A model test device and method for studying the effect of stratum loss rate on surface subsidence

Abstract

The present invention provides a model test device and a method for using the device for studying the effect of stratum loss rate on surface subsidence. The model test device includes a sand particle holding device, a test support platform, a tunnel shrinkage simulation device, a front transparent plate, a rear transparent plate, a strong magnet, and a camera. The test support platform is respectively provided with a front transparent plate and a rear transparent plate. The sand particle holding device is mounted on the test support platform. A through hole is provided at the bottom of the sand particle holding device. One end of the tunnel shrinkage simulation device is mounted within the sand particle holding device, and the other end is exposed through the through hole. The strong magnet is used to adsorb and fix the tunnel shrinkage simulation device located within the sand particle holding device to an appropriate position within the sand particle holding device. The camera is used to photograph and record the morphological changes and subsidence of the soil subsidence trough above the tunnel shrinkage simulation device. The present invention has the following beneficial effects: the model test device is simple, and the loading and unloading of soil particles does not require repeated disassembly of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering, and in particular to a model test device and a use method thereof that can be used to study the influence of stratum loss rate on surface settlement. Background Art

[0002] Most existing test devices used to study the relationship between ground loss rate and ground deformation after shield tunneling are based on sand test model boxes. The sand within the model box is passed through a sand spreading device and an embedded tunnel simulator to simulate tunnel excavation within the sand. A monitoring system then monitors the sand within the box and analyzes the data. However, the tunnel devices used in previous test devices were unable to control the specific shrinkage rate of the shield tunnel. Furthermore, most test methods involved complex procedures. Loading and unloading soil particles required repeated disassembly of the device, and the sand filling process also struggled to achieve significant pre-consolidation due to the natural fall of sand particles from the same height. Consequently, test results were unclear and failed to effectively simulate ground loss caused by tunnel shrinkage.

[0003] Therefore, it is urgent to propose a simple and practical model test device that can be used to study the influence of formation loss rate on surface subsidence.

[0004] Problems and defects of existing technologies:

[0005] 1. The test method is cumbersome and the device needs to be disassembled repeatedly during the loading and unloading of soil particles;

[0006] 2. It is difficult to achieve the natural fall of sand particles from the same height during the filling process, which leads to greater early consolidation;

[0007] 3. It is impossible to control the specific shrinkage rate of the shield tunnel. Summary of the Invention

[0008] The present invention provides a model test device that can be used to study the influence of stratum loss rate on surface settlement, comprising a sand and soil particle holding device, a test support platform, a tunnel shrinkage simulation device, a front transparent plate, a rear transparent plate, a strong magnet, and a camera. The front transparent plate and the rear transparent plate are respectively installed on the front and back of the test support platform. The sand and soil particle holding device is installed on the test support platform. A through hole is provided at the bottom of the sand and soil particle holding device. One end of the tunnel shrinkage simulation device is installed in the sand and soil particle holding device, and the other end passes through the through hole and is exposed to the outside. The strong magnet is used to adsorb and fix the tunnel shrinkage simulation device located in the sand and soil particle holding device to an appropriate position of the sand and soil particle holding device. The camera is used to shoot and record the morphological change process and settlement of the covering settlement trough above the tunnel shrinkage simulation device.

[0009] As a further improvement of the present invention, the sand and soil particle holding device includes a first block, a second block, and a model part, the second block is installed on the top of the model part, the first block is installed on the second block, and the through hole is provided at the bottom of the model part; the model part includes a first panel, a second panel, a third panel, and a fourth panel, the second panel and the third panel are respectively installed on both sides of the first panel, the fourth panel is installed at the bottom of the first panel, and the second block is installed on the top of the first panel; the sand and soil particle holding device also includes a rubber plug, the rubber plug is installed at the through hole, and the rubber plug is provided with an opening.

[0010] As a further improvement of the present invention, the test support platform includes a first support block, a second support block, and a first support plate, and the first support block and the second support block are respectively installed on both sides of the first support plate; the test support platform also includes a third support block and a fourth support block, and the third support block and the fourth support block are respectively installed on both sides of the first support plate. The third support block and the fourth support block are connected to the second support block; the test support platform also includes a pad block, and the pad block is placed on the top of the first support block and the second support block; the test support platform also includes a first support rod and a second support rod, the first support rod is installed on the top of the first support block, and the second support rod is installed on the top of the second support block; the test support platform also includes a first pad plate and a second pad plate, the first pad plate is installed between the first support block and the first support plate, and the second pad plate is installed between the second support block and the first support plate; the test support platform also includes wheels, and the wheels are installed below the third support block and the fourth support block; the test support platform also includes a first ruler and a second ruler, the first ruler is installed on the front of the first support block, and the second ruler is installed on the front of the second support block.

