A tunnel excavation construction method suitable for grade IV and V surrounding rock

Abstract

The invention provides a tunnel excavation construction method suitable for IV and V grade surrounding rocks, and the construction method comprises the following steps: step 1, construction preparation, formulating construction plans and construction measures, formulating construction monitoring and measurement plans and settlement observation plans; step 2, measurement and setting out; step 3, IV and V grade surrounding rock tunnels adopt three-step method construction technology, drilling blastholes, and ventilating the tunnel after the blastholes are completed; step 4, charging, blasting and re-evacuating the blastholes; the drilling and blasting design adopts multi-hole dense hole blasting technology, strictly following the principle of short footage and weak blasting; step 5, slag discharge, slag discharge adopts a loader and a dump truck to load and transport slag; step 6, after excavation, timely initial spraying of concrete, laying of steel mesh, installation of steel frame, and setting of locking foot anchor pipes to fix the steel frame; setting of system anchor rods, and then spraying of concrete for sealing; step 7, excavation and pouring of invert arches. The construction method improves production efficiency, accelerates construction progress and saves project costs.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel excavation, and in particular relates to a tunnel excavation construction method suitable for IV and V grade surrounding rocks. Background Art

[0002] With the development of my country's railway construction, railway engineering transportation infrastructure has gradually shifted from plain areas to mountainous areas. The number of tunnel constructions has increased, and various geological structures have appeared in tunnel construction. Among them, horizontal jointed rock formations have become the focus of tunnel builders. Excavation, as the first link in horizontal jointed rock formation tunnels, plays a vital role in "safety", "cost" and "progress" in construction. Therefore, ensuring the quality of tunnel excavation has become the primary goal of tunnel builders.

[0003] Horizontal jointed rock strata are mostly mudstone and siltstone, which are cemented with mud and have well-developed joints and fissures. They are in fragmented form and are prone to falling off and collapse. This leads to serious over-excavation and under-excavation during smooth blasting.

[0004] Therefore, it is necessary to provide an improved technical solution to address the above-mentioned deficiencies in the prior art. Summary of the invention

[0005] The purpose of the present invention is to provide a tunnel excavation construction method suitable for grade IV and V surrounding rock, so as to at least solve the current problems of serious over-excavation and under-excavation of tunnels.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A tunnel excavation construction method applicable to grade IV and V surrounding rock, the construction method comprising the following steps:

[0008] Step 1: Construction preparation: understand the engineering geology and hydrogeology information according to the design data, formulate construction plans and construction measures, and formulate construction monitoring and measurement plans and settlement observation plans;

[0009] Step 2: measure and stake out the tunnel face, stake out the excavation contour, and arrange blasthole positions on the tunnel face;

[0010] Step 3: For tunnels with rock mass of level IV and V, three-step construction technology is adopted to drill blastholes, and tunnel ventilation is performed after the blastholes are completed;

[0011] Step 4: Charge, blast, and clear the danger in the blastholes; the drilling and blasting design adopts multi-hole dense hole blasting technology and strictly follows the principle of short footage and weak blasting;

[0012] Step 5: slag removal, which is carried out by using a loader and a dump truck to load and transport the slag;

[0013] Step 6: After excavation, spray concrete in time, lay steel mesh, install steel frame, and install locking anchor pipes to fix the steel frame; then install system anchor rods and spray concrete to seal;

[0014] Step 7: Excavation and pouring of the invert.

[0015] As described above, the tunnel excavation construction method applicable to grade IV and V surrounding rock is preferably such that in step 2, the excavation contour line laid out is enlarged by at least 5CM to ensure the thickness of the secondary lining.

[0016] The tunnel excavation construction method applicable to Class IV and V surrounding rock as described above, preferably, in step 2, when the tunnel is in a Class V surrounding rock environment;

[0017] The blastholes on the upper step are divided into a left center hole, a right center hole, two rows of peripheral holes and two rows of lower holes. The two rows of peripheral holes are arranged along the contour line of the upper step of the tunnel, and the two rows of lower holes are arranged at the bottom of the upper step. The left center hole and the right center hole are arranged between the two rows of peripheral holes and the two rows of lower holes. The left center hole and the right center hole are symmetrically arranged along the vertical center line of the tunnel. The left center hole and the right center hole include multiple rows of blastholes, and the blastholes in the same vertical direction among the multiple rows of blastholes are in the same detonator section;

[0018] The middle step blastholes are divided into multiple rows of middle holes and one row of peripheral holes. The middle holes at the same horizontal position are in the same detonator section, and the number of multiple rows of middle holes increases step by step from top to bottom.

