Ground settlement compensation method for soft rock tunnel

Abstract

The application discloses a surface subsidence compensation method for soft rock tunnels and relates to the technical field of soft rock tunnel construction, wherein the surface subsidence compensation method for soft rock tunnels comprises the following steps: according to the geological conditions of soft rock in a soft rock tunnel, the section of the soft rock tunnel is divided into a plurality of excavation units; a quantitative relationship model of the excavation units and surface subsidence areas is established; the excavation result is predicted according to the quantitative relationship model, and the excavation sequence is obtained according to the prediction result; each excavation unit is excavated according to the excavation sequence, dynamic pressure balance compensation is implemented, and an excavation part is formed; the surface subsidence area corresponding to the excavation part is gradually backfilled and solidified, and the surface subsidence compensation of the soft rock tunnel is completed. Through the division of the excavation units with uniform geological conditions and the establishment of the quantitative relationship model, the dynamic pressure balance compensation and the layered backfilling and solidification technology are combined, the solidification effect of the surface subsidence position of the soft rock tunnel is improved, and the safety of the soft rock tunnel is improved.

Description

Technical Field

[0001] This invention relates to the field of soft rock tunnel construction technology, and in particular to a method for compensating for surface settlement in soft rock tunnels. Background Technology

[0002] Soft rock tunnel engineering is an important component of underground engineering construction. However, due to the characteristics of soft rock strata, such as low strength, poor stability, and easy deformation, significant surface settlement often occurs during tunnel excavation. This settlement can not only lead to tunnel structural instability but also cause serious damage to surface buildings and infrastructure, and even trigger safety accidents.

[0003] Currently, existing technologies are not ideal for solidification in the treatment of surface subsidence compensation, and secondary subsidence is prone to occur, posing safety hazards. Summary of the Invention

[0004] The main objective of this invention is to propose a method for compensating for surface settlement in soft rock tunnels, aiming to improve the solidification effect at the surface settlement points of soft rock tunnels and enhance their safety.

[0005] To achieve the above objectives, the present invention proposes a surface settlement compensation method for soft rock tunnels, comprising:

[0006] Based on the geological conditions of the soft rock in the soft rock tunnel, the cross-section of the soft rock tunnel is divided into multiple excavation units;

[0007] Establish a quantitative relationship model between the excavation unit and the surface subsidence area;

[0008] The excavation results are predicted based on the quantitative relationship model, and the excavation sequence is obtained based on the prediction results;

[0009] Each of the excavation units is excavated according to the excavation sequence, and dynamic pressure balance compensation is implemented to form an excavation section;

[0010] The surface settlement area corresponding to the excavation section is gradually backfilled and solidified to complete the surface settlement compensation of the soft rock tunnel.

[0011] In one embodiment, the step of dividing the cross-section of the soft rock tunnel into multiple excavation units based on the geological conditions of the soft rock in the soft rock tunnel includes:

[0012] Based on the hardness, water content, and joint development of the soft rock in the soft rock tunnel, the cross-section of the tunnel is divided into multiple excavation units with uniform geological conditions.

[0013] In one embodiment, the step of establishing a quantitative relationship model between the excavation unit and the surface subsidence area includes:

[0014] Set up settlement observation points in the aforementioned surface subsidence area;

[0015] Stress monitoring points are set up inside the soft rock tunnel at locations corresponding to the surface subsidence zone.

[0016] Monitoring data are obtained using the settlement observation points and the stress monitoring points;

[0017] A quantitative relationship model between the excavation unit and the surface subsidence area is established based on the monitoring data.

[0018] In one embodiment, the steps of predicting excavation results based on the quantitative relationship model and obtaining the excavation sequence based on the prediction results include:

[0019] When the predicted excavation result is an area with a predicted settlement of A, the excavation unit is excavated in layers according to the thickness B, and the excavation interval between each layer is H1 hours; wherein, 10mm < A; 0.5m ≤ B ≤ 0.7m; 1.5h ≤ H ≤ 2h.

[0020] In one embodiment, the steps of excavating each of the excavation units according to the excavation sequence and implementing dynamic pressure balance compensation to form the excavation section include:

[0021] Drill holes at the locations corresponding to the excavation units above the top of the soft rock tunnel;

[0022] Drilling is paused after reaching 80% of the target depth. The remaining 20% ​​of drilling is completed after the excavation face of the soft rock tunnel reaches directly below the borehole, forming a compensation channel.

[0023] Each of the excavation units shall be excavated in accordance with the excavation sequence;

[0024] When the settlement rate of the surface area corresponding to the excavation unit exceeds 0.5 mm / h for three consecutive times or the cumulative settlement value exceeds 70% of the design value, compensation grout is injected into the compensation channel and pressurized in stages to form the excavation section.

[0025] In one embodiment, the compensating grout comprises, by weight, 100 parts silicate cement, 20-30 parts bentonite, 80-100 parts water, and 0.5-1 parts polycarboxylate superplasticizer.

[0026] In one embodiment, when the settlement rate of the surface area corresponding to the excavation unit exceeds 0.5 mm / h three times consecutively or the cumulative settlement value exceeds 70% of the design value, the step of injecting compensation grout into the compensation channel and pressurizing it in stages to form the excavation section includes:

[0027] When the settlement rate of the surface area corresponding to the excavation unit exceeds 0.5 mm / h for three consecutive times or the cumulative settlement value exceeds 70% of the design value, the compensation grout is injected into the compensation channel and initial pressurization is performed. The initial pressurization pressure value is P1, which lasts for 10 minutes, so that the compensation grout penetrates into the micro-cracks of the excavation unit; 0.1 MPa ≤ P1 ≤ 0.3 MPa;

[0028] After the initial pressurization is completed, the compensation grout is injected again into the compensation channel and stable pressurization is performed. The stable pressurization pressure value is P2, which lasts for 30 minutes to offset the stress loss in the excavation unit; 0.3MPa≤P2≤0.8MPa;

[0029] After the stabilization pressurization is completed, the compensation grout is injected into the compensation channel again and enhanced pressurization is performed. The pressure value of the enhanced pressurization is P3, until the settlement rate of the surface settlement area corresponding to the excavation unit is reduced to V, forming the excavation section; 0.8MPa≤P3≤1.5MPa, V<0.1mm / h.

[0030] In one embodiment, the step of progressively backfilling and solidifying the surface settlement area corresponding to the excavation section to complete the surface settlement compensation of the soft rock tunnel includes:

[0031] When the distance between the excavation face of the soft rock tunnel and the compensation channel is D, clean the inner wall of the compensation channel and apply an interface agent; 50m≤D≤80m;

[0032] The surface subsidence area corresponding to the excavation section is backfilled in three layers from bottom to top, forming a bottom backfill layer, a middle backfill layer, and a top backfill layer.

[0033] In one embodiment, the backfilling construction interval H2 between the bottom backfill layer, the middle backfill layer and the top backfill layer is 2h≤H2≤6h.

[0034] In one embodiment, the bottom backfill layer comprises, by weight, 100 parts rapid-hardening sulfoaluminate cement, 50 parts quartz sand, 1-2 parts early-strength agent, and 25-30 parts water;

[0035] The intermediate backfill layer comprises, by weight, 100 parts ordinary Portland cement, 30 parts fly ash, 0.3 parts retarder, and 40-45 parts water;

[0036] The top backfill layer comprises, by weight, 100 parts bentonite, 5 parts flexible latex powder, and 120-150 parts water.

[0037] The technical solution of this invention effectively solves the problem of uneven settlement caused by differences in geological conditions during the construction of soft rock tunnels by dividing the excavation units with uniform geological conditions and establishing a quantitative relationship model, combined with dynamic pressure balance compensation and layered backfilling and solidification technology. The zoned excavation strategy improves construction controllability, the dynamic compensation mechanism achieves real-time stress balance, and the layered backfilling method ensures the coordination between the solidified layer and the deformation of the strata, thereby reducing the incidence of secondary settlement, improving the long-term stability of the tunnel structure, enhancing the solidification effect at the surface settlement points of soft rock tunnels, and improving the safety of soft rock tunnels. Attached Figure Description

[0038] 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.

[0039] Figure 1 This is a schematic flowchart of an embodiment of the surface settlement compensation method for soft rock tunnels provided by the present invention.

[0040] 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

[0041] 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.

[0042] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications 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 indications will also change accordingly.

[0043] 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.

[0044] In existing technologies, soft rock tunnel engineering faces the challenge of controlling surface settlement. Traditional methods employ a uniform backfilling approach, failing to adequately consider the impact of varying geological conditions on settlement distribution. This leads to a mismatch between backfill materials and strata characteristics, causing stress concentration in the solidified layer and subsequently triggering secondary settlement. Particularly in soft rock strata with well-developed joints and uneven water content distribution, conventional construction methods struggle to achieve differentiated settlement compensation control.

[0045] To address this technical problem, this invention proposes a method for compensating for surface settlement in soft rock tunnels.

[0046] Please see Figure 1 In one embodiment of the present invention, the surface settlement compensation method for soft rock tunnels includes:

[0047] Step S10: Based on the geological conditions of the soft rock in the soft rock tunnel, the cross-section of the soft rock tunnel is divided into multiple excavation units.

[0048] Step S20: Establish a quantitative relationship model between the excavation unit and the surface subsidence area;

[0049] Step S30: Predict the excavation results based on the quantitative relationship model, and obtain the excavation sequence based on the prediction results;

[0050] Step S40: Excavate each of the excavation units according to the excavation sequence and implement dynamic pressure balance compensation to form an excavation section;

[0051] Step S50: The surface settlement area corresponding to the excavation section is gradually backfilled and solidified to complete the surface settlement compensation of the soft rock tunnel.

[0052] The excavation unit division refers to spatial zoning based on differences in rock mass mechanical properties. For example, zoning is conducted when the hardness difference of soft rock does not exceed a certain value or the water content difference between adjacent units reaches a specific threshold. This helps establish a precise unit-surface correspondence. The quantitative relationship model obtains data by deploying surface settlement observation points and tunnel stress monitoring points, reflecting the dynamic impact of excavation activities on surface deformation. Dynamic pressure balance compensation involves real-time monitoring of the settlement rate during excavation. When the rate exceeds a set threshold, compensation grout injection is initiated. The compensation grout can be a cement-based material with micro-expansion properties. Progressive backfilling and solidification refers to implementing backfill layers with different proportions in stages according to the excavation progress. For example, the bottom layer uses early-strength materials to quickly form support, while the upper layer uses flexible materials to adapt to subsequent deformation.

[0053] Specifically, the tunnel cross-section is first geologically zoned based on parameters such as rock hardness, water content, and joint density, forming multiple excavation units. A mathematical model of the relationship between excavation units and surface deformation is constructed by synchronously monitoring surface settlement and tunnel stress changes. This model is used to simulate surface settlement distribution under different excavation sequences to select the optimal excavation scheme. During construction, units are excavated in a predetermined sequence. When abnormal settlement is detected, compensating grout is immediately injected through pre-set channels. Under pressure, the compensating grout seeps into rock fissures to form a reinforcement layer. After excavation, based on the actual settlement of the corresponding surface area of ​​each unit, different proportions of solidification materials are backfilled in layers. For example, the bottom layer uses fast-hardening materials to quickly stabilize the foundation, the middle layer uses conventional materials to fill the main body, and the surface layer uses flexible materials to absorb residual deformation.

[0054] Compared with existing technologies, this method achieves refined control through geological zoning, establishes a direct correlation between excavation units and surface deformation, and overcomes the drawbacks of the "one-size-fits-all" approach in traditional methods. The dynamic pressure compensation mechanism can promptly repair the stress imbalance caused by excavation, and the progressive backfilling strategy achieves differential compensation through material ratio optimization, forming a multi-layered, collaborative, and stable structure.

[0055] This application effectively solves the problem of non-uniform settlement caused by differences in geological conditions during the construction of soft rock tunnels by dividing the excavation into uniformly geological units and establishing a quantitative relationship model, combined with dynamic pressure balance compensation and layered backfilling and solidification technology. The zoned excavation strategy improves construction controllability, the dynamic compensation mechanism achieves real-time stress balance, and the layered backfilling method ensures the coordination between the solidified layer and the deformation of the strata, thereby reducing the incidence of secondary settlement, improving the long-term stability of the tunnel structure, enhancing the solidification effect at the surface settlement points of soft rock tunnels, and improving the safety of soft rock tunnels.

[0056] In an embodiment of the present invention, the step of dividing the cross-section of the soft rock tunnel into multiple excavation units according to the geological conditions of the soft rock in the soft rock tunnel includes:

[0057] Step S11: Based on the hardness, water content, and joint development of the soft rock in the soft rock tunnel, the cross-section of the tunnel is divided into multiple excavation units with uniform geological conditions.

[0058] Among these, hardness refers to the rock's ability to resist external forces, which can be achieved using uniaxial compressive strength testing. Dividing the rock into hardness ranges ensures relative stability of the mechanical properties within each excavation unit. Moisture content refers to the mass ratio of water in the rock, which can be determined using an oven-drying method. Controlling the difference in moisture content between adjacent units avoids uneven settlement caused by different permeability zones. Joint development refers to the number of rock fissures per unit area, which can be statistically analyzed using core drilling combined with image analysis. Setting a joint density difference threshold effectively distinguishes regions with different structural stability. Uniform geological conditions mean that the fluctuation range of rock mass parameters within the divided excavation units is controllable. This can be achieved through 3D geological modeling combined with clustering algorithms, resulting in a compensation model with higher reliability.

[0059] Specifically, in the process of tunnel cross-section division, data on rock hardness, water content, and joint density are first obtained through geological exploration. For hardness parameters, for example, differences in test values ​​are controlled within 5 MPa to form independent excavation units; for water content parameters, for example, adjacent areas are designated as different units when the difference in water content reaches 15%; for joint density parameters, for example, three fractures per square meter are used as the boundary standard. This multi-dimensional division method can accurately reflect the heterogeneous characteristics of the strata, laying the foundation for establishing accurate settlement compensation relationships in the future.

[0060] Compared with existing technologies, traditional methods typically divide regions based on only a single geological parameter, easily overlooking the coupling effect between different parameters. This scheme comprehensively considers three key indicators—hardness, water content, and joint density—and uses a quantified threshold to control the division accuracy, ensuring both the uniformity of geological conditions within a unit and highlighting the significant differences between adjacent units.

[0061] Through the above technical solution, this application can effectively solve the problem of insufficient targeting of compensation measures caused by incomplete identification of geological parameters in the prior art. By scientifically dividing the excavation unit, compensation strategies corresponding to different geological regions can be accurately matched, significantly reducing compensation deviations caused by parameter fluctuations and providing a reliable geological basis for implementing dynamic pressure balance compensation.

[0062] In an embodiment of the present invention, the step of establishing a quantitative relationship model between the excavation unit and the surface subsidence area includes:

[0063] Step S21: Set up settlement observation points in the surface subsidence area;

[0064] Step S22: Stress monitoring points are set up inside the soft rock tunnel at locations corresponding to the surface subsidence zone.

[0065] Step S23: Obtain monitoring data using the settlement observation points and the stress monitoring points;

[0066] Step S24: Establish a quantitative relationship model between the excavation unit and the surface subsidence area based on the monitoring data.

[0067] Settlement observation points refer to displacement monitoring devices installed within the surface settlement area, which can be implemented using total stations or GPS positioning equipment, to acquire real-time vertical displacement data of the surface. Stress monitoring points refer to stress sensors deployed inside the tunnel surrounding rock, which can be implemented using vibrating wire sensors or fiber optic grating sensors, to collect data on stress changes within the surrounding rock. Monitoring data refers to the synchronously acquired displacement and stress changes, which can be achieved using a data acquisition instrument, to establish the correlation between the excavation unit and surface settlement.

[0068] Specifically, settlement observation points are arranged in a grid pattern in the surface settlement area, for example, total station prisms are set up at 5m×5m intervals, and vibrating wire stress gauges are installed in the corresponding areas inside the tunnel. During excavation, surface displacement data and surrounding rock stress change data corresponding to each excavation unit are recorded simultaneously, and a displacement-stress coupling model is established through data fitting. As the excavation unit advances, the model parameters are dynamically adjusted based on real-time monitoring data to predict the settlement distribution pattern under different excavation sequences, providing data support for optimizing the excavation sequence.

[0069] Compared with existing technologies, which typically rely solely on single-dimensional surface displacement monitoring or manual experience-based judgment, this approach fails to establish a quantitative relationship between excavation units and surface settlement. This application constructs a dual-parameter dynamic monitoring system by simultaneously collecting surface displacement and surrounding rock stress data. This system accurately reflects the spatiotemporal correlation of ground response during excavation unit advancement, overcoming the problems of single monitoring dimensions and data lag inherent in traditional methods.

[0070] Through the above technical solution, this application achieves dynamic correlation modeling between excavation units and surface settlement areas, enabling accurate prediction of the impact of different excavation sequences on surface settlement and providing a scientific basis for optimizing the excavation sequence. The dual-parameter monitoring system effectively captures the coupling relationship between surrounding rock stress release and surface displacement, significantly improving the accuracy of settlement prediction and avoiding delays in compensation measures due to data gaps.

[0071] In an embodiment of the present invention, the steps of predicting the excavation result based on the quantitative relationship model and obtaining the excavation sequence based on the prediction result include:

[0072] Step S31: When the predicted excavation result is an area with a predicted settlement of A, the excavation unit is excavated in layers according to the thickness B, and the excavation interval between each layer is H1 hours; wherein, 10mm < A; 0.5m ≤ B ≤ 0.7m; 1.5h ≤ H ≤ 2h.

[0073] Among them, the predicted settlement A refers to the predicted surface settlement value calculated through a quantitative relationship model, which can be achieved by combining finite element numerical simulation with measured data correction. This parameter is used to determine whether layered excavation measures are needed. Thickness B refers to the thickness of the rock layer in a single excavation, which can be determined by ground-penetrating radar scanning combined with borehole sampling. This parameter is used to control the degree of disturbance to the surrounding rock in a single excavation. Excavation interval H1 refers to the waiting time between two adjacent layered excavations, which can be adjusted by real-time monitoring of the surrounding rock deformation rate. This parameter is used to ensure that the stratum stress is redistributed within a controllable range.

[0074] Specifically, when the predicted settlement output by the quantitative relationship model exceeds 10 mm, it indicates a significant risk of ground disturbance in the area. In this case, the excavation unit is divided into several layers with a thickness between 0.5 and 0.7 meters; for example, 0.6 meters can be used as a typical layer thickness. After each layer is excavated, a stabilization period of 1.5 to 2 hours is maintained; for example, 1.8 hours can be chosen as a typical interval. During this period, the deformation of the surrounding rock is tracked in real time using a stress monitoring system. This staged excavation method allows ground stress to be released gradually, avoiding sudden settlement caused by concentrated excavation.

[0075] Compared to existing technologies, traditional methods often employ fixed layer thicknesses and excavation rhythms, failing to dynamically adjust construction parameters based on predicted settlement. This solution establishes a correlation mechanism between predicted values ​​and construction parameters, achieving coordinated control of layer thickness and excavation intervals. This ensures construction efficiency while effectively suppressing stress abrupt changes during excavation.

[0076] Through the above technical solution, this application can automatically match the optimal excavation parameter combination for different predicted settlement areas, thereby improving excavation efficiency while ensuring construction safety. By precisely controlling the single excavation thickness and process interval, the risk of cascading settlement caused by improper excavation procedures is significantly reduced, creating favorable conditions for subsequent dynamic pressure balance compensation.

