Hole entering method for cliff hole of highway tunnel

Abstract

The invention discloses a hole entering method for a highway tunnel cliff hole, relates to the technical field of highway engineering construction, and aims to solve the problems of poor construction conditions, tedious procedures, high cost, slow progress and large potential safety hazards of a traditional construction method under complex terrain conditions. According to the method, by building a construction adit, the construction process is optimized and comprises the steps of determining the adit position and design parameters, building a construction shortcut, constructing an adit top water interception gutter and a protection project, excavating an adit blind hole, carrying out primary support and secondary lining, entering a main hole for construction and blocking the adit. Scientific calculation methods, such as blasting parameters, support parameters and concrete mix proportion, are adopted in construction, so that the construction safety and quality are ensured. Compared with a traditional method, the construction period is remarkably shortened, investment is saved, the construction risk is reduced, and the project quality and durability are improved; and meanwhile, the influence on the environment is reduced, technical reference is provided for tunnel construction under similar complex terrain conditions, and remarkable economic and social benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of highway engineering construction, in particular to a method for entering a cliff hole of a highway tunnel. Background Art

[0002] In complex terrain areas such as the Hengduan Mountains, due to the steep terrain and crisscrossing mountains, some highway tunnel entrances are located on cliffs, and the construction environment is extremely harsh. Traditional tunnel construction methods usually rely on building a construction platform at the entrance and creating construction conditions by backfilling the slope foot and setting up retaining walls. However, this traditional method has many problems when facing cliff terrain:

[0003] 1. Construction access roads and platforms are difficult to build: Building construction access roads and work platforms on cliffs faces great technical difficulties and safety risks, and the construction cost is high.

[0004] 2. Complicated procedures and slow progress: Traditional methods require large-scale backfilling of earth and stone, and the backfill height generally does not exceed 10 meters, which not only increases the complexity of the construction process, but also significantly prolongs the construction period.

[0005] 3. Prominent safety hazards: The cliff terrain itself is highly risky, and the frequent high-altitude operations required during the construction process further aggravate the safety hazards of construction workers.

[0006] 4. Poor economic efficiency: Traditional construction methods require a large amount of manpower, material resources and time resources, resulting in high project costs. Especially in areas where bridges and tunnels overlap and geological conditions are complex, the construction costs increase exponentially.

[0007] Therefore, how to efficiently and safely complete the tunnel entrance construction under cliff terrain conditions has become a technical problem that needs to be solved urgently in the current highway tunnel construction. Summary of the invention

[0008] The objective of the present invention is to provide a highway tunnel entrance construction method suitable for cliff terrain, so as to solve the problems existing in traditional construction methods, such as poor construction conditions, complicated procedures, slow progress, great safety hazards and high costs, and to provide scientific basis and technical support for similar projects.

[0009] The technical solution adopted by the present invention is:

[0010] A method for entering a cave at a cliff entrance of a highway tunnel, the method comprising the following steps:

[0011] Step 1: According to the two-stage construction drawing design documents and the actual on-site measurement results, determine the location, line shape and cross-sectional form of the tunnel entry construction branch hole, and determine the plane design drawing, longitudinal section design drawing and cross-sectional design drawing of the construction branch hole;

[0012] Step 2: Build a construction access road to the entrance of the construction branch tunnel, and harden the surrounding area to ensure a certain slope for easy drainage;

[0013] Step 3, construct the water cutoff ditch on the top of the construction branch tunnel, the tunnel entrance protection, and the open tunnel;

[0014] Step 4: Construction of branch tunnels and blind tunnels; excavation of the tunnel body is carried out by drilling and blasting with an excavator and a manual pneumatic drill; wet spraying is used for tunnel body support, and grouting anchors are drilled with a down-the-hole drill and grouting is done with a grouting machine; the secondary lining is cast with C30 waterproof reinforced concrete using a steel membrane trolley;

[0015] Step 5, enter the main tunnel for construction; the main tunnel is constructed using the New Austrian Tunneling Method. During the construction process, the self-bearing capacity of the surrounding rock and the restraining effect of the excavation surface are utilized. Anchor rods and shotcrete are used as the main construction support means to reinforce the surrounding rock in time, restrain the relaxation and deformation of the surrounding rock, and measure and monitor the surrounding rock and support;

[0016] Step 6: After the main tunnel construction is completed, 1m thick C30 plain concrete is used to seal both ends of the construction branch tunnel.

