Multi-point vane shear apparatus and undrained shear strength parameter measurement method

Abstract

The invention provides a multi-point vane shear apparatus and an undrained shear strength parameter measurement method. The vane shear apparatus comprises a plurality of groups of vane optical fiber shear sensors; each group of vane optical fiber shear sensors comprises a vane head, a dowel bar and a torque measuring unit; a protective sleeve is arranged in the torque measuring unit; the vane head comprises vane blades and a vane shaft lever; the rectangular cross section of the torque measuring unit is provided with a fiber grating. The fiber bragg grating is embedded in the protective sleeve; in each group of vane optical fiber shear sensors, a vane shaft lever, a dowel bar and a torque measuring unit are coaxially connected in sequence, and vane blades are located on the same straight line. According to the method, the defect that only undrained shear strength parameters of a single point position can be measured in an on-site in-situ test is overcome by utilizing a plurality of groups of connected vane optical fiber shear sensors, quasi-distributed measurement of the soil layer strength in the depth direction is realized, and the method has the advantages of high precision, high efficiency and low cost.

Description

Technical Field

[0001] The invention relates to the technical field of engineering geological in-situ survey, and in particular to a multi-point cross-plate shear instrument and an undrained shear strength parameter measurement method. Background Art

[0002] The undrained shear strength parameter is an important parameter to describe the ability of low permeability soil to resist shear failure. Accurately measuring the distribution of undrained shear strength of in-situ marine clay along the depth direction is a prerequisite for the design and construction of various marine infrastructure.

[0003] In the prior art, indoor tests and in-situ tests are used to obtain the undrained shear strength parameters of marine clay. However, it is difficult for indoor tests to accurately simulate the stress conditions on site, and the sample collection cost is expensive and is easily disturbed during transportation. In the in-situ penetration test, a structure of known geometric shape is vertically penetrated into the soil at a uniform speed, and the undrained shear strength of soil layers at each depth is indirectly obtained through the bearing coefficient and penetration resistance. However, the soil damage form is complex during the penetration process, and the bearing coefficient needs to be corrected by considering the shape of the penetration structure, the properties of the soil, and the stress state on site.

[0004] Therefore, the prior art needs to be further improved. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a multi-point cross-plate shear instrument and an undrained shear strength parameter measurement method to solve the defects of high measurement cost, low efficiency and low measurement accuracy in the prior art.

[0006] In a first aspect, the present embodiment discloses a multi-point cross-plate shear instrument, which includes: a plurality of groups of cross-plate optical fiber shear sensors; each group of cross-plate optical fiber shear sensors includes: a cross-plate head, a force transmission rod and a torque measurement unit; a protective cover is arranged inside the torque measurement unit; the cross-plate head includes a cross-plate blade and a cross-plate shaft rod; a fiber Bragg grating is arranged on a rectangular cross section of the torque measurement unit; the fiber Bragg grating is embedded in the protective cover;

[0007] In each group of cross-plate optical fiber shear sensors: the cross-plate shaft rod, the force transmission rod and the torque measurement unit are coaxially connected in sequence, and the cross-plate blades in the multiple groups of cross-plate optical fiber shear sensors are located in a straight line.

[0008] Optionally, the cross plate head and the force transmission rod, the force transmission rod and the torque measuring unit, and the cross plate head and the torque measuring unit are all detachably connected.

[0009] Optionally, the fiber Bragg gratings are respectively arranged on four rectangular sections of the torque measurement unit, and the angle between the fiber Bragg gratings on one group of relative rectangular sections and the center line is 45°, and the angle between the fiber Bragg gratings on another group of relative rectangular sections and the center line is 135°.

[0010] Optionally, the protective cover is provided with an opening, and the fiber Bragg grating is connected to the signal transmission grating through the opening, and passes through the gap between the cross plate shaft, the force transmission rod and the cross plate blades to be connected to an external fiber Bragg grating demodulator.

[0011] Optionally, the material of the protective cover is plastic or metal sheet; the protective cover is fixedly packaged on the surface of the torque measuring unit.

[0012] Optionally, the diameters of the cross plate shaft, force transmission rod and torque measurement unit are equal or gradually increase from bottom to top along the connection sequence; the sizes of the cross plate blades are equal from bottom to top or gradually increase from bottom to top along the arrangement sequence.

