Pore water pressure sensor

Abstract

The utility model discloses a pore water pressure sensor, comprising a permeation plate gland; the permeation plate is ellipsoidal, spherical or inverted conical; a supporting groove, a first inner threaded hole and a containing cavity are formed in the outer protection cylinder, the permeation plate is arranged in the supporting groove in a shape fit mode, and the permeation plate gland is connected to the upper portion of the outer protection cylinder and presses the permeation plate; the sensor comprises a pressure-bearing medium bin, a sensing piece, a transition section and an external thread column which are sequentially connected from top to bottom, the pressure-bearing medium bin is arranged in the containing cavity, an external thread head is arranged on the upper portion of the pressure-bearing medium bin, the interior of the pressure-bearing medium bin is communicated with the pressure-bearing medium bin, a semi-permeable membrane is arranged on the upper end face of the external thread head, and the external thread head is screwed into the first internal thread hole; the upper portion of the sealing cover is connected to the lower portion of the outer protection cylinder, a limiting hole and a second inner threaded hole which are communicated are formed in the sealing cover, the transition section is matched in the limiting hole, and the outer threaded column is in threaded connection with the second inner threaded hole. The device can avoid stress loss and improve the accuracy of a measurement result.

Description

Technical Field

[0001] The utility model relates to the technical field of frozen soil measurement, in particular to a pore water pressure sensor. Background Art

[0002] In 1923, Terzaghi proposed the famous effective stress principle, which laid the foundation for soil mechanics. For saturated thawed soil, after the soil is subjected to external force, the total stress it is subjected to will inevitably be borne by the soil skeleton and pore water. The stress borne by the soil skeleton is transmitted through the contact surface between particles and is called effective stress; the stress borne by the pore water is borne by the water between the connected pores and is called pore water pressure. In actual engineering applications, effective stress is not easy to measure directly, and pore water pressure is usually used to infer effective stress.

[0003] In the field of frozen soil, water in the soil condenses into ice, forming a three-phase, four-component material. The instability and reversibility of the ice-water phase transition make frozen soil research extremely difficult. Many scholars have proved that the pores in frozen soil are connected and there is unfrozen water, and the effective stress is still applicable. Understanding the stress state of frozen soil is of great significance to the study of frozen soil strength and deformation, and its measurement method is still to measure its pore water pressure to infer the effective stress. At present, there are many pore water pressure sensors suitable for frozen soil in the industry, and the internal pressure medium can ensure that it will not freeze at low temperatures, but in actual experiments, the pore water pressure output value is always fluctuating or even chaotic, which has attracted our attention.

[0004] After sufficient verification, we found that the frost heave of frozen soil is the root cause of the problem of pore pressure sensors. Buildings in frozen soil areas will be destroyed by the huge frost heave force of the soil. When conducting frozen soil experiments, sensors are often placed directly inside the soil, and the pore pressure sensors are not structurally protected. The frost heave force will affect the accuracy of the pore pressure sensor and even destroy the sensor structure, causing sensor damage; secondly, the measurement of saturated soil pore water pressure in limited environments such as laboratories often adopts the principle of liquid pressure transmission, that is, the pore water in the soil acts on the saturated pressure medium inside the sensor, and then the pressure change of the saturated pressure medium will be captured by other devices inside the sensor and converted into an electrical signal, but the existing pressure abdominal cavity is prone to other external forces, affecting the measurement results; in addition, commonly used micro pore water pressure sensors will have a permeable plate installed on the surface to prevent the influence of soil particles, but currently they are all in the shape of a circular plate. In saturated thawed soil, there is basically no effect due to the high water content, but in frozen soil, there is little unfrozen water. If the circular plate shape is still used, it will cause a large pore water stress loss, resulting in errors in the measurement results. Utility Model Content

[0005] In view of the deficiencies in the prior art, the utility model aims to provide a pore water pressure sensor.

