Underground Space Construction Catastrophe Influence on Surface Simulation Experiment System and Its Working Method

Abstract

The present invention belongs to the technical field of geotechnical and underground engineering tests, and provides a simulation experiment system for the influence of underground space construction disasters on the ground surface and its working method, including a formation distribution simulation device, a traffic load simulation device, and a ground surface deformation monitoring device; the formation distribution simulation device includes a simulation experiment box, and the internal of the simulation experiment box simulates the soil layer structure; a traffic load simulation device is arranged on the upper surface of the simulation experiment box; the traffic load simulation device includes a load loading block and a static and dynamic load loading device, the load loading block is placed on the upper surface of the simulation experiment box, and the static and dynamic load loading device is arranged on the load loading block to control the load loading block; the ground surface deformation monitoring device is arranged on one side of the ground surface soil layer simulation device for real-time obtaining of the ground surface soil layer deformation data.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical and underground engineering tests, and particularly relates to a simulation experiment system for the influence of underground space construction disasters on the ground surface and a working method thereof. Background Technique

[0002] The statements in this part only provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] Under the background of complex urban traffic road networks, when underground space construction passes under the main surface roads, construction disasters in the lower space (such as sand collapse and water and mud inrush) may cause formation displacement, which is very likely to cause ground surface settlement or collapse after developing to the ground surface, affecting surface traffic. Existing simulation experiment systems mainly focus on geomechanical model tests, which can better simulate underground space construction disasters. The simulation of surface dynamic and static traffic loads mainly focuses on the influence of traffic loads on the deformation of subgrade and pavement, but the influence of surface dynamic and static traffic loads is less considered in geomechanical model tests, and it is impossible to simulate the scenario of coexistence of underground space construction disasters and complex surface traffic road networks. Summary of the Invention

[0004] To solve the above problems, the present invention proposes a simulation experiment system for the influence of underground space construction disasters on the ground surface and a working method thereof. The present invention establishes a mapping relationship between construction disasters such as sand collapse and the surface traffic passing capacity to realize the simulation of different geological environment conditions.

[0005] According to some embodiments, the first solution of the present invention provides a simulation experiment system for the influence of underground space construction disasters on the ground surface, and adopts the following technical solutions:

[0006] The simulation experiment system for the influence of underground space construction disasters on the ground surface includes a formation distribution simulation device, a traffic load simulation device, and a ground surface deformation monitoring device;

[0007] The formation distribution simulation device includes a simulation experiment box, and the internal of the simulation experiment box simulates the soil layer structure; the upper surface of the simulation experiment box is sealed, and a traffic load simulation device is arranged on the upper surface of the simulation experiment box;

[0008] The traffic load simulation device includes a load loading block and a dynamic and static load loading device. The load loading block is placed on the upper surface of the simulation experiment box, and the dynamic and static load loading device is arranged on the load loading block to control the load loading block;

[0009] The ground surface deformation monitoring device is arranged on one side of the formation distribution simulation device for obtaining ground surface soil layer deformation data in real time.

[0010] The simulation test box is composed of multiple frames. A transparent acrylic board is connected to the frame on the front side of the simulation test box, and the remaining three sides of the simulation test box are made of steel plates;

[0011] The bottom plate of the simulation test box adopts a steel plate structure.

[0012] Furthermore, multiple frames between the four sides of the simulation test box are connected by bolts; the frames between the side surface and the bottom plate of the simulation test box are connected by bolts;

[0013] The transparent acrylic board and the frame on the front side of the simulation test box are bonded through a silica gel strip and glass glue.

[0014] Furthermore, three water injection holes are vertically arranged on the left side surface of the simulation test box, and the three water injection holes are located on a vertical straight line.

[0015] Furthermore, a tunnel opening is provided on the right side surface of the simulation test box, and a detachable plate is arranged on the tunnel opening.

[0016] Furthermore, the load loading blocks include a small passenger car simulation load loading block, a large passenger car simulation load loading block, and an articulated passenger car / train simulation load loading block.

[0017] Furthermore, the static and dynamic load loading device includes a reaction frame. The reaction frame is fixed on the top of the simulation test box, and a servo motor is fixed on the reaction frame. The servo motor is electrically connected to a servo loading control terminal;

[0018] A stress sensor is further connected to the bottom of the reaction frame, and the stress sensor is electrically connected to the servo loading control terminal.

[0019] Furthermore, the servo loading control terminal is externally connected to a display screen.

[0020] According to some embodiments, the second solution of the present invention provides a working method for a simulation experiment system for the impact of underground space construction disasters on the ground surface, adopting the following technical solutions:

[0021] The working method of the simulation experiment system for the impact of underground space construction disasters on the ground surface includes:

[0022] The formation distribution simulation process is specifically as follows:

[0023] According to the actual formation distribution of the project, soil layer simulation materials with different thicknesses are filled layer by layer from bottom to top. After the lower soil layer is compacted, another round of soil layer simulation material configuration is carried out;

[0024] The inclination angle between the fault and the surrounding rock is controlled by a wooden board;

[0025] After the soil layer is consolidated for 24 hours, a rectangular groove is excavated in the topmost layer of the soil layer, the subgrade simulation material is filled in the rectangular groove, and reflective sheets are arranged on the surface of the simulated subgrade.

[0026] The excavation simulation is carried out through the tunnel opening on the right side of the simulation test box, and the deformation of the soil body in the front side is observed through the transparent acrylic board.

