阅读说明：本技术 一种等高隧洞交岔口开挖支护施工方法 (Equal-height tunnel intersection excavation supporting construction method ) 是由 王海涛 马文贤 于曼丽 刘飞 旦正杰 卢世鸿 韩常智 张世安 于 2021-09-09 设计创作，主要内容包括：本发明涉及隧道开挖技术领域,具体涉及一种等高隧洞交岔口开挖支护施工方法。具体施工方法为：反推45°开挖、测量放样、主洞钢拱架加工及安装、喷射混凝土、岔口开挖、副拱安装、支洞开口、锁脚锚杆施工及支洞钢拱架施工。本发明方法中,反推出大断面到45°扩挖断面里程,完成小断面变大断面的转换,充分发挥人工和机械的最大优势,在保证安全的前提下,经济、高效地完成施工任务。等高支洞开挖时,通过连立三榀钢拱架同时,在两侧副拱之间平缓部位架设横梁,保证将交岔口拱架所受压力通过横梁传导至副拱钢拱架上,减少洞口钢支撑受力。另外,副供还解决了大断面开挖时原初支收敛、沉降问题,节约因隧洞沉降而引起的返工费用,降低了安全风险,保证施工质量。(The invention relates to the technical field of tunnel excavation, in particular to a construction method for excavating and supporting a intersection of a tunnel with equal height. The specific construction method comprises the following steps: the method comprises the following steps of backward-pushing 45-degree excavation, measurement lofting, main tunnel steel arch frame processing and installation, concrete spraying, fork excavation, auxiliary arch installation, branch tunnel opening, foot locking anchor rod construction and branch tunnel steel arch frame construction. In the method, the mileage from the large section to the enlarged excavation section of 45 degrees is reversely deduced, the conversion from the small section to the enlarged section is completed, the maximum advantages of manpower and machinery are fully exerted, and the construction task is economically and efficiently completed on the premise of ensuring safety. When the equal-height branch tunnel is excavated, three steel arches are connected, and a beam is erected at a gentle position between the two side auxiliary arches, so that the pressure applied to the intersection arch is transmitted to the auxiliary arch steel arch through the beam, and the stress of the steel support at the tunnel opening is reduced. In addition, the problem of convergence and settlement of the original primary support during large-section excavation is solved by the auxiliary supply, the rework cost caused by tunnel settlement is saved, the safety risk is reduced, and the construction quality is ensured.)

1. The construction method for excavating and supporting the intersection of the equal-height tunnel is characterized by comprising the following specific steps of:

step 1, reversely deducing 45-degree excavation mileage: when a small section is enlarged and a section is enlarged when a single-side variable section of the tunnel is constructed by enlarging a roof truss one by one, gradually enlarging and excavating by using a variable section enlarging and excavating angle of 45 degrees, increasing the excavating width of each steel arch by 0.75m, and enlarging the arch crown height and the clear distance of a side wall one by one in the enlarging and excavating process; when the excavation span is larger than 9.0m, the steel arch is constructed by adopting a large-section steel arch;

step 2, measurement lofting: firstly, positioning a lofting blasthole by a measurer by using a total station, accurately drawing a central line and a contour line of an excavated section by using red paint, marking the position of the blasthole, and keeping the error to be less than 5 cm; punching holes at an angle of 45 degrees outside the excavation surface according to the position of the blast hole, and judging and determining the footage according to the grade condition of the surrounding rock;

step 3, processing and installing a main tunnel steel arch frame: the variable section steel arch is enlarged along with the gradual expansion of the section, the small section of the steel arch is supported by an I16 steel arch, and the row spacing is 0.75 m; the cross section with the span of more than 12m is supported by an I18 steel arch center, and the row spacing is 0.5 m; the section of the clear span 15.5m is supported by an I20 steel arch frame, and the row spacing is 0.5 m; the steel arch frame is processed in a segmented mode outside the tunnel, the steel arch frame is bent in a segmented mode through a rail bending machine, trial assembly is carried out after the steel arch frame is finished, and the allowable error is that the error along the peripheral outline of the tunnel is not more than 3 cm;

