Shear strength testing device and testing method

Abstract

The present invention relates to the field of strength measurement technology, and in particular to a shear strength testing device and a testing method. A shear strength testing device comprises: a rod body, the interior of which is hollow; a strain structure, comprising at least two strain gauges arranged at intervals, the strain gauges being arranged on the outer peripheral wall of the rod body and arranged along the length direction of the rod body; a hole sensor, which is arranged on the outer peripheral wall of the rod body. In a test state, the hole sensor is inserted into a soil sample to sense the pressure of the soil sample, and the strain gauge measures the shear strength of the soil sample. The present invention solves the problem that the existing testing device cannot sense the pressure of the hole.

Description

Technical Field

[0001] The invention relates to the technical field of strength measurement, and in particular to a shear strength testing device and a testing method. Background Art

[0002] In geotechnical engineering design, the undrained shear strength of marine soft soil is an essential mechanical parameter. In-situ tests and laboratory tests are important ways to obtain the undrained shear strength of marine soft soil.

[0003] Existing in-situ tests all involve vertically pressing into the foundation soil, and then measuring the soil strength by measuring the resistance during the pressing process (pore pressure static penetration test) or the rotational shear resistance after pressing into the foundation (cross-plate shear test). During the test, the human eye cannot observe the state of the hole after pressing into the foundation, resulting in the test device being unable to sense the pressure in the hole. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the testing device in the prior art cannot sense the pressure of the hole, thereby providing a shear strength testing device and a testing method.

[0005] In order to solve the above problems, the present invention provides a shear strength testing device, comprising:

[0006] A rod body, wherein the interior of the rod body is hollow;

[0007] The strain structure comprises at least two strain gauges arranged at intervals, wherein the strain gauges are arranged on the outer peripheral wall of the rod body and along the length direction of the rod body;

[0008] The hole sensor is arranged on the outer peripheral wall of the rod body. Under the test state, the hole sensor is inserted into the soil sample to sense the pressure of the soil sample, and the strain gauge measures the shear strength of the soil sample.

[0009] Optionally, an embedding groove is provided on the outer peripheral wall below the rod body, and the hole sensor is arranged in the embedding groove.

[0010] Optionally, a protective layer is further included, and the protective layer is sleeved on the outer circumference of the rod body.

[0011] Optionally, the strain gauge and the hole sensor are communicatively connected via a signal line.

[0012] A testing method for a shear strength testing device comprises the following steps: selecting at least two points at a testing site, pressing down a rod at each point and waiting, and a hole sensor measuring pore pressure data; after the excess pore pressure dissipates, performing several horizontal cyclic slidings in an undrained soil state until the data measured by the strain gauge decays to a stable state to measure the data; then, preparing for the next point test.

[0013] Optionally, the horizontal resistance F between adjacent strain gauges is calculated based on the bending moment difference measured by two adjacent strain gauges in the length direction of the rod, and a relationship curve between the horizontal resistance F exerted on the rod and the horizontal sliding distance S between the strain gauges at each adjacent distance in the length direction of the rod is drawn, and the horizontal resistance peak value Fp is extracted from the relationship curve, and a relationship diagram between Fp and the number of cycles n is drawn.

[0014] Optionally, soil samples are obtained on site and subjected to undrained cyclic shear tests in the laboratory to measure the residual undrained shear strength sur of the soft soil after multiple cyclic shearing.

[0015] Optionally, according to the formula Fp=NsuA=NsuDΔL, the positive correlation between the peak horizontal resistance Fp of the rod with a length ΔL and the undrained shear strength su of the soft soil is obtained.

[0016] Optionally, based on the first horizontal sliding resistance Fp1=Nsu0D△L, and the ratio of Fp formula Fp1 / Fpn=su0 / sur, su0=Fp1 / Fpnsur is obtained.

[0017] Optionally, the horizontal sliding speed of the rod body needs to satisfy vD / Cv>20.

[0018] The technical solution of the present invention has the following advantages:

[0019] 1. The shear strength test device provided by the present invention comprises: a rod body, the interior of which is hollow; a strain structure, comprising at least two strain gauges arranged at intervals, which are arranged on the outer peripheral wall of the rod body and arranged along the length direction of the rod body; a hole sensor, which is arranged on the outer peripheral wall of the rod body. In the test state, the hole sensor is inserted into the soil sample to sense the soil sample pressure, and the strain gauge measures the shear strength of the soil sample. In the test state, the hole sensor is inserted into the soil sample to sense the soil sample pressure, so that the on-site personnel can understand the state of the hole after the rod body is pressed into the foundation through the hole sensor, and then the shear strength of the soil sample is measured by the strain gauge.

