Hole-entering construction method for shallow-buried tunnel under residual, broken and accumulated geological conditions

Abstract

The invention provides a shallow-buried tunnel hole-entering construction method under the residual, broken and accumulated geological condition. The shallow-buried tunnel hole entering construction method under the residual and broken accumulation geological conditions comprises the following steps that S1, surveying and setting out are conducted, the light and shade boundary mileage and the excavation outer contour line and the plane position of a hidden hole are set out, and marking is conducted in a drawing; s2, lofting and measuring the elevation of the catchwater at the top of the tunnel by measuring personnel, and cleaning the surface of the catchwater at the top of the tunnel before excavation. According to the shallow-buried tunnel entering construction method under the broken and accumulated geological conditions, a pipe shed lengthening mode is adopted for firstly excavating a pipe shed working chamber in a tunnel, then single-layer pipe shed and advanced small guide pipe construction is adopted, different excavation modes are adopted, V-grade surrounding rock soil and stones are used in a left-right layered mode, and a single-side-wall pilot tunnel and short step method is adopted; and in addition, the method of double-layer pipe shed construction and cover arch construction is adopted, so that the supporting safety is better guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering, and in particular relates to a shallow tunnel entry construction method under residual and broken geological conditions. Background Art

[0002] A shallow buried tunnel is a tunnel project under specific conditions, with a burial depth less than twice the tunnel diameter. Its construction is not only restricted by the geological factors of the covering layer, but also affected by the ground environment. The shallow buried tunnel does not simply mean that the thickness of the top stratum is small, but should also be comprehensively judged in combination with the engineering geological conditions of the overlying strata, including the structural characteristics of the surrounding rock structure, the degree of weathering, fragmentation, fault influence, structural strength, looseness, and groundwater.

[0003] The site of a certain tunnel belongs to the low mountain and hilly landform. The structural traces are mainly manifested in the development of joints and fissures, and the geological conditions are poor. The surrounding rock level of the fully weathered mixed granite at the entrance and exit is V grade. The fully weathered mixed granite at the tunnel entrance is thick, loose in structure, and easy to collapse, which makes the stability of the back slope rock and soil at the entrance extremely poor. Construction and excavation are very likely to cause shallow engineering landslides or large collapses. The Quaternary residual slope accumulation layer above the exit is thick and loose in structure. The strongly weathered rock mass is broken by joints, cracks and weathering, and it is easy to soften when it comes into contact with water, resulting in a rapid decrease in strength. Construction and excavation are very likely to cause shallow engineering collapses. During tunnel construction, it is necessary to remove the surface residual slope deposits, and take grouting and stone masonry slope protection measures on the surface of the strongly weathered rock layer. Therefore, higher requirements are put forward for the construction method.

[0004] For tunnels with entrances mainly composed of residual slope soil and a large number of boulders, or structural broken zones, and broken rock masses with an overall fragmented structure, there is a possibility of collapse during excavation. It is necessary to strengthen monitoring and measurement, provide timely support, and ensure construction safety. Therefore, a new construction method is needed to enter the tunnel.

[0005] Therefore, it is necessary to provide a new shallow tunnel construction method under residual geological conditions to solve the above technical problems. Summary of the invention

[0006] The technical problem solved by the present invention is to provide a method adopting double-layer pipe-roof construction + sleeve arch construction to better ensure the safety of support. The pipe-roof extension method is used to first excavate the pipe-roof studio in the tunnel, and then a single-layer pipe-roof + advanced small guide tube construction is used. Different excavation methods are adopted. V-grade surrounding rock soil and stone are used in layers on the left and right, a single side wall pilot pit + short step method, and V-grade surrounding rock soft and broken strata are used: a double side wall pilot pit method, V-grade surrounding rock soil and stone are used in layers up and down, and a double side wall pilot pit + upper and lower step method is used for shallow tunnel entry construction under broken geological conditions.

[0007] In order to solve the above technical problems, the shallow tunnel construction method under residual and broken geological conditions provided by the present invention comprises the following steps: S1. measuring and staking out the mileage of the light and dark boundary and the outer contour line and plane position of the dark tunnel excavation, and marking them in the drawing;

[0008] S2. The surveying personnel shall lay out the intercepting ditch on the cave roof and measure its elevation. Before excavation, the intercepting ditch on the cave roof shall be cleared and the shrubs and dangerous rocks on the hillside shall be removed. The ditch shall be excavated manually and the isolated rocks shall be dismantled by pneumatic picks. Masonry shall be carried out in time after excavation.

