Flat plate penetrometer and effective stress parameter measuring method thereof

Abstract

The invention discloses a flat plate penetrometer and an effective stress parameter measuring method thereof. The flat plate penetrometer comprises a frame, a plurality of sensors and a plurality of sensors, the conical tip resistance sensor is arranged at the lower end of the frame; the pore water pressure sensor is positioned in the frame and is connected with the cone of the conical tip resistance sensor; the effective stress sensor is arranged on the first side surface of the frame; the shear strength sensor is arranged on the second side surface of the frame; the penetration resistance sensor is arranged at the upper end of the frame; the first side face and the second side face are parallel to each other. The flat plate penetrometer can measure effective stress, shear strength, conical tip resistance, pore water pressure and total penetration resistance at the same time, and can calculate an effective friction angle and effective cohesive force of a tested soil sample according to a Moire-Coulomb failure criterion.

Description

Technical Field

[0001] The invention relates to the technical field of penetrometers, and in particular to a flat 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. After the flat shovel lateral expansion test, the sensor is inserted into the soil, and the resistance of the metal film at the center of the sensor is measured by actively expanding the film to resist the deformation of the soil. After that, the shear strength τ and the effective friction angle can be calculated through empirical formulas. and the lateral earth pressure coefficient K 0 .

[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, a flat 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] A flat 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 effective stress sensor, disposed on a first side of the frame;

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

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

[0015] Wherein, the first side surface and the second side surface are parallel to each other.

[0016] The flat plate penetrometer, wherein the frame comprises:

[0017] substrate;

[0018] A first column and a second column are both arranged on the lower surface of the substrate;

[0019] A connecting beam has two ends respectively connected to the first column and the second column.

[0020] The flat-plate penetrometer, wherein the cone tip resistance sensor comprises:

[0021] A silicone pad is disposed on the lower surface of the first column and the lower surface of the second column, and the silicone pad forms a via hole;

[0022] A cone is disposed below the silicone pad, a boss is formed on one side of the cone facing the silicone pad, and the boss passes through the via hole;

[0023] 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 connecting beam;

[0024] The first strain sensing element is disposed on the arched beam structure and along the length direction of the arched beam structure.

[0025] The flat-plate penetrometer has two arched beam structures, which are symmetrically arranged, and the arched beam structure includes: a first arched beam and a contact plate; the first arched beam and the contact plate are integrally formed, and the contact plate is located below the first arched beam.

[0026] The flat plate penetrometer, wherein the connecting beam forms a through hole, and the boss forms a channel; the pore water pressure sensor comprises:

[0027] A first permeable stone is located between the cone and the silicone pad and corresponds to the position of the channel;

[0028] a water-permeable pipe, disposed on the boss and connected to the channel;

[0029] A pore water pressure sensor body is arranged at one end of the water permeable pipe away from the boss;

[0030] Wherein, the water-permeable pipe passes through the through hole and is located between the two arched beam structures.

[0031] The flat-plate penetrometer, wherein the frame further comprises: a first side plate, connected to the base plate, the first column and the second column respectively;

[0032] A circular groove and a plurality of mounting grooves are formed on the first side plate, an annular groove is formed on the groove wall of the circular groove, and the mounting groove is connected to the annular groove;

[0033] The effective stress sensor comprises:

[0034] A circular structure is installed in the circular 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 annular groove and the cavity;

[0035] A second strain sensing element is disposed on the inner side of the sensing surface of the circular structure and along the radial direction of the circular structure;

[0036] A plurality of second permeable stones are installed in corresponding installation grooves.

[0037] The flat plate penetrometer, wherein the frame further comprises: a second side plate, mounted on the first column and the second column; a sliding channel and an opening are formed on the second side plate, and the sliding channel is connected to the opening;

[0038] The shear strength sensor comprises:

[0039] A fixed block, fixedly connected to the sliding channel;

[0040] A sliding block, located in the sliding channel;

[0041] a friction plate, located in the opening and connected to the sliding block;

[0042] A beryllium copper sheet, two ends of which are respectively connected to the sliding block and the fixed block;

[0043] A third strain sensing element is disposed on the beryllium copper sheet and is disposed along the length direction of the beryllium copper sheet;

[0044] Wherein, the beryllium copper sheet and the third strain sensing element are both located between the sliding block and the friction plate.

