Inclined plate penetrometer and effective stress parameter measuring method thereof

Abstract

The invention discloses a swash plate penetrometer and an effective stress parameter measuring method thereof. The swash plate penetrometer comprises a frame, a conical tip resistance sensor, a pore water pressure sensor, an effective stress sensor array, a shear strength sensor array and a penetration resistance sensor. The distance between the first side surface and the second side surface is gradually reduced from top to bottom; and the positions of the effective stress sensors in the effective stress sensor array are the same as the positions of the corresponding shear strength sensors in the shear strength sensor array. The inclined plate penetrometer can measure effective stress, shear strength, conical tip resistance, pore water pressure and total penetration resistance at the same time, and the distances between the effective stress sensors and the central axis of the penetrometer and between the shear strength sensors and the central axis of the penetrometer are different. The in-situ undisturbed effective stress and the in-situ undisturbed shear strength when the distance is 0 can be calculated; the effective friction angle and the effective cohesive force can be calculated according to the Moire-Coulomb failure criterion.

Description

Technical Field

[0001] The invention relates to the technical field of penetrometers, and in particular to an inclined plate penetrometer and a method for measuring effective stress parameters thereof. Background Art

[0002] In the field of geotechnical and marine engineering, the measurement of foundation soil strength parameters is crucial, among which the effective stress generated by the contact of soil particle skeletons directly affects the strength of foundation soil. At present, the means of measuring soil strength parameters are mainly unit tests in laboratories. In order to simulate the stress state of soil samples in real environments, it is usually necessary to apply a certain effective stress / effective confining pressure to the unit samples. Common laboratory measurement methods include triaxial compression tests, direct shear tests, and unconfined compression tests. However, before the test, it is necessary to take samples from the site. During this process, the samples will be affected by human or mechanical equipment interference, loss during transportation, and environmental factors, resulting in differences between the soil samples and the in-situ state. Especially in the marine environment, sampling is difficult, and the soil samples are mostly soft soils, which are more susceptible to interference from the external environment, ultimately leading to inaccurate measurement results.

[0003] In order to obtain more accurate soil strength parameters, in-situ measurement technology is widely used in various engineering environments. Compared with laboratory measurement methods, in-situ measurement technology reduces the interference to the sample during sampling and transportation, and can directly obtain the strength parameters of the soil sample in the in-situ state. Especially in wide water environments such as oceans, lakes and rivers, the cost of using laboratory methods to evaluate soil strength parameters is relatively high, and the in-situ test method can better reflect the advantages. At present, the mainstream in-situ test methods are cone tip penetration test (CPTu), cross plate shear test (VST) and flat shovel lateral expansion test (DMT). The above methods all penetrate the probe into the soil and actively or passively measure the pressure exerted on it by the soil. The cone tip penetration test continuously penetrates the probe into the soil at a constant rate. This test can directly measure the cone tip resistance q c , sleeve friction force f s and pore water pressure u, and then calculate the effective friction angle of the soil based on the empirical formula and empirical coefficient Effective stress parameters such as effective cohesion c' and shear strength τ. For the cross-plate shear test, a cross blade is inserted into the undisturbed soil and the blade is rotated at a constant speed to measure the torque required to shear the soil with the blade. By using limit equilibrium analysis, the torque or moment is converted into the shear strength τ of the soil. In the flat shovel lateral expansion test, after the sensor is inserted into the soil, the metal film at the center of the sensor is actively expanded to measure the resistance of the film to the deformation of the soil. After that, the shear strength τ and the effective friction angle can be calculated through empirical formula calculation. And the lateral earth pressure coefficient K0.

[0004] Although the above-mentioned in-situ test method solves the problem of excessive disturbance of soil samples by laboratory test methods, it is still necessary to use multiple in-situ test methods to obtain multiple formation parameters of a certain soil layer, and the effective stress parameters need to be calculated based on empirical coefficients, and the accuracy of the data cannot be guaranteed. Furthermore, unlike the in-situ measurement method on land, the in-situ measurement method under marine conditions is more expensive and requires the assistance of a complex measurement system.

[0005] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0006] The technical problem to be solved by the present invention is that, in view of the above-mentioned defects of the prior art, an inclined plate penetrometer and an effective stress parameter measurement method thereof are provided, aiming to solve the problem in the prior art that the accuracy of the data needs to be improved due to the use of different test methods to measure various formation parameters.

[0007] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0008] An inclined plate penetrometer, comprising:

[0009] frame;

[0010] A cone tip resistance sensor is arranged at the lower end of the frame;

[0011] A pore water pressure sensor is located in the frame and connected to the cone of the cone tip resistance sensor;

[0012] an array of effective stress sensors disposed on a first side of the frame;

[0013] a shear strength sensor array, disposed on the second side of the frame;

[0014] A penetration resistance sensor is arranged at the upper end of the frame;

[0015] Wherein, from top to bottom, the distance between the first side surface and the second side surface gradually decreases;

[0016] The effective stress sensors in the effective stress sensor array and the shear strength sensors in the shear strength sensor array are both arranged from top to bottom;

[0017] The positions of the effective stress sensors in the effective stress sensor array are the same as the positions of the corresponding shear strength sensors in the shear strength sensor array.

[0018] The inclined plate penetrometer, wherein the effective stress sensor array has three effective stress sensors, the first side surface of the frame forms three main mounting grooves, and each main mounting groove is connected to a plurality of auxiliary mounting grooves;

[0019] The effective stress sensor comprises:

[0020] A circular structure is installed in the main installation groove, a cavity is formed in the circular structure, and a plurality of water holes are formed on the side wall of the circular structure, and two ends of the water holes are respectively connected to the auxiliary installation groove and the cavity;

[0021] A first strain sensing element is disposed inside the circular structure and along the radial direction of the circular structure;

[0022] A plurality of first permeable stones are installed in corresponding auxiliary installation grooves.

