A method for judging instability of surrounding rock of joint development stratum tunnel

Abstract

The present application relates to a kind of joint development stratum tunnel surrounding rock instability determination method, comprising the following steps: based on the joint occurrence information of working face based on multiple data acquisition;Based on the joint occurrence information of working face, draw the isodensity map, group joint, and the grouping result includes single group joint, two group joints and three groups and above joint;Based on different joint grouping situation, using corresponding tunnel surrounding rock instability determination method obtains instability determination result, specifically: for single group joint, respectively, the crushing and bending of weak part are calculated and the sliding failure calculation of structure surface shear strength control, judge its instability mode and instability range;For two group joints, on the basis of judging the instability block of tunnel free face, using cyclic search method, realize the determination of tunnel collapse range;For three groups and above joint, based on the homogenization thought, the broken surrounding rock is equivalent to homogeneous medium calculation, obtains instability determination result.Compared with prior art, the present application has the advantages of rapid determination, improve calculation efficiency and the like.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering technology and relates to a method for determining the instability of surrounding rock in tunnels, particularly a method for determining the instability of surrounding rock in tunnels with well-developed joints. Background Technology

[0002] Constantly monitoring the stability of the surrounding rock in tunnels is crucial for ensuring safe tunnel construction. For hard surrounding rock containing joints, the traditional method is to obtain joint orientation information based on advanced geological forecasting and geological sketching, and then assess the stability of key blocks based on block theory.

[0003] Currently, the main methods for analyzing the stability of blocks include stereographic projection analysis, solid scale projection analysis, and block analysis theory. Stereographic projection analysis is a qualitative method, while quantitative analysis is mainly represented by block analysis theory. In recent years, some scholars have combined the two methods to form a new stereographic projection analytical method, which is widely used in the fields of tunnels and slopes. The main operation process and technical solution of this method are as follows:

[0004] (1) Information collection on the structural characteristics of the surrounding rock. Based on geological mapping, drilling data, geological sketches of the tunnel face, and other means, information on the joint orientation within a certain range of the tunnel face area is obtained, dominant joints are extracted and joint groups are divided.

[0005] (2) Analysis of finite movable blocks. Draw the stereographic projection diagram. First, through geometric and kinematic analysis, exclude all infinite blocks, immobile blocks and stable blocks.

[0006] (3) Analysis and identification of key blocks. Based on the kinematic principles of block theory, mechanical analysis is performed on potentially unstable blocks to identify key blocks.

[0007] (4) Calculation of stability coefficient of movable block. Calculate gravity, determine sliding mode and calculate anti-slip force for each movable block; calculate the stability coefficient of key block based on known sliding force and anti-slip force.

[0008] (5) Block stability judgment. An instability index is set artificially. When the block stability coefficient reaches the instability index, the block is judged to be unstable.

[0009] Based on publicly available technical information, patents, and literature, the main technical features of the existing methods are as follows:

[0010] (1) Influence of joint orientation parameters on the stability of surrounding rock

[0011] The article "Numerical Analysis of Roadway Surrounding Rock Stability under Different Dip Angle Structural Surface Combinations" uses the large-scale general-purpose finite element software Abaqus to simulate and analyze the deformation and failure characteristics of the surrounding rock of a wedge-shaped roadway under five different dip angle structural surface combinations, as well as the stress and displacement at characteristic points around the roadway. The results show that as the dip angle of the combined structural surface increases, the stress on the roadway floor gradually increases, while the stress on the roof increases in the opposite direction; the displacement changes at each key location all increase with the increase of the dip angle of the combined structural surface.

[0012] The article "Study on the Stability of Large-Section Tunnels in Layered Rock Masses Based on Joint Dip Angle" uses the Daliangshan Tunnel Project in Shaanxi Province as the research object to study the stability of the surrounding rock and the corresponding tunnel instability modes under different joint dip angles. The results show that joint surfaces are the key to tunnel instability and failure; when the dip angle is small, the arch is prone to bending failure.

