A vertical reverse-slope fault tunnel portal safety construction system and method

Abstract

The application discloses a vertical reverse-slope fault tunnel portal safety construction system and method, and relates to the field of tunnel construction. The system comprises the following modules: an engineering geological model construction module for identifying fault structures and constructing a three-dimensional engineering geological model; an advanced geological prediction module for ascertaining fault influence width, fragmentation degree and groundwater occurrence conditions; a tunnel portal slope and slope body directional reinforcement system for establishing a three-dimensional reinforcement system for the slope, including high-position danger removal, slope surface protection, deep anchoring and slope toe locking; a low-disturbance excavation into a tunnel and advanced support system for implementing advanced support, short footage weak blasting excavation and initial support; a monitoring and measurement and dynamic feedback system for establishing a comprehensive monitoring system in combination with fault occurrence and fragmentation zone width and their spatial positional relationship with the tunnel portal, and for adjusting support parameters and excavation methods in real time according to monitoring data. The system can realize whole-process cooperation of geological accurate identification, multi-level directional reinforcement, low-disturbance excavation and dynamic monitoring and feedback.

Description

Technical Field

[0001] This invention relates to the field of tunnel entrance safety construction technology, and in particular to a system and method for safe construction of tunnel entrances with vertical reverse slope faults. Background Technology

[0002] With the continuous advancement of transportation infrastructure construction in my country, tunnel projects are increasingly extending into the high mountain and canyon areas of western China. In these regions, tunnel entrances often face the combined effects of multiple unfavorable factors, including steep slopes, deep valleys, and complex geological structures. Particularly when tunnel entrances are located in canyon areas with faults perpendicular to the slope direction, the fault zone exhibits fractured rock masses and well-developed structural surfaces. Furthermore, the fault dips in the opposite direction to the slope, making it highly susceptible to slope collapses and landslides at the tunnel entrance under the combined effects of river erosion, weathering, and excavation disturbances. This poses a serious threat to tunnel construction safety and long-term operational stability.

[0003] Currently, for tunnel portal slope protection and tunnel construction, existing technologies typically employ single or combined conventional methods, such as retaining walls, anti-slide piles, anchor (cable) frame beams, active / passive protection nets, and advanced pipe roof support. However, when facing the unique and complex engineering geological conditions of a vertical reverse slope towards the fault strike, existing technologies still have the following shortcomings: Insufficient precision and lack of systematic understanding in geological identification: Traditional engineering geological surveys often focus on macro-regional geological investigations or localized drilling verification, lacking refined identification methods for the spatial distribution, occurrence, properties, and spatial correlation of small and medium-sized fault structures at the kilometer to hundred-meter scale with respect to tunnel entrances (such as fault-controlled sharp bends in rivers, the relationship between fault undercuts and slope toes, etc.). Existing methods struggle to accurately distinguish between weathering unloading fractures and structural joints caused by fault structure failure, resulting in a lack of accurate geological model support for subsequent reinforcement designs, easily leading to problems such as deviations in reinforcement scope or inappropriate parameters.

[0004] The disconnect between advanced forecasting and dynamic feedback, coupled with low levels of information-based construction practices, leads to several problems. While existing advanced geological forecasting technologies are widely used, geophysical exploration and drilling methods often operate independently, with insufficient data fusion and analysis. This results in limited accuracy in detecting fault fracture zone width, water abundance, and groundwater conditions. Furthermore, monitoring data is primarily used for post-event warnings, failing to effectively establish a closed-loop control mechanism of "construction-monitoring-feedback-adjustment." This hinders the dynamic optimization of support parameters and excavation methods based on real-time deformation rates and stress states, resulting in delayed construction risk management.

[0005] The reinforcement measures lack specificity and multi-layered, three-dimensional coordination: For steep canyon slopes controlled by vertical reverse-slope faults, existing protection technologies are mostly general-purpose designs that do not fully consider the unique damage patterns of such slopes, characterized by "upper danger, middle fracturing, and lower erosion." There is a lack of systematic integration between measures such as removing loose rocks at the top of the slope, flexible slope protection, deep anchoring, and scour-resistant locking at the toe. Each reinforcement unit operates independently, failing to form a self-stabilizing reinforced body. Especially in water-rich fault zones on concave riverbanks, the synergistic effect of gabion mesh for lateral erosion prevention and large-diameter anti-slide piles for toe support has not been fully emphasized, resulting in insufficient guarantee of toe stability.

