A soft-contact soil pressure sensor and soil pressure sensor calibration method

Abstract

The present invention discloses a soft-contact earth pressure sensor and an earth pressure sensor calibration method. The earth pressure sensor includes: a soft contact layer, a piezoresistive sensitive element, a sensor main shell, a pagoda-shaped anti-breakage structure, and a threaded protective shell. In the present invention, the earth pressure sensor and the soil contact surface adopt a soft contact method. The arc-shaped columnar sensor main shell is filled in through a window on the front. The soft contact layer on the surface of the earth pressure sensor is affected by the upper filling soil layer and deformed and flexed to form a shape flush with the sensor main shell, so that the earth pressure acts on the piezoresistive sensitive element. The soft contact layer of the earth pressure sensor is made of a high-elastic material. The density of the high-elastic material is between dry sand and saturated sand. Compared with aluminum alloy and stainless steel materials, the use of a high-elastic material in the soft contact layer can effectively reduce the stiffness matching problem between the earth pressure sensor and the soil medium, thereby improving the test accuracy of the earth pressure sensor and making the earth pressure data measured by the earth pressure sensor have higher accuracy and reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of soil pressure sensors, and more particularly to a soft-contact soil pressure sensor and a soil pressure sensor calibration method. Background Art

[0002] The high-gravity centrifuge model test relies on the high-speed rotation of the geotechnical centrifuge to generate high centrifugal force, compensate for the stress loss of the soil layer or geotechnical structure in the high-gravity centrifuge model, and achieve a stress level similar to or equal to that of the prototype. When a stable high centrifugal acceleration condition is reached (such as 50g~100g), by applying a compressive seismic load (with "high frequency 10~300Hz", "instantaneous ≤1s", and "strong vibration up to 30g~60g"), the actual prototype dynamic characteristics and failure mechanism can be more accurately presented. It is also an important research method in the field of geotechnical engineering and has played an important role in basic theoretical research and engineering application research.

[0003] However, due to the small size of the ultra-gravity centrifugal model (mostly 700 (length) * 300 (width) * 400mm (height)), and the micro-earth pressure sensor, as a key measuring sensor for monitoring earth pressure and lateral earth pressure in saturated / unsaturated soil, has significant differences from the measurement media of conventional pressure sensors such as air pressure and water pressure (soil is a non-uniform and inelastic medium, and gas and liquid are uniform media). Affected by many factors such as embedding effect, contact interface, size effect, waterproof structure, etc., the accuracy and reliability of the earth pressure data measured by the micro-earth pressure sensor in the ultra-gravity centrifugal test have large errors (the maximum error can reach 50%). Summary of the Invention

[0004] In view of this, the present invention discloses a soft-contact earth pressure sensor and an earth pressure sensor calibration method to improve the test accuracy of the earth pressure sensor and make the earth pressure data measured by the earth pressure sensor have higher accuracy and reliability.

[0005] A soft-contact earth pressure sensor, comprising: a soft contact layer, a piezoresistive sensitive element, a sensor main housing, a pagoda-shaped anti-breakage structure and a threaded protective housing;

[0006] The soft contact layer is used as the direct contact body between the earth pressure sensor and the soil. It is made of highly elastic material and is installed at the front window of the sensor main housing to directly transmit the physical changes of the earth pressure to the piezoresistive sensitive element.

[0007] The piezoresistive sensitive element is the core part of the soil pressure sensor, which is used to convert the physical change of the soil pressure into a voltage signal output;

[0008] The sensor main housing has an internal thread, which is used to match the threaded protective shell through the internal thread to install and protect the piezoresistive sensitive element; it is also used as a carrier for the soft contact layer;

[0009] The pagoda-type anti-breakage structure is used to match the main housing of the sensor to install a Teflon waterproof tube.

[0010] Optionally, the contact surface between the soft contact layer and the soil is an arc surface, and the contact surface between the soft contact layer and the piezoresistive sensitive element is a parallel surface;

[0011] The arc surface is used to deform when soil pressure is detected to disperse the additional stress and transfer it to the parallel surface.

[0012] Optionally, the piezoresistive sensitive element includes: a high-pressure chamber, a sensitive diaphragm, a vacuum chamber, a gold wire, a stress-free adhesive, a terminal block, a conversion circuit board, and a silicon diaphragm protective shell;

[0013] The high-pressure chamber is a transparent pressure chamber, which is used to contact the soil pressure to be measured;

[0014] The vacuum chamber is a transparent pressure chamber used to output a zero point with the vacuum environment as a reference;

[0015] The high-pressure cavity and the vacuum cavity are respectively provided on both sides of the sensitive diaphragm, for generating strain changes when the pressures in the high-pressure cavity and the vacuum cavity are different, and converting the strain changes into voltage signals for output;

[0016] The gold wire is used to connect multiple equal-value resistors provided in the sensitive diaphragm to form a Wheatstone bridge;

[0017] The connection terminal is arranged on the conversion circuit board and is connected to the gold wire;

[0018] The conversion circuit board is used to be fixedly connected to the four-core shielded cable outside the piezoresistive sensitive element;

[0019] The silicon diaphragm protective shell has a window on the front and a cavity structure inside. The cavity structure is used to install the high-pressure cavity, the sensitive diaphragm and the vacuum cavity, and is filled with the stress-free glue around and on the surface as a protective layer.

