Tunnel construction method for shallow-buried water-rich section underneath passing existing expressway

Abstract

The invention discloses a tunnel construction method for a shallowly-buried water-rich section to pass through an existing expressway. The tunnel construction method comprises the following steps that firstly, an arch part is subjected to advanced supporting through advanced small guide pipe grouting; secondly, tunnel blasting is conducted through the water pressure smooth blasting technology, and a blasting parameter structure is designed; thirdly, blasting tunneling is conducted through a double-side-wall pilot tunnel method, and excavation supporting construction is conducted; a left upper pilot tunnel is firstly excavated, and then a left lower pilot tunnel, a right upper pilot tunnel, a right lower pilot tunnel, a middle upper pilot tunnel and a middle lower pilot tunnel are excavated and subjected to primary support; and fourthly, secondary lining construction is conducted. The defects that in construction in the prior art, air pollution is large, the structural stability is poor, and the risk is high are overcome.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology. More specifically, this invention relates to a method for constructing a shallow-buried, water-rich section tunnel under an existing highway. Background Technology

[0002] In highway construction, tunnel or culvert excavation technology is a crucial link, especially for the construction of underpasses in shallow buried sections. Due to the thin strata and complex geological conditions, problems such as collapse and ground subsidence are prone to occur during construction, posing great challenges to the construction.

[0003] Traditional tunneling methods for shallow buried sections typically employ open-cut and backfilling, cut-and-cover, or shield tunneling. However, open-cut and backfilling methods have been gradually phased out due to their significant ground disturbance, long construction period, and substantial environmental impact. While cut-and-covering and shield tunneling methods can reduce ground impact in shallow buried sections, they still present challenges such as unstable ground conditions and groundwater leakage. To address these issues, the engineering field has been continuously exploring new construction methods in recent years to improve tunneling efficiency and safety. For example, in the construction of shallow buried sections crossing existing highways, the project's characteristics—rich in fissure water, fractured rock mass, highly developed joints and fissures, small clearance, and complex environment beneath the tunnel—pose significant construction challenges. Therefore, a tunnel construction method for shallow buried water-rich sections crossing existing highways needs to be designed to overcome the technical deficiencies of existing technologies, such as structural instability and high construction risks. Summary of the Invention

[0004] One objective of this invention is to provide a method for constructing a shallow-buried, water-rich section tunnel under an existing highway, thereby addressing the shortcomings of existing technologies, such as high air pollution, poor structural stability, and high risks.

[0005] To address the aforementioned technical problems, this invention provides a method for constructing a shallow-buried, water-rich section tunnel under an existing highway, comprising the following steps: Step 1: Use advanced small-diameter pipes for grouting to provide advanced support for the arch; Step 2: Tunnel blasting is carried out using hydraulic smooth blasting technology, and the blasting parameters and structure are designed. Step 3: Use the double-sided pilot tunnel method for blasting and excavation, and carry out excavation and support construction. The excavation and initial support of the left upper pilot tunnel shall be carried out in the following order: first excavate the left lower pilot tunnel, then the left upper pilot tunnel, the right upper pilot tunnel, the right lower pilot tunnel, the middle upper pilot tunnel, and the middle lower pilot tunnel. Step 4: Secondary lining construction.

[0006] Preferably, in step three, during the initial support process, anchor bolt reinforcement is carried out. Three-dimensional laser scanning technology is used to identify structural surfaces, and the anchor bolts are then placed at the joints and fissures based on the joints and fissures between the structural surfaces. The specific method is as follows: First, multiple scanning stations are set up on the surface of the tunnel pilot pit, and high reflectivity targets are evenly distributed. Each station cloud covers ≥5 non-coplanar targets. The control point-based ICP algorithm is used to stitch the multi-station clouds to a unified coordinate system, and the stitching error is controlled within 3mm. Secondly, a 99th percentile threshold is used for hard rock areas and a 95th percentile threshold is used for soft rock areas. Statistical filtering is used to remove flying points while retaining microcrack edge points, thus preserving the main tunnel structure. Then, structural surface recognition: deep learning algorithms are used to train the point cloud data to automatically identify structural surfaces; by setting an appropriate threshold, the structural surfaces are separated from the background noise. Finally, joint and crack extraction: on the identified structural surface, joint and crack information is further extracted; by calculating the point cloud density change on the structural surface, the location and width of the joint and crack are determined.

