Support structure and construction method for complex geological structure mountain tunnel

Abstract

The application provides a supporting structure and a construction method for a mountain tunnel with a complex geological structure, wherein the supporting structure comprises a steel corrugated pipe piece and connecting bolts, further comprises fixing piles, the steel corrugated pipe piece is connected and fixed with the fixing piles and the connecting bolts to form a cylindrical corrugated pipe, grouting pipes are arranged at the lower part and the middle parts on both sides of the cylindrical corrugated pipe, a detection pipe is arranged on the top of the cylindrical corrugated pipe, drainage holes are uniformly arranged on the side wall of the top of the detection pipe, the middle part and the bottom of the detection pipe are provided with external threads, the bottom of the detection pipe is used for being rotatably matched with a detection pipe cap, gap maintaining blocks are uniformly arranged on the outer surface of the cylindrical corrugated pipe, and a cylindrical concrete supporting layer is arranged between the cylindrical corrugated pipe and the tunnel wall; and the construction method of the supporting structure is further provided. The supporting structure can form a complete cylindrical concrete supporting layer, and a supporting structure with high bearing capacity is obtained.

Description

Technical Field

[0001] This invention relates to the field of mountain tunnel construction, and in particular to a support structure and construction method for mountain tunnels with complex geological structures. Background Technology

[0002] my country has a vast territory and a complex and diverse geological structure. Transportation construction often involves building tunnels through mountains and valleys. With the continuous advancement of transportation network construction, the number of tunnels encountering adverse geological conditions is increasing. For example, some mountainous areas contain mixed soil and rock strata, weakly cemented gravel strata, etc. Although these strata have a certain strength, they are prone to localized collapses during construction due to disturbance, forming large cavities and posing construction risks. This results in unreasonable stress distribution on the tunnel during later use. Therefore, strengthening initial support is particularly important in such strata. Existing initial support structures for mined tunnels mainly consist of steel grating, systematic anchor bolts, steel mesh, and shotcrete. This type of support structure involves many procedures, long construction time, high construction difficulty, slow construction speed, and a poor construction environment. The excessive time spent on initial support often leads to collapses and falls in the fractured surrounding rock.

[0003] In view of the above problems, our R&D team developed a solution that involves assembling corrugated steel segments inside the tunnel and fixing them with anchor bolts, followed by grouting behind the segments to quickly form a support structure. However, in actual trials, it was found that the above solution still has certain drawbacks and problems. For example, during the installation of anchor bolts, vibration can easily cause the cemented layer or soil-rock mixture layer around the anchor bolts to detach; and after the support structure is completed, during subsequent construction, there have been instances of the top of the corrugated segments detaching, leading to their collapse.

[0004] After disassembly and creative analysis by technicians, it was discovered that at some anchoring locations, the geological structure was inherently unstable. The disturbance during anchor installation exacerbated the already loose connection and balance of the surrounding geological structure, making it more prone to fracture and collapse. Furthermore, technicians found that the concrete layer on the outside of the corrugated segment was not a continuous ring in some areas, but rather distributed in patches. After further analysis, technicians concluded that due to the complex geological structure, areas with more soil in the tunnel were more flat, resulting in a relatively tight fit between the corrugated segment and the tunnel wall, preventing or eliminating the need for grouting cement to pass through. While a cement layer of sufficient thickness can form effective support, there are sometimes weakly cemented gravel and sand behind the soil layer with poor stability. This is especially true for the corrugated pipe segments at the top. When this happens, the cement layer adheres to the corrugated pipe segments, and the sheet-like cement layer not only fails to form a ring-shaped support but also presses down on the corrugated pipe segments, becoming a burden on them. Another minor influencing factor is that the corrugated openings of the pipe segments are arc-shaped, and the bonding strength with the cement layer is not ideal. When the top stratum collapses and falls, the corrugated pipe segments on both sides are relatively easy to detach from the cement layer, reducing the supporting and pulling effect on the middle corrugated pipe segments. Summary of the Invention

[0005] The purpose of this invention is to provide a support structure and construction method for mountain tunnels with complex geological structures, so as to solve the problems in the prior art.

