Terminological dictionary for construction in 12 languages ​​(VNIIIS Gosstroy of the USSR)] angle ... ... Technical Translator's Handbook

    The maximum angle of inclination of the slope, folded by the gp, at which they are in balance, i.e., they do not crumble, do not creep. Depends on the composition and condition of the settlements that make up the slope, their water content, and for clayey settlements, the height of the slope. Geological … Geological Encyclopedia

    Angle of (natural) repose- (Böschungswinkel) - the angle relative to the horizontal, formed when bulk material is poured. [STB EN1991 1 1 20071.4] Term heading: General, placeholders Encyclopedia headings: Abrasive equipment, Abrasives, Roads … Encyclopedia of terms, definitions and explanations of building materials

    angle of repose- The ultimate steepness of the slope, at which the loose deposits composing it are in equilibrium (do not crumble). Syn.: natural slope… Geography Dictionary

    angle of repose- 3.25 angle of repose: The angle formed by the generatrix of the slope with a horizontal surface during the dumping of bulk material (soil) and close to the value of its angle of internal friction. Source … Dictionary-reference book of terms of normative and technical documentation

    ANGLE OF REVERSE- the angle at which the unreinforced slope of sandy soil still maintains balance, or the angle at which freely poured sand is located. U.e.o. determined in air-dry state and under water ... Dictionary of hydrogeology and engineering geology

    angle of repose- the angle at the base of the cone, formed during the free pouring of bulk material on a horizontal plane; characterizes the flowability of this material; See also: Angle contact angle contact angle … Encyclopedic Dictionary of Metallurgy

    The limiting angle formed by a free slope of loose soil with a horizontal plane, at which there is no violation of the stable state (Bulgarian; Bulgarian) ъгъл on a natural slope (Czech; Čeština) úhel přirozeného… … Construction dictionary

    Ecological dictionary

    SOIL SLOPE- (soil) the largest possible angle that a stable slope of an embankment of dry soil (soil), or wet soil (soil) under water, forms with a horizontal surface. Ecological Dictionary, 2001 The angle of repose of the soil (soil) ... ... Ecological dictionary


The angle of repose of the soil is the largest value of the angle that forms with the horizontal plane the surface of the soil, poured without shocks; tremors and vibrations.
The angle of repose depends on the soil's shear resistance. To establish this dependence, let us imagine a soil body dissected by a plane a - a, inclined to the horizon at an angle a (Fig. 22).

Part of the soil above the plane a - a, considered as a single massif, can remain at rest or move under the action of the force P - its own weight and the impact of the structure erected on it.
We decompose P into two forces: N \u003d P cos a, directed normally to the plane a - a, and the force T \u003d P sin a, parallel to the plane a - a. The force T tends to move the cut off part, which is held by the forces of cohesion and friction in the plane a - a.
In the state of limit equilibrium, when the shear force is balanced by the resistance of friction and adhesion, but when there is no shift yet, equality 26 is satisfied, i.e. T = N tg f + CF.
In clayey soils, shear is mainly counteracted by cohesion.


There is almost no cohesion in dry sand and the state of limit equilibrium is characterized by the relation T = N tg f. Substituting the values ​​of N and T, we obtain P sin a \u003d P cos a tg f or tg a \u003d tg f and a \u003d f, i.e., the angle a corresponds to the angle of internal friction of the soil f in the state of limit equilibrium of an array of non-cohesive soil.
Determining the angle of repose of sand is shown in fig. 23. The angle of repose of sand is determined twice - for the state of natural humidity and under water. To do this, sandy soil is poured into a glass rectangular vessel, as shown in Fig. 23, a. Then the vessel is tilted at an angle of at least 45° and carefully returned to its original position (Fig. 23b). Next, the angle a between the formed slope of sandy soil and the horizontal is determined; the magnitude of the angle a can be judged by the ratio hl, equal to tg a.

In recent years, a number of new methods have been proposed to determine the characteristics of soil shear resistance: according to soil testing in stabilometers (see Fig. 11), by pressing a ball stamp into the soil (Fig. 24), similarly to determining hardness according to Brinell and others.
Soil testing by the ball test method (Fig. 24) consists in measuring the ball settlement S under the action of a constant load p.
The value of equivalent soil cohesion is determined by the following formula:


where P is the total load on
D - ball diameter, cm;
S - ball draft, see

The adhesion value ssh takes into account not only the adhesion forces of the soil, but also internal friction.
To determine the specific adhesion c, the value of csh is multiplied by the coefficient K, which depends on the angle of internal friction φ (deg).

