Shallow-buried tunnel excavation and primary support construction method

Abstract

The invention discloses a shallow-buried tunnel excavation and primary support construction method. The method comprises the following steps that excavation and masonry of a top intercepting ditch of a tunnel and a tunnel opening drainage project are carried out; excavating earth and stone at the hole, and performing temporary protection on a side slope and a hole forming face; constructing an entrance hole-entering auxiliary measure; excavating a hole body; primarily supporting the tunnel body; constructing a pipe shed on an upward slope of an exit edge; performing inverted arch and backfill construction; tunnel body waterproof and drainage construction; performing open cut tunnel molded lining construction and tunnel portal construction; carrying out secondary lining; and pavement in the tunnel. The construction method has the advantages that the new Austrian method principle is adopted, the tunnel is divided into the left part and the right part to be excavated in the construction process, three-part layered excavation, primary support construction and mid-partition wall temporary support construction are adopted on one side of the tunnel, then the other side of the tunnel is excavated by steps, and the corresponding primary support construction method is carried out. Large-section tunnel construction is divided into small-section cavern construction through the mid-partition wall method, the early construction time of surrounding rock excavation is shortened, and therefore the stress change of surrounding rock excavation is stopped, and safe tunnel construction is facilitated.

Description

Technical Field

[0001] The present application belongs to the technical field of tunnel construction, and specifically relates to a shallow tunnel excavation and initial support construction method. Background Art

[0002] The tunnel construction industry is a large and important field, covering a variety of types such as traffic tunnels, hydraulic tunnels, municipal tunnels, mining tunnels, and military tunnels. This industry is closely related to the urbanization process, infrastructure construction, and the growth of transportation demand, and has broad market prospects and huge development potential. In the economic development landscape, road traffic is like the blood of the country, running through every corner and connecting the prosperity of urban and rural areas. As a key link in improving traffic smoothness and driving safety, highway tunnels play an indispensable role in it. With the acceleration of urbanization and the advancement of regional economic integration, the demand for highway tunnel construction has also shown a steady growth trend. Such a development background not only highlights the important strategic position of the highway tunnel construction industry, but also makes its research value more significant. Summary of the invention

[0003] The purpose of this application is to provide a shallow tunnel excavation and initial support construction method, which is based on the principle of the traditional excavation method "New Austrian Tunneling Method", improves the traditional excavation and support technology, and consists of several major processes such as advance support, tunnel excavation and construction, and initial tunnel support to carry out construction operations for shallow tunnels, so as to maximize the original rock strength of the surrounding rock around the tunnel, which can not only improve construction efficiency, improve the stability and safety of the tunnel structure, but also help reduce the use of support materials and reduce engineering costs.

[0004] The purpose of this application is achieved through the following technical solutions:

[0005] A shallow tunnel excavation and initial support construction method comprises the following steps:

[0006] Step S01, excavation and construction of the intercepting ditch on the cave roof and drainage works at the cave entrance;

[0007] Step S02, excavation of earth and stone at the tunnel entrance, and temporary protection of the side slope and the tunnel surface;

[0008] Step S03, construction of auxiliary measures for entrance into the hole;

[0009] Step S04, tunnel excavation;

[0010] Step S05A, initial support of the tunnel body; Step S05B, construction of the pipe shed on the exit side;

[0011] Step S06, invert and backfill construction;

[0012] Step S07A, tunnel body waterproofing and drainage construction; Step S07B, open hole formwork lining construction and tunnel gate construction;

[0013] Step S08, secondary lining;

[0014] Step S09, road surface inside the tunnel.

[0015] Furthermore, according to the shallow tunnel excavation and initial support construction method of claim 1, it is characterized in that: the tunnel entrance engineering includes tunnel entrance drainage engineering construction, tunnel entrance side slope construction, pipe shed construction, open tunnel construction and end wall type tunnel portal construction;

[0016] Construction of tunnel entrance drainage project: The tunnel entrance drainage works include intercepting ditch outside the side slope excavation line, drainage ditch at the side wall corner and outside the tunnel and ditch on the top of the end wall, which are connected with the drainage system of the road outside the tunnel of the tunnel project; the slope of the intercepting ditch is set according to the terrain, not less than 5m away from the edge of the side slope excavation, and the slope is not less than 3%; the intercepting ditch on the top of the side slope of the tunnel entrance section is built in advance in combination with the permanent drainage system, and is completed before the tunnel enters the tunnel, and the outlet must prevent the water from flowing down the slope; the drainage outlet of the tunnel entrance must form a drainage system with the drainage network of the road outside the tunnel, and its water flow must not scour the road and damage the environment; the surface water within the intercepting ditch of the tunnel entrance is introduced into the road drainage ditch through the ditch on the top of the end wall; the intercepting ditch is located 5m outside the side slope excavation line, the slope is guaranteed to be flat and stable, and it is strictly forbidden to stick to the slope; the longitudinal slope is strictly constructed according to the drawing, the ditch bottom is flat, the drainage is unobstructed, and there is no water blocking.

[0017] Furthermore, according to the shallow tunnel excavation and initial support construction method described in claim 2, it is characterized by: construction of the tunnel entrance side slope: the slope rate of the tunnel entrance side slope is coordinated with the roadbed outside the tunnel, and after the tunnel construction is completed, the exposed temporary side slope is greened to make it coordinated with the surrounding natural environment; in order to prevent the weathering and peeling or instability of the slope rock or soil, and at the same time not to destroy and change the original landform and vegetation growth conditions of the slope, clearing measures are taken for the slope above the top of the tunnel where there is a risk of falling rocks and collapse; the process flow is: measurement and layout → side slope excavation → inspection of slope and stability → initial concrete spraying → drilling → hole cleaning → installation of mortar anchor rods → laying of steel mesh → concrete spraying.