[0006] The technical solution for the expanded-body pile of this invention is implemented as follows:

[0007] The support structure for mountain tunnels with complex geological structures includes corrugated steel segments and connecting bolts, as well as fixing piles. The corrugated steel segments are fixed by the fixing piles and connecting bolts to form a cylindrical corrugated pipe. Grouting pipes are installed at the bottom and the middle of both sides of the cylindrical corrugated pipe. A detection pipe is screwed onto the top of the cylindrical corrugated pipe. Drainage holes are evenly distributed on the top side wall of the detection pipe, and external threads are provided in the middle and bottom. The bottom of the detection pipe is used to screw onto the detection pipe cap. Gap retaining blocks are evenly fixed on the outer surface of the cylindrical corrugated pipe. A cylindrical concrete support layer is provided between the cylindrical corrugated pipe and the tunnel wall.

[0008] Preferably, the gap retaining block is a columnar, hemispherical, or frustum-shaped rubber block bonded to the outer surface of the cylindrical corrugated pipe, or a hollow metal block bonded to the outer surface of the cylindrical corrugated pipe.

[0009] Preferably, the corrugated steel pipe sheet is a corrugated steel pipe sheet with uniformly distributed trapezoidal grooves, and the width of the opening of the trapezoidal groove is smaller than the width of the bottom of the groove.

[0010] Preferably, the fixed pile includes a pile hole and a pile assembly inserted into the pile hole. The pile assembly includes a cylindrical pile core, a grout-stopping ring sleeved on the upper end of the pile core, and at least two grouting components inserted into the pile core. The grouting components include multiple arc-shaped plates with the same curvature as the inner wall of the pile core and multiple grouting rods located in the lower part of the arc-shaped plates and communicating with the concave surface of the arc-shaped plates. The grouting rods are hollow structures and include a conical body with a grout outlet hole at the end and a tubular body with a grout outlet hole on the side wall connecting the arc-shaped plates and the conical body. The upper end of the pile core has an external thread for cooperating with the pile end cap and the pile end nut. The lower part of the side wall of the pile core has multiple through holes for the corresponding grouting rods to pass through. There are grouting holes on the side wall of the pile core between adjacent arc-shaped plates. The pile core has a concrete core inside and a root-like concrete fixing structure on the outside of the pile core.

[0011] The construction method for the support structure includes the following steps:

[0012] S1. Excavation of the tunnel arch and treatment of the tunnel walls

[0013] Excavate the upper arch of the tunnel. After the excavation is completed, remove any loose rocks from the tunnel walls of the upper arch.

[0014] S2. Install the upper fixing stake.

[0015] Piling holes are drilled on the upper left and upper right sides of the tunnel arch, and then pile components are inserted. A grout-stopping ring is fitted on the pile core to seal the gap between the pile hole and the pile core. The arc-shaped plates of each grouting component are squeezed onto the side wall of the pile core by inserting a hole expander into the pile core. At this time, the grouting rod passes through the side wall of the pile core and is inserted into the side wall of the pile hole. Then, double-fast cement mortar is injected through the pile core to form a tree root-like concrete fixing structure on the outside of the pile core. Finally, the pile end cap is screwed on to seal the structure.

[0016] S3. Install the corrugated steel pipe segments of the upper arch.

[0017] First, apply emulsified asphalt or hot asphalt evenly to the inside and outside of the corrugated steel pipe segment. Then, after the grout has solidified and hardened, unscrew the pile end cap, connect the corrugated steel pipe segment with connecting bolts, fit the reserved installation hole on the corrugated steel pipe segment onto the pile core, and fix it to the pile core with the pile end nut.

[0018] S4. Excavation of the tunnel invert and treatment of the tunnel walls.

[0019] Excavate the tunnel invert section, and after the excavation is completed, remove any loose rocks from the tunnel walls of the invert section.

[0020] S5. Install the lower fixing pile.

[0021] Piling holes are drilled at the lower left and lower right of the tunnel invert, and then pile components are inserted. A grout-stopping ring is fitted on the pile core to seal the gap between the pile hole and the pile core. The arc-shaped plates of each grouting component are squeezed onto the side wall of the pile core by inserting a hole expander into the pile core. At this time, the grouting rod passes through the side wall of the pile core and is inserted into the side wall of the pile hole. Then, double-fast cement mortar is injected through the pile core to form a tree root-like concrete fixing structure on the outside of the pile core. Finally, the pile end cap is screwed on to seal the structure.

