A nondestructive detection device for loess structure collapse under water-heat-force coupling

Abstract

The invention discloses a nondestructive detection device for loess structure collapsibility under water-heat-force coupling, comprising a pressure chamber, a consolidation box, a loading unit and an electric heating unit, wherein the pressure chamber is a closed chamber, and a water inlet and a water outlet are provided at the bottom to communicate with the inside of the consolidation box; the consolidation box comprises a pressure plate, a permeable stone, a ring knife and a clay plate, and a bending element transmitting end is installed on the permeable stone and extends into the box; the ring knife is installed directly under the permeable stone to form a consolidation box body; the clay plate is installed under the ring knife to form a consolidation box bottom plate, and a bending element receiving end is installed on the clay plate and extends into the box; the loading unit is a loading rod that passes through the top of the pressure chamber; and the electric heating unit is used to heat the loess sample in the consolidation box body. The invention can detect the change characteristics of loess collapsible structure under high stress environment, has high heating efficiency, and can conveniently control different loess collapsible temperature environments, so as to realize continuous nondestructive quantitative detection of different stages of the whole process of loess structure collapsibility.

Description

Technical Field

[0001] The invention belongs to the technical field of soil detection, and in particular relates to a nondestructive detection device for loess structure collapse under water-heat-force coupling. Background Art

[0002] Loess is a special type of unsaturated soil that is widely distributed in my country. Under the influence of the geological sedimentary environment, loess has a special soil structure, which makes it have significant collapsible characteristics, that is, when it is soaked by water under a certain pressure, the soil structure is rapidly destroyed and produces significant additional sinking characteristics. Loess collapse can cause a variety of geological disasters such as ground subsidence, surface cracking, slope instability, and uneven settlement, which brings great challenges to the smooth development of engineering construction and disaster prevention and mitigation work in loess areas.

[0003] The consolidation instrument is an industrial instrument, which is divided into saturated consolidation instrument and unsaturated consolidation instrument. It can perform normal slow consolidation test and rapid consolidation test. It is usually used to measure the compression performance of soil under different loads and confined conditions, and to detect parameters such as the initial consolidation pressure, compression index and rebound index of the soil. For loess, the consolidation test can determine the collapsibility parameters such as the collapsibility coefficient and the initial collapsibility pressure, and is usually used to detect the collapsibility characteristics of loess.

[0004] The existing loess structure collapse detection technology usually has a relatively simple control method for collapse environmental factors. For example, the traditional unsaturated consolidation instrument and the unsaturated consolidation instrument equipped with a bending element probe can detect the deformation characteristics and small strain shear modulus of collapsed loess, but can only control the changes in the load and water content of the loess, ignoring the influence of the temperature environment. More importantly, even if the unsaturated consolidation instrument equipped with a temperature control device can detect the collapse deformation characteristics of loess under the conditions of load, water content and temperature environment changes, the existing loess structure collapse detection technology can only compare and analyze the soil structure before and after collapse by further destructive sampling of the soil after the collapse is completed. Therefore, the existing technology has neither formed a multi-factor coupling detection technology for loess structure collapse, nor a non-destructive detection method to achieve continuous detection of different stages of the entire process of structural collapse.

[0005] It is also worth noting that the existing unsaturated temperature-controlled consolidation instrument uses a water bath heating method to control the sample temperature, and uses the high specific heat capacity of water to keep the sample temperature relatively constant for a long time. However, this heating equipment and method are relatively backward and cannot accurately control the temperature. In addition, the heating time is long, which prolongs the test cycle. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a nondestructive detection device for loess structure collapse under the action of water-heat-force coupling. The present invention can conveniently realize nondestructive quantitative detection of the deformation characteristics and structural change characteristics of the loess collapse process under the action of water-heat-force coupling.

[0007] The present invention is achieved in that:

[0008] The present invention first provides a nondestructive detection device for loess structure collapse under water-heat-force coupling, comprising a pressure chamber, a consolidation box, a loading unit and an electric heating unit, wherein:

[0009] The pressure chamber is a closed chamber, with an air inlet at the top connected to the interior of the pressure chamber, and a water inlet and a water outlet at the bottom connected to the interior of the consolidation box;

[0010] The consolidation box is installed in the pressure chamber, including the pressure plate, permeable stone, ring knife and clay plate, and:

[0011] The pressure plate is stacked on the permeable stone, and together with the permeable stone, it forms the top cover of the consolidation box. The permeable stone is equipped with a bending element transmitting end which extends into the box, and the bending element transmitting end and the permeable stone are sealed.

[0012] The ring cutter is installed directly under the permeable stone to form a consolidation box body, in which the loess sample is placed;

[0013] The clay plate is installed on the base of the pressure chamber below the ring knife to form the bottom plate of the consolidation box. The bending element receiving end is installed on the clay plate and extends into the box. The bending element receiving end and the clay plate are sealed.

[0014] The loading unit is a loading rod that passes through the top of the pressure chamber and is vertically opposite to the pressure plate, and the loading rod and the top of the pressure chamber are sealed;

[0015] The electric heating unit is used to heat the loess sample in the consolidation box.