[0023] The inclined plate penetrometer, wherein the shear strength sensor array has three shear strength sensors, the second side of the frame forms a sliding channel, and the sliding channel has three openings;

[0024] The shear strength sensor comprises:

[0025] A fixed block, fixedly connected to the sliding channel;

[0026] A sliding block, located in the sliding channel;

[0027] a friction plate, located in the corresponding opening and connected to the sliding block;

[0028] A beryllium copper sheet, two ends of which are respectively connected to the sliding block and the fixed block;

[0029] A second strain sensing element is disposed on the beryllium copper sheet and is disposed along the length direction of the beryllium copper sheet;

[0030] Wherein, the beryllium copper sheet and the second strain sensing element are both located between the sliding block and the friction plate.

[0031] The inclined plate penetrometer, wherein the pore water pressure sensor comprises:

[0032] a second permeable stone, located between the frame and the cone;

[0033] A water-permeable pipe, arranged on the cone and connected with the second water-permeable stone;

[0034] The pore water pressure sensor body is arranged at one end of the permeable pipe away from the second permeable stone.

[0035] The inclined plate penetrometer, wherein the cone tip resistance sensor comprises:

[0036] A cone, which is in close contact with the lower surface of the second permeable stone;

[0037] A silicone pad is located between the frame and the second permeable stone, the silicone pad forms a through hole, the cone forms a boss on one side facing the silicone pad, the boss passes through the through hole, and a channel is formed in the boss to connect the permeable pipe and the second permeable stone;

[0038] An arched beam structure, wherein the lower end of the arched beam structure is placed on the boss, and the upper end of the arched beam structure is against the frame;

[0039] The third strain sensing element is disposed on the arched beam structure and along the length direction of the arched beam structure.

[0040] The oblique plate penetrometer, wherein the first strain sensing element, the second strain sensing element and the third strain sensing element are all selected from fiber Bragg gratings or resistive strain gauges.

[0041] The inclined plate penetrometer, wherein the penetration resistance sensor comprises:

[0042] A first support cylinder is mounted on the frame;

[0043] A second support cylinder;

[0044] A plurality of second arched beams, two ends of the second arched beams are respectively connected to the first support tube and the second support tube;

[0045] a fourth strain sensing element, disposed on the second arched beam and arranged along the length direction of the second arched beam;

[0046] A sleeve is arranged on the frame and sleeved outside the second arched beam and the second supporting tube.

[0047] A method for measuring effective stress parameters of an inclined plate penetrometer as described in any one of the above, comprising the steps of:

[0048] The inclined plate penetrometer was injected with water and soaked, and then sealed with a plastic film to keep the pore water pressure sensor and the effective stress sensor saturated;

[0049] Fix the electric cylinder above the saturated soil sample to be tested, fix the inclined plate penetrometer at the bottom of the electric cylinder, and connect the signal transmission cable of the cone tip resistance sensor, the signal transmission cable of the pore water pressure sensor, the signal transmission cable of the effective stress sensor array, the signal transmission cable of the shear strength sensor array, and the signal transmission cable of the penetration resistance sensor to a signal demodulator; wherein there is water on the saturated soil sample to be tested, and the inclined plate penetrometer is located in the water;

[0050] After removing the plastic film, the electric cylinder is started, and the inclined plate penetrometer is penetrated into the saturated soil sample to be tested at a constant speed, and the pore water pressure, cone tip resistance, penetration resistance, effective stress and shear strength at a certain moment are collected through the signal demodulator;

[0051] Determine the in-situ undisturbed effective stress and the in-situ undisturbed shear strength according to the effective stress and the shear strength; determine the effective friction angle and the effective cohesion according to the in-situ undisturbed effective stress and the in-situ undisturbed shear strength;

[0052] The consolidation coefficient is determined based on the pore water pressure and the initial pore water pressure.

[0053] The effective stress parameter measurement method of the inclined plate penetrometer, wherein the in-situ undisturbed effective stress is:

[0054]

[0055]

[0056] The in-situ undisturbed shear strength is:

[0057]

[0058] The effective friction angle and the effective cohesion satisfy the following relationship:

[0059]

[0060] Where σ'0 represents the in-situ undisturbed effective stress, represents the mean effective stress, σ i ' represents the effective stress of the ith effective stress sensor at a certain moment, τ0 represents the in-situ undisturbed shear strength, represents the average shear strength, τ i represents the shear strength of the ith shear strength sensor at a certain moment, β1 represents the slope of the effective stress-distance relationship, β2 represents the slope of the shear strength-distance relationship, n represents the number of effective stress sensors, represents the average distance from the effective stress sensor to the center axis of the inclined plate penetrometer, d i represents the distance from the ith effective stress sensor to the central axis of the inclined plate penetrometer, ∑ represents the summation, tan(·) represents the tangent function, represents the effective friction angle, and c' represents the effective cohesion.

[0061] The effective stress parameter measurement method of the inclined plate penetrometer, wherein the consolidation coefficient is:

[0062]

[0063] Among them, c h represents the consolidation coefficient, w represents the width, T * Indicates the time coefficient, time coefficient T * According to the numerical table of time coefficient and soil consolidation degree and soil consolidation degree U v OK, I r represents the stiffness coefficient of the saturated soil sample to be tested, f represents the correction coefficient, t represents the measurement time, U v represents the degree of soil consolidation, u i represents the initial pore water pressure, u e Represents the pore water pressure at a certain moment.