[0022] S6. Install the corrugated steel pipe segments of the invert arch.

[0023] First, apply emulsified asphalt or hot asphalt evenly to the inside and outside of the corrugated steel pipe segment. Then, after the grout has solidified and hardened, unscrew the pile end cap and connect the corrugated steel pipe segments with connecting bolts. Fit the reserved installation holes on the corrugated steel pipe segments onto the pile core and fix them to the pile core with pile end nuts. Connect the upper and lower corrugated steel pipe segments with connecting bolts to finally form a cylindrical corrugated pipe.

[0024] S7. Install a concrete support layer.

[0025] First, inject quick-setting cement mortar into the gap between the end of the cylindrical corrugated pipe and the tunnel wall to form an end sealing layer, sealing the gap between the end of the cylindrical corrugated pipe and the tunnel wall. After the end sealing layer solidifies, grout is injected into the cylindrical corrugated pipe through the grouting pipe. Ordinary cement mortar or quick-setting cement mortar with retarder is injected. The grouting sequence is from bottom to top. Each grouting must be symmetrical and simultaneous from left to right. When grouting the uppermost grouting pipe, the pressure is gradually increased, so that the grout is compacted downward and flows upward and gradually reaches the top. After the detection pipe collects normal grout, the detection pipe cap is screwed to seal the detection pipe. Then, the grouting pressure and grouting flow rate are observed. When the grouting pressure gradually increases and the flow rate gradually decreases, and when the grouting pressure reaches the set requirement, it can be stopped after stabilizing for 3 minutes. After solidification, a concrete support layer is formed.

[0026] The support structure of this invention features uniformly fixed gap-maintaining blocks on the outer surface of the cylindrical corrugated pipe, ensuring a continuous gap of at least the length of the gap-maintaining blocks between the cylindrical corrugated pipe and the tunnel wall. This prevents the cylindrical corrugated pipe from being tightly pressed against the tunnel wall, providing space for the formation of a cylindrical concrete support layer. Grouting pipes are installed at the lower part and the middle of both sides of the cylindrical corrugated pipe. Grouting is performed in stages from bottom to top, first filling the lower space, then the middle sections. This sequential, multi-point grouting, combined with the interconnected gap structure of a certain width, facilitates the formation of a seamless, dead-angle-free coverage, preventing... In cases where dead zones and localized air pockets cause discontinuities in the concrete support layer, the pressure is gradually increased during grouting through the uppermost grouting pipe. This causes the grout to compact downwards and flow upwards, gradually reaching the top. Once the detection pipe has collected normal grout, the cap is screwed off to seal the pipe. Because the detection pipe rests against the uppermost tunnel wall, and drainage holes are evenly distributed on the top sidewall of the pipe, the collection of normal grout indicates that the cylindrical corrugated pipe and the uppermost tunnel wall are filled with grout, ultimately forming a complete cylindrical concrete support layer, thus achieving a high-bearing-capacity support structure.

[0027] Furthermore, the corrugated steel pipe segments are corrugated steel pipe segments with evenly distributed trapezoidal grooves. The width of the opening of the trapezoidal groove is smaller than the width of the bottom of the groove. In this way, the corrugated steel pipe segments form an interlocking structure with the solidified concrete, making it difficult for the corrugated pipe segments to separate from the concrete layer, greatly increasing the stability and enhancing the compressive and tensile strength.

[0028] Furthermore, the structure of the fixed piles results in less construction disturbance. After the grout is injected, it not only forms an expanded pile, but the grout is also deeply injected into the surrounding strata through the grouting rod, penetrating the gaps between the gravel and soil, forming a root-like concrete fixing structure. This more firmly binds together the strata structure that has been loosened during construction, greatly increasing the stability of the strata and reducing the possibility of local collapse. At the same time, it greatly increases the stability of the fixed piles, laying a solid foundation for the stability of the support structure.