[0006] In order to achieve the above purpose, the technical solution provided by an embodiment of the present utility model is as follows:

[0007] A pore water pressure sensor, comprising:

[0008] A permeation plate gland, wherein the permeation plate gland is hollow inside;

[0009] A permeable plate, wherein the permeable plate is in an ellipsoidal, spherical or inverted conical shape;

[0010] An outer casing, wherein a support groove, a first internal threaded hole connected to the bottom of the support groove, and a receiving cavity connected to the first internal threaded hole are sequentially arranged inside the outer casing from top to bottom, the permeable plate is fitted in the support groove, and the permeable plate gland is connected to the upper part of the outer casing and presses the permeable plate;

[0011] A sensor, the sensor comprising a pressure medium bin, a sensing element, a transition section and an external thread column connected in sequence from top to bottom, the pressure medium bin being arranged in the accommodating cavity, a hollow external thread head being arranged at the upper portion of the pressure medium bin, the interior of the external thread head being connected to the pressure medium bin, a semi-permeable membrane being arranged at the upper end surface of the external thread head, and the external thread head being screwed into the first internal thread hole;

[0012] A sealing cover, wherein the upper portion of the sealing cover is connected to the lower portion of the outer casing, a limiting hole and a second internal threaded hole are provided in the sealing cover, the transition section is fitted in the limiting hole, and the external threaded column is threadedly connected to the second internal threaded hole.

[0013] As a further improvement of the utility model, the lower part of the permeation plate pressure cover is provided with a first external thread, the upper part of the outer casing is provided with an internal thread groove, the first external thread is connected to the internal thread groove, and the internal thread groove is located at the upper periphery of the support groove.

[0014] As a further improvement of the utility model, a first through hole and a second through hole connected to each other are arranged inside the permeation plate pressure cover from top to bottom, the aperture of the first through hole is smaller than the aperture of the second through hole, and a first step is formed at the connection between the first through hole and the second through hole.

[0015] As a further improvement of the present invention, a sealing gasket is provided at the first step.

[0016] As a further improvement of the utility model, the outer diameter of the upper part of the permeation plate gland is the same as the outer diameter of the outer casing.

[0017] As a further improvement of the present invention, the aperture of the accommodating cavity is larger than the outer diameter of the pressure medium bin.

[0018] As a further improvement of the utility model, the lower part of the outer casing is provided with an internal thread, the upper part of the sealing cover is provided with a second external thread, and the second external thread is connected to the internal thread.

[0019] As a further improvement of the utility model, the outer diameter of the outer casing is the same as the outer diameter of the lower part of the sealing cover.

[0020] As a further improvement of the present invention, the transition section and the limiting hole are both in the shape of an inverted frustum.

[0021] As a further improvement of the present invention, the bottom end of the external threaded column extends out of the sealing cover.

[0022] The beneficial effects of the utility model are:

[0023] (1) The permeable plate is placed in the support groove on the upper part of the outer casing. The permeable plate and the support groove are matched to make the pore water gather to the middle semipermeable membrane, reduce stress loss, make the sensor more sensitive when the water content is low, and improve the measurement accuracy. The permeable plate gland is connected to the outer casing through threads. It is hollow inside and a step hole is formed in the upper part. The permeable plate is pressed by the first step to achieve the stability of the permeable plate while preventing water from flowing in and out through the gap between the upper end of the permeable plate and the side wall of the support groove of the outer casing, avoiding the small experimental results and ensuring the accuracy of pressure measurement.

[0024] (2) The sensor has an external thread head on the upper part, which is hollow inside and connected to the pressure medium chamber. The upper surface of the external thread head is a semi-permeable membrane, which allows silicone oil to pass through when the sensor is saturated and is used to accumulate pore water. The sensor is threadedly connected to the first internal thread hole of the outer casing through the external thread head to achieve sealing.