[0020] Optionally, the sensor main housing includes: a soft contact layer positioning groove, a soft contact layer support beam, a sensitive element installation cavity and a sensitive element positioning groove, wherein the internal thread is provided inside the sensitive element installation cavity;

[0021] The soft contact layer positioning groove is used to position the soft contact layer;

[0022] The soft contact layer support beam is used to support the soft contact layer;

[0023] The sensor installation cavity is used to place the piezoresistive sensor and is used to position the piezoresistive sensor in combination with the sensor positioning groove. After the piezoresistive sensor is positioned and installed, epoxy resin is filled in the remaining space.

[0024] Optionally, the thread protection housing includes: a connecting external thread and a sensitive element support column;

[0025] The threaded protection housing is matched with the sensor main housing through the connecting external thread, and supports and fixes the piezoresistive sensitive element through the sensitive element support column.

[0026] Optionally, it also includes: four-core shielded cable;

[0027] The four-core shielded cable is fixedly connected to the piezoresistive sensitive element.

[0028] Optionally, it also includes: the Teflon waterproof tube.

[0029] Optionally, the piezoresistive sensitive element is a miniature high-frequency response piezoresistive sensitive diaphragm.

[0030] A soil pressure sensor calibration method is applied to a data acquisition instrument, wherein the data acquisition instrument is connected to the soil pressure sensor described above. The soil pressure calibration method includes:

[0031] The maximum theoretical earth pressure value of the soil layer required to be measured by the earth pressure sensor to be calibrated is divided into M levels, where M is a positive integer;

[0032] When the earth pressure sensor to be calibrated is buried to the soil layer depth corresponding to the actual test, centrifugal acceleration load is applied to the earth pressure sensor to be calibrated step by step to a preset value based on the M levels, and the output voltage signal of the earth pressure sensor to be calibrated at each level and the theoretical earth pressure value corresponding to the soil layer depth under each centrifugal acceleration are obtained;

[0033] Based on the theoretical earth pressure values ​​corresponding to the respective levels, a least squares curve fitting method is used to obtain an average calibration coefficient between the earth pressure output voltage signals of each level of the earth pressure sensor to be calibrated and the theoretical earth pressure values ​​under the corresponding centrifugal acceleration conditions;

[0034] Multiplying the earth pressure output voltage signals of each level of the earth pressure sensor to be calibrated by the corresponding average calibration coefficient to obtain the measured output earth pressure values ​​of the earth pressure sensor to be calibrated at each level;

[0035] Calculating the deviation between the measured output earth pressure value and the corresponding theoretical earth pressure value corresponding to each level of the earth pressure sensor to be calibrated;

[0036] A target coefficient of the earth pressure sensor to be calibrated after calibration is determined based on the respective deviation amounts.

[0037] From the above technical solution, it can be seen that the present invention discloses a soft-contact soil pressure sensor and a soil pressure sensor calibration method. The soil pressure sensor includes: a soft contact layer, a piezoresistive sensitive element, a sensor main shell, a pagoda-shaped anti-breakage structure and a threaded protective shell. The soft contact layer serves as the direct contact body between the soil pressure sensor and the soil. It is made of highly elastic material and is installed at the front window of the sensor main shell to directly transmit the physical changes in soil pressure to the piezoresistive sensitive element. The piezoresistive sensitive element, as the core part of the soil pressure sensor, converts the physical changes in soil pressure into voltage signal output. The sensor main shell can not only serve as a carrier of the soft contact layer, but also can be matched with the threaded protective shell through the internal thread to install and protect the piezoresistive sensitive element, thereby reducing the influence of external force on the piezoresistive sensitive element. The pagoda-shaped anti-breakage structure is matched with the sensor main shell to install the Teflon waterproof pipe. In the present invention, the contact surface between the earth pressure sensor and the soil adopts a soft contact method, and the arc-shaped cylindrical sensor main shell is filled in through a window on the front. The soft contact layer on the surface of the earth pressure sensor is deformed and flexed by the upper filling soil layer to form a shape flush with the sensor main shell, so that the earth pressure acts on the piezoresistive sensitive element; the soft contact layer of the earth pressure sensor adopts a high elastic material, and the density of the high elastic material is between dry sand and saturated sand. Compared with aluminum alloy and stainless steel materials, the high elastic material used in the soft contact layer can effectively reduce the stiffness matching problem between the earth pressure sensor and the soil medium, thereby improving the test accuracy of the earth pressure sensor, and making the earth pressure data measured by the earth pressure sensor have higher accuracy and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the disclosed drawings without any creative work.

