CN-117890225-B - Method for analyzing bearing and supporting effects of spray anchor support in large-size tunnel model test

CN117890225BCN 117890225 BCN117890225 BCN 117890225BCN-117890225-B

Abstract

The invention belongs to the technical field of tunnel engineering tests and discloses a method for analyzing bearing and supporting effects of a large-size tunnel model test anchor support, which comprises the steps of S1) determining a model test loading device and parameters thereof, S2) manufacturing a strain brick test block, a spray layer test block and carrying out a tensile test on an anchor rod, S3) filling surrounding rock materials and fine river sand, S4) burying the strain brick test block and a soil pressure box, S5) burying a tunnel die and the anchor rod, S6) applying a spray layer material, S7) installing a displacement meter, S8) carrying out graded loading until the spray anchor support material is damaged, S9) monitoring stress and strain of surrounding rock in the process of observing whether the surrounding rock or the spray layer structure is damaged, and the method can directly observe and monitor deformation, damage process and bearing capacity of the spray anchor support under different working conditions, can more accurately predict and evaluate the bearing capacity and supporting effect of the spray anchor support, is beneficial to understanding the working mechanism and performance of the spray anchor support in depth, and the accuracy and reliability of engineering design are improved.

Inventors

CUI LAN
YAN QINGMING
SHENG QIAN
CHEN JIAN
GUAN KAI

Assignees

中国科学院武汉岩土力学研究所

Dates

Publication Date: 20260505
Application Date: 20240117

Claims (10)