[0077] In an embodiment of the present invention, the steps of excavating each of the excavation units according to the excavation sequence and implementing dynamic pressure balance compensation to form the excavation section include:

[0078] Step S41: Drill a hole at the position corresponding to the excavation unit above the top of the soft rock tunnel;

[0079] Step S42: Drilling is paused after reaching 80% of the target depth. The remaining 20% ​​of drilling is completed after the excavation face of the soft rock tunnel reaches directly below the borehole, forming a compensation channel.

[0080] Step S43: Excavate each of the excavation units according to the excavation sequence;

[0081] Step S44: When the settlement rate of the surface area corresponding to the excavation unit exceeds 0.5 mm / h for three consecutive times or the cumulative settlement value exceeds 70% of the design value, compensation grout is injected into the compensation channel and pressurized in stages to form the excavation section.

[0082] The drilling location refers to the depth of the tunnel above the top, between 1 / 3 and 1 / 2 of its burial depth. This is determined by ground-penetrating radar to identify the rock strata structure and select a suitable location that balances construction efficiency with rock stability. The compensation channel formation involves drilling in two stages. For example, only 80% of the drilling is completed before the tunnel face is reached, and the remaining 20% ​​is completed once the face is directly below. This method avoids premature drilling, which could lead to stress imbalance in the rock strata. Dynamic pressure balance compensation involves injecting grout and pressurizing it in stages based on surface settlement data. For example, compensation is initiated when the settlement rate or cumulative value exceeds a threshold, gradually offsetting the stress release caused by excavation through staged pressurization.

[0083] Specifically, after selecting borehole locations within the burial depth range above the tunnel top, a staged drilling process is used to form compensation channels. During excavation, surface settlement data is monitored in real time. When the settlement rate continuously exceeds a threshold or the cumulative settlement approaches the design limit, grout is immediately injected through the compensation channels. After grout injection, pressure is applied in stages. For example, initial pressurization allows the grout to penetrate into micro-fractures in the rock mass, stable pressurization compensates for stress loss, and intensified pressurization further suppresses settlement. By controlling pressure in stages, the deformation of the rock strata caused by excavation can be dynamically matched, forming a stable excavation section structure.

[0084] Compared to existing technologies, which typically employ single-pressure grouting or fail to adjust compensation timing based on real-time settlement data, this approach can easily lead to uneven grout diffusion or delayed compensation. This new method combines staged drilling with dynamic pressurization to precisely create compensation channels after the excavation face reaches a specific location. Furthermore, it adjusts the pressure in gradients based on real-time monitoring data, ensuring that grout filling and stress compensation more closely match the actual deformation state of the rock strata.

[0085] Through the above technical solution, this application can effectively suppress the surface settlement rate during soft rock tunnel excavation and avoid secondary settlement caused by compensation lag or improper pressure control. The combination of staged drilling and dynamic pressurization can improve the filling efficiency of grout into rock fissures, enhance the overall stability of the rock mass surrounding the excavation section, and thus reduce the risk of damage to surface structures.

[0086] In an embodiment of the present invention, the compensating grout comprises, by weight, 100 parts silicate cement, 20-30 parts bentonite, 80-100 parts water and 0.5-1 parts polycarboxylate superplasticizer.

[0087] Among them, silicate cement refers to a hydraulic cementitious material with calcium silicate as its main component, specifically ordinary silicate cement or rapid-hardening silicate cement, used to provide the basic bonding strength of the grout. Bentonite refers to a clay mineral with montmorillonite as its main component, specifically sodium-based bentonite or calcium-based bentonite, used to increase the fluidity and thixotropy of the grout and reduce bleeding. Polycarboxylate superplasticizer refers to a high-molecular-weight surfactant containing carboxylic acid groups, specifically polycarboxylate ether superplasticizers, used to reduce the water-cement ratio of the grout and improve its fluidity, preventing the compensation channels from becoming blocked due to excessive grout viscosity.

[0088] Specifically, silicate cement, as the main cementing material, reacts with water to form hydration products, providing early and later strength to the grout. The addition of bentonite adsorbs a large amount of free water, forming a stable colloidal structure that allows the grout to diffuse evenly into the micro-cracks of the excavation unit under pressure. Polycarboxylate superplasticizer disperses cement particles through steric hindrance, reducing water consumption while maintaining grout fluidity, thereby lowering the shrinkage rate after curing. During the dynamic pressure balance compensation process, the grout penetrates cracks, fills voids, and forms a dense structure through staged pressurization, ultimately achieving effective compensation of stress loss.

[0089] Compared to existing technologies, which typically use single cement grout or ordinary concrete as backfill material without considering the development of micro-fractures in soft rock formations, resulting in insufficient grout permeability or shrinkage cracking after curing, this solution utilizes the synergistic effect of silicate cement, bentonite, and polycarboxylate superplasticizer to achieve a grout with high fluidity, low shrinkage, and anti-bleeding properties, making it suitable for the complex working conditions of soft rock formations.

[0090] Through the above technical solution, this application effectively solves the problems of poor permeability and easy shrinkage of traditional compensation grout in soft rock formations, significantly improves the filling effect of grout on micro fractures, reduces the risk of secondary settlement, and at the same time ensures the unobstructed flow of compensation channels by optimizing the material ratio, making the dynamic pressure balance compensation process more controllable.

[0091] In an embodiment of the present invention, when the settlement rate of the surface area corresponding to the excavation unit exceeds 0.5 mm / h for three consecutive times or the cumulative settlement value exceeds 70% of the design value, the step of injecting compensation grout into the compensation channel and pressurizing it in stages to form the excavation section includes:

[0092] Step S441: When the settlement rate of the surface area corresponding to the excavation unit exceeds 0.5 mm / h for three consecutive times or the cumulative settlement value exceeds 70% of the design value, the compensation grout is injected into the compensation channel and initial pressurization is applied. The initial pressurization pressure value is P1, which lasts for 10 minutes, allowing the compensation grout to penetrate into the micro-cracks of the excavation unit; 0.1 MPa ≤ P1 ≤ 0.3 MPa;

[0093] Step S442: After the initial pressurization is completed, the compensation grout is injected into the compensation channel again and stable pressurization is performed. The stable pressurization pressure value is P2, which lasts for 30 minutes to offset the stress loss in the excavation unit; 0.3MPa≤P2≤0.8MPa;

[0094] Step S443: After the stabilization pressurization is completed, the compensation grout is injected into the compensation channel again and enhanced pressurization is performed. The pressure value of the enhanced pressurization is P3, until the settlement rate of the surface settlement area corresponding to the excavation unit is reduced to V, forming the excavation section; 0.8MPa≤P3≤1.5MPa, V<0.1mm / h.

