Static soil pressure measuring device based on curved surface pressure sensor and testing method thereof

Abstract

The invention discloses a static soil side pressure measuring device and testing method based on a curved surface pressure sensor. Horizontal openings are symmetrically cut in the middle of a sample pressure chamber to penetrate through the inner wall and the outer wall, and the curved surface pressure sensor is embedded; the sample base penetrates through an avoiding hole in the middle of the pressure chamber fixing ring and is fixed to the upper portion of the base through a bolt, and the pressure chamber is arranged on the fixing ring; the sample base is placed in an avoiding hole in the middle of the gravity balance foam; the curved surface pressure sensor is formed by sealing a stress component, a square tubular cavity and a packaging base, and the cavity is filled with silicone oil; the outer surface of the stressed part is a curved surface, a strain gauge is pasted at the center of the inner surface, intracavity silicone oil is communicated with a pressure controller, and the strain gauge is connected to a strain collector. The device solves the problem of uneven stress and strain caused by mismatching of a conventional plane pressure sensor and the inner wall of a consolidometer, ensures the non-deformation requirement of a static soil side pressure test, remarkably reduces the friction resistance of the side wall, and can meet the test requirements of various soil bodies under the conditions from low pressure to high pressure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geotechnical engineering and soil mechanics, and particularly relates to a static soil pressure measuring device based on a curved surface pressure sensor and a testing method thereof. BACKGROUND

[0002] The static soil lateral pressure coefficient has important significance in geotechnical engineering, and it is the key to understanding and calculating the original stress state of the soil body when the lateral restriction does not deform. Its core value lies in providing accurate design benchmarks for various underground engineering, such as deep foundation pit supporting walls and basement side walls. Therefore, the accurate selection of the static soil pressure coefficient value is directly related to the safety and economy of the structural design. Underestimation may lead to risks, while overestimation may result in waste. In addition, it is also an indispensable parameter for defining the initial stress field in numerical simulation, ensuring the reliability of the simulation prediction of the construction process (such as excavation and tunneling), and deeply affecting the accurate judgment of the stress history of the soil body, the strength evaluation, and the control of the surrounding environment settlement.

[0003] The current common method for measuring the soil lateral pressure coefficient is to add a horizontal soil pressure sensor to the consolidation instrument for measurement. However, this method has several obvious defects: on the one hand, the conventional consolidation instrument is usually circular in cross-section, while the conventional soil pressure sensor usually has a planar contact surface, which easily causes local unevenness in stress and strain distribution in the measurement area; on the other hand, the measurement of the static soil pressure lateral coefficient has strict requirements for the deformation tolerance of the sample, and the strain level usually needs to be controlled at about 10 -5 .

[0004] The existing conventional soil pressure sensor relies on the deformation of the elastic body to sense the pressure, and its inherent stiffness is often insufficient to suppress the deformation of the soil body under full range, thereby causing the deformation of the sensor membrane surface during the stress process and inducing the soil arching effect, which further affects the measurement results of the true soil pressure. In addition, since the sensor needs to be arranged on the side wall of the consolidation instrument, the sample height of the consolidation instrument needs to be increased, which further amplifies the influence of the sample side friction, and there is still a significant deficiency in effectively reducing the side wall friction in the existing device. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a static soil pressure measuring device based on a curved surface pressure sensor and a testing method thereof, which can solve the problem of uneven stress and strain caused by the mismatch between the conventional soil pressure sensor and the surface of the consolidation instrument, ensure the static soil pressure testing conditions that the sensor hardly deforms during the full range measurement process, effectively reduce the interference of the sample side friction on the test results, and be compatible with the high-precision sample preparation of various types of soil, and adapt to the testing requirements under low pressure to high pressure conditions.