[0011] As a further improvement of the present invention, the raising block is a magnet; the magnet is a concave magnet, and the number of the concave magnets is multiple, and every two of the concave magnets are combined into a group and sequentially installed on the first support rod and the second support rod, and the number of the concave magnets can be appropriately adjusted according to the test requirements; the model test device also includes a plurality of fixing parts, and the fixing parts are used to fix the first ruler, the second ruler, and the front transparent plate on the first support block and the second support block, and to fix the rear transparent plate on the first support block and the second support block; the first support block and the second support block are respectively provided with a plurality of first through holes, the first ruler and the second ruler are respectively provided with a plurality of third through holes corresponding to the first through holes, the front transparent plate is respectively provided with a plurality of second through holes corresponding to the first through holes on both sides, and the rear transparent plate is respectively provided with a plurality of second through holes corresponding to the first through holes on both sides. There are multiple fourth through holes corresponding to the first through holes, and the fixing parts include multiple hexagonal nuts and multiple bolts, one of the bolts sequentially extends into the third through hole on the first ruler, the second through hole on the left side of the front transparent plate, the first through hole on the first support block, and the fourth through hole on the left side of the rear transparent plate, and the hexagonal nuts are installed at both ends of the bolt to fix the first ruler, one side of the front transparent plate, and one side of the rear transparent plate to the first support block, and the other bolt sequentially extends into the third through hole on the second ruler, the second through hole on the right side of the front transparent plate, the first through hole on the second support block, and the fourth through hole on the right side of the rear transparent plate, and the hexagonal nuts are installed at both ends of the bolt to fix the second ruler, the other side of the front transparent plate, and the other side of the rear transparent plate to the second support block.

[0012] As a further improvement of the present invention, the tunnel contraction simulation device includes an airbag bag, a test block, a metal block, a first water pipe, a second water pipe, a first syringe, a second syringe, a first water stop clamp, and a second water stop clamp. The metal block is installed inside the test block, and the airbag bag is installed on the outer surface of the test block; a first interface and a second interface are provided on the airbag bag, and one end of the first water pipe and the second water pipe are connected to the first interface and the second interface respectively, and the other end of the first water pipe and the second water pipe are connected to the first syringe and the second syringe respectively through the opening on the rubber stopper; the first water stop clamp is installed between the first water pipe and the first syringe, and the second water stop clamp is installed between the second water pipe and the second syringe.

[0013] As a further improvement of the present invention, the airbag bag is provided with a plurality of trapezoidal prism air chambers, each air chamber is connected by a channel, and the air chamber can expand after being injected with water; the airbag bag is a trapezoidal airbag bag, the airbag bag is about 320 mm long and 100 mm wide, and the airbag bag is made of foam material; the test block is a cylindrical acrylic test block with an inner diameter of 40 mm and an outer diameter of 100 mm; the metal block is a cylindrical metal block with a diameter of 40 mm; the diameters of the first water pipe and the second water pipe are 3 mm respectively; the first syringe and the second syringe are large syringes of 200 ml or more.

[0014] As a further improvement of the present invention, the model test device also includes an outer slide groove sheet, which includes a first outer slide groove sheet, a second outer slide groove sheet, a third outer slide groove sheet, and a fourth outer slide groove sheet. The first outer slide groove sheet and the second outer slide groove sheet are respectively installed on the outside of the second panel, and the third outer slide groove sheet and the fourth outer slide groove sheet are respectively installed on the outside of the third panel; the model test device also includes a support block slide, which includes a left support block slide and a right support block slide. The left support block slide is installed on the right side of the first support block, and the right support block slide is installed on the left side of the second support block; the outer slide groove sheet and the support block slide are metal groove sheets with pulleys.

[0015] As a further improvement of the present invention, the first block and the second block are respectively rectangular metal blocks; the first block is 1400 mm long, 100 mm wide, and 30 mm high; the second block is 990 mm long, 100 mm wide, and 100 mm high; the through hole size is 30 mm*30 mm; the model part is made of acrylic material; the first panel, the second panel, the third panel, and the fourth panel are integrally formed.

[0016] As a further improvement of the present invention, the through hole is arranged at the center position of the fourth panel, and the through hole is square; the strong magnet is horseshoe-shaped; the front transparent plate and the rear transparent plate are transparent glass plates; the camera includes a camera control system; the first support block, the second support block, the third support block, and the fourth support block are respectively rectangular metal blocks; the dimensions of the first support block and the second support block are respectively 8000mm high*80mm long*100mm wide; the dimensions of the first support plate are 1280mm*180mm*20mm; the dimensions of the third support block and the fourth support block are respectively 80mm*500mm*40mm; the first raising plate and the second raising plate are concave metal plates; the first support rod and the second support rod are respectively metal screws; the exposed length of the first support rod and the second support rod is 200mm; the thickness of the magnet is 20mm; the first raising plate and the second raising plate are concave metal plates; the sand particle holding device is easy to disassemble and can move up and down.

