purpose of work:
Determine the angle of repose of the test soil in laboratory conditions in a dry state and under water.
The essence of the method:
Angle of repose of sands is the limiting angle of free sand pouring at which the soil mass is in a stable state. This indicator is determined both in dry condition and under water.
The angle of repose of the test soil is determined in laboratory conditions by a device for determining the angle of repose, which is part of the Litvinov PLL-9 field laboratory.
The angle of repose of sand in a dry state is equal to the angle of internal friction of this sand
Equipment:
A device for determining the angle of repose;
Funnel;
Straight Blade Knife;
Measuring vessel.
Fig. 5. A device for determining the angle of repose of sands
1- retractable sash;
2- small office.
Determination of the angle of repose of sands in a dry state
Operating procedure:
3. Smooth out the sand with a knife.
4. After that, gradually raise the sliding sash, making sure that there are no jolts; while holding the device with your hand.
5. The sand is partially poured into another compartment until a stable equilibrium position is reached; the angle between the plane of the free slope and the horizontal plane is the angle of repose.
6. By divisions on the bottom and side wall, the height and location of the slope are counted and the tangent of the angle of repose is calculated. The readings are carried out with an accuracy of 1 mm.
7. The tests are carried out two times.
8. The numerical value of the tangent of the angle of repose is determined as the arithmetic mean of the results of two measurements.
9. The results of the determinations are recorded in table 5.
Determination of the angle of repose of underwater sands
Operating procedure:
1. The device is placed on a table or other horizontal surface. At the same time, the retractable sash is lowered to the bottom.
2. Sand is poured into the small compartment of the device in small portions through a funnel flush with the edges.
3. Smooth out the sand with a knife.
4. After the test soil has been poured into the small compartment of the instrument, water is poured into the large compartment to the top.
5. Thereafter, the sliding sash is raised a few millimeters so that water can enter the small compartment.
6. When the soil is saturated with water, gradually raise the retractable sash, making sure that there are no jolts; while holding the device with your hand.
7. The sand is partially poured into another compartment until a stable equilibrium position is reached; the angle between the plane of the free slope and the horizontal plane is the angle of repose.
8. By divisions on the bottom and side wall, the height and location of the slope are counted and the tangent of the angle of repose is calculated. The readings are carried out with an accuracy of 1 mm.
9. The tests are carried out twice.
10. The numerical value of the tangent of the angle of repose is determined as the arithmetic mean of the results of two measurements.
11. The results of the determinations are recorded in table 5.
Table 5 Results of determining the angle of repose.
Laboratory work No. 6
Determination of the filtration coefficient of sandy soil
Purpose of work:
Determine the filtration coefficient of the tested sandy soil in laboratory conditions.
The essence of the method:
Filtration coefficient K f is a numerical characteristic of water permeability (the ability of the soil to filter water). It represents the filtration rate and is usually expressed in cm / s or m / day.
The filtration coefficient is determined on disturbed soils at optimal moisture content and maximum standard density, the values of which are preliminarily determined in laboratory work No. 4.
The filtration coefficient is used when calculating groundwater reserves, determining the flow of water into construction pits and mine workings, when calculating water leaks from reservoirs, designing drainage structures and filters, as well as in a number of other calculations.
In this laboratory work, the procedure for determining the filtration coefficient of sandy soils and building sands used in construction is established.
Equipment:
Soyuzdorniya PKF-SD device;
Scales with an accuracy of 0.01 g;
Metal cups with a capacity of at least 5 liters;
Measuring cylinders with a spout with a capacity of 100 and 500 ml;
Spatula - trowel;
Metal ruler 30 cm long;
Stopwatch;
Thermometer;
Rubber pear.
Fig 6. General view of the device PKF-SD to determine the filtration coefficient.
1- working cylinder; 2- piezometer; 3- perforated bottom;
10- anvil; 11-drummer; 12-handle.
The device consists of the following main parts: a filter tube assembly, a loading funnel, a stand, a rammer, a glass, and a bath.
The filter tube assembly includes a working cylinder 1, on which a piezometer is located 2. A perforated bottom 3 with a mesh is screwed to the bottom of the cylinder 4. After compaction of the soil, the filter tube is installed on a stand 6. The ramming device consists of a guide rod 9, an anvil 10, a striker 11 with a mass 500 gr and handles 12.
To conduct an experiment to determine the filtration coefficient K f with hydraulic gradient i = 1, the filter tube with support is placed in beaker 7. With a hydraulic gradient i = 2, the filter tube with support is placed directly in the bath 8.