[0025] (3) The outer wall of the sealing cover of the utility model has a second external thread, which is connected to the outer casing through the thread. The diameter gradient limit hole at the upper end of the sealing cover perfectly corresponds to the transition section at the lower part of the sensor body, which is used to fix the sensor and prevent the sensor from moving. The lower end of the sealing cover has an internal thread, which is used to connect the external thread column of the sensor to achieve sealing.

[0026] (4) The utility model is suitable for frozen soil environment. The protective shell is formed by the cooperation of the permeable plate pressure cover, the outer casing and the sealing cover to prevent the soil from freezing and squeezing the sensor, thereby causing measurement result deviation or even sensor damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 It is a schematic diagram of the structure of the utility model;

[0029] Figure 2 This is a schematic diagram of the exploded structure of a preferred embodiment of the utility model;

[0030] Figure 3 It is a bottom view structural schematic diagram of the permeation plate gland of the preferred embodiment of the utility model;

[0031] In the figure: 1. permeation plate pressure cap, 11. first external thread, 12. first through hole, 13. second through hole, 14. first step, 15. sealing gasket, 2. permeation plate, 3. outer casing, 31. supporting groove, 32. first internal thread hole, 33. accommodating chamber, 34. internal thread groove, 35. internal thread, 4. sensor, 40. pressure medium bin, 41. sensing element, 42. transition section, 43. external thread column, 44. external thread head, 45. semipermeable membrane, 5. sealing cover, 51. limiting hole, 52. second internal thread hole, 53. second external thread. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0033] See also Figure 1-Figure 3The embodiment of the present application discloses a pore water pressure sensor, including: a permeable plate gland 1, the permeable plate gland 1 is hollow inside; a permeable plate 2, the permeable plate 2 is ellipsoidal, spherical or inverted conical; an outer casing 3, the inner part of the outer casing 3 is provided with a support groove 31, a first internal threaded hole 32 connected to the bottom of the support groove 31 and a receiving cavity 33 connected to the first internal threaded hole 32 in sequence from top to bottom, the permeable plate 2 is fitted in the support groove 31, the permeable plate gland 1 is connected to the upper part of the outer casing 3 and presses the permeable plate 2; a sensor 4, the sensor 4 includes a pressure medium bin 40, a pressure medium bin 41 connected in sequence from top to bottom, A sensing element 41, a transition section 42 and an external threaded column 43, a pressure medium bin 40 is arranged in the accommodating chamber 33, a hollow external threaded head 44 is arranged on the upper part of the pressure medium bin 40, the interior of the external threaded head 44 is connected to the pressure medium bin 40, a semi-permeable membrane 45 is arranged on the upper end surface of the external threaded head 44, and the external threaded head 44 is screwed into the first internal threaded hole 32; a sealing cover 5, the upper part of the sealing cover 5 is connected to the lower part of the outer casing 3, a connecting limiting hole 51 and a second internal threaded hole 52 are arranged inside the sealing cover 5, the transition section 42 is fitted in the limiting hole 51, and the external threaded column 43 is threadedly connected to the second internal threaded hole 52.

[0034] The permeable plate gland 1 is threadedly sealed with the outer casing 3. In the present embodiment, the permeable plate 2 is ellipsoidal, and the support groove 31 is ellipsoidal, which matches the permeable plate 2. However, it is not limited to the ellipsoidal shape, and can also be spherical or inverted conical. The permeable plate gland 1 is pressed on the upper end of the permeable plate 2, which can prevent the pore water from flowing directly from the gap between the upper end of the permeable plate 2 and the side wall of the support groove 31, avoid the loss of pore water on the side wall of the support groove 31, avoid stress loss, and avoid the measured pore water pressure numerical result being less than the true value. Since the permeable plate 2 is ellipsoidal, the pore water flowing from the permeable plate 2 to the side wall of the support groove 31 can move downward along the side wall of the support groove 31, and finally gather in the middle and accumulate on the semipermeable membrane 45, further ensuring the accuracy of the pressure measurement. The setting of the semipermeable membrane 45 enables the silicone oil used for saturation to pass through the semipermeable membrane 45 to block the pore water. The semipermeable membrane 45 can be made of a hydrophobic material such as polytetrafluoroethylene or polypropylene, which can form water droplets and is not easily penetrated by water, but allows silicone oil with lower viscosity to pass through. In this way, the pressure medium chamber 40 and the external threaded head 44 are saturated with silicone oil to avoid the presence of air in the pressure medium chamber 40 and the external threaded head 44.