[0019] The lower step blastholes are divided into multiple rows of bottom holes and a row of peripheral holes. The bottom holes at the same horizontal position are in the same detonator section, and the number of multiple rows of bottom holes decreases gradually from top to bottom.

[0020] The tunnel excavation construction method applicable to the surrounding rock of grade IV and V as described above is preferably such that, in the upper step, the number of blastholes of the left center hole and the right center hole gradually decreases from the center of the tunnel to both sides and the detonator sections gradually increase; the detonator sections of the two rows of peripheral holes gradually increase from the inside to the outside, and the detonator sections of the two rows of lower holes gradually increase from the top to the bottom;

[0021] In the middle step, the detonator segments of multiple rows of middle holes gradually increase from top to bottom;

[0022] On the lower steps, the detonator segments of the multiple rows of bottom holes gradually become larger from top to bottom.

[0023] The tunnel excavation construction method applicable to the IV and V grade surrounding rock as described above is preferably such that the peripheral holes located in the outermost circle on the upper, middle and lower steps are in the same detonator section, and the spacing between the peripheral holes in the outermost circle is within 40 cm, and small explosive rolls are used for interval charging, and the unit consumption of explosives is 0.6 kg / m 3The excavation progress of the upper step is within 0.6m, and the middle step and the lower step are constructed by staggered excavation on both sides, with a staggered distance of more than 3 steel frames. The excavation progress of each cycle ranges from 1.2m to 2.0m.

[0024] The tunnel excavation construction method applicable to grade IV and V surrounding rock as described above, preferably, in step 6, C25 concrete is used for the surrounding rock sprayed concrete, the thickness of the arch wall sprayed concrete is at least 28 cm, the thickness of the invert arch sprayed concrete is at least 28 cm, and the grade V surrounding rock adopts a full-ring I20a / I20b steel frame with a steel frame spacing of 0.6 m; the length of the locking foot anchor pipe is at least 5 m, and at least 8 locking foot anchor pipes are arranged on each steel frame, and the locking foot anchor pipe is fixedly connected to the steel frame at the end position with a U-shaped steel bar.

[0025] The tunnel excavation construction method applicable to Class IV and V surrounding rock as described above, preferably, in step 2, when the tunnel is in a Class IV surrounding rock environment;

[0026] The blastholes on the upper step are divided into multiple rows of peripheral holes, groove holes, two groups of first auxiliary holes, one group of second auxiliary holes and two groups of third auxiliary holes. Multiple rows of peripheral holes are arranged along the contour line of the upper step of the tunnel. Multiple groove holes are evenly distributed in the center of the upper step. Two groups of first auxiliary holes are respectively arranged at the upper left and upper right parts of the groove holes. One group of second auxiliary holes is arranged in a semi-enclosed arrangement at the middle and lower part of the groove holes. Two groups of third auxiliary holes are respectively arranged at the lower left and lower right parts of the second auxiliary holes.

[0027] The middle step blastholes are divided into multiple rows of middle holes and two rows of peripheral holes. The middle holes at the same horizontal position are in the same detonator section, and the number of the two rows of peripheral holes increases step by step from the inside to the outside.

[0028] The lower step blastholes are divided into multiple rows of bottom holes and two rows of peripheral holes. The bottom holes at the same horizontal position are in the same detonator section. The number of the two rows of peripheral holes increases step by step from the inside to the outside, and the number of the multiple rows of bottom holes decreases step by step from top to bottom.

[0029] The tunnel excavation construction method applicable to the surrounding rock of level IV and V as described above, preferably, in the upper step, the detonator sections of the blasthole from the inside to the outside are gradually enlarged;

[0030] In the middle step, the detonator segments of multiple rows of middle holes gradually increase from top to bottom;

[0031] On the lower steps, the detonator segments of the multiple rows of bottom holes gradually become larger from top to bottom.