[0017] Furthermore, in step 4, when the tunnel is excavated by drilling and blasting with an excavator or a manual pneumatic drill, blasting parameter calculation is required; blasting parameter calculation includes blasthole depth calculation and charge quantity calculation;

[0018] The formula for calculating the depth of the blasthole is:

[0019] H=K·B

[0020] In the formula, H is the depth of the blasthole; K is the empirical coefficient, which is generally 1.0 to 1.2; B is the excavation footage;

[0021] The formula for calculating the charge amount is:

[0022] Q=q·V

[0023] Where Q is the charge of a single hole; q is the unit explosive consumption, which is determined according to the surrounding rock grade; V is the blasting volume of a single hole.

[0024] Furthermore, in step 4, before the wet spraying operation of the tunnel support, the support parameter calculation needs to be performed; the support parameter calculation includes the calculation of the shotcrete thickness, the anchor rod length and spacing;

[0025] The design of shotcrete thickness needs to be determined according to the surrounding rock pressure and support strength requirements. The calculation formula is:

[0026]

[0027] Where, t is the thickness of shotcrete; P is the surrounding rock pressure; σ c is the compressive strength of shotcrete;

[0028] The design of anchor bolts must meet the requirements of surrounding rock reinforcement, and their length and spacing are calculated using the following formula;

[0029] Anchor rod length calculation formula:

[0030] L=L a +L b +L c

[0031] Where, L is the total length of the anchor rod; a L is the length of the anchoring section, generally 1 to 1.5 m; b is the free section length, which is determined according to the relaxation range of the surrounding rock; L c The length of the exposed section is generally 0.1 to 0.2 m;

[0032] Anchor spacing calculation formula:

[0033]

[0034] Where S is the anchor spacing; T is the bearing capacity of a single anchor; τ is the bond strength between the anchor and the surrounding rock.

[0035] Furthermore, the concrete mix design of the concrete used in step 4, step 5, and step 6 must meet the requirements of strength, durability, and workability, and the specific calculation is as follows:

[0036] f cu,0 =f cu,k +1.645·σ

[0037] In the formula, f cu,0 The strength of concrete mix; f cu,k is the design strength of concrete, which is 30MPa for C30 concrete; σ is the standard deviation, which is generally 5MPa.

[0038] Furthermore, in step 6, the blocking construction adopts a blocking wall, and the thickness of the blocking wall must meet the requirements of compression and shear resistance; the calculation formula of the compressive thickness of the blocking wall is as follows:

[0039]

[0040] Where, t is the thickness of the blocking wall; F is the force acting on the blocking wall; σ cis the compressive strength of concrete; b is the width of the blocking wall.

[0041] The beneficial effects of the present invention are:

[0042] The present invention solves the technical problem of tunnel entrance construction under cliff terrain conditions by designing and implementing the construction of branch tunnels, and has the following significant effects:

[0043] 1. Improve efficiency and shorten construction period: The entry method of the cliff cave entrance of the highway tunnel avoids the complicated procedures of building construction access roads, backfilling the slope foot and retaining wall protection in the traditional method by building a construction branch tunnel, which can shorten the construction period by 2 to 3 months.

[0044] 2. Reduce costs and save investment: The entry method of the cliff entrance of the highway tunnel does not require large-scale earth and stone backfilling and retaining wall construction, which reduces resource input and saves project investment of 3.5 million to 6.28 million yuan.

[0045] 3. Improve safety: The entry method of the cliff entrance of the highway tunnel reduces the risk of high-altitude operations, scientifically designs support parameters, such as: shotcrete thickness, anchor arrangement, and ensures the stability of the surrounding rock through dynamic monitoring to ensure construction safety.

[0046] 4. Adapt to complex terrain: The entry method of the cliff entrance of this highway tunnel is suitable for complex terrain conditions such as cliffs, solving problems that are difficult to implement with traditional methods, and has high technical feasibility.

[0047] 5. Ensure quality and durability: The entry method of the cliff entrance of the highway tunnel ensures construction quality and structural strength by accurately calculating blasting parameters, support parameters and concrete mix ratio; the blocking wall is reasonably designed to enhance the safety of the tunnel during operation.

[0048] 6. Significant environmental and social benefits: The entry method of the cliff entrance of the highway tunnel reduces the damage to the ecological environment, provides technical reference for similar projects, and promotes the advancement of tunnel construction technology.