[0013] Optionally, the cross-plate blades on each cross-plate head are aligned with each other and are located on the same straight line.

[0014] In a second aspect, the present application further discloses a method for measuring undrained shear strength parameters, wherein the method is applied to the multi-point cross plate shear instrument, and the steps of the method for measuring undrained shear strength parameters include:

[0015] Push the cross-plate shear instrument vertically and uniformly into the target detection position in the soil;

[0016] Controlling the cross-plate shear instrument to rotate at a constant speed at a preset angular velocity, and collecting the torque applied to each torque measuring unit;

[0017] The undrained shear strength parameters of the soil at each cross-plate blade position are calculated based on the torque applied to each torque measuring unit.

[0018] Optionally, the step of calculating the undrained shear strength parameter of the soil at each cross-plate blade position according to the torque received by each torque measuring unit comprises:

[0019] The undrained shear strength of the soil at the location measured by the corresponding cross-plate head is calculated based on the diameter of the cross-plate blade, the height of the cross-plate blade, the diameter of the cross-plate shaft, and the torque measured by the corresponding torque measurement unit.

[0020] Optionally, the specific method for calculating the undrained shear strength of the soil body measured by the corresponding cross-plate head at the position thereof according to the diameter of the cross-plate blade, the height of the cross-plate blade, the diameter of the cross-plate shaft, and the torque measured by the corresponding torque measurement unit is as follows: using the undrained shear strength calculation formula, it is calculated that the undrained shear strength of the soil body measured by the Nth cross-plate head from bottom to top is:

[0021]

[0022] Among them, M N is the torque on the Nth cross-plate blade, M N-1 is the torque on the N-1th cross plate blade, D N is the diameter of the Nth cross plate blade, H N is the height of the Nth cross plate blade, d N is the diameter of the Nth cross plate shaft, where N ≥ 2.

[0023] Beneficial effect: the present invention provides a multi-point cross-plate shear instrument and an undrained shear strength parameter measurement method, the cross-plate shear instrument includes multiple groups of cross-plate optical fiber shear sensors; each group of cross-plate optical fiber shear sensors includes: a cross-plate head, a force transmission rod and a torque measurement unit; a protective cover is arranged inside the torque measurement unit; the cross-plate head includes a cross-plate blade and a cross-plate shaft; a fiber grating is arranged on the rectangular cross-section of the torque measurement unit; the fiber grating is embedded in the protective cover; in each group of cross-plate optical fiber shear sensors: the cross-plate shaft, the force transmission rod and the torque measurement unit are coaxially connected in sequence, and the cross-plate blades in the multiple groups of cross-plate optical fiber shear sensors are located in a straight line. In this embodiment, multiple groups of connected cross-plate optical fiber shear sensors are used to overcome the deficiency that the on-site in-situ test can only measure the undrained shear strength parameters of a single point, and the distributed measurement of soil layer strength is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a partial structural schematic diagram of the multi-point cross plate shearing instrument provided by the present invention;

[0025] Figure 2 It is a schematic diagram of the overall structure of the multi-point cross plate shearing instrument provided by the present invention;

[0026] Figure 3 It is a schematic diagram of the torque measurement unit and fiber Bragg grating arrangement of the multi-point cross plate shear instrument provided by the present invention;

[0027] Figure 4 It is a schematic diagram of the principle of measuring the distribution of undrained shear strength parameters by the multi-point cross-plate shear instrument provided by the present invention;

[0028] Figure 5It is a schematic diagram for calculating the cross plate area ratio provided by the present invention;

[0029] Figure 6 is a flowchart of the steps of the undrained shear strength parameter measurement method in an embodiment of the present invention;

[0030] Figure 7 It is a schematic diagram of the first cross plate head structure from bottom to top of the multi-point cross plate shearing instrument provided by the present invention;

[0031] Figure 8 1 is a schematic diagram of the structure of the Nth cross plate head from bottom to top of the multi-point cross plate shearing instrument in an embodiment of the present invention;

[0032] Fig. 9 It is a reference data table of the dimensions of the multi-point cross plate shearing instrument in the embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention clearer and more specific, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] Before designing and constructing various types of marine infrastructure, it is necessary to conduct engineering geological surveys on the target sites for infrastructure construction to provide data on geotechnical parameters and properties of the target sites under actual conditions. The distribution of undrained shear strength of marine clay along the depth direction is one of the key parameters.