[0017] The present invention also discloses a method for using a model test device for studying the influence of formation loss rate on surface subsidence, comprising sequentially performing the following steps:

[0018] Step 1: Installation of the model test device; overlap the test support platform with the sand and soil particle holding device, put all the multiple magnets on the first support block and the second support block, and at the same time place the tunnel contraction simulation device in the sand and soil particle holding device, and fix it to the appropriate position of the sand and soil particle container through the strong magnet outside the front transparent plate or the rear transparent plate. During the process, pay attention to pass the first water pipe and the second water pipe of the tunnel contraction simulation device through the rubber stopper of the opening. One end of the first water pipe and the second water pipe are connected to the airbag bag, and the other end is connected to the first syringe and the second syringe respectively through the first water stop clamp and the second water stop clamp. The rubber stopper larger than the opening is adhered to the fourth panel, and the first nut and the second nut on both sides of the second block are tightened.

[0019] Step 2: Inject water to simulate tunnel pre-contraction; remove the first syringe and draw water into the syringe, taking care to ensure that no bubbles are generated in the syringe during the pumping process. Disconnect the second syringe and start injecting water into the tunnel contraction simulation device until no bubbles are observed in the first water pipe, the second water pipe, and the airbag. Drain the air from the second syringe and connect it, close the first and second water-stop clamps to ensure that the device is leak-proof.

[0020] Step 3: Make a sample of the sand system; slowly pour the sand particles into the device in batches according to the sand filling amount set for each time, observe the first ruler and the second ruler on both sides, and each time the sand of the set height is poured in, remove the required number of magnets above the first support block and the second support block to make the sand body holding device in the device fall naturally through the first outer slide plate with pulleys, the second outer slide plate, the third outer slide plate, the fourth outer slide plate, the left support block slide plate, and the right support block slide plate. After the fall is stable, pour the sand particles of the set height again, and repeat the cycle until the sand particles in the device reach the test cover thickness.

[0021] Step 4: Remove the strong magnet outside the model test device and let the model test device stand still until the tunnel contraction simulation structure in the device is stable and the sand particles do not slide.

[0022] Step 5: Set up the camera and turn it on to prepare for recording. The recording content should include the morphological changes of the soil settlement trough above the tunnel shrinkage simulation device and the final maximum settlement value. The camera image must include rulers on both sides to facilitate subsequent computer image analysis.

[0023] Step 6: Pump water to simulate tunnel shrinkage; open only the second water-stop clamp on one side of the second syringe. Simultaneously, start the camera to take continuous photos or record video. Then, use the second syringe to pump water from the second water pipe and the airbag bag. Record the amount of water pumped using the scale on the second syringe. This value is the tunnel shrinkage test value. The corresponding tunnel shrinkage rate can be calculated based on the tunnel diameter and the lateral thickness of the sand particle holding device in the device. The calculation formula under the conditions of this device size is as follows:

[0024]

[0025] η is tunnel shrinkage rate; V is pumping volume, in ml.

[0026] Step 7: Change the covering depth, repeat the test, and make multiple records. If the fluidity of the sand used in the test is good, the device can be left in place. By removing the magnets above the first and second support blocks, the sand holding device can be made to slide downward to increase the covering depth. Water can be injected and pumped out to repeat the test.

[0027] Step 8: Analyze and process the photographic records or video recordings before and after the second syringe pumping, and compare and study the changes in the morphology of the upper cover soil settlement trough and the maximum surface settlement value during the process of tunnel shrinkage at different cover soil depths.

[0028] The beneficial effects of the present invention are: 1. The model test device of the present invention is simple, and the process of loading and unloading soil particles does not require repeated disassembly of the device; 2. The model test device of the present invention can realize the natural fall of sand particles from the same height during the sand filling process without causing large premature consolidation; 3. The model test device of the present invention can control the specific shrinkage rate of the shield tunnel shrinkage. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is an overall structural diagram of the model test device of the present invention;

[0030] Figure 2 This is a structural diagram of the sand particle holding device of the present invention;

[0031] Figure 3 This is a structural diagram of the test support platform of the present invention;

[0032] Figure 4 This is an exploded structural diagram of the tunnel contraction simulation device of the present invention;

[0033] Figure 5 This is an assembly structure diagram of the tunnel contraction simulation device of the present invention;

[0034] Figure 6 This is a structural diagram of the outer slide plate with a small pulley of the present invention;

[0035] Figure 7 This is a structural diagram of the support block slide of the present invention;

[0036] Figure 8 This is a structural diagram of a tunnel shrinkage simulation device installed in a sand and soil particle receiving device of the present invention;

[0037] Figure 9 It is the overall structural diagram of the test support platform of the present invention. DETAILED DESCRIPTION

[0038] The present invention provides a model test device and an installation and use method that can be used to study the influence of stratum loss rate on surface settlement. It uses a drawer-like method to keep sand and soil particles falling from the same horizontal height and control the burial depth of tunnel cover. It simulates the shrinkage caused by the tunnel excavation process by injecting and pumping water through a syringe. It uses a camera to record the surface settlement morphology and settlement depth above the container, effectively simulating stratum loss in tunnel excavation projects, and then analyzing and studying the influence of different shrinkage rates and different burial depths on the horizontal surface settlement depth and settlement trough morphology.