[0006] Excavation methods cause significant disturbance to the surrounding rock and have poor adaptability to geological conditions: In fault fracture zones and steep slopes, traditional excavation methods cause considerable disturbance to the surrounding rock, easily leading to secondary relaxation deformation. The selection of existing advanced support and excavation methods largely relies on experience-based judgment, lacking differentiated, low-disturbance tunneling technology solutions based on refined geological models and advanced forecasting results. This is especially true in steep canyon slopes without working platforms, where specialized tunneling methods such as inclined shaft entry or transverse tunnel return access have not yet formed standardized integrated procedures.

[0007] In summary, current technologies lack a systematic and integrated safety protection and construction method for steep tunnel entrances in canyon areas with vertical reverse slope faults. There is an urgent need to develop a technical system capable of coordinating the entire process, from precise geological identification and multi-level directional reinforcement to low-disturbance excavation and dynamic monitoring feedback, to solve the problem of tunnel entrance collapse protection under such special geological conditions and ensure project safety and quality. Summary of the Invention

[0008] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a safe construction system for vertical reverse-slope fault tunnel entrances, which can achieve full-process coordination of accurate geological identification, multi-level directional reinforcement, low-disturbance excavation, and dynamic monitoring feedback.

[0009] This invention also proposes a safe construction method for tunnel entrances to vertical reverse slope faults.

[0010] A safe construction system for vertical reverse-slope fault tunnel entrances according to a first aspect of the present invention includes: The engineering geological model construction module is used to construct a three-dimensional engineering geological model that includes the combined relationship between faults, river channels, and tunnel entrance slopes, based on the spatial distribution, occurrence, nature, and scale of fault structures identified by engineering geological mapping and their spatial correlation with tunnel entrances. The advanced geological prediction module is used to determine the fault width, degree of fragmentation, and groundwater occurrence based on the engineering geological model by using a combination of transient electromagnetic, ground-penetrating radar, and advanced horizontal drilling technologies. The tunnel entrance slope and slope directional reinforcement system is used to establish a multi-layered three-dimensional reinforcement system for steep slopes, including high-level hazard removal, slope protection, deep anchoring and slope toe locking. The low-disturbance excavation and advanced support system is used to implement advanced support, short-cut weak blasting excavation and initial support after the prediction results of the advanced geological prediction module and the reinforcement of the directional reinforcement system are completed. The monitoring and dynamic feedback system is used to establish a comprehensive monitoring system for surface displacement, deep hole displacement, tunnel settlement and convergence, and steel arch contact stress by combining fault attitude and fracture zone width and their spatial relationship with the tunnel entrance. The system provides real-time feedback based on the monitoring data to adjust support parameters and excavation methods, forming a closed-loop control of construction-monitoring-feedback-adjustment.

[0011] In some embodiments, in the engineering geological model construction module, the scale of the engineering geological survey is 1:500 to 1:2000, and the survey range is 500 to 1000 meters around the tunnel entrance.

[0012] In some embodiments, in the advanced geological prediction module, the electrode spacing of the transient electromagnetic field is 5 to 10 meters, and the drilling depth of the advanced horizontal drill is 30 to 50 meters.

[0013] In some embodiments, the portal slope and slope directional reinforcement system includes: The high-level hazard removal unit is used for the manual removal of dangerous rocks at the top of steep slopes and on the upper part of the slope. The slope toe locking unit is used to lay gabion mesh on the concave bank of the river to prevent lateral erosion by river water, and to install anti-sliding piles on the outside of the tunnel near the riverbank for support and toe locking. The slope protection unit is used to set up an active protective net to cover the slope in the middle and upper part of the tunnel entrance slope, and to close the slope with the help of the hanging net and shotcrete anchor. It also sets up a passive protective net to intercept falling rocks for tunnel entrances with high risk of rockfall. The deep anchoring unit is used to install circumferential uphill anchor cables and vertical high-strength prestressed steel cables at the lower part of the tunnel entrance slope to form a cross-arranged anchoring system.

[0014] In some embodiments, the slope toe locking unit also includes a double-pipe jet grouting pile forming a water-stop curtain in the water-rich fault zone on the concave bank of the river.

[0015] In some embodiments, in the deep anchoring unit, the anchor cable anchoring adopts secondary high-pressure grouting, the secondary high-pressure grouting pressure is not less than 2.0 MPa, and the anchor cable tension locking value is 60% to 75% of the ultimate bearing capacity.

[0016] In some embodiments, the low-disturbance excavation and advance support system includes: Advanced support units are used to perform advanced large pipe shed or double-layer small pipe grouting before entering the tunnel. For extremely broken geological bodies, surface drilling grouting and tunnel secondary splitting grouting are used for comprehensive reinforcement. For water-rich fault zones, full-section curtain grouting is used for water plugging and reinforcement. Excavation unit is used to carry out short-foot, weak-blasting excavation by employing the three-stage temporary horizontal bracing method or the ring excavation method with reserved core soil. The initial support unit is used to immediately implement the combined support of anchor mesh and shotcrete with steel arch frame after excavation and pour concrete to form a pipe roof structure.

[0017] In some embodiments, the monitoring and dynamic feedback system collects data 3 to 5 times a day during peak construction periods, 1 to 2 times a day during normal construction periods, and once a week after the tunnel has stabilized. The threshold for dynamic feedback is determined based on the ratio of the reserved deformation amount to the deformation rate at the tunnel entrance, with the reserved deformation amount being 120 to 150 mm and the deformation rate ratio being 0.05.

[0018] A safe construction method for a vertical reverse-slope fault tunnel entrance according to a second aspect of the present invention includes the following steps: S1. Geological Identification: Through engineering geological mapping, identify the spatial distribution, occurrence, nature and scale of fault structures and their spatial relationship with tunnel entrances, and construct a three-dimensional engineering geological model that includes the combined relationship of faults, river channels and tunnel entrance slopes. S2. Advanced geological prediction: Using a comprehensive prediction technology that combines transient electromagnetic, ground-penetrating radar and advanced horizontal drilling, the width of fault influence, degree of fragmentation and groundwater occurrence are determined. S3. Directional reinforcement of tunnel entrance slope and slope body: Multi-level three-dimensional reinforcement of steep slopes, including high-level hazard removal, slope protection, deep anchoring and slope toe locking; S4. Low-disturbance excavation and tunnel entry: After advanced geological forecasting and directional reinforcement are completed, advanced support, short-foot weak blasting excavation and initial support are implemented. S5. Monitoring and Dynamic Feedback: Combining the fault attitude and fracture zone width and their spatial relationship with the tunnel entrance, establish a comprehensive monitoring system for surface displacement, deep hole displacement, tunnel settlement and convergence, and steel arch contact stress. Adjust support parameters and excavation methods in real time based on monitoring data to form a closed-loop control of construction-monitoring-feedback-adjustment.

[0019] The present invention has at least the following beneficial effects: The safe construction method for vertical reverse-slope fault tunnel entrances according to embodiments of the present invention, through the organic combination of geological identification and advanced prediction, can determine the spatial distribution, occurrence, and groundwater occurrence of fault structures in advance, providing accurate geological basis for subsequent construction; through multi-layered three-dimensional protection of the tunnel entrance slope and slope body directional reinforcement, the stability of steep slopes is effectively improved, reducing the risk of landslides during tunnel entry construction; through low-disturbance excavation and timely follow-up of initial support, the exposure time and disturbance range of surrounding rock are reduced, ensuring the construction safety of the tunnel entrance section; through closed-loop control of monitoring measurement and dynamic feedback, the stress and deformation state of the surrounding rock and support structure can be grasped in real time, and construction parameters can be adjusted in a timely manner, thereby effectively avoiding engineering risks caused by sudden changes in geological conditions.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a safe construction system for a vertical reverse slope fault tunnel entrance according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a tunnel entrance slope and slope directional reinforcement system according to an embodiment of the present invention; Figure 3 This is a flowchart of a safe construction method for a vertical reverse slope fault tunnel entrance according to an embodiment of the present invention. Detailed Implementation