[0018] Furthermore, according to the shallow buried tunnel excavation and initial support construction method described in claim 2, it is characterized by: pipe-roof construction: before the construction of the pipe-roof, a sleeve arch is first constructed, and the sleeve arch is used as the fixed end of the pipe-roof and for guidance, and at the same time, the back slope mountain is stabilized with the help of the concrete sleeve arch; measurement and layout are carried out to calibrate the boundary line between the sleeve arch and the blind hole excavation; the sleeve arch part and the side back slope are excavated and repaired, and the side back slope is reinforced according to the design requirements, and the core soil of the tunnel body is reserved when the sleeve arch position is excavated; the sleeve arch is constructed close to the heading face outside the open hole contour line. During the sleeve arch construction, a steel arch frame is first supported and installed, and each unit of the steel frame is fixed and formed by a connecting plate, and the tunnel entrance and exit between the units are supported in advance by a pipe-roof; the drilling adopts a pipe-roof drilling rig, which is driven in at one time. During the drilling construction process, a short drill rod is repeatedly added to the rod to extend the length; the grouting adopts cement slurry segmented grouting; longitudinal connecting steel bars are arranged between the steel frames, and the slope of the connecting line on the outer surface of the steel frame is consistent with the external insertion angle of the pipe-roof; after the installation of the guide pipe, both ends are used The slurry stopper is used to block the concrete and prevent the concrete from flowing into the pipe. The sleeve arch is cast with concrete. The inner and outer molds of the sleeve arch and the plug molds are all processed and installed with wooden molds or bamboo plywood. The bottom mold of the sleeve arch is positioned with steel supports, and steel pipes are set up for reinforcement and support to ensure that the mold position is accurate and does not deform during concrete pouring. No external mold is used within 40° of the top of the guide wall, and manual finishing is adopted to ensure that the structural surface is flat and smooth. Commercial concrete is used for concrete. Concrete is transported to the site by concrete tankers and pumped into the mold by concrete pump trucks. The pouring sequence is strictly controlled during construction and the pouring is completed before the concrete begins to set. In order to avoid excessive eccentric load during concrete pouring, the left and right sides rise alternately during concrete pouring, and the height difference of the concrete surfaces on both sides does not exceed 50cm. During the concrete pouring process, the formwork support is observed and any deformation is handled to ensure the accurate position of the sleeve arch. When the strength of the sleeve arch concrete reaches 85%, the long pipe shed construction begins.

[0019] Further, according to the shallow tunnel excavation and initial support construction method described in claim 2, it is characterized by: open hole construction: the open hole construction of the tunnel follows the principle of continuity, lining after excavation, and backfilling after lining, so as to avoid the slope being exposed to the outside and enhance the stability of the tunnel entrance; the open hole lining is used for the open excavation section of the entrance and exit, and a reinforced concrete structure is adopted; when performing structural calculations, the design load considers the backfill soil load, the deadweight of the structure and the construction load, and the elastic resistance of the foundation is considered for the invert and the side wall part backfilled with plain concrete; during the open hole construction process, the construction is strictly carried out according to the drawings, the plain concrete backfill of the side wall is dense, and the top backfill is symmetrically backfilled, and it is not allowed to exceed the designed backfill thickness and the designed backfill soil cross slope, so as to ensure that the structural working conditions are consistent with the structural design mode; the process flow is: excavation and support of the tunnel entrance section and foundation trench → base geophysical exploration and bearing capacity test → invert construction → filling concrete → template trolley in place → template inspection → steel bar binding → erection of external template → pouring lining concrete → waterproofing layer, connection of drainage pipes → arch backfill;

[0020] End wall portal construction: The tunnel entrance and exit are both end wall portals with reinforced concrete structure, and the wall and open hole lining are connected with steel bars; process flow: construction preparation interception and drainage ditch construction → excavation of the entrance section and portal foundation → base bearing capacity testing → tying steel bars and supporting formwork → inspection of reserved holes → pouring reinforced concrete → dismantling formwork → connecting drainage facilities → making portal nameplate.

[0021] Furthermore, according to the shallow tunnel excavation and initial support construction method described in claim 1, it is characterized in that: the construction process of tunnel excavation is: use the steel frame erected in the previous cycle to apply advance support; excavate the first part → spray concrete on the face → apply initial support and temporary support around the first pilot tunnel → apply system anchors and then spray concrete to the designed thickness; lag behind the first part by a set distance, excavate the second part → spray concrete on the face → apply initial support and temporary support around the second pilot tunnel → apply system anchors and then spray concrete to the designed thickness; lag behind the second part by a set distance, excavate the third part → spray concrete on the face → apply the third pilot tunnel Initial support face spraying concrete and temporary support around → After installing system anchors, spray concrete to the designed thickness; after excavating the set distance of the third lag, excavate the fourth part, and its construction steps and procedures are the same as the first part; after the set distance of the fourth lag, excavate the fifth part, and its construction steps and procedures are the same as the second part; after the set distance of the fifth lag, excavate the sixth part, and its construction steps and procedures are the same as the third part; according to the monitoring and measurement results, after the initial support converges, remove the temporary steel frame, and integrally pour the bottom invert and invert filling concrete; after the invert length meets the construction length of the secondary lining, use the integral hydraulic lining template trolley to cast the secondary lining at one time;

[0022] Excavation of the tunnel:

[0023] Process flow: The construction sequence of the exit is exit construction preparation → exit intercepting ditch and temporary drainage → exit side slope construction → exit guide wall construction → exit large pipe shed construction → exit from the tunnel → open tunnel and tunnel door construction; the construction process and parameters of the exit section tunnel entrance engineering are the same as those of the entrance section; before exiting the tunnel, the tunnel entrance intercepting ditch, temporary drainage measures and side slope protection measures must be completed, and then the guide wall must be constructed. After the exit large pipe shed is constructed and grouting is completed, the tunnel entrance is closed with shotcrete;

[0024] Pilot pit construction: prepare drainage at the exit tunnel, side slope protection, and pipe shed construction in advance. Excavation can only be continued after confirming that the side slope at the exit tunnel is stable and there is no impact of geological disasters such as collapse or landslide. After each excavation of the exit tunnel, observe the bedding and cracks of the excavation surface, judge the stability of the surrounding rock, and apply initial support after excavation. The initial support is closely followed by the heading face, and blind excavation is strictly prohibited. To ensure the safety of the exit tunnel, set a distance from the penetration surface, slow down the excavation speed, and observe at any time. After the upper pilot pit on the left is excavated, it will be initially supported to complete the safe exit. After the exit construction of the upper pilot pit is completed, the remaining pilot pits will be gradually advanced to the tunnel entrance to complete the exit construction.

[0025] Tunnel entrance project: After exiting the tunnel, complete the construction of the tunnel entrance project of the open tunnel and tunnel gate.

[0026] Further, according to the shallow tunnel excavation and initial support construction method of claim 1, it is characterized in that: the support includes advanced small pipe support, initial support and temporary support;

[0027] The process flow of advanced small-pipe support is as follows: construction preparation → measurement and positioning → drilling operation → hole cleaning → drilling acceptance → pipe lowering and hole plugging after passing the inspection, and return to drilling operation if unqualified → spraying concrete to plug the working surface → connection and debugging of grouting pipeline → grouting operation → grouting effect analysis → welding of pipe tail and steel frame if the requirements are met → end; grouting effect analysis → adjusting grouting parameters if the requirements are not met → slurry preparation → grouting operation; construction preparation → small-pipe preparation → pipe lowering and hole plugging; construction preparation → raw material inspection → slurry ratio design → grouting test → slurry preparation → grouting operation;

[0028] The initial support process is: excavation of surrounding rock → finding the top → initial spraying of shotcrete on the rock surface of the tunnel body → erection of steel frame → driving of radial anchor rods → hanging of steel mesh → re-spraying of concrete to the designed thickness → inspection and acceptance;

[0029] The temporary support process is: construction preparation → drilling → hole cleaning → delivering anchor coil → pushing anchor rod and stirring anchor coil → anchor agent reaches strength.