[0006] In order to solve the above technical problems, the application provides a static soil pressure measuring device based on a curved surface pressure sensor, which comprises a perspex container, a sample pressure chamber and a sample base are arranged in the perspex container, a cylindrical hole is arranged in the sample pressure chamber, the sample base is fixed at the bottom of the perspex container and extends into the bottom of the cylindrical hole, a sample top cover and an upper pressure applying assembly are arranged above the cylindrical hole, the sample top cover, the sample base and the sample pressure chamber cooperatively form a pressure measuring cavity; Two openings are arranged on the surface of the sample pressure chamber in a radial direction and penetrate the inner wall and the outer wall, and two curved surface pressure sensors are arranged in the two openings; The curved surface pressure sensor is connected with a volume pressure controller and a strain acquisition instrument, the volume pressure controller is used for controlling the output pressure value of the curved surface pressure sensor, and the strain acquisition instrument is used for acquiring the value of the curved surface pressure sensor; The upper pressure applying assembly, the volume pressure controller and the strain acquisition instrument are connected with a measuring controller; A gravity balance foam is further sleeved on the sample base, a pressure chamber fixing ring is arranged on the sample base, the pressure chamber fixing ring is fixed on the sample base through bolts, and the sample pressure chamber is placed on the upper surface of the pressure chamber fixing ring.

[0007] Further, the volume V of the gravity balance foam is p The design is as follows: ; Wherein, M c is the mass of the pressure chamber, M f is the mass of the pressure chamber fixing ring, p w is the density of water, and p p is the density of the gravity balance foam.

[0008] Further, the curved surface pressure sensor comprises a force receiving component, a square tubular cavity and a packaging base, the outer surface of the force receiving component is curved and consistent with the shape of the inner wall of the sample pressure chamber, the inner surface of the force receiving component is flat and sealingly connected with one end of the square tubular cavity, the other end of the square tubular cavity is sealingly connected with the packaging base, and the internal space formed by the force receiving component, the square tubular cavity and the packaging base is filled with silicon oil as a working medium; A strain gauge is further pasted at the center of the inner surface of the force receiving component, and the deformation direction of the strain gauge is horizontal.

[0009] Further, a hydraulic sleeve assembly is arranged on the packaging base, so as to communicate the silicon oil in the sensor with the volume pressure controller; a sealing lead device is arranged on the packaging base, so as to connect the lead wire of the strain gauge; and the packaging base is fixedly connected with the outer wall of the sample pressure chamber through a plurality of screws.

[0010] Further, the outer surface of the force receiving component is pasted with a polyester film through vacuum silicone grease.

[0011] Further, the square tubular cavity is sealed and connected with the force receiving component and the packaging base through epoxy resin at both ends.

[0012] Further, the height of the acrylic container is higher than the height of the top surface of the sample pressure chamber.

[0013] Further, the upper pressure applying assembly comprises an upper hydraulic cylinder, and an upper pressure increasing pressure sensor is arranged between the upper hydraulic cylinder and the sample top cover.

[0014] A static soil pressure testing method based on a curved surface pressure sensor, comprising the following steps: Step 1) calibrate two groups of curved surface pressure sensors to obtain calibration functions F1 and F2; Step 2) set the output of the volume pressure controller connected with the two groups of curved surface pressure sensors to 0 kPa, and record the initial readings of the strain gauges in the two curved surface pressure sensors as ε 01 and ε 02 respectively; Step 3) preparation: install the sample pressure chamber, prepare the soil sample in the sample pressure chamber and cover the sample top cover, and in this process, the output pressures of the two volume pressure controllers are adjusted synchronously by the measuring controller to ensure that the readings of the two curved surface pressure sensors are always ε 01 and ε 02 ; Step 4) when testing the dry sample, inject water in the acrylic container chamber so that the water level is above the bottom of the sample pressure chamber and below the top of the sample base; when testing the saturated sample, inject water in the acrylic container chamber so that the water level is above the top of the sample pressure chamber; The water injected in the acrylic container chamber makes the gravity balance foam float up and abut against the bottom surface of the pressure chamber fixing ring; in this process, the output pressures of the two volume pressure controllers are adjusted synchronously by the measuring controller to ensure that the readings of the two curved surface pressure sensors are always ε 01 and ε 02 ; Step 5) slowly rotate and remove the bolts on the pressure chamber fixing ring, so that the gravity balance foam directly supports the sample pressure chamber and the pressure chamber fixing ring; in this process, the output pressures of the two volume pressure controllers are adjusted synchronously by the measuring controller to ensure that the readings of the two curved surface pressure sensors are always ε 01 and ε 02 ; Step 6) Apply vertical load to the soil sample by the upper pressure assembly, and simultaneously adjust the output pressure of the two volumetric pressure controllers by the measurement controller to ensure that the readings of the two curved surface pressure sensors are always ε 01 and ε 02 ; after the vertical load is stabilized, the static earth lateral pressure coefficient K is calculated by the following formula: ; wherein F1 and F2 are calibration functions of the two sets of curved surface pressure sensors, respectively; σ a1 and σ a2 are the output pressure values of the volumetric pressure controllers connected to the two curved surface pressure sensors, respectively; F v is the pressure value of the upper pressure assembly; and d is the inner diameter of the sample pressure chamber. Step 7) Increase or decrease the vertical load step by step, and repeat step 6 to obtain the static earth lateral pressure coefficients corresponding to different vertical pressure levels under normal consolidation, over-consolidation and other states.