the steel arch is formed by splicing arch parts and side walls by connecting steel plates, and when the steel arch is horizontally placed, the plane warpage is less than +/-2 cm; welding reinforcing steel bars 200-300 mm are additionally welded in grooves on two sides of a steel arch frame, in order to ensure that the steel arch frame is arranged on a stable foundation, an original foundation of 0.15-0.2 m is reserved at the base foot part of the steel arch frame in construction, the grooves are dug in place when the steel arch frame is erected, and channel steel is arranged at the base foot part of the steel arch frame to increase the bearing capacity of the foundation; the plane of the steel arch is vertical to the center line of the tunnel, the inclination of the steel arch is not more than 2 degrees, and any part of the steel arch deviates from the vertical plane by not more than 5 cm;

and 4, spraying concrete: firstly cleaning the surface of a rock stratum, then carrying out primary spraying, installing a steel arch frame, then carrying out secondary spraying, wherein before spraying, a sprayed surface has no loose rock blocks and wall feet have no loose slag accumulation, and when spraying, the air pressure is changed from high to low from an arch part to a side wall foot, so that the pressure at a spray head is ensured to be 0.1-0.15 MPa, and the spraying direction is vertical to the rock surface; the concrete spraying operation is carried out in a segmented and segmented mode, and the once spraying thickness is controlled to be as follows: the arch part is 3-5 cm and the wall part is 6-8 cm; when spraying in layers, the later layer is finally set in the former layer;

step 5, mounting the auxiliary arch: the auxiliary arch adopts I18 steel arch frames with the spacing of 50cm and 4 frames in total, and phi 22 steel bars are adopted between each two frames as longitudinal connecting bars to connect the 4 steel arch frames into a whole to bear force, and in addition, in order to ensure that the pressure borne by the steel arch frames can be transmitted to the underground, a foot locking anchor rod is additionally arranged at the connecting plate of each steel arch frame and the bottom of the steel arch frame; then connecting the installed auxiliary arch with the main tunnel steel arch frame and the mountain body, and hanging a net and spraying concrete after the connection is finished so as to integrate the auxiliary arch and the main tunnel steel arch frame and the mountain body, and integrally stressing the auxiliary arch;

step 6, opening branch holes: erecting the main tunnel steel arch in the step 3 by cutting, erecting a beam at the gentle part of the main tunnel steel arch in time while cutting the main tunnel steel arch, erecting the main tunnel steel arch on the beam and welding;

step 7, construction of a foot locking anchor rod: the drilling angle of the foot-locking anchor rod is larger than 30 degrees, and the foot-locking anchor rod and the tunnel steel arch are welded after drilling is finished;

step 8, constructing a steel arch center of the branch tunnel: the verticality and the space between every two trusses need to meet the design requirements when the supporting tunnel steel arch is installed, the bottom of the supporting tunnel steel arch is located on a solid foundation surface, the gap between the supporting tunnel steel arch and the rock surface is densely filled by spraying concrete, a steel base plate at the joint of the supporting tunnel steel arch is reinforced by high-strength bolts, and the periphery of a staggered base plate is welded; the steel arch frame of the branch tunnel supports the rock surface.

2. The construction method for excavating and supporting the intersection of the equal-height tunnel according to claim 1, wherein emulsion explosive is adopted at the blast hole in the step 2.

3. The method for supporting and protecting the excavation of the intersection of the equal-height tunnels according to claim 1, wherein in the step 4, when spraying in layers, the spraying of the later layer is carried out after the final setting of the concrete of the former layer, and the maximum thickness of the spraying is as follows: the arch part should not exceed 10cm, and the side wall should not exceed 15 cm.