[0007] Preferably, based on the results of structural surface identification, the joints and fissures between structural surfaces are observed, and the system anchors are evenly distributed at the joints and fissures. Specifically: for a single structural surface, if the joint and fissure direction is parallel to the tunnel axis (i.e., within the range of θ≤10°), the anchors are arranged perpendicular to the structural surface, with a dipping angle of ±90° and an anchor length ≥2 times the structural surface spacing; if the joint and fissure direction is perpendicular to the tunnel axis (i.e., within the range of θ≥80°), the anchors are arranged parallel to the structural surface, with a dipping angle of ±10° and an anchor spacing of 0.6 times the structural surface spacing; for inclined structural surfaces (i.e., within the range of 10°<θ<80°), the angle β between the anchor direction and the normal vector of the structural surface is 50°±3°, forming an "oblique anchoring". For composite structural surfaces, for intersecting cracks (i.e., the included angle is ≤20°), double rows of anchor bolts are arranged on both sides of the intersection line, with a row spacing of 0.5 times the crack spacing, and the anchor bolt direction is at a 20° angle to the intersection line; for en echelon cracks (i.e., the spacing changes periodically), the anchor bolt spacing is arranged in a gradient of 0.8 times the crack spacing to form a sparse-dense-sparse transition zone.

[0008] Preferably, in step two, the charge structure used for water-pressure smooth blasting during excavation is as follows: For the peripheral holes and slotted holes, a first water bag, a shaped charge tube, and a second water bag are arranged sequentially from the inside to the outside in the charging channel. The hole opening is provided with sealing mud. V-shaped shaped charge grooves are symmetrically opened on both sides of the shaped charge tube. The shaped charge tube is filled with explosive and has a continuous, uncoupled structure. A pair of arc-shaped water bags are arranged on the outer periphery of the shaped charge tube at positions other than the V-shaped shaped charge grooves. They form an integral structure with the outer wall of the shaped charge tube. The pair of arc-shaped water bags are symmetrically arranged on both sides of the pair of V-shaped shaped charge grooves. For auxiliary holes and bottom holes, a first water bag, a shaped charge tube, and a second water bag are arranged sequentially from the inside to the outside in the charging channel. The hole opening is provided with sealing mud. V-shaped shaped charge grooves are symmetrically opened on both sides of the shaped charge tube. The shaped charge tube is filled with explosive and has a continuous uncoupled structure.

[0009] Preferably, the arc-shaped water bags cover the outer periphery of all energy-concentrating tubes except for the V-shaped energy-concentrating groove. Multiple arc-shaped water bags are spaced apart along the length of the energy-concentrating tube. Multiple guide columns are provided on the outer wall of the energy-concentrating tube at its upper end, lower end, and between adjacent arc-shaped water bags. These guide columns are set close to the inner wall of the charging channel to guide the energy-concentrating tube, so that the central axis of the energy-concentrating tube coincides with the central axis of the charging channel.

[0010] Preferably, the opening direction of the pair of V-shaped energy-concentrating grooves of the energy-concentrating tube is consistent with the tunnel outline, that is, aligned with the tangential direction of the tunnel outline.

[0011] Preferably, the loading of the propellant into the loading channel is achieved through an auxiliary mechanism. This auxiliary mechanism includes a portal-shaped fixing component, comprising a pair of fixing posts and a horizontal column connecting the top ends of the pair of fixing posts as a single unit. The bottom ends of the pair of fixing posts are connected by an elastic rope. One end of the elastic rope is fixed to the lower end of one of the fixing posts, and the other end is integrally connected to a connecting block. The connecting block has a concave internal threaded groove. The other fixing post has a through channel inside, within which a screw is installed. The lower end of the screw is threaded into the groove of the connecting block, and the upper end is threaded through the top of the fixing post. Inside the fixed nut, the connecting block is pulled into the through channel of the fixed column by the screw when the elastic rope is stretched. The lower part of the through channel that mates with the connecting block has an enlarged diameter structure and fits tightly with the connecting block. The lower part of the pair of fixed columns is provided with a slot on its side. A pair of semi-circular arc plates are arranged opposite each other and are engaged in the slot on the same side of the pair of fixed columns, so that the lower part of the pair of fixed columns forms a space for placing the first water bag. The inner sidewalls of the pair of fixed columns are provided with protrusions that mate with the V-shaped energy-gathering groove. The pair of fixed columns are provided with scale lines.

[0012] The present invention has at least the following beneficial effects: 1. This invention uses hydraulic smooth blasting technology to improve the utilization rate of explosives, reduce harmful gases and dust, and protect the health of construction workers.

[0013] 2. Traditional tunnel reinforcement methods involve arranging anchor bolts at equal longitudinal and circumferential intervals on the surrounding rock and drilling holes according to uniform design requirements. This method may involve drilling through entire sections of rock, thus reducing the stability of the surrounding rock. Furthermore, grouting the arranged mortar anchor bolts is not practically meaningful. Traditional methods not only fail to increase the stability of the surrounding rock but also increase labor and material costs. This application, however, uses 3D point cloud-based structural surface identification and arranges anchor bolts based on the identification results, effectively solving the aforementioned drawbacks.

