A method for reinforcing an extremely broken soft rock tunnel face by advanced chemical grouting

Abstract

This invention discloses a method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock, including the steps of grouting conduit installation, grouting pipeline connection, hole sealing operation, and grout injection. After tunnel excavation, the locations of the advanced grouting holes are marked on the tunnel face. Holes are drilled in a staggered arrangement of long and short grouting pipes, and long and short grouting pipes are installed. Grouting solution A and grout B are injected simultaneously in a 1:1 ratio. Grout A is an isocyanate aqueous solution with a density of 1.05±0.05 g / cm3, and grout B is a combined polyether aqueous solution with a density of 1.23±0.05 g / cm3. The mixed grout has a setting time of 15 to 20 seconds, an expansion ratio of 22 to 25 times, and a bond strength ≥3.0 MPa. This invention uses a combined polyether polyol chemical grout, which has low viscosity and strong permeability, and can effectively inject into the micro-fractures in extremely broken soft rock. Not only is the gelation time controllable, but it also has sufficient long-term strength and durability after curing, which can provide a lasting reinforcement effect for the surrounding rock and meet the safety requirements of the entire life cycle of the tunnel.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering, specifically to a method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock. Background Technology

[0002] In tunnel construction, traversing fractured and weak surrounding rock strata is an extremely common and challenging condition. Such surrounding rock typically exhibits low strength, poor self-stability, and is prone to softening and disintegration upon contact with water. Under the disturbance of tunnel excavation, the tunnel face is highly susceptible to instability or even collapse, seriously threatening construction safety and progress. Therefore, pre-reinforcement of the tunnel face in extremely fractured and soft rock tunnels is essential.

[0003] To ensure the safe excavation of tunnels in fractured soft rock, the previous main pre-reinforcement strategy combined with advance support and face sealing was adopted. Timely shotcrete sealing of the face is the first step in stabilizing it; however, for extremely fractured soft rock, simple surface sealing is often insufficient to prevent the continued deterioration and deformation of the deeper surrounding rock. Therefore, advance grouting reinforcement technology for the face has been widely used. This technology aims to inject grout into the surrounding rock in front of the face to form a "reinforced arch" with a certain strength and thickness, thereby improving the integrity and self-stabilizing capacity of the surrounding rock. Currently, commonly used advance grouting reinforcement methods still have significant shortcomings when dealing with extremely fractured soft rock. These shortcomings mainly manifest in the high viscosity and poor permeability of commonly used cement-based grouts, making it difficult to effectively inject into micro-fractures. While some chemical grouts have good permeability, they suffer from problems such as difficulty in controlling gelation time, low strength of the aggregate, or poor environmental friendliness, failing to meet the needs of both rapid sealing and long-term reinforcement.

[0004] For the reasons mentioned above, there is an urgent need to develop a targeted, systematic, and material-compatible method for pre-reinforcement of the tunnel face in extremely fractured soft rock tunnels, in order to overcome the limitations of existing technologies in terms of grouting reinforcement effect, material properties, and construction technology, and to provide reliable technical support for the safe and efficient excavation of extremely fractured soft rock tunnels. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock tunnels, in order to overcome the challenge of preventing collapse and instability at the tunnel face in extremely fractured soft rock tunnels.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for pre-treatment chemical grouting reinforcement of the tunnel face in extremely fractured soft rock, characterized by the following steps: 【1】Installation of grouting conduit: After the tunnel excavation is completed, the tunnel face is sealed with shotcrete; the positions of the advanced grouting holes are marked on the tunnel face, and holes are drilled in a staggered arrangement of long and short grouting pipes, and long and short grouting pipes are installed. [2] Grouting pipe connection: The exposed end of the grouting conduit is sealed and connected to the output port of the four-way connector. The three input ