Excavation and support construction method and support system for highly altered rock mass roof cavern section

Abstract

The invention relates to the technical field of tunnel excavation construction, and discloses an excavation support construction method and support system for a highly altered rock mass roof caving tunnel section, and the excavation support construction method comprises the following steps: respectively supporting a combined support structure consisting of a steel arch frame and a system anchor rod on rock walls of tunnel sections A m away from two sides of a highly altered rock mass; after supporting of the combined supporting structure is completed, a large pipe shed is arranged above the combined supporting structure and obliquely penetrates through the strong alteration rock mass in the length direction of the tunnel based on a set rule; and after the large pipe shed is arranged, the strong alteration rock mass is excavated, and the excavated place is supported in the excavation process until the top caving hole section of the strong alteration rock mass is completely excavated and supported. According to the method, detailed supporting parameters of the strong alteration rock mass hole section and the complete rock mass within the range of A m on the two sides are provided, and the hole section can be effectively supported through the supporting parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel excavation construction, and particularly relates to an excavation support construction method and a support system for a roof-falling section of strongly altered rock mass. Background Art

[0002] During the tunnel excavation process, strongly altered rock mass is a common engineering problem. Such rock mass is usually formed by the superposition of multiple geological factors such as water-rock interaction, metamorphism, surficial weathering, and tectonic activities, and has the characteristics of extremely low strength and extremely poor stability. During the excavation process, such rock mass is extremely prone to instability problems such as roof fall due to unloading effect, seriously threatening construction safety and project progress.

[0003] Currently, there is no good construction treatment method for the strongly altered rock mass section with roof fall phenomenon or roof fall risk. The commonly used construction treatment method is to first carry out consolidated grouting and then carry out excavation. However, it is difficult to effectively support a relatively large strongly altered rock mass section by using this treatment method, that is, there is still a relatively large roof fall risk for the section. Summary of the Invention

[0004] To effectively solve this problem, an excavation support construction method and a support structure for a roof-falling section of strongly altered rock mass are proposed. By optimizing the construction technology and the support system, the safety and stability during the tunnel excavation process are ensured.

[0005] The present invention is realized by the following technical solutions: An excavation support construction method for a roof-falling section of strongly altered rock mass, comprising: Joint support structures composed of steel arch frames and system bolts are respectively supported on the rock walls of the tunnel sections at a distance of A meters from both sides of the strongly altered rock mass, where A≥5; After the joint support structure is supported, large pipe roofs are obliquely penetrated through the strongly altered rock mass along the tunnel length direction based on a set rule above the joint support structure; After the large pipe roofs are set, the strongly altered rock mass is excavated, and the excavated places are supported during the excavation process until the entire excavation support of the roof-falling section of the strongly altered rock mass is completed.

[0006] As an optimization, several of the combined support structures are arranged at intervals of B meters along the length direction of the tunnel. Each combined support structure includes a steel arch, several top arch system bolts, several side wall system bolts, a steel mesh, and several foot-locking bolts. Among them, along the length direction of the tunnel, several cross braces evenly distributed at intervals are fixedly connected between two adjacent steel arches. Several of the top arch system bolts are evenly spaced at the crown position of the steel arch. Several of the side wall system bolts are evenly spaced at the side wall position of the steel arch. And several foot-locking bolts are fixed at the bottom of the steel arch. And concrete is sprayed on the outer side of the steel arch, and the steel mesh is arranged in the concrete.

[0007] As an optimization, the distance between two adjacent top arch system bolts on the same steel arch is 1.5 m. And several top arch system bolts of several steel arches are arranged in a rectangular network. And the diameter of the top arch system bolt is φ32, and the length of the top arch system bolt is 9 m.

[0008] As an optimization, the distance between two adjacent side wall system bolts on the same steel arch is 1.5 m. And several top arch system bolts of several steel arches are arranged in a plum blossom-shaped network. And the diameter of the side wall system bolt is φ28, and the length of the side wall system bolt is 6 m.

[0009] As an optimization, the specific setting rule is as follows: The large pipe shed uses a perforated pipe with a diameter of d. And the length of the large pipe shed anchors the intact rock mass on both sides of the strongly altered rock mass for at least A meters. And the spacing between two adjacent large pipe sheds is twice the diameter of the large pipe shed. The diameter of the large pipe shed follows the principle that the higher the degree of alteration of the strongly altered rock mass, the smaller the diameter. Its calculation formula is: d = 100 + 5 * (R b - 5); In the formula: d is the diameter of the large pipe shed, with the unit of mm; R b is the saturated uniaxial compressive strength of the rock, with the unit of Mpa. This index can be used as a quantitative index for the degree of rock alteration. And the diameter of the large pipe shed is not less than 89 mm. And the spacing between two top arch system bolts divided by twice the diameter of the large pipe shed is equal to a positive integer. From the side with higher elevation to the side with lower elevation, the installation elevation angle of the large pipe shed , i represents the slope drop of the tunnel chamber, represents the length of the tunnel section of the strongly altered rock mass in the horizontal direction.

[0010] As an optimization, after the installation of the large pipe shed is completed, fixed connection grouting is carried out, and the grouting pressure range is 0.5 MPa to 1 MPa. The grouting liquid is grouted in the order from thin to thick.

[0011] As an optimization, the strongly altered rock mass is excavated, and the excavated area is supported during the excavation process until the entire excavation and support of the roof caving section of the strongly altered rock mass are completed. The specific process is as follows: The excavation footage of the strongly altered rock mass is not allowed to exceed 0.5 m, and the excavation direction is from the side with a higher elevation to the side with a lower elevation; The layered excavation method is adopted to divide the strongly altered rock mass into an upper layer area, a middle layer area, and a lower layer area; The upper layer area is excavated by the method of leaving a core soil and manually chiseling with a pneumatic pick, and after the upper layer excavation is completed, the upper layer area is supported by the combined support method of shotcrete with wire mesh + steel arch frame; For the excavation of the middle layer area and the lower layer area, the excavation is carried out in the order of layer by layer from the middle to both sides, and the support is carried out along with the excavation, and the support parameters are the same as those of the upper layer; Repeat the above steps until the excavation of the roof caving section of the strongly altered rock mass is completed.

