Soil sampling for laboratory research. Guidelines for the selection of soil samples for laboratory analysis and testing during detailed technical surveys of highways

GOST 12071-2014 "Soils. Selection, packaging, transportation and storage of samples"

4.1 General

1. Soil sampling and the volume of samples of disturbed or natural composition (monoliths) is carried out to describe soils and determine their properties in laboratory conditions in accordance with GOST 5180, GOST 12248, GOST 12536, GOST 22733, GOST 23161, GOST 23740, GOST 24143, GOST 26263, GOST 30416.
2. Soil samples are taken from cleaned faces and walls of mine workings (pits, pits, boreholes, etc.), natural and artificial outcrops and the bottom of water areas.
3. To determine the full range of physical and mechanical properties of soils, the sample should consist of one or more monoliths, depending on the composition of the planned laboratory work.
4. Monoliths should be oriented immediately after selection (mark the top of the monolith).

1. For the selection of monoliths from open mine workings, a shovel, knife, cutting rings and soil carriers of various types are used.

1. To isolate the monoliths of thawed soils, paraffin of the oil grade HB 56-58 according to GOST 23683 with the addition of 35% - 50% (by weight) of tar, gauze, insulating tape, and also ceresin according to GOST 2488 is used.

Number of soil monoliths for laboratory testing

OSN APK 2.10.01.001-04 "Design of shallow foundations
low-rise rural buildings on heaving soils"

Chapter 4

1. When conducting engineering and geological surveys at the site of the planned construction, soil sampling for laboratory testing should be carried out every 25 cm along the depth of workings in the seasonal freezing layer.
   The normative freezing depth d fh is determined according to the instructions of SNiP 2.02.01-83 *.
   If groundwater is detected in the surveyed area, the depth of the workings should be increased in accordance with the data in Table. 2, characterizing the minimum distance Z between the standard freezing depth d fh and the depth of groundwater d w .

table 2

Soil sampling from pits for laboratory testing

Instructions for field documentation of engineering and geological
and exploration work during surveys highways

When taking soil samples, the requirements of GOST 12071-60 should be taken into account.
Soil sampling from the pits is carried out in layers. If the layer thickness is more than 1 meter, it can be characterized by several samples.
Samples with a disturbed structure are taken in a depth interval of 10 cm.
For example, the sample was taken from a depth of 1.10-1.20 m.
Your sample should be about 500 grams, in the case of fine soils, and if necessary, sampling for standard compaction (for example, for excavation soils) - 3-3.5 kg.
The selection of samples of coarse soils is carried out by the furrow method. The selected samples are subjected to screening to separate into fractions. Pieces larger than 100 mm should be selected manually. From fine fractions of soils that have passed through a sieve of 20 mm, an average sample weighing 3 kg is taken by quartering for testing in the laboratory.
Sampling of soils with an undisturbed structure (monoliths) is carried out in two ways:

1. with cutting rings. This method is used in cases where it is not necessary to determine the compression properties of the soil, but only the coefficient of porosity of the soil is required to be determined. The cutting rings are made of metal and have walls no more than 2 mm thick.
   At one end, the ring is pointed due to the outer diameter, and a cover with a small hole for air to escape is put on the other.
   The inner diameter of the cutting rings must be at least 10 mm. The height of the ring should not exceed the diameter.
   Rings of smaller diameter are used when taking monoliths of clay and loamy soils, larger ones - sandy and sandy soils.
   Before taking the monolith, the wall of the pit is leveled and cleaned; the ring at a given depth is leaned closely with a sharp end against the wall of the pit and pressed into the ground until the cover sinks a little into the ground.
   After that, the ring with soil is carefully removed with a soil knife, the cover is removed, excess soil is cut flush with the edges of the ring, and the ring with soil is weighed, after wiping it from the outside of the adhering soil, on technical or pharmaceutical scales with an accuracy of 0.1 gram. Subtracting the weight of the ring from the weight of the ring with soil, determine the weight of the soil; by dividing the weight of the soil by the volume of the ring, the volumetric weight of the soil is obtained.
   Weighing is carried out three times.
   At the same time, a soil sample is taken from the same depth to determine the natural moisture content and a soil sample of a disturbed structure weighing 0.5 kg to determine specific gravity soil, granulometric composition, plasticity.