[0045] The flat plate penetrometer, wherein the frame further comprises: a mounting tube, disposed on the upper surface of the substrate;

[0046] The penetration resistance sensor comprises:

[0047] A first supporting cylinder, installed in the installation cylinder;

[0048] A second support cylinder;

[0049] 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;

[0050] a fourth strain sensing element, disposed on the second arched beam and arranged along the length direction of the second arched beam;

[0051] A sleeve is arranged on the installation tube and sleeved outside the second arched beam and the second supporting tube.

[0052] A method for measuring effective stress parameters of a flat plate penetrometer as described in any one of the above, comprising the steps of:

[0053] The flat plate penetrometer is filled with water and soaked, and then sealed with a plastic film to keep the pore water pressure sensor and the effective stress sensor saturated;

[0054] Fix the electric cylinder above the saturated soil sample to be tested, fix the flat 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, the signal transmission cable of the shear strength sensor, 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 flat plate penetrometer is located in the water;

[0055] After removing the plastic film, starting the electric cylinder, penetrating the flat plate penetrometer into the saturated soil sample to be tested at a constant speed, and collecting pore water pressure, cone tip resistance, penetration resistance, effective stress at at least two depths, and shear strength at at least two depths through the signal demodulator;

[0056] Determining an effective friction angle and an effective cohesion according to the effective stress at the at least two depth positions and the shear strength at the at least two depth positions;

[0057] 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.

[0058] The effective stress parameter measurement method of the flat plate penetrometer, wherein the effective friction angle and the effective cohesion satisfy the following relationship:

[0059]

[0060] Among them, τ represents the shear strength, σ' represents the effective stress, represents the effective friction angle, c' represents the effective cohesion;

[0061] 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 eRepresents the pore water pressure at a certain moment.

[0064] Beneficial effects: The flat plate penetrometer can simultaneously measure effective stress, shear strength, cone tip resistance, pore water pressure and overall penetration resistance, and can calculate the effective friction angle and effective cohesion of the soil sample through the Mohr-Coulomb failure criterion. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0067] Figure 3 1 is a first structural schematic diagram of a flat plate penetrometer in an embodiment of the present invention.

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

[0069] Figure 5 4 is a cross-sectional view of a flat plate penetrometer according to an embodiment of the present invention.

[0070] Figure 6 yes Figure 5 Enlarged view of point A in the middle.

[0071] Figure 7 1 is an exploded view of a flat plate penetrometer according to an embodiment of the present invention.

[0072] Figure 8 It is a first structural diagram of the framework in an embodiment of the present invention.

[0073] Fig. 9 2 is a schematic diagram of the second structure of the framework in an embodiment of the present invention.

[0074] Fig.10 Schematic diagram of the internal structure of the shear strength sensor in an embodiment of the present invention.

[0075] Fig.11 is an exploded view of the shear strength sensor in an embodiment of the present invention.

[0076] Fig.12 Schematic diagram of the structure of the first side plate in an embodiment of the present invention.

[0077] Fig.13 Schematic diagram of the structure of the pore water pressure sensor in the embodiment of the present invention.

[0078] Fig.14 Schematic diagram of the first structure of the cone in the embodiment of the present invention.

[0079] Fig.15 2 is a second structural schematic diagram of a cone in an embodiment of the present invention.

[0080] Fig.16 Schematic diagram of the flat plate penetrometer penetrating a soil sample in an embodiment of the present invention.

[0081] Fig.17 Schematic diagram of the relationship between the effective friction angle and the effective cohesion in the embodiment of the present invention.

