Visual simulation device and test method for shield tunnel seepage fields in different stratums

Abstract

The invention relates to the technical field of underground engineering visualization, and provides a visual simulation device and test method for shield tunnel seepage fields in different stratums.The device comprises an underground water simulation system, a model box and a data monitoring system, and the underground water simulation system comprises a water inlet mechanism and a water outlet mechanism; the water inlet mechanism and the water outlet mechanism are arranged on the two opposite sides of the model box and communicate with the model box. The model box is filled with transparent soil, and a tunnel model is embedded in the transparent soil; and the data monitoring system is used for acquiring a seepage field speed cloud picture by shooting speckle field images of the transparent soil. According to the scheme, shield tunnel seepage field research on different stratums can be carried out, internal association between stratum permeability characteristics and seepage field distribution is revealed, and early warning mechanisms of underground water levels and flow velocities in various stratums are perfected.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underground engineering visualization, in particular to a visualization simulation device and test method for seepage field of shield tunnel in different strata. BACKGROUND

[0002] In the construction of urban underground engineering, the shield method is widely used in underground engineering construction because it can adapt to various strata, effectively deal with complex geological conditions, and has little interference to ground traffic and residents' life. At present, the mileage of China's subway has broken through 9000 kilometers, among which more than 60% of the tunnels need to pass through complex strata such as sand layer, pebble layer and clay layer. The permeability of different strata is significantly different, the high permeability of sand layer is easy to form concentrated seepage channel, and the low permeability of clay layer may lead to long-term accumulation of pore water pressure. In addition, the tunnel diseases caused by groundwater seepage during operation account for more than 35%, the groundwater erosion of tunnel lining structure leads to the decrease of lining strength, the appearance of cracks and even local damage, which affects the overall stability of the tunnel; the water pressure generated by groundwater seepage may produce additional lateral pressure on the tunnel lining, further aggravating the deformation and damage of the lining; long-term erosion of groundwater to stratum fine particles leads to imbalance of soil pressure around the tunnel, causing the stability of surrounding rock to decrease.

[0003] At present, the research on the influence of seepage on shield tunnel mainly focuses on the seepage law of single stratum, lacks systematic understanding of the evolution mechanism of seepage field under the condition of stratum combination, and it is difficult to accurately predict the seepage risk of tunnel in complex strata such as silt-clay interbedded layer and pebble-bedrock contact zone. At the same time, the existing technology mainly focuses on the research of excavation face stability and soil displacement during tunnel construction, lacks direct monitoring of groundwater seepage field, and it is difficult to directly and effectively reveal the failure mode and key control factors of tunnel under the action of seepage during operation.

[0004] The above defects directly restrict the improvement of the safety risk prevention and control ability of tunnel in whole life cycle. Therefore, it is urgent to develop an innovative test system combining multi-stratum simulation and seepage field visualization monitoring to reveal the seepage disaster mechanism under complex hydrogeological conditions. SUMMARY

[0005] In order to solve the problems in the background art, the present application provides a visualization simulation device and test method for seepage field of shield tunnel in different strata, which can carry out seepage field research of shield tunnel in different strata, reveal the internal correlation between stratum permeability and seepage field distribution, and perfect the early warning mechanism of groundwater level and flow rate in various strata, providing experimental support for improving tunnel drainage design theory, establishing seepage disaster early warning system and providing tunnel site selection basis.

[0006] In order to achieve the above purpose, the present application adopts the following scheme: The application discloses a visual simulation device for seepage field of shield tunnel in different strata.

[0007] Optionally, the model box is a transparent acrylic box, and the transparent soil is homogeneous sandy soil stratum, homogeneous clay stratum, layered non-homogeneous sandy soil stratum, layered non-homogeneous clay stratum or sandy-clay composite stratum.

[0008] Optionally, the data monitoring system comprises a laser, an industrial camera and a post-processing mechanism electrically connected with the laser and the industrial camera respectively, the laser is arranged on one side of the model box communicating with the water outlet mechanism, is used for emitting sheet laser to irradiate the transparent soil to form a speckle field, and the industrial camera is arranged opposite to the model box and is used for continuously collecting speckle field images; the post-processing mechanism adopts particle image velocimetry (PIV) software, and a seepage field velocity nephogram is obtained by analyzing the speckle images through a cross-correlation principle.