[0032] The tunnel excavation construction method applicable to grade IV and V surrounding rock as described above, preferably, in step 6, C25 concrete is used for the surrounding rock sprayed concrete, the thickness of the arch wall sprayed concrete is at least 25 cm, the thickness of the invert arch sprayed concrete is at least 10 cm, and the grade V surrounding rock adopts a full-ring I18 steel frame with a steel frame spacing of 1.0 m; the length of the locking foot anchor pipe is at least 4 m, and at least 8 locking foot anchor pipes are arranged on each steel frame, and the locking foot anchor pipe is fixedly connected to the steel frame at the end position with a U-shaped steel bar.

[0033] The tunnel excavation construction method applicable to the surrounding rock of grade IV and V as described above, preferably, in step 6, the shotcrete is sprayed in sections, slices and layers, from bottom to top, from the area without water or less water to the area with water or more water, and the nozzle of the shotcrete is substantially perpendicular to the sprayed surface, and the distance is kept between 1.5 and 2.0 m;

[0034] The sprayed concrete covers the steel frame with a protective layer of no less than 4cm. The nozzle moves slowly and evenly in a spiral shape, pressing the front half circle each time. The circle diameter ranges from 25-35cm. The thickness of one spraying is controlled at no more than 6cm for the arch wall and no more than 10cm for the side wall.

[0035] Beneficial effects: The tunnel over-excavation and under-excavation, tunnel surrounding rock stability, and initial support quality all meet the design requirements, the tunneling effect is good, the first-time inspection pass rate is 100%, and the construction effect is perfectly achieved. This construction method ensures product quality, improves production efficiency, speeds up construction progress, saves project costs, and achieves significant social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0037] Figure 1 This is a blasthole layout diagram of the tunnel face under the condition of Grade V surrounding rock in an embodiment of the present invention;

[0038] Figure 2 This is a layout diagram of step blastholes on the tunnel face under the condition of Grade IV surrounding rock in an embodiment of the present invention;

[0039] Figure 3 This is a layout diagram of the middle step blastholes of the tunnel face under the condition of Grade IV surrounding rock in the embodiment of the present invention;

[0040] Figure 4 This is a layout diagram of the step blastholes under the tunnel face under the condition of Grade IV surrounding rock in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0042] In the description of the present invention, the terms "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on the present invention. The terms "connected" and "connected" used in the present invention should be understood in a broad sense. For example, they can be fixed connections or detachable connections; they can be directly connected or indirectly connected through intermediate components. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0043] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0044] According to a specific embodiment of the present invention, Figure 1-4 As shown, the present invention provides a tunnel excavation construction method applicable to grade IV and V surrounding rock, and the construction method comprises the following steps:

[0045] Step 1, construction preparation, understand the engineering geology and hydrogeology information according to the design data, formulate construction plans and construction measures, and formulate construction monitoring and measurement plans and settlement observation plans. Lay water pipes and wires, construction access roads, layout of construction sites, mechanical equipment, personnel allocation, material preparation, construction of drainage facilities, construction of environmental protection and water conservation facilities. Pneumatic drills, trolleys and other equipment are overhauled and placed near the face; prepare for subsequent construction.

[0046] Step 2: measure and stake out the tunnel face, stake out the excavation contour line, and arrange the blasthole positions on the tunnel face; the staked out excavation contour line is enlarged by at least 5CM to ensure the thickness of the secondary lining.

[0047] When the tunnel is in a Grade V surrounding rock environment; the upper step blastholes are divided into a left center eye, a right center eye, two rows of peripheral eyes and two rows of lower eyes. The two rows of peripheral eyes are arranged along the contour line of the upper step of the tunnel, and the two rows of lower eyes are arranged at the bottom of the upper step. The left center eye and the right center eye are arranged between the two rows of peripheral eyes and the two rows of lower eyes. The left center eye and the right center eye are symmetrically arranged along the vertical center line of the tunnel. The left center eye and the right center eye include multiple rows of blastholes. The blastholes in the multiple rows of blastholes in the same vertical direction are in the same detonator section; the middle step blastholes are divided into multiple rows of middle eyes and a row of peripheral eyes. The middle eyes at the same horizontal position are in the same detonator section, and the number of multiple rows of middle eyes increases step by step from top to bottom; the lower step blastholes are divided into multiple rows of bottom eyes and a row of peripheral eyes. The bottom eyes at the same horizontal position are in the same detonator section, and the number of multiple rows of bottom eyes decreases step by step from top to bottom.