[0012] The present invention also discloses a support system for supporting the tunnel sections on both sides of the strongly altered rock mass with a length of A meters in the excavation and support construction method for the roof caving section of the strongly altered rock mass as described above. The support system includes a combined support structure and a number of large pipe sheds. Among them, the combined support structure includes a steel arch frame, a number of top arch system anchor bolts, a number of side wall system anchor bolts, a steel wire mesh, and a number of locking foot anchor bolts. Along the length direction of the tunnel, a number of uniformly spaced cross braces are fixedly connected between two adjacent steel arch frames. A number of the top arch system anchor bolts are evenly spaced and arranged at the crown position of the steel arch frame, a number of the side wall system anchor bolts are evenly spaced and arranged at the side wall position of the steel arch frame, and a number of locking foot anchor bolts are fixed at the bottom of the steel arch frame. And concrete is sprayed on the outside of the steel arch frame, and the steel wire mesh is arranged in the concrete. A number of the large pipe sheds penetrate the strongly altered rock mass obliquely along the length direction of the tunnel, and one end of the large pipe shed on the side with a higher elevation is lower than one end of the large pipe shed on the side with a lower elevation.

[0013] As an optimization, the distance between two adjacent top arch system anchor bolts on the same steel arch frame is 1.5 m, and a number of the top arch system anchor bolts of a number of the steel arch frames are arranged in a rectangular network. The diameter of the top arch system anchor bolt is φ32, and the length of the top arch system anchor bolt is 9 m.

[0014] As an optimization, the distance between two adjacent side wall system bolts on the same steel arch is 1.5 m. The roof arch system bolts of several steel arches are arranged in a plum blossom-shaped network. The diameter of the side wall system bolts is φ28, and the length of the side wall system bolts is 6 m.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The load-bearing system of the present invention is a combined load-bearing system of large pipe roofs + intact surrounding rocks at both ends + steel arches, which makes use of the self-bearing capacity of the surrounding rocks to a certain extent. Compared with the support system that solely relies on the support structure for load-bearing, the project investment is saved. This load-bearing system can effectively support strongly altered rock masses and greatly reduce the risk of roof caving of the strongly altered rock masses during excavation; 2. On the premise of effective support, the length of the pipe roof required for the present invention to drill the large pipe roof from the side with a higher elevation to the side with a lower elevation is shorter than that required to drill from the side with a lower elevation to the side with a higher elevation. Therefore, adopting this construction direction can save the construction period and project investment; 3. The elevation angle calculated by the formula proposed in the present invention can ensure that, on the basis of effectively utilizing the bearing capacity of the intact surrounding rocks, the length of the large pipe roof is minimized as much as possible, thereby saving the construction period and project investment; 4. The pipe diameter of the large pipe roof determined by the method proposed in the present invention can adapt to strongly altered rock masses with different degrees of alteration to form effective support. At the same time, the pipe spacing calculated by the formula proposed in the present invention can avoid damage to the system bolts of the intact rock masses on both sides during the construction of the pipe roof; 5. The present invention can effectively consolidate the strongly altered rock mass section of the tunnel through consolidated grouting with large pipe roofs (perforated pipes). Compared with the traditional advanced grouting with small pipes, the combined support system formed by the large pipe roof and the grouting body has a better effect than the support system of the single grouting body, and the large pipe roof grouting is more convenient and the construction period is shorter; 6. Excavating the strongly altered rock mass section of the tunnel from the side with a higher elevation to the side with a lower elevation can relatively reduce the risk of landslide of the strongly altered rock mass, that is, reduce the construction risk and ensure the construction safety; 7. The detailed support parameters of the strongly altered rock mass section of the tunnel and the intact rock masses within A m on both sides proposed in the present invention can effectively support the tunnel section in the background technology of the present invention, and the relevant support parameters can be used for reference in other similar cases. In summary, the present invention has its advantages in ensuring construction safety, saving project costs and construction periods, and has obvious economic benefits and practical values. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings: Figure 1 It is a schematic cross-sectional view of the chamber combined support structure; Figure 2 Schematic diagram of partial enlargement of the chamber support structure Figure 3 Schematic diagram of the construction axis profile of the large pipe shed Figure 4 Schematic diagram of the construction section of the large pipe shed Figure 5 Schematic diagram of the excavation sequence of the strongly altered rock mass

[0017] Markings in the attached drawings and corresponding names of components 1 - Roof arch system bolt; 2 - Side wall system bolt; 3 - Reinforcement mesh; 4 - Concrete; 5 - Steel arch frame; 6 - Foot-locking bolt Specific implementation mode

[0018] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments and the attached drawings. The illustrative implementation modes of the present invention and their descriptions are only used to explain the present invention and are not used to limit the present invention

[0019] Embodiment 1 of the present invention provides an excavation support construction method for the roof caving section of a strongly altered rock mass, which is characterized by including: Step 1: Support a combined support structure composed of a steel arch frame and a system bolt on the rock walls of the tunnel sections A meters away from both sides of the strongly altered rock mass respectively. Both A and B are positive numbers

[0020] Specifically, the support needs to be completed within at least 5 m on both sides of the strongly altered rock mass, that is, A≥5, to provide a bearing structure for the subsequent construction of the large pipe shed

