A construction method for a tunnel portal section through a traction-type landslide body

Abstract

The application relates to the technical field of tunnels, and provides a tunnel portal section construction method through a pulling type landslide body, which comprises the following steps: constructing a first reinforcing component, a second reinforcing component, a third reinforcing component and a fourth reinforcing component at a tunnel portal section to be constructed, constructing an intermediate cross support component and an inclined support component at a landslide main influence open tunnel section, constructing an open tunnel lining structure of the landslide main influence open tunnel section, and constructing a bias retaining wall outside the open tunnel lining structure; backfilling soil from the outer contour of the open tunnel lining structure to the top of the first reinforcing component and the top of the second reinforcing component; vertically excavating at an open-dark interface; adopting anchor net spraying support for the interface; constructing a sleeve arch between the two third reinforcing components; constructing an advanced pipe shed by using the sleeve arch; and excavating the landslide main influence dark tunnel section and the landslide secondary influence dark tunnel section. The application breaks the conventional construction idea, does not need large excavation, realizes safe passing of the tunnel portal section through the pulling type landslide body, is high in convenience, and is controllable in construction.

Description

Technical Field

[0001] This invention relates to the field of tunnel technology, and in particular to a method for constructing a tunnel portal section using a traction-type landslide. Background Technology

[0002] Landslides are generally classified into traction landslides and push-moving landslides based on their formation mechanism. In traction landslides, the front of the slope bottom is exposed due to excavation or erosion, leading to unloading and relaxation of the slope body, weakening its mechanical properties, and gradually developing upwards. Especially when encountering large landslide sections, the affected area of ​​the landslide body is large, and how to ensure the safe passage of tunnel entrance sections through traction landslide bodies has become an urgent problem to be solved.

[0003] There are three main existing methods for constructing tunnels through traction-type landslides:

[0004] First, the large-scale excavation of the traction-type landslide body turns the tunnel into a road cut. The treatment plan of large-scale excavation of the tunnel is too much of a change to the existing natural environment, which is not environmentally friendly. Moreover, in the later operation stage of the large-scale excavation, as the road cut slope is exposed, it is subject to erosion and infiltration by rainwater, and the landslide surface is prone to develop into deeper layers, which seriously threatens the operational safety of the existing road.

[0005] Secondly, the tunnel is used to reinforce and improve the landslide body through the tunnel crossing and the anti-slide pile reinforcement. By reinforcing and improving the landslide body, the soil mechanical parameters are enhanced. The tunnel is a tunnel crossing, which requires high grouting technology during construction. The tunnel construction method is complicated, costly and has extremely high construction risks. In addition, the tunnel structure is prone to cracking and water leakage in the later operation stage.

[0006] Thirdly, a combined construction method of anti-slide piles and open-cut excavation is adopted. However, the existing anti-slide pile + open-cut method requires large-sized anti-slide piles and generally uses manual excavation techniques, which carries extremely high risks when constructing within the landslide body. Due to terrain conditions, conventional anti-slide piles used as retaining structures are often large in size, making mechanical construction impossible and resulting in poor construction convenience.

[0007] In view of this, it is necessary to propose a construction method for the tunnel portal section using a traction-type landslide body to solve or at least alleviate the above-mentioned defects. Summary of the Invention

[0008] The main objective of this invention is to provide a construction method for tunnel portal sections using traction-type landslide bodies, in order to solve the technical problems of high construction risk and low convenience in existing tunnel portal section traction-type landslide body schemes.

[0009] To achieve the above objectives, the present invention provides a method for constructing a tunnel portal section using a traction-type landslide, comprising the following steps:

[0010] S1. Based on the positional relationship between the proposed tunnel portal section and the landslide body and the extent of the landslide, the tunnel portal section is determined to include the landslide-affected open tunnel section, the landslide-affected closed tunnel section, and the landslide-affected secondary closed tunnel section, which are connected in sequence.

[0011] S2, a first reinforcement component and a second reinforcement component are respectively installed on both sides of the main affected open tunnel section of the landslide, a third reinforcement component is respectively installed on both sides of the main affected dark tunnel section of the landslide, and a fourth reinforcement component is respectively installed on both sides of the secondary affected dark tunnel section of the landslide.

[0012] S3, excavation of the section of the tunnel mainly affected by the landslide;

[0013] S4. Vertical excavation is carried out at the interface between the main impact open tunnel section and the main impact dark tunnel section of the landslide. Anchor mesh spraying support is used for the interface. Then, a sleeve arch is constructed between the two third reinforcement components, and then the sleeve arch is used to construct the advanced pipe roof.

[0014] S5, excavation of the main tunnel section affected by the landslide;

[0015] S6, excavation of the section of the tunnel affected by the landslide.

[0016] Preferably, step S3 specifically includes the following steps:

[0017] S31, remove the landslide body within the tunnel section mainly affected by the landslide, and construct intermediate cross bracing components and diagonal bracing components in the tunnel section mainly affected by the landslide; wherein, the intermediate cross bracing components are located above the tunnel outline, the intermediate cross bracing components are connected between the first reinforcement component and the second reinforcement component, the diagonal bracing components are located on the back side of the tunnel section mainly affected by the landslide, and the diagonal bracing components are supported on the outside of the second reinforcement component;

[0018] S32, construct the tunnel lining structure for the tunnel section mainly affected by the landslide and construct an eccentric retaining wall on the outside of the tunnel lining structure, and then backfill the gap between the eccentric retaining wall and the second reinforcement component.

[0019] S33, backfill soil is used to backfill from the outer contour of the tunnel lining structure to the top of the first reinforcement component and the top of the second reinforcement component.

[0020] Preferably, step S5 specifically includes the following steps:

[0021] S51, first, grouting reinforcement is carried out on the surface of the back side of the tunnel section mainly affected by the landslide;

[0022] S52, in each cycle of advance, the arch wall area is first excavated using the pre-reserved core soil bench method, specifically including:

[0023] S521: First, excavate the first upper bench, then construct the initial support for the first upper bench, and then excavate the reserved core soil for the first upper bench.

[0024] S522, Construct the first temporary invert arch at the junction of the first upper step and the first lower step; wherein, the two ends of the first temporary invert arch are respectively connected to the initial support of the first upper step;

[0025] S523, after the first upper step is excavated to a certain distance, the first lower step is excavated, the initial support of the first lower step is then constructed, and the core soil reserved for the first lower step is then excavated.

[0026] S53, after the second distance of the first lower step is excavated, the first invert arch area is excavated, and then the initial support of the first invert arch and the first invert arch filling layer are constructed in sequence.

[0027] S54, Perform secondary lining of the arch wall corresponding to the current cycle advance.

