Children often break toys, disassembling them into their component parts in order to find out how they work. So geological engineers “take apart” selected rock and water samples into parts to find out what they are made of. Soil sampling is carried out while drilling a well or digging a hole. The monoliths are carefully removed and carefully packaged. As a result of the compression test, or shear resistance test, the sample breaks, but we obtain the necessary information.
In the laboratory, the selected samples are dried, weighed, and crushed. The granulometric composition is determined. Organic content is determined. They press, they cut.
Water samples are taken from wells and watercourses. The selected water is divided into portions to determine the content of various components. In conventional chemical analysis, the content of bicarbonates, chlorine, calcium, magnesium and some other components is determined. The water is given a name and classified according to its aggressive properties.
What do laboratory determinations provide?
Indicators of aggressive water qualities make it possible to prepare in advance for the fact that seasonal changes in groundwater levels will adversely affect the condition of concrete structures located in the area of its influence. You can take a more durable brand of concrete for such structures.
The deformation and strength characteristics of the soil, determined either in the laboratory or using tables (based on physical and mechanical properties established in the same laboratory), make it possible to calculate strong, reliable foundations.
Why and in what volumes are soil and water samples taken?
Soil samples, depending on the purposes for which they are taken, are taken at different depths. Thus, specimens of the damaged structure, selected to determine the corrosive activity of soils in relation to the lead sheath of the cable, are taken at the cable depth specified in the technical specifications. To carry out this experiment, a large amount of soil is required, so two or three standard sampling bags are taken in one place (from the same depth).
To determine the granulometric composition, one bag at a time is taken from the sand thickness in the right places (when changing the grain composition, for testing a layer, etc.). If it is necessary to determine the moisture content of sand, a small sample (1 bottle) should be hermetically sealed.
Water samples are collected in well-closed containers.
How are selected samples identified?
Each soil and water sample is signed. The label accompanying the sample must state the following:
- object cipher;
- well number;
- sampling depth;
- name of the soil;
- test date;
- geologist's signature.
The field journal must indicate the location where the sample was taken.
The collected water and soil samples are delivered to the laboratory. The geologist, in office conditions, prepares an assignment for the laboratory, indicating in the statement the place where the sample was taken, its size and the definitions that he needs.
Every year the level of soil pollution is increasing. This occurs due to the deposition of emissions from operating industrial enterprises and the accumulation of radionuclides. The reason is also the presence of pathogenic microorganisms in the soil and acidification as a result of excessive application of mineral fertilizers. That is why soil sampling is more relevant now than ever. It is necessary to monitor pollution levels.
Selected samples undergo laboratory analysis to assess the quantitative and qualitative composition of the soil according to the following indicators:
- pH level (acid-base balance);
- chlorides;
- pesticides;
- ammonium nitrogen ((NH4)+);
- ratio of protein to organic nitrogen;
- sulfur compounds;
- heavy metals;
- cyanide and arsenic;
- oil and petroleum products;
- phenols;
- carcinogenic and radioactive substances;
- anionic and cationic detergents.
Depending on what type of research will be carried out, soil samples are taken at varying intervals.
Selection of territory and location of sampling sites
A group of people goes to the selection site, and based on the results of their work, a passport is drawn up for the plot of land under study. The passport contains the following information:
- departure date, address and area of the site;
- the nature of the terrain and the names of the soils present;
- presence of plants, groundwater level, parent and underlying rock, as well as visible indicators of salinity and waterlogging;
- results of analysis of the soil horizon by color, humidity, composition and structure, composition, density, presence of inclusions, nature of the horizon transition;
- data characterizing the source of pollutants: scope of production, quantity of products produced, volume of emitted gas, liquid and solid substances, distance to nearby residential buildings, organizations and water intake sites.
When collecting soil samples near manufacturing plants, various meteorological data must be taken into account. This applies primarily to the strength and direction of the winds characteristic of the study area. The distribution of pollutants depends on these indicators.
Soil sampling terms
Based on the data from the passport, a plan or map is developed, on which the source of pollution, probable sample sites and marks for taking point soil samples are plotted. Test sites are marked on a coordinate grid. The uniformity of the distribution of pollutants determines the distance between the grid lines. If some areas are unevenly polluted, the spacing between the lines will also vary.
Another method of selecting sections is also used - concentric circles. With this method, the “epicenter” is first determined - the point of concentration of pollution, for example, the location of an industrial enterprise. Then circles are drawn with a larger diameter the further from the center of the circle.
The test site, which is laid out for a factory or plant that pollutes the soil, should occupy an area equal to three times the area of the sanitary protection zone. In order for the selected samples to give an objective idea of the qualities of the soil, the sites are laid on plots of land with the same type of plant and soil layers.