[0013] The article "Study on the Influence of Spatial Combination Relationship of Structural Surfaces on the Stability of Tunnel Surrounding Rock" investigates the impact of the spatial combination relationship of structural surfaces on the stability of tunnel surrounding rock. Based on the engineering geological conditions of the Xiangjiawan Tunnel of the Zhengzhou-Wanzhou Railway, the article uses UDEC discrete element software to numerically simulate the stability of the surrounding rock under full-section excavation. The study focuses on analyzing the influence of the spatial combination relationship of two sets of structural surfaces on the shear slip of the structural surfaces, the plastic failure of the surrounding rock, and the displacement. The results show that the deformation and failure of the tunnel surrounding rock mainly occur under the spatial combination conditions where the spacing between the structural surfaces is less than 1.5m and the dip angle of J1 is 45°~75° and the dip angle of J2 is 103°~133°.

[0014] However, existing methods still have the following problems: research on the stability of tunnel surrounding rock under conditions of joint parameter variation or different joint combinations is relatively superficial, mostly based on specific engineering projects to study the laws of stress and deformation of surrounding rock, ultimately leading to some qualitative research conclusions. Currently, there is a lack of summarizing and refining the research results, or even proposing a general stability prediction method or approach.

[0015] (2) Block stability analysis method

[0016] The patent application "A method for evaluating the stability of rock slopes" (application number: 202110809237.4) addresses the issue that traditional stereographic projection methods can only perform stereographic projection analysis by combining structural planes in pairs, without considering the relationship between the inclination angle of structural planes and intersection lines and the stability of slopes. The method divides the base circle of the stereographic projection into regions with varying degrees of stability, thereby enabling rapid assessment of the stability of hard rock slope blocks.

[0017] The article "Steleographic Projection Method for Surrounding Rock Stability Analysis" is based on a tunnel project. It uses stereographic projection to mark the rock mass structure plane and the tunnel free face. By determining the angle between the two and their combination relationship on the projection map, the potential stability state of the cutting body is determined.

[0018] The article "Stability Analysis of Surrounding Rock of No. 1 Flood Discharge Tunnel Based on Block Theory Stereoscopic Projection Method" is based on the No. 1 flood discharge tunnel project. Based on geological survey and surrounding rock exploration data, the article uses the block theory stereoscopic projection method to determine the possible unstable blocks and their volumes formed by joint combinations, and proposes corresponding support suggestions.

[0019] The article "Prediction and Analysis of Jointed and Fractured Rock Mass Failure Based on Block Theory Stereoscopic Analysis" is based on a tunnel engineering project. It uses the stereoscopic analysis method of block theory to study the distribution law of movable blocks in the tunnel. The article clearly states that block theory can only predict the stability trend of movable blocks, but cannot provide quantitative analysis of the stability of blocks or even the tunnel itself.

[0020] However, existing methods still have the following problems: Current theoretical analysis methods cannot accurately determine or predict the instability form and extent of tunnels under joint combinations. The DDA numerical calculation method based on block analysis theory requires the construction of a global stiffness matrix, handling contacts, and performing opening and closing iterations. When dealing with a large number of blocks and contact surfaces generated by multiple joint combinations, the computational load is large and the computational efficiency is low. Summary of the Invention

[0021] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for determining the instability of the surrounding rock of tunnels in jointed strata that is fast and has improved computational efficiency.

[0022] The objective of this invention can be achieved through the following technical solutions:

[0023] A method for determining the instability of surrounding rock in tunnels with well-developed joints includes the following steps:

[0024] Information on joint orientation of the working face is obtained based on multi-source data;

[0025] Based on the joint orientation information of the working face, an isodensity map is drawn, and the joints are grouped. The grouping results include single joints, two joints, and three or more joints.

[0026] Based on different joint groupings, corresponding tunnel surrounding rock instability assessment methods are used to obtain instability assessment results, specifically:

[0027] For a single joint, crushing and bending calculations of weak points and sliding failure calculations controlled by the shear strength of the structural surface are performed to determine its instability mode and instability range.