[0030] Furthermore, according to the shallow tunnel excavation and initial support construction method of claim 1, it is characterized in that: the invert and backfill construction includes the leveling layer construction: the invert construction is carried out after the open hole excavation is completed to prevent rainwater from soaking the foundation pit; the leveling layer construction can be carried out only after the bearing capacity of the excavated foundation reaches the design requirements or reaches the design requirements after treatment;

[0031] Rebar processing and binding: welding is used to overlap the steel bars; structural limit steel bars are set between the inner and outer layers of annular stress-bearing steel bars, and the limit steel bars are welded to the annular stress-bearing steel bars and the distribution steel bars; double-layer steel bars are pre-buried at the portal and connected to the portal; lining steel bars meet the design and specification requirements; steel bars are straightened before processing and bending; oil stains and rust on the surface of steel bars are clean; cold processing is used for straightening, hooking, bending and bending of steel bars; steel bars are pre-made outside the tunnel according to the arc shape of the inverted arch. When installing steel bars, each node bar of the transverse steel bars and the longitudinal steel bars must be tied or welded; the overlapping positions of adjacent main bars are staggered; the connection points of the steel bars are at the intersection of the longitudinal and transverse bars, which must be tied or welded;

[0032] Install the formwork: When installing the formwork, ensure that the support is firm and the joints are tight, so that there will be no expansion or leakage. After the formwork is installed, check the center line, elevation, section and clearance dimensions; the contact surface between the formwork and the concrete must be coated with an isolation agent;

[0033] Concrete pouring: Before pouring concrete, the slag, dirt and water in the foundation pit must be drained away. It is strictly forbidden to pour concrete into a foundation pit with water. The slump and workability parameters of the concrete must be controlled. A forced concrete mixer is used for mixing, and an electronic meter is provided. Concrete is transported by a concrete transport truck to prevent segregation of the concrete during transportation. A vibrating vibrator is used to vibrate the bottom of the invert first, and then gradually vibrate towards the arch foot of the tunnel body to ensure the compactness of the concrete.

[0034] Backfill of the invert: The backfill concrete is poured after the initial setting of the poured concrete of the invert. The pouring of the filling concrete is carried out in two times: the first time is to install the curb and formwork, and pour to the ditch bottom elevation; the second time is to install the ditch formwork, tie the ditch and curb reinforcement, and then pour to the designed elevation; the filling concrete is poured using a delivery pump and manual vibrator to ensure the pouring thickness of the invert concrete during construction; when backfilling the invert, pay attention to controlling the top surface elevation to avoid intrusion into the pavement structure layer.

[0035] Furthermore, according to the shallow tunnel excavation and initial support construction method described in claim 1, it is characterized by: tunnel body drainage construction: waterproof membrane construction preparation; waterproof membrane fixation: waterproof membrane is laid without nails, that is, the cut membrane is hot-melt pasted on the plastic round gasket using a hot air welding gun; when the membrane is fixed on the plastic round gasket, it must not be tightened or bulged, and the membrane at the corners must be tightly attached to the corners to avoid affecting the size of the poured concrete or tearing the membrane; waterproof membrane seam welding; protective measures for waterproof membrane to avoid damage; buried waterstop construction; back-sticked waterstop construction.

[0036] Furthermore, according to the shallow tunnel excavation and initial support construction method described in claim 1, it is characterized in that: the secondary lining process flow is: spray concrete surface treatment → drainage blind pipe installation → inspection, if unqualified, re-spray concrete surface treatment → lay waterproof board → inspection, if unqualified, re-lay waterproof board → manufacture and install steel bars → inspection, if unqualified, re-manufacture and install steel bars → if qualified, put the secondary lining trolley in place → decontamination, brush release agent → trolley positioning → embedded parts installation → erecting plug plate, installing water stop → inspection, if unqualified, re-position the trolley → pouring concrete if qualified → demolding after maintenance → continue maintenance after demolding.

[0037] Beneficial effects of this application:

[0038] (1) This application adopts the principle of "New Austrian Tunneling Method". During construction, the tunnel is divided into two parts, left and right, for excavation. First, three-part layer excavation is adopted on one side of the tunnel, and initial support and temporary support of the middle partition wall are applied. Then, the other side of the tunnel is excavated in steps, and the corresponding initial support construction method is carried out. The middle partition wall method divides the large-section tunnel construction into small-section cavern construction, shortens the early construction time of the excavated surrounding rock, thereby stopping the stress change of the excavated surrounding rock, which is beneficial to the safe construction of the tunnel. Dividing the tunnel into multiple caverns increases the construction work surface, and rationally organizes the construction, which is beneficial to speeding up the construction progress of large-section tunnels with poor geological conditions.

[0039] (2) Weak surrounding rock is an unfavorable geological condition often encountered in tunnel construction, which poses a serious threat to the stability and safety of the tunnel structure. The middle partition wall method can better adapt to the soft surrounding rock environment by adding support structures to improve the overall stiffness and stability of the tunnel. In addition, this method can also flexibly cope with surrounding rocks of different degrees of weakness by adjusting support parameters and construction processes.

[0040] (3) When constructing tunnels in soft strata or densely populated urban areas, ground settlement is a key factor that must be strictly controlled. The intermediate wall method can effectively disperse and transfer the load generated by tunnel excavation by adding a supporting structure, reduce the disturbance to the surrounding soil, and thus significantly suppress ground settlement. This is crucial to protecting the safety of ground buildings, roads, and pipelines.

[0041] The aforementioned main scheme of the present application and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection in the present application; and in the present application, (non-conflicting options) can also be freely combined with each other and with other options. After understanding the scheme of the present application, those skilled in the art can understand that there are many combinations based on the prior art and common knowledge, all of which are technical schemes to be protected by the present application, and they are not exhaustively listed here. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the process flow of this application.

[0043] Figure 2 It is a diagram of the pipe-roof conduit structure of the present application.

[0044] Figure 3 It is a cross-sectional view of the pipe-roof conduit of the present application.

[0045] Figure 4 This is the open hole lining reinforcement layout diagram of this application.

[0046] Figure 5 It is a schematic diagram of the process flow of the advanced small-duct support of the present application.

[0047] Figure 6 It is a cross-sectional view of the advanced small catheter support of the present application.

[0048] Figure 7 It is the waterproof structure diagram of this application.

[0049] Figure 8 It is a schematic diagram of fixing the waterproof membrane of the present application.