[0039] like Figure 1 、 Figure 7As shown, the present invention discloses a model test device that can be used to study the influence of stratum loss rate on surface settlement, comprising three main parts: a sand and soil particle holding device that can be easily disassembled and moved up and down, a test support platform, and a tunnel contraction simulation device, as well as various small parts installed when the device is installed. The test support platform is respectively equipped with a front transparent plate 41 and a rear transparent plate 42. The sand and soil particle holding device is installed on the test support platform. A through hole 6 is provided at the bottom of the sand and soil particle holding device. One end of the tunnel contraction simulation device is installed in the sand and soil particle holding device, and the other end passes through the through hole 6 and is exposed to the outside. The strong magnet 43 is used to adsorb and fix the tunnel contraction simulation device located in the sand and soil particle holding device to an appropriate position of the sand and soil particle holding device. The shooting device is used to shoot and record the morphological changes and settlement of the soil settlement trough above the tunnel contraction simulation device.

[0040] like Figure 2 As shown, the first body: the sand and soil particle holding device consists of a first block 1 (a rectangular metal block) with a length of 1400mm, a width of 100mm, and a height of 30mm; a second block 2 (a rectangular metal block) with a length of 990mm, a width of 100mm, and a height of 100mm; and an integrally formed acrylic mold 60 composed of four panels (a first panel 4, a second panel 3, a third panel 5, and a fourth panel 61). The fourth panel 61 has a 30mm*30mm square opening in the center. The acrylic mold 60 is spliced with the second block 2, which is then spliced with the first block 1 to form the sand and soil particle holding device. The sand and soil particle holding device can be customized by a processing factory through integrated splicing.

[0041] like Figure 3 、 Figure 8As shown, the second main body: the test support platform is composed of two 8000mm*80mm*100mm first support blocks 9 (rectangular metal blocks), a second support block 10 (rectangular metal block), a 1280mm*180mm*20mm first support plate 13 (metal plate), an 80mm*500mm*40mm third support block 14 (rectangular metal block), a fourth support block 15 (rectangular metal block), a first padding plate 11 (concave metal plate), a second padding plate 12 (concave metal plate), four wheels fixed at the bottom (first wheel 16, second wheel 17, third wheel 18, fourth wheel 19) and two first support rods 7 (long metal screws) and second support rods 8 (long metal screws) of moderate length. Among them, the first support block 9 and the second support block 10 are respectively punched with 6 first through holes for the bolts 40 to pass through, and the first support rod 7 (long metal screw) is embedded on the top, and the exposed length of the first support rod 7 (long metal screw) is 200 mm. At the same time, the first support block 9 (rectangular metal block) and the second support block 10 (rectangular metal block) pass through the first support plate (metal plate) and are respectively spliced with the third support block 14 (rectangular metal block) and the fourth support block 15 (rectangular metal block). Four wheels (first wheel 16, second wheel 17, third wheel 18, and fourth wheel 19) are fixed with screws below the third support block 14 (rectangular metal block) and the fourth support block 15 (rectangular metal block). Two concave metal plates (first raising plate 11 and second raising plate 12) are lightly placed on the first support plate 13 (metal plate) to raise it so that the water injection pipes (first water pipe 23 and second water pipe 24) can pass through to form a test support platform. The test support platform can be customized by integrated splicing at a processing factory.

[0042] like Figure 4-5As shown, the third main body: the tunnel contraction simulation device consists of a trapezoidal airbag bag 20, two large syringes with a capacity of more than 200 ml (a first syringe 25 and a second syringe 26), two thin water pipes with a diameter of about 3 mm (a first water pipe 23 and a second water pipe 24), a metal block 22 (a cylindrical iron block) with a length of 100 mm and a diameter of 40 mm, a cylindrical acrylic test block 21 with a length of 100 mm, an inner diameter of 40 mm and an outer diameter of 100 mm, and two water-stopping clamps (a first water-stopping clamp 45 and a second water-stopping clamp 46). The metal block 22 fits neatly within the cylindrical acrylic test block 21, simulating the excavated tunnel surface. The trapezoidal airbag 20 is attached to the outer diameter of the cylindrical acrylic test block 21 and connected to the thin water pipes (first water pipe 23 and second water pipe 24) via interfaces. The first syringe 25 and second syringe 26 are connected to the other ends of the first water pipe 23 and second water pipe 24, respectively. The first waterstop clamp 45 is installed between the first water pipe 23 and the first syringe 25, and the second waterstop clamp 46 is installed between the second water pipe 24 and the second syringe 26, forming a sealed structure. Waterproof tape or other tools can be used at the interface connection locations to ensure the sealing of the device. The metal block 22 can include iron, aluminum, copper, or other metal blocks, preferably iron.

