CN112229981A - Device for simulating comprehensive influence of foundation pit excavation and multi-gradient precipitation on tunnel - Google Patents
Device for simulating comprehensive influence of foundation pit excavation and multi-gradient precipitation on tunnel Download PDFInfo
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- 238000009412 basement excavation Methods 0.000 title claims abstract description 39
- 238000001556 precipitation Methods 0.000 title claims abstract description 32
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 150
- 239000002689 soil Substances 0.000 claims abstract description 61
- 238000012360 testing method Methods 0.000 claims abstract description 31
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- 229910001220 stainless steel Inorganic materials 0.000 claims description 3
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- 239000004746 geotextile Substances 0.000 claims description 2
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Abstract
The invention provides a device for simulating comprehensive influence of foundation pit excavation and multi-gradient precipitation on a tunnel, which mainly comprises a model box, a tunnel structure system, an underground water control system, a foundation pit structure system and a measuring system: a foundation pit structure and a tunnel structure are arranged, a pressure-bearing water layer is simulated by utilizing sandy soil, a pressure-bearing water head of the pressure-bearing water layer is simulated by a groundwater control system, and various data in the test process are collected in real time by combining a measurement system. Through the system, the influence of the coupling effect of foundation pit excavation and pressure reduction precipitation on the proximity tunnel can be simulated, the influence of the multi-gradient pressure reduction precipitation of the foundation pit on the regional seepage field is researched, and the evaluation of the influence of the local seepage of the tunnel or the foundation pit on the structure safety is carried out.
Description
Technical Field
The invention belongs to the fields of civil construction, tunnel and underground space engineering and environmental engineering, and particularly relates to a device for simulating comprehensive influence of foundation pit excavation and multi-gradient precipitation on a tunnel.
Background
The urban traffic system is developed rapidly, the problem that the overground space cannot meet the requirement of traffic line expansion is more and more obvious, and the development of underground space becomes a necessary trend of urban development in the region. In recent years, foundation pit engineering in coastal areas along rivers has the characteristics of depth, large size, near size and tightness, and the influence of foundation pit excavation on the surrounding environment is more and more complicated. The underground water level in coastal areas along rivers is high, mostly sedimentary river floodbeach mucky soil and cohesive soil, the stratum is complex and changeable, and the stratum often contains a shallow water layer and a plurality of confined aquifers. When the deep foundation pit excavation is carried out in the area, the confined aquifer is required to be subjected to pressure reduction and precipitation frequently, and the coupling effect of the foundation pit excavation and the pressure reduction and precipitation tends to cause deformation of the surrounding soil layer, so that the long-term operation safety of the existing tunnel is influenced. Therefore, how to evaluate the coupling effect of excavation and pressure reduction and precipitation has important significance on ensuring the construction safety of the foundation pit engineering and the long-term operation safety of the existing close-proximity tunnel.
Through the research on technical documents, a great deal of research is carried out on the influence of foundation pit dewatering or foundation pit excavation on a proximity tunnel at home and abroad, various simulation equipment such as water tanks and soil boxes are developed, and physical simulation tests are carried out on the problems of ground settlement environment caused by foundation pit excavation or foundation pit dewatering, the problems of deformation control of existing structures, pollutant migration and the like, but most of the model equipment are one-dimensional or two-dimensional flow simulation of underground water without distinguishing confined aquifers and water barriers, or simulation of single underground structures such as only foundation pits or tunnels. For example, chinese patent document No. CN110221042A describes a device for simulating the coupling effect between the stress field of excavation of a foundation pit and the underground seepage field, but the lateral water source supply condition of the device cannot satisfy the water head control for the confined water layer, and the device does not consider the arrangement of a flexible tunnel structure, so that the influence of the coupling effect between excavation of the foundation pit and pressure reduction and precipitation on the tunnel cannot be simulated. In view of the above, there is an urgent need to develop a device for simulating the comprehensive influence of excavation of a foundation pit and multi-gradient precipitation on a tunnel so as to further explore the engineering problems.