[0039] Figure 1 An exploded view of the main structure of a soft-contact earth pressure sensor disclosed in an embodiment of the present invention;

[0040] Figure 2 An exploded view of the main structure of another soft-contact earth pressure sensor disclosed in an embodiment of the present invention;

[0041] Figure 3A front view of the main structure of a soft-contact earth pressure sensor disclosed in an embodiment of the present invention;

[0042] Figure 4 A cross-sectional view of the main structure of a soft-contact earth pressure sensor disclosed in an embodiment of the present invention;

[0043] Figure 5 A front view of a soft contact layer disclosed in an embodiment of the present invention;

[0044] Figure 6 A side view of a soft contact layer disclosed in an embodiment of the present invention;

[0045] Figure 7 A schematic diagram of the connection between a piezoresistive sensor and a four-core shielded cable disclosed in an embodiment of the present invention;

[0046] Figure 8 A cross-sectional view of a piezoresistive sensor disclosed in an embodiment of the present invention;

[0047] Figure 9 A schematic diagram of the connection between a sensor main housing and a pagoda-shaped anti-breakage structure disclosed in an embodiment of the present invention;

[0048] Figure 10 A perspective view of the connection between a sensor main housing and a pagoda-shaped anti-breakage structure disclosed in an embodiment of the present invention;

[0049] Figure 11 A cross-sectional view of the connection between a sensor main housing and a pagoda-shaped anti-breakage structure disclosed in an embodiment of the present invention;

[0050] Figure 12 This is a structural schematic diagram of a threaded protective housing disclosed in an embodiment of the present invention;

[0051] Figure 13 A Fujian standard quartz sand particle size gradation curve diagram disclosed in an embodiment of the present invention;

[0052] FIG14( a ) is a layout diagram of a soft-contact soil pressure sensor disclosed in an embodiment of the present invention;

[0053] FIG14( b ) is a schematic diagram of centrifugal acceleration graded loading disclosed in an embodiment of the present invention;

[0054] FIG15( a ) is a diagram showing the centrifugal acceleration calibration results of a soft-contact earth pressure sensor T1 disclosed in an embodiment of the present invention;

[0055] FIG15( b ) is a diagram showing the theoretical earth pressure calibration results of a soft-contact earth pressure sensor T1 disclosed in an embodiment of the present invention;

[0056] FIG15( c ) is a diagram showing the centrifugal acceleration calibration results of a soft-contact earth pressure sensor T2 disclosed in an embodiment of the present invention;

[0057] FIG15( d ) is a diagram showing the theoretical earth pressure calibration results of a soft-contact earth pressure sensor T2 disclosed in an embodiment of the present invention;

[0058] FIG15( e ) is a diagram showing the centrifugal acceleration calibration results of a soft-contact earth pressure sensor T3 disclosed in an embodiment of the present invention;

[0059] FIG15( f ) is a diagram showing the theoretical earth pressure calibration results of a soft-contact earth pressure sensor T3 disclosed in an embodiment of the present invention;

[0060] Figure 16 This is a flow chart of a soil pressure sensor calibration method disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0062] An embodiment of the present invention discloses a soft-contact earth pressure sensor and an earth pressure sensor calibration method. The earth pressure sensor includes: a soft contact layer, a piezoresistive sensitive element, a sensor main shell, a pagoda-shaped anti-breakage structure and a threaded protective shell. The soft contact layer serves as the direct contact body between the earth pressure sensor and the soil. It is made of highly elastic material and is installed at the front window of the sensor main shell to directly transmit the physical changes in earth pressure to the piezoresistive sensitive element. The piezoresistive sensitive element, as the core part of the earth pressure sensor, converts the physical changes in earth pressure into voltage signal output. The sensor main shell can not only serve as a carrier of the soft contact layer, but also can be matched with the threaded protective shell through the internal thread to install and protect the piezoresistive sensitive element, thereby reducing the influence of external force on the piezoresistive sensitive element. The pagoda-shaped anti-breakage structure is matched with the sensor main shell to install a Teflon waterproof pipe. In the present invention, the contact surface between the earth pressure sensor and the soil adopts a soft contact method, and the arc-shaped cylindrical sensor main shell is filled in through a window on the front. The soft contact layer on the surface of the earth pressure sensor is deformed and flexed by the upper filling soil layer to form a shape flush with the sensor main shell, so that the earth pressure acts on the piezoresistive sensitive element; the soft contact layer of the earth pressure sensor adopts a high elastic material, and the density of the high elastic material is between dry sand and saturated sand. Compared with aluminum alloy and stainless steel materials, the high elastic material used in the soft contact layer can effectively reduce the stiffness matching problem between the earth pressure sensor and the soil medium, thereby improving the test accuracy of the earth pressure sensor, and making the earth pressure data measured by the earth pressure sensor have higher accuracy and reliability.

[0063] See also Figure 1 , an exploded diagram of the main structure of a soft-contact earth pressure sensor disclosed in an embodiment of the present invention, the earth pressure sensor includes: a soft contact layer 01, a piezoresistive sensitive element 02, a sensor main shell 04, a pagoda-shaped anti-breakage structure 05 and a threaded protective shell 07.

[0064] Among them, the soft contact layer 01 serves as the direct contact body between the soil pressure sensor and the soil. It is made of highly elastic material and is installed at the front window of the sensor main shell 04 to directly transmit the physical changes of soil pressure to the piezoresistive sensitive element 02.