[0016] In some embodiments, a through hole is provided on the permeable stone for the bending element transmitting end to pass through, one end of the bending element transmitting end is fixedly mounted on the pressure plate, and the other end passes through the through hole, and the through hole is filled with epoxy resin;

[0017] A through hole is provided on the clay plate for the receiving end of the bending element to pass through. One end of the receiving end of the bending element is fixedly installed at the bottom of the pressure chamber, and the other end passes through the through hole. The through hole is filled with epoxy resin.

[0018] In some embodiments, the bending element transmitting end is installed on the pressure plate through a sealing unit, and the sealing unit includes a fixed shell, a fixed body and epoxy resin. The fixed shell is a cylindrical structure with a bottom at one end. The bottom end of the bending element transmitting end is fixedly installed on the bottom of the fixed shell through the fixed body. The lead wire of the bending element transmitting end passes through the bottom of the fixed shell, and the top end of the bending element transmitting end protrudes from the fixed shell. The remaining space in the fixed shell is filled with epoxy resin; a sealing ring is provided on the outside of the fixed shell, and a through hole for the fixed shell to pass through is opened on the permeable stone, and the fixed shell and the through hole are sealed by a sealing ring;

[0019] The receiving end of the bending element is installed at the bottom of the pressure chamber in the same way, and a through hole for the fixed shell to pass through is opened on the clay plate;

[0020] Preferably, the length of the bottom end of the bending element emitting end located at the fixed body does not exceed three quarters of the length of the bending element emitting end, and the length of the top end of the bending element emitting end protruding from the fixed housing is 2-3 mm;

[0021] The bottom end of the bending element receiving end is located at a length of the fixed body that does not exceed three quarters of the length of the bending element receiving end, and the top end of the bending element receiving end protrudes from the fixed housing by 2-3 mm;

[0022] Preferably, the fixing body is made of plastic.

[0023] In some embodiments, a thermocouple is further included, which is disposed at the bottom of the pressure chamber and located at the center of the clay plate. The thermocouple penetrates the clay plate and extends into the consolidation box. The thermocouple is sealed from the clay plate.

[0024] In some embodiments, the electric heating unit adopts an electric heating ring, which is arranged on the periphery of the ring knife in the pressure chamber, and includes an annular shell and an electric heating wire, the annular shell has an inner cavity, the electric heating wire is arranged in the inner cavity, the annular shell is coaxially arranged with the clay plate, and the inner diameter of the annular shell is not less than the diameter of the clay plate; the lower end of the annular shell is sealed and connected to the bottom of the pressure chamber;

[0025] Preferably, the lower end of the annular shell is detachably sealed to the bottom of the pressure chamber, the lower end of the annular shell is provided with a step, a sealing ring is sleeved on the outer surface of the step, and a groove for embedding the step is provided at the bottom of the pressure chamber.

[0026] In some embodiments, the pressure chamber includes a pressure chamber upper cover, an annular side wall and a pressure chamber base, the pressure chamber upper cover and the pressure chamber base are fixed to the top and bottom of the annular side wall by bolts, and sealing rings are provided on the contact surface between the pressure chamber upper cover and the top of the annular side wall and on the contact surface between the pressure chamber base and the bottom of the annular side wall;

[0027] Preferably, the clay plate is arranged on the pressure chamber base and located at the center of the annular side wall, the thermocouple and the receiving end of the bending element are both arranged on the pressure chamber base, and the pressure chamber base is provided with a channel for the lead wires of the thermocouple and the receiving end of the bending element to pass through;

[0028] Preferably, the water inlet and the water outlet are provided on the pressure chamber base.

[0029] In some embodiments, it also includes a gas circulation pump, an inlet and outlet water controller, and a temperature controller. The gas circulation pump is connected to the air inlet, the inlet and outlet water controller is connected to the water inlet and outlet, and the electric heating ring and the thermocouple are both connected to the temperature controller.

[0030] In some embodiments, a signal generator and an oscilloscope are also included, the transmitting end of the bending element is connected to the signal generator, and the receiving end of the bending element is connected to the oscilloscope.

[0031] In some embodiments, a displacement sensor is further included, which is mounted on the loading rod and has a probe in contact with the top of the pressure chamber.

[0032] The present invention also provides a nondestructive detection method for loess structure collapse under water-heat-force coupling, based on the detection device, comprising the following steps:

[0033] (1) Prepare a sample of a certain size, use a ring knife to obtain a sample of the required size from the large soil sample retrieved in situ, and put the soil sample wrapped by the ring knife into the pressure chamber to complete the sample loading process;

[0034] (2) Connecting the air inlet, water inlet, water outlet, bending element transmitting end, and bending element receiving end;

[0035] (3) Apply load to target load and monitor the collapsibility process in real time;

[0036] (4) Set the target temperature and keep it stable during the collapse process;

[0037] (5) Apply a set water pressure to the pressure chamber until the water volume is stable, so as to control the initial water content of the soil sample; apply a set air pressure to the pressure chamber so that the gas acts evenly on the upper surface of the sample through the holes of the permeable stone until the required matrix suction is reached;

[0038] (6) The transmitting end of the bending element excites the signal, and the receiving end of the bending element receives the signal, thereby realizing the measurement of the initial small strain shear modulus of the soil and the non-destructive testing of the initial structure;

[0039] (7) Changing the water pressure applied to the pressure chamber to simulate the next stage of the collapsible process, after the water volume is stable, repeating step (6) to excite and record the bending element signal once, thereby achieving the measurement of the small strain shear modulus of the soil at this stage of collapsible and the non-destructive detection of the structural collapsible process;

[0040] (8) Repeat step (7) until the soil sample is saturated, thereby achieving the determination of the shear modulus of the soil at different stages of the whole process of loess structure collapse and the non-destructive testing of the whole process of structure collapse.