[0064] Beneficial effects: The inclined plate penetrometer can simultaneously measure effective stress, shear strength, cone tip resistance, pore water pressure and overall penetration resistance. Since multiple effective stress sensors and multiple shear strength sensors are at different distances from the central axis of the penetrometer, the effective stress and shear strength when the distance is 0 can be calculated according to the extrapolation method, that is, the effective stress and shear strength without disturbance in situ; further, the effective friction angle and effective cohesion without disturbance in situ can be calculated according to the Mohr-Coulomb failure criterion. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a schematic diagram of the connection between the inclined plate penetrometer and the signal demodulator in an embodiment of the present invention.

[0066] Figure 2 is a photograph of the inclined plate penetrometer in an embodiment of the present invention in an experimental scenario.

[0067] Figure 3 It is a first structural schematic diagram of the inclined plate penetrometer in an embodiment of the present invention.

[0068] Figure 4 2 is a second structural schematic diagram of the inclined plate penetrometer in an embodiment of the present invention.

[0069] Figure 5 1 is an exploded view of the inclined plate penetrometer in an embodiment of the present invention.

[0070] Figure 6 is a cross-sectional view of the inclined plate penetrometer in an embodiment of the present invention.

[0071] Figure 7 yes Figure 6 Magnified image of .

[0072] Figure 8 Schematic diagram of the structure of the main installation slot in an embodiment of the present invention.

[0073] Fig. 9 Schematic diagram of the structure of the pore water pressure sensor in the embodiment of the present invention.

[0074] Fig.10 It is a first structural diagram of the framework in an embodiment of the present invention.

[0075] Fig.11 2 is a schematic diagram of the second structure of the framework in an embodiment of the present invention.

[0076] Fig.12 Schematic diagram of the structure of the cone in the embodiment of the present invention.

[0077] Fig.13 Schematic diagram of the relationship between effective stress, shear strength and the distance from the central axis in an embodiment of the present invention.

[0078] Fig.14 It is a schematic diagram of the principle of effective stress at different depths in an embodiment of the present invention.

[0079] Fig.15 is a graph of effective stress at different depths in an embodiment of the present invention.

[0080] Fig.16 It is a schematic diagram of the principle of shear strength at different depths in an embodiment of the present invention.

[0081] Fig.17 is a graph of shear strength at different depths in an embodiment of the present invention.

[0082] Description of reference numerals:

[0083] 10. frame; 11. main mounting groove; 12. auxiliary mounting groove; 13. sliding channel; 14. opening; 20. cone tip resistance sensor; 21. cone; 211. boss; 212. channel; 22. silicone cushion; 23. contact plate; 24. first arched beam; 30. pore water pressure sensor; 31. second permeable stone; 32. permeable pipe; 33. pore water pressure sensor body; 4. effective stress sensor array; 40. effective stress sensor; 4 1. Circular structure; 411. Cavity; 412. Water hole; 42. First permeable stone; 5. Shear strength sensor array; 50. Shear strength sensor; 51. Fixed block; 52. Sliding block; 53. Friction plate; 54. Beryllium copper sheet; 55. Cable fixing plate; 60. Penetration resistance sensor; 61. First support tube; 62. Second support tube; 63. Second bow beam; 64. Sleeve; 71. Extension tube; 72. Electric cylinder; 73. Signal demodulator. DETAILED DESCRIPTION

[0084] 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.

[0085] Please also see Figure 1-Figure 17 , the present invention provides some embodiments of an inclined plate penetrometer.

[0086] like Figure 1 and Figure 6 As shown, the inclined plate penetrometer of the present invention comprises:

[0087] Frame 10;

[0088] A cone tip resistance sensor 20 is disposed at the lower end of the frame 10;

[0089] The pore water pressure sensor 30 is located in the frame 10 and connected to the cone 21 of the cone tip resistance sensor 20;

[0090] An effective stress sensor array 4 is disposed on a first side surface of the frame 10;

[0091] A shear strength sensor array 5 is arranged on the second side surface of the frame 10;

[0092] a penetration resistance sensor 60 , disposed at the upper end of the frame 10 ;

[0093] Among them, from top to bottom, the distance between the first side surface and the second side surface gradually decreases; the effective stress sensor 40 in the effective stress sensor array 4 and the shear strength sensor 50 in the shear strength sensor array 5 are both arranged from top to bottom; the position of the effective stress sensor 40 in the effective stress sensor array 4 is the same as the position of the corresponding shear strength sensor 50 in the shear strength sensor array 5.

[0094] Specifically, the frame 10 provides support force to facilitate the assembly of various sensors. The frame 10 has a certain strength and can penetrate the soil sample smoothly. The cone tip resistance sensor 20 is used to detect the cone tip resistance, the pore water pressure sensor 30 is used to detect the pore water pressure, the effective stress sensor array 4 is used to detect the effective stress, the shear strength sensor array 5 is used to detect the shear strength, and the penetration resistance sensor 60 is used to detect the penetration resistance. The cone tip sensor is located at the lower end of the frame 10, and the cone tip sensor first contacts and penetrates the soil sample; the penetration resistance sensor 60 is located at the upper end of the frame 10, and the penetration resistance sensor 60 is connected to the telescope, and the telescope realizes the penetration of the inclined plate penetrometer by telescoping. Figure 2 As shown, the telescopic device can be an electric cylinder 72, and the electric cylinder 72 is connected to the penetration resistance sensor 60 through an extension tube 71. Figure 1As shown, the signal transmission cables of each sensor can be connected to the signal demodulator 73 for data collection. The pore water pressure sensor 30 is located in the frame 10 and is connected to the cone 21 of the cone tip resistance sensor 20. The cone 21 is not only conducive to penetrating the soil sample, but also conducive to the circulation of water, so that the pore water pressure sensor 30 can detect the pore water pressure. The effective stress sensor 40 and the shear strength sensor 50 are respectively located on both sides of the frame 10, namely the first side and the second side. The first side and the second side form an angle, forming an inclined plate penetrometer.