[0095] Initial pressurization refers to the process of filling micro-fractures in the rock mass with grout through low-pressure permeation. This can be achieved using a hydraulic pump in a stepped pressurization manner, and this pressure range avoids damage to the rock mass structure. Stabilization pressurization refers to the process of compensating for stress loss in the formation through medium pressure, which can be achieved using a pressure stabilization control system. This pressure range can balance the stress release caused by excavation. Enhanced pressurization refers to the process of suppressing the continuous deformation trend of the formation through high pressure, which can be achieved using a closed-loop feedback control system. This pressure range ensures that the settlement rate reaches a stable threshold.

[0096] Specifically, when the surface settlement rate or cumulative settlement value triggers a threshold, grout is first injected at a low pressure to allow it to fully penetrate the micro-fractures in the rock mass and form initial support. The pressure is then gradually increased to a medium level to compensate for stress losses in the surrounding rock caused by excavation. Finally, even higher pressure is used for dynamic adjustment until the surface deformation rate drops to a safe range, forming a stable reinforced structure.

[0097] Compared with existing technologies, traditional methods often use a single pressure value for grouting, which can easily lead to uneven grout distribution or insufficient pressure to effectively compensate for stress loss. This solution, through staged pressure control, not only ensures the penetration and diffusion of grout in the rock mass but also achieves a dynamic balance between stress compensation and deformation control.

[0098] Through the above technical solution, this application can effectively control the gradual deformation of soft rock strata during the excavation process, prevent secondary settlement caused by local stress concentration, and ensure that the surface settlement compensation effect matches the excavation progress synchronously.

[0099] In an embodiment of the present invention, the step of progressively backfilling and solidifying the surface settlement area corresponding to the excavation section to complete the surface settlement compensation of the soft rock tunnel includes:

[0100] Step S51: When the distance between the excavation face of the soft rock tunnel and the compensation channel is D, clean the inner wall of the compensation channel and apply an interface agent; 50m≤D≤80m;

[0101] Step S52: The surface settlement area corresponding to the excavation section is backfilled in three layers from bottom to top to form a bottom backfill layer, a middle backfill layer and a top backfill layer.

[0102] Interface agents are chemical coatings used to enhance the adhesion between the inner wall of the compensation channel and the backfill material. These can be achieved using epoxy resin or polyurethane-based materials, and their function is to prevent delamination between the backfill material and the rock mass. Progressive backfilling refers to controlling the stress release rate of the stratum through layered construction. This can be achieved by implementing three layers sequentially: bottom, middle, and top, with each layer's thickness controlled within the range of 0.5–1.0 m, thereby balancing the backfill's self-weight with the stratum's bearing capacity.

[0103] Specifically, when the tunnel excavation face advances to within 50-80 meters of the compensation channel, high-pressure water jets are first used to remove debris from the inner wall of the compensation channel, followed by the uniform application of an interface agent using spraying equipment. The backfilling operation is divided into three stages: the bottom backfill layer uses a fast-setting material to quickly form a support structure; the middle backfill layer uses conventional materials to achieve stress transition; and the top backfill layer uses a flexible material to absorb residual deformation. After each layer is completed, a waiting period of 2-6 hours is required for the material to initially solidify before proceeding to the next layer, thus forming a composite backfill body with gradient properties.

[0104] Compared to existing technologies, current backfilling methods typically employ monolithic casting of a single material, which is prone to internal voids due to material shrinkage and cannot adapt to the mechanical properties of strata at different depths. This solution enhances bonding strength through interface treatment and combines a layered backfilling process to match the material properties of each layer with the deformation characteristics of the corresponding strata, effectively avoiding the problem of coordinated deformation between the backfill and the surrounding rock.

[0105] Through the above technical solution, this application solves the problem of secondary settlement caused by the single material properties of traditional backfilling methods. By enhancing the bonding strength of the contact surface with an interface agent and realizing stress gradient release through a layered backfilling structure, the collaborative bearing capacity of the backfill and the surrounding rock is significantly improved, ensuring the long-term stability of the surface settlement compensation effect.

[0106] In an embodiment of the present invention, the backfilling construction interval H2 between the bottom backfill layer, the middle backfill layer and the top backfill layer is 2h≤H2≤6h.

[0107] H2 duration refers to the construction interval between adjacent backfill layers, which can be controlled using timers or construction schedules. For example, after completing the bottom backfill layer, wait 2-6 hours before constructing the middle backfill layer. This time range is set to allow the previous layer to initially solidify but not fully harden, thus ensuring interlayer bonding strength. The bottom, middle, and top backfill layers refer to structural layers formed by backfilling from bottom to top, which can be achieved using layered pouring equipment. Different backfill layers use differentiated material ratios; for example, the bottom backfill layer uses fast-setting materials to quickly form support, while the top backfill layer uses flexible materials to accommodate deformation.

[0108] Specifically, after completing the dynamic pressure balance compensation of the excavation section, the inner wall of the compensation channel is first cleaned and an interface agent is applied. Then, backfilling is carried out in layers in the order of bottom, middle, and top. After the bottom backfill layer is completed, an H2 time (e.g., 3 hours) must be waited before the middle backfill layer is constructed. Similarly, after the middle backfill layer is completed, an H2 time (e.g., 4 hours) must be waited before the top backfill layer is constructed. By controlling the interval time, the previous layer of material can reach a preliminary solidification state, avoiding disturbance to it during subsequent construction, while ensuring a tight bond between layers.

[0109] In some specific implementations, the duration of H2 can be dynamically adjusted according to the ambient temperature and material properties. For example, in low-temperature environments (such as below 5°C), H2 can be extended to 6 hours to ensure the curing effect; in high-temperature environments (such as above 30°C), H2 can be shortened to 2 hours to avoid premature hardening of the material leading to a decrease in interlayer adhesion.

[0110] Compared to existing technologies, traditional backfilling methods typically employ continuous construction or lack clear interval control, leading to mismatches in the curing states of interlayer materials and a tendency for surface cracking or insufficient overall strength. This application, however, solves the problems of interlayer delamination and secondary settlement by setting an H2 time range, allowing each layer of material to be stacked under optimal bonding conditions.

[0111] Through the above technical solution, this application achieves progressive and synergistic curing of the backfill layer structure, effectively improving the overall stability of the multi-layer backfill system. By controlling the construction interval, the materials in each layer form a gradient strength distribution during the curing process, which can quickly provide initial support and adapt to deformation coordination under long-term loads, thereby significantly reducing the risk of secondary ground subsidence.