[0020] 2. In the shear strength testing device provided by the present invention, an embedding groove is provided on the outer peripheral wall below the rod body, and the hole sensor is arranged in the embedding groove, and the embedding groove is used to install the hole sensor.

[0021] 3. The shear strength testing device provided by the present invention also includes a protective layer, which is sleeved on the outer periphery of the rod body and is used to protect the strain gauge on the outer peripheral wall of the rod body.

[0022] 4. In the shear strength testing device provided by the present invention, the strain gauge and the hole sensor are connected through a signal line communication to transmit measured data information.

[0023] 5. The test method of the shear strength test device provided by the present invention is to select at least two points at the test site, press the rod down at each point and wait, and the hole sensor measures the pore pressure data. After the excess pore pressure dissipates, the soil is undrained for several times of horizontal cyclic sliding until the data measured by the strain gauge decays to a stable state to measure the data; then, prepare for the next point test. The soil resistance measured by horizontal sliding replaces the previous vertical pressure resistance, reducing the impact of the pressure process and the change of the overlying soil pressure on the measurement results, ensuring that the test structure at the test site more truly reflects the original soft soil strength.

[0024] 6. The testing method of the shear strength testing device provided by the present invention calculates the horizontal resistance F between adjacent strain gauges based on the bending moment difference measured by two adjacent strain gauges in the length direction of the rod body, draws a relationship curve between the horizontal resistance F exerted on the rod body and the horizontal sliding distance S between the strain gauges at each adjacent distance in the length direction of the rod, extracts the horizontal resistance peak value Fp from the relationship curve, draws a relationship diagram between Fp and the number of cycles n, performs data processing on the test results, and obtains the corresponding relationship diagram.

[0025] 7. The testing method of the shear strength testing device provided by the present invention obtains field soil samples and conducts undrained cyclic shear tests in the laboratory to measure the residual undrained shear strength sur of the soft soil after multiple cyclic shearing, ignoring the influence of the disturbance of the soil samples during sampling, storage and transportation.

[0026] 8. The testing method of the shear strength testing device provided by the present invention obtains the positive correlation between the horizontal resistance peak Fp of the rod with a length △L and the undrained shear strength su of soft soil according to the formula Fp=NsuA=NsuD△L, and the first horizontal sliding resistance Fp1=Nsu0D△L is used to make a ratio with the Fp formula Fp1 / Fpn=su0 / sur, and su0=Fp1 / Fpnsur is obtained. By making a ratio between the first and final semi-rigid pile horizontal resistance peaks, the influence of the empirical coefficient is eliminated. At the same time, the residual undrained shear strength measured by indoor tests is used to eliminate the influence of soil sampling disturbance, and finally a reliable original undrained shear strength of soft soil is obtained.

[0027] 9. In the testing method of the shear strength testing device provided by the present invention, the horizontal sliding speed of the rod body needs to satisfy vD / Cv>20 to ensure that the sliding speed is large enough to keep the soil around the rod body in an undrained state. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 A front view of a shear strength testing device provided in an embodiment of the present invention;

[0030] Figure 2 A schematic diagram of on-site sampling of a shear strength testing device provided in an embodiment of the present invention;

[0031] Figure 3 A cyclic load variation diagram of a shear strength testing device provided in an embodiment of the present invention;

[0032] Figure 4 A peak load attenuation diagram of a shear strength testing device provided in an embodiment of the present invention;

[0033] Explanation of the accompanying reference numerals: 1. rod body; 2. strain gauge; 3. embedded groove; 4. hole sensor; 5. signal line; 6. protective layer; 7. soil sampling point; 8. surface of soft soil layer. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0036] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] Example 1

[0039] The shear strength test device provided by the present invention comprises: a rod body 1, the interior of the rod body 1 is hollow; a strain structure, comprising at least two strain gauges 2 arranged at intervals, the strain gauges 2 are arranged on the outer peripheral wall of the rod body 1, and are arranged along the length direction of the rod body 1; a hole sensor 4 is arranged on the outer peripheral wall of the rod body 1, and in the test state, the hole sensor 4 is inserted into the soil sample to sense the soil sample pressure, and the strain gauge 2 measures the shear strength of the soil sample. In the test state, the hole sensor 4 is inserted into the soil sample to sense the soil sample pressure, so that the on-site personnel can understand the state of the hole after the rod body 1 is pressed into the foundation through the hole sensor 4, and then the strain gauge 2 measures the shear strength of the soil sample.