[0035] There are two methods in the prior art to obtain the undrained shear strength parameters of marine clay: indoor tests and field in-situ tests. Indoor tests such as direct shear tests and triaxial compression are difficult to simulate the stress conditions on site, and the sample collection cost is expensive. At the same time, a single indoor experiment can only measure the undrained shear strength within a limited location, and a large number of tests are required to obtain the spatial distribution of the undrained shear strength. Field in-situ test methods such as CPT penetration tests, T-bar penetration tests, and Ball-bar penetration tests penetrate structures of known geometric shapes vertically into the soil at a uniform speed, and indirectly obtain the undrained shear strength of soil layers at each depth through the bearing coefficient and penetration resistance. However, the soil damage during the penetration process is complex, and the bearing coefficient needs to be corrected considering the shape of the penetration structure, the nature of the soil, and the on-site stress state, and the process is cumbersome.

[0036] In order to overcome the above problems, the present invention utilizes the advantages of high precision, strong waterproof and anti-corrosion performance and quasi-distributed measurement of fiber Bragg grating, and provides a multi-point cross-plate shear instrument and undrained shear strength parameter measurement method, the cross-plate shear instrument includes multiple groups of coaxially connected cross-plate fiber optic shear sensors; each group of cross-plate fiber optic shear sensors includes: a cross-plate head, a force transmission rod and a torque measurement unit; a protective sleeve is arranged inside the torque measurement unit; the cross-plate head includes a cross-plate blade and a cross-plate shaft rod; a fiber Bragg grating is arranged on the rectangular cross section of the torque measurement unit; the fiber Bragg grating is embedded in the protective sleeve; in each group of cross-plate fiber optic shear sensors: the cross-plate blades in multiple groups of cross-plate fiber optic shear sensors are located in a straight line. In this embodiment, by measuring the resisting torque received by multiple groups of connected cross-plate fiber optic shear sensors when rotating in clay, the undrained shear strength parameters of multiple discrete points can be calculated, and the distributed measurement of soil layer strength is realized, which improves the measurement efficiency, and the cross-plate shear instrument provided in this embodiment has low cost, clear soil shear failure mechanism, and can obtain more accurate measurement results.

[0037] The cross shear apparatus and the undrained shear strength parameter measurement method provided in this embodiment are further described in detail below in conjunction with the accompanying drawings.

[0038] This embodiment discloses a multi-point cross plate shear instrument, comprising: a plurality of groups of cross plate optical fiber shear sensors; each group of cross plate optical fiber shear sensors comprises: a cross plate head, a force transmission rod and a torque measuring unit; a protective cover is arranged inside the torque measuring unit. The cross plate head comprises a cross plate blade and a cross plate shaft rod; a fiber Bragg grating is arranged on a rectangular cross section of the torque measuring unit; and the fiber Bragg grating is embedded in the protective cover.

[0039] In each group of cross-plate optical fiber shear sensors: the cross-plate shaft rod, force transmission rod and torque measurement unit are coaxially connected in sequence, and the cross-plate blades in multiple groups of cross-plate optical fiber shear sensors are located in a straight line. Figure 1 and Figure 2 As shown, taking the cross-plate shear instrument including three sets of cross-plate optical fiber shear sensors as an example, Figure 2The cross-plate shear meter is composed of three groups of cross-plate optical fiber shear sensors connected together, each group of cross-plate optical fiber shear sensors includes: a cross-plate head, a force transmission rod and a torque measurement unit, wherein the first cross-plate optical fiber shear sensor located at the bottom includes: a first cross-plate head, a first force transmission rod 31 and a first torque measurement unit 51. The first cross-plate head includes: a first cross-plate blade 11, a first cross-plate shaft rod 21, and a first protective cover 41 is arranged inside the first torque measurement unit 51. A first optical fiber grating 61 is arranged on the rectangular cross section of the first torque measurement unit 51. Since there are four rectangular cross sections of the first torque measurement unit 51, the first optical fiber grating 61 is arranged on the four rectangular cross sections.