[0015] Further, the calibration steps of the curved surface pressure sensor are as follows: a. Place the curved surface pressure sensor in the calibration pressure chamber, and set the hydraulic output of the calibration pressure chamber to 0 kPa, and simultaneously set the output pressure of the volumetric pressure controller to 0 kPa, and record the output reading of the curved surface pressure sensor as ε0; b. Increase the output pressure of the calibration pressure chamber to σ r step by step, and correspondingly adjust the output pressure of the volumetric pressure controller to keep the reading of the curved surface pressure sensor at ε0, and record the output pressure of the volumetric pressure controller as σ a ; c. Increase the output pressure of the calibration pressure chamber step by step, and repeat the operation of step b until the maximum range of the curved surface pressure sensor is reached; d. On the basis of the existing data points of σ r and σ a , the function relationship F of σ r and σ a is constructed by the two-point linear interpolation method to obtain the calibration function, i.e. .

[0016] Advantages of the present application: The device of the present application breaks through the limitation of traditional soil pressure sensors that can only be applied to plane pressure measurement, and can accurately measure the horizontal soil pressure under the curved surface state of the circular consolidation instrument, avoiding the problem of uneven stress and strain caused by the inconsistency between the conventional soil pressure sensor and the inner surface of the consolidation pressure chamber.

[0017] The device of the present application adds strain gauges in the curved surface pressure sensor and introduces an independent volume pressure controller to servo-balance the deformation of the surface stress component of the sensor, thereby realizing the harsh working condition of almost no deformation of the sensor during full-range measurement. This design effectively overcomes the local soil arching effect caused by membrane deformation in the measurement of traditional soil pressure sensors, and improves the accuracy of static soil lateral pressure coefficient measurement.

[0018] The device of the present application realizes the self-adaptive lifting of the sample pressure chamber during the consolidation test loading process, overcomes the obvious side wall friction caused by the fixed bottom of the pressure chamber in the traditional rigid wall consolidation test, and further eliminates the drag friction of the sample side wall caused by its own gravity when the sample pressure chamber is in a suspended state, thereby maintaining an approximately frictionless contact interface between the sample and the sample pressure chamber side wall.

[0019] The device and test method of the present application use an adjustable sample pressure chamber fixing ring to effectively overcome the side wall friction while maintaining the feasibility of high-precision sample preparation, which is beneficial to the development of high-precision geotechnical test experiments. During sample preparation, the pressure chamber fixing ring is fixed by manual bolts to provide stable support for the sample pressure chamber, facilitating the preparation of various types of soil samples. After sample preparation is completed, the pressure chamber fixing ring is slowly released using manual bolts, resulting in less disturbance to the sample during the entire process, which is particularly important for preparing high-quality non-adhesive soil samples.

