A construction method suitable for tunnel in denudation hilly landform

Abstract

The present application relates to a kind of construction methods suitable for denudation hilly land tunnel, comprising the following steps: making roof water interception gutter, layered excavation side slope from top to bottom, open cut excavation, making entrance large pipe shed support;Making tunnel body long pipe shed support, making advance small guide pipe support, burying monitoring survey point, taking advance geological forecast and geological verification work, tunnel excavation;Initial support, radial grouting, curtain grouting, laying waterproof layer, secondary lining, construction ditch cable trough, tunnel pavement.The present application carries out reinforcement treatment to surrounding rock by radial grouting and curtain grouting water plugging measures, ensures smooth passing through fault fracture zone;When construction through granite residual soil and completely weathered, strong weathered rock, tectonic fissure, rock broken section, do advance support well, control collapse, ensure construction safety;When construction, take advance geological forecast and geological verification work, and strengthen surrounding rock metamorphic monitoring, overcome the harm brought by adverse geological conditions.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and specifically to a construction method suitable for tunnels in eroded hilly terrain. Background Technology

[0002] With the increasing demand for travel among the people, my country is constructing numerous mountain highways and tunnels across the country. Some tunnel sites are located in eroded hilly terrain, where the soil and rock are primarily residual granite soil and completely weathered or strongly weathered rock. This soil is prone to disintegration and softening when exposed to water, leading to reduced strength and bearing capacity. Secondly, granite exhibits uneven weathering, easily forming spherical weathered rocks (isolated boulders) in the residual soil and completely weathered layers. Furthermore, the uneven weathering of granite makes it highly susceptible to rockfalls along joints and fissures. Additionally, structural fissures and broken rocks allow surface water to easily flow along fracture channels, and the deep burial depth of the tunnel can result in high water pressure, making water control difficult. Therefore, the unique soil and rock conditions and unfavorable geological conditions of the tunnel sites significantly impact tunnel construction.

[0003] Therefore, there is an urgent need to provide a construction method suitable for tunnels in eroded hilly terrain in order to solve the above problems. Summary of the Invention

[0004] In view of the above problems, the present invention is proposed to provide a construction method for tunnels in eroded hilly terrain that overcomes or at least partially solves the above problems.

[0005] The construction method for tunnels in eroded hilly terrain includes the following steps:

[0006] During the construction of the tunnel entrance section, a water interception ditch was constructed on the tunnel roof according to the actual terrain. Unstable rocks on the tunnel roof were removed, and the surface was reinforced. Surface reinforcement was carried out in sections, with a settlement joint reserved every 15 meters and filled with asphalt-impregnated hemp fiber. Before excavating the side slopes, surface settlement observation points were installed at the tunnel entrance, and exposed boulders on the slope were cleared for data monitoring. The side slopes were excavated in layers from top to bottom, with each layer supported and shotcrete applied promptly. When the open tunnel reached the arch height, the guide wall construction trench was excavated, and shotcrete was applied for support. A core section was reserved in the center. The subsoil is excavated into a stepped shape to facilitate the installation of the guide wall arch frame and the support of the guide wall formwork; the invert arch and arch wall lining of the open tunnel are constructed; after the open tunnel construction is completed, the tunnel portal, the waterproof layer of the open tunnel, and the backfilling of the open tunnel are constructed; the large pipe shed support at the tunnel entrance is constructed. First, a guide hole larger than the diameter of the pipe shed steel pipe is drilled. Then, using the impact and thrust of the drilling rig, the pipe shed steel pipe with the working pipe head is drilled along the guide hole, and the pipe fittings are extended until the bottom of the hole is reached; the initial grouting pressure is 0.5-1.0 MPa, and the final pressure is 2.0-2.5 MPa. After grouting is completed, the steel pipe is filled with cement mortar to form steel pipe concrete;

[0007] Advanced support is implemented by constructing long pipe roof support for the tunnel body. The plane position of the guide pipe is determined on the I-beam steel frame. The inclination angle and external insertion angle of the borehole pipe are set. After drilling, the steel pipe is pushed in slowly using the impact and thrust of the drilling rig. According to the pipe roof layout diagram, steel flower pipes are used for odd numbers and steel pipes are used for even numbers. During construction, the steel flower pipes are installed first and grouting is performed. Then the steel pipes are installed and filled with cement mortar to enhance the strength of the pipe roof. Advanced small guide pipe support is implemented. The small guide pipes are used in conjunction with the steel frame. When installing the small guide pipes, the angle is controlled by a directional device. The external insertion angle is 5° to 10°. After the small guide pipes are installed, the borehole and surrounding cracks are sealed with plastic putty. The tail of the small guide pipe is exposed 30cm and supported on the steel frame behind the excavation face. It is connected to the steel frame as a whole to form a pre-support system.

[0008] Before tunnel excavation, monitoring and measurement points are installed, and advanced geological forecasting and verification are conducted. Smooth blasting is employed, and laser profilers are used to promptly correct the drilling and blasting design. Different tunnel excavation methods are adopted according to the surrounding rock grade. Specifically, full-face excavation is used for Class II and III surrounding rock sections, three-stage or bench excavation is used for Class IV surrounding rock sections, and three-stage and temporary invert arch or three-stage excavation is used for Class V surrounding rock sections. After excavation, monitoring and measurement points are set up inside the tunnel, and monitoring data is recorded in a timely manner during construction.

[0009] Initial support: After the tunnel is excavated, wet shotcrete should be sprayed in time, with a thickness of 4-8cm. Remove the slag at the arch foot, erect the steel frame, and set up longitudinal connections between the steel frames. Install steel mesh and longitudinal connecting bars. Spray wet shotcrete to fill the gaps on the back of the steel frame and steel mesh. Install anchor bolts and anchor bolt pads. The steel frame should be firmly welded to the anchor bolts at the foot.

[0010] Radial grouting is performed on the back side of the initial support. Radial grouting holes, 3m deep, are drilled at 120-150cm intervals around the tunnel perimeter in a quincunx pattern. After acceptance, the borehole pipes are installed and anchored with anchoring agent. Intermittent grouting is carried out using a skip-hole method, with the grouting sequence proceeding from both sides to the arch crown according to the zones. The grouting pressure is 1-1.5 MPa. Anchoring agent is used to fill the gap between the grouting hole wall and the borehole pipe. A grout stop plug is installed at the borehole opening. After grouting is completed, the water inflow per meter of tunnel should not exceed 2m³. 3 If the grouting time is 24 hours, it is determined that the grouting has achieved the desired effect; otherwise, additional grouting should be performed.

[0011] Curtain grouting, specifically for areas with well-developed groundwater, involves advanced curtain grouting reinforcement around the tunnel perimeter and at the excavation face. Prior to construction, advanced geological forecasting is conducted. The grouting reinforcement zone extends 3 meters beyond the excavation outline. Each grouting cycle is 27 meters long, with 24 meters of excavation and a 3-meter retaining rock mass as a grout stop. In the first cycle, a 1.5-meter thick cast-in-place concrete grout stop is constructed at the tunnel face. Subsequent cycles utilize the 3-meter of grouted but unexcavated rock mass to replace the grout stop, sealing the tunnel face with shotcrete. The concrete grout diffusion radius is 2-3 meters, and the spacing between grouting holes is 3-4 meters. Drilling and grouting proceed from the outside in, with alternating holes within the same ring. After grouting, inspection holes are drilled within the excavation outline to check the grouting effect. Once the advanced curtain grouting reinforcement achieves its intended effect, cyclic excavation continues. After the grouting effect check is completed, the inspection holes should be sealed with cement mortar.