4. The method for supporting and excavating the intersection of the equal-height tunnel according to claim 1, wherein in the step 4, when a gap is formed in the back of the steel arch frame, the spray head keeps a distance of 0.6-1.0 m from the rock surface, the material bundle moves in an S-shaped rotating track, the material bundle is pressed into a half circle, the material bundle is longitudinally shaped like a snake, the snake-shaped spray length is 3-4 m each time, the spray head slowly moves, the material bundle leaves after spraying for a certain thickness, the spray range is expanded in a sheet mode, and concrete is sprayed to the concave portion of the rock surface for leveling.

5. The excavation supporting construction method for the intersection of the equal-height tunnels as claimed in claim 1, wherein the foot-locking anchor rods are phi 22 steel bars, and the length of the foot-locking anchor rods is 6 m.

Technical Field

The invention relates to the technical field of tunnel excavation, in particular to a construction method for excavating and supporting a intersection of a tunnel with equal height.

Background

When a multi-section tunnel in an alpine region is excavated, due to poor geological conditions, rocks are mainly composed of slates and sandstone, and the grades of surrounding rocks are IV grade and V grade. The tunnel excavation is divided into a main channel and branch tunnels, a plurality of small sections and large sections are directly converted in the excavation process, for example, when the small sections enter the large sections, construction is carried out according to a conventional construction method of a reverse expanding excavation method, namely when the large sections are excavated to reach the mileage, expanding excavation is carried out towards an angle of 30 degrees outside a palm surface, when the large sections are expanded and excavated in place, a 3m construction platform is reserved, excavation of gradually changed triangular parts is started, and reverse excavation of the triangular parts is carried out. When the rock mass is II, III grades, rely on the rock self-stability ability, adopt reverse to expand to dig can effectual assurance construction progress, when the rock is V grade, when carrying out reverse expansion and digging, because of the rock mass is poor from the stability ability, need carry out preliminary bracing to the face of digging according to strutting the requirement, still need demolish to the first branch after reverse expansion is dug in place, demolish the incident that appears easily in-process. When the tunnel is excavated to a branch tunnel, because the section span at the intersection is large and the arch part is gentle, when the branch tunnel is excavated, a supporting measure needs to be strengthened at the part; in addition, after the expansion and excavation of the intersection are completed, it is important to prevent the deformation convergence of the intersection.

Disclosure of Invention

Based on the technical problems, the invention compares the two excavation modes of 'reverse expanding excavation' and 'advance expanding excavation' in the aspect of safety, quality, progress and the like during excavation, and finally determines to adopt 'advance expanding excavation'; before the branch tunnel is excavated, an auxiliary arch is added at the branch tunnel mouth, so that the stress of primary support is reduced. The aim is to provide a construction method for excavating and supporting a turnout of a tunnel with the same height.

The invention provides a construction method for excavating and supporting a turnout of a tunnel with equal height, which comprises the following specific steps:

step 1, reversely deducing 45-degree excavation mileage: when a small section is enlarged and a section is enlarged when a single-side variable section of the tunnel is constructed by enlarging a roof truss one by one, gradually enlarging and excavating by using a variable section enlarging and excavating angle of 45 degrees, increasing the excavating width of each steel arch by 0.75m, and enlarging the arch crown height and the clear distance of a side wall one by one in the enlarging and excavating process; when the excavation span is larger than 9.0m, the steel arch is constructed by adopting a large-section steel arch;

step 2, measurement lofting: firstly, positioning a lofting blasthole by a measurer by using a total station, accurately drawing a central line and a contour line of an excavated section by using red paint, marking the position of the blasthole, and keeping the error to be less than 5 cm; punching holes at an angle of 45 degrees outside the excavation surface according to the position of the blast hole, and judging and determining the footage according to the grade condition of the surrounding rock;