[0009] Optionally, the water inlet mechanism comprises a water inlet box and a water inlet pipe, the water inlet end of the water inlet pipe communicates with the water inlet box, the water outlet end of the water inlet pipe communicates with the transparent soil below the tunnel model in the model box, and the water inlet pipe is sequentially connected with a water inlet valve, a water inlet pump and a water inlet flowmeter along the water flow direction.

[0010] Optionally, the water outlet mechanism comprises a water outlet box and a water outlet pipe, the water outlet end of the water outlet pipe communicates with the water outlet box, the water inlet end of the water outlet pipe communicates with the transparent soil below the tunnel model in the model box, and the water outlet pipe is sequentially connected with a water outlet flowmeter and a water outlet valve along the water flow direction.

[0011] The application further discloses a test method of the visual simulation device for seepage field of shield tunnel in different strata. Step 1, transparent sandy soil and transparent clay are prepared respectively; Step 2, the transparent soil required by the test is filled in the model box by using the transparent sandy soil or the transparent clay, and the tunnel model is buried; Step 3, the water inlet mechanism, the model box and the water outlet mechanism are sequentially connected, the data monitoring system is installed, and water is injected into the water inlet box; Step 4, at least one stratum seepage simulation is performed, the laser irradiates the transparent soil, the industrial camera is synchronously controlled to collect speckle field images at a frequency of 10-30 frames, and the speckle field images are transmitted to the post-processing mechanism; Step 5, the post-processing mechanism analyzes the speckle field image by PIV software, and obtains the velocity nephogram of the seepage field based on the principle of cross-correlation analysis.

[0012] Optionally, in step 1, the transparent sand is prepared by the following steps: step 1.1a, mixing n-dodecane and white oil at a mass ratio of 1:4 to form a pore fluid; step 1.2a, adding 0.05%-0.2% of tracer particles to the pore fluid; step 1.3a, mixing the fused quartz sand and the pore fluid obtained in step 1.2a at a solid-liquid ratio of 2:1-3:1 to form a mixture; The transparent clay is prepared by the following steps: Step 1.1b, mixing n-dodecane and white oil at a mass ratio of 1:4 to form a pore fluid; step 1.2b, adding 0.05%-0.2% of tracer particles to the pore fluid; step 1.3b, mixing the amorphous silicon powder and the pore fluid obtained in step 1.2b at a solid-liquid ratio of 1:1-1:1.5 to form a mixture.

[0013] Optionally, in step 2, the method for filling the transparent soil required for the test and burying the tunnel model specifically includes: Step 2.1, filling the transparent sand or transparent clay in layers to the height at which the tunnel model is placed; Step 2.2, placing the tunnel model; Step 2.3, continuing to fill the transparent sand or transparent clay to a height higher than the preset height; Step 2.4, placing the model box into the vacuum box and vacuumizing to medium transparency; Step 2.5, performing a consolidation operation for stratum property adaptation; Step 2.6, finally adjusting to the preset height of the test.

[0014] Optionally, in step 4, the soil layer seepage simulation includes homogeneous sand layer seepage field simulation, homogeneous clay layer seepage field simulation, layered non-homogeneous sand layer seepage field simulation, layered non-homogeneous clay layer seepage field simulation, and sand-clay composite layer seepage field simulation, wherein, When performing homogeneous sand layer seepage field simulation, open the water inlet valve and close the water outlet valve, and inject water into the model box to form an initial underground water level with the water level reaching 30%-50% of the height of the transparent soil, simultaneously open the water inlet valve and the water outlet valve, and adjust the flow of the water inlet pump to make the readings of the water inlet flow meter and the water outlet flow meter equal, thereby forming a stable seepage field; When performing homogeneous clay layer seepage field simulation, simultaneously open the water inlet valve and the water outlet valve, and adjust the flow of the water inlet pump to make the readings of the water inlet flow meter and the water outlet flow meter stable at the order of m / s, thereby forming a low-speed seepage field; When simulating the seepage field of layered heterogeneous sandy soil, the water inlet valve is opened and the water outlet valve is closed, water is injected into the model box until the water level reaches 30-50% of the height of the fine sand layer, the water inlet valve is closed and the water outlet valve is opened until the water in the coarse sand layer is drained, and then the water outlet valve and the water inlet valve are opened synchronously, and the flow of the water inlet pump is adjusted to make the water inlet flow meter smaller than the water outlet flow meter, thereby forming an unsteady seepage field. When simulating the seepage field of layered heterogeneous clay soil, the water inlet valve is opened and the water outlet valve is closed, the flow of the water inlet pump is adjusted to make the water inlet flow meter stable at the order of m / s, thereby forming a low-speed one-way infiltration field. When simulating the seepage field of layered heterogeneous clay soil, the water inlet valve is opened and the water outlet valve is closed, the flow of the water inlet pump is adjusted to make the water inlet flow meter stable at the order of m / s, thereby forming a low-speed one-way infiltration field. When simulating the seepage field of sand-clay composite stratum, the water inlet valve is opened and the water outlet valve is closed, water is injected into the model box until the water level reaches the top of the sand layer to form an initial groundwater level, then the water inlet valve is closed and the water outlet valve is opened to form a one-way seepage field.