[0040] Similarly, the second cross-plate optical fiber shear sensor connected to the first cross-plate optical fiber shear sensor is also provided with a second cross-plate head, a second force transmission rod 32 and a second torque measuring unit 52. The second cross-plate head includes: a second cross-plate blade 12, a second cross-plate shaft rod 22, and a second protective cover 42 is provided inside the second torque measuring unit 52. A second optical fiber Bragg grating 62 is provided on the rectangular cross section of the second torque measuring unit 52. Since the second torque measuring unit 52 has four rectangular cross sections, the second optical fiber Bragg grating 62 is provided on each of the four rectangular cross sections.

[0041] The third cross plate optical fiber shear sensor connected to the second cross plate optical fiber shear sensor is also provided with a third cross plate head, a third force transmission rod 33 and a third torque measuring unit 53. The third cross plate head includes: a third cross plate blade 13, a third cross plate shaft rod 23, and a third protective cover 43 is provided inside the third torque measuring unit 53. A third optical fiber Bragg grating 63 is provided on the rectangular cross section of the third torque measuring unit 53. Since there are four rectangular cross sections of the third torque measuring unit 53, the third optical fiber Bragg grating 63 is provided on each of the four rectangular cross sections.

[0042] Specifically, for hard soil layers, the diameter of the cross-plate blade ranges from 35 to 50 mm, and for soft soil layers, the diameter of the cross-plate blade ranges from 75 to 100 mm. The height-to-diameter ratio of the cross-plate blade ranges from 1 to 2.5. The thickness of the cross-plate blade ranges from 0.8 to 3 mm. The diameter of the cross-plate shaft ranges from 14 to 20 mm. The diameter of the force transmission rod ranges from 18 to 36 mm. The cross-plate area ratio is less than or equal to 10%.

[0043] Furthermore, combined with Figure 2 As shown, the first fiber grating 61, the second fiber grating 62, and the third fiber grating 63 located in the protective cover are all connected to the signal transmission optical cable 7. The signal transmission optical cable 7 passes through the opening of the protective cover, passes through the gap between the cross plate shaft rod, the force transmission rod and the cross plate head, and is connected to the fiber grating demodulator.

[0044] Furthermore, since the size range of the cross plate blades is 1-2 mm, in the specific implementation, the cross plate blades are welded to the cross plate shaft rod. This ensures that the cross plate blades can be stably fixed on the cross plate shaft rod, and the welding speed is fast, which can improve the manufacturing efficiency. In addition, the cross plate blades and the cross plate shaft rod on the cross plate head can also be obtained by an integrated molding process, that is, the cross plate head including the cross plate blades and the cross plate shaft rod can be directly processed.

[0045] Furthermore, the cross plate head and the force transmission rod, the force transmission rod and the torque measurement unit, and the cross plate head and the torque measurement unit can be detachably connected.

[0046] The cross plate head, the force transmission rod and the torque measurement unit are arranged to be detachably connected. In one embodiment, in a group of cross plate optical fiber shear sensors, the cross plate shaft rod of the cross plate head and the force transmission rod are detachably connected by threaded connection, and the force transmission rod and the torque measurement unit are threadedly connected. Between two groups of cross plate optical fiber shear sensors, the cross plate head in the cross plate optical fiber shear sensor located above and the torque measurement unit of the cross plate optical fiber shear sensor located below are detachably connected, thereby realizing the connection of multiple groups of cross plate optical fiber shear sensors in sequence. In one embodiment, for the cross plate shaft rod of the bottom cross plate head, the cross plate shaft rod is docked with the force transmission rod in the manner of stud fitting screw hole, and the other end of the force transmission rod is docked with the torque measurement unit in the manner of stud fitting screw hole; for the cross plate shaft rod of the middle cross plate head, one cross plate shaft rod is docked with the force transmission rod in the manner of stud fitting screw hole, and the other cross plate shaft rod is docked with the bottom torque measurement unit in the manner of stud fitting screw hole, and the combination obtains a cross plate shear instrument.

[0047] In detail, the diameters of the cross plate shaft, the force transmission rod and the torque measuring unit are equal or gradually increase from bottom to top in the connection sequence; the sizes of the cross plate blades are equal from bottom to top or gradually increase from bottom to top in the arrangement sequence. The cross plate blades on each cross plate head are aligned with each other and are on the same straight line.