[0095] From bottom to top, the first side surface and the second side surface are both inclined in a direction away from the central axis of the inclined plate penetrometer. The effective stress sensor array 4 has at least two effective stress sensors 40 arranged from bottom to top on the first side surface. The shear strength sensor array 5 has at least two shear strength sensors 50 arranged from bottom to top on the second side surface. The positions of the effective stress sensors 40 and the corresponding positions of the shear strength sensors 50 are symmetrical about the central axis of the inclined plate penetrometer, and the penetration depths of the two are the same.

[0096] The inclined plate penetrometer can simultaneously measure effective stress, shear strength, cone tip resistance, pore water pressure and overall penetration resistance. Since the multiple effective stress sensors 40 and the multiple shear strength sensors 50 are at different distances from the central axis of the penetrometer, the effective stress and shear strength when the distance is 0 can be calculated according to the extrapolation method, that is, the effective stress and shear strength of the in-situ undisturbed state; further, the effective friction angle and effective cohesion of the in-situ undisturbed state can be calculated according to the Mohr-Coulomb failure criterion.

[0097] In a preferred implementation of the embodiment of the present invention, Figure 3 , Figure 5 , Figure 6 as well as Figure 8 As shown, there are three effective stress sensors 40 in the effective stress sensor array 4 , and three main installation slots 11 are formed on the first side surface of the frame 10 . Each main installation slot 11 is connected to a plurality of auxiliary installation slots 12 .

[0098] Specifically, a main mounting groove 11 and an auxiliary mounting groove 12 are formed on the first side of the frame 10. The number of the main mounting grooves 11 is determined according to the number of effective stress sensors 40. Each main mounting groove 11 is installed with a corresponding effective stress sensor 40. Each main mounting groove 11 corresponds to a plurality of auxiliary mounting grooves 12. The auxiliary mounting grooves 12 are connected to the main mounting grooves 11, and external water can flow from the auxiliary mounting grooves 12 into the main mounting grooves 11.

[0099] In a preferred implementation of the embodiment of the present invention, Figure 3 , Figure 5 , Figure 7 as well as Fig.11As shown, the effective stress sensor 40 includes:

[0100] A circular structure 41 is installed in the main installation groove 11, a cavity 411 is formed in the circular structure 41, and a plurality of water holes 412 are formed on the side wall of the circular structure 41, and two ends of the water holes 412 are respectively connected to the auxiliary installation groove 12 and the cavity 411;

[0101] A first strain sensing element is disposed inside the circular structure 41 and along the radial direction of the circular structure 41;

[0102] A plurality of first permeable stones 42 are installed in corresponding auxiliary installation grooves 12 .

[0103] Specifically, the circular structure 41 is circular in shape, and a cavity 411 is formed inside, and water can be contained in the cavity 411. The side of the circular structure 41 that faces away from the shear strength sensor 50 is a sensing surface, and a first strain sensing element is arranged on the inner side of the sensing surface. The first strain sensing element is arranged along the radial direction of the circular structure 41 to measure the radial strain change on the sensing surface, thereby realizing the detection of effective stress. There can be multiple first strain sensing elements on each sensing surface. The circular structure 41 is located in the main mounting groove 11, and multiple water holes 412 are formed on the side wall of the circular structure 41. The two ends of the water holes 412 are respectively connected to the auxiliary mounting groove 12 and the cavity 411 of the circular structure 41, and the water in the auxiliary mounting groove 12 can enter the cavity 411 through the water holes 412. The number of the first permeable stones 42 is consistent with the number of the auxiliary mounting grooves 12, and the first permeable stones 42 are installed in the auxiliary mounting grooves 12.

[0104] In a preferred implementation of the embodiment of the present invention, Figure 4 , Figure 5 , Figure 6 as well as Fig.10 As shown, there are three shear strength sensors 50 in the shear strength sensor array 5 , and the second side surface of the frame 10 forms a sliding channel 13 , and the sliding channel 13 has three openings 14 .

[0105] Specifically, the number of the shear strength sensors 50 is consistent with the number of the effective stress sensors 40 . The second side surface of the frame 10 forms a slide channel 13 , and the slide channel 13 has three openings 14 , and the positions of the openings 14 correspond to the positions of the effective stress sensors 40 .

[0106] In a preferred implementation of the embodiment of the present invention, Figure 4 , Figure 5 , Figure 7 as well as Fig.10 As shown, the shear strength sensor 50 includes:

[0107] A fixing block 51, fixedly connected to the sliding channel 13;

[0108] A sliding block 52, located in the sliding channel 13;

[0109] The friction plate 53 is located in the corresponding opening 14 and connected to the sliding block 52;

[0110] A beryllium copper sheet 54, two ends of which are respectively connected to the sliding block 52 and the fixed block 51;

[0111] A second strain sensing element is disposed on the beryllium copper sheet 54 and is disposed along the length direction of the beryllium copper sheet 54;

[0112] The beryllium copper sheet 54 and the second strain sensing element are both located between the sliding block 52 and the friction plate 53 .