[0023] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0024] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. Additionally, examples of various specific processes and materials are provided in this invention; however, those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0025] Below, refer to Figure 1 A safety construction system for a vertical reverse-slope fault tunnel entrance according to an embodiment of the first aspect of the present invention is described, comprising: The engineering geological model construction module is used to construct a three-dimensional engineering geological model that includes the combined relationship between faults, river channels, and tunnel entrance slopes, based on the spatial distribution, occurrence, nature, and scale of fault structures identified by engineering geological mapping and their spatial correlation with tunnel entrances. The advanced geological prediction module is used to determine the fault width, degree of fragmentation, and groundwater occurrence based on the engineering geological model by using a combination of transient electromagnetic, ground-penetrating radar, and advanced horizontal drilling technologies. The tunnel entrance slope and slope directional reinforcement system is used to establish a multi-layered three-dimensional reinforcement system for steep slopes, including high-level hazard removal, slope protection, deep anchoring and slope toe locking. The low-disturbance excavation and advanced support system is used to implement advanced support, short-cut weak blasting excavation and initial support after the prediction results of the advanced geological prediction module and the reinforcement of the directional reinforcement system are completed. The monitoring and dynamic feedback system is used to establish a comprehensive monitoring system for surface displacement, deep hole displacement, tunnel settlement and convergence, and steel arch contact stress by combining fault attitude and fracture zone width and their spatial relationship with the tunnel entrance. The system provides real-time feedback based on the monitoring data to adjust support parameters and excavation methods, forming a closed-loop control of construction-monitoring-feedback-adjustment.

[0026] For example, the engineering geological model building module includes: The fault structure interpretation unit is used to interpret the width, dip, dip angle and the angle with the tunnel axis of the fault fracture zone based on the results of surface geological mapping, drilling and geophysical exploration, and to delineate the range of the fault influence zone accordingly. The river channel correlation analysis unit is used to analyze the river channel direction, cutting depth and spatial intersection with faults, and to assess the hydraulic recharge of the river channel to the fault fracture zone and its potential impact on the stability of the tunnel entrance slope. The tunnel entrance slope stability coupling analysis unit is used to couple the fault structure interpretation results with the river channel correlation analysis results to construct a three-in-one stability coupling analysis model of fault-river-slope, evaluate the instability mode and risk level of the tunnel entrance slope under different working conditions, and determine the key areas and priorities for tunnel entrance slope reinforcement accordingly.

[0027] The engineering geological model construction module uses AutoCAD and 3D MAX to construct engineering geological models composed of faults, river channels, and tunnel entrance slopes, which guides the selection of advanced geological prediction technologies and methods and provides a basis for slope toe reinforcement strength and curtain grouting depth.

[0028] In some embodiments, the engineering geological model construction module uses an engineering geological mapping scale of 1:500 to 1:2000, with a mapping range of 500 to 1000 meters around the tunnel entrance. This allows for a precise depiction of the spatial distribution of the fault fracture zone and its geometric relationship with the tunnel entrance slope and river channel, providing high-precision geometric boundary conditions for subsequent numerical simulations and stability analyses.

[0029] For example, the advanced geological prediction module includes: The fault zone integrated detection unit is used to lay transient electromagnetic survey lines and ground-penetrating radar survey lines along the tunnel axis at the tunnel entrance. Combined with the core sampling verification of advanced horizontal drilling, it comprehensively determines the width of the fault fracture zone, the nature of the filling material, the degree of cementation and the water-rich section, and classifies the advanced prediction level accordingly, and determines the prediction accuracy requirements and detection spacing for different sections. The groundwater occurrence status assessment unit is used to comprehensively determine the groundwater occurrence status, water pressure, and hydraulic connection with surface water bodies based on transient electromagnetic apparent resistivity anomaly zones, ground-penetrating radar reflection wave group characteristics, and drilling water inflow conditions. Based on this, high-risk sections for water and mud inrush are delineated, providing a basis for subsequent drainage and grouting reinforcement schemes.

[0030] In some embodiments, in the advanced geological prediction module, the electrode spacing of the transient electromagnetic field is 5–10 meters, and the drilling depth of the advanced horizontal drill is 30–50 meters. This enables the detection of water-bearing structures and water-rich sections within fault fracture zones with high spatial resolution. Simultaneously, combined with a high-frequency ground-penetrating radar antenna for fine scanning of shallow fracture zones, a multi-layered detection system from deep to shallow and from far to near is formed. This achieves a three-dimensional and accurate depiction of the spatial distribution and water-bearing properties of fault fracture zones, effectively reducing the risk of missed or misjudged predictions in advanced geological forecasting.