[0020] The device of the present application adopts a rigid wall structure, and the size of the curved surface pressure sensor can be customized as needed, suitable for tests of fine-grained soil and coarse-grained soil. Since the range of the curved surface pressure sensor is determined by the range of the volume pressure controller, it has a wide test range and can test soil under low pressure to high pressure conditions, with high applicability and flexibility. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is the overall structure schematic diagram of the static soil pressure measurement device of the present application; Figure 2 is the top view schematic diagram of the static soil pressure measurement device of the present application; Figure 3is a side view schematic diagram of the static earth pressure testing device of the present application; Figure 4 is a structural schematic diagram of the curved surface pressure sensor of the present application; Figure 5 is a rear view schematic diagram of the curved surface pressure sensor of the present application; Figure 6 is a schematic diagram of the pressure sensor calibration of the present application; Figure 7 is a graph of the relationship between the static earth side pressure coefficient and the vertical stress of loose sand soil samples in the process of loading, unloading and reloading according to the present application; Figure 8 is a graph of the relationship between the static earth side pressure coefficient and the vertical stress of dense sand soil samples in the process of loading, unloading and reloading according to the present application. DETAILED DESCRIPTION

[0022] The present application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not limiting to the present application.

[0023] Referring to Figures 1 to 3 An embodiment of the static earth side pressure measuring device based on the curved surface pressure sensor of the present application is shown in the drawings, which comprises an upper hydraulic cylinder 1, an upper pressurizing pressure sensor 2, a sample top cover 3, a sample base 5, a sample pressure chamber 4, two sets of curved surface pressure sensors A, a pressure chamber fixing ring 6, a gravity balance foam 7, an acrylic container chamber 10, two volume pressure controllers 12, a strain acquisition instrument 11 and a measurement controller 13; the upper hydraulic cylinder 1, the upper pressurizing pressure sensor 2, the two volume pressure controllers 12 and the strain acquisition instrument 11 are connected to the measurement controller 13 for control.

[0024] The sample pressure chamber 4 described above is formed by a through cylinder cut from the top middle of a cuboid steel block to form a space for accommodating the soil sample; the sample top cover 3 and the sample base 5 are both cylindrical, with a diameter slightly smaller than the inner diameter of the sample pressure chamber 4, and can be inserted into the sample pressure chamber 4; the sample pressure chamber 4, the sample top cover 3 and the sample base 5 are placed in the acrylic container chamber 10; the sample top cover 3 is connected to the upper pressurizing assembly above it, which comprises the upper hydraulic cylinder 1 and the upper conventional pressure sensor 2; a horizontal opening is symmetrically cut in the middle of the sample pressure chamber 4, penetrating the inner wall and the outer wall, i.e. the opening is in the same diameter direction, and two sets of curved surface pressure sensors A are embedded in the opening; the bottom of the curved surface pressure sensor A is fixedly connected to the outer wall of the sample pressure chamber 4 through a screw 8, ensuring stability after installation.

[0025] The middle part of the pressure chamber fixing ring 6 is provided with an avoiding hole, the diameter of which is slightly larger than the diameter of the sample base 5, so that the sample base can pass through the avoiding hole; the pressure chamber fixing ring 6 is fixedly connected to the sample base 5 through a manually rotatable bolt 9, and the sample pressure chamber 4 is directly placed on the upper part of the pressure chamber fixing ring 6, that is, the sample pressure chamber 4 can move in the axial direction of the sample base 5 and cannot move in the radial direction, and the bottom is limited by the pressure chamber fixing ring 6. During the preparation of the sample, the sample pressure chamber is fixed by the manual bolt, which provides stable support for the sample pressure chamber, and facilitates the preparation of various soil samples, that is, soil samples; after the sample preparation is completed, the connection between the pressure chamber fixing ring 6 and the sample base 5 is released by using the bolt 9, and the operation needs to be slowly released, so that the disturbance to the sample during the whole process is small, which is particularly important for preparing high-quality non-adhesive soil samples.