In recent years, the ball test method has been applied in the field. In this case, hemispherical dies up to 1 m in size are used (Fig. 25).
Shear characteristics f and c are called strength characteristics and the accuracy of their determination is of great importance when calculating the foundations of structures in terms of strength and stability. SP 48.13330.2011 Organization of construction; SP 50.101.2004 Design and installation of bases and foundations for buildings and structures; STO NOSTROY 2.3.18.2011 Strengthening of soils by injection methods in construction

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1. General Provisions

Purpose and types of earthworks

The volume of earthworks is very large, it is available during the construction of any building and structure. Earthworks account for 10% of the total labor intensity in construction.

The following main types of earthworks are distinguished:

Site layout;

Pit and trenches;

Roadbeds;

Dams;

Dams;

Channels, etc.

Earthworks are divided into:

Permanent;

Temporary.

Constants include pits, trenches, embankments, excavations.

Requirements for permanent earthworks:

Must be durable, i.e. resist temporary and permanent loads;

sustainable;

Good resistance to atmospheric influences;

Good resistance to erosive action;

Must be infallible.

Temporary earthworks are carried out for subsequent construction and installation works. These are trenches, pits, lintels, etc.

Basic building properties and soil classification

The soil is called the rocks occurring in the upper layers of the earth's crust. These include: vegetable soil, sand, sandy loam, gravel, clay, loess-like loam, peat, various rocky soils and quicksand.

According to the size of mineral particles and their interconnection, the following soils are distinguished :

Connected - clay;

Non-cohesive - sandy and loose (in a dry state), coarse-grained non-cemented soils containing more than 50% (by weight) of fragments of crystalline rocks larger than 2 mm;

Rocky - igneous, metamorphic and sedimentary rocks with a rigid connection between the grains.

The main properties of soils that affect the production technology, labor intensity and cost of earthworks include:

Bulk weight;

Humidity;

Blurring

Clutch;

looseness;

Angle of repose;

Volumetric mass is the mass of 1 m3 of soil in its natural state in a dense body.
The bulk density of sandy and clay soils is 1.5 - 2 t/m3, rocky soils are not loosened up to 3 t/m3.
Humidity - the degree of saturation of the soil pores with water


g b - g c - mass of soil before and after drying.

At humidity up to 5% - soils are called dry.

With a moisture content of 5 to 15%, soils are called low-moisture.

At humidity from 15 to 30% - soils are called wet.

With a moisture content of more than 30%, the soils are called wet.

Cohesion - the initial resistance of the soil to shear.

Soil adhesion force:

Sandy soils 0.03 - 0.05 MP

Clay soils 0.05 - 0.3 MP

Semi-rocky soils 0.3 - 4 MPa

Rocky more than 4 MPa.

In frozen soils, the adhesion force is much greater.

Looseness- this is the ability of the soil to increase in volume during development, due to the loss of communication between the particles. The increase in soil volume is characterized by the coefficient of loosening K p.

After compaction of the loosened soil is called the residual loosening K op.

soils

Initial

looseness

K r

Residual

looseness

K or

sandy soils

1,08 - 1,17

1,01 - 1,025

loams

1,14 - 1,28

1,015 - 1,05

Clay

1,24 - 1,30

1,04 - 1,09

Mergeli

1,30 - 1,45

1,10 - 1,20

rocky

1,45 - 1,50

1,20 - 1,30

Angle of repose characterized by the physical properties of the soil.

The value of the angle of repose depends on the angle of internal friction, the adhesion force and the pressure of the overlying layers.

In the absence of adhesion forces, the limiting angle of repose is equal to the angle of internal friction.

The steepness of the slope depends on the angle of repose. The steepness of the slopes of cuts and embankments is characterized by the ratio of height to foundation m - slope factor.