If soil samples are taken to monitor the cultivated areas of agricultural institutions, then sites, each of which occupies one hundred square meters, are planned for every 0.5~20 hectares. The number of sites depends on what crops are grown on the territory, as well as on the terrain.
To take soil samples near kindergartens, schools, etc., which are done for sanitary soil control, sample areas with an area of 25 square meters are required.
Soil sampling rules
Soil samples are taken from successive layers in the area selected at the exploration stage. Each sample must show the overall properties of the test site in accordance with the data of the site passport, and also be consistent with the purpose of the study according to the table below.
There are general rules for sampling:
- If the depression exceeds 40 cm, then at least two samples must be made.
- If the soil is contaminated with microorganisms, it is important to follow the rules of asepsis.
- For chemical analysis you need to take at least 5 samples. They are taken with a spatula, knife or special sampler. The selected samples are mixed into one, the weight of which should be 1 kg or more.
- If the soil is contaminated with oil or petroleum products, including gasoline, diesel fuel, fuel oil, etc., samples should be taken at different depths from 0 to 5 cm and from 5 to 20 cm.
- If the soil contains heavy metals, samples are taken with a plastic sampler. The use of a metal product may affect the reliability of laboratory test results.
- If the soil is tested for the presence of easily evaporating substances, then the selected samples are immediately tightly sealed in glass laboratory containers.
- To conduct a microbiological analysis of soil, you will need at least 10 samples taken with a sterile instrument and placed in sterile containers. The combined sample is made up of three samples weighing about 250 g, and sampling is done from two layers: 0~5 and 5~20 cm.
- For helminthological analysis, a combined sample is required, corresponding to 10 samples weighing 200 g, selected at depths from 0 to 5 cm and from 5 to 20 cm. Such samples are taken using a shortened soil drill.
Preparation of samples for laboratory testing
Regardless of what type of analysis the sample is subject to, it must be recorded in a journal and assigned a number. In addition, a special coupon is drawn up for each sample containing the following information:- date and time of selection;
- site address;
- number of sample, site, site;
- layer depth;
- description of meteorological conditions at the time the sample was taken;
- the name of the person who carried out the fence.
Samples intended for helminthological analysis must be examined immediately upon delivery. They are stored at a temperature of 4~5 °C in a laboratory refrigerator.
Samples for quantitative and qualitative studies of bacteria are transported in special cooler bags. They can be stored for no more than a day. If samples are to be tested for E. coli, the permissible storage time is 72 hours.
In special cases, soil samples are preserved using formalin or hydrochloric acid. This is done if it is expected that the period between sampling and the beginning of their analysis may be up to 30 days.
For chemical studies and determination of humidity by thermogravimetric method, a sample weighing 10~20 g is taken from the combined sample and dried in an oven at a temperature of 105°C.
Samples delivered to the laboratory are prepared for analysis. The soil is evenly laid out on paper and crushed if necessary. If there are pebbles, debris, insects, etc. in the samples, they are removed. Then the soil samples are ground in a mortar and sifted through a sieve with cells with a diameter of 1 mm.
Methodological manual for laboratory work on soil mechanics for students of specialty 270105 “Urban construction and management” of all forms of education
Compiled by V.P. Tkachenko, M.G. Onoprienko, N.A. Ivanenko
Reviewer: Professor, Honored Scientist of Kuban E.N. Peresypkin
Sochi – RIO SSU 2014
Introduction
To design the foundations of buildings and structures, it is necessary to determine the physical and mechanical properties of soils and the conditions of their occurrence. They are determined in the process of engineering geological surveys using field and laboratory research methods. Laboratory research methods make it possible to determine the physical and mechanical properties of soils taken in the form of samples and monoliths during geotechnical surveys. The accuracy of calculations, reliability and technical and economic indicators of construction and operation of structures depend on the accuracy of the obtained values.
The guidelines introduce students to the basic methods and techniques of performing laboratory soil analyzes within the approved training programs. Before starting laboratory work, the student must first study the relevant theoretical material, familiarize himself with these guidelines, and then perform the work in the training laboratory. At the end of each lesson, the student must fill out 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 is required to tidy up his/her workplace and hand it over to the laboratory assistant.
Selection of soil samples for laboratory work.
Selection, packaging, transportation and storage of soil samples for laboratory research are carried out in accordance with GOST 12071 - 72.
