Visual movable door test device for soil arching effect evolution

Abstract

The invention relates to a visual movable door test device for soil arching effect evolution, and belongs to the technical field of tunnel engineering and geotechnical engineering.The visual movable door test device comprises a transparent model box, a movable door adjusting assembly comprises a semicircular shell cylindrical movable door block and a constant-speed loading instrument, and the constant-speed loading instrument is arranged at the bottom of the inner side of the transparent model box; the semi-circular shell cylindrical movable door block is horizontally arranged right above the constant-speed loading instrument, the two supporting plates are horizontally arranged on the two sides of the semi-circular shell cylindrical movable door block respectively, and the transparent soil is filled into the transparent model box layer by layer in the vertical direction. The constant-speed loading instrument drives the semicircular shell cylindrical movable door block to move up and down to simulate stratum loss or grouting lifting, so that the difference of the loss of the stratum caused by test and shield tunnel construction is avoided, and transparent soil is utilized to form overlying soil of a shield tunnel. And the visual observation of the gradual response of the soil body of the shield tunnel under the loss or expansion of different stratums is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of tunnel engineering and geotechnical engineering, and particularly relates to a visual movable door test device for soil arching effect evolution. BACKGROUND

[0002] With the acceleration of urbanization process in China, traffic congestion is becoming increasingly serious, which has become one of the key factors restricting the further development of cities. Urban rail transit is considered as an effective way to alleviate and solve the problem of traffic congestion in large cities due to its advantages of land saving, large capacity, no pollution, etc., and has been developed vigorously. Shield method is the main construction method of urban rail transit. In shield tunnel construction, different overburden soil displacement will lead to different vertical loads on the shield shell, vertical loads on the segment, and vertical loads on the shield shell when the attitude deviates, which indirectly affects the construction parameters such as shield shell friction force calculation, grouting pressure analysis, and partition pressure of correction jack.

[0003] In order to realize the fine control of construction parameters, Terzaghi's ultimate loose soil pressure theory is often used to analyze the actual soil pressure during shield tunnel construction. Due to the factors such as excavation diameter, mechanical diameter, segment diameter, grouting characteristics, and imbalance between excavation face support pressure and initial ground stress, ground loss inevitably occurs, causing ground movement and stress release. However, in Terzaghi's ultimate loose soil pressure theory, the overburden soil is in a limit state. For normal construction state, due to the support of shield shell or pipe ring, the displacement and stress release of soil around the tunnel are limited, which leads to incomplete development of arching effect in overburden soil, and the developed shear stress of soil is less than its shear strength, resulting in that Terzaghi's ultimate loose soil pressure theory cannot accurately analyze the actual soil pressure during shield tunnel construction, and further cannot meet the fine control of construction parameters.

[0004] On the other hand, in view of the problem that shield tunnel in operation period is easily affected by surrounding environment changes, resulting in large displacement and excessive longitudinal uneven settlement deformation, micro-disturbance double-liquid grouting lifting adjustment method is often used. In this grouting lifting adjustment method, the setting of grouting parameters is related to the change of overburden soil pressure caused by the interaction between tunnel and soil. There is no calculation method for predicting the internal force and deformation of tunnel lifting structure in the prior art, which cannot accurately obtain the response characteristics of overburden soil in the gradual lifting process of shield tunnel, and it is difficult to evaluate and estimate the safety of the structure in the tunnel lifting process. At the same time, according to the actual engineering experience, the single lifting amount of the tunnel is small, and the overburden soil has not reached the limit bearing state, which cannot provide a theoretical basis for the safety evaluation of the structure in the grouting process.

[0005] At present, in order to provide a theoretical basis for accurately analyzing the actual earth pressure of the shield tunnel construction period and evaluating the structural safety during the grouting process in the prior art, an active door test device is used to simulate the soil arching effect in the shield tunnel construction. The tunnel excavation is simulated by the sinking of the active door, and the stratum loss caused by the tunnel construction is simulated by the movement of the active door. However, the existing active door test device has the following disadvantages when simulating:

[0006] (10) The existing active door test device mainly uses a flat active door to simulate the stratum loss, which is different from the stratum loss caused by the shield tunnel construction; (11) The front of the active door test device is transparent glass, and the movement of the soil particles can be observed during the test. Due to the boundary effect, the observation results on the front of the test device cannot reflect the actual movement of the soil in the test device; In summary, the existing active door test device has poor simulation effect on the soil arching effect in the shield tunnel construction. SUMMARY

[0007] Therefore, the present application provides a visual active door test device for soil arching effect evolution, which can avoid the difference between the test and the stratum loss caused by the shield tunnel construction, and avoid the boundary effect that the observation results on the front of the test device cannot reflect the actual movement of the soil in the test device, thereby improving the simulation effect on the soil arching effect in the shield tunnel construction.