[0012] Secondary lining and invert construction: First, the surface of the initial support concrete at the tunnel bottom is treated. Large pits are filled with sprayed concrete to smooth the surface, ensuring a flat surface without sharp edges. A waterproof layer is laid, reinforcing bars are tied, invert formwork is installed, concealed works are monitored, invert concrete is poured, concrete is cured, filling and bottom formwork are installed, formwork installation is checked, filling concrete is poured, lining cross-section is inspected, tracks are laid, a traveling full-section hydraulic formwork lining trolley is positioned, construction joints in the arch wall are treated, steel formwork end templates, waterstops, embedded parts, and spacers are installed, the arch wall concrete is poured continuously and symmetrically from both sides simultaneously, tamping is done with an immersion vibrator, demolding and concrete curing are performed; the concrete is waterproof concrete.

[0013] Ancillary works include the construction of drainage ditches, cable trenches, and tunnel pavement.

[0014] In one embodiment, the construction of the large pipe shed support at the tunnel entrance includes the following steps: surveying and setting out, positioning and fixing of the guide pipe, laying the guide pipe at 140° circumferential angle, positioning the drilling rig, drilling and cleaning the holes, installing the pipe shed and grouting pipes, preparing cement grout, grouting the pipe shed, filling with cement mortar, and forming steel pipe concrete; the large pipe shed support at the tunnel entrance uses hot-rolled seamless steel pipes with an outer diameter of 108mm and a wall thickness of 6mm, with grouting holes of 12mm diameter drilled around the pipe wall at a spacing of 15cm; the steel pipes are arranged in a quincunx pattern, with a 110cm un-drilled section reserved at the tail as a grout-stopping section; during the construction of the long pipe shed support in the tunnel body, the steel pipes are driven into the surrounding rock at an outward insertion angle of 1° to 3° along the tunnel perimeter, and the water-cement ratio of the grouting cement grout is 1:1.

[0015] In one embodiment, the tunnel long pipe shed support uses hot-rolled seamless steel pipes and steel perforated pipes with an outer diameter of 89mm and a wall thickness of 5mm. Each section of hot-rolled seamless steel pipe is 10m long. Seamless steel pipes with an outer diameter of 95mm and a wall thickness of 6mm are used as joints. The number of joints in the same cross section of the steel pipes and steel perforated pipes is no more than 50% of the number of pipes. The circumferential spacing of the steel pipes is 30-40cm.

[0016] In one embodiment, the advanced small guide pipe is made of hot-rolled seamless steel pipe with an outer diameter of 50mm and a wall thickness of 3.5mm. Grouting holes with a diameter of 10mm and a spacing of 15cm are drilled at the front of the steel pipe in a quincunx pattern. The front end of the steel pipe is processed into a cone shape, and the length of the un-drilled section of the grout-stopping section at the tail end is not less than 30cm. The advanced small guide pipes are arranged at 150° circumferentially with a circumferential spacing of 40cm, and the horizontal overlap length of two adjacent rows of small guide pipes is not less than 150cm. The grouting pressure of the advanced small guide pipe support is 0.5-1MPa.

[0017] In one embodiment, the monitoring and measurement points include surface settlement monitoring points, tunnel arch settlement monitoring points, tunnel clearance convergence monitoring points, and stratum displacement monitoring points; the surface settlement monitoring points and tunnel arch settlement monitoring points are arranged on the same cross section in the cut-and-cover section; the surface settlement monitoring points are arranged on cross sections perpendicular to the tunnel centerline, with a spacing of 2 to 5 meters; the monitoring and measurement points arranged inside the tunnel are installed in the rock mass; the initial readings of the monitoring and measurement points should be taken within 12 hours after the measurement points are installed, and before the next cycle of excavation.

[0018] In one embodiment, the advanced geological forecasting is carried out through geological sketching, advanced geological drilling, deepening borehole detection, elastic wave reflection, and ground-penetrating radar detection.

[0019] In one embodiment, the advanced curtain grouting reinforcement includes the following steps: advanced geological prediction, measurement of borehole layout, construction of grout stop wall, drilling of test holes, selection of grouting scheme based on the water pressure test results of the test holes, such as using the forward grouting method when the rock strata are fractured and prone to borehole collapse, and using the backward grouting method when the surrounding rock is fractured but not prone to borehole collapse, and after grouting is completed, inspection holes are drilled within the excavation outline area to test the grouting effect.

[0020] In one embodiment, the forward grouting method involves grouting in sections, with each section being 3-5m long, until the borehole reaches the designed depth. The backward grouting method involves inserting a sleeve valve pipe at the borehole opening after drilling to the designed depth, followed by inserting a grouting pipe with a grout stop plug. Rubber sleeves are installed at both ends of the sleeve valve pipe to prevent grout leakage. The grouting pipeline is then connected, and backward grouting is performed in sections from the bottom of the borehole to the borehole opening, with each section being 2-3m long.

[0021] In one embodiment, the waterproofing layer installation includes the following steps: base surface treatment to ensure no obvious water leakage, installation of longitudinal drainage blind pipes and circumferential drainage boards, installation of the waterproofing board using a hanging process of bonding the waterproofing board body and self-adhesive cloth, hot-melt welding between the waterproofing boards using an automatic double-seam hot-melt welding machine, quality inspection of the waterproofing board, and repair of any damaged parts of the waterproofing board.

[0022] In one embodiment, the waterstop is an embedded self-adhesive rubber waterstop or a back-adhesive self-adhesive rubber waterstop; the waterstop is installed at the circumferential construction joints of the arch wall and the invert arch, the longitudinal construction joints of the arch wall and the invert arch, the deformation joints of the arch wall, and the deformation joints of the invert arch.

[0023] The construction method applicable to tunnels in eroded hilly terrain involves timely correction of drilling and blasting designs using laser profilers at the excavation cross-section, and the adoption of different excavation methods based on the surrounding rock grade, strictly controlling over- and under-excavation. When traversing granite residual soil, completely weathered and strongly weathered rock, structural fissures, and fractured rock sections, advanced support is implemented to control collapses and ensure construction safety. Radial grouting and curtain grouting are used to reinforce the surrounding rock, ensuring smooth passage through fault fracture zones. Advanced geological forecasting and verification are conducted during construction, and monitoring of surrounding rock deformation is strengthened to overcome the hazards posed by adverse geological conditions. To ensure the tunnel is free from seepage, leakage, and cracking, the principle of "primarily blocking with limited discharge" is adopted in moderately water-rich areas, while in other weakly water-rich and water-poor areas, the principle of "combining prevention, drainage, interception, and blocking, adapting to local conditions, and comprehensive management" is adopted. Attached Figure Description

[0024] The accompanying drawings, which form part of the specification, are used to provide a further understanding of the embodiments of this application and illustrate the implementation methods of this application, together with the textual description, to explain the principles of this application. Obviously, the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any creative effort. In the drawings:

[0025] Figure 1 This is a schematic diagram of the cross-section of the guide wall at the tunnel entrance side slope according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the arrangement of the long pipe roof support pipe roof in the tunnel body according to an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the longitudinal arrangement of the long pipe roof support pipe roof in the tunnel body according to an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the transverse cross-section of the advanced small catheter arrangement in an embodiment of the present invention;

[0029] Figure 5 This is a schematic diagram of the longitudinal section of the advanced small catheter arrangement according to an embodiment of the present invention;

[0030] Figure 6 This is a schematic diagram of the transverse cross-section of radial grouting in an embodiment of the present invention;

[0031] Figure 7 This is a schematic diagram of the longitudinal section of radial grouting in an embodiment of the present invention;

[0032] Figure 8 This is a schematic diagram of the longitudinal section of the curtain grouting in an embodiment of the present invention;

[0033] Figure 9 This is a schematic diagram of the transverse cross-section of the curtain grouting in an embodiment of the present invention;

[0034] Figure 10 This is a schematic diagram of the layout of monitoring and measurement points inside the tunnel according to an embodiment of the present invention. Detailed Implementation

[0035] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments.