[0026] The gravity balance foam 7 is placed in the middle of the acrylic container chamber 10, and an avoiding hole is formed in the middle part, the diameter of which is slightly larger than the diameter of the sample base 5, and the sample base 5 is placed in the avoiding hole; the gravity balance foam 7 needs to support and support the disconnected pressure chamber fixing ring 6 through its buoyancy, and the volume Vp of the gravity balance foam 7 is designed as: Where M c is the mass of the sample pressure chamber, M f is the mass of the sample pressure chamber fixing ring, p w is the density of water, and p p is the density of the gravity balance foam. Based on this design, after the balance foam 7 is completely immersed in water, the buoyancy provided can just balance the gravity of the sample pressure chamber 4, the pressure chamber fixing ring 6 and the balance foam itself, so as to offset the drag friction force generated by the gravity of the sample pressure chamber in suspension on the soil sample.

[0027] Referring to FIGS. 1, 2 and 3, Figure 4 and Figure 5 The curved surface pressure sensor A is composed of a force receiving part 14, a square tube cavity 15 and a packaging base 16; the outer surface of the force receiving part 14 is a curved surface, which is designed according to the shape of the opening of the inner wall of the sample pressure chamber 4, can exactly fill the gap of the inner wall of the sample pressure chamber 4, play a complementary role, and fill the opening position, so that the inner wall of the sample pressure chamber 4 forms a complete columnar surface; the inner surface of the force receiving part 14 is a plane, and one end of the square tube cavity 15 is sealed and connected through epoxy resin, and the other end of the square tube cavity 15 is also sealed and connected with the packaging base 16 through epoxy resin, and the internal space formed by the three is filled with silicone oil as working medium; here, the working medium can also use gas pressure, and the corresponding volume pressure controller 12 also needs to be replaced with gas pressure, and the benefit of using oil pressure here is that a wider pressure range of the curved surface pressure sensor can be provided.

[0028] A strain gauge 17 is pasted at the center of the inner surface of the force receiving part 14, which measures the change direction of the outer surface curve of the force receiving part 14, i.e. the deformation direction of the strain gauge during the measurement of the instrument is horizontal; when the outer surface of the force receiving part 14 is subjected to pressure, the strain gauge 17 will be stretched to produce strain and generate a signal for the data acquisition instrument 11 to collect; The packaging base 16 is provided with a hydraulic sleeve 18 for connecting the silicon oil in the sensor with the volume pressure controller 12; the packaging base 16 is provided with a sealed lead device 19 for connecting the strain gauge 17 with the external strain acquisition instrument, which can collect data while avoiding the leakage of silicon oil; the packaging base 16 is also provided with a plurality of holes for the screws 8 to pass through and be fixed with the outer wall of the sample pressure chamber 4; A polyester film 20 is pasted on the outer surface of the force receiving part 14 of the curved surface pressure sensor A through vacuum silicon grease, which does not directly contact with the sample; on the one hand, the polyester film can play a protective role to prevent larger sharp particles from scratching and damaging the outer surface of the curved surface sensor, and on the other hand, the polyester film can have relative displacement with the outer surface of the curved surface sensor, which can reduce the friction of the outer surface of the curved surface sensor, so that the outer surface is mainly subjected to pressure perpendicular to the outer surface.

[0029] Based on the above measurement device, calibration operation is also needed before testing, as shown in Figure 6 , the steps are as follows: First, place the curved surface pressure sensor A in a calibration pressure chamber 21 with precise oil pressure output capability, and set the hydraulic output of the calibration pressure chamber to 0 kPa, and at the same time, set the output pressure of the volume pressure controller 12 connected with the curved surface pressure sensor A to 0 kPa, and record the output reading of the strain gauge 17 in the curved surface pressure sensor A, which is denoted as ε0.

[0030] Then gradually increase the output pressure of the calibration pressure chamber 21 to σ r kPa, and adjust the output pressure of the volume pressure controller 12 connected with the curved surface pressure sensor A correspondingly, so that the strain gauge reading in the curved surface pressure sensor A always maintains at ε0, and record the output pressure of the volume pressure controller 12 as σ a kPa.

[0031] Subsequently, gradually increase the output pressure of the calibration pressure chamber 21, and repeat the above operation until the maximum range required by the curved surface pressure sensor A is reached. Based on the existing data points of σ r and σ a , a two-point linear interpolation method is used to construct the functional relationship F between σ r and σ a , which is named as "calibration function", i.e. The calibration functions of the two sets of curved surface pressure sensors A are denoted as F1 and F2.