[0041] The beneficial effects of the present invention relative to the prior art are:

[0042] The closed pressure chamber that can withstand high pressure can detect the changing characteristics of loess collapsible structure under high stress environment. By setting up an electric heating ring, a ring knife can be placed inside the electric heating ring. The electric heating ring can directly heat the soil in the ring knife, which improves the heating efficiency. In conjunction with a thermocouple, the soil in the ring knife can be tested in real time using a thermocouple. The soil in the ring knife can be quickly heated to the preset temperature, which can easily realize the detection of loess collapsible structure at different temperatures, because temperature has a great influence on the strength and collapsibility of unsaturated loess. By introducing a bending element system, the change of small strain shear modulus during loess collapsibility is measured, and continuous non-destructive quantitative detection of different stages of the whole process of loess structure collapsibility is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0044] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment in size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0045] Figure 1 It is a schematic diagram of the main part of a detection device according to an embodiment of the present invention;

[0046] Figure 2 is a partial cross-sectional view of a consolidation box in one embodiment of the present invention;

[0047] Figure 3 is a schematic diagram of a bending element probe in an embodiment of the present invention;

[0048] Figure 4 This is a cross-sectional view of an electric heating ring according to an embodiment of the present invention;

[0049] Figure 5It is an overall schematic diagram of a detection device according to an embodiment of the present invention;

[0050] Wherein: 1- loading rod, 2- loading rod head, 3- displacement sensor, 4- air inlet, 5- bending element transmitting end lead, 6- pressure plate, 7- bending element transmitting end, 8- ring knife, 9- electric heating ring, 9-1- ring shell, 9-2- electric heating wire, 9-3- step, 10- permeable stone, 11- thermocouple, 12- bending element receiving end, 13- thermocouple and bending element receiving end lead, 14- water inlet, 15- water outlet, 16- clay plate, 17- pressure chamber base, 18- connecting bolt, 19- pressure chamber cover, 20- gas circulation pump, 21- water inlet and outlet controller, 22- loading frame, 23- signal amplifier, 24- oscilloscope, 25- temperature controller, 26- sealing ring, 27- epoxy resin, 28- fixed shell, 29- fixed body. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0052] In the description of the present invention, the terms "include / comprise", "consist of..." or any other variations thereof are intended to cover non-exclusive inclusion, so that a product, device, process or method including a series of elements includes not only those elements, but also other elements not explicitly listed when necessary, or also includes elements inherent to such product, device, process or method. In the absence of further restrictions, the elements defined by the sentences "include / comprise...", "consist of..." do not exclude the presence of other identical elements in the product, device, process or method including the elements.

[0053] It should be understood that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0054] It should also be understood that terms such as "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", and "center" to indicate directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only used to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the device, component or structure referred to must have a specific direction, be constructed or operate in a specific direction, and should not be understood as a limitation on the present invention.

[0055] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0056] The implementation of the present invention is described in detail below in conjunction with preferred embodiments.

[0057] See also Figure 1 , a nondestructive detection device for loess structure collapse under water-heat-force coupling, comprising a pressure chamber, a consolidation box, a loading unit and an electric heating unit, wherein:

[0058] The pressure chamber is a closed chamber, with an air inlet 4 at the top connected to the interior of the pressure chamber, and a water inlet 14 and a water outlet 15 at the bottom connected to the interior of the consolidation box;

[0059] The consolidation box is installed in the pressure chamber, including a pressure plate 6, a permeable stone 10, a ring knife 8 and a clay plate 16, and:

[0060] The pressure plate 6 is stacked on the permeable stone 10, and together with the permeable stone 10, it forms the top cover of the consolidation box. The permeable stone 10 is equipped with a bending element emitting end 7 and extends into the box. The bending element emitting end 7 and the permeable stone 10 are sealed.

[0061] The ring cutter 8 is installed directly under the permeable stone 10 to form a consolidation box body, and the loess sample is placed in the box body;

[0062] The clay plate 16 is installed on the base of the pressure chamber below the ring knife 8 to form the bottom plate of the consolidation box. The bending element receiving end 12 is installed on the clay plate 16 and extends into the box. The bending element receiving end 12 and the clay plate 16 are sealed.

[0063] The loading unit is a loading rod 1 that passes through the top of the pressure chamber and is vertically opposite to the pressure plate 6, and the loading rod 1 is sealed with the top of the pressure chamber;

[0064] The electric heating unit is used to heat the loess sample in the consolidation box.

[0065] Collapse is completed after the soil is compressed and moistened. The present invention provides the historical stress of the soil sample through a loading rod, simulates the moistening process through the lower water inlet, and provides air pressure through the air inlet to make the pore air pressure in the soil sample reach a set value, and then cooperates with the water pressure to obtain the required matrix suction. Matrix suction is an important angle for analyzing the collapsibility of unsaturated loess.