[0027] Furthermore, it also includes:

[0028] The traffic load simulation process is specifically as follows:

[0029] The sensor feeds back the loading force value to the servo loading control terminal in real time through a pulse signal, and then the servo loading control terminal adjusts the servo motor to form a closed-loop loading control system;

[0030] Replace different types of load loading blocks, and through the display screen, set the loading frequency, set force magnitude, and load action time of the controllable load to simulate different vehicle types, load weights, and vehicle speeds respectively;

[0031] The application direction of the load is controlled by setting the magnitude of the force. When the pressure value reaches the simulated vehicle load value, the loading surface moves away from the road surface direction to complete one vehicle load application;

[0032] The vehicle load is simplified to a rectangular load, and the load action area is the length and width of the simulated vehicle.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] Through the simulation experiment system for the influence of underground space construction disasters on the ground surface, the present invention can simulate the scenario of the coexistence of complex surface traffic road networks and underground space construction disasters, obtain the surface deformation and stratum displacement caused by different surface traffic flows during underground space construction, establish the mapping relationship between construction disasters such as sand boiling and collapse and the surface traffic passing capacity, and can realize the real-time simulation of the surface traffic load flow, the real-time monitoring and acquisition of the surface settlement amount, and the real-time observation and recording of the stratum deformation range. At the same time, through different soil layer simulation materials, it can simulate the excavation of tunnels with different geological conditions (including poor geological conditions such as groundwater and sand layers) and different buried depths. Description of the Drawings

[0035] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0036] Figure 1 It is a three-dimensional view of the simulation experiment system for the influence of underground space construction disasters on the ground surface described in the embodiment of the present invention;

[0037] Figure 2 It is the left view of the simulation experiment system for the impact of underground space construction disasters on the ground surface described in the embodiments of the present invention;

[0038] Figure 3 It is the right view of the simulation experiment system for the impact of underground space construction disasters on the ground surface described in the embodiments of the present invention;

[0039] Figure 4 It is the front view of the simulation experiment system for the impact of underground space construction disasters on the ground surface described in the embodiments of the present invention;

[0040] Figure 5 It is the schematic diagram of the traffic load simulation method described in the embodiments of the present invention;

[0041] Figure 6 It is the simulation curve of the surface traffic flow load loading described in the embodiments of the present invention;

[0042] Figure 7 It is the schematic diagram of the lateral formation displacement range described in the embodiments of the present invention;

[0043] Figure 8 It is the curve of the vehicle type load changing with the vehicle speed and traffic flow described in the embodiments of the present invention;

[0044] Figure 9 It is the relationship curve between the surface collapse and the traffic flow and vehicle speed described in the embodiments of the present invention;

[0045] In the figure, 1 - simulation experiment box; 2 - frame; 3 - cross beam; 4 - transparent acrylic board; 5 - right side; 6 - load loading block; 7 - stress sensor; 8 - servo motor; 9 - reaction frame; 10 - tunnel entrance; 11 - water injection hole; 12 - left side. Detailed implementation manners

[0046] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0047] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further descriptions of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0048] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or their combinations.

[0049] Without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0050] Embodiment 1

[0051] As Figures 1 - 6 shown, this embodiment provides a simulation experiment system for the impact of underground space construction disasters on the ground surface, including a formation distribution simulation device, a traffic load simulation device, and a ground surface deformation monitoring device;

[0052] The formation distribution simulation device includes a simulation experiment box, and the internal of the simulation experiment box simulates the soil layer structure; the upper surface of the simulation experiment box is sealed, and a traffic load simulation device is arranged on the upper surface of the simulation experiment box;

[0053] The traffic load simulation device includes a load loading block and a static and dynamic load loading device. The load loading block is placed on the upper surface of the simulation experiment box, and the static and dynamic load loading device is arranged on the load loading block to control the load loading block;

[0054] The ground surface deformation monitoring device is arranged on one side of the formation distribution simulation device for real-time ground surface soil layer deformation data. Among them, the total station is used for the ground surface deformation monitoring device, and by setting the measurement interval time and automatically capturing the center position of the reflector arranged at the monitoring point, the full-automatic, whole-process continuous dynamic monitoring of the ground surface deformation is realized.

[0055] The simulation experiment system also includes a lateral soil layer displacement monitoring device, specifically a high-definition camera, which is placed directly in front of the transparent acrylic plate of the formation distribution simulation device to record the soil layer displacement process in real time and analyze the soil layer displacement curve.

[0056] Specifically, the simulation experiment box is composed of multiple frames. The frame on the front side of the simulation experiment box is connected with a transparent acrylic plate, and the other three sides of the simulation experiment box adopt steel plates;

[0057] The bottom plate of the simulation experiment box adopts a steel plate structure. The frames adopt angle irons, and the angle irons and the steel plates are connected by bolts.

[0058] The multiple frames between the four sides of the simulation experiment box are connected by bolts; the frames between the side surface and the bottom plate of the simulation experiment box are connected by bolts;

[0059] The transparent acrylic plate and the frame on the front side of the simulation experiment box are bonded by silicone strips and glass glue.

[0060] Among them, three water injection holes are vertically arranged on the left side surface of the simulation experiment box, and the three water injection holes are on a vertical straight line; a tunnel opening is arranged on the right side surface of the simulation experiment box, and a detachable plate is arranged on the tunnel opening.

[0061] Specifically, the load loading blocks include a small passenger car simulation load loading block, a large passenger car simulation load loading block, and an articulated bus / train simulation load loading block.