[0028] For the two sets of joints, based on the judgment of the unstable blocks on the free face of the tunnel, the cyclic search method is used to determine the range of tunnel collapse;

[0029] For three or more joints, the fractured surrounding rock is treated as a homogeneous medium based on the homogenization concept to obtain the instability judgment result.

[0030] Furthermore, the multi-source data includes field measurement records, advanced geological forecast data, borehole exploration data, and drilling face data.

[0031] Furthermore, the on-site measurement and recording data are obtained using contact measurement methods or non-contact measurement methods.

[0032] Furthermore, the joint occurrence information of the tunnel face includes the joint characteristics of the rock mass surface, the joint combination morphology, spatial distribution, and roughness of the tunnel face.

[0033] Furthermore, for a single joint, the instability modes include block crushing instability and block sliding instability, and the method for determining the block crushing instability is as follows:

[0034] Weak blocks around the tunnel are searched, and the maximum tensile stress is calculated based on a simply supported beam calculation model. If the maximum tensile stress exceeds the allowable tensile strength of the surrounding rock, the block is judged to be instability due to bending failure.

[0035] The method for determining the block's sliding instability is as follows:

[0036] Blocks around the holes that are movable from both geometric and mechanical angles are selected, and their structural shear strength is evaluated to determine whether the structural surfaces on both sides of the block are damaged. When the shear strength of the structural surfaces on both sides of the block reaches the limit, it is determined that the block has experienced structural surface failure and instability.

[0037] Furthermore, the formula for determining whether the bending failure has occurred is as follows:

[0038]

[0039] Where γ is the unit weight of the surrounding rock, L is the calculated length of the joint block, H is the burial depth of the center of gravity of the calculated block, α is the joint dip angle, μ is the cross-sectional equivalence coefficient, b is the tunnel cross-sectional width, and [σ] is the allowable tensile strength of the surrounding rock.

[0040] Furthermore, the selection of the perimeter block that is movable from both geometric and mechanical angles specifically includes:

[0041] Based on traditional block theory, the blocks around the tunnel are judged one by one. First, blocks that can slide in terms of geometric structure are selected. Based on the selected blocks, mechanical analysis is performed to calculate the sliding force and anti-slip force. The stability coefficient of the blocks is calculated according to traditional block analysis theory. Blocks around the tunnel that can move from both geometric and mechanical angles are selected.

[0042] Furthermore, the surrounding rock instability range of the block crushing instability is calculated based on the composite beam theory, and the surrounding rock instability range of the block sliding instability is the range of the sliding block.

[0043] Furthermore, the loop retrieval method specifically includes:

[0044] Based on the parameters of each joint group, the constitutive parameters of the structural plane, the tunnel outline and the center position of the tunnel, the surrounding rock cutting model is automatically generated, the surrounding rock within the tunnel outline is removed, and the tunnel excavation model is formed.

[0045] The blocks around the tunnel were searched one by one, and the joint combination analysis of each block was carried out using the stereographic projection analysis method to screen out the blocks that were geometrically unstable.

[0046] Based on the screening of blocks, traditional block analysis theory is used to determine the key unstable blocks from a mechanical perspective and identify the unstable parts of the tunnel.

[0047] The key blocks are deleted, and the instability of the resulting free-standing blocks is determined by using the extreme burial depth method in a cyclical manner, thereby determining the extent of tunnel collapse.

[0048] Furthermore, the steps for determining the extent of the tunnel collapse include:

[0049] The first joint group is labeled s1, and the second joint group is labeled s2. If the sliding surface of the free block is s1, the ultimate burial depth H1 of the block is calculated using the following formula:

[0050]

[0051] If the sliding surface of the free-standing block is s2, then the ultimate burial depth H2 of the block is calculated using the following formula:

[0052]

[0053] Where H1 is the ultimate burial depth of the block sliding along surface s1, and H2 is the ultimate burial depth of the block sliding along surface s2. α is the internal friction angle of the first joint group, c1 is the cohesion of the first joint group, α is the dip angle of the first joint group, and d1 is the joint spacing of the first joint group. β is the internal friction angle of the second joint group, c2 is the cohesion of the second joint group, β is the dip angle of the second joint group, and d2 is the spacing between the second joint groups.