[0066] In addition, temperature has a great influence on the strength of unsaturated loess. When the temperature is above 0 degrees Celsius, the shear strength of the soil will increase with the increase of temperature. This is mainly because the viscosity of water decreases with the increase of temperature, and the permeability coefficient increases, which reduces the porosity of the soil and increases the strength. Reflecting on the collapsibility, the temperature increases, the soil structure is further damaged, the degree of soil agglomeration increases, and the collapsibility is enhanced. The present invention can quickly heat the soil in the ring cutter to a preset temperature through an electric heating unit, and can conveniently realize the loess collapsibility test at different temperatures and the detection of the collapsible structure.

[0067] See also Figure 2 In the present invention, a through hole is provided on the permeable stone 10 for the bending element transmitting end 7 to pass through, one end of the bending element transmitting end 7 is fixedly mounted on the pressure plate 6, and the other end passes through the through hole, and the through hole is filled with epoxy resin 27; a through hole is provided on the clay plate 16 for the bending element receiving end 12 to pass through, one end of the bending element receiving end 12 is fixedly mounted on the bottom of the pressure chamber, and the other end passes through the through hole, and the through hole is filled with epoxy resin 27. By providing through holes in the permeable stone 10 and the clay plate 16, the bending element transmitting end 7 and the bending element receiving end 12 are penetrated, and the bending element transmitting end 7 and the bending element receiving end 12 are directly fixed on the pressure plate 6 and the bottom of the pressure chamber, the structure is simpler and the installation is convenient.

[0068] Furthermore, since the bending element sheet at the bending element transmitting end is relatively fragile and easily damaged during use, the bending element transmitting end of the present invention is installed on the pressure plate 6 through a sealing unit to improve the reliability of installation and sealing.

[0069] like Figure 3As shown, in one embodiment, the sealing unit includes a fixed shell 28, a fixed body 29 and an epoxy resin 27. The fixed shell 28 is a cylindrical structure with a bottom at one end, and the bottom is upward as shown in the figure. The bottom end of the bending element transmitting end 7 is fixedly installed on the bottom of the fixed shell through the fixed body 29, and the lead of the bending element transmitting end 7 passes through the bottom of the fixed shell. The top of the bending element transmitting end 7 protrudes from the fixed shell, and the remaining space in the fixed shell is filled with epoxy resin 27; a sealing ring 26 is provided on the outside of the fixed shell, and a through hole for the fixed shell to pass through is opened on the permeable stone 10, and the fixed shell and the through hole are sealed by the sealing ring 26; the present invention wraps the bending element piece by the fixed body, and when installing, it only needs to align the component with the hole pre-punched in the bottom permeable stone and then insert it as a whole. In this way, on the one hand, the performance of the bending element transmitting end after installation is guaranteed, and the installation is convenient. On the other hand, if the material of the bending element piece itself is damaged, or it needs to be replaced to maintain accuracy after a period of use, it can be replaced at any time after plugging and unplugging the wiring when there is a problem with the bending element piece, which is more superior than the traditional design that the bending element piece is fixed in the center of the base and cannot be replaced.

[0070] Likewise, the bending element receiving end 12 is mounted on the bottom of the pressure chamber in the same manner, and a through hole is provided on the clay plate 16 for the fixed housing to pass through.

[0071] In the present invention, the fixing body 29 is made of plastic, which will not damage the bending element piece and can also effectively fix the bending element piece.

[0072] Furthermore, the length of the bottom end of the bending element transmitting end 7 located at the fixed body does not exceed three quarters of the length of the bending element transmitting end 7, and the top end of the bending element transmitting end 7 protrudes from the fixed shell by 2-3mm; by designing that the length of the bottom end of the bending element transmitting end located at the fixed body does not exceed three quarters of the length of the bending element transmitting end, the vibration of the bending element transmitting end can be guaranteed, so that the received signal is relatively good; the top end of the bending element transmitting end protrudes from the fixed shell by 2-3mm, and during installation, the end face of the fixed shell is generally aligned with the surface of the permeable stone 10, so that the length of the top end of the bending element transmitting end 7 extending into the soil in the ring cutter is 2-3mm, which can not only ensure the measurement but also prevent the bending element transmitting end from excessively disturbing the soil in the ring cutter, so that the measurement result is more accurate and the measurement effect is guaranteed.

[0073] The length of the bottom end of the bending element receiving end 12 located at the fixed body does not exceed three quarters of the length of the bending element receiving end 12, and the length of the top end of the bending element receiving end 12 protruding from the fixed shell is 2-3mm. By designing that the length of the bottom end of the bending element receiving end located at the fixed body does not exceed three quarters of the length of the bending element receiving end, the vibration of the bending element receiving end can be guaranteed, so that the received signal is relatively good, and the length of the top end of the bending element receiving end protruding from the fixed shell is 2-3mm. During installation, the end face of the fixed shell is generally aligned with the surface of the clay plate 16, so that the length of the top end of the bending element receiving end 12 extending into the soil in the ring cutter is 2-3mm, which can ensure the measurement and prevent the bending element receiving end from excessively disturbing the soil in the ring cutter, so that the measurement result is more accurate and the measurement effect is guaranteed.