[0112] In an embodiment of the present invention, the bottom backfill layer comprises, by weight, 100 parts of rapid-hardening sulfoaluminate cement, 50 parts of quartz sand, 1-2 parts of early-strength agent and 25-30 parts of water;

[0113] The intermediate backfill layer comprises, by weight, 100 parts ordinary Portland cement, 30 parts fly ash, 0.3 parts retarder, and 40-45 parts water;

[0114] The top backfill layer comprises, by weight, 100 parts bentonite, 5 parts flexible latex powder, and 120-150 parts water.

[0115] Rapid-hardening sulfoaluminate cement refers to a hydraulic cementitious material with high early strength and short setting time. Specifically, it can be achieved using cement containing calcium sulfoaluminate minerals. Its function is to quickly form the supporting structure of the bottom backfill layer, reducing the exposure time of the strata after excavation. Quartz sand refers to a uniformly sized siliceous particle material, specifically quartz sand with a 0.5–1.0 mm gradation. Its function is to enhance the compressive strength of the bottom backfill layer and adjust the material's flowability. Early-strength agents are chemical additives that accelerate the cement hydration reaction. Specifically, they can be calcium nitrate or calcium formate compounds. Their function is to shorten the initial setting time of the bottom backfill layer, meeting the need for rapid closure after soft rock tunnel excavation. Ordinary silicate cement refers to a conventional silicate-based cementitious material, specifically PO 42.5 grade cement. Its function is to provide basic strength for the intermediate backfill layer and balance costs. Fly ash refers to solid waste from coal-fired power plants, specifically secondary fly ash. Its function is to improve the workability of the intermediate backfill layer and reduce cement usage. Retarder refers to an additive that delays the setting time of cement. It can be achieved using sodium gluconate or lignin sulfonate. Its function is to extend the workability time of the intermediate backfill layer and ensure the continuity of layered backfilling. Bentonite refers to clay minerals mainly composed of montmorillonite. It can be achieved using sodium-based bentonite. Its function is to impart water absorption and expansion properties to the top backfill layer, compensating for voids caused by surface subsidence. Flexible latex powder refers to dispersible polymer powder. It can be achieved using ethylene-vinyl acetate copolymer powder. Its function is to improve the crack resistance and deformation adaptability of the top backfill layer.

[0116] Specifically, the bottom backfill layer, through the synergistic effect of rapid-hardening sulfoaluminate cement and an early-strength agent, quickly forms a high-strength sealing layer after excavation, suppressing immediate deformation of soft rock. The middle backfill layer, utilizing ordinary silicate cement and a retarder, provides continuous and stable support after the bottom backfill layer has solidified, while fly ash improves the material density. The top backfill layer, leveraging the expansibility of bentonite and the elasticity of flexible latex powder, forms a flexible buffer layer in the later stages of surface settlement, absorbing residual deformation of the strata. The three layers are constructed in a bottom-up sequence, with each layer thickness controlled between 0.5 and 1.0 meters, and construction intervals between layers of 2 to 6 hours, ensuring interlayer bonding strength and the continuity of the overall structure.

[0117] Compared to existing technologies, those using a single backfill material cannot simultaneously address the differences in mechanical response at different soil depths. For example, traditional cement mortar backfill layers struggle to meet the demands of rapid bottom support, mid-section stabilization and reinforcement, and top deformation adaptation, easily leading to secondary settlement due to the limited material properties. This solution, however, employs a layered material design, prioritizing rapid curing in the bottom backfill layer, long-term stability in the middle backfill layer, and enhanced deformation coordination in the top backfill layer, forming a composite structure with gradient performance matching.

[0118] Through the above technical solution, this application can effectively solve the problem of mismatch between backfill materials and stratum deformation characteristics in soft rock tunnels. The bottom backfill layer quickly seals the excavation face, preventing immediate collapse of soft rock; the middle backfill layer provides continuous support, inhibiting the development of plastic deformation; and the top backfill layer absorbs residual stress through flexible deformation. The synergistic effect of these three layers can significantly reduce the risk of secondary settlement and improve the reliability of surface settlement compensation.

[0119] Based on the above embodiments, a specific implementation method is shown here for ease of understanding:

[0120] This invention provides a method for surface settlement compensation in soft rock tunnels. This method organically combines three core technical steps: predictive layered excavation control, dynamic pressure balance compensation, and progressive backfilling and solidification. This achieves proactive control and effective compensation for surface settlement during soft rock tunnel construction. The core of this method lies in transforming the traditional passive response to settlement into proactive prevention and compensation. Through precise construction timing control and a pressure balance mechanism, it minimizes the impact of surface settlement on the surrounding environment.

[0121] Logical relationship of the main technical steps:

[0122] The technical solution of the present invention includes three interrelated main steps: first, a predictive layered excavation control step is performed, which provides an accurate data basis and construction space for subsequent compensation work; second, a dynamic pressure balance compensation step is implemented, which performs real-time compensation operation based on the data obtained in the first step; and finally, a progressive backfilling and solidification step is performed, which ensures the long-term stability of the compensation effect.

[0123] Specifically, the first core step: predictive stratified excavation control

[0124] The predictive layered excavation control step is the foundation of the entire compensation method. The innovation of this step lies in closely integrating the tunnel excavation process with the prediction of surface settlement, and actively influencing the development trend of surface settlement by precisely controlling the excavation rhythm and excavation method.

[0125] In the specific implementation process, a detailed stratified analysis of the soft rock geology is first required. Based on the geological characteristics of the rock strata, such as hardness, water content, and joint development, the tunnel excavation section is divided into several independent yet interconnected excavation units. The principle for dividing each excavation unit is to ensure that the geological conditions within the unit are relatively uniform, while the geological differences between units are significant. This division method provides a clear operational interface for subsequent precise control.

[0126] Once the excavation units are determined, it is necessary to establish the settlement influence relationship between each unit and the corresponding area on the surface. This relationship is not a simple vertical correspondence, but rather takes into account the complexity and nonlinear characteristics of stress transmission in soft rock geology. Several settlement observation points are set up on the surface before tunnel excavation, arranged according to a grid principle to ensure a comprehensive reflection of the spatial distribution characteristics of surface settlement. Simultaneously, stress monitoring points are set up at corresponding locations inside the tunnel. By synchronously monitoring surface settlement and stress changes inside the tunnel, a quantitative relationship model between the two is established.

