A soil strength weakening-recovering characteristic testing device

Abstract

The present application belongs to the field of geotechnical, geological and environmental research, and provides a soil strength weakening-recovery characteristic testing device, which comprises an actuation and collection system, a soil disturbance system and a soil strength measurement system. The soil disturbance system adopts a net-like grid structure, and realizes the remolding of soil through rotating the grid; the soil sample strength measurement system mainly refers to the traditional vane shear apparatus, and installs a pore water pressure sensor on the top of the vane head to test the consolidation state of the soil. For the soil at the same position, the process of soil strength measurement-remolding-resting (for different time)-strength measurement is repeatedly carried out to analyze the weakening and recovery law of soil strength. The method of the present application makes up for the lack of effective technical means in the field of current geotechnical investigation in the aspect of soil strength weakening-recovery characteristic testing, and based on the method, the soil strength weakening characteristics and strength recovery law can be quickly and accurately obtained, which provides an important reference for geotechnical engineering design and engineering stability analysis.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical and geological technology, and specifically relates to a soil strength weakening-recovery characteristic testing device. Background Technology

[0002] The marine process is developing rapidly, with marine engineering projects such as foundation design and submarine pipelines flourishing. In marine engineering, the design and safety / stability of marine structural foundations and submarine pipelines place stringent requirements on the mechanical properties of the soil, necessitating accurate interpretation of these properties. Marine clay is characterized by high water content, large void ratio, and significant strain softening; therefore, the soil's strength weakening and recovery characteristics are crucial for marine engineering design. Current in-situ cone penetration tests (CBPTs) and laboratory experiments primarily include vane shear tests, T-bar cone penetration tests, ball cone penetration tests, and CPT and CPTu cone penetration tests. However, these existing methods cannot accurately determine the soil's strength weakening and recovery characteristics. Obtaining these characteristics through CBPTs is of great significance, providing crucial support for the rational design and stability of underwater engineering facilities such as subsea oil and gas drilling platforms, submarine pipelines, and submarine cables.

[0003] Evaluation methods for structural soil samples include the drop cone test, full-flow cone penetrometer test, and vane shear test. The vane shear test was hypothesized and validated by Terzaghi et al. (1994) in "Soil mechanics in engineering practice." Because the strength of undisturbed clay decreases after remolding, exhibiting certain sensitivity and structural characteristics, Terzaghi (1944) proposed an index for evaluating sensitivity in "Ends and means in soil mechanics," namely, sensitivity S. t This index specifies the peak strength S of undisturbed soil. u,0 and peak strength S of remolded soil u,rem The ratio. Sensitivity, as an important mechanical parameter of soil samples, requires the measurement of peak strength of undisturbed and remolded soils. The vane shear test is commonly used, but it is difficult to determine whether the soil sample is completely remolded, thus hindering the determination of soil strength weakening characteristics and strength recovery patterns. Considering the problems encountered in current structural soil sample evaluation methods, there is an urgent need to find a soil strength weakening-recovery characteristic testing device to serve the determination of basic mechanical parameters of soil samples. Summary of the Invention

[0004] To address the limitations of existing methods for structural soil samples in achieving complete remolding and thus failing to determine soil strength weakening characteristics and recovery patterns, this invention proposes a soil strength weakening-recovery test method. This method is applicable to the determination of soil sample sensitivity in geotechnical laboratories, as well as the peak undrained shear strength of undisturbed and remolded soils. It serves the evaluation of structural soil samples, providing experimental basis and important reference for the rational design and stability assessment of marine engineering projects.

[0005] The technical solution of this invention:

[0006] A soil strength weakening-recovery characteristic testing device includes three parts: an actuation and acquisition system I, a remolded soil sample system II, and a penetration testing system III;

[0007] The actuation and acquisition system I includes an acquisition device 1, a cable 2, a working platform 3, and an actuation device 4. The acquisition device 1 is used to acquire data generated by the cross-plate shearing device. The upper end of the cable 2 is connected to the acquisition device 1, and the lower end is connected to the actuation device 4. The working platform 3 is used to support the acquisition device 1 and the cross-plate shearing device. The actuation device 4 is connected to the cross-plate shearing device and provides power to the cross-plate shearing device.

