Anti-seismic toughness improving method for additionally arranging rubber sand walls on two sides of existing shallow-buried underground structure

Abstract

The invention discloses an anti-seismic toughness improving method for additionally arranging rubber sand walls on two sides of an existing shallow buried underground structure, and belongs to the technical field of tunnel engineering. Aiming at the existing underground structure with seismic reinforcement requirements, the method comprises the following steps: firstly, determining parameters of rubber sand to be adopted according to basic physical property indexes of rubber particles, basic physical property indexes of sand, field engineering conditions and the seismic grade of the existing shallow buried underground structure to be reinforced, and preparing a rubber sand shock-absorbing material; determining design parameters of a rubber sand wall according to geometric parameters, field engineering conditions and a construction scheme of the to-be-reinforced existing shallow buried underground structure, additionally arranging the vertical and continuous rubber sand wall with proper rigidity and thickness on the field close to the two sides of the underground structure, and utilizing the characteristics of deformation absorption, damping energy consumption and the like of the rubber sand wall to reinforce the existing shallow buried underground structure. Seismic energy transmitted to the underground structure from surrounding sites is reduced, so that the seismic response of the tunnel structure is reduced, and the aim of improving the seismic toughness of the existing tunnel is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering, and in particular relates to a method for improving the seismic toughness by adding rubber sand walls on both sides of an existing shallow buried underground structure. Background Art

[0002] Tunnels are key carriers of urban transportation and important lifeline projects. Repeated earthquake disasters in recent years have shown that tunnel structures are often severely damaged under strong earthquake loads. However, due to the small number of tunnels in the early days and the fact that they were basically not tested by major earthquakes, people have long ignored the seismic design of tunnels. In addition, with the improvement of my country's seismic fortification level and the improvement of seismic calculation methods, some existing tunnels that take seismic effects into consideration cannot meet the requirements of current seismic fortification-related specifications, and there is a high risk of earthquake damage, which urgently requires seismic reinforcement. Under the action of an earthquake, the deformation and damage of the tunnel structure are obviously constrained and affected by the surrounding site soil. The relevant specifications for seismic resistance of underground structures suggest that a shock-absorbing layer can be laid between the tunnel and the site to absorb the seismic deformation transmitted from the site to the tunnel, so as to reduce the seismic response of the tunnel structure.

[0003] At present, the existing tunnel seismic isolation technology is mostly aimed at newly built tunnels, such as the use of rubber shock-absorbing layers (see Figure 1 ) or EPS foam backfill, and a few also use flexible materials such as foam concrete. However, for existing tunnels, due to limitations in line operation and construction technology, a fully wrapped annular rubber shock-absorbing layer is basically not feasible for construction. On the other hand, existing technologies usually use polyurethane or cement grouting to reinforce adjacent sites. This method can effectively reduce the seismic response of the tunnel structure, but some sites are difficult to use grouting technology due to geological conditions, and the cost of polyurethane and cement is high, and there is a risk of groundwater pollution.

[0004] In 2022, my country produced 13.5 million tons of waste tires, but the recycling rate was less than 50%, causing serious environmental pollution and waste of resources. At present, "low carbon and resilience" has become an important development direction of civil engineering. How to achieve low-carbon resource utilization of waste tires in civil engineering resilience disaster reduction has become an important issue. Studies have shown that rubber sand, which is formed by mixing rubber particles formed by crushing and screening waste tires with natural sand in a certain proportion, has the characteristics of light density, low modulus and high damping. It is a green, low-cost seismic isolation material. The seismic isolation effect in engineering structures such as houses, docks, abutments and retaining walls has been widely studied and verified. However, there are no reports on the shock-absorbing application of rubber sand in tunnel structures.

[0005] Therefore, how to use rubber sand to improve the seismic toughness of existing tunnels has become a technical problem that needs to be urgently solved in this field. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a method for improving the seismic toughness by adding rubber sand walls on both sides of an existing shallow underground structure.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for improving the seismic toughness of an existing shallow underground structure by adding rubber sand walls on both sides of the existing shallow underground structure. Flexible rubber sand walls are respectively arranged on both sides of the existing shallow underground structure; the depth of the rubber sand walls is greater than 1 times the diameter of the invert arch of the existing shallow underground structure.