[0062] Specifically, the static and dynamic load loading device includes a reaction frame fixed on the top of the simulation test box. A servo motor is fixed on the reaction frame and is electrically connected to a servo loading control terminal. The servo loading control terminal is externally connected to a display screen.

[0063] A stress sensor is further connected to the bottom of the reaction frame and is electrically connected to the servo loading control terminal.

[0064] To study the influence mechanism of underground space construction disasters on surface traffic capacity under the specific scenario of the coexistence of complex urban surface traffic road networks and subway construction below, a model test system for the influence of underground space construction disasters on surface traffic is developed.

[0065] It is intended to establish a mapping relationship between construction disasters such as sand boiling and collapse and surface traffic capacity through simulation tests. For this purpose, the test device has the following functions:

[0066] (1) Real-time simulation of surface traffic load flow;

[0067] (2) Real-time monitoring and acquisition of surface settlement;

[0068] (3) Real-time observation and recording of formation deformation range;

[0069] (4) Capable of simulating the excavation of tunnels with different geological conditions (including poor geological conditions such as groundwater and sand layers) and different burial depths;

[0070] (5) During the test, it is possible to adjust the external force (surface static and dynamic loads, water pressure) state;

[0071] (6) The stiffness and sealing performance meet the test requirements;

[0072] (7) Capable of simulating multiple sand boiling and collapse disasters and recycling.

[0073] The influence of underground chamber excavation is generally less than 5% beyond 3 times the tunnel diameter and less than 1% beyond 5 times the tunnel diameter. When designing the model test system, a semi-structure is adopted to observe the formation deformation range. Finally, the size of the model test box is determined to be 0.6×0.8×1.0 m. The model test frame is connected and sealed by angle iron + bolts, and a high-strength sealant is applied to the contact surface. Transparent acrylic plates are placed on the symmetry plane to observe the formation deformation range. Three water injection holes are provided on the back plate of the tunnel entrance. During the test, a water storage tank with a corresponding water head height is set outside the model box according to the underground water level to inject water into the model box to simulate groundwater.

[0074] The model device is as follows Figure 1 , Figure 2 , Figure 3 and Figure 4 as shown in the figure, specifically including:

[0075] (1) The internal size of the model is 0.6×0.8×1.0m, taking a semi-structure.

[0076] (2) The bottom edge of the model frame is made of steel plate, the symmetry plane is made of transparent acrylic plate for observing the deformation of the soil layer, and the other three sides are made of steel plates to ensure the stiffness of the model. The frame is made of angle iron.

[0077] (3) The sides of the model box are connected to each other and to the ground by bolts through angle iron. Silicone strips are laid between the angle iron and the acrylic plate, and glass glue is evenly laid on both sides of the silicone strip with a glue gun. The joints of the rubber strips are cut at a 45° angle to ensure good sealing.

[0078] (4) Cross beams (angle iron) are set on the outer wall of the model frame, and the intersections of the angle iron are welded to jointly resist the lateral stress generated by the test with the test bench and prevent the lateral deformation of the test bench caused by soil pressure and water pressure.

[0079] (5) The tunnel entrance is horseshoe-shaped, located above the first layer of bedrock, and the tunnel burial depth is controlled by the soil layer thickness.

[0080] (6) Three water injection holes are opened on the back of the tunnel entrance. During the test, water is injected through a water pipe to simulate the groundwater environment, and the groundwater level is controlled by the water head height.

[0081] (7) The back panel of the tunnel entrance is set as a detachable plate with bolts, and a sealing rubber strip with bolt holes is additionally equipped to facilitate repeated experiments and reduce the workload.

[0082] For the development of the traffic load simulation device

[0083] Common traffic load classification

[0084] At present, the simulation of traffic load is roughly divided into three categories according to its action mode: dead load action, moving dead load action, and vibrating moving load. A brief introduction is as follows:

[0085] (1) Dead load action

[0086] The surface traffic flow changes continuously with time. The dead load action is often applicable to the simulation of traffic flow load over a long time span. At this time, the continuously changing traffic load can be simplified into a uniform load or a concentrated load acting on the road surface, and the magnitude of the load does not change with time. The load weight is often the self-weight of the vehicle itself.

[0087] (2) Moving dead load action

[0088] The above-mentioned constant load is moved in a certain direction to simulate the load of a moving vehicle. The force on the same point on the ground surface is expressed as a uniformly distributed load that occurs at a certain frequency. Its load value is the same as the constant load and cannot reflect the changes in the load generated by the vehicle during driving.

[0089] (3) Vibration moving load

[0090] Vibrating moving load can better simulate the characteristics related to vehicle dynamic load. It refers to the load simulation applied by the vehicle to the surface road surface by using a periodic load with a certain frequency and amplitude. The load size and action frequency can be changed according to the traffic map of different traffic flows in a certain area to simulate the traffic flow of different models and speeds.

[0091] like Figure 5 As shown in the figure, the common vibration moving load fitting methods can be roughly divided into two forms: sinusoidal steady-state vibration and random vibration. Among them, random vibration is the traffic load simulation method that is closest to the actual stress condition of the surface. However, in the actual simulation, since the flatness of the surface road itself is random, the various changes in the random vibration load simulation method have transient randomness. Only with the help of statistics, a series of tedious tasks such as actual measurement, classification and statistics of various different situations can the relevant model be established. This method consumes a lot of computing resources and requires a lot of data support. In addition, the established model is often of limited applicability, and it is difficult to draw conclusions with practical application value.

[0092] Therefore, this embodiment uses a sinusoidal steady-state curve to simulate the traffic load.