Operating procedure:
Sample formation
1. Fill the first hitch into the working cylinder, insert a rammer (load weight 0.5 kg, drop height 0.3 m), carry out 40 blows on the compacted soil.
2. Measure with a ruler with an accuracy of 1 mm at three points the distance from the surface of the compacted soil to the top of the cylinder. Record the measurement results in table 6.2 and determine the average value.
3. Loosen the surface of the compacted layer with a knife to a depth of 1-2mm. Pour the second sample into the working cylinder, repeat the compaction of the sample and measure the distance from the surface of the compacted soil to the top of the cylinder. Record the measurement results in table 6.2 and determine the average value.
4. Pour the third sample into the working cylinder, repeat the compaction and measurement operations. Record the results in Table 6.2 and determine the average.
5. After completion of soil compaction operations, weigh the working cylinder with soil with an accuracy of 1 g. Enter the weighing results in table 6.2.
6. On the surface of the compacted soil in the working cylinder, pour gravel with a particle size of 2-5 mm so that the thickness of the gravel layer is 5-10 mm.
Saturation of the sample with water.
1. Place the filtration tube with compacted soil into the metal cup 7, which is supplied with the device, the height of which corresponds to the upper level of the soil in the working cylinder. Fill this glass with water to 2/3 of the height and stand for 15 minutes before carrying out the next operation.
2. Transfer the glass with the filter tube placed in it to the water tank with a capacity of 8-10 liters and bring the water level in this tank to a height of 10-15 mm above the upper edge of the glass.
3. Keep the glass in a tank with water until a water mirror appears above the gravel layer and record the time of saturation of the soil with water in table 6.2.
Testing.
1. Carefully add water to the inner cavity of the filtration tube by 1/3 of its height and transfer the device together with a metal glass to the bath for measuring the filtration duration, positioning it so that the zero mark of the water meter is at eye level.
2. Add water to the inner cavity of the filter tube to a level that is at least 0.5 cm higher than the zero mark of the water tube (each division on the water tube corresponds to 0.5 cm).
3. Check the water level in the metal glass and, if necessary, fill it up to the top with water.
4. Install a thermometer in a metal glass to measure the temperature of the water during the test.
5. Carry out the first measurement of the filtration duration using a stopwatch, turn on the latter when the water level in the water meter reaches zero division, and turn it off when it reaches 5 cm, and record the water temperature. The water level in the filter tube during the test should not drop below the surface of the gravel bed.
6. If the filtration time exceeds 2 minutes, carry out the second measurement when the water level drops to the 2cm mark. Otherwise, all subsequent measurements should be carried out when the level falls to the 5 cm mark, in all cases registering the loss of water. The water level in the filter tube during the test should not drop below the surface of the gravel bed.
7. If the filtration duration for the previous item exceeds two minutes, all subsequent measurements should be carried out when the water level drops to 1cm. Otherwise, all subsequent measurements should be carried out when the level falls to the 2 cm mark, in all cases registering the water temperature. The water level in the filter tube during the test should not drop below the surface of the gravel bed.
8. If the filtration duration according to the previous point exceeds 10 minutes, the pressure gradient during the test must be taken equal to 2. For this, the filtration tube together with the stand must be removed from the metal beaker and installed in the bath without the beaker.
9. Enter the results of each measurement and the recorded water temperature in the table 6.2.
Processing of results:
where K 10 - filtration coefficient, m / day;
I is the height of the filtering layer of sand, determined as the difference between the total height of the filtration tube H o and the distance from the upper end of the tube to the soil surface h 3, cm.
t m - average filtration time, sec;
T cf - water temperature, ˚С;
The value of the water level drop function, determined according to table 6.1;
S is the drop in the water level in the water-measuring tube, cm;
h o - the height of the initial water pressure in the device from its bottom to zero division of the water tube, equal to 10 for a pressure gradient 1 or 20 for a pressure gradient 2.
2. Enter the obtained values into Table 6.2 with results rounded to 0.1m / day if the filtration coefficient is less than 5m / day, and the results are rounded to whole numbers if the filtration coefficient is more than 5m / day.
3. After carrying out the calculations, compare the results obtained with the averaged values of the filtration coefficient of various types of soils:
Clean pebble …………………………… more than 100 m3 / day;
Pebble with sandy aggregate .. ……… 100-200 m3 / day;
Clean sands of various sizes …………… 50-2 m3 / day;
Clay sands, sandy loam ……………. ……… 2-0.1 m / day;
Loams ………………………… ... ………… less than 0.1 m / day;
Clays …………………………… ... ………… .. less than 0.01 m / day.