[0050] Fig. 9 It is the secondary lining process flow chart of this application. DETAILED DESCRIPTION

[0051] The following non-limiting examples are provided to illustrate the present application.

[0052] Example 1

[0053] refer to Figures 1 to 9 As shown, a shallow buried tunnel excavation and initial support construction method includes the following steps: step S01, excavation of the intercepting ditch on the top of the tunnel, masonry and construction of the tunnel entrance drainage project; step S02, excavation of earth and stone at the tunnel entrance, and temporary protection construction of the side slope and the tunnel surface; step S03, construction of auxiliary measures for entering the tunnel entrance; step S04, excavation of the tunnel body; step S05A, initial support of the tunnel body; step S05B, construction of the pipe shed on the side slope of the exit; step S06, arch and backfill construction; step S07A, tunnel body drainage construction; step S07B, open hole formwork lining construction and tunnel gate construction; step S08, secondary lining; step S09, road surface construction in the tunnel.

[0054] The tunnel entrance project includes tunnel entrance drainage construction, tunnel entrance side slope construction, pipe shed construction, open tunnel construction and end wall tunnel portal construction.

[0055] Construction of tunnel entrance drainage project: The tunnel entrance drainage works include intercepting ditch outside the side slope excavation line, side wall corner and tunnel drainage ditch and end wall top ditch, and are connected with the tunnel road drainage system outside the tunnel. The slope of the intercepting ditch is set according to the terrain, not less than 5m away from the edge of the side slope excavation, and the slope is not less than 3%. The intercepting ditch on the top of the side slope of the tunnel entrance section is built in advance in combination with the permanent drainage system, and is completed before the tunnel enters the tunnel. The outlet must prevent the flow along the slope. The drainage outlet of the tunnel entrance must form a drainage system with the drainage network of the road outside the tunnel, and its water flow must not scour the road and damage the environment. The surface water within the intercepting ditch of the tunnel entrance is introduced into the road drainage ditch through the end wall top ditch. The intercepting ditch is located 5m outside the side slope excavation line, and the side slope is guaranteed to be flat and stable, and it is strictly forbidden to stick to the slope. The longitudinal slope is strictly constructed according to the drawing, the ditch bottom is flat, the drainage is unobstructed, and there is no water blocking. The drainage of the entire drainage system is reasonable.

[0056] Construction of tunnel entrance side slope: The slope of the tunnel entrance side slope is coordinated with the roadbed outside the tunnel. After the tunnel construction is completed, the exposed temporary side slope is greened to make it coordinated with the surrounding natural environment. In order to prevent the weathering and peeling or instability of the slope rock or soil, and at the same time not to destroy and change the original landform of the slope and the growth conditions of vegetation, clearing measures are taken for the slope above the cave top that is in danger of falling rocks and collapse.

[0057] The construction process of the side slope of the tunnel entrance is as follows: measurement and layout → excavation of the side slope → inspection of slope and stability → initial spraying of concrete → drilling → hole cleaning → installation of mortar anchors → laying of steel mesh → spraying of concrete.

[0058] Pipe shed construction: Before the construction of the pipe shed, the sleeve arch is constructed first, and the sleeve arch is used as the fixed end of the pipe shed and for guidance. At the same time, the concrete sleeve arch is used to stabilize the mountain on the slope. Measure and stake out, and mark the boundary between the sleeve arch and the blind hole excavation. Excavate and repair the sleeve arch and the side slope, and reinforce the side slope according to the design requirements. When excavating the sleeve arch position, reserve the core soil of the cave.

[0059] The arch is constructed outside the outline of the open tunnel and close to the face. The length is 2 meters. During the construction of the arch, four I22b steel arch frames are first supported and installed. The steel arch frames are processed into semi-finished products in the processing plant and then transported to the site for installation. Each unit of the steel frame is welded and fixed by the connecting plate. The entrance and exit of the tunnel between the units are supported by pipe sheds. The pipe shed uses φ108 seamless steel pipes with a wall thickness of 6mm and a circumferential spacing of 50cm. The drilling is done with a pipe shed drilling rig, which is driven in at one time. During the drilling construction process, the short drill rod is repeatedly extended by adding rods. The steel pipe joints are connected with 114 steel pipes with threads. The thread length is 15cm, and the steel pipe joints are staggered. Grouting uses cement slurry for segmented grouting, with a water-cement ratio of 1:0.5 and a grouting pressure of 0.5~1MPa, which can be increased to 2MPa when necessary. The connections between I-beams and connecting steel plates are all welded, and the weld grade is level 2.

[0060] The steel frame unit is made of hot-rolled ordinary I-beams, with the ends welded to the steel plates. The steel arch frame is connected between units with S8.8 grade bolts. Longitudinal connecting steel bars are set between the steel frames, with a circumferential spacing of 1.0m (alternated inside and outside), and the connection between the steel frame and the longitudinal connecting steel bars is welded, with a weld height of 10mm. The slope of the connecting line on the outer surface of the steel frame is consistent with the external insertion angle of the pipe shed. After the circumferential points are measured to meet the requirements, the 108 pipes are welded to the steel frame one by one with a 40cm ring spacing. The orifice pipe and the 122b I-beam are welded as a whole and fixed with fixed steel bars. The fixed steel bars are double-sided welded with the orifice pipe and the I22b I-shaped steel arch, and the weld length is greater than 5 times the diameter of the steel bar; after the installation of the guide pipe is completed, the two ends are blocked with slurry stoppers to prevent concrete from flowing into the pipe.

[0061] The arch is cast with C30 concrete. The inner and outer formworks and plug formworks of the arch are all processed and installed with 5cm wooden formworks or bamboo plywood. The bottom formwork of the arch is positioned with steel supports, and steel pipes are set up for reinforcement and support to ensure the accurate position of the formwork and no deformation during concrete pouring. No external formwork is used within 40° of the top of the guide wall, and manual finishing is used to ensure a smooth and flat structural surface.

[0062] Commercial concrete is used. Concrete is transported to the site by concrete tank trucks and pumped into the mold by concrete pump trucks. The pouring sequence is strictly controlled during construction and the pouring is completed before the initial setting of the concrete. In order to avoid excessive eccentric load during the concrete pouring process, the left and right sides are alternately raised during the concrete pouring, and the height difference of the concrete surface on both sides does not exceed 50cm. During the concrete pouring process, the formwork support is observed and deformation is handled to ensure the accurate position of the arch; the long pipe shed construction begins when the concrete strength of the arch reaches 85%. Before the construction of the pipe shed, the machinery and materials for construction are prepared, and the construction personnel of the pipe shed are technically trained to be familiar with the operating points and technical parameters of each process. The drilling hole position is measured with a total station and marked on the face with red paint. The inclination angle of the pipe shed is 2°.