[0032] After calibration, the test can be carried out by the above method, and the test steps are as follows: The output of the volume pressure controller connected with the two sets of curved surface pressure sensors A is set to 0 kPa, and the initial readings of the strain gauges in the two curved surface pressure sensors A are recorded as ε 01 and ε 02 .

[0033] The soil sample is prepared, the bolt 9 of the pressure chamber fixing ring 6 is first tightened to stabilize the support of the sample pressure chamber 4; the soil sample is prepared between the sample pressure chambers 4, which allows various sample preparation methods, including layered compaction of cohesionless soil and placement of undisturbed cohesive soil samples, etc., and the sample top cover 3 is covered after preparation. During this process, the output pressures of the two volume pressure controllers 12 are adjusted synchronously by the measuring controller 13 to ensure that the readings of the strain gauges in the two curved surface pressure sensors A are always ε 01 and ε 02 .

[0034] For dry samples, water is injected into the acrylic container chamber 10 to cover the pressure chamber fixing ring 6 and be below the top of the sample base 5; for saturated samples, water is injected into the acrylic container chamber 10 to cover the sample pressure chamber 4. The above two cases make the gravity balance foam 7 float up and rest under the pressure chamber fixing ring 6; during this process, the output pressures of the two volume pressure controllers 12 are adjusted synchronously by the measuring controller 13 to ensure that the readings of the strain gauges in the two curved surface pressure sensors A are always ε 01 and ε 02 .

[0035] After the above operation, the bolt 9 needs to be slowly rotated and removed, the bolt 9 can be located in the acrylic container chamber 10, which has a simple structure, but has a large disturbance to water, or the bolt 9 can pass through the acrylic container chamber 10 to the outside, which can be operated outside with less disturbance to water, such a design needs to set a sealing structure on the corresponding position of the acrylic container chamber 10 to ensure that the connection between the bolt 9 and the acrylic container chamber 10 will not leak during rotation, for example, a sealing ring is added. After the fixation is released, the sample pressure chamber 4 and the pressure chamber fixing ring 6 will move down due to gravity, but the gravity balance foam 7 can directly support the sample pressure chamber 4 and the pressure chamber fixing ring 6 due to the use of the gravity balance foam 7, during this process, the output pressures of the two volume pressure controllers 12 are adjusted synchronously by the measuring controller 13 to ensure that the readings of the strain gauges in the two curved surface pressure sensors A are always ε 01 and ε 02 .

[0036] Subsequently, the pressure test is carried out, the vertical load is applied to the soil sample by the upper hydraulic cylinder 1, and the output pressure of the two volume pressure controllers 12 is synchronously adjusted by the measurement controller 13, so that the respective readings of the strain gauges in the two curved surface pressure sensors A are always ε 01 and ε 02 ; after the vertical load is stabilized, the static soil lateral pressure coefficient K is calculated by the following formula: Wherein, F1 and F2 are the calibration functions of the two groups of curved surface pressure sensors A respectively; σ a and σ a2 are the output pressure values of the volume pressure controllers 12 connected to the two curved surface pressure sensors A respectively; F v is the pressure value of the upper conventional pressure sensor 2; and d is the inner diameter of the sample pressure chamber 4.

[0037] The vertical load is gradually increased or decreased, and the above operation is repeatedly performed, so as to obtain the static soil lateral pressure coefficients corresponding to different vertical pressure levels in the normal consolidation and over-consolidation states.