[0014] 3. This invention can monitor tunnels based on scanned 3D point cloud models, improving the efficiency of traditional monitoring methods.

[0015] 4. This invention reduces the impact on the existing highway above, which is beneficial to the stability of the excavation face.

[0016] 5. This invention achieves stability and safety in blasting by setting up a charging structure and charging auxiliary mechanisms, while also achieving precise charging positioning.

[0017] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0018] Figure 1 This is a flowchart of the blasting process of the present invention; Figure 2 This is a schematic diagram of the rhomboid groove of the present invention; Figure 3 This is a schematic diagram of the borehole arrangement using the double-side-wall guide pit method of the present invention; Figure 4 This is a schematic diagram of part of the point cloud data of the present invention; Figure 5 This is a diagram showing the structural surface identification results of the present invention; Figure 6 This is a diagram showing the arrangement of the anchor bolts in this invention; Figure 7 This is a schematic diagram of the charge channel structure of the present invention; Figure 8 This is a cross-sectional view of the energy-concentrating tube of the present invention; Figure 9 This is a plan view of the fastener of the present invention; Figure 10 This is a cross-sectional schematic diagram of the fastener of the present invention.

[0019] Explanation of reference numerals in the attached figures: 1. First water bag, 2. Energy-concentrating tube, 3. Arc-shaped water bag, 4. Second water bag, 5. Guide column, 6. Fixing column, 7. Horizontal column, 8. Elastic rope, 9. Through channel, 10. Connecting block, 11. Internal threaded groove, 12. Nut, 13. Raised strip, 14. Semi-circular arc plate. Detailed Implementation

[0020] To better understand the purpose, structure, and function of this invention, the invention will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0021] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] like Figures 1 to 6 As shown, this invention provides a method for constructing a shallow-buried, water-rich section tunnel under an existing highway, comprising the following steps: S1: Advanced support for the arch is achieved using pre-grouting with small guide pipes. Hot-rolled seamless steel pipes (Φ50×5mm) are selected, with a single pipe length of 5.0m, a circumferential spacing of 40cm, an outward insertion angle of 15°, a longitudinal overlap length of not less than 1m, and a longitudinal spacing of 3.0m. The tail of the pre-grouting pipes is firmly welded to the initial support steel arch frame to enhance overall rigidity. Cement grout is used as the grouting material, and the mix proportion is determined by laboratory testing. A grouting test is required before grouting construction to adjust the grouting parameters. The water-cement ratio for this segment is 0.5:1, and the grouting pressure is 0.5~1.0MPa.

[0023] S2: Tunnel blasting employs hydraulic smooth blasting technology, primarily by placing explosives in a water-filled borehole, utilizing water as a medium to transfer the energy and pressure generated during the explosion. For example... Figure 1 The diagram shown is the overall flowchart of the blasting process.

[0024] (1) Make water bags. The water bag material is polyethylene plastic bag, which is made using a filling and sealing machine; (2) Hole layout: Before laying out the boreholes and drilling, the surveyors mark the centerline and outline of the excavation section according to the blasting design plan, and mark the slotting holes, auxiliary holes, peripheral holes and bottom holes respectively. The hole layout points should be clearly marked. In this project, the double-side wall pilot tunnel method is used for blasting excavation in Class V surrounding rock areas such as shallow buried sections with severe bias pressure, small clearance sections, and sections passing under the main line of Shenhai Expressway. The designed borehole diameter is 42mm, the peripheral holes and auxiliary holes are 0.6m deep, and the slotting holes are 0.7m deep. Because the excavation advance of this method is relatively small, the design hole spacing of smooth holes is 0.45m, the thickness of the smooth blasting layer is 0.5m, the hole spacing of auxiliary holes is 0.6m and the row spacing is 0.5m, the hole spacing of bottom holes is 0.5m, and the slotting holes adopt a diamond-shaped slotting pattern. Figure 2 As shown in the diagram. Due to the development of joints and fractures, the design charge per hole for the peripheral holes is Q = 0.1 kg, for the auxiliary holes Q = 0.3 kg, for the bottom holes Q = 0.4 kg, and for the slotted holes Q = 0.5 kg. Based on the above hole layout principles, the hole layout diagram is as follows. Figure 3 As shown in Table 1, the blasting parameters are as follows.