step 3, processing and installing a main tunnel steel arch frame: the variable section steel arch is enlarged along with the gradual expansion of the section, the small section of the steel arch is supported by an I16 steel arch, and the row spacing is 0.75 m; the cross section with the span of more than 12m is supported by an I18 steel arch center, and the row spacing is 0.5 m; the section of the clear span 15.5m is supported by an I20 steel arch frame, and the row spacing is 0.5 m; the steel arch frame is processed in a segmented mode outside the tunnel, the steel arch frame is bent in a segmented mode through a rail bending machine, trial assembly is carried out after the steel arch frame is finished, and the allowable error is that the error along the peripheral outline of the tunnel is not more than 3 cm;

the steel arch is formed by splicing arch parts and side walls by connecting steel plates, and when the steel arch is horizontally placed, the plane warpage is less than +/-2 cm; welding reinforcing steel bars 200-300 mm are additionally welded in grooves on two sides of a steel arch frame, in order to ensure that the steel arch frame is arranged on a stable foundation, an original foundation of 0.15-0.2 m is reserved at the base foot part of the steel arch frame in construction, the grooves are dug in place when the steel arch frame is erected, and channel steel is arranged at the base foot part of the steel arch frame to increase the bearing capacity of the foundation; the plane of the steel arch is vertical to the center line of the tunnel, the inclination of the steel arch is not more than 2 degrees, and any part of the steel arch deviates from the vertical plane by not more than 5 cm;

and 4, spraying concrete: firstly cleaning the surface of a rock stratum, then carrying out primary spraying, installing a steel arch frame, then carrying out secondary spraying, wherein before spraying, a sprayed surface has no loose rock blocks and wall feet have no loose slag accumulation, and when spraying, the air pressure is changed from high to low from an arch part to a side wall foot, so that the pressure at a spray head is ensured to be 0.1-0.15 MPa, and the spraying direction is vertical to the rock surface; the concrete spraying operation is carried out in a segmented and segmented mode, and the once spraying thickness is controlled to be as follows: the arch part is 3-5 cm and the wall part is 6-8 cm; when spraying in layers, the later layer is finally set in the former layer;

step 5, mounting the auxiliary arch: the auxiliary arch adopts I18 steel arch frames with the spacing of 50cm and 4 frames in total, and phi 22 steel bars are adopted between each two frames as longitudinal connecting bars to connect the 4 steel arch frames into a whole to bear force, and in addition, in order to ensure that the pressure borne by the steel arch frames can be transmitted to the underground, a foot locking anchor rod is additionally arranged at the connecting plate of each steel arch frame and the bottom of the steel arch frame; then connecting the installed auxiliary arch with the main tunnel steel arch frame and the mountain body, and hanging a net and spraying concrete after the connection is finished so as to integrate the auxiliary arch and the main tunnel steel arch frame and the mountain body, and integrally stressing the auxiliary arch;

step 6, opening branch holes: erecting the main tunnel steel arch in the step 3 by cutting, erecting a beam at the gentle part of the main tunnel steel arch in time while cutting the main tunnel steel arch, erecting the main tunnel steel arch on the beam and welding;

step 7, construction of a foot locking anchor rod: the drilling angle of the foot-locking anchor rod is larger than 30 degrees, and the foot-locking anchor rod and the tunnel steel arch are welded after drilling is finished;

step 8, constructing a steel arch center of the branch tunnel: the verticality and the space between every two trusses need to meet the design requirements when the supporting tunnel steel arch is installed, the bottom of the supporting tunnel steel arch is located on a solid foundation surface, the gap between the supporting tunnel steel arch and the rock surface is densely filled by spraying concrete, a steel base plate at the joint of the supporting tunnel steel arch is reinforced by high-strength bolts, and the periphery of a staggered base plate is welded; the steel arch frame of the branch tunnel supports the rock surface.

Further, in the step 2, emulsion explosive is adopted at the blast hole.

Further, in the step 4, in the layered spraying, the spraying of the next layer is performed after the final setting of the concrete of the previous layer, and the maximum thickness of the spraying at one time is as follows: the arch part should not exceed 10cm, and the side wall should not exceed 15 cm.