[0065] The soft contact layer 01 in the present invention is mainly installed at the front window of the sensor main housing 04, which is the direct contact body between the sensor and the soil. The high elastic material used is mainly silicone rubber (that is, the preferred high elastic silicone material in the present invention). It has good high temperature resistance, high pressure resistance, water and oil resistance, strong corrosion resistance, electrical insulation, high dielectric strength, etc. Its density can be adjusted according to the soil type in the range of 1.7g~2.5g / cm 3 The Shore hardness range is 45 to 65, and the shear and tensile strength are ≥ 2.0 MPa. The density of dry sand with a soil particle size of 0.08 mm to 2.0 mm is approximately 1.4 g / cm 3~1.7g / cm 3 , the density of saturated sand is about 1.8g / cm 3 ~2.1g / cm 3 Therefore, the density of the high elastic material is between dry sand and saturated sand, and is similar to that of aluminum alloy (density is about 2.7g / cm 3 , Rockwell hardness is about 90) and stainless steel (density is about 7.8g / cm 3 , Rockwell hardness is about 201), the high elastic material used on the front of the earth pressure sensor can effectively reduce the stiffness matching problem between it and the soil medium.

[0066] The soft contact layer 01, a low-stiffness elastomer, directly transmits the soil pressure to the piezoresistive sensor 02, thereby improving the sensitivity and frequency response rate of the soil pressure sensor. Furthermore, the soft contact layer 01 is made of highly elastic silicone rubber, minimizing the inherent stiffness error of the soil. This reduces stress redistribution in the existing sand stress field, thereby improving the test accuracy of the soil pressure sensor.

[0067] The piezoresistive sensitive element 02 is the core part of the soil pressure sensor, which is used to convert the physical changes of soil pressure into voltage signal output.

[0068] The sensor main housing 04 has an internal thread for matching with the threaded protective shell 07 through the internal thread to install and protect the piezoresistive sensitive element 02 and reduce the influence of external force on the piezoresistive sensitive element 02.

[0069] The sensor main housing 04 is also used as a carrier of the soft contact layer 01 .

[0070] It should be noted that the sensor main housing 04 is an arc-shaped cylinder.

[0071] The pagoda-type anti-break structure 05 is used to match the sensor main housing 04 to install the Teflon waterproof tube.

[0072] In summary, the present invention discloses a soft-contact soil pressure sensor, comprising: a soft contact layer 01, a piezoresistive sensitive element 02, a sensor main shell 04, a pagoda-shaped anti-breakage structure 05 and a threaded protective shell 07. The soft contact layer 01 serves as the direct contact body between the soil pressure sensor and the soil. It is made of highly elastic material and is installed at the front window of the sensor main shell 04 to directly transmit the physical changes in soil pressure to the piezoresistive sensitive element 02. The piezoresistive sensitive element 02, as the core part of the soil pressure sensor, converts the physical changes in soil pressure into voltage signal output. The sensor main shell 04 can not only serve as a carrier of the soft contact layer 01, but also can be matched with the threaded protective shell 07 through the internal thread to install and protect the piezoresistive sensitive element 02, thereby reducing the influence of external force on the piezoresistive sensitive element 02. The pagoda-shaped anti-breakage structure 05 is matched with the sensor main shell 04 to install a Teflon waterproof pipe. In the present invention, the contact surface between the earth pressure sensor and the soil adopts a soft contact method, and the arc-shaped cylindrical sensor main shell 04 is filled in through the front window. The soft contact layer 01 on the surface of the earth pressure sensor is deformed and flexed by the upper filling soil layer to form a shape flush with the sensor main shell 04, so that the earth pressure acts on the piezoresistive sensitive element 02; the soft contact layer 01 of the earth pressure sensor adopts a high elastic material, and the density of the high elastic material is between dry sand and saturated sand. Compared with aluminum alloy and stainless steel materials, the high elastic material used in the soft contact layer 01 can effectively reduce the stiffness matching problem between the earth pressure sensor and the soil medium, thereby improving the test accuracy of the earth pressure sensor, and making the earth pressure data measured by the earth pressure sensor have higher accuracy and reliability.

[0073] To further optimize the above embodiment, see Figure 2 , an exploded diagram of the main structure of another soft contact earth pressure sensor disclosed in an embodiment of the present invention, Figure 1 On the basis of the illustrated embodiment, the soil pressure sensor may further include: a four-core shielded cable 03 , wherein the four-core shielded cable 03 is fixedly connected to the piezoresistive sensitive element 02 .

[0074] To further optimize the above embodiment, the soil pressure sensor may further include: a Teflon waterproof tube 06;

[0075] The pagoda-type anti-breakage structure 05 is matched with the sensor main housing 04 to install the Teflon waterproof tube 06.

[0076] in, Figure 2 The connection relationship between the main structures of the soil pressure sensor in the embodiment shown can also be seen in Figure 3 and Figure 4 The front view and cross-sectional view of the main structure of the soil pressure sensor are shown respectively.

[0077] The following is a detailed description of the main structures of the earth pressure sensor, as follows:

[0078] See also Figure 5 and Figure 6 , are respectively a front view and a side view of a soft contact layer disclosed in an embodiment of the present invention, wherein the contact surface of the soft contact layer 01 with the soil is an arc surface 011, and the contact surface with the piezoresistive sensitive element 02 is a parallel surface 012;

[0079] The arc surface 011 is used to deform when soil pressure is detected to disperse the additional stress and transfer it to the parallel surface 012.