[0015] Optionally, in step 5, the specific method for the post-processing mechanism to obtain the seepage field velocity cloud map comprises the following steps: 5.1, dividing the speckle field image into a plurality of grid units; 5.2, performing cross-correlation operation on the speckle field images of adjacent time in the same sub-region; 5.3, locating the peak value coordinates of the cross-correlation function, calculating the average displacement vector of the particles in the sub-region, and obtaining the seepage field velocity cloud map in the stratum.

[0016] The present application has the beneficial effects that: first, the present application constructs a device capable of reproducing the seepage environment of shield tunnels in different strata during operation in the test environment through the underground water simulation system, the model box, the transparent soil and the data monitoring system, and can simulate the tunnel segment seepage field of various strata by adjusting the type, height and proportion of the transparent soil in the model box and cooperating with the adjustment of the underground water simulation system, thereby revealing the internal correlation between the stratum permeation characteristics and the seepage field distribution, and perfecting the early warning mechanism of the groundwater level and flow rate in various strata.

[0017] Secondly, the present application combines the transparent soil technology with the optical measurement system to construct a non-invasive, full-face and full-process seepage field visualization observation platform, which breaks through the deficiencies of the traditional soil test, such as invasive interference, low quantitative analysis accuracy and observation limitations, can quantitatively analyze the seepage velocity and the dynamic change of the underground water, and provides a new visual analysis method for the seepage mechanism research of shield tunnels, and the full-field, dynamic and digital seepage data obtained significantly improve the accuracy and reliability of the seepage field analysis, and lay a solid foundation for establishing a more scientific seepage early warning model for tunnel engineering.

[0018] In addition, the device has simple structure, when simulating the seepage field of each stratum, only the flow of the water inlet valve, the water outlet valve and the water inlet pump needs to be adjusted to form the relevant seepage field, so that the test operation is convenient, and the test period is shortened and the research efficiency is improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a whole structure schematic view of the visual simulation device of the application. Figure 2 It is a flow chart of the test method of the application.

[0020] The reference signs in the drawing are as follows: 1, water inlet tank; 2, water inlet conduit; 3, water inlet valve; 4, water inlet pump; 5, water inlet flowmeter; 6, water outlet flowmeter; 7, water outlet valve; 8, model tank; 9, tunnel model; 10, transparent soil; 11, laser; 12, industrial camera; 13, post-processing mechanism; 14, water outlet tank; 15, water outlet conduit. DETAILED DESCRIPTION

[0021] In order to make the application clearer and more understandable, the application is optionally and in detail described below in combination with the drawings and examples, and it should be understood that the given examples are only one of the implementation manners and do not represent all the examples.

[0022] Example 1 In combination Figure 1 The example provides a visual simulation device of a shield tunnel seepage field in different strata, which comprises a groundwater simulation system, a model tank 8 and a data monitoring system, the groundwater simulation system comprises a water inlet mechanism and a water outlet mechanism, the water inlet mechanism and the water outlet mechanism are arranged on opposite sides of the model tank 8 and communicate with the model tank 8, the model tank 8 is filled with transparent soil 10, the tunnel model 9 is embedded in the transparent soil 10, and the data monitoring system is used for obtaining a seepage field velocity nephogram by shooting a speckle field image of the transparent soil 10.

[0023] The example constructs a device capable of reproducing the seepage environment of a shield tunnel in operation in different strata in a test environment through the groundwater simulation system, the model tank 8, the transparent soil 10 and the data monitoring system, the tunnel segment seepage field of various strata can be simulated by adjusting the type, height and proportion of the transparent soil 10 in the model tank 8 and cooperating with the adjustment of the groundwater simulation system, the internal correlation between the stratum permeation characteristics and the seepage field distribution is revealed, and the early warning mechanism of the groundwater level and flow rate in various strata is improved.