[0008] The technical scheme of the present application is: a visual active door test device for soil arching effect evolution, comprising a transparent model box, an active door adjusting assembly comprising a semi-circular shell column-shaped active door block and an equal-speed loading instrument, the equal-speed loading instrument is arranged on the inner bottom of the transparent model box, the semi-circular shell column-shaped active door block is horizontally arranged above the equal-speed loading instrument, the opening of the semi-circular shell column-shaped active door block is downwardly arranged, the output end of the equal-speed loading instrument is connected with the semi-circular shell column-shaped active door block, for driving the semi-circular shell column-shaped active door block to move up and down, so as to simulate the stratum loss or grouting uplift through the up-and-down movement of the semi-circular shell column-shaped active door block, two supporting plates are respectively horizontally arranged on the two sides of the semi-circular shell column-shaped active door block, the ends of the two supporting plates away from each other are respectively connected with the transparent model box, and the other ends are respectively abutted with the outer sides of the semi-circular shell column-shaped active door block, the upper side of the supporting plate is flush with the edge of the opening of the semi-circular shell column-shaped active door block, the transparent soil is filled into the transparent model box layer by layer along the vertical direction, and is located on the upper side of the semi-circular shell column-shaped active door block and the supporting plate, so as to constitute the overburden soil of the shield tunnel, thereby realizing the visual test of the progressive response of the shield tunnel to the stratum loss or grouting uplift of the overburden soil.

[0009] Preferably, the test process monitoring assembly further comprises a displacement sensor and a load sensor, which are arranged on the output end of the constant rate of loading instrument to collect the distance value of the up-and-down movement of the semi-cylindrical shell column-shaped movable door block and the load pressure value applied by the constant rate of loading instrument to the semi-cylindrical shell column-shaped movable door block.

[0010] Preferably, the test process monitoring assembly further comprises a matrix thin film pressure sensor, a plurality of LVDT displacement sensors, and a plurality of groups of BW type resistance strain soil pressure sensors. The matrix thin film pressure sensor is arranged on the outside of the semi-cylindrical shell column-shaped movable door block to collect the pressure value on the outside of the semi-cylindrical shell column-shaped movable door block. The plurality of LVDT displacement sensors are arranged in an equidistant array along the length and width of the transparent model box at the top thereof to collect the overlying soil settlement or uplift height value of the shield tunnel. The plurality of groups of BW type resistance strain soil pressure sensors are arranged in an equidistant array along the length and width of the transparent model box at the upper side of each layer of transparent soil and flush with the upper side of each layer of transparent soil to collect the soil stress value of each layer of transparent soil.

[0011] Preferably, the upper side of the matrix thin film pressure sensor is provided with two Teflon membranes, and the two Teflon membranes are sealedly connected to each other.

[0012] Preferably, the test process monitoring assembly further comprises two lasers and two CCD cameras. The two lasers are arranged on the outside of the adjacent two sides of the transparent model box to emit light to form a speckle field in the transparent soil. The two CCD cameras are arranged on the outside and the top of the transparent model box. The CCD camera arranged on the outside of the transparent model box is opposite to one of the lasers to collect the image of the transparent soil.

[0013] Preferably, the movable door adjusting assembly further comprises a rectangular block, which is horizontally arranged between the semi-cylindrical shell column-shaped movable door block and the output end of the constant rate of loading instrument. The rectangular block is flush with and fixedly connected to the outside edge of the mouth of the semi-cylindrical shell column-shaped movable door block. The lower side of the rectangular block is connected to the output end of the constant rate of loading instrument.

[0014] Preferably, two oil-proof sealing rings are horizontally sleeved around the outside of the rectangular block near the upper and lower end faces of the rectangular block, and the oil-proof sealing rings abut against the supporting plate.

[0015] Preferably, the transparent soil is one of transparent sandy soil and transparent clay.

[0016] Preferably, the transparent sandy soil is composed of solid-phase fused quartz sand, No. 15 white mineral oil, and n-dodecane.

[0017] Preferably, the transparent clay is composed of amorphous silica powder, No. 15 white mineral oil and n-dodecane.

[0018] Compared with the prior art, the visual movable door test device for soil arching effect evolution provided by the application uses the semi-circular shell column movable door block, the constant speed loading instrument and the supporting plate, and the transparent soil in cooperation with the transparent model box and the movable door adjusting assembly to simulate the boundary of the shield tunnel by the semi-circular shell column movable door block and the two supporting plates, which is more in line with the boundary conditions of the shield tunnel than the flat movable door, to simulate the stratum loss or grouting uplift by driving the semi-circular shell column movable door block to move up and down by the constant speed loading instrument, so as to avoid the difference between the stratum loss caused by the test and the shield tunnel construction, fill the transparent soil into the transparent model box layer by layer to form the overburden of the shield tunnel, thereby realizing the visual observation of the progressive response of the soil body of the shield tunnel under different stratum loss or expansion, avoiding that the observation results of the front of the test device cannot reflect the actual movement of the soil body in the test device due to the boundary effect, and further improving the simulation effect of the soil arching effect in the shield tunnel construction. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the front view of the movable door test device of the application; Figure 2 is the side view of the movable door test device of the application; Figure 3 is the top view of the movable door test device of the application; Figure 4 is the arrangement schematic view of the semi-circular shell column movable door block and the supporting plate of the application; Figure 5 is the connection schematic view of the matrix type thin film pressure sensor and the Teflon film of the application; Figure 6 is the arrangement schematic view of the laser and the CCD camera of the application; Figure 7 is the flow chart of the test process monitoring assembly of the application. DETAILED DESCRIPTION

[0020] The application provides a visual movable door test device for soil arching effect evolution. Figures 1 to 7 The application will be described below in combination with the structural schematic view.