[0021] In some embodiments, as Figure 1 - Figure 2 shown, a plurality of the combined support structures are arranged at intervals of B meters along the length direction of the tunnel. Each combined support structure includes a steel arch frame, a plurality of roof arch system bolts, a plurality of side wall system bolts, a reinforcement mesh and a plurality of foot-locking bolts. Among them, along the length direction of the tunnel, a plurality of cross braces are fixedly connected between adjacent two steel arch frames at evenly distributed intervals. A plurality of the roof arch system bolts are evenly spaced at the arch crown position of the steel arch frame. A plurality of the side wall system bolts are evenly spaced at the side wall position of the steel arch frame. And a plurality of foot-locking bolts are fixed at the bottom of the steel arch frame. And concrete is sprayed on the outside of the steel arch frame, and the reinforcement mesh is arranged in the concrete

[0022] In some embodiments, the distance between adjacent two of the roof arch system bolts on the same steel arch frame is 1.5 m, and a plurality of the roof arch system bolts of a plurality of the steel arch frames are arranged in a rectangular network. And the diameter of the roof arch system bolt is φ32, and the length of the roof arch system bolt is 9 m

[0023] In some embodiments, the distance between two adjacent sidewall system bolts on the same steel arch is 1.5 m. A number of top arch system bolts of several steel arches are arranged in a plum blossom-shaped network. The diameter of the sidewall system bolts is φ28, and the length of the sidewall system bolts is 6 m.

[0024] For example, A is 5 and B is 0.5. A should not be too large. If A is too large, it will lead to a large increase in cost while the function improvement is very small.

[0025] That is to say, during the excavation and support of the tunnel sections on both sides of the strongly altered rock mass, the tunnel sections within 5 m on both sides of the strongly altered rock mass are excavated and supported. The support adopts a combined support form of steel arch + system bolts. For the top arch, system bolts with φ32 and L = 9 m are set, with a spacing of 1.5 m between rows and columns, arranged in a rectangular pattern. For the sidewalls, system bolts with φ28 and L = 6 m are set, with a spacing of 1.5 m between rows and columns, arranged in a plum blossom-shaped pattern. The steel arch is supported by I20b steel arches, with a spacing of 0.50 m between each arch. The steel arches should extend along with the excavation of the lower layer of the tunnel body to the sidewall floor. Adjacent steel arches are welded with Φ28 (grade III steel) steel bars to form cross braces, with a cross brace spacing of 1 m. The steel arches should be welded to the existing system bolts as much as possible. Each steel arch is provided with 22 lock-foot bolts with φ28 and L = 6 m. A φ8@20 cm×20 cm steel mesh is laid closely against the rock wall, and 27 cm thick C25 concrete is sprayed. The sprayed concrete should cover the arch and ensure density.

[0026] Step 2: After the combined support structure is completed, a large pipe shed is inclined and drilled through the strongly altered rock mass along the tunnel length direction above the combined support structure based on a set rule.

[0027] When drilling the large pipe shed, drill in the gap between two steel arches, with the direction along the tunnel length direction, and drill from the side with a higher elevation to the side with a lower elevation.

[0028] In some embodiments, the set rule is specifically: The large pipe shed uses a perforated pipe with a diameter of d, and the length of the large pipe shed anchors at least A meters of the intact rock mass on both sides of the strongly altered rock mass. The distance between two adjacent large pipe sheds is twice the diameter of the large pipe shed; The so-called twice here refers to the distance between the axes of the pipe sheds. In engineering (especially in pipe shed support in tunnel engineering, foundation pit support, etc.), the distance between two pipe sheds usually refers to the distance between the centers, that is, the center distance.

[0029] The diameter of the large pipe shed follows the principle that the higher the degree of alteration of the strongly altered rock mass, the smaller the diameter. And the diameter of the large pipe shed is not less than 89 mm, and the distance between two top arch system bolts divided by twice the diameter of the large pipe shed is an integer; ; In the formula: is a positive integer, is the spacing of the anchor rods of the crown system of the intact rock mass on both sides.

[0030] The pipe diameter of the large pipe shed is obtained according to the following formula: d = 100 + 5 * (R b - 5); In the formula: d is the pipe diameter of the large pipe shed, with the unit of mm; R b is the uniaxial compressive strength of the saturated rock, with the unit of Mpa, and this index can be used as a quantitative index for the degree of rock alteration.

[0031] From the side with a higher elevation to the side with a lower elevation, the installation elevation angle of the large pipe shed , i represents the slope drop of the tunnel chamber, represents the length of the tunnel section of the strongly altered rock mass in the horizontal direction. The schematic diagram of the construction axis section of the large pipe shed is as Figure 3 shown. The schematic diagram of the construction section of the large pipe shed is as Figure 4 shown.

[0032] In some embodiments, after the installation of the large pipe shed is completed, solidifying grouting is carried out, and the grouting pressure range is 0.5 MPa to 1 MPa. The grouting fluid is grouted in the order of from thin to thick. For example, the mixing ratio between the solvent and the solute in the grouting fluid is grouted in the order of 2:1, 1:1, 0.5:1.

[0033] The composition of the grouting fluid is prior art and will not be elaborated here.

[0034] Purpose of the slurry ratio from thin to thick: Initial penetration (thin slurry): Expand the reinforcement range: The thin slurry (such as cement slurry with a high water-cement ratio) has strong fluidity, can penetrate into fine cracks, initially fill the loose rock and soil mass, and form a wide-area reinforcement.

[0035] Reduce resistance: The thin slurry has a small penetration resistance to the rock formation, avoiding premature sealing of cracks and preventing subsequent slurry from spreading.

[0036] Subsequent strengthening (thick slurry): Improve strength: Gradually increase the slurry concentration (such as adding a setting accelerator or reducing the water-cement ratio), form a high-strength consolidation body in the penetrated area, and enhance the bearing capacity.

[0037] Control the diffusion radius: The thick slurry has low fluidity, can concentrate on reinforcing key areas, and avoid excessive loss of slurry to non-target areas.

[0038] The benefits of this are: Stratified reinforcement: The thin slurry fills deep fissures, and the thick slurry strengthens the shallow layer, forming a gradient strength distribution to match the stress characteristics of the surrounding rock.