[0009] Preferably, the rubber particle content in the raw material of the rubber sand wall is 20-50%.

[0010] Preferably, the maximum particle size of the rubber particles is 0.250 mm, the median particle size is 0.137 mm, and the minimum particle size is 0.100 mm. 。

[0011] Optionally, the maximum particle size of the raw sand of the rubber sand wall is 1.0 mm, the median particle size is 0.176 mm, and the minimum particle size is 0.075 mm.

[0012] Optionally, the thickness of the rubber sand wall is 1 / 3 of the diameter of the existing shallow buried underground structure, and the longitudinal length is the same as that of the existing shallow buried underground structure.

[0013] Optionally, the construction method for building the rubber sand wall includes drilling, hole cleaning, pipe lowering, rubber sand pouring, pile building and continuous wall building.

[0014] Preferably, the existing shallow underground structure includes but is not limited to a tunnel.

[0015] Preferably, the method for improving the seismic toughness of adding rubber sand walls on both sides of an existing shallow buried underground structure provided by the present invention comprises the following steps:

[0016] (1) crushing, grinding and screening waste tires to obtain rubber particles of different particle sizes, and testing the basic physical properties of the obtained rubber particles;

[0017] (2) Select sand according to on-site engineering conditions and test the basic physical properties of the selected sand;

[0018] (3) determining the static and dynamic parameters of the required rubber sand according to the seismic reinforcement target of the existing shallow underground structure to be reinforced; determining the parameters of the rubber sand to be used according to the determined static and dynamic parameters of the rubber sand and the basic physical properties of the rubber particles in step (1) and the basic physical properties of the sand in step (2); preparing the rubber sand shock-absorbing material according to the parameters of the obtained rubber sand;

[0019] (4) Determine the design parameters of the rubber sand wall based on the geometric parameters of the existing shallow underground structure to be reinforced, on-site engineering conditions and construction plan;

[0020] (5) According to the construction plan and the design parameters of the rubber sand wall determined in step (4), the rubber sand shock-absorbing material prepared in step (3) is used to construct the rubber sand wall, thereby improving the seismic toughness of the existing shallow underground structure.

[0021] The present invention aims at existing underground structures that require seismic reinforcement. First, the parameters of rubber sand to be used are determined according to the basic physical properties of rubber particles, the basic physical properties of sand, on-site engineering conditions and the seismic grade of the existing shallow underground structure to be reinforced, and the rubber sand shock-absorbing material is made. Then, the design parameters of the rubber sand wall are determined according to the geometric parameters of the existing shallow underground structure to be reinforced, the on-site engineering conditions and the construction plan. By adding vertical, continuous rubber sand walls with appropriate stiffness and thickness at sites close to both sides of the underground structure, the deformation absorption and damping energy dissipation characteristics of the rubber sand walls are utilized to reduce the seismic energy transmitted from the surrounding sites to the underground structure, thereby reducing the seismic response of the tunnel structure and achieving the purpose of improving the seismic toughness of the existing tunnel.

[0022] Optionally, in step (1), the basic physical properties of the rubber particles include particle size, specific gravity, non-uniformity coefficient, curvature coefficient, maximum dry density and minimum dry density.

[0023] Optionally, in step (2), the basic physical properties of the sand include particle size, specific gravity, uniformity coefficient, curvature coefficient, maximum dry density and minimum dry density.

[0024] Optionally, in step (3), the static and dynamic parameters of the rubber sand include stiffness, density, dynamic elastic modulus, damping ratio and Poisson's ratio.

[0025] Optionally, in step (3), the static and dynamic parameters of the required rubber sand are determined according to the seismic level of the existing shallow underground structure to be reinforced. The basic principle is that the higher the seismic reinforcement target, the greater the deformation absorption and energy dissipation capacity of the rubber sand. The static and dynamic parameters are determined based on site conditions, structural characteristics, seismic reinforcement targets, etc., combined with numerical analysis and rubber sand unit test results.

