Intrusion limit surrounding rock excavation method for large deformation section of soft rock

Abstract

The invention discloses an invasion limit surrounding rock excavation method for a large deformation section of soft rock, and relates to the technical field of invasion limit surrounding rock excavation construction for the large deformation section of the soft rock. The invasion limit surrounding rock excavation method for the large deformation section of the soft rock comprises the steps that refined partitioning of an invasion limit body is achieved through dense scanning and loose circle testing; dividing the invasion limiting body into a core pressure-bearing area and a peripheral stress relaxation area; a main stress diversion arch crossing an invasion limit section is constructed through full-ring radial grouting reinforcement and erection of a strong profile steel temporary cover arch, and effective stress transfer is achieved; the mode of subarea gradual type dismantling and chiseling and instant supporting is adopted, a peripheral stress relaxation area is treated firstly, then a core pressure-bearing area is treated, and surrounding rock disturbance is reduced; the circumferential stress equalization is realized by compensating grouting in stages and dynamically adjusting the grouting pressure according to real-time monitoring data. According to the method, the excavation construction safety of the invasion limit surrounding rock of the large deformation section of the soft rock can be improved, surrounding rock disturbance is reduced, stress distribution is optimized, and the treatment efficiency of the invasion limit surrounding rock is improved.

Description

Technical Field

[0001] This invention relates to the field of excavation technology for encroaching surrounding rock in soft rock sections with large deformation, and particularly to a method for excavating encroaching surrounding rock in soft rock sections with large deformation. Background Technology

[0002] In tunnel construction, soft rock strata, due to their inherent characteristics such as significantly low surrounding rock strength, severely insufficient self-stabilizing capacity, and prominent rheological behavior, are prone to large-scale deformation after excavation, which can lead to structural instability or even collapse in severe cases. When the initial support structure of the tunnel intrudes into the design outline due to continuous compression from the surrounding rock, how to efficiently complete the removal and re-support of the intruding surrounding rock while ensuring construction safety has become a long-standing technical bottleneck in the field of tunnel engineering. To address this challenge, engineering practice and technical research have gradually shifted from a passive response mode to an active control strategy, and from single reinforcement methods to a systematic and comprehensive management system.

[0003] In current engineering practice, handling the encroachment sections of tunnels with large deformations in soft rock mainly relies on two methods: overall demolition and reconstruction, and local reinforcement. The overall demolition and reconstruction method involves erecting temporary support structures at both ends of the encroached section, completely removing the damaged initial support, re-excavating to the design cross-section, and installing new support. The local reinforcement method employs measures such as adding steel frames, installing systematic anchor bolts, and grouting the surrounding rock to locally strengthen the encroached area while retaining part of the original support. In some complex conditions, prestressed anchor cable reinforcement or advanced pipe roof support are also used to improve the overall stability of the surrounding rock. In the construction monitoring stage, the conventional approach is to rely on manually collected convergence deformation data and crown settlement measurements as the main basis for assessing the stability of the surrounding rock.

[0004] However, existing technologies still face multiple technical obstacles when dealing with large deformation encroachment sections in soft rock. The primary problem is the lack of refined quantitative analysis and scientific zoning of the stress distribution within the encroaching surrounding rock. This makes it difficult to accurately match reinforcement measures to the actual mechanical properties of the surrounding rock, and hinders the effective guidance of stress redistribution and balanced transmission. Secondly, while overall demolition can completely solve the encroachment problem, the prolonged exposure time of the surrounding rock during construction significantly increases safety risks. Local reinforcement methods, due to their limited depth, often fail to eradicate the encroachment phenomenon, easily leading to repeated deformation or even continuous deterioration. Furthermore, traditional demolition operations generally employ a large-scale, rapid-advance construction mode, causing severe disturbance to the surrounding rock and easily inducing secondary deformation or local instability. Finally, monitoring methods suffer from significant timeliness deficiencies, failing to capture the dynamics of stress transfer in the surrounding rock and the stress changes in the support structure in real time, resulting in delayed construction decisions and hindering dynamic adjustment and refined control. These technical deficiencies directly lead to longer processing cycles for encroaching sections, increased engineering costs, and persistently high safety risks, resulting in a significant gap between these factors and the comprehensive requirements of modern tunnel engineering for efficiency, safety, and economy. Summary of the Invention

[0005] The main objective of this invention is to propose a method for excavating encroaching surrounding rock in soft rock sections with large deformation. This method aims to improve the safety of excavation in soft rock sections with large deformation, reduce disturbance to the surrounding rock, optimize stress distribution, and improve the processing efficiency of encroaching surrounding rock.

[0006] To achieve the above objectives, the present invention proposes a method for excavating confined surrounding rock in soft rock sections with large deformation. The method includes: Intensive scanning and loosening zone testing of the encroached section were carried out. The geometric boundary of the encroached body was determined based on the scanning data. At the same time, based on the loosening zone test results, the encroached body was divided into a core pressure zone and a peripheral stress relaxation zone on the cross section. Full-ring radial grouting reinforcement is implemented for the outer stress relaxation zone; at the same time, a strong steel temporary arch is erected in the undeformed section before and after the encroachment section. The strong steel temporary arch is rigidly connected to the stable initial support on both sides of the encroachment section through longitudinal connecting beams to form the main stress diversion arch spanning the encroachment section. After monitoring and confirming that the stress transfer is stable, the initial support corresponding to the outer stress relaxation zone is broken and dismantled. Then, the encroaching surrounding rock of the outer stress relaxation zone is chiseled away to the design outline, and a new initial support for the outer stress relaxation zone is immediately constructed. After the new initial support reaches the predetermined strength, the core pressure zone is treated in the same way. After the initial support of the core pressure zone is completed, compensation grouting is carried out in stages and areas behind the full ring support through pre-embedded grouting pipes. The grouting pressure is adjusted according to the real-time monitoring data of the internal force of the support.

[0007] In one embodiment, the steps of performing intensive scanning and surrounding rock loosening zone testing on the confined section, determining the geometric boundary of the confined body based on the scanning data, and dividing the confined body into a core pressure zone and a peripheral stress relaxation zone on the cross-section based on the loosening zone test results include: The surrounding rock area where the rate of decrease in acoustic wave velocity is higher than the first threshold is defined as the peripheral stress relaxation zone. The surrounding rock area whose sound wave velocity decreases between the first threshold and the second threshold is defined as the core pressure zone.

[0008] In one embodiment, the section modulus of the high-strength steel temporary arch is not less than 1.5 times the section modulus of the original design initial support steel frame; the arch foot of the high-strength steel temporary arch is situated on stable bedrock reinforced by radial grouting and is anchored by multiple rows of large-diameter anchor pipes.

[0009] In one embodiment, after monitoring confirms that stress transfer is stable, the steps of breaking and dismantling the initial support corresponding to the peripheral stress relaxation zone, subsequently chiseling away the encroaching surrounding rock of the peripheral stress relaxation zone to the design outline, and immediately constructing new initial support for the peripheral stress relaxation zone include: The depth of chiseling in a single cycle should be controlled between 30 and 50 cm. After completing one cycle of chiseling and initial spraying, the operation should be paused. Once the detected deformation rate is below the safety threshold, the next cycle of operation will begin.

[0010] In one embodiment, before treating the core pressure zone in the same manner after the new initial support has reached a predetermined strength, the method for excavating confined surrounding rock in soft rock sections with large deformation further includes: Before the removal work begins, a ring of pre-stress relief holes is made outside the design outline of the core pressure-bearing area.

