A Robust Locking and Progressive Bolt Support Design Method for a Block Group in an Underground Chamber

Abstract

The present invention relates to a robust locking and progressive bolt support design method for a block group in an underground chamber. First, according to the time sequence and the breadth-first search algorithm, the unstable blocks are divided into the first batch, the second batch, and the third batch. For different instability batches under the instability of key blocks, the bolt support parameters are optimized and adjusted, including changing the longitudinal spacing, circumferential spacing, length, and bolt angle of the bolts. By comprehensively considering the geometric parameters of the structural planes (structural plane spacing, rock bridge) under different surrounding rock grades, as well as the bolt spacing and length, and taking the vertical displacement value of the block under limited conditions as the robustness index, an anchoring optimization design method based on the robust locking of the block system is proposed. The present invention comprehensively considers the surrounding rock instability mechanism and the bolt support mechanism, establishes a bolt support system and a support method applicable to different surrounding rock conditions, and greatly improves the construction safety and economy.

Description

Technical Field

[0001] The present invention relates to a robust locking and progressive bolt support design method for a block group in an underground chamber, belonging to the technical field of surrounding rock tunnel excavation support. Background Technique

[0002] With the increase in mountain tunnel projects, the geological conditions faced in construction are becoming increasingly complex, and the resulting support methods are more difficult. For tunnels of grade IV or even grade V, choosing a reasonable support method is a key and difficult content, and to a certain extent, it affects the project budget and construction progress.

[0003] Currently, for the bolt support of fractured rock mass instability, common theories include the suspension theory, combined arch theory, combined beam theory, etc. Based on these theories, bolt support design can be guided, but they do not have universal applicability, and the surrounding rock conditions they target are relatively single. Tunnel support often determines the entire project duration and benefits. Once the support is not timely or inaccurate, it is extremely easy to produce block falling and overall collapse phenomena, which will not only affect the project progress, but seriously affect life safety. Therefore, if the traditional block theory and support theory can be broken through, and the coupling effect between bolts and blocks under different rock mass structure characteristics can be deconstructed again, considering both the direct anchoring effect of bolts and the resulting embedding effect, the construction efficiency and safety can be greatly improved. In order to achieve the optimal design of uncertain parameters, a method must be found to overcome the instability effect of uncertain parameters on the structural design results and achieve the robust support of tunnel surrounding rock. Summary of the Invention

[0004] In order to solve the above problems, the present invention discloses a robust locking and progressive bolt support design method for a block group in an underground chamber.

[0005] The technical solution adopted by the present invention to solve the above technical problems is:

[0006] A robust locking and progressive bolt support design method for a block group in an underground chamber proposed by the present invention, the method comprises the following steps:

[0007] Step 1. Using the time sequence and breadth-first search algorithm, divide the unstable blocks into the first batch, the second batch, and the third batch;

[0008] Step 2. Optimize the systematic bolt support for the unstable blocks in the first batch, and change the longitudinal and circumferential pitches of the bolts on the premise of ensuring safety;

[0009] Step 3. Conduct precise support for the unstable blocks in the second batch, and adjust the bolt length so that the bolt length covers the unstable blocks in the second batch;

[0010] Step 4. Conduct targeted support for the unstable blocks in the third batch, and adjust the bolt angle;

[0011] Step 5. Synthesize the geometric parameters of structural planes under different surrounding rock grades, and establish a robust locking method for the risk resistance ability of a group of unstable blocks including the first batch of unstable blocks, the second batch of unstable blocks, and the third batch of unstable blocks.

[0012] As a further technical solution, according to the time sequence that the vertical displacement S of the block is greater than 1 / 3 of the designed ultimate displacement value S max , after a time node of the tunnel face excavation, the blocks that meet S≥S max / 3 are the first batch of unstable blocks.

[0013] As a further technical solution, after two time nodes of the tunnel face excavation, taking the first batch of blocks and the original range of the tunnel face as the starting contour, use the breadth-first search algorithm of the unweighted undirected graph to realize the geometric search of the key blocks in the rock mass around the excavated tunnel, and record their distribution forms and geometric attributes in the spatial dimension. Among the obtained key blocks, the blocks that meet S≥S max / 3 are the second batch of unstable blocks.