2. In cases where it is necessary to determine the compressive properties of the soil, the angle of internal friction, cohesion, tensile strength, etc., in a sample with an undisturbed structure, a monolith is selected in the form of a cube or parallelepiped with side dimensions for rocky soils of at least 100 × 100 × 100 mm , for coarse fragments cemented by permafrost, gruss and gravel 200 × 200 × 200 mm crushed stone and pebble - 300 × 300 × 300 mm, sandy cemented by permafrost and clay 200 × 200 × 200 mm.
   In the event of difficulties, it is allowed to take samples of arbitrary shape while maintaining the indicated dimensions of the sides as minimal.
   The wall of the pit is leveled, cleaned and, at a given depth, a square slightly larger than the required size is marked with a soil knife. As it deepens into the wall of the pit, the sample is gradually given the correct shape and the required size.
   To avoid drying, the monolith taken here at the pit is waxed and carefully packed according to the rules set forth in GOST 12071-66.

Description of pits

Methodical manual for laboratory work on soil mechanics for students of the specialty 270105 "Urban construction and economy" of all forms of education

Compiled by V.P. Tkachenko, M.G. Onoprienko, N.A. Ivanenko

Reviewer: Professor, Honored Worker of Science of Kuban E.N. Peresypkin

Sochi – RIO SSU 2014

Introduction

For the design of foundations and foundations of buildings and structures, it is necessary to determine the physical and mechanical properties of soils and the conditions for their occurrence. They are determined in the process of engineering and geological surveys using field and laboratory research methods. Laboratory methods studies make it possible to determine the physical and mechanical properties of soils taken in the form of samples and monoliths in the process of performing engineering and geological surveys. The accuracy of the obtained values ​​depends on the accuracy of calculations, reliability and technical and economic indicators of the construction and operation of structures.

Guidelines introduce students to the basic methods and techniques for performing laboratory soil analyzes within the approved training programs. Before starting the laboratory work, the student must first work out the relevant theoretical material, familiarize himself with these guidelines, and then complete the work in the educational laboratory. At the end of the next lesson, the student must draw up a laboratory journal and show it to the teacher. The journal contains the necessary calculation equations and graphical results of the experiment. At the end of the lesson, the student must put his workplace and hand it over to the lab.

Soil sampling for laboratory work.

Selection, packaging, transportation and storage of soil samples for laboratory research is carried out in accordance with GOST 12071 - 72.

Soil samples are taken undisturbed (monoliths) or disturbed in addition from cleaned faces, walls of mine workings (clearings, pits, pipes, pits, etc.) and boreholes. Their number, type, size are determined by the research program, and can be specified during laboratory work. The number and type of samples should be sufficient for laboratory studies and control determinations. Monoliths from pits, pits, as a rule, are taken in a prismatic shape, and from wells with soil carriers - a cylindrical shape. A monolith that does not retain its shape without a rigid container is selected by the cutting ring method according to GOST 5182-78. The inner diameter of the cutting ring when selecting monoliths of large-block soil must be at least 200 mm and at least 90 mm for other types of soil. The ring height must be at least one and no more than two ring diameters.

Selection of monoliths of non-frozen sandy and clayey soils is carried out from wells in the process of drilling without the use of flushing fluid with overlapping of water-saturated layers with casing pipes.

After selecting the monoliths, they immediately begin to isolate them from the outside air by wrapping them with gauze soaked in paraffin. A label wrapped in tracing paper and soaked in paraffin lies on the upper face of the monolith. The monolith to the gauze is lowered into molten paraffin, removed from it, and then covered with a second layer of gauze and waxed again. The waxed monolith is covered with a second label, which is covered with a thin layer of paraffin, which ensures the reading of the inscription on the label. 35-50% (by weight) of tar is added to the paraffin used for isolation of monoliths in order to increase its plasticity.

The label of the monolith indicates the organization that performs the survey, the name of the object, its location, the name and number of the working, the number of the monolith, the depth of sampling, the name of the soil by visual determination, the position and surname of the person who conducted the sampling of the monolith, his signature and date of sampling. Labels are filled with a simple graphite pencil.

Soil samples intended for transportation are packed in boxes with free space filled with sawdust, shavings, and other materials with similar properties. Under the top cover of the box lies a list of samples wrapped in tracing paper with the information indicated on the labels. The boxes are numbered, provided with the inscriptions "Top", "Do not turn over", "Do not throw", the addresses of the recipient and sender.