[0038] Specifically, the static soil lateral pressure coefficients of two groups of dry samples (loose sand and dense sand) are measured by using the above device, the sample diameter d = 8 cm, the initial height h = 6 cm, the relative densities of the loose sand and the dense sand are 25% and 80% respectively, and the sand is prepared by the sand dropping method. Figure 7 and Figure 8 The relationship diagrams of the static soil lateral pressure coefficients and the vertical stresses of the two soil samples in the loading, unloading and reloading processes are given. Firstly, the vertical stress is increased from 25 kPa to 300 kPa, then unloaded to 25 kPa, and then reloaded, the vertical stress is gradually increased to and exceeds 300 kPa, and finally reaches 500 kPa. The observation results are consistent with the common sense: in the initial loading stage, the static soil lateral pressure coefficients of the two groups of samples are approximately constant, and the lateral pressure coefficient of the loose sand is significantly higher than that of the dense sand; in the unloading process, the soil enters the over-consolidation state, the static soil lateral pressure coefficient gradually increases, then presents a downward trend in the reloading stage, and as the vertical stress exceeds the previous maximum value, the static soil lateral pressure coefficient tends to fall back and approaches the trend value in the initial loading stage, showing the characteristics of approximately constant.

[0039] In summary, the application breaks through the limitation of the traditional soil pressure sensor which can only be applied to plane pressure measurement, and has accurate measurement, good popularization and applicability.

[0040] The above examples are only preferred embodiments for fully illustrating the application, and the protection scope of the application is not limited thereto. Any equivalent replacement or transformation made by the person skilled in the art on the basis of the application is within the protection scope of the application.

Claims

1. A static earth pressure measuring device based on a curved surface pressure sensor, characterized by, The application relates to a pressure measuring device for measuring the static earth lateral pressure coefficient of a soil sample, which comprises an acrylic container, a sample pressure chamber and a sample base arranged in the acrylic container, a cylindrical hole is hollowly arranged in the sample pressure chamber, the sample base is fixed at the bottom of the acrylic container and extends into the bottom of the cylindrical hole, a sample top cover and an upper pressure applying assembly are arranged above the cylindrical hole, the sample top cover, the sample base and the sample pressure chamber cooperatively form a pressure measuring cavity; Two openings are arranged on the surface of the sample pressure chamber in a radial direction and penetrate the inner wall and the outer wall, and two curved surface pressure sensors are arranged in the openings; The curved surface pressure sensors are connected with a volume pressure controller and a strain acquisition instrument, the volume pressure controller is used for controlling the output pressure number of the curved surface pressure sensor, and the strain acquisition instrument is used for acquiring the number of the curved surface pressure sensor; The upper pressure applying assembly, the volume pressure controller and the strain acquisition instrument are connected with a measuring controller; A gravity balance foam is further sleeved on the sample base, a pressure chamber fixing ring is arranged on the sample base, the pressure chamber fixing ring is fixed on the sample base through bolts, and the sample pressure chamber is placed on the upper surface of the pressure chamber fixing ring.

2. The apparatus for measuring static earth pressure based on a curved pressure sensor according to claim 1, wherein, The volume V of the gravity balanced foam p is designed to: ； where M c is the mass of the pressure chamber, M f is the mass of the pressure chamber stationary ring, p w is the density of water, p p is the density of the gravity balanced foam.

3. The apparatus according to claim 1, wherein The curved surface pressure sensor comprises a stress component, a square tubular cavity and a packaging base, the outer surface of the stress component is a curved surface and is consistent with the shape of the inner wall of the sample pressure chamber, the inner surface of the stress component is a plane and is sealingly connected with one end of the square tubular cavity, the other end of the square tubular cavity is sealingly connected with the packaging base, and the internal space formed by the stress component, the square tubular cavity and the packaging base is filled with silicon oil as a working medium; A strain gauge is further pasted at the center of the inner surface of the stress component, and the deformation direction of the strain gauge is horizontal.

4. The apparatus according to claim 3, wherein the curved pressure sensor is a flexible printed circuit board. A hydraulic sleeve is arranged on the packaging base and is used for connecting the silicon oil in the sensor with the volume pressure controller; a sealing lead device is arranged on the packaging base and is used for connecting the lead wire of the strain gauge; and the packaging base is fixedly connected with the outer wall of the sample pressure chamber through a plurality of screws.

5. The apparatus according to claim 3, wherein the curved pressure sensor is a flexible printed circuit board. The outer surface of the stress component is pasted with a polyester film through vacuum silicon grease.

6. The apparatus according to claim 3, wherein the curved pressure sensor is a flexible printed circuit board. The two ends of the square tubular cavity are sealingly connected with the stress component and the packaging base through epoxy resin.