[0048] In the upper step, the number of blastholes in the left and right center holes gradually decreases from the center of the tunnel to both sides, and the detonator section gradually increases; the detonator section of the two rows of peripheral holes gradually increases from the inside to the outside, and the detonator section of the two rows of lower holes gradually increases from top to bottom. In the middle step, the detonator section of multiple rows of middle holes gradually increases from top to bottom; in the lower step, the detonator section of multiple rows of bottom holes gradually increases from top to bottom.

[0049] The peripheral holes on the upper, middle and lower steps are in the same detonator section, and the spacing between the peripheral holes in the outermost circle is within 40cm. Small explosive rolls are used for interval loading, and the unit consumption of explosives is 0.6Kg / m 3 The excavation progress of the upper step is within 0.6m, and the middle step and the lower step are constructed by staggered excavation on both sides, with a staggered distance of more than 3 steel frames. The excavation progress of each cycle ranges from 1.2m to 2.0m.

[0050] In the upper step of the present embodiment, the left center eye and the right center eye are each arranged in four rows, with a row spacing of 50cm*50cm, and the detonator segments are 1, 3, 5, and 7, respectively; the detonator segments of the two rows of lower eyes are 13 and 15, respectively from top to bottom, the spacing of the lower eyes located above is 60cm, and the spacing of the upper eyes located below is 70cm; the detonator segments of the two rows of peripheral eyes are 9 and 11, respectively, from inside to outside; the spacing of the peripheral eyes located on the inner side is 80cm.

[0051] In the middle step, there are four rows of middle eyes. The detonator sections of the four rows of middle eyes from top to bottom are 1, 5, 7, and 13 respectively. The row spacing between any two rows of middle eyes is 100 cm, and the spacing between the four rows of middle eyes is 100 cm; the detonator section of the peripheral eyes is 11.

[0052] In the lower steps, there are three rows of bottom holes. The detonator sections of the three rows of bottom holes are 1, 5, and 7 respectively. The spacing between the three rows of bottom holes is 100cm; the detonator section of the peripheral holes is 11.

[0053] When the tunnel is in a Grade IV surrounding rock environment; the upper step blastholes are divided into multiple rows of peripheral holes, groove holes, two groups of first auxiliary holes, one group of second auxiliary holes and two groups of third auxiliary holes. Multiple rows of peripheral holes are set along the contour line of the upper step of the tunnel, and multiple groove holes are evenly distributed in the center of the upper step. Two groups of first auxiliary holes are respectively set at the upper left and upper right parts of the groove holes, one group of second auxiliary holes is set in a semi-enclosed arrangement at the middle and lower parts of the groove holes, and two groups of third auxiliary holes are respectively set at the lower left and lower right parts of the second auxiliary holes; the middle step blastholes are divided into multiple rows of middle holes and two rows of peripheral holes. The middle holes at the same horizontal position are in the same detonator section, and the number of the two rows of peripheral holes increases step by step from the inside to the outside; the lower step blastholes are divided into multiple rows of bottom holes and two rows of peripheral holes. The bottom holes at the same horizontal position are in the same detonator section, the number of the two rows of peripheral holes increases step by step from the inside to the outside, and the number of multiple rows of bottom holes decreases step by step from top to bottom.

[0054] In the upper step, the detonator sections of the blast holes from the inside to the outside gradually increase in size; in the middle step, the detonator sections of multiple rows of middle holes gradually increase in size from top to bottom; in the lower step, the detonator sections of multiple rows of bottom holes gradually increase in size from top to bottom.

[0055] In the upper step of this embodiment, the detonator segment of the groove eye is 1, and the detonator segments of the first auxiliary eye, the second auxiliary eye and the third auxiliary eye are 3, 5, and 7 respectively; the detonator segments of the three rows of peripheral eyes are 9, 11, and 13 from the inside to the outside; the spacing of the outermost peripheral eyes is 500mm, and the spacing of the other two peripheral eyes is 800mm.

[0056] In the middle step, there are three rows of central holes, and the detonator sections are 1, 3, and 5 from top to bottom. The spacing between the holes is 1000mm, and the detonator sections of the two rows of peripheral holes are 5 and 7 from inside to outside.

[0057] In the lower step, there are two rows of bottom holes, and their detonator sections are 1 and 3 from top to bottom, and the spacing between the holes is 1000mm. The detonator sections of the two rows of peripheral holes are 5 and 7 from inside to outside, and the spacing between the outermost peripheral holes is 650mm.