[0035] Preferably, the lower part of the permeable plate gland 1 is provided with a first external thread 11, and the inner part of the outer casing 3 is provided with an internal thread groove 34, the first external thread 11 is connected to the internal thread groove 34, and the internal thread groove 34 is located at the upper periphery of the support groove 31. The lower part of the permeable plate gland 1 is threadedly connected with the upper part of the outer casing 3, so as to realize the tight and sealed connection between the permeable plate gland 1 and the outer casing 3.

[0036] Preferably, the inside of the permeation plate gland 1 is provided with a first through hole 12 and a second through hole 13 connected from top to bottom, the aperture of the first through hole 12 is smaller than the aperture of the second through hole 13, and a first step 14 is formed at the connection between the first through hole 12 and the second through hole 13. The first step 14 is pressed on the upper end of the permeation plate 2.

[0037] In order to ensure the sealing between the first step 14 and the upper end of the permeation plate 2 , a sealing gasket 15 is preferably provided at the first step 14 .

[0038] The upper outer surface of the permeable plate gland 1 is smooth. Preferably, the upper outer diameter of the permeable plate gland 1 is the same as the outer diameter of the outer casing 3 to avoid the presence of a step between the outer wall of the permeable plate gland 1 and the outer wall of the outer casing 3, so as to facilitate rapid placement into the soil to be measured.

[0039] In order to better improve the sealing performance between the external thread head 44 and the first internal thread hole 32 , thread glue may be provided on the external thread head 44 or the first internal thread hole 32 to ensure the sealing performance.

[0040] Preferably, the diameter of the accommodating cavity 33 is larger than the diameter of the first internal threaded hole 32 .

[0041] In order to avoid the external force of the outer casing 3 on the pressure medium bin 40, the aperture of the accommodating cavity 33 is preferably larger than the outer diameter of the pressure medium bin 40. Since there is a gap between the accommodating cavity 33 and the pressure medium bin 40, the external force borne by the outer casing 3 will not be transmitted to the pressure medium bin 40.

[0042] Preferably, the lower portion of the outer casing 3 is provided with an internal thread 35 , and the upper portion of the sealing cover 5 is provided with a second external thread 53 , and the second external thread 53 is connected to the internal thread 35 , so as to achieve a sealed connection between the outer casing 3 and the sealing cover 5 .

[0043] In order to avoid the existence of a step between the outer wall of the outer casing 3 and the outer wall of the sealing cover 5 and facilitate rapid insertion into the soil to be measured, the outer diameter of the outer casing 3 is preferably the same as the outer diameter of the lower part of the sealing cover 5 .

[0044] Preferably, the transition section 42 and the limiting hole 51 are both in the shape of an inverted cone. In this way, the transition section 42 of the sensor 4 is supported and limited at the limiting hole 51. At the same time, the upper part of the sensor 4 is fastened to the first internal thread hole 32 through the external thread head 44, and the lower part of the sensor 4 is fastened to the second internal thread hole 52 through the external thread column 43, so that the sensor 4 is fixed, avoiding the movement of the sensor 4 in the accommodating cavity 33, and improving the stability of the measurement.

[0045] Preferably, the sensor 41 is a strain gauge sensor element.

[0046] Preferably, the bottom end of the external threaded column 43 extends out of the sealing cover 5, so that the transmission line connected to the sensor 41 can be connected to an external data acquisition system to collect signals.