Disclosure of Invention
In order to solve the problems, the invention discloses a device for simulating comprehensive influence of foundation pit excavation and multi-gradient dewatering on a tunnel, which can simulate the influence of a stress field and a seepage field coupling effect generated by the foundation pit excavation and the multi-gradient dewatering on a close-connected tunnel and solve the technical problem that the existing test device cannot well simulate the comprehensive influence of the foundation pit excavation and the multi-gradient dewatering on the existing tunnel.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a device for simulating comprehensive influence of foundation pit excavation and multi-gradient precipitation on a tunnel comprises a model box, a tunnel structure system, an underground water control system, a foundation pit structure system and a measuring system;
a sandy soil layer and a cohesive soil layer are arranged in the model box at intervals, wherein the sandy soil layer simulates a confined aquifer, and the cohesive soil layer simulates a relative water-resisting layer;
the tunnel structure system and the foundation pit structure system are correspondingly arranged in the soil layer according to the relative position, the embedding depth (excavation depth), the enclosing form and the like;
the underground water control system controls the water heads of different aquifers by adjusting the position of the annular water pipe and the size of the water supply head; the system also comprises a dewatering well and a recharging well, wherein the dewatering well and the recharging well are arranged in corresponding areas according to simulated working conditions;
the measuring system comprises a testing element and a data acquisition system, wherein the testing element is arranged in the tunnel structure system, the foundation pit structure system, the underground water control system and the soil layer, monitors the dynamic change of each part in real time and transmits data to the data acquisition system.
Furthermore, in the invention, side wall holes are distributed on four sides of the model box, the holes are communicated with external water pipes so as to simulate different groundwater supply conditions, and idle holes can be used as water pressure monitoring points. Meanwhile, a tunnel structure arrangement area formed by splicing a plurality of pieces of organic glass with the same area is divided on the front surface and the rear surface of the model box, side wall holes in the organic glass in the area are arranged and unified in other areas of the model box, and the organic glass blocks with the tunnel sections which are chiseled out can be repeatedly used in different working conditions.
Further, in the invention, the tunnel structure system is formed by connecting a plurality of sections of tunnel models through flexible rubber rings so as to simulate the differential deformation of two sides of a tunnel deformation joint. Each tunnel model is made of particle concrete, for example, a double-layer galvanized wire netting is arranged in the concrete, and a leakage area can be arranged at a specific position of the tunnel model according to requirements so as to simulate the influence of tunnel seepage on a seepage field. In addition, the section form, size and whether the cross-over tunnel is the overpass tunnel can be arranged according to the simulation working condition.
Further, in the invention, the enclosure wall in the foundation pit structure system is made of particle concrete with a built-in double-layer galvanized wire netting, the secondary water stop wall is made of plain particle concrete, and the waist beam and the support are made of a wooden frame and are embedded in the soil body together with the underground diaphragm wall structure. The enclosure wall and the secondary water stop wall are buried deeply, the distance between the enclosure wall and the secondary water stop wall, the foundation pit supporting form and the like are arranged according to the simulation working condition. In addition, a leakage area can be arranged at a specific position of the enclosure wall according to the requirement so as to simulate the influence of the leakage of the enclosure wall on the precipitation of the foundation pit.
Furthermore, the underground water control system comprises an annular water pipe, a water head control water tank, a booster pump, a flow meter, a pressure gauge, a dewatering well and a recharge well. The water pipes are arranged on the inner sides of the annular water pipes and are connected with side wall holes on the model box, the annular water pipes are connected with the side wall holes on the model box at the same height through the water pipes, and the side, facing the soil, of each connecting water pipe is wrapped with a stainless steel filter screen. The water head controls the height of the water tank to be lifted, the water tank is connected with a water inlet at the outer side of the annular water pipe through a water pipe, and a flow meter and a pressure gauge are arranged on the connected water pipe; if the water tank cannot meet the requirement of water supply pressure only by adopting the lifting water head control, the booster pump can be combined to supply water, and the power of the booster pump is dynamically adjusted through the pressure gauge.
Furthermore, in the invention, PVC pipes are adopted for the dewatering well and the recharging well, filtering holes are drilled in the corresponding filtering areas, the geotechnical cloth is bound by using iron wires outside the filtering holes to form a filter screen, and the pipe bottoms are blocked by rubber plugs; in the foundation pit dewatering process, the height of the water head control box is adjusted, so that the size of the boundary water head of the model, the reading of the flow meter at the water inlet and the reading of the flow meter of the dewatering well are stable, and the stable seepage field is formed by the model.