[0039] Adaptive adjustment: Dynamically adjust the ratio according to the feedback of grouting pressure, flow rate, etc. to cope with different geological conditions (such as porosity changes).

[0040] Economy: The thin slurry reduces the initial material consumption, and the thick slurry provides targeted reinforcement to optimize resource utilization.

[0041] Since the slurry is grouted from thin to thick during the grouting process, therefore, the ratio of each stage of the slurry, the grouting time of each stage, and the type of slurry will vary due to different geological conditions.

[0042] Therefore, how to find the best parameter combination is usually determined based on experience in the existing situation, which has strong subjectivity. Therefore, the present invention determines the best parameter combination through a parameter optimization algorithm, which will be more objective.

[0043] The parameter optimization algorithm of the present invention is a genetic algorithm.

[0044] Suppose the slurry goes through a total of 3 stages from thin to thick, the grouting time of each stage is T1, T2, T3 respectively, the geological condition (geological type) is DL, the type of solute in the grouting liquid is RL, and the ratios are b1:a1, b2:a2, b3:a3 respectively. Here, a is the solvent, generally the mass of water, and b is the mass of the solute. One of the constraint conditions is b1:a1 < b2:a2 < b3:a3. That is, the slurry concentration in the three stages is from thin to thick.

[0045] Let these parameters be the gene coding positions of the genetic algorithm, and these parameters form a chromosome individual.

[0046] The process of optimizing these parameters through the genetic algorithm is specifically as follows: A1. Set the number of iterations of the genetic algorithm and the number of chromosome individuals in each generation of the population; among them, several chromosomes jointly form a population; A2. Establish an objective function and constraint conditions, where the objective function is: ; ; Among them, is the solid connection strength, is the minimum actual penetration range of the grouting liquid, It represents the penetration threshold of the grouting fluid; the consolidation strength (or grouting consolidation strength) refers to the mechanical properties of the consolidated body formed after injecting the grout (such as cement slurry, chemical slurry, etc.) into the rock and soil mass or structural cracks through the grouting process (such as grouting, injecting slurry, etc.). It usually includes indicators such as its compressive strength, shear strength, and bond strength. In the present invention, it can be the sum of these three strengths (compressive strength, shear strength, and bond strength).

[0047] A3. Encode all gene coding positions to obtain the coding value of the chromosome individual, and randomly generate an initial population formed by several chromosome individuals based on the constraint conditions. Let this initial population be the parental population, and let the chromosome individuals in the parental population be parental individuals. Each parental individual includes a set of all gene coding positions; A4. Conduct grouting tests according to the coding values of the parental individuals in the parental population. After the grouting tests, obtain the test results composed of the solidification strength , the minimum actual penetration range of the grouting fluid ; A5. Calculate the fitness function according to the test results on the premise of satisfying , and calculate the fitness values of each parental individual in the parental population that satisfy and sort them; A6. Save the first M parental individuals with the largest fitness values in the parental population. Select parental individuals from all parental individuals except the first M parental individuals with the largest fitness values through roulette wheel selection for crossover and mutation operations to obtain offspring individuals. Then calculate the fitness values of the offspring individuals after crossover and mutation and sort them. Reinsert the offspring individuals into the parental population according to the fitness values, select a set number of individuals to be solved to form a new parental population, and then return to A4; A7. Repeat A4 - A6 until the iteration number is reached or the objective function value is within the specified threshold range. The finally obtained parental population is the optimal combination.

[0048] Through optimization by the genetic algorithm, the optimal grouting parameter combinations of different grouting fluids corresponding to each geological type can be objectively obtained.

[0049] That is to say, during the construction of the large pipe shed, after the excavation and support of the tunnel section within 5 m on both sides of the strongly altered rock mass are completed, the construction of the large pipe shed is carried out. The large pipe shed uses a perforated pipe (with holes on the steel pipe for grouting) with a diameter of d. The length is based on at least anchoring 5 m of intact rock. The pipe shed spacing is twice the diameter. The construction is carried out from the side with a higher elevation to the side with a lower elevation, and the upward angle is , which is determined by Equation 1 below. The diameter of the large pipe shed is determined according to the alteration degree of the tunnel section in the strongly altered rock mass and the bolt spacing of the intact rock mass system on both sides. It follows the principle that the higher the alteration degree of the strongly altered rock mass, the smaller the diameter, but it should not be less than 89 mm. The diameter of the large pipe shed should also comply with the principle of Equation 2. If the bolt spacing of the intact rock mass system on both sides divided by twice the diameter is not a positive integer, the pipe shed construction will damage the bolts of the intact rock mass system on both sides.

[0050] After the installation of the large pipe shed is completed, consolidated grouting is carried out. The grouting pressure is controlled at 0.5 MPa to 1 MPa, and the slurry is grouted from thin to thick according to the mixing ratios of 2:1, 1:1, and 0.5:1.

[0051] Of course, the determination of the grouting time can also be carried out under the following conditions. For example, the slurry is grouted from thin to thick according to the mixing ratios of 2:1, 1:1, and 0.5:1.

[0052] Control of the grouting time and grouting pressure for each mixing ratio slurry: There is no absolute fixed time for slurry conversion. It is mainly judged and controlled comprehensively based on the changes in grouting pressure, slurry absorption rate (slurry intake per unit time), and the specified stable time in the design. The specific principles are as follows: 1. Initial perfusion (thin slurry: 2:1): Starting condition: Start grouting with 2:1 thin slurry.

[0053] Duration: Continuously perfusion until one of the following conditions is met: 1) Design stable time: Under the design pressure of 0.5 to 1 MPa, the slurry absorption volume remains stable (without obvious decrease) and reaches the minimum stable time specified in the design or specification (usually 15 to 30 minutes). This is the basic requirement.