[0028] Preferably, step S6 specifically includes the following steps:

[0029] S61, first perform radial grouting reinforcement on the mountainside outside the outline of the secondary impact tunnel section of the landslide;

[0030] S62, in each cycle of advance, the arch wall area is first excavated using the pre-reserved core soil bench method, specifically including:

[0031] S621, first excavate the second upper bench, then construct the initial support for the second upper bench, and then excavate the reserved core soil for the second upper bench;

[0032] S622, Construct a second temporary invert at the junction of the second upper step and the second lower step; wherein, the two ends of the second temporary invert are respectively connected to the initial support of the second upper step;

[0033] S623, after the second upper step is excavated to a third distance, the second lower step is excavated, the initial support of the second lower step is then constructed, and the core soil reserved for the second lower step is then excavated.

[0034] S63, after the fourth distance of the second lower step excavation, the second invert arch area is excavated, and then the initial support of the second invert arch and the filling layer of the second invert arch are constructed in sequence.

[0035] S64, Perform secondary lining of the arch wall corresponding to the current cycle advance.

[0036] Preferably, the lining structure of the open-cut tunnel in step S32 is obtained through the following design steps:

[0037] S321, Select the first reinforcement component of the tunnel section mainly affected by the landslide as the object, determine the lowest position of the tunnel lining structure, simplify the connection between the first reinforcement component and the soil corresponding to the lowest position as a fixed support, simplify the connection between the first reinforcement component and the intermediate cross brace component as a first hinge support, simplify the adjacent part of the first reinforcement component and the tunnel lining structure as a second hinge support, and apply the remaining sliding force P of the landslide body to the first reinforcement component;

[0038] S322, the lateral pressure F2 on the second hinge support is calculated using the formula Ph0≤K(F1h1+F2h2), where h0 is the vertical distance from the point where the remaining sliding force P acts to the fixed support, K ​​is the safety factor of the landslide, F1 is the axial force of the cross brace of the first hinge support, h1 is the vertical distance from the intermediate cross brace assembly to the fixed support, and h2 is the vertical distance from the second hinge support to the fixed support.

[0039] S323, simplify the lateral pressure F2 as a uniformly distributed load acting on the tunnel lining structure, calculate the lateral uniformly distributed pressure on the second hinge support, and then calculate the backfill pressure on the upper part of the tunnel lining structure.

[0040] S324. Using the finite element method, the connection between the perimeter of the tunnel lining structure and the soil is simplified to only the compressed foundation spring, and the internal forces on the tunnel lining structure are calculated.

[0041] S325 uses the comprehensive safety factor method to verify the bearing capacity and reinforcement of the tunnel lining structure, thereby obtaining the design dimensions and reinforcement of the tunnel lining structure.

[0042] Preferably, the first reinforcement component includes a first cap beam and a plurality of first reinforcement pile units interlocked along the tunnel extension direction, the plurality of first reinforcement pile units together forming a mountain-side reinforcement wall, and the first cap beam is connected to the top of the mountain-side reinforcement wall; wherein, the bottom of each first reinforcement pile unit is embedded in the soil and rock mass for not less than 0.3 times the excavation depth, and the top of the first reinforcement pile unit extends to the ground surface;

[0043] And / or each of the third reinforcement components includes a second cap beam and a plurality of second reinforcement pile units interlocked along the tunnel extension direction, the plurality of second reinforcement pile units together forming a reinforcement wall, the second cap beam being connected to the top of the reinforcement wall; wherein, the bottom of each second reinforcement pile unit is embedded in the soil and rock mass for not less than 0.3 times the excavation depth, and the top of the second reinforcement pile unit extends to the ground surface.

[0044] Preferably, the second reinforcement component includes a plurality of pile units spaced apart along the tunnel extension direction, each pile unit including a bored interlocking pile and a reinforced concrete column connected to the top of the bored interlocking pile; wherein, the top of the reinforced concrete column is not less than 1m higher than the intermediate cross bracing component, and the bottom of the bored interlocking pile is embedded in the soil and rock mass for not less than 0.3 times the excavation depth.

[0045] Preferably, the bracing assembly includes multiple bracing units arranged in a one-to-one correspondence with the pile column units, and each bracing unit includes a bracing support and a reinforced concrete pier; wherein, the reinforced concrete pier is buried in the soil and rock mass to a depth of not less than 2m, the lower end of the bracing support is connected to the reinforced concrete pier, and the upper end of the bracing support is connected to the reinforced concrete column.

[0046] Preferably, the step between step S2 and step S3 further includes the following step:

[0047] S21, three anchor cable rows are constructed sequentially from top to bottom; wherein, each anchor cable row includes anchor cables that are laid out one-to-one with the first reinforced pile unit, each anchor cable includes an anchoring end and a connecting end that are arranged opposite to each other along its own extension direction, the connecting end is connected to the corresponding first reinforced pile unit, and the anchoring end extends downward from the connecting end toward the interior of the rock and soil mass on the mountain side and anchors into the interior of the rock and soil mass;

[0048] S22, a through hole for water supply and drainage pipes is drilled in the first reinforced pile unit, and a drainage pipe is buried; wherein, the drainage pipe passes through the through hole and is inclined, the lower end of the drainage pipe is located on the back side of the first reinforced pile unit and is connected to the tunnel drainage system, and the upper end of the drainage pipe is located on the mountain-facing side of the first reinforced pile unit.

[0049] Preferably, the tunnel lining structure is an irregular structure, which includes a mountain-side arch wall lining and a back-mountain-side arch wall lining. The thickness of the mountain-side arch wall lining is greater than that of the back-mountain-side arch wall lining, and the thickness of the mountain-side arch wall lining gradually increases from the arch top to the first reinforcing pile unit.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] This invention provides a method for constructing a tunnel portal section through a traction-type landslide. The method involves constructing a first, second, third, and fourth reinforcement component at the planned tunnel portal section; constructing intermediate horizontal and diagonal bracing components in the main landslide-affected open tunnel section; constructing the open tunnel lining structure for the main landslide-affected open tunnel section; and constructing an eccentric retaining wall on the outside of the open tunnel lining structure. Backfill soil is used to backfill from the outer contour of the open tunnel lining structure to the top of the first and second reinforcement components. Vertical excavation is employed at the interface between the open and dark sections, and anchor mesh and shotcrete support are applied to the interface. An arch is then constructed between the two third reinforcement components, and an advanced pipe roof is constructed using the arch. The main landslide-affected dark tunnel section and the secondary landslide-affected dark tunnel section are excavated, thereby traversing the traction-type landslide.

[0052] This application breaks with conventional construction methods, eliminating the need for large-scale excavation and grouting reinforcement of the landslide body. It enables the safe passage of the tunnel portal through the traction landslide, offering high convenience and controllable construction. The first, second, third, and fourth reinforcement components of this application facilitate mechanized construction, ensuring high convenience and controllable construction. Furthermore, the increased structural strength and stiffness compensate for the shortcomings of conventional anti-slide pile construction. In addition, the main and secondary affected tunnel sections, relying on innovative tunnel construction methods combined with an excavation and support system, effectively resist the lateral thrust of the traction landslide on the mountainside, ensuring the safety of the tunnel portal construction in the traction landslide section. Attached Figure Description

[0053] 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.