[0082] Description of reference numerals:

[0083] 10. frame; 11. base plate; 12. first column; 13. second column; 14. connecting beam; 15. first side plate; 151. circular groove; 152. mounting groove; 153. annular groove; 16. second side plate; 161. sliding channel; 162. opening; 17. mounting tube; 20. cone tip resistance sensor; 21. silicone cushion; 22. cone; 221. boss; 222. channel; 23. contact plate; 24. first arched beam; 30. pore water pressure sensor; 31. first permeable stone; 32 , permeable pipe; 33, pore water pressure sensor body; 40, effective stress sensor; 41, circular structure; 411, cavity; 412, water hole; 42, second permeable stone; 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 a flat plate penetrometer.

[0086] like Figure 1 and Figure 5 As shown, the flat 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 22 of the cone tip resistance sensor 20;

[0090] An effective stress sensor 40 is disposed on a first side surface of the frame 10;

[0091] A shear strength sensor 50 is disposed 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] Wherein, the first side surface and the second side surface are parallel to each other.

[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 40 is used to detect the effective stress, the shear strength sensor 50 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 flat penetrometer by telescoping. The telescope can use an electric cylinder 72, and the electric cylinder 72 is connected to the penetration resistance sensor 60 through an extension tube 71, such as Figure 2 As shown. Figure 1 As shown, the signal transmission cables of each sensor can be connected to the signal demodulator 73 to collect data. The pore water pressure sensor 30 is located in the frame 10 and connected to the cone 22 of the cone tip resistance sensor 20. The cone 22 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. Figure 3 and Figure 4 As shown, the effective stress sensor 40 and the shear strength sensor 50 are respectively located on two sides of the frame 10, namely the first side and the second side. The first side and the second side are two parallel sides, thus forming a flat plate penetrometer. The position of the effective stress sensor 40 and the position of the shear strength sensor 50 are symmetrical about the central axis of the flat plate penetrometer, and the penetration depths of the two are the same.

[0095] The flat plate penetrometer can simultaneously measure effective stress, shear strength, cone tip resistance, pore water pressure and overall penetration resistance, and can calculate the effective friction angle and effective cohesion of the soil sample through the Mohr-Coulomb failure criterion.

[0096] In a preferred implementation of the embodiment of the present invention, Figure 8 and Fig. 9 As shown, the frame 10 comprises:

[0097] substrate 11;

[0098] The first column 12 and the second column 13 are both arranged on the lower surface of the substrate 11;

[0099] The connecting beam 14 has two ends respectively connected to the first column 12 and the second column 13 .

[0100] Specifically, the first column 12 and the second column 13 are both arranged on the lower surface of the substrate 11, and the penetration resistance sensor 60 is located above the substrate 11. The cone tip resistance sensor 20 is located at the bottom of the first column 12 and the bottom of the second column 13. The two ends of the connecting beam 14 are respectively connected to the first column 12 and the second column 13, and the connecting beam 14 is conducive to improving the strength of the frame 10. The connecting beam 14 is also connected to the cone tip resistance sensor 20 to provide support for the cone tip resistance sensor 20.

[0101] In a preferred implementation of the embodiment of the present invention, Figure 3-Figure 5 , Fig.14 as well as Fig.15 As shown, the cone tip resistance sensor 20 includes:

[0102] A silicone pad 21 is provided on the lower surface of the first column 12 and the lower surface of the second column 13, and the silicone pad 21 forms a via hole;

[0103] A cone 22 is disposed below the silicone pad 21, and a boss 221 is formed on one side of the cone 22 facing the silicone pad 21, and the boss 221 passes through the via hole;

[0104] An arched beam structure, wherein the lower end of the arched beam structure is placed on the boss 221, and the upper end of the arched beam structure abuts against the connecting beam 14;

[0105] The first strain sensing element is disposed on the arched beam structure and along the length direction of the arched beam structure.