[0080] The soft contact layer 01 in the present invention can effectively reduce the "arch effect" phenomenon of the original sand stress field through the arc-shaped design (i.e., the arc surface 011) and the selection of materials (highly elastic materials), thereby improving the test accuracy of the soil pressure sensor.

[0081] Specifically, when the overlying soil layer is filled, the soil will be disturbed. At this time, the earth pressure sensor will bear more of the stress in the soil. The contact surface between the soft contact layer 01 and the soil adopts the arc surface 011 design, so that when the overlying soil pressure directly acts on the arc surface 011, the arc surface 011 can disperse the additional stress through its own slight flexural deformation (the arc angle is reduced, but only the slight deformation of the contact surface occurs) and evenly apply it to the soft contact layer 01 of the earth pressure sensor, and then transmit it to the parallel surface 012. This process can reduce the stress concentration phenomenon that causes the sensor measurement data to be too large, and protect the piezoresistive sensitive element 02 inside the earth pressure sensor from damage; secondly, compared with the use of aluminum alloy and stainless steel materials (high stiffness, which can easily lead to insensitive response of sensitive elements), the soft contact layer 01 (low stiffness, elastic body) can directly physically change the soil pressure to the piezoresistive sensitive element 02, thereby improving the sensitivity and frequency response rate of the earth pressure sensor.

[0082] See also Figure 7 , a schematic diagram of a connection between a piezoresistive sensitive element and a four-core shielded cable disclosed in an embodiment of the present invention, combined with Figure 8 As shown in the cross-sectional view of the piezoresistive sensitive element, the piezoresistive sensitive element 02, as the core part of the soil pressure sensor, includes: a high-pressure chamber 021, a sensitive diaphragm 022, a vacuum chamber 023, a gold wire 024, a stress-free glue 025, a terminal 026, a conversion circuit board 027 and a silicon diaphragm protective shell 028.

[0083] The high-pressure chamber 021 is a transparent pressure chamber used to be in contact with the soil pressure to be measured.

[0084] The vacuum chamber 023 is a transparent pressure chamber used to output a zero point with the vacuum environment as a reference.

[0085] In practical applications, the materials of the high-pressure chamber 021 and the vacuum chamber 023 can both be expanded glass.

[0086] The sensitive diaphragm 022 is made of semiconductor material (silicon). A high-pressure cavity 021 and a vacuum cavity 023 are respectively provided on both sides of the sensitive diaphragm 022. When the pressures in the high-pressure cavity 021 and the vacuum cavity 023 are different, strain changes are generated and the strain changes are converted into voltage signals for output.

[0087] The gold wire 024 is used to connect multiple equal-value resistors provided in the sensitive diaphragm 022 to form a Wheatstone bridge.

[0088] The connection terminal 026 is provided on the conversion circuit board 027 and is connected to the gold wire 024 .

[0089] The conversion circuit board 027 is used to be fixedly connected to the four-core shielded cable 03 outside the piezoresistive sensitive element 02 .

[0090] The silicon diaphragm protective shell 028 has a window on the front and a cavity structure inside. The cavity structure is used to install the high-pressure chamber 021, the sensitive diaphragm 022 and the vacuum chamber 023, and is filled with stress-free glue 025 around and on the surface as a protective layer.

[0091] Preferably, the piezoresistive sensitive element 02 can be a miniature high-frequency response piezoresistive sensitive diaphragm, the natural frequency of which can be as high as 700kHz.

[0092] Specifically, the sensitive diaphragm 022 is used to generate strain changes when the pressures applied to the high-pressure chamber 021 and the vacuum chamber 023 are different, and the strain changes are converted into voltage signal outputs. A plurality of equivalent resistors (for example, four equivalent resistors R1=R2=R3=R4=5kΩ) are set on the sensitive diaphragm 022 using an ion implantation process, and the four equivalent resistors are connected using a gold wire 024 to form a Wheatstone bridge. The gold wire 024 is then connected to the terminal 026 on the conversion circuit board 027, and then the internal cable of the conversion circuit board 028 is soldered to the external four-core shielded cable 03. When the pressures (soil pressure changes) exerted on the high-pressure cavity 021 and the vacuum cavity 023 on both sides of the sensitive diaphragm 022 are different, the sensitive diaphragm 022 produces strain changes and converts the strain changes into voltage signal output; the silicon diaphragm protective shell 028 has a window on the front and a cavity structure inside. The cavity structure is used to install the high-pressure cavity 021, the sensitive diaphragm 022, and the vacuum cavity 023, and is filled with stress-free glue 025 on all sides and the surface as a protective layer. The upper surface of the stress-free glue 025 is bonded to the parallel surface 012 of the soft contact layer 01, so that the entire cavity surface is evenly stressed.