[0021] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the technical solutions of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0022] Referring to Figure 1 , Figure 4 , Figure 1 is a front view of the activity door test device of the present embodiment, Figure 4 is a schematic view of the arrangement of the semi-circular shell column-shaped activity door block and the supporting plate, a visual activity door test device for soil arching effect evolution, comprising a transparent model box 1, an activity door adjusting assembly comprising a semi-circular shell column-shaped activity door block 5 and an equal-speed loading instrument 10, the equal-speed loading instrument 10 is arranged at the inner bottom of the transparent model box 1, the semi-circular shell column-shaped activity door block 5 is horizontally arranged directly above the equal-speed loading instrument 10, the opening of the semi-circular shell column-shaped activity door block 5 is arranged downward, the output end of the equal-speed loading instrument 10 is connected with the semi-circular shell column-shaped activity door block 5, for driving the semi-circular shell column-shaped activity door block 5 to move up and down, so as to simulate the stratum loss or grouting uplift through the up-and-down movement of the semi-circular shell column-shaped activity door block 5, two supporting plates 7 are respectively horizontally arranged at the two sides of the semi-circular shell column-shaped activity door block 5, the mutually faraway ends of the two supporting plates 7 are respectively connected with the transparent model box 1, and the other ends are respectively abutted with the outer sides of the semi-circular shell column-shaped activity door block 5, the upper side of the supporting plate 7 is flush with the edge of the opening of the semi-circular shell column-shaped activity door block 5, the transparent soil 2 is filled into the transparent model box 1 layer by layer along the vertical direction, and is located at the upper side of the semi-circular shell column-shaped activity door block 5 and the supporting plate 7, so as to constitute the overburden of the shield tunnel, thereby realizing the visual test of the progressive response of the shield tunnel to the stratum loss or grouting uplift of the overburden.

[0023] In the present embodiment, the visual activity door test device for soil arching effect evolution, compared with the existing activity door test device which uses a flat plate activity door to simulate the soil arching effect caused by stratum loss, uses the semi-circular shell column-shaped activity door block 5 and two supporting plates to simulate the stratum loss or grouting uplift of the overburden under the driving of the equal-speed loading instrument 10, which is closer to the stress state change condition of the real circular tunnel stratum loss or grouting process, and realizes a closer simulation of the stratum loss and the real tunnel stratum loss.

[0024] Specifically, by changing the shape of the movable door in the embodiment, different shield tunnel cross-section forms can be simulated. In this way, the shape of the movable door can adopt semi-circular shell column, horseshoe, triangle, rectangle, etc., so as to explore the influence of the shape of the movable door on the simulation of the lowering or lifting of the shield tunnel.

[0025] Specifically, in the test of the progressive response of the shield tunnel to the stratum loss or the grouting lifting of the overlying soil, the key of the tunnel construction simulation is to control the stratum loss, the tunnel excavation is simulated by the sinking of the two supporting plates and the semi-circular shell column movable door block, and the semi-circular shell column movable door block is more in line with the boundary condition.

[0026] Specifically, in most movable door tests, the front of the model box is made of transparent organic glass so that the movement of the soil particles can be visually observed during the test. However, due to the boundary effect, the observation results of the front cannot reflect the actual movement of the soil inside the model box. Therefore, in order to reduce the influence of the boundary effect on the test results, the transparent soil 2 and the transparent model box 1 are matched in the embodiment to realize the visual test of the shield tunnel to the progressive response of the stratum loss or the grouting lifting of the overlying soil, and the observation of the internal displacement of the soil.

[0027] The embodiment can realize the visual measurement of the progressive response of the soil to the stratum loss or the expansion of the shield tunnel, and provides a simulation test device for studying the disturbance mechanism of the soil caused by the stratum loss of the shield tunnel or the progressive lifting of the shield tunnel, the stress state and displacement field change of the soil, the local deformation and progressive shear slip failure of the soil, the load change characteristics of the tunnel, and the development law of the uneven settlement of the ground surface.

[0028] Specifically, the transparent soil in the embodiment is obtained by mixing crystal or powder particle materials with a pore fluid having the same refractive index as the crystal or powder particle materials and expelling air. By adjusting different pre-consolidation pressures, the transparent saturated soil can have similar geotechnical engineering properties as natural soil.

[0029] Specifically, the transparent model box 1 in the embodiment is composed of a tempered glass cover or a tempered glass cylinder and a test table 15, the tempered glass cover or the tempered glass cylinder is vertically arranged on the test table 15 and connected with the test table 15 through flanges, the test table 15 is provided with pulleys 4 around the bottom, which facilitates the fixation or movement of the position of the test table 15, the length, width and height of the tempered glass cover or the tempered glass cylinder are 600*300*700mm, and the thickness of the tempered glass is 20mm. The tempered glass cover or the tempered glass cylinder and the transparent soil 2 are used together to realize the full environmental visualization of the simulation test.

[0030] Specifically, in order to strengthen the stability of the tempered glass cover or the tempered glass cylinder, a triangular reinforcing partition plate 3 is arranged around the tempered glass cover or the tempered glass cylinder, one side of the tempered glass cover or the tempered glass cylinder is provided with a plurality of wire holes, the aperture of the wire hole is 5mm, and the ends of the supporting plates 7 away from each other are fixedly connected with the test table 15 through connecting pieces.

[0031] In order to minimize the influence of the boundary (inner wall) of the transparent model box 1 on the test results, in this embodiment, vaseline is applied to the side wall of the transparent model box 1, plastic film is pasted, and the like, to reduce the friction between the boundary of the transparent model box 1 and the transparent soil 2, and further improve the test accuracy.