[0029] The construction method of the support structure, which proceeds from the upper arch of the tunnel to the lower arch, greatly reduces the impact of the lower construction on the upper construction and significantly increases the safety factor during the lower construction. Injecting quick-setting cement mortar into the pile core significantly accelerates the construction progress. In the concrete support layer installation step, quick-setting cement mortar is first injected between the end of the cylindrical corrugated pipe and the tunnel wall to form an end sealing layer. This ensures the subsequent pressurized grouting within the cylindrical corrugated pipe, preventing the grout from being squeezed out from both ends, which would lead to insufficient grouting pressure and prevent the grout from being compacted downwards or flowing upwards. Due to the segregation phenomenon during grouting, a certain amount of low-concentration mixed liquid will occur at the top. Therefore, the detection pipe first collects the upper low-concentration water-bearing layer. The detection pipe can discharge the low-concentration water-bearing layer to prevent wide gaps after solidification. Simultaneously, the collection of normal grout reflects the grouting filling status at the top. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the support structure after grouting in an embodiment of the present invention;

[0032] Figure 2 for Figure 1 Enlarged structural diagram at point A in the middle;

[0033] Figure 3 This is a schematic diagram of the support structure before grouting in an embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram of the pile assembly in an embodiment of the present invention;

[0035] Figure 5 This is a schematic diagram of the grouting component in an embodiment of the present invention;

[0036] Figure 6 This is a schematic diagram of the structure of the pile assembly after grouting and the pile end cap in an embodiment of the present invention;

[0037] Figure 7 This is a schematic diagram of the structure of the pile assembly after grouting and the pile end nut in an embodiment of the present invention;

[0038] Figure 8 This is a partial structural schematic diagram of the corrugated steel pipe segment in an embodiment of the present invention;

[0039] Figure 9 This is a schematic diagram of the structure of the hole expander in an embodiment of the present invention.

[0040] The components are as follows: stratum 1; grouting pipes 2, 8, 10; concrete support layer 3; fixed piles 4, 6, 7, 9; cylindrical corrugated pipe 5; gap retaining block 11; tunnel wall 12; detection pipe 13; drainage hole 14; fixed pipe 15; connecting bolt 16; L-shaped connecting plate 17; detection pipe cap 18; arc plate 19; tubular body 20; conical body 21; grout outlet hole 22; grouting rod 23; pile core 24; 25 pile end external thread; grouting hole 26; perforation 27; plug 28; pile end cap 29; concrete fixing structure 30; pile end nut 31; steel corrugated pipe segment 32; trapezoidal groove 33; grout stop ring 34; hole enlarging rod 35; hinged rod 36; fan-shaped hole enlarging plate 37; sliding sleeve 38; positioning pin 39; comb-shaped positioning hole 40; force application sleeve 41. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Support structures used for mountain tunnels with complex geological structures, such as Figure 1-7As shown, the structure includes corrugated steel pipe segments 32, connecting bolts 16, and four fixing piles 4, 6, 7, and 9, distributed at the upper left, upper right, lower left, and lower right positions of the tunnel wall 12. The corrugated steel pipe segments have L-shaped connecting plates 17 at both transverse ends. The corrugated steel pipe segments also have mounting holes. The connecting bolts 16 connect to the L-shaped connecting plates 17, and the fixing piles pass through the corresponding mounting holes and are fixed in place. Each corrugated steel pipe segment 32 is fixed by the fixing piles and connecting bolts 16 to form a cylindrical corrugated pipe 5. Grouting pipes 8, 10, and 2 are installed at the bottom and middle of both sides of the cylindrical corrugated pipe. A detection pipe 13 is screwed onto the top of the cylindrical corrugated pipe. Drainage holes 14 are evenly arranged on the top side wall of the detection pipe, and external threads are provided in the middle and bottom. The bottom of the detection pipe is used to screw into the detection pipe cap 18. The cylindrical corrugated pipe has an insertion hole at this point, and a fixing pipe 15 with internal threads is welded into the insertion hole. The detection pipe 13 is screwed into the fixing pipe 15. This allows the size of the gap between the cylindrical corrugated pipe and the top of the tunnel wall to be adjusted. By adjusting the screw-in depth of the detection tube 13, the detection tube 13 is pressed against the top of the tunnel wall. Gap retaining blocks 11 are uniformly fixed on the outer surface of the cylindrical corrugated pipe. The gap retaining blocks are columnar, hemispherical, or frustum-shaped rubber blocks or hollow metal blocks bonded to the outer surface of the cylindrical corrugated pipe. In this embodiment, hemispherical rubber blocks are used, and the radius is set as needed, such as 3cm or 5cm, etc., to ensure that a certain width of interconnected gap is formed between the cylindrical corrugated pipe and the tunnel wall. There is a cylindrical concrete support layer 3 between the cylindrical corrugated pipe and the tunnel wall.