[0036] This invention provides a construction method for tunnels in eroded hilly terrain, comprising the following steps:

[0037] During the construction of the tunnel entrance section, a water interception ditch was constructed on the tunnel roof according to the actual terrain. Unstable rocks on the tunnel roof were removed, and the surface was reinforced. Surface reinforcement was carried out in sections, with a settlement joint reserved every 15 meters and filled with asphalt-impregnated hemp fiber. Before excavating the side slopes, surface settlement observation points were installed at the tunnel entrance, and exposed boulders on the slope were cleared for data monitoring. The side slopes were excavated in layers from top to bottom, with each layer supported and shotcrete applied promptly. When the open tunnel reached the arch height, the guide wall construction trench was excavated, and shotcrete was applied for support. A core section was reserved in the center. The subsoil is excavated into a stepped shape to facilitate the installation of the guide wall arch frame and the support of the guide wall formwork; the invert arch and arch wall lining of the open tunnel are constructed; after the open tunnel construction is completed, the tunnel portal, the waterproof layer of the open tunnel, and the backfilling of the open tunnel are constructed; the large pipe shed support at the tunnel entrance is constructed. First, a guide hole larger than the diameter of the pipe shed steel pipe is drilled. Then, using the impact and thrust of the drilling rig, the pipe shed steel pipe with the working pipe head is drilled along the guide hole, and the pipe fittings are extended until the bottom of the hole is reached; the initial grouting pressure is 0.5-1.0 MPa, and the final pressure is 2.0-2.5 MPa. After grouting is completed, the steel pipe is filled with cement mortar to form steel pipe concrete;

[0038] Advanced support is implemented by constructing long pipe roof support for the tunnel body. The plane position of the guide pipe is determined on the I-beam steel frame. The inclination angle and external insertion angle of the borehole pipe are set. After drilling, the steel pipe is pushed in slowly using the impact and thrust of the drilling rig. According to the pipe roof layout diagram, steel flower pipes are used for odd numbers and steel pipes are used for even numbers. During construction, the steel flower pipes are installed first and grouting is performed. Then the steel pipes are installed and filled with cement mortar to enhance the strength of the pipe roof. Advanced small guide pipe support is implemented. The small guide pipes are used in conjunction with the steel frame. When installing the small guide pipes, the angle is controlled by a directional device. The external insertion angle is 5° to 10°. After the small guide pipes are installed, the borehole and surrounding cracks are sealed with plastic putty. The tail of the small guide pipe is exposed 30cm and supported on the steel frame behind the excavation face. It is connected to the steel frame as a whole to form a pre-support system.

[0039] Before tunnel excavation, monitoring and measurement points are installed, and advanced geological forecasting and verification are conducted. Smooth blasting is employed, and laser profilers are used to promptly correct the drilling and blasting design. Different tunnel excavation methods are adopted according to the surrounding rock grade. Specifically, full-face excavation is used for Class II and III surrounding rock sections, three-stage or bench excavation is used for Class IV surrounding rock sections, and three-stage and temporary invert arch or three-stage excavation is used for Class V surrounding rock sections. After excavation, monitoring and measurement points are set up inside the tunnel, and monitoring data is recorded in a timely manner during construction.

[0040] Initial support: After the tunnel is excavated, wet shotcrete should be sprayed in time, with a thickness of 4-8cm. Remove the slag at the arch foot, erect the steel frame, and set up longitudinal connections between the steel frames. Install steel mesh and longitudinal connecting bars. Spray wet shotcrete to fill the gaps on the back of the steel frame and steel mesh. Install anchor bolts and anchor bolt pads. The steel frame should be firmly welded to the anchor bolts at the foot.

[0041] Radial grouting is performed on the back side of the initial support. Radial grouting holes, 3m deep, are drilled at 120-150cm intervals around the tunnel perimeter in a quincunx pattern. After acceptance, the borehole pipes are installed and anchored with anchoring agent. Intermittent grouting is carried out using a skip-hole method, with the grouting sequence proceeding from both sides to the arch crown according to the zones. The grouting pressure is 1-1.5 MPa. Anchoring agent is used to fill the gap between the grouting hole wall and the borehole pipe. A grout stop plug is installed at the borehole opening. After grouting is completed, the water inflow per meter of tunnel should not exceed 2m³. 3 If the grouting time is 24 hours, it is determined that the grouting has achieved the desired effect; otherwise, additional grouting should be performed.

[0042] Curtain grouting, specifically for areas with well-developed groundwater, involves advanced curtain grouting reinforcement around the tunnel perimeter and at the excavation face. Prior to construction, advanced geological forecasting is conducted. The grouting reinforcement zone extends 3 meters beyond the excavation outline. Each grouting cycle is 27 meters long, with 24 meters of excavation and a 3-meter retaining rock mass as a grout stop. In the first cycle, a 1.5-meter thick cast-in-place concrete grout stop is constructed at the tunnel face. Subsequent cycles utilize the 3-meter of grouted but unexcavated rock mass to replace the grout stop, sealing the tunnel face with shotcrete. The concrete grout diffusion radius is 2-3 meters, and the spacing between grouting holes is 3-4 meters. Drilling and grouting proceed from the outside in, with alternating holes within the same ring. After grouting, inspection holes are drilled within the excavation outline to check the grouting effect. Once the advanced curtain grouting reinforcement achieves its intended effect, cyclic excavation continues. After the grouting effect check is completed, the inspection holes should be sealed with cement mortar.

[0043] Secondary lining and invert construction: First, the surface of the initial support concrete at the tunnel bottom is treated. Large pits are filled with sprayed concrete to smooth the surface, ensuring a flat surface without sharp edges. A waterproof layer is laid, reinforcing bars are tied, invert formwork is installed, concealed works are monitored, invert concrete is poured, concrete is cured, filling and bottom formwork are installed, formwork installation is checked, filling concrete is poured, lining cross-section is inspected, tracks are laid, a traveling full-section hydraulic formwork lining trolley is positioned, construction joints in the arch wall are treated, steel formwork end templates, waterstops, embedded parts, and spacers are installed, the arch wall concrete is poured continuously and symmetrically from both sides simultaneously, tamping is done with an immersion vibrator, demolding and concrete curing are performed; the concrete is waterproof concrete.

[0044] Ancillary works include the construction of drainage ditches, cable trenches, and tunnel pavement.

[0045] Preferably, the construction of the large pipe shed support at the tunnel entrance includes the following steps: surveying and setting out, positioning and fixing of the guide pipe, laying the guide pipe at 140° circumferential angle, positioning the drilling rig, drilling and cleaning the holes, installing the pipe shed and grouting pipe, preparing cement grout, grouting the pipe shed, filling with cement mortar, and forming steel pipe concrete; the large pipe shed support at the tunnel entrance uses hot-rolled seamless steel pipes with an outer diameter of 108mm and a wall thickness of 6mm, with grouting holes of 12mm diameter drilled around the pipe wall at a spacing of 15cm; the steel pipes are arranged in a quincunx pattern, with a 110cm un-drilled section reserved at the tail as a grout-stopping section; during the construction of the long pipe shed support in the tunnel body, the steel pipes are driven into the surrounding rock at an outward insertion angle of 1° to 3° around the tunnel perimeter, and the water-cement ratio of the grouting cement grout is 1:1.

[0046] Preferably, the tunnel long pipe shed support uses hot-rolled seamless steel pipes and steel perforated pipes with an outer diameter of 89mm and a wall thickness of 5mm. Each section of hot-rolled seamless steel pipe is 10m long. Seamless steel pipes with an outer diameter of 95mm and a wall thickness of 6mm are used as joints. The number of joints in the same cross section of the steel pipes and steel perforated pipes is no more than 50% of the number of pipes. The circumferential spacing of the steel pipes is 30-40cm.