[0106] Specifically, the silicone cushion 21 can be deformed. When the cone 22 contacts the soil sample, it is subjected to the pressure of the soil sample, and the cone 22 moves toward the connecting beam 14. The silicone cushion 21 is compressed, and the arched beam structure is deformed under pressure, and is sensed by the first strain sensing element. The cone 22 can be a quadrangular pyramid with an inclination angle of 60°. The first strain sensing element is arranged along the length direction of the arched beam structure, that is, in the vertical direction. A boss 221 is formed on the upper side of the cone 22, and the boss 221 can be abutted against by the arched beam structure. When the cone 22 is pressed and moved, the arched beam structure will be squeezed and deformed. The boss 221 and the cone 22 are integrally formed.

[0107] In a preferred implementation of the embodiment of the present invention, Fig.13As shown, there are two arched beam structures, which are symmetrically arranged. 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 .

[0108] Specifically, there are two arched beam structures, which are symmetrically arranged, which is conducive to uniform stress on the arched beam structure. A first strain sensing element can be arranged on each arched beam structure. The contact plate 23 abuts against the boss 221; the upper end of the first arched beam 24 contacts the connecting beam 14.

[0109] In a preferred implementation of the embodiment of the present invention, Figure 5 , Figure 6 , Figure 8 as well as Fig.13 As shown, the connecting beam 14 forms a through hole, and the boss 221 forms a channel 222; the pore water pressure sensor 30 includes:

[0110] A first permeable stone 31 is located between the cone 22 and the silicone pad 21 and corresponds to the position of the channel 222;

[0111] A water-permeable pipe 32, disposed on the boss 221 and connected to the channel 222;

[0112] The pore water pressure sensor body 33 is arranged at one end of the water permeable pipe 32 away from the boss 221;

[0113] The water-permeable pipe 32 passes through the through hole and is located between the two arched beam structures.

[0114] Specifically, a channel 222 is formed in the boss 221 for water circulation, and the water in the soil sample reaches the boss 221 through the cone 22, and enters the water-permeable pipe 32 and the pore water pressure sensor body 33 from the channel 222. A fifth strain sensing element is provided on the sensing surface of the pore water pressure sensor body 33, which is used to sense the strain change on the sensing surface to detect the pore water pressure.

[0115] In a preferred implementation of the embodiment of the present invention, Figure 3 , Figure 7 , Fig. 9 as well as Fig.12 As shown, the frame 10 also includes: a first side plate 15, which is respectively connected to the base plate 11, the first column 12 and the second column 13; wherein a circular groove 151 and a plurality of mounting grooves 152 are formed on the first side plate 15, an annular groove 153 is formed on the groove wall of the circular groove 151, and the mounting groove 152 is connected to the annular groove 153.

[0116] Specifically, the first side plate 15 is located on the first side surface of the frame 10. The first side plate 15 is connected to the base plate 11, the first column 12 and the second column 13 respectively. The first side plate 15 is used to install the effective stress sensor 40. The first side plate 15, the base plate 11, the first column 12 and the second column 13 can be integrally formed or fixedly connected. A circular groove 151 and a plurality of mounting grooves 152 are formed on the first side plate 15. An annular groove 153 is formed on the groove wall of the circular groove 151. The annular groove 153 is connected to the mounting groove 152. Water in any mounting groove 152 can enter the annular groove 153, so as to be evenly distributed in the circular groove 151. The mounting grooves 152 are arranged around the circular groove 151. The number of the mounting grooves 152 can be configured as needed. For example, there are four mounting grooves 152.

[0117] In a preferred implementation of the embodiment of the present invention, Figure 3 , Figure 5 , Figure 6 , Fig. 9 as well as Fig.12 As shown, the effective stress sensor 40 comprises:

[0118] A circular structure 41 is installed in the circular groove 151. A cavity 411 is formed in the circular structure 41. A plurality of water holes 412 are formed on the side wall of the circular structure 41. Two ends of the water holes 412 are connected to the annular groove 153 and the cavity 411 respectively.

[0119] A second strain sensing element is disposed on the inner side of the sensing surface of the circular structure 41 and is disposed along the radial direction of the circular structure 41;

[0120] A plurality of second permeable stones 42 are installed in corresponding installation grooves 152 .