[0008] The remolded soil sampling system II includes a cross-shaped top cover 6, a fishing line mesh grid 7, an outer steel hoop 8, an inner steel hoop 9, and a cross-shaped bottom cover 10. The fishing line mesh grid 7 includes two intersecting wing plates, each wing plate being a rectangular structure with a hollow center, woven using a fishing line diamond pattern. The fishing line mesh grid 7 has a U-shaped structure with a hollow center to reduce torque during the remolding rotation process. The side of the fishing line mesh grid 7 perpendicular to the probe rod 5 is divided into an outer side and an inner side, with half of the outer side having a dimension of... The dimensions of half of the inner edge are Where D = 75mm is the standard crosshead diameter and H = 150mm is the standard crosshead height; the soil sample is reshaped by rotating the fishing line mesh 7 without taking the soil sample away; the cross-shaped top cover 6 and the cross-shaped bottom cover 10 are used to connect and fix the two ends of the fishing line mesh 7. The two are cross-shaped, the same as the shape of the cross, and the same in size as the cross shearing device 12. The purpose is to allow the soil sample within the shearing range of the cross to be completely reshaped without increasing the penetration resistance of the cross shearing device 12; the outer steel hoop 8 is placed on the outside of the fishing line mesh 7 to fix the fishing line and increase its rigidity; the inner steel hoop 9 is placed in the middle of the fishing line mesh 7 to increase its rigidity.

[0009] The penetration test system III includes a penetration probe 5, a strain gauge 11, a vane shear apparatus 12, and a pore water pressure sensor 13. The penetration probe 5 is composed of a steel pipe, inside which the connecting lines of the pore water pressure sensor 13 and the strain gauge 11 are placed. From top to bottom, the penetration probe 5 is connected to a cross-shaped top cover 6, a fishing line mesh grid 7, an outer steel hoop 8, an inner steel hoop 9, a cross-shaped bottom cover 10, the strain gauge 11, the vane shear apparatus 12, and the pore water pressure sensor 13. The vane shear apparatus 12 has dimensions of D×H=75×150mm. The strain gauge 11 is connected at the upper connection between the vane shear apparatus 12 and the penetration probe 5. By collecting the strain generated during the vane shearing process, the undrained shear strength of the soil sample is obtained through formula conversion. The pore water pressure sensor 13 is connected at the lower connection between the penetration probe 5 and the vane shear apparatus 12 to collect pore water pressure.

[0010] The distance between the remolded soil sample system (II) and the probing system (III) is greater than or equal to 6 cm.

[0011] The beneficial effects of this invention are:

[0012] 1) The cross-plate shearing device for completely reshaping soil samples proposed in this invention combines the idea of ​​soil sample reshaping. For the same soil location, the process of soil strength measurement-reshaping-resting (at different times)-strength measurement is repeated to analyze the weakening and recovery law of soil strength, solve the problem that soil samples cannot be completely reshaped, and a pore water pressure sensor is installed at the top of the plate to test the consolidation state of the soil.

[0013] 2) The vane shearing device for fully reshaping soil samples proposed in this invention has significant innovation. It uses a fishing line mesh grid as the soil reshaping device, which solves the problem that the traditional vane shearing device cannot reshape the soil at the boundary of its shearing surface, resulting in excessive strength of the fully reshaped soil. It not only saves time in judging whether the soil sample has been reshaped, but also avoids the problem that the soil sample will not be fully reshaped. Attached Figure Description

[0014] Figure 1 This is a schematic diagram illustrating the practical engineering application of the present invention;

[0015] Figure 2 This is a schematic diagram of the overall three-dimensional structure of the present invention;

[0016] Figure 3 This is a longitudinal cross-sectional view of the reconstituted soil sample system II and the penetration test system III of the present invention;

[0017] Figure 4 This is a cross-sectional view of the reconstituted soil sampling system II and the penetration testing system III of the present invention;

[0018] Figure 5 This is a detailed drawing of the reconstituted soil sample system II of the present invention;

[0019] Figure 6 This is a detailed drawing of the probe system III of the present invention;

[0020] Figure 7(a) is a schematic diagram showing the relationship between torque and rotation angle of the vane shearing device provided in an embodiment of the present invention;

[0021] Figure 7(b) is a schematic diagram showing the relationship between the undrained shear strength of soil and the rotation angle of the vane shear apparatus provided in the embodiment of the present invention.