[0043] In this embodiment, fixed piles 4, 6, 7, and 9 include pile holes and pile assemblies inserted into the pile holes. Each pile assembly includes a cylindrical pile core 24, a grout-stopping ring 34 fitted over the upper end of the pile core, and at least two grouting components inserted into the pile core. The outer diameter of the pile core can be 4.5 cm, and the inner diameter can be 4.3 cm. The grouting components include multiple arc-shaped plates 19 with the same curvature as the inner wall of the pile core, and multiple grouting rods 23 located in the lower part of the arc-shaped plates and communicating with the concave surface of the arc-shaped plates. The grouting rods are hollow structures, and their length and diameter can be set as needed to meet the requirements of insertion and grouting, such as lengths of 1 cm, 1.3 m, or 1.5 cm, and diameters from 0.3 cm. The grouting rod is selected as needed within the range of m-0.8cm. It includes a conical body 21 with a grout outlet hole at the end and a tubular body 20 with a grout outlet hole 22 on the side wall connecting the arc plate and the conical body. The upper end of the pile core has an external thread 25 that mates with the pile end cap 29 and the pile end nut 31. The pile end cap has a U-shaped plug 28 inside. The middle and lower part of the pile core side wall has multiple through holes 27 for the corresponding grouting rods to pass through. There are grouting holes 26 on the pile core side wall between adjacent arc plates. The pile core has a concrete core (the concrete core is not shown in the figure for easy reading). The pile core has a root-like concrete fixing structure 30 on the outside, which greatly enhances the bearing capacity.

[0044] In this embodiment, the support structure features uniformly fixed gap-maintaining blocks on the outer surface of the cylindrical corrugated pipe. This ensures a continuous gap between the cylindrical corrugated pipe and the tunnel wall, at least the length of the gap-maintaining blocks, preventing the cylindrical corrugated pipe from being tightly pressed against the tunnel wall and providing space for the formation of a cylindrical concrete support layer. Grouting pipes are installed at the lower part and the middle of both sides of the cylindrical corrugated pipe. Grouting is performed in stages from bottom to top, first filling the lower space, then the middle sections. This sequential, multi-point grouting, combined with the interconnected gap structure of a certain width, facilitates the formation of a seamless coverage, preventing leaks. In cases where dead zones and localized air pockets cause discontinuities in the concrete support layer, the pressure is gradually increased during grouting through the uppermost grouting pipe. This causes the grout to compact downwards and flow upwards, gradually reaching the top. Once the detection pipe collects normal grout, the cap is tightened to seal it. Because the detection pipe rests against the uppermost tunnel wall, and drainage holes are evenly distributed on its top sidewall, the collection of normal grout indicates that the cylindrical corrugated pipe and the uppermost tunnel wall are filled with grout, ultimately forming a complete cylindrical concrete support layer, resulting in a high-bearing-capacity support structure. The fixed pile structure experiences less construction disturbance. After grout injection, it not only forms an expanded pile, but the grout is also deeply injected into the surrounding strata through the grouting rod, penetrating the gaps between gravel and soil, forming a root-like concrete fixing structure. This more firmly binds together the strata structure loosened during construction, greatly increasing the stability of the strata and reducing the possibility of localized collapse. Simultaneously, it significantly increases the stability of the fixed pile, laying a solid foundation for the stability of the support structure.

[0045] Unlike Example 1, the fixed pile can use a locking anchor rod. The diameter of the locking anchor rod is smaller than that of the pile core in Example 1. It has a simple structure, low cost, and convenient and quick construction. However, the anchoring effect is not as good as that of the fixed pile, and it has a greater impact on the cemented layer or soil-rock mixture structure during construction. The probability of rockfall and local collapse during construction is also greater.