[0026] Preferably, in step (3), the parameters of the rubber sand include the mix ratio of rubber particles and sand, the gradation of rubber particles and sand, the particle size of the rubber particles and the particle size of the sand.

[0027] The content of rubber particles in rubber sand is a key factor affecting its static and dynamic properties such as stiffness, density and damping. Theoretically, the higher the content of rubber particles, the more significant its shock absorption effect. However, too many rubber particles will cause excessive compression deformation of the material, resulting in settlement or damage to the surrounding site, which is not conducive to the service safety of the tunnel structure. However, the content of rubber particles should not be too low, otherwise it will lead to poor shock absorption effect.

[0028] Optionally, in step (4), the geometric parameters of the existing shallow underground structure to be reinforced include the longitudinal length of the underground structure, the interval between two adjacent underground structures, and the spacing between the underground structure and the supporting structure.

[0029] Optionally, in step (4), the design parameters of the rubber sand wall include spatial position, geometric parameters and density.

[0030] When designing the spatial position and geometric parameters of the rubber sand wall, the tunnel seismic reinforcement objectives, hydrogeological and engineering geological conditions, adjacent structures, construction environment and technology and other factors should be comprehensively considered, and the depth, thickness, length and distance of the rubber sand wall from the underground structure should be determined with the help of numerical analysis and other methods. With regard to its spatial position, it should be as close to the underground structure as possible without compromising the safe operation of the existing underground structure, and the depth should not be less than 1 times the diameter of the underground structure invert, so as to absorb the deformation of the site in a larger range.

[0031] Optionally, in step (4) or step (5), the construction plan includes the following steps: rotary drilling to form holes, hole cleaning, lowering guide tubes, pouring rubber sand, forming piles and continuously forming walls according to the design parameters of the rubber sand wall.

[0032] Further preferably, a continuous rubber sand wall is formed through the construction process of bite piles.

[0033] Compared with the prior art, the present invention has the following advantages and technical effects:

[0034] The present invention achieves the purpose of improving the seismic toughness of existing tunnels by supplementing the seismic reinforcement measures of flexible rubber sand walls on both sides of existing tunnel sites that require seismic reinforcement. The method provided by the present invention has important engineering application value in reducing the risk of earthquake damage to tunnel structures and improving the level of resource utilization of waste tires.

[0035] The method proposed by the invention uses waste tires as the main raw material, and has lower cost compared with traditional shock absorption methods such as rubber cushions, foam concrete, etc.

[0036] The method proposed by the present invention can be used in combination with existing site reinforcement methods such as drilling and grouting to form a rubber sand wall. The construction technology is mature and the application range of sites is wide. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0038] Figure 1 A schematic diagram of the structure of a new tunnel rubber cushion for shock absorption in the prior art;

[0039] Figure 2 It is a schematic diagram of the structure of the existing tunnel rubber sand wall shock absorption in the present invention;

[0040] Figure 3 A schematic diagram of a process for improving the seismic toughness of an existing shallow underground structure by adding rubber sand walls on both sides provided by the present invention;

[0041] Figure 4 It is a schematic diagram of the construction scheme in the present invention;

[0042] Figure 5 A real-life picture of the sand-rain method of molding;

[0043] Figure 6 It is a structural schematic diagram of the tunnel model box with and without rubber sand wall;

[0044] Figure 7 is the gradation curve of Fujian standard sand and rubber particles;

[0045] Figure 8 This is a live picture of the production process of the rubber sand wall;

[0046] Fig. 9 Schematic diagram of the arrangement of sensors on the four sections of the tunnel model box with or without rubber sand wall, where (a) is a schematic diagram of the arrangement of strain gauges on section 1 or section 4, (b) is a schematic diagram of the arrangement of acceleration, displacement and earth pressure sensors on section 2, (c) is a schematic diagram of the arrangement of acceleration, displacement and earth pressure sensors on section 3, and (d) is a distribution diagram of the four sections;

[0047] Fig.10 This is a schematic diagram of the arrangement of strain gauges for tunnel structures;