Angles of repose of soils and the ratio of slope height to foundation

soils

The value of the angles of repose and the ratio of the height of the slope to its inception at different soil moisture

Dry

Wet

Wet

Angle to degrees

Height to lay ratio

Angle to degrees

Height to lay ratio

Angle to degrees

Height to lay ratio

Clay

1: 1

1: 1,5

1: 3,75

Loam medium

1: 0,75

1: 1,25

1: 1,75

Light loam

1: 1,25

1: 1,75

1: 2,75

Fine-grained sand

1: 2,25

1: 1,75

1: 2,75

Medium sand

1: 2

1: 1,5

1: 2,25

Sand coarse-grained

1: 1,75

1: 1,6

1: 2

plant soil

1: 1,25

1: 1,5

1: 2,25

bulk soil

1: 1,5

1: 1

1: 2

Gravel

1: 1,25

1: 1,25

1: 1,5

Pebble

1: 1,5

1: 1

1: 2,25

Soil erosion - entrainment of particles by flowing water. For fine sands, the highest water velocity should not exceed 0.5-0.6 m/s, for coarse sands 1-2 m/s, for clay soils 1.5 m/s.

According to production standards, all soils are grouped and classified according to the degree of difficulty of development by various earthmoving machines and manually.:

For single-bucket excavators - 6 groups;

For multi-bucket excavators - 2 groups;

For manual development - 7 groups, etc.

Calculation of volumes of earthworks

In construction practice, it is mainly necessary to calculate the volume of work on the vertical layout of sites, the volume of pits and the volume of linear structures (trench, roadbeds, embankments, etc.).

The volume is calculated in the working drawings and specified in the project for the production of works.

Excavation projects should include an excavation cartogram, a bill of fill and cut volumes, and a general soil balance sheet.

The project must have the volume and direction of movement of soil masses in the form of a sheet or cartogram.

The technology of development, soil transportation, backfilling and compaction should be thought out.

The project should include a calendar schedule for earthworks, human and material resources and the choice of a set of machines should be indicated.

When calculating the volume of excavation of pits, trenches, excavations of embankments, all known geometry formulas are used.

With complex forms of cuts and embankments, they are divided into a number of simpler geometric bodies, which are then summarized.

Determination of the volumes of soil masses in the development of pits

In most cases, the pit is a truncated rectangular pyramid, the volume of which is determined by the formula :





The entrance trench is determined by the formula:


Determination of the volumes of soil masses in the construction of linear structures

The volume of earthworks for linear structures of embankment, excavation, trench can be calculated by the formula:



With a slope not exceeding 0.1, you can use the formula F.F. Murzo:


m - slope factor.

If the slope exceeds 0.1, then use the formula




Calculation of volume on curves (Thulden's formula):

r- radius of curves

α - central angle of rotation

Calculation of earthwork volumes in site planning

It is most expedient to design the layout of the site in such a way that a zero balance of earth masses is observed, i.e. redistribution of earth masses on the site itself, without the import or export of soil.

The volume of earthworks is determined on the basis of the cartogram.

The site plan is divided into squares with a side of 10 to 50 m, depending on the terrain. With a more complex terrain, the squares are divided into triangles.

The average mark of the surface of the site, when broken down into squares, is determined by the formula:


ΣH 1- the sum of marks of points where there is one vertex of the square;

ΣH2- the sum of marks of points where there are two vertices of the square;

ΣH4- the sum of marks of points where there are four vertices of the square;

n- The number of squares.

When broken down into triangles, according to the formula:

ΣH 1- the sum of marks of points where there is one vertex of the triangle;

ΣH2- the sum of the marks of the points where there are two vertices of the triangle;

ΣH 3- the sum of marks of points where there are three vertices of the triangle;

ΣH 6- the sum of the marks of the points where there are six vertices of the triangle;
n- the number of squares.

As a rule, additional earthworks in the form of embankments and excavations are always erected on the planned site.

To ensure a zero balance of earthworks, the construction of these structures is taken into account by introducing an amendment to the average planning mark and the coefficient of residual loosening of the soil.

Distribution of earth masses on the site.

After the volumes of earthworks are calculated, they begin to distribute the earth masses. From which area where to transport the land.

Before this, it is necessary to draw up a balance of earthworks. How much excavation will be, how much embankment.

When distributing earth masses, it is necessary to take into account the profile volume of earthworks and the working volume of earthworks. The worker is larger, it takes into account the slopes.

Distribution of earth masses in a linear structure

Taken into account:

Longitudinal transportation of soil;

Cross transportation of soil.

Which way to take can be decided using the inequality:

C vk + C nr ≤ C vn

Свк - the cost of developing excavation and laying the soil in the cavalier;

С нр - the cost of dumping into the embankment from the reserve;

C vn - the cost of developing the soil and filling it into an embankment.

The correct calculation of the cost of transportation for certain distances is important.

