A method for simulating cross-fault tunnel tests under the combined action of earthquake motion and fault slip

Abstract

The present invention discloses a method for simulating cross-fault tunnel tests under the combined effects of earthquake motion and fault movement, belonging to the technical field of tunnel engineering model tests. The method comprises the following steps: step one: determining the similarity relationship of the models; step two: making a tunnel lining test model; step three: making a test model box; step four: pouring surrounding rock; step five: pressurizing the model box to simulate the tunnel burial depth; step six: simulating fault movement; and step seven: applying earthquake motion. In the present invention, a horseshoe-shaped flexible model box is designed to replace the rigid model box used in conventional model tests. The test cost is low and can be completed on a set of test systems without the need to design several additional devices. The operation process is simple and the feasibility is strong. Based on the characteristics of tunnels crossing active faults, the influence of ground stress is considered, and the deformation and damage evolution laws of the tunnel under the combined effects of earthquake motion and fault movement are comprehensively analyzed to better reflect the actual site conditions.

Description

Technical Field

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

[0002] With the rapid development of land transportation networks, more and more tunnel projects are being constructed, such as mountain tunnels, urban subway tunnels, and submarine tunnels. In mountainous areas with complex and dangerous geological conditions, mountain tunnels often need to pass through faults or fault fracture zones. This is especially true in southwest my country, where a large number of active faults are distributed. Because of its location in the Eurasian and Himalayan seismic belts, tunnel construction in this area must consider the seismic and anti-fault requirements of underground structures. Therefore, studying the mechanical characteristics and failure modes of tunnels crossing active faults has important theoretical significance and engineering value. Currently, methods for studying the seismic and anti-fault performance of tunnels crossing faults include theoretical analysis, numerical simulation, and model testing. Theoretical analysis requires a series of pre-set assumptions, and the results often deviate significantly from actual results. Numerical simulation requires high operator skills and incurs high computational costs, resulting in certain limitations in the application of both methods. Model testing, based on similarity theory and using similar materials for casting surrounding rock and lining, can more intuitively and concisely represent the evolution of the mechanical properties of underground structures.

[0003] The prior art discloses several invention patents in the field of tunnel engineering model testing technology. Among them, patent publication number CN118624268A discloses a test apparatus and method for simulating cross-fault tunnel motion. The apparatus comprises: a first active surface defining a sidewall of a test cavity, capable of applying a constant first loading force to the test cavity horizontally during the test; a second active surface defining an end surface of the test cavity, capable of applying a second loading force vertically to the test cavity. The second loading force has a switchable vertical upward / downward or stationary direction, respectively, to create an upward / downward or stationary interval within the test cavity. When both the stationary interval and the upward interval are formed within the test cavity, the test cavity simulates reverse fault motion; and when both the stationary interval and the downward interval are formed within the test cavity, the test cavity simulates normal fault motion, thereby improving the simulation effect of normal and reverse fault motion tests.

[0004] When tunnels cross active faults, they are simultaneously exposed to the hazards of seismic motion and fault dislocation. Currently, most experiments consider the two separately, using vibration tables or centrifuges to study the mechanical response characteristics of cross-fault tunnels under seismic motion, and using self-designed fault dislocation simulation devices to simulate fault dislocation. This 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 stresses. Existing devices that simulate the deep-buried state of tunnels use external airbags to simulate the deep-buried stress field. This method requires the coordination of multiple devices and is cumbersome to operate. Therefore, it is necessary to propose a new experimental simulation method to study the mechanical response characteristics of cross-fault tunnels under the combined action of seismic motion and fault dislocation. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of tunnels being simultaneously subjected to earthquake motion and fault dislocation when crossing an active fault. Currently, most experiments consider the two separately, using a vibration table or 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 buried at great depths and are significantly affected by high ground stress. Existing devices for simulating the deep-buried state of tunnels use external air bags to simulate the deep-buried stress field. This method requires the cooperation of multiple devices and is cumbersome to operate. Therefore, it is necessary to propose a new experimental simulation method to study the problem of the mechanical characteristics of cross-fault tunnels under the combined action of earthquake motion and fault dislocation, and a method for experimental simulation of cross-fault tunnels 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 comprises the following steps:

[0008] S1: Use river sand, gypsum, cement and water as raw materials to cast the segmental circular tunnel lining model. The total length of the spliced ​​circular tunnel lining model 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 indenter 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. Attach transverse and longitudinal strain gauges and acceleration sensors to the segmental circular tunnel lining model. After attaching the acceleration sensors, assemble the segmental circular tunnel lining model into a whole and place it in the middle of the horseshoe-shaped flexible model box. Continue backfilling with similar surrounding rock and compacting until the horseshoe-shaped flexible model box is completely cast.

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

[0013] S6: Determine the fault displacement position, adjust the indenter at the corresponding position to the displacement control mode, extend and move the indenter at the corresponding position of the test system to simulate the displacement of the active fault, and use the vibration platform below to complete the ground motion simulation. This allows for a cross-fault tunnel test under the combined effects of ground motion and fault displacement, and records the data monitored by the sensors.

[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 between 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 stiffness of the rubber plate sandwiched between the metal skeleton layers is equivalent to the stiffness of similar surrounding rocks on both sides of the fault, and the thickness of the rubber plate 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 segmented circular tunnel lining model is spliced ​​together by epoxy resin glue.

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

[0030] The stiffness of the rubber sheet sandwiching the metal skeleton layer needs to be measured through 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 designed replaces the rigid model box used in conventional model tests, which has a low test cost and saves test expenses. Moreover, the test can be completed on a set of test systems without the need to design several additional devices. The operation process is simple and the feasibility is strong.