[0048] Fig.11 It is a schematic diagram of a Wheatstone full bridge;

[0049] Fig.12 Two loading modes used for strain gauge calibration;

[0050] Fig.13 for Fig.12 Internal force analysis of two loading modes;

[0051] Fig.14The dynamic earth pressure time history with and without rubber wall under the action of Sin-Leap waves of different amplitudes;

[0052] Fig.15 The dynamic earth pressure time history with and without rubber wall under the action of El Centro waves of different amplitudes;

[0053] Fig.16 The surface settlement time history at three different positions on the ground with and without rubber walls under the action of Sin-Leap waves of different amplitudes, where a is 0.1g Sin-Leap, b is 0.2g Sin-Leap, and c is 0.3g Sin-Leap;

[0054] Fig.17 The surface settlement time histories at three different locations on the ground with and without the rubber wall under the action of El Centro waves of different amplitudes, where a is 0.1g El Centro, b is 0.2g El Centro, and c is 0.3g El Centro;

[0055] Fig.18 is the acceleration response of the tunnel structure with and without rubber wall under Sin-Leap waves of different amplitudes;

[0056] Fig.19 It is the acceleration time history of the tunnel structure with and without rubber wall under real earthquake shaking;

[0057] Fig. 20 The axial force time history at four locations of the tunnel structure with and without rubber walls under the action of El Centro wave (a), Kobe wave (b), and Chi-Chi wave (c);

[0058] Fig.21 The axial force time history at four locations of the tunnel structure with and without rubber walls under the action of Wolong wave (a), Parkfield wave (b), and Northridge wave (c);

[0059] Fig. 22 is the maximum dynamic axial force of the tunnel under the real earthquake and its damping coefficient β. DETAILED DESCRIPTION

[0060] 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.

[0061] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0062] Rubber sand: A lightweight shock-absorbing material formed by mixing rubber particles formed by crushing and screening waste tires with sand in a certain proportion.

[0063] Shear modulus: refers to the ratio of peak shear stress to shear strain of a material under shear stress. A large modulus indicates a high stiffness of the material.

[0064] Sand rain method: Utilize the free fall of soil and the conversion of gravitational potential energy into kinetic energy to obtain the drop distance-density relationship curve, thereby making a model soil sample of a specific density. It is one of the commonly used modeling methods for centrifuge tests.

[0065] Dynamic earth pressure: The total earth pressure during an earthquake minus the initial earth pressure caused by static loads.

[0066] Centrifuge shaking table test: Place a 1:N times scaled model of the similarity law in a rotating centrifuge shaking table system, obtain centrifugal acceleration Ng through high-speed rotation to simulate a high gravity field, and load the seismic load through the centrifugal shaking table system after reaching the preset centrifugal acceleration Ng, so as to accurately simulate the dynamic characteristics and failure mechanism of the in-situ engineering site under the action of seismic loads. With the help of the high-speed rotation of the geotechnical centrifuge system, the stress field with the same stress level as the horizontal engineering site can be effectively reproduced 1:1, and compressive seismic loads can be applied under high centrifugal field conditions, so that the dynamic characteristics or physical and mechanical phenomena of the prototype can be reproduced.

[0067] Shock absorption coefficient: the ratio of the maximum dynamic internal force of the shock-absorbing tunnel to the maximum dynamic internal force of the non-shock-absorbing tunnel at the same position. If it is greater than 1, it means that the rubber sand wall increases the seismic response of the tunnel internal force; if it is less than 1, it means that the seismic response of the tunnel is reduced. The smaller the shock absorption coefficient, the better the shock absorption effect.