To correctly determine the length of the movement of the soil, the centers of gravity of the embankment and excavation are taken and this will be the average distance for transportation.

General information about machines designed for earthworks

Soils are developed by mechanical, hydromechanical, explosive, combined and other special methods.

mechanical method- 80-85% is done in this way, by separating the soil by cutting with the help of earth-moving machines (single-bucket and multi-bucket excavators) working for transport or dumping, or earth-moving machines: bulldozers, scrapers, graders, graders-elevators and ditchers.

Hydromechanical method- hydraulic monitors - they erode the soil, transport and stack or suck the soil from the bottom of the reservoir with dredgers.

Explosive way- based on the use of the force of the blast wave of various explosives placed in specially arranged wells, is one of the powerful means of mechanizing labor-intensive and hard work.

Combined method- combines mechanical with hydromechanical or mechanical with explosive.

Special Ways- destroy the soil with ultrasound, high-frequency current, thermal installations, etc.

For preparatory work, brush cutters, rooters, rippers, etc. are used.

The soil is transported by dump trucks, trailer, conveyors, railway. transport and hydraulic method.

All kinds of rollers, rammers and vibration machines are used to compact the soil.

Single bucket excavator- self-propelled earth-moving machine of cyclic action; attachments: front shovel, backhoe, dragline, grapple, plow and backfiller.

In addition, replaceable equipment is used: a crane, a pile driver, a tamper plate, a stump remover, a concrete breaker, etc.

With a bucket capacity of 0.25; 0.3; 0.4; 0.5; 0.65; one; 1.25; 2.5; 3; 4.5 m 3 - used in construction, and 40; fifty; 100; 140 m 3 is used in overburden work.

The maximum at the construction site is usually 2.5 m 3 .

Bucket excavator- self-propelled earth-moving machine of continuous action. There are chain and rotary.

Bulldozer- the knife blade is hung to the tractor. Tractor power 55 - 440 kW (from 75 to 60 hp).

Bulldozers are used for digging, moving and leveling the soil, as well as cleaning it up in pits.

Scrapers- consist of a bucket and a running gear on a pneumatic duct. There are trailed scrapers with a bucket capacity of 2.25 - 15 m 3, self-propelled 4.5 - 60 m 3. Working speed of movement is 10 - 35 km/h.

They are used for layer-by-layer digging, transportation and backfilling with soil layers. (The cheapest in earthworks).

road graders- self-propelled machine on the frame of which there is a blade with a cutting knife. Designed for planning and profiling work with soil.

Elevator graders- equipped with a disc plow. They are used for layer-by-layer cutting of soil and moving it to a dump or vehicles.

2. The device of cuts and embankments

Pit device

A pit is a recess intended for the construction of a part of a building or structure located below the surface of the earth, for the construction of foundations.

Pit pits come with vertical walls, with fasteners and with slopes.

According to SNiP, it is allowed to dig pits with vertical walls without fastenings in soils of natural moisture with an undisturbed structure, in the absence of groundwater and the depth of pits in bulk, sandy and gravelly soils is not more than 1 m; in sandy and loamy 1.25 m; in clay 1.5 m and extra-dense 2 m.

Mounts are:


strut anchor sheet pile

But it is better to carry out a pit with slopes. The highest allowable steepness of slopes of pits in soils of natural moisture and in the absence of groundwater is taken for excavations

Depth up to 1.5 m from 1: 0.25 to 1: 0;
depth 1.3 - 3 m from 1: 1 to 1: 0.25;
depth 3 - 5 m from 1: 1.25 to 1: 1.5.

For deeper pits, slopes are calculated.

Pit development includes the following work steps:

Development of soil with unloading on the edge or loading into vehicles;

Soil transportation;

The layout of the bottom of the pit;

Backfill with trimming and compaction.

Digging a pit is the leading process. The pits are developed with a single-bucket excavator, scraper, bulldozer and hydromechanical method.

Single bucket excavator used:

During the construction of housing 0.3 - 1 m 3;

In industrial construction 0.5 - 2.5 m 3 sometimes 4 m 3.

trenching

Trenches are temporary excavations intended for laying strip foundations in them or installing pipelines and cables.

There are 3 types of trenches : vertical walls, sloped, and mixed trenches:


Most trenches with vertical walls require fastening, which means additional consumption of materials, additional labor costs

Without fastening, you can dig from 1 to 2 m, depending on the density of the soil. But they recommend immediately laying pipelines or building a foundation.

