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A test method for simulating the change of shear strength of dewatered soil in foundation pit

A technology of shear strength and test method, which is used in the application of stable shear force to test the strength of materials and the preparation of test samples, can solve the problems of not considering the influence of the shear strength of foundation pit precipitation and the unreasonable results.

Inactive Publication Date: 2011-11-30
TONGJI UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

At present, in the design and calculation of deep foundation pits in soft soil and water-rich strata, the selection of soil shear strength indexes mostly adopts the material parameters before precipitation, or is selected only based on experience, without considering the influence of foundation pit precipitation on soil shear strength. The result is obviously not reasonable enough

Method used

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  • A test method for simulating the change of shear strength of dewatered soil in foundation pit
  • A test method for simulating the change of shear strength of dewatered soil in foundation pit
  • A test method for simulating the change of shear strength of dewatered soil in foundation pit

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Experimental program
Comparison scheme
Effect test

Embodiment 1

[0030] Specific steps are as follows:

[0031] (1) Take the undisturbed soil sample, and prepare a soil column with a diameter of φ39.1mm and a height of 80mm with equipment such as a wire saw, a soil cutter, and a soil cutter;

[0032] (2) After putting the sample into the vacuum tank, carry out pumping and water saturation;

[0033] (3) Install the specimen in the triaxial pressure chamber. When installing, first put the latex film on the film support tube, use a suction ball to inhale air from the air nozzle, make the latex film close to the tube wall, and cover the outside of the prepared sample; then open the pore water pressure valve, After filling and exhausting the permeable stone at the sample base of the pressure chamber and the piping system connected to it, close the valve, put a piece of filter paper on the permeable stone, put the sample covered with latex film on the base of the pressure chamber, turn over Tie the lower end of the lower latex membrane with the...

Embodiment 2

[0039] The sample is the undisturbed soil taken from a deep foundation pit in the urban area of ​​Shanghai. The sample soil is gray muddy clay of layer ④, with a buried depth of 9.5-17.5m and a weight of 16.7kN / m 3 , the average self-weight stress is 100.0kPa. The test simulated four working conditions of no precipitation and 2.0m, 4.0m, and 8.0m of precipitation, and the corresponding consolidation pressures were 100.0kPa, 120.0kPa, 140.0kPa, and 180.0kPa; The precipitation samples were consolidated in two stages; a total of 4 groups of tests were done. Table 1 shows the shear strength index of gray muddy clay soil in layer ④ before and after precipitation measured according to the above test procedures. The cohesion c and internal friction angle φ of layer ④ gray silty clay change with precipitation depth, see Figure 4~5 shown.

Embodiment 3

[0041] The sample is the undisturbed soil taken from a deep foundation pit in the urban area of ​​Shanghai. The sample soil is ⑤-1 layer of gray clay, with a buried depth of 17.5-22.0m and a weight of 17.5kN / m 3 , the average self-weight stress is 150.0kPa. The test simulated four working conditions of no precipitation and 2.0m, 4.0m, and 8.0m of precipitation, and the corresponding consolidation pressures were 150.0kPa, 170.0kPa, 190.0kPa, and 230.0kPa; The precipitation samples were consolidated in two stages; a total of 4 groups of tests were done. Table 1 shows the shear strength indexes of the gray clay layer ⑤-1 before and after precipitation measured according to the above test procedures. ⑤ The cohesion c and internal friction angle φ of gray clay layer 1 vary with precipitation depth, see Figure 6~7 shown.

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Abstract

The invention relates to a test method for simulating the shear resistant strength change of foundation pit precipitation soil. The test method comprises the following steps of: firstly, preparing an original-shape soil sample by using a fret saw, a soil cutter, a soil cutting disk, and the like; secondly, carrying out exhausting and water injection on the sample in a vacuum tank to be saturated;thirdly, mounting a test sample in which a latex film is sleeved in a three-axle pressure chamber; fourthly, solidifying the test sample at two phases through a three-axle ambient pressure system, wherein the test sample is restored to be in a natural self-weight stress state of a soil body by using the first-time solidification and the stress state of the soil body subjected to precipitation is simulated by using secondary solidification; fifthly, carrying out an un-drained shear test on the test sample through an axial loading system; and sixthly, after the test is ended, closing a motor and a valve and detaching the test sample. According to the test method disclosed by the invention, the influence of the reduction for water content of the foundation pit precipitation soil, the increase of effective stress and soil solidification and compaction on the soil shear resistant stretch is considered so as to provide reference for accurately selecting shear resistant strength indexes of the foundation pit precipitation soil and further provide guarantee for designing and constructing deep foundation pits of soft soil water-rich stratum safely, economically and reasonably.

Description

technical field [0001] The invention relates to an indoor geotechnical test method, in particular to a test method for simulating changes in the shear strength of precipitation soil in foundation pits on soft ground. Background technique [0002] The shear strength of soil is an important mechanical property of soil. It includes two basic indicators of soil cohesion c and internal friction angle φ. These two indicators must be used for the earth pressure of the building envelope. However, there are many factors that affect the shear strength index, including: soil type, compactness, water content, pore water pressure, structure and so on. Therefore, the correct determination of the shear strength of soil is of great significance in engineering, and it is related to the accuracy of foundation pit design and calculation and the safety and reliability of foundation pit engineering. [0003] For deep foundation pits in coastal soft soil and water-rich strata, precipitation mea...

Claims

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Application Information

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IPC IPC(8): G01N3/24G01N1/28
Inventor 丁春林叶丹赵军朱恺孟晓红舒进
Owner TONGJI UNIV
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