[0068] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0069] Example 1

[0070] A method for improving the seismic toughness of an existing shallow underground structure by adding rubber sand walls on both sides. The process diagram is shown in Figure 3 , including the following steps:

[0071] (1) crushing, grinding and screening waste tires to obtain rubber particles of different particle sizes, and testing the particle size, density, hardness, elasticity and strength of the obtained rubber particles;

[0072] (2) Select sand according to on-site engineering conditions and test the particle size, apparent density, porosity and moisture content of the selected sand;

[0073] (3) determining the stiffness, density, dynamic elastic modulus, damping ratio and Poisson's ratio of the required rubber sand according to the seismic reinforcement target of the existing shallow tunnel to be reinforced; determining the mix ratio of rubber particles and sand, the gradation of rubber particles and sand, the particle size of rubber particles and the particle size of sand in the proposed rubber sand according to the determined static and dynamic parameters of the rubber sand and the basic physical properties of the rubber particles in step (1) and the basic physical properties of the sand in step (2); and uniformly mixing the rubber particles and sand according to the parameters of the obtained rubber sand to obtain the rubber sand shock-absorbing material;

[0074] (4) Determine the spatial position, geometric parameters and density of the rubber sand wall according to the longitudinal length of the existing shallow tunnel to be reinforced, the interval between two adjacent tunnels, the spacing between the tunnel and the supporting structure, as well as the on-site engineering conditions and the construction plan; the geometric parameters of the rubber sand wall include the depth, thickness, length and distance of the rubber sand wall from the tunnel;

[0075] (5) According to the construction plan and the design parameters of the rubber sand wall determined in step (4), the rubber sand shock-absorbing material prepared in step (3) is used to construct the rubber sand wall, thereby improving the seismic toughness of the existing shallow buried tunnel. The construction plan specifically includes: drilling holes, cleaning holes, lowering guide tubes, pouring rubber sand shock-absorbing materials, piling and continuous walling according to the design parameters of the rubber sand wall. The schematic diagram of the construction plan is shown in FIG. Figure 4 .

[0076] In order to illustrate the effectiveness of the method of the present invention, a centrifugal shaking table model test was performed to verify the method, focusing on the lateral seismic response of the tunnel structure. The deformation and internal force of the tunnel are important evaluation indicators. The specific steps are as follows:

[0077] (1) Test equipment

[0078] The test used the large centrifuge vibration table system of the Institute of Engineering Mechanics - DCIEM-40-300 geotechnical centrifuge, with a centrifuge system capacity of 300gt and a vibration table effective vibration capacity of 40gt. In order to reduce the test error, a layered shear deformation model box was used to carry out the model test. The model box size was 1.2m×0.5m×0.6m, and the similarity ratio used was 1:50 (model: prototype).

[0079] (2) Model site preparation and structural design

[0080] The model site mainly includes the model foundation and rubber sand wall. The model foundation depth is 500mm, the relative density Dr = 60%, and it is made of pure sand and soil by the sand rain method. The actual picture of the sand rain method modeling is shown in Figure 5. Aluminum alloy round tubes are used to simulate the prototype tunnel structure, and its parameters are determined according to the similarity relationship between geometry and bending stiffness. The model box used in the test is large in size, and the cost of multiple sets of centrifuge vibration table model tests is high and will lead to certain test errors. Two model tunnels are buried in the middle of the model box along the width direction of the model box, and rubber sand walls are placed symmetrically on both sides of one of the model tunnels to obtain a tunnel model box with or without rubber sand walls. The structural schematic diagram of the tunnel model box with or without rubber sand walls is shown in Figure 6 Among them, the longitudinal length of a single tunnel is 200mm, the distance between two tunnels, and the distance between the front and rear walls of the tunnel and the model box are all 24mm. In order to prevent the inflow of model soil, plastic film is covered at both ends of the tunnel and a 10mm thick cover-shaped acrylic plate is used.