Further, in the step 4, when a gap at the back of the steel arch frame is sprayed, the spray head and the rock surface keep a distance of 0.6-1.0 m, the material beam moves in an S-shaped rotating track, a half circle is pressed for one circle, the material beam is vertically shaped like a snake, the snake-shaped spray length is 3-4 m each time, the spray head slowly moves, the material beam leaves after spraying a certain thickness, the spray range is expanded in a sheet mode, and concrete is sprayed at a concave part of the rock surface for leveling.

Further, the foot-locking anchor rod is a phi 22 steel bar, and the length of the foot-locking anchor rod is 6 m.

Compared with the prior art, the invention has the following beneficial effects:

(1) and reversely pushing out the mileage of the enlarged excavation section from the large section to 45 degrees, increasing the excavation section from the small section to the truss pin by pin when the enlarged excavation section reaches the preset length, and just enlarging the excavation section when the enlarged excavation section reaches the corresponding pile number to finish the conversion of the small section into the enlarged section. The greatest advantages of manpower and machinery can be fully exerted in the construction of 'expanding excavation in advance', and the construction task can be economically and efficiently completed on the premise of ensuring safety. (2) When equal-height branch tunnels are excavated, three steel arch supports are connected, and beams are erected at the gentle parts between the two side auxiliary arches, so that the pressure applied to the intersection arch support can be transmitted to the auxiliary arch steel supports through the beams, and the stress of the tunnel portal steel supports is reduced. In addition, the problem of convergence and settlement of an original primary support during large-section excavation is solved by 'auxiliary supply', the safety risk is reduced, and the construction quality is guaranteed. (3) The 'auxiliary supply' saves nearly millions of rework cost caused by tunnel settlement, and greatly saves project expenses.

Drawings

FIG. 1 is a flow chart of the construction method of the present invention;

FIG. 2 is a schematic view of the present invention illustrating a construction of enlarging and digging 45 degrees ahead of time;

FIG. 3 is a schematic diagram of a pre-reaming cross-sectional structure according to the present invention.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

A construction method for excavating and supporting a turnout of a tunnel with equal height comprises the following specific steps:

step 1, reversely deducing 45-degree excavation mileage: when a small section is enlarged and a section is enlarged when a single-side variable section of the tunnel is constructed by enlarging a roof truss one by one, gradually enlarging and excavating by using a variable section enlarging and excavating angle of 45 degrees, increasing the excavating width of each steel arch by 0.75m, and enlarging the arch crown height and the clear distance of a side wall one by one in the enlarging and excavating process; when the excavation span is larger than 9.0m, the steel arch is constructed by adopting a large-section steel arch;

step 2, measurement lofting: firstly, positioning a lofting blasthole by a measurer by using a total station, accurately drawing a central line and a contour line of an excavated section by using red paint, marking the position of the blasthole, and keeping the error to be less than 5 cm; punching holes at an angle of 45 degrees outside the excavation surface according to the position of a blast hole, judging and determining the footage according to the grade condition of surrounding rocks, and adopting emulsion explosives at the blast hole;

step 3, processing and installing a main tunnel steel arch frame: the variable section steel arch is enlarged along with the gradual expansion of the section, the small section of the steel arch is supported by an I16 steel arch, and the row spacing is 0.75 m; the cross section with the span of more than 12m is supported by an I18 steel arch center, and the row spacing is 0.5 m; the section of the clear span 15.5m is supported by an I20 steel arch frame, and the row spacing is 0.5 m; the steel arch frame is processed in a segmented mode outside the tunnel, the steel arch frame is bent in a segmented mode through a rail bending machine, trial assembly is carried out after the steel arch frame is finished, and the allowable error is that the error along the peripheral outline of the tunnel is not more than 3 cm;