Further, in the present invention, the test element includes a micro displacement meter, an osmometer, an earth pressure meter, a piezometer tube, a resistivity probe and a strain gauge. The miniature displacement meter, the osmometer, the earth pressure meter, the pressure measuring pipe and the resistivity probe are buried in different positions in the earth; the strain gauge is adhered to different positions of the tunnel structure system and the foundation pit structure system. The data acquisition system mainly comprises an automatic data acquisition instrument and an automatic resistivity tester, the miniature displacement meter, the osmometer, the earth pressure meter, the pressure measuring tube and the strain gauge are respectively connected with the automatic data acquisition instrument through leads, and the resistivity probe is connected with the automatic resistivity tester through leads. Through the cooperation of various test elements and automatic data acquisition, real-time dynamic monitoring can be carried out in the model box.
The invention has the beneficial effects that:
the test device solves the problem that the comprehensive effect of foundation pit excavation and precipitation on the tunnel is difficult to simulate for a long time, and can simulate various water flow pressure conditions by randomly adjusting the height of the box body of the confined water head control water tank and adjusting the positions of the annular water pipes in multiple stages; the simulation of multi-gradient pressure reduction and precipitation of the foundation pit can be realized through the buried depth of the enclosure wall and the second-stage water stop wall and the distance between the enclosure wall and the second-stage water stop wall; by replacing organic glass in the tunnel region, simulation of different tunnel section forms, section sizes and embedding depths can be realized. The device has practical significance for researching the influence of the coupling effect of foundation pit excavation and pressure reduction and precipitation on the adjacent tunnel engineering, the influence of the multi-gradient pressure reduction and precipitation of the foundation pit on the regional seepage field, the evaluation of the safety influence of the local seepage of the tunnel (foundation pit) on the tunnel (foundation pit) structure and the like. The whole testing device is high in modular design degree, strong in controllability, rich in functions, capable of simulating various working conditions and easy to operate and use.
Drawings
FIG. 1 is a three-dimensional schematic view of a mold box of the present invention;
FIG. 2 is a top view of a mold box of the present invention;
FIG. 3 is a schematic longitudinal section of a mold box according to the invention;
FIG. 4 is a schematic view of a tunnel region of the model of the present invention;
FIG. 5 is a schematic cross-sectional view of an organic glass spliced channel steel in a tunnel region according to the invention;
FIG. 6 is a schematic diagram of a tunnel structure of the model of the present invention.
List of reference numerals:
1 is a model box; 2 is a tunnel structure; 3, a foundation pit enclosure wall structure; 4, a secondary water stop wall structure; 5 is a dewatering well; 6 is a recharging well; 7 is an annular water pipe; 8 is a water supply valve; 9 is a flow meter; 10 is a pressure gauge; 11 water head control water supply tank; 12 is a connecting water pipe; 13 is a side wall hole of the mold box; 14 is organic glass in a tunnel region; 15 is a flexible rubber ring; 16 is a pressure water layer; 17 is a water-resisting layer; 18 is a micro displacement meter; 19 is an osmometer; 20 is a strain gauge; 21 is a piezometer tube; 22 is a soil pressure meter; 23 is a resistivity probe; 24 is a lead; 25 is a DataTaker automatic data acquisition instrument; 26 is an automatic resistivity tester; 27 is an I-shaped channel steel; 28 is a double-groove slide rail; and 29 is a tunnel leakage area.
Detailed Description
The present invention will be further illustrated with reference to the accompanying drawings and specific embodiments, which are to be understood as merely illustrative of the invention and not as limiting the scope of the invention. It should be noted that the terms "front," "back," "left," "right," "upper" and "lower" used in the following description refer to directions in the drawings, and the terms "inner" and "outer" refer to directions toward and away from, respectively, the geometric center of a particular component.