[0025] Table 1. Blasting Parameters for Double-Side Wall Pilot Tunnel Method (3) Drilling and cleaning: The design adopts a pneumatic leg-type air drill for drilling. In order to reduce the friction between the hole wall and the water bag, water pressure is used to clean the hole first, and then air pressure is used to remove the water accumulated in the hole. (4) Water bag and blasting mud installation: water pressure blasting is continuous charging in the slotted hole, auxiliary hole and bottom edge hole. The detonating cord is used for detonation. Before charging, a section of water hose is installed at the bottom of the blast hole. Then the explosive is continuously and evenly distributed into the blast hole. After charging, multiple sections of water bag are installed. Finally, blasting mud is used to plug the hole. like Figure 7 and Figure 8 As shown, the charge structure is as follows: For the peripheral holes and slotted holes, a first water bag 1, a shaped charge tube 2, and a second water bag 4 are sequentially arranged from the inside to the outside within the charging channel. Sealing mud is provided at the hole opening. V-shaped shaped charge grooves are symmetrically opened on both sides of the shaped charge tube. The shaped charge tube is filled with explosive and has a continuous, uncoupled structure. A pair of arc-shaped water bags 3 are arranged on the outer periphery of the shaped charge tube at positions other than the V-shaped shaped charge grooves. They form an integral structure with the outer wall of the shaped charge tube. The pair of arc-shaped water bags are symmetrically arranged on both sides of the pair of V-shaped shaped charge grooves. The opening direction of the pair of V-shaped shaped charge grooves of the shaped charge tube is consistent with the tunnel outline, that is, aligned with the tangent direction of the tunnel outline. The arc-shaped water bags cover the outer periphery of all the energy-concentrating tubes except for the V-shaped energy-concentrating groove. Multiple arc-shaped water bags are spaced apart along the length of the energy-concentrating tube. Multiple guide posts 5 are provided on the outer wall of the energy-concentrating tube at its upper end, lower end and between adjacent arc-shaped water bags. These guide posts are set close to the inner wall of the charging channel to guide the energy-concentrating tube, so that the central axis of the energy-concentrating tube coincides with the central axis of the charging channel.

[0026] For auxiliary holes and bottom holes, a first water bag, a shaped charge tube, and a second water bag are arranged sequentially from the inside to the outside in the charging channel. The hole opening is provided with sealing mud. V-shaped shaped charge grooves are symmetrically opened on both sides of the shaped charge tube. The shaped charge tube is filled with explosive and has a continuous uncoupled structure.

[0027] Given the unique construction environment of this application—a shallow-buried tunnel with a water-rich section and passing under an existing highway—it is crucial to ensure the stability of the blasting process, maintain a smooth blast surface, and control the stability of the tunnel structure. This application, building upon the existing conventional combination of water bags, explosives, and water bags, utilizes a shaped charge tube for the central explosive charge. This significantly improves the blasting direction, controls the blast surface outline, and ensures tunnel structural stability. Furthermore, based on the different functions of each charging duct, the charging structure within each duct needs to be differentiated and rationally zoned. During blasting, the peripheral holes and cut holes generate more dust; therefore, additional arc-shaped water bags are installed around the corresponding shaped charge tubes to better control dust and enhance the water wedge effect, resulting in higher explosive utilization, better blasting effect, and reduced damage to the surrounding rock.

[0028] like Figure 9 and Figure 10As shown, loading the propellant into the loading channel is achieved through an auxiliary mechanism. This auxiliary mechanism includes a portal-shaped fixing component, comprising a pair of fixing posts 6 and a horizontal post 7 connecting the top ends of the pair of fixing posts as a single unit. The bottom ends of the pair of fixing posts are connected by an elastic rope 8. One end of the elastic rope is fixed to the lower end of one of the fixing posts, and the other end is integrally connected to a connecting block 10. The connecting block has a concave internal threaded groove 11. The other fixing post has a through channel 9 inside, within which a screw is installed. The lower end of the screw is threaded into the groove of the connecting block, and the upper end is threaded through the top of the fixing post. Inside the fixed nut 12, the connecting block is pulled into the through channel of the fixed column by the screw when the elastic rope is stretched. The lower part of the through channel that cooperates with the connecting block has an enlarged diameter structure and fits tightly with the connecting block. The lower part of the pair of fixed columns is provided with a slot on its side. A pair of semi-circular arc plates 14 are arranged opposite each other and are both engaged in the slot on the same side of the pair of fixed columns, so that the lower part of the pair of fixed columns forms a space for placing the first water bag. The inner sidewalls of the pair of fixed columns are provided with protrusions 13 that cooperate with the V-shaped energy-gathering groove. The pair of fixed columns are provided with scale lines.