the steel arch is formed by splicing arch parts and side walls by connecting steel plates, and when the steel arch is horizontally placed, the plane warpage is less than +/-2 cm; welding reinforcing steel bars are additionally welded in grooves on two sides of a steel arch frame by 200mm, in order to ensure that the steel arch frame is arranged on a stable foundation, a 0.15m original foundation is reserved at the base foot part of the steel arch frame in construction, a groove is dug in place when the steel arch frame is erected, and channel steel is arranged at the base foot part of the steel arch frame to increase the bearing capacity of the foundation; the plane of the steel arch is vertical to the center line of the tunnel, the inclination of the steel arch is not more than 2 degrees, and any part of the steel arch deviates from the vertical plane by not more than 5 cm;

and 4, spraying concrete: firstly cleaning the surface of a rock stratum, then carrying out primary spraying, installing a steel arch frame, then carrying out secondary spraying, wherein before spraying, a sprayed surface has no loose rock blocks and wall feet have no loose slag accumulation, and when spraying, the air pressure is changed from high to low from an arch part to a side wall foot, so that the pressure at a spray head is ensured to be 0.1-0.15 MPa, and the spraying direction is vertical to the rock surface; the concrete spraying operation is carried out in a segmented and segmented mode, and the once spraying thickness is controlled to be as follows: the arch part is 3cm and the wall part is 6 cm; when spraying in layers, the later layer is finally set in the former layer; maximum thickness of one shot: the arch part is not more than 10cm, and the side wall is not more than 15 cm; when a gap at the back of the steel arch frame is sprayed, the distance between the spray head and the rock surface is kept at 0.6m, the material beam moves in an S-shaped rotating track, a circle is pressed for a half circle, the material beam is longitudinally shaped in a snake shape, the snake-shaped spraying length is 3m each time, the spray head slowly moves, the material beam leaves after being sprayed for a certain thickness, the spraying range is expanded in a piece mode, and concrete is firstly sprayed at a concave part of the rock surface for leveling;

step 5, mounting the auxiliary arch: the auxiliary arch adopts I18 steel arch frames with the spacing of 50cm and 4 frames in total, the 4 steel arch frames are connected into a whole to bear force by adopting phi 22 steel bars as longitudinal connecting bars among each two frames, in addition, in order to ensure that the pressure borne by the steel arch frames can be transmitted to the underground, a foot locking anchor rod is additionally arranged at the connecting plate of each steel arch frame and the bottom of the steel arch frame, the foot locking anchor rod is phi 22 steel bars, and the length of the foot locking anchor rod is 6 m; then connecting the installed auxiliary arch with the main tunnel steel arch frame and the mountain body, and hanging a net and spraying concrete after the connection is finished so as to integrate the auxiliary arch and the main tunnel steel arch frame and the mountain body, and integrally stressing the auxiliary arch;

step 6, opening branch holes: erecting the main tunnel steel arch in the step 3 by cutting, erecting a beam at the gentle part of the main tunnel steel arch in time while cutting the main tunnel steel arch, erecting the main tunnel steel arch on the beam and welding;

step 7, construction of a foot locking anchor rod: the drilling angle of the foot-locking anchor rod is larger than 30 degrees, and the foot-locking anchor rod and the tunnel steel arch are welded after drilling is finished;

step 8, constructing a steel arch center of the branch tunnel: the verticality and the space between every two trusses need to meet the design requirements when the supporting tunnel steel arch is installed, the bottom of the supporting tunnel steel arch is located on a solid foundation surface, the gap between the supporting tunnel steel arch and the rock surface is densely filled by spraying concrete, a steel base plate at the joint of the supporting tunnel steel arch is reinforced by high-strength bolts, and the periphery of a staggered base plate is welded; the steel arch frame of the branch tunnel supports the rock surface.