As shown in the figure, the device for simulating the comprehensive influence of the excavation of the foundation pit and the multi-gradient dewatering on the tunnel, disclosed by the invention, is characterized in that a model box is organically combined with five modules, namely a tunnel structure system, an underground water control system, a foundation pit structure system and a measuring system, so that the simulation of the comprehensive influence of the excavation of the foundation pit and the multi-gradient dewatering on the existing tunnel is realized: the model box is a carrier of each module; the tunnel structure system and the foundation pit structure system are correspondingly arranged in the soil layer according to the relative position, the embedding depth (excavation depth), the enclosing form and the like; controlling the distribution of water heads at each position in the soil body by adjusting the thickness and the distribution of sandy soil and controlling the position of a ring-shaped water pipe in a groundwater control system, the size of a water supply water head and the amount of water pumping (dropping); the measuring system completes dynamic tests of water level, structural stress, deformation and the like in the test process.
As shown in fig. 1, the model box 1 is made of organic glass into a cuboid, and the length, width and height of the cuboid are 3.5 mx 2 m; the side wall of the model box is provided with a side wall hole 13, the aperture is 2cm, and the arrangement transverse and longitudinal distance is 20cm x 20 cm; the side wall holes 13 of the model box can be connected with the connecting water pipe 12 to be used as an external water source inlet channel, can also be externally connected with a vertical water pipe to measure a water head at the position, can also be used as a wire outlet, and can be sealed by a rubber plug when not in use.
Five soil bodies of cohesive soil (a relative water-resisting layer 17), sandy soil (a confined aquifer 16), cohesive soil (a relative water-resisting layer 17), sandy soil (a confined aquifer 16) and cohesive soil (a relative water-resisting layer 17) can be layered from top to bottom in the model box 1 according to simulation requirements; the thickness of each layer of soil can be adjusted according to the simulation working condition, but the side wall hole 13 of the model box is required to be ensured in the thickness range of each layer of soil, and the side wall hole is used for controlling the water head pressure of each layer of soil by a later-stage underground water control system.
Symmetrically arranging a tunnel structure arrangement area of 1.4 mx 1.4m on the front and back surfaces of the model box 1, and splicing the tunnel structure arrangement area by 16 organic glasses 14 with the area of 34 mx 34 cm; the organic glass 14 in the tunnel region is horizontally overlapped by a double-groove slide rail 28, and water leakage is prevented by sealant; the vertical joint of the organic glass 14 in the tunnel region is bordered by an I-shaped channel steel 27, and water leakage is prevented by sealant; the arrangement of the side wall holes on the organic glass 14 in the tunnel region is unified with other regions of the model box, the organic glass 14 at the corresponding position is selected to chisel the tunnel section according to the form of the tunnel section, the size of the section and the embedding depth, and the tunnel structure 2 is arranged between the two tunnel sections.
The tunnel structure 2 is formed by connecting a plurality of sections of tunnel models through flexible rubber rings 15, each tunnel model is made of particle concrete, and a double-layer galvanized wire netting is arranged in the particle concrete; the section form, section size, buried depth, tunnel line shape and whether the tunnel is a multilayer interchange tunnel can be adjusted according to the simulation working condition; a leakage area 29 can be arranged at a specific part of the tunnel structure 2 according to requirements so as to simulate the tunnel leakage condition; the strain gauges 20 are adhered to different positions of the top, the side wall and the bottom of the inner wall of the tunnel structure 2, and lead wires of the strain gauges to the automatic data acquisition instrument through the side wall holes 13 of the mold box.
The enclosure wall 3 in the foundation pit structure system is made of particle concrete with a built-in double-layer galvanized wire netting, the secondary water stop wall 4 is made of plain particle concrete, and the waist beam and the support are made of a wooden frame and are embedded in the soil body together with the enclosure wall 3. The enclosure wall 3 and the secondary water stop wall 4 are arranged according to the simulated working condition, such as the buried depth, the distance between the two walls, the foundation pit supporting form and the like; in addition, a leakage area can be arranged at a specific position of the enclosure wall 3 according to the requirement so as to simulate the influence of the leakage of the enclosure wall 3 on the precipitation of the foundation pit.