Soil samples are taken of undisturbed (monoliths) or disturbed composition from cleared faces, walls of mine workings (clearings, pits, pipes, pits, etc.) and boreholes. Their number, type, and dimensions are determined by the research program and can be specified during laboratory work. The number and type of samples must be sufficient for laboratory research and control determinations. Monoliths from pits and pits, as a rule, are taken in a prismatic shape, and from wells using soil carriers - in a cylindrical shape. A monolith that does not retain its shape without a rigid container is selected using the cutting ring method according to GOST 5182-78. The internal 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 height of the ring must be at least one and no more than two ring diameters.
The selection of monoliths of non-frozen sandy and clayey soils is carried out from wells in the process of drilling them without the use of flushing fluid and covering the 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 is placed on the upper edge of the monolith. The monolith to the gauze is dipped into molten paraffin, removed from it, and then covered with a second layer of gauze and paraffinized again. A second label is placed on the waxed monolith, which is covered with a thin layer of paraffin, ensuring that the inscription on the label is readable. In order to increase its plasticity, 35–50% (by weight) of tar is added to paraffin used for insulating monoliths.
The label of the monolith indicates the organization performing the survey, the name of the object, its location, the name and number of the excavation, the number of the monolith, the depth of selection, the name of the soil by visual determination, the position and surname of the person who carried out the selection of the monolith, his signature and the date of selection. Labels are filled in with a simple graphite pencil.
Soil samples intended for transportation are packed in boxes with the free space filled with sawdust, shavings, and other materials with similar properties. Under the top lid of the box there is a list of samples wrapped in tracing paper with the information indicated on the labels. The boxes are numbered and marked with the inscriptions “Top”, “Do not tip”, “Do not throw”, and the addresses of the recipient and sender.
During transportation, soil monoliths should not be subjected to sudden dynamic and temperature influences. Before 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, packaging and storage defects are prohibited from being accepted for laboratory testing. They are used as samples of soil with a disturbed structure.
The physical state of the soil is determined by the following defining characteristics: natural density, particle density, humidity, granulometric composition. The strength of soils is assessed by certain characteristics of soil compression and shear resistance. The filtration properties of soils are characterized by certain values of their permeability.
Calculated soil characteristics include:
· Porosity coefficient;
· Porosity;
· Degree of humidity;
· Turnover rate;
· Plasticity number;
· Heterogeneity coefficient of sandy soil.
In accordance with the determined and calculated characteristics of soils according to SNiP 2.02.01 - 82, they are classified according to type, type and condition. Soil characteristics are used in calculations to determine the bearing capacity, strength and settlement of structure foundations, slope stability, pressure on enclosing structures, etc.
GOST 12071-2014 "Soils. Selection, packaging, transportation and storage of samples"
4.1 General provisions
- The selection of soil samples 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.
- Soil samples are taken from cleared faces and walls of mine workings (pits, ditches, boreholes, etc.), natural and artificial outcrops and the bottom of water areas.
- To determine the full range of physical and mechanical properties of soils, the sample must consist of one or more monoliths, depending on the composition of the planned laboratory work.
- Monoliths must be oriented immediately after selection (mark the top of the monolith).
- To select monoliths from open-pit mines, a shovel, a knife, cutting rings and various types of soil carriers are used.
- To isolate monoliths of thawed soils, paraffin oil grade NV 56-58 according to GOST 23683 with the addition of 35% - 50% (by weight) tar, gauze, insulating tape, as well as ceresin according to GOST 2488 are used.
For dimensions of monoliths for determining soil density and moisture content, see the website page "Methods for determining soil characteristics"
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. p.:
- When carrying out engineering-geological surveys at the site of the planned construction, soil samples for laboratory tests should be taken every 25 cm along the depth of excavations in the seasonal freezing layer.
The standard 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 excavations should be increased in accordance with the data in Table. 2, characterizing the minimum distance Z between the standard freezing depth dfh and the depth of groundwater dw.
Table 2
Sampling of soil from pits for laboratory testing
Guidelines for field documentation of engineering-geological
and prospecting and exploration work during highway surveys
When taking soil samples, the requirements of GOST 12071-60 should be taken into account.
Soil samples are taken from pits 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 at a depth interval of 10 cm.
For example, a sample was taken from a depth of 1.10-1.20 m.
Your sample should be about 500 grams, in the case of fine-earth soils, and if it is necessary to take samples for standard compaction (for example, for excavation soils) - 3-3.5 kg.
Sampling of coarse soils is carried out using the furrow method. Selected samples are screened to separate into fractions. Pieces larger than 100 mm should be selected manually. From the small fractions of soil that have passed through a sieve, 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:
- Using cutting rings. This method is used in cases where it is not necessary to determine the compression properties of the soil, but only the porosity coefficient of the soil needs 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 its outer diameter; at the other end a cap with a small hole for air outlet is put on.
The internal diameter of the cutting rings must be at least 10 mm. The height of the ring should not be more than the diameter.