[0054] Figure 1 This is a schematic diagram of a process in one embodiment of the present invention;

[0055] Figure 2 This is a schematic diagram of the influence range of a traction-type landslide in one embodiment of the present invention;

[0056] Figure 3 This is a schematic diagram of the plan layout after construction step S7 in one embodiment of the present invention;

[0057] Figure 4 This is a schematic elevation view of the main impact tunnel section of the landslide after construction step S7 in one embodiment of the present invention.

[0058] Figure 5 This is a schematic elevation view of the main impact tunnel section of a landslide in one embodiment of the present invention;

[0059] Figure 6 This is a schematic elevation view of the landslide secondary impact cavity section in one embodiment of the present invention;

[0060] Figure 7 This is a schematic diagram of the excavation elevation of the main impact tunnel section of a landslide in one embodiment of the present invention;

[0061] Figure 8 This is a schematic elevation view after construction step S4 is completed in one embodiment of the present invention;

[0062] Figure 9 This is a schematic diagram of the force applied to the first reinforcing component in one embodiment of the present invention;

[0063] Figure 10 This is a schematic diagram of the stress on the tunnel lining structure in one embodiment of the present invention.

[0064] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings.

[0065] Explanation of icon numbers:

[0066] 110. First reinforcement component; 111. First capping beam; 112. First reinforcement pile unit; 120. Second reinforcement component; 1211. Bored interlocking pile; 1212. Reinforced concrete column; 130. Intermediate cross brace component; 131. Diagonal brace component; 1311. Diagonal support; 1312. Reinforced concrete pier; 140. Open-cut tunnel lining structure; 141. Mountain-side arch wall lining; 142. Back-mountain-side arch wall lining; 150. Eccentric retaining wall; 160. Backfill soil; 170. Anchor cable; 210. Third reinforcement component ; 211, Second Crown Beam; 212, Second Reinforcing Pile Unit; 220, Arch Jacket; 230, Advanced Pipe Shed; 241, First Upper Step; 242, Initial Support of the First Upper Step; 243, Reserved Core Soil for the First Upper Step; 244, First Temporary Invert Arch; 245, First Lower Step; 246, Initial Support of the First Lower Step; 247, Initial Support of the First Invert Arch; 248, Filling Layer of the First Invert Arch; 249, Secondary Lining of the Arch Wall; 250, Steel Pipe; 310, Fourth Reinforcing Component; 320, Grouting Pipe. Detailed Implementation

[0067] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0068] 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.

[0069] In this invention, the terms "first," "second," etc., are used 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. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Furthermore, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. If 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.

[0070] Please see the appendix Figures 1 to 10 The present invention provides a method for constructing a tunnel portal section using a traction-type landslide in one embodiment, comprising the following steps:

[0071] S1. Based on the positional relationship between the proposed tunnel portal section and the landslide body and the extent of the landslide, the tunnel portal section is determined to include the landslide-affected open tunnel section, the landslide-affected closed tunnel section, and the landslide-affected secondary closed tunnel section, which are connected in sequence.

[0072] It is worth noting that this application addresses a scenario where the slope of the proposed tunnel portal section experiences a severe traction landslide. This type of traction landslide has a significant impact on the portal section, specifically manifested in the entire open-cut section being within the main landslide influence zone, while some concealed sections are also within the main influence zone and others within a general influence zone. The length of the general influence zone is typically three to five times the tunnel excavation width B, i.e., 3B to 5B. For tunnel portal sections traversing this scenario, this application proposes a construction method for tunnel portal sections passing through traction landslide bodies.

[0073] S2, a first reinforcement component 110 and a second reinforcement component 120 are respectively installed on both sides of the main impact tunnel section of the landslide, a third reinforcement component 210 is respectively installed on both sides of the main impact tunnel section of the landslide, and a fourth reinforcement component 310 is respectively installed on both sides of the secondary impact tunnel section of the landslide.

[0074] S3, excavation of the section of the tunnel mainly affected by the landslide;

[0075] In a preferred embodiment, step S3 specifically includes the following steps:

[0076] S31, remove the landslide body within the tunnel section mainly affected by the landslide, and construct an intermediate cross brace assembly 130 and an inclined brace assembly 131 in the tunnel section mainly affected by the landslide; wherein, the intermediate cross brace assembly 130 is located above the tunnel outline, the intermediate cross brace assembly 130 is connected between the first reinforcement assembly 110 and the second reinforcement assembly 120, the inclined brace assembly 131 is located on the back side of the tunnel section mainly affected by the landslide, and the inclined brace assembly 131 is supported on the outside of the second reinforcement assembly 120;

[0077] Specifically, after completing step S2, a continuous reinforcement wall was built on the mountainside of the tunnel entrance section to be constructed. At this time, the landslide body in the open tunnel section that mainly affected the landslide can be gradually removed to provide construction space for subsequent components. In order to accurately describe the location of different components, the mountainside referred to in this application is the side of the mountain where the landslide occurred, and the back mountainside is the side of the mountain away from the landslide.

[0078] As a preferred example, an intermediate cross bracing assembly 130 can be installed 2m away from the tunnel arch in the main affected section of the tunnel. Preferably, the intermediate cross bracing assembly 130 includes multiple reinforced concrete cross braces spaced apart along the tunnel extension direction, each reinforced concrete cross brace having a width × height of 0.7m × 0.9m. The intermediate cross bracing assembly 130 can transfer part of the traction landslide thrust to the outer second reinforcement assembly 120 and the inclined bracing assembly 131, effectively distributing part of the traction landslide thrust to both the second reinforcement assembly 120 and the inclined bracing assembly 131, improving the stress system. Furthermore, the first reinforcement assembly 110 and the intermediate cross bracing assembly 130 together form a three-dimensional support system, effectively improving tunnel safety.

[0079] S32, construct the tunnel lining structure 140 of the tunnel section mainly affected by the landslide and construct the biased retaining wall 150 on the outside of the tunnel lining structure 140, and then backfill the gap between the biased retaining wall 150 and the second reinforcement component 120.

[0080] S33, backfill soil 160 is used to backfill from the outer contour of the tunnel lining structure 140 to the top of the first reinforcement component 110 and the top of the second reinforcement component 120.

[0081] As a preferred example, backfill soil 160 with a cement content of 8% can be used to backfill from the outer contour of the tunnel lining structure 140 to the top of the first reinforcement component 110 and the top of the second reinforcement component 120.

[0082] S4, vertical excavation is carried out at the interface between the main impact open tunnel section and the main impact dark tunnel section of the landslide, anchor mesh spraying support is used at the interface, and then a sleeve arch 220 is constructed between the two third reinforcement components 210, and then the sleeve arch 220 is used to construct the advanced pipe roof 230.