The underground water control system comprises an annular water pipe 7, a pressure-bearing water head control water tank 11, a flow meter 9, a pressure meter 10, a dewatering well 5 and a recharging well 6. Each layer of soil body corresponds to an annular water pipe 7 which is made of a PVC pipe, and the corners are connected by adopting a bent double-pass pipe; if the hydraulic boundary conditions on four sides in the simulated working condition are the same, each annular water pipe 7 passes through a water inlet and a pressure-bearing water head control box 11; if the water conservancy conditions on four sides in the simulated working condition are different, the bent double-way pipe is plugged, the water conservancy relation of four sections of water pipes of the annular water pipe 7 is cut off, and each boundary is independently controlled by one pressure-bearing water head control box 11; and a connecting water pipe 13 with the diameter of 2cm is distributed on the inner side of the annular water pipe 7 and is connected with a side wall hole 13 of the model box, the annular water pipe 7 is connected with all model box wall holes 13 at the same height through a connecting water pipe 12, and the soil facing side of the connecting water pipe 12 is wrapped with a stainless steel filter screen.
The pressure-bearing water head control water tank 11 can be lifted and lowered, and the height control precision is in mm level; the water pipe is connected with a water inlet at the outer side of the annular water pipe 7, and a flow meter 9 and a pressure meter 10 are arranged on the connected water pipe, so that the water inflow and the pressure can be conveniently recorded; if the water tank cannot meet the requirement of water supply pressure only by adopting lifting of the confined water head, the booster pump can be combined for supplying water, and the power of the booster pump is dynamically adjusted through the pressure gauge 10.
The dewatering well 5 and the recharging well 6 are both made of hollow PVC pipes, and the depth and the position are determined according to the simulation working condition; plugging the bottom ends of the dewatering well 5 and the recharge well 6, wherein the dewatering well 5 is used as a filtering section within a range of 200mm from the bottom end to the top, and the recharge well 6 is used as a filtering section within a range of 2/3 pipe lengths from the bottom end to the top; and 2 mm-diameter filter holes are distributed in the filter section at intervals of 5mm in transverse and longitudinal intervals, and the geotextile is wrapped by using a wire mesh in the range of the filter section to form a filter screen.
As shown in fig. 3, the measurement system comprises a test element and a data acquisition system, wherein the test element monitors dynamic changes in the model box 1 in real time and transmits data to the data acquisition system; the test elements comprise a micro displacement meter 18, a osmometer 19, an earth pressure meter 22, a piezometer tube 21, a resistivity probe 23 and a strain gauge 20. The micro displacement meter 18, the osmometer 19, the earth pressure meter 22, the piezometer tube 21 and the resistivity probe 23 are all buried at different positions in the earth; the strain gauge 20 is adhered at different locations of the tunnel structure 2 and the foundation pit structure system. The data acquisition system mainly comprises a DataTaker automatic data acquisition instrument 25 and an automatic resistivity tester 26, the micro displacement meter 18, the osmometer 19, the earth pressure meter 22, the piezometer tube 21 and the strain gauge 20 are respectively connected with the DataTaker automatic data acquisition instrument 25 through a lead 24, and the resistivity probe 23 is connected with the automatic resistivity tester 26 through the lead 24.
The specific functions of the various test elements described above are as follows: the micro displacement meter 18 can measure the deformation of the soil body at different positions; the osmometer 19 can give the water level change by conversion; the soil pressure gauge 22 can measure the soil pressure at different positions; the pressure measuring pipe 21 can measure the water head change of the pressure-bearing water layer; the strain gage 20 may give strain to the tunnel structure measurement point.
The using method of the device comprises the following steps:
1. a test preparation stage: the method comprises the steps of laying a cohesive soil layer and a sandy soil layer in layers, setting the thickness of the cohesive soil layer and the sandy soil layer according to a simulation working condition, placing a tunnel structure and a foundation pit structure in a soil body according to position requirements in the simulation working condition, burying a micro displacement meter 18, an osmometer 19, a soil pressure meter 22, a pressure measuring pipe 21, a strain gauge 20, a dewatering well 5 and a recharge well 6 at designed positions, and leading out a lead 24 of a test element from a model box 1 through a side wall hole 13 of the model box in a concentrated mode and connecting the lead with an automatic data acquisition instrument 25. After all the soil layers are laid and the test elements are laid, the water supply valve 8 is opened to supply water to the model. When water seeps from the surface of the soil layer and the model boundary water head is stable after the water supply valve 8 is closed, the soil body is solidified by self weight.