[0032] The existing movable door test device cannot obtain the whole process data of the displacement of the movable door and the deformation of the soil by controlling the movable door to move downward to a certain position to collect the corresponding deformation data, which limits the analysis of the evolution law of the soil arching effect.

[0033] As a further optimization scheme, the test process monitoring assembly is further included in this embodiment, and the test process monitoring assembly includes a displacement sensor 9 and a load sensor 11, and the displacement sensor 9 and the load sensor 11 are arranged on the output end of the constant speed loading instrument 10 to collect the distance value of the up-down movement of the semicircular shell column movable door block 5 and the load pressure value of the constant speed loading instrument 10 applied to the semicircular shell column movable door block 5.

[0034] In this embodiment, the displacement sensor 9 and the load sensor 11 of the test process monitoring assembly constitute a movable door displacement and load measurement control system, the distance value of the up-down movement of the semicircular shell column movable door block 5 and the load pressure value of the constant speed loading instrument 10 applied to the semicircular shell column movable door block 5 are collected, so that the whole process data of the displacement of the movable door and the deformation of the soil are obtained, and the analysis of the evolution law of the soil arching effect is avoided.

[0035] When measuring the pressure at the bottom of the movable door, the existing movable door test device arranges a plurality of pressure sensors (single points) at certain intervals, which is difficult to obtain the space-time distribution of the contact pressure of the soil arching effect evolution and the structure interface in the unloading process of the movable door, and further cannot analyze the space-time evolution law of the contact pressure distribution.

[0036] Referring to Figure 2 , Figure 3 , Figure 2 is a side view of the movable door test device of the present embodiment, Figure 3As a further optimization scheme, the test process monitoring assembly in the embodiment further comprises: a matrix type thin film pressure sensor 12, a plurality of LVDT displacement sensors 13, and a plurality of groups of BW type resistance strain soil pressure sensors 14. The matrix type thin film pressure sensor 12 is covered on the outer side of the semi-cylindrical shell column-shaped movable door block 5 to collect the pressure value on the outer side of the semi-cylindrical shell column-shaped movable door block 5. The plurality of LVDT displacement sensors 13 are arranged in an equidistant array along the length and width directions of the transparent model box 1 on the top of the transparent model box 1 to collect the overburden soil settlement or uplift height value of the shield tunnel. The plurality of groups of BW type resistance strain soil pressure sensors 14 are respectively arranged in an equidistant array along the length and width directions of the transparent model box 1 on the upper side of each layer of transparent soil 2 and flush with the upper side of each layer of transparent soil 2 to collect the soil stress value of each layer of transparent soil 2.

[0037] In the embodiment, the pressure value on the outer side of the semi-cylindrical shell column-shaped movable door block 5 is collected by the matrix type thin film pressure sensor 12, the overburden soil settlement or uplift height value of the shield tunnel is collected by the LVDT displacement sensor 13, and the soil stress value of each layer of transparent soil 2 is collected by the BW type resistance strain soil pressure sensor 14. The matrix type thin film pressure sensor 12 and the data collection handle constitute a movable door surface pressure distribution measurement system, the LVDT displacement sensor 13 and the displacement data collection instrument constitute a soil surface settlement measurement system, and the BW type resistance strain soil pressure sensor 14 and the pressure data collection instrument constitute a soil pressure test system. The collected data is processed by using the movable door surface pressure distribution measurement system, the soil surface settlement measurement system, and the soil pressure test system in cooperation with the corresponding application analysis software, and then the stress field of the stratum soil, the soil surface settlement and uplift, and the movable door surface pressure distribution are respectively obtained. Thus, the time and space distribution of the soil arching effect evolution and the contact pressure of the structure interface in the movable door unloading process are obtained, and the time and space evolution law of the contact pressure distribution can be analyzed.

[0038] Specifically, according to the size of the semi-cylindrical shell column-shaped movable door block 5, the size of the matrix type thin film pressure sensor 12 is selected so that the matrix type thin film pressure sensor 12 is uniformly laid on the outer surface of the semi-cylindrical shell column-shaped movable door block 5. A plurality of crossbeams are arranged on the top of the transparent model box 1, the crossbeams are fixedly connected with the test table 15 through the columns at both ends, and the LVDT displacement sensor 13 is arranged on the crossbeams.

[0039] Referring to Figure 5 , Figure 5 It is a connection diagram of the matrix type thin film pressure sensor and the Teflon film. As a further optimization scheme, the upper two sides of the matrix type thin film pressure sensor 12 are respectively provided with Teflon films 22, the Teflon film 22 has a larger area than the matrix type thin film pressure sensor 12, and the edges of the two Teflon films 22 are sealingly connected with each other.

[0040] In this embodiment, the matrix thin film pressure sensor 12 is wrapped with two pieces of 0.1mm thick Teflon film 22, and the edges of the two Teflon films 22 are sealed with transparent tape.

[0041] Referring to Figure 6 , Figure 6 The laser and CCD camera arrangement of this embodiment is shown in the schematic diagram. As a further optimization, the test process monitoring assembly in this embodiment also includes two lasers 19 and two CCD cameras 20. The two lasers 19 are arranged on the outside of the two adjacent sides of the transparent model box 1 to emit sheet light from the side of the transparent model box 1 to form a speckle field in the transparent soil 2. The two CCD cameras 20 are arranged on the outside and on the top of the transparent model box 1. The CCD camera 20 arranged on the outside of the transparent model box 1 is opposite to one of the lasers 19 to capture the image of the transparent soil 2.