[0054] Determine whether H>=H1 or H>=H2 exists, where H is the burial depth of the block center. If so, the block in the open space is determined to be an unstable block.

[0055] Delete the unstable blocks, and repeat the above steps for newly generated free blocks until all unstable blocks are removed, and determine the scope of the unstable collapse.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] 1. Based on mechanics and instability mechanisms, this invention classifies joints into three forms: single-group joints, combinations of two-group joints, and combinations of three or more-group joints. For each form, an instability determination method is proposed, and targeted analysis is conducted. The determination is accurate and reliable, and it can quickly determine the instability and the instability range.

[0058] 2. This invention proposes a judgment method and judgment criteria based on joint parameters for two failure modes of single joints, so as to realize the rapid determination of the unstable part and scale of tunnel excavation under single joints.

[0059] 3. For tunnels with two sets of joint combinations, this invention establishes a standard cutting block stress analysis model. After identifying the key blocks that are unstable on the free face of the tunnel, it proposes a cyclic retrieval method for judging block instability, which avoids the large amount of calculation work in traditional DDA analysis and improves calculation efficiency. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the process of the present invention;

[0061] Figure 2 This is a schematic diagram of the calculation location of the jointed block;

[0062] Figure 3 This is a schematic diagram of the calculation model for a simply supported beam with jointed blocks;

[0063] Figure 4 This is a schematic diagram of the crush instability range;

[0064] Figure 5 This is a schematic diagram of a tunnel excavation model with two sets of joint combinations;

[0065] Figure 6 This is a schematic diagram of the stress analysis of a surrounding rock block at a burial depth of H;

[0066] Figure 7 Schematic diagram of the arch waist crushing and instability range;

[0067] Figure 8 This is a schematic diagram showing the range of sliding instability in the arched waist area.

[0068] Figure 9 This is a schematic diagram showing the range of sliding instability at the crown.

[0069] Figure 10 This is a schematic diagram showing the extent of damage caused by horizontal and vertical joints. Detailed Implementation

[0070] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0071] Terminology Explanation

[0072] Structural planes: These are discontinuous surfaces with extremely low or no tensile strength. They are various structural planes formed after the rock mass is formed under tectonic forces, including faults, joints, cleavage, and inter-layer slip.

[0073] Joints: Joints, also known as fissures, are small fracture structures in which the rock blocks on either side of a rock mass do not experience significant displacement after fracturing under stress. Joints are a very common geological phenomenon; they are the cracks we see on rock outcrops, or simply fissures in rocks.

[0074] Block analysis theory: Due to the presence of various structural planes (weak interlayers, fissures, joints, etc.), rock masses are not homogeneous wholes, but rather aggregates of rock blocks of varying shapes cut by these structural planes. When artificial excavation is carried out on slopes, foundations, or underground caverns, or when new loads are applied to the rock mass, some blocks exposed on the free face lose their original static equilibrium state. Consequently, some blocks first slip and become unstable along the structural planes, leading to a chain reaction and ultimately causing the destruction of the entire rock mass engineering project.

[0075] Example

[0076] This embodiment provides a method for determining the instability of surrounding rock in tunnels with well-developed joints. Based on the joint occurrence parameters obtained from the geological sketch of the tunnel face, the joint forms are classified according to mechanics and instability mechanisms, including three forms: single joints, combinations of two joints, and combinations of three or more joints. Different methods for determining the instability of surrounding rock are used for different types of joint combinations. For single joints and two joints, the determination is made from the mechanical perspective of the cut blocks. For broken to relatively broken surrounding rock cut by three or more joints, the homogenization concept is used for equivalent analysis.

[0077] like Figure 1 As shown, the method includes the following steps:

[0078] S1. Obtain joint orientation information at the tunnel face based on multi-source data. Multi-source data includes field measurement records, advanced geological prediction data, borehole exploration data, and drilling data at the tunnel face. Joint orientation information at the tunnel face includes the characteristics of joints on the rock mass surface, the morphology of joint connections at the tunnel face, spatial distribution, and roughness.