2. And (3) test development stage: after consolidation is completed, reading and recording initial values of all test parameters of the test element, and then carrying out pre-precipitation before excavation of the foundation pit according to a simulation working condition. When the water level is deepened to meet the requirement, the size of a model boundary water head, the reading of a flow meter at the water inlet and the reading of a flow meter of a dewatering well are stable, namely the model is proved to form a stable seepage field, and then the first layer excavation of the foundation pit can be started. The device can be used for researching the influence of the coupling effect of foundation pit excavation and pressure reduction and precipitation on the proximity tunnel, and can also be used for designing different experimental research contents, such as: and evaluating the influence of the multi-echelon pressure reduction and precipitation of the foundation pit on the regional seepage field, the influence of the local seepage of the tunnel (foundation pit) on the safety of the tunnel (foundation pit) structure and the like. In view of the versatility of the device, various test conditions can be designed for each research content.
The technical means disclosed in the invention scheme are not limited to the technical means disclosed in the above embodiments, but also include the technical scheme formed by any combination of the above technical features.
Claims (10)
1. The utility model provides a device that simulation foundation ditch excavation and many terraces precipitation comprehensively influenced tunnel which characterized in that: the system comprises a model box, a tunnel structure system, an underground water control system, a foundation pit structure system and a measuring system;
a sandy soil layer and a cohesive soil layer are arranged in the model box at intervals, wherein the sandy soil layer simulates a confined aquifer, and the cohesive soil layer simulates a relative water-resisting layer;
the tunnel structure system and the foundation pit structure system are correspondingly arranged in the soil layer according to the relative position, the embedding depth and the enclosure form;
the underground water control system controls the water heads of different aquifers by adjusting the position of the annular water pipe and the size of the water supply head, and the underground water level control in the foundation pit construction process is completed through the dewatering well and the recharge well; arranging the dewatering well and the recharge well in corresponding areas of the soil layer according to the simulated working conditions;
the measuring system comprises a testing element and a data acquisition system, wherein the testing element is arranged in the tunnel structure system, the foundation pit structure system, the underground water control system and the soil layer, monitors the dynamic change of each part in real time and transmits data to the data acquisition system.
2. The device of claim 1 for simulating the comprehensive influence of excavation of a foundation pit and multi-gradient precipitation on a tunnel, wherein: side wall holes are distributed on four sides of the model box, the hole part is communicated with an external annular water pipe to simulate different groundwater supply conditions, and the other part of the side wall holes are used as water pressure monitoring points.
3. The device of claim 1 for simulating the comprehensive influence of excavation of a foundation pit and multi-gradient precipitation on a tunnel, wherein: symmetrically arranging a tunnel structure arrangement area on the front surface and the rear surface of the model box, splicing the tunnel structure arrangement area by a plurality of pieces of organic glass with the same area, overlapping all horizontal seams of the tunnel structure arrangement area by double-groove sliding rails, and connecting the organic glass and the double-groove sliding rails by sealing glue; all vertical seams of the area are connected with a sealant through I-shaped channel steel, and the tunnel structure system is arranged between the front area and the rear area.
4. The device of claim 1 for simulating the comprehensive influence of excavation of a foundation pit and multi-gradient precipitation on a tunnel, wherein: the tunnel structure system is formed by flexibly connecting multiple sections of tunnel models, each tunnel model is made of particle concrete, double-layer galvanized wire nets are arranged in the particle concrete, each section of tunnel is connected through a flexible rubber ring, a leakage area is arranged at a specific position of the tunnel structure, strain gauges are pasted at different positions of the top, the side wall and the bottom of the inner wall of the tunnel structure, and a lead of the strain gauge leads to the automatic data acquisition instrument through a side wall hole of the model box.
5. The device of claim 1 for simulating the comprehensive influence of excavation of a foundation pit and multi-gradient precipitation on a tunnel, wherein: the underground continuous wall in the foundation pit structure system is made of particle concrete, and a double-layer galvanized wire netting is arranged in the particle concrete; the second-level plain water stop wall is made of plain particle concrete; the waist beam and the support are made of wood frames and are embedded into the soil body together with the ground wall structure.