[0043] The trapezoidal airbag bag 20 in the tunnel contraction simulation device is a foam airbag that is about 320 mm long and 100 mm wide, and has an air inlet and an air outlet (the first interface 211 is the air inlet and the second interface 212 is the air outlet). It is divided into 12 trapezoidal prism air chambers, and the 12 air chambers are connected by small channels. At the same time, it can ensure the smooth flow of liquid in them, and after water is injected, the air chamber can expand laterally to a maximum height of about 9 mm.

[0044] like Figure 6 As shown, the combined installation of the sand and soil particle holding device and the test support platform also requires the installation of an outer slide plate with a small pulley (including a first outer slide plate 30, a second outer slide plate 31, a third outer slide plate 32, and a fourth outer slide plate 33), and the outer slide plate is made of metal material; a support block slide plate with a small pulley (a left support block slide plate 34, a right support block slide plate 35, and the left support block slide plate 34 and the right support block slide plate 35 have the same structure), and the support block slide plate is made of metal material; wherein, The first outer slide plate 30 and the second outer slide plate 31 are fixed to the second panel 3 (acrylic panel) on the left side of the sand and soil particle holding device with screws, the third outer slide plate 32 and the fourth outer slide plate 33 are fixed to the third panel 5 (right acrylic panel) of the sand and soil particle holding device with screws, the left support block slide 34 is fixed to the first support block 9 on the left side of the test support platform with screws, and the right support block slide 35 is fixed to the second support block 10 on the right side of the test support platform with screws.

[0045] There are also a front transparent plate 41 and a rear transparent plate 42 with small openings in front and behind the test support platform (the front transparent plate 41 and the rear transparent plate 42 are transparent glass plates) and a first ruler 37 and a second ruler 38, which are fixed to the first support block 9 and the second support block 10 on both sides through hexagonal nuts 39 and bolts 40. Among them, transparent glass plates (front transparent plate 41 and rear transparent plate 42) are fixed on the front and back of the test support platform, but only the front transparent plate is in contact and fixed with the first ruler 37 and the second ruler 38.

[0046] Fourteen magnets 36 are placed above the first support block 9 and the second support block 10 on either side of the test support platform. Each magnet is identical in size and 20 mm thick. The magnets 36 serve to elevate the sand and soil particle containment device. During the soil loading process, the magnets 36 can be gradually removed to ensure that the soil particles fall from the same height as much as possible. The number of magnets 36 can be increased as appropriate based on test requirements. The magnets 36 are concave magnets.

[0047] The model test device also includes a strong magnet 43 and a camera 44 for photographing. The strong magnet 43 is required to ensure that when the device is not filled with soil particles, the magnetic force is sufficient to fix the tunnel contraction simulation device without sliding. The camera 44 also includes a camera control system so that the surface settlement morphology and settlement height above the container can be truly recorded using a video camera.

[0048] The present invention also discloses a method for using a model test device for studying the influence of formation loss rate on surface subsidence, comprising sequentially performing the following steps:

[0049] Step 1: Installation of the model test device; overlap the test support platform and the sand and soil particle holding device, put all the multiple magnets 36 on the first support block 9 and the second support block 10, and at the same time place the tunnel contraction simulation device in the sand and soil particle holding device, and fix it to the appropriate position of the sand and soil particle container through the strong magnet 43 outside the front transparent plate 41 or the rear transparent plate 42. During the process, pay attention to passing the first water pipe 23 and the second water pipe 24 of the tunnel contraction simulation device through the open rubber stopper 29. One end of the first water pipe 23 and the second water pipe 24 are connected to the airbag bag 20, and the other end is connected to the first syringe 25 and the second syringe 26 respectively through the first water stop clamp 45 and the second water stop clamp 46. The rubber stopper 29 larger than the opening is adhered to the fourth panel 61, and the first nut 27 and the second nut 28 on both sides of the second block 2 are fastened.

[0050] Step 2: Inject water to simulate tunnel pre-contraction; remove the first syringe 25, draw water into the syringe, and pay attention to ensuring that no bubbles are generated in the syringe during the water extraction process. Disconnect the second syringe 26 and start injecting water into the tunnel contraction simulation device until no bubbles are observed in the first water pipe 23, the second water pipe 24 and the airbag bag 20. Drain the air from the second syringe 26 and connect it, close the first water stop clamp 45 and the second water stop clamp (46) to ensure that the device is leak-proof.

[0051] Step 3: Make samples of sand and soil; to ensure that the sand and soil fall from the same height as much as possible during the sand filling process, pour the sand and soil particles slowly into the device in batches according to the filling amount of about 20 mm each time, observe the first ruler 37 and the second ruler 38 on both sides, and remove two pieces of magnets 36 above the first support block 9 and the second support block 10 every time 20 mm of sand and soil are poured in, so that the sand and soil body holding device in the device as a whole can fall naturally through the first outer slide 30, the second outer slide 31, the third outer slide 32, the fourth outer slide 33, the left support block slide 34, and the right support block slide 35 with pulleys. After the fall is stable, pour in sand and soil particles of about 20 mm in height again, and repeat the cycle until the sand and soil particles in the device reach the test cover thickness.