[0014] As a further technical solution, after three time nodes of the tunnel face excavation, taking the first batch of unstable blocks, the second batch of unstable blocks and the original range of the tunnel face as the starting contour, use the breadth-first search algorithm of the unweighted undirected graph to realize the geometric search of the key blocks in the rock mass around the excavated tunnel, and record their distribution forms and geometric attributes in the spatial dimension. Among the obtained key blocks, the blocks that meet S≥S max / 3 are the third batch of unstable blocks.

[0015] As a further technical solution, for the second batch of unstable blocks, the length L of the anchor bolt for support is greater than the perpendicular length N from the midpoint of the outermost side line of the unstable blocks to the tunnel contour, and is greater than twice the average spacing d of the structural planes; the bonding tension F 拉 generated by the insertion of the anchor bolt into the stable block should be sufficient to support the gravity G of the anchored block.

[0016] As a further technical solution, in Step 5, taking the vertical displacement value of the blocks after three time nodes of the tunnel face excavation as the robustness index, regardless of the vertical displacement value S of the blocks obtained with any anchor bolt parameters, it shall not be greater than 1 / 3 of the designed ultimate displacement value S max , that is:

[0017] S = max{S i (i = 1, 2, 3,..., n)} ≤ S 标 (1)

[0018] Where: S i is the vertical displacement value of the blocks under the i-th anchor bolt parameter combination; n is the total number of anchor bolt support parameter combinations; S标 is the limit value of the expected vertical displacement of the block, S 标 = S max / 3;

[0019] When the stability of the tunnel surrounding rock meets Equation (1), there is an allowable uncertainty change amplitude for the uncertain parameters, that is, the robust reliability index. The uncertain parameters include the design variable q and the design parameter u; the robust evaluation index of the tunnel surrounding rock stability is a function of the limit value of the vertical displacement of the block, the geometric parameters of the structural planes of different grades of surrounding rock, and the design parameters of the bolts, expressed as:

[0020]

[0021] where α is the information difference between the design value and the true value; is the robust reliability index, that is, the allowable change range of the uncertain parameters for the tunnel surrounding rock stability; there is a relationship between the two:

[0022]

[0023] As a further technical solution, the design parameters of the bolts are expressed as the values within the specification interval, that is:

[0024] μ = [u 1 , u u (4)

[0025] In the formula: u 1 is the lower limit of the design parameter, u u is the upper limit of the design parameter; the median value of the design parameter interval number is used as its nominal value, that is

[0026]

[0027] As a further technical solution, the initial value of the said α is taken as the median value within the specified interval.

[0028] As a further technical solution, determine the vertical displacement value S of the block under different bolt support conditions i , since the design value is expressed as an interval number, the obtained number of block collapses is still an interval number:

[0029]

[0030] As a further technical solution, to ensure the robustness of the tunnel surrounding rock stability under bolt support conditions, it is necessary to ensure:

[0031] max S i (α) = max S i [B] ≤ S 标 (7).

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The robust locking and progressive bolt support design method for the block group in the underground chamber proposed by the present invention can, on the one hand, accurately divide the unstable blocks into batches and reasonably optimize the bolt support in a targeted manner. On the other hand, it proposes a robust locking domain for the bolt support to maximize the stability of the support structure and achieve the robust control of the stability of the tunnel surrounding rock. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flowchart of the present invention.

[0035] Figures 2(a) and 2(b) are schematic diagrams of different instability batches of the blocks;

[0036] Figure 3 It is a schematic cross-sectional view of the first-batch unstable blocks;

[0037] Figures 4(a) and 4(b) are schematic diagrams of the breadth-first search algorithm for the unweighted undirected graph;

[0038] Figures 5(a) and 5(b) are schematic diagrams of the bolt support optimization;

[0039] Figure 6 It is a schematic diagram of the locking domain of the bolt support;

[0040] Wherein: 1. The first-batch unstable blocks, 2. The second-batch unstable blocks, 3. The third-batch unstable blocks, 4. The relatively large spacing between the blocks of this batch, 5. The dangerous rocks searched out, 6. The new contour after identifying the first-batch unstable blocks, 7. The identified second-batch dangerous rocks; 8. Adjust the bolt spacing, 9. Adjust the bolt length, 10. The ineffective support design, 11. The targeted support area, 12. The unreasonable support design, 13. The reasonable support design. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0042] It should be noted that the terms used herein are only for describing the specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the present invention otherwise clearly indicates, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of the features, steps, operations, devices, components, and / or combinations thereof;

[0043] This embodiment discloses a robust locking and progressive bolt support design method for a block group in an underground chamber. According to the time sequence and the breadth - first search algorithm, the unstable blocks are divided into the first batch, the second batch, and the third batch; the bolt support parameters are optimized and adjusted for different instability batches under the instability of key blocks, including changing the longitudinal pitch, circumferential pitch, length, and bolt angle of the bolts; considering the geometric parameters of the structural planes (structural plane spacing, rock bridge) under different surrounding rock grades, as well as the bolt spacing and length, and taking the vertical displacement value of the block under limited conditions as the robustness index, an anchoring optimization design method based on the robust locking of the block system is proposed.

[0044] Specifically, the method includes the following steps:

[0045] a. Determine different instability batches

[0046] The instability mode of the heading tunnel is related to the construction progress and organization design of the tunnel. In this embodiment, the unstable blocks are divided into three batches, making full use of the spatio - temporal migration law to summarize the instability mode of the surrounding rock and divide the unstable blocks, in order to provide a basis for subsequent support.

[0047] Taking every 6 hours after the excavation of the heading face as a time node for analysis, according to the time sequence when the vertical displacement S of the block is greater than 1 / 3 of the design limit displacement value S max (i.e., S≥S max / 3), it is stipulated that after 6 hours of excavation of the heading face, S≥S max / 3 are the unstable blocks 1 in the first batch; after 12 hours of excavation of the heading face, taking the blocks in the first batch and the original range of the heading face as the starting contour, using the breadth - first search algorithm for an unweighted undirected graph (as shown in Figures 4(a) and 4(b)), the geometric search of the key blocks in the surrounding rock of the excavated tunnel is realized, and their distribution patterns and geometric properties in the spatial dimension are recorded. Among the obtained key blocks, the blocks with S≥S max / 3 are the unstable blocks 2 in the second batch; except for the blocks in the first two batches, after 18 hours of excavation of the heading face, taking the blocks in the first two batches and the original range of the heading face as the starting contour, using the breadth - first search algorithm for an unweighted undirected graph to realize the geometric search of the key blocks in the surrounding rock of the excavated tunnel, and recording their distribution patterns and geometric properties in the spatial dimension. Among the obtained key blocks, the blocks with S≥S max / 3 are the unstable blocks 3 in the third batch. Finally, the unstable blocks in the three batches are shown in Figures 2(a) and 2(b).

[0048] Specifically, the operation steps for block search are as follows:

[0049] 1) First, number each fracture in Figure 4, assuming Set{n1,n2,n3,…,n m}, where each n tIt contains two intersection points x1 and x2.

[0050] 2) Find all the fissures intersecting with this tunnel, and sort them in ascending order according to the distance between the intersection points and the leftmost tunnel edge, obtaining the set Set{e1, e2, ……, e m}.

[0051] 3) Start searching from e1, find all the fissures intersecting with e1, and retrieve them in ascending order according to the distance between the intersection points of the fissures and the intersection point O0 of e1 and the tunnel edge (breadth-first), obtaining the fissure set Set{p1, p2…, p m}.

[0052] 4) Check if there are fissures in set E in set P. If there are, find the smallest block, end the retrieval, and return to step 3. If not, start from set P (replace e1 with P1 and continue step 3) from 1 and continue the process of step 3 until the fissures in set E are found to complete the calculation or an empty set is obtained to end.

[0053] 5) After all the loops are completed, display the blocks.