[0024] As a preferred solution, the model box 8 is a whole cube composed of transparent acrylic plates with a thickness of 10 mm, so as to observe the dynamic changes of the internal soil body and the tunnel model 9, and the size is 600 mm long x 400 mm wide x 600 mm high. The connection between the side plate and the bottom plate is treated with waterproof sealant to ensure the water tightness of the device. The preparation method of the tunnel model 9 used in the embodiment is to mix gypsum 50%-70%, diatomite 10%-30% and water 20%-40% uniformly, then pour the mold and demold. The size of the tunnel model 9 in the embodiment is 64 mm in outer diameter and 58 mm in inner diameter. The distance between the center of the tunnel and the two side surfaces of the model box 8 is 300 mm, the distance from the bottom of the model box 8 is 150 mm, and the distance from the upper surface of the transparent soil 10 is 150 mm. The water inlet mechanism, the model box 8 and the water outlet mechanism form a water circulation system, realizing the reuse of water resources. As shown in Figure 1 the left side of the tunnel model 9, the water is transported into the transparent soil 10 on the left side of the model box 8, so as to form a seepage path from left to right, simulate the scouring of groundwater seepage on the tunnel, and the seepage path of groundwater flowing from the side of the tunnel to the bottom. The water outlet mechanism is located on the right side of the tunnel model 9, and the water from the left side of the stratum is discharged, which is used to simulate the flow path of the groundwater.

[0025] Specifically, the transparent soil 10 is one of homogeneous sandy soil stratum, homogeneous clay stratum, layered non-homogeneous sandy soil stratum, layered non-homogeneous clay stratum or sandy-clay composite stratum. This embodiment mainly simulates the seepage field of these strata.

[0026] Specifically, the data monitoring system includes a laser 11, an industrial camera 12 and a post-processing mechanism 13 electrically connected with the laser 11 and the industrial camera 12 respectively. The laser 11 is arranged on one side of the model box 8 connected with the water outlet mechanism, for emitting a sheet laser to irradiate the transparent soil 10 to form a speckle field. The industrial camera 12 is arranged opposite to the model box 8, for continuously collecting speckle field images. The post-processing mechanism 13 adopts particle image velocimetry (PIV) software to analyze the speckle images to obtain the seepage field velocity cloud image through the cross-correlation principle. Here, the industrial camera 12 adopts a CCD industrial camera.

[0027] Specifically, the water inlet mechanism comprises a water inlet tank 1 and a water inlet conduit 2, the water inlet end of the water inlet conduit 2 communicates with the water inlet tank 1, the water outlet end of the water inlet conduit 2 communicates with the transparent soil 10 below the tunnel model 9 in the model tank 8; the water inlet conduit 2 is sequentially connected with a water inlet valve 3, a water inlet pump 4 and a water inlet flowmeter 5 along the water flow direction. The water outlet mechanism comprises a water outlet tank 14 and a water outlet conduit 15, the water outlet end of the water outlet conduit 15 communicates with the water outlet tank 14, the water inlet end of the water outlet conduit 15 communicates with the transparent soil 10 below the tunnel model 9 in the model tank 8, the water outlet conduit 15 is sequentially connected with a water outlet flowmeter 6 and a water outlet valve 7 along the water flow direction. When simulating the tunnel segment seepage field of various strata, the formation of the relevant seepage field can be realized by adjusting the flow of the water inlet valve 3, the water outlet valve 7 and the water inlet pump 4.

[0028] Embodiment two The embodiment provides a test method of a visualization simulation device of a shield tunnel seepage field of different strata, and comprises the following steps: Step 1, transparent sand and transparent clay are respectively prepared. The transparent sand is prepared through the following steps: step 1.1a, dodecane and No. 15 white oil are mixed in a mass ratio of 1:4 to form a pore fluid; step 1.2a, 0.05%-0.2% of tracer particles are added into the pore fluid; step 1.3a, fused quartz sand and the pore fluid obtained through step 1.2a are mixed in a solid-liquid ratio of 2:1-3:1 to form a mixture. The transparent clay is prepared through the following steps: step 1.1b, dodecane and white oil are mixed in a mass ratio of 1:4 to form a pore fluid; step 1.2b, 0.05%-0.2% of tracer particles are added into the pore fluid; step 1.3b, amorphous silica powder and the pore fluid obtained through step 1.2b are mixed in a solid-liquid ratio of 1:1-1:1.5 to form a mixture. Here, hollow glass microbeads can be selected as the tracer particles, so that the fluid forms a speckle plane under laser.