[0052] Step 4: Remove the strong magnet 43 outside the model test device and let the model test device stand still until the tunnel contraction simulation structure in the device is stable and the sand particles do not slide.

[0053] Step 5: Set up the camera 44 and turn it on to prepare for recording. The recording content includes the morphological changes of the soil settlement trough above the tunnel shrinkage simulation device and the final maximum settlement value. The camera image must include rulers on both sides to facilitate subsequent computer image analysis.

[0054] Step 6: Pump water to simulate tunnel shrinkage; open only the second water-stop clamp 46 on one side of the second syringe 26, and simultaneously turn on the camera 44 to take continuous photos or videos. Then, use the second syringe 26 to extract water from the second water pipe 24 and the airbag 20. Record the amount of water pumped using the scale on the second syringe 26. This value is the tunnel shrinkage test value. The corresponding tunnel shrinkage rate can be calculated based on the tunnel diameter and the lateral thickness of the sand particle holding device in the device. The calculation formula under the conditions of this device size is as follows:

[0055]

[0056] η-tunnel shrinkage rate; V-pumping volume, unit is ml;

[0057] Step 7: Change the soil covering depth, repeat the test, and record multiple times. If the test sand has good fluidity, the device can be left unassembled. By removing the magnets 36 above the first support block 9 and the second support block 10, the sand body holding device can be slid downward to increase the soil covering depth. Water is then injected and pumped out to repeat the test.

[0058] Step 8: Analyze and process photographs or videos taken before and after the second syringe 26 pumps water, and compare the changes in the overburden settlement trough morphology and maximum ground settlement values during the tunnel shrinkage process at different overburden depths. Note: The first syringe 25 only serves to introduce water and does not participate in shrinkage control.

[0059] The beneficial effects of the present invention are as follows: 1. The model test device of the present invention is simple, and the process of loading and unloading soil particles does not require repeated disassembly of the device; 2. The model test device of the present invention can realize the natural fall of sand particles from the same height during the sand filling process without causing large premature consolidation; 3. The model test device of the present invention can control the specific shrinkage rate of the shield tunnel shrinkage.

[0060] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A model test device for studying the effect of stratum loss rate on surface subsidence, characterized by: The invention comprises a sand and soil particle accommodating device, a test support platform, a tunnel contraction simulation device, a front transparent plate (41), a rear transparent plate (42), a strong magnet (43), and a camera (44). The front transparent plate (41) and the rear transparent plate (42) are respectively installed at the front and rear of the test support platform. The sand and soil particle accommodating device is installed on the test support platform. A through hole (6) is provided at the bottom of the sand and soil particle accommodating device. One end of the tunnel contraction simulation device is installed in the sand and soil particle accommodating device, and the other end passes through the through hole (6) and is exposed to the outside. The strong magnet (43) is used to adsorb and fix the tunnel contraction simulation device located in the sand and soil particle accommodating device to an appropriate position of the sand and soil particle accommodating device. The camera (44) is used to photograph and record the morphological change process and settlement of the soil subsidence trough above the tunnel contraction simulation device. The sand and soil particle accommodating device comprises a first block (1), a second block (2), and a mold part (60); the second block (2) is mounted on the top of the mold part (60); the first block (1) is mounted on the second block (2); and the through hole (6) is provided at the bottom of the mold part (60); the mold part (60) comprises a first panel (4), a second panel (3), a third panel (5), and a fourth panel (61); the second panel (3) and the third panel (5) are mounted on both sides of the first panel (4), the fourth panel (61) is mounted on the bottom of the first panel (4), and the second block (2) is mounted on the top of the first panel (4); the sand and soil particle accommodating device further comprises a rubber plug (29); the rubber plug (29) is mounted at the through hole (6), and the rubber plug (29) is provided with an opening; The test support platform includes a first support block (9), a second support block (10), and a first support plate (13), and the first support block (9) and the second support block (10) are respectively installed above both sides of the first support plate (13); the test support platform also includes a third support block (14) and a fourth support block (15), and the third support block (14) and the fourth support block (15) are respectively installed below both sides of the first support plate (13), and the third support block (14) is connected to the first support block (9), and the fourth support block (15) is connected to the second support block (10); the test support platform also includes a padding block, and the padding block is placed on the top of the first support block (9) and the second support block (10); the test support platform also includes a first support rod (7) and a second support rod (8), The first support rod (7) is installed at the top of the first support block (9), and the second support rod (8) is installed at the top of the second support block (10); the test support platform also includes a first raising plate (11) and a second raising plate (12), the first raising plate (11) is installed between the first support block (9) and the first support plate (13), and the second raising plate (12) is installed between the second support block (10) and the first support plate (13); the test support platform also includes wheels, and the wheels are installed below the third support block (14) and the fourth support block (15); the test support platform also includes a first ruler (37) and a second ruler (38), the first ruler (37) is installed on the front of the first support block (9), and the second ruler (38) is installed on the front of the second support block (10).