[0079] Specifically, contact measurement methods such as geological compasses, geological hammers, and measuring tapes, or non-contact technologies such as three-dimensional laser scanning and digital close-range photogrammetry are used to measure and record the joint characteristics of the exposed rock surface in the surrounding rock. At the same time, by combining multi-source data such as advanced geological prediction data, borehole exploration data, and drilling face data, the occurrence information such as joint morphology, spatial distribution, and roughness of the face is extracted.

[0080] S2, joint grouping and dominant joint classification.

[0081] Based on the joint attitude information of the working face, isodensity maps are drawn to group the joints. The grouping results include single-group joints, two-group joints, and three or more-group joints. Specifically, based on the extracted raw data of joint development characteristics of the working face, a joint attitude record table is compiled; the attitude of the joint surface and its normal poles are projected onto a Schnetter diagram of equal area, and the grouping of the joint surfaces is determined according to the isodensity map of the poles; at the same time, the aggregation regions where the poles are mainly concentrated are divided on the isodensity map, and these regions are the dominant joint surfaces.

[0082] S3, Determination of instability of surrounding rock in tunnels.

[0083] Based on the joint orientation parameters, a joint group diagram is drawn, and a tunnel outline diagram is also drawn. Surrounding rock blocks within the tunnel excavation area are removed. Based on the joint grouping and joint coordinates, a two-dimensional joint combination and tunnel outline diagram are drawn. According to the joint form, the corresponding tunnel surrounding rock instability judgment method is used to obtain the instability judgment result. Specifically:

[0084] For a single joint, crushing and bending calculations of weak points and sliding failure calculations controlled by the shear strength of the structural surface are performed to determine its instability mode and instability range.

[0085] For the two sets of joints, based on the judgment of the unstable blocks on the free face of the tunnel, the cyclic search method is used to determine the range of tunnel collapse;

[0086] For three or more joints, the fractured surrounding rock is treated as a homogeneous medium based on the concept of homogenization to obtain the instability judgment result. This calculation process can be implemented using existing technology and will not be described in detail in this invention.

[0087] 1. Method for determining tunnel instability under single-joint combinations

[0088] For surrounding rock cut by a single set of joints, tunnel excavation mainly results in two types of failure: block bending failure and structural surface failure. From the perspective of instability failure mechanism, the instability modes are divided into two forms: block crushing instability and block sliding instability. Weak blocks around the tunnel are searched, and the maximum bending moment and maximum tensile stress are calculated based on a simply supported beam calculation model to determine whether block crushing instability has occurred. Based on traditional block analysis theory, geometrically movable blocks around the tunnel are searched, and mechanically movable blocks are further searched. Finally, the shear strength of the structural surface is verified to determine whether block sliding instability has occurred. Subsequently, the instability range is determined according to the failure mode.

[0089] (1) Determination of instability location and pattern

[0090] The methods for determining the instability sites and patterns under this type of joint combination are as follows:

[0091] 1) Draw the tunnel outline diagram, and at the same time draw the joint group according to the joint dip angle, spacing and location;

[0092] 2) First, determine the bending failure mode of the jointed block. The specific determination method is as follows:

[0093] Locate the surrounding rock blocks around the tunnel outline, and perform calculations on the weakest points within these blocks, such as... Figure 2 As shown, if there are multiple weak points, they can be calculated simultaneously.

[0094] like Figure 3 As shown, the cut block is simplified as a simply supported beam, and the maximum tensile stress of the beam is calculated. When the maximum tensile stress exceeds the tensile strength of the surrounding rock, bending failure is considered to have occurred.

[0095] The determination formula is:

[0096]

[0097] in:

[0098] γ—Unit weight of surrounding rock;

[0099] L—Calculated length of the jointed block;

[0100] H — Burial depth of the center of gravity of the calculation block;

[0101] α — Joint dip angle;

[0102] μ—the cross-sectional equivalence coefficient, which can be converted using the principle of area equivalence;

[0103] b—Tunnel cross-section width;

[0104] [σ]——Allowable tensile strength of surrounding rock.