[0042] In this embodiment, the laser 19 emits sheet light from the side of the transparent model box 1 to form a speckle field in the transparent soil 2. The image of the transparent soil 2 is captured by the CCD camera 20. The image processing technology of particle image velocimetry (PIV) is used to divide the image, analyze and match the pixels, and determine the transient displacement of the entire flow field. The laser irradiation in the transparent soil can form a speckle field, and the high-precision picture is captured by the CCD camera 20. The displacement field of the soil at different times can be analyzed by combining the PIV technology. This technology is suitable for indoor model test research, and the transparent soil 2 and the particle image velocimetry (PIV) technology can realize non-contact observation of the continuous displacement field inside the soil and eliminate the boundary effect of the model test.

[0043] Referring to Figure 7 , Figure 7 The flow chart of the test process monitoring assembly of this embodiment is shown. The various sensors of the test process monitoring assembly are arranged at the corresponding positions of the test device according to the requirements, and are connected to the acquisition instrument and the computer through the corresponding acquisition interface. The laser 19 is arranged on the side of the transparent model box, and the CCD camera 20 is arranged on the corresponding vertical section. The CCD camera 20 is connected to the computer 21 on which the PIV digital image processing system is installed.

[0044] The test process monitoring assembly is composed of the movable gate displacement and load measurement control system, the soil surface settlement measurement system, the soil internal displacement field measurement system, and the movable gate surface pressure distribution measurement system. The data collected by each subsystem can be displayed in real time on the screen of the computer 21, and is finally used for data analysis. The existing application software is used for data analysis.

[0045] The movable door displacement and load measurement control system comprises a displacement sensor 9, a load sensor 11 and corresponding displacement control data acquisition instrument and load control data acquisition instrument. The displacement sensor 9 and the load sensor 11 are installed at the connecting position of the output end of the constant speed loading instrument 10 and the rectangular block 6, and can measure the displacement of the semicircular shell column movable door block 5 when it is lowered or raised and the load pressure applied on the semicircular shell column movable door block 5 in real time.

[0046] Specifically, the output end of the constant speed loading instrument 10 is connected with the bottom of the rectangular block 6 through a bolt rod 8. The displacement sensor 9 and the load sensor 11 are installed at the end of the bolt rod 8 close to the rectangular block 6 and connected with the rectangular block 6.

[0047] The soil surface settlement measurement system comprises a plurality of LVDT displacement sensors 13 and a displacement data acquisition instrument. The plurality of LVDT displacement sensors 13 are arranged on the top of the transparent model box 1 along the length and width of the transparent model box 1. The displacement data acquisition instrument is connected with the LVDT displacement sensors 13 and the computer 21. The height data of the ground settlement and uplift during the lowering or lifting of the semicircular shell column movable door block 5 can be measured and displayed on the screen of the computer 21 in real time.

[0048] The soil internal displacement measurement system comprises a PIV digital image processing system, a laser 19 and a CCD camera 20. The laser 19 is arranged on the side of the transparent model box 1. The CCD camera 20 is used to shoot the two-dimensional image of a certain section of the transparent soil layer under the sheet light source. The image gray and the soil displacement field are matched by the PIV digital image processing application software connected with the computer 21, so as to obtain the soil displacement field of the section of the soil layer during the lowering or lifting of the semicircular shell column movable door block 5. The velocity field is obtained by dividing the displacement field by time.

[0049] The soil pressure test system comprises a plurality of BW type resistance strain soil pressure sensors 14 and a pressure data acquisition instrument. The BW type resistance strain soil pressure sensors 14 are connected with the computer 21 through the acquisition instrument. The BW type resistance strain soil pressure sensors 14 are horizontally buried in different layers of the transparent soil. The soil pressure test system is used to measure the stress state change of the soil layer during the lowering or lifting of the semicircular shell column movable door block 5.

[0050] The movable door surface pressure distribution measurement system comprises a matrix type thin film pressure sensor 12 and a data acquisition handle and I-Scan software. One end of the data acquisition handle is connected to the matrix type thin film pressure sensor 12, and the other end is connected to the computer 21 running the I-Scan software. The size of the matrix type thin film pressure sensor 12 is selected according to the size of the outer surface of the semicircular shell column movable door block 5, and the matrix type thin film pressure sensor 12 is uniformly laid on the outer surface of the semicircular shell column movable door block 5. The pressure distribution of the outer surface of the semicircular shell column movable door block 5 during the lowering or lifting of the semicircular shell column movable door block 5 can be obtained.

[0051] The matrix thin film pressure sensor 12, the LVDT displacement sensor 13 and the BW type resistance strain soil pressure sensor 14 need to be calibrated in the transparent soil 2 respectively before the test, and the position of the CCD camera is calibrated.

[0052] The visual movable door test device for soil arching effect evolution in the above embodiment can be used in different properties of strata and different shield depths, and can be used in a visual environment by means of a movable door displacement and load measurement control system, a soil surface settlement measurement system, a soil internal displacement field measurement system and a movable door surface pressure distribution measurement system, so as to observe and record the stress state of strata soil, the displacement field change and the development trend of uneven ground surface settlement of the shield tunnel under different strata loss or expansion, and provide theoretical guidance for tunnel settlement deformation prediction and operation and maintenance and optimization of construction control measures, which has far-reaching significance for the development of urban rail transit and underground engineering.