[0113] Specifically, the fixed block 51 and the sliding block 52 are both located in the sliding channel 13, the fixed block 51 is fixed relative to the sliding channel 13, and the sliding block 52 slides relative to the sliding channel 13. The friction plate 53 is located in the opening 14, and there is a gap between the upper surface of the friction plate 53 and the side wall of the opening 14. When the friction plate 53 moves upward due to the friction force, the gap avoids the friction plate 53. The two ends of the beryllium copper sheet 54 are respectively connected to the sliding block 52 and the fixed block 51. When the friction plate 53 moves upward due to the friction force, the sliding block 52 is driven to move upward, thereby stretching the beryllium copper sheet 54 and the second strain sensing element. The second strain sensing element detects the strain change of the beryllium copper sheet 54 to achieve the shear strength detection. The second strain sensing element is located on the outer side of the beryllium copper sheet 54, that is, the side of the beryllium copper sheet 54 facing the friction plate 53. The beryllium copper sheet 54 can be connected to the sliding block 52 and the fixed block 51 respectively using a cable fixing plate 55.

[0114] In a preferred implementation of the embodiment of the present invention, Figure 6 , Figure 7 as well as Fig. 9 As shown, the pore water pressure sensor 30 includes:

[0115] A second permeable stone 31, located between the frame 10 and the cone 21;

[0116] A water-permeable pipe 32 is provided on the cone 21 and communicated with the second water-permeable stone 31;

[0117] The pore water pressure sensor body 33 is disposed at one end of the water permeable pipe 32 away from the second water permeable stone 31 .

[0118] Specifically, water from the outside can penetrate the second permeable stone 31 and enter the sensor body through the permeable pipe 32. A fifth strain sensing element is provided on the sensing surface of the pore water pressure sensor body 33 to sense the strain change on the sensing surface and realize the detection of pore water pressure.

[0119] In a preferred implementation of the embodiment of the present invention, Figure 7 , Fig. 9 as well as Fig.12 As shown, the cone tip resistance sensor 20 includes:

[0120] The cone 21 is in close contact with the lower surface of the second permeable stone 31;

[0121] A silicone pad 22 is located between the frame 10 and the second permeable stone 31. The silicone pad 22 forms a through hole. A boss 211 is formed on a side of the cone 21 facing the silicone pad 22. The boss 211 passes through the through hole. A channel 212 is formed in the boss 211 to connect the permeable pipe 32 and the second permeable stone 31.

[0122] An arched beam structure, wherein the lower end of the arched beam structure is placed on the boss 211 and the upper end of the arched beam structure is against the frame 10;

[0123] The third strain sensing element is disposed on the arched beam structure and along the length direction of the arched beam structure.

[0124] Specifically, the silicone cushion 22 can be deformed. When the cone 21 contacts the soil sample, it is subjected to the pressure of the soil sample, the cone 21 moves upward, the silicone cushion 22 is compressed, the arched beam structure is deformed under pressure, and is sensed by the third strain sensing element. The cone 21 can be a tetrahedron, and the inclination angle of the tetrahedron is 60°. The third strain sensing element is arranged along the length direction of the arched beam structure, that is, along the vertical direction. A boss 211 is formed on the upper side of the cone 21, and the boss 211 can be used for the arched beam structure to abut against. When the cone 21 is pressed and moved, the arched beam structure will be squeezed and deformed. The boss 211 and the cone 21 are integrally formed, and a channel 212 is formed in the boss 211 to realize the connection between the second permeable stone 31 and the permeable pipe 32. After the external water passes through the second permeable stone 31, it enters the channel 212 and reaches the permeable pipe 32 and the pore water pressure sensor body 33. The arched beam structure includes: a first arched beam 24 and a contact plate 23 ; the first arched beam 24 and the contact plate 23 are integrally formed, and the contact plate 23 is located below the first arched beam 24 .

[0125] In a preferred implementation manner of the embodiment of the present invention, the first strain sensing element, the second strain sensing element and the third strain sensing element are all selected from fiber Bragg gratings or resistive strain gauges.

[0126] Specifically, the first strain sensing element, the second strain sensing element, and the third strain sensing element may be the same strain sensing element or different strain sensing elements, and the strain sensing element is selected from a fiber Bragg grating (FBG) and a resistive strain gauge.

[0127] In a preferred implementation of the embodiment of the present invention, Figure 1 and Figure 6 As shown, the penetration resistance sensor 60 includes:

[0128] A first support tube 61 is mounted on the frame 10;

[0129] A second support tube 62;

[0130] A plurality of second arched beams 63, two ends of the second arched beams 63 are respectively connected to the first support tube 61 and the second support tube 62;

[0131] a fourth strain sensing element, disposed on the second arched beam 63 and arranged along the length direction of the second arched beam 63;

[0132] The sleeve 64 is disposed on the frame 10 and sleeved outside the second arched beam 63 and the second supporting tube 62 .

[0133] Specifically, the first support tube 61 is installed on the installation tube, and the second support tube 62 is connected to the telescopic device (or electric cylinder 72). The second support tube 62 can adopt a threaded structure and be threadedly connected to the extension tube 71. The extension tube 71 is connected to the electric cylinder 72, and the inclined plate penetrometer penetrates the soil sample through the electric cylinder 72. The electric cylinder 72 can adopt a servo electric cylinder 72, which is conducive to controlling the penetration speed of the inclined plate penetrometer. The two ends of the second arched beam 63 are respectively connected to the first support tube 61 and the second support tube 62. When the second support tube 62 is forced to move downward, the second arched beam 63 is compressed and deformed, and the fourth strain sensing element detects the strain change of the second arched beam 63 to detect the penetration resistance.

[0134] The fourth strain sensing element and the fifth strain sensing element may be the same strain sensing element or different strain sensing elements, and the strain sensing element is selected from a fiber Bragg grating (FBG) and a resistive strain gauge.

[0135] The thickness of the first arched beam 24, the thickness of the second arched beam 63, the thickness of the sensing surface in the circular structure 41, the thickness of the beryllium copper sheet 54, and the thickness of the sensing surface in the pore water pressure sensor body 33 can all be adjusted according to different stress / resistance measurement ranges to adapt to soil samples with different parameters.

