CN102943460A - Pore pressure cross plate device capable of evaluating sand liquefaction potentiality - Google Patents

Abstract

The invention discloses a pore pressure cross plate device that can continuously and qualitatively evaluate the liquefaction potential of saturated sandy soil. The lower part of the pipe (32) is connected with the lower threaded round pipe (31), and the pore water pressure sensor (2) is arranged in the upper threaded round pipe (32) and the shaft (4), and the upper part of the pore water pressure sensor (2) Connect the power cable (1); connect the shaft (4) to the lower part of the lower threaded pipe (31), and set the non-hole plate head (52) and the hole plate head (51) on the outside of the shaft rod (4). The set cross plate head is provided with water permeable holes (6) along the radial direction of the lower threaded circular pipe (31) in the middle of the hole plate head (51), and the bottom end of the shaft rod (4) is an impermeable plug ( 7). The device has the characteristics of in-situ, fast, accurate, and convenient, and provides a powerful detection tool for tailings dam evaluation, sand earthquake liquefaction evaluation, and geotechnical engineering foundation treatment practice.

Description

A pore pressure cross plate device that can evaluate the liquefaction potential of sandy soil

technical field

The invention relates to a pore pressure cross plate device, which belongs to a test device capable of accurately and quantitatively evaluating the liquefaction potential of saturated sandy soil in the field of civil engineering.

Background technique

Since Casagrande proposed in 1976 that it is necessary to develop in-situ testing sand liquefaction potential technology, many testing techniques have been applied in this area, the most common of which are standard penetration test (SPT) and pore pressure static penetration test ( CPT). These two tests mainly evaluate the liquefaction potential of sandy soil based on experience, which makes the test technology have great limitations. At present, the dilation/shrinkage trend and steady-state shear strength of sandy soil are mainly obtained through laboratory tests and related field test indicators. The measurement of in-situ pore water pressure in the soil layer is helpful to evaluate the liquefaction potential of sandy soil, because the change of pore water pressure is the basis of sandy soil liquefaction. Many scholars have tried to measure the pore water pressure change caused by the penetration of the probe by using pore pressure static sounding technology, and then evaluate the sand liquefaction potential. Factors such as the uncertainty of the location of the water pressure measurement complicate the theoretical interpretation of the sand liquefaction potential. The cross-plate shear test (VST) is suitable for in-situ determination of the undrained shear strength of saturated soils, and the measured shear strength value is equivalent to the undrained shear strength of the natural soil layer consolidated under in-situ pressure at the test depth. shear strength. VST does not need to collect soil samples, and avoids soil sample disturbance, natural stress state changes and tedious indoor tests, and is an effective in-situ test method.

Based on the conventional cross-plate shearing instrument, the present invention proposes an accurate, quantitative and quick in-situ testing device, providing an accurate and effective quantitative evaluation tool for sand earthquake liquefaction evaluation and geotechnical engineering foundation treatment.

Contents of the invention

Technical problem: The technical problem to be solved in this invention is to propose a method that can be used in the field of geotechnical engineering to quantitatively evaluate the liquefaction potential of saturated sand in situ, aiming at the in-situ quantitative evaluation of the liquefaction potential of saturated sand that cannot be carried out in China at present. Hole pressure cross plate device.

Technical solution: The upper part of the pore pressure cross plate device of the present invention that can evaluate the liquefaction potential of sand and soil is an upper threaded round pipe, the lower part is a lower threaded round pipe, the lower part of the upper threaded round pipe is connected with the lower threaded round pipe, and the upper threaded round pipe is connected to the lower threaded round pipe. A pore water pressure sensor is installed in the round tube and the shaft, and the upper part of the pore water pressure sensor is connected to the power cable; the lower part of the lower threaded round tube is connected to the shaft, and the outer part of the shaft is equipped with a non-porous plate head and a holed plate head. The vertically arranged cross plate head is provided with water permeable holes along the radial direction of the lower threaded circular pipe in the middle part of the perforated plate head, and the bottom end of the shaft rod is an impermeable plug.

There are two permeable holes in the middle of each perforated plate head, the hole diameter is 1.5mm, and the spacing is 20mm.

The height of the cross head is 100mm, the diameter is 50mm, and the thickness is 3mm.

The diameter of the shaft is 20mm.

The diameter of the upper threaded round pipe is 20mm, and the diameter of the lower threaded round pipe is 25mm.

The pore pressure cross plate device of the present invention that can evaluate the liquefaction potential of saturated sandy soil, the pore water pressure measurement is mainly completed by the pore water pressure sensor, the permeable hole and the shaft rod and other measurement systems, and its steady state soil shear strength The measurement is mainly completed by the conventional cross board part. By applying external torque, turning the cross plate, shearing the soil, and recording the torque, pore water pressure and rotational angular velocity during the shearing process of the soil, the shear strength of the soil in steady state can be calculated and the liquefaction potential can be evaluated according to relevant theories. A large number of theoretical studies and measured data show that when saturated sand is sheared, the rise/fall of pore water pressure is closely related to the liquefaction potential. When the pore water pressure increases during shearing, it appears as liquefiable potential sandy soil; when the pore water pressure decreases during shearing, it appears as non-liquefiable potential sandy soil.