[0058] Step 3: For tunnels with rock masses of level IV and V, three-step construction technology is used to drill blastholes. After the blastholes are completed, the tunnel is ventilated to eliminate smoke and dust.

[0059] Step 4, charge, blast and clear the danger in the blast hole; the drilling and blasting design adopts multi-hole dense hole blasting technology and strictly follows the principle of short footage and weak blasting.

[0060] The excavation height of the upper step is 6.5m. The excavation footage is dynamically adjusted according to the geological forecast and the actual geological conditions of the face. The integrity, bedding distribution, joint development and hardness of the rock mass of the arch are fully considered to make flexible adjustments to minimize the disturbance to the arch rock mass. The drilling and blasting design is modified according to the construction phenomenon and the changes of the surrounding rock, and the blasting design is optimized. After each blasting, the blasting effect is evaluated, including the residual eye rate, blasthole utilization rate, charge size, charge structure, blasting depth, ballast throwing distance and ballast block size. By statistics, evaluation and optimization of blasting design, the self-bearing capacity of the surrounding rock is maximized and the advance support effect is tested.

[0061] Step 5: slag removal. The slag is removed by a loader and a dump truck.

[0062] Step 6, after excavation, spray concrete in time, lay steel mesh, install steel frame, and install locking foot anchor pipe to fix the steel frame; then install system anchor rods, and then spray concrete to seal. When the bottom of the steel frame is not dense or suspended, install concrete pads at the bottom of the steel frame. In this embodiment, after the concrete spraying machine is installed and debugged, install a vibrating screen (sieve hole 10mm) on the hopper to prevent oversized aggregate from entering the spraying machine; before spraying, the rock surface must be trimmed, loose rocks must be removed, individual under-excavated protruding parts must be chiseled off, and individual over-excavated parts must be sprayed with sprayed concrete to level them; use high-pressure air to clean the rock surface; check whether the spraying machine is working normally; and conduct a spraying test. After everything is normal, concrete spraying can be carried out. Shotcrete is sprayed in sections, slices and layers, from bottom to top, from waterless and low-water areas to water-rich and high-water areas. The nozzle of the shotcrete is basically vertical to the sprayed surface, and the distance is maintained between 1.5 and 2.0 m. The gap between the steel frame and the rock surface is filled densely with shotcrete. The spraying sequence is symmetrical, from bottom to top. First, the gap between the steel frame and the surrounding rock is sprayed, and then the gap between the steel frames is sprayed. The shotcrete covers the steel frame with a protective layer of not less than 4 cm. Before spraying, the concave part of the sprayed surface is leveled first, and the nozzle moves slowly and evenly in a spiral shape, pressing the front half a circle each time. The circle diameter range is 25-35 cm, and the thickness of one spraying is controlled to not exceed 6 cm for the arch wall and not more than 10 cm for the side wall.

[0063] When the tunnel is in a Grade V surrounding rock environment, C25 concrete is used for the surrounding rock spraying, the thickness of the arch wall spraying is at least 28cm, the thickness of the invert arch spraying is at least 28cm, the arch wall Φ8 steel mesh, the grid spacing is 20cm×20cm. Grade V surrounding rock uses a full ring I20a / I20b steel frame with a steel frame spacing of 0.6m; the length of the locking foot anchor pipe is at least 5m, and at least 8 locking foot anchor pipes are set for each steel frame. The locking foot anchor pipe is fixedly connected to the steel frame with a U-shaped steel bar at the end.

[0064] When the tunnel is in a Grade IV surrounding rock environment, C25 concrete is used for the surrounding rock shotcrete, the thickness of the arch wall shotcrete is at least 25cm, the thickness of the invert shotcrete is at least 10cm, and the Grade V surrounding rock adopts a full-ring I18 steel frame with a steel frame spacing of 1.0m. The length of the locking foot anchor pipe is at least 4m, and each steel frame is equipped with at least 8 locking foot anchor pipes. The locking foot anchor pipe is fixedly connected to the steel frame at the end with a U-shaped steel bar, so that the steel frame is firmly connected to the steel frame to form a whole, so as to prevent sinking during tunnel excavation.

[0065] The support should be implemented promptly following the excavation surface to minimize the exposure time of the surrounding rock, inhibit the deformation of the surrounding rock, and prevent the surrounding rock from loosening and peeling off in a short period of time.