[0054] b. Bolt support methods for each instability batch

[0055] After determining the instability batch of the surrounding rock, carry out targeted initial support for the tunnel, and the support methods are as follows:

[0056] According to the spatial position and range of the distribution of the first batch of unstable blocks, adjust the longitudinal and circumferential spacings of the systematic bolts: for the case where the first batch of unstable blocks are not all adjacent during the actual construction process (as Figure 3 shown), appropriately increase the longitudinal and circumferential spacings of the systematic bolts, and the stable support for the unstable blocks can also be achieved.

[0057] In actual engineering, the existence of the second batch of unstable blocks is crucial. If these blocks cannot be well supported, they will not only collapse along with the collapse of the first batch of blocks but also be difficult to support the surrounding third batch of unstable blocks. Therefore, for the second batch of unstable blocks, the bolt length should be mainly considered. According to the Technical Code for Rock and Soil Bolts and Shotcrete Lining Engineering GB50086 - 2015, for grade IV surrounding rock with an excavation span between 5m and 10m, the bolt support length L = 2.0 - 3.0m; for grade V surrounding rock with an excavation span between 5m and 10m, the bolt support length L = 2.5 - 3.5m. However, in actuality, there are some unstable blocks whose positions exceed the length range of the standard bolts.

[0058] For the second batch of unstable blocks, first, support is provided by the anchoring effect of the systematic bolts applied to the first batch of unstable blocks. Secondly, the anchoring of the blocks is achieved by specifically increasing the bolt length.

[0059] For the length of the anchor bolts used to anchor the second batch of blocks, the following specific requirements are made:

[0060] (1) The length L of the anchor bolts for supporting the unstable blocks in the second batch should be greater than the perpendicular length N from the midpoint of the outermost side line of this batch of blocks to the tunnel contour, and greater than twice the average spacing d of the structural planes;

[0061] (2) The bonding tensile force F generated by the anchor bolts anchored into the stable rock mass 拉 should be greater than the gravity G of the supported blocks, that is:

[0062] F 拉 >G

[0063] At the same time, the length l of the anchor bolts anchored into the stable rock mass should satisfy:

[0064]

[0065] where D is the diameter of the anchor bolt, [σ t is the tensile strength of the anchor bolt steel, and [C] is the designed bonding strength between the mortar and the anchor bolt.

[0066] For the unstable blocks in the third batch, generally there are fewer such blocks. According to their positions, the angles of individual anchor bolts can be adjusted to anchor this batch of blocks.

[0067] c. Robust locking domain of anchor bolt support

[0068] Tunnel engineering passes through mountains and ridges, and the mountain conditions faced are relatively complex. The surrounding rock grades change dynamically, and it is impossible to construct with a constant support method. In order to achieve the optimal design of uncertain parameters, a method must be found to overcome the instability impact of uncertain parameters on the structural design results, which is the robust optimization design, that is, the robust support of tunnel surrounding rock. Therefore, according to the actual surrounding rock conditions, a robust locking domain of anchor bolt support is proposed to scientifically guide the anchor bolt support under different surrounding rock grades.

[0069] (1) Robust evaluation model

[0070] The most direct description method of the stability of tunnel surrounding rock is the vertical displacement value of the blocks. In this embodiment, the vertical displacement value of the blocks 18 hours after the actual excavation of the tunnel face is studied. The vertical displacement value S of the blocks obtained with any anchor bolt parameters shall not be greater than 1 / 3 of the designed limit displacement value S max . Therefore, the expected function to meet the stability of the tunnel surrounding rock is that the vertical displacement value of the blocks is greater than the settlement displacement limit value, that is:

[0071] S = max{S i (i = 1, 2, 3,..., n)} ≤ S标

[0072] Where: S i is the vertical displacement value of the block under the i-th bolt parameter combination; n is the total number of bolt support parameter combinations; S 标 is the limit value of the expected vertical displacement of the block, S 标 = S max / 3.