Rings of smaller diameter are used when taking monoliths of clayey and loamy soils, while larger ones are used for sandy loam and sandy soils.
Before taking the monolith, the wall of the pit is leveled and cleaned; the ring at a given depth is pressed closely with its sharp end against the wall of the pit and pressed into the ground until the lid is slightly submerged in the ground.
After this, the ring with soil is carefully removed using a soil knife, the cover is removed, the excess soil is cut off flush with the edges of the ring, and the ring with soil is weighed, having previously wiped it off the outside from adhering soil, on a technical or pharmaceutical scale with an accuracy of 0.1 grams. By subtracting the weight of the ring from the weight of the ring with soil, the weight of the soil is determined; By dividing the weight of the soil by the volume of the ring, the volumetric weight of the soil is obtained.
Weighing is done three times.
At the same time, a soil sample is taken from the same depth to determine natural moisture and a soil sample of disturbed structure weighing 0.5 kg to determine the specific gravity of the soil, particle size distribution, and plasticity. - In cases where it is necessary to determine the compression properties of the soil, the angle of internal friction, adhesion, temporary crushing resistance, etc. in a sample with an undisturbed structure, the 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, sand cemented by permafrost and clay 200×200×200 mm.
If difficulties arise, it is allowed to take samples of arbitrary shape while maintaining the specified side dimensions 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 out with a soil knife. As the sample is deepened into the wall of the pit, it is gradually given the correct shape and required size.
To avoid drying out, the monolith taken here at the pit is waxed and carefully packaged according to the rules set out in GOST 12071-66.
Description of pits
A description and sketch of the pit is made as it is excavated.The pit is fixed after the rocks have been described, their sketches have been made and soil samples have been taken for laboratory testing. The described depth interval should not exceed 2 m.
Before describing the wall, the pits must be cleared of adhering rock and prepared with a knife so that the contacts of the layers and the structure of the soil are clearly visible. The average thickness of the layer and its depth are determined as the arithmetic mean of measurements taken at 3 and 4 characteristic inflection points. Determination of the density of cohesive soils is carried out according to table No. 4. When describing pits, in addition to describing the rocks, digger passages, worms, and fracturing are noted.
The pit is sketched, as a rule, one wall at a time. Four walls are sketched if the rocks lie obliquely or lens-shaped, while measurements are taken to the bottom of the formation at the corners of the pit, and if necessary, in the middle of the wall. When sketching along four walls, the walls of the pit should be oriented according to the cardinal points. The sketch is made in the accepted conventions (see Fig. 3) on a scale of 1:20, 1:50, 1:100.
Within the framework of which we are engaged in soil sampling. In the field of construction, soil is understood as the study of the upper layer of the lithosphere, consisting of rocky, semi-rocky and loose rocks.
For what purpose do geologists take samples?
— To classify and determine the composition of a section containing strata and sedimentary layers.
To calculate the optimal size of slopes associated with excavation work.
To describe the characteristics (the possibility of their use in construction as materials).
Determination of bearing capacity through geological surveys of the soil located at the base of the foundation.
When sampling, various methods are used, determined in accordance with the soils being studied. For selection, soils that have either a disturbed or undisturbed structure are used.
When working with loose rocks, for example, sand, you can use samples with a disturbed structure for research. To work with cohesive rocks, only a monolithic structure is used.
If geologists want to preserve the monolithic structure, professional drilling of engineering wells should be provided. You can use any methods designed to obtain a sample that has retained its intact structure. To ensure a high-quality sample, it is necessary to drill a well with an optimal diameter in the range from 108 to 168 millimeters. In field testing of soils, a soil carrier is used, that is, a device designed to obtain a high-quality sample. A soil sample taken from a well must have a cube or cylinder shape.
There are several common methods for collecting soil samples.
Using the point method is more effective when taking small soil samples.
The use of the furrow method involves plowing furrows along the entire length of the formation. Sampling is carried out at various places in the furrow.
The use of the bulk method makes it possible to use all excavated soil during research.
Soil selection is carried out in compliance with basic rules and in a certain sequence.
Care must be taken to exclude the entry of random elements and to ensure consistency between the soil layer and the sampling location.
Sampling is accompanied by keeping a journal in which information about the work site and the time when sampling is carried out is recorded, with the drawing up of a corresponding report.
Samples are taken to the extent necessary to carry out all studies planned to ensure quality engineering studies. In order to provide the laboratory with the most reliable information, care must be taken to preserve the samples. We are talking only about undisturbed soils. The main goal of conservation is to preserve the primary structure with the natural moisture content of the sample. During transportation, it is necessary to ensure that samples are protected from negative environmental influences.