[0011] In one embodiment, after the initial support of the core pressure-bearing zone is completed, compensatory grouting is performed behind the full ring support in stages and areas through pre-embedded grouting pipes, and the grouting pressure is adjusted according to the real-time monitored internal force data of the support. The steps include: Low-pressure grouting was carried out within 24 hours after the initial support and closure of the entire ring. After the low-pressure grouting is completed, targeted pressure grouting is carried out in areas with smaller support internal forces based on the continuously monitored support internal force data.

[0012] In one embodiment, before the steps of performing intensive scanning and loosening zone testing on the confined section, determining the geometric boundary of the confined body based on the scanning data, and dividing the confined body into a core pressure zone and a peripheral stress relaxation zone on the cross-section based on the loosening zone test results, the method for excavating confined surrounding rock for large deformation sections of soft rock further includes: The distribution of cracks and the deformation state of the steel frame on the initial support surface of the section before and after the encroachment section were investigated and recorded, and the investigation and recording results were obtained. Based on the survey records, the key areas for the full-ring radial grouting reinforcement and the arch foot installation positions of the high-strength steel temporary arch were determined.

[0013] In one embodiment, before the step of adjusting the grouting pressure according to the real-time monitored internal force data of the support after the new initial support in the core pressure zone is completed, the method for excavating the confined surrounding rock for soft rock with large deformation further includes: Convergence measurement points are set up in each newly excavated or newly supported section and measurements are taken regularly. Strain measurement elements were installed at key stress points of each newly erected steel arch frame, and data was collected periodically. A cross-sectional scan is performed on the work section at predetermined time intervals.

[0014] In one embodiment, after the step of performing a cross-sectional scan of the working section at predetermined time intervals, the method for excavating confined surrounding rock in soft rock sections with large deformation further includes: When the deformation rate increment of a certain zone exceeds 1.5 times that of the deformation rate increment of the adjacent zone, and the strain data of the corresponding steel arch increases abnormally at the same time, the forward excavation operation of the zone is suspended. A set of radial prestressed anchor bolts is installed in the adjacent supported area of ​​the partition. After completing the installation of additional radial prestressed anchor bolts, the suspended excavation work will resume once the deformation rate returns to the permissible range.

[0015] In one embodiment, the new initial support includes an arc-shaped steel arch frame, a steel mesh pre-welded to the arc-shaped steel arch frame, and a bundled quick-setting agent pack; After monitoring confirms that the stress transfer is stable, the steps of breaking and removing the initial support corresponding to the outer stress relaxation zone, then chiseling away the encroaching surrounding rock of the outer stress relaxation zone to the design outline, and immediately constructing new initial support for the outer stress relaxation zone include: After chiseling out a working area, the new initial support was hoisted into place and sealed with shotcrete.

[0016] The technical solution of this invention achieves fine division of surrounding rock through quantification of encroachment and stability zoning, and forms a main stress diversion arch by combining pre-reinforcement and stress transfer path. It adopts zonal progressive demolition and chiseling and immediate support to reduce disturbance and close the area immediately. Finally, it optimizes the grouting process by constructing circumferential stress equalization, thereby efficiently treating encroaching surrounding rock. It has the advantages of improving construction safety, reducing surrounding rock disturbance, optimizing stress distribution, and achieving efficient excavation. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of an embodiment of the method for excavating encroaching surrounding rock in soft rock sections with large deformation provided by the present invention.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0022] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0023] Existing methods for handling encroachment sections in soft rock tunnels with large deformation lack detailed zoning assessments of the internal stress state of the encroaching surrounding rock, resulting in weak targeting of reinforcement measures and difficulty in achieving effective stress transfer and balanced distribution. Overall demolition methods pose construction safety risks, while local reinforcement methods cannot completely solve the encroachment problem. Traditional demolition and chiseling operations cause significant disturbance to the surrounding rock, easily triggering secondary deformation. Existing monitoring methods are relatively outdated, making it difficult to achieve dynamic adjustment and refined control of the construction process.

[0024] To address this technical problem, this invention proposes a method for excavating encroaching surrounding rock in soft rock sections with large deformation.

[0025] Please see Figure 1 In one embodiment of the present invention, the method for excavating confined surrounding rock in soft rock sections with large deformation includes: S10, Perform intensive scanning and surrounding rock loosening zone testing on the encroachment section, determine the geometric boundary of the encroachment body based on the scanning data, and divide the encroachment body into a core pressure zone and a peripheral stress relaxation zone on the cross section based on the loosening zone test results; S20, full-ring radial grouting reinforcement is carried out for the outer stress relaxation zone; at the same time, a strong steel temporary arch is erected in the undeformed section before and after the intrusion section. The strong steel temporary arch is rigidly connected to the stable initial support on both sides of the intrusion section through longitudinal connecting beams to form the main stress diversion arch that spans the intrusion section. S30, after monitoring and confirming that the stress transfer is stable, the initial support corresponding to the outer stress relaxation zone is broken and dismantled. Then, the encroaching surrounding rock of the outer stress relaxation zone is chiseled away to the design outline, and a new initial support for the outer stress relaxation zone is immediately constructed. After the new initial support reaches the predetermined strength, the core pressure zone is treated in the same way. S40 After the initial support of the core pressure zone is completed, compensation grouting is carried out behind the full ring support in stages and areas through the pre-embedded grouting pipes. The grouting pressure is adjusted according to the real-time monitoring data of the internal force of the support.

[0026] For ease of understanding, the following explains some key terms in this embodiment: An encroachment section refers to a specific section where the surrounding rock of a tunnel deforms beyond the design outline and encroaches on the tunnel's clearance.

[0027] The loosening zone test is a technique that uses geophysical methods to assess the internal structural integrity and stress state of surrounding rock, and is used to determine the degree of loosening and bearing capacity of the surrounding rock.

[0028] The core pressure zone refers to the relatively dense, stress-concentrated, and high-bearing-capacity area within the confined surrounding rock.

[0029] The peripheral stress relaxation zone refers to a relatively loose area in the confined surrounding rock where stress is released and bearing capacity is relatively weak.

[0030] A high-strength steel temporary arch is a temporary support structure set before and after the encroachment section, used to transfer the load of the surrounding rock to a stable surrounding rock area before the encroachment surrounding rock is removed.

[0031] The main stress diversion arch, through the connection of the strong steel temporary arch and the stable initial support, forms a structural system that can bypass the encroaching section and transfer the load of the surrounding rock above the encroaching section to the stable surrounding rock on both sides.

[0032] New initial support refers to a new type of initial support structure that meets design requirements and is constructed immediately after the encroaching surrounding rock is removed.

[0033] Compensation grouting refers to the technique of grouting behind the support structure to fill voids, compact the surrounding rock, adjust the stress state of the support, and achieve circumferential stress equalization.

[0034] This embodiment provides a method for excavating confined surrounding rock in soft rock sections with large deformation.

[0035] First, quantification and stability zoning are performed on the encroached section. Intensive scanning and loosening zone testing of the surrounding rock are conducted. Based on the scan data, the geometric boundaries of the encroached body are determined. Simultaneously, based on the loosening zone test results, the encroached body is divided into a core bearing zone and a peripheral stress relaxation zone on the cross-section. Specifically, intensive scanning can be performed using a laser scanner or 3D photogrammetry equipment to obtain the surface geometry data of the encroached section. Loosening zone testing of the surrounding rock can be conducted using ground-penetrating radar or elastic wave testing methods. Based on the scan data, the geometric boundaries of the encroached body can be identified through manual interpretation or image processing algorithms. The stability zoning of the surrounding rock can be determined empirically, for example, based on visually observed crack distribution, the degree of rock fragmentation, or simple geological survey results, dividing the encroached body into an internal bearing zone and an external relaxation zone.