In viscous soils, rotary excavators dig up to 3 meters, laying pipelines (gas pipelines, oil pipelines, etc.), fastenings are performed where people descend.

When constructing trenches with slopes, the greatest steepness is taken in accordance with the angle of repose and weather conditions.

Mixed-type trenches are arranged with great depth and the presence of groundwater, the level of which is higher than the bottom of the trench.

Trench fastenings are:

Horizontal or vertical;

With gaps or solid;

Inventory or non-inventory.

Inventory fences consist of collapsible frames and inventory boards, inventory spacers.

For the development of trenches, single-bucket excavators are used: a backhoe or a dragline with a bucket capacity of 0.3 - 1 m 3.

The backhoe can be developed with vertical walls. Dragline with slopes and in the presence of groundwater.

If the trenches are not deep, then the dump is organized next to the trench (lateral or end movement).

If the trench is deep, then the blade is on both sides and the excavator moves in a zigzag.

A bucket-wheel excavator is used in the development of trenches for laying pipelines.

Operational changeable productivity of bucket-wheel excavator:


c- the duration of the shift;

n 1 - the number of unloaded buckets per minute depends on the speed of movement and the distance between them;

k1- excavator utilization rate;

k3- bucket load factor;

g- bucket capacity.

If the soil in the trench is moved, then sand or small gravel is laid and it is rammed (but not the soil). When developing trenches for foundations, the soil from under the excavator is usually taken away by dump trucks.

Sometimes in very cramped conditions or when pipelines pass through a road or other obstacles, adits are dug or a puncture is performed (trenchless laying).

The fastening of the trenches is dismantled from the bottom up, but they can also be left (for example, in quicksand).

Backfilling of trenches is carried out after geodetic survey of laid pipelines or other communications.

Backfilling is carried out in two stages: first, the pipe is sprinkled with 0.2 m sand or fine gravel, and then everything else with layer-by-layer compaction.

The device of underwater trenches

Underwater trenches are arranged for laying siphons.

A trench is always developed with slopes, the steepness of which is taken for sandy soils from 1:1.5 to 1:3, for sandy loam and loam 1:1 - 1:2, for clays 1:0.5 - 1:1.
With the width of the development of trenches, the speed of the river flow is taken into account (for small rivers, the channel is diverted).

The development of underwater trenches, depending on local conditions, is carried out by an excavator, a rope-scraper installation, dredgers, and hydraulic monitors.

In some cases, trenches are developed manually.

Ground bed device

The subgrade is the base of the upper structure of roads and railways, consists of embankments and excavations.

The steepness of the slope is taken depending on the type of soil and the height of the embankment.

For non-cohesive soils with an embankment height of up to 6 m, a slope of 1: 1.5 is recommended.

Embankments from 6 m and above should have slopes of a broken profile, more gentle in the lower part.

The process of arranging the subgrade consists of 2 works : preparatory and main.

Preparatory- cleaning of the route and breakdown of the canvas.

Main- development, movement, planning and compaction of soil.

On each section of the subgrade, the soil is developed by machines of one or more types, which are selected taking into account the conditions of their use and ensuring the highest productivity.

Bulldozers used in the construction of excavations up to 2 m and embankments with a height of 1 - 1.5 m with a travel length of 80 - 100 m.

Scrapers are used for longitudinal movement of soil from excavations to an embankment at a distance of movement of more than 100 m, as well as when embankments are arranged from lateral reserves.

Elevator graders- it is advisable to use in the construction of low (up to 1 meter) embankments from reserves in flat terrain. The front of the work of each machine should be within 1.2 - 3 km, the length of the grip should be at least 400 m.

Graders and Motor Graders are mainly intended for planning and profiled works, they can also be used as main machines in the construction of subgrades with an embankment height of up to 0.75 m.

Excavators- a straight shovel or dragline is used where the concentrated masses of soil are not less than a normal face in height.

Means of hydromechanization apply if there are natural reservoirs and sources of electricity in the area of ​​work on the subgrade.

Fixing slopes of permanent earthworks and banks

During the construction of subgrade, canals, water supply and sewerage and other structures, it is necessary to carry out work on fixing slopes and banks.

The soil of the slopes and banks is fixed with organic binders (bitumen), grass sowing, protective clothing in the form of turf, as well as brushwood, stone, reinforced concrete slabs and special protective structures.

A more durable fastening is paving or riprap in wattle cages ranging in size from 1 x 1 to 1.2 x 1.2 m.