[0127] The excavation process employs an asymmetric timing control method, which is the first innovative aspect of this step. Traditional tunnel excavation typically uses a symmetrical or regular excavation sequence, while this method consciously adjusts the excavation sequence based on geological conditions and settlement prediction results, resulting in a controllable distribution pattern of surface settlement in both space and time. Specifically, for areas with better geological conditions, the excavation speed can be appropriately accelerated to allow time for slower excavation in areas with poorer geological conditions. For tunnel sections corresponding to surface areas with predicted large settlement, a more meticulous layered excavation is adopted, with the thickness of each layer controlled at 50%–70% of the conventional thickness, and the excavation interval extended to 1.5–2 times the conventional interval. This timing arrangement allows sufficient stress adjustment time for soft rock, avoiding sudden and significant settlement caused by stress concentration.

[0128] During excavation, the contribution of each excavation unit to surface settlement is monitored in real time. If the surface settlement caused by the excavation of a certain unit exceeds a preset threshold, excavation of that unit is immediately suspended, and other units are started instead. By dynamically adjusting the excavation sequence in this way, surface settlement is kept within a controllable range. This real-time adjustment mechanism requires construction personnel to have rapid decision-making capabilities and a robust information transmission system to ensure that surface monitoring data can be transmitted to the construction site inside the tunnel in a timely manner.

[0129] The second core step: Dynamic pressure balance compensation

[0130] The dynamic pressure balance compensation step is the core innovation of this invention. This step achieves active control of surface subsidence by simultaneously implementing pressure compensation operations during tunnel excavation. The theoretical basis for this step is the stress transmission mechanism and pressure balance principle in soft rock geology.

[0131] Traditional surface settlement treatment typically involves passive repair after settlement occurs. This method, however, implements active compensation in the intermediate layer between the surface and the tunnel during tunnel excavation. Specifically, a compensation operation channel is established via drilling at a depth of 1 / 3 to 1 / 2 of the tunnel top. This location is chosen based on the characteristics of stress transmission in soft rock: it effectively influences the stress redistribution caused by tunnel excavation and directly affects the formation process of surface settlement.

[0132] The compensation channel is established using a staged drilling method. First, drilling proceeds from the surface down to 80% of the predetermined depth. Drilling is then paused, and the tunnel excavation is allowed to advance directly below this location before completing the remaining 20% ​​of the drilling. This staged drilling method avoids adverse effects on tunnel excavation while ensuring the precise positioning of the compensation channel. The borehole diameter is determined based on the compensation requirements, generally controlled between 150 and 300 mm. The borehole spacing is determined based on geological conditions and predicted settlement, typically ranging from 3 to 8 meters.

[0133] The pressure compensation is implemented using a gradual pressurization method, which is the core technical feature of this step. When the surface settlement rate in a certain area exceeds the preset value due to tunnel excavation, pressurization is immediately implemented in the corresponding compensation channel for that area. The pressurizing medium uses controllable flowable materials, such as cement mortar or bentonite slurry, which have good flowability and controllable solidification characteristics. The pressurization process is divided into three stages: the initial pressurization stage, where the pressure is controlled at 0.1-0.3 MPa, mainly to fill micro-cracks and voids in soft rock; the stabilization pressurization stage, where the pressure is increased to 0.3-0.8 MPa, using continuous pressure to offset the stress loss caused by tunnel excavation; and the intensified pressurization stage, where the pressure is increased to 0.8-1.5 MPa as needed to achieve active compensation for the settlement that has already occurred.

[0134] The timing of pressure compensation is crucial, requiring the establishment of an automatic triggering mechanism based on real-time monitoring data. The pressure compensation program should automatically initiate when the surface settlement rate exceeds a preset threshold three times consecutively, or when the cumulative settlement reaches 70% of a preset limit. The magnitude of the compensation pressure is determined based on the settlement amount and geological parameters. The calculation formula considers key parameters such as the deformation modulus, Poisson's ratio, and burial depth of soft rock, ensuring that the compensation pressure effectively offsets the settlement without adversely affecting surrounding structures.

[0135] During the pressure compensation process, it is necessary to continuously monitor changes in surface subsidence. When the subsidence rate decreases to a safe range, the compensation pressure is gradually reduced until a stable equilibrium pressure level is maintained. The determination of this equilibrium pressure requires comprehensive consideration of the progress of tunnel excavation, changes in geological conditions, and the development trend of surface subsidence, and is usually 30% to 50% of the maximum compensation pressure.

[0136] The third core step: progressive backfilling and curing.

[0137] The progressive backfilling and curing process is a key step in ensuring the long-term stability of the compensation effect. This process, through a carefully designed backfilling and curing procedure, transforms temporary stress compensation into permanent structural support.

[0138] Unlike traditional one-time backfilling methods, this method employs a gradual backfilling strategy synchronized with the tunnel excavation progress. When the tunnel excavation advances to within 50-80 meters of a certain compensation point, backfilling and solidification operations are initiated at that compensation point. This distance is selected based on the analysis results of the stress influence range in soft rock, ensuring that the backfilling and solidification operation will not adversely affect the ongoing tunnel excavation, while simultaneously ensuring timely solidification of the compensation effect.

[0139] The selection and proportioning of backfill materials are of significant technical importance, requiring compliance with requirements in terms of strength, deformation, and durability. A layered configuration is employed for the backfill materials: the bottom layer uses high-strength, fast-setting materials, such as fast-setting cement mortar, primarily providing structural support; the middle layer uses medium-strength, retarding materials, such as ordinary cement mortar with added retarder, mainly serving as a transition and buffer; the top layer uses low-strength, flexible materials, such as bentonite cement grout, primarily adapting to minor surface deformations. This layered configuration creates a support system that combines rigidity and flexibility, ensuring sufficient load-bearing capacity while possessing good deformation adaptability.

[0140] The backfilling and solidification process employs a bottom-up, layered backfilling method. Each layer is controlled to be 0.5–1.0 meters thick, with an interval of 2–6 hours between layers to ensure the lower layer has reached initial setting before the next layer is applied. During backfilling, strict control of the backfill pressure is crucial to prevent excessive pressure from causing further disturbance to the already stabilized surface. The backfill pressure is controlled using a gradually decreasing approach: the bottom layer pressure remains consistent with the previous compensation pressure; the middle layer pressure is 70%–80% of the bottom layer pressure; and the top layer pressure is 40%–50% of the bottom layer pressure.

[0141] To ensure a good bond between the backfill material and the surrounding soft rock, the walls of the compensation channel need to be pre-treated before backfilling. Pre-treatment includes cleaning loose materials from the channel, rinsing the channel walls with low-pressure water, and applying an interface treatment agent. The interface treatment agent is a cement-based penetrating crystallizing material that can penetrate into the micro-fractures of the soft rock to form a strong bonding interface.