Example 2

A construction method for excavating and supporting a turnout of a tunnel with equal height comprises the following specific steps:

step 1, reversely deducing 45-degree excavation mileage: when a small section is enlarged and a section is enlarged when a single-side variable section of the tunnel is constructed by enlarging a roof truss one by one, gradually enlarging and excavating by using a variable section enlarging and excavating angle of 45 degrees, increasing the excavating width of each steel arch by 0.75m, and enlarging the arch crown height and the clear distance of a side wall one by one in the enlarging and excavating process; when the excavation span is larger than 9.0m, the steel arch is constructed by adopting a large-section steel arch;

step 2, measurement lofting: firstly, positioning a lofting blasthole by a measurer by using a total station, accurately drawing a central line and a contour line of an excavated section by using red paint, marking the position of the blasthole, and keeping the error to be less than 5 cm; punching holes at an angle of 45 degrees outside the excavation surface according to the position of the blast hole, and judging and determining the footage according to the grade condition of the surrounding rock; emulsion explosive is adopted at the blast hole;

step 3, processing and installing a main tunnel steel arch frame: the variable section steel arch is enlarged along with the gradual expansion of the section, the small section of the steel arch is supported by an I16 steel arch, and the row spacing is 0.75 m; the cross section with the span of more than 12m is supported by an I18 steel arch center, and the row spacing is 0.5 m; the section of the clear span 15.5m is supported by an I20 steel arch frame, and the row spacing is 0.5 m; the steel arch frame is processed in a segmented mode outside the tunnel, the steel arch frame is bent in a segmented mode through a rail bending machine, trial assembly is carried out after the steel arch frame is finished, and the allowable error is that the error along the peripheral outline of the tunnel is not more than 3 cm;

the steel arch is formed by splicing arch parts and side walls by connecting steel plates, and when the steel arch is horizontally placed, the plane warpage is less than +/-2 cm; welding reinforcing steel bars 300mm in grooves on two sides of a steel arch frame, reserving an original foundation of 0.2m at the base foot part of the steel arch frame during construction, digging grooves in place when erecting the steel arch frame, and arranging channel steel at the base foot part of the steel arch frame to increase the bearing capacity of the foundation; the plane of the steel arch is vertical to the center line of the tunnel, the inclination of the steel arch is not more than 2 degrees, and any part of the steel arch deviates from the vertical plane by not more than 5 cm;

and 4, spraying concrete: firstly cleaning the surface of a rock stratum, then carrying out primary spraying, installing a steel arch frame, then carrying out secondary spraying, wherein before spraying, a sprayed surface has no loose rock blocks and wall feet have no loose slag accumulation, and when spraying, the air pressure is changed from high to low from an arch part to a side wall foot, so that the pressure at a spray head is ensured to be 0.1-0.15 MPa, and the spraying direction is vertical to the rock surface; the concrete spraying operation is carried out in a segmented and segmented mode, and the once spraying thickness is controlled to be as follows: the arch part is 5cm and the wall part is 8 cm; when spraying in layers, the later layer is finally set in the former layer of concrete, and the maximum thickness of one-time spraying is as follows: the arch part is not more than 10cm, and the side wall is not more than 15 cm; when a gap at the back of the steel arch frame is sprayed, the distance between the spray head and the rock surface is kept at 1.0m, the material beam moves in an S-shaped rotating track, a circle is pressed for a half circle, the material beam is longitudinally shaped in a snake shape, the snake-shaped spraying length is 4m each time, the spray head slowly moves, the material beam leaves after being sprayed for a certain thickness, the spraying range is expanded in a piece mode, and concrete is firstly sprayed at a concave part of the rock surface for leveling;

step 5, mounting the auxiliary arch: the auxiliary arch adopts I18 steel arch frames with the spacing of 50cm and 4 frames in total, the 4 steel arch frames are connected into a whole to bear force by adopting phi 22 steel bars as longitudinal connecting bars among each two frames, in addition, in order to ensure that the pressure borne by the steel arch frames can be transmitted to the underground, a foot locking anchor rod is additionally arranged at the connecting plate of each steel arch frame and the bottom of the steel arch frame, the foot locking anchor rod is phi 22 steel bars, and the length of the foot locking anchor rod is 6 m; then connecting the installed auxiliary arch with the main tunnel steel arch frame and the mountain body, and hanging a net and spraying concrete after the connection is finished so as to integrate the auxiliary arch and the main tunnel steel arch frame and the mountain body, and integrally stressing the auxiliary arch;