2. The model test device according to claim 1, characterized in that: The padding block is a magnet (36); the magnet (36) is a concave magnet, and the number of the concave magnets is multiple, and every two of the concave magnets are combined into a group and sequentially installed on the first support rod (7) and the second support rod (8), and the number of the concave magnets can be appropriately adjusted according to the test requirements; the model test device also includes a plurality of fixing members, and the fixing members are used to fix the first ruler (37), the second ruler (38), and the front transparent plate (41) on the first support block (9) and the second support block (10), and to fix the rear transparent plate (42) on the first support block (9) and the second support block (10); the first support block (9) and the second support block (10) are respectively provided with a plurality of first through holes, the first ruler (37) and the second ruler (38) are respectively provided with a plurality of third through holes corresponding to the first through holes, the front transparent plate (41) is respectively provided with a plurality of second through holes corresponding to the first through holes on both sides, and the rear transparent plate (42) is respectively provided with a plurality of fourth through holes corresponding to the first through holes on both sides. The fixing member includes a plurality of hexagonal nuts (39) and a plurality of bolts (40), wherein one of the bolts (40) is sequentially inserted into the third through hole on the first ruler (37), the second through hole on the left side of the front transparent plate (41), the first through hole on the first support block (9), and the fourth through hole on the left side of the rear transparent plate (42), and the hexagonal nuts (39) are installed at both ends of the bolt (40) to fix the first ruler (37), one side of the front transparent plate (41), and one side of the rear transparent plate (42) to the On the first support block (9), another bolt (40) is sequentially extended into the third through hole on the second ruler (38), the second through hole on the right side of the front transparent plate (41), the first through hole on the second support block (10), and the fourth through hole on the right side of the rear transparent plate (42). The hexagonal nuts (39) are installed at both ends of the bolt (40) to fix the second ruler (38), the other side of the front transparent plate (41), and the other side of the rear transparent plate (42) on the second support block (10).

3. The model test device according to claim 1, characterized in that: The tunnel contraction simulation device comprises an air bag (20), a test block (21), a metal block (22), a first water pipe (23), a second water pipe (24), a first syringe (25), a second syringe (26), a first water stop clamp (45), and a second water stop clamp (46); the metal block (22) is installed inside the test block (21); the air bag (20) is installed on the outer surface of the test block (21); the air bag (20) is provided with a first interface (211) and a second interface (212); the first water pipe (23), the second syringe (25), the second syringe (26), a first water stop clamp (45), and a second water stop clamp (46); One end of the second water pipe (24) is connected to the first interface (211) and the second interface (212) respectively, and the other ends of the first water pipe (23) and the second water pipe (24) are connected to the first syringe (25) and the second syringe (26) respectively through the opening on the rubber stopper (29); the first water stop clamp (45) is installed between the first water pipe (23) and the first syringe (25), and the second water stop clamp (46) is installed between the second water pipe (24) and the second syringe (26).

4. The model test device according to claim 3, characterized in that: The airbag bag (20) is provided with a plurality of trapezoidal prism air chambers, each of which is connected by a channel, and the air chambers can expand after being injected with water; the airbag bag (20) is a trapezoidal airbag bag, the airbag bag (20) is about 320 mm long and 100 mm wide, and the airbag bag (20) is made of foam material; the test block (21) is a cylindrical acrylic test block with an inner diameter of 40 mm and an outer diameter of 100 mm; the metal block (22) is a cylindrical metal block with a diameter of 40 mm; the first water pipe (23) and the second water pipe (24) have diameters of 3 mm respectively; the first syringe (25) and the second syringe (26) are large syringes with a capacity of more than 200 ml.

5. The model testing device according to claim 1, characterized in that: The model test device also includes an outer slide plate, the outer slide plate includes a first outer slide plate (30), a second outer slide plate (31), a third outer slide plate (32), and a fourth outer slide plate (33), the first outer slide plate (30) and the second outer slide plate (31) are respectively installed on the outside of the second panel (3), the third outer slide plate (32) and the fourth outer slide plate (33) are respectively installed on the outside of the third panel (5); the model test device also includes a support block slide plate, the support block slide plate includes a left support block slide plate (34) and a right support block slide plate (35), the left support block slide plate (34) is installed on the right side of the first support block (9), and the right support block slide plate (35) is installed on the left side of the second support block (10); the outer slide plate and the support block slide plate are metal groove plates with pulleys.

6. The model testing device according to claim 1, characterized in that: The first block (1) and the second block (2) are respectively rectangular metal blocks; the first block (1) is 1400 mm long, 100 mm wide and 30 mm high; the second block (2) is 990 mm long, 100 mm wide and 100 mm high; the through hole size is 30 mm*30 mm; the model part (60) is made of acrylic material; the first panel (4), the second panel (3), the third panel (5) and the fourth panel (61) are integrally formed.