[0009] S3. Analyze the drawings and the detected data and select the appropriate method for excavation, starting from open excavation to the mileage pile number at the junction of open and dark areas. When excavating, pay attention to the step-by-step excavation of the foundation, and strengthen the support of the slope and the wall foot. If necessary, add locking anchor rods for locking and fixing. The locking anchor rods are made of Φ22 steel bars with a length of 3.5m. After being driven into the surrounding rock, they are anchored with anchoring agents;

[0010] S4. The advance support of the left and right tunnels at the exit adopts a double-layer large pipe shed. C20 concrete is sprayed on the soil around the exit to seal the surrounding slope, which serves as a temporary grouting wall during grouting and ensures the stability of the surrounding rock on the slope. I-beams are used as supports and positioning frames, large pipe shed orifice pipes are installed, and C30 concrete is poured in the formwork;

[0011] S5. During excavation, the inclination angle of the borehole should be parallel to the longitudinal slope of the route, and the direction should be parallel to the center line of the route. Drilling can only be started after the strength of the arch concrete reaches the design requirements. Before drilling, check whether the mechanical condition of the drilling rig is normal. If a hole cannot be drilled, add a sleeve or weld the drill bit directly to the front end of the steel pipe for drilling;

[0012] S6. After the drilling rig is in place, the drilling position is measured and laid out in advance. When drilling, the face of the tunnel should be pressed tightly to improve the drilling accuracy. The drilling speed should be low when the drilling rig is drilling. After the drilling depth reaches 20cm, the normal drilling speed should be switched. The drilling direction of the drilling rig should be adjusted continuously during the drilling process. The drilling should be stopped when there is 20-30cm left.

[0013] S7. Drill the first section of drill pipe into the tail of the rock formation, use two pipe clamps to manually clamp the drill pipe, reverse the drill rig at a low speed, disengage the drill pipe, return the drill rig to its original position along the guide rail, manually install the second section of drill pipe, and install the connecting sleeve at the front end of the drill pipe. The drill rig is sent to the tail of the first borehole at a low speed, and the directions are aligned and connected into one. Each time the drill pipe is extended, it should be carried out according to the above method. When changing the drill pipe, pay attention to check whether the drill pipe is bent, damaged, and whether the central water hole is unobstructed. If it does not meet the requirements, it should be replaced to ensure normal operation;

[0014] S8. When drilling, the straightener should be placed on the drill pipe and moved forward with the drill pipe to prevent the drill pipe from vibrating up and down under the dual effects of thrust and vibration, which may cause the hole to be not straight.

[0015] S9. After drilling, clean each pipe to prevent debris from clogging the pipe and making subsequent work impossible;

[0016] S10. When delivering the pipe, the drill moves forward at a low speed and aims at the end of the steel pipe, strictly controlling the angle, and then the drill pushes the steel pipe at a low speed with impact pressure and thrust pressure;

[0017] S11. Steel pipes must be numbered hole by hole and pipe by pipe before installation. Pipes must be connected and pushed forward in the order of numbers. Mixing is not allowed. After the pipe shed is in place, the gap between the steel pipe and the guide pipe must be tightly blocked with quick-setting cement or other materials to prevent slurry from overflowing. When blocking, slurry inlet holes and exhaust holes should be set;

[0018] S12. After the pipe jacking construction is completed, each pipe is cleaned to prevent debris from clogging the pipe, which may cause the subsequent pipe shed grouting work to be unable to proceed and achieve the ideal grouting effect;

[0019] S13. Before grouting, check the pipeline and mechanical conditions first, and conduct grouting tests after confirming that they are normal, and determine reasonable grouting parameters before construction can begin;

[0020] S14. During the grouting process, check the hole mouth, adjacent holes, and areas with thinner covering layers at any time to see if there is any grouting;

[0021] S15. Grouting shall be carried out by single liquid grouting and by segmented grouting to ensure that the grouting can be fully filled into the surrounding rock;

[0022] S16. A dedicated person should be assigned to fill in the Grouting Record Form during the grouting process, record the grouting time, slurry consumption, grouting pressure and other data in detail, observe the pressure gauge value, monitor the connecting device, avoid abnormal situations caused by a sudden increase in pressure, and take corresponding emergency measures for special situations that may occur on site;

[0023] S17. After grouting is completed, clean the steel pipe hole first.

[0024] As a further solution of the present invention, the following requirements should be noted in the masonry in step S2:

[0025] (1) The selected stone should be hard, not easily weathered, without cracks, and the middle thickness should not be less than 15cm. The surface should be clean. If there is dirt, it should be washed clean with high-pressure water. The strength of the stone should not be less than 30Mpa;

[0026] (2) When laying mortar slabs, the bottom layer should face downwards, interlaced and connected with each other, with tight overlap. The steps are as follows:

[0027] 1). First lay 3-4cm mortar on the bottom layer, then place stones of roughly equal height, press the mortar by hand, fill the gaps with thicker mortar first, and then fill it tightly with appropriate small stones to make the mortar full; then lay the upper layer of mortar, and lay the upper layer of stones in the same way;

[0028] (3) After the masonry is completed and the mortar has finally set, a 2cm thick layer of mortar is laid on the surface to prevent water seepage;

[0029] (4) The water ditch is located 5m outside the top of the slope and is constructed with M7.5 mortar-laid rubble. The excavated earth and stone must be dumped in a safe area. It is prohibited to dump them as they are dug, which may cause safety accidents. The side slopes on the outside of the intercepting ditch should be smoothed so that the water collected on the slope can flow smoothly into the intercepting ditch.