[0031] In some embodiments, refer to Figure 2 The tunnel entrance slope and slope directional reinforcement system includes: The high-level hazard removal unit is used to manually remove dangerous rocks from the top and upper part of steep slopes to prevent them from suddenly rolling or collapsing and affecting the safety of construction personnel and machinery.

[0032] The slope toe locking unit is used to deploy gabion mesh on the concave bank of a river to prevent lateral erosion by river water, and to install anti-slide piles near the riverbank outside the tunnel entrance for support and toe locking. Specifically, gabion mesh is a flexible structure formed by galvanized steel wire mesh boxes filled with stones. It is suitable for slope toe erosion protection. During construction, the river is first diverted and the foundation is excavated, then geotextile is laid, gabion mesh is installed, stones are filled, and the boxes are sealed and connected. It must be placed on a stable foundation, and the filling stones should be firm and weather-resistant. Adjacent mesh boxes are firmly tied together to form a whole. The anti-slide piles are large-diameter bored cast-in-place piles, arranged in single or double rows near the riverbank outside the tunnel entrance, with the pile ends embedded into stable bedrock to a certain depth.

[0033] In some embodiments, the slope toe locking unit is further equipped with double-pipe jet grouting piles to form a water-stop curtain in the water-rich fault zone on the concave bank of the river. This effectively cuts off the seepage path of groundwater in the fault zone towards the tunnel entrance, reduces the water pressure and softening degree of the rock mass at the slope toe, thereby enhancing the overall stability of the rock mass at the slope toe and preventing slope toe instability and landslides caused by increased water pressure or weakened rock mass strength. At the same time, the water-stop curtain works in synergy with the anti-slide piles and gabion mesh to form a three-in-one slope toe protection system of "scour prevention - support - water interception", comprehensively improving the long-term stability of the tunnel entrance slope under complex hydrogeological conditions.

[0034] The slope protection unit is used to cover the upper part of the slope at the tunnel entrance with an active protective net, which, together with the netting and shotcrete, seals the slope. For tunnel entrances with a high risk of rockfall, a passive protective net is used to intercept falling rocks. The active protective net uses a high-strength, flexible steel wire rope net to cover the slope and is fixed with anchor bolts to limit weathering and erosion of the soil and rock. During construction, the slope is first cleaned, then holes are drilled and grouted to install anchor bolts. Next, support ropes are tensioned, the steel wire rope net is laid, and secured with stitching ropes. The anchor bolts are anchored into the rock to a depth of not less than 60 cm. The steel wire rope net must be tensioned tightly against the slope, and the steel wire rope is hot-dip galvanized for corrosion protection. The passive protective net is laid along contour lines at appropriate locations on the upper part of the tunnel entrance slope. An RXI series ring net is used to intercept falling rocks from higher elevations. During construction, the steel column foundation is first poured, then the anchor ropes are fixed. Subsequently, pressure-reducing rings are precisely installed, and the ring net is spliced ​​and adjusted. The installation direction of the pressure-reducing rings is specified. The tension is the core control point. The foundation must be laid along contour lines and avoid large topographical undulations. It is suitable for steep slopes with serious rockfalls. The mesh-and-shotcrete combination is for weathered, fractured, and jointed rock slopes. Through the combined action of anchor bolts, steel mesh, and shotcrete, a composite protective layer with both flexibility and rigid constraint is formed on the slope. During construction, the slope is first trimmed and loose soil and rocks are removed. Then, holes are drilled according to the design, anchor bolts are installed, and 1:3 cement mortar is injected for consolidation. Then, steel mesh is hung and welded firmly to the anchor bolt heads to ensure close contact with the slope. Then, shotcrete is sprayed in layers. The initial spray thickness is not less than 5 cm, and the total thickness after the second spray is not less than 12 cm. Drainage holes are reserved to prevent groundwater blockage. During the curing period, the sprayed layer is kept moist to avoid early cracking. Subsequent construction procedures can only be carried out after the concrete reaches the design strength. The length and diameter of the anchor bolts are determined based on the thickness of the fractured layer. The anchor bolts are spaced in a 1.5m x 1.5m staggered pattern. The angle between the anchor bolts and the horizontal plane is controlled between 15° and 20° to enhance the anchoring effect. The exposed ends of the anchor bolts are equipped with hooks or pads and welded to the steel mesh to form an integral load-bearing system, ensuring that the shotcrete layer and the slope rock mass deform in tandem and improving the overall support rigidity.