[0036] Secondly, pre-reinforcement and stress transfer path construction are carried out. Full-ring radial grouting reinforcement is implemented in the outer stress relaxation zone. Simultaneously, a high-strength temporary steel arch is erected in the undeformed sections before and after the encroachment section. This temporary steel arch is rigidly connected to the stable initial supports on both sides of the encroachment section via longitudinal connecting beams, forming a main stress diversion arch spanning the encroachment section. Specifically, the full-ring radial grouting reinforcement can be carried out using conventional cement grout or cement-water glass dual-liquid grout, injected into the surrounding rock through drilling to improve the overall strength and density of the surrounding rock. The high-strength temporary steel arch can be made of H-beams or I-beams and erected in the relatively stable surrounding rock areas before and after the encroachment section. This temporary arch can be connected to the existing initial support structures on both sides of the encroachment section by welding or bolting to form a temporary support system capable of sharing the surrounding rock load. The longitudinal connecting beam can be made of steel bars or steel plates to connect the temporary arch to the stable initial supports.

[0037] Next, a phased, progressive demolition and immediate support process is implemented. After monitoring and confirming the stability of stress transfer, the initial support corresponding to the outer stress relaxation zone is broken and removed. Subsequently, a pneumatic drill is used to remove the encroaching surrounding rock in the outer stress relaxation zone down to the design outline using a shallow peeling and multi-cycle operation method. New initial support for the outer stress relaxation zone is then immediately constructed. Once the new initial support reaches the predetermined strength, the core pressure zone is treated in the same manner. Specifically, the stability of stress transfer can be confirmed by manually observing the surrounding rock deformation or by using a simple displacement gauge. The initial support can be broken and removed using a hydraulic breaker or manual chiseling. The encroaching surrounding rock can be removed using a pneumatic drill, with small advances and multiple cycles to gradually peel away the surrounding rock. The depth of each chiseling operation can be adjusted based on field experience. After chiseling is completed, new initial support can be constructed immediately, for example, by spraying concrete or installing steel mesh and steel arches. When treating the core pressure zone, similar chiseling and support methods as those used for the outer stress relaxation zone can be employed.

[0038] Finally, circumferential stress equalization is constructed. After the initial support in the core pressure zone is completed, compensatory grouting is performed behind the entire ring support in stages and areas through pre-embedded repeatable grouting pipes. The grouting pressure is adjusted based on real-time monitoring of the support's internal force data. Specifically, after the initial support in the core pressure zone is completed, grouting can be performed behind the support through pre-set grouting holes or pipes. Grouting can be completed in one go or in stages according to the construction progress. The grouting pressure can be controlled based on empirical values ​​or through a simple pressure gauge to ensure that the grout fully fills the voids behind the support. Support internal force data can be obtained through stress sensors installed on the support structure and used to guide the adjustment of the grouting pressure.

[0039] The encroaching surrounding rock excavation method proposed in this embodiment achieves effective transfer and balanced distribution of the surrounding rock load by finely dividing the encroaching surrounding rock into zones and constructing principal stress diversion arches. The zoned, progressive demolition and immediate support strategy significantly reduces disturbance to the surrounding rock during construction and avoids secondary deformation. Compensatory grouting combined with real-time monitoring data dynamically adjusts the support stress state, effectively solving the problems of high safety risks, long construction periods, and incomplete treatment effects in the treatment of encroaching surrounding rock in soft rock sections with large deformation.

[0040] In an embodiment of the present invention, the steps of performing intensive scanning and surrounding rock loosening zone testing on the encroachment section, determining the geometric boundary of the encroachment body based on the scanning data, and dividing the encroachment body into a core pressure-bearing zone and a peripheral stress relaxation zone on the cross-section based on the loosening zone test results include: S11, the surrounding rock area where the rate of decrease in sound wave velocity is higher than the first threshold is defined as the peripheral stress relaxation zone; S12, the surrounding rock area where the sound wave velocity decrease rate is between the first threshold and the second threshold is defined as the core pressure zone.

[0041] The acoustic wave velocity reduction rate is a quantitative indicator measuring the degree of loosening or damage to the surrounding rock. It is determined by comparing the difference in acoustic wave propagation speed between loosened and intact surrounding rock. When the surrounding rock structure changes, such as the appearance of cracks, pores, or stress relaxation, the acoustic wave propagation speed decreases; a higher reduction rate indicates a greater degree of loosening. The first and second thresholds are preset critical values ​​used to accurately define surrounding rock areas with different stability. The first threshold is typically set at a higher reduction rate, such as 25% to 35%, to identify severely loosened surrounding rock areas where stress has been fully released. The second threshold is set at a reduction rate lower than the first threshold, such as 10% to 20%, to distinguish surrounding rock areas affected by stress but not yet completely loosened. By designating surrounding rock areas with an acoustic wave velocity reduction rate higher than the first threshold as the peripheral stress relaxation zone, areas requiring priority grouting reinforcement and shallow peeling / removal can be accurately identified. Meanwhile, defining the surrounding rock area where the sound wave velocity decrease rate is between the first and second thresholds as the core pressure zone clarifies that this area still bears significant stress and requires different excavation and support strategies.

[0042] Through the above technical solution, this application can objectively and accurately classify the stability of the encroaching surrounding rock. This quantitative zoning method effectively avoids the problems of vague zoning boundaries and strong subjectivity in traditional methods, ensuring that the boundaries between the core pressure zone and the peripheral stress relaxation zone are accurately identified. Therefore, subsequent targeted full-ring radial grouting reinforcement, the erection of high-strength steel temporary arches, and zonal progressive demolition and immediate support measures can be accurately applied to the target area, significantly improving the scientific nature, safety, and efficiency of excavation and support of the encroaching surrounding rock, optimizing resource allocation, and effectively controlling the deformation of the surrounding rock.

[0043] In an embodiment of the present invention, the section modulus of the high-strength steel temporary arch is not less than 1.5 times the section modulus of the original design initial support steel frame; the arch foot of the high-strength steel temporary arch is situated on stable bedrock reinforced by radial grouting and is anchored by multiple rows of large-diameter anchor pipes.

[0044] Specifically, the section modulus of the high-strength temporary steel arch is not less than 1.5 times the section modulus of the original initial support steel frame, meaning that the bending stiffness and load-bearing capacity of the temporary arch are significantly enhanced. Section modulus is a key parameter for measuring a component's resistance to bending deformation. Designing it to be more than 1.5 times the section modulus of the original initial support steel frame can be achieved by selecting larger-sized steel sections (e.g., H-beams, I-beams), increasing the thickness of the steel sections, or using a composite steel structure. For example, if the original initial support steel frame uses I20 I-beams, the high-strength temporary steel arch can use I30 or larger I-beams, or double I20 I-beams, etc. This aims to ensure that the temporary arch does not undergo excessive deformation or buckling failure when bearing and transferring the stress of the surrounding rock, thereby providing stable boundary conditions for subsequent excavation and support.