[0029] Existing blasting processes typically involve manual loading, which is cumbersome, inefficient, and lacks reliable installation and positioning. Therefore, this application proposes an auxiliary mechanism to facilitate the loading process during blasting. First, the first water bag is assembled. The elastic rope is stretched, connecting the screw and the connecting block. The elastic rope is then stretched further, and the connecting block is assembled into the through-channel. The elastic rope forms a barrier at the bottom of a pair of fixing posts. The connecting block and the enlarged diameter structure at the bottom of the through-channel fit tightly, ensuring that the friction between the connecting block and the through-channel is greater than the threaded connection force between the threaded groove of the connecting block and the screw. Next, a pair of semi-circular arc plates are engaged in slots. The lower end of the semi-circular arc plates has a detachable protrusion that can be inserted into the slot. The first water bag is placed within the space formed by the elastic rope, the pair of semi-circular arc plates, and the pair of fixing posts. The entire bag is inserted into the borehole. The markings on the fixing posts indicate whether the first water bag has reached the bottom of the borehole. After placement, the screw is rotated, causing the connecting block to detach from the screw. Under the rebound of the elastic rope, the connecting block detaches from the through-channel of the fixing posts. Then, the pair of fixing posts are pulled outwards, simultaneously pulling out the elastic rope, completing the installation of the first water bag. At the same time, the pair of semi-circular arc plates are removed. A pair of fixed posts, with their protruding strips engaging with the V-shaped energy-concentrating grooves of the shaped charge tube, are assembled into the borehole. The outer walls of the fixed posts are flush with the inner walls of the borehole, and the outer diameter of the fixed posts is equal to the inner diameter of the borehole. Guided by the fixed posts, the central axis of the shaped charge tube coincides with the central axis of the borehole, achieving precise positioning and installation of the shaped charge tube. Simultaneously, the graduations on the fixed posts allow for precise positioning and monitoring of the shaped charge tube's installation position. By monitoring the installation angle of the fixed posts, the orientation of the V-shaped energy-concentrating grooves on the shaped charge tube towards the designated tunnel outline can be accurately determined. Furthermore, the guide posts on the shaped charge tube do not interfere with the fixed posts. After the shaped charge tube is positioned, the fixed posts are removed, and the guide posts provide support and positioning for the shaped charge tube.

[0030] (5) Detonation: After the charge is completed, the detonation network is connected using the cluster method. The network is divided into three larger networks: upper, middle, and lower. After connecting the detonating cords in each borehole together, the detonating cords are connected to the detonator for detonation. (6) Slag removal: Excavators, loaders and slag removal trucks are used for slag removal.

[0031] S3: The double-sided wall pilot tunnel method is used for excavation and support. The upper left section is excavated, initial shotcrete is applied, the first layer of steel mesh is installed, steel arch frame is erected, the second layer of steel mesh is installed, the anchor bolts are installed, shotcrete is applied again, and system anchor bolts and interlocking rock guide pipes are constructed. (1) The upper left pilot tunnel was scanned using a 3D laser scanner to obtain its 3D point cloud data. The tunnel can then be precisely monitored based on the 3D point cloud data.

[0032] (2) Shotcrete construction uses a shotcrete machine. Before construction, the rock surface is first cleaned from top to bottom with high-pressure air, and marker nails are embedded to control the thickness of the shotcrete. If there is dripping or gushing water on the working face, drainage work is carried out in advance by drilling and embedding pipes. Wet spraying method is used for shotcrete, which has a fast spraying speed, less rebound, and less dust. Concrete is centrally mixed at the mixing plant outside the tunnel and transported to the working face by concrete transport trucks. After each cycle of excavation is completed, initial shotcrete is carried out immediately, with an initial shotcrete thickness of about 4cm. Markers are set to control the thickness of the shotcrete to ensure the thickness of the shotcrete. Short steel bars are inserted into the rock surface for marking during the initial shotcrete operation. The shotcrete operation is carried out from bottom to top from the arch foot or wall foot, in sections and pieces, to prevent the upper shotcrete rebound material from not covering the arch foot and not being dense, resulting in insufficient strength and instability; the pit and depression parts are leveled first, and then shotcrete is sprayed to make it smooth and continuous. The spraying operation involves moving the nozzle horizontally in a spiral motion, keeping it as perpendicular as possible to the surface being sprayed. The distance from the nozzle to the surface should be 0.6–1.2 m. After the support structure is completed, layers of concrete should be sprayed to the designed thickness, each layer being 5–6 cm thick and covering the steel frame with a thickness of at least 2 cm. For the supporting steel frame, the back of the frame should be sprayed densely, ensuring a tight and secure bond.

[0033] (3) Lay the first layer of steel mesh, using A8 type steel welded mesh with a steel diameter of Φ80mm and a spacing of 20cm*20cm. The intersections are resistance welded and set on the arch wall. The welded length of the steel mesh should not be less than 2.0m. It should be centrally processed in the steel component processing plant using mesh processing molds. The overlap length of the steel mesh should not be less than 30d (d is the steel diameter), i.e., 24cm, and should not be less than the size of one long side of the mesh. (4) The steel frame is made of shaped steel, which is manufactured in sections in the factory and assembled on site. It is then transported to the site for installation and use. A settlement allowance of 15cm is reserved. The steel arch frame is made of I-22b steel and I-18 steel for temporary steel supports, with a longitudinal spacing of 0.5m / frame. Φ22HRB400 longitudinal connecting steel bars are set at a circumferential spacing of 1m and a longitudinal spacing of 0.5m. After the steel frame is installed, anchor bolts are installed on the arch wall and temporary side wall.