[0083] like Figure 8 As shown, for construction safety, considering that the traction landslide mainly exerts a thrust along the transverse direction of the tunnel and the longitudinal tunnel experiences less force, it is preferable to install a third reinforcement component 210 on both sides and longitudinal slope free face anchor mesh spraying support at the interface between the main affected open tunnel section and the main affected closed tunnel section of the landslide (i.e., the open-closed boundary position). Preferably, the third reinforcement component 210 adopts bored piles with a pile diameter of 1.2m and a pile overlap of 0.4m. The bored piles are embedded in the rock and soil for no less than 0.3 times the excavation depth. The anchor mesh spraying uses 10cm thick C20 steel fiber shotcrete, φ8mm steel mesh, and 4m long, φ22 diameter mortar anchor rods.

[0084] Furthermore, such as Figure 8 As shown, a 220-type arch and a φ108 advanced long pipe roof can be used, with the long pipe roof being 30m in length. Furthermore, reinforcement bars can be installed inside the bored pile, and connecting steel plates can be installed at both ends of the 220-type arch to connect the two.

[0085] S5, excavation of the main tunnel section affected by the landslide;

[0086] S6, excavation of the section of the tunnel affected by the landslide.

[0087] In this application, the impact of the traction landslide on different sections of the tunnel is divided into three categories: the main impact open tunnel section, the main impact closed tunnel section, and the secondary impact closed tunnel section. First reinforcement component 110, second reinforcement component 120, third reinforcement component 210, and fourth reinforcement component 310 are specifically constructed in each section. The intermediate cross bracing component 130, diagonal bracing component 131, and second reinforcement component 120 form a spatial three-dimensional support structure, transferring some of the traction landslide thrust to the second reinforcement component 120 and diagonal bracing component 131, forming a distributed stress structure. The open tunnel lining structure 140 is located between the reinforcement components, preventing all traction landslide thrust from directly acting on the open tunnel lining structure 140, effectively protecting the open tunnel lining structure 140.

[0088] At the interface between the main landslide-affected open tunnel section and the main landslide-affected concealed tunnel section, vertical excavation combined with anchor mesh and shotcrete support is employed to avoid disturbing the traction-type landslide body by traditional bench excavation. Simultaneously, the use of the arch 220 and the advanced pipe roof 230 forms a protective shell, providing safe conditions for the excavation of the concealed tunnel section. The eccentric retaining wall 150 can withstand the remaining landslide thrust, and the backfill soil 160 balances the soil pressure behind the eccentric retaining wall 150 through its own weight. The eccentric retaining wall 150 can also prevent the displacement of the open tunnel lining structure 140.

[0089] This application breaks with conventional construction methods, eliminating the need for large-scale excavation and grouting reinforcement of the landslide body. It not only allows for the safe passage of the tunnel portal through the traction landslide, but the first reinforcement component 110, second reinforcement component 120, third reinforcement component 210, and fourth reinforcement component 310 facilitate mechanized construction, offering high convenience and controllable construction. Furthermore, the increased structural strength and stiffness compensate for the shortcomings of conventional anti-slide pile construction. In addition, the main and secondary affected tunnel sections can effectively resist the lateral thrust of the traction landslide on the mountainside by combining innovative construction methods and excavation support systems, ensuring the safety of the tunnel portal construction in the traction landslide section.

[0090] In a preferred embodiment, step S5 specifically includes the following steps:

[0091] S51, first, grouting reinforcement is carried out on the surface of the back side of the tunnel section mainly affected by the landslide;

[0092] S52, in each cycle of advance, the arch wall area is first excavated using the pre-reserved core soil bench method, specifically including:

[0093] S521, first excavate the first upper bench 241, then construct the initial support 242 for the first upper bench, and then excavate the reserved core soil 243 for the first upper bench; preferably, the initial support 242 for the first upper bench can be anchor mesh shotcrete + 22b I-beams, with the longitudinal spacing of the 22b I-beams being 0.5m.

[0094] S522, construct a first temporary invert arch 244 at the junction of the first upper step 241 and the first lower step 245; wherein, the two ends of the first temporary invert arch 244 are respectively connected to the initial support 242 of the first upper step; preferably, the first temporary invert arch 244 is made of 20b I-beams with a longitudinal spacing of 0.5m.

[0095] S523, after the first upper step 241 is excavated at a first distance, the first lower step 245 is excavated, the initial support 246 of the first lower step is then constructed, and the core soil reserved for the first lower step is then excavated; preferably, the first distance is 5m, and the initial support 246 of the first lower step can be made of anchor mesh spraying + 22b I-beams with a longitudinal spacing of 0.5m.

[0096] S53, after excavating the first lower step 245 at a second distance, excavate the first invert arch area, and then sequentially construct the first invert arch initial support 247 and the first invert arch filling layer 248; preferably, the second distance is 6m.

[0097] S54, Perform secondary lining of the arch wall corresponding to the current cycle advance 249.

[0098] Furthermore, two φ50mm, 4m long locking steel pipes with a longitudinal spacing of 0.5m can be used at the connection between the upper and lower steps and at the bottom of the side wall to enhance the overall strength of the steel frame.

[0099] This embodiment injects grout (such as cement grout, chemical grout, etc.) into the surface of the back side of the main landslide-affected tunnel section to fill the cracks in the rock and soil, improve the strength of the surface soil, reduce surface subsidence caused by excavation disturbance, reduce groundwater seepage channels, and enhance the overall anti-sliding capacity.

[0100] To simplify the construction process, this embodiment describes the construction steps for each cycle of advance. The entire landslide's main affected tunnel section can be repeated multiple times until completion; this approach is conventional in the field and will not be elaborated upon here. This embodiment divides the tunnel face into upper and lower steps, excavating in stages to reduce disturbance to the surrounding rock from a single excavation, utilizing the unexcavated core soil to maintain tunnel face stability. Initial support (such as anchor bolts, steel frames, and shotcrete) is immediately implemented after each excavation step to form a load-bearing structure and control surrounding rock deformation. The first temporary invert arch 244 connects to the initial support 242 of the first upper step, forming a closed loop in the area of ​​the first upper step 241, enhancing structural integrity and preventing arch crown subsidence and convergence deformation. After advancing a certain distance in the first lower step 245, the invert arch is excavated, forming a complete tunnel invert arch area structure, which, together with the initial support, constitutes a closed load-bearing ring, significantly improving structural stability.

[0101] In a preferred embodiment, step S6 specifically includes the following steps:

[0102] S61, first perform radial grouting reinforcement on the mountainside outside the outline of the landslide secondary impact tunnel section; preferably, grouting reinforcement can be performed using grouting pipe 320.

[0103] S62, in each cycle of advance, the arch wall area is first excavated using the pre-reserved core soil bench method, specifically including:

[0104] S621, first excavate the second upper bench, then construct the initial support for the second upper bench, and then excavate the reserved core soil for the second upper bench; preferably, the initial support for the second upper bench can be anchor mesh shotcrete + 22b I-beams, with the longitudinal spacing of the 22b I-beams being 0.5m.