[0035] Deep anchoring units are used to install circumferential uphill anchors and vertical high-strength prestressed steel cables at the lower part of the tunnel entrance slope, forming a cross-arranged anchoring system. The circumferential uphill anchors are laid out along the contour lines of the slope, anchoring the unstable block to deep, stable rock mass. The anchor angle is determined based on the rock strata's attitude. The anchoring section must penetrate the potential sliding surface into the stable rock strata by at least 4 meters. The anchoring section adopts a pressure-dispersing structure, dispersing stress through multiple independent anchoring units to avoid stress concentration leading to anchoring failure. Before construction, underground pipelines and other obstacles must be identified. The slope should be leveled according to the principle of "one level of excavation, one level of protection," and loose soil and loose rocks should be removed. Depressions should be backfilled with concrete of at least C20 grade. Subsequently, surveying and layout should be conducted to accurately mark the hole positions, with a positional error not exceeding ±50mm. After the drilling rig is in place, the drilling inclination and azimuth angles must be strictly controlled, with an inclination error not exceeding ±1° and an azimuth error not exceeding ±2°. The hole depth should not be less than the design value and should be over-drilled by 20-50cm. The bottom deviation should not exceed 3% of the length. After drilling, the hole must be cleaned with high-pressure air, and anchor bolt installation and grouting must be completed within 24 hours to prevent hole collapse. The anchor bolts must be straight, free of rust, and must not be welded. During installation, they should be pushed into the hole at a uniform speed. If resistance is encountered, the hole must be re-drilled and cleaned; forced penetration is strictly prohibited. Anchor hole grouting is the core step in anchor cable construction. The normal pressure grouting pressure is controlled at 0.2–0.4 MPa. After thick grout overflows from the borehole, a second high-pressure grouting is performed at a pressure of no less than 2.0 MPa to fully fill the fissures within the borehole, ensuring a tight bond between the grout and the borehole wall rock mass, forming a complete anchoring force transmission system. The water-cement ratio of the grout should be 0.4–0.5, and the cement-sand ratio 1:1–1:2. The grout filling coefficient should be 1.1–1.3. After grouting, tensioning and locking can only be carried out after the grout strength reaches at least 80% of the design value. Tensioning and locking are performed in 3–5 stages, with each stage held for at least 5 minutes. The locking value is taken as 60%–75% of the anchor cable's ultimate bearing capacity. After tensioning, excess steel strands are cut off, the anchor head is treated with anti-corrosion sealing, and permanent markings are installed for later monitoring.

[0036] In some embodiments, the deep anchoring unit employs secondary high-pressure grouting for anchor cable anchoring. The secondary high-pressure grouting pressure is not less than 2.0 MPa, and the anchor cable tensioning lock value is 60% to 75% of the ultimate bearing capacity. This ensures that the secondary high-pressure grouting fully fills the surrounding rock fissures, significantly improving the bond strength between the anchor body and the borehole wall, thus guaranteeing reliable transmission of anchoring force. Through staged tensioning and a reasonable lock value setting, prestress is effectively applied while avoiding anchor cable loosening or rock mass damage due to over-tensioning, thereby ensuring the stability and durability of the anchoring system during long-term operation.

[0037] In some embodiments, the low-disturbance excavation and advance support system includes: The advanced support unit is used to perform advanced large pipe roof or double-layer small pipe grouting before entering the tunnel. For extremely fractured geological bodies, a combination of surface drilling grouting and tunnel secondary splitting grouting is used for comprehensive reinforcement. For water-rich fault zones, full-section curtain grouting is used for water plugging reinforcement. The advanced large pipe roof uses hot-rolled seamless steel pipes with a circumferential spacing of 30~40cm, an external insertion angle of 1°~3°, and the length of the pipe roof is determined in combination with the geological conditions.

[0038] The excavation unit is used to carry out short-advance, weak-blasting excavation using the three-stage temporary cross bracing method or the ring excavation method with reserved core soil. When using the stage method, the advance of the upper stage is controlled at the spacing of 1 to 2 steel arch frames per cycle, while the middle and lower stages can be appropriately increased but not exceeding 3 frames. When using the core soil method, the width of the core soil should be 1 / 3 to 1 / 2 of the tunnel excavation width, and the height should not be less than 2.5m to maintain the stability of the tunnel face.

