Fault-crossing tunnel test simulation method under combined action of ground vibration and fault movement

Abstract

The invention discloses a cross-fault tunnel test simulation method under the combined action of ground vibration and fault movement, and belongs to the technical field of tunnel engineering model tests.The method comprises the following steps that firstly, the similarity relation of models is determined; 2, manufacturing a tunnel lining test model; 3, manufacturing a test model box; fourthly, surrounding rock is poured; 5, pressurizing the model box to simulate the tunnel burial depth; step 6, simulating fault dislocation; and step 7, applying seismic oscillation. In the invention, the designed horseshoe-shaped flexible model box replaces a rigid model box adopted by a conventional model test, the test cost is low, the test can be completed on one set of test system without designing several additional devices for cooperation, the operation process is simple, the feasibility is high, and the test efficiency is improved by considering the influence of ground stress aiming at the characteristic that the tunnel passes through the active fault. The deformation and failure evolution law of the tunnel under the combined action of seismic oscillation and fault movement is comprehensively analyzed, and the real site condition is better reflected.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering model tests, and in particular relates to a simulation method for a cross-fault tunnel test under the combined action of earthquake motion and fault dislocation. Background Art

[0002] With the rapid development of land transportation network, more and more tunnel projects are being built, such as mountain tunnels, urban subway tunnels and undersea tunnels. In difficult mountainous areas with complex geological conditions, mountain tunnels usually need to pass through faults or fault fracture zones, especially in southwest my country, where there are a large number of active faults. In addition, due to the Eurasian continent and the Himalayas seismic belt, the construction of tunnel projects here has to consider the requirements of earthquake resistance and fault resistance of underground structures. Therefore, the study of the mechanical characteristics and failure forms of tunnels across active faults has important theoretical significance and engineering value. At present, the methods for studying the earthquake resistance and fault resistance of tunnels across faults include theoretical analysis, numerical simulation and model tests. Among them, the theoretical analysis method requires a series of assumptions to be set in advance, and the research results obtained are often greatly deviated from the actual results. The numerical simulation method has high requirements on the skills of the operators and requires a large calculation cost, which leads to certain limitations in the application of the two methods. The model test uses similar materials to cast surrounding rock and lining according to the similarity theory, which can more intuitively and concisely show the evolution process of the mechanical properties of underground structures.

[0003] The prior art discloses some invention patents in the field of tunnel engineering model test technology, among which the invention patent with publication number CN118624268A discloses a test device and method for simulating the dislocation of a cross-fault tunnel, comprising: a first active surface, which is given a side wall surface defining a test cavity, and during the test, the first active surface can form a first loading force that acts constantly on the test cavity in the horizontal direction; a second active surface, which is given an end surface defining the test cavity, and the second active surface forms a second loading force that acts on the test cavity in the vertical direction, and the second loading force has a switchable vertical upward / downward or static action direction, so that the test cavity forms an upward / downward or static interval, respectively, wherein when the static interval and the upward interval are formed in the test cavity at the same time, the test cavity is used to simulate the dislocation of a reverse fault, and when the static interval and the downward interval are formed in the test cavity at the same time, the test cavity is used to simulate the dislocation of a normal fault, which can improve the simulation effect of normal and reverse fault dislocation tests.

[0004] When a tunnel crosses an active fault, it is simultaneously exposed to the hazards of earthquake motion and fault dislocation. At present, most experiments consider the two separately, using a vibration table or centrifuge to study the mechanical response characteristics of a cross-fault tunnel under earthquake motion, and using a self-designed fault dislocation simulation device to simulate fault dislocation. The separate consideration of the two limits the application of research results in tunnel projects crossing active faults. In addition, tunnels built in western my country are often buried at great depths and are significantly affected by high ground stress. The existing device for simulating the deep buried state of the tunnel uses an external air bag to simulate the deep buried stress field. This method requires multiple devices to cooperate with each other and is cumbersome to operate. Therefore, it is necessary to propose a new experimental simulation method to study the mechanical response characteristics of a cross-fault tunnel under the combined action of earthquake motion and fault dislocation. Summary of the invention