[0063] Open-hole construction: Rational organization of open-hole construction of tunnels speeds up construction, follows the principle of continuity, lining after excavation and backfilling after lining to avoid exposing the slope and enhance the stability of the tunnel entrance.

[0064] The open hole lining is used for the open cut section of the entrance and exit, and adopts C35 reinforced concrete structure. When performing structural calculations, the design load takes into account the backfill soil load, the deadweight of the structure and the construction load, and the elastic resistance of the foundation is considered for the invert and the side wall part backfilled with C20 plain concrete. During the construction of the open hole, the construction is strictly carried out according to the drawings, the C20 plain concrete backfill of the side wall is dense, and the top backfill soil is symmetrically backfilled, and it is not allowed to exceed the designed backfill thickness and the designed backfill soil cross slope to ensure that the structural working conditions are consistent with the structural design mode.

[0065] The construction process of the open tunnel is as follows: excavation and support of the tunnel entrance section and foundation trench → geophysical exploration and bearing capacity test of the base → construction of the invert arch → filling with concrete → positioning of the formwork trolley → formwork inspection → steel bar binding → erection of external formwork → pouring of lining concrete → application of waterproof layer and connection of drainage pipes → backfilling of the arch.

[0066] End wall portal construction: The tunnel entrance and exit are both end wall portals with C30 reinforced concrete structure, the foundation is 2.1×1m, the inward slope is 1:10, the wall thickness is 1.6m, the slope is 1:0.1, and the wall and the open hole lining are connected with double-layer C22 steel bars. The length of the connecting bar is 80cm, the longitudinal spacing is 50cm, and the circumferential spacing is 25cm.

[0067] The construction process of end wall portal is as follows: Construction preparation: Construction of drainage ditch → Excavation of portal section and portal foundation → Testing of base bearing capacity → Binding of steel bars and erection of formwork → Inspection of reserved holes → Pouring of reinforced concrete → Removal of formwork → Connection of drainage facilities → Installation of portal nameplate.

[0068] The construction process of tunnel excavation is as follows: use the steel frame erected in the previous cycle to apply advance support (φ42 small duct on the tunnel side wall and φ42 small duct on the pilot pit side wall); excavate the first part → spray concrete on the heading (thickness 8cm, construction once every 2m, the same below) → apply initial support and temporary support around the first pilot pit (initially spray 4cm thick concrete, lay steel mesh, erect steel frame and I22b temporary vertical support, apply locking anchor rods and pilot pit φ22 drug roll anchor rods) → apply system anchor rods and then spray concrete again to the designed thickness of 28cm (re-spray the middle partition wall to 22cm).

[0069] After lagging the set distance of 5m behind the first part, the second part is excavated → concrete is sprayed on the face → initial support and temporary support are constructed around the second pilot pit (initially spray 4cm thick concrete, lay steel mesh, extend steel frame and I22b temporary vertical support, and construct φ22 drug-coated anchor rods for the pilot pit) → after constructing system anchor rods, re-spray concrete to the designed thickness of 28cm (re-spray the middle partition wall to 22cm).

[0070] After lagging the set distance of 5m behind the second part, the third part is excavated → concrete is sprayed on the face → initial support and temporary support are constructed around the third part pilot pit (4cm thick concrete is sprayed initially, steel mesh is laid, side wall and invert steel frames are constructed, I22b temporary vertical support steel frames are extended, side wall foot locking anchors and φ22 drug roll anchors are constructed) → system anchors are constructed and then concrete is sprayed again to a designed thickness of 28cm (middle partition walls are sprayed to 22cm).

[0071] After the third section is excavated and set at a distance of 10m, the fourth section is excavated, and its construction steps and procedures are the same as those of the first section. After the fourth section is excavated and set at a distance of 5m, the fifth section is excavated, and its construction steps and procedures are the same as those of the second section. After the fifth section is excavated and set at a distance of 5m, the sixth section is excavated, and its construction steps and procedures are the same as those of the third section.

[0072] According to the monitoring and measurement results, after the initial support converges, the temporary steel frame is removed, and the bottom invert and invert filling concrete are poured integrally. When the invert length meets the construction length of the secondary lining, the 9m integral hydraulic lining formwork trolley is used to pour the secondary lining in one go (the arch wall lining is constructed in one go).

[0073] Exit construction during tunnel excavation: The process flow of exit construction: The order of exit construction is exit construction preparation → exit intercepting ditch and temporary drainage → exit side slope construction → exit guide wall (arch) construction → exit large pipe shed construction → exit from the tunnel to the exit → open tunnel and tunnel gate construction.

[0074] The construction technology and parameters of the exit section are the same as those of the entrance section. Before exiting the tunnel, the tunnel entrance interception ditch, temporary drainage measures and side slope protection measures must be completed, and then the guide wall must be constructed. After the exit large pipe shed is constructed and grouting is completed, 5cm, C25 shotcrete is used to close the tunnel entrance. Continue to excavate from the inside of the tunnel to the entrance, and the exit mileage is K0+815 (light and dark junction mileage).

[0075] Construction of the pilot pit for exit construction: prepare drainage at the exit tunnel, side slope protection, and pipe shed construction (same construction process as above) in advance. Excavation can only be continued on the premise that the slope at the exit tunnel is stable and there is no impact of geological disasters such as collapse and landslide. After each excavation of the exit section tunnel, observe the bedding and cracks of the excavation surface, judge the stability of the surrounding rock, and apply initial support after excavation. The initial support follows the heading face, and blind excavation is strictly prohibited. To ensure the safety of the exit, set a distance of 10 meters from the through face, slow down the excavation speed, and observe at any time. After the upper pilot pit on the left is excavated, it is initially supported to complete a safe exit. After the exit construction of the upper pilot pit is completed, the remaining pilot pits are gradually advanced to the entrance to complete the exit construction.

[0076] Entrance works for exiting the tunnel: After exiting the tunnel, complete the construction of the entrance works of the open tunnel and tunnel gate.

[0077] The support includes advance small-duct support, initial support and temporary support.

[0078] The process flow of advanced small-pipe support is as follows: construction preparation → measurement and positioning → drilling operation → hole cleaning → drilling acceptance → pipe lowering and hole plugging after passing the test, and return to drilling operation if unqualified → spray concrete to plug the working surface → connect and debug the grouting pipeline → grouting operation → grouting effect analysis → welding the pipe tail to the steel frame if the requirements are met → end. Grouting effect analysis → adjust the grouting parameters if the requirements are not met → slurry preparation → grouting operation. Construction preparation → small-pipe preparation → pipe lowering and hole plugging. Construction preparation → raw material inspection → slurry ratio design → grouting test → slurry preparation → grouting operation.