[0045] Meanwhile, the arch foot of the high-strength steel temporary arch rests on stable bedrock reinforced by radial grouting. The arch foot is the key part of the arch structure that transfers load to the foundation. Resting it on stable bedrock reinforced by radial grouting means pre-grouting the surrounding rock area below the arch foot before installing the temporary arch. Radial grouting reinforcement effectively fills cracks in the surrounding rock, cements loose rock masses, and improves the overall strength, stiffness, and bearing capacity of the surrounding rock, thus forming a solid and stable foundation. Stable bedrock typically refers to rock mass that has not been affected by large-scale erosion deformation and has high integrity and mechanical properties. In this way, it can be ensured that the arch foot can reliably transfer the stress borne by the temporary arch to the stable surrounding rock, avoiding the failure of the entire temporary arch due to instability of the arch foot foundation.

[0046] Furthermore, the high-strength steel temporary arch is anchored using multiple rows of large-diameter anchor pipes. Anchor pipes are components used to anchor the support structure to the surrounding rock, providing pull-out and shear resistance and enhancing the overall stability of the support structure and the surrounding rock. Using multiple rows of large-diameter anchor pipes means the anchoring system has higher load-bearing capacity and stronger pull-out and shear resistance. The multiple rows allow for a more even distribution of anchoring force in the surrounding rock, while the large diameter increases the contact area and friction between the anchor pipe and the grouting body and the surrounding rock, thus significantly improving anchoring strength. Anchor pipes are typically made of high-strength steel and are anchored through drilling, pipe insertion, and grouting consolidation. This anchoring method effectively resists horizontal thrust, vertical loads, and torque that may be generated during stress transfer in the temporary arch, ensuring a reliable connection between the arch foot and the surrounding rock and preventing slippage or uplift of the arch foot.

[0047] Through the aforementioned technical solution, the section modulus of the high-strength steel temporary arch is designed to be significantly higher than that of the original initial support steel frame, significantly improving its bending stiffness and load-bearing capacity. This enables it to effectively resist the enormous loads generated during the stress transfer process in the soft rock large deformation section, preventing deformation or failure of the temporary arch due to insufficient strength. Simultaneously, by placing the arch foot of the temporary arch on stable bedrock reinforced by radial grouting and anchoring it with multiple rows of large-diameter anchor pipes, the connection strength and stability between the arch foot and the surrounding rock are greatly enhanced. This ensures that the temporary arch can reliably and effectively transfer the stress of the encroaching section's surrounding rock to the stable surrounding rock on both sides, constructing a robust and reliable principal stress diversion arch. This provides stable boundary conditions and safety guarantees for subsequent zonal progressive demolition and immediate support operations in the encroaching section, effectively avoiding the risk of secondary deformation or collapse due to the failure of the temporary support system, and significantly improving the safety and controllability of the entire excavation method.

[0048] In an embodiment of the present invention, after monitoring and confirming that the stress transfer is stable, the steps of breaking and dismantling the initial support corresponding to the peripheral stress relaxation zone, subsequently chiseling away the encroaching surrounding rock of the peripheral stress relaxation zone to the design outline, and immediately applying new initial support to the peripheral stress relaxation zone include: S31, the depth of chiseling in a single cycle is controlled at 30-50cm. After completing one cycle of chiseling and initial spraying, the operation is suspended. S32, the next cycle of operation will only begin after the detected deformation rate is below the safety threshold.

[0049] Specifically, the depth of each excavation cycle is controlled within 30-50 cm to limit the range and extent of disturbance to the surrounding rock caused by each excavation. In soft rock sections with large deformation, excessively deep single excavations can easily lead to stress concentration and rapid deformation of the surrounding rock. Controlling the excavation depth within a narrow range of 30-50 cm can effectively slow down the rate of stress release in the surrounding rock, providing time for the surrounding rock to gradually adapt to the new stress state, thereby reducing the risk of instability. The determination of this depth range can be optimized based on on-site geological conditions, rock mechanics parameters, and numerical simulation results.

[0050] Furthermore, pausing operations after completing a cycle of excavation and initial shotcrete sealing allows the surrounding rock and newly applied initial support time to stabilize and respond. After excavation to a certain depth and completion of the initial shotcrete sealing, the stress in the surrounding rock will redistribute, and the newly shotcrete also needs time to harden and perform its supporting function. Pausing operations avoids secondary disturbance to the still unstable surrounding rock and support caused by continuous excavation, providing a necessary time window for subsequent deformation monitoring and decision-making.

[0051] Based on this, the next cycle of operation will only proceed after the monitored deformation rate falls below a safety threshold. This is a dynamic control strategy based on real-time monitoring data. During the pause in operation, the deformation rate of the surrounding rock is continuously monitored by deployed monitoring equipment (such as convergence meters, multi-point displacement meters, etc.). Only when the deformation rate decreases below a preset safety threshold, indicating that the surrounding rock has reached a relatively stable state, is the next cycle of excavation allowed. This safety threshold is usually determined based on engineering experience, design requirements, and risk assessment, aiming to ensure that the surrounding rock reaches an acceptable level of stability after each excavation cycle.

[0052] The aforementioned technical solution refines the excavation operation into a cyclical process characterized by shallow depths, intermittent operations, and real-time deformation monitoring. This refined control method effectively avoids rock instability and support failure caused by rapid, large-scale excavation in soft rock sections with large deformation. By limiting the depth of each excavation, the rate of stress release in the surrounding rock is slowed down, reducing the magnitude of instantaneous deformation. Pausing operations after each cycle provides sufficient stabilization time for the surrounding rock and initial support. Furthermore, the dynamic decision-making mechanism based on deformation rate ensures that each excavation is carried out under the premise of relatively stable surrounding rock, thereby achieving effective control over surrounding rock deformation, guaranteeing construction safety and support effectiveness, and significantly improving the stability and reliability of excavation in soft rock sections with large deformation.

[0053] In an embodiment of the present invention, before the step of treating the core pressure zone in the same manner after the new initial support has reached the predetermined strength, the method for excavating the confined surrounding rock for large deformation sections of soft rock further includes: S301, Before the excavation work begins, a ring of pre-stress relief holes is made outside the design outline of the core pressure-bearing area.

[0054] Specifically, pre-drilled stress relief holes refer to a series of holes pre-drilled in front of the excavation face or the area to be excavated. The main function of these holes is to induce or guide the redistribution of high stress within the surrounding rock to the area around the holes by altering the stress boundary conditions, thereby reducing the stress concentration in the surrounding rock near the excavation face and achieving the purpose of releasing or adjusting the stress in the surrounding rock. They are typically constructed using conventional drilling equipment, and the hole diameter, depth, and spacing need to be designed according to the geological conditions of the surrounding rock, the stress state, and the excavation dimensions. "Outside the design outline" means that these stress relief holes are located in the surrounding rock area outside the final excavation outline. The purpose of this arrangement is to pre-treat the high stress within the core pressure-bearing zone without affecting the final structural dimensions. By forming a stress adjustment zone outside the design outline, the stress concentration within the core pressure-bearing zone can be effectively reduced, creating a relatively low-stress environment for subsequent chiseling operations. "Before the start of chiseling operations" refers to before the actual mechanical chiseling or blasting operations are carried out on the core pressure-bearing zone. This timing arrangement ensures that stress relief holes can function in advance, adjusting the stress state of the surrounding rock before it is disturbed by excavation, thereby minimizing the risk of high stress that may be encountered during excavation.