Table 6.1. Dependence of the magnitude of the drop in water level on the initial head.
| S / h 0 | φ (S / h 0) | S / h 0 | φ (S / h 0) | S / h 0 | φ (S / h 0) | S / h 0 | φ (S / h 0) |
| 0,01 | 0,010 | 0,26 | 0,301 | 0,51 | 0,713 | 0,76 | 1,427 |
| 0,02 | 0,020 | 0,27 | 0,315 | 0,52 | 0,734 | 0,77 | 1,470 |
| 0,03 | 0,030 | 0,28 | 0,329 | 0,53 | 0,755 | 0,78 | 1,514 |
| 0,04 | 0,040 | 0,29 | 0,346 | 0,54 | 0,777 | 0,79 | 1,561 |
| 0,05 | 0,051 | 0,3 | 0,357 | 0,55 | 0,799 | 0,8 | 1,609 |
| 0,06 | 0,062 | 0,31 | 0,371 | 0,56 | 0,821 | 0,81 | 1,661 |
| 0,07 | 0,073 | 0,32 | 0,385 | 0,57 | 0,844 | 0,82 | 1,715 |
| 0,08 | 0,083 | 0,33 | 0,400 | 0,58 | 0,863 | 0,83 | 1,771 |
| 0,09 | 0,094 | 0,34 | 0,416 | 0,59 | 0,892 | 0,84 | 1,838 |
| 0,1 | 0,105 | 0,35 | 0,431 | 0,6 | 0,916 | 0,85 | 1,897 |
| 0,11 | 0,117 | 0,36 | 0,446 | 0,61 | 0,941 | 0,86 | 1,966 |
| 0,12 | 0,128 | 0,37 | 0,462 | 0,62 | 0,957 | 0,87 | 2,040 |
| 0,13 | 0,139 | 0,38 | 0,478 | 0,63 | 0,994 | 0,88 | 2,120 |
| 0,14 | 0,151 | 0,39 | 0,494 | 0,64 | 1,022 | 0,89 | 2,207 |
| 0,15 | 0,163 | 0,4 | 0,510 | 0,65 | 1,050 | 0,9 | 2,303 |
| 0,16 | 0,174 | 0,41 | 0,527 | 0,66 | 1,079 | 0,91 | 2,408 |
| 0,17 | 0,186 | 0,42 | 0,545 | 0,67 | 1,109 | 0,92 | 2,526 |
| 0,18 | 0,196 | 0,43 | 0,562 | 0,68 | 1,139 | 0,93 | 2,659 |
| 0,19 | 0,210 | 0,44 | 0,580 | 0,69 | 1,172 | 0,94 | 2,813 |
| 0,2 | 0,223 | 0,45 | 0,593 | 0,7 | 1,204 | 0,95 | 2,996 |
| 0,21 | 0,236 | 0,46 | 0,616 | 0,71 | 1,238 | 0,96 | 3,219 |
| 0,22 | 0,248 | 0,47 | 0,635 | 0,72 | 1,273 | 0,97 | 3,507 |
| 0,23 | 0,261 | 0,48 | 0,654 | 0,73 | 1,309 | 0,98 | 3,912 |
| 0,24 | 0,274 | 0,49 | 0,673 | 0,74 | 1,347 | 0,99 | 4,605 |
| 0,25 | 0,288 | 0,5 | 0,693 | 0,75 | 1,386 | - | - |
Table 6.2. Results of determining the filtration coefficient.
| op. | Soil moisture, W,% | Weight, gr. | Filtration tube height, cm. | Soil density, g / cm 3 | Filtration time, sec. | Falling water level in the tube, see | Water temperature, ˚С | Pressure gradient | Filtration coefficient, m / day | ||||||
| Cylinder | cylinder with soil | soil | Initial, h 0. | Above a compacted soil sample, h 3. | Wet | Sukhoi | Separate measurement | Mean | Separate measurement | Mean | |||||
The measurement of the filtration duration at the selected levels of water drop and pressure gradient should be carried out at least 2 times, after which the average value should be calculated.
Laboratory work No. 7
Angle of repose
Angle of repose
Angle of repose- the angle formed by the free surface of a loose rock mass or other bulk material with a horizontal plane. Sometimes the term "angle of internal friction" can 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 on the specific gravity of the material.