[0053] As a further optimization scheme, the movable door adjusting assembly in the embodiment further includes a rectangular block 6, which is horizontally arranged between the semicircular shell column movable door block 5 and the output end of the constant rate of loading apparatus 10, is flush with and fixedly connected to the outer side edge of the mouth of the semicircular shell column movable door block 5, and is connected to the output end of the constant rate of loading apparatus 10.

[0054] In the embodiment, the rectangular block 6 arranged at the bottom of the semicircular shell column movable door block 5 enables the constant rate of loading apparatus 10 to stably drive the semicircular shell column movable door block 5 to move up and down, and further improves the accuracy of the test.

[0055] Specifically, the outer diameter of the semicircular shell column movable door block 5 is 200 mm, the maximum vertical progress is 100 mm, the width of the rectangular block 6 is 200 mm, and the two are connected by bolts. During the test, the constant rate of loading apparatus 10 connected to the lower end of the bolt rod 8 is controlled to descend or ascend. Here, different displacements of the semicircular shell column movable door block 5 represent different degrees of strata loss or grouting uplift. Therefore, the response process of various physical quantities in the entire process can be analyzed by measuring the corresponding physical quantities by using the following measurement systems at different displacements.

[0056] As a further optimization scheme, the outer sides of the rectangular block 6 are respectively horizontally sleeved with two oil-proof sealing rings 16 around the circumferences thereof, and the oil-proof sealing rings 16 are located close to the upper and lower end faces of the rectangular block 6 and abut against the supporting plate 7.

[0057] In the embodiment, the two oil-proof sealing rings 16 sleeved on the outer sides of the rectangular block 6 can play an oil-proof role when the semicircular shell column movable door block 5 moves up and down between the two oil-proof sealing rings 16.

[0058] As a further optimization scheme, the transparent soil 2 in the embodiment is one of transparent sand and transparent clay.

[0059] The transparent soil 2 in the embodiment can use transparent sand or transparent clay, so that the corresponding transparent soil 2 is selected according to the soil layer where the shield tunnel is located, and the transparent soil 2 is suitable for sand and clay layers and has good universality.

[0060] As a further optimization scheme, the transparent sand in the embodiment is composed of solid-phase fused quartz sand, No. 15 white mineral oil and n-dodecane.

[0061] In the embodiment, the particle size of the solid-phase fused quartz sand is 0.5mm-1mm, the density of the solid-phase fused quartz sand is 60%, and the refractive index of the solid-phase fused quartz sand at 20℃ is 1.4585. In order to achieve the best transparency effect, the No. 15 white mineral oil and the n-dodecane are liquid phases, and the refractive index of the mixed oil is also 1.4585. By trial selection, the mass ratio of n-dodecane and No. 15 white mineral oil is 16:1, the volume ratio of quartz sand and mixed oil is controlled to be 1:1, and the transparent sand is prepared by mixing the solid-phase fused quartz sand, the No. 15 white mineral oil and the n-dodecane.

[0062] As a further optimization scheme, the transparent clay in the embodiment is composed of amorphous silicon powder, No. 15 white mineral oil and n-dodecane.

[0063] In the embodiment, the particle size of the amorphous silicon powder is 2000 mesh (6.5μm), the refractive index of the amorphous silicon powder at 20℃ is 1.4476, and the mass ratio of n-dodecane and No. 15 white mineral oil is 1:2.5. The mass ratio of amorphous silicon powder and mixed oil is 1:5, and the transparent clay is prepared by mixing the amorphous silicon powder, the No. 15 white mineral oil and the n-dodecane.

[0064] The properties of the prepared transparent sand and transparent clay are similar to those of real sand and clay, and can be used to simulate sand and clay layers, and carbon nanotube particles are added as tracer particles.