[0030] (5) After the construction of the intercepting ditch on the top of the cave is completed, a 5cm thick M5 mortar protective layer is applied on the inside, and then a 2.5mm thick SBS waterproof membrane is laid.

[0031] As a further solution of the present invention, core soil should be reserved during the excavation, and the core soil should be used as the inner soil formwork of the sleeve arch. If the core soil is unstable and cannot be used as the soil formwork, it should be processed to meet the quality requirements for setting up the inner formwork of the sleeve arch.

[0032] As a further solution of the present invention, the double-layer large pipe rack with an outer diameter of Φ108mm, a wall thickness of 10mm, and a length of 600cm (or 300cm) is adopted. A Φ12mm grouting hole is drilled outside the steel pipe within 437cm from the tail end. The circumferential spacing of the steel pipe is about 40cm. The external insertion angle is parallel to the longitudinal slope of the route, and the direction is parallel to the center line of the route. The tail end is supported on a steel frame, and the steel flower pipe is connected by threaded connection.

[0033] As a further solution of the present invention, the thread is 15 cm long, the steel pipe joints should be staggered, the number of joints in the same longitudinal cross section is not more than 50%, and the joints of adjacent steel pipes are staggered by at least 1 m.

[0034] As a further solution of the present invention, if slurry leakage occurs in step S14, grouting should be performed simultaneously under the condition of multiple grouting machines. If the conditions are not met, the grouting should be stopped immediately or intermittent grouting should be used to block the slurry leakage. Linen yarn, wooden wedges, fast-hardening cement mortar or anchoring agents can also be used to block the slurry leakage until the grouting is no longer continued. If the pressure suddenly increases during the grouting process, pipe blockage may occur and the machine should be stopped for inspection.

[0035] As a further solution of the present invention, in step S15, if the amount of cement slurry fed is large and the pressure does not increase for a long time, the slurry concentration and mix ratio should be adjusted to shorten the gel time, and small pump volume and low pressure grouting or intermittent grouting should be carried out to allow the slurry to have a relative residence time in the cracks to facilitate gelation, and the residence time does not exceed the gel time of the mixed slurry.

[0036] As a further solution of the present invention, the grouting sequence is from bottom to top, skip-hole grouting, the grouting parameters are cement slurry water-cement ratio: 0.8:1, and an accelerating setting agent is added when necessary, and the grouting pressure is an initial pressure of 0.5 to 1 MPa.

[0037] As a further scheme of the present invention, in step S4, the I-beam arch frame is as follows: center radius: 963.7 cm, 180° semicircular, eight I-beam arch frames of No. 122b are erected in the sleeve arch at the outlet end (longitudinal spacing 0.80 m, 20 cm away from the edge of the sleeve arch), and the I-beam arch frame is as follows: center radius of the outer arch frame: 1032.7 cm, 180° semicircular, center radius of the outer arch frame: 962.7 cm, 180° semicircular, and three I-beam arch frames of No. 120a are erected in the sleeve arch at the inlet end (longitudinal spacing 0.80 m, 20 cm away from the edge of the sleeve arch).

[0038] As a further solution of the present invention, the large pipe shed is constructed by relaying, firstly a 60m double-layer large pipe shed is built and then a 35m single-layer large pipe shed is connected, which can avoid the problem of drilling difficulty or serious deviation during the construction of the pipe shed.

[0039] Compared with the related art, the shallow tunnel construction method under residual and broken geological conditions provided by the present invention has the following beneficial effects:

[0040] 1. The advance support of the tunnel entrance in the present invention adopts the method of double-layer pipe shed construction + sleeve arch construction, which further ensures the safety of the support;

[0041] 2. After entering the cave, the present invention adopts the method of pipe shed extension to firstly excavate the pipe shed studio in the cave, and then adopts single-layer pipe shed + advanced small guide tube construction;

[0042] 3. The present invention adopts different excavation methods according to different geological conditions: V-level surrounding rock soil and stone are used in left and right layers, single side wall pilot pit + short step method, V-level surrounding rock soft and broken strata are used, double side wall pilot pit method, V-level surrounding rock soil and stone are used in upper and lower layers, double side wall pilot pit + upper and lower step method. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0044] Figure 1 This is a schematic diagram of the double-layer large pipe shed arch protection for entering the cave entrance in the present invention;

[0045] Figure 2 This is a schematic diagram of the pipe shed construction in the present invention;

[0046] Figure 3 It is a schematic diagram of the vault grouting arrangement in the present invention;

[0047] Figure 4 Schematic diagram of the cofferdam excavation method at different levels in the present invention. DETAILED DESCRIPTION