[0047] Preferably, the advanced small guide pipe is made of hot-rolled seamless steel pipe with an outer diameter of 50mm and a wall thickness of 3.5mm. Grouting holes with a diameter of 10mm and a spacing of 15cm are drilled at the front of the steel pipe in a quincunx pattern. The front end of the steel pipe is processed into a cone shape, and the length of the un-drilled section at the tail end is not less than 30cm. The advanced small guide pipes are arranged at 150° circumferentially with a circumferential spacing of 40cm. The horizontal overlap length of two adjacent rows of small guide pipes is not less than 150cm. The grouting pressure of the advanced small guide pipe support is 0.5~1MPa.

[0048] Preferably, the monitoring and measurement points include surface settlement monitoring points, tunnel arch settlement monitoring points, tunnel clearance convergence monitoring points, and stratum displacement monitoring points; the surface settlement monitoring points and tunnel arch settlement monitoring points are arranged on the same cross section in the cut-and-cover section; the surface settlement monitoring points are arranged on cross sections perpendicular to the tunnel centerline, with a spacing of 2-5m; the monitoring and measurement points arranged inside the tunnel are installed in the rock mass; the initial readings of the monitoring and measurement points should be taken within 12 hours after the measurement points are installed, and before the next cycle of excavation.

[0049] Preferably, the advanced geological forecasting is carried out through geological sketching, advanced geological drilling, deepening borehole detection, elastic wave reflection, and ground-penetrating radar detection.

[0050] Preferably, the advanced curtain grouting reinforcement includes the following steps: advanced geological prediction, measurement of borehole layout, construction of grout stop wall, drilling of test holes, selection of grouting scheme based on the water pressure test results of the test holes, such as using the forward grouting method when the rock strata are fractured and prone to borehole collapse, and using the backward grouting method when the surrounding rock is fractured but not prone to borehole collapse. After grouting is completed, inspection holes are drilled within the excavation outline to test the grouting effect.

[0051] The forward grouting method involves grouting in sections, with each section being 3-5m long, until the borehole reaches the designed depth. The backward grouting method involves drilling to the designed depth, inserting a sleeve valve pipe at the borehole opening, and then inserting a grouting pipe with a grout stop plug. Rubber sleeves are installed at both ends of the sleeve valve pipe to prevent grout leakage. The grouting pipeline is then connected, and backward grouting is performed in sections from the bottom of the borehole to the borehole opening, with each section being 2-3m long.

[0052] Preferably, the waterproofing layer installation includes the following steps: base surface treatment to ensure no obvious water leakage, installation of longitudinal drainage blind pipes and circumferential drainage boards, installation of the waterproofing board using a hanging process of bonding the waterproofing board body and self-adhesive cloth, hot-melt welding between the waterproofing boards using an automatic double-seam hot-melt welding machine, quality inspection of the waterproofing board, and repair of any damaged parts of the waterproofing board.

[0053] Preferably, the waterstop is an embedded self-adhesive rubber waterstop or a back-adhesive self-adhesive rubber waterstop; the waterstop is installed at the circumferential construction joints of the arch wall and the invert arch, the longitudinal construction joints of the arch wall and the invert arch, the deformation joints of the arch wall, and the deformation joints of the invert arch.

[0054] This embodiment utilizes a laser profiler to promptly correct the drilling and blasting design at the excavation cross-section, and employs different excavation methods based on the surrounding rock grade to strictly control over- and under-excavation. When traversing granite residual soil, completely weathered and strongly weathered rock, structural fissures, and fractured rock sections, advanced support is implemented to control collapses and ensure construction safety. Radial grouting and curtain grouting are used to reinforce the surrounding rock, ensuring smooth passage through fault fracture zones. Advanced geological forecasting and verification are conducted during construction, and monitoring of surrounding rock deformation is strengthened to overcome the hazards posed by adverse geological conditions. To ensure the tunnel is leak-proof, seepage-free, and crack-free, the principle of "primarily blocking with limited discharge" is adopted in moderately water-rich areas, while in other weakly water-rich and water-poor areas, the principle of "combining prevention, drainage, interception, and blocking, adapting to local conditions, and comprehensive management" is adopted.

[0055] The following section provides a more detailed description of the construction methods for tunnels in low-mountain areas affected by karst dissolution and denudation, using specific engineering examples.

[0056] A certain tunnel project, with a total length of 4291 meters, is a single-track tunnel. The tunnel site area is characterized by eroded hilly terrain, with well-developed vegetation, including shrubs and weeds. The ground elevation ranges from 31 to 130 meters, and the natural slope ranges from 10 to 30 degrees. The surface water system in the tunnel site area is relatively developed, and the groundwater is mainly bedrock fissure water. The special soil and rock in the tunnel site area are mainly residual granite soil and completely weathered and strongly weathered rocks, which are prone to disintegration and softening when exposed to water, resulting in reduced strength and bearing capacity. Secondly, granite has the characteristic of uneven weathering, which easily forms spherical weathered rocks (isolated rocks) in residual soil and completely weathered layers. Moreover, the unevenly weathered granite rocks are very likely to form dangerous rocks along joints and fissures, and the vibration of blasting can easily cause dangerous rocks to roll down steep slopes. Furthermore, the tectonic fissures and broken rocks allow surface water to easily flow along the fracture channels, and the large burial depth of the tunnel results in high water head pressure, making it difficult to stop water in the tunnel. Therefore, the special soil and soil conditions and unfavorable geological conditions in the tunnel site area have a significant impact on tunnel construction.

[0057] A construction method applicable to tunnels in eroded hilly terrain includes the following steps:

[0058] 1) Construction of the tunnel entrance section

[0059] Based on the actual terrain at the tunnel entrance, a water interception ditch was constructed at the tunnel top; loose rocks at the tunnel top were removed, and the surface was reinforced. Surface reinforcement was carried out in sections, with a settlement joint reserved every 15 meters and filled with asphalt-impregnated hemp fiber. Before excavating the side slopes, surface settlement observation points were installed at the tunnel entrance, and exposed boulders on the slope were cleared for data monitoring. The side slopes were excavated in layers from top to bottom, with each layer supported and shotcrete applied promptly. When the open tunnel reached the arch height, the guide wall construction trench was excavated, and shotcrete was applied for support. Core soil was reserved in the central area. The excavation is stepped to facilitate the installation of the guide wall arch frame and the support of the guide wall formwork; construction of the invert arch and arch wall lining of the open tunnel; after the construction of the open tunnel is completed, the tunnel entrance, the waterproof layer of the open tunnel, and the backfilling of the open tunnel are constructed; the large pipe shed support at the tunnel entrance is constructed. First, a guide hole larger than the diameter of the pipe shed steel pipe is drilled. Then, using the impact and thrust of the drilling rig, the pipe shed steel pipe with the working pipe head is drilled along the guide hole, and the pipe fittings are extended until the bottom of the hole is reached; the initial grouting pressure is 0.5-1.0 MPa, and the final pressure is 2.0-2.5 MPa. After the grouting is completed, the steel pipe is filled with cement mortar to form steel pipe concrete.

[0060] The slope protection at the tunnel entrance is graded at a height of 2-3m and is protected by shotcrete mesh. The anchor rods are φ22mm reinforced mortar anchor rods. The steel mesh is φ8mm in diameter with a longitudinal and transverse spacing of 20cm. When laying the steel mesh, the distance between it and the contact surface should not exceed 3cm, and it should be firmly connected to the anchor rods. When performing shotcrete operations, vibration of the mesh should be minimized to reduce rebound. The guide wall is made of C20 concrete with a cross-sectional dimension of 1m×1m. Two I18 steel frames are installed inside the guide wall. Φ140×5mm guide steel pipes with a length of 1m are installed on the outer edge of the steel frames. The steel pipes are fixed to the steel frames with Φ12mm stiffening hoops.