7. The model testing device according to claim 2, characterized in that: The through hole is provided at the center of the fourth panel (61), and the through hole is square; the strong magnet (43) is horseshoe-shaped; the front transparent plate (41) and the rear transparent plate (42) are transparent glass plates; the camera (44) includes a camera control system; the first support block (9), the second support block (10), the third support block (14), and the fourth support block (15) are rectangular metal blocks; the first support block (9) and the second support block (10) are respectively 8000mm high*80mm long*100mm wide; the first support plate (13) is 1280mm* 180mm*20mm; the dimensions of the third support block (14) and the fourth support block (15) are 80mm*500mm*40mm respectively; the first raising plate (11) and the second raising plate (12) are concave metal plates; the first support rod (7) and the second support rod (8) are metal screws respectively; the exposed length of the first support rod (7) and the second support rod (8) is 200mm; the thickness of the magnet (36) is 20mm; the first raising plate (11) and the second raising plate (12) are concave metal plates; the sand particle holding device is easy to disassemble and can move horizontally up and down.

8. A method for using a model test device for studying the effect of formation loss rate on surface subsidence, characterized in that: It includes performing the following steps in sequence: Step 1: Installation of the model test device; the test support platform is overlapped with the sand and soil particle holding device, and the multiple magnets (36) on the first support block (9) and the second support block (10) are all placed. At the same time, the tunnel contraction simulation device is placed in the sand and soil particle holding device, and is adsorbed and fixed to the appropriate position of the sand and soil particle container by the strong magnet (43) outside the front transparent plate (41) or the rear transparent plate (42). During the process, it is noted that the first water pipe (23) and the second water pipe (24) of the tunnel contraction simulation device are passed through the rubber stopper (29) of the opening. One end of the first water pipe (23) and the second water pipe (24) are connected to the air bag (20), and the other end is connected to the first syringe (25) and the second syringe (26) respectively through the first water stop clamp (45) and the second water stop clamp (46). The rubber stopper (29) larger than the opening is adhered to the fourth panel (61), and the first nut (27) and the second nut (28) on both sides of the second block (2) are fastened; Step 2: inject water to simulate tunnel pre-contraction; remove the first syringe (25), pump water into the syringe, and pay attention to ensuring that no bubbles are generated in the syringe during the pumping process. Disconnect the second syringe (26) and start injecting water into the tunnel contraction simulation device until no bubbles are observed in the first water pipe (23), the second water pipe (24) and the air bag (20). Drain the air from the second syringe (26) and connect it, close the first water stop clamp (45) and the second water stop clamp (46) to ensure that the device is leak-proof. Step 3: making a sand sample; slowly pouring sand particles into the device in batches according to the sand filling amount set each time, observing the first ruler (37) and the second ruler (38) on both sides, and removing the required number of blocks of the magnets (36) above the first support block (9) and the second support block (10) each time the sand of the set height is poured in, so that the sand body holding device in the device as a whole can fall naturally through the first outer slide plate (30) with pulleys, the second outer slide plate (31), the third outer slide plate (32), the fourth outer slide plate (33), the left support block slide plate (34), and the right support block slide plate (35), and pouring sand particles of the set height again after the fall is stable, and repeating the cycle until the sand particles in the device reach the test cover thickness; Step 4: Remove the strong magnet (43) outside the model test device and let the model test device stand until the tunnel contraction simulation structure in the device is stable and the sand particles do not slide; Step 5: Set up a camera (44) for filming and turn it on, and prepare to film and record. The filming record content includes the morphological change process of the soil settlement trough above the tunnel contraction simulation device and the final maximum settlement value. The camera image must include rulers on both sides to facilitate subsequent computer image analysis; Step 6: Pumping water to simulate tunnel contraction; only open the second water-stopping clamp (46) on one side of the second syringe (26), open the second water-stopping clamp (46) and simultaneously turn on the camera (44) to take continuous photos or videos, then use the second syringe (26) to extract water from the second water pipe (24) and the air bag (20), and record the amount of water pumped by the scale on the second syringe (26). This value is the tunnel contraction test value. The corresponding tunnel contraction rate can be calculated by the tunnel diameter and the lateral thickness of the sand particle holding device in the device. The calculation formula under the size conditions of this device is as follows: η - tunnel shrinkage; V-pumping volume, in ml; Step 7: Change the soil covering depth, repeat the test, and record multiple times. If the fluidity of the test sand is good, the device can be left unassembled. By removing the magnets (36) above the first support block (9) and the second support block (10), the sand body receiving device can be slid downward to increase the soil covering depth, and water can be injected and pumped out to repeat the test. Step 8: Analyze and process the photographic records or video recordings before and after the second syringe (26) pumps water, and compare and study the changes in the morphology of the upper cover soil settlement trough and the maximum surface settlement value during the process of tunnel shrinkage at different cover soil depths.

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