[0055] By constructing a ring of pre-stress relief holes outside the designed outline of the core pressure zone before excavation begins, the high stress within the core pressure zone can be effectively pre-adjusted and released. These holes create local weak surfaces in the surrounding rock, inducing the transfer and redistribution of high stress around the holes, thereby reducing stress concentration near the excavation face of the core pressure zone. This significantly improves the stability of the surrounding rock in the core pressure zone, reducing the risk of local instability, rock bursts, or large deformations during excavation, allowing subsequent excavation operations to be carried out more safely and efficiently. Simultaneously, pre-releasing stress provides a more favorable stress environment for the new initial support in the core pressure zone, helping the support structure to function better and ensuring the smooth implementation of the entire encroaching surrounding rock excavation process and the long-term stability of the structure.

[0056] In an embodiment of the present invention, after the initial support of the core pressure-bearing zone is completed, compensation grouting is performed behind the full ring support in stages and areas through pre-embedded grouting pipes, and the grouting pressure is adjusted according to the real-time monitored internal force data of the support. The steps include: S41, low-pressure grouting shall be carried out within 24 hours after the initial support of the full ring is closed; S42, after the low-pressure grouting is completed, based on the continuously monitored support internal force data, targeted pressure grouting is carried out in areas with smaller support internal forces.

[0057] The first stage of grouting aims to quickly fill the voids between the support and the surrounding rock, forming a preliminary dense layer and applying a basic, uniform prestress to the surrounding rock. Low-pressure grouting is performed within 24 hours of the initial closure of the full-ring support to capitalize on the opportunity when the initial support strength has not yet fully reached its design value but already possesses a certain bearing capacity. This early intervention suppresses initial deformation of the surrounding rock and lays the foundation for subsequent refined grouting. Low-pressure grouting typically refers to grouting pressure controlled between 0.5 MPa and 1.5 MPa, with specific values ​​adjusted according to surrounding rock conditions, grout type, and initial support strength. Early-strength cement grout or cement-water glass dual-liquid grout can be used to ensure a certain consolidation effect is achieved in a short time. The grouting pipeline is connected via pre-embedded reusable grouting pipes to ensure uniform grout injection.

[0058] The second-stage grouting is crucial for achieving circumferential stress equalization. After the first-stage low-pressure grouting forms the foundation support, continuous monitoring of the support's internal force data identifies areas with uneven stress distribution. Targeted pressurized grouting is then performed on areas with lower internal forces to reinforce these understressed areas, improving their bearing capacity and thus achieving a more uniform stress distribution across the entire circumferential support, preventing localized stress concentration or support failure. Continuously monitored support internal force data can be obtained by pre-embedding stress sensors, strain gauges, and other monitoring elements in the initial support. This data is transmitted in real-time to the monitoring system for analysis. Areas with significantly lower support internal forces than the design value or adjacent areas are identified as having lower internal forces. The pressure of the targeted pressurized grouting will be higher than in the first stage, potentially reaching 2MPa to 5MPa or even higher, depending on the bearing capacity of the surrounding rock and the required stress level. Higher-strength, more permeable cement-based or chemical grouts can be used. By using pre-embedded re-grouting pipes, grouting can be performed multiple times on a specific area until the internal support force of that area reaches the target value or tends to be in equilibrium with the surrounding area.

[0059] The above technical solution involves first performing low-pressure grouting, which quickly fills voids and provides basic support, effectively suppressing initial deformation of the surrounding rock. Subsequently, based on continuously monitored support internal force data, targeted pressurized grouting is performed in areas with lower stress levels, accurately adjusting the stress distribution behind the support. This dynamic, feedback-based, staged grouting strategy effectively avoids the problems of local over-grouting or under-grouting that may occur with traditional one-time grouting, significantly improving the overall stress uniformity of the support structure. This results in more effective circumferential stress equalization, enhancing the overall stability and bearing capacity of the initial support, extending the service life of the support structure, and improving the safety of excavating soft rock sections with large deformation.

[0060] In an embodiment of the present invention, before the steps of performing intensive scanning and loosening zone testing on the confined section, determining the geometric boundary of the confined body based on the scanning data, and dividing the confined body into a core pressure zone and a peripheral stress relaxation zone on the cross-section based on the loosening zone test results, the method for excavating the confined surrounding rock for large deformation sections of soft rock further includes: S101, Investigate and record the crack distribution and steel frame deformation state on the initial support surface of the section before and after the encroachment section, and obtain the investigation and record results; S102, Based on the survey record results, determine the key area of ​​the full-ring radial grouting reinforcement and the arch foot installation position of the strong steel temporary arch.

[0061] Specifically, the investigation and recording of crack distribution and steel frame deformation on the initial support surface of the sections before and after the encroachment zone aims to obtain damage and deformation information on the initial support of the encroachment zone and its adjacent areas, providing data support for subsequent reinforcement and support schemes. This investigation can be conducted using various methods. For example, for crack distribution, visual inspection, crack width measuring instruments, or ultrasonic flaw detectors can be used to record in detail the cracks appearing on the initial support surface, including their location, direction, length, width, depth, and development trend. For steel frame deformation, total stations, laser scanners, or deformation measuring rulers can be used to measure and record the geometry, displacement, tilt, and torsion of the initial support steel frame, paying particular attention to the deformation of the steel frame's connection points, stress concentration areas, and the contact surface with the surrounding rock. All investigation data are compiled into charts, reports, and other forms, forming a detailed investigation record.

[0062] Based on this, the key areas for the full-ring radial grouting reinforcement and the installation positions of the arch feet of the high-strength steel temporary arch are determined according to the survey records. This step utilizes the damage and deformation data obtained from the preliminary investigation to guide the accurate implementation of subsequent reinforcement measures, ensuring the effectiveness of resource investment and the reliability of structural support. For example, based on the distribution of cracks and the severity of steel frame deformation, areas with the most severe initial support damage and the worst surrounding rock stability can be identified, such as areas with dense cracks, large crack widths, and significant steel frame deformation. These areas indicate loosening of the surrounding rock or stress concentration and should be identified as key areas for radial grouting reinforcement to restore the integrity and bearing capacity of the surrounding rock. Simultaneously, the arch feet of the high-strength steel temporary arch are the critical parts where the temporary arch transfers loads to the surrounding rock. Based on the survey records, areas with relatively small initial support deformation, relatively stable surrounding rock, and sufficient bearing capacity should be selected as the installation positions for the arch feet. For example, areas with dense cracks and severely deformed areas should be avoided, and areas with good surrounding rock integrity and relatively intact initial support structures should be selected to ensure that the arch feet can be reliably anchored and effectively transfer stress.

[0063] By employing the aforementioned technical solution, before conducting intensive scanning and loosening zone testing of the surrounding rock in the encroached section, the crack distribution and steel frame deformation status of the initial support surface in the sections before and after the encroachment are investigated and recorded. Based on these investigation and recording results, the key areas for full-ring radial grouting reinforcement and the installation positions of the arch feet of the high-strength steel temporary arch are determined. This application can more accurately identify the weak points of the surrounding rock and the initial support. This forward-looking investigation and assessment allows subsequent full-ring radial grouting reinforcement to concentrate resources on the areas most in need of reinforcement, effectively improving the integrity and bearing capacity of the surrounding rock, and avoiding the waste of resources and poor results caused by blind grouting. At the same time, the arch feet of the high-strength steel temporary arch can be installed on stable bedrock that has been fully evaluated, ensuring the reliability of the main stress diversion arch and the effectiveness of the stress transfer path, thereby significantly enhancing the safety, economy, and construction efficiency of the entire encroached surrounding rock excavation method, and providing a more solid foundation for subsequent zonal progressive demolition and immediate support.