[0022] Figure 8 This is a schematic diagram showing the relationship between the undrained shear strength of soil under different thixotropic times and the rotation angle of the vane shear apparatus, provided as an embodiment of the present invention.

[0023] In the diagram: 1. Data acquisition device; 2. Cable; 3. Working platform; 4. Actuating device; 5. Penetration probe; 6. Cross-shaped top cover; 7. Fishing net grid; 8. Outer steel hoop; 9. Inner steel hoop; 10. Cross-shaped bottom cover; 11. Strain gauge; 12. Cross-plate shearing device; 13. Pore water pressure sensor. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0025] like Figure 1 The image shows the practical application of a vane shearing device for completely reshaped soil samples. The device was inserted into marine clay to measure the undrained shear strength.

[0026] like Figure 2 The illustrated vane shearing device for completely remodeling soil samples includes two parts: a soil remodeling system II and a penetration testing system III.

[0027] Combination Figure 3 , Figure 4 , Figure 5 , Figure 6 As shown, the remolded soil sample system II and the penetration test system III include a penetration probe 5, a cross-shaped top cover 6, a fishing line grid 7, an outer steel hoop 8, an inner steel hoop 9, a cross-shaped bottom cover 10, a strain gauge 11, a vane shear tester 12, and a pore water pressure sensor 13.

[0028] Referring to the attached diagrams and technical solutions, the operation of the vane shearing device for completely reshaping soil samples includes the following steps:

[0029] The first step is to process and assemble the experimental apparatus.

[0030] See Figure 5The fishing lines are woven into a diamond-shaped fishing net. The fishing net grid 7 is connected to the cross-shaped top cover 6 and the cross-shaped bottom cover 10. An inner steel hoop 9 is connected in the middle of the fishing net grid 7 to increase its rigidity. Finally, an outer steel hoop 8 is connected to the outside of the fishing net grid 7 to fix it in place. The fishing net grid 7 has a U-shaped structure with a hollow center to reduce the torque during the reshaping and rotation process. Its outer rectangular dimensions are... The internal rectangle has the following dimensions: Where D = 75 mm is the standard vane head diameter and H = 150 mm is the standard vane head height, connecting the remolded soil sample system II and the penetration test system III together;

[0031] See Figure 6 The strain gauge 11 is attached to the upper connection between the penetrometer rod 5 and the vane shear apparatus 12 to measure strain; the pore water pressure sensor 13 is installed at the lower connection between the vane shear apparatus 12 and the penetrometer rod 5 to measure pore water pressure.

[0032] The second step is experimental preparation.

[0033] Combination Figure 1 On the working platform 3, the acquisition device 1 is connected to the actuation device 4 by the cable 2, and then the remolded soil sample system II and the penetration system III are connected to it and pre-buried in the marine clay. It is necessary to ensure that the pre-buried penetration process is horizontal. The vane shearing instrument 12 is penetrated into the soil surface to a certain depth, and the device is left to stand for 2-3 minutes to check whether the connection is normal.

[0034] The third step is to measure the undrained shear strength of the undisturbed soil and the remolded soil.

[0035] The vane shear apparatus 12, fishing line grid 7, cross-shaped top cover 6, and vane bottom cover 10 are rotated at a rotation rate of 6°-12° / min. When the reading reaches its peak value, the peak value is the measured undrained shear strength of the undisturbed soil sample. The soil is completely remodeled using the remodeled soil sample system II and left to stand for different times. Then, the vane shear apparatus 12 is moved to the completely remodeled soil sample and the measurement is performed again. The peak value is the measured undrained shear strength of the remodeled soil sample. That is, for the same soil sample, the process of soil strength measurement-remodeling-standing (different times)-strength measurement is repeated to obtain the mechanical parameters of the undisturbed soil sample and the remodeled soil sample. In addition, the pore water pressure sensor 13 at the bottom of the vane shear apparatus 12 can measure the consolidation state of the soil, providing experimental basis and numerical reference for the design and evaluation of marine engineering.