[0079] The initial support process is as follows: excavation of surrounding rock → finding the top → initial spraying of 4cm C25 shotcrete on the rock surface of the tunnel body → erection of steel frame → driving of radial anchor rods → hanging of steel mesh → re-spraying of C25 concrete to the designed thickness → inspection and acceptance.

[0080] The temporary support is Φ22 drug coil anchor, double-layer Φ8 steel mesh, I22b I-beam steel frame, C25 shotcrete 26cm. The temporary support process is: construction preparation → drilling → hole cleaning → anchor coil delivery → anchor rod advancement, anchor coil mixing → anchor agent reaches strength.

[0081] The construction of invert and backfill includes the construction of leveling layer: the invert construction is carried out after the open hole excavation is completed to prevent rainwater from soaking the foundation pit. The leveling layer construction can be carried out only after the excavated foundation bearing capacity reaches the design requirements or reaches the design requirements after treatment. The leveling layer uses 10cm thick C25 concrete and the horizontal pouring width is 1620cm.

[0082] Rebar processing and binding for leveling layer construction: welding overlap is adopted between the steel bars, and the length of the weld is not less than 10d. The circumferential steel bars are arranged at equal intervals of 15cm in the longitudinal direction, and the stirrups are arranged at equal intervals of 25cm (along the inner circumferential bars). The net protective layer thickness of the main bars is ≥4cm. Structural limit steel bars are set between the inner and outer layers of circumferential force-bearing steel bars. The steel bar diameter is 16, and the longitudinal and transverse spacing is 2.0m×2.0m. The limit steel bars are welded with the circumferential force-bearing steel bars and the distribution steel bars. Double-layer C22 steel bars are pre-buried at the portal to connect with the portal. The length of the connecting bars is 80cm, the longitudinal spacing is 50cm, and the circumferential spacing is 25cm.

[0083] The lining steel bars meet the design and specification requirements. The steel bars are straightened before processing and bending. The oil stains and rust on the surface of the steel bars are clean. The steel bars are straightened, hooked, bent and bent by cold processing. The steel bars are made in advance outside the hole according to the arc shape of the invert. When installing the steel bars, each node bar of the transverse steel bars and the longitudinal steel bars must be tied or welded. The lap positions of adjacent main bars are staggered, and the staggered distance is not less than 1m. The two lap distances of the same stress-bearing steel bars are not less than 1.5m. The connection points of the steel bars must be tied or welded at the cross connection of the longitudinal and transverse bars. The welding at the joints must ensure the weld length requirements (5d or 10d), the weld is full, and the welding slag on the weld is chiseled off.

[0084] Installation formwork for leveling layer construction: The invert lining formwork and bracket must have sufficient strength, rigidity and stability. When installing the formwork, ensure that the support is firm and the joints are tight, and there will be no expansion and leakage. After the formwork is installed, check the center line, elevation, section and clearance size. The contact surface between the formwork and the concrete must be coated with an isolation agent;

[0085] Concrete pouring for leveling layer construction: Before pouring concrete, the slag, dirt and water in the foundation pit must be drained away. It is strictly forbidden to pour concrete into the foundation pit with water. The slump and workability parameters of the concrete must be controlled. A forced concrete mixer is used for mixing, and an electronic meter is provided. The concrete is transported by a concrete transport truck to prevent the concrete from segregating during transportation. A vibrating vibrator is used to vibrate the bottom of the invert first, and then gradually vibrate towards the arch foot of the tunnel body to ensure the compactness of the concrete.

[0086] Backfilling of the inverted arch during the construction of the leveling layer: The backfilling concrete of the inverted arch is carried out after the initial setting of the poured concrete of the inverted arch. The pouring of the filling concrete is carried out in two times: the first time is to install the curbstone and formwork, and pour to the ditch bottom elevation; the second time is to install the ditch formwork, tie the ditch and curbstone steel bars, and pour to the designed elevation. The C20 concrete pouring is filled with a delivery pump and tamped with a manual vibrator. The pouring thickness of the inverted arch concrete is guaranteed during construction. Pay attention to controlling the top surface elevation during the backfilling of the inverted arch to avoid intrusion into the pavement structure layer.

[0087] Tunnel body drainage construction: Preparation for waterproof membrane construction; Fixing of waterproof membrane: Waterproof membrane is laid without nails, that is, the cut membrane is hot-melt pasted on the plastic round gasket with a hot air welding gun; when fixing the membrane on the plastic round gasket, it must not be tightened or bulged, and the membrane at the corners must be close to the corners to avoid affecting the size of the poured concrete or tearing the membrane; Welding of waterproof membrane seams; Protection measures for waterproof membrane to avoid damage: The quality of waterproof membrane protection is related to the success or failure of the waterproof project. Any small damage may cause water leakage in the project. Therefore, it is the focus of the waterproof project to strengthen the protection of waterproof membrane. Due to the use of flow operation, the various processes are frequently crossed and the waterproof material is easily damaged; Construction of embedded waterstop; Construction of back-sticked waterstop.

[0088] The secondary lining process flow is: spray concrete surface treatment → installation of drainage blind pipe → inspection, if unqualified, re-spray concrete surface treatment → laying of waterproof board → inspection, if unqualified, re-laying of waterproof board → manufacturing and installation of steel bars → inspection, if unqualified, re-manufacturing and installation of steel bars → secondary lining trolley in place → decontamination, brushing of release agent → trolley positioning → embedded parts installation → erecting plugging plate, installing water stop → inspection, if unqualified, re-positioning of trolley → pouring of concrete if qualified → demoulding after curing → continue curing after demoulding.

[0089] The aforementioned basic examples and their further selected examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed for protection in this application. In the scheme of this application, each selected example can be arbitrarily combined with any other basic examples and selected examples.

[0090] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A shallow tunnel excavation and initial support construction method, characterized in that: The steps include: Step S01, excavation and construction of the intercepting ditch on the cave roof and drainage works at the cave entrance; Step S02, excavation of earth and stone at the tunnel entrance, and temporary protection of the side slope and the tunnel surface; Step S03, construction of auxiliary measures for entrance into the hole; Step S04, tunnel excavation; Step S05A, initial support of the tunnel body; Step S05B, construction of the pipe shed on the exit side; Step S06, invert and backfill construction; Step S07A, tunnel body waterproofing and drainage construction; Step S07B, open hole formwork lining construction and tunnel gate construction; Step S08, secondary lining; Step S09, road surface inside the tunnel.