[0065] The operation method of the visualization activity door test device for soil arching effect evolution provided in the embodiment is first divided into a test in a sand layer and a test in a clay layer according to different simulated strata. For the test in the sand layer, the following steps are included: Step one: Before the test, the transparent sand similar to the properties of the real soil is prepared by taking the basic physical and mechanical properties of the soil as control indexes, and the specific operation is as follows: (1) Select solid-phase fused quartz sand with a particle size of 0.5mm-1mm, and control the density to be 60%; (2) First, n-dodecane and No. 15 white mineral oil are mixed in a mass ratio of 16:1, and stirred uniformly to obtain mixed oil; (3) Solid fused quartz sand is mixed with the mixed oil in a volume ratio of 1:1 to obtain transparent sand, and carbon nanotube particles are added as tracer particles; (4) The just-mixed transparent sand is quickly and uniformly stirred with a high-power stirring rod; (5) The preliminarily stirred transparent sand is placed in a self-made vacuum stirring device for vacuumizing and secondary stirring; (6) The transparent sand required for the test is obtained by standing; Step two: calibrate and debug the matrix thin film pressure sensor, BW type resistance strain soil pressure sensor, and LVDT displacement sensor, check the connection of the BW type resistance strain soil pressure sensor to be buried in the soil layer, and number it, and uniformly lay the matrix thin film pressure sensor on the outer surface of the semi-circular shell column movable door block after surface sealing and oil-proof treatment; Step three: arrange the laser on the side of the transparent model box, set the CCD camera on the corresponding vertical section to prepare for shooting two-dimensional images, and calibrate and debug the PIV digital image processing system, and connect the equal-speed loading instrument, displacement sensor and load sensor to the rectangular block through the bolt rod; Step four: fill the prepared transparent sand into the transparent model box according to the set density requirement, symmetrically and uniformly, bury a number of numbered BW type resistance strain soil pressure sensors in the layer after each layer is added, and compact and level them, and fill the soil layer by layer uniformly to the specified burial depth, and install the LVDT displacement sensor on the beam above the transparent model box; Step five: when all the measurement systems are debugged, wait for the test instrument data to be stable, record the readings of each pressure sensor and displacement sensor, which are used as the initial readings during each test, set the displacement sensor and load sensor to zero, control the equal-speed loading instrument to drop (or lift) to the set ground loss or grouting process corresponding height according to the test condition, simulate different ground loss or grouting process of shield tunnel, and record the displacement of the load sensor every 0.05mm in the range of 0 to 0.2mm, every 0.1mm in the range of 0.2 to 1mm, every 0.5mm in the range of 1 to 3mm, and every 1mm in the range of 3 to 5mm; Step six: During the test, the data of the matrix film pressure sensor is analyzed to obtain the variation law of the earth pressure on the semi-cylindrical movable door block and the distribution of the earth pressure, the LVDT displacement sensor is used to measure the development of the ground settlement or uplift, the BW type resistance strain soil pressure sensor is used to measure the stress state variation of the stratum soil, the laser is used to emit a sheet of light from the side of the model box into the transparent soil containing carbon nanotube particles, the CCD camera is used to capture the distribution and movement images of the carbon nanotube particles in the transparent soil during the lowering (or raising) of the semi-cylindrical movable door block, the data processing software is used to control the image acquisition on the computer, and the variation law of the surrounding soil displacement field is obtained by further processing the image data. Step seven: After each working condition test is completed, the readings of the sensors of the measurement system should be recorded after being stable, and then the main test instruments are removed, the soil is excavated, the sensors are taken out, the test parameters are adjusted, and another set of working condition tests is repeated.

[0066] For the test in the clay layer, the specific test steps are similar to those of the transparent sand soil, but the transparent clay needs to be pre-layered and consolidated, and steps one and three need to be adjusted accordingly. The specific adjustments are as follows: Adjusted step one: Before the test, the transparent clay similar to the real soil in terms of basic physical and mechanical properties is prepared according to the ratio, and the specific operation is as follows: (1) Select the solid amorphous silicon powder with a particle size of 2000 mesh (6.5 μm); (2) First, mix n-dodecane and No. 15 white mineral oil according to a mass ratio of 1:2.5, and stir evenly to obtain a mixed oil; (3) Slowly mix the solid amorphous silicon powder with the mixed oil at a mass ratio of 1:5 to obtain transparent clay, and add carbon nanotube particles as tracer particles; (4) Use a high-power stirring rod to quickly and uniformly stir the just-mixed transparent clay; (5) Put the preliminarily stirred transparent soil into the self-made vacuum stirring device for vacuumizing and secondary stirring; (6) After standing, the transparent clay required for the test is obtained; Adjusted step three: Put the transparent clay after vacuum stirring and standing in adjusted step one into a vacuum consolidation device with the same size as the transparent model box, layer by layer according to the selected layering height, and consolidate under the selected consolidation pressure. The specific operation of consolidation is as follows: (1) Put the transparent clay to be consolidated into the vacuum consolidation device, level the upper surface of the transparent clay, and measure the height H of the transparent clay filling at this time; (2) lay the force transmission film flat on the surface of the transparent clay, lay a steel pad plate on the upper surface, use a measuring head fixed on a magnetic dial gauge to press against the steel pad plate, measure and record the initial reading h1 of the dial gauge; (3) calculate the required weight to be applied for the pile load consolidation according to the required consolidation pressure value; (4) read the dial gauge reading every hour after oil discharge, when the difference between the current reading and the last reading is less than 0.0005H, consider that the consolidation is completed.

[0067] In particular, when consolidating the lowermost layer (the semicircular shell column-shaped movable door block), a model of the same size as the movable door needs to be placed at the corresponding position of the vacuum consolidation device for filling, and after each layer is consolidated, it is transferred to the transparent model box, and similarly, a plurality of BW type electric resistance strain soil pressure sensors are embedded and leveled in each layer, and then the soil is filled to the specified burial depth, and the LVDT displacement sensor is installed on the beam above the transparent model box.

[0068] The visual movable door test device for soil arching effect evolution has the following advantages: 1) The transparent soil and PIV and other visualization technologies can realize the complete visualization of the stratum soil body response of the shield tunnel under different stratum loss or expansion; 2) The test device of the present application can be used in the test research method to observe and record in detail the progressive evolution characteristics of the overlying soil pressure of the tunnel and the change law of the ground settlement during the shield tunneling process, and analyze and research the stratum load-displacement change curve, the stress state of the soil body and the displacement field change in the whole process; 3) By changing the filling height of the transparent soil in the transparent model box, the situation of the shield tunnel under different burial depths is simulated, so as to study the progressive evolution mechanism of the overlying soil pressure of the tunnel, the stress state of the stratum soil body and the displacement field under different burial depths; 4) By changing the shape of the semicircular shell column-shaped movable door block, the influence of the shape of the movable door on the simulation of the shield tunnel lowering or lifting is explored; 6) The device has comprehensive design functions, reasonable structure layout and can be reused.