[0039] The initial support unit is used immediately after excavation to implement combined support of anchor mesh, shotcrete, and steel arch frames, followed by concrete pouring to form a pipe roof structure. The initial support employs a wet shotcrete process, with the shotcrete strength grade not lower than C25. The initial shotcrete thickness is controlled at 3-5 cm, followed by re-shotcrete to the designed thickness. The steel arch frames are made of fabricated steel sections, with longitudinal spacing matching the excavation cycle advance. Longitudinal connecting bars are installed between the arch frames and firmly welded to the anchor pipes to form an integral load-bearing skeleton.

[0040] In some embodiments, the monitoring and dynamic feedback system collects data at the following frequencies: 3-5 times per day during peak construction periods, 1-2 times per day during normal construction periods, and once per week after the tunnel has stabilized. The dynamic feedback threshold is determined based on the ratio of the reserved deformation amount to the deformation rate at the tunnel entrance, with the reserved deformation amount being 120-150 mm and the deformation rate ratio being 0.05. Thus, through high-frequency, multi-level monitoring data collection, subtle changes in the deformation of the surrounding rock and the stress state of the support structure can be captured in a timely manner, providing reliable data support for dynamic control.

[0041] Reference Figure 3 According to a second aspect of the present invention, a safe construction method for a vertical reverse-slope fault tunnel entrance includes the following steps: S1. Geological Identification: Through engineering geological mapping, identify the spatial distribution, occurrence, nature and scale of fault structures and their spatial relationship with tunnel entrances, and construct a three-dimensional engineering geological model that includes the combined relationship of faults, river channels and tunnel entrance slopes. S2. Advanced geological prediction: Using a comprehensive prediction technology that combines transient electromagnetic, ground-penetrating radar and advanced horizontal drilling, the width of fault influence, degree of fragmentation and groundwater occurrence are determined. S3. Directional reinforcement of tunnel entrance slope and slope body: Multi-level three-dimensional reinforcement of steep slopes, including high-level hazard removal, slope protection, deep anchoring and slope toe locking; S4. Low-disturbance excavation and tunnel entry: After advanced geological forecasting and directional reinforcement are completed, advanced support, short-foot weak blasting excavation and initial support are implemented. S5. Monitoring and Dynamic Feedback: Combining the fault attitude and fracture zone width and their spatial relationship with the tunnel entrance, establish a comprehensive monitoring system for surface displacement, deep hole displacement, tunnel settlement and convergence, and steel arch contact stress. Adjust support parameters and excavation methods in real time based on monitoring data to form a closed-loop control of construction-monitoring-feedback-adjustment.

[0042] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0043] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A safe construction system for vertical reverse slope fault tunnel entrances, characterized in that, include: The engineering geological model construction module is used to construct a three-dimensional engineering geological model that includes the combined relationship between faults, river channels, and tunnel entrance slopes, based on the spatial distribution, occurrence, nature, and scale of fault structures identified by engineering geological mapping and their spatial correlation with tunnel entrances. The advanced geological prediction module is used to determine the fault width, degree of fragmentation, and groundwater occurrence based on the engineering geological model by using a combination of transient electromagnetic, ground-penetrating radar, and advanced horizontal drilling technologies. The tunnel entrance slope and slope directional reinforcement system is used to establish a multi-layered three-dimensional reinforcement system for steep slopes, including high-level hazard removal, slope protection, deep anchoring and slope toe locking. The low-disturbance excavation and advanced support system is used to implement advanced support, short-cut weak blasting excavation and initial support after the prediction results of the advanced geological prediction module and the reinforcement of the directional reinforcement system are completed. The monitoring and dynamic feedback system is used to establish a comprehensive monitoring system for surface displacement, deep hole displacement, tunnel settlement and convergence, and steel arch contact stress by combining fault attitude and fracture zone width and their spatial relationship with the tunnel entrance. The system provides real-time feedback based on the monitoring data to adjust support parameters and excavation methods, forming a closed-loop control of construction-monitoring-feedback-adjustment.

2. The safe construction system for vertical reverse slope fault tunnel entrances according to claim 1, characterized in that, In the engineering geological model construction module, the scale of the engineering geological survey is 1:500 to 1:2000, and the survey range is 500 to 1000 meters around the tunnel entrance.