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

[0034] Figure 1 This is 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 This is a schematic diagram of the arrangement of sensors on the left and right side walls of a circular tunnel lining in a simulation method for a cross-fault tunnel test under the combined action of earthquake motion and fault movement proposed in the present invention;

[0036] Figure 3 This is a schematic diagram of the state of the pressure head assembly for simulating the deep-buried stress field in a tunnel under the combined action of earthquake motion and fault dislocation proposed by the present invention;

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

[0038] Figure 5 This is a flow chart of an embodiment of a method for simulating a cross-fault tunnel test under the combined action 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 movement simulation position. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making any creative efforts shall fall within the scope of protection of the present invention.

[0042] A servo-controlled variable stiffness tunnel lining static-dynamic loading test system was 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 regulating cylinder in real time according to the displacement monitored by the displacement sensor and the pre-set stiffness value to ensure constant stiffness loading during the test;

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

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

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

[0048] Example 1:

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

[0050] Taking length, density and elastic modulus as basic physical quantities, and 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 table below:

[0051]

[0052]

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

[0054] River sand, gypsum, cement and water were used as raw materials to cast 100*100*100mm cubic specimens. The proportions of the four raw materials were adjusted, and the mix ratio of 1 / 20 of the C25 concrete strength was determined through uniaxial compression tests. 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 with 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 mix 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 wet.

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

[0056] A horseshoe-shaped flexible model box is made. 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 between metal skeleton layers. 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 between metal skeleton layers to determine its stiffness and to ensure that the stiffness is equivalent to the stiffness of the surrounding rocks 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 rocks 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. Every 50mm thickness is laid and compacted. When the surrounding rock height is 225mm, the lining model is divided into 9 monitoring sections. The No. 5 monitoring section is located inside the fault. The distance between the No. 3-4, No. 4-5, No. 5-6, and No. 6-7 monitoring sections is 116.5mm. The No. 1-2 monitoring sections are 116.5mm apart. The distance between monitoring sections 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 side walls of sections 4-6. The longitudinal strain gauges are pasted on the left and right side walls of sections 1-3 and 7-9. The strain gauge model is BFH120-50AA-R1-D150. The acceleration sensors are pasted on the left and right side walls of sections 1-9. The acceleration sensor model is 1C302. The pasted segmental circular tunnel lining is connected as a whole with 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 rock is backfilled and acrylic panels are installed until the horseshoe-shaped flexible model box is completely filled. The acrylic panels are connected with epoxy resin glue. After the model is left to stand for 24 hours and formed, the extended indenter is retracted.

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

[0060] In this example, the tunnel depth is 100m, and the vertical stress field σ of the tunnel under study in the real site is calculated. h =γh, where γ is the bulk density of the surrounding rock and h is the depth of the tunnel. The horizontal stress field and vertical stress field in the actual 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, fitted with the horseshoe-shaped flexible model box, and the pressure size is set to this value, such as Figure 3 As shown, connect the data transmission lines of the strain gauge and acceleration sensor to the data acquisition system and perform zero adjustment;

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

[0062] The eight indenters of the test system were used to simulate the movement of the fault using the displacement loading mode. 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 earthquake motion;

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

[0065] Example 2:

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

[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 and h is the depth of the tunnel. The horizontal and vertical stress fields in the actual site are equal. The stress field magnitude during the indoor test is determined according to the stress similarity ratio. All indenter components are set to pressure control mode and fitted to the horseshoe-shaped flexible model box. The pressure magnitude is set to this value. The data transmission lines of the strain gauge and accelerometer are connected to the data acquisition system and zeroed.

[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, such as Figure 4 As shown, the displacement loading mode was used to simulate the dislocation of the fault, with a loading rate of 0.01 mm / s and loading levels of 2 mm, 5 mm, 10 mm, and 15 mm. An 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 embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection 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: Use river sand, gypsum, cement and water as raw materials to cast the segmental circular tunnel lining model. The total length of the spliced ​​circular tunnel lining model 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 indenter 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. Attach transverse and longitudinal strain gauges and acceleration sensors to the segmental circular tunnel lining model. After attaching the acceleration sensors, assemble the segmental circular tunnel lining model into a whole and place it in the middle of the horseshoe-shaped flexible model box. Continue backfilling with similar surrounding rock and compacting until the horseshoe-shaped flexible model box is completely cast. S5: Calculate the stress field of the tunnel under study in the actual site. Determine the stress field magnitude during the indoor test according to the stress similarity ratio. Set all indenter components to pressure control mode, fit them to the horseshoe-shaped flexible model box, and set the pressure magnitude to this value. S6: Determine the fault displacement position, adjust the indenter at the corresponding position to the displacement control mode, extend and move the indenter at the corresponding position of the test system to simulate the displacement of the active fault, and use the vibration platform below to complete the ground motion simulation. This allows for a cross-fault tunnel test under the combined effects of ground motion and fault displacement, and records the data monitored by the sensors. S7: Take out the circular tunnel lining model from 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 displacement 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 displacement 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 displacement according to claim 1 is characterized in that: The horseshoe-shaped flexible model box is made of a rubber plate sandwiched between 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 stiffness of the rubber plate sandwiched between the metal skeleton layers is equivalent to the stiffness of similar surrounding rocks on both sides of the fault, and the thickness of the rubber plate 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 displacement according to claim 1, 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 displacement according to claim 6, 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 displacement according to claim 1, characterized in that: The segmented circular tunnel lining model is spliced ​​together by epoxy resin glue.

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

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