6. The device of claim 1 for simulating the comprehensive influence of excavation of a foundation pit and multi-gradient precipitation on a tunnel, wherein: the underground water control system comprises an annular water pipe, a water head control water tank, a booster pump, a flow meter, a pressure gauge, a dewatering well and a recharge well, wherein the inner side of the annular water pipe is provided with a connecting water pipe which is connected with a side wall hole on the model box, and the side, facing the soil, of the connecting water pipe is wrapped with a stainless steel filter screen.
7. The device of claim 1 for simulating the comprehensive influence of excavation of a foundation pit and multi-gradient precipitation on a tunnel, wherein: the test element comprises a micro displacement meter, an osmometer, a soil pressure meter, a piezometer tube, a resistivity probe and a strain gauge, and the micro displacement meter, the osmometer, the soil pressure meter, the piezometer tube and the resistivity probe are all embedded at different positions in soil; the strain gauge is adhered to different positions of the tunnel structure system and the foundation pit structure system, the data acquisition system comprises an automatic data acquisition instrument and an automatic resistivity tester, the miniature displacement meter, the osmometer, the soil pressure meter, the pressure measuring tube and the strain gauge are respectively connected with the automatic data acquisition instrument through wires, and the resistivity probe is connected with the automatic resistivity tester through wires.
8. The device of claim 6 for simulating the comprehensive influence of excavation of a foundation pit and multi-gradient precipitation on a tunnel, wherein: the water head control water tank is characterized in that the height can be lifted, the water head control water tank is connected with a water inlet at the outer side of the annular water pipe through a water pipe, and a flow meter and a pressure gauge are arranged on the connected water pipe; if the water tank cannot meet the requirement of water supply pressure only by adopting a lifting water head to control the water tank, the combined water supply of the booster pump is needed, and the power of the booster pump is dynamically adjusted through the pressure gauge.
9. The device of claim 1 for simulating the comprehensive influence of excavation of a foundation pit and multi-gradient precipitation on a tunnel, wherein: the dewatering well and the recharging well are both made of hollow PVC pipes, the bottom ends of the dewatering well and the recharging well are plugged, the dewatering well is used as a filtering section within a range of 200mm from the bottom end to the top, and the recharging well is used as a filtering section within a range of 2/3 pipe lengths from the bottom end to the top; and 2 mm-diameter filter holes are distributed in the filter section at intervals of 5mm in transverse and longitudinal intervals, and the geotextile is wrapped by using a wire mesh in the range of the filter section to form a filter screen.
10. The use method of the device for simulating the comprehensive influence of foundation pit excavation and multi-gradient precipitation on the tunnel according to claim 1 is characterized in that: the method comprises the following steps:
(1) and a test preparation stage: paving a cohesive soil layer and a sandy soil layer in a model box in a layered manner, placing a tunnel structure and a foundation pit structure in a soil body according to the position requirement in a simulation working condition, simultaneously embedding a micro displacement meter, an osmometer, a soil pressure meter, a pressure measuring pipe, a strain gauge, a dewatering well and a recharge well at a designed position, leading out a wire of a test element from the model box in a concentrated manner through a side wall hole of the model box, connecting the wire with an automatic data acquisition instrument, opening a water supply valve to supply water to the model after the laying of all the soil layers and the laying of the test element are finished, and enabling the soil body to be solidified by self weight when the water seeps out from the surface of the soil layer and the boundary water head of the model is stable after the water supply;
(2) and a test development stage: after the consolidation is finished, reading and recording initial values of all test parameters of the test element, then pre-dewatering the foundation pit before excavation according to a simulation working condition, when the water level is deepened to meet the requirement, and the size of a model boundary water head, the reading of a flow meter at the water inlet and the reading of a flow meter of a dewatering well are stable, namely, the model is shown to form a stable seepage field, and then the first-layer excavation of the foundation pit is started, and the device can also carry out the following experimental research contents:
influence of multi-gradient pressure reduction and precipitation of the foundation pit on the regional seepage field;
and (4) evaluating the influence of local leakage of the tunnel or the foundation pit on the safety of the structure.
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