[0066] Step 7, excavation and pouring of the invert. In this embodiment, the excavation length of each cycle of the invert is 3m, the invert steel frame is installed, connected with the lower step steel frame, and initial support is applied to make the initial support closed into a ring; pouring the invert concrete, each group of invert concrete pouring length is 6m.

[0067] The technical parameters for smooth blasting of surrounding rock are determined according to the surrounding rock grade, and the excavation contour line is set on the side. Professional blasting personnel monitor the entire process from blasthole position, inclination, blasthole depth, charging to detonation, and correct the blasting parameters in time according to the actual situation of the surrounding rock and blasting.

[0068] 1. Increase the slurry coagulation degree from 1.1 to about 1.3 and continue spraying.

[0069] 2. Pour clay slurry or add fine sand or medium sand, and continue normal spraying after the gaps are filled.

[0070] 3. Add fine aggregate to the slurry.

[0071] 4. Add mud balls to seal and continue spraying normally.

[0072] 5. After pouring cement mortar, replace the cement slurry in the hole with clay slurry, and continue normal spraying after the pores are filled.

[0073] In summary, the technical solution of the tunnel excavation construction method suitable for IV and V grade surrounding rock provided by the present invention saves a lot of manpower, materials, machines and other resources compared with the traditional tunnel excavation method. The conventional excavation method has serious over-excavation in the horizontal rock layer excavation process, and the over-excavation is generally about 15cm. Compared with the conventional excavation method, the present method improves the effect of ordinary drilling and blasting excavation of the tunnel, can control the over-excavation within 5cm, reduces the over-excavation phenomenon, saves a lot of shotcrete, and can save 2774m3 of concrete per kilometer of double-track tunnels. The construction safety is effectively controlled, safe and reliable, and at the same time, the construction period is greatly shortened, the labor cost is reduced, and the economic benefits are significant.

[0074] It should be understood that the above description is merely exemplary and the embodiments of the present application do not limit this.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A tunnel excavation construction method suitable for surrounding rock of grade IV and V, characterized in that: The construction method comprises the following steps: Step 1: Construction preparation: understand the engineering geology and hydrogeology information according to the design data, formulate construction plans and construction measures, and formulate construction monitoring and measurement plans and settlement observation plans; Step 2: measure and stake out the tunnel face, stake out the excavation contour, and arrange blasthole positions on the tunnel face; Step 3: For tunnels with rock mass of level IV and V, three-step construction technology is adopted to drill blastholes, and tunnel ventilation is performed after the blastholes are completed; Step 4: Charge, blast, and clear the danger in the blastholes; the drilling and blasting design adopts multi-hole dense hole blasting technology and strictly follows the principle of short footage and weak blasting; Step 5: slag removal, which is carried out by using a loader and a dump truck to load and transport the slag; Step 6: After excavation, spray concrete in time, lay steel mesh, install steel frame, and install locking anchor pipes to fix the steel frame; then install system anchor rods and spray concrete to seal; Step 7, excavation and pouring of the invert; In step 2, when the tunnel is in a Class V surrounding rock environment; The blastholes on the upper step are divided into a left center hole, a right center hole, two rows of peripheral holes and two rows of lower holes. The two rows of peripheral holes are arranged along the contour line of the upper step of the tunnel, and the two rows of lower holes are arranged at the bottom of the upper step. The left center hole and the right center hole are arranged between the two rows of peripheral holes and the two rows of lower holes. The left center hole and the right center hole are symmetrically arranged along the vertical center line of the tunnel. The left center hole and the right center hole include multiple rows of blastholes, and the blastholes in the same vertical direction among the multiple rows of blastholes are in the same detonator section; The middle step blastholes are divided into multiple rows of middle holes and one row of peripheral holes. The middle holes at the same horizontal position are in the same detonator section, and the number of multiple rows of middle holes increases step by step from top to bottom. The lower step blastholes are divided into multiple rows of bottom holes and one row of peripheral holes. The bottom holes at the same horizontal position are in the same detonator section, and the number of multiple rows of bottom holes decreases step by step from top to bottom. In the upper steps, the number of blastholes in the left and right center holes gradually decreases from the center of the tunnel to both sides, and the detonator sections gradually increase; the detonator sections of the two rows of peripheral holes gradually increase from the inside to the outside, and the detonator sections of the two rows of lower holes gradually increase from top to bottom; In the middle step, the detonator segments of multiple rows of middle holes gradually increase from top to bottom; In the lower steps, the detonator segments of multiple rows of bottom holes gradually increase in size from top to bottom; In step 2, when the tunnel is in the Class IV surrounding rock environment; The blastholes on the upper step are divided into multiple rows of peripheral holes, groove holes, two groups of first auxiliary holes, one group of second auxiliary holes and two groups of third auxiliary holes. Multiple rows of peripheral holes are arranged along the contour line of the upper step of the tunnel. Multiple groove holes are evenly distributed in the center of the upper step. Two groups of first auxiliary holes are respectively arranged at the upper left and upper right parts of the groove holes. One group of second auxiliary holes is arranged in a semi-enclosed arrangement at the middle and lower part of the groove holes. Two groups of third auxiliary holes are respectively arranged at the lower left and lower right parts of the second auxiliary holes. The middle step blastholes are divided into multiple rows of middle holes and two rows of peripheral holes. The middle holes at the same horizontal position are in the same detonator section, and the number of the two rows of peripheral holes increases step by step from the inside to the outside. The lower step blastholes are divided into multiple rows of bottom holes and two rows of peripheral holes. The bottom holes at the same horizontal position are in the same detonator section. The number of the two rows of peripheral holes increases from the inside to the outside, and the number of the multiple rows of bottom holes decreases from the top to the bottom. In the upper steps, the detonator sections of the blasthole from the inside to the outside become larger step by step; In the middle step, the detonator segments of multiple rows of middle holes gradually increase from top to bottom; On the lower steps, the detonator segments of the multiple rows of bottom holes gradually become larger from top to bottom.