[0093] The traffic load simulation is as follows:

[0094] Traffic loads on urban roads are generated by various vehicles traveling at different speeds. To simulate traffic loads in a certain area of ​​the surface, it is actually to simulate the force process of the vehicle load on the road when it is traveling on the urban road. In actual situations, the dynamic load of the vehicle is a random load. This paper uses the commonly used sinusoidal steady-state curve to simulate the surface traffic load. When simulating vehicle loads with sinusoidal steady-state fluctuations, the vehicle load is generally divided into static load and dynamic load. For the value of static load, the current method is to convert it according to the vehicle load in the specification. If a car is used as the research object, it is generally 20kN, while for large cars, it is 100kN. For the value of the dynamic load, there is still a lot of controversy among relevant scholars. In summary, it is because the type of vehicle, the hardness of the suspension, the speed, etc. are very random.

[0095] The developed surface dynamic and static traffic load simulation device sets the static load part as the vehicle's own weight and the dynamic load part as the vehicle's load. During the actual driving process of the vehicle, the force change on the surface within a vehicle length area as the vehicle passes is a process from zero to the highest point and then back to zero, rather than a continuously acting static load. To make the traffic load simulation closer to the actual situation, the sum of the static load value and the dynamic load value is used as the vertex of the sine steady-state curve.

[0096] In actual working conditions, since the force on the surface during vehicle loading is affected by vehicle speed, road smoothness, stiffness, strength, flatness, and the strength of the soil layer under the road surface, the detected traffic load spectrum does not strictly follow a sine wave. During the actual model test loading process, the change trend of the interaction force between the simulated traffic load and the soil layer also does not completely follow the sine steady-state curve. During the traffic load loading process, the ground force will change due to the unevenness and deformation of the surface. To better control the loading process, the sine steady-state curve is further simplified to a trapezoidal load here. The peak value of the load is the maximum value of the sine steady-state load, the maximum value acting time is 1 / 3 of the loading period, and the loading period of the load is the same as that of the sine steady-state loading. Specifically, as Figure 6 shown.

[0097] Based on this, the traffic load data at different time nodes collected in actual projects are fitted to obtain the real load loading process of the vehicle during driving. The real-time control of the servo motor is achieved through programming on the intelligent control terminal. The sensor feeds back the loading force value to the control terminal in real time through a pulse signal, and then the control terminal adjusts the servo motor to form a closed-loop loading control system.

[0098] The functions and working processes of the traffic load simulation device are introduced as follows:

[0099] (1) Connect to the external control instrument display screen. Through programming, set the loading frequency, size, and time of the controllable load to simulate different vehicle types, loads, and vehicle speeds.

[0100] (2) Control the application direction of the load by setting the force size. When the pressure value reaches the simulated vehicle load value, the loading surface moves away from the road surface direction to complete one vehicle load loading.

[0101] (3) The vehicle load is simplified to a rectangular load, and the load acting area is the length and width of the simulated vehicle.

[0102] As shown in Table 1 and Table 2, according to the "Technical Standard for Highway Engineering" (JTG B01—2014), the surface traffic flow is divided into small passenger cars, large passenger cars, trucks, articulated buses, and articulated trains according to the outer contour dimensions of the designed vehicles. When simulating vehicle loads, considering the similarity scale of the model test and the outer contour dimensions of the designed vehicles, and considering the most unfavorable loading conditions, the acting area of the vehicle load is enlarged, and the projected area of the vehicle on the ground surface is used as the acting area of the load, without considering the load distribution of the front axle, middle axle, and rear axle of the vehicle.

[0103] Outer contour dimensions of representative vehicle models in Table 1 (unit: m)

[0104] Vehicle type Overall length (m) Overall width (m) Overall height (m) Front overhang (m) Wheelbase (m) Rear overhang (m) Passenger car 6 1.8 2 0.8 3.8 1.4 Large bus 13.7 2.55 4 2.6 6.5+1.5 3.1 Articulated bus 18 2.5 4 1.7 5.8+6.7 3.8 Truck 12 2.5 4 1.5 6.5 4 Articulated train 18.1 2.55 4 1.5 3.3+11 2.3

[0105] Outer contour dimensions of the loading blocks for simulating vehicle loads in Table 2

[0106] Vehicle type Simulated length (cm) Simulated width (cm) Passenger car 8.6 2.5 Large bus, truck 17.1 3.6 Articulated train, articulated bus 25.7 3.6

[0107] Example 2

[0108] This example provides a working method for a simulation experiment system of the impact of underground space construction disasters on the ground surface, including:

[0109] Process of simulating the surface soil layer, specifically:

[0110] According to the actual engineering stratum distribution, soil layer simulation materials with different thicknesses are filled layer by layer from bottom to top. After the lower soil layer is compacted, a new round of soil layer simulation material configuration is carried out;

[0111] The inclination angle between the fault and the surrounding rock is controlled by a wooden board;

[0112] After the soil layer is consolidated for 24 hours, a rectangular groove is excavated on the topmost soil layer, and subgrade simulation materials are filled in the rectangular groove, and reflective sheets are arranged on the surface of the simulated subgrade;

[0113] By carrying out excavation simulation at the tunnel entrance on the right side of the simulation test box, the deformation of the soil body inside the front side is observed through a transparent acrylic board.