[0049] In summary, the entry method of the cliff entrance of the highway tunnel achieved comprehensive optimization of construction period, cost, safety and quality, with significant economic and social benefits and important promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 It is a plan view schematic diagram of a method for entering a cliff cave entrance of a highway tunnel according to the present invention;

[0052] Figure 2 It is a longitudinal section schematic diagram of a method for entering a cliff entrance of a highway tunnel according to the present invention;

[0053] Figure 3 It is a cross-sectional schematic diagram of a method for entering a cliff cave entrance of a highway tunnel according to the present invention;

[0054] Figure 4 It is a schematic diagram of the location of the blocking wall of the method for entering the cliff hole of the highway tunnel of the present invention;

[0055] In the figure, 1. anchor rod, 2. main hole, 3. branch hole, 4. blocking wall. DETAILED DESCRIPTION

[0056] The following will be combined with the accompanying drawings of the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] In view of the problems of poor construction conditions, complicated procedures, high costs, slow progress and great safety hazards of traditional construction methods under complex terrain conditions, this embodiment provides a method for entering a cliff entrance of a highway tunnel, and the method for entering a cliff entrance of a highway tunnel includes the following steps:

[0058] Step 1: According to the two-stage construction drawing design documents and the actual on-site measurement results, determine the location, line shape and cross-sectional form of the tunnel entry construction tunnel, and determine the plan design drawing, longitudinal section design drawing and cross-sectional design drawing of the construction tunnel.

[0059] Specifically, based on the two-stage construction drawing design documents and actual on-site measurement results, combined with the geological survey report, which includes surrounding rock classification, groundwater distribution, surface water impact, etc., the location, line shape and cross-sectional form of the construction branch tunnel are determined.

[0060] For location selection: give priority to areas with relatively flat terrain and good geological conditions as the entrance of the construction branch tunnel, and avoid high and steep slopes or landslides. For linear design: the construction branch tunnel should be designed as straight or gentle curves as much as possible to reduce the difficulty of construction. The slope is controlled at 3% to 5% to facilitate the passage of mechanical equipment. For section form: determine the reasonable section size according to construction requirements and geological conditions. Generally, a three-center circular arch section is used, with a net width of 4.56 meters and a net height of 4 to 5 meters to meet the passage requirements of transportation vehicles and equipment.

[0061] Finally, optimization is carried out. Considering the project construction period, the design scheme of the construction access tunnel is optimized multiple times through BIM technology or numerical simulation software such as FLAC3D and ANSYS to ensure its economy and feasibility. The final plane design drawing of the construction access tunnel is determined as shown in Figure 1 . In the figure, A is the starting point of the construction access tunnel, B is the ending point of the construction access tunnel, and C is the ending point of the tunnel; the longitudinal section design drawing is as shown in Figure 2 . In the figure, the vertical line on the left is the reference elevation, and D is the outlet of the construction access tunnel; the cross-section design drawing is as shown in Figure 3 , and it is implemented after being submitted to the supervision unit for approval.

[0062] Step 2: Build a construction access road to the entrance of the construction access tunnel of the tunnel, and harden the surrounding site to ensure a certain slope for drainage.

[0063] Specifically, the construction of the construction access road includes route planning, width and slope, and structural design. For route planning: The construction access road is led out from the existing road and arranged along the relatively flat area of the terrain, avoiding steep slopes, landslide bodies, and poor geological sections as much as possible. For width and slope: The width of the construction access road is 4.5 - 6 meters, the maximum longitudinal slope does not exceed 8%, and the turning radius is not less than 15 meters to meet the passing requirements of large transport vehicles. For structural design: The base of the access road is compacted with graded gravel, and the surface is paved with 20 - centimeter - thick C20 concrete to ensure that the bearing capacity meets the requirements of construction machinery and vehicle loads.

[0064] Finally, the site is hardened. A hardened site is set around the entrance of the construction access tunnel for material stacking, mechanical equipment parking, and construction operations. The site is hardened with 15 - centimeter - thick C20 concrete, and a 2% - 3% drainage slope is set on the surface to prevent water accumulation. Drainage ditches are set around to introduce rainwater into the intercepting gutter to avoid scouring the construction site.

[0065] Step 3: Construct the intercepting gutter on the top of the construction access tunnel, the entrance protection, and the open cut tunnel.