[0105] S622, construct a second temporary invert arch at the junction of the second upper step and the second lower step; wherein, the two ends of the second temporary invert arch are respectively connected to the initial support of the second upper step; preferably, the second temporary invert arch is made of 20b I-beams with a longitudinal spacing of 0.5m.

[0106] S623, after the second upper step is excavated at a third distance, the second lower step is excavated, the initial support of the second lower step is then constructed, and the core soil reserved for the second lower step is then excavated; preferably, the third distance is 5m, and the initial support of the second lower step can be anchor mesh spray + 22b I-beams with a longitudinal spacing of 0.5m.

[0107] S63, after the fourth distance of the second lower step excavation, the second invert arch area is excavated, and then the initial support of the second invert arch and the filling layer of the second invert arch are constructed in sequence; preferably, the second distance is 6m.

[0108] S64, Perform secondary lining of the arch wall corresponding to the current cycle advance 249.

[0109] To simplify the construction process, this embodiment describes the construction steps for each cycle of advance. The entire landslide secondary impact tunnel section can be repeated multiple times until completion, which is a conventional approach in this field and will not be elaborated upon here. In this embodiment, grout is injected into the mountainside outside the outline of the landslide secondary impact tunnel section to fill the cracks in the rock and soil, improve the strength and self-stabilizing capacity of the rock and soil between the fourth reinforcement component 310, reduce the risk of landslides caused by excavation disturbance, and together with the fourth reinforcement component 310, form a three-dimensional reinforcement structure.

[0110] By dividing the tunnel face into upper and lower benches and excavating in stages, the disturbance to the surrounding rock from each excavation is reduced, and the unexcavated core soil is used to maintain the stability of the tunnel face. Initial support (such as anchor bolts, steel frames, and shotcrete) is immediately implemented after each excavation step to form a load-bearing structure and control surrounding rock deformation. A second temporary invert arch connects to the initial support of the second upper bench, forming a closed loop in the second upper bench area, enhancing the overall structural integrity and preventing arch crown settlement and convergence deformation. After advancing a certain distance in the second lower bench, the invert arch is excavated, forming a complete tunnel invert arch area structure. Together with the initial support, this forms a closed load-bearing ring, significantly improving structural stability.

[0111] In a preferred embodiment, the first reinforcement component 110 includes a first cap beam 111 and a plurality of first reinforcement pile units 112 interlocked along the tunnel extension direction. The plurality of first reinforcement pile units 112 together form a mountain-side reinforcement wall, and the first cap beam 111 is connected to the top of the mountain-side reinforcement wall. The bottom of each first reinforcement pile unit 112 is embedded in the soil and rock mass for no less than 0.3 times the excavation depth, and the top of the first reinforcement pile unit 112 extends to the ground surface. The excavation depth is the maximum depth from the ground surface to the bottom of the open-cut tunnel lining structure 140.

[0112] And / or each of the third reinforcement components 210 includes a second cap beam 211 and a plurality of second reinforcement pile units 212 interlocked along the tunnel extension direction, the plurality of second reinforcement pile units 212 together forming a reinforcement wall, the second cap beam 211 being connected to the top of the reinforcement wall; wherein, the bottom of each second reinforcement pile unit 212 is embedded in the soil and rock mass for not less than 0.3 times the excavation depth, the top of the second reinforcement pile unit 212 extending to the ground surface, the excavation depth being the maximum depth from the ground surface to the bottom of the open-cut tunnel lining structure 140.

[0113] like Figure 3 As shown, the first reinforcement pile unit 112 is set on the mountain side outside the outer contour of the tunnel. Preferably, each first reinforcement pile unit 112 includes a reinforced concrete pile and a plain pile. The first reinforcement pile unit 112 adopts drilled interlocking piles 1211, which are connected by interlocking piles along the extension direction of the tunnel to form a continuous and closed mountain-side reinforcement wall, effectively blocking potential sliding surfaces, significantly improving the slope's anti-sliding capacity, and preventing mountain instability.

[0114] like Figure 5 As shown, third reinforcement components 210 are respectively set on both sides of the tunnel section mainly affected by the landslide. Preferably, the third reinforcement components 210 are formed by drilled interlocking piles 1211 to form a reinforcement wall. Furthermore, φ50mm steel pipes 250 can be used to reinforce the soil and rock mass of the shallow buried tunnel on the back side of the tunnel section mainly affected by the landslide by cement grouting: the spacing of φ50mm steel pipes 250 is set to 1.5m×1.5m, and the length of steel pipe 250 is 10m, to strengthen the soil and rock mass of the tunnel section mainly affected by the landslide and ensure the safety and stability of the tunnel during construction.

[0115] Preferably, the diameter of the reinforced concrete piles and plain piles is 1.2m, and the width × height of the first capping beam 111 is 1.6m × 1m. The first capping beam 111 is used to enhance the overall integrity of the piles. The pile bottom is embedded in the soil and rock to a depth ≥ 0.3 times the excavation depth to ensure that the pile has sufficient uplift bearing capacity to resist the risk of uplift caused by groundwater buoyancy and lateral pressure from the mountain. The pile top extends to the ground surface, forming full-height support from the ground surface to the deep layer, effectively restraining the deformation of shallow loose soil and preventing surface collapse. In addition, the first reinforced pile unit 112 adopts bored interlocking piles 1211, which can also act as a water-stop curtain, reducing the additional load of pore water pressure on the support structure. Furthermore, the bored interlocking pile 1211 technology is mature and can be mechanized, which can effectively improve the convenience of construction.

[0116] In a preferred embodiment, the second reinforcement component 120 includes a plurality of pile units spaced apart along the tunnel extension direction. Each pile unit includes a drilled interlocking pile 1211 and a reinforced concrete column 1212 connected to the top of the drilled interlocking pile 1211. The top of the reinforced concrete column 1212 is at least 1m higher than the intermediate cross bracing component 130, and the bottom of the drilled interlocking pile 1211 is embedded in the soil and rock mass at least 0.3 times the excavation depth, which is the maximum depth from the ground surface to the bottom of the open-cut tunnel lining structure 140.

[0117] like Figure 3 As shown, the pile-column unit is located on the back side of the mountain outside the outer contour of the tunnel, that is, on the opposite side of the first reinforced pile unit 112. Each pile-column unit includes a drilled interlocking pile 1211 and a reinforced concrete column 1212 connected to the top of the drilled interlocking pile 1211. Preferably, the reinforced concrete column 1212 is rigidly connected to the drilled interlocking pile 1211, so as to directly transfer the upper load (such as part of the traction landslide thrust transmitted by the intermediate cross brace component 130) to the pile foundation, forming a pile-column-cross brace three-dimensional force system, which significantly enhances the overall overturning and sliding resistance of the structure.