[0093] In summary, the sensing element of the soil pressure sensor in the present invention can be a miniature high-frequency response piezoresistive sensitive diaphragm. A plurality of equivalent resistors (for example, four equivalent resistors) are provided on the sensitive diaphragm 022 by using an ion implantation process, and a plurality of equivalent circuits are connected using a gold wire 024 to form a Wheatstone bridge. Two pressure cavities, a high-pressure cavity 021 and a vacuum cavity 023, are provided on both sides of the sensitive diaphragm 022. When the pressures of the two pressure cavities are different, the sensitive diaphragm 022 generates strain, thereby improving the frequency response performance and sensitivity of the soil pressure sensor.

[0094] In addition, through the design in this embodiment and the miniaturization of the piezoresistive sensitive diaphragm, the volume of the soil pressure sensor can be reduced, the diameter can be controlled within 10 mm, and the output voltage signal can reach more than 100 mV.

[0095] Furthermore, the present invention utilizes the design of the inner chamber of the shell to fix the sensitive diaphragm 022, and covers the surface and surrounding areas of the sensitive diaphragm 022 with a layer of stress-free protective glue 025. This not only reduces the damage to the sensitive diaphragm 022 caused by the "stress concentration" generated by the compaction of the overlying soil layer and avoids direct contact between the soil and the sensitive diaphragm 022, thereby increasing the life cycle of the earth pressure sensor, but also makes the entire inner chamber surface evenly stressed, thereby improving the test accuracy of the earth pressure sensor.

[0096] See also Figures 9 to 11 , respectively, are a schematic diagram of the connection between a sensor main housing and a pagoda-type anti-breakage structure disclosed in an embodiment of the present invention, a perspective view of the connection between the sensor main housing and the pagoda-type anti-breakage structure, and a cross-sectional view of the connection between the sensor main housing and the pagoda-type anti-breakage structure. The sensor main housing 04 includes: a soft contact layer positioning groove 041, a soft contact layer support beam 042, a sensitive element mounting cavity 043 and a sensitive element positioning groove 044, wherein the sensitive element mounting cavity 043 is internally provided with an internal thread 045.

[0097] The soft contact layer positioning groove 041 is used to position the soft contact layer 01 .

[0098] The soft contact layer support beam 042 is used to support the soft contact layer 01 .

[0099] Sensor mounting cavity 043 is used to house piezoresistive sensor 02 and is positioned in conjunction with sensor positioning groove 044. After piezoresistive sensor 02 is positioned and installed, the remaining space is filled with epoxy resin to further secure and waterproof piezoresistive sensor 02 and isolate it from any lateral stress.

[0100] Specifically, the sensor main housing 04 is matched with the pagoda-type anti-breakage structure 05 to install the Teflon waterproof tube 06, thereby protecting the four-core shielded cable 03 from breakage and the cable waterproof function.

[0101] In summary, the cable fixing and sealing method of the soil pressure sensor in the present invention adopts a pagoda-type anti-breakage structure 05 design, which can effectively improve the shear strength and tensile strength of the cable of the soil pressure sensor, and can improve the sealing effect of the soil pressure sensor; and combined with the Teflon cable protective layer, it can protect the exposed cables and reduce the interference with the original flow field and stress field and the wear of the sensor cable.

[0102] See also Figure 12 , a structural diagram of a thread protection shell disclosed in an embodiment of the present invention, the thread protection shell 07 mainly includes: a connecting external thread 071 and a sensitive element support column 072.

[0103] The threaded protection housing 07 is matched with the sensor main housing 04 by connecting the external thread 071 , and supports and fixes the piezoresistive sensitive element 02 through the sensitive element support column 072 .

[0104] It should be noted that the present invention adopts a split structure of the threaded protection housing 07 and the sensor main housing 04, which can increase the maintenance capability of the earth pressure sensor and improve the utilization rate of the piezoresistive sensitive element 02.

[0105] In order to improve the reliability of the soil pressure sensor, the soil pressure sensor needs to be calibrated before use. During calibration, a geotechnical centrifuge can be used for calibration.

[0106] See also Figure 16 , a flow chart of a soil pressure sensor calibration method disclosed in an embodiment of the present invention, the method is applied to a data acquisition instrument, the data acquisition instrument is connected to the soil pressure sensor in the above embodiment, the soil pressure calibration method may include:

[0107] Step S101: Divide the maximum theoretical earth pressure value of the soil layer required to be measured by the earth pressure sensor to be calibrated into M levels.

[0108] The maximum theoretical earth pressure is the maximum earth pressure value at the prototype depth under the preset centrifugal acceleration conditions.

[0109] Wherein, M is a positive integer.

[0110] In practical applications, each level corresponds to a calibrated earth pressure output voltage signal.

[0111] Step S102: determining the theoretical earth pressure value corresponding to the output voltage signal of the earth pressure sensor to be calibrated at each level and the depth of the soil layer under each centrifugal acceleration.

[0112] Specifically, when the soil pressure sensor to be calibrated is buried to the soil layer depth corresponding to the actual test, based on M levels, the centrifugal acceleration load is applied to the soil pressure sensor to be calibrated step by step to the preset value, and the output voltage signal of the soil pressure sensor to be calibrated at each level and the theoretical soil pressure value corresponding to the soil layer depth under each centrifugal acceleration are obtained.