[0061] Furthermore, the construction of the large pipe shed support at the tunnel entrance includes the following steps: surveying and setting out, positioning and fixing of the guide pipe, laying the guide pipe along a 140° circumferential direction, positioning the drilling rig, drilling and cleaning the holes, installing the pipe shed and grouting pipes, preparing cement grout, grouting the pipe shed, filling with cement mortar, and forming steel pipe concrete; the large pipe shed support at the tunnel entrance uses hot-rolled seamless steel pipes with an outer diameter of 108mm and a wall thickness of 6mm. Grouting holes with a diameter of 12mm are drilled around the pipe wall, with a hole spacing of 15cm; the steel pipes are arranged in a quincunx pattern, with a 110cm un-drilled section reserved at the tail as a grout-stopping section; during the construction of the long pipe shed support in the tunnel body, the steel pipes are driven into the surrounding rock along the tunnel perimeter at an outward insertion angle of 1° to 3°, and the water-cement ratio of the grouting cement grout is 1:1.

[0062] 2) Advance support

[0063] Construct long pipe roof support for the tunnel body, and use the total station coordinate method to determine the plane position of the guide pipe on the I-beam frame; use a leveling rod and slope plate to set the inclination angle of the orifice pipe, and use the front-to-back difference method to set the external insertion angle of the orifice pipe; adopt the casing follow-up method for drilling; after drilling is completed, use the impact force and thrust of the drilling rig to push the steel pipe in at low speed, according to the pipe roof layout diagram ( Figure 2 , Figure 3 The pipe shed is constructed using steel perforated pipes for odd-numbered sections and steel pipes for even-numbered sections. During construction, the steel perforated pipes are installed first and grouted, followed by the installation of the steel pipes and filling with cement mortar to enhance the strength of the pipe shed. Pre-support is provided by small guide pipes, which are used in conjunction with the steel frame. When installing the small guide pipes, an directional device is used to control the angle, with an external insertion angle of 5° to 10°. The small guide pipes are installed by drilling. After the installation of the small guide pipes, the openings and surrounding cracks are sealed with plastic putty. The tail of the small guide pipe protrudes 30cm and is supported on the steel frame behind the excavation face, and connected to the steel frame as a whole to form a pre-support system.

[0064] The tunnel's long pipe roof support uses hot-rolled seamless steel pipes and steel perforated pipes with an outer diameter of 89mm and a wall thickness of 5mm. Each section of the hot-rolled seamless steel pipe is 10m long, using seamless steel pipes with an outer diameter of 95mm and a wall thickness of 6mm as joints. The number of joints in the same cross-section of the steel pipes and steel perforated pipes does not exceed 50% of the total number of pipes. Adjacent steel pipe joints are staggered by more than 1m, and the circumferential spacing between the steel pipes is 30-40cm. The advanced small guide pipes are made of hot-rolled seamless steel pipes with an outer diameter of 50mm and a wall thickness of 3.5mm. A hole with a diameter of 10mm is drilled at the front of the steel pipe. Grouting holes with a diameter of mm and a spacing of 15cm are arranged in a quincunx pattern. The front end of the steel pipe is processed into a cone shape, and the un-drilled length of the grout-stopping section at the tail end is not less than 30cm. The advanced small guide pipes are set at 150° circumferentially with a circumferential spacing of 40cm, and the horizontal overlap length of two adjacent rows of small guide pipes is not less than 150cm. The small guide pipes need to be equipped with grout-stopping valves. A water pressure test is carried out before grouting to check whether the mechanical equipment is normal and whether the pipeline connection is correct. In order to speed up the grouting speed and maximize the efficiency of the equipment, group pipe grouting can be used, and the grouting pressure is 0.5~1MPa.

[0065] 3) Tunnel excavation

[0066] Before construction, monitoring and measurement points were installed, and advanced geological forecasting and verification were carried out. Smooth blasting was adopted, and the drilling and blasting design was promptly corrected using a laser profiler. Different excavation methods were used for tunnel excavation according to the surrounding rock grade. Specifically, full-face excavation was used for Class II and III surrounding rock sections, three-stage or bench excavation was used for Class IV surrounding rock sections, and three-stage and temporary invert arch or three-stage excavation was used for Class V surrounding rock sections. After excavation, monitoring and measurement points were set up inside the tunnel, and monitoring data was recorded in a timely manner during construction.

[0067] The monitoring and measurement points include surface settlement monitoring points, tunnel arch settlement monitoring points, tunnel clearance convergence monitoring points, and stratum displacement monitoring points. Surface settlement monitoring points and tunnel arch settlement monitoring points are arranged on the same cross-section in the cut-and-cover section. Surface settlement monitoring points are arranged on cross-sections perpendicular to the tunnel centerline, with a spacing of 2–5 m, with the monitoring points closer together near the centerline and gradually sparser on the outer edges. In representative sections, stratum displacement monitoring points are buried every 10–20 m, with 5 monitoring points buried per cross-section. Monitoring and measurement points inside the tunnel are installed in the rock mass; the arrangement of monitoring and measurement points varies depending on the tunnel excavation method, as detailed in [link to relevant documentation]. Figure 10 Different monitoring and measurement points utilize different monitoring equipment. For example, digital cameras, geological compasses, and measuring rods are used to observe the geological conditions inside and outside the tunnel; DINI03 electronic levels, indium steel tapes, and Leica TCRA1201 total stations are used for surface settlement monitoring; Leica TCRA1201 total stations are used for monitoring tunnel arch settlement and tunnel clearance convergence; and inclinometers are used for ground displacement monitoring. Initial readings for monitoring and measurement points should be taken within 12 hours of the point's installation and before the next excavation cycle. A comprehensive judgment is made based on the monitoring data, combined with the displacement management level table and displacement control benchmark table (see Tables 1 and 2 for details), to determine the deformation management level and guide construction.

[0068] Management level <![CDATA[Distance from the excavation section 1B(U 1B )]]> <![CDATA[Distance from the excavation section 2B(U 2B )]]> Construction status Ⅲ <![CDATA[U<U 1B / 3]]> <![CDATA[U<U 2B / 3]]> Normal construction is possible Ⅱ <![CDATA[(U 1B / 3)≤U≤(2U 1B / 3)]]> <![CDATA[(U 2B / 3)≤U≤(2U 2B / 3)]]> Support should be strengthened Ⅰ <![CDATA[U0>(2U 1B / 3)]]> <![CDATA[U0>(2U 1B / 3)]]> Special measures should be taken.

[0069] Table 1

[0070] category <![CDATA[Distance from the excavation section 1B(U 1B )]]> <![CDATA[Distance from the excavation section 2B(U 2B )]]> Far from the excavation section Allowed values <![CDATA[65%U0]]> <![CDATA[90% U0]]> <![CDATA[100%U0]]>

[0071] Table 2

[0072] The monitoring frequency can be determined based on the distance between the monitoring and measurement points and the excavation section, as well as the displacement velocity. Table 3 shows the monitoring and measurement frequency determined based on the distance between the monitoring and measurement points and the excavation section, while Table 4 shows the monitoring and measurement frequency determined based on the displacement velocity.

[0073] Distance from monitoring section to excavation section (m) Monitoring frequency (0～1)B 2 times / day (1～2)B 1 time / day (2～5)B 1 time / (2-3 days) ＞5B 1 time / 7 days

[0074] Table 3

[0075] Displacement velocity (mm / day) Monitoring frequency ≥5 2 times / day 1～5 1 time / day 0.5～1 1 time / (2-3 days) 0.2～0.5 1 time / 3 days ＜0.2 1 time / 7 days

[0076] Table 4

[0077] In Tables 1, 2, and 3, B represents the tunnel excavation span, U0 represents the ultimate relative displacement value, and U represents the measured displacement value.