[0034] (5) Lay another layer of steel mesh. The steel mesh should be laid with the undulation of the sprayed surface and connected with the steel arch and anchor as much as possible to ensure that the steel mesh does not shake when the shotcrete is sprayed.

[0035] (6) For example Figures 4 to 6 As shown, based on 3D point cloud data, Cloudcompare software is used for filtering and noise reduction, followed by structural surface recognition. The specific method is as follows: First, multiple scanning stations are set up on the surface of the tunnel pilot pit, and high reflectivity targets are evenly distributed. Each station cloud covers ≥5 non-coplanar targets. The control point-based ICP algorithm is used to stitch the multi-station clouds to a unified coordinate system, and the stitching error is controlled within 3mm. Secondly, a 99th percentile threshold is used for hard rock areas and a 95th percentile threshold is used for soft rock areas. Statistical filtering is used to remove flying points while retaining microcrack edge points, thus preserving the main tunnel structure. Then, structural surface recognition: Deep learning algorithms (such as convolutional neural networks CNN) are used to train the point cloud data to automatically identify structural surfaces; by setting an appropriate threshold, structural surfaces are separated from background noise; Finally, joint and crack extraction: Joint and crack information is further extracted from the identified structural surfaces. The location and width of joints and cracks are determined by calculating the point cloud density changes on the structural surfaces. The local point cloud density (neighborhood radius = 1cm) of each point on the structural surface is calculated, generating a density gradient map. Edge points with gradient magnitude > 0.5 are extracted as candidate crack regions. For each candidate crack region, two parallel straight lines are fitted (least square method), and the distance between the lines is the crack width. False cracks (such as construction scratches) with width < 1cm are filtered out. The crack points are projected onto a two-dimensional plane (expanded along the tunnel axis), and Hough transform is used to detect straight line segments. Adjacent line segments with a strike deviation < 10° are merged to generate a continuous crack strike curve.

[0036] Based on the results of structural surface identification, joints and fissures between structural surfaces can be seen. The system anchors are then evenly distributed at the joints and fissures. Specifically: For single structural surfaces, where the joint fracture direction is parallel to the tunnel axis (θ≤10°), anchor bolts are arranged perpendicular to the structural surface, with a dip angle of ±90° and an anchor bolt length ≥2 times the structural surface spacing; where the joint fracture direction is perpendicular to the tunnel axis (θ≥80°), anchor bolts are arranged parallel to the structural surface, with a direction angle of ±10° and an anchor bolt spacing of 0.6 times the structural surface spacing; for inclined structural surfaces (10°<θ<80°), the anchor bolt direction is at an angle β of 50°±3° with the structural surface normal vector, forming "oblique anchoring"; for combined structural surfaces, for intersecting fractures (angle ≤20°), double rows of anchor bolts are arranged on both sides of the intersection line, with a row spacing of 0.5 times the fracture spacing and an anchor bolt direction at a 20° angle with the intersection line; for en echelon fractures (spacing varies periodically), the anchor bolt spacing is arranged in a gradient of 0.8 times the fracture spacing, forming a "sparse-dense-sparse" transition zone. Using the uniformity of stress in the compression zone formed by the anchor bolt group as the objective function, the particle swarm optimization (PSO) algorithm is used to adjust the anchor bolt spacing (range 20-200cm) and length (range 1-5m) so that the standard deviation of stress in the compression zone is ≤10%.

[0037] In one specific implementation scheme, a ring is formed with a longitudinal spacing of 50cm, and the circumferential spacing of each ring is set to 1m. Based on the identification results, anchor points are placed in areas with more joints and fissures, and can be fine-tuned according to the actual situation. Each ring has no less than 27 anchor rods. The anchor rods are Φ25mm hollow grouting anchor rods. The tensile breaking strength of a single anchor body should be no less than 180KN, the anchor pull-out resistance should be no less than 80KN, the cement mortar strength should be no less than M20, the water-cement ratio should be 0.4~0.5, the sand-cement ratio should be 0~1, and the sand diameter should be less than 1mm. Before drilling, the anchor rod hole positions are measured and marked with paint. The allowable deviation of the hole position is ±150mm. After the excavation trolley is in place, a pneumatic rock drill is used to align with the marked positions and drill. The drilling direction should be along the normal direction of the excavation contour (the vertical deviation should not exceed 20°), and the hole diameter should be 15mm larger than the anchor rod diameter. After drilling is completed, high-pressure air is used to blow away debris and gravel from the hole, and the borehole is checked for unobstructed flow. The drilling depth is also checked (within 5cm of the allowable deviation from the designed anchor length). Hollow anchors are pre-assembled at the steel component processing plant, consisting of the anchor head, vent pipe, grout stop plug, and hollow rod body, and transported to the site for installation. Before grouting, the grouting pipe is securely connected to the grout stop valve at the anchor pipe opening, and the anchor hole is cleared by blowing air or injecting water. After clearing, grout is injected into the hole using a grouting pump, using cement mortar. Grouting can be stopped once grout appears in the vent hole. The grout stop valve is closed promptly after grouting is completed. After the mortar has fully set, the anchor plate is installed and the nuts are tightened. The anchor plate should be in close contact with the shotcrete layer. If the plate is not completely flush with the shotcrete layer, it should be filled with cement mortar.