[0074] Furthermore, the present invention also includes a thermocouple 11, which is arranged at the bottom of the pressure chamber and located at the center of the clay plate 16. The thermocouple 11 penetrates the clay plate 16 and extends into the consolidation box, and the thermocouple 11 is sealed with the clay plate 16. The thermocouple is used to detect the temperature of the soil in the ring cutter in real time, and the soil in the ring cutter can be quickly heated to a preset temperature in conjunction with the electric heating unit, so as to conveniently realize the detection of loess collapsible structure at different temperatures.

[0075] like Figure 4 As shown, in one embodiment, the electric heating unit adopts an electric heating ring 9, which is arranged on the periphery of the ring knife 8 in the pressure chamber, and includes an annular shell 9-1 and an electric heating wire 9-2. The annular shell 9-1 has an inner cavity, and the electric heating wire 9-2 is arranged in the inner cavity. The annular shell 9-1 is coaxially arranged with the clay plate 16, and the inner diameter of the annular shell 9-1 is not less than the diameter of the clay plate 16; the lower end of the annular shell 9-1 is sealed and connected to the bottom of the pressure chamber. By arranging the electric heating ring, the ring knife can be placed inside the electric heating ring, and the soil in the ring knife can be directly heated by the electric heating ring, thereby improving the heating efficiency.

[0076] Furthermore, the lower end of the annular housing 9-1 is detachably sealed to the bottom of the pressure chamber, the lower end of the annular housing 9-1 is provided with a step 9-3, the outer surface of the step 9-3 is provided with a sealing ring 26, and the bottom of the pressure chamber is provided with a groove for embedding the step 9-3. The step and groove structure facilitates the quick installation of the annular housing 9-1, and the outer surface cooperates with the sealing ring 26 to facilitate the sealed connection with the bottom of the pressure chamber.

[0077] Continue to see Figure 1In the present invention, the pressure chamber includes a pressure chamber upper cover 19, an annular side wall and a pressure chamber base 17. The pressure chamber upper cover 19 and the pressure chamber base 17 are connected and fixed to the top and bottom of the annular side wall by bolts 18. The contact surface between the pressure chamber upper cover 19 and the top of the annular side wall and the contact surface between the pressure chamber base 17 and the bottom of the annular side wall are provided with sealing rings. A stable pressure chamber space is formed by the upper cover, the side wall, the base and the matching sealing structure. The entire structure is located on a larger loading frame 22, and the base with a larger dead weight is used as a support. After the loading rod and the pressure chamber upper cover are assembled, the base is covered as a whole, connected to the base with four long bolts, and a seal is formed by the O-ring on the base. The matrix suction control part is connected to the pressure chamber through a pipeline, and the temperature control part is connected to the base.

[0078] Furthermore, the clay plate 16 is disposed on the pressure chamber base 17 and is located at the center of the annular side wall, the thermocouple 11 and the bending element receiving end 12 are both disposed on the pressure chamber base 17, and the pressure chamber base 17 is provided with a channel for the lead wires of the thermocouple 11 and the bending element receiving end 12 to pass through;

[0079] Furthermore, the water inlet 14 and the water outlet 15 are provided on the pressure chamber base 17 .

[0080] See also Figure 5 The present invention also includes a gas circulation pump 20, an inlet and outlet water controller 21, and a temperature controller. The gas circulation pump 20 is connected to the air inlet 4, the inlet and outlet water controller 21 is connected to the water inlet 14 and the water outlet 15, and the electric heating ring 9 and the thermocouple 11 are connected to the temperature controller. The gas circulation pump 20 applies a set air pressure to the pressure chamber through the air inlet 4 at the upper cover 19 of the pressure chamber, and the gas acts evenly on the upper surface of the sample through the holes of the permeable stone to control the suction of the sample; the target temperature is set by the temperature controller, and it is always kept stable during the collapse process; the inlet and outlet water controller 21 applies a set water pressure to the pressure chamber through the water inlet 14, and after the water volume is stable, the initial water content condition of the soil sample is controlled.

[0081] Furthermore, the present invention also includes a signal generator 23 and an oscilloscope 24, the bending element transmitting end 7 is connected to the signal generator 23, and the bending element receiving end 12 is connected to the oscilloscope 24. The leads of the bending element transmitting end 7 and the bending element receiving end 12 are respectively connected to the signal generator and the oscilloscope, the bending element transmitting end excites the signal, which is received by the bending element receiving end and the oscilloscope, and an image is formed on the oscilloscope, so as to realize the measurement of the initial small strain shear modulus of the soil and the non-destructive detection of the initial structure.

[0082] like Figure 1The present invention further includes a displacement sensor 3, which is mounted on the loading rod 1, and its probe is in contact with the top of the pressure chamber. The displacement sensor uses an LVDT (Linear Variable Differential Transformer), which is mounted on the loading rod, and the core of the LVDT is in contact with the top of the pressure chamber. The displacement sensor measures the vertical displacement change of the sample and records the change data at the same time.