[0046] In this embodiment, as Figure 8 As shown, the corrugated steel pipe segment 32 is a corrugated steel pipe segment with uniformly distributed trapezoidal grooves 33. The width of the opening of the trapezoidal groove is smaller than the width of the bottom of the groove. The two transverse ends of the corrugated steel pipe segment have L-shaped connecting plates 17. In this way, the corrugated steel pipe segment forms an interlocking structure with the solidified concrete, making it difficult for the corrugated pipe segment to detach from the concrete layer, greatly increasing the stability and enhancing the compressive and tensile strength. In order to achieve continuous connection in the axial direction, the corrugated steel pipe segments of this structure need to be provided with two pluggable specifications, which are alternately plugged in in the axial direction.

[0047] Construction methods for support structures, such as Figure 1-9 As shown, it includes the following steps:

[0048] S1. Excavation of the tunnel arch and treatment of the tunnel walls

[0049] Excavate the upper arch of the tunnel. After the excavation is completed, remove any loose rocks from the tunnel walls of the upper arch.

[0050] S2. Install the upper fixing stake.

[0051] In this embodiment, pile holes are drilled on the upper left and upper right sides of the tunnel arch. The drilling is carried out in two steps. First, a cylindrical drill bit is used to drill an annular hole in the tunnel wall, forming a columnar body in the middle. This process causes minimal disturbance. Then, the columnar body is broken up using the cylindrical drill bit. Due to the weak cementation of stratum 1, the columnar body is easily broken. In this step, due to the isolation gap formed by the annular hole, there is basically no impact on the circumferential stratum structure. Although vibrations can be transmitted axially to deeper layers, the deeper strata are more stable and easier to withstand and absorb. Moreover, the vibrations transmitted to deeper strata through the columnar body will also be significantly attenuated. Compared with directly setting anchor bolts, this greatly reduces the disturbance and damage to the surrounding stratum structure and rockfall. The probability of collapse is greatly reduced. After the pile hole is drilled, the pile assembly is inserted and a grout stop ring is fitted on the pile core to seal the gap between the pile hole and the pile core. If necessary, the pile assembly can be fixed in the pile hole by fitting a pad behind the grout stop ring and using a hydraulic mechanism to hold the pad. The reamer (not shown in the figure) is inserted into the pile core to squeeze the arc plates of each grouting component onto the side wall of the pile core. At this time, the grouting rod passes through the side wall of the pile core and is inserted into the side wall of the pile hole. Then, double-fast cement mortar is injected through the pile core to form a root-like concrete fixing structure on the outside of the pile core. Then, the pile end cap is tightened to seal the hole. The reamer includes a heart-shaped or conical reamer body at the front end and a connecting rod at the rear end. Existing reamers can be used. Lubricating oil is applied when using them.

[0052] To prevent the pile assembly from being unable to be pulled out after insertion or from experiencing excessive pulling force during extraction, a special hole expander can be designed, such as... Figure 9 As shown, the device includes a reaming rod 35 with a conical head, multiple fan-shaped reaming plates 37 with their lower ends hinged to the reaming rod behind the conical head, a force-applying sleeve 41 slidably sleeved on the upper part of the reaming rod, and a sliding sleeve 38 fixed to the lower end of the force-applying sleeve. The sliding sleeve is hinged to the middle of each of the fan-shaped reaming plates through a hinge rod 36. The force-applying sleeve has a comb-shaped positioning hole 40, which includes a vertical elongated hole and a horizontal elongated hole communicating with the vertical elongated hole. The upper end of the reaming rod has a positioning pin 39 inserted into the comb-shaped hole. Each fan-shaped reaming plate is evenly distributed along the circumference of the reaming rod, and the gap between each fan-shaped reaming plate gradually increases as the positioning pin moves axially upward away from the lower edge of the comb-shaped hole. When using it, place the positioning pin in the corresponding horizontal elongated hole according to the required hole size, and open the fan-shaped hole expander. After use, rotate the force-applying sleeve to place the positioning pin in the vertical elongated hole, and then pull it upwards to retract the fan-shaped hole expander, making it easy to remove the hole expander from the pile core.

[0053] S3. Install the corrugated steel pipe segments of the upper arch.

[0054] First, apply emulsified asphalt or hot asphalt evenly inside and outside the corrugated steel pipe segment. Then, after the grout has solidified and hardened, unscrew the pile end cap and pad. The pad can be reused. Connect the corrugated steel pipe segment with connecting bolts. Fit the reserved installation hole on the corrugated steel pipe segment onto the pile core and fix it to the pile core with the pile end nut.