[0038] (7) Small-diameter pipe reinforcement was carried out on the section between the left and right tunnels where the interbedded rock thickness was less than 20m. The vertical reinforcement range of the sidewall was 5m. Seamless steel pipes with an outer diameter of 50mm and a wall thickness of 5mm were used for the small-diameter pipes. The pipes were 5m long, with a circumferential spacing of 70cm and a longitudinal spacing of 1.0m, and a horizontal insertion angle of 45°. The top end was a 10cm cone. Φ8mm holes were drilled in the middle, with a spacing of 15cm, arranged in a quincunx pattern, and a 100cm grout stop section was reserved at the tail. Cement grout was used for drilling and grouting, with a water-cement ratio of 0.5:1 and a grouting pressure of 0.5~1MPa.

[0039] (8) Re-spraying of concrete: Depending on the design thickness of the sprayed concrete, the spraying location, and the setting of the steel frame and reinforcing mesh, re-spraying can be carried out in one operation or in layers. When spraying in layers, the thickness of each re-spraying on the arch should not exceed 100mm, the thickness of each spraying on the sidewall should not exceed 150mm, and the minimum thickness of the re-spraying should not be less than 50mm. The subsequent layer of spraying should be carried out after the final setting of the previous layer of concrete. If the final setting time exceeds 1 hour, the rock surface should be treated first. In the spraying operation, the concrete between the steel frame and the rock surface should be sprayed first, and then the concrete between the two steel frames should be sprayed. When spraying, the nozzle should be perpendicular to the sprayed surface, and the distance between the nozzle and the sprayed surface should be 0.6~1.2m.

[0040] Repeat the above construction process.

[0041] S4: Construction of the secondary lining of the tunnel, monitoring and measurement to determine the construction time of the secondary lining, followed by the construction of geotextile waterproof membrane, secondary lining reinforcement, track laying, trolley positioning and adjustment, waterstop installation, end plate installation, pumping concrete pouring, formwork removal and concrete curing.

[0042] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention, and other modifications can be easily implemented by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A method for constructing a shallow-buried, water-rich section tunnel under an existing highway, characterized in that, Includes the following steps: Step 1: Use advanced small-diameter pipes for grouting to provide advanced support for the arch; Step 2: Tunnel blasting is carried out using hydraulic smooth blasting technology, and the blasting parameters and structure are designed. Step 3: Use the double-sided pilot tunnel method for blasting and excavation, and carry out excavation and support construction. The excavation and initial support of the left upper pilot tunnel shall be carried out in the following order: first excavate the left lower pilot tunnel, then the left upper pilot tunnel, the right upper pilot tunnel, the right lower pilot tunnel, the middle upper pilot tunnel, and the middle lower pilot tunnel. Step 4: Secondary lining construction.

2. The tunnel construction method for a shallow-buried, water-rich section tunnel passing under an existing highway as described in claim 1, characterized in that, In step three, during the initial support process, anchor bolt reinforcement is carried out. Three-dimensional laser scanning technology is used to identify structural surfaces, and then the anchor bolts are placed at the joints and cracks between the structural surfaces. The specific method is as follows: First, multiple scanning stations are set up on the surface of the tunnel pilot pit, and high reflectivity targets are evenly distributed. Each station cloud covers ≥5 non-coplanar targets. The control point-based ICP algorithm is used to stitch the multi-station clouds to a unified coordinate system, and the stitching error is controlled within 3mm. Secondly, a 99th percentile threshold is used for hard rock areas and a 95th percentile threshold is used for soft rock areas. Statistical filtering is used to remove flying points while retaining microcrack edge points, thus preserving the main tunnel structure. Then, structural surface recognition: deep learning algorithms are used to train the point cloud data to automatically identify structural surfaces; by setting an appropriate threshold, the structural surfaces are separated from the background noise. Finally, joint and crack extraction: on the identified structural surface, joint and crack information is further extracted; by calculating the point cloud density change on the structural surface, the location and width of the joint and crack are determined.