[0073] When the stability of the tunnel surrounding rock satisfies Equation (3), there exists an allowable uncertainty variation amplitude for the uncertain parameters, that is, the robust reliability index. The uncertain parameters include the design variable q and the design parameter u. The robust evaluation index of the tunnel surrounding rock stability is a function of the vertical displacement limit of the block, the geometric parameters of the structural planes of different grades of surrounding rock, and the bolt design parameters, and can be expressed as:

[0074]

[0075] Among them, α is the information difference between the design value and the true value; is the robust reliability index, that is, the allowable variation range of the uncertain parameters for the tunnel surrounding rock stability. There is a relationship between the two:

[0076]

[0077] (2) Robust reliability index

[0078] There are many geometric parameters of the fissures. The most common ones in practical engineering are dip angle, dip direction, spacing, rock bridge, etc. Among them, the dip angle and dip direction have little influence on the classification of the surrounding rock grade. Therefore, the joint spacing and joint rock bridge are selected as the key factors to analyze the corresponding bolt support. The design variable q includes the average spacing d of the structural plane and the rock bridge s, expressed as q[d, s]; the design parameter u includes the hoop spacing m, longitudinal spacing n of the bolts, and the bolt length L, all of which are random variables and follow a normal distribution, and can be expressed as μ = {m, n, L}. According to the Engineering Rock Mass Classification Standard (GB50218-94), for grade IV surrounding rock, d = [0.4, 1.0], and for grade V surrounding rock, d = [0.2, 0.4]. According to the Technical Code for Rock Bolt and Shotcrete Support Engineering (GB50086-2015), for a tunnel with an excavation span of 5m to 10m, for grade IV surrounding rock, m = [1.0, 1.25], n = [1.0, 1.25], L = [2.0, 3.0]; for grade V surrounding rock, m = [0.75, 1.0], n = [0.75, 1.0], L = [2.5, 3.5].

[0079] In practical engineering, the design parameters are expressed as the values within the specification intervals, that is:

[0080] μ = [u 1 , u u ​

[0081] where: u 1 is the lower limit of the design parameter, and u u is the upper limit of the design parameter. The median value of the design parameter interval is taken as its nominal value, that is

[0082]

[0083] The requirements for the robust reliability index of the rock bolt support for tunnel surrounding rock need to meet the predetermined function of surrounding rock stability and safety. The specific analysis is as follows:

[0084] Given the initial value α0 of the uncertainty parameter α. Since the specified tunnel settlement values are different under different surrounding rock grades, the initial value of the uncertainty parameter can be taken as the median value within the specified interval.

[0085] Determine the vertical displacement value S of the block under different rock bolt support conditions i . Since the design value is represented by an interval number, the obtained number of block collapses is still an interval number:

[0086]

[0087] To ensure the robustness of the tunnel surrounding rock stability under the rock bolt support, it is necessary to ensure:

[0088] max S i (α) = max S i [B] ≤ S 标

[0089] By judging the robustness of the tunnel surrounding rock stability under the rock bolt support as described above, a robust locking domain of the tunnel rock bolt support can be formed, as Figure 6 shown, which can not only reduce the over-effective support design and discard unreasonable support methods, but also target the surrounding rock for targeted support, realizing the precise support of the rock bolt.