[0048] Please refer to Figure 1 , Figure 2 , Figure 3 and Figure 4 ,in, Figure 1 This is a schematic diagram of the double-layer large pipe shed arch protection for entering the cave entrance in the present invention; Figure 2 This is a schematic diagram of the pipe shed construction in the present invention; Figure 3 It is a schematic diagram of the vault grouting arrangement in the present invention; Figure 4 Schematic diagram of the cofferdam excavation method at different levels in the present invention. The shallow buried tunnel construction method under the residual geological conditions includes the following steps:

[0049] S1. Measure and lay out the mileage of the light and dark boundary and the outer contour line and plane position of the dark hole excavation, and mark them on the drawings;

[0050] S2. The surveying personnel shall lay out the intercepting ditch on the cave roof and measure its elevation. Before excavation, the intercepting ditch on the cave roof shall be cleared and the shrubs and dangerous rocks on the hillside shall be removed. The ditch shall be excavated manually and the isolated rocks shall be dismantled by pneumatic picks. Masonry shall be carried out in time after excavation.

[0051] S3. Analyze the drawings and the detected data and select the appropriate method for excavation, starting from open excavation to the mileage pile number at the junction of open and dark areas. When excavating, pay attention to the step-by-step excavation of the foundation, and strengthen the support of the slope and the wall foot. If necessary, add locking anchor rods for locking and fixing. The locking anchor rods are made of Φ22 steel bars with a length of 3.5m. After being driven into the surrounding rock, they are anchored with anchoring agents;

[0052] S4. The advance support of the left and right tunnels at the exit adopts a double-layer large pipe shed. C20 concrete is sprayed on the soil around the exit to seal the surrounding slope, which serves as a temporary grouting wall during grouting and ensures the stability of the surrounding rock on the slope. I-beams are used as supports and positioning frames, large pipe shed orifice pipes are installed, and C30 concrete is poured in the formwork;

[0053] S5. During excavation, the inclination angle of the borehole should be parallel to the longitudinal slope of the route, and the direction should be parallel to the center line of the route. Drilling can only be started after the strength of the arch concrete reaches the design requirements. Before drilling, check whether the mechanical condition of the drilling rig is normal. If a hole cannot be drilled, add a sleeve or weld the drill bit directly to the front end of the steel pipe for drilling;

[0054] S6. After the drilling rig is in place, the drilling position is measured and laid out in advance. When drilling, the face of the tunnel should be pressed tightly to improve the drilling accuracy. The drilling speed should be low when the drilling rig is drilling. After the drilling depth reaches 20cm, the normal drilling speed should be switched. The drilling direction of the drilling rig should be adjusted continuously during the drilling process. The drilling should be stopped when there is 20-30cm left.

[0055] S7. Drill the first section of drill pipe into the tail of the rock formation, use two pipe clamps to manually clamp the drill pipe, reverse the drill rig at a low speed, disengage the drill pipe, return the drill rig to its original position along the guide rail, manually install the second section of drill pipe, and install the connecting sleeve at the front end of the drill pipe. The drill rig is sent to the tail of the first borehole at a low speed, and the directions are aligned and connected into one. Each time the drill pipe is extended, it should be carried out according to the above method. When changing the drill pipe, pay attention to check whether the drill pipe is bent, damaged, and whether the central water hole is unobstructed. If it does not meet the requirements, it should be replaced to ensure normal operation;

[0056] S8. When drilling, the straightener should be placed on the drill pipe and moved forward with the drill pipe to prevent the drill pipe from vibrating up and down under the dual effects of thrust and vibration, which may cause the hole to be not straight.

[0057] S9. After drilling, clean each pipe to prevent debris from clogging the pipe and making subsequent work impossible;

[0058] S10. When delivering the pipe, the drill moves forward at a low speed and aims at the end of the steel pipe, strictly controlling the angle, and then the drill pushes the steel pipe at a low speed with impact pressure and thrust pressure;

[0059] S11. Steel pipes must be numbered hole by hole and pipe by pipe before installation. Pipes must be connected and pushed forward in the order of numbers. Mixing is not allowed. After the pipe shed is in place, the gap between the steel pipe and the guide pipe must be tightly blocked with quick-setting cement or other materials to prevent slurry from overflowing. When blocking, slurry inlet holes and exhaust holes should be set;

[0060] S12. After the pipe jacking construction is completed, each pipe is cleaned to prevent debris from clogging the pipe, which may cause the subsequent pipe shed grouting work to be unable to proceed and achieve the ideal grouting effect;

[0061] S13. Before grouting, check the pipeline and mechanical conditions first, and conduct grouting tests after confirming that they are normal, and determine reasonable grouting parameters before construction can begin;

[0062] S14. During the grouting process, check the hole mouth, adjacent holes, and areas with thinner covering layers at any time to see if there is any grouting;

[0063] S15. Grouting shall be carried out by single liquid grouting and by segmented grouting to ensure that the grouting can be fully filled into the surrounding rock;

[0064] S16. A dedicated person should be assigned to fill in the Grouting Record Form during the grouting process, record the grouting time, slurry consumption, grouting pressure and other data in detail, observe the pressure gauge value, monitor the connecting device, avoid abnormal situations caused by a sudden increase in pressure, and take corresponding emergency measures for special situations that may occur on site;

[0065] S17. After grouting is completed, clean the steel pipe hole first.