7. The apparatus according to claim 1, wherein The height of the acrylic container is higher than the height of the top surface of the sample pressure chamber.

8. The apparatus for measuring earth pressure based on a curved pressure sensor and a method for testing the same according to claim 1, wherein, The upper pressure applying assembly comprises an upper hydraulic cylinder, and an upper pressure increasing pressure sensor is arranged between the upper hydraulic cylinder and the sample top cover.

9. A static earth pressure test method based on a curved surface pressure sensor, characterized by, The application further discloses a method for measuring the static earth lateral pressure coefficient of a soil sample, which comprises the following steps: Step 1, calibrating two groups of curved surface pressure sensors to obtain calibration functions F1 and F2; Step 2) Set the output of the volumetric pressure controller connected to the two sets of curved surface pressure sensors to 0 kPa, and simultaneously record the initial readings of the strain gauges in the two curved surface pressure sensors as ε. 01 and ε 02 ; Step 3) Preparation: Install the sample pressure chamber, prepare the soil sample in the sample pressure chamber and cover the sample top cover, during which the output pressure of the two volume pressure controllers is adjusted synchronously by the measurement controller to ensure that the readings of the two curved pressure sensors are always ε 01 and ε 02 ; Step 4, when testing a dry sample, water is injected into the acrylic container chamber so that the water level is above the bottom of the sample pressure chamber and below the top of the sample base; when testing a saturated sample, water is injected into the acrylic container chamber so that the water level is above the top of the sample pressure chamber; The water injected into the acrylic container chamber makes the gravity balance foam float up and rest on the bottom surface of the pressure chamber fixed ring; in this process, the output pressure of the two volume pressure controllers is adjusted synchronously by the measurement controller to ensure that the readings of the two curved pressure sensors are always ε 01 and ε 02 ; Step 5) Slowly unscrew and remove the bolts on the pressure chamber fixing ring, so that the gravity directly supports the sample pressure chamber and the pressure chamber fixing ring. In this process, the output pressure of the two volume pressure controllers is adjusted synchronously by the measuring controller to ensure that the readings of the two curved pressure sensors are always ε 01 and ε 02 ; Step 6) Apply vertical load to the soil sample by the upper pressure assembly, while synchronously adjusting the output pressure of the two volumetric pressure controllers by the measurement controller, to ensure that the readings of the two curved pressure sensors are always ε 01 and ε 02 ; after the vertical load is stable, the static soil lateral pressure coefficient K is calculated by the following formula: ； where F1 and F2 are calibration functions of the two sets of curved surface pressure sensors, respectively; σ a1 and σ a1 are output pressure values of the volume pressure controllers connected to the two curved surface pressure sensors, respectively; F v is the pressure value of the upper pressure applying assembly; and d is the inner diameter of the sample pressure chamber. Step 7, gradually increasing or decreasing the vertical load and repeatedly executing step 6 to obtain the static earth lateral pressure coefficient corresponding to different vertical pressure levels under normal consolidation and over-consolidation states.

10. The static earth pressure test method based on the curved surface pressure sensor according to claim 9, wherein, The calibration steps of the curved surface pressure sensor are as follows: a. Place the diaphragm pressure sensor in the calibration pressure chamber and set the hydraulic output of the calibration pressure chamber to 0 kPa, while also setting the output pressure of the volumetric pressure controller to 0 kPa, and record the output reading of the diaphragm pressure sensor, denoted ε0; b. The output pressure of the calibration pressure chamber is gradually increased to σ r and the output pressure of the volumetric pressure controller is correspondingly increased, so that the reading of the curved pressure sensor is always maintained at ε0, and the output pressure of the volumetric pressure controller is recorded as σ a ; c. Increase the output pressure of the calibration pressure chamber in steps and repeat the procedure of step b until the maximum range of the diaphragm pressure sensor is reached; d. In the existing σ r With σ a Based on the data points, the two-point linear interpolation method is used to construct the function relationship F of σ r With σ a The calibration function is obtained, that is: 。

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