[0048] Specifically, the two ends of the cross-plate shaft and the torque measuring unit in each cross-plate optical fiber shear sensor in the present embodiment are equal-diameter round rods, the force transmission rod is an equal-diameter round rod or a variable-diameter round rod (the cross-sectional diameter of the bottom surface gradually increases from bottom to top), and the cross-plate shaft, the force transmission rod and the torque measuring unit are coaxially connected, that is, the axes (or center lines) of the cross-plate shaft, the force transmission rod and the torque measuring unit are consistent to form a common axis.

[0049] Furthermore, the fiber Bragg gratings are respectively arranged on four rectangular sections of the torque measurement unit, and the angle between the fiber Bragg gratings on one set of the rectangular sections and the center line is 45 degrees, and the angle between the fiber Bragg gratings on the other set of the rectangular sections and the center line is 135 degrees. Figure 3 As shown, Figure 2 Taking the third cross-plate optical fiber shear sensor as an example, four third optical fiber gratings 63 with the same sensitivity are respectively arranged on the four rectangular sections of the third torque measuring unit 53. The four rectangular sections are respectively regarded as A, B, C, and D. The angle between the third optical fiber gratings 63 on one set of opposite faces A and C and the center line is 45°, and the angle between the third optical fiber gratings 63 on the other set of opposite faces B and D and the center line is 135°.

[0050] Furthermore, the protective cover is provided with an opening, through which the fiber Bragg grating is connected to the signal transmission grating, and passes through the gap between the cross plate shaft, the force transmission rod and the cross plate blades, and is connected to an external fiber Bragg grating demodulator. Figure 3 As shown, the third fiber Bragg grating 63 is connected to the signal transmission cable 7. After the signal transmission cable 7 passes through the opening of the protective cover 4, it passes through the gap between the cross plate shaft rod, the force transmission rod and the cross plate blades and is connected to the fiber Bragg grating demodulator.

[0051] In one embodiment, the protective cover can be a hard plastic tube or a bendable metal sheet. After the fiber grating is arranged in the protective cover, the protective cover is fixed on the torque measurement unit and sealed with epoxy resin glue to prevent water leakage.

[0052] Combination Figure 4 and Figure 5 As shown, when the cross-plate shear instrument disclosed in this embodiment is used, the cross-plate shear instrument is placed in the soil layer, and the cross-plate shear instrument is controlled to rotate at a constant speed at a specified angular velocity in the soil layer. During the uniform rotation of the cross-plate shear instrument, the torque received by the torque measuring unit at the top is the cumulative value of the soil shear failure resistance received by all the cross-plate blades at the bottom of the torque measuring unit. Therefore, by measuring the torque received by each torque measuring unit at the top, the soil shear failure resistance received by each cross-plate blade can be calculated, thereby calculating the undrained shear strength parameter of the soil measured by each cross-plate blade.

[0053] The multi-point cross-plate shear instrument disclosed in this embodiment utilizes the characteristics of high precision, strong waterproof and anti-corrosion ability of fiber Bragg grating, and accurate distributed measurement, overcomes the defect that the penetration test can only indirectly measure the distribution value of the undrained shear strength parameter along the depth, and makes up for the deficiency that the traditional on-site in-situ test can only measure the undrained shear strength parameter of a single point, and the size of the cross-plate blades in the cross-plate shear instrument disclosed in this embodiment is set to be equal or gradually increase from bottom to top, which conforms to the characteristics that the undrained shear strength of marine clay increases along the depth, and ensures the accuracy requirements of distributed measurement of undrained shear strength. After the cross-plate shear instrument disclosed in the present invention is installed, each cross-plate blade is aligned in a straight line, and the diameter of the cross-plate shaft rod, force transmission rod, torque measurement unit, and the screw rod and screw hole of each structure are designed to be gradually increased from bottom to top, which not only meets the demand for increasing the bearing capacity of the upper instrument structure due to torque superposition, but also ensures that the penetration process of the multi-point cross-plate shear instrument will not cause additional disturbance to the measured soil layer.

[0054] Based on the above multi-point cross plate shear instrument, the present application also discloses a method for measuring undrained shear strength parameters, such as Figure 6 As shown, the method for measuring the undrained shear strength parameters is applied to the multi-point cross plate shear instrument provided in the above embodiment, and the steps include:

[0055] Step S1, placing the cross-plate shear instrument at a target detection position in the soil.