[0029] Step 2, the transparent soil 10 required by the test is filled in the model tank 8 by using transparent sand or transparent clay, and the tunnel model 9 is buried. In the embodiment, the seepage field simulation is mainly performed on homogeneous sand stratum, homogeneous clay stratum, layered non-homogeneous sand stratum, layered non-homogeneous clay stratum and sand-clay composite stratum, so the method for filling and burying the tunnel model 9 specifically comprises the following steps: When the transparent soil 10 is a homogeneous sand stratum, step 2.1a, the transparent sand is filled in layers to the height at which the tunnel model 9 is placed; step 2.2a, the tunnel model 9 is placed; step 2.3a, because the pressurized consolidation operation is not needed, the transparent sand is directly continuously filled to the preset height of the test; step 2.4a, the model tank 8 is placed in a vacuum tank to be vacuumized at-1MPa for 2 hours until the medium is transparent.

[0030] It should be noted that based on the size of the tunnel model 9 in Example 1, the placement height of the tunnel model 9 is the distance from the top of the first layer of transparent sand or transparent clay to the bottom of the model box 8, that is, 118 mm; the preset height of the test is the distance from the top of the final transparent sand or transparent clay in the model box 8 to the bottom of the model box 8, that is, 300 mm. The following stratum heights are based on this standard.

[0031] When the transparent soil 10 is a homogeneous clay stratum, step 2.1b, layer-by-layer filling of transparent clay to the placement height of the tunnel model 9, which is slightly greater than 118 mm from the bottom of the model box 8, gives a certain margin for the subsequent pressure consolidation operation; step 2.2b, placing the tunnel model 9; step 2.3b, continuing to fill the transparent clay to slightly higher than the preset height, that is, the top of the transparent clay is slightly higher than 300 mm from the bottom of the model box 8; step 2.4b, placing the model box 8 into the vacuum box to extract vacuum at -1 MPa for 2 hours to make the medium transparent; step 2.5b, consolidating at 3 MPa for 5 days; step 2.6b, adjusting the final height of the transparent clay in the model box 8 to the test preset height.

[0032] When the transparent soil 10 is a layered and non-homogeneous sand stratum, step 2.1c, layer-by-layer filling of coarse-grained transparent sand (2-4 mm quartz sand preparation) to the placement height of the tunnel model 9; step 2.2c, placing the tunnel model 9; step 2.3c, layer-by-layer filling of fine-grained transparent sand (0.25-0.5 mm quartz sand preparation) to the test preset height.

[0033] When the transparent soil 10 is a layered and non-homogeneous clay stratum, step 2.1d, layer-by-layer filling of transparent clay to the placement height of the tunnel model 9, which is slightly greater than 118 mm from the bottom of the model box 8, gives a certain margin for the subsequent pressure consolidation operation; step 2.2d, extracting vacuum at -1 MPa in the vacuum box for 2 hours to make the medium transparent, and consolidating at 3 MPa for 5 days to adjust the transparent clay in the model box 8 to the tunnel placement height; step 2.3d, placing the tunnel model 9, step 2.4d, continuing to fill the transparent clay to slightly higher than the preset height; step 2.5d, consolidating at 2 MPa for 2 days after secondary vacuum extraction in the vacuum box; step 2.6b, adjusting the final height of the transparent clay in the model box 8 to the test preset height.

[0034] When the transparent soil 10 is a sand-clay composite stratum, step 2.1e, layer-by-layer fill the transparent sand soil to the tunnel placement height; step 2.2e, place the tunnel model 9; step 2.3e, layer-by-layer fill the transparent clay soil to slightly higher than the preset height; step 2.4e, vacuumize in the vacuum box at -1 MPa for 2 hours to make the medium transparent; step 2.5e, consolidate at 3 MPa for 5 days; and step 2.6e, adjust the final height of the transparent soil 10 in the model box 8 to the preset height of the test.

[0035] Step 3, sequentially connect the water inlet mechanism, the model box 8 and the water outlet mechanism, and install the data monitoring system, and fill water into the water inlet box 1; Step 4, perform at least one stratum seepage simulation, start the laser 11 to irradiate the transparent soil 10, synchronously control the industrial camera 12 to collect speckle field images at a frequency of 10-30 frames, and transmit the speckle field images to the post-processing mechanism 13.