[0069] The above disclosure is only the preferred specific embodiment of the present application, but the embodiments of the present application are not limited thereto, and any changes that can be thought of by those skilled in the art should fall within the protection scope of the present application.

Claims

1. A visual movable gate test device for the evolution of soil arching effect, characterized in that, include; Transparent model box (1); The movable gate adjustment assembly includes a semi-circular shell cylindrical movable gate block (5) and a constant velocity loading device (10). The constant velocity loading device (10) is located at the bottom inside the transparent model box (1). The semi-circular shell cylindrical movable gate block (5) is horizontally located directly above the constant velocity loading device (10). The opening of the semi-circular shell cylindrical movable gate block (5) is arranged downward. The output end of the constant velocity loading device (10) is connected to the semi-circular shell cylindrical movable gate block (5) to drive the semi-circular shell cylindrical movable gate block (5) to move up and down, so as to simulate formation loss or grouting up by moving the semi-circular shell cylindrical movable gate block (5) up and down. Two support plates (7) are horizontally arranged on both sides of the semi-circular shell cylindrical movable door block (5). The ends of the two support plates (7) that are far apart from each other are connected to the transparent model box (1), and the other ends are respectively abutted against the outer side of the semi-circular shell cylindrical movable door block (5). The upper side of the support plate (7) is flush with the edge of the opening of the semi-circular shell cylindrical movable door block (5). Transparent soil (2) is filled into the transparent model box (1) layer by layer in the vertical direction and is located on the upper side of the semi-circular shell columnar movable gate block (5) and support plate (7) to form the overburden of the shield tunnel, thereby realizing the visualization test of the progressive response of the shield tunnel to the overburden under stratum loss or grouting lifting.

2. The visual movable gate test device for the evolution of soil arching effect according to claim 1, characterized in that, Also includes: The test process monitoring component includes a displacement sensor (9) and a load sensor (11). The displacement sensor (9) and the load sensor (11) are respectively set on the output end of the constant velocity loading instrument (10) to collect the distance value of the vertical movement of the semi-circular shell cylindrical movable gate block (5) and the load pressure value applied by the constant velocity loading instrument (10) to the semi-circular shell cylindrical movable gate block (5).

3. The visual movable gate test device for the evolution of soil arching effect according to claim 2, characterized in that, The test process monitoring components also include: a matrix-type thin-film pressure sensor (12), multiple LVDT displacement sensors (13), and multiple sets of BW-type resistance strain gauge earth pressure sensors (14). The matrix-type thin-film pressure sensor (12) covers the outside of the semi-circular shell cylindrical movable gate block (5) to collect the pressure value on the outside of the semi-circular shell cylindrical movable gate block (5). Multiple LVDT displacement sensors (13) are arranged in an array at equal intervals along the length and width of the transparent model box (1) on its top to collect the settlement or uplift height value of the overlying soil of the shield tunnel. Multiple BW-type resistance strain gauge earth pressure sensors (14) in each set are arranged in an array at equal intervals along the length and width of the transparent model box (1) on the upper side of each layer of transparent soil (2) and are flush with the upper side of each layer of transparent soil (2) to collect the soil stress value of each layer of transparent soil (2).

4. The visual movable gate test device for the evolution of soil arching effect according to claim 3, characterized in that, The matrix-type thin-film pressure sensor (12) has Teflon membranes (22) on both sides of its upper side. The Teflon membranes (22) have a larger area than the matrix-type thin-film pressure sensor (12), and the edges of the two Teflon membranes (22) are sealed to each other.

5. The visual movable gate test device for the evolution of soil arching effect according to claim 2, characterized in that, The test process monitoring component also includes two lasers (19) and a CCD camera (20). The two lasers (19) are respectively arranged on the outer sides of the transparent model box (1) to emit sheet light from the side of the transparent model box (1) into the transparent soil (2) to form a speckle field. The two CCD cameras (20) are respectively arranged on the outside and top of the transparent model box (1). The CCD camera (20) arranged on the outside of the transparent model box (1) is directly opposite to one of the lasers (19) to acquire images of the transparent soil (2).

6. The visual movable gate test device for the evolution of soil arching effect according to claim 1, characterized in that, The movable door adjustment assembly further includes a rectangular block (6), which is horizontally positioned between the semi-circular shell cylindrical movable door block (5) and the output end of the constant velocity loading device (10). The rectangular block (6) is flush with and fixedly connected to the outer edge of the opening of the semi-circular shell cylindrical movable door block (5). The lower side of the rectangular block (6) is connected to the output end of the constant velocity loading device (10).

7. The visual movable gate test device for soil arching effect evolution according to claim 6, characterized in that, Two oil-proof sealing rings (16) are respectively horizontally sleeved around the outer side of the rectangular block (6) and located near the upper and lower end faces of the rectangular block (6). The oil-proof sealing rings (16) abut against the support plate (7).

8. The visual movable gate test device for the evolution of soil arching effect according to claim 1, characterized in that, The transparent soil (2) is one of transparent sand or transparent clay.

9. The visual movable gate test device for the evolution of soil arching effect according to claim 1, characterized in that, The transparent sand is composed of solid-phase fused silica sand, No. 15 white mineral oil, and n-dodecane.

10. The visual movable gate test device for the evolution of soil arching effect according to claim 1, characterized in that, The transparent clay is composed of amorphous silica powder, No. 15 white mineral oil, and n-dodecane.

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