[0066] The following requirements should be noted in the masonry in step S2:

[0067] (1) The selected stone should be hard, not easily weathered, without cracks, and the middle thickness should not be less than 15cm. The surface should be clean. If there is dirt, it should be washed clean with high-pressure water. The strength of the stone should not be less than 30Mpa;

[0068] (2) When laying mortar slabs, the bottom layer should face downwards, interlaced and connected with each other, with tight overlap. The steps are as follows:

[0069] 1). First lay 3-4cm mortar on the bottom layer, then place stones of roughly equal height, press the mortar by hand, fill the gaps with thicker mortar first, and then fill it tightly with appropriate small stones to make the mortar full; then lay the upper layer of mortar, and lay the upper layer of stones in the same way;

[0070] (3) After the masonry is completed and the mortar has finally set, a 2cm thick layer of mortar is laid on the surface to prevent water seepage;

[0071] (4) The water ditch is located 5m outside the top of the slope and is constructed with M7.5 mortar-laid rubble. The excavated earth and stone must be dumped in a safe area. It is prohibited to dump them as they are dug, which may cause safety accidents. The side slopes on the outside of the intercepting ditch should be smoothed so that the water collected on the slope can flow smoothly into the intercepting ditch.

[0072] (5) After the construction of the intercepting ditch on the top of the cave is completed, a 5cm thick M5 mortar protective layer is applied on the inside, and then a 2.5mm thick SBS waterproof membrane is laid.

[0073] During the excavation, core soil should be reserved and used as the inner soil formwork of the arch. If the core soil is unstable and cannot be used as the soil formwork, it should be processed to meet the quality requirements for setting up the inner formwork of the arch.

[0074] The double-layer large pipe rack with an outer diameter of Φ108mm, a wall thickness of 10mm, and a length of 600cm (or 300cm) is made of hot-rolled seamless steel pipes. Φ12mm grouting holes are drilled outside the steel pipe within 437cm from the tail end. The circumferential spacing of the steel pipes is about 40cm. The external insertion angle is parallel to the longitudinal slope of the route, and the direction is parallel to the center line of the route. The tail end is supported on a steel frame, and the steel flower pipe is connected with threaded connections.

[0075] The thread is 15 cm long, the steel pipe joints should be staggered, the number of joints in the same longitudinal cross section should not exceed 50%, and the joints of adjacent steel pipes should be staggered by at least 1 m.

[0076] If grouting occurs in step S14, grouting should be performed simultaneously with multiple grouting machines. If this is not possible, grouting should be stopped immediately or intermittent grouting should be used to block the grouting outlet. Linen yarn, wooden wedges, fast-hardening cement mortar or anchoring agents can also be used to block the grouting until there is no more grouting. If the pressure suddenly increases during the grouting process, pipe blockage may occur and the machine should be stopped for inspection.

[0077] In step S15, if the amount of cement slurry fed is large and the pressure does not increase for a long time, the slurry concentration and mix ratio should be adjusted to shorten the gel time, and low-pressure grouting or intermittent grouting with a small pump volume should be performed to allow the slurry to have a relative residence time in the cracks to facilitate gelation, and the residence time should not exceed the gel time of the mixed slurry.

[0078] The grouting sequence is from bottom to top, skipping holes, the grouting parameters are cement slurry water-cement ratio: 0.8:1, adding accelerating setting agent when necessary, and the grouting pressure is an initial pressure of 0.5-1MPa.

[0079] In step S4, the I-beam arch frame is as follows: center radius: 963.7 cm, 180° semicircular, eight I-beam arch frames of No. 122b are erected in the sleeve arch at the exit end (longitudinal spacing 0.80 m, 20 cm away from the edge of the sleeve arch), and the I-beam arch frame is as follows: center radius of the outer arch frame: 1032.7 cm, 180° semicircular, center radius of the outer arch frame: 962.7 cm, 180° semicircular, and three I-beam arch frames of No. 120a are erected in the sleeve arch at the entry end (longitudinal spacing 0.80 m, 20 cm away from the edge of the sleeve arch).

[0080] The large pipe shed is constructed in relay, where a 60m double-layer large pipe shed is first constructed and then a 35m single-layer large pipe shed is connected, which can avoid problems such as drilling difficulties or serious deviations during the construction of the pipe shed.