[0047] When the utility model is in use, a vacuum saturation machine is used to evacuate and saturate the pressure medium bin 40 and the external threaded head 44 inside the sensor 4, and the saturated pressure medium bin 40 and the external threaded head 44 are filled with silicone oil to avoid the presence of air in the pressure medium bin 40. After saturation is completed, the pore water pressure sensor is inserted into the frozen soil, and the pore water in the frozen soil enters the permeable plate 2 through the first through hole 12 and the second through hole 13 of the permeable plate gland 1, and then enters the supporting groove 31 through the permeable plate 2, and finally gathers on the semi-permeable membrane 45, so that the stress is accurately transmitted to the pressure medium bin 40, and the sensor 41 at the lower part of the pressure medium bin 40 can sense the change, generate an electrical signal, and transmit the signal to the external data acquisition system through the transmission line.

[0048] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-restrictive from any point of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention. Any reference numeral in a claim should not be regarded as limiting the claim to which it relates.

[0049] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A pore water pressure sensor, characterized in that: include: A permeation plate gland, wherein the permeation plate gland is hollow inside; A permeable plate, wherein the permeable plate is in an ellipsoidal, spherical or inverted conical shape; An outer casing, wherein a support groove, a first internal threaded hole connected to the bottom of the support groove, and a receiving cavity connected to the first internal threaded hole are sequentially arranged inside the outer casing from top to bottom, the permeable plate is fitted in the support groove, and the permeable plate gland is connected to the upper part of the outer casing and presses the permeable plate; A sensor, the sensor comprising a pressure medium bin, a sensing element, a transition section and an external thread column connected in sequence from top to bottom, the pressure medium bin being arranged in the accommodating cavity, a hollow external thread head being arranged at the upper portion of the pressure medium bin, the interior of the external thread head being connected to the pressure medium bin, a semi-permeable membrane being arranged at the upper end surface of the external thread head, and the external thread head being screwed into the first internal thread hole; A sealing cover, wherein the upper portion of the sealing cover is connected to the lower portion of the outer casing, a limiting hole and a second internal threaded hole are provided in the sealing cover, the transition section is fitted in the limiting hole, and the external threaded column is threadedly connected to the second internal threaded hole.

2. A pore water pressure sensor according to claim 1, characterized in that: The lower part of the permeation plate pressure cap is provided with a first external thread, the upper part of the outer casing is provided with an internal thread groove, the first external thread is connected to the internal thread groove, and the internal thread groove is located at the upper periphery of the support groove.

3. A pore water pressure sensor according to claim 2, characterized in that: A first through hole and a second through hole are connected to each other from top to bottom inside the permeation plate gland. The aperture of the first through hole is smaller than the aperture of the second through hole. A first step is formed at the connection between the first through hole and the second through hole.

4. A pore water pressure sensor according to claim 3, characterized in that: A sealing gasket is arranged at the first step.

5. The pore water pressure sensor according to claim 2, characterized in that: The outer diameter of the upper portion of the permeation plate gland is the same as the outer diameter of the outer casing.

6. The pore water pressure sensor according to claim 1, characterized in that: The aperture of the accommodating cavity is larger than the outer diameter of the pressure medium bin.

7. The pore water pressure sensor according to claim 1, characterized in that: The lower part of the outer casing is provided with an internal thread, and the upper part of the sealing cover is provided with a second external thread, and the second external thread is connected to the internal thread.

8. The pore water pressure sensor according to claim 1, characterized in that: The outer diameter of the outer casing is the same as the outer diameter of the lower portion of the sealing cover.

9. The pore water pressure sensor according to claim 1, characterized in that: The transition section and the limiting hole are both in the shape of an inverted frustum.

10. The pore water pressure sensor according to claim 1, characterized in that: The bottom end of the external thread column extends out of the sealing cover.

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