[0081] Fujian standard sand with a median particle size of 0.176 mm is selected. The grading curve of the sand is shown in Figure 7 , the gradation of sand is: d 60 =0.193mm, d 50 =0.176mm, d 30 =0.145mm, d 10 =0.113mm; the basic physical properties of sand are shown in Table 1; the rubber particles with a median particle size of 0.137mm are selected, and the grading curve of the rubber particles is shown in Figure 7 , the gradation of rubber particles is: d 60 =0.150mm,d 50 =0.137mm, d 30 =0.112mm, d 10 =0.090mm; the basic physical properties of rubber particles are shown in Table 2. It should be pointed out that since the particle size of the Fujian standard sand used in the test is small, rubber particles with smaller particle size are also selected to prevent the separation of sand-rubber particles and the accumulation of fine sand particles at the bottom of the shock-absorbing wall; the above sand and rubber particles are mixed evenly in a mass ratio of 50%:50% to obtain rubber sand shock-absorbing material. The rubber sand shock-absorbing material obtained is used to build rubber sand walls on both sides of the tunnel. The production process of the rubber sand wall is shown in Figure 8 The design parameters of the rubber sand wall are determined according to the size of the model box and the geometric parameters of the model tunnel. The specific thickness of the rubber sand wall is 1 / 3 of the tunnel diameter, the depth exceeds 1 times the diameter of the tunnel bottom, the longitudinal length is equal to the tunnel model, and the rubber sand wall is set at a position 1 times the diameter of the tunnel outside. According to the similarity relationship, the corresponding geometric parameters of the rubber sand wall model are: thickness t = 40mm, depth Lw = 320mm, and distance from the outside of the lining e = 120mm.

[0082] Table 1 Basic physical properties of sand

[0083]

[0084] Table 2 Basic physical properties of rubber particles

[0085]

[0086] (3) Sensor layout and calibration

[0087] Sensors are arranged on the four sections of the tunnel model box with and without rubber sand walls. The schematic diagram of sensor arrangement is shown in Fig. 9 , the distribution diagrams of the four sections are shown in Fig. 9 In (d), sections 1 and 2 are sections where the shock-absorbing tunnel is located, and the sensor names all start with the letter A; sections 3 and 4 are sections where the non-shock-absorbing tunnel is located, and the sensor names all start with the letter B. The schematic diagram of the arrangement of strain gauges on section 1 or section 4 is shown in Fig. 9 (a) in the figure. The schematic diagram of the arrangement of acceleration, displacement and earth pressure sensors on section 2 is shown in Fig. 9 In (b), section 2 is the shock-absorbing tunnel site, where 15 horizontal accelerometers and 2 vertical accelerometers are arranged. The schematic diagram of the arrangement of acceleration, displacement and earth pressure sensors on section 3 is shown in Fig. 9 In (c), section 3 is a non-shock-absorbing tunnel site. The same sensors as those in the shock-absorbing tunnel site are arranged at the same position in the non-shock-absorbing tunnel site. Three rows of displacement sensors are arranged at the top of the model to monitor the vertical settlement curves of the model during the accelerated loading stage and the vibration stage. Three earth pressure boxes are arranged at a 45° interval on one side of the tunnel. The calibration of the earth pressure box uses the controllable high-precision earth pressure sensor calibration equipment independently developed by the Institute of Engineering (the applied load range is 1kPa~2MPa and the accuracy is 0.1%) to obtain a more accurate earth pressure sensor calibration coefficient. On the shock-absorbing tunnel monitoring surface 1 (section 1) and the non-shock-absorbing monitoring surface 4 (section 4), 8 pairs of strain gauges are arranged in a full-bridge manner at a 45° oblique position inside and outside the tunnel. Each bridge consists of four bridge arms (two double-grid strain gauges). By gluing one pair of bridge arms (R2-R3) to the inner surface and the other pair of bridge arms (R1-R4) to the outer surface, a pressure gauge is arranged to measure the bending strain. The layout diagram is shown in Fig.10 , see the schematic diagram of the Wheatstone full bridge Fig.11 By applying a voltage V across the bridge a and b ab , use an ammeter to measure the voltage change ΔV between point c and point d cd By processing the voltage signals collected during the test and converting them into theory, the internal force results at the key positions of the tunnel structure can be obtained. The strain gauge used in the test is a double-grid strain gauge (BF120-2FB(11)P50) produced by AVIC Electro-Mechanical Measurement. The two loading modes used for strain gauge calibration are shown in Fig.12 , Fig.12 The internal force analysis of the two loading modes is shown in Fig.13 .