[0081] 1). Construction of pipe shed studio in the cave. The design drawings did not specify the relay construction of the extra-long pipe shed in the tunnel. However, based on past experience, in order to ensure the smooth progress of the construction, it was initially decided to temporarily excavate a pipe shed relay studio in the tunnel at a mileage section with better surrounding rock in the tunnel. After comprehensively considering various issues such as the structural size of the pipe shed machinery, the length of the steel pipe, the external insertion angle, the lap length, the difficulty of jacking, etc., the pipe shed studio was initially designed to be 100cm higher than the original lining section, with a length of about 6m. The excavation section was expanded to reserve construction space for the pipe shed overlap. An I20a steel frame was set up in the studio, and Ф22 connecting reinforcement was welded to the inner flange of the steel arch frame in an inner eight-shaped shape to connect the two arch frames. φ8 steel mesh was laid on both sides of the arch frame, with a grid spacing of 200*200mm in double layers, and then C25 concrete was sprayed with a thickness of 30cm. The steel frame used 42 steel pipe locking feet (L-4.5m), with 4 feet per frame. After the pipe shed construction was completed, the studio was poured at the same time as the second lining concrete of the main tunnel. The specific section selection is based on the geological surrounding rock conditions of each tunnel. At that time, the owner, design, supervision and construction units will conduct on-site research and decide on the specific construction plan for the tunnel pipe shed;

[0082] 2). The construction and reinforcement of the drilling rig working platform. After the construction of the pipe shed studio is completed, the drilling rig working platform will be set up. The working platform is constructed with φ50mm steel pipes. In order to ensure that the erected working platform has sufficient bearing capacity, 2.0m mortar anchor rods are set in a plum blossom shape on both sides of the tunnel side wall. In order to make use of the mortar anchor rods for later use, 30cm is exposed, and hooks are made on the exposed heads to reinforce the drilling rig working platform, making it more stable and safe. After the platform is set up, the casing is installed on the steel frame to facilitate the positioning of the drill bit. The casing is made of φ150mm, 3mm thick seamless steel pipe;

[0083] 3). Hole opening positioning, drilling and hole cleaning. After the drilling platform is set up, drilling work will be carried out. First, the hole position, hole opening and hole axis are positioned according to the hole spacing using a combination of total station, hanging line and drill rod. The position and contour line of the pipe shed hole are drawn within the range of the face arch. The circumferential spacing of the pipe shed is 40cm. Since the pipe shed is long, the angle between the axis of the pipe shed and the outer edge of the lining is controlled at 1°;

[0084] 4). After drilling, jack up the pipe shed. After drilling, number each hole. The jacking steel pipes are numbered as odd numbers and the jacking steel pipes are numbered as even numbers. During the construction process, the steel pipes are jacked in first and grouting is performed, and then the steel pipes are jacked in to check the grouting quality of the steel pipes. The jacking of the pipe shed adopts a combination of winch and drilling rig, and the number of joints in the same section cannot exceed 50% of the total. The gap between the steel pipes of the pipe shed and the connecting steel pipes is sealed with high-strength cement mortar or quick-setting agent to prepare for the next step of grouting;

[0085] 5). Grouting of pipe shed. After the top of the pipe shed is completed, inject cement slurry in time. Before injecting cement slurry, conduct a water pressure test to check whether the mechanical equipment is normal and the pipeline connection status. After all indicators are confirmed to be normal, grouting is carried out. The water-cement ratio of grouting cement slurry is: 0.8:1. When the amount of slurry consumed by the broken zone is too large, the grouting pressure is used as the main control method during grouting. The grouting pressure is maintained at 0.5-2.0MPa. After the slurry is filled, the pressure is maintained for 2-3 minutes to increase the diffusion range of the slurry and ensure that the slurry in the pipe shed is full. During the grouting process, check whether there is slurry leakage at the orifice at any time. If there is slurry leakage, stop grouting immediately, and take measures such as linen yarn and anchoring agents to seal it until there is no slurry leakage before continuing grouting. After the grouting is completed, M20 cement mortar is used to fill the steel pipe to enhance the strength of the pipe shed;

[0086] 6). During the construction of the pipe shed in the tunnel, especially when constructing in the tunnel through the broken zone, the choice of drilling rig is particularly important. First of all, consider using a down-the-hole drill, which is best for coring. This will give a better hole-making effect and reduce the possibility of the drill getting stuck. Controlling the drilling angle when drilling holes in the pipe shed in the tunnel is an important part of the pipe shed construction results. Installing the casing is an effective means to control the angle. The longer the casing, the easier it is to control the drilling angle. In tunnel construction, the surrounding rock conditions are complex and changeable. It is necessary to go deep into the excavation line, fully grasp the actual situation of the surrounding rock, and conduct dynamic monitoring. Advanced geological predictions and forecasts must also be followed up in a timely manner. According to the specific situation, appropriate countermeasures must be taken in a timely manner to ensure the normal progress of the construction and achieve the expected quality and safety goals, thereby obtaining the maximum benefit of the construction.

[0087] The present invention adopts the advanced large pipe shed pre-support + double side wall pilot pit excavation method in the Class V soft rock section at the entrance and exit of the tunnel. The principle of "weak blasting, short footage, strong support, early closure, and frequent measurement" is adhered to during construction. Weak blasting or mechanical excavation is used for excavation. The depth of the blasthole and the amount of charge are strictly controlled during blasting. During construction, monitoring and measurement should be carried out according to the requirements of relevant specifications and standard drawings, and the results should be fed back in time to analyze the stability of the tunnel structure, so as to provide a basis for adjusting the support parameters and pouring the secondary lining.