[0066] Specifically, a water interception gutter is set above the top of the construction branch tunnel to prevent surface water from flowing into the tunnel. The gutter is 0.81 meters wide and 0.6 to 0.8 meters deep, and is built with M7.5 mortar-laid rubble. A longitudinal slope is set at the bottom of the gutter, with a slope of not less than 2%, to divert the water flow to the natural drainage system or sedimentation tank. Retaining walls are set on both sides of the tunnel opening. The height of the retaining wall is determined according to the terrain, generally 2 to 3 meters, and is built with M10 mortar-laid rubble. A reinforced concrete arch is set at the top of the tunnel opening, with a thickness of 0.5 meters and a span consistent with the tunnel opening to ensure the stability of the tunnel opening. The length of the open tunnel is determined according to the geological conditions, generally 5 to 10 meters. The open excavation method is adopted for construction, and the initial support and secondary lining are applied in time after the excavation is completed. The initial support adopts the joint support of shotcrete + anchor rod + steel mesh. The thickness of the shotcrete is 10 cm, the length of the anchor rod is 2.5 to 3 meters, and the spacing is 1.2×1.2 meters. The secondary lining is made of C30 waterproof reinforced concrete with a thickness of 0.5 meters.

[0067] Step 4, construct branch tunnel and blind tunnel engineering;

[0068] The tunnel excavation is carried out in stages by using an excavator and a manual hand-drill for drilling and blasting, and the advance per cycle is controlled at 1.5 to 2 meters. The blasting parameters are adjusted according to the surrounding rock grade. For the III. level surrounding rock, the blasthole spacing is 0.81 meters and the hole depth is 2 meters. For the IV. level surrounding rock, the blasthole spacing is 0.6 to 0.8 meters and the hole depth is 1.5 meters. Finally, a loader and a dump truck are used to transport the slag to the designated waste dump.

[0069] The initial support uses a wet spraying machine to spray concrete, with a spraying thickness of 10 to 15 cm and a strength grade of C25. The grouting anchor 1 is drilled with a down-the-hole drill and grouting is done with a grouting machine. The diameter of the anchor 1 is Φ22, the length is 2.5 to 3 meters, and the spacing is 1.2×1.2 meters. The steel mesh is welded into a grid shape with Φ8 steel bars, and the grid size is 20×20 cm, which is fixed on the anchor 1.

[0070] Before the wet spraying operation of the tunnel support, the support parameter calculation needs to be carried out; the support parameter calculation includes the calculation of the thickness of the shotcrete, the length and spacing of the anchor rods;

[0071] The design of shotcrete thickness needs to be determined according to the surrounding rock pressure and support strength requirements. The calculation formula is:

[0072]

[0073] Where, t is the thickness of shotcrete; P is the surrounding rock pressure; σ c is the compressive strength of shotcrete.

[0074] Assuming the surrounding rock pressure is 0.2MPa and the compressive strength of shotcrete is 25MPa, the thickness of shotcrete is:

[0075]

[0076] In actual construction, taking into account safety reserves and construction errors, the thickness of shotcrete is usually 10 to 15 cm.

[0077] The design of anchor bolts must meet the requirements of surrounding rock reinforcement, and their length and spacing are calculated using the following formula;

[0078] Anchor rod length calculation formula:

[0079] L=L a +L b +L c

[0080] Where, L is the total length of the anchor rod; a L is the length of the anchoring section, generally 1 to 1.5 m; b is the free section length, which is determined according to the relaxation range of the surrounding rock; L c The length of the exposed section is generally 0.1 to 0.2 m;

[0081] Anchor spacing calculation formula:

[0082]

[0083] Where S is the anchor spacing; T is the bearing capacity of a single anchor; τ is the bond strength between the anchor and the surrounding rock.

[0084] Assuming that the bearing capacity of a single anchor is 100kN and the bonding strength is 300kPa, the anchor spacing is:

[0085]

[0086] Therefore, considering the safety factor and construction convenience, the anchor spacing can be 1.2×1.2m.

[0087] Furthermore, when the tunnel is excavated by drilling and blasting with an excavator or a manual pneumatic drill, blasting parameter calculation is required; blasting parameter calculation includes calculation of blasthole depth and charge amount;

[0088] The formula for calculating the depth of the blasthole is:

[0089] H=K·B

[0090] In the formula, H is the depth of the blasthole; K is the empirical coefficient, generally taken as 1.0~1.2; B is the excavation footage.

[0091] The formula for calculating the charge amount is:

[0092] Q=q·V

[0093] Where Q is the charge of a single hole; q is the unit explosive consumption, which is determined according to the surrounding rock grade; V is the blasting volume of a single hole.