[0064] In an embodiment of the present invention, before the completion of the new initial support construction in the core pressure-bearing zone, and before the step of adjusting the grouting pressure according to the real-time monitored internal force data of the support, the method for excavating the confined surrounding rock in soft rock with large deformation further includes: S401, Convergence measuring points are set up in each newly excavated or newly supported section and measurements are taken regularly; S402, strain measuring elements are installed at the key stress points of each newly erected steel arch frame and data is collected regularly; S403, a cross-sectional scan of the work section is performed at predetermined time intervals.

[0065] Specifically, convergence measuring points are deployed and measured periodically in each newly excavated or newly supported section to monitor the radial deformation of the surrounding rock and initial support in real time. Convergence measuring points typically consist of markers fixed to the surrounding rock or support structure, such as rebar ends, bolts, or reflectors. In each newly excavated or newly supported section, these measuring points are evenly distributed circumferentially along the tunnel cross-section, usually selecting key locations such as the arch crown, arch waist, sidewalls, and arch feet. During measurement, precision measuring equipment such as convergence meters, total stations, or laser scanners can be used to periodically measure the distance changes between measuring points or the displacement of the measuring points relative to a fixed reference point. The measurement frequency can be adjusted according to the surrounding rock deformation rate and construction stage, for example, once a day or once per shift, to ensure timely acquisition of deformation data.

[0066] Simultaneously, strain measurement elements are installed at key stress-bearing locations on each newly erected steel arch frame, and data is collected periodically to directly monitor the stress state of the steel arch frame. The strain measurement elements can be resistance strain gauges or fiber optic strain sensors, which can measure the minute deformations of materials under stress. These elements are typically bonded or welded to areas of concentrated stress or high bending moment, such as the arch crown, arch waist, and arch foot. Connecting the strain measurement elements to a data acquisition device allows for real-time or periodic readings of strain data, thereby assessing the bearing capacity and stress distribution of the support structure and determining whether it has reached its design strength or exhibits abnormal stress concentration. The frequency of data acquisition can also be adjusted according to the construction stage and changes in the surrounding rock conditions.

[0067] In addition, a cross-sectional scan is performed on the working section at predetermined time intervals to obtain the overall geometry and deformation of the section. Cross-sectional scanning typically employs a high-precision 3D laser scanner or photogrammetry system to perform non-contact measurements of the excavation cross-section of the tunnel or underground engineering project, acquiring high-precision point cloud data. The predetermined scanning time interval can be set after each excavation cycle, weekly, or dynamically adjusted according to the surrounding rock deformation. The scanning range should cover the excavation face, the supported area, and the surrounding rock. The acquired point cloud data is then imported into specialized software for processing, generating cross-sectional diagrams and deformation cloud maps, which are compared with the design cross-section to visually assess surrounding rock convergence, over-excavation / under-excavation, and the overall deformation of the support structure.

[0068] By employing the aforementioned technical solutions, convergence measurement points are strategically placed in each newly excavated or supported section and measured periodically. This allows for real-time monitoring of the overall deformation trend of the surrounding rock and initial support, providing macroscopic data support for assessing rock stability. Simultaneously, strain measurement elements are installed at key stress-bearing locations of each newly erected steel arch frame, and data is collected periodically. This directly monitors changes in the internal forces of the steel arch frame, accurately assesses the load-bearing state and stress distribution of the support structure, and promptly identifies potential stress concentrations or overloads. Furthermore, a cross-sectional scan of the work section is performed at predetermined time intervals to obtain the overall geometry and deformation of the section, providing a direct assessment of rock convergence, over-excavation / under-excavation, and the overall deformation of the support structure. These three monitoring methods complement each other, constructing a comprehensive and refined monitoring system. This enables construction personnel to accurately and in real-time grasp the dynamic response of the surrounding rock and support system, allowing for timely adjustments to construction parameters and support measures. This effectively avoids construction risks caused by information lag, ensures the stability of the stress transfer process and the safety of subsequent construction, and significantly improves the refined management level and engineering reliability of excavation in soft rock sections with large deformation.

[0069] In an embodiment of the present invention, after the step of performing a cross-sectional scan of the working section at predetermined time intervals, the method for excavating confined surrounding rock for soft rock sections with large deformation further includes: S404. When the deformation rate increment of a certain zone exceeds 1.5 times the deformation rate increment of the adjacent zone, and the strain data of the corresponding steel arch increases synchronously and abnormally, the forward excavation operation of the zone is suspended. S405, install a set of radial prestressed anchor bolts in the adjacent supported area of ​​the partition; S406. After completing the work of installing additional radial prestressed anchor bolts, wait for the deformation rate to drop back to the permissible range before resuming the suspended excavation work.

[0070] Specifically, when the monitoring system analyzes convergent measuring points, strain measurement elements, and cross-sectional scanning data and finds that the deformation rate increment of a certain zone exceeds 1.5 times that of adjacent zones, and the strain data of the corresponding steel arch also shows a synchronous abnormal increase, this indicates that the stability of the surrounding rock in that area may be locally deteriorating, the stress on the support structure has exceeded the normal range, and there is a risk of local overload or deformation concentration. At this point, forward excavation work in that zone should be immediately suspended to avoid further disturbance of the surrounding rock, buy time for subsequent treatment, and prevent the danger from escalating.

[0071] Subsequently, a set of radial prestressed anchors is installed in the adjacent supported areas of the locally unstable zone (i.e., areas with abnormal deformation rate increments). Radial prestressed anchors are an active support measure; by applying prestress to the anchors, a squeezing effect is created between the anchors and the surrounding rock, thereby improving the overall stability and bearing capacity of the surrounding rock. Installing additional anchors in adjacent supported areas utilizes the relative stability of the supported areas, connecting the surrounding rock of the locally unstable zone to the more stable deeper surrounding rock through the anchors, forming a more robust whole and thus inhibiting further deformation of the unstable zone. The length, spacing, and prestress magnitude of the anchors can be optimized based on site geological conditions and monitoring data.

[0072] After completing the installation of additional radial prestressed anchor bolts, the deformation rate of the affected area needs to be continuously monitored. Only when the deformation rate significantly decreases and stabilizes within an acceptable safety threshold can it be considered that the reinforcement measures have been effective and the surrounding rock stability has been restored. At this point, the suspended excavation work can be resumed to ensure the safety of the construction process.

[0073] The aforementioned technical solutions enable timely identification and effective response to potential localized rock instability issues during the excavation of soft rock sections with large deformation. By setting clear early warning indicators (deformation rate increments and strain data), early warning and rapid response to potential risks are achieved. Suspending excavation prevents the escalation of the danger, while installing additional radial prestressed anchors provides targeted proactive reinforcement, effectively controlling localized deformation and improving the overall stability of the surrounding rock and the safety of the support structure. This dynamic adjustment and intervention mechanism significantly reduces construction risks, ensures the continuity and safety of excavation operations, and avoids project delays or accidents caused by localized instability.

[0074] In an embodiment of the present invention, the new initial support includes an arc-shaped steel arch frame, a steel mesh pre-welded to the arc-shaped steel arch frame, and a bundled quick-setting agent pack; After monitoring confirms that the stress transfer is stable, the steps of breaking and removing the initial support corresponding to the outer stress relaxation zone, then chiseling away the encroaching surrounding rock of the outer stress relaxation zone to the design outline, and immediately constructing new initial support for the outer stress relaxation zone include: S310, after chiseling out a working area, the new initial support is hoisted into place and sealed with shotcrete.