[0088] Test conditions

[0089] The seismic excitation uses the Sin-Leap wave commonly used in centrifugal shaking table model tests and six real ground motions. The Sin-Leap wave has a single frequency (1Hz) and clear peaks and troughs, which is convenient for subsequent research and inversion analysis of the dynamic characteristics of site soil and rubber sand. The peak values ​​of the Sin-Leap wave were adjusted to 0.1g, 0.2g, and 0.3g respectively; after adjustment based on the similarity relationship, the load was increased in a step-by-step manner. The real ground motion was input from small to large according to the Arenas intensity, and white noise sweep frequency was performed before and after loading, for a total of 14 working conditions. The working condition details are shown in Table 3.

[0090] Table 3

[0091]

[0092] Note: The values ​​in the table represent the frequency or amplitude of the prototype ground motion.

[0093] Test results

[0094] a. Earthquake pressure response

[0095] According to the three earth pressure sensors arranged on each tunnel in the model test, namely the sensors at the upper left position (AT1 and BT1), the left position (AT2 and BT2) and the lower left position (AT3 and BT3) of the tunnel, the dynamic earth pressure time history curves with and without rubber walls under the action of Sin-Leap waves or El Centro waves of different amplitudes are tested. The results are shown in Fig.14 and Fig.15 Among them, the BT3 sensor is damaged and has been removed from the picture.

[0096] Fig.14 It is the earth pressure time history with and without rubber wall under the action of Sin-Leap waves of different amplitudes. Among them, shock absorption refers to the case with rubber wall, and non-shock absorption refers to the case without rubber wall. Fig.15 is the earth pressure time history with and without rubber wall under the action of El Centro waves of different amplitudes, where shock absorption refers to the presence of rubber wall and non-shock absorption refers to the absence of rubber wall. Fig.14 and Fig.15 It can be found that with the increase of burial depth and input earthquake amplitude, the dynamic earth pressure gradually increases. Comparing the dynamic earth pressure peaks with and without rubber sand walls, it can be found that the presence of rubber sand walls significantly reduces the dynamic earth pressure of the tunnel. The dynamic earth pressure at the left spandrel of the tunnel structure is most significantly reduced, and the degree of reduction in dynamic earth pressure is greater with the increase of earthquake intensity. Under the action of 0.3g earthquake motion, the dynamic earth pressure of the tunnel with rubber sand walls is reduced by about 50% compared with the non-seismic tunnel.

[0097] b. Vertical settlement reaction of the ground surface

[0098] Fig.16 Figure 2 shows the surface settlement time history at three different locations on the ground with and without the rubber wall under the action of Sin-Leap waves of different amplitudes, where a is 0.1g Sin-Leap, b is 0.2g Sin-Leap, and c is 0.3g Sin-Leap. Fig.17 The surface settlement time history at three different locations on the ground with and without rubber walls under the action of ElCentro waves of different amplitudes, where a is 0.1g ElCentro, b is 0.2g El Centro, and c is 0.3g El Centro. Overall, with the continuous vibration, the soil layer (i.e., the model foundation) condition becomes more and more dense, and the settlement becomes smaller and smaller. In the first half of the loading, the settlement of the shock-absorbing section (AL1-AL3) is significantly greater than that of the non-shock-absorbing section (BL1-BL3). This is because in the initial stage of loading (Sin-Leap wave), the soil layer and the rubber sand wall are in a relatively loose state, but the compressibility of the rubber sand is significantly higher than that of pure sand, and it is easier to undergo elastic deformation and be compressed. Therefore, the settlement of the rubber sand wall and the surrounding site (i.e., the shock-absorbing section) is significantly greater than that of the site without the rubber sand wall (i.e., the non-shock-absorbing section). Under the subsequent real earthquake, due to the site densification caused by the earthquake history, the rubber sand and the pure sand in the foundation are in a relatively dense state, and the vertical deformation of the same position of the site around the rubber sand wall and the non-rubber sand wall is relatively close (see Fig.17 The above comparison shows that when adding the rubber sand wall with a higher density, the vertical settlement of the rubber sand wall and the surrounding site will not increase significantly under the action of a strong earthquake, and the settlement is basically the same as that of the site without the rubber sand wall.