[0094] Assume that the excavation depth is 2m, the surrounding rock grade is III., and the unit explosive consumption is 0.3kg / m 3 , then the blasthole depth:

[0095] H = 1.1 2 = 2.2 m

[0096] Assuming the hole spacing is 1m, the single hole blasting volume is:

[0097] V=π·r 2 H = π (0.05) 2 2.2≈0.017m 3

[0098] The charge per hole is:

[0099] Q = 0.3 0.017 = 0.0051 kg

[0100] For the secondary lining, a steel membrane trolley is used to cast C30 waterproof reinforced concrete with a thickness of 0.5 meters. During the casting process, the slump of the concrete is strictly controlled at 16 to 18 centimeters, and the quality of vibration is controlled to ensure that the lining is dense and free of voids.

[0101] Step 5, enter the main tunnel for construction; the main tunnel is constructed using the New Austrian Tunneling Method. During the construction process, the self-bearing capacity of the surrounding rock and the restraining effect of the excavation surface are utilized. Anchor rods and shotcrete are used as the main construction support means to reinforce the surrounding rock in time, restrain the relaxation and deformation of the surrounding rock, and measure and monitor the surrounding rock and support.

[0102] Specifically, the main tunnel was constructed using the New Austrian Tunneling Method, which fully utilized the self-bearing capacity of the surrounding rock and adopted a construction method of short footage, weak blasting, strong support, and frequent measurement. The footage of each cycle was controlled at 1.5 to 2 meters, and initial support was carried out in a timely manner after blasting.

[0103] The thickness of the initial support shotcrete is 10-15 cm, and the strength grade is C25. The anchor rods are Φ22 hollow grouting anchor rods, with a length of 3-4 meters and a spacing of 1.2×1.2 meters. The steel mesh uses Φ8 steel bars with a mesh size of 20×20 cm.

[0104] Set up surrounding rock deformation monitoring points once a day, focusing on monitoring the arch subsidence and peripheral convergence. Dynamically adjust support parameters based on monitoring data to ensure construction safety.

[0105] Step 6, sealing the branch hole;

[0106] like Figure 4As shown in the figure, after the construction of the main tunnel 2 is completed, the two ends of the construction branch tunnel 3 are blocked. The blocking wall 4 is 1 meter thick and is cast with C30 plain concrete. Drain holes with a diameter of Φ100 mm and a spacing of 2 meters are set on the top of the blocking wall 4 to prevent water accumulation. Clean the loose rock mass at the blocking position, install the formwork and reinforce it; vibrate the concrete in layers when pouring to ensure that it is dense and has no voids; the concrete curing time is not less than 7 days, and the formwork is removed after reaching the design strength.

[0107] Furthermore, the blocking construction adopts a blocking wall, and the thickness of the blocking wall needs to meet the requirements of compression and shear resistance;

[0108] The calculation formula of the compressive thickness of the blocking wall is as follows:

[0109]

[0110] Where, t is the thickness of the blocking wall; F is the force acting on the blocking wall; σ c is the compressive strength of concrete; b is the width of the blocking wall.

[0111] Assuming the force is 1000kN, the concrete compressive strength is 30MPa, and the width of the blocking wall is 5m; then the thickness of the blocking wall is:

[0112]

[0113] The thickness of the blocking wall can be greater than 6.67cm, but in actual construction, considering safety reserves and construction errors, 1m is usually taken as the thickness of the blocking wall.

[0114] The specific steps and implementation of the above-mentioned highway tunnel cliff cave entry method not only solved the problem of cliff cave entry construction, but also significantly improved construction efficiency and safety, providing valuable experience and technical support for similar projects.

[0115] Furthermore, the concrete mix design of the concrete used in step 4, step 5, and step 6 of the above-mentioned highway tunnel cliff entrance method needs to meet the strength, durability and workability requirements, and the specific calculation is as follows:

[0116] f cu,0 =f cu,k +1.645·σ

[0117] In the formula, f cu,0 The strength of concrete mix; f cu,k is the design strength of concrete; σ is the standard deviation, which is generally 5MPa.

[0118] Assuming that C30 concrete is used, the concrete design strength of C30 concrete is 30MPa, then the concrete mix strength is:

[0119] fcu,0 =30+1.645·5=30+8.225=38.225Mpa

[0120] According to the test data, determine the cement dosage, water-cement ratio and aggregate ratio. For example: cement dosage: 400kg / m 3 , water-cement ratio: 0.45, sand rate: 40%, aggregate ratio: sand: stone = 1:2.