[0113] The value of the preset value is determined according to actual needs and is not limited in the present invention.

[0114] Step S103: Based on the theoretical earth pressure values ​​corresponding to each level, the least squares curve fitting method is used to obtain the average calibration coefficient of the earth pressure output voltage signals of each level of the earth pressure sensor to be calibrated and the theoretical earth pressure values ​​under the corresponding centrifugal acceleration conditions.

[0115] Among them, the average calibration coefficient is the ratio of the theoretical soil pressure value of each level (kPa) to the soil pressure sensor to be calibrated (mV).

[0116] Step S104: multiplying the earth pressure output voltage signals of each level of the earth pressure sensor to be calibrated by the corresponding average calibration coefficient to obtain the measured output earth pressure values ​​of the earth pressure sensor to be calibrated at each level.

[0117] Step S105 : Calculate the deviation between the measured output earth pressure value and the corresponding theoretical earth pressure value corresponding to each level of the earth pressure sensor to be calibrated.

[0118] Step S106: determining a target coefficient of the earth pressure sensor to be calibrated after calibration based on each deviation amount.

[0119] In summary, the present invention connects the earth pressure sensor to be calibrated with a data acquisition instrument, and the data acquisition instrument processes the data collected from the earth pressure sensor to be calibrated to obtain the deviation between the measured output earth pressure value corresponding to each level of the earth pressure sensor to be calibrated and the corresponding theoretical earth pressure value, thereby obtaining the target coefficient of the earth pressure sensor to be calibrated after calibration based on each deviation, completing the calibration of the earth pressure sensor to be calibrated, so as to further improve the test accuracy of the earth pressure sensor, and make the earth pressure data measured by the earth pressure sensor have higher accuracy and reliability.

[0120] The soil pressure sensor calibration process is illustrated as follows:

[0121] 1) The soil sample material can be selected according to the actual test soil type. This embodiment takes the soil sample material as Fujian standard quartz sand as an example for explanation. The particle size distribution curve of Fujian standard quartz sand is as follows: Figure 13 As shown in Table 1, the basic physical parameters are as follows:

[0122] Table 1 Main physical parameters of Fujian standard quartz sand

[0123]

[0124] Relative density of sand D r The dry sand model is divided into 5 layers in the model box, and the sensor burial depths are 50 mm (number T1), 150 mm (number T2), 250 mm (number T3), 350 mm (number T4), and 450 mm (number T5), respectively. One soft-contact earth pressure sensor to be calibrated is placed in the center of each layer. A total of 5 sensors are placed, and each sensor is placed vertically upward. Then, the model box, soft-contact earth pressure sensor and cable are hoisted onto the geotechnical centrifuge and connected to the data acquisition instrument.

[0125] 2) After preheating the five soft-contact earth pressure sensors for 60 minutes, set the sampling rate of the data acquisition instrument to 5 Hz, set the initial calibration factor (ICF) of the soft-contact earth pressure sensor to 1.0, and set the initial value of the soft-contact earth pressure sensor to "NULL" (i.e., balance reset) on the data acquisition instrument; after the soft-contact earth pressure sensor is set to "NULL", monitor the soft-contact earth pressure sensor to be calibrated in real time on the display screen of the data acquisition instrument, and then check whether the output voltage signal of the soft-contact earth pressure sensor is in a stable state and the degree of noise interference.

[0126] 3) The geotechnical centrifuge will be loaded with centrifugal acceleration in stages (number of stages ≥ 5), namely 5g, 10g, 15g, 20g, 30g, 40g, and 50g. After each stage of centrifugal acceleration is maintained for ≥ 5 minutes, the next stage of centrifugal acceleration will be applied after the soil layer reaches a stable state and the output voltage of the soft contact earth pressure sensor reaches a stable state. Figure 14(a) and 14(b) As shown in Figure 1, centrifugal acceleration is applied repeatedly 2 to 3 times to obtain the average output voltage value of the soft contact earth pressure sensor under each level of centrifugal acceleration.

[0127] 4) Finally, use formula (1) to calculate the calibration coefficient ACF (unit: kPa / mV) of the soft contact earth pressure sensor (i.e., draw a calibration comparison curve between the output voltage value (abscissa) of the soft contact earth pressure sensor recorded by the data acquisition instrument and the theoretical earth pressure value (ordinate) corresponding to each soil layer under each level of centrifugal acceleration), and perform curve fitting and conversion correlation coefficient R based on the calibration curve. 2 ,get Figures 15(a) to 15(f) Calibration results of representative soft-contact earth pressure sensors No. T1, T2, and T3 are shown.

[0128]

[0129] Where N is the centrifugal acceleration at each stage, ρ is the density of each soil layer (kg / m 2 ), g cis the acceleration due to gravity (m / s 2 )(take 9.8), h is the buried height of the soft contact earth pressure sensor (m), N is the number of measurement points recorded during the calibration process; X is the output voltage signal of the soft contact earth pressure sensor, in mV; Y is the theoretical earth pressure value corresponding to each soil layer under each level of centrifugal acceleration, in kPa.