[0054] 2) Significant decrease in slurry absorption volume: After reaching the design pressure, the slurry absorption volume continuously decreases significantly (for example, drops to 1 / 4 or lower of the initial slurry absorption rate) and maintains for a period of time (such as 10 to 15 minutes), indicating that the pores in the formation have been initially filled or the passage has been partially blocked.

[0055] 3) Cumulative grouting volume meets the standard: When the cumulative grouting volume reaches the designed estimated volume or it is judged according to experience that the slurry of this gradation has been effectively injected into the predetermined range.

[0056] 2. Conversion to medium concentration (1:1): Starting condition: After meeting the end condition of the 2:1 slurry.

[0057] Duration: Also perfusion under the pressure of 0.5 to 1 MPa until the following is met again: 1) The stable time required by the design (such as 15 to 30 minutes).

[0058] 2) There is a significant and continuous decline in the slurry absorption volume again.

[0059] 3) The cumulative grouting volume reaches the expectation.

[0060] 3. Switch to thick slurry (0.5:1): Starting condition: After the end condition of 1:1 slurry is met.

[0061] End condition (final grouting standard): 1) Main standard: Under the design pressure of 0.5 - 1 MPa, the slurry absorption volume drops to the design-specified end standard (usually a very low rate, such as less than 0.4 L / min or 1 L / min) and remains stable for a specified time (such as 30 minutes). This indicates that the formation has been basically filled and reaches a relatively dense state.

[0062] 2) Pressure compliance: Reach the design maximum pressure (1 MPa), and the slurry absorption volume is very small and remains stable continuously.

[0063] 3) Special situation: If the slurry absorption volume is still large and the pressure cannot rise after grouting thick slurry for a long time, it may indicate the existence of large cavities or channels. Measures such as intermittent grouting, adding accelerators, waiting for setting and re-grouting need to be taken, rather than grouting indefinitely.

[0064] Key control points: Pressure is the prerequisite: It must be on the premise of reaching and stabilizing in the design pressure range (0.5 - 1 MPa), and then judged according to the slurry absorption volume and time.

[0065] The change in slurry absorption volume is the core index: The conversion of slurry concentration mainly depends on whether there is a significant and continuous decline in the slurry absorption volume under a constant pressure.

[0066] The stable time is the basic requirement: After each gradation of slurry reaches the design pressure, it needs to maintain a specified stable time (check the design or specification, usually 15 - 30 minutes), which is the basic condition to ensure the effective diffusion and filling of this gradation of slurry.

[0067] Gradually change level by level, and do not skip levels: It must be strictly changed in the order of 2:1 -> 1:1 -> 0.5:1. Only after the previous level of slurry reaches the end standard can it be changed to the next level of thicker slurry.

[0068] Dynamic adjustment: It needs to be flexibly adjusted according to the on-site geological conditions (such as large fissures with large slurry absorption volume), but the change principle remains the same. When the slurry absorption volume is abnormally large, it may be necessary to extend the grouting time of thin slurry or take special measures.

[0069] Adopting the grouting sequence with the water-cement ratio from large to small (that is, the slurry from thin to thick: 2:1 -> 1:1 -> 0.5:1) has the following significant advantages: 1. Improve groutability and permeability: The thin slurry (2:1) has low viscosity and good fluidity, making it easier to enter the fine rock fractures, pores, and the contact gaps between the pipe shed and the soil. This is crucial for initially opening the grouting channels, wetting the fracture surfaces, and establishing a slurry flow network. If thick slurry is used at the beginning, it may quickly block the surface or narrow channels, resulting in ineffective perfusion in the deep part.

[0070] 2. Reduce leakage losses and waste: The thin slurry can preferentially seal smaller fractures and leakage channels. Under pressure, the fine particles and colloidal components in the thin slurry are more likely to enter the small fractures and initially fill and seal them. This creates conditions for subsequent perfusion of thicker slurry and reduces the waste caused by the thicker slurry flowing into non-target areas during perfusion.

[0071] 3. Ensure the uniformity and density of grouting: The thin slurry first fills the small gaps, the medium-concentration slurry (1:1) further expands the filling range and increases the density of the slurry stone body. Finally, the thick slurry (0.5:1) effectively fills the larger voids on the basis of the formed channels and filling, and forms a high-strength stone body under pressure. This progressive filling method enables pores of different sizes to be more fully and evenly filled, with higher overall density.

[0072] 4. Effectively control the grouting pressure and prevent formation splitting: The thin slurry has good fluidity and can start effective perfusion and diffusion at relatively low pressure. If thick slurry is directly used, due to its high viscosity and large resistance, a higher pressure may be required to achieve the same diffusion range, which greatly increases the risk of accidentally splitting (cracking) the surrounding rock and soil mass, resulting in ineffective loss of slurry and even damage to the formation stability. Starting from thin to thick can more gently increase the grouting resistance and safely reach the design pressure.

[0073] 5. Improve the strength and durability of the stone body: Although the thick slurry stone body has higher strength, the thin slurry can better penetrate into the micro-fractures to form foundation reinforcement. The thick slurry mainly fills the large voids and forms a skeleton in the later stage. This combination makes the finally formed stone body network more complete, with better overall strength and impermeability. The thick slurry solidifies in a relatively closed environment, and moisture is not easily precipitated, resulting in a denser stone.

[0074] 6. Facilitate construction control and judgment: By observing the changes in pressure and slurry absorption volume during the perfusion of the thin slurry, information such as the permeability of the formation and the location of the main leakage channels can be initially judged, providing a basis for adjusting subsequent perfusion parameters. The change process of the slurry absorption volume from large to small and the pressure from small to large also makes it easier to intuitively judge whether the grouting is gradually approaching completion (meeting the standards).