Beneficial effects: In geotechnical engineering practice, the evaluation of sand liquefaction potential is very important. Currently commonly used in-situ evaluation techniques mainly include standard penetration test (SPT) and pore pressure static penetration test (CPT). limitation. The liquefaction trend and steady state shear strength of sandy soil can be obtained through laboratory tests and related in-situ test parameters. However, affected by factors such as sampling disturbance and test methods, the process is time-consuming and laborious, and the reliability of the test results is low. The invention solves the defect that the existing domestic in-situ test technology cannot better, accurately and quantitatively evaluate the liquefaction potential of saturated sandy soil, so that the cross-plate shear test technology can more comprehensively serve the field of geotechnical engineering.

Description of drawings

Fig. 1 is a component device diagram of the present invention;

Wherein there are: power cable 1, pore water pressure sensor 2, lower threaded round pipe 31, upper threaded round pipe 32, shaft rod 4, plate head with orifice 51, head without orifice 52, permeable hole 6, impermeable plug 7.

Fig. 2 is a sectional view of A-A in Fig. 1 of the present invention.

Detailed ways

The pore pressure cross plate device of the present invention that can evaluate the liquefaction potential of saturated sandy soil includes a power cable 1, a pore water pressure sensor 2, a lower threaded round pipe 31, an upper threaded round pipe 32, a shaft rod 4, and a holed plate head 51, No-hole plate head 52, permeable hole 6, impermeable plug 7; The top of this device is the upper threaded round pipe 32, the bottom is the lower threaded round pipe 31, the bottom of the upper threaded round pipe 32 is connected with the lower threaded round pipe 31, in A pore water pressure sensor 2 is arranged in the upper threaded round pipe 32 and the shaft 4, and the upper part of the pore water pressure sensor 2 is connected to the power cable 1; the lower part of the lower threaded round pipe 31 is connected to the shaft 4, and a The non-porous plate head 52 and the cross plate head with orifice 51 are arranged perpendicularly to each other. In the middle of the perforated plate head 51, a water permeable hole 6 is provided along the radial direction of the lower threaded round pipe 31. At the bottom end of the shaft rod 4 For impermeable plug 7.

The number of permeable holes 6 is 4, the aperture is 1.5mm, and the spacing is 20mm.

The height of the cross head is 100mm, the diameter is 50mm, and the thickness is 3mm.

The shaft rod 4 has a diameter of 20 mm.

The diameters of the two threaded round pipes are 20mm and 25mm respectively.

A large number of theoretical studies and measured data show that when saturated sand is sheared, the increase/decrease of pore water pressure is closely related to the liquefaction potential. The pore water pressure decreases, showing the non-liquefaction potential sandy soil.

At the same time, the cross-plate shearer is an effective in-situ test instrument for testing the undrained shear strength of soil. According to the calculation method of shear strength proposed by Cadling and Odenstad (1950), it is obtained:

S _h =S _v /K

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; /</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; D.</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; h</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 6</span>}\mathrm{<span\; class="notranslate">\; K</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

where _Sh is the horizontal shear strength, S _v is the vertical shear strength, K is the horizontal earth pressure coefficient, M is the applied torque, H is the height of the cross blade, and D is the diameter of the cross blade.

According to the requirements of the conventional cross-plate shear test, insert the pore pressure cross-plate device to the designated test position and stay there for 2-3 minutes. After the pore water pressure caused by the penetration is basically dissipated, the shear test starts. The shear angular velocity is approximately 90° /s, and record the torque, pore water pressure and angular velocity at the same time every 16ms.

Combined with the liquefaction theory proposed by Castro and Poulos (1977) and the above shear strength calculation method, the liquefaction potential and steady state shear strength of saturated sandy soil can be determined. Liquefiable soils; Potentially non-liquefiable soils are identified when pore water pressure decreases.

Claims (5)

1. A pore pressure cross plate device capable of evaluating the liquefaction potential of sand and soil, characterized in that the upper part of the device is an upper threaded round pipe (32), the lower part is a lower threaded round pipe (31), and the upper threaded round pipe (32 ) is connected to the lower threaded round pipe (31), the upper threaded round pipe (32) and the shaft (4) are provided with a pore water pressure sensor (2), and the upper part of the pore water pressure sensor (2) is connected to the power cable (1); the shaft (4) is connected to the lower part of the lower threaded round pipe (31), and the outside of the shaft (4) is provided with a cross vertically arranged by the non-porous plate head (52) and the perforated plate head (51) The plate head is provided with water permeable holes (6) along the radial direction of the lower threaded pipe (31) in the middle part of the perforated plate head (51), and the bottom end of the shaft rod (4) is an impermeable plug (7). 2. The pore pressure cross plate device capable of evaluating the liquefaction potential of saturated sandy soil according to claim 1, characterized in that each perforated plate head (51) has two water permeable holes (6) in the middle part, and the hole diameter is 1.5mm , the spacing is 20mm. 3. The pore pressure cross plate device capable of evaluating the liquefaction potential of saturated sand and soil according to claim 1, characterized in that the height of the cross plate head is 100 mm, the diameter is 50 mm, and the thickness is 3 mm. 4. The pore pressure cross plate device capable of evaluating the liquefaction potential of saturated sandy soil according to claim 1, characterized in that the diameter of the shaft (4) is 20 mm. 5. The pore pressure cross plate device capable of evaluating the liquefaction potential of saturated sand and soil according to claim 1, characterized in that the diameter of the upper threaded round pipe (32) is 20 mm, and the diameter of the lower threaded round pipe (31) is 25 mm .