[0130] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0131] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0132] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A soft contact earth pressure sensor, characterized in that: include: Soft contact layer, piezoresistive sensitive element, sensor main housing, pagoda-type anti-breakage structure and threaded protection housing; The soft contact layer serves as the direct contact between the earth pressure sensor and the soil, and is made of a highly elastic material with a density between dry sand and saturated sand. The soft contact layer is installed at the front window of the sensor main housing to directly transmit the physical changes in earth pressure to the piezoresistive sensitive element. The piezoresistive sensitive element is the core part of the soil pressure sensor, which is used to convert the physical change of the soil pressure into a voltage signal output; The sensor main housing has an internal thread, which is used to match the threaded protective shell through the internal thread to install and protect the piezoresistive sensitive element; it is also used as a carrier for the soft contact layer; The pagoda-shaped anti-breakage structure is used to match the main housing of the sensor to install a Teflon waterproof tube; The thread protection housing includes: a connecting external thread and a sensitive element support column; The threaded protection housing is matched with the sensor main housing through the connecting external thread, and supports and fixes the piezoresistive sensitive element through the sensitive element support column.

2. The soil pressure sensor according to claim 1, wherein: The contact surface between the soft contact layer and the soil is an arc surface, and the contact surface between the soft contact layer and the piezoresistive sensitive element is a parallel surface; The arc surface is used to deform when soil pressure is detected to disperse the additional stress and transfer it to the parallel surface.

3. The soil pressure sensor according to claim 1, wherein: The piezoresistive sensitive element comprises: a high-pressure cavity, a sensitive diaphragm, a vacuum cavity, a gold wire, a stress-free adhesive, a terminal block, a conversion circuit board and a silicon diaphragm protective shell; The high-pressure chamber is a transparent pressure chamber, which is used to contact the soil pressure to be measured; The vacuum chamber is a transparent pressure chamber used to output a zero point with the vacuum environment as a reference; The high-pressure cavity and the vacuum cavity are respectively provided on both sides of the sensitive diaphragm, for generating strain changes when the pressures in the high-pressure cavity and the vacuum cavity are different, and converting the strain changes into voltage signals for output; The gold wire is used to connect multiple equal-value resistors provided in the sensitive diaphragm to form a Wheatstone bridge; The connection terminal is arranged on the conversion circuit board and is connected to the gold wire; The conversion circuit board is used to be fixedly connected to the four-core shielded cable outside the piezoresistive sensitive element; The silicon diaphragm protective shell has a window on the front and a cavity structure inside. The cavity structure is used to install the high-pressure cavity, the sensitive diaphragm and the vacuum cavity, and is filled with the stress-free glue around and on the surface as a protective layer.

4. The soil pressure sensor according to claim 1, wherein: The sensor main housing comprises: a soft contact layer positioning groove, a soft contact layer support beam, a sensitive element installation cavity and a sensitive element positioning groove, wherein the internal thread is provided inside the sensitive element installation cavity; The soft contact layer positioning groove is used to position the soft contact layer; The soft contact layer support beam is used to support the soft contact layer; The sensor installation cavity is used to place the piezoresistive sensor and is used to position the piezoresistive sensor in combination with the sensor positioning groove. After the piezoresistive sensor is positioned and installed, epoxy resin is filled in the remaining space.

5. The soil pressure sensor according to claim 1, wherein: Also includes: Four-core shielded cable; The four-core shielded cable is fixedly connected to the piezoresistive sensitive element.

6. The soil pressure sensor according to claim 1, wherein: Also includes: The Teflon waterproof tube.

7. The soil pressure sensor according to claim 1, characterized in that: The piezoresistive sensitive element is a miniature high-frequency response piezoresistive sensitive diaphragm.

8. A soil pressure sensor calibration method, characterized in that: Applied to a data acquisition instrument, the data acquisition instrument is connected to the earth pressure sensor according to any one of claims 1 to 7, and the earth pressure calibration method includes: The maximum theoretical earth pressure value of the soil layer required to be measured by the earth pressure sensor to be calibrated is divided into M levels, where M is a positive integer; When the earth pressure sensor to be calibrated is buried to the soil layer depth corresponding to the actual test, centrifugal acceleration load is applied to the earth pressure sensor to be calibrated step by step to a preset value based on the M levels, and the output voltage signal of the earth pressure sensor to be calibrated at each level and the theoretical earth pressure value corresponding to the soil layer depth under each centrifugal acceleration are obtained; Based on the theoretical earth pressure values ​​corresponding to the respective levels, a least squares curve fitting method is used to obtain an average calibration coefficient between the earth pressure output voltage signals of each level of the earth pressure sensor to be calibrated and the theoretical earth pressure values ​​under the corresponding centrifugal acceleration conditions; Multiplying the earth pressure output voltage signals of each level of the earth pressure sensor to be calibrated by the corresponding average calibration coefficient to obtain the measured output earth pressure values ​​of the earth pressure sensor to be calibrated at each level; Calculating the deviation between the measured output earth pressure value and the corresponding theoretical earth pressure value corresponding to each level of the earth pressure sensor to be calibrated; A target coefficient of the earth pressure sensor to be calibrated after calibration is determined based on the respective deviation amounts.

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