[0075] In summary, the grouting sequence from thin to thick follows the objective law of "first infiltrating and filling small fissures, and then squeezing and filling large pores". It is the most effective and commonly used method to ensure the grouting effect (improve injectability, reduce loss, and ensure uniform compaction), control construction risks (prevent formation fracturing), optimize material use, and final reinforcement quality (improve overall strength and durability). It is crucial to strictly implement this sequence in the consolidated grouting of large pipe roofs.

[0076] Step 3: After the large pipe roof is set up, excavate the strongly altered rock mass, and support the excavated area during the excavation process until the entire roof caving section of the strongly altered rock mass is excavated and supported.

[0077] In some embodiments, the specific process of excavating the strongly altered rock mass and supporting the excavated area during the excavation process until the entire roof caving section of the strongly altered rock mass is excavated and supported is as follows: Let the excavation footage of the strongly altered rock mass not exceed 0.5 m, and the excavation direction is from the side with higher elevation to the side with lower elevation, which can reduce construction safety risks; Adopt a layered excavation method to divide the strongly altered rock mass into an upper layer area, a middle layer area, and a lower layer area; on the premise that the height of the upper layer area is greater than the height from the crown to the shoulder of the arch, divide it equally into upper, middle, and lower parts; otherwise, first ensure the height of the upper layer area, and then divide it equally into middle and lower parts.

[0078] The upper layer area is excavated by the method of leaving a core soil and manually chiseling with a pneumatic pick, and after the upper layer excavation is completed, the upper layer area is supported by the combined support method of shotcrete with wire mesh + steel arch frame; The middle layer area and the lower layer area are excavated in a layered sequence from the middle to both sides, and the support is carried out along with the excavation, and the support parameters are the same as those of the upper layer; Repeat the above steps until the excavation of the roof caving section of the strongly altered rock mass is completed.

[0079] Adopt a layered excavation method to divide the strongly altered rock mass into an upper layer area, a middle layer area, and a lower layer area; Let the excavation footage of the strongly altered rock mass not exceed 0.5 m; The upper layer area is excavated by the method of leaving a core soil and manually chiseling with a pneumatic pick, and after the upper layer excavation is completed, the upper layer area is supported by the combined support method of shotcrete with wire mesh + steel arch frame; Specifically, the purpose of leaving a core soil is to reduce the disturbance of the excavation face to the surrounding rock, prevent the collapse of the heading face, and the core soil serves as a temporary support to balance the formation pressure.

[0080] The operation method is to only excavate the part outside the tunnel contour line during excavation (such as circular excavation), and retain the central core soil (usually with a width of 3 - 5m). The core soil is removed in blocks after the support is completed.

[0081] The tool used for manual pneumatic pick chiseling is a pneumatic pick. The excavation is carried out in layers from top to bottom, with each layer having a height of about 0.5 - 1m.

[0082] Shotcrete with wire mesh: The wire mesh is made of φ6 - φ8mm steel bars, with a grid spacing of 15×15cm or 20×20cm, covering the excavation surface. Its function is to enhance the crack resistance of the shotcrete and prevent surface spalling.

[0083] The shotcrete (sprayed concrete) has a thickness of 10 - 15cm, a strength of C20 - C25, and a quick - setting agent is added (3 - 5% of the cement dosage) to quickly seal the rock surface. Steel arch: The type is I - shaped steel (I18 - I20) or lattice steel arch, with a spacing of 0.5 - 1.5m (depending on the degree of rock mass fragmentation). The key points for installation are: the arch feet need to be padded solid, and when necessary, locking bolts (such as φ25mm, L = 3m) are set to prevent sinking. The steel arches are welded with cross braces to form an integral whole.

[0084] Combined support process: 1. Immediately spray a layer of concrete (3 - 5cm) after excavation to seal the rock surface; 2. Hang the wire mesh, install the steel arch and fix it; 3. Re - spray the concrete to the designed thickness to cover the steel arch and the wire mesh.

[0085] The support effect is that the shotcrete provides surface support, the steel arch bears the main load, and the wire mesh coordinates the deformation.

[0086] The technical advantages are: Reducing disturbance: Manual excavation + retaining the core soil maximally protects the self - stability of the surrounding rock.

[0087] Quick sealing: Shotcrete + steel arch can promptly inhibit the deformation of the surrounding rock.

[0088] Strong adaptability: The combined support can cope with problems such as rheology and softening of strongly altered rock masses.

[0089] During the excavation of the middle - layer area and the lower - layer area, the excavation is carried out in layers from the middle to both sides, and the support is carried out along with the excavation. The support parameters are the same as those of the upper layer.

[0090] (1) Excavation from the middle to both sides: Excavation sequence (taking the middle layer as an example): First, excavate the middle part (core soil area) to form a temporary working space.

[0091] Expand to both sides (excavate with a left - right stagger) to avoid instability of the surrounding rock caused by simultaneous unloading on both sides.

[0092] Advantages: Reduce the free face of the surrounding rock and prevent the deformation of the steel arch due to lateral pressure.

[0093] Facilitate mucking and support operations, and improve construction efficiency.

[0094] 2. Support is carried out simultaneously with excavation (timely support) Principle: "Excavate a section and support a section" to avoid long - term exposure of the surrounding rock.

[0095] Specific steps: For every 1 - 2 m of excavation, immediately carry out support (install wire mesh and spray concrete + steel arch).

[0096] The steel arch is closed into a ring as soon as possible (connect the top support with the side - wall support) to form a stable structure.

[0097] When necessary, add locking foot bolts to prevent the steel arch from sinking or squeezing inwards.

[0098] 3. The support parameters are the same as those of the upper layer The support parameters include: Steel arch model (such as I20 I - beam, spacing 0.5 m).

[0099] Shotcrete thickness (such as 12 cm, C25 concrete).

[0100] Reinforcement mesh specification (such as φ6@15×15 cm).

[0101] Locking foot bolts (such as φ25 mm, L = 3 m, 2 bolts at each arch foot).

[0102] Reasons for keeping the support parameters consistent: Ensure uniform support stiffness for the entire cross - section and avoid deformation caused by local weakness.