[0005] The purpose of the present invention is to solve the harm caused by earthquake motion and fault dislocation when tunnels cross active faults. At present, most experiments consider the two separately, using a vibration table or a centrifuge to study the mechanical response characteristics of cross-fault tunnels under earthquake motion, and using a self-designed fault dislocation simulation device to simulate fault dislocation. The separate consideration of the two limits the application of research results in tunnel projects crossing active faults. In addition, tunnels built in western my country are often in a state of great burial depth and are significantly affected by high ground stress. In the existing device for simulating the deep buried state of tunnels, an external air bag is used to simulate the deep buried stress field. This method requires multiple devices to cooperate with each other and is cumbersome to operate. Therefore, it is necessary to propose a new experimental simulation method to study the problem of mechanical characteristics of cross-fault tunnels under the combined action of earthquake motion and fault dislocation, and a cross-fault tunnel experimental simulation method under the combined action of earthquake motion and fault dislocation is proposed.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for simulating a cross-fault tunnel test under the combined action of earthquake motion and fault dislocation, the method comprising the following steps:

[0008] S1: River sand, gypsum, cement and water are used as raw materials to cast the segmental circular tunnel lining model. The total length of the circular tunnel lining model after splicing is 2000mm;

[0009] S2: Make a horseshoe-shaped flexible model box with a height of 870 mm, a width of 1140 mm, and a length of 2000 mm;

[0010] S3: Standard sand, gypsum and water are used as raw materials to simulate similar surrounding rocks within the fault, and standard sand, gypsum, lime, barite powder and water are used as raw materials to simulate similar surrounding rocks on both sides of the fault;

[0011] S4: Place the horseshoe-shaped flexible model box into the servo-controlled variable stiffness tunnel lining static-dynamic loading test system, fit the pressure head assembly in the test system to the outer surface of the horseshoe-shaped flexible model box, then lay a certain thickness of test surrounding rock and compact it, paste the transverse and longitudinal strain gauges and acceleration sensors on the segmental circular tunnel lining model, and after the acceleration sensors are pasted, splice the segmental circular tunnel lining model into a whole and place it in the middle of the horseshoe-shaped flexible model box, and continue to backfill similar surrounding rock and compact until the horseshoe-shaped flexible model box is completely poured;

[0012] S5: Calculate the stress field of the studied tunnel in the site, determine the stress field size during the indoor test according to the stress similarity ratio, adjust all the pressure head components to the pressure control mode, fit them with the horseshoe-shaped flexible model box, and set the pressure size to this value;

[0013] S6: Determine the displacement position of the fault, adjust the pressure head at the corresponding position to the displacement control mode, extend and move the pressure head at the corresponding position of the test system to simulate the displacement of the active fault, use the vibration platform at the bottom to complete the ground motion simulation, realize the cross-fault tunnel test under the combined action of ground motion and fault displacement, and record the data monitored by the sensor;

[0014] S7: Take out the circular lining model from the horseshoe-shaped flexible model box, observe and record the development of the circular tunnel lining cracks, and end the test.

[0015] As a further description of the above technical solution:

[0016] In step S1, the particle size of the river sand is between 0.8 and 2 mm, and the gypsum is glue-free quick-drying gypsum.

[0017] As a further description of the above technical solution:

[0018] The strike of the fault is 0°, and the dip angle of the fault is 90°.

[0019] As a further description of the above technical solution:

[0020] The horseshoe-shaped flexible model box is made of a rubber plate sandwiched with a metal frame layer. Transparent acrylic covers are provided at both ends of the horseshoe-shaped flexible model box. The outer diameter of the acrylic cover is the same as that of the horseshoe-shaped flexible model box, and the inner diameter is the same as that of the circular tunnel lining model.

[0021] As a further description of the above technical solution:

[0022] The rigidity of the rubber sheet sandwiched between the metal skeleton layers is equivalent to the rigidity of similar surrounding rocks on both sides of the fault, and the thickness of the rubber sheet sandwiched between the metal skeleton layers is 50 mm.

[0023] As a further description of the above technical solution:

[0024] The acrylic cover plates at both ends of the horseshoe-shaped flexible model box are respectively formed by splicing three acrylic plates with a height of 25.67 cm, and the spliced ​​parts are connected into a whole by epoxy resin glue.

[0025] As a further description of the above technical solution:

[0026] The horseshoe-shaped flexible model box is hinged to the acrylic cover plate.

[0027] As a further description of the above technical solution:

[0028] The segmental circular tunnel lining model is spliced ​​together by epoxy resin glue.

[0029] As a further description of the above technical solution:

[0030] The rigidity of the rubber sheet sandwiching the metal skeleton layer needs to be measured by a uniaxial compression test.

[0031] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0032] 1. In the present invention, the horseshoe-shaped flexible model box is designed to replace the rigid model box used in conventional model tests, so the test cost is low, the test expenses are saved, and it can be completed on a set of test systems without the need to design several additional devices to cooperate with each other. The operation process is simple and the feasibility is strong.