During transportation, soil monoliths should not be subjected to sharp dynamic and temperature effects. Prior to analysis, they are stored in rooms with a relative humidity of 50 - 60% at a temperature of 2 - 20 0 C. Frozen soil monoliths are stored in chambers with a relative humidity of 80 - 90% at a negative temperature. The shelf life of monoliths is 1.5 - 3 months, depending on the condition and type of soil.

Soil monoliths with damage to the waterproofing layer, defects in packaging and storage are prohibited from accepting for laboratory testing. They are used as soil samples with a disturbed structure.

The physical state of the soil is established by the following defining characteristics: natural density, particle density, moisture, granulometric composition. The strength of soils is evaluated according to certain characteristics of soil resistance to compression and shear. The filtration properties of soils are characterized by certain values ​​of their permeability.

The calculated characteristics of the soil include:

· Porosity coefficient;

· Porosity;

Degree of humidity;

· Fluidity index;

plasticity number;

· Coefficient of heterogeneity of sandy soil.

In accordance with the determined and calculated characteristics of soils according to SNiP 2.02.01 - 82, they are classified by type, type and condition. Soil characteristics are used in calculations to determine bearing capacity, strength and settlement of structures foundations, slope stability, pressure on building envelopes, etc.

Soil sampling is carried out in conjunction with engineering and geological surveys. Under the soil in construction is understood the upper layer of the lithosphere, which includes rocky, as well as semi-rocky and loose rocks.

Purpose of sampling

The main purposes of soil sampling include:

• classification of soil rocks and determination of the composition of the section (or sedimentary layers and layers);
• identification of the optimal value of slopes during earthworks;
• description of the characteristics, properties of the soil and its components in terms of the possibility of their use as building materials;
• establishing the physical and mechanical characteristics of the soil to determine its bearing capacity (the so-called soil sample for the foundation).

Soil sampling methods

The methods used to take soil samples depend on the type of soil being examined. Soils are selected from:

• broken structure;
• with undisturbed or monolithic structure.

When sampling loose rocks, for example, sandy ones, samples of a disturbed structure can be taken, and for the study of cohesive rocks, such as loose soils, clay, etc., it is necessary to take undisturbed, i.e. monolithic structure. For such samples it is required to drill wells. Any drilling method allows obtaining a high-quality sample with an undisturbed structure and ensuring compliance with the properties of the layers from which soil samples are taken.

Selection methods are varied, among them:

• point method for taking small soil samples;
• furrow, based on plowing furrows along the entire length of the reservoir;
• gross, which allows using the entire worked-out soil for analysis.

How to take samples correctly?

When selecting soils, you should:

• completely eliminate the ingress of accidental inclusions;
• ensure that the soil sample matches the soil layer of the sampling site;
• do not smoke during sampling;

As a rule, when sampling, a log is kept, in which marks are made about the place, time of sampling and compiled relevant act. With regard to the volume of the sample taken, it should ensure the possibility of all planned studies. For soils of a disturbed structure, this value is at least 2000 cm², and for monoliths it is more than 500 cm².

Soil samples, depending on the need for certain determinations, are taken in glass (plastic) containers or plastic bags.

A necessary condition for soil sampling is their protection from secondary pollution (including precipitation) at all stages of sampling.

For soil sampling, it is necessary to use equipment made of metal (stainless steel), ceramics, plastics, etc. All work surfaces must be thoroughly cleaned of dirt and free of signs of corrosion and rust.

Conducting laboratory studies of soils is a labor-intensive process that requires a professional approach already at the sampling stage. GC "Specialist" is ready to provide its customers with such an approach: having worked in the field of subsoil use for many years, we know all the nuances of laboratory testing.

Depending on the tasks set for laboratory studies, samples are taken with a disturbed or undisturbed (monoliths) structure. To do this, use one of the following methods:

• point (one or more samples are taken from the whole mineral layer);
• furrow (furrows are located along the reservoir and selections are already made from them);
• gross (examine the entire soil from the working).

In the case when the selection of monoliths is not possible (the soil is loose or sandy), field tests are carried out to determine the natural density of the rock.

Basic Sampling Rules

Highly qualified specialists of our company follow all the necessary rules when taking samples for laboratory research:

1. The sample must have all specific traits layer from which it is taken, and do not contain impurities.
2. Sample packaging is carried out immediately, each sample is marked in accordance with accepted standards, recorded in a log and marked on a map, plan or sketch of the site.
3. Immediately after packaging, the sample, without violating its safety, is sent to a laboratory or storage place with appropriate conditions.