[0103] The middle and lower layers also face the problem of softness of strongly altered rock and require the same strength of support.

[0104] 4. Example of construction process (mid - layer excavation and support): Excavate the middle part (the remaining part of the core soil) → Initially spray concrete for sealing.

[0105] Excavate the left side (1 - 2 m) → Install the left - hand steel arch → Install wire mesh → Spray concrete → Drive locking foot bolts.

[0106] Excavate the right side (staggered by 3 - 5 m) → Follow the same support process as the left side.

[0107] Check the closure of the support to ensure firm connection between the steel arch and the upper layer.

[0108] That is to say, during the excavation and support of strongly altered rock masses, after the construction of large pipe roofs is completed, the excavation of strongly altered rock masses is carried out. The excavation is carried out in layers. The upper layer uses the method of leaving a core soil and manually chiseling with pneumatic picks to reduce excavation disturbance. After the upper layer excavation is completed, the upper layer support is carried out. The support adopts the combined support method of shotcrete with wire mesh + steel arch. The wire mesh uses φ8@20cm×20cm wire mesh, and the steel arch uses I20b steel arch. The middle and lower layers are excavated in sequence from the middle to both sides in layers, and the support is carried out along with the excavation. The support parameters are the same as those of the upper layer. The excavation generally follows the principle of short advance footage, weak blasting or no blasting, and the excavation advance footage is controlled within 0.5m. The excavation sequence is shown in Figure 5 .

[0109] Example 2 discloses a support system for supporting a tunnel section with a length of A meters on both sides of a strongly altered rock mass in the excavation support construction method for a strongly altered rock mass roof caving section described in Example 1. The support system includes a combined support structure and a number of large pipe roofs. Among them, the combined support structure includes steel arches, a number of top arch system bolts, a number of side wall system bolts, wire mesh, and a number of foot-locking bolts. Along the length direction of the tunnel, a number of cross braces are fixedly connected between adjacent two steel arches at evenly distributed intervals. A number of the top arch system bolts are evenly spaced at the crown position of the steel arch. A number of the side wall system bolts are evenly spaced at the side wall position of the steel arch. And a number of foot-locking bolts are fixed at the bottom of the steel arch. And concrete is sprayed on the outside of the steel arch. The wire mesh is arranged in the concrete. A number of the large pipe roofs obliquely penetrate through the strongly altered rock mass along the length direction of the tunnel, and one end of the large pipe roof on the side with a higher elevation is lower than one end of the large pipe roof on the side with a lower elevation.

[0110] In some embodiments, the distance between adjacent two of the top arch system bolts on the same steel arch is 1.5m, and a number of the top arch system bolts of a number of the steel arches are arranged in a rectangular network, and the diameter of the top arch system bolt is φ32, and the length of the top arch system bolt is 9m.

[0111] In some embodiments, the distance between adjacent two of the side wall system bolts on the same steel arch is 1.5m, and a number of the top arch system bolts of a number of the steel arches are arranged in a plum blossom-shaped network, and the diameter of the side wall system bolt is φ28, and the length of the side wall system bolt is 6m.

[0112] In summary, the key points of the present invention are as follows: 1) An effective support for the strongly altered rock mass is provided through a common load-bearing system of large pipe roofs + intact surrounding rocks at both ends + steel arches, thereby providing conditions for the excavation of the strongly altered rock mass; 2) The construction sequence of the pipe shed is proposed, that is, drilling from the side with higher elevation to the side with lower elevation. Adopting this construction direction can save the construction period and project investment; 3) The calculation formula for the upward angle of the large pipe shed determined according to the slope drop of the cavern and the length of the section with strongly altered rock mass is proposed. The upward angle calculated according to this formula can ensure saving the construction period and project investment as much as possible on the basis of effectively utilizing the bearing capacity of the intact surrounding rock; 4) The determination method of the diameter of the large pipe shed and the determination method of the pipe spacing of the large pipe shed are proposed, that is, the diameter of the large pipe shed is determined according to the degree of alteration of the section with strongly altered rock mass and the bolt spacing of the intact rock mass system on both sides, and the pipe spacing of the large pipe shed is determined by twice the diameter of the large pipe shed. The diameter of the large pipe shed and the pipe spacing determined by this method can effectively support the strongly altered rock mass with different degrees of alteration, and can avoid damaging the bolts of the intact rock mass system on both sides during the construction of the pipe shed; 5) It is proposed that the large pipe shed is a perforated pipe, and the strongly altered rock mass section can be effectively consolidated through the consolidation grouting of the perforated pipe, providing conditions for the excavation of the strongly altered rock mass; 6) The construction direction of the excavation of the section with strongly altered rock mass is proposed, that is, excavating from the side with higher elevation to the side with lower elevation. Adopting this construction direction can reduce the construction risk; 7) The detailed support parameters of the section with strongly altered rock mass and the intact rock mass within Am on both sides are proposed. Using these support parameters, the above-mentioned section can be effectively supported.

[0113] It should be noted that the method of the present invention can be used for the excavation support of the roof caving section of the strongly altered rock mass, including but not limited to engineering fields such as water conservancy and hydropower projects, transportation projects, mining projects, and energy storage projects.

[0114] The specific embodiments described above further elaborate on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A construction method for excavation and support of the roof caving section of a strongly altered rock mass, characterized in that Including: Joint support structures composed of steel arch frames and systematic rock bolts are respectively supported on the rock walls of the tunnel sections at a distance of A meters from both sides of the strongly altered rock mass, where A ≥ 5; After the joint support structures are supported, large pipe roofs are inclined and penetrated through the strongly altered rock mass along the tunnel length direction above the joint support structures based on set rules; After the large pipe roofs are set, the strongly altered rock mass is excavated, and the excavated areas are supported during the excavation process until all the caving sections of the strongly altered rock mass are completely excavated and supported.