1. The method for analyzing the bearing and supporting effects of the spray anchor support in the large-size tunnel model test is characterized by comprising the following steps: s1), determining a model test loading device and parameters thereof; s2) manufacturing a strain brick test block, a spray layer test block and carrying out a tensile test on the anchor rod; s3) filling surrounding rock materials and fine river sand; S4), burying a strain brick test block and a soil pressure box; s5), embedding a tunnel mould and an anchor rod; S6), applying a spray layer material; s7), installing a displacement meter; s8), carrying out graded loading until the shotcrete support material is damaged; s9), monitoring stress and strain of surrounding rock, observing whether a surrounding rock or a spraying layer structure is damaged, recording vertical load born when the surrounding rock or the spraying layer structure is damaged, and respectively analyzing the stress, the displacement, the bearing arch internal force, the anchor rod axial force and the spraying layer stress of the surrounding rock arch; the step S9) includes: s91), determining bearing capacity, and determining a corresponding vertical load when a spraying layer first breaks in the loading process as the bearing capacity of the spraying anchor support; s92), vault surrounding rock stress analysis, namely calculating tangential stress and radial stress in surrounding rock at the embedded position through the following formula (1) (2) And (3) with Respectively representing the maximum and minimum principal stresses, E is the elastic modulus of surrounding rock material, In order to be the poisson ratio of the surrounding rock material, Is a horizontal strain of 0 deg., Is a strain of 45 deg.. Is a 90 ° vertical strain; Respectively making a vertical load-tangential stress variation curve graph and a vertical load-radial stress variation curve graph, and analyzing the variation conditions of radial stress and tangential stress at the vault along with the increase of the vertical load; S93), analyzing the vault displacement of the surrounding rock, extracting data monitored by a vault displacement meter, making a vertical load-vault displacement change curve graph, and analyzing the change condition of the vault displacement along with the increase of the vertical load; S94), analyzing the internal force of the bearing arch, converting according to the formula (1) to obtain tangential stress, calculating according to the assumption of the plane section to obtain the axial force and the bending moment at the center of the bearing arch, finally making an internal force and bending moment diagram of the bearing arch when the bearing arch of the spray-anchor surrounding rock reaches the bearing capacity, and analyzing the stress condition in the bearing arch; s95), analyzing the axial force of the anchor rods, making the axial force condition of each anchor rod when the spraying layer-anchor rock bearing arch reaches the bearing capacity, and calculating the ultimate strength of each anchor rod when the spraying layer-anchor rock bearing arch reaches the bearing capacity; S96), analyzing the inner and outer side strain data of the sprayed layer test block, calculating the axial force and bending moment of the sprayed layer, and making a sprayed layer axial force and bending moment diagram when the sprayed layer anchor-rock bearing arch reaches the bearing capacity.
2. The method for analyzing the bearing and supporting effects of the large-size tunnel model test anchor support according to claim 1, wherein in the step S1), the model test loading device comprises a loading bench, a model box and a hydraulic loading system.
3. The method for analyzing the bearing and supporting effects of the large-size tunnel model test anchor support according to claim 1, wherein the step S2) includes: s21), respectively manufacturing a strain brick test block and a spray layer test block by using a die; s22), carrying out a tensile test on the selected anchor rod material, respectively attaching strain gauges on the upper part, the middle part and the lower part of the selected anchor rod material before the test, and stretching the selected anchor rod material by a universal testing machine to obtain a stress-strain curve of the anchor rod material, and simultaneously calculating according to the stress-strain curve to obtain the elastic modulus, the tensile rigidity and the ultimate tensile strength of the anchor rod material.
4. The method for analyzing the bearing and supporting effects of the large-size tunnel model test anchor support according to claim 1, wherein the step S3) includes: S31), separating surrounding rock materials from fine river sand by using a steel baffle, filling the surrounding rock materials in layers in the middle of the model box, and repeatedly paving and tamping by using a tamping hammer; s32), when the surrounding rock material is tamped to reach the designed elevation of each layer, removing the steel baffle plates, and placing PET sheets on two sides of the surrounding rock material; s33), filling fine river sand on two sides of the model box after the PET thin sheet is placed, and paving and tamping.
5. The method for analyzing the bearing and supporting effects of the large-size tunnel model test anchor spraying support according to claim 1, wherein in the step S4), when the surrounding rock is filled to a designated height, the strain bricks and the soil pressure box are buried at the designated elevation to monitor the stress condition inside the surrounding rock.
6. The method for analyzing the bearing and supporting effects of the large-size tunnel model test anchor support according to claim 1, wherein the step S5) includes: S51), when surrounding rock materials are filled to the arch bottom, embedding a cylindrical foam mold with the same shape as the section of the tunnel, and marking the positions of all anchor rods on the tunnel mold; S52), 6 monitoring anchor rods are respectively arranged at the vault, the arch shoulder and the arch waist according to the anchor rod arrangement scheme, and strain gauges are attached to the upper part, the middle part and the lower part of the monitoring anchor rods; S53), before surrounding rock is filled, one end of an iron pipe with the outer diameter larger than the outer diameter of the anchor rod material is inserted into a mark point of a tunnel mould, and the iron pipe is ensured to keep a vertical relationship with a tangent plane at the mark point on the tunnel mould; s54), filling surrounding rock materials around the iron pipe and tamping, and when the other end of the iron pipe is about to be filled and buried by the surrounding rock materials, pulling out the iron pipe to form a hole with the outline consistent with the outline of the anchor rod; s55), injecting an anchor rod binder at the hole, inserting the anchor rod into the hole, and bringing the binder into the hole until the other end of the anchor rod contacts the surface of the tunnel mould; S56), after the surrounding rock is completely filled, placing for 12 hours, melting the foam mould by using a hot air gun, and bonding the anchor rod tray at a position close to the wall of the tunnel after tunnel forming.
7. The method for analyzing the bearing and supporting effects of the large-size tunnel model test anchor support according to claim 1, wherein the step S6) includes: s61), spraying a layer of gypsum on the wall surface of the tunnel by using a syringe; S62), after the gypsum is solidified and air-dried, respectively adhering the sprayed test block adhered with the strain gauge and the soil pressure box to the surface of the gypsum according to a monitoring arrangement scheme; s63), fixing the wire netting, and then coating the spraying material to a specified thickness; s64), finally standing, and waiting for the spray layer material to be completely air-dried and solidified.
8. The method for analyzing the bearing and supporting effects of the large-size tunnel model test spray anchor according to claim 1, wherein in the step S7), displacement meters are arranged in the 45 ° directions of the arch crown, the arch bottom and the arch shoulder to capture the displacement of the tunnel during the loading process of the model test.
9. The method for analyzing the bearing and supporting effects of the large-size tunnel model test anchor spraying support according to claim 1, wherein in the step S8), the top surface and the side jacks of the model box are loaded simultaneously; the load of each stage is maintained for 10 minutes, when the tunnel has no obvious damage phenomenon or deformation is not obvious, the load is continuously increased, if the tunnel is continuously and rapidly deformed, the current load is maintained until the current load is stable, and the load of the next stage is increased; In the loading process, the damage condition of surrounding rock and a spraying layer supporting structure is recorded by using a camera, and meanwhile, the damage phenomenon generated in the test process is recorded in detail on a test record table; when the surrounding rock cannot maintain the existing section form to be damaged, a certain section of the spraying layer structure is damaged firstly, or the tunnel collapses, the tunnel is considered to reach the bearing capacity until the tunnel collapses completely, and the loading is finished.
10. The method for analyzing the bearing and supporting effects of the large-size tunnel model test spray anchor according to claim 1, wherein, S95) analyzing the axial force of the anchor rod, extracting 6 pieces of monitoring anchor rod strain data buried in the vault, the vault shoulder and the vault waist, comparing the stress-strain curves of the anchor rods obtained by the tensile test in the step to respectively obtain the stress of each anchor rod in the loading process, multiplying the stress by the cross section area of the anchor rod material to obtain the axial force of the anchor rod, making the axial force condition of each anchor rod when the spray-anchor bearing arch reaches the bearing capacity, and calculating the ultimate strength of each anchor rod when the spray-anchor bearing arch reaches the bearing capacity according to the following formula: (2) Kappa is the exertion degree of the anchor rods, and N 1 and N 2 are the maximum axial force of each anchor rod and the ultimate strength of the anchor rod when the spray-layer-anchor rock bearing arch reaches the ultimate bearing capacity; s96), respectively calculating the axial force and the bending moment of the spray layer according to formulas (3) and (4): (3) (4) wherein E is the elastic modulus of the spray layer; the strain is the inner side of the spray layer test block; the strain of the outer side of the spray layer test block, b is the unit length, and 1;h is the spray layer thickness.