[0142] After backfilling and solidification are completed, effectiveness verification and long-term monitoring are required. Effectiveness verification includes testing the strength of the backfill, checking its bonding with the surrounding rock mass, and assessing the stability of surface settlement. Long-term monitoring should last for at least one complete seasonal cycle, and should include monitoring trends in surface settlement, the stability of the backfill, and the impact on the surrounding environment.

[0143] The three core steps generated a synergistic effect, enabling proactive control of surface settlement in soft rock tunnels throughout the entire process. The predictive layered excavation control step provided a precise data foundation and a controllable construction environment for the entire compensation process; the dynamic pressure balance compensation step enabled real-time intervention and proactive control of settlement; and the progressive backfilling and solidification step ensured the long-term stability and reliability of the compensation effect.

[0144] Compared to traditional passive response methods, this proactive, end-to-end control approach offers significant advantages, including strong preventative capabilities, high control precision, and excellent adaptability. Through precise timing control and pressure balancing mechanisms, surface subsidence can be kept within design limits, effectively protecting the safety of surface structures and infrastructure. Furthermore, this method is economically efficient, reducing post-construction repair costs through proactive prevention and improving the overall efficiency of tunnel construction.

[0145] 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 ground settlement compensation method for a soft rock tunnel, characterized by, include: Based on the geological conditions of the soft rock in the soft rock tunnel, the cross-section of the soft rock tunnel is divided into multiple excavation units; Establish a quantitative relationship model between the excavation unit and the surface subsidence area, and set up subsidence observation points in the surface subsidence area; Stress monitoring points are set up at locations corresponding to the surface subsidence area within the soft rock tunnel; monitoring data are obtained using the subsidence observation points and the stress monitoring points. A quantitative relationship model between the excavation unit and the surface subsidence area is established based on the monitoring data. The excavation results are predicted based on the quantitative relationship model, and the excavation sequence is obtained based on the prediction results; Each of the excavation units is excavated according to the excavation sequence, and dynamic pressure balance compensation is implemented to form an excavation section; The surface settlement area corresponding to the excavation section is gradually backfilled and solidified to complete the surface settlement compensation of the soft rock tunnel.

2. The ground settlement compensation method for a soft rock tunnel according to claim 1, wherein, Based on the geological conditions of the soft rock in the soft rock tunnel, the step of dividing the cross-section of the soft rock tunnel into multiple excavation units includes: Based on the hardness, water content, and joint development of the soft rock in the soft rock tunnel, the cross-section of the tunnel is divided into multiple excavation units with uniform geological conditions.

3. The ground settlement compensation method for a soft rock tunnel according to claim 1, wherein, The steps of predicting the excavation results based on the quantitative relationship model and obtaining the excavation sequence based on the prediction results include: When the predicted excavation result is an area with a predicted settlement of A, the excavation unit is excavated in layers according to the thickness B, and the excavation interval between each layer is H1 hours; wherein, 10mm < A; 0.5m ≤ B ≤ 0.7m; 1.5h ≤ H1 ≤ 2h.

4. The ground settlement compensation method for a soft rock tunnel according to claim 3, wherein, The steps of excavating each of the excavation units according to the excavation sequence and implementing dynamic pressure balance compensation to form the excavation section include: Drill holes at the locations corresponding to the excavation units above the top of the soft rock tunnel; Drilling is paused after reaching 80% of the target depth. The remaining 20% ​​of drilling is completed after the excavation face of the soft rock tunnel reaches directly below the borehole, forming a compensation channel. Each of the excavation units shall be excavated in accordance with the excavation sequence; When the settlement rate of the surface settlement area corresponding to the excavation unit exceeds 0.5 mm / h for three consecutive times or the cumulative settlement value exceeds 70% of the design value, compensation grout is injected into the compensation channel and pressurized in stages to form the excavation section.

5. The ground settlement compensation method for a soft rock tunnel according to claim 4, wherein, The compensating grout comprises, by weight, 100 parts silicate cement, 20-30 parts bentonite, 80-100 parts water, and 0.5-1 parts polycarboxylate superplasticizer.

6. The ground settlement compensation method for a soft rock tunnel according to claim 5, wherein, When the settlement rate of the surface settlement area corresponding to the excavation unit exceeds 0.5 mm / h for three consecutive times or the cumulative settlement value exceeds 70% of the design value, the steps of injecting compensation grout into the compensation channel and pressurizing it in stages to form the excavation section include: When the settlement rate of the surface settlement area corresponding to the excavation unit exceeds 0.5 mm / h for three consecutive times or the cumulative settlement value exceeds 70% of the design value, the compensation grout is injected into the compensation channel and initial pressurization is performed. The initial pressurization pressure value is P1, which lasts for 10 minutes, so that the compensation grout penetrates into the micro-cracks of the excavation unit; 0.1 MPa ≤ P1 ≤ 0.3 MPa; After the initial pressurization is completed, the compensation grout is injected again into the compensation channel and stable pressurization is performed. The stable pressurization pressure value is P2, which lasts for 30 minutes to offset the stress loss in the excavation unit; 0.3MPa≤P2≤0.8MPa; After the stabilization pressurization is completed, the compensation grout is injected into the compensation channel again and enhanced pressurization is performed. The pressure value of the enhanced pressurization is P3, until the settlement rate of the surface settlement area corresponding to the excavation unit is reduced to V, forming the excavation section; 0.8MPa≤P3≤1.5MPa, V<0.1mm / h.

7. The ground settlement compensation method for a soft rock tunnel according to claim 6, wherein, The steps for progressively backfilling and solidifying the surface settlement area corresponding to the excavation section to complete the surface settlement compensation of the soft rock tunnel include: When the distance between the excavation face of the soft rock tunnel and the compensation channel is D, clean the inner wall of the compensation channel and apply an interface agent; 50m≤D≤80m; The surface subsidence area corresponding to the excavation section is backfilled in three layers from bottom to top, forming a bottom backfill layer, a middle backfill layer, and a top backfill layer.

8. The ground settlement compensation method for a soft rock tunnel according to claim 7, wherein, The backfilling construction interval H2 between the bottom backfill layer, the middle backfill layer and the top backfill layer is 2h≤H2≤6h.

9. The ground settlement compensation method for a soft rock tunnel according to claim 8, wherein, The bottom backfill layer comprises, by weight, 100 parts rapid-hardening sulfoaluminate cement, 50 parts quartz sand, 1-2 parts early-strength agent, and 25-30 parts water; The intermediate backfill layer comprises, by weight, 100 parts ordinary Portland cement, 30 parts fly ash, 0.3 parts retarder, and 40-45 parts water; The top backfill layer comprises, by weight, 100 parts bentonite, 5 parts flexible latex powder, and 120-150 parts water.

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