[0056] First, install the cross-plate shear instrument section by section according to the connection relationship from bottom to top, and make sure that the installed cross-plate shear instrument is vertical and stable. Then insert the installed cross-plate shear instrument into the soil at the predetermined depth. During the insertion process, the cross-plate shear instrument needs to be kept vertical to avoid bending.

[0057] Step S2, controlling the cross-plate shear instrument to rotate at a constant speed at a preset angular velocity, and collecting the torque applied to each torque measuring unit.

[0058] After standing still for a period of time, the cross-plate shear instrument is controlled to rotate at a preset angular velocity, and the central wavelength change of each fiber grating is collected. Based on the central wavelength change, the shear modulus of each torque measurement unit, and the torsional section coefficient of each torque measurement unit, the torque measured by each torque measurement unit is calculated.

[0059] Step S3: Calculate the undrained shear strength parameters of the soil at the location of each cross-plate blade according to the torque applied to each torque measuring unit.

[0060] According to the torque applied to each torque measuring unit obtained in the above steps, the undrained shear strength parameters of the soil at the location of each cross-plate blade are calculated.

[0061] Specifically, the step of calculating the undrained shear strength parameters of the soil at each cross-plate blade position according to the torque received by each torque measuring unit includes:

[0062] The undrained shear strength of the soil measured by the corresponding cross plate head is calculated based on the diameter of the cross plate blade, the height of the cross plate blade, the diameter of the cross plate shaft, and the torque measured by the corresponding torque measurement unit.

[0063] The specific method for calculating the undrained shear strength of the soil measured by the corresponding cross-plate head according to the diameter of the cross-plate blade, the height of the cross-plate blade, the diameter of the cross-plate shaft, and the torque measured by the corresponding torque measurement unit is as follows: using the undrained shear strength calculation formula, the undrained shear strength of the soil measured by the Nth cross-plate head from bottom to top is calculated as:

[0064]

[0065] Among them, M N is the torque on the Nth cross-plate blade, M N-1 is the torque on the N-1th cross plate blade, D N is the diameter of the Nth cross plate blade, H N is the height of the Nth cross plate blade, d N is the diameter of the N+1th cross plate shaft, where N≥2.

[0066] If the cross-plate shear instrument includes N groups, the central wavelength of the fiber Bragg grating set on the four surfaces of the Nth torque measurement unit changes by Δλ AN , Δλ BN , Δλ CN , Δλ DN They are:

[0067] Δλ AN =k ε (ε t45°-N +ε b45°-N )+k T ΔT (1)

[0068] Δλ BN =k ε (ε t135°-N +ε b135°-N )+k T ΔT (2)

[0069] Δλ CN =k ε (ε t45°-N -ε b45°-N )+k T ΔT (3)

[0070] ΔλDN =k ε (ε t135°-N -ε b135°-N )+k T ΔT (4)

[0071] Among them, ε t45°-N and ε t135°-N are the strains at 45° and 135° directions of the centerline caused by torque, ε t45°-N =-ε t135°-N , ε b45°-N and ε b135°-N are the strains at 45° and 135° of the centerline caused by the bending moment, ΔT is the temperature change during the measurement, k ε and k T are the strain sensitivity coefficient and temperature sensitivity coefficient of the fiber Bragg grating respectively.

[0072] The torque M measured by the Nth torque measuring unit from bottom to top N for: (5)

[0074] M N =2G N W pN ε t45°-N

[0075] In the above formula, G N is the shear modulus of the Nth torque measurement unit, W pN is the torsional section coefficient of the Nth torque measurement unit.

[0076] Formula (1) + (3) - (2) - (4) gives

[0077]

[0078] Substituting formula (6) into formula (5), we can obtain the torque M measured by the Nth torque measurement unit from bottom to top: N for

[0079]

[0080] The undrained shear strength C of the soil measured by the first cross plate head from bottom to top u1 for:

[0081]

[0082] Where G1 is the shear modulus of the material of the Nth torque measurement unit, W p1 is the torsional section coefficient of the Nth torque measurement unit, D1 is the diameter of the first cross plate blade 11, H1 is the height of the first cross plate blade 11, d1 is the diameter of the first cross plate shaft 21 (such as Figure 7As shown), Δλ A1 , Δλ B1 , Δλ C1 and Δλ D1 They are the changes of the central wavelength of the fiber Bragg grating on the four surfaces of cross section A, B, C, and D respectively.