step 6, opening branch holes: erecting the main tunnel steel arch in the step 3 by cutting, erecting a beam at the gentle part of the main tunnel steel arch in time while cutting the main tunnel steel arch, erecting the main tunnel steel arch on the beam and welding;

step 7, construction of a foot locking anchor rod: the drilling angle of the foot-locking anchor rod is larger than 30 degrees, and the foot-locking anchor rod and the tunnel steel arch are welded after drilling is finished;

step 8, constructing a steel arch center of the branch tunnel: the verticality and the space between every two trusses need to meet the design requirements when the supporting tunnel steel arch is installed, the bottom of the supporting tunnel steel arch is located on a solid foundation surface, the gap between the supporting tunnel steel arch and the rock surface is densely filled by spraying concrete, a steel base plate at the joint of the supporting tunnel steel arch is reinforced by high-strength bolts, and the periphery of a staggered base plate is welded; the steel arch frame of the branch tunnel supports the rock surface.

Example 3

1. The economic benefits of the two processes of reverse excavation and advanced excavation are compared, and a Tibet Gonga project is taken as an example.

(1) Reverse enlarging and digging

Back shoveling: 1, loader: 1, hand pneumatic drill: 6, 6 excavating persons, 8 erecting persons and 6 spraying anchors. According to the field construction condition, an expanding excavation section is formed; the planning period is 7 days, the excavation angle is 30 degrees, the original designed section can be excavated at 9m, and the used materials, machinery and manual calculation are as follows:

mechanical cost: backhoe-7-450-3150; loader 7 × 450 × 3150; hand pneumatic drilling: 6, 7, 220, 9240; material cost: 22.35 × 2 × 1582.68 ═ 70745.8 for sprayed concrete; i18 steel arch 0.578 × 17 × 4780 ═ 46968.3; labor cost: 26 × 300 × 7 ═ 54600;

because the engineering has 19 expanding and digging sections, the cost for reverse expanding and digging is 3509377.9 yuan.

(2) Expanding and digging in advance:

back shoveling: 1, loader: 1, hand pneumatic drill: 6, 6 excavating persons, 8 erecting persons and 6 spraying anchors. According to the field construction condition, an expanding excavation section is formed; the practical construction period is 4 days, the excavation angle is 45 degrees, 5m is excavated to the original design section, and the used materials, machinery and manual calculation are as follows:

mechanical cost: backhoe-7-450-3150; loader 7 × 450 × 3150; hand pneumatic drilling: 6, 7, 220, 9240; material cost: sprayed concrete 12.35 × 1582.68 ═ 19546.1; i18 steel arch 0.578 × 5 × 4780 ═ 13814.2; labor cost: 26 × 300 × 4 ═ 31200;

calculating the total 19 expanding excavation sections according to the project, wherein the cost required by expanding excavation in advance is 1462055.7 yuan;

compared with the forward excavation expanding and the reverse excavation expanding, the cost of the forward excavation expanding is saved in 3509377.9-1462055.7-2047322.2 Yuan.

2. Economic benefit measurement and calculation for 'auxiliary arch' construction

The 'auxiliary arch' construction can effectively reduce the settlement and convergence of the primary support of the tunnel, save the rework cost caused by the settlement of the tunnel, and increase the analysis of the construction benefits of the auxiliary arch as follows:

(1) and (3) the rework cost of main hole support line invasion:

rework processing time: 14 d; manual work: 7 persons/d; total 14 × 7 × 300 — 29000; mechanically: the breaking hammer is 14 × 480 × 6720, and the loader is 14 × 450 × 6300; material cost: the C25 sprayed concrete is 57.7 × 2 × 1582.68 ═ 182641.3, the I18 steel arch frame is 0.578 × 20 × 4780 ═ 55256.8, and the phi 22 system anchor rod is 41443.2;

the engineering has 13 equal-height excavation sections, and if the engineering is reworked, the reworking cost is 4090336.9 yuan.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.