[0033] 2. In the present invention, the characteristics of tunnels crossing active faults are taken into account, the influence of ground stress is considered, and the deformation and damage evolution law of the tunnel under the combined action of ground motion and fault dislocation are comprehensively analyzed to better reflect the actual site conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of the state of the pressure head assembly during the model casting process in a cross-fault tunnel test simulation method under the combined action of earthquake motion and fault dislocation proposed by the present invention;

[0035] Figure 2 A schematic diagram of the arrangement of sensors on the left and right side walls of a circular tunnel lining in a cross-fault tunnel test simulation method under the combined action of ground motion and fault dislocation proposed by the present invention;

[0036] Figure 3 A schematic diagram of the state of a pressure head assembly for simulating a tunnel deep-buried stress field in a cross-fault tunnel test simulation method under the combined action of ground motion and fault dislocation proposed by the present invention;

[0037] Figure 4 A schematic diagram of the state of a simulated fault displacement pressure head assembly in a cross-fault tunnel test simulation method under the combined action of ground motion and fault displacement proposed by the present invention;

[0038] Figure 5 The present invention is a schematic flow chart of an embodiment of a method for simulating a cross-fault tunnel test under the combined effects of earthquake motion and fault dislocation proposed by the present invention.

[0039] Legend:

[0040] 1. Horseshoe-shaped flexible model box; 2. Acrylic cover; 3. Circular tunnel lining model; 4. Fault dislocation simulation position. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The servo-controlled variable stiffness tunnel lining static-dynamic loading test system is used to conduct cross-fault tunnel tests under the combined action of ground motion and fault displacement. The test system includes:

[0043] Servo electric cylinders are used for test loading, which can realize displacement or force loading modes and effectively maintain constant displacement when the test is paused;

[0044] The control system adjusts the pressure of the stiffness adjustment cylinder in real time according to the displacement monitored by the displacement sensor and the preset stiffness value to ensure constant stiffness loading during the test;

[0045] The variable stiffness test loading system contains 36 pressure heads, each of which can be controlled individually or simultaneously;

[0046] The vibration frequency of the vibration platform is within the range of 0-20Hz, which meets the input requirement that the main frequency of the real seismic wave is within the range of 0-10Hz.

[0047] The present invention will be further described below in conjunction with the accompanying drawings.

[0048] Embodiment 1:

[0049] (1) Step 1: Determine the similarity relationship of the model;

[0050] Taking length, density and elastic modulus as basic physical quantities, according to the Bukingham principle, the relationship between other physical quantities is derived. In this example, the similarity relationship of length is determined to be 1 / 30, density is 1 / 1, and elastic modulus is 1 / 20, as shown in the following table:

[0051]

[0052]

[0053] (2) Step 2: Make a tunnel lining test model;

[0054] River sand, gypsum, cement and water were selected as raw materials to cast 100*100*100mm cubic specimens, the proportions of the four raw materials were adjusted, and the ratio of 1 / 20 of the C25 concrete strength was determined through uniaxial compression test. A steel cylinder with a length of 500mm, a diameter of 320mm and a thickness of 5mm was selected as the external mold of the segmental circular tunnel lining, and a steel cylinder with a length of 500mm, a diameter of 288mm and a thickness of 3mm was selected as the internal mold of the segmental circular tunnel lining. The external mold and the internal mold were cut into two parts on average, and the cut parts were re-fixed by bolts and nuts. After that, the spliced ​​external mold and internal mold were fixed on a concentric base, and a wire mesh with a diameter of 1mm was placed inside. According to the predetermined lining simulation materials and ratios, several lining models were cast for repeated and controlled tests. After three days, the molds were removed and placed in a dryer for drying. After drying, a layer of varnish was applied on the surface to prevent it from getting damp.

[0055] (3) Step 3: Making a test model box;

[0056] A horseshoe-shaped flexible model box is manufactured. The height of the model box is 870mm, the width is 1140mm, the length is 2000mm, and the thickness is 50mm. It is made of a rubber plate sandwiched by a metal skeleton layer. The metal skeleton can play a certain supporting role to prevent the rubber plate from deforming and failing to reach the preset shape. A uniaxial compression test is carried out on the rubber plate sandwiched by a metal skeleton layer to determine its stiffness and satisfy the requirement that the stiffness is equivalent to the stiffness of the surrounding rock on both sides of the fault. The manufactured horseshoe-shaped flexible model box is placed in a servo-controlled variable stiffness tunnel lining static-dynamic loading test system. The pressure head assembly in the test system is fitted to the outer surface of the horseshoe-shaped flexible model box, but no displacement is applied. Figure 1 As shown;