[0055] S4. Excavation of the tunnel invert and treatment of the tunnel walls.

[0056] Excavate the tunnel invert section, and after the excavation is completed, remove any loose rocks from the tunnel walls of the invert section.

[0057] S5. Install the lower fixing pile.

[0058] Piling holes are drilled at the lower left and lower right of the tunnel invert. The remaining operations are the same as in step S2 and will not be described in detail here.

[0059] S6. Install the corrugated steel pipe segments of the invert arch.

[0060] The operation is the same as step S3, so I will not repeat it here;

[0061] S7. Install a concrete support layer.

[0062] First, inject quick-setting cement mortar between the end of the cylindrical corrugated pipe and the tunnel wall to form an end sealing layer, sealing the gap between the end of the cylindrical corrugated pipe and the tunnel wall. After the end sealing layer solidifies, grout is injected into the cylindrical corrugated pipe through the grouting pipe. Ordinary cement mortar or quick-setting cement mortar with retarder is injected to avoid uneven grouting due to rapid solidification. The grouting sequence is from bottom to top, and each grouting must be symmetrical and simultaneous. When grouting the uppermost grouting pipe, the pressure is gradually increased, so that the grout is compacted downwards and flows upwards and gradually reaches the top. After the detection pipe collects normal grout, the detection pipe cap is screwed to seal the detection pipe. Then, the grouting pressure and grouting flow rate are observed. When the grouting pressure gradually increases and the flow rate gradually decreases, and when the grouting pressure reaches 0.5MPa and stabilizes for 3 minutes, the grouting can be stopped. After solidification, a concrete support layer is formed.