At the angles of repose, the maximum permissible angles of the slopes of benches and sides of open pits, embankments, dumps and stacks are determined. angle of repose made of various materials
A list of the various materials and their angle of repose. Data are approximate.
| Material (conditions) | Angle of repose(degrees) |
|---|---|
| Ash | 40 ° |
| Asphalt (crushed) | 30-45 ° |
| Bark (wood waste) | 45 ° |
| Bran | 30-45 ° |
| chalk | 45 ° |
| Clay (dry lump) | 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 (wet) | 34 ° |
| Sand (with water) | 15-30 ° |
| Sand (wet) | 45 ° |
| Dry wheat | 28 ° |
| Dry corn | 27 ° |
see also
Notes (edit)
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See what "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 USSR)] angle ... ... Technical translator's guide
The maximum angle of inclination of the slope, folded by the g. P., At which they are in equilibrium, that is, they do not crumble, do not slide. Depends on the composition and state of the g. P., Composing the slope, their water content, and for clay p. And the height of the slope. Geological ... Geological encyclopedia
Angle of (natural) slope- (Böschungswinkel) - the angle relative to the horizontal, formed when pouring bulk material. [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 extreme steepness of the slope, at which the loose sediments 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 when filling bulk material (soil) and close to the value of its angle of internal friction. A source … Dictionary-reference book of terms of normative and technical documentation
ANGLE OF NATURAL SLOPE- the angle at which the unreinforced sandy slope still maintains equilibrium, or the angle at which the freely poured sand is located. U. e. O. determined in an air dry state and under water ... Dictionary of Hydrogeology and Engineering Geology
angle of repose- the angle at the base of the cone, formed when free pouring 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 disturbance of the stable state (Bulgarian; Български) ъгъл on a natural slope (Czech; Čeština) úhel přirozeného ... ... Construction vocabulary
Ecological Dictionary
ANGLE OF NATURAL SOIL SLOPE- (soil) the largest possible angle that forms a stable slope with a horizontal surface of an embankment of dry soil (soil), or wet soil (soil) under water. Ecological Dictionary, 2001 Angle of natural slope of the soil (ground) ... ... Ecological Dictionary
Purpose of work:
Acquaintance with the method for determining the angle of repose for sandy soils.
Acquisition of skills in working with the device for determining the angle of repose of loose soils.
Determination of the angle of repose of air-dry and underwater sand.
Necessary equipment and materials
Methodical instructions for performing the work.
Laboratory work journal.
A device for determining the angle of repose of the Litvinov field laboratory.
A container with water.
The lack of adhesion in sands allows you to determine the angle of internal friction φ 0 by the angle of the natural slope of the soil under conditions of extreme equilibrium (Fig. 2.3.).
Figure 2.3. Scheme for determining the angle of repose of a sandy grant.
T 1 = 
where φ - angle of internal friction; tg φ - coefficient of friction
The angle of repose of sandy soil is called the maximum value of the angle formed with the horizontal plane, the surface of the soil, poured without jolts and dynamic influences.
The angle of repose is determined for sandy soil in an air-dry state and under water. We use Litvinov's device for testing.
Work order
Determination of the angle of repose of the soil in the air-dry state is carried out as follows. The device is placed on a table, while the sliding sash is lowered to the bottom. The test sand is poured into the small compartment of the device to the top (Figure 2.4). After that, the sliding sash is gradually raised without jolting; while holding the device with your hand. The soil is gradually partially poured into the other compartment until the equilibrium position is reached.
Rice. 2.4. General view of the device for determining the angle of repose of sands (Pendant's Box).
The angle between the plane of the free slope and the horizontal plane is the angle of the repose. By divisions on the bottom and side wall, the height and location of the slope are counted and the tangent of the angle of repose is calculated; readings are accurate to 1mm.
The determination of the angle of repose of the soil in the underwater state differs from the previous one in that after the test soil is poured into the small compartment of the device, water is poured into the large compartment to the top. The top flap is raised a few millimeters so that water can enter the small compartment. When all the soil is saturated with water, the sash is raised higher and the test is continued in the same way as the previous one. The test results are recorded in table 2.4.
When building foundations or laying communications in the ground, it is required to dig pits and trenches. Excavation works are necessarily accompanied by safety measures. They define the rules for securing the sides and bottom. To determine the angle of the pit slope, a table is used. Its application allows for the soil at the construction site to select the desired level of inclination of the walls of the dug recess to its bottom, so that collapse does not occur.
Types of earth structures
The construction of buildings and communication structures is associated with labor-intensive earthworks. They mean the development of soil when digging pits and trenches, its transportation, storage.