[0114] Specifically, this method further includes:

[0115] Process of simulating traffic loads, specifically:

[0116] The sensor feeds back the loading force value to the servo loading control terminal in real time through a pulse signal, and then the servo loading control terminal adjusts the servo motor to form a closed-loop loading control system;

[0117] Replace different types of load loading blocks, and through the display screen, set the controllable loading frequency, set force magnitude, and load acting time of the load to simulate different vehicle models, load weights, and vehicle speeds respectively;

[0118] By setting the magnitude of the force to control the application direction of the load, when the pressure value reaches the simulated vehicle load value, the loading surface moves away from the road surface direction to complete one vehicle load application.

[0119] The vehicle load is simplified to a rectangular load, and the load acting area is the length and width of the simulated vehicle.

[0120] Specific embodiments are as follows:

[0121] 1. The process of simulating the stratum distribution is as follows:

[0122] (1) Stratum filling

[0123] According to the actual engineering stratum distribution, simulate materials with different thicknesses (medium weathered granite, sandy layer containing clay, plain fill) are filled from bottom to top in sequence. The density of the layer is controlled by controlling the filling quality.

[0124] To ensure the stability of the material properties during the filling process, the filling is carried out in layers. The thickness of each filling is 10 cm. The filling quality can be determined according to the density of the simulated material. Weigh and mix the simulated material according to the aforementioned relevant ratio until it is uniform, and then pour it into the model test box. After the filling is completed, use a hammer and an iron block to assist in ramming. Ram one layer at a time. After the underlying soil layer is compacted, configure and fill another round of simulated material. The inclination angle between the fault and the surrounding rock is controlled by a wooden board to reduce the influence of the artificial layering of the filling material on the test results.

[0125] When filling the overlying stratum of the tunnel, a dyed soil layer is filled every 10 cm to facilitate further observation of the lateral deformation of the soil body.

[0126] (2) Subgrade filling and maintenance

[0127] The subgrade is harder than the surface miscellaneous fill. Quick-hardening and early-strength sulphoaluminate cement is mixed with small stone chips for filling simulation. When filling the subgrade, in order to ensure that the shear force at the acrylic board of the symmetry plane is 0, vaseline is pre-applied on the inner side of the acrylic board before laying.

[0128] The specific filling method is as follows:

[0129] After the filling soil layer is consolidated for 24 h, a rectangular groove with a width of 15 cm (one-way four lanes) and a depth of 1 cm is excavated on the upper part of the first layer of soil, and the subgrade simulation material is filled and consolidated for 24 h. During the consolidation period, sprinkle water for maintenance to prevent cracking and deformation.

[0130] (3) Monitoring point layout

[0131] Reflective sheets are arranged on the subgrade surface. The reflective sheets are pasted on cardboard and inserted into the ground surface. During the test, the vertical displacement of the surface soil layer is recorded by a Leica high-precision total station. Taking the settlement amount as the Z value and the measuring point coordinates as the X and Y values, the settlement diagram is fitted through origin, and the deformation surface diagrams in the pre-, mid- and post-tunnel passing stages are established to analyze the settlement deformation characteristics of the surface subgrade in different stages.

[0132] (5) Excavation simulation

[0133] The excavation is carried out by using a self-made small iron shovel to simulate the drill and blast method, and the excavation step length is 3 cm each time.

[0134] (6) After the excavation is completed, record the surface settlement amount and the settlement amount of the subgrade part.

[0135] Observe the deformation of the side soil through a transparent acrylic board, record the displacement process by a high-definition camera, and draw the soil layer displacement curve through Origin according to the deformation of the dyed soil layer laid during the process of filling the simulated material. According to the relationship between the formation displacement range and size and the surface settlement range and settlement amount, the formula is obtained by fitting.

[0136] 2. The process of traffic load simulation is as follows:

[0137] According to the vehicle type, the traffic load is divided into three levels from low to high risk:

[0138] Level 3 traffic load: Passenger car, speed 60 km / h, vehicle weight 1.5 t, load 0.5 t

[0139] Level 2 traffic load: Large bus, truck, speed 40 km / h, vehicle weight 6 t, load 2.5 t

[0140] Level 1 traffic load: Articulated train, articulated bus, speed 20 km / h, vehicle weight 10 t, load 10 t.

[0141] The vehicle weight and load in the above data are referenced from "Limits for Dimensions, Axle Loads and Masses of Motor Vehicles, Trailers and Semi-trailers" (GB 1589 - 2016).

[0142] Using the relationship formula between driving speed and loading time

[0143]

[0144] In the formula, L is the vehicle length.

[0145] According to the above formula, the loading times of the traffic loads under the three levels are 0.4 s, 1.2 s, and 1.7 s in sequence.

[0146] After the similarity ratio conversion, the simulation situations of the traffic loads of the three risk levels are shown in Table 3 below.

[0147] Table 3 Outer contour dimensions of the simulated vehicle load loading block

[0148] Traffic load risk level Maximum load application (N) Single - cycle load application time (s) Level 3 (safest) 286 0.4 Level 2 1214 1.2 Level 1 (most dangerous) 2857 1.7

[0149] After testing with the simulation experimental system for the impact of underground space construction disasters on the ground surface described in Example 1, it is not difficult to find that the shape of the stratum displacement in the cross-section parallel to the tunnel excavation direction after sand bursting and collapse is approximately composed of two trapezoids. In the actual engineering excavation process, support measures will be taken for the tunnel surrounding rock in the excavated part, and there will be no large-area exposure of the surrounding rock in this model test. After the support is applied, the stability of the rock mass is good, and it is difficult for a large area of soil layer to drop above it under the action of surface traffic load.