3. The safe construction system for vertical reverse slope fault tunnel entrances according to claim 1, characterized in that, In the advanced geological prediction module, the electrode spacing of the transient electromagnetic system is 5 to 10 meters, and the drilling depth of the advanced horizontal drill is 30 to 50 meters.

4. The safe construction system for vertical reverse slope fault tunnel entrances according to claim 1, characterized in that, The tunnel entrance slope and slope directional reinforcement system includes: The high-level hazard removal unit is used for the manual removal of dangerous rocks at the top of steep slopes and on the upper part of the slope. The slope toe locking unit is used to lay gabion mesh on the concave bank of the river to prevent lateral erosion by river water, and to install anti-sliding piles on the outside of the tunnel near the riverbank for support and toe locking. The slope protection unit is used to set up an active protective net to cover the slope in the middle and upper part of the tunnel entrance slope, and to close the slope with the help of the hanging net and shotcrete anchor. It also sets up a passive protective net to intercept falling rocks for tunnel entrances with high risk of rockfall. The deep anchoring unit is used to install circumferential uphill anchor cables and vertical high-strength prestressed steel cables at the lower part of the tunnel entrance slope to form a cross-arranged anchoring system.

5. The safe construction system for vertical reverse slope fault tunnel entrances according to claim 4, characterized in that, In the slope toe locking unit, double-pipe jet grouting piles are also installed in the water-rich fault zone on the concave bank of the river to form a water-stop curtain.

6. The safe construction system for vertical reverse slope fault tunnel entrances according to claim 4, characterized in that, In the deep anchoring unit, the anchor cable anchoring adopts secondary high-pressure grouting, the secondary high-pressure grouting pressure is not less than 2.0MPa, and the anchor cable tension locking value is 60% to 75% of the ultimate bearing capacity.

7. The safety construction system for vertical reverse slope fault tunnel entrances according to claim 1, characterized in that, The low-disturbance excavation and pre-support system includes: Advanced support units are used to perform advanced large pipe shed or double-layer small pipe grouting before entering the tunnel. For extremely broken geological bodies, surface drilling grouting and tunnel secondary splitting grouting are used for comprehensive reinforcement. For water-rich fault zones, full-section curtain grouting is used for water plugging and reinforcement. Excavation unit is used to carry out short-foot, weak-blasting excavation by employing the three-stage temporary horizontal bracing method or the ring excavation method with reserved core soil. The initial support unit is used to immediately implement the combined support of anchor mesh and shotcrete with steel arch frame after excavation and pour concrete to form a pipe roof structure.

8. The safety construction system for vertical reverse slope fault tunnel entrances according to claim 1, characterized in that, In the monitoring and dynamic feedback system, the monitoring data collection frequency is: 3 to 5 times a day during the peak construction period, 1 to 2 times a day during the normal construction period, and once a week after the tunnel has entered a stable state; the threshold for dynamic feedback is determined based on the ratio of the reserved deformation amount and the deformation rate at the tunnel entrance, with the reserved deformation amount being 120 to 150 mm and the deformation rate ratio being 0.

05.

9. A safe construction method for a vertical reverse slope tunnel entrance, characterized in that, Includes the following steps: S1. Geological Identification: Through engineering geological mapping, identify the spatial distribution, occurrence, nature and scale of fault structures and their spatial relationship with tunnel entrances, and construct a three-dimensional engineering geological model that includes the combined relationship of faults, river channels and tunnel entrance slopes. S2. Advanced geological prediction: Using a comprehensive prediction technology that combines transient electromagnetic, ground-penetrating radar and advanced horizontal drilling, the width of fault influence, degree of fragmentation and groundwater occurrence are determined. S3. Directional reinforcement of tunnel entrance slope and slope body: Multi-level three-dimensional reinforcement of steep slopes, including high-level hazard removal, slope protection, deep anchoring and slope toe locking; S4. Low-disturbance excavation and tunnel entry: After advanced geological forecasting and directional reinforcement are completed, advanced support, short-foot weak blasting excavation and initial support are implemented. S5. Monitoring and Dynamic Feedback: Combining the fault attitude and fracture zone width and their spatial relationship with the tunnel entrance, establish a comprehensive monitoring system for surface displacement, deep hole displacement, tunnel settlement and convergence, and steel arch contact stress. Adjust support parameters and excavation methods in real time based on monitoring data to form a closed-loop control of construction-monitoring-feedback-adjustment.

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