[0090] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A robust locking and progressive bolt support design method for a block group in an underground chamber, characterized in that it includes the following steps: Step 1. Using the time sequence and breadth-first search algorithm, divide the unstable blocks into the first batch, the second batch, and the third batch; According to the vertical displacement of the block S Greater than the design ultimate displacement value S max In the time sequence of 1 / 3 of S ≥ S max / 3 of the blocks are the first batch of unstable blocks; After two time nodes of tunnel face excavation, taking the first batch of blocks and the original range of the tunnel face as the starting contour, the geometric search of key blocks in the surrounding rock mass of the excavated tunnel is realized by using the breadth-first search algorithm of an undirected graph without weights, and their distribution patterns and geometric properties in the spatial dimension are recorded. Among the obtained key blocks, the blocks that meet S ≥ S max / 3 are the unstable blocks of the second batch; After three time nodes of the tunnel face excavation, taking the first batch of unstable blocks, the second batch of unstable blocks and the original range of the tunnel face as the starting contour, the geometric search of key blocks in the surrounding rock of the excavated tunnel is realized by using the breadth-first search algorithm of the undirected graph without weights, and their distribution forms and geometric properties in the spatial dimension are recorded. Among the obtained key blocks, the blocks that meet S ≥ S max / 3 are the third batch of unstable blocks; Step 2. Optimize the systematic bolt support for the unstable blocks in the first batch. On the premise of ensuring safety, change the longitudinal pitch and circumferential pitch of the bolts. Specifically: According to the spatial position and range of the unstable blocks in the first batch, adjust the longitudinal pitch and circumferential pitch of the systematic bolts: For the situation where the unstable blocks in the first batch are not all adjacent during the actual construction process, appropriately increase the longitudinal pitch and circumferential pitch of the systematic bolts to achieve stable support for the unstable blocks; Step 3. Carry out precise support for the unstable blocks in the second batch and adjust the bolt length so that the bolt length covers the unstable blocks in the second batch; Step 4. Carry out targeted support for the unstable blocks in the third batch and adjust the bolt angle; Step 5. Establish a robust locking design criterion for the jointed rock mass tunnel block group related to the joint spacing and rock bridge, including the unstable blocks in the first batch, the second batch, and the third batch, according to the geometric conditions of the structural planes under different surrounding rock grades.

2. The robust locking and progressive bolt support design method for the underground chamber block group according to claim 1, characterized in that, The length L of the anchor rod for supporting the instable blocks in the second batch is greater than the perpendicular length N from the midpoint of the outermost side line of the instable blocks in this batch to the tunnel contour, and is also greater than twice the average spacing d of the structural planes; the bonding tension F generated by inserting the anchor rod into the stable block 拉 should be sufficient to support the gravity G of the anchored blocks.

3. The robust locking and progressive bolt support design method for a block group in an underground chamber according to claim 1, characterized in that In the said step 5, taking the vertical displacement values of the block after three time nodes of the tunnel face excavation as the robustness index, no matter what the bolt parameters are, the vertical displacement value of the block S shall not be greater than 1 / 3 of the designed ultimate displacement value, that is: S max ​ （1） In the formula: S i is the vertical displacement value of the block under the i th combination of bolt parameters; n is the total number of combinations of bolt support parameters; S 标 is the limit value of the expected vertical displacement of the block, S 标 = S max / 3; When the stability of the tunnel surrounding rock meets Equation (1), there exists an allowable uncertainty variation amplitude for the uncertain parameters, namely the robust reliability index. The uncertain parameters include design variables q and design parameters u ; The robustness evaluation index of the tunnel surrounding rock stability is a function of the vertical displacement limit of the block, the geometric parameters of the structural planes of surrounding rocks of different grades, and the bolt design parameters, expressed as: （2） wherein, is the information difference between the design value and the true value; is the robust reliability index, that is, the allowable variation range of uncertain parameters for the stability of tunnel surrounding rock; there is a relationship between the two: （3）。 4. The robust locking and progressive bolt support design method for the underground chamber block group according to claim 3, characterized in that, the bolt design parameters are expressed by the values within the specification range, that is: μ =[ u 1 , u u ]（4） In the formula: u 1 is the lower limit of the design parameter, u u is the upper limit of the design parameter; Take the median value of the design parameter interval number as its nominal value, that is （5）。 5. The robust locking and progressive bolt support design method for the underground chamber block group according to claim 3, characterized in that, The described α initial value α 0 takes the median value within a specified range.

6. The robust locking and progressive bolt support design method for the block group in the underground chamber according to claim 3, characterized in that, Determine the vertical displacement values of blocks under different bolt support conditions S i , since the design values are represented by interval numbers, the obtained number of block collapses is still an interval number: （6）。 7. The robust locking and progressive bolt support design method for underground chamber block groups according to claim 5, characterized in that, To ensure the robustness of the tunnel surrounding rock stability under bolt support conditions, it is necessary to ensure: max S i ( α ) = max S i [B]≤ S 标 (7)。

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