The basic rule of sampling, which is strictly observed by the employees of the Specialist Group of Companies, is that they should be enough to study all the necessary characteristics of the soil and conduct tests. For rocky and coarse-grained rocks, at least 2000 square meters are selected. cm, for sandy - 1000 sq. cm and for clay - 500 sq. cm.

Monoliths in the form of a prism or a cylinder selected from wells are cleaned and preserved in one of two ways:

• waxing ("soldering" in three layers of paraffin, separated by gauze);
• rigid packaging.

When packing a monolith in one of the above ways, it is worth noting the top of the sample and orientation to the cardinal points. Transportation is carried out in wooden boxes with sawdust or shavings between the samples, which will avoid damage. The selection, transportation and storage of rock samples in our company is carried out in accordance with GOST 12071 - 72.

The urgency in this case is due to the need to preserve the structure of the soil and its natural moisture content. In addition, when transporting thawed rocks, it must be taken into account that freezing will change the structure of the soil. The same will happen with thawed frozen soil. All these details can seriously affect the results of soil laboratory tests, and as a result, lead to incorrect conclusions. Our geologists will not tolerate a violation of the procedure, so we can vouch for the reliability of the results of our tests.

Sampling Rules

For laboratory studies of the physical and mechanical properties of soils, samples are taken with a disturbed or undisturbed (monoliths) structure. The type of sample depends on the purpose of the study of the rock and its condition, and the method of sampling depends on the type of exploration working from which the sample is taken. In engineering and geological surveys, three sampling methods are used: point, furrow and gross. The point method consists in the fact that the rock layer is characterized by one or more samples of relatively small size. With the furrow method, furrows are made across the entire tested formation across its strike, from which soil is taken for sampling. Gross method consists in the study of all the soil extracted from the development. The last two methods are commonly used in the exploration of building materials.

The physical and mechanical properties of soils during engineering and geological surveys are investigated for the following purposes:

• · classification of rocks and selection of lithological layers, layers and other elements of the geological section;
• · determination of the design characteristics of the physical and mechanical properties of soils that form the basis of the design structures, natural and artificial slopes;
• Determination of the characteristics of soils intended for use as building materials.

Monoliths are selected to determine the calculated characteristics of the physical and mechanical properties of cohesive rocks. For loose sandy rocks, monoliths can be replaced by samples with a disturbed structure, but in this case, it is necessary to determine the density of soils in their natural occurrence by field methods.

When sampling, the following basic rules must be observed:

• · the sample should be characteristic of the layer from which it was taken, and should not contain random inclusions and contaminants;
• Each sample must be immediately packaged, labeled according to prescribed form, entered in the exploration working log and marked with a sketch of the working;
• · After packaging and registration, the sample should be immediately sent to the field laboratory or to an appropriate storage location.

The volume of samples taken should be sufficient to perform all determinations. The volume of samples with a disturbed structure for rocky and coarse fragments should be at least 2000 cm 2, for sandy - at least 1000 cm 2, for clay - at least 500 cm 2.

Monoliths taken from mine workings may have the shape of a cube or a cylinder (taken from boreholes).

Preservation of monoliths.

After being removed from the soil carrier, the monolith is cleaned of sludge and immediately preserved to preserve the structure and natural soil moisture. There are two methods of preservation: waxing and packaging in rigid containers. When packing a monolith, its top should be noted and, if necessary, an orientation to the cardinal points should be given.

A monolith taken from a rigid container is covered with a layer of tightly wrapped gauze pre-impregnated with molten paraffin. Then, over the gauze, it is covered with another layer of paraffin, wrapped again with gauze and covered with a third layer of paraffin. Before waxing, a label wrapped in tracing paper is placed on the upper face of the sample, which is also covered with paraffin. The second copy of the label is moistened with molten paraffin, attached to the surface of the waxed sample and also covered with a thin layer of paraffin.

Soil monoliths taken into a rigid container (cage) or specially made metal or wooden boxes are packed in the same container. A label is placed on the upper face of the sample between the rubber and the lid, and the second label is attached to the surface of the rigid container.

For waxing monoliths, a mixture is used, consisting of two parts of paraffin and one part of tar, which is heated to a temperature of 60-65 degrees. It is necessary to transport monoliths in wooden boxes. In order to avoid damage to the packaging, the gaps between the monoliths are covered with sawdust. Samples of thawed rocks must be protected from freezing, and frozen ones from thawing, since in this case they lose their structure.