3. The tunnel construction method for a shallow-buried, water-rich section passing under an existing highway as described in claim 2, characterized in that, Based on the structural surface identification results, the joints and fissures between the structural surfaces are observed. System anchors are then evenly distributed at these joints and fissures. Specifically: for a single structural surface, if the joint / fissure direction is parallel to the tunnel axis (θ≤10°), the anchors are arranged perpendicular to the structural surface, with a dip angle of ±90° and an anchor length ≥2 times the structural surface spacing; if the joint / fissure direction is perpendicular to the tunnel axis (θ≥80°), the anchors are arranged parallel to the structural surface, with a dip angle of ±10° and an anchor spacing of 0.6 times the structural surface spacing; for inclined structural surfaces (10°<θ<80°), the angle β between the anchor direction and the structural surface normal vector is 50°±3°, forming an "oblique anchoring". For composite structural surfaces, for intersecting cracks (i.e., the included angle is ≤20°), double rows of anchor bolts are arranged on both sides of the intersection line, with a row spacing of 0.5 times the crack spacing, and the anchor bolt direction is at a 20° angle to the intersection line; for en echelon cracks (i.e., the spacing changes periodically), the anchor bolt spacing is arranged in a gradient of 0.8 times the crack spacing to form a sparse-dense-sparse transition zone.

4. The construction method for a shallow-buried, water-rich section tunnel passing under an existing highway as described in claim 1, characterized in that, In step two, the charge structure used for hydraulic smooth blasting during the excavation process is as follows: For the peripheral holes and slotted holes, a first water bag, a shaped charge tube, and a second water bag are arranged sequentially from the inside to the outside in the charging channel. The hole opening is provided with sealing mud. V-shaped shaped charge grooves are symmetrically opened on both sides of the shaped charge tube. The shaped charge tube is filled with explosive and has a continuous, uncoupled structure. A pair of arc-shaped water bags are arranged on the outer periphery of the shaped charge tube at positions other than the V-shaped shaped charge grooves. They form an integral structure with the outer wall of the shaped charge tube. The pair of arc-shaped water bags are symmetrically arranged on both sides of the pair of V-shaped shaped charge grooves. For auxiliary holes and bottom holes, a first water bag, a shaped charge tube, and a second water bag are arranged sequentially from the inside to the outside in the charging channel. The hole opening is provided with sealing mud. V-shaped shaped charge grooves are symmetrically opened on both sides of the shaped charge tube. The shaped charge tube is filled with explosive and has a continuous uncoupled structure.

5. The tunnel construction method for a shallow-buried, water-rich section passing under an existing highway as described in claim 4, characterized in that, The arc-shaped water bags cover the outer periphery of all the energy-concentrating tubes except for the V-shaped energy-concentrating groove. Multiple arc-shaped water bags are spaced apart along the length of the energy-concentrating tube. Multiple guide columns are provided on the outer wall of the energy-concentrating tube at its upper end, lower end, and between adjacent arc-shaped water bags. These guide columns are set close to the inner wall of the charging channel to guide the energy-concentrating tube, so that the central axis of the energy-concentrating tube coincides with the central axis of the charging channel.

6. The tunnel construction method for a shallow-buried, water-rich section passing under an existing highway as described in claim 4, characterized in that, The opening direction of the pair of V-shaped energy-concentrating grooves of the energy-concentrating tube is consistent with the tunnel outline, that is, aligned with the tangent direction of the tunnel outline.

7. The construction method for a shallow-buried, water-rich section tunnel passing under an existing highway as described in claim 5, characterized in that, The loading of explosives into the loading channel is achieved through an auxiliary mechanism, which includes a portal-shaped fixing component. This component comprises a pair of fixing posts and a horizontal column connecting the top ends of the pair of fixing posts as a single unit. The bottom ends of the pair of fixing posts are connected by an elastic rope. One end of the elastic rope is fixed to the lower end of one of the fixing posts, and the other end is integrally connected to a connecting block. The connecting block has a concave internal threaded groove. The other fixing post has a through channel inside, within which a screw is installed. The lower end of the screw is threaded into the groove of the connecting block, and the upper end is threaded through the top of the fixing post for fixation. Inside the nut, the connecting block is pulled into the through channel of the fixed column by the screw when the elastic rope is stretched. The lower part of the through channel that mates with the connecting block has an enlarged diameter structure and fits tightly with the connecting block. The lower part of the pair of fixed columns is provided with a slot on its side. A pair of semi-circular arc plates are arranged opposite each other and are engaged in the slot on the same side of the pair of fixed columns, so that the lower part of the pair of fixed columns forms a space for placing the first water bag. The inner sidewalls of the pair of fixed columns are provided with protrusions that mate with the V-shaped energy-gathering groove. The pair of fixed columns are provided with scale lines.

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