3. Auxiliary work in the production of earthworks

Drainage

Excavations in aquifers are developed using open drainage or artificial dewatering of the groundwater level.

Drainage is used when there is a small flow of water.

Disadvantages of drainage:

Blurs the walls of recesses;

The influx of water makes excavation difficult;

The bottom of the pit is not always dry.

Therefore, they arrange an artificial lowering of the groundwater level.

Dewatering

The lowering of the groundwater level is carried out : with the use of light wellpoints, providing a single-tier lowering of the groundwater level to 4 - 5 m, and with a two-tier one by 7 - 9 m; ejector wellpoints, allowing a single-tier lowering of the groundwater level to 15 - 20 m; and tubular wells with deep pumps.

Lightweight wellpoints consist of a set of wellpoints, a suction manifold and pumps.

Pipes are immersed by hydraulic method or drilling. For deep pits, there can be 2 and 3 tiers.

For trenches, it is possible to arrange from one side.

Wellpoints with an ejector device are used to lower the groundwater level in one tier to a depth of 15–20 m.

Deep tubular wells carry out a single-tier lowering of groundwater to a depth of 60 m or more.

Submersible pumps are installed in pre-drilled filtered wells (casing pipes) d 200 - 400 mm.

Artesian pumps are also used.

Artificial fencing of excavations from groundwater

Soil excavations during penetration of layers with a significant influx of water can be carried out under the protection of an ice waterproof wall of frozen soil or with the help of thixotropic impervious screens.

Artificial freezing of soils is used in the development of recesses in quicksand in order to create a temporary waterproof ice wall.

Thixotropic screens are made from bentonite clays or from simple clays mixed with cement 1:2.

Clays absorb water up to 7 times their own weight and, after saturation with water, thicken, acquiring a water-repellent quality.

4. Features of earthworks in winter conditions

General information

In winter, the structure of the soil changes: the mechanical strength, as well as the specific resistance to cutting and digging, increases sharply (several times).

Therefore, earthworks are very different from summer ones.

But sometimes winter conditions favor earthworks. For example, in swamps, when developing silty soils, soils saturated with water.

Due to groundwater in spring, the soil thaws from below. Therefore, at the time of thawing, groundwater rises.

The first ice crystals in groundwater appear at t = -0.1°C. Ground freezing begins at -6°C and below.

In loose soils, sand, sandy loam, water freezes at t = (- 2°С - 5°С), in clay soils at t = (- 7°С - 10°С).

The temperature inside the soil is distributed depending on the depth.

ground temperature,

in °С

Depth, in m

Without snow

Snow 35 cm

0,75

0,75

1,25

1,15

1,85

1,75

2,25

The depth of soil freezing depends on:

Humidity - the higher the humidity, the greater the depth. At a humidity of 30 - 40% leads to heaving of the soil;

Groundwater level - the closer the groundwater to the surface, the less freezing;

The nature of winter and the time of snowfall. The sharper the fluctuations of the outside air, the greater the depth of freezing.

The depth of freezing can be determined by the following formula (the ground is not covered with snow):

H- freezing depth

k- coefficient taking into account the characteristics of the soil:

Clay - 1;

Loam - 1.06;

Sandy loam - 1.08;

Sand - 1.12.

z- the number of days of winter before the settlement day.

t- the average outdoor temperature for the period from the beginning of winter to the settlement day.

In addition, the freezing depth can be determined from various graphs and tables. In general, the depth of freezing is determined in kind.

Protecting the soil from freezing

In general, it is difficult to protect the soil from freezing.

The simplest is loosening: harrowing with a depth of 0.15 - 0.2 m, plowing 0.25 - 0.35 m, deep loosening with an excavator up to 1.5 m.

Provide drainage of autumn waters.

They arrange snow retention with a thickness of 0.5 - 1.0 m. For insulation, they cover with dry peat, foliage, slag (sawdust is not allowed).

Water-air coating with foam from surface-active substances (surfactants), arranged with the help of foam generators with a layer of 30 - 40 cm, reduces the freezing depth by 10 times.

But warming the soil is advisable only in the first half of winter.

Loosening frozen soil

When the soil freezes up to 0.1 m, it is developed without loosening.

Frozen soil is loosened by explosive or mechanically.

The explosive method of loosening is beneficial at a freezing depth of more than 0.8 m (the method is cheap).