2. The shallow tunnel excavation and initial support construction method according to claim 1 is characterized in that: The tunnel entrance project includes tunnel entrance drainage construction, tunnel entrance side slope construction, pipe shed construction, open tunnel construction and end wall tunnel door construction; Construction of tunnel entrance drainage project: The tunnel entrance drainage works include intercepting ditch outside the side slope excavation line, drainage ditch at the side wall corner and outside the tunnel and ditch on the top of the end wall, which are connected with the drainage system of the road outside the tunnel of the tunnel project; the slope of the intercepting ditch is set according to the terrain, not less than 5m away from the edge of the side slope excavation, and the slope is not less than 3%; the intercepting ditch on the top of the side slope of the tunnel entrance section is built in advance in combination with the permanent drainage system, and is completed before the tunnel enters the tunnel, and the outlet must prevent the water from flowing down the slope; the drainage outlet of the tunnel entrance must form a drainage system with the drainage network of the road outside the tunnel, and its water flow must not scour the road and damage the environment; the surface water within the intercepting ditch of the tunnel entrance is introduced into the road drainage ditch through the ditch on the top of the end wall; the intercepting ditch is located 5m outside the side slope excavation line, the slope is guaranteed to be flat and stable, and it is strictly forbidden to stick to the slope; the longitudinal slope is strictly constructed according to the drawing, the ditch bottom is flat, the drainage is unobstructed, and there is no water blocking.

3. The shallow tunnel excavation and initial support construction method according to claim 2 is characterized in that: Construction of tunnel entrance side slope: The slope rate of the tunnel entrance side slope is coordinated with the roadbed outside the tunnel. After the tunnel construction is completed, the exposed temporary side slope is greened to make it coordinated with the surrounding natural environment. In order to prevent the weathering and peeling or instability of the rock or soil on the slope, and at the same time not to destroy and change the original landform and vegetation growth conditions of the slope, clearing measures are taken for the slope above the tunnel top that is in danger of falling rocks and collapse. The process flow is: measurement and layout → excavation of side slope → inspection of slope and stability → initial spraying of concrete → drilling → cleaning of holes → installation of mortar anchors → laying of steel mesh → spraying of concrete.

4. The shallow tunnel excavation and initial support construction method according to claim 2 is characterized in that: Pipe shed construction: Before the construction of the pipe shed, the sleeve arch is constructed first, and the sleeve arch is used as the fixed end of the pipe shed and for guidance. At the same time, the concrete sleeve arch is used to stabilize the back slope of the mountain; survey and layout, and mark the boundary line between the sleeve arch and the blind tunnel excavation; excavate and repair the sleeve arch and the side back slope, and reinforce the side back slope according to the design requirements. When excavating the sleeve arch position, reserve the core soil of the tunnel body; the sleeve arch is constructed outside the outline of the open tunnel and close to the heading face. During the sleeve arch construction, the steel arch frame is first supported and installed. Each unit of the steel frame is fixed and formed by a connecting plate. The tunnel entrance and exit between the units are supported in advance by the pipe shed; the drilling is carried out by a pipe shed drilling rig, which is driven in at one time. During the drilling construction process, the short drill rod is extended multiple times by adding rods; the grouting is carried out in sections by cement slurry; longitudinal connecting steel bars are set between the steel frames, and the slope of the connecting line on the outer surface of the steel frame is consistent with the external insertion angle of the pipe shed; after the installation of the guide pipe is completed, the two ends are blocked with slurry stoppers to prevent concrete from flowing into the pipe; sleeve arch Concrete pouring is adopted. The inner and outer formworks of the sleeve arch and the plug formwork are all processed and installed with wooden formworks or bamboo plywood. The formwork at the bottom of the sleeve arch is positioned with steel supports, and steel pipes are set up for reinforcement and support to ensure that the formwork is accurately positioned and does not deform during concrete pouring. No external formwork is used within 40° of the top of the guide wall, and manual finishing is adopted to ensure that the structural surface is flat and smooth. Commercial concrete is used. Concrete is transported to the site by concrete tankers and pumped into the formwork by concrete pump trucks. The pouring sequence is strictly controlled during construction, and the pouring is completed before the concrete begins to set. In order to avoid excessive eccentric load during concrete pouring, the left and right sides rise alternately during concrete pouring, and the height difference of the concrete surfaces on both sides does not exceed 50cm. During the concrete pouring process, the formwork support is observed and any deformation is dealt with to ensure the accurate position of the sleeve arch. When the strength of the sleeve arch concrete reaches 85%, the construction of the long pipe shed begins.

5. The shallow tunnel excavation and initial support construction method according to claim 2 is characterized in that: Open-cut construction: Open-cut construction of tunnels follows the principle of continuity, with lining after excavation and backfill after lining to avoid exposing the slope and enhance the stability of the tunnel entrance. Open-cut lining is used for the open-cut sections of the entrance and exit, and a reinforced concrete structure is used. When calculating the structure, the design load takes into account the backfill soil load, the deadweight of the structure and the construction load, and the elastic resistance of the foundation is taken into account for the invert and the side wall backfilled with plain concrete. During the construction of the open-cut tunnel, the construction is strictly carried out according to the drawings, the plain concrete backfill of the side wall is dense, and the top backfill is symmetrically backfilled, and the designed backfill thickness and the designed backfill soil cross slope are not allowed to be exceeded to ensure that the structural working conditions are consistent with the structural design model. The process flow is: excavation and support of the tunnel entrance section and foundation trench → base geophysical exploration and bearing capacity test → invert construction → filling concrete → formwork trolley in place → formwork inspection → steel bar binding → erection of external formwork → pouring of lining concrete → waterproofing layer and connection of drainage pipes → backfilling of the arch top. End wall portal construction: The tunnel entrance and exit are both end wall portals with reinforced concrete structure, and the wall and open hole lining are connected with steel bars; process flow: construction preparation interception and drainage ditch construction → excavation of the entrance section and portal foundation → base bearing capacity testing → tying steel bars and supporting formwork → inspection of reserved holes → pouring reinforced concrete → dismantling formwork → connecting drainage facilities → making portal nameplate.