[0136] The inclined plate penetrometer of the present application has the following technical effects:

[0137] (1) The inclined plate penetrometer of the present invention integrates multiple sensors and can simultaneously obtain multiple parameters in one test; the present invention is equipped with an effective stress sensor, which can simplify the calculation process of the effective stress and improve the test efficiency.

[0138] (2) The effective stress sensors and shear strength sensors on both sides of the present invention are arranged at an angle, so that the data measured by the sensors at the upper position will not be disturbed by the sensors at the lower position; and through the extrapolation method, the in-situ undisturbed strength parameters and effective stress parameters can be calculated.

[0139] (3) The sensing elements in all sensors of the present invention have simple structures, low costs, strong environmental adaptability, are not easily damaged, and are easy to replace, and can be applied to different working conditions.

[0140] Based on the inclined plate penetrometer described in any of the above embodiments, the present invention also provides a preferred embodiment of a method for measuring effective stress parameters of an inclined plate penetrometer:

[0141] The effective stress parameter measurement method of the inclined plate penetrometer according to the embodiment of the present invention comprises the following steps:

[0142] Step S100, injecting water into the inclined plate penetrometer and soaking it, and wrapping and sealing it with a plastic film to keep the pore water pressure sensor and the effective stress sensor saturated;

[0143] Step S200, fixing the electric cylinder above the saturated soil sample to be tested, fixing the inclined plate penetrometer at the bottom of the electric cylinder, connecting the signal transmission cable of the cone tip resistance sensor, the signal transmission cable of the pore water pressure sensor, the signal transmission cable of the effective stress sensor array, the signal transmission cable of the shear strength sensor array and the signal transmission cable of the penetration resistance sensor to a signal demodulator; wherein there is water on the saturated soil sample to be tested, and the inclined plate penetrometer is located in the water;

[0144] Step S300, after removing the plastic film, start the electric cylinder, penetrate the inclined plate penetrometer into the saturated soil sample to be tested at a constant speed, and collect the pore water pressure, cone tip resistance, penetration resistance, effective stress and shear strength at a certain moment through the signal demodulator;

[0145] Step S400: determining an in-situ undisturbed effective stress and an in-situ undisturbed shear strength according to the effective stress and the shear strength; determining an effective friction angle and an effective cohesion according to the in-situ undisturbed effective stress and the in-situ undisturbed shear strength;

[0146] Step S500: determining a consolidation coefficient according to the pore water pressure and the initial pore water pressure.

[0147] Specifically, when injecting water, the first permeable stone, the second permeable stone and the cone can be removed, and the first permeable stone and the second permeable stone can be ultrasonically cleaned and injected with water; water can also be injected into the cavity of the circular structure through the self-supporting mounting groove, and water can be injected into the permeable pipe until no bubbles are generated. Then, after the first permeable stone, the second permeable stone and the cone are assembled, they are soaked so that the pore water pressure sensor and the effective stress sensor are saturated. The gaps of the effective stress sensor and the gaps of the shear strength sensor can be filled with vacuum sealing paste for sealing to prevent soil particles from entering the inclined plate penetrometer during the penetration process, affecting the accuracy of the measurement data. In order to maintain the saturated state, the inclined plate penetrometer is wrapped with a plastic film so that the injected and soaked water is not easy to lose.

[0148] When the electric cylinder is fixed, it is in a vertical state, and the electric cylinder is extended and retracted in the vertical direction to move the inclined plate penetrometer, so that the inclined plate penetrometer can penetrate in the vertical direction without eccentricity. The signal transmission cables of each sensor are connected to the signal demodulator, and the signal demodulator collects the data detected by each sensor. There is water on the saturated soil sample to be tested, and the water surface is above the inclined plate penetrometer, which is conducive to maintaining the saturation of the inclined plate penetrometer. In actual application, there can be water above the soil sample; during the experiment, water needs to be added above the soil sample.

[0149] After removing the plastic film, start the electric cylinder, penetrate the inclined plate penetrometer into the saturated soil sample to be tested, and detect it through various sensors. Specifically, the cone tip resistance sensor is used to detect the cone tip resistance, the pore water pressure is detected by the pore water pressure sensor, the effective stress at different positions at a certain moment is detected by the effective stress sensor array, the shear strength at different positions at a certain moment is detected by the shear strength sensor array, and the penetration resistance is detected by the penetration resistance sensor. The collected data can be a curve distributed along the depth of the soil sample, with the ordinate of the curve being the soil layer depth z, and the abscissa being the strain change value Δε measured by the sensor. The stress measured by each sensor is then calculated based on the strain value, such as Fig.15 and Fig.17 The positions of the effective stress sensors and the corresponding shear strength sensors are symmetrical about the central axis of the inclined plate penetrometer, while the positions of different effective stress sensors are at different distances from the central axis of the inclined plate penetrometer, and the positions of different shear strength sensors are at different distances from the central axis of the inclined plate penetrometer, as shown in Fig. Fig.13 , Fig.14 as well as Fig.16As shown, when three effective stress sensors and three shear strength sensors are used, the distances between the positions of the effective stress sensors (or shear strength sensors) and the central axis of the inclined plate penetrometer are d1, d2, and d3, respectively. At a certain moment in the penetration process, the effective stresses σ1', σ'2, σ'3 of different effective stress sensors and the shear strengths τ1, τ2, τ3 of different shear strength sensors can be obtained. For this reason, the relationship between the distance between the sensor and the central axis and the measured stress can be obtained, and then according to the extrapolation method, the in-situ undisturbed effective stress σ'0 and the in-situ undisturbed shear strength τ0 can be calculated when the distance is 0. After obtaining the in-situ undisturbed effective stress σ'0 and the in-situ undisturbed shear strength τ0, the effective friction angle is determined based on the in-situ undisturbed effective stress σ'0 and the in-situ undisturbed shear strength τ0 through the Mohr-Coulomb failure theory. and effective cohesion c'.