[0040] Example 2

[0041] like Figure 1 - Figure 4 A specific embodiment of the shear strength test device shown in FIG. 1 includes a rod body 1, and a strain structure is provided on the outer peripheral wall of the rod body 1. Figure 1 As shown, the strain structure is a plurality of strain gauges 2 arranged along the length direction of the rod body 1. Specifically, the rod body 1 is a semi-rigid pile body. In order to sense the hole pressure of the rod body 1 after being inserted into the soft soil layer, Figure 1 , Figure 2 As shown, an embedding groove 3 is provided on the outer peripheral wall below the rod body 1, and a hole sensor is provided in the embedding groove 3. In order to protect the strain gauge 2, a protective layer 6 is also included which is sleeved on the outer periphery of the rod body 1. Specifically, the material of the protective layer 6 is epoxy resin. In order to transmit the data of the strain gauge 2 and the hole sensor 4, a signal line 5 which is connected to the strain gauge 2 and the hole sensor 4 for communication is also included.

[0042] A testing method for a shear strength testing device comprises the following steps:

[0043] 1) Design the test points, determine the stratum properties and soil classification according to the on-site drilling results, understand the depth distribution and general properties of the shallow marine soft soil to be tested, and determine the number of test measurement points and the specific location of each measurement point;

[0044] 2) Design the test process to Figure 2 For example, a strength test is carried out near points a and b. The rod 1 test mainly includes two steps: rod 1 pressing in and horizontal cyclic sliding: rod 1 is pressed in from the surface 8 of the soft soil layer, and the pressing process is slow to ensure that the vertical pressing depth L1 does not deviate, and at the same time, it can also reduce the disturbance to the surrounding soil; after rod 1 is pressed in, it waits still, and according to the pore pressure data measured by the hole sensor 4, after the excess pore pressure is dissipated, horizontal cyclic sliding is carried out between points a and b at the Sab distance. It should be noted that the horizontal sliding speed must be large enough, that is, the horizontal sliding speed must satisfy vD / Cv>20, where v is the horizontal sliding speed, D is the diameter of rod 1, and Cv is the consolidation coefficient of soft soil. The cyclic sliding is carried out to the nth cycle. When the data measured by the strain gauge 2 of rod 1 decays to a stable state and no longer changes, the horizontal sliding ends, and then rod 1 is extracted to prepare for the next point test;

[0045] 3) Calculate the resistance between two adjacent strain gauges, the bending moment difference measured by the length △L between two adjacent strain gauges in the length direction of the rod body 1, calculate the horizontal resistance F between two adjacent strain gauges, and draw the relationship curve between the horizontal resistance F and the horizontal sliding distance S of the rod body 1 between two adjacent strain gauges in the length direction of the rod;

[0046] 4) Obtain the peak resistance Fp of each cycle, extract the peak horizontal resistance Fp of the rod body 1 of each ΔL length from the curve diagram in step 3), and draw a relationship diagram between Fp and the number of cycles n;

[0047] 5) Take soil samples on site, determine the location for indoor test soil sample selection, select soil samples at the soil sampling point 7 of the field test attachment, select the soil sample at the middle position of the △L length rod 1, and at least 10D away from the sliding position to represent the strength of the soil sample;

[0048] 6) Indoor test to determine the undrained shear strength of soft soil. The soil samples obtained on site are brought back to the laboratory, and the undrained cyclic shear test is carried out in the laboratory to measure the residual undrained shear strength sur of the soft soil after multiple cyclic shearing. The influence of the sampling, storage and transportation processes on the soil sample disturbance is ignored in the whole process;

[0049] 7) The sliding resistance of the pile body comes from the horizontal resistance peak Fp of the △L length rod body 1 and the product of the undrained shear strength su of the soft soil and the cross-sectional area A of the section, that is, Fp=NsuA=NsuD△L, where N is the empirical coefficient and su is measured by indoor tests;

[0050] 8) The first horizontal sliding resistance of the test is Fp1=Nsu0DΔL, where su0 is the undisturbed original undrained shear strength. At the end of the cycle, the nth horizontal sliding resistance is Fpn=NsurDΔL, where sur is the residual undrained shear strength of soft soil measured in the laboratory. The ratio of the two formulas is Fp1 / Fpn=su0 / sur, that is, su0=Fp1 / Fpnsur.