[0121] 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 facing away from the shear strength sensor 50 is a sensing surface, and a second strain sensing element is arranged on the inner side of the sensing surface. The second 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 second strain sensing elements. The circular structure 41 is located in the circular groove 151, 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 annular groove 153 and the cavity 411 of the circular structure 41, and the water in the annular groove 153 can enter the cavity 411 through the water holes 412. The number of the second permeable stones 42 is consistent with the number of the mounting grooves 152, and the second permeable stones 42 are installed in the mounting grooves 152.

[0122] In a preferred implementation of the embodiment of the present invention, Figure 4-Figure 7 , Fig.10 as well as Fig.11 As shown, the frame 10 further includes: a second side plate 16 mounted on the first column 12 and the second column 13 ; a sliding channel 161 and an opening 162 are formed on the second side plate 16 , and the sliding channel 161 is connected to the opening 162 .

[0123] Specifically, the second side plate 16 is located on the second side surface of the frame 10, and the second side plate 16 is used to install the shear strength sensor 50. The second side plate 16 is detachably arranged on the first column 12 and the second column 13. A sliding channel 161 is formed in the second side plate 16, and an opening 162 is formed on the surface of the second side plate 16, and the sliding channel 161 is connected to the opening 162.

[0124] In a preferred implementation of the embodiment of the present invention, Figure 6 , Figure 7 , Fig.10 as well as Fig.11 As shown, the shear strength sensor 50 includes:

[0125] A fixing block 51, fixedly connected to the sliding channel 161;

[0126] A sliding block 52, located in the sliding channel 161;

[0127] A friction plate 53, located in the opening 162 and connected to the sliding block 52;

[0128] A beryllium copper sheet 54, two ends of which are respectively connected to the sliding block 52 and the fixed block 51;

[0129] A third strain sensing element is disposed on the beryllium copper sheet 54 and is disposed along the length direction of the beryllium copper sheet 54;

[0130] The beryllium copper sheet 54 and the third strain sensing element are both located between the sliding block 52 and the friction plate 53 .

[0131] Specifically, the fixed block 51 and the sliding block 52 are both located in the sliding channel 161, the fixed block 51 is fixed relative to the sliding channel 161, and the sliding block 52 slides relative to the sliding channel 161. The friction plate 53 is located in the opening 162, and there is a gap between the upper surface of the friction plate 53 and the side wall of the opening 162. 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 third strain sensing element. The third strain sensing element detects the strain change of the beryllium copper sheet 54 to achieve the shear strength detection. The third 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.

[0132] In a preferred implementation of the embodiment of the present invention, Figure 1 , Figure 3 as well as Figure 5 As shown, the frame 10 further includes: a mounting tube 17 disposed on the upper surface of the substrate 11 .

[0133] Specifically, the mounting tube 17 is disposed on the upper surface of the substrate 11 and is used to mount the penetration resistance sensor 60. A through hole is formed on the substrate 11, and the mounting tube 17 surrounds the through hole. The inner diameter of the mounting tube 17 is larger than the aperture of the through hole.

[0134] In a preferred implementation of the embodiment of the present invention, Figure 1 , Figure 3 as well as Figure 5 As shown, the penetration resistance sensor 60 includes:

[0135] A first support tube 61 is installed in the installation tube 17;

[0136] A second support tube 62;

[0137] 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;

[0138] a fourth strain sensing element, disposed on the second arched beam 63 and arranged along the length direction of the second arched beam 63;

[0139] The sleeve 64 is disposed on the installation tube 17 and sleeved outside the second arched beam 63 and the second supporting tube 62 .

[0140] Specifically, the first support tube 61 is installed on the installation tube 17, 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 flat 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 flat 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.

[0141] 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.

[0142] The first strain sensing element, the second strain sensing element, the third strain sensing element, 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.

[0143] The flat plate penetrometer of this application has the following technical effects:

[0144] (1) The flat-plate penetrometer of the present invention integrates multiple sensors and can simultaneously obtain multiple parameters in one test.