[0083] See also Figures 1 to 5 During the test of the loess structure wetting nondestructive detection device of the present invention, the loading rod 1 is installed on the pressure chamber cover 19, the displacement sensor LVDT is installed on the loading rod 1, the loading rod head 2 is screwed on the lower end of the loading rod 1, the ring knife 8 is placed in the heating ring 9, the ring knife 8 is placed on the clay plate 16, the clay plate 16 is embedded in the center of the upper surface of the pressure chamber base 17, the soil sample is placed in the ring knife 8, and the permeable stone 10 is adhered to the pressure plate 6 and placed on the soil sample.

[0084] The thermocouple 11 is installed in the center of the clay plate 16, with the top exposed 3 mm from the clay plate, and is sealed between the clay plate 16 with an O-ring and epoxy resin.

[0085] like Figure 2 As shown, one installation method of the bending element transmitting end 7 and the bending element receiving end 12 is: the bottom of the bending element receiving end 12 is installed on the pressure chamber base 17, a hole is punched at the corresponding position of the clay plate 16 to expose the head of the bending element receiving end 12, and the hole is filled with epoxy resin to facilitate the fixation and sealing of the bending element. The bottom of the bending element transmitting end 7 is installed on the pressure plate 6, a hole is punched at the corresponding position of the permeable stone to expose the transmitting end, and the hole is filled with epoxy resin. The height of the head of the bending element transmitting end 7 exposed from the permeable stone 10 is 3mm, and the height of the head of the bending element receiving end 12 exposed from the clay plate 16 is 3mm.

[0086] like Figure 3 As shown, another installation method of the bending element transmitting end 7 and the bending element receiving end 12 is: the top of the bending element transmitting end 7 and the receiving end 12 is exposed to 3mm of epoxy resin, and the bottom 5mm of the bending element is wrapped with a plastic body, which will not damage the bending element piece and can also effectively fix the bending element piece. The plastic body is wrapped with aluminum alloy, and the wire is left at the bottom. The 13mm above the clamping part is wrapped with epoxy resin, and this part and the top exposed 3mm are the vibration part of the bending element piece. This part is a movable part, which is easy to replace.

[0087] The lead wire 5 at the transmitting end of the bending element is led out through a hole punched in the upper cover 19 of the pressure chamber and is sealed with an O-ring and a steel hoop. The lead wire 13 at the receiving end of the thermocouple and the bending element is led out through a channel punched in the base 17 of the pressure chamber and is sealed with an O-ring and a steel hoop at the outlet.

[0088] The pressure chamber is placed on a loading rack, which is an existing product. The thermocouple 11 and the heating ring 9 are connected to the temperature controller 25 outside the pressure chamber, which is an existing product. The water inlet 14 and the water outlet 15 are connected to the water inlet and outlet controller 21, and the water supply and drainage are controlled by the water inlet and outlet controller 21. The bending element transmitting end 7 and the receiving end 12 are respectively connected to the signal amplifier 23 and the oscilloscope 24 through the lead wire. The air inlet 4 at the upper cover 19 of the pressure chamber is connected to the gas circulation pump 20 to control the suction of the sample.

[0089] The temperature controller 25 sets the temperature, the heating ring 9 heats up the sample, and the temperature of the sample is measured and fed back through the thermocouple 11 to complete the temperature control.

[0090] The method for detecting the collapsibility characteristics of loess structures at different temperatures using the nondestructive detection device for collapsible loess structures of the present invention comprises the following steps:

[0091] (1) Prepare a sample of a certain size, specifically, use a ring knife to obtain a sample of a required size from a large piece of soil sample retrieved in situ, place the soil sample wrapped by the ring knife in the electric heating ring 9 on the base, cover the pressure chamber cover, tighten the bolts to form a seal, and complete the sample loading process;

[0092] (2) Each structure is connected to a computer, that is, the air inlet, the water inlet, the water outlet, the bending element transmitting end, the bending element receiving end, and the computer;

[0093] (3) The load is applied to the target load through the loading frame, that is, the load is applied to the historical overburden pressure. At the beginning of the test, a vertical pressure of 0.1 MPa is applied to the specimen step by step. The wetting process is monitored in real time and remains stable at all times;

[0094] (4) The target temperature is set by the temperature controller and remains stable during the wetting process;

[0095] (5) Use pipelines to connect the water inlet 14 on the base of the pressure chamber and the water inlet controller, apply a set water pressure to the pressure chamber, and after the water inlet volume stabilizes, the initial water content of the soil sample is controlled; at the same time, use pipelines to connect the air inlet on the upper cover of the pressure chamber to the air pressure controller, apply a set air pressure to the pressure chamber, and make the gas pass through the holes of the permeable stone and evenly act on the upper surface of the sample;

[0096] (6) The lead wire 5 of the transmitting end of the bending element is connected to the signal generator 23, and the lead wire 13 of the receiving end of the thermocouple and the bending element is connected to the oscilloscope. The excitation signal of the transmitting end of the bending element is received by the receiving end of the bending element and the oscilloscope, and an image is formed on the oscilloscope, thereby realizing the measurement of the initial small strain shear modulus of the soil and the non-destructive detection of the initial structure;

[0097] (7) Changing the water pressure applied to the pressure chamber to simulate the next stage of the collapsible process, after the water volume is stable, repeating step (6) to excite and record the bending element signal once, thereby achieving the measurement of the small strain shear modulus of the soil at this stage of collapsible and the non-destructive detection of the structural collapsible process;

[0098] (8) Repeat step (7) until the soil sample is saturated, thereby achieving the determination of the shear modulus of the soil at different stages of the whole process of loess structure collapse and the non-destructive testing of the whole process of structure collapse.