[0150] Therefore, in this embodiment, only the stratum displacement of the part close to the ground surface, that is, the upper trapezoid, is analyzed to obtain the theoretical model of stratum displacement settlement considering the action of surface traffic load. The analysis of the shape of the stratum displacement of the part close to the ground surface is as Figure 7 shown. In the figure, l is the length of the short side of the trapezoid, φ0 is the loosening angle of the sand bursting and collapse body of the stratum, which can be taken as the internal friction angle of the sand and soil mass in the sand layer, S max is the maximum ground surface settlement after sand bursting and collapse, b0 is the ground surface settlement range, and σ v is the load value generated by the surface traffic flow.

[0151] Considering the discriminant of the passing capacity of large buses, five sets of ground surface collapse settlement data are selected for analysis under the condition of ensuring the same stratum distribution.

[0152] Analysis of the value of the short side l of the model

[0153] The length l of the short side of the trapezoid is related to the vehicle type acting on the ground surface after the sand bursting and collapse disaster of the stratum. l can be approximately the axis length of the simulated vehicle type. The explanation from the mechanism of sand bursting and collapse of the stratum is as follows:

[0154] In the analysis of the formation displacement model, the quicksand collapse disaster occurring after the excavation of the lower tunnel is caused by the reciprocating action of surface traffic loads. Considering the most unfavorable stress condition, it is assumed that the tunnel is just excavated directly below the traffic load action surface. According to the aforementioned analysis of the mechanism of lateral formation quicksand collapse, under the action of traffic loads, the formation experiences three stages: elastic-elastic plastic-plastic and finally loses stability. Since the action area of the traffic load is the projection of the corresponding vehicle type in the vertical road surface direction, after the quicksand collapse occurs, the vehicle load displaces downward with the formation due to the loss of the support of the surface soil layer. The gravity of the vehicle itself exerts a load on the upper part of the loose formation of the collapse, accelerating the downward displacement of the formation. When the volume of the quicksand collapse accumulated in the lower tunnel is large enough, the soil medium accumulation body can reach equilibrium with the upper loose soil layer and the vehicle load as a counter-pressure body. At this time, the vehicle acts as a dense block to block the channel for the loose quicksand collapse body to continue to displace downward, and the collapse process ends. Therefore, the length of the short side of the trapezoid in the model can be approximately the vehicle axis length.

[0155] Maximum surface settlement S max Research on the value of

[0156] Traffic flow load σ v Affected by three factors: vehicle type, vehicle speed and traffic flow, the empirical formula of formation loss ratio and surface load is as follows:

[0157] V L =1.33(σ s +γH - σ T ) / τ f -1.4 (2)

[0158] In the formula, γ is the unit weight of soil; H is the buried depth of the tunnel axis; σ s is the ground load; T is the tunnel support pressure; τ f is the undrained shear strength of the soil at the tunnel axis depth.

[0159] In this embodiment, it is intended to equivalently replace the traffic flow load σ v with the ground load σ s in formula (2). Therefore, it is necessary to correct it according to the three influencing factors of σ v .

[0160] Formation loss ratio V l refers to the ratio of the loss of the surface soil layer during tunnel excavation to the nominal excavation area of the tunnel, which is obtained by integrating both ends of the Peck formula. Among them, the Peck formula is as follows:

[0161]

[0162] In the formula, s maxis the maximum surface settlement at the tunnel centerline after tunnel excavation; i is the width of the settlement trough; x is the horizontal distance between the surface settlement point and the tunnel centerline, and the maximum surface settlement is s max is related to the tunnel excavation radius R and the ground loss ratio V l and the width i of the settlement trough have the following relationship:

[0163]

[0164] The width i of the settlement trough is mainly related to the buried depth H of the tunnel axis, the tunnel radius R and the internal friction angle of the stratum. In order to describe the width of the surface settlement trough more simply, let the settlement trough width coefficient k = i / H.

[0165] Since the displacement stratum simulated in this paper is mainly sandy soil containing clay, the formula (5) is proposed to be applicable to the settlement trough width coefficient of sandy soil in the model test, as follows:

[0166] k = 0.2047 + 0.3361 / H (5)

[0167] When the buried depth H is 7m, the settlement trough width coefficient k is 0.253, and the corresponding settlement trough width i is 1.769m calculated according to the stratum distribution corresponding to the five load combinations.

[0168] The stratum distribution and the maximum surface settlement under the five combinations are shown in Table 4 below,

[0169] Table 4 Maximum surface settlement under different load combinations

[0170]

[0171]

[0172] According to the above data, the corresponding ground load σ under the 5 combinations can be obtained from Equation (2) and Equation (3) s The values are shown in Table 5 below. The τf values in the table refer to the direct shear test data in Chapter 2.

[0173] Table 5 Corresponding ground load σ under different load combinations s

[0174]

[0175] According to the traffic load simulation described above, the stress generated by the large bus model on the ground is the ratio of the vehicle load to the acting area. It can be calculated that the stress value generated by the large bus model is 2.614 kPa. Figure 7 The ground load σ in v can be expressed as the vehicle type load σ c , the vehicle speed correction factor α v and the traffic flow correction factor βt The function is as follows:

[0176] σ v = f(σ c , α v , β t ) (6)

[0177] In the formula, the vehicle type load σ c can be determined according to the vehicle load values of cars, buses, and articulated trucks, and can be considered as a constant term. Therefore, the ground load σ v can be regarded as a binary function of the vehicle speed correction factor α v and the traffic flow correction factor β t , σ v = f(α v , β t ). According to the model test results, when the vehicle speed correction factor σ v is a constant, σ v can be approximately regarded as an exponential function of the traffic flow correction factor β t :

[0178]

[0179] When the traffic flow correction factor β t is a constant, σ v can be approximately regarded as a quadratic function of the vehicle speed correction factor α v :

[0180]

[0181] Combining formula (7) and formula (8), the functional form of σ v = f(α v , β t ) can be obtained as:

[0182]

[0183] In the formula, A, B, C, and D are all undetermined constants. Using the Origin data analysis software, non-linear data fitting is performed on σ v under different α t and β v according to formula (9), and the obtained result is as shown in formula (10). The corrected determination coefficient R of the fitting result is 0.87038.