[0083] The undrained shear strength C of the soil measured by the Nth (N≥2) cross plate head from bottom to top uN for:

[0084]

[0085] Among them, G N is the shear modulus of the material of the Nth torque measurement unit, W pN is the torsional section coefficient of the Nth torque measuring unit, D N H is the diameter of the cross plate blade 1N, N is the height of the cross plate blade 1-N, d N is the diameter of the cross plate shaft 2N (such as Figure 8 As shown), Δλ AN , Δλ BN , Δλ CN and Δλ DN They are the changes of the central wavelength of the fiber Bragg grating on the four surfaces of cross section A, B, C, and D respectively.

[0086] In the specific operation, the cross-plate shear instrument is pushed vertically into the soil at a specified depth, left to stand for 2 minutes, and then rotated at a constant angular speed of 6-12° / min within 5 minutes to record C uN Data changing with rotation angle until the undrained shear strength peak C uN-p After that, continue to rotate for 1-2 minutes. Then quickly rotate the cross plate shear instrument for 5-10 turns to measure the undrained shear strength peak value C uN-p The angular velocity used to measure the residual value of undrained shear strength C uN-r , soil sensitivity (S t ) Available S t =C uN-p / C uN-r Perform calculations.

[0087] In a specific embodiment, the following steps can be used to measure the undrained shear strength parameters using the cross plate shear instrument provided in this embodiment:

[0088] First, determine the maximum range Cmax-N (Pa) of each cross-plate head of the cross-plate shear instrument for measuring undrained shear strength.

[0089] Secondly, refer to Fig. 9According to the specification requirements listed in Table 1, the size of the first cross plate blade 11 is selected, including the diameter, height and thickness of the cross plate blade; also refer to Table 1 to select the diameter of the first cross plate shaft rod 21 and the first force transmission rod 31;

[0090] Among them, the cross plate area ratio

[0091] Combination Figure 4 and Figure 8 As shown, the first cross plate shaft rod 21 is a round rod with a uniform cross section, and the distance H' from the top of the first cross plate shaft rod 21 to the upper surface of the first cross plate blade 11 is N Should be larger than its diameter (d' N ), the length of the first force transmission rod 31 can be adjusted arbitrarily according to measurement requirements.

[0092] Next, calculate the maximum torque T that the Nth segment can withstand. max-N The maximum torque received by the first cross plate shaft 21, the first force transmission rod 31 and the first torque measurement unit 51 is:

[0093]

[0094] The maximum torque on the Nth (N≧2) cross plate shaft 2N, force transmission rod 3N, and Nth torque measurement unit 5N is:

[0095]

[0096] From this, calculate the 2N torque T of the Nth cross plate shaft max-N Is the shear stress under the action less than the maximum shear stress limit of the material used for processing? The shear stress under the torque of the Nth cross plate shaft is;

[0097]

[0098] Finally, if the elastic modulus E and Poisson's ratio μ of the material used for the torque measuring unit are known, the finite element software can be used to calculate the torque measuring unit 5N under torque T max-N and T max-(N-1) Shear strain ε under (N≥2) 45°-N (με) and ε 45°-(N-1) (με), ε 45°-N It should be less than the maximum shear strain limit of the material used for processing.

[0099] The accuracy of the undrained shear strength measured by the Nth cross plate head is (Pa / με), which can also be expressed as k ε (pm / με)) is the strain sensitivity coefficient of the fiber Bragg grating.

[0100] The present invention provides a multi-point cross-plate shear instrument and an undrained shear strength parameter measurement method, the cross-plate shear instrument includes multiple groups of cross-plate optical fiber shear sensors; each group of cross-plate optical fiber shear sensors includes: a cross-plate head, a force transmission rod and a torque measurement unit; a protective cover is arranged inside the torque measurement unit; the cross-plate head includes a cross-plate blade and a cross-plate shaft rod; a fiber grating is arranged on the rectangular cross section of the torque measurement unit; the fiber grating is embedded in the protective cover; in each group of cross-plate optical fiber shear sensors: the cross-plate shaft rod, the force transmission rod and the torque measurement unit are coaxially connected in sequence, and the cross-plate blades in the multiple groups of cross-plate optical fiber shear sensors are located in a straight line. In this embodiment, multiple groups of connected cross-plate optical fiber shear sensors are used to overcome the deficiency that the on-site in-situ test can only measure the undrained shear strength parameters of a single point, and the distributed measurement of soil layer strength is realized.