[0118] The interlocking piles are embedded to a depth ≥ 0.3 times the excavation depth, ensuring the pile bottom is located in a stable soil and rock layer. This utilizes the resistance of the soil and rock mass to limit pile deformation and effectively control surface settlement caused by tunnel excavation. The reinforced concrete column 1212 extends at least 1m above the intermediate cross bracing assembly 130, forming a portal frame structure. The intermediate cross bracing assembly 130 and the stable load-bearing area of ​​the reinforced concrete column 1212 are connected, enhancing lateral stiffness and creating vertical backfill space. Later backfilling with 160mm backfill soil further improves the overall lateral resistance of the structure. Furthermore, the bored interlocking piles 1211 and the reinforced concrete column 1212 utilize mature technologies and can be mechanized, effectively improving construction convenience.

[0119] Furthermore, fourth reinforcement components 310 are installed on both sides of the tunnel section affected by the landslide. Preferably, the fourth reinforcement components 310 are bored piles with a diameter of 1.2m and a spacing of 1.6m. The piles are embedded in the soil and rock mass for no less than 0.3 times the excavation depth. Simultaneously, after excavation, radial grouting is performed to reinforce the arch wall on the mountain-side of the tunnel's soil and rock mass. Figure 6 As shown, preferably, φ50mm steel pipe 250, 5m in length, is used with a reinforcement spacing of 1m×1.5m to strengthen the strength of the soil and rock between piles and ensure construction safety.

[0120] Furthermore, the inclined bracing assembly 131 includes multiple inclined bracing units arranged one-to-one with the pile column units. Each inclined bracing unit includes an inclined support 1311 and a reinforced concrete pier 1312. The reinforced concrete pier 1312 is buried in the soil and rock mass to a depth of not less than 2m. The lower end of the inclined support 1311 is connected to the reinforced concrete pier 1312, and the upper end of the inclined support 1311 is connected to the reinforced concrete column 1212.

[0121] The inclined bracing assembly 131 in this embodiment includes multiple inclined bracing units arranged one-to-one with the pile column units. Specifically, the reinforced concrete pier 1312 has a embedment depth of ≥2m. This deep embedment significantly increases the side friction and end passive earth pressure of the pier, effectively resisting the horizontal force of the landslide. The inclined bracing assembly 131 of this application can transfer part of the traction landslide thrust to the reinforced concrete pier 1312 embedded in the soil, improving the overall stress and enhancing the safety of the tunnel entrance section. Preferably, the reinforced concrete pier 1312 is in the form of a square pier, with an inclined surface on the side near the reinforced concrete column 1212, and the lower end of the inclined bracing 1311 is connected to the inclined surface. Preferably, the dimensions of the inclined bracing 1311 are width × height = 0.7m × 0.9m.

[0122] In a preferred embodiment, the following step is further included between step S2 and step S3:

[0123] S21, three anchor cable rows are constructed sequentially from top to bottom; wherein, each anchor cable row includes anchor cables 170 that are arranged one-to-one with the first reinforced pile unit 112, each anchor cable 170 includes an anchoring end and a connecting end that are arranged opposite to each other along its own extension direction, the connecting end is connected to the corresponding first reinforced pile unit 112, and the anchoring end extends downward from the connecting end toward the interior of the rock and soil mass on the mountain side and anchors into the interior of the rock and soil mass;

[0124] S22, a through hole for water supply and drainage pipes is drilled in the first reinforced pile unit 112, and a drainage pipe is buried; wherein, the drainage pipe passes through the through hole and is inclined, the lower end of the drainage pipe is located on the back side of the first reinforced pile unit 112 and is connected to the tunnel drainage system, and the upper end of the drainage pipe is located on the mountain-facing side of the first reinforced pile unit 112.

[0125] In this embodiment, three rows of prestressed anchor cables 170 are installed from the top of the pile downwards in the main impact section of the landslide tunnel to transfer part of the pile-driven landslide thrust into the deep rock strata on the mountainside. Preferably, the anchoring end is anchored into the strongly weathered rock strata for no less than 5m, the vertical spacing of the anchor cables 170 is 4m, and the horizontal spacing is 3m.

[0126] The drainage pipes are installed at an angle, utilizing gravity for natural drainage, effectively reducing pore water pressure in the soil and rock on the mountain side and minimizing additional water load. The drainage pipes can be connected to the tunnel drainage network to form a complete drainage path, such as connecting to tunnel side ditches or intercepting ditches, to promptly discharge water from the mountain side.

[0127] Furthermore, the tunnel lining structure 140 is an irregular structure, which includes a mountain-side arch wall lining 141 and a back-mountain-side arch wall lining 142. The thickness of the mountain-side arch wall lining 141 is greater than that of the back-mountain-side arch wall lining 142, and the thickness of the mountain-side arch wall lining 141 gradually increases from the arch top to the first reinforcing pile unit 112.

[0128] like Figure 4 As shown, to ensure the tunnel structure of the main affected section during operation can withstand the landslide's traction force for a long period and prevent structural damage or destruction, the tunnel lining structure 140 adopts an asymmetrical structure with a thin arch and thick wall on the inner side near the mountain. Specifically, the thickness of the arch wall lining 141 on the mountain side is greater than the thickness of the arch wall lining 142 on the back side, and the thickness of the arch wall lining 141 on the mountain side gradually increases from the arch crown to the reinforcing pile unit. For example, the thickness of the arch wall lining 142 on the back side is set to 1.1m, while the thickness of the arch wall lining 141 on the mountain side is set to 2.6m. An eccentric retaining wall 150 is used on the outer side (back side) to prevent the tunnel lining from shifting, further dispersing the traction thrust of the landslide. Finally, soil is backfilled from the arch crown of the tunnel lining structure 140 to further resist the traction thrust of the landslide. The thin-arch, thick-wall, irregularly shaped open-cut tunnel lining structure 140 of this embodiment can enhance the structural rigidity of the tunnel on the mountain-side, compensate for the damage or destruction of the open-cut tunnel lining structure 140 caused by the increased traction landslide thrust due to extreme weather and other adverse factors during the operation period, improve the safety and toughness of the tunnel structure, and ensure the long-term safety of the tunnel structure.