[0036] In this embodiment, seepage field simulation of shield tunnels in various strata including homogeneous sand stratum, homogeneous clay stratum, layered non-homogeneous sand stratum, layered non-homogeneous clay stratum and sand-clay composite stratum can be performed, and different seepage field simulation conditions are realized according to different groundwater levels and seepage characteristics in different strata.

[0037] When performing seepage field simulation of the homogeneous sand stratum, since the sand soil has large pores, good connectivity and high permeability coefficient, and the sand stratum usually has an original groundwater level, a stable seepage with the original groundwater level needs to be formed during simulation. During the test, the water inlet valve 3 is opened and the water outlet valve 7 is closed, water is filled into the model box 8 to form an initial water level of the sand stratum where the tunnel structure is located, the water inlet valve 3 and the water outlet valve 7 are synchronously opened, the flow of the water inlet pump 4 is adjusted, the readings of the water inlet flow meter 5 and the water outlet flow meter 6 are equal, a stable seepage field is formed, and it can be used for studying the seepage field of the homogeneous sand stratum under general conditions.

[0038] When performing seepage field simulation of the homogeneous clay stratum, since the clay particles are fine and the pores are small, the permeability coefficient is extremely low, and the original water level of the clay stratum is not obvious, a low-speed seepage without the original groundwater level needs to be formed during simulation. During the test, the water inlet valve 3 and the water outlet valve 7 are synchronously opened, the flow of the water inlet pump 4 is adjusted, the readings of the water inlet flow meter 5 and the water outlet flow meter 6 are synchronously and stably in the order of m / s, a low-speed seepage field is formed, and it can be used for studying the influence of pore water pressure dissipation on the stability of the tunnel.

[0039] ​When simulating the seepage field of layered heterogeneous sandy soil, the sandy soil layer forms a layered structure of fine sand on top and coarse sand on bottom due to water flow deposition and wind deposition. The grain size and permeability of different layers of sandy soil are different. The upper fine sand layer has low permeability and blocks water, while the lower coarse sand layer has high permeability and fast drainage. Therefore, the original water level is in the fine sand layer during simulation. Under natural conditions, rainfall first seeps through the fine sand layer and then continues to seep downward through the coarse sand layer. The infiltration rate is less than the exfiltration rate, which is unsteady seepage. During the test, the water inlet valve 3 is opened and the water outlet valve 7 is closed. Water is injected into the model box 8 until the water level reaches 30%-50% of the height of the fine sand layer. Then the water inlet valve 3 is closed and the water outlet valve 7 is opened until the water in the coarse sand layer is drained, and then the water outlet valve 7 is closed. Finally, the water outlet valve 7 and the water inlet valve 3 are opened synchronously, and the flow of the water inlet pump 4 is adjusted to make the water inlet flow meter 5 smaller than the water outlet flow meter 6. A non-steady seepage field is formed, which can be used to study the seepage field of sandy soil layers with different degrees of weathering under natural conditions such as rainfall.

[0040] When simulating the seepage field of layered heterogeneous clay soil, the lower layer of clay bears more overburden pressure for a long time, so it hardens more and has smaller permeability. Therefore, during simulation, a low-speed one-way infiltration without original groundwater level is needed. During the test, the water inlet valve 3 is opened and the water outlet valve 7 is closed. The flow of the water inlet pump 4 is adjusted to make the water inlet flow meter 5 stable at the order of m / s, forming a low-speed one-way infiltration field.

[0041] When simulating the seepage field of sandy-clay composite stratum, the permeability coefficient of sandy soil is much larger than that of clay. Therefore, under natural conditions, the sandy soil layer easily forms a free water level, and the clay layer can be regarded as an impermeable layer. Therefore, during simulation, the original water level is at the interface between the clay layer and the sandy soil layer, and under natural conditions, rainfall forms a stagnant water on the surface of the clay layer, and then continues to seep downward through the sandy soil layer. The seepage is only exfiltration. During the test, the water inlet valve 3 is opened and the water outlet valve 7 is closed. After the water level in the model box 8 reaches the top of the sandy soil layer to form an initial groundwater level, the water inlet valve 3 is closed and the water outlet valve 7 is opened to form a one-way exfiltration field.