[0057] (4) Step 4: pouring surrounding rock;

[0058] Install a layer of acrylic board. The acrylic board and the horseshoe-shaped flexible model box are connected by hinges. The test surrounding rock on both sides of the fault and the test surrounding rock inside the fault are laid respectively. The fault is located in the middle of the model box. The width is 100mm. Compact once every 50mm thickness. When the surrounding rock height is 225mm, divide the lining model into 9 monitoring sections. Monitoring section 5 is located inside the fault. The distance between monitoring sections 3-4, 4-5, 5-6, and 6-7 is 116.5mm, and 1-2 The distance between the monitoring sections No. 1, 2-3, 7-8, and 8-9 is 333 mm. The longitudinal and circumferential strain gauges are respectively pasted on the left and right walls of the sections No. 4-6. The longitudinal strain gauges are pasted on the left and right walls of the sections No. 1-3 and 7-9. The strain gauge model is BFH120-50AA-R1-D150. The acceleration sensors are pasted on the left and right walls of the sections No. 1-9. The acceleration sensor model is 1C302. The pasted segmental circular tunnel lining is connected as a whole by epoxy resin glue. Figure 2 As shown, the circular tunnel lining model is placed in the middle of the horseshoe-shaped flexible model box, and similar surrounding rocks are backfilled and acrylic plates are installed until the horseshoe-shaped flexible model box is completely filled. The acrylic plates are connected by epoxy resin glue. After the model is left to stand for 24 hours and formed, the extended pressure head is retracted.

[0059] (5) Step 5: Pressurizing the model box to simulate the stress field of the deep buried tunnel;

[0060] In this example, the tunnel depth is taken as 100m, and the vertical stress field σ of the studied tunnel in the real site is calculated. h =γh, where γ is the bulk density of the surrounding rock, h is the buried depth of the tunnel, the horizontal stress field and the vertical stress field of the real site are equal, and the stress field size during the indoor test is determined according to the stress similarity ratio. All pressure head components are adjusted to the pressure control mode, fit with the horseshoe-shaped flexible model box, and the pressure size is set to this value, such as Figure 3 As shown, the data transmission lines of the strain gauge and acceleration sensor are connected to the data acquisition system, and the zeroing operation is performed;

[0061] (6) Step 6: Simulate fault movement;

[0062] The 8 indenters of the test system were called, and the displacement loading mode was used to simulate the movement of the fault. The loading rate was 0.01 mm / s and the loading displacement was 15 mm. Figure 4 As shown, the development of cracks on the inner surface of a circular tunnel lining was recorded using an endoscope;

[0063] (7) Step 7: Applying ground motion;

[0064] The seismic waves are filtered to retain only those within the 20 Hz range. The acceleration waveform is quadratically integrated to obtain its displacement time history curve, which is then reduced using the displacement similarity ratio and input into the vibration platform through the control system. The changes in the values ​​of the strain gauge and acceleration sensor are recorded, and the deformation and vibration response characteristics of different parts of the lining are compared. The development of cracks on the inner surface of the circular tunnel lining is recorded using an endoscope, and the circular tunnel lining model in the horseshoe-shaped flexible model box is taken out to observe and record the development of cracks in the circular tunnel lining to complete the test. Figure 5 A schematic flow chart of this embodiment of a method for simulating a cross-fault tunnel test under the combined effects of earthquake motion and fault dislocation is provided.

[0065] Embodiment 2:

[0066] To observe the effect of fault displacement on tunnel response characteristics at different tunnel burial depths, steps (1) to (4) in Example 1 were repeated;

[0067] (5) Pressurizing the model box to simulate the stress field of a deep buried tunnel;

[0068] In this example, the tunnel depths are taken as 20, 40, 60, 80, and 100 m respectively, and the vertical stress field σ of the studied tunnel in the real site is calculated. h =γh, where γ is the bulk density of the surrounding rock, h is the buried depth of the tunnel, the horizontal stress field and the vertical stress field of the real site are equal, the stress field size during the indoor test is determined according to the stress similarity ratio, all the pressure head components are adjusted to the pressure control mode, fit with the horseshoe-shaped flexible model box, and the pressure size is set to this value, the data transmission line of the strain gauge and acceleration sensor is connected to the data acquisition system, and the zeroing operation is performed;

[0069] (6) Observe the tunnel response characteristics under different tunnel depths and different fault displacements;

[0070] For the above four tunnel depths, the eight pressure heads of the test system are used to apply displacement to the flexible model box. Figure 4 As shown, the displacement loading mode was used to simulate the dislocation of the fault, the loading rate was 0.01mm / s, the loading levels were 2mm, 5mm, 10mm, and 15mm, and the endoscope was used to record the development of cracks on the inner surface of the circular tunnel lining to complete the test.