[0150] The in-situ undisturbed effective stress is:

[0151]

[0152] The in-situ undisturbed shear strength is:

[0153]

[0154]

[0155] The effective friction angle and the effective cohesion satisfy the following relationship:

[0156]

[0157] Where σ'0 represents the in-situ undisturbed effective stress, represents the mean effective stress, σ i ' represents the effective stress of the ith effective stress sensor at a certain moment, τ0 represents the in-situ undisturbed shear strength, represents the average shear strength, τ i represents the shear strength of the ith shear strength sensor at a certain moment, β1 represents the slope of the effective stress-distance relationship, β2 represents the slope of the shear strength-distance relationship, n represents the number of effective stress sensors, represents the average distance from the effective stress sensor to the center axis of the inclined plate penetrometer, d i represents the distance from the ith effective stress sensor to the central axis of the inclined plate penetrometer, ∑ represents the summation, tan(·) represents the tangent function, represents the effective friction angle, and c' represents the effective cohesion.

[0158] When the inclined plate penetrometer is tested in clay soil, the pore water pressure value measured by the pore water pressure sensor can be used to calculate the consolidation coefficient c of the soil layer. h , the consolidation coefficient is:

[0159]

[0160] Among them, c h represents the consolidation coefficient, w represents the width, T * Indicates the time coefficient, time coefficient T * According to the numerical table of time coefficient and soil consolidation degree and soil consolidation degree U v OK, I r represents the stiffness coefficient of the saturated soil sample to be tested, f represents the correction coefficient, t represents the measurement time, U v represents the degree of soil consolidation, u i represents the initial pore water pressure, u e Represents the pore water pressure at a certain moment.

[0161] The inclined plate penetrometer and the effective stress parameter measurement method of the present invention are used to conduct tests in a square model box. The model box is 1000 mm long, 600 mm wide, and 800 mm high. The saturated soil sample to be tested is sand with a particle size range of 0.25-0.5 mm. In the model box, the saturated soil sample to be tested is prepared by layered compaction. After each layer of the saturated soil sample to be tested is prepared, it needs to be soaked in clean water for 12 hours to ensure that the saturated soil sample to be tested is completely saturated. The final height of the saturated soil sample to be tested is 600 mm. The subsequent testing method of the inclined plate penetrometer is as follows:

[0162] (1) The inclined plate penetrometer is completely immersed in water, and water is injected into the auxiliary installation groove and the permeable pipe with a syringe until no bubbles are generated in the water. The inclined plate penetrometer is continuously immersed in water for 12 hours, and the first permeable stone and the second permeable stone are placed in an ultrasonic water tank for cleaning to fully saturate the effective stress sensor array, the pore water pressure sensor, the first permeable stone, and the second permeable stone;

[0163] (2) After the sensor is saturated, the first permeable stone, the second permeable stone and the cone are placed into the inclined plate penetrometer, and the inclined plate penetrometer is wrapped and sealed with a plastic film to prevent the sensor saturation from decreasing.

[0164] (3) Fix the servo electric cylinder above the saturated soil sample to be tested, and leave a height of 600 mm between the bottom of the electric cylinder and the top of the soil sample. Then fix the inclined plate penetrometer at the bottom of the servo electric cylinder, connect the signal transmission cables of each sensor to the signal demodulator, and check whether each sensor is working properly.

[0165] (4) After the inclined plate penetrometer is debugged, clean water is injected into the saturated soil sample to be tested, so that the water level is 200 mm above the sample surface and just covers the inclined plate penetrometer, and the plastic film is removed;

[0166] (5) Set the descending speed of the servo electric cylinder to 2 mm / s, and set the sampling frequency of the signal demodulator to 0.1 s; start sampling while penetrating, and stop when the penetration displacement reaches 450 mm. This is to prevent the bottom boundary effect of the model box from affecting the results.

[0167] (6) Taking the moment when the sensor is completely buried in the soil as the initial state, the distance between the bottom effective stress sensor and the shear strength sensor and the central axis of the penetrometer is 16.7 mm, the distance between the middle effective stress sensor and the shear strength sensor and the central axis of the penetrometer is 20.63 mm, and the distance between the top effective stress sensor and the shear strength sensor and the central axis of the penetrometer is 24.48 mm. According to the linear regression relationship, the relationship between stress and distance is obtained. Then, according to the extrapolation method, the soil stress state when the distance is 0 mm, that is, the original undisturbed state, is obtained.

[0168] (7) According to the estimated data, the soil layer depth ranges from 187 mm to 475 mm, the effective stress range inside the model box is 50-150 kPa, and the shear strength range is 20-30 kPa.

[0169] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. An inclined plate penetrometer, characterized in that: include: frame; A cone tip resistance sensor is arranged at the lower end of the frame; A pore water pressure sensor is located in the frame and connected to the cone of the cone tip resistance sensor; an array of effective stress sensors disposed on a first side of the frame; a shear strength sensor array, disposed on the second side of the frame; A penetration resistance sensor is arranged at the upper end of the frame; Wherein, from top to bottom, the distance between the first side surface and the second side surface gradually decreases; The effective stress sensors in the effective stress sensor array and the shear strength sensors in the shear strength sensor array are both arranged from top to bottom; The positions of the effective stress sensors in the effective stress sensor array are the same as the positions of the corresponding shear strength sensors in the shear strength sensor array.