[0078] If excessive surface displacement or unstable subsidence rate is found, excavation inside the tunnel should be stopped, and reinforcement measures should be taken for the substructure; the thickness of shotcrete should be increased, or the anchor bolts should be lengthened and densified, or a denser and thicker steel mesh should be added; secondary lining should be constructed in advance, and the strength of the secondary lining should be checked through back analysis; and the invert arch should be constructed in advance.

[0079] Furthermore, advanced geological forecasting employs methods such as geological sketching, advanced geological drilling, deepening borehole detection, elastic wave reflection, and ground-penetrating radar detection to conduct geological forecasting work. Tunnel geological sketching is a method of accurately recording and drawing charts of the lithology, geological structure, structural plane occurrence, location and state of groundwater outcrops, water volume, coal seams, karst caves, etc., exposed by the tunnel. It is part of geological survey work and includes geological sketching of the excavation face and the tunnel body. Advanced geological drilling is suitable for advanced geological prediction of tunnels under various geological conditions. It must be used in complex geological conditions such as water-rich weak fault fracture zones, water-rich karst development areas, coal seam gas development areas, and areas with major geophysical anomalies. Deepened borehole detection is suitable for advanced geological exploration of tunnels under various geological conditions, especially for karst development areas. Elastic wave reflection is suitable for delineating stratigraphic boundaries, finding geological structures, and detecting the thickness and extent of adverse geological bodies. Ground-penetrating radar detection is mainly used for karst detection, and can also be used for detecting heterogeneous geological bodies such as weak interlayers in fault fracture zones.

[0080] 4) Initial support

[0081] After the tunnel is excavated, wet shotcrete should be applied promptly. Before spraying, large depressions on the rock surface should be filled and the concrete thickness should be 4-8cm. Remove the loose debris at the arch foot, erect the steel frame, and make longitudinal connections between the steel frames. Install steel mesh and longitudinal connecting bars. Apply wet shotcrete to fill the gaps on the back of the steel frame and steel mesh. Install anchor rods and anchor rod pads. The steel frame should be firmly welded to the anchor rods at the foot.

[0082] 5) Radial grouting

[0083] Radial grouting was performed on the back side of the initial support. Radial grouting holes were drilled around the tunnel perimeter at intervals of 120-150 cm, with a depth of 3 m, arranged in a quincunx pattern. After acceptance, the borehole pipes were installed and anchored with anchoring agent. Intermittent grouting was carried out using the skip-hole method, with the grouting sequence proceeding from both sides to the arch crown according to the zones. The grouting pressure was 1-1.5 MPa. The space between the grouting hole wall and the borehole pipe was filled with anchoring agent, and a grout stop plug was installed at the borehole opening. After grouting was completed, the water inflow per meter of tunnel should not exceed 2 m³. 3 If the grouting time is 24 hours, it is determined that the grouting has achieved the desired effect; otherwise, additional grouting should be performed.

[0084] Radial grouting behind the initial support of the tunnel can enhance the adhesion between the initial support and the surrounding rock, improve the bearing capacity and self-stabilizing force of the surrounding rock, effectively control the settlement and deformation of the initial support structure of the tunnel, and achieve the purpose of water blocking, thereby ensuring construction safety, construction period, and improving the construction environment.

[0085] 6) Curtain grouting

[0086] For areas with well-developed groundwater, advanced curtain grouting reinforcement is carried out around the tunnel and at the excavation face. Advanced geological forecasting is conducted before construction. The grouting reinforcement zone extends 3 meters beyond the excavation outline. Each grouting cycle is 27 meters long, with 24 meters of excavation and a 3-meter retaining rock mass for grout stopping. In the first cycle, a 1.5-meter thick cast-in-place concrete grout stopping wall is constructed at the tunnel face. In subsequent cycles, the 3-meter grouting but unexcavated rock mass is used to replace the grout stopping wall, and the tunnel face is sealed with shotcrete. The concrete grout diffusion radius is 2-3 meters, and the spacing between grouting holes is 3-4 meters. The drilling and grouting sequence is from the outside in, with holes in the same ring being constructed at intervals. After grouting is completed, inspection holes are drilled within the excavation outline to check the grouting effect. After the advanced curtain grouting reinforcement achieves the desired grouting effect, cyclic excavation continues. After the grouting effect check is completed, the inspection holes should be completely sealed with cement mortar.

[0087] Tunnel cross-section curtain grouting reinforcement involves grouting along the excavation outline, with holes arranged radially from the working face towards the excavation direction. The grout penetrates and diffuses into the pores of the fractured zone, solidifying with the surrounding fractured rock blocks to form a bond with a certain strength. This creates a water-blocking curtain (reinforced zone) around the tunnel and at the excavation face, cutting off the flow path of groundwater and solidifying with the surrounding soil or rock mass. This achieves the purpose of consolidation and water stoppage, maintaining the stability of the surrounding rock and enhancing construction safety.

[0088] The advanced curtain grouting reinforcement includes the following steps: advanced geological prediction, borehole layout measurement, construction of grout stop walls, drilling test holes, and selection of grouting scheme based on the water pressure test results of the test holes. For example, if the rock strata are fractured and prone to borehole collapse, the forward grouting method is used; if the surrounding rock is fractured but not prone to borehole collapse, the backward grouting method is used. The forward grouting method involves grouting in sections, with each section being 3-5 meters long, until the borehole reaches the designed depth. The backward grouting method involves drilling to the designed depth, inserting a sleeve valve pipe at the borehole opening, and then inserting a grouting pipe with a grout stop plug. The sleeve valve pipe is equipped with... Rubber sleeves are used to prevent grout leakage. The grouting pipeline is connected, and grouting is performed in segments, with each segment controlled to be 2-3 meters long, from the bottom to the opening. After grouting, inspection holes are drilled within the excavation outline to check the grouting effect. Five inspection holes are set per cycle: two at the arch, one on each sidewall, and one at the bottom. The inspection holes are 110 mm in diameter and approximately 27 meters long, with an average water outflow of less than 0.2 L / min. A water pressure test is conducted at 1.0 MPa, with an absorption rate of less than 2 L / min. The compressive strength of the solidified body is not less than 3 MPa, and the rock mass RQD index reaches 75-80. If the above conditions are met, the grouting is considered effective, and excavation can only proceed after the grouting effect is confirmed. After the grouting effect check is completed, the inspection holes should be completely sealed with M10 cement mortar.

[0089] 7) Secondary lining

[0090] For the invert construction, the initial support concrete surface at the tunnel bottom is first treated. Larger depressions are filled with sprayed concrete to smooth the surface, ensuring a flat surface without sharp edges. A waterproof layer is then laid, reinforcing bars are tied, invert formwork is installed, concealed works are monitored, invert concrete is poured, concrete is cured, infill and bottom formwork are installed, formwork installation is checked, infill concrete is poured, lining cross-section is inspected, tracks are laid, a traveling full-section hydraulic formwork lining trolley is positioned, construction joints in the arch wall are treated, steel formwork end templates, waterstops, embedded parts, and spacers are installed, the arch wall concrete is poured continuously and symmetrically from both sides simultaneously, tamping is done with an immersion vibrator, demolding and concrete curing are performed; the concrete is waterproof.

[0091] Secondary lining is generally constructed after the surrounding rock deformation has basically stabilized. The deformation should meet one of the following requirements when it is stable: (1) The deformation rate around the tunnel decreases significantly and tends to be moderate, that is, the horizontal deformation rate is less than 0.2 mm / d and the arch settlement rate is less than 0.15 mm / d; (2) The cumulative displacement value before the construction of secondary lining has reached more than 80% of the limit displacement value.