[0101] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the protection scope of the claims attached to the present invention.

Claims

1. A multi-point cross plate shear instrument, characterized in that: include: Multiple sets of cross-plate optical fiber shear sensors; Each set of cross-plate optical fiber shear sensor includes: a cross-plate head, a force transmission rod and a torque measurement unit; A protective cover is provided inside the torque measuring unit; the cross plate head includes a cross plate blade and a cross plate shaft; a fiber Bragg grating is provided on the rectangular cross section of the torque measuring unit; the fiber Bragg grating is embedded in the protective cover; In each group of cross-plate optical fiber shear sensors: the cross-plate shaft rod, the force transmission rod and the torque measurement unit are coaxially connected in sequence, and the cross-plate blades in the multiple groups of cross-plate optical fiber shear sensors are located in a straight line.

2. The multi-point cross plate shearing instrument according to claim 1, characterized in that: The cross plate head and the force transmission rod, the force transmission rod and the torque measuring unit, and the cross plate head and the torque measuring unit can be detachably connected.

3. The multi-point cross plate shearing instrument according to claim 1, characterized in that: The fiber gratings are respectively arranged on four rectangular sections of the torque measurement unit, and the angle between the fiber gratings on one group of relative rectangular sections and the center line is 45°, and the angle between the fiber gratings on the other group of relative rectangular sections and the center line is 135°.

4. The multi-point cross plate shearing instrument according to claim 1, characterized in that: The protective cover is provided with an opening, through which the fiber Bragg grating is connected to the signal transmission grating, and passes through the gap between the cross plate shaft rod, the force transmission rod and the cross plate blades to be connected to the fiber Bragg grating demodulator.

5. The multi-point cross plate shearing instrument according to claim 1, characterized in that: The material of the protective cover is plastic or metal sheet; the protective cover is fixedly packaged on the surface of the torque measuring unit.

6. The multi-point cross plate shearing instrument according to any one of claims 1 to 5, characterized in that: The diameters of the cross plate shaft, force transmission rod and torque measurement unit are equal or gradually increase from bottom to top along the connection sequence; the sizes of the cross plate blades are equal from bottom to top or gradually increase from bottom to top along the arrangement sequence.

7. The multi-point cross plate shearing instrument according to claim 6, characterized in that: The cross plate blades on each cross plate head are aligned and located on the same straight line.

8. A method for measuring undrained shear strength parameters, characterized in that: Applied to the multi-point cross plate shear instrument according to any one of claims 1 to 7, the steps of the undrained shear strength parameter measurement method include: Push the cross-plate shear instrument vertically and uniformly into the target detection position in the soil; Controlling the cross-plate shear instrument to rotate at a constant speed at a preset angular velocity, and collecting the torque applied to each torque measuring unit; The undrained shear strength parameters of the soil at each cross-plate blade position are calculated based on the torque applied to each torque measuring unit.

9. The undrained shear strength parameter measurement method according to claim 8, characterized in that: The step of calculating the undrained shear strength parameters of the soil at the target detection position received by each cross-plate blade according to the torque received by each torque measuring unit comprises: The undrained shear strength of the soil at the location measured by the corresponding cross-plate head is calculated based on the diameter of the cross-plate blade, the height of the cross-plate blade, the diameter of the cross-plate shaft, and the torque measured by the corresponding torque measurement unit.

10. The undrained shear strength parameter measurement method according to claim 9, characterized in that: The specific method for calculating the undrained shear strength of the soil body measured by the corresponding cross-plate head according to the diameter of the cross-plate blade, the height of the cross-plate blade, the diameter of the cross-plate shaft, and the torque measured by the corresponding torque measurement unit is as follows: using the undrained shear strength calculation formula, the undrained shear strength of the soil body measured by the Nth cross-plate head from bottom to top is calculated as: Among them, M N is the torque on the Nth cross-plate blade, M N-1 is the torque on the N-1th cross plate blade, D N is the diameter of the Nth cross plate blade, H N is the height of the Nth cross plate blade, d N is the diameter of the Nth cross plate shaft, where N ≥ 2.

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