[0075] The arched steel arch is a prefabricated or on-site bent steel frame that serves as the main load-bearing component of the initial support, resisting rock pressure and maintaining the stability of the excavation profile. This arch can be made of H-beams, I-beams, or channel steel, connected by welding or bolting to form an arch structure. Its cross-sectional dimensions and steel strength are optimized according to the rock pressure and design requirements. The pre-welded steel mesh on the arched steel arch is a mesh structure formed by cross-welding of reinforcing bars, integrated with the steel arch in a factory or prefabrication yard. Together with the steel arch, it forms a composite support structure, enhancing the overall integrity and shear resistance of the support, providing an adhesion surface for shotcrete, and effectively dispersing stress. The steel mesh can use reinforcing bars of different diameters and spacings, fixed to the inner or outer side of the steel arch by spot welding or binding. Pre-welding ensures installation accuracy and connection strength. The aforementioned accelerator package refers to a package containing an accelerator (such as an alkaline accelerator or an alkali-free accelerator) pre-packaged according to a specific ratio and dosage, and then tied and fixed to the reinforcing mesh or steel arch frame. Its function is to break open and mix with the concrete during shotcrete construction, accelerating the setting and hardening of the concrete, allowing the initial support to quickly form load-bearing capacity, and effectively controlling surrounding rock deformation. The accelerator package can be packaged using easily breakable film materials and tied to the reinforcing mesh with thin wire or cable ties to ensure uniform release upon impact of the shotcrete.

[0076] After excavating a designated working face, the new initial support is hoisted into place as a whole, aiming for rapid installation. Specifically, after the excavation face is formed, prefabricated integral support units, including steel arches, steel mesh, and accelerator packages, are hoisted to the designated location and accurately positioned using lifting equipment (such as gantry cranes, cantilever cranes, or specialized trolleys). This requires high dimensional accuracy of the prefabricated components and sufficient load-bearing capacity and positioning accuracy of the hoisting equipment. Subsequently, shotcrete sealing is performed to tightly bond the hoisted support structure with the surrounding rock, forming a continuous and dense initial support layer. Wet or dry shotcrete processes can be used, where the concrete mixture is sprayed at high speed onto the positioned steel arches and steel mesh using shotcrete equipment, ensuring close contact with the surrounding rock surface and filling uneven areas. The addition of the accelerator ensures rapid concrete setting and quick formation of support strength.

[0077] The aforementioned technical solution designs the new initial support as a combination of prefabricated arched steel arches, pre-welded steel mesh, and bound quick-setting agent packages. After excavating the working face, the entire structure is hoisted into place and then sealed with shotcrete, significantly shortening the on-site support construction time. Prefabrication and overall hoisting reduce on-site assembly steps, improving construction efficiency and safety. The introduction of quick-setting agent packages ensures that the shotcrete can quickly set and achieve early strength, providing effective support in the early stages of surrounding rock deformation, rapidly controlling rock deformation, preventing further loosening and encroachment, and ensuring the stability and safety of the excavation face. This rapid and efficient support method effectively addresses the challenge of rapid deformation in soft rock sections with large deformation, enhancing the adaptability and reliability of the overall excavation method.

[0078] The following example will provide a more detailed explanation of the above technical solution: In a tunnel project, a section of soft rock strata (hereinafter referred to as the encroachment section) experienced deformation due to complex geological conditions, causing the initial support to encroach on the tunnel's design outline. To address this encroachment section, the following methods were adopted: First, a preliminary investigation was conducted. The distribution of surface cracks and the deformation state of the steel frame on the initial support surface in the sections before and after the encroachment zone were investigated and recorded. Based on these records, the key areas for full-ring radial grouting reinforcement and the installation positions of the arch feet of the temporary high-strength steel arch were determined. This step provided fundamental data for subsequent reinforcement and support.

[0079] Next, quantification of encroachment and stability zoning are performed. Dense scanning is conducted on the encroached section to acquire geometric boundary data of the encroached body. Simultaneously, a loosening zone test is performed, assessing the degree of loosening of the surrounding rock using the sonic velocity reduction rate. Areas with a sonic velocity reduction rate exceeding a first threshold are designated as peripheral stress relaxation zones, indicating a high degree of loosening. Areas with a sonic velocity reduction rate between the first and second thresholds are designated as core pressure zones, indicating that the surrounding rock still possesses bearing capacity. This zoning method provides a detailed division of the internal stress state of the surrounding rock, unlike existing technologies that lack such assessments.

[0080] Subsequently, a pre-reinforcement and stress transfer path was constructed. For the peripheral stress relaxation zone, full-ring radial grouting reinforcement was implemented to improve the overall strength and stability of the surrounding rock in this area. Simultaneously, a high-strength temporary steel arch was erected in the undeformed sections before and after the encroachment section. The section modulus of this temporary steel arch is no less than 1.5 times that of the original initial support steel frame, providing higher load-bearing capacity. The arch foot of this temporary steel arch rests on the stable bedrock reinforced by radial grouting and is anchored by multiple rows of large-diameter anchor pipes to ensure the stability of the arch foot. This temporary steel arch is rigidly connected to the stable initial supports on both sides of the encroachment section via longitudinal connecting beams, forming a main stress diversion arch spanning the encroachment section. This diversion arch transfers the surrounding rock pressure to the stable areas on both sides of the encroachment section, reducing the load on the surrounding rock in the encroachment section, which differs from the construction safety risks associated with existing overall demolition methods.

[0081] Continuous monitoring was implemented throughout the construction process. Convergence measuring points were deployed in each newly excavated or newly supported section, and measurements were taken periodically. Strain measuring elements were installed at key stress points of each newly erected steel arch frame, and data was collected periodically. A cross-sectional scan of the work section was performed at predetermined time intervals. This monitoring system provides real-time data, unlike existing monitoring methods which are relatively lagging, and can dynamically grasp the stress transfer process of the surrounding rock and the stress state of the support.

[0082] After monitoring and confirming that stress transfer has stabilized, a phased, progressive demolition and immediate support system is implemented. First, the initial support corresponding to the outer stress relaxation zone is broken and removed. Before the demolition begins, a ring of pre-stress relief holes is constructed outside the design outline of the core pressure zone to pre-release stress in the core pressure zone. Subsequently, pneumatic drills are used to demolish the encroaching surrounding rock of the outer stress relaxation zone down to the design outline using a shallow peeling and multi-cycle operation method. The depth of each cycle is controlled at 30-50 cm. After completing one cycle of demolition and initial spraying closure, work is paused. The next cycle is only started after the monitored deformation rate is below the safety threshold. This shallow peeling and multi-cycle operation method causes minimal disturbance to the surrounding rock, unlike traditional large-scale, rapid-advance demolition methods, reducing the risk of secondary deformation. The new initial support system includes an arched steel frame, pre-welded steel mesh on the arched steel frame, and bundled quick-setting agent packages. After clearing a working area, the new initial support is hoisted into place and sealed with shotcrete to provide immediate support. Once the new initial support in the outer stress relaxation zone reaches the predetermined strength, the core pressure zone is treated in the same way.