[0092] The invert arch reinforcement cage is tied at intersections, and the positioning reinforcement is welded to the I-beam steel frame of the initial support invert arch using short steel bars. When installing the bottom layer of reinforcement, the longitudinal reinforcement is above the circumferential reinforcement; when installing the upper layer of reinforcement, the longitudinal reinforcement is below the circumferential reinforcement, that is, the longitudinal reinforcement is inside the two layers of circumferential reinforcement. After the upper and lower layers of reinforcement are installed, the stirrups are tied, and stirrups are installed at each intersection, and the stirrups are hooked to the main reinforcement. After inspection and approval, the invert arch and side wall foundation concrete is poured. The invert arch concrete is poured symmetrically from the middle to both sides as a whole, and is compacted with an immersion vibrator.

[0093] The waterproofing layer installation includes the following steps: Base surface treatment, ensuring the base surface is free of significant water leakage; the depth-to-width ratio of pits should be controlled within 1:10; pits with a depth-to-width ratio greater than 1:10 should be leveled with cement mortar; large pits should be smoothed and repaired with sprayed concrete to ensure a smooth surface without sharp edges; installation of longitudinal drainage blind pipes and circumferential drainage boards; installation of the waterproofing board using a self-adhesive fabric bonding process; welding of the waterproofing boards together using an automatic double-seam hot-melt welding machine; quality inspection of the waterproofing board; repair of any damaged areas; the length of the waterproofing layer laid in both longitudinal and transverse directions should exceed the length of the secondary lining.

[0094] Embedded self-adhesive rubber waterstops and back-adhesive self-adhesive rubber waterstops are installed at the circumferential construction joints of the arch wall and invert. Embedded self-adhesive rubber waterstops and concrete interface agents are installed at the longitudinal construction joints. For waterproofing, embedded self-adhesive rubber waterstops, back-adhesive self-adhesive rubber waterstops, and medium-density polyethylene (MDPE) boards are used to seal the expansion joints of the arch wall. An additional embedded self-adhesive rubber waterstop is installed along the inner edge of the lining at the expansion joints of the arch wall, and the gaps are filled tightly with sealant. Embedded self-adhesive rubber waterstops and back-adhesive self-adhesive rubber waterstops are installed at the expansion joints of the invert. MDL boards are used to seal the gaps, and double-layered shear reinforcement is installed circumferentially for waterproofing. To reduce settlement on both sides of the expansion joint of the invert, Φ50 double-layered shear reinforcement is installed in the secondary lining of the invert, with a circumferential spacing of 50cm. The gaps in the expansion joint of the invert are filled tightly with sealant.

[0095] The concrete should be cured within 12 hours after it is poured. During the curing period, the temperature difference between the inside and surface of the concrete, and the temperature difference between the surface and the ambient temperature should not exceed 20°C. The temperature difference between the curing water and the surface temperature of the concrete should not exceed 15°C.

[0096] 8) Ancillary works

[0097] Construction of drainage ditches, cable trenches, and tunnel pavement.

[0098] This embodiment utilizes a laser profiler to promptly correct the drilling and blasting design at the excavation cross-section, and employs different excavation methods based on the surrounding rock grade to strictly control over- and under-excavation. When traversing granite residual soil, completely weathered and strongly weathered rock, structural fissures, and fractured rock sections, advanced support is implemented to control collapses and ensure construction safety. Radial grouting and curtain grouting are used to reinforce the surrounding rock, ensuring smooth passage through fault fracture zones. Advanced geological forecasting and verification are conducted during construction, and monitoring of surrounding rock deformation is strengthened to overcome the hazards posed by adverse geological conditions. To ensure the tunnel is leak-proof, seepage-free, and crack-free, the principle of "primarily blocking with limited discharge" is adopted in moderately water-rich areas, while in other weakly water-rich and water-poor areas, the principle of "combining prevention, drainage, interception, and blocking, adapting to local conditions, and comprehensive management" is adopted.

[0099] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for constructing a tunnel in a denudation hilly landscape, characterized in that, The method comprises the following steps: The hole opening section construction is performed according to the actual terrain of the hole opening, and a hole top water intercepting gutter is constructed; dangerous rocks on the hole top are removed, and the ground surface is reinforced, the ground surface reinforcement is performed by sectional construction, a settlement joint is reserved every 15 m, and pitch asphalt is filled in the joint; before the side slope is excavated, ground surface settlement observation points are buried at the hole opening, and the hole opening slope surface is cleaned to remove exposed isolated rocks, and data monitoring is performed; the side slope is excavated from top to bottom in layers, one level of support is excavated at a time, and concrete is sprayed in time; when the tunnel is excavated to the height of the arch top, the base groove of the guide wall is excavated, and concrete is sprayed in time for support, the core soil at the center is reserved, the excavation is in a step shape, the installation of the guide wall arch frame and the support of the guide wall formwork are facilitated, the tunnel invert and the arch wall lining are constructed, after the tunnel construction is completed, the hole opening, the tunnel waterproof layer and the tunnel backfill are constructed, the hole opening large pipe shed support is constructed, a guide hole larger than the diameter of the pipe shed steel pipe is drilled first, then the pipe shed steel pipe with a working pipe head is drilled along the guide hole by using the impact and thrust of the drilling machine, the pipe is lengthened, and until the bottom of the hole; the initial pressure of the grouting is 0.5-1.0 MPa, the final pressure is 2.0-2.5 MPa, after the grouting is completed, the steel pipe is filled with cement mortar to form a steel pipe concrete; The advanced support is performed, the hole body long pipe shed support is constructed, and the position of the guide pipe is determined on the I-shaped steel frame; the inclination angle and the external insertion angle of the hole opening pipe are set, after the drilling is completed, the steel pipe is slowly pushed in by using the impact and thrust of the drilling machine, the pipe shed is arranged according to the pipe shed arrangement diagram, odd numbers are arranged by using steel flower pipes, even numbers are arranged by using steel pipes, the steel flower pipe is installed first and grouting is performed, then the steel pipe is installed, and the cement mortar is filled to enhance the strength of the pipe shed; the advanced small guide pipe support is constructed, the small guide pipe is used in cooperation with the steel frame, the angle is controlled by using a directional device when the small guide pipe is installed, the external insertion angle is 5°-10°, after the small guide pipe installation is completed, the hole opening and the surrounding cracks are sealed by using plastic cement, the tail of the small guide pipe is exposed by 30 cm, is supported on the steel frame behind the excavation surface, and is connected with the steel frame as a whole to form a pre-support system; The tunnel is excavated, before the construction, the monitoring and measuring points are buried, the advanced geological prediction and geological verification work are performed, the smooth blasting is adopted, the laser section instrument is used to correct the drilling and blasting design in time, and different tunnel excavation methods are adopted according to the surrounding rock grade to excavate the hole body; among them, the whole section method is adopted to excavate the II and III grade surrounding rock section, the three-step method or bench method is adopted to excavate the IV grade surrounding rock section, and the three-step and temporary invert method or three-step method is adopted to excavate the V grade surrounding rock section; after the excavation, the monitoring and measuring points are arranged in the hole, and the monitoring data is recorded in time during the construction process; The initial support is performed, the hole body is excavated in time, the concrete is wet sprayed, the concrete thickness is 4-8 cm, the arch foot dregs are removed, the steel frame is erected, the longitudinal connection should be arranged between the steel frames, the steel mesh and the longitudinal connecting rib are installed, the steel frame, the steel mesh and the gap back surface are filled and compacted by wet spraying concrete, the anchor rod and the anchor rod pad are installed, and the steel frame should be firmly welded with the lock foot anchor rod; Radial grouting, radial grouting is carried out at the back side of the primary support, radial grouting holes are drilled at the periphery of the tunnel body at intervals of 120-150 cm, the hole depth is 3 m, the holes are arranged in a quincunx shape, the orifice pipe is installed after acceptance, and is anchored with anchoring agent, interval grouting is carried out by the skip-hole method, the grouting sequence is from both sides to the vault according to the partition, the grouting pressure is 1-1.5 MPa, the hole wall and the orifice pipe are filled with anchoring agent, a grout stopper is arranged at the orifice, and the grouting is completed 3 If the water inflow per meter of tunnel is not greater than 2 m / 24 h, it is judged that the grouting achieves the effect, otherwise, supplementary grouting should be carried out; The curtain grouting is used for the section with developed groundwater, and the advanced curtain grouting is used for reinforcing the tunnel periphery and the excavation face, and the advanced geological prediction is carried out before the construction; the consolidation range of the grouting reinforcement ring is 3 m outside the excavation contour line; the length of each cycle grouting is 27 m, the excavation is 24 m, 3 m rock disc is reserved for stopping grouting, the first cycle sets a 1.5 m thick mold built concrete stopping grouting wall at the working face, and then the 3 m rock mass which is not excavated after the grouting is used to replace the stopping grouting wall, the working face is closed by using the sprayed concrete, the diffusion radius of the concrete slurry is 2-3 m, the hole bottom spacing of the grouting hole is 3-4 m, the drilling and grouting sequence is from outside to inside, and the holes in the same ring are constructed with interval; after the grouting is completed, the inspection holes are drilled in the range of the excavation contour line to detect the grouting effect; after the advanced curtain grouting reinforcement reaches the grouting effect, the cycle excavation is continuously carried out, and the cement mortar should be used to seal the whole hole in time after the inspection hole is used to detect the grouting effect; The secondary lining is constructed by the inverted arch, the concrete surface of the initial support of the tunnel bottom is treated, the concave pits which are too large are supplemented by spraying concrete and are smoothed, and it is ensured that the concrete surface is flat and has no sharp edges and corners; the waterproof layer is laid, the steel bars are bound, the inverted arch formwork is installed, the concealed engineering is monitored, the inverted arch concrete is poured, the concrete is maintained, the filling and bottom laying formwork is installed, the installation situation of the formwork is checked, the filling concrete is poured, the lining section is checked, the track is laid, the walking type full-face hydraulic formwork lining trolley is positioned, the construction joint of the arch wall is treated, the steel formwork head formwork, water stop belt, embedded part and cushion block are installed, the arch wall concrete is integrally and continuously poured, the left and right sides are simultaneously and symmetrically poured, the inserted type vibrating rod is used to consolidate the concrete, the demolding and concrete maintenance are carried out; the concrete is waterproof concrete; The auxiliary engineering is constructed by the water ditch cable groove and the tunnel pavement.