[0071] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for simulating a cross-fault tunnel test under the combined action of earthquake motion and fault dislocation, characterized in that: The method comprises the following steps: S1: River sand, gypsum, cement and water are used as raw materials to cast the segmental circular tunnel lining model. The total length of the circular tunnel lining model after splicing is 2000mm; S2: Make a horseshoe-shaped flexible model box with a height of 870 mm, a width of 1140 mm, and a length of 2000 mm; S3: Standard sand, gypsum and water are used as raw materials to simulate similar surrounding rocks within the fault, and standard sand, gypsum, lime, barite powder and water are used as raw materials to simulate similar surrounding rocks on both sides of the fault; S4: Place the horseshoe-shaped flexible model box into the servo-controlled variable stiffness tunnel lining static-dynamic loading test system, fit the pressure head assembly in the test system to the outer surface of the horseshoe-shaped flexible model box, then lay a certain thickness of test surrounding rock and compact it, paste the transverse and longitudinal strain gauges and acceleration sensors on the segmental circular tunnel lining model, and after the acceleration sensors are pasted, splice the segmental circular tunnel lining model into a whole and place it in the middle of the horseshoe-shaped flexible model box, and continue to backfill similar surrounding rock and compact until the horseshoe-shaped flexible model box is completely poured; S5: Calculate the stress field of the studied tunnel in the real site, determine the stress field size during the indoor test according to the stress similarity ratio, adjust all the pressure head components to the pressure control mode, fit them with the horseshoe-shaped flexible model box, and set the pressure size to this value; S6: Determine the displacement position of the fault, adjust the pressure head at the corresponding position to the displacement control mode, extend and move the pressure head at the corresponding position of the test system to simulate the displacement of the active fault, use the vibration platform at the bottom to complete the ground motion simulation, realize the cross-fault tunnel test under the combined action of ground motion and fault displacement, and record the data monitored by the sensor; S7: Take out the circular tunnel lining model in the horseshoe-shaped flexible model box, observe and record the development of the circular tunnel lining cracks, and end the test.

2. The method for simulating a cross-fault tunnel test under the combined action of earthquake motion and fault dislocation according to claim 1 is characterized in that: In step S1, the particle size of the river sand is between 0.8 and 2 mm, and the gypsum is glue-free quick-drying gypsum.

3. The method for simulating a cross-fault tunnel test under the combined action of earthquake motion and fault dislocation according to claim 1 is characterized in that: The strike of the fault is 0°, and the dip angle of the fault is 90°.

4. The method for simulating a cross-fault tunnel test under the combined effects of earthquake motion and fault dislocation according to claim 1 is characterized in that: The horseshoe-shaped flexible model box is made of a rubber plate sandwiched with a metal frame layer. Transparent acrylic covers are provided at both ends of the horseshoe-shaped flexible model box. The outer diameter of the acrylic cover is the same as that of the horseshoe-shaped flexible model box, and the inner diameter is the same as that of the circular tunnel lining model.

5. The method for simulating a cross-fault tunnel test under the combined effects of earthquake motion and fault displacement according to claim 4 is characterized in that: The rigidity of the rubber sheet sandwiched between the metal skeleton layers is equivalent to the rigidity of similar surrounding rocks on both sides of the fault, and the thickness of the rubber sheet sandwiched between the metal skeleton layers is 50 mm.

6. The method for simulating a cross-fault tunnel test under the combined effects of earthquake motion and fault dislocation according to claim 1 is characterized in that: The acrylic cover plates at both ends of the horseshoe-shaped flexible model box are respectively formed by splicing three acrylic plates with a height of 25.67 cm, and the spliced ​​parts are connected into a whole by epoxy resin glue.

7. The method for simulating a cross-fault tunnel test under the combined effects of earthquake motion and fault dislocation according to claim 6 is characterized in that: The horseshoe-shaped flexible model box is hinged to the acrylic cover plate.

8. The method for simulating a cross-fault tunnel test under the combined effects of earthquake motion and fault dislocation according to claim 1 is characterized in that: The segmental circular tunnel lining model is spliced ​​together by epoxy resin glue.

9. The method for simulating cross-fault tunnel test under the combined action of earthquake motion and fault displacement according to claim 5, characterized in that: The rigidity of the rubber sheet sandwiching the metal skeleton layer needs to be measured by a uniaxial compression test.

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