[0099] c. Tunnel structure acceleration response

[0100] Fig.18 Figure 2 is the acceleration response of the tunnel structure with and without rubber walls under Sin-Leap waves of different amplitudes. A17 and A18 are tunnel structures with rubber walls, and B17 and B18 are tunnel structures without rubber walls. Fig.19 The acceleration time history of the tunnel structure with and without rubber walls under real earthquakes, among which A17 and A18 are tunnel structures with rubber walls, and B17 and B18 are tunnel structures without rubber walls. It can be found that the acceleration response of the tunnel arch bottom is basically the same under the conditions with and without rubber sand walls. However, when rubber sand walls are added on both sides of the tunnel, the acceleration response of the structural arch increases to a certain extent. This shows that the existence of the rubber sand wall has little effect on the seismic response of the arch bottom, increases the seismic response of the arch, and increases the overall sway (rather than structural deformation) response of the tunnel structure. Therefore, the constraint force exerted by the surrounding soil on the tunnel structure is smaller, which helps to reduce the dynamic earth pressure and dynamic internal force in certain parts of the tunnel structure.

[0101] d. Tunnel structure internal force response

[0102] Fig. 20 The axial force time history at four locations of the tunnel structure with and without rubber walls under the action of El Centro wave (a), Kobe wave (b), and Chi-Chi wave (c). Fig.21 The axial force time history at four locations of the tunnel structure with and without rubber walls under the action of Wolong wave (a), Parkfield wave (b), and Northridge wave (c). Fig. 20 and Fig.21 It can be seen that the existence of the rubber sand wall increases the dynamic internal force of the tunnel structure at the axial force of the structure at the left and right spandrels of the tunnel. At the left and right arch feet, the addition of rubber sand walls can significantly reduce the internal force response of the tunnel. It should be pointed out that regardless of whether the rubber sand wall is added, the dynamic internal force at the left and right arch feet of the tunnel is greater than that at the left and right spandrels, which is the control section of the tunnel seismic design. Therefore, after adding the rubber sand wall, the internal force of the control section is reduced, which has a shock-absorbing effect.

[0103] Fig. 22 is the maximum dynamic axial force of the tunnel under the real earthquake and its damping coefficient β. Fig. 22 It can be found that the maximum dynamic axial force of the tunnel can be reduced by 20 to 30%.

[0104] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for improving the seismic toughness of an existing shallow underground structure by adding rubber sand walls on both sides, characterized in that: Flexible rubber sand walls are respectively arranged on both sides of the existing shallow buried underground structure; the depth of the rubber sand wall is greater than 1 times the diameter of the invert arch of the existing shallow buried underground structure.

2. The method for improving the seismic toughness of an existing shallow underground structure by adding rubber sand walls on both sides according to claim 1, characterized in that: The rubber particle content in the raw materials of the rubber sand wall is 20-50%.

3. According to the method for improving the seismic toughness of adding rubber sand walls on both sides of an existing shallow buried underground structure as described in claim 2, the maximum particle size of the rubber particles is 0.250 mm, the median particle size is 0.137 mm, and the minimum particle size is 0.100 mm 。 4. According to the method for improving the seismic toughness of adding rubber sand walls on both sides of an existing shallow underground structure as described in claim 1, the maximum particle size of the raw sand of the rubber sand wall is 1.0 mm, the median particle size is 0.176 mm, and the minimum particle size is 0.075 mm.

5. According to the method for improving the seismic toughness of an existing shallow underground structure by adding rubber sand walls on both sides of the existing shallow underground structure as described in claim 1, the thickness of the rubber sand wall is 1 / 3 of the diameter of the existing shallow underground structure, and the longitudinal length is the same as that of the existing shallow underground structure.

6. The method for improving the seismic toughness of an existing shallow underground structure by adding rubber sand walls on both sides according to claim 1, characterized in that: The construction method for building the rubber sand wall comprises hole forming, hole cleaning, pipe lowering, rubber sand pouring, pile forming and continuous wall forming.

7. The method for improving the seismic toughness of an existing shallow underground structure by adding rubber sand walls on both sides according to claim 1, characterized in that: The existing shallow underground structure includes a tunnel.

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