[0121] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for entering a cliff entrance of a highway tunnel, characterized by: The method for entering the cliff entrance of the highway tunnel comprises the following steps: Step 1: According to the two-stage construction drawing design documents and the actual on-site measurement results, determine the location, line shape and cross-sectional form of the tunnel entry construction branch hole, and determine the plane design drawing, longitudinal section design drawing and cross-sectional design drawing of the construction branch hole; Step 2: Build a construction access road to the entrance of the construction branch tunnel, and harden the surrounding area to ensure a certain slope for easy drainage; Step 3, construct the water cutoff ditch on the top of the construction branch tunnel, the tunnel entrance protection, and the open tunnel; Step 4: Construction of branch tunnels and blind tunnels; excavation of the tunnel body is carried out by drilling and blasting with an excavator and a manual pneumatic drill; wet spraying is used for tunnel body support, and grouting anchors are drilled with a down-the-hole drill and grouting is done with a grouting machine; the secondary lining is cast with C30 waterproof reinforced concrete using a steel membrane trolley; Step 5, enter the main tunnel for construction; the main tunnel is constructed using the New Austrian Tunneling Method. During the construction process, the self-bearing capacity of the surrounding rock and the restraining effect of the excavation surface are utilized. Anchor rods and shotcrete are used as the main construction support means to reinforce the surrounding rock in time, restrain the relaxation and deformation of the surrounding rock, and measure and monitor the surrounding rock and support; Step 6: After the main tunnel construction is completed, 1m thick C30 plain concrete is used to seal both ends of the construction branch tunnel.

2. The method for entering a cliff entrance of a highway tunnel according to claim 1, characterized in that: In step 4, when the tunnel is excavated by drilling and blasting with an excavator or a manual pneumatic drill, blasting parameter calculation is required; blasting parameter calculation includes blasthole depth calculation and charge calculation; The formula for calculating the depth of the blasthole is: H=K·B In the formula, H is the depth of the blasthole; K is the empirical coefficient, which is generally 1.0 to 1.2; B is the excavation footage; The formula for calculating the charge amount is: Q=q·V Where Q is the charge of a single hole; q is the unit explosive consumption, which is determined according to the surrounding rock grade; V is the blasting volume of a single hole.

3. The method for entering a cliff entrance of a highway tunnel according to claim 1, characterized in that: In step 4, before the wet spraying operation of the tunnel support, the support parameter calculation needs to be carried out; the support parameter calculation includes the calculation of the thickness of the shotcrete, the length and spacing of the anchor rods; The design of shotcrete thickness needs to be determined according to the surrounding rock pressure and support strength requirements. The calculation formula is: Where, t is the thickness of shotcrete; P is the surrounding rock pressure; σ c is the compressive strength of shotcrete; The design of anchor bolts must meet the requirements of surrounding rock reinforcement, and their length and spacing are calculated using the following formula; Anchor rod length calculation formula: L=L a +L b +L c Where, L is the total length of the anchor rod; a L is the length of the anchoring section, generally 1 to 1.5 m; b is the free section length, which is determined according to the relaxation range of the surrounding rock; L c The length of the exposed section is generally 0.1 to 0.2 m; Anchor spacing calculation formula: Where S is the anchor spacing; T is the bearing capacity of a single anchor; τ is the bond strength between the anchor and the surrounding rock.

4. The method for entering a cliff entrance of a highway tunnel according to claim 1, characterized in that: The concrete mix design of the concrete used in step 4, step 5, and step 6 must meet the requirements of strength, durability and workability. The specific calculation is as follows: f cu,0 =f cu,k +1.645·s In the formula, f cu,0 The strength of concrete mix; f cu,k is the design strength of concrete, which is 30MPa for C30 concrete; σ is the standard deviation, which is generally 5MPa.

5. The method for entering a cliff entrance of a highway tunnel according to claim 1, characterized in that: In step 6, the blocking construction adopts a blocking wall, and the thickness of the blocking wall must meet the requirements of compression and shear resistance; The calculation formula of the compressive thickness of the blocking wall is as follows: Where, t is the thickness of the blocking wall; F is the force acting on the blocking wall; σ c is the compressive strength of concrete; b is the width of the blocking wall.

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