One: Geotechnical test
I. Three-phase composition of soil (solid phase, liquid phase and gas phase)
Soil physical property index:
1 density of soil: refers to the density variation range of quality soil per unit volume of soil, generally 16-22kN/m? 0? six
2 Specific gravity (or density of soil particles) Gs: refers to the ratio of the mass of soil solid particles per unit volume to the mass of water per unit volume at 4℃.
The specific gravity of soil depends on the mineral composition of soil, and its variation range is generally between 26.0 and 27.5.
Soil water content w: refers to the ratio of the mass of water to the mass of solid particles in the soil, usually expressed as a percentage.
Water content is an index of soil moisture. The natural water content of soil varies greatly, from dry sand close to zero to saturated clay of several hundred percent.
Dry density: refers to the ratio of the solid particle mass of soil to the total volume of soil.
The greater the dry density, the denser the soil, so the dry density is often used as the control index of soil compaction.
Saturation density: refers to the density of soil when all gaps are filled with water.
Where the density of water is =9.8 1KN/m? 0? 6=9.8 1* 10-3N/cm？ 0? six
6 Floating density or immersion density: refers to the mass per unit volume when the soil is immersed in water and subjected to the buoyancy of water.
7 Pore ratio E: It is the ratio of pore volume to solid particle volume in soil.
Pore ratio is a widely used index, which can be used to evaluate the compactness of soil.
Porosity n: refers to the ratio of pore volume to total volume in soil;
There is the following conversion relationship between porosity and porosity.
Saturation Sr: refers to the ratio of water volume in pores to pore volume.
Saturation is used to describe the degree to which water fills soil pores. When Sr=0, the soil is completely dry, and when Sr= 1, the soil is completely saturated. According to saturation, sand can be divided into three states:
0 & ltSr≤0.5 slightly wet
0.5 & ltSr≤0.8 Humidity
0.8 & ltSr≤ 1.0 saturation
Transformation relation of physical expression of index symbols
Soil physical properties test:
Water content test:
Drying method: Drying method is a standard method for measuring water content, which is suitable for clay, silt, sandy soil and organic soil.
Instruments and equipment:
1, oven: ignition oven or other energy oven, the temperature is 105- 1 10.
2. Balance: sensitivity 0.01g.
3. Others: dryers, weighing boxes, etc.
Test steps
1, take representative samples, including 15-30g fine-grained soil, 50g sandy soil and 50g organic soil, put them into a weighing box, immediately cover the box cover and weigh their mass. When weighing, put a weight with the same mass as the weighing box at one end of the balance, and move the sky to translate the code, and the weighing result is the wet soil mass.
2. Uncover the box cover, put the sample and the box into the oven, and dry at constant temperature 105- 1 10. For fine-grained soil, it shall not be less than 8h; for soil with organic matter content exceeding 5%, it shall be dried at constant temperature of 65-70℃.
3. Take out the dried samples and boxes and put them in the dryer for cooling (generally only 0.5- 1h). After cooling, cover the box cover, and accurately weigh the mass to 0.01g.
Alcohol combustion method
Adding alcohol to the soil sample can burn on the soil, so that the water in the soil will evaporate. The soil sample should be dried, usually three times.
Instruments and equipment
1 weighing box
2 balance: sensitivity 0.01g.
3 Alcohol: purity 95%
4 droppers, matches, earth knives, etc.
experimental procedure
1, take a representative sample (clay 5- 10g sand 20-30g) and put it into the weighing box to weigh the wet soil.
2. Use the dropper to inject alcohol into the weighing box containing the sample until a free liquid level appears in the box. In order to make the alcohol fully and evenly mixed in the sample, tap the box on the table.
3. Light the box until the flame goes out.
4. Cool the sample for a few minutes and reburn it twice in steps 2 and 3.
5. After the third flame is extinguished, cover it and immediately weigh the dry soil with an accuracy of 0.01g..
This method is suitable for cohesionless soil, which is generally cohesive soil, but it is not suitable for soil containing organic matter, soil with high salt content and heavy clay.
Other test methods for water content:
1, infrared irradiation method: infrared irradiation method is to dry the soil sample under infrared light. Usually, the soil sample can be dried by irradiation at a distance of about 5- 15cm from the light source1h. Experiments show that the water content of this method is slightly higher than that of drying method by about 65438 0%.
2. Specific gravity method: put the soil sample into a glass bottle with a certain volume, calculate the floating weight of unearthed particles in water, and then calculate the unearthed water content. It is suitable for sandy soil.
3. Microwave heating method: Compared with the standard drying method, the relative error of most soils is less than 65438 0.5%, but it is not suitable for some soils containing metal minerals.
4 calcium carbide pneumatic method: calcium carbide is a water-absorbing substance. A certain amount of wet soil samples and calcium carbide are put into a sealed container with a certain volume, and the water absorbent reacts with water in the soil to generate acetylene gas. The pressure generated by acetylene gas in a sealed container is directly proportional to the mass of water molecules in the soil.
Testing method of special soil water content;
1, test method for water content of gypsum-containing soil and organic soil
When the drying temperature of gypsum-containing soil and organic soil is 1 10, gypsum-containing soil will lose crystal water and organic components will burn, and the test results are inconsistent with the definition of water content. It is best to dry this kind of samples in a vacuum drying box under the action of near 1 atmosphere, or to control the oven temperature at 60-70℃ for more than 8 hours.