[0099] By setting different temperatures in step (4) for each test, nondestructive testing of the entire loess structure collapse process at different temperatures can be performed.

[0100] It can be seen from the above scheme that the present invention has the following advantages:

[0101] (A) A ring knife is used to obtain a sample of a required size from the large block of soil sample retrieved in situ. At this time, the soil sample in the ring knife is the same as the original soil sample except for the temperature. During the test, the ring knife and the soil sample are placed in a pressure chamber for testing, which can be regarded as a non-destructive soil sample. The present invention does not damage the soil sample before and after the structural collapse test, and can directly perform structural testing on the sample in the collapse test, thereby realizing in-situ, non-destructive testing;

[0102] (B) The present invention controls the temperature of the sample through an electric heating ring, and uses a thermocouple and a temperature controller to feedback control the center temperature of the soil sample in real time, so that the soil sample is heated evenly, and the accuracy can be controlled within ±1 degree, with high accuracy, fast heating, and more accurate consideration of temperature effects;

[0103] (C) The present invention introduces a bending element system, which can be started at any time for detection. The detection can be performed before wetting, when wetting with water, and after wetting. The change of small strain shear modulus during loess wetting is measured. The small strain shear modulus parameter reflects the structural properties of the soil. The structural changes of the soil during wetting can be quantitatively evaluated, and continuous non-destructive quantitative detection of different stages of the whole process of loess structural wetting can be achieved.

[0104] (D) The bending element is a movable part. Since the bending element is relatively fragile and easily damaged during use, the present invention designs this part as a movable part for easy replacement;

[0105] (E) The matrix suction control part and consolidation stress of the present invention can be monitored in real time by a computer, which is convenient for recording and control;

[0106] (F) The scheme of the present invention is reasonable, the structure is clear, and it is easy to operate. By fully considering the various factors that affect the collapse of loess, the entire collapse process of unsaturated loess is accurately characterized.

[0107] The present invention fully considers the unsaturated state of loess in actual working conditions such as engineering construction and disaster prevention and mitigation, as well as the influence of humidity and temperature environment that changes with seasons, and possible changes in overlying loads. It proposes a multi-factor coupling detection method that simultaneously considers the influence of moisture content, temperature and load during the loess collapse process.

[0108] It is easy for those skilled in the art to understand that, under the premise of no conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A nondestructive detection device for loess structure collapse under water-heat-force coupling, comprising a pressure chamber, a consolidation box, a loading unit and an electric heating unit, in: The pressure chamber is a closed chamber, with an air inlet (4) at the top connected to the interior of the pressure chamber, and a water inlet (14) and a water outlet (15) at the bottom connected to the interior of the consolidation box; The consolidation box is installed in the pressure chamber, and includes a pressure plate (6), a permeable stone (10), a ring knife (8) and a clay plate (16), and: The pressure plate (6) is stacked on the permeable stone (10) and together with the permeable stone (10) forms a top cover of the consolidation box. The permeable stone (10) is equipped with a bending element emitting end (7) and extends into the box. The bending element emitting end (7) and the permeable stone (10) are sealed. The ring cutter (8) is installed directly opposite to the permeable stone (10) and below the permeable stone (10) to form a consolidation box body, in which the loess sample is placed; The clay plate (16) is installed on the base of the pressure chamber below the ring knife (8) to form the bottom plate of the consolidation box. The clay plate (16) is equipped with a bending element receiving end (12) and extends into the box. The bending element receiving end (12) and the clay plate (16) are sealed. The loading unit is a loading rod (1) that passes through the top of the pressure chamber and is vertically opposite to the pressure plate (6), and the loading rod (1) and the top of the pressure chamber are sealed; The electric heating unit is used to heat the loess sample in the consolidation box.

2. The detection device according to claim 1, Features: The permeable stone (10) is provided with a through hole for the bending element emitting end (7) to pass through, one end of the bending element emitting end (7) is fixedly mounted on the pressure plate (6), and the other end passes through the through hole, and the through hole is filled with epoxy resin; A through hole is provided on the clay plate (16) for the bending element receiving end (12) to pass through. One end of the bending element receiving end (12) is fixedly mounted on the bottom of the pressure chamber, and the other end passes through the through hole. The through hole is filled with epoxy resin.