[0184]

[0185] The variation of σ v obtained from the fitting formula with α v and β is as shown in Figure 8 , σ vIt has a positive correlation with the traffic flow. The relationship with the vehicle speed is affected by the traffic flow. When the traffic flow is low, the influence of the vehicle speed on σv is very small. As the traffic flow increases, the relationship between the vehicle speed and σ v tends to be positively correlated.

[0186] Define the right side of the equal sign in Equation (10) as the surface traffic flow correction factor T, and then we get:

[0187] σ v = Tσ c (11)

[0188] From Equations (2), (3), and (11), the maximum displacement S of the stratum collapse loose body considering the surface traffic flow can be obtained max as shown in the following formula:

[0189]

[0190] The meanings of the symbols in the formula are the same as those in the previous text.

[0191] Specifically, the method for judging whether there is surface collapse

[0192] From the results of the aforementioned model tests, for the typical vehicle load of a large bus, it is impossible to determine whether it can safely pass through the underpass construction section. Therefore, the load influencing factors are further divided, and two traffic flow factors, vehicle speed and traffic flow, are introduced. The relationship between whether there is surface collapse and the vehicle load traffic flow under the action of a large bus (secondary traffic load) is established as Figure 9 shown, and this figure can be used as a basis for preliminarily judging whether the surface collapses.

[0193] From Figure 9 as shown, when the combination of traffic flow and vehicle speed exceeds the surface traffic capacity, surface collapse occurs. When the combination is within the safe range, surface settlement occurs, and the maximum value of surface deformation can be calculated by Equation (12).

[0194] Specific application examples

[0195] Based on the case of the sand and collapse accident in the Jingsha section of Qingdao Metro Line 4, the applicability of the theoretical model is verified from the aspects of the collapse result and the collapse range.

[0196] Engineering geological conditions

[0197] The right line of the tunnel from Jinggang Road Station to Shazikou Section of Qingdao Metro Line 4 is 1143m long, and the left line is 1123m long. The mining method + shield method is used for construction. When constructing under the Fishing Port Road, a sudden sand and collapse accident occurred at the tunnel face. The buried depth of the arch crown of the underlying stratum is 18m, the excavation diameter is 6m, and the cave-in in the tunnel developed to the surface. There is a ground collapse of about 591m2 on the surface, with a depth of about 10m and a width of about 25m - 31m, showing an irregular shape.

[0198] Analysis of the Causes of Collapse Disasters

[0199] The content of cohesive soil in the sand layer exposed at the tunnel vault is relatively low, and the cementing ability of the sand layer is weak. The tunnel excavation axis passes under the main urban traffic artery, and the surface traffic flow is large, with reciprocating traffic loads. When a free surface is generated during the excavation of the lower tunnel, under the action of the surface traffic load, the fine cohesive soil particles inside the sand layer at the vault area move relative to each other, resulting in the appearance of a fracture surface inside the sand layer. As the fracture surface continues to expand, the cementing ability between the sand layers is further reduced. Eventually, when the sand layer in the vault area cannot bear the surface traffic load and the gravity of the overlying strata, the sand layer undergoes shear failure, and a sand collapse and loosening body appears on the surface, and the sand collapse disaster occurs.

[0200] Calculation of the Results and Scope of Surface Collapse

[0201] The Yugang Road passing through this section is a four-lane two-way road with a designed speed of 60 - 80 km / h. Since its location is not a main urban artery, the daily traffic volume can be considered average. According to Figure 9 the relationship between whether surface collapse occurs and traffic volume and vehicle speed shown, it is preliminarily judged that a collapse accident is extremely likely to occur under this working condition. According to the calculation of the maximum surface subsidence depth S max = 8.29 m by formulas (10) - (12), the actual maximum settlement at the accident site is 10 m. Compared with the actual maximum settlement of the project, the calculation result of the theoretical formula is on the small side, but the error is controlled within 20%, verifying the accuracy of the theoretical formula, which can be used as a reference for the safe excavation of related projects.

[0202] Based on the results of the model test, a theoretical model of the vertical displacement of the surface soil under the combined action of shallow tunnel excavation and upper traffic flow is established. The main conclusions are as follows:

[0203] (1) After the sand collapse of the lower tunnel is caused by the surface traffic flow, the shape of the collapse and loosening body near the ground is approximately a trapezoid with a longer upper side and a shorter lower side. The shorter side of the trapezoid is approximately the vehicle length of the vehicle type corresponding to the traffic load acting on the upper part at the time of collapse.

[0204] (2) The influencing factors of the surface traffic load are divided into vehicle type, vehicle speed, and traffic volume. Based on this, taking the load of a large bus, a typical uncertain vehicle type, as an example, a preliminary judgment method for whether surface collapse occurs under different combinations of vehicle speed and traffic volume is proposed, and a quantitative relationship formula between the maximum vertical deformation of the surface under the action of traffic load and traffic load is established. The formula is verified through actual projects, and the error between the calculated displacement of the theoretical formula and the actual displacement of the project is within 20%.