[0145] (2) The present invention is equipped with an effective stress sensor, which can simplify the calculation process of effective stress and improve test efficiency.

[0146] (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.

[0147] Based on the flat 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 a flat plate penetrometer:

[0148] The effective stress parameter measurement method of the flat plate penetrometer according to the embodiment of the present invention comprises the following steps:

[0149] Step S100, injecting water into the flat 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;

[0150] Step S200, fixing the electric cylinder above the saturated soil sample to be tested, fixing the flat 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, the signal transmission cable of the shear strength sensor, 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 flat plate penetrometer is located in the water;

[0151] Step S300, after removing the plastic film, start the electric cylinder, penetrate the flat plate penetrometer into the saturated soil sample to be tested at a constant speed, and collect pore water pressure, cone tip resistance, penetration resistance, effective stress at at least two depths, and shear strength at at least two depths through the signal demodulator;

[0152] Step S400, determining an effective friction angle and an effective cohesion according to the effective stress at the at least two depth positions and the shear strength at the at least two depth positions;

[0153] Step S500: 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.

[0154] 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 from the installation groove into the cavity of the circular structure, 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 flat plate penetrometer during the penetration process, affecting the accuracy of the measurement data. In order to maintain the saturated state, the flat plate penetrometer is wrapped with a plastic film so that the injected and soaked water is not easy to lose.

[0155] 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 flat plate penetrometer, so that the flat 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 covers the flat plate penetrometer, which is conducive to maintaining the saturation of the flat 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.

[0156] After removing the plastic film, start the electric cylinder, penetrate the flat 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 at least two depths is detected by the effective stress sensor, the shear strength at at least two depths is detected by the shear strength sensor, 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. The ordinate of the curve is the soil layer depth z, and the abscissa is the strain change value Δε measured by the sensor. The stress measured by each sensor is then calculated based on the strain value. The positions of the effective stress sensors and the shear strength sensors on both sides are symmetrical about the central axis of the flat plate penetrometer. Therefore, the effective stress σ' and shear strength τ at the same depth can be measured respectively. Fig.16 As shown, data at three depth positions can be measured, for example, three depth positions (z 1 、z 2 and z 3 ) when the measured effective stress (σ 1 ', σ' 2 and σ 3 ') and the measured shear strength (τ 1 , τ 2 and τ 3 ), and assuming that the soil is uniform between the three depths, the effective friction angle is calculated based on the Mohr-Coulomb failure theory. and effective cohesion c', as Fig.17 shown.

[0157] The effective friction angle and the effective cohesion satisfy the following relationship:

[0158]

[0159] Among them, τ represents the shear strength, σ' represents the effective stress, represents the effective friction angle, and c' represents the effective cohesion.

[0160] When the 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 Therefore, when the saturated soil sample to be tested is clay, the consolidation coefficient is:

[0161]

[0162] 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 vOK, I r It indicates the stiffness coefficient of the saturated soil sample to be tested. The value range of the stiffness coefficient is 25-500. f indicates the correction coefficient. t indicates 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.

[0163] like Figure 2 As shown, the effective stress parameter measurement method of the flat plate penetrometer of the present invention is used to conduct an experiment in a square model box. The model box is 1000mm long, 600mm wide, and 800mm high. The saturated soil sample to be tested is sand with a particle size range of 0.25-0.5mm. 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 600mm. The test method of the flat plate penetrometer is as follows:

[0164] (1) The flat plate penetrometer is completely immersed in water, and water is injected into the installation groove and the permeable pipe with a syringe until no bubbles are generated in the water. The flat 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, the pore water pressure sensor, the first permeable stone, and the second permeable stone;

[0165] (2) After the sensor is saturated, the first permeable stone, the second permeable stone and the cone are placed into the flat plate penetrometer, and the flat plate penetrometer is wrapped and sealed with a plastic film to prevent the sensor saturation from decreasing.