3. The detection device according to claim 1, Features: The bending element transmitting end (7) is installed on the pressure plate (6) through a sealing unit, and the sealing unit includes a fixed shell (28), a fixed body (29) and an epoxy resin (27). The fixed shell (28) is a cylindrical structure with a bottom at one end. The bottom end of the bending element transmitting end (7) is fixedly installed on the bottom of the fixed shell through the fixed body (29). The lead wire of the bending element transmitting end (7) passes through the bottom of the fixed shell, and the top end of the bending element transmitting end (7) protrudes from the fixed shell. The remaining space in the fixed shell is filled with epoxy resin (27); a sealing ring (26) is provided on the outside of the fixed shell, and a through hole for the fixed shell to pass through is opened on the permeable stone (10), and the fixed shell and the through hole are sealed by the sealing ring (26); The bending element receiving end (12) is installed at the bottom of the pressure chamber in the same manner, and a through hole is provided on the clay plate (16) for the fixed housing to pass through; Preferably, the length of the bottom end of the bending element emitting end (7) located at the fixed body does not exceed three quarters of the length of the bending element emitting end (7), and the top end of the bending element emitting end (7) protrudes from the fixed housing by 2-3 mm; The bottom end of the bending element receiving end (12) is located at a length of the fixed body that does not exceed three quarters of the length of the bending element receiving end (12), and the top end of the bending element receiving end (12) protrudes from the fixed housing by 2-3 mm; Preferably, the fixing body (29) is made of plastic.

4. The detection device according to claim 1, It is characterized in that It also includes a thermocouple (11) which is arranged at the bottom of the pressure chamber and located at the center of the clay plate (16). The thermocouple (11) penetrates the clay plate (16) and extends into the consolidation box. The thermocouple (11) and the clay plate (16) are sealed.

5. The detection device according to claim 4, It is characterized in that The electric heating unit adopts an electric heating ring (9), which is arranged on the periphery of the ring knife (8) in the pressure chamber, and comprises an annular shell (9-1) and an electric heating wire (9-2); the annular shell (9-1) has an inner cavity, and the electric heating wire (9-2) is arranged in the inner cavity; the annular shell (9-1) and the clay plate (16) are coaxially arranged, and the inner diameter of the annular shell (9-1) is not less than the diameter of the clay plate (16); the lower end of the annular shell (9-1) is sealed and connected to the bottom of the pressure chamber; Preferably, the lower end of the annular housing (9-1) is detachably sealed to the bottom of the pressure chamber, the lower end of the annular housing (9-1) is provided as a step (9-3), a sealing ring (26) is sleeved on the outer surface of the step (9-3), and the bottom of the pressure chamber is provided with a groove for embedding the step (9-3).

6. The detection device according to any one of claims 1 to 5, It is characterized in that The pressure chamber comprises a pressure chamber upper cover (19), an annular side wall and a pressure chamber base (17); the pressure chamber upper cover (19) and the pressure chamber base (17) are connected and fixed to the top and bottom of the annular side wall by bolts (18); sealing rings are provided on the contact surface between the pressure chamber upper cover (19) and the top of the annular side wall and on the contact surface between the pressure chamber base (17) and the bottom of the annular side wall; Preferably, the clay plate (16) is arranged on the pressure chamber base (17) and is located at the center of the annular side wall, the thermocouple (11) and the bending element receiving end (12) are both arranged on the pressure chamber base (17), and the pressure chamber base (17) is provided with a channel for the lead wires of the thermocouple (11) and the bending element receiving end (12) to pass through; Preferably, the water inlet (14) and the water outlet (15) are provided on the pressure chamber base (17).

7. The detection device according to claim 6, It is characterized in that It also includes a gas circulation pump (20), an inlet and outlet water controller (21), and a temperature controller. The gas circulation pump (20) is connected to the gas inlet (4), the inlet and outlet water controller (21) is connected to the water inlet (14) and the water outlet (15), and the electric heating ring (9) and the thermocouple (11) are both connected to the temperature controller.

8. The detection device according to claim 1, It is characterized in that It also includes a signal generator (23) and an oscilloscope (24), wherein the bending element transmitting end (7) is connected to the signal generator (23), and the bending element receiving end (12) is connected to the oscilloscope (24).

9. The detection device according to claim 1, It is characterized in that It also includes a displacement sensor (3) which is mounted on the loading rod (1) and whose probe contacts the top of the pressure chamber.

10. A nondestructive detection method for loess structure collapse under water-heat-mechanical coupling, based on the detection device according to any one of claims 1 to 9, comprising the following steps: (1) Prepare a sample of a certain size, use a ring knife to obtain a sample of the required size from the large soil sample retrieved in situ, and put the soil sample wrapped by the ring knife into the pressure chamber to complete the sample loading process; (2) Connecting the air inlet, water inlet, water outlet, bending element transmitting end, and bending element receiving end; (3) Apply load to target load and monitor the collapsibility process in real time; (4) Set the target temperature and keep it stable during the collapse process; (5) Apply a set water pressure to the pressure chamber until the water volume is stable, so as to control the initial water content of the soil sample; apply a set air pressure to the pressure chamber so that the gas acts evenly on the upper surface of the sample through the holes of the permeable stone until the required matrix suction is reached; (6) The transmitting end of the bending element excites the signal, and the receiving end of the bending element receives the signal, thereby realizing the measurement of the initial small strain shear modulus of the soil and the non-destructive testing of the initial structure; (7) Changing the water pressure applied to the pressure chamber to simulate the next stage of the collapsible process, after the water volume is stable, repeating step (6) to excite and record the bending element signal once, thereby achieving the measurement of the small strain shear modulus of the soil at this stage of collapsible and the non-destructive detection of the structural collapsible process; (8) Repeat step (7) until the soil sample is saturated, thereby achieving the determination of the shear modulus of the soil at different stages of the whole process of loess structure collapse and the non-destructive testing of the whole process of structure collapse.

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