[0036] Step 4: Equipment recycling

[0037] After the test is completed, slowly pull the device upwards and clean the cross-plate shearer 12 and the fishing line mesh 7 to remove the clay and prevent corrosion.

[0038] Step 5: Processing the measurement data

[0039] The data obtained from the experiment needs to be analyzed and processed. The specific steps are as follows:

[0040] (1) Undrained shear strength of soil

[0041] The undrained shear strength of soil is one of the important mechanical parameters, and its strength is mainly estimated by the following formula:

[0042]

[0043] In the formula, S u Let T be the undrained shear strength of the soil, T be the torque value measured by the vane shear apparatus, D be the diameter of the vane shear apparatus, and H be the height of the vane shear apparatus.

[0044] (2) Soil sensitivity

[0045] The sensitivity of the soil can be obtained by the following formula:

[0046]

[0047] In the formula, S t For the sensitivity of the soil, S u,0 S represents the initial undrained shear strength of the soil. u,rem It represents the undrained shear strength of the soil under fully remodeled conditions.

[0048] The above are merely preferred technical solutions of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A soil strength weakening-recovery characteristic testing device, characterized in that, The soil strength weakening-recovery characteristic testing device consists of three parts: an actuation and acquisition system (I), a remolded soil sample system (II), and a probing system (III). The actuation and acquisition system (I) includes an acquisition device (1), a cable (2), a working platform (3), and an actuation device (4). The acquisition device (1) is used to acquire data generated by the vane shearing device. The upper end of the cable (2) is connected to the acquisition device (1), and the lower end is connected to the actuation device (4). The working platform (3) is used to support the acquisition device (1) and the vane shearing device. The actuation device (4) is connected to the vane shearing device and provides power to the vane shearing device. The soil reshaping system (II) includes a cross-shaped top cover (6), a fishing line grid (7), an outer steel hoop (8), an inner steel hoop (9), and a cross-shaped bottom cover (10). The fishing line grid (7) includes two cross-shaped wing plates, each of which is a rectangular structure with a hollow center, and is made of fishing line diamond weaving. The fishing line grid (7) is a square-shaped structure with a hollow center. The soil sample is reshaped by rotating the fishing line grid (7) without taking the soil sample away. The cross-shaped top cover (6) and the cross-shaped bottom cover (10) are used to connect and fix the two ends of the fishing line grid (7). The two are cross-shaped, the same as the shape of the cross plate, and the same size as the cross plate shearing instrument (12). The outer steel hoop (8) is placed on the outside of the fishing line grid (7) to fix the fishing line, and the inner steel hoop (9) is placed in the middle of the fishing line grid (7). The penetrometer system (III) includes a penetrometer probe (5), a strain gauge (11), a vane shearing device (12), and a pore water pressure sensor (13). The penetrometer probe (5) is made of a steel pipe, inside which the connecting lines of the pore water pressure sensor (13) and the strain gauge (11) are placed. The penetrometer probe (5) is connected from top to bottom to the following components: a cross-shaped top cover (6), a fishing line net grid (7), an outer steel hoop (8), an inner steel hoop (9), a cross-shaped bottom cover (10), a strain gauge (11), and a vane shearing device. The shearing instrument (12) and the pore water pressure sensor (13) are used. The dimensions of the vane shearing instrument (12) are D×H=75×150mm. The strain gauge (11) is connected to the upper connection between the vane shearing instrument (12) and the penetrometer rod (5). The strain generated during the vane shearing process is collected and the undrained shear strength of the soil sample is obtained by formula conversion. The pore water pressure sensor (13) is connected to the lower connection between the penetrometer rod (5) and the vane shearing instrument (12) to collect pore water pressure.

2. The soil strength weakening-recovery characteristic testing device according to claim 1, characterized in that, The fishing line mesh (7) is divided into an outer edge and an inner edge perpendicular to the side where the probe (5) is located. The dimension of half of the outer edge is... The dimensions of half of the inner edge are Where D = 75mm is the standard crosshead diameter and H = 150mm is the standard crosshead height.

3. The soil strength weakening-recovery characteristic testing device according to claim 1, characterized in that, The distance between the remolded soil sample system (II) and the probing system (III) is greater than or equal to 6 cm.

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