2. The tunnel excavation construction method applicable to grade IV and V surrounding rock according to claim 1, characterized in that: In step 2, the excavation contour line is enlarged by at least 5CM to ensure the thickness of the secondary lining.

3. The tunnel excavation construction method applicable to grade IV and V surrounding rock according to claim 1, characterized in that: The peripheral holes on the upper, middle and lower steps are in the same detonator section, and the spacing between the peripheral holes in the outermost circle is within 40cm. Small explosive rolls are used for interval loading, and the unit consumption of explosives is 0.6Kg / m 3 The excavation progress of the upper step is within 0.6m, and the middle step and the lower step are constructed by staggered excavation on both sides, with a staggered distance of more than 3 steel frames. The excavation progress of each cycle ranges from 1.2m to 2.0m.

4. The tunnel excavation construction method applicable to grade IV and V surrounding rock according to claim 1, characterized in that: In step 6, C25 concrete is used for surrounding rock shotcrete, the thickness of arch wall shotcrete is at least 28 cm, the thickness of invert shotcrete is at least 28 cm, and the V-level surrounding rock adopts full-ring I20a / I20b steel frame with a steel frame spacing of 0.6 m. The length of the locking foot anchor pipe is at least 5 m, and at least 8 locking foot anchor pipes are set for each steel frame. The locking foot anchor pipe is fixedly connected to the steel frame with U-shaped steel bars at the end.

5. The tunnel excavation construction method applicable to grade IV and V surrounding rock according to claim 1, characterized in that: In step 6, C25 concrete is used for surrounding rock shotcrete, the thickness of arch wall shotcrete is at least 25 cm, the thickness of invert shotcrete is at least 10 cm, and full-ring I18 steel frame is used for Grade V surrounding rock, with a steel frame spacing of 1.0 m; the length of the locking foot anchor pipe is at least 4 m, and at least 8 locking foot anchor pipes are set for each steel frame. The locking foot anchor pipe is fixedly connected to the steel frame at the end with a U-shaped steel bar.

6. The tunnel excavation construction method applicable to grade IV and V surrounding rock according to any one of claims 1 to 5, characterized in that: In step 6, the spraying of concrete is carried out in sections, slices and layers, from bottom to top, from areas without water or with little water to areas with water or with much water. During the spraying, the nozzle of the spraying concrete is basically vertical to the sprayed surface, and the distance is kept between 1.5 and 2.0 m. The sprayed concrete covers the steel frame with a protective layer of no less than 4cm. The nozzle moves slowly and evenly in a spiral shape, pressing the front half circle each time. The circle diameter ranges from 25-35cm. The thickness of one spraying is controlled at no more than 6cm for the arch wall and no more than 10cm for the side wall.

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