Earthen structures are embankments, excavations. They can be of a permanent type or temporary. The first ones are made for long-term operation. These include:
- channels;
- dams;
- reservoirs;
- dams and other structures.
Temporary excavations are trenches and pits. They are intended for subsequent construction work.
A pit is a recess, the width and length of which practically do not differ noticeably in size. They are necessary for the construction of foundations for buildings.
The trench, on the other hand, is a long furrow in comparison with its cross-section. It is intended for the installation of communication systems.
According to the requirements of GOST 23407-78, digging of pits, trenches in settlements, places of traffic, or people, must be accompanied by the creation of protective fences. They are installed along the perimeter of the working area. Warning signs and inscriptions are placed on them, and even signal lighting is used at night. Also specially equipped bridges for the movement of people.
Slopes are sloped sidewalls of cut or fill. An important characteristic is their slope (steepness). The horizontal surfaces surrounding the slopes are called berms.
The bottom of a recess is understood to mean its lower, flat part. The brow is the top edge of the created slope and the sole is the bottom.
When operating earthen structures, they should not:
- change their outlines and linear dimensions;
- sink down;
- be washed away by water or succumb to the action of precipitation.
The laying of water pipelines, underground power lines, sewerage systems, the construction of foundations for buildings cannot do without digging trenches or foundation pits. In construction, special definitions have been adopted to designate structural elements of this type. All work must be carried out in strict compliance with safety rules in order to minimize the possibility of accidents.
Varieties of foundation pits
Digging recesses for the base of a structure is a responsible business that requires a lot of time, money, and labor. It is customary to divide pits today according to the following criteria:
- the presence of slopes;
- the use of fasteners designed to prevent soil crumbling;
- type of side surfaces (walls).
The walls of the pits can be:
- vertical;
- inclined;
- stepped.
In order to carry out excavation work correctly, first conduct research on the construction site. These activities include the following operations:
- analysis of soil properties: establishing its group and type;
- determination of loads from the building being erected;
- calculating the depth of the excavation;
- establishing the presence of old communications;
- determination of the depth of groundwater;
- analysis of weather conditions of the area.
The choice of the method of carrying out the work is determined depending on the following factors:
- the type and dimensions of the structure being built;
- the depth of the foundation;
- the volume of upcoming activities.
If it is planned to build a shallow base of a tape or columnar type, then the soil can be developed without involving equipment, manually. When it is necessary to build a house with a basement, or a basement, then earth-moving mechanisms will need to be involved in the work.
To extract the bulk of the soil from the excavation, excavators of various types are often used, equipped with a backward or forward shovel. Work associated with digging a foundation pit should be performed without disturbing the density of the soil at the bottom of the foundation. This requirement is implemented in practice through its shortage, the value of which ranges from 5 to 20 cm.
Workers manually clean the ground from the sides and from the bottom of the excavation to the planned mark. In this case, it is imperative to monitor the strengthening of its walls with the help of slopes, or by installing special structures. The fallout of precipitation and the rise of groundwater in spring and summer, the impact of frost in winter - all this contributes to the destruction of the foundation pit.
The soil from the pit must be immediately removed or placed on the construction site no closer than 1 m from its edge. A drainage system is created to drain soil water.
An important point when digging pits is the creation of a working space of the sizes required according to the rules. It should take at least half a meter from the foundation formwork to the bottom of the slope. The steepness of the pit slopes is selected according to the tables or graphs given in SNiP 3.02.01-87.
Types and purpose of trenches
Trenching for various communications is the most common type of excavation. Digging them by hand is slow and expensive, so they often use equipment that is bought or rented.
According to the purpose, excavations of this type are divided into the following types:
- for grounding;
- plumbing;
- cable;
- gas pipelines;
- drainage (drainage);
- sewer.
By design, trenches are of 3 types:
- rectangular;
- trapezoidal;
- mixed.
Spacers are installed inside trenches without sidewall slopes to increase the level of safety for people. Strengthening the slopes is not required, because they are done in order to protect against landslides. Trenches designed for laying communications are dug at various depths using different techniques.
Soil: groups and types
Due to the fact that earthen structures are created in soils, it is imperative to know their main characteristics. The suitable type of foundation directly depends on them. The choice is made taking into account the achievement of the highest possible level of reliability and durability of the base being erected.
The main properties of the soil are determined by the following factors:
- shape, size, strength, arrangement of particles that make up its composition;
- the degree of relationship between them;
- the ability of the constituent substances to solubility, moisture absorption.