[0205] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications or deformations that can be made without creative efforts on the basis of the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. The simulation experiment system for the influence of underground space construction disasters on the ground surface is characterized in that It includes a formation distribution simulation device, a traffic load simulation device, and a ground surface deformation monitoring device; The formation distribution simulation device includes a simulation test box, and the internal of the simulation test box simulates the soil layer structure; the traffic load simulation device is arranged on the upper surface of the simulation test box, and the upper surface is sealed; The simulation test box is composed of multiple frames. The frame on the front side of the simulation test box is connected with a transparent acrylic board, and the other three sides of the simulation test box adopt steel plates; The bottom plate of the simulation test box adopts a steel plate structure; cross beams are arranged on the outer wall of the model frame. The cross beams adopt angle irons, and the intersections of the angle irons are welded to jointly resist the lateral stress generated by the test with the test bench and prevent the lateral deformation of the test bench caused by soil pressure and water pressure; The simulation experiment system also includes a lateral soil layer displacement monitoring device, specifically a high-definition camera, which is placed directly in front of the transparent acrylic board of the formation distribution simulation device to record the process of soil layer displacement in real time and analyze the soil layer displacement curve; The traffic load simulation device includes a load loading block and a static and dynamic load loading device. The load loading block is placed on the upper surface of the simulation test box, and the static and dynamic load loading device is arranged on the load loading block to control the load loading block; A sine steady-state curve is used to simulate the traffic load; the sine steady-state curve is simplified into a trapezoidal load. The peak value of the load action is the maximum value of the sine steady-state load, the maximum value action time is 1 / 3 of the loading period, and one loading period of the load is the same as one period time of the sine steady-state loading; An external control instrument display screen is connected. Through programming, the loading frequency, size, and time of the controllable load are set to realize the simulation of different vehicle types, load weights, and vehicle speeds; the application direction of the load is controlled by setting the size of the force. When the pressure value reaches the simulated vehicle load value, the loading surface moves away from the road surface direction to complete one vehicle load loading; the vehicle load is simplified into a rectangular load, and the load action area is the length and width of the simulated vehicle; The ground surface deformation monitoring device is arranged on one side of the formation distribution simulation device to obtain the ground surface soil layer deformation data in real time; The ground surface deformation monitoring device adopts a total station. By setting the measurement interval time and automatically capturing the center position of the reflection sheet arranged at the monitoring point, the full-automatic whole-process continuous dynamic monitoring of the ground surface deformation is realized; Three water injection holes are vertically arranged on the left side surface of the simulation test box, and the three water injection holes are on a vertical straight line; A tunnel opening is provided on the right side surface of the simulation test box, and a detachable plate is arranged on the tunnel opening; The load loading block includes a small passenger car simulation load loading block, a large passenger car simulation load loading block, and an articulated bus / train simulation load loading block.

2. The simulation experiment system for the impact of underground space construction disasters on the ground surface according to claim 1, characterized in that, The multiple frames between the four side surfaces of the simulation test box are connected by bolts; the frames between the side surface and the bottom plate of the simulation test box are connected by bolts; The transparent acrylic board and the frame on the front side surface of the simulation test box are bonded by a silica gel strip and glass glue.

3. The simulation experiment system for the impact of underground space construction disasters on the ground surface according to claim 1, characterized in that, The static and dynamic load loading device includes a reaction frame fixed on the top of the simulation test box, and a servo motor is fixed on the reaction frame and electrically connected to a servo loading control terminal; A stress sensor is further connected to the bottom of the reaction frame and electrically connected to the servo loading control terminal.

4. The simulation experiment system for the influence of underground space construction disasters on the ground surface according to claim 3, characterized in that, The servo loading control terminal is externally connected to a display screen.

5. The working method of the simulation experiment system for the impact of underground space construction disasters on the ground surface according to any one of claims 1-4, characterized in that, It includes: The process of simulating the formation distribution, specifically: According to the actual engineering formation distribution, soil layer simulation materials with different thicknesses are filled layer by layer from bottom to top. After the lower soil layer is compacted, another round of soil layer simulation material configuration is carried out; The inclination angle between the fault and the surrounding rock is controlled by a wooden board; After the soil layer is consolidated for 24 hours, a rectangular groove is excavated on the topmost layer of the soil layer, and subgrade simulation materials are filled in the rectangular groove, and reflective sheets are arranged on the surface of the simulated subgrade; Excavation simulation is carried out through the tunnel entrance on the right side of the simulation test box, and the deformation of the soil body inside the front side is observed through a transparent acrylic board.

6. The working method of the simulation experiment system for the impact of underground space construction disasters on the ground surface according to claim 5, characterized in that, It also includes: The process of simulating traffic loads, specifically: The sensor feeds back the loading force value to the servo loading control terminal in real time through a pulse signal, and then the servo loading control terminal adjusts the servo motor to form a closed-loop loading control system; Replace different types of load loading blocks, and through the display screen, set the controllable loading frequency, set force magnitude and load action time of the load to simulate different vehicle types, load weights and vehicle speeds respectively; Control the application direction of the load by setting the magnitude of the force. When the pressure value reaches the simulated vehicle load value, the loading surface moves away from the road surface direction to complete one vehicle load loading; The vehicle load is simplified to a rectangular load, and the load acting area is the length and width of the simulated vehicle.

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