[0051] The testing method of the shear strength testing device provided by the present invention eliminates the influence of the empirical coefficient by making a ratio between the first and final horizontal resistance peak values ​​of the rod body 1, and simultaneously uses the residual undrained shear strength measured by indoor tests to eliminate the influence of soil sampling disturbance, and finally obtains a reliable original undrained shear strength of soft soil.

[0052] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A shear strength test method, characterized in that: The test equipment used includes: A rod body (1), wherein the interior of the rod body (1) is hollow; The strain structure comprises at least two strain gauges (2) arranged at intervals, wherein the strain gauges (2) are arranged on the outer peripheral wall of the rod body (1) and are arranged along the length direction of the rod body (1); A hole sensor (4) is arranged on the outer peripheral wall of the rod body (1); in a test state, the hole sensor (4) is inserted into a soil sample to sense the pressure of the soil sample, and the strain gauge (2) measures the shear strength of the soil sample; The test method comprises the following steps: 1) Design the test points, determine the stratum properties and soil classification according to the on-site drilling results, understand the depth distribution and general properties of the shallow marine soft soil to be tested, and determine the number of test measurement points and the specific location of each measurement point; 2) Designing a test process, performing strength tests near points a and b, the rod (1) test mainly includes two steps: pressing the rod (1) in and horizontal cyclic sliding: the rod (1) is pressed in from the surface of the soft soil layer, and the pressing process is slow to ensure that the vertical pressing depth does not deviate and reduce the disturbance to the surrounding soil; after the rod (1) is pressed in, it waits for a while, and after the excess pore pressure is dissipated according to the pore pressure data measured by the hole sensor (4), horizontal cyclic sliding is performed between points a and b at the Sab distance; the horizontal sliding speed must be large enough to satisfy vD / Cv>20, where v is the horizontal sliding speed, D is the diameter of the rod (1), and Cv is the soft soil consolidation coefficient; after the cyclic sliding reaches the nth cycle, when the data measured by the strain gauge (2) of the rod (1) decays to a stable state and no longer changes, the horizontal sliding is terminated, and the rod (1) is extracted to prepare for the next point test; 3) calculating the resistance between adjacent strain gauges (2), calculating the horizontal resistance F between adjacent strain gauges (2) according to the bending moment difference measured by the length △L between two adjacent strain gauges (2) in the length direction of the rod body (1), and drawing a relationship curve between the horizontal resistance F and the horizontal sliding distance S of the rod body (1) between the strain gauges (2) at each adjacent distance in the length direction of the rod; 4) Obtaining the peak resistance Fp of each cycle, extracting the peak horizontal resistance Fp of each ΔL length rod (1) from the curve diagram in step 3), and drawing a relationship diagram between Fp and the number of cycles n; 5) Take soil samples on site, determine the location for indoor test soil sample selection, and select soil samples at the soil sampling point of the field test attachment. Select the soil sample at the middle position of the △L length rod (1) and at least 10D away from the sliding position to represent the soil sample strength; 6) Indoor test to determine the undrained shear strength of soft soil. The soil samples obtained on site are brought back to the laboratory, and the undrained cyclic shear test is carried out in the laboratory to measure the residual undrained shear strength sur of the soft soil after multiple cyclic shearing. The influence of sampling, storage and transportation on the disturbance of soil samples is ignored in the whole process; 7) The sliding resistance of the pile body comes from the horizontal resistance peak Fp of the △L length rod (1), which is positively correlated with the product of the undrained shear strength su of the soft soil and the cross-sectional area A of the rod body of this section, that is, Fp=NsuA=NsuD△L, where N is the empirical coefficient and su is measured through indoor tests; 8) The first horizontal sliding resistance of the test is Fp1=Nsu0DΔL, where su0 is the undisturbed original undrained shear strength. At the end of the cycle, the nth horizontal sliding resistance is Fpn=NsurDΔL, where sur is the residual undrained shear strength of soft soil measured in the laboratory. Comparing the two formulas, we get Fp1 / Fpn=su0 / sur, that is, su0=Fp1 / Fpnsur.

2. The shear strength testing method according to claim 1, characterized in that: An embedding groove (3) is provided on the outer peripheral wall below the rod body (1), and the hole sensor (4) is arranged in the embedding groove (3).

3. The shear strength testing method according to claim 1, characterized in that: It also comprises a protective layer (6), wherein the protective layer (6) is sleeved on the outer circumference of the rod body (1).

4. The shear strength testing method according to claim 1, characterized in that: The strain gauge (2) and the hole sensor (4) are communicatively connected via a signal line (5).

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