[0088] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A shallow tunnel construction method under residual geological conditions, characterized in that: The following steps are involved: S1. Measure and lay out the mileage of the light and dark boundary and the outer contour line and plane position of the dark hole excavation, and mark them on the drawings; S2. The surveying personnel shall lay out the intercepting ditch on the cave roof and measure its elevation. Before excavation, the intercepting ditch on the cave roof shall be cleared and the shrubs and dangerous rocks on the hillside shall be removed. The ditch shall be excavated manually and the isolated rocks shall be dismantled by pneumatic picks. Masonry shall be carried out in time after excavation. S3. Analyze the drawings and the detected data and select the appropriate method for excavation, starting from open excavation to the mileage pile number at the junction of open and dark areas. When excavating, pay attention to the step-by-step excavation of the foundation, and strengthen the support of the slope and the wall foot. If necessary, add locking anchor rods for locking and fixing. The locking anchor rods are made of Φ22 steel bars with a length of 3.5m. After being driven into the surrounding rock, they are anchored with anchoring agents; S4. The advance support of the left and right tunnels at the exit adopts a double-layer large pipe shed. C20 concrete is sprayed on the soil around the exit to seal the surrounding slope, which serves as a temporary grouting wall during grouting and ensures the stability of the surrounding rock on the slope. I-beams are used as supports and positioning frames, large pipe shed orifice pipes are installed, and C30 concrete is poured in the formwork; S5. During excavation, the inclination angle of the borehole should be parallel to the longitudinal slope of the route, and the direction should be parallel to the center line of the route. Drilling can only be started after the strength of the arch concrete reaches the design requirements. Before drilling, check whether the mechanical condition of the drilling rig is normal. If a hole cannot be drilled, add a sleeve or weld the drill bit directly to the front end of the steel pipe for drilling; S6. After the drilling rig is in place, the drilling position is measured and laid out in advance. When drilling, the face of the tunnel should be pressed tightly to improve the drilling accuracy. The drilling speed should be low when the drilling rig is drilling. After the drilling depth reaches 20cm, the normal drilling speed should be switched. The drilling direction of the drilling rig should be adjusted continuously during the drilling process. The drilling should be stopped when there is 20-30cm left. S7. Drill the first section of drill pipe into the tail of the rock formation, use two pipe clamps to manually clamp the drill pipe, reverse the drill rig at a low speed, disengage the drill pipe, return the drill rig to its original position along the guide rail, manually install the second section of drill pipe, and install the connecting sleeve at the front end of the drill pipe. The drill rig is sent to the tail of the first borehole at a low speed, and the directions are aligned and connected into one. Each time the drill pipe is extended, it should be carried out according to the above method. When changing the drill pipe, pay attention to check whether the drill pipe is bent, damaged, and whether the central water hole is unobstructed. If it does not meet the requirements, it should be replaced to ensure normal operation; S8. When drilling, the straightener should be placed on the drill pipe and moved forward with the drill pipe to prevent the drill pipe from vibrating up and down under the dual effects of thrust and vibration, which may cause the hole to be not straight. S9. After drilling, clean each pipe to prevent debris from clogging the pipe and making subsequent work impossible; S10. When delivering the pipe, the drill moves forward at a low speed and aims at the end of the steel pipe, strictly controlling the angle, and then the drill pushes the steel pipe at a low speed with impact pressure and thrust pressure; S11. Steel pipes must be numbered hole by hole and pipe by pipe before installation. Pipes must be connected and pushed forward in the order of numbers. Mixing is not allowed. After the pipe shed is in place, the gap between the steel pipe and the guide pipe must be tightly blocked with quick-setting cement or other materials to prevent slurry from overflowing. When blocking, slurry inlet holes and exhaust holes should be set; S12. After the pipe jacking construction is completed, each pipe is cleaned to prevent debris from clogging the pipe, which may cause the subsequent pipe shed grouting work to be unable to proceed and achieve the ideal grouting effect; S13. Before grouting, check the pipeline and mechanical conditions first, and conduct grouting tests after confirming that they are normal, and determine reasonable grouting parameters before construction can begin; S14. During the grouting process, check the hole mouth, adjacent holes, and areas with thinner covering layers at any time to see if there is any grouting; S15. Grouting shall be carried out by single liquid grouting and by segmented grouting to ensure that the grouting can be fully filled into the surrounding rock; S16. A dedicated person should be assigned to fill in the Grouting Record Form during the grouting process, record the grouting time, slurry consumption, grouting pressure and other data in detail, observe the pressure gauge value, monitor the connecting device, avoid abnormal situations caused by a sudden increase in pressure, and take corresponding emergency measures for special situations that may occur on site; S17. After grouting is completed, clean the steel pipe hole first.