6. The shallow tunnel excavation and initial support construction method according to claim 1 is characterized in that: The construction process of tunnel excavation is as follows: use the steel frame erected in the previous cycle to apply advance support; excavate the first part → spray concrete on the face → apply initial support and temporary support around the first pilot tunnel → apply system anchors and then spray concrete to the designed thickness; lag behind the first part by a set distance, excavate the second part → spray concrete on the face → apply initial support and temporary support around the second pilot tunnel → apply system anchors and then spray concrete to the designed thickness; lag behind the second part by a set distance, excavate the third part → spray concrete on the face → apply initial support around the third pilot tunnel, spray concrete on the face and temporary support Protection → After the system anchor rods are constructed, concrete is sprayed to the designed thickness; after the third lagging part is excavated to a set distance, the fourth part is excavated, and the construction steps and procedures are the same as the first part; after the fourth lagging part is excavated to a set distance, the fifth part is excavated, and the construction steps and procedures are the same as the second part; after the fifth lagging part is excavated to a set distance, the sixth part is excavated, and the construction steps and procedures are the same as the third part; according to the monitoring and measurement results, after the initial support converges, the temporary steel frame is removed, and the bottom invert and invert filling concrete are poured integrally; after the invert length meets the construction length of the secondary lining, the secondary lining is poured at one time using the integral hydraulic lining template trolley; Excavation of the tunnel: Process flow: The construction sequence of the exit is exit construction preparation → exit intercepting ditch and temporary drainage → exit side slope construction → exit guide wall construction → exit large pipe shed construction → exit from the tunnel → open tunnel and tunnel door construction; the construction process and parameters of the exit section tunnel entrance engineering are the same as those of the entrance section; before exiting the tunnel, the tunnel entrance intercepting ditch, temporary drainage measures and side slope protection measures must be completed, and then the guide wall must be constructed. After the exit large pipe shed is constructed and grouting is completed, the tunnel entrance is closed with shotcrete; Pilot pit construction: prepare drainage at the exit tunnel, side slope protection, and pipe shed construction in advance. Excavation can only be continued after confirming that the side slope at the exit tunnel is stable and there is no impact of geological disasters such as collapse or landslide. After each excavation of the exit tunnel, observe the bedding and cracks of the excavation surface, judge the stability of the surrounding rock, and apply initial support after excavation. The initial support is closely followed by the heading face, and blind excavation is strictly prohibited. To ensure the safety of the exit tunnel, set a distance from the penetration surface, slow down the excavation speed, and observe at any time. After the upper pilot pit on the left is excavated, it will be initially supported to complete the safe exit. After the exit construction of the upper pilot pit is completed, the remaining pilot pits will be gradually advanced to the tunnel entrance to complete the exit construction. Tunnel entrance project: After exiting the tunnel, complete the construction of the tunnel entrance project of the open tunnel and tunnel gate.

7. The shallow tunnel excavation and initial support construction method according to claim 1 is characterized in that: Support includes advance small-duct support, initial support and temporary support; The process flow of advanced small-pipe support is as follows: construction preparation → measurement and positioning → drilling operation → hole cleaning → drilling acceptance → pipe lowering and hole plugging after passing the inspection, and return to drilling operation if unqualified → spraying concrete to plug the working surface → connection and debugging of grouting pipeline → grouting operation → grouting effect analysis → welding of pipe tail and steel frame if the requirements are met → end; grouting effect analysis → adjusting grouting parameters if the requirements are not met → slurry preparation → grouting operation; construction preparation → small-pipe preparation → pipe lowering and hole plugging; construction preparation → raw material inspection → slurry ratio design → grouting test → slurry preparation → grouting operation; The initial support process is: excavation of surrounding rock → finding the top → initial spraying of shotcrete on the rock surface of the tunnel body → erection of steel frame → driving of radial anchor rods → hanging of steel mesh → re-spraying of concrete to the designed thickness → inspection and acceptance; The temporary support process is: construction preparation → drilling → hole cleaning → delivering anchor coil → pushing anchor rod and stirring anchor coil → anchor agent reaches strength.

8. The shallow tunnel excavation and initial support construction method according to claim 1 is characterized in that: The construction of invert and backfill includes the construction of leveling layer: the invert construction is carried out after the open hole excavation is completed to prevent rainwater from soaking the foundation pit; the leveling layer construction can be carried out only after the bearing capacity of the excavated foundation reaches the design requirements or reaches the design requirements after treatment; Rebar processing and binding: welding is used to overlap the steel bars; structural limit bars are set between the inner and outer layers of annular stress-bearing steel bars, and the limit bars are welded to the annular stress-bearing steel bars and distribution steel bars; double-layer steel bars are pre-buried at the portal and connected to the portal; lining steel bars meet the design and specification requirements; steel bars are straightened before processing and bending; The oil stains and rust on the surface of the steel bar are clean; the steel bar is straightened, hooked, bent and bent by cold processing; the steel bar is made in advance outside the hole according to the arc shape of the inverted arch. When installing the steel bar, each node bar of the transverse steel bar and the longitudinal steel bar must be tied or welded; the overlapping positions of adjacent main bars are staggered; the connection points of the steel bar must be tied or welded at the intersection of the longitudinal and transverse bars; Install the formwork: When installing the formwork, ensure that the support is firm and the joints are tight, so that there will be no expansion or leakage. After the formwork is installed, check the center line, elevation, section and clearance dimensions; the contact surface between the formwork and the concrete must be coated with an isolation agent; Concrete pouring: Before pouring concrete, the slag, dirt and water in the foundation pit must be drained away. It is strictly forbidden to pour concrete into a foundation pit with water. The slump and workability parameters of the concrete must be controlled. A forced concrete mixer is used for mixing, and an electronic meter is provided. Concrete is transported by a concrete transport truck to prevent segregation of the concrete during transportation. A vibrating vibrator is used to vibrate the bottom of the invert first, and then gradually vibrate towards the arch foot of the tunnel body to ensure the compactness of the concrete. Backfill of the invert: The backfill concrete is poured after the initial setting of the poured concrete of the invert. The pouring of the filling concrete is carried out in two times: the first time is to install the curb and formwork, and pour to the ditch bottom elevation; the second time is to install the ditch formwork, tie the ditch and curb reinforcement, and then pour to the designed elevation; the filling concrete is poured using a delivery pump and manual vibrator to ensure the pouring thickness of the invert concrete during construction; when backfilling the invert, pay attention to controlling the top surface elevation to avoid intrusion into the pavement structure layer.

9. The shallow tunnel excavation and initial support construction method according to claim 1, characterized in that: Tunnel body drainage construction: preparation for waterproof membrane construction; fixing of waterproof membrane: waterproof membrane is laid without nails, that is, the cut membrane is hot-melt pasted on the plastic round gasket with a hot air welding gun; when fixing the membrane on the plastic round gasket, it must not be tightened or bulged, and the membrane at the corners must be tightly attached to the corners to avoid affecting the size of the poured concrete or tearing the membrane; welding of waterproof membrane seams; protective measures for waterproof membrane to avoid damage; construction of embedded waterstop; construction of back-sticked waterstop.

10. The shallow tunnel excavation and initial support construction method according to claim 1, characterized in that: The secondary lining process flow is: spray concrete surface treatment → installation of drainage blind pipe → inspection, if unqualified, re-spray concrete surface treatment → laying of waterproof board → inspection, if unqualified, re-laying of waterproof board → manufacturing and installation of steel bars → inspection, if unqualified, re-manufacturing and installation of steel bars → secondary lining trolley in place → decontamination, brushing of release agent → trolley positioning → embedded parts installation → erecting plugging plate, installing water stop → inspection, if unqualified, re-positioning of trolley → pouring of concrete if qualified → demoulding after curing → continue curing after demoulding.

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