The soil is characterized using the following coefficients:
- compressibility;
- friction;
- plasticity;
- loosening.
The classification provides for the division of soils according to various criteria. There are the following types:
- sandy;
- dusty;
- clayey;
- rocky;
- clastic.
Depending on the water content, soil is distinguished:
- dry (up to 5% moisture present);
- wet (5-30%);
- wet (contains more than 30% water).
The division into groups is presented in the table below.
| Category | Incoming soil varieties |
|---|---|
| 1 | sandy loam, sand, light loam (wet), peat, soil of the vegetation layer |
| 2 | light wet clay, fine and medium gravel, loam |
| 3 | dense loam, medium and heavy (loosened) clay |
| 4 | frozen soils (clay, loamy, peat, sandy, sandy loam, vegetation layer), heavy clay |
| 5 | fragile limestone and sandstone, strong clay shale, permafrost (with admixtures of crushed stone, pebbles, boulders, gravel up to 10%), moraine and river (with a content of large boulders and pebbles up to 30%) |
| 6 | strong shale, clayey sandstone, marly limestone, fragile serpentine and dolomite, river and moraine (inclusions of boulders and pebbles - up to 50%), permafrost (with a fraction of gravel, boulders, pebbles, crushed stone - up to 20%) |
| 7 | hard limestone and sandstone, dolomite, serpentine, mica and silicified shale, marble, permafrost (stone components account for up to 70% of the volume) |
Also, soils are divided into the following types:
- quicksand;
- soft;
- medium;
- strong.
The structure and properties of the soil on the building site play a major role in the calculations during the design of the foundation. This is due to the fact that depending on the type of soil, its bearing capacity is located. Also, each species reacts differently to weather conditions.
Earthwork plan, requirements for them
Excavation works in a number of stages. They are spelled out in SNiP 3.02.01-87. The main stages of the process are as follows:
- implementation of preparatory activities;
- experimental and production part;
- creation of a pit or trench;
- control activities;
- acceptance of work performed.
SNiP 3.02.01-87 provides for the following requirements:
- to develop a working project is allowed only by specialists who have the necessary qualifications and experience;
- communication and coordination of actions in matters of design, construction, engineering solutions should be ensured between them;
- it is constantly necessary to control the quality of construction work on the site;
- the project must be carried out by appropriately qualified personnel;
- the erected structure is allowed to be used only for its intended purpose in accordance with the project;
- measures for the maintenance of the structure and associated engineering communications must maintain it in a safe, working condition during the entire operation.
When digging pits and trenches, you must adhere to the instructions:
- rules for organizing their construction;
- norms for conducting geodetic works;
- labor protection standards;
- sections of the fire safety rules relating to the conduct of construction work.
Earthen structures must be created strictly according to the current project.
Conducting work with an explosive sweep requires compliance with the relevant safety rules during their production.
The materials, structures, products used in the work must meet the requirements of the standards and the project. Their replacement is allowed only after preliminary agreement with the organization that developed the documentation, the customer.
There are the following types of control during excavation work:
- input;
- operating;
- acceptance.
Control is carried out in accordance with SP 48.13330.
Acceptance of works takes place with the registration of the necessary documentation (acts) confirming their implementation.
The considered requirements in individual construction are greatly simplified. Small buildings are often erected without any projects, and the depth of the excavations does not exceed 1.5-2 m, but safety precautions must always be observed.
Safety measures when digging pits
The soil from the side walls of the pit or trench, as a result of the action of gravity on them, can move and fill the bottom of the excavation. Accidents with people are possible due to uncontrolled collapse of earth masses. Also, destruction leads to an increase in labor costs and funds: it will be necessary to restore the planned contour of the excavation, to backfill the base with a large volume of soil.
To prevent shedding and reduce the possibility of material losses to a minimum, it is necessary to correctly calculate, at the design stage, according to SNiP 111-4-80, the steepness of the slopes of the excavation being created.
If the depth of a trench or foundation pit, on average, exceeds 1.25 meters, then it is necessary to strengthen their walls in order to prevent possible collapses and earth slides. Along the contour of the dug structures, strips should remain free from the excavated soil mass, the minimum width of which is more than 0.6 m. The earth from the excavation should not roll back.
The parameters of the side slopes before excavating the excavation must be determined correctly. This will allow:
- prevent the possibility of collapse;
- perform the optimal amount of earthwork;
- will save you from the cost of reworking slopes during construction work.
Landslide prevention is a major safety concern for personnel.