2. The shallow tunnel construction method under residual geological conditions according to claim 1 is characterized by: The following requirements should be noted in the masonry in step S2: (1) The selected stone should be hard, not easily weathered, without cracks, and the middle thickness should not be less than 15cm. The surface should be clean. If there is dirt, it should be washed clean with high-pressure water. The strength of the stone should not be less than 30Mpa; (2) When laying mortar slabs, the bottom layer should face downwards, interlaced and connected with each other, with tight overlap. The steps are as follows: 1). First lay 3-4cm mortar on the bottom layer, then place stones of roughly equal height, press the mortar by hand, fill the gaps with thicker mortar first, and then fill it tightly with appropriate small stones to make the mortar full; then lay the upper layer of mortar, and lay the upper layer of stones in the same way; (3) After the masonry is completed and the mortar has finally set, a 2cm thick layer of mortar is laid on the surface to prevent water seepage; (4) The water ditch is located 5m outside the top of the slope and is constructed with M7.5 mortar-laid rubble. The excavated earth and stone must be dumped in a safe area. It is prohibited to dump them as they are dug, which may cause safety accidents. The side slopes on the outside of the intercepting ditch should be smoothed so that the water collected on the slope can flow smoothly into the intercepting ditch. (5) After the construction of the intercepting ditch on the top of the cave is completed, a 5cm thick M5 mortar protective layer is applied on the inside, and then a 2.5mm thick SBS waterproof membrane is laid.

3. The shallow tunnel construction method under residual geological conditions according to claim 1 is characterized by: During the excavation, core soil should be reserved and used as the inner soil formwork of the arch. If the core soil is unstable and cannot be used as the soil formwork, it should be processed to meet the quality requirements for setting up the inner formwork of the arch.

4. The shallow tunnel construction method under residual geological conditions according to claim 1 is characterized by: The double-layer large pipe rack with an outer diameter of Φ108mm, a wall thickness of 10mm, and a length of 600cm (or 300cm) is made of hot-rolled seamless steel pipes. Φ12mm grouting holes are drilled outside the steel pipe within 437cm from the tail end. The circumferential spacing of the steel pipes is about 40cm. The external insertion angle is parallel to the longitudinal slope of the route, and the direction is parallel to the center line of the route. The tail end is supported on a steel frame, and the steel flower pipe is connected with threaded connections.

5. The shallow tunnel construction method under residual geological conditions according to claim 4 is characterized by: The thread is 15 cm long, the steel pipe joints should be staggered, the number of joints in the same longitudinal cross section should not exceed 50%, and the joints of adjacent steel pipes should be staggered by at least 1 m.

6. The shallow tunnel construction method under residual geological conditions according to claim 1 is characterized by: If grouting occurs in step S14, grouting should be performed simultaneously with multiple grouting machines. If this is not possible, grouting should be stopped immediately or intermittent grouting should be used to block the grouting outlet. Linen yarn, wooden wedges, fast-hardening cement mortar or anchoring agents can also be used to block the grouting until there is no more grouting. If the pressure suddenly increases during the grouting process, pipe blockage may occur and the machine should be stopped for inspection.

7. The shallow tunnel construction method under residual geological conditions according to claim 1 is characterized by: In step S15, if the amount of cement slurry fed is large and the pressure does not increase for a long time, the slurry concentration and mix ratio should be adjusted to shorten the gel time, and low-pressure grouting or intermittent grouting with a small pump volume should be performed to allow the slurry to have a relative residence time in the cracks to facilitate gelation, and the residence time should not exceed the gel time of the mixed slurry.

8. The shallow tunnel construction method under residual geological conditions according to claim 1 is characterized by: The grouting sequence is from bottom to top, skipping holes, and the grouting parameters are the water-cement ratio of cement slurry: 0.8:1, add accelerating setting agent if necessary, and the initial grouting pressure is 0.5~1MPa.

9. The shallow tunnel construction method under residual geological conditions according to claim 1 is characterized by: In step S4, the I-beam arch frame is as follows: center radius: 963.7 cm, 180° semicircular, eight I-beam arch frames of No. 122b are erected in the sleeve arch at the exit end (longitudinal spacing 0.80 m, 20 cm away from the edge of the sleeve arch), and the I-beam arch frame is as follows: center radius of the outer arch frame: 1032.7 cm, 180° semicircular, center radius of the outer arch frame: 962.7 cm, 180° semicircular, and three I-beam arch frames of No. 120a are erected in the sleeve arch at the entry end (longitudinal spacing 0.80 m, 20 cm away from the edge of the sleeve arch).

10. The shallow tunnel construction method under residual geological conditions according to claim 1 is characterized by: The large pipe shed is constructed in relay, where a 60m double-layer large pipe shed is first constructed and then a 35m single-layer large pipe shed is connected, which can avoid problems such as drilling difficulties or serious deviations during the construction of the pipe shed.

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