2. The inclined plate penetrometer according to claim 1, characterized in that: There are three effective stress sensors in the effective stress sensor array, three main installation slots are formed on the first side of the frame, and each main installation slot is connected to a plurality of auxiliary installation slots; The effective stress sensor comprises: A circular structure is installed in the main installation groove, a cavity is formed in the circular structure, and a plurality of water holes are formed on the side wall of the circular structure, and two ends of the water holes are respectively connected to the auxiliary installation groove and the cavity; A first strain sensing element is disposed inside the circular structure and along the radial direction of the circular structure; A plurality of first permeable stones are installed in corresponding auxiliary installation grooves.

3. The inclined plate penetrometer according to claim 2, characterized in that: There are three shear strength sensors in the shear strength sensor array, and the second side surface of the frame forms a sliding channel, and the sliding channel has three openings; The shear strength sensor comprises: A fixed block, fixedly connected to the sliding channel; A sliding block, located in the sliding channel; a friction plate, located in the corresponding opening and connected to the sliding block; A beryllium copper sheet, two ends of which are respectively connected to the sliding block and the fixed block; A second strain sensing element is disposed on the beryllium copper sheet and is disposed along the length direction of the beryllium copper sheet; Wherein, the beryllium copper sheet and the second strain sensing element are both located between the sliding block and the friction plate.

4. The inclined plate penetrometer according to claim 3, characterized in that: The pore water pressure sensor comprises: a second permeable stone, located between the frame and the cone; A water-permeable pipe, arranged on the cone and connected with the second water-permeable stone; The pore water pressure sensor body is arranged at one end of the permeable pipe away from the second permeable stone.

5. The inclined plate penetrometer according to claim 4, characterized in that: The cone tip resistance sensor comprises: A cone, in close contact with the lower surface of the second permeable stone; A silicone pad is located between the frame and the second permeable stone, the silicone pad forms a through hole, the cone forms a boss on one side facing the silicone pad, the boss passes through the through hole, and a channel is formed in the boss to connect the permeable pipe and the second permeable stone; An arched beam structure, wherein the lower end of the arched beam structure is placed on the boss, and the upper end of the arched beam structure is against the frame; The third strain sensing element is disposed on the arched beam structure and along the length direction of the arched beam structure.

6. The inclined plate penetrometer according to claim 5, characterized in that: The first strain sensing element, the second strain sensing element and the third strain sensing element are all selected from fiber Bragg gratings or resistive strain gauges.

7. The inclined plate penetrometer according to any one of claims 1 to 6, characterized in that: The penetration resistance sensor comprises: A first support cylinder is mounted on the frame; A second support cylinder; A plurality of second arched beams, two ends of the second arched beams are respectively connected to the first support tube and the second support tube; a fourth strain sensing element, disposed on the second arched beam and arranged along the length direction of the second arched beam; A sleeve is arranged on the frame and sleeved outside the second arched beam and the second supporting tube.

8. A method for measuring effective stress parameters of an inclined plate penetrometer according to any one of claims 1 to 7, characterized in that: Includes steps: The inclined plate penetrometer was injected with water and soaked, and then sealed with a plastic film to keep the pore water pressure sensor and the effective stress sensor saturated; Fix the electric cylinder above the saturated soil sample to be tested, fix the inclined plate penetrometer at the bottom of the electric cylinder, and connect the signal transmission cable of the cone tip resistance sensor, the signal transmission cable of the pore water pressure sensor, the signal transmission cable of the effective stress sensor array, the signal transmission cable of the shear strength sensor array, and the signal transmission cable of the penetration resistance sensor to a signal demodulator; wherein there is water on the saturated soil sample to be tested, and the inclined plate penetrometer is located in the water; After removing the plastic film, the electric cylinder is started, and the inclined plate penetrometer is penetrated into the saturated soil sample to be tested at a constant speed, and the pore water pressure, cone tip resistance, penetration resistance, effective stress and shear strength at a certain moment are collected through the signal demodulator; Determine the in-situ undisturbed effective stress and the in-situ undisturbed shear strength according to the effective stress and the shear strength; determine the effective friction angle and the effective cohesion according to the in-situ undisturbed effective stress and the in-situ undisturbed shear strength; When the saturated soil sample to be tested is clay, the consolidation coefficient is determined according to the pore water pressure and the initial pore water pressure.

9. The effective stress parameter measurement method of the inclined plate penetrometer according to claim 8, characterized in that: The in-situ undisturbed effective stress is: The in-situ undisturbed shear strength is: The effective friction angle and the effective cohesion satisfy the following relationship: Where σ'0 represents the in-situ undisturbed effective stress, represents the mean effective stress, σ i ' represents the effective stress of the ith effective stress sensor at a certain moment, τ0 represents the in-situ undisturbed shear strength, represents the average shear strength, τ i represents the shear strength of the ith shear strength sensor at a certain moment, β1 represents the slope of the effective stress-distance relationship, β2 represents the slope of the shear strength-distance relationship, n represents the number of effective stress sensors, represents the average distance from the effective stress sensor to the center axis of the inclined plate penetrometer, d i represents the distance from the ith effective stress sensor to the central axis of the inclined plate penetrometer, ∑ represents the summation, tan(·) represents the tangent function, represents the effective friction angle, and c' represents the effective cohesion.

10. The effective stress parameter measurement method of the inclined plate penetrometer according to claim 8, characterized in that: The consolidation coefficient is: Among them, c h represents the consolidation coefficient, w represents the width, T * Indicates the time coefficient, time coefficient T * According to the numerical table of time coefficient and soil consolidation degree and soil consolidation degree U v OK, I r represents the stiffness coefficient of the saturated soil sample to be tested, f represents the correction coefficient, t represents the measurement time, U v represents the degree of soil consolidation, u i represents the initial pore water pressure, u e Represents the pore water pressure at a certain moment.

Images