[0129] like Figure 9 and Figure 10 As shown, in a preferred embodiment, the open-cut lining structure 140 in step S32 is specifically obtained through the following design steps:

[0130] S321, taking the first reinforcement component 110 of the tunnel section mainly affected by the landslide as the object, determining the lowest position of the tunnel lining structure 140, simplifying the connection between the first reinforcement component 110 and the soil corresponding to the lowest position as a fixed support, simplifying the connection between the first reinforcement component 110 and the intermediate cross brace component 130 as a first hinge support, simplifying the adjacent part of the first reinforcement component 110 and the tunnel lining structure 140 as a second hinge support, and applying the remaining sliding force P of the landslide body to the first reinforcement component 110;

[0131] Specifically, slope stability calculations typically employ the limit equilibrium method. Depending on different assumptions regarding the forces between the landslide blocks, landslide calculation theories such as the Bishop method, the simple strip method, and the transfer coefficient method can be used. The transfer coefficient method is employed for landslide stability analysis and calculation, specifically the residual sliding force P = TF (where T is the slope sliding force and F is the slope resisting force). Specific slope calculations can be performed according to Appendix A of the "Technical Specification for Slope Engineering (GB 50330-2013)" for slope stability calculations with different sliding surface morphologies. Therefore, the residual sliding force P of the landslide body can be obtained using existing techniques, which will not be elaborated upon here.

[0132] Based on the structural relationship and stress characteristics of the tunnel lining structure 140 and the first reinforcement component 110, this embodiment simplifies the connection between the first reinforcement component 110 and the soil corresponding to the lowest position as a fixed support, the connection between the first reinforcement component 110 and the intermediate cross brace component 130 as a first hinge support, and the adjacent connection between the first reinforcement component 110 and the tunnel lining structure 140 as a second hinge support. The remaining sliding force P of the landslide body is applied to the first reinforcement component 110 for easy calculation.

[0133] S322, the lateral pressure F2 on the second hinge support is calculated using the formula Ph0≤K(F1h1+F2h2), where h0 is the vertical distance from the point of application of the remaining sliding force P to the fixed support (in meters), K is the safety factor of the landslide (generally taken as 1.35), and F1 is the axial force of the cross brace of the first hinge support. Preferably, F1=EAδ / L, where E is the elastic modulus of the material (in kN / m). 2 A represents the cross-sectional area of ​​the intermediate cross brace component 130 (unit: m²). 2 δ represents the displacement at the first hinge support, in meters (m), which can be obtained by installing a displacement measuring point at this support point based on actual field measurements. h1 represents the vertical distance from the intermediate cross brace assembly 130 to the fixed support, in meters (m), and h2 represents the vertical distance from the second hinge support to the fixed support, in meters (m).

[0134] S323, simplify the lateral pressure F2 as a uniformly distributed load acting on the tunnel lining structure 140, calculate the lateral uniformly distributed pressure on the second hinge support, and then calculate the pressure of the backfill soil 160 above the tunnel lining structure 140.

[0135] Preferably, the lateral uniformly distributed pressure e on the second hinge support is calculated using the formula F2=e1h2. 1， (Unit: KN / m); Preferably, the pressure q1 of the upper backfill soil 160 of the tunnel lining structure 140 is calculated using the formula q1=γh3 (where γ is the unit weight of the backfill soil 160, generally 15~18 KN / m). 2 h3 is the height of the backfill soil (160 m), and q1 is in kN / m.

[0136] S324, using the finite element method, the connection between the perimeter of the tunnel lining structure 140 and the soil is simplified to be only subjected to the compression of the foundation spring, and the internal forces on the tunnel lining structure 140 are calculated; preferably, the internal forces include bending moment M and axial force N;

[0137] S325, using the comprehensive safety factor method, the bearing capacity and reinforcement of the tunnel lining structure 140 are verified, thereby obtaining the design dimensions and reinforcement of the tunnel lining structure 140.

[0138] Specifically, the preliminary dimensions and reinforcement of the tunnel lining structure 140 can be designed based on experience. The bearing capacity and reinforcement of the tunnel lining structure 140 can then be verified using the comprehensive safety factor method. It can be determined whether the preliminary dimensions and reinforcement meet the requirements. If they do, the current dimensions and reinforcement are used as the final design dimensions and reinforcement. If not, the dimensions or reinforcement are readjusted until the design requirements are met. The comprehensive safety factor method can be used according to Appendix N.0.8-2 of the "Highway Tunnel Design Specification, Volume 1, Civil Engineering" (JTG3370.1-2018). This method is used to verify the bearing capacity and reinforcement of the tunnel lining structure 140, thereby obtaining the designed structural dimensions and reinforcement. This part is the technical content recorded in the existing specifications and will not be elaborated here.

[0139] Due to the unique location of the tunnel lining structure 140, and the fact that its safety directly impacts the tunnel's internal safety, this embodiment uses load-bearing capacity and reinforcement calculations to ensure that the tunnel lining structure 140 has a certain safety reserve when bearing the design load, thereby improving design safety. Through repeated calculations and adjustments to design dimensions or reinforcement, dimensions or reinforcement that meet design requirements and are relatively economical can be found, thus optimizing the structural design. Precise calculations and adjustments during the design phase can reduce uncertainties and risks during construction, improving construction efficiency and quality.

[0140] The above are merely preferred embodiments of the present invention and do not limit the scope of protection of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention’s specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for constructing a tunnel portal section using a traction-type landslide, characterized in that, Includes the following steps: S1. Based on the positional relationship between the proposed tunnel portal section and the landslide body and the extent of the landslide, the tunnel portal section is determined to include the landslide-affected open tunnel section, the landslide-affected closed tunnel section, and the landslide-affected secondary closed tunnel section, which are connected in sequence. S2, a first reinforcement component and a second reinforcement component are respectively installed on both sides of the main affected open tunnel section of the landslide, a third reinforcement component is respectively installed on both sides of the main affected dark tunnel section of the landslide, and a fourth reinforcement component is respectively installed on both sides of the secondary affected dark tunnel section of the landslide. S3, excavation of the section of the tunnel mainly affected by the landslide; S4. Vertical excavation is carried out at the interface between the main impact open tunnel section and the main impact dark tunnel section of the landslide. Anchor mesh spraying support is used for the interface. Then, a sleeve arch is constructed between the two third reinforcement components, and then the sleeve arch is used to construct the advanced pipe roof. S5, excavation of the main tunnel section affected by the landslide; S6, excavation of the section of the tunnel affected by the landslide; Step S3 specifically includes the following steps: S31, remove the landslide body within the tunnel section mainly affected by the landslide, and construct intermediate cross bracing components and diagonal bracing components in the tunnel section mainly affected by the landslide; wherein, the intermediate cross bracing components are located above the tunnel outline, the intermediate cross bracing components are connected between the first reinforcement component and the second reinforcement component, the diagonal bracing components are located on the back side of the tunnel section mainly affected by the landslide, and the diagonal bracing components are supported on the outside of the second reinforcement component; S32, construct the tunnel lining structure for the tunnel section mainly affected by the landslide and construct an eccentric retaining wall on the outside of the tunnel lining structure, and then backfill the gap between the eccentric retaining wall and the second reinforcement component. S33, backfill soil is used to backfill from the outer contour of the tunnel lining structure to the top of the first reinforcement component and the top of the second reinforcement component.