Correspondence of slopes to optimal slope angles for a given type of soil minimizes money and labor costs for backfilling and reworking.
Before starting work, geological and hydrological surveys of the building site are carried out. In the presence of soil water, unstable soils, or if it is necessary to dig an excavation more than 5 m deep, a project is created for the identified individual conditions.
According to SNiP 111-4-80, for non-wet soils with a uniform structure, it is possible to leave vertical side walls when digging trenches or pits. At the same time, there should be no structures near the excavations and groundwater. The permissible excavation depth for different soils with vertical walls is for:
- gravel, sand - 1 m;
- sandy loam - 1.25 m;
- clay and loamy - no more than 1.5 m;
- very dense - 2 m.
In pits with a depth of about 1.25 m, it is required to use ladders that will rise above the ground to a height of at least 1 m. In deeper recesses, stair flights are used.
The side surfaces of the pits are allowed to be strengthened with edging. In case of the possibility of additional loads, or wash-out of slopes, they are covered with a film or shotcrete (concreting with a thin layer) is carried out.
Slope table
When you need to dig a hole from 1.5 m deep, then you should take the angle of the pit slope according to the table given in SNiP 111-4-80. It takes into account both the type of soil and the depth of the foundation.
In the construction literature, regulations, rules, the steepness of the slope of the excavation is measured in degrees (angle), or the ratio of its height to the position.
A table of the steepness of the slopes for pits of different depths and on different types of soil is presented below.
Despite the presence of slopes, there is a possibility that the ground mass will collapse under the influence of the weight of the equipment involved. Therefore, the distance from the parking of cars to their soles is also regulated by SNiP.
When different types of soil are present on the construction site, then the steepness of the slopes is chosen according to its most unstable variety.
Existing inclusions of boulders, stones are recommended to be removed using an excavator to prevent the possibility of landslides, collapses.
The walls of the recesses up to 3 m deep are fixed in accordance with the design guidelines.
If the soil connectivity changes for the worse in the working area when water gets into it, during drying, under the influence of low temperatures, then it is recommended to equip slopes of less steepness, or with indents.
When the side surfaces of pits up to 3 m deep with steps are formed, the width of the latter should be at least 1.5 m. In this case, the slopes should also be made.
If the design depth of the excavation exceeds 5 m, or the slope of the pit wall differs from the table value, then the stability of the slopes must be calculated.
Pits, or trenches dug in autumn or winter frosts, must be examined during the spring thaws and the stability of their slopes is determined.
With the slope angles considered in the table for each type of soil and the depth of the excavation, workers can be in the excavation without the need to fix the slopes. If the slopes have been moistened, then before starting work, they are inspected for cracks, delamination.
Excavation methods, used mechanisms
Depending on the soil, different techniques are used in the works on the arrangement of trenches and pits, different methods of development of plots for construction are used. They differ in labor intensity and the level of required material costs. According to SNiP 111-4-80, the following methods are distinguished:
- hydromechanical;
- mechanical;
- blasting operations.
The mechanical method of excavating pits and trenches is the main one. Its essence lies in digging soil using earth-moving (excavators) machines, or earth-moving transport (scrapers, bulldozers, graders).
The hydromechanical method is based on the erosion of the soil mass by a jet of water from a water jet. Then there is a suction of the resulting solution by a dredger.
Blasting works are mainly used in suburban construction. Holes (wells) are drilled in the ground. Then explosives are placed in them and detonated. The resulting loose mass is removed with the help of technology.
The mechanical method consists of a number of stages:
- loosening the soil;
- development of rock mass;
- its transportation;
- leveling, compaction of side slopes and the bottom.
Hydromechanical excavation works are carried out in the following sequence:
- designate the area of the working area with the help of fences, inscriptions, warning signs;
- according to the standards, a hydromonitor is installed, manually controlled by the operator: the distance from its nozzle to the wall of the excavation should be at least the height of the excavation, and to the nearest air power line - at least two gaps to which the water jet can be supplied by this technique;
- behind the security perimeter of power transmission lines, slurry pipelines, water conduits are placed;
- protect the places of dumps of reclaimed earth mass;
- erosion and excavation are performed.
Do not operate the jet monitor during a thunderstorm.
Blasting operations are regulated by the relevant rules.
When the mechanical loosening of the earth mass is carried out by the shock method, then the workers should not be within a radius of 5 m from the place of loosening.
Any equipment must be positioned during work in accordance with applicable standards and rules. Departure from them often causes accidents.