The volume is divided into grips, holes are drilled, explosives are laid, blown up and developed in the usual way.

Mechanized loosening at a depth of 0.25 - 0.4 m with a ripper or an excavator with a bucket of 0.5 - 1 m 3.

If the freezing depth is 0.5 - 0.7 m and the volume is not large, free-fall hammers are used, which are in the form of a wedge or ball, concrete breakers based on a hydraulic excavator.

With a freezing depth of up to 1.3 m, it is better to use a diesel hammer with a wedge.

In addition, frozen soil can be cut into blocks with a bar, which are then removed.

A small amount of work is carried out with jackhammers.

Thawing of frozen ground

This method is used for small amounts of work, usually in cramped conditions.

The soil can be thawed:

hot water;

Ferry;

Electric shock;

fire way;

Chemical way (quicklime).

hot water or steam is fed through needles placed in pre-drilled boreholes.

electric current- electric needles, electric furnaces, heating elements, coaxial heaters, horizontal or driving electrodes.

fire method- burning any fuel (peat, coal, firewood, wood chips, diesel fuel, etc.) under a metal box or pipe.

Excavation, backfilling and embankment

In winter, the soil is developed in the usual way.

Excavation is carried out consistently, quickly and the foundations are laid while the soil is warm.

Shallow trenches (up to 1.5 m deep) for foundations are insulated.

backfilling is carried out in compliance with the following requirements: when backfilling the sinuses of pits and trenches, frozen clods should be no more than 15% of the backfill volume, inside the building they are covered only with thawed soil.

Pipelines of 0.5 m are covered with thawed soil.

Above, you can fill it with frozen soil that does not contain clods larger than 5-10 cm.

Erection of subgrade embankments in winter conditions: when constructing a road embankment, up to 20% of frozen soil is allowed, and a railway embankment - up to 30%.

Clay soils in the embankment should be no more than 4.5 m.

The top layer of the embankment is thawed soil 1 m thick.

When planning the site, up to 60% of frozen soil is allowed.

The foundation for foundations can be rented frozen, but not in heaving soils.

5. Organization of a complex-mechanized process of erection of earthworks

With complex mechanization, all earthwork processes are carried out mechanized: loosening, excavation, soil transportation, leveling, compaction.

The leading machine is selected, which should be used to the fullest.

The rest of the set of cars is selected for it.

The cost of 1 m 3 of processed soil is determined and the set of machines is compared with another set.

C with- specific costs per 1 m 3

From 0- total cost of earthworks

V- overall volume

With m.sm.- the cost of a machine shift in rubles.

T- the duration of the machine at this facility

C d- additional costs associated with the organization of earthworks, rubles (road construction, road maintenance, etc.)

Z- Wages of workers not included in the cost of machines.

6. Quality control of earthworks and their acceptance

It is necessary to systematically check the performance of project documentation and the requirements of SNiP 3.02.01-87 "Earth structures, bases and foundations".

It is necessary to keep a work log, which reflects the properties of the soil (plasticity, moisture content, viscosity, etc.).

After the excavation is completed, a tripartite act (customer, contractor, geologist or designer) is drawn up on the compliance of the supporting base with the project in order to be able to carry out further work.

When handing over earthworks, the contractor must submit to the commission executive drawings, in which all changes, deviations from the project, acts of hidden work, acts of testing the soil, acts of geodetic surveys are applied.

Angle of repose- this is the largest angle that can be formed by a slope of freely poured soil in equilibrium with a horizontal plane.

The angle of repose depends on particle size distribution and particle shape. As the grain size decreases, the angle of repose becomes flatter.
In the air-dry state, the angle of repose of sandy soil is 30-40°, under water - 24-33°. For non-cohesive (loose) soils, the angle of repose does not exceed the angle of internal friction

To determine the angle of repose of sandy soil in an air-dry state, the UVT device is used ( rice. 9.11, 9.12), under water - VIA ( rice. 9.13).

According to rice. 9.12 when the box is tilted, the sand crumbles and, loosening, forms a slope with an angle that can be determined by a protractor or by the formula

The concept of angle of repose applies only to dry loose soils, and for cohesive clay soils it loses all meaning, since in the latter it depends on moisture content, slope height and slope load and can vary from 0 to 90 °.