2, inorganic binder stabilized soil water content test method
Inorganic binder is often called hydraulic binder abroad, which mainly refers to cement, lime, fly ash and lime or cement fly ash. The terms used are cement stabilized soil, lime stabilized soil and lime stabilized soil.
When the moisture content of inorganic binder is measured by drying method, the oven temperature should be raised to 1 10 in advance, so that the inorganic binder can start drying at 105- 1 10. In addition, silica gel should be used as desiccant after drying.
If the oven temperature does not rise to 1 10, the measured water content is often very small.
Density test method
The common methods for measuring density include ring knife method, wax sealing method, sand filling method and irrigation method. The circular knife method is simple and accurate, and is widely used indoors and outdoors. Hard, fragile, coarse-grained, irregular-shaped soil that cannot be cut with a ring knife can be sealed with wax; Sand filling method and irrigation method are generally used in the field.
In density test, m is easy to obtain, but the value of v is difficult to obtain. The detection operation of V value is greatly influenced by human factors and soil particle size composition.
Ring knife method:
This method is to cut the soil sample with a certain volume ring knife, so that the soil is filled with it according to the shape of the ring knife. The weight of soil is measured in the ring knife. According to the known volume of the ring knife, the unearthed density can be calculated according to the definition. There are different types of ring knives to choose from. In indoor testing, we can choose cutting, pressurizing and infiltrating ring knives according to the situation of domestic instruments and equipment. When checking the density of the filled soil in the construction site, due to the uneven compaction degree of each layer of soil, the compaction thickness of each layer is 20-30cm, the volume of the ring cutter is too small, the depth of the soil layer changes slightly, and the measured density error is large. Therefore, the ring cutter with large volume can be selected to improve the test accuracy.
1. Instruments and equipment
(1) ring cutter: inner diameter 6-8cm, height 2-3m, wall thickness 1.5-2mm.
(2) Balance: sensitivity 0.1g.
(3) Others: soil trimmer, wire saw, vaseline, etc.
2. Test steps
(1) According to the engineering requirements, take the undisturbed soil or disturbed soil sample in the required state, level both ends, coat a thin layer of vaseline on the inner wall of the ring cutter, and put it on the soil sample with the edge facing down. In direct proportion. The corresponding water content can be converted by measuring the gas pressure.
(2) Use a soil trimmer or wire saw to cut the upper part of the soil sample into a soil column slightly larger than the diameter of the ring cutter, then press the ring cutter vertically and cut while pressing until the soil sample extends out of the upper part of the ring cutter, cut off the residual soil at both ends to make it flush with the surface of the ring cutter, and measure the water content with the residual soil sample.
(3) Wipe the outer wall of the circular knife, and weigh the mass of the circular knife and the soil to the accuracy of 0.1g..
Collate results
4. Poor precision and tolerance
The second parallel determination shall be conducted in this test, and the arithmetic mean shall be taken, and the parallel difference shall not be greater than 0.03g/cm3.
(3) wax sealing method
In this legal system, irregular soil samples (the volume is not less than 5cm3) are weighed according to their natural mass, then immersed in melted paraffin, so that the soil samples are wrapped by paraffin, and then weighed according to air weight and water weight, and the density of the soil samples is calculated according to the formula.
The density value obtained by this method is always greater than that obtained by other methods, because it is difficult to avoid melting wax from soaking into the pores of human soil under any circumstances.
1. Instruments and equipment
(1) balance: sensitivity 0.0 1.
(2) Beakers, thin wires, paraffin, needles, knives, etc.
2. Test steps
(1) Cut the specimen with a volume greater than 30 "with a soil cutter to remove loose soil, loose soil and sharp edges and corners on the surface of the specimen, and weigh it on the balance with an accuracy of 0.01g. Take a representative sample to measure the hydration quantity.
(2) The paraffin wax is heated to just over the melting point, and the specimen is tied with thin wires and intruded, so that the surface of the specimen is covered with a thin layer of dense paraffin wax. If there are bubbles on the wax film of the specimen, the bubbles must be broken with a hot needle, and then the pinhole and Tu Ping hole must be filled with paraffin.
(3) After cooling, weigh the wax seal sample on the balance with an accuracy of 0.01g..
(4) Place the wax-sealed sample on one end of the balance with a thin thread to make it float in a beaker filled with distilled water. Be careful not to touch the beaker wall, weigh the underwater mass of the wax sealed sample to the accuracy of 0.0 1g, and measure the temperature of distilled water.
(5) Take the wax seal specimen out of the water, dry the water on the wax surface, weigh its mass in the air, and compare it with the mass mentioned in (3). If the mass increases, it means that water has entered the specimen; If the soaking water quality exceeds 0.03g, it should be redone.
3 Results collation
Calculate the wet density according to the following formula
Field pit test method:
If the upper layer contains broken gravel or the artificially filled upper layer cannot be sampled by ring cutter, a measuring pit can be dug at the site, and the quality and water content of the excavated earth and rock can be measured at the same time. The excavated soil is generally not less than 300kg. For irregular test pits, you can put an impermeable film bag in the pit, then fill the bag with water and measure the volume of water, and calculate the density of soil according to the definition. Volume can also be measured by sand filling method.
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