Soil consolidation technologies
Depending on the geological characteristics of the construction site and the climatic features of the terrain, the depth of excavation, the characteristics of the constructed or reconstructed building, various methods of soil consolidation are used in practice. Technology can improve them in terms of resistance to destruction. SNiP111-4-80 identifies the following fixing methods:
- thermal;
- cement;
- using cement mortar.
Various types of mechanical fasteners are often used. By design, the following types are distinguished:
- braced;
- cantilever-spacer;
- spacer;
- cantilever-anchor;
- console.
The choice of the type of fastening is made on the basis of the above factors that affect the correct performance of the work.
According to the design and the possibility of quick installation and dismantling, the following types of fasteners are distinguished:
- stationary;
- inventory;
- at intervals;
- solid.
The upper part of the fasteners after their installation should rise above the edge of the pit or trench by more than 0.15 m. In this case, the installation itself is performed from top to bottom during excavation of earth masses, and disassembly in the opposite direction when backfilling.
The spacer type of fasteners is most widespread. This option is used if the depth of the trench does not exceed 3 m.The structure consists of the following elements:
- shields;
- screw spacers or frames;
- racks.
Fastening of the side surfaces of the trenches is carried out immediately after their fragments.
On weak, wet soils, cantilever-spacer or cantilever types of fasteners are used. In this case, the depth of the grooves should be within 3 m.
A variety of cantilever fasteners are tongue-and-groove. They fix the walls of deep pits, where there is a lot of pressure from the sides and difficult hydrogeological conditions.
Sash barriers are rarely used, because they make it difficult to carry out work.
The fixing method is determined by the project documentation. If you need these measures during individual development, you can rent various fasteners, or make metal or wooden counterparts of factory products yourself. Determining the choice in favor of one or another option of fasteners is required depending on the conditions at the construction site.
The videos below show the different ways of fixing the soil of the slopes of the excavation.
The process of forming a slope with an excavator is demonstrated in the following videos.
Giving stability to the side surfaces of the pits is the first requirement that is presented when creating them. In order to ensure safe working conditions, prevent debris and comply with construction technology, excavations are erected with slopes of the required steepness.
If the depth of the pit does not exceed 1 m, then on any type of soil, the slope on the side surfaces is not made, and for hard rocks, vertical walls of the excavation are left even at depths of up to 2 m.The slopes of the pits are formed according to the SNiP tables, if the depth is up to 5 m.After exceeding this value - perform special calculations.
Grading. In practice, the nature and quality of rock destruction is clearly determined by its granulometric composition. It characterizes the loosened rock in terms of the percentage of particles of various sizes in it and can be depicted by a curve (Fig.2.1) if the diameter of the particles, mm, is plotted along the abscissa axis, and the total content of particles with a diameter smaller than that given, in percent, on the ordinate axis.
To characterize the heterogeneity of loose rocks, the ratio d60 / d10 = Kн is used, called the coefficient of heterogeneity (d60, d10 are the maximum diameters of pieces, making up 60 and 10% of the total volume of loose rock, respectively).
Particularly important is the granulometric composition of the rock in the processes of hydromechanization. The specific water consumption for development and transportation, the smallest permissible slope of the bottom of the face and trays, and the critical water velocity depend on it.
The angle of repose φ is the maximum angle formed by the free surface of loose crushed rock with a horizontal plane. The rock particles located on this surface experience a state of ultimate equilibrium. If the weight of the particle is P (Fig. 2.2), then in the state of limiting equilibrium on the free surface the following forces act on the particle: Pn is the force of normal pressure, which presses the particle to the free surface; Рτ - force tending to move the particle down; Ft is the friction force depending on Pn and the friction coefficient ffr, R is the support reaction. Since the particle is in equilibrium, we have
i.e.
Thus, the angle of repose depends on the coefficient of friction between the rock pieces and the surface on which it can slide. For a loose (free-flowing) medium, such as sand, it can be determined using a cylindrical container without a bottom. The container is installed on a horizontal platform and filled with rock. Then the container is raised and the rock forms a free surface corresponding to the angle of repose.
In the general case, the angle of repose depends on the roughness of the grains, the degree of their moisture, particle size distribution and shape, as well as on the density of the material. With an increase in moisture to a certain limit in rocks such as coal or sand, the angle of repose increases. With an increase in the size and angularity of particles, it also increases. In general, in loose rocks, it is in the range of 0-40 °.
At the angles of the natural slope, the maximum permissible angles of the slopes of ledges and sides of open pits, embankments, dumps and stacks are determined.