[0105] 3) Determine the structural failure mode of the jointed blocks. The specific determination method is as follows:

[0106] 3.1) Based on traditional block theory, the blocks around the hole are judged one by one, and the blocks that can slide in terms of geometric structure are first screened out;

[0107] 3.2) Based on the selected blocks, perform mechanical analysis, calculate the sliding force and anti-slip force, calculate the block stability coefficient according to the traditional block analysis theory, and further screen out the key blocks that can move mechanically;

[0108] 3.3) For the selected key blocks, the shear strength of the structural surfaces is evaluated for each block to determine whether the structural surfaces on both sides of the block are damaged; when the shear strength of the structural surfaces on both sides of the block reaches the limit, it is determined that the block has experienced sliding instability in the form of structural surface failure.

[0109] When the project object is a deep-buried two-lane highway tunnel, the standards in Table 1 can be directly used to determine whether it is unstable and the type of damage.

[0110] Table 1 Criteria for Judging Tunnel Instability under Single Joints

[0111] Joint dip angle Joint spacing (m) Structural surface bonding degree Destruction Mode 0-20° <1 _ The vault collapsed 20°-60° _ Terrible ~ Very bad Sidewall block sliding 60°-90° <0.6 _ Side wall crushed

[0112] (2) Determination of the range of instability

[0113] For tunnels cut by a single set of joints, the range of surrounding rock instability is determined according to the block instability mode, as follows:

[0114] 1) For a block that slips and becomes unstable due to structural surface failure, the range of instability is the range of the sliding block.

[0115] 2) For crushed blocks, the instability failure range can be calculated based on composite beam theory, as shown in the figure. Figure 4 As shown in the figure. Points A and B are where the cross-section changes. The angle is the internal friction angle of the surrounding rock. Lines AD and BC are the shear failure traces, and the angle between them and the horizontal direction is... The specific determination method is as follows: starting from points A and B along... Draw a shear failure line at an angle. The failure lines AD and BC are of the same length and are determined by the local load. Extend DA to intersect CB at point O. Draw an arc with point O as the center and OC as the radius. The area ABCD is the crushing instability failure range.

[0116] 2. Method for determining tunnel instability under two sets of joint combinations

[0117] For the surrounding rock cut by two sets of joints, tunnel excavation mainly results in block sliding instability at the outline, which in turn causes chain instability of internal blocks. The instability determination of the tunnel under the combination of two sets of joints is as follows: the mobility of blocks at the tunnel excavation outline is calculated successively, and the shear strength of the structural surface is calculated based on the block anti-sliding force to determine the instability location; a standard analysis model of the cut blocks is established, and the ultimate burial depth of the instable blocks is calculated from the perspective of mechanical mechanism; the instable blocks are removed, and the newly generated free blocks are judged for sliding instability using the ultimate burial depth; the instable blocks are further removed, and the above method is used for iterative retrieval to quickly determine the instability area.

[0118] Traditional DDA calculation methods require constructing a global stiffness matrix, handling contact, and performing opening and closing iterations, resulting in a large computational load. This embodiment proposes a cyclic retrieval method, with the specific determination method as follows:

[0119] 1) Input the parameters of each joint group (including joint spacing and dip angle), the constitutive parameters of the structural surface (internal friction angle and cohesion), the tunnel outline and the location of the tunnel center;

[0120] 2) Automatically generate a surrounding rock cutting model, removing the surrounding rock within the tunnel outline to form a tunnel excavation model, such as... Figure 5 As shown;

[0121] 3) Search each block around the tunnel, and use the stereographic projection analysis method to analyze the joint combination of each block to screen out the blocks that are geometrically unstable;

[0122] 4) Based on the blocks selected above, traditional block analysis theory is further used to determine the key unstable blocks from a mechanical perspective, thereby determining the unstable parts of the tunnel;

[0123] 5) Delete the critical unstable block and further determine whether its adjacent blocks are unstable; the method for determining the instability of internal adjacent blocks is as follows:

[0124] 5.1) Label joint group 1 as s1 and joint group 2 as s2;

[0125] 5.2) Determine the free surface and sliding surface of adjacent blocks: when the free surface is s1, the sliding surface is s2; when the free surface is s2, the sliding surface is s1.