[0166] (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 flat penetrometer on 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.

[0167] (4) After the flat 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 flat plate penetrometer, and the plastic film is removed;

[0168] (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.

[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. A flat 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 effective stress sensor, disposed on a first side of the frame; a shear strength sensor, disposed on the second side surface of the frame; A penetration resistance sensor is arranged at the upper end of the frame; Wherein, the first side surface and the second side surface are parallel to each other.

2. The flat plate penetrometer according to claim 1, characterized in that: The framework includes: substrate; A first column and a second column are both arranged on the lower surface of the substrate; A connecting beam has two ends respectively connected to the first column and the second column.

3. The flat plate penetrometer according to claim 2, characterized in that: The cone tip resistance sensor comprises: A silicone pad is disposed on the lower surface of the first column and the lower surface of the second column, and the silicone pad forms a via hole; A cone is disposed below the silicone pad, a boss is formed on one side of the cone facing the silicone pad, and the boss passes through the via hole; 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 connecting beam; The first strain sensing element is disposed on the arched beam structure and along the length direction of the arched beam structure.

4. The flat plate penetrometer according to claim 3, characterized in that: There are two arched beam structures, which are symmetrically arranged. The arched beam structure includes: a first arched beam and a contact plate; the first arched beam and the contact plate are integrally formed, and the contact plate is located below the first arched beam.

5. The flat plate penetrometer according to claim 4, characterized in that: The connecting beam forms a through hole, and the boss forms a channel; the pore water pressure sensor includes: A first permeable stone is located between the cone and the silicone pad and corresponds to the position of the channel; a water-permeable pipe, disposed on the boss and connected to the channel; A pore water pressure sensor body is arranged at one end of the water permeable pipe away from the boss; Wherein, the water-permeable pipe passes through the through hole and is located between the two arched beam structures.

6. The flat plate penetrometer according to any one of claims 2 to 5, characterized in that: The frame further includes: a first side plate, connected to the base plate, the first column and the second column respectively; A circular groove and a plurality of mounting grooves are formed on the first side plate, an annular groove is formed on the groove wall of the circular groove, and the mounting groove is connected to the annular groove; The effective stress sensor comprises: A circular structure is installed in the circular 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 annular groove and the cavity; A second strain sensing element is disposed on the inner side of the sensing surface of the circular structure and along the radial direction of the circular structure; A plurality of second permeable stones are installed in corresponding installation grooves.

7. The flat plate penetrometer according to claim 6, characterized in that: The frame further includes: a second side plate mounted on the first column and the second column; a sliding channel and an opening are formed on the second side plate, and the sliding channel is connected to the opening; 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 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 third 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 third strain sensing element are both located between the sliding block and the friction plate.

8. The flat plate penetrometer according to any one of claims 2 to 5, characterized in that: The frame further comprises: a mounting tube, which is arranged on the upper surface of the substrate; The penetration resistance sensor comprises: A first supporting cylinder, installed in the installation cylinder; 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 installation tube and sleeved outside the second arched beam and the second supporting tube.

9. A method for measuring effective stress parameters of a flat plate penetrometer according to any one of claims 1 to 8, characterized in that: Includes steps: The flat plate penetrometer is filled 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 flat 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, the signal transmission cable of the shear strength sensor, 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 flat plate penetrometer is located in the water; After removing the plastic film, starting the electric cylinder, penetrating the flat plate penetrometer into the saturated soil sample to be tested at a constant speed, and collecting pore water pressure, cone tip resistance, penetration resistance, effective stress at at least two depths, and shear strength at at least two depths through the signal demodulator; Determining an effective friction angle and an effective cohesion according to the effective stress at the at least two depth positions and the shear strength at the at least two depth positions; 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.

10. The effective stress parameter measurement method of a flat plate penetrometer according to claim 9, characterized in that: The effective friction angle and the effective cohesion satisfy the following relationship: Among them, τ represents the shear strength, σ' represents the effective stress, represents the effective friction angle, c' represents the effective cohesion; 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.

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