Description

Method for analyzing bearing and supporting effects of spray anchor support in large-size tunnel model test Technical Field The invention belongs to the technical field of tunnel engineering tests, and particularly relates to a method for analyzing bearing and supporting effects of a spray anchor support in a large-size tunnel model test. Background The spray anchor support is a support mode commonly used in tunnel engineering, and the spray anchor support forms an integral structure by combining an anchor rod, a spray layer and surrounding rock, and the three functions together to improve the bearing capacity and stability along with the tunnel so as to prevent collapse and slippage of the tunnel due to insufficient bearing capacity. After the anchor rod and the spray layer support are applied, the surrounding rock with a certain thickness can be converted into a self-supporting arch, so that the surrounding rock is effectively stabilized. The anchoring section of the anchor rod can effectively transmit load with surrounding rock soil body in a friction manner, lateral limiting force of surrounding rock is improved, the spraying layer maintains a tunnel free face, and when the rock body is broken, small rock blocks between the anchor rods can be pulled and blocked by utilizing the wire mesh, so that supporting effect of the spraying layer on the rock body is enhanced. The load-bearing capacity of the shotcrete support system has an important influence on the safety and the economy of tunnel engineering. The bearing capacity of the spray anchor support system is closely related to the mechanical properties such as tensile strength, shearing resistance, bending resistance and the like of the components such as the anchor rods, the spray layers, the reinforcing steel bar meshes and the like. In actual engineering, when the bearing capacity of a designed shotcrete support system is insufficient, the problems of deformation, damage, collapse and the like of a tunnel during operation are caused, so that the safety of the tunnel engineering is influenced. When the bearing capacity of the designed shotcrete support system is overlarge, the engineering cost is greatly increased, and unnecessary waste is caused. Therefore, a method for accurately calculating and analyzing the bearing capacity of the spray anchor support is needed in engineering, however, a precise quantitative analysis method is not available in the bearing capacity of the spray anchor support at the present stage, the traditional spray anchor support design often depends on an empirical formula and theoretical calculation, and the method has certain limitations in practical application, such as poor accuracy, high calculation complexity and the like, and cannot meet engineering requirements. Disclosure of Invention In order to solve the technical problems, the invention provides a method for analyzing the bearing and supporting effects of a large-size tunnel model test anchor spraying support, which solves the problems in the prior art, and adopts the following technical scheme: The method for analyzing the bearing and supporting effects of the spray anchor support in the large-size tunnel model test comprises the following steps: s1), determining a model test loading device and parameters thereof; s2) manufacturing a strain brick test block, a spray layer test block and carrying out a tensile test on the anchor rod; s3) filling surrounding rock materials and fine river sand; S4), burying a strain brick test block and a soil pressure box; s5), embedding a tunnel mould and an anchor rod; S6), applying a spray layer material; s7), installing a displacement meter; s8), carrying out graded loading until the shotcrete support material is damaged; s9), monitoring the stress and strain of the surrounding rock, observing whether the surrounding rock or the spraying layer structure is damaged, recording the vertical load born when the surrounding rock or the spraying layer structure is damaged, and respectively analyzing the vault stress, the vault displacement, the bearing arch internal force, the anchor rod axial force and the spraying layer stress of the surrounding rock. The invention has the following beneficial effects that the invention relates to a method for analyzing the bearing capacity and the supporting effect of the spray anchor supporting based on a large-size model test. Through a large-size model test, the deformation, damage process and bearing capacity of the spray anchor support under different working conditions can be directly observed and monitored, so that the bearing capacity and the support effect of the spray anchor support can be more accurately predicted and estimated, the deep understanding of the working mechanism and the performance of the spray anchor support is facilitated, and the accuracy and the reliability of engineering design are improved. Meanwhile, different design schemes and optimization schemes can be explored by