2. The excavation support construction method for the roof caving section of a strongly altered rock mass according to claim 1, characterized in that, A number of the joint support structures are arranged at intervals of B meters along the tunnel length direction. Each joint support structure includes a steel arch frame, a number of top arch systematic rock bolts, a number of side wall systematic rock bolts, a steel mesh, and a number of foot-locking rock bolts. Among them, along the tunnel length direction, a number of evenly spaced cross braces are fixedly connected between adjacent steel arch frames. A number of the top arch systematic rock bolts are evenly spaced at the crown position of the steel arch frame. A number of the side wall systematic rock bolts are evenly spaced at the side wall position of the steel arch frame. And a number of foot-locking rock bolts are fixed at the bottom of the steel arch frame. And concrete is sprayed on the outside of the steel arch frame, and the steel mesh is arranged in the concrete.

3. The excavation and support construction method for the roof caving section of a strongly altered rock mass according to claim 2, characterized in that, The distance between adjacent two of the top arch systematic rock bolts on the same steel arch frame is 1.5m, and a number of the top arch systematic rock bolts of a number of the steel arch frames are arranged in a rectangular network. And the diameter of the top arch systematic rock bolt is φ32, and the length of the top arch systematic rock bolt is 9m.

4. The excavation and support construction method for the roof caving section of a strongly altered rock mass according to claim 2, characterized in that, The distance between adjacent two of the side wall systematic rock bolts on the same steel arch frame is 1.5m, and a number of the top arch systematic rock bolts of a number of the steel arch frames are arranged in a plum blossom-shaped network. And the diameter of the side wall systematic rock bolt is φ28, and the length of the side wall systematic rock bolt is 6m.

5. The excavation and support construction method for the roof caving section of a strongly altered rock mass according to claims 2 and 3, characterized in that, The specific set rules are as follows: The large pipe roofs adopt perforated pipes with a diameter of d, and the length of the large pipe roofs anchors at least A meters of the intact rock mass on both sides of the strongly altered rock mass, and the spacing between adjacent two of the large pipe roofs is twice the diameter of the large pipe roofs; The calculation formula for the diameter of the large pipe roofs is: d = 100 + 5 * (R b - 5); where: d is the pipe diameter of the large pipe shed, with the unit of mm; R b is the uniaxial compressive strength of the rock under saturation, with the unit of Mpa, and this index can be used as a quantitative index for the degree of rock alteration; And the diameter of the large pipe roofs is not less than 89mm, and the spacing between two of the top arch systematic rock bolts divided by twice the diameter of the large pipe roofs is equal to a positive integer; From the side with a higher elevation to the side with a lower elevation, the installation elevation angle of the large pipe shed , where i represents the slope of the tunnel chamber, represents the length of the tunnel section of the strongly altered rock mass in the horizontal direction.

6. The excavation and support construction method for the roof caving section of a strongly altered rock mass according to claim 5, characterized in that, After the large pipe roofs are installed, fixed grouting is carried out, and the grouting pressure range is 0.5MPa to 1MPa, and the grouting liquid is grouted in the state from thin to thick in sequence.

7. The excavation support construction method for the roof caving section of a strongly altered rock mass according to claim 1, characterized in that, The specific process of excavating the strongly altered rock mass and supporting the excavated areas during the excavation process until all the caving sections of the strongly altered rock mass are completely excavated and supported is as follows: Let the excavation footage of the strongly altered rock mass not exceed 0.5m, and the excavation direction is from the side with higher elevation to the side with lower elevation; Adopt a layered excavation method to divide the strongly altered rock mass into an upper area, a middle area, and a lower area; The upper area is excavated by the method of leaving a core soil and manually chiseling with a pneumatic pick, and after the upper layer excavation is completed, the upper area is supported by the combined support method of shotcrete with wire mesh + steel arch frame; For the excavation of the middle and lower regions, the excavation is carried out in layers from the middle to both sides in sequence, and the support is carried out simultaneously with the excavation. The support parameters are the same as those of the upper layer. Repeat the above steps until the excavation of the crown caving section of the strong alteration rock mass is completed.

8. A support system for supporting the tunnel section with a length of A meters on both sides of the strong alteration rock mass in the excavation support construction method of the crown caving section of the strong alteration rock mass according to any one of claims 1-7, characterized in that it includes a combined support structure and a number of large pipe roofs. Among them, the combined support structure includes steel arch frames, a number of top arch system anchor bolts, a number of side wall system anchor bolts, steel wire meshes and a number of foot-locking anchor bolts. Along the length direction of the tunnel, a number of cross braces evenly distributed at intervals are fixedly connected between two adjacent steel arch frames. The number of top arch system anchor bolts are evenly spaced at the crown position of the steel arch frame. The number of side wall system anchor bolts are evenly spaced at the side wall position of the steel arch frame. And a number of foot-locking anchor bolts are fixed at the bottom of the steel arch frame. And concrete is sprayed on the outside of the steel arch frame, and the steel wire mesh is arranged in the concrete. A number of large pipe roofs penetrate through the strong alteration rock mass obliquely along the length direction of the tunnel, and one end of the large pipe roof on the side with a higher elevation is lower than one end of the large pipe roof on the side with a lower elevation.

9. A support system according to claim 8, characterized in that, The distance between two adjacent top arch system anchor bolts on the same steel arch frame is 1.5m, and the top arch system anchor bolts of a number of steel arch frames are arranged in a rectangular network. And the diameter of the top arch system anchor bolt is φ32, and the length of the top arch system anchor bolt is 9m.

10. A support system according to claim 8, characterized in that, The distance between two adjacent side wall system anchor bolts on the same steel arch frame is 1.5m, and the top arch system anchor bolts of a number of steel arch frames are arranged in a plum blossom-shaped network. And the diameter of the side wall system anchor bolt is φ-28, and the length of the side wall system anchor bolt is 6m.

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