Rice. 9.11. UVT-2 device: 1 - scale; 2 - tank; 3 - measuring table; 4 - clip; 5 - support; 6 - sand sample

Rice. 9.12. Determining the angle of repose by rotating the container (a) and slowly removing the plate (b): A - axis of rotation of the container

Rice. 9.13. VIA device: 1 - VIA box; 2 - sand sample; 3 - container with water; 4 - protractor; 5 - axis of rotation; 6- piezometer; 7- tripod

During the development and shrinkage of the loosened soil cuts and embankments form natural slopes of various steepness. The greatest steepness of flat slopes of earthworks, trenches and pits, arranged without fasteners, should be taken according to tab. 9.2. When ensuring the natural steepness of the slopes, the stability of earthen embankments and excavations is ensured.

Table 9.2. The greatest steepness of slopes of trenches and pits, hail.

soils Slope steepness at excavation depth, m (ratio of height to foundation)
1,5 3,0 5,0
Bulk unconsolidated 56(1:0,67) 45(1:1) 38(1:1,25)
Sandy and gravel wet 63(1:0,5) 45(1:1) 45(1:1)
Clay:
sandy loam 76(1:0,25) 56(1:0,67) 50(1:0,85)
loam 90(1:0) 63(1:0,5) 53 (1:0,75)
clay 90(1:0) 76(1:0,25) 63(1:0,5)
Loesses and loess-like dry 90(1:0) 63(1:0,5) 63(1:0,6)
Moraine:
sandy, sandy 76(1:0,25) 60(1:0,57) 53 (1:0,75)
loamy 78(1:0,2) 63(1:0,5) 57(1:0,65)

The slopes of embankments of permanent structures are performed more gentle than the slopes of excavations.

Lab #1

Determination of the granulometric composition of sand and the degree of its homogeneity

Objective: determination of soil (sand) properties by its granulometric composition. Knowing its composition and the content of the definition of fractions in it, one can judge its properties and application in construction practice (mortars, sand cushions, foundations, etc.).

Work tasks: to gain skills in determining the percentage of each fraction, quartering, determining the homogeneity and heterogeneity of soils according to the schedule.

Providing funds: sieves, electronic scales, weighing of air-dry sand.

Name of definitions Fraction size Sum of fraction weights Loss
> 2,0 1,0 0,5 0,25 0,1 < 0,1
Fraction weight, g (1 plumb line)
Fraction weight, g (2 plumb)
Fraction weight, g (3 plumb)
Fraction weight, g (average value)
% of total
Sum % less than given diameter

U = d60/d10 = 0.35/0.14 = 2.5 ≤ 3

Conclusion (conclusion): Since U< 3 – песок по составу однородный. Согласно ГОСТ песок средней крупности, так как содержание фракций крупнее d 0,25 больше 50 %.

Performers: Selkov D.M., Starchenko V.P., Yakovleva N.V.


Lab #2

Determination of the angle of repose of sandy soil in dry and wet conditions

Objective: to investigate the dependence of the change in the angle of repose of sand on its moisture content.

Work tasks: gain skills in working with the Litvinov device, learn how to take readings correctly and determine the angle of repose in degrees.

Providing funds: device of the Litvinov system, scoop, vessel with water, sandy soil.

Table for determining the angle of repose

Conclusion (conclusion):

The angle of repose, the angle of internal friction (in soil mechanics) is the angle formed by the free surface of a loose rock mass or other granular substance with a horizontal plane. Sometimes the term "angle of external friction" may be used.


Particles of matter located on the free surface of the embankment experience a state of limiting (critical) equilibrium. The angle of repose is related to the coefficient of friction and depends on the roughness of the grains, the degree of their moisture, particle size distribution and shape, as well as the specific gravity of the material.

The angle of repose is a measure of the strength of soils and is used to describe the frictional resistance to soil shear together with the normal effective stress.

According to the angles of repose, the maximum allowable angles of slopes of ledges and sides of quarries, embankments, dumps and piles are determined.

During development (cutting), soils loosen, their structure is disturbed, and they lose their cohesion. The forces of friction and cohesion also change, decreasing with increasing humidity. Therefore, the stability of loose slopes is also unstable and remains temporarily until the physical and chemical properties of the soil change, which is mainly associated with precipitation in the summer and a subsequent increase in soil moisture. Thus, the angle of repose φ for dry sand is 25...30°, wet sand is 20°, dry clay is 45°, and wet clay is 15°. Establishing a safe bench height and slope angle is an important task. The safety of excavation, a quarry depends on the correct choice of slope angle.

Performers: Melekhin S.A., Morokhin A.V.

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