[0083] After the initial support in the core pressure zone is completed, circumferential stress equalization is achieved. Compensatory grouting is performed behind the full ring support in stages and by area using pre-embedded, repeatable grouting pipes. The first stage of grouting is performed under low pressure within 24 hours of the initial ring support closure. The second stage of grouting, after the low-pressure grouting, involves targeted pressurized grouting in areas with lower support internal forces based on continuously monitored support internal force data. The grouting pressure is adjusted according to real-time monitored support internal force data. This staged, area-specific compensatory grouting method, combined with pressure adjustment based on real-time monitoring data, achieves a balanced distribution of pressure behind the support, unlike existing reinforcement measures that lack specificity.

[0084] During construction, if the deformation rate increment of a certain zone exceeds 1.5 times that of the adjacent zones, and the strain data of the corresponding steel arch increases abnormally, the forward excavation work in that zone is suspended. A set of radial prestressed anchors is then installed in the adjacent supported area of ​​that zone. After the installation of the additional radial prestressed anchors is completed, excavation work resumes once the deformation rate returns to the permissible range. This dynamic adjustment and emergency response mechanism ensures control over the construction process.

[0085] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural transformations made based on the technical concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

Claims

1. A method for excavating confined surrounding rock in soft rock sections with large deformation, characterized in that, The method for excavating confined surrounding rock in soft rock sections with large deformation includes: Intensive scanning and loosening zone testing of the encroached section were carried out. The geometric boundary of the encroached body was determined based on the scanning data. At the same time, based on the loosening zone test results, the encroached body was divided into a core pressure zone and a peripheral stress relaxation zone on the cross section. Full-ring radial grouting reinforcement is implemented for the outer stress relaxation zone; at the same time, a strong steel temporary arch is erected in the undeformed section before and after the encroachment section. The strong steel temporary arch is rigidly connected to the stable initial support on both sides of the encroachment section through longitudinal connecting beams to form the main stress diversion arch spanning the encroachment section. After monitoring and confirming that the stress transfer is stable, the initial support corresponding to the outer stress relaxation zone is broken and dismantled. Then, the encroaching surrounding rock of the outer stress relaxation zone is chiseled away to the design outline, and a new initial support for the outer stress relaxation zone is immediately constructed. After the new initial support reaches the predetermined strength, the core pressure zone is treated in the same way. After the initial support of the core pressure zone is completed, compensation grouting is carried out in stages and areas behind the full ring support through pre-embedded grouting pipes. The grouting pressure is adjusted according to the real-time monitoring data of the internal force of the support.

2. The method for excavating confined surrounding rock in large deformation sections of soft rock as described in claim 1, characterized in that, The steps of conducting intensive scanning and loosening zone testing on the confined section, determining the geometric boundary of the confined body based on the scanning data, and dividing the confined body into a core bearing zone and a peripheral stress relaxation zone on the cross-section based on the loosening zone test results include: The surrounding rock area where the rate of decrease in acoustic wave velocity is higher than the first threshold is defined as the peripheral stress relaxation zone. The surrounding rock area whose sound wave velocity decreases between the first threshold and the second threshold is defined as the core pressure zone.

3. The method for excavating confined surrounding rock in large deformation sections of soft rock as described in claim 1, characterized in that, The section modulus of the high-strength steel temporary arch is not less than 1.5 times the section modulus of the original design initial support steel frame; the arch foot of the high-strength steel temporary arch is located on stable bedrock reinforced by radial grouting and is anchored by multiple rows of large-diameter anchor pipes.

4. The method for excavating confined surrounding rock in large deformation sections of soft rock as described in claim 1, characterized in that, After monitoring confirms that the stress transfer is stable, the steps of breaking and removing the initial support corresponding to the outer stress relaxation zone, then chiseling away the encroaching surrounding rock of the outer stress relaxation zone to the design outline, and immediately constructing new initial support for the outer stress relaxation zone include: The depth of chiseling in a single cycle should be controlled between 30 and 50 cm. After completing one cycle of chiseling and initial spraying, the operation should be paused. Once the detected deformation rate is below the safety threshold, the next cycle of operation will proceed.

5. The method for excavating confined surrounding rock in large deformation sections of soft rock as described in claim 1, characterized in that, Before proceeding with the step of treating the core pressure zone in the same manner after the new initial support has reached the predetermined strength, the method for excavating confined surrounding rock in soft rock sections with large deformation further includes: Before the removal work begins, a ring of pre-stress relief holes is made outside the design outline of the core pressure-bearing area.

6. The method for excavating confined surrounding rock in large deformation sections of soft rock as described in claim 1, characterized in that, After the initial support in the core pressure-bearing zone is completed, compensatory grouting is performed behind the full ring support in stages and areas through pre-embedded grouting pipes. The steps for adjusting the grouting pressure based on real-time monitored support internal force data include: Low-pressure grouting was carried out within 24 hours after the initial support and closure of the entire ring. After the low-pressure grouting is completed, targeted pressure grouting is carried out in areas with smaller support internal forces based on the continuously monitored support internal force data.

7. The method for excavating encroaching surrounding rock in large deformation sections of soft rock as described in claim 1, characterized in that, Before the steps of conducting intensive scanning and loosening zone testing of the confined section, determining the geometric boundary of the confined body based on the scanning data, and dividing the confined body into a core pressure zone and a peripheral stress relaxation zone on the cross-section based on the loosening zone test results, the method for excavating the confined surrounding rock for large deformation sections of soft rock further includes: The distribution of cracks and the deformation state of the steel frame on the initial support surface of the section before and after the encroachment section were investigated and recorded, and the investigation and recording results were obtained. Based on the survey records, the key areas for the full-ring radial grouting reinforcement and the arch foot installation positions of the high-strength steel temporary arch were determined.

8. The method for excavating confined surrounding rock in large deformation sections of soft rock as described in claim 1, characterized in that, After the initial support of the core pressure-bearing zone is completed, compensation grouting is performed behind the full ring support in stages and areas through pre-embedded grouting pipes. Before the step of adjusting the grouting pressure according to the real-time monitored internal force data of the support, the method for excavating the confined surrounding rock for soft rock with large deformation also includes: Convergence measurement points are set up in each newly excavated or newly supported section and measurements are taken regularly. Strain measurement elements were installed at key stress points of each newly erected steel arch frame, and data was collected periodically. A cross-sectional scan is performed on the work section at predetermined time intervals.

9. The method for excavating confined surrounding rock in large deformation sections of soft rock as described in claim 8, characterized in that, After performing a cross-sectional scan of the work section at predetermined time intervals, the method for excavating confined surrounding rock in soft rock sections with large deformation further includes: When the deformation rate increment of a certain zone exceeds 1.5 times that of the deformation rate increment of the adjacent zone, and the strain data of the corresponding steel arch increases abnormally at the same time, the forward excavation operation of the zone is suspended. A set of radial prestressed anchor bolts is installed in the adjacent supported area of ​​the partition. After completing the installation of additional radial prestressed anchor bolts, the suspended excavation work will resume once the deformation rate returns to the permissible range.

10. The method for excavating confined surrounding rock in large deformation sections of soft rock as described in claim 1, characterized in that, The new initial support includes an arc-shaped steel arch frame, steel mesh pre-welded to the arc-shaped steel arch frame, and bundled quick-setting agent packs; After monitoring confirms that the stress transfer is stable, the steps of breaking and removing the initial support corresponding to the outer stress relaxation zone, then chiseling away the encroaching surrounding rock of the outer stress relaxation zone to the design outline, and immediately constructing new initial support for the outer stress relaxation zone include: After chiseling out a working area, the new initial support was hoisted into place and sealed with shotcrete.

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