[0042] Step 5, the post-processing mechanism 13 analyzes the speckle field images through PIV software and obtains the seepage field velocity cloud map based on the cross-correlation analysis principle. By analyzing multiple speckle field images taken during the test through PIV software, the images are divided into several grid units. The cross-correlation analysis principle is used to calculate the average displacement vector of the same sub-region in two images with adjacent time intervals. The cross-correlation operation is performed on the same sub-region of adjacent time images. The peak value coordinates of the cross-correlation function are located. The seepage field velocity cloud map in each stratum is obtained. By comparing and analyzing the seepage field velocity cloud maps obtained above, the change process of the seepage field under the influence of different strata is obtained, and the test is completed.

[0043] ​The specific embodiments of the present application are described above with reference to the drawings, but the present application is not limited to the described embodiments. Various changes, modifications, replacements, and variations of the embodiments can be made by those skilled in the art without departing from the principles and spirit of the present application, and still fall within the protection scope of the present application.

Claims

1. A device for visualizing simulation of seepage field of shield tunnel in different strata, characterized in that: The groundwater simulation system comprises a water inlet mechanism and a water outlet mechanism, which are arranged on opposite sides of the model box (8) and communicate with the model box (8); the model box (8) is filled with transparent soil (10), and a tunnel model (9) is embedded in the transparent soil (10); the data monitoring system is used to obtain a seepage field velocity nephogram by shooting speckle field images of the transparent soil (10). The model box (8) is a transparent acrylic box, and the transparent soil (10) is a homogeneous sandy soil layer, a homogeneous clay soil layer, a layered non-homogeneous sandy soil layer, a layered non-homogeneous clay soil layer, or a sandy-clay composite soil layer.

2. The device for visualizing simulation of seepage field of different strata of shield tunnel according to claim 1, characterized in that: The data monitoring system comprises a laser (11), an industrial camera (12), and a post-processing mechanism (13) electrically connected with the laser (11) and the industrial camera (12); the laser (11) is arranged on the side of the model box (8) communicating with the water outlet mechanism, and is used to emit sheet laser to irradiate the transparent soil (10) to form a speckle surface; the industrial camera (12) is arranged opposite to the model box (8), and is used to continuously collect speckle field images; the post-processing mechanism (13) adopts particle image velocimetry (PIV) software, and obtains a seepage field velocity nephogram by analyzing the speckle images based on a cross-correlation principle.

3. The device for visualizing simulation of seepage field of different strata of shield tunnel according to claim 1, characterized in that: The water inlet mechanism comprises a water inlet tank (1) and a water inlet conduit (2); the water inlet end of the water inlet conduit (2) communicates with the water inlet tank (1); the water outlet end of the water inlet conduit (2) communicates with the transparent soil (10) below the tunnel model (9) in the model box (8); the water inlet conduit (2) is sequentially connected with a water inlet valve (3), a water inlet pump (4), and a water inlet flowmeter (5) along the water flow direction.

4. The device for visualizing simulation of seepage field of different strata shield tunnel according to claim 3, characterized in that: The water outlet mechanism comprises a water outlet tank (14) and a water outlet conduit (15); the water outlet end of the water outlet conduit (15) communicates with the water outlet tank (14); the water inlet end of the water outlet conduit (15) communicates with the transparent soil (10) below the tunnel model (9) in the model box (8); the water outlet conduit (15) is sequentially connected with a water outlet flowmeter (6) and a water outlet valve (7) along the water flow direction.

5. The device for visualizing simulation of seepage field of different strata of shield tunnel according to claim 4, characterized in that: The method comprises the following steps:

6. The test method for visualizing the seepage field of a shield tunnel in different strata according to claim 5, wherein, Step 1, transparent sandy soil and transparent clay are prepared respectively; Step 2, the transparent soil (10) required by the test is filled in the model box (8) by using the transparent sandy soil or the transparent clay, and the tunnel model (9) is embedded; Step 3, the water inlet mechanism, the model box (8), and the water outlet mechanism are sequentially connected, and the data monitoring system is installed, and water is injected into the water inlet tank (1); Step 4, at least one stratum seepage simulation is performed, the laser (11) irradiates the transparent soil (10), the industrial camera (12) is synchronously controlled to collect speckle field images at a frequency of 10-30 frames, and the speckle field images are transmitted to the post-processing mechanism (13); Step 5, the post-processing mechanism (13) analyzes the speckle field images by using the PIV software, and obtains a seepage field velocity nephogram based on a cross-correlation analysis principle. In step 1, the transparent sandy soil is prepared by the following steps:

