Geology of a site in Moscow
How are the subsidence properties of loess rocks determined
The geology of the site in Moscow includes the definition of soil types. Different breeds have distinctive properties. It is important to know the possible occurrence of various natural phenomena in them. Loess rocks have distinctive characteristics, they are studied by compression tests.
Rocks are compressed in volume when loads are applied to them. During compression tests, rocks are forced to experience loads. At the same time limit the ability of the sample to expand on the sides, using a device (odometer), where the walls are hard. A soil sample is placed on the odometer. The pressure increases in steps. Maintain under pressure until oscillations from deformations damp out. This type of testing in the laboratory is often used to determine how much soil can be deformed. The rock is not destroyed during compression.
Loess deposits placed in the odometer are compacted by directional loads. The sample is soaked with water.Relative subsidence depends on height changes (in centimeters) when a certain pressure is applied to a sample. From the height of the sample with natural humidity, the height, but already wetted, is removed, the pressure is maintained. The height difference is divided by the height of the same sample, but not additionally moistened (sample with natural moisture). Loess are considered not subsidence if the result of division is less than 0.01 and are subsidence if the coefficient is more than 0.01. According to the data obtained, a graph of changes in the properties of the soil under pressure in a normal and in a moist state is plotted.
Physico-chemical structural features of loess soils, methods for testing them
The geology of the site in Moscow when studying loess soils is faced with significant variations in their parameters:
- Silicon dioxide can range from 43.1 to seventy-eight percent.
- Aluminum oxide Al2O3 ranges from four to 17.54%.
- Iron oxide ranges from 0.4 to 9.79%.
- Calcium oxide varies between 2.68 and 15.9%, etc.
These significant fluctuations are associated with different conditions of formation of minerals, their particle size, chemical composition. The content of carbonate salts in loess ranges from four to twenty percent (sometimes up to thirty).The highest value is noted in the driest places. Most of the carbonate particles are of silty dimension. In classical loess soils, a large part is a dust fraction. In them, from fifty to eighty-four percent are carbonates. The fine fraction contains carbonates slightly, but in the clay part it can reach up to forty percent.
The percentage of carbonate particles depends on the strength properties of the rock. The highly dispersed carbonate component forms a solid crystallization bond bonding the particles of loess soils. The calcium content contributes to the clay and calloid fractions to reduce their plastic characteristics. Of the sulfates in loess there can be gypsum, mainly with a dimension greater than 0.01mm. Gypsum are medium soluble salts. If the areas are dry - gypsum is always found in loess soils. In the northern regions, in the forest zone, loess does not contain this mineral. Loess rocks contain an insignificant amount of salts, they easily dissolve (sodium carbonates, sulfates, chlorides, etc.).
Loess rocks have a natural moisture content from 0.05 to 0.25.In the laboratory, the thermostatic method is used to determine the humidity. Less moisture in subsided loess rocks. In the geological section, the moisture content of the overlying loess rocks may be different than that of the underlying layers. Humidity may vary depending on the season, the time of day, precipitation. Usually the humidity of the loess increases with depth. At an average depth of about 0.12. When the humidity is increased, soils compressibility is also increased, but their shear resistance decreases. Non-swelling loess rocks have an average total capacity from 0.13 to 0.16. In clay and heavy loess loam this value is within 0.14 - 0.21. Loess has a capillary moisture capacity of up to 0.4, and loess rocks range from 0.2 to 0.33. Conventional soils have approximately the same full and capillary moisture capacity. The difference between them in loess rocks is significant.
Geology of a site in Moscowuses a radioisotope surface-depth moisture meter to examine the moisture of rocks in the field. The device can be used to a depth of one hundred meters for measurements at depth and up to fifty meters for measurements at the surface. The device is not dangerous for personnel by radioactive indicators.
Samples of rocks are trying to select in their natural occurrence and trying to preserve their natural characteristics. For example, keep their natural moisture. If the loess rocks are dried, the bonds between the particles and the particle complexes are broken. In this case, the properties of the soil change significantly and it will be impossible to reliably determine the limit of plasticity. There is a correlation between the plasticity number and the moisture at the yield boundary, which can vary for different areas. The plasticity of loess rocks is small due to the low content of the clay component, due to the significant content of calcium compounds, due to the content of water-soluble salts. The plasticity of loess increases from north to south.
TheDGI Construction LLCresearches various soils both in the laboratory and in the field.
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