2. The method according to claim 1, wherein, The construction of the large pipe shed support at the hole includes the following steps: measurement and setting out, positioning and fixing of the guide pipe, arrangement of the guide pipe along the ring direction by 140°, positioning of the drilling machine, drilling and hole cleaning, installation of the pipe shed and grouting pipe, configuration of the cement slurry, pipe shed grouting, filling of the cement mortar, and formation of the steel pipe concrete; the large pipe shed support at the hole adopts the hot-rolled seamless steel pipe with an outer diameter of 108 mm and a wall thickness of 6 mm, the pressure grouting holes with a diameter of 12 mm are drilled on the four walls of the steel pipe, and the hole spacing is 15 cm; the steel pipe is arranged in the plum blossom type, and a 110 cm non-hole section is reserved at the tail as a grouting stopping section; when the long pipe shed support in the hole body is constructed, the steel pipe is punched into the surrounding rock along the tunnel periphery with an outward insertion angle of 1°-3°, and the water-cement ratio of the grouting cement slurry is 1:

1.

3. The method according to claim 1, wherein the method is applied to a tunnel in a denudation hill landscape. The long pipe shed support in the hole body adopts the hot-rolled seamless steel pipe with an outer diameter of 89 mm and a wall thickness of 5 mm and the steel flower pipe, each section of the hot-rolled seamless steel pipe is 10 m long, the seamless steel pipe with an outer diameter of 95 mm and a wall thickness of 6 mm is used as the joint, the number of joints in the same section of the steel pipe and the steel flower pipe is not more than 50% of the number of the pipes, and the ring direction spacing of the steel pipe is 30-40 cm.

4. The method according to claim 1, wherein the method is applied to a tunnel in a denudation hill landscape. The super small duct adopts a hot-rolled seamless steel pipe with an outer diameter of 50 mm and a wall thickness of 3.5 mm, and a grouting hole with a diameter of 10 mm and a spacing of 15 cm is drilled in the front of the steel pipe, and the steel pipe is arranged in a quincunx shape, the front end of the steel pipe is processed into a cone shape, and the non-drilling length of the tail end of the grouting stop section is not less than 30 cm; the super small duct is arranged at 150° in the circumferential direction, the circumferential spacing is 40 cm, and the horizontal overlap length of the adjacent two rows of small ducts is not less than 150 cm; and the grouting pressure of the super small duct support is 0.5-1 MPa.

5. The method as claimed in claim 1, wherein the method is suitable for construction of a tunnel in a denudation hill landscape. The monitoring measurement points include surface subsidence monitoring points, tunnel vault subsidence monitoring points, tunnel clearance convergence monitoring points and stratum displacement monitoring points; the surface subsidence monitoring points and the tunnel vault subsidence monitoring points are arranged on the same cross section in the underground excavation section; the surface subsidence monitoring points are arranged on the cross section perpendicular to the tunnel center line, and the spacing is 2-5 m; the in-hole monitoring measurement point installation is arranged in the rock mass; and the initial reading of the monitoring measurement points should be within 12 hours after the measurement point is buried and before the next cycle of excavation.

6. The method according to claim 1, wherein: The super geological prediction is performed by a geological sketch method, a super geological drilling method, a deepening blast hole detection method, an elastic wave reflection method and a geological radar detection method.

7. The method according to claim 1, wherein, The super curtain grouting reinforcement comprises the following steps: super geological prediction, hole arrangement, grouting stop wall construction, test hole drilling, selection of a grouting scheme according to the water pressure test results of the test holes, such as the use of a forward grouting method when the rock stratum is broken and easy to cause hole collapse, or the use of a backward grouting method when the surrounding rock is broken but not easy to cause hole collapse, and inspection hole setting and grouting effect detection within the excavation contour line range after grouting is completed.

8. The method according to claim 7, wherein the method is applied to the construction of a tunnel in a denudation hill landscape. The forward grouting method adopts a drilling and grouting segmented manner, each segment has a length of 3-5 m, and the drilling and grouting is performed until the designed depth; the backward grouting method is that a sleeve valve pipe is inserted at the hole mouth after drilling to the designed hole depth, a grouting pipe with a grouting stop plug is inserted, rubber sheaths are installed at both ends of the sleeve valve pipe to prevent grouting slurry from leaking out, a grouting pipeline is connected, and backward segmented grouting is performed from the hole bottom to the hole mouth, and each segment has a length of 2-3 m.

9. The method according to claim 1, wherein, The waterproof layer laying comprises the following steps: base surface treatment, keeping the base surface free of obvious water leakage, installing longitudinal drainage blind pipes and circumferential drainage plates, laying waterproof plates by using a laying process of a waterproof plate body and self-adhesive cloth sticking, hot fusion welding of the waterproof plates by using an automatic double-seam hot fusion welding machine, quality inspection of the waterproof plates, and repair of damaged parts of the waterproof plates.

10. The method according to claim 1, wherein the method is applied to the construction of a tunnel in a denudation hill landscape. The water stop belt is a middle-buried self-adhesive rubber water stop belt or a back-sticking self-adhesive rubber water stop belt; and the water stop belt is arranged at the circumferential construction joints of the arch wall and inverted arch, the longitudinal construction joints of the arch wall and inverted arch, the deformation joints of the arch wall and inverted arch.

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