7. The test method of the apparatus for visualizing simulation of seepage field of different strata shield tunnel according to claim 6, characterized in that: ​ Step 1.1a, mixing n-dodecane and white oil in a mass ratio of 1:4 to form a pore fluid; Step 1.2a, adding 0.05%-0.2% of tracer particles to the pore fluid; Step 1.3a, mixing fused quartz sand and the pore fluid obtained in step 1.2a in a solid-liquid ratio of 2:1-3:1 to form a mixture; The transparent clay is prepared by the following steps: Step 1.1b, mixing n-dodecane and white oil in a mass ratio of 1:4 to form a pore fluid; Step 1.2b, adding 0.05%-0.2% of tracer particles to the pore fluid; Step 1.3b, mixing amorphous silicon powder and the pore fluid obtained in step 1.2b in a solid-liquid ratio of 1:1-1:1.5 to form a mixture.

8. The test method of the apparatus for visualizing simulation of seepage field of different strata of shield tunneling according to claim 6, characterized in that: In step 2, the method for filling the transparent soil (10) required for the test and burying the tunnel model (9) includes: Step 2.1, filling the transparent sand or transparent clay in layers to the height at which the tunnel model (9) is placed; Step 2.2, placing the tunnel model (9); Step 2.3, continuing to fill the transparent sand or transparent clay to a height higher than the preset height; Step 2.4, placing the model box (8) into the vacuum box and vacuumizing to medium transparency; Step 2.5, performing a consolidation operation for stratum property adaptation; Step 2.6, finally adjusting to the preset height of the test.

9. The test method of the apparatus for visualizing simulation of seepage field of different strata of shield tunneling according to claim 6, characterized in that: In step 4, the stratum seepage simulation includes homogeneous sand stratum seepage field simulation, homogeneous clay stratum seepage field simulation, layered non-homogeneous sand stratum seepage field simulation, layered non-homogeneous clay stratum seepage field simulation, and sand-clay composite stratum seepage field simulation, wherein, When performing homogeneous sand stratum seepage field simulation, open the water inlet valve (3) and close the water outlet valve (7), and inject water into the model box (8) until the water level reaches 30%-50% of the height of the transparent soil (10) to form an initial underground water level, and simultaneously open the water outlet valve (7) and the water inlet valve (3), and adjust the flow of the water inlet pump (4) to make the readings of the water inlet flowmeter (5) and the water outlet flowmeter (6) equal, thereby forming a stable seepage field; When simulating the seepage field of homogeneous clay, the water inlet valve (3) and the water outlet valve (7) are opened simultaneously, the flow of the water inlet pump (4) is adjusted, and the readings of the water inlet flowmeter (5) and the water outlet flowmeter (6) are stabilized simultaneously on the order of m / s, forming a low-speed seepage field. When performing layered non-homogeneous sand stratum seepage field simulation, open the water inlet valve (3) and close the water outlet valve (7), and inject water into the model box (8) until the water level reaches 30%-50% of the height of the fine sand layer, close the water inlet valve (3) and open the water outlet valve (7), and close the water outlet valve (7) after the coarse sand layer is drained; finally, simultaneously open the water outlet valve (7) and the water inlet valve (3), and adjust the flow of the water inlet pump (4) to make the reading of the water inlet flowmeter (5) less than that of the water outlet flowmeter (6), thereby forming a non-stable seepage field; When simulating the seepage field of layered heterogeneous clay, open the water inlet valve (3) and close the water outlet valve (7), adjust the flow of the water inlet pump (4) to make the water inlet flow meter (5) stable at the order of m / s, forming a low-speed one-way infiltration field; When performing sand-clay composite stratum seepage field simulation, open the water inlet valve (3) and close the water outlet valve (7), and inject water into the model box (8) until the water level reaches the top of the sand layer to form an initial underground water level, then close the water inlet valve (3) and open the water outlet valve (7), thereby forming a one-way seepage field.

10. The method of testing the device for visualizing the seepage field of a shield tunnel in different strata according to claim 6, wherein: In step 5, the specific method for the post-processing mechanism (13) to obtain the seepage field velocity cloud chart includes: step 5.1, dividing the speckle field image into a plurality of grid cells; step 5.2, performing cross-correlation operation on the speckle field images of adjacent time instants in the same sub-region; step 5.3, locating the peak value coordinates of the cross-correlation function, calculating the average displacement vector of the particles in the sub-region, and obtaining the seepage field velocity cloud chart in the formation.

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