[0063] The construction method of the support structure in this embodiment, which follows the construction sequence of the upper arch of the tunnel before the lower arch, greatly reduces the impact of the lower construction on the upper construction and significantly increases the safety factor during the lower construction. The injection of double-fast cement mortar into the pile core greatly accelerates the construction progress. In the step of setting the concrete support layer, double-fast cement mortar is first injected between the end of the cylindrical corrugated pipe and the tunnel wall to form an end sealing layer, which provides a guarantee for the subsequent pressurized grouting in the cylindrical corrugated pipe. This prevents the grout from being squeezed out from both ends, which would result in the inability to guarantee the grouting pressure and the inability of the grout to be compacted downwards and flow upwards. Due to the segregation phenomenon during the grouting process, there will be a certain amount of low-concentration mixed liquid at the top. Therefore, the detection tube first collects the low-concentration water-bearing layer at the top. The detection tube can discharge the low-concentration water-bearing layer to prevent wide gaps after solidification. At the same time, the collection of normal grout can reflect the filling situation of the grouting at the top.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction method for a support structure used in mountain tunnels with complex geological structures. The support structure includes corrugated steel pipe segments and connecting bolts, as well as fixing piles. The corrugated steel pipe segments are fixed by the fixing piles and connecting bolts to form a cylindrical corrugated pipe. Grouting pipes are installed at the lower part and the middle of both sides of the cylindrical corrugated pipe. A detection pipe is screwed onto the top of the cylindrical corrugated pipe. Drainage holes are evenly distributed on the top sidewall of the detection pipe, and external threads are present in the middle and bottom. The cylindrical corrugated pipe has insertion holes at these points, and a fixing pipe with internal threads is welded into the insertion holes. The detection pipe is screwed into the fixing pipe, and the bottom of the detection pipe is used to screw onto the detection pipe cap. Gap retaining blocks are evenly fixed on the outer surface of the cylindrical corrugated pipe. A cylindrical concrete support layer exists between the cylindrical corrugated pipe and the tunnel wall. The gap retaining blocks are columnar, hemispherical, or frustum-shaped rubber blocks or hollow metal blocks bonded to the outer surface of the cylindrical corrugated pipe. The structure is as follows: The corrugated steel pipe segment is a corrugated steel pipe segment with uniformly distributed trapezoidal grooves, the width of the opening of the trapezoidal groove is smaller than the width of the bottom of the groove; The fixed pile includes a pile hole and a pile assembly inserted into the pile hole. The pile assembly includes a cylindrical pile core, a grout-stopping ring sleeved on the upper end of the pile core, and at least two grouting components inserted into the pile core. The grouting components include multiple arc-shaped plates with the same curvature as the inner wall of the pile core and multiple grouting rods located in the lower part of the arc-shaped plates and communicating with the concave surface of the arc-shaped plates. The grouting rods are hollow structures, including a conical body with a grout outlet hole at the end and a tubular body with a grout outlet hole on the side wall connecting the arc-shaped plates and the conical body. The upper end of the pile core has an external thread for cooperating with the pile end cap and the pile end nut. The lower part of the side wall of the pile core has multiple through holes for the corresponding grouting rods to pass through. There are grouting holes on the side wall of the pile core between adjacent arc-shaped plates. The pile core has a concrete core inside and a root-like concrete fixing structure on the outside of the pile core. The construction method includes the following steps: S1. Excavation of the tunnel arch and treatment of the tunnel walls Excavate the upper arch of the tunnel. After the excavation is completed, remove any loose rocks from the tunnel walls of the upper arch. S2. Install the upper fixing stake. Piling holes are drilled on the upper left and upper right sides of the tunnel arch, and then pile components are inserted. A grout-stopping ring is fitted on the pile core to seal the gap between the pile hole and the pile core. The arc-shaped plates of each grouting component are squeezed onto the side wall of the pile core by inserting a hole expander into the pile core. At this time, the grouting rod passes through the side wall of the pile core and is inserted into the side wall of the pile hole. Then, double-fast cement mortar is injected through the pile core to form a tree root-like concrete fixing structure on the outside of the pile core. Finally, the pile end cap is screwed on to seal the structure. S3. Install the corrugated steel pipe segments of the upper arch. First, apply emulsified asphalt or hot asphalt evenly to the inside and outside of the corrugated steel pipe segment. Then, after the grout has solidified and hardened, unscrew the pile end cap, connect the corrugated steel pipe segment with connecting bolts, fit the reserved installation hole on the corrugated steel pipe segment onto the pile core, and fix it to the pile core with the pile end nut. S4. Excavation of the tunnel invert and treatment of the tunnel walls. Excavate the tunnel invert section, and after the excavation is completed, remove any loose rocks from the tunnel walls of the invert section. S5. Install the lower fixing pile. Piling holes are drilled at the lower left and lower right of the tunnel invert, and then pile components are inserted. A grout-stopping ring is fitted on the pile core to seal the gap between the pile hole and the pile core. The arc-shaped plates of each grouting component are squeezed onto the side wall of the pile core by inserting a hole expander into the pile core. At this time, the grouting rod passes through the side wall of the pile core and is inserted into the side wall of the pile hole. Then, double-fast cement mortar is injected through the pile core to form a tree root-like concrete fixing structure on the outside of the pile core. Finally, the pile end cap is screwed on to seal the structure. S6. Install the corrugated steel pipe segments of the invert arch. First, apply emulsified asphalt or hot asphalt evenly to the inside and outside of the corrugated steel pipe segment. Then, after the grout has solidified and hardened, unscrew the pile end cap and connect the corrugated steel pipe segments with connecting bolts. Fit the reserved installation holes on the corrugated steel pipe segments onto the pile core and fix them to the pile core with pile end nuts. Connect the upper and lower corrugated steel pipe segments with connecting bolts to finally form a cylindrical corrugated pipe. S7. Install a concrete support layer. First, inject quick-setting cement mortar into the gap between the end of the cylindrical corrugated pipe and the tunnel wall to form an end sealing layer, sealing the gap between the end of the cylindrical corrugated pipe and the tunnel wall. After the end sealing layer solidifies, grout is injected into the cylindrical corrugated pipe through the grouting pipe. Ordinary cement mortar or quick-setting cement mortar with retarder is injected. The grouting sequence is from bottom to top. Each grouting must be symmetrical and simultaneous from left to right. When grouting the uppermost grouting pipe, the pressure is gradually increased, so that the grout is compacted downward and flows upward and gradually reaches the top. After the detection pipe collects normal grout, the detection pipe cap is screwed to seal the detection pipe. Then, the grouting pressure and grouting flow rate are observed. When the grouting pressure gradually increases and the flow rate gradually decreases, and when the grouting pressure reaches the set requirement, it can be stopped after stabilizing for 3 minutes. After solidification, a concrete support layer is formed.

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