2. The construction method for the tunnel portal section via a traction-type landslide body according to claim 1, characterized in that, Step S5 specifically includes the following steps: S51, first, grouting reinforcement is carried out on the surface of the back side of the tunnel section mainly affected by the landslide; S52, in each cycle of advance, the arch wall area is first excavated using the reserved core soil bench method, specifically including: S521, first excavate the first upper bench, then construct the initial support of the first upper bench, and then excavate the reserved core soil of the first upper bench; S522, Construct the first temporary invert arch at the junction of the first upper step and the first lower step; wherein, the two ends of the first temporary invert arch are respectively connected to the initial support of the first upper step; S523, after the first upper step is excavated to a certain distance, the first lower step is excavated, the initial support of the first lower step is then constructed, and the core soil reserved for the first lower step is then excavated. S53, after the second distance of the first lower step is excavated, the first invert arch area is excavated, and then the initial support of the first invert arch and the first invert arch filling layer are constructed in sequence. S54, Perform secondary lining of the arch wall corresponding to the current cycle advance.

3. The construction method for the tunnel portal section via a traction-type landslide body according to claim 2, characterized in that, Step S6 specifically includes the following steps: S61, first perform radial grouting reinforcement on the mountainside outside the outline of the secondary impact tunnel section of the landslide; S62, in each cycle of advance, the arch wall area is first excavated using the pre-reserved core soil bench method, specifically including: S621, first excavate the second upper bench, then construct the initial support for the second upper bench, and then excavate the reserved core soil for the second upper bench; S622, Construct a second temporary invert at the junction of the second upper step and the second lower step; wherein, the two ends of the second temporary invert are respectively connected to the initial support of the second upper step; S623, after the second upper step is excavated to a third distance, the second lower step is excavated, the initial support of the second lower step is then constructed, and the core soil reserved for the second lower step is then excavated. S63, after the fourth distance of the second lower step excavation, the second invert arch area is excavated, and then the initial support of the second invert arch and the filling layer of the second invert arch are constructed in sequence. S64, Perform secondary lining of the arch wall corresponding to the current cycle advance.

4. The construction method for the tunnel portal section via a traction-type landslide body according to claim 1, characterized in that, The lining structure of the open-cut tunnel in step S32 is obtained through the following design steps: S321, Select the first reinforcement component of the tunnel section mainly affected by the landslide as the object, determine the lowest position of the tunnel lining structure, simplify the connection between the first reinforcement component and the soil corresponding to the lowest position as a fixed support, simplify the connection between the first reinforcement component and the intermediate cross brace component as a first hinge support, simplify the adjacent part of the first reinforcement component and the tunnel lining structure as a second hinge support, and apply the remaining sliding force P of the landslide body to the first reinforcement component; S322, the lateral pressure F2 on the second hinge support is calculated using the formula Ph0≤K(F1h1+F2h2), where h0 is the vertical distance from the point where the remaining sliding force P acts to the fixed support, K ​​is the safety factor of the landslide, F1 is the axial force of the cross brace of the first hinge support, h1 is the vertical distance from the intermediate cross brace assembly to the fixed support, and h2 is the vertical distance from the second hinge support to the fixed support. S323, simplify the lateral pressure F2 as a uniformly distributed load acting on the tunnel lining structure, calculate the lateral uniformly distributed pressure on the second hinge support, and then calculate the backfill pressure on the upper part of the tunnel lining structure. S324. Using the finite element method, the connection between the perimeter of the tunnel lining structure and the soil is simplified to only the compressed foundation spring, and the internal forces on the tunnel lining structure are calculated. S325 uses the comprehensive safety factor method to verify the bearing capacity and reinforcement of the tunnel lining structure, thereby obtaining the design dimensions and reinforcement of the tunnel lining structure.

5. The construction method for the tunnel portal section via a traction-type landslide body according to claim 1, characterized in that, The first reinforcement component includes a first cap beam and multiple first reinforcement pile units interlocked along the tunnel extension direction. The multiple first reinforcement pile units together form a mountain-side reinforcement wall. The first cap beam is connected to the top of the mountain-side reinforcement wall. The bottom of each first reinforcement pile unit is embedded in the soil and rock mass for no less than 0.3 times the excavation depth, and the top of the first reinforcement pile unit extends to the ground surface. And / or each of the third reinforcement components includes a second cap beam and a plurality of second reinforcement pile units interlocked along the tunnel extension direction, the plurality of second reinforcement pile units together forming a reinforcement wall, the second cap beam being connected to the top of the reinforcement wall; wherein, the bottom of each second reinforcement pile unit is embedded in the soil and rock mass for not less than 0.3 times the excavation depth, and the top of the second reinforcement pile unit extends to the ground surface.

6. The construction method for the tunnel portal section via a traction-type landslide body according to claim 1, characterized in that, The second reinforcement component includes multiple pile units spaced apart along the tunnel extension direction. Each pile unit includes a drilled interlocking pile and a reinforced concrete column connected to the top of the drilled interlocking pile. The top of the reinforced concrete column is at least 1m higher than the intermediate cross bracing component, and the bottom of the drilled interlocking pile is embedded in the soil and rock mass at least 0.3 times the excavation depth.

7. The construction method for the tunnel portal section via a traction-type landslide body according to claim 6, characterized in that, The inclined bracing assembly includes multiple inclined bracing units arranged in a one-to-one correspondence with the pile column units. Each inclined bracing unit includes an inclined support and a reinforced concrete pier. The reinforced concrete pier is buried in the soil and rock mass to a depth of not less than 2m. The lower end of the inclined support is connected to the reinforced concrete pier, and the upper end of the inclined support is connected to the reinforced concrete column.

8. The construction method for the tunnel portal section via a traction-type landslide body according to claim 5, characterized in that, The following steps are also included between steps S2 and S3: S21, three anchor cable rows are constructed sequentially from top to bottom; wherein, each anchor cable row includes anchor cables that are laid out one-to-one with the first reinforced pile unit, each anchor cable includes an anchoring end and a connecting end that are arranged opposite to each other along its own extension direction, the connecting end is connected to the corresponding first reinforced pile unit, and the anchoring end extends downward from the connecting end toward the interior of the rock and soil mass on the mountain side and anchors into the interior of the rock and soil mass; S22, a through hole for water supply and drainage pipes is drilled in the first reinforced pile unit, and a drainage pipe is buried; wherein, the drainage pipe passes through the through hole and is inclined, the lower end of the drainage pipe is located on the back side of the first reinforced pile unit and is connected to the tunnel drainage system, and the upper end of the drainage pipe is located on the mountain-facing side of the first reinforced pile unit.

9. The construction method for the tunnel portal section via a traction-type landslide body according to claim 5, characterized in that, The tunnel lining structure is an irregular structure, which includes a mountain-side arch wall lining and a back-mountain-side arch wall lining. The thickness of the mountain-side arch wall lining is greater than that of the back-mountain-side arch wall lining, and the thickness of the mountain-side arch wall lining gradually increases from the arch top to the first reinforcing pile unit.

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