[0126] 5.3) Establish a block sliding dynamics model, such as... Figure 6 As shown, the limit burial depth H1 of the sliding block on surface s1 is calculated using equation (2); the limit burial depth H2 of the sliding block on surface s2 is calculated using equation (3).

[0127] 5.4) Compare the burial depth of the block to determine whether it is unstable; for the block, if its potential sliding surface is s1, then determine the burial depth H of the block center. If H>=H1, the block is unstable and slides down; for the block, if its potential sliding surface is s2, then determine the burial depth H of the block center. If H>=H2, the block is unstable and slides down.

[0128] 5.5) Delete the unstable blocks, and repeat steps 5.1 to 5.5 for newly generated free blocks until all unstable blocks are removed, then the scope of the unstable collapse can be determined.

[0129]

[0130]

[0131] Where: H1——the ultimate burial depth of the block sliding along surface s1;

[0132] H2—The ultimate burial depth of the block sliding along the s2 surface;

[0133] —Angle of friction within joint group 1;

[0134] c1—Cohesion of the first joint group;

[0135] α — dip angle of the first joint group;

[0136] d1—Joint spacing of group 1;

[0137] —Angle of friction within joint group 2;

[0138] c2—Cohesion of joint group 2;

[0139] β—Dip angle of the second joint group;

[0140] d2 — the spacing between the second group of joints.

[0141] When the project object is a deep-buried two-lane highway tunnel, the standards in Table 2 can be directly used to determine whether it is unstable and the type of damage.

[0142] Table 2 Criteria for Determining Tunnel Instability under Two Sets of Joints

[0143]

[0144]

[0145] For the instability failures shown in Table 2, the following method can be used to quickly determine the instability range:

[0146] 1) For the collapse and instability of the arch waist, the instability range is as follows: Figure 7 The diagram shows region ABC. Point A is the midpoint of the arch's waist, and point B is the apex of the arch; the angle between line segment AC and the horizontal direction is... in Let be the internal friction angle of the surrounding rock; point O is the midpoint of line segment AB, and line segments BC and AC are symmetrical about OC.

[0147] 2) For the sliding instability of the arch waist, the instability range is as follows: Figure 8 As shown, this is region ABC. Point A is the apex of the arch, and point B is the intersection of the joint group and the arch foot; BC is a single joint, that is, a sliding failure surface, with a dip angle of β; the block where point C is located is at the ultimate burial depth H2.

[0148] 3) For the sliding instability of the arch, the instability range is as follows: Figure 9 As shown, this is region ABC. The block where point C is located satisfies the limit burial depth H1; tangents are drawn from point C to both sides of the tunnel, compared to points A and B.

[0149] 4) For horizontal and vertical joints, the instability range is as follows: Figure 10 As shown, this is region ABCD. Points A and B are the intersections of vertical joints and the tunnel outline; AD and BC are vertical joints, i.e., sliding failure surfaces; DC is the horizontal line of the ground surface.

[0150] If the above methods are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0151] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for determining instability of a tunnel surrounding rock of a joint development stratum, characterized in that, The method comprises the following steps: obtaining information on the occurrence of the joint of the working face based on multi-source data; drawing an isodensity map based on the information on the occurrence of the joint of the working face, grouping the joints, and the grouping result comprising single-group joints, two-group joints, and three-group or more joints; based on different joint grouping conditions, obtaining a failure determination result by using a corresponding tunnel surrounding rock instability determination method, specifically: for single-group joints, respectively performing crushing and bending calculation of the weak part and sliding failure calculation controlled by the shear strength of the structural plane, determining the instability mode and instability range; for two-group joints, based on the instability block of the tunnel free face, using a cyclic search method to determine the tunnel collapse range; for three-group or more joints, based on the homogenization idea, the broken surrounding rock is equivalent to a homogeneous medium for calculation, and the instability determination result is obtained; the cyclic search method specifically comprises: based on the parameters of each joint group, the constitutive parameters of the structural plane, the tunnel contour line and the tunnel center position, a surrounding rock cutting model is automatically generated, the surrounding rock inside the tunnel contour line is removed, and a tunnel excavation model is formed; each block around the tunnel is searched, and the joint combination of each block is analyzed by using the gnomonic projection analysis method, and the blocks that can be unstable in terms of geometric structure are screened out; based on the screened blocks, the key blocks that are unstable are determined from the mechanical point of view by using the traditional block analysis theory, and the instability position of the tunnel is determined; the key blocks are deleted, and the limit buried depth method is used to cyclically determine the instability of the generated free block, and the determination of the tunnel collapse range is realized; the determination of the tunnel collapse range comprises: If the sliding surface of the free block is s1, the following formula is used to calculate the limit depth of the block H 1: If the sliding surface of the free block is s2, the following formula is used to calculate the limit depth of the block H 2: wherein, H 1 is the limit depth of the block along the s1 plane, H 2 is the limit depth of the block along the s2 plane, is the internal friction angle of the first group of joint sets, c 1 is the cohesion of the first group of joint sets, is the dip angle of the first group of joint sets, d 1 is the spacing of the first group of joints, is the internal friction angle of the second group of joint sets, c 2 is the cohesion of the second group of joint sets, is the dip angle of the second group of joint sets, d 2 is the spacing of the second group of joints; determining whether there is H >= H 1 or H >= H 2, H is the center depth of the block, if yes, the free block is determined as an unstable block; the instability blocks are deleted, and the above steps are cyclically performed on the newly generated free blocks until all the instability blocks are removed, and the instability collapse range is determined.

2. The method according to claim 1, wherein, The multi-source data comprises field measurement record data, advanced geological prediction data, drilling detection data and working face while-drilling data.

3. The method according to claim 2, wherein, The field measurement record data is obtained by using a contact measurement method or a non-contact measurement method.

4. The method according to claim 1, wherein, The information on the occurrence of the joint of the working face comprises the joint characteristics of the rock mass surface, the joint combination form of the working face, the spatial distribution and the roughness.

5. The method according to claim 1, wherein, For single-group joints, the instability mode comprises block crushing instability and block sliding instability, and the determination mode of the block crushing instability is: searching for the weak blocks around the hole, calculating the maximum tensile stress based on the simply supported beam calculation model, and if the maximum tensile stress exceeds the allowable tensile strength of the surrounding rock, it is determined that the block crushing instability in the form of bending failure occurs; the determination mode of the block sliding instability is: screening out the blocks around the hole that can move in terms of geometric angle and mechanical angle, evaluating the shear strength of the structural plane, and determining whether the structural plane on both sides of the block is damaged, and when the shear strength of the structural plane on both sides of the block reaches the limit, it is determined that the block sliding instability in the form of structural plane damage occurs.

6. The method according to claim 5, wherein, The determination formula for the bending failure is: wherein, is the surrounding rock density, L is the joint block calculation length, H is the calculation block center of gravity burial depth, is the joint dip angle, is the cross-section equivalent coefficient, b is the tunnel cross-section width, is the surrounding rock allowable tensile strength.

7. The method according to claim 5, wherein, screening out the blocks around the hole that can move in terms of geometric angle and mechanical angle specifically comprises: based on the traditional block theory, the blocks around the hole are determined block by block, firstly, the blocks that can slide in terms of geometric structure are screened out, based on the screened blocks, the mechanical analysis is performed, the sliding force and the anti-sliding force are calculated, the block stability coefficient is calculated according to the traditional block analysis theory, and the blocks around the hole that can move in terms of geometric angle and mechanical angle are screened out.

8. The method according to claim 5, wherein, The block crushing instability surrounding rock instability range is obtained based on the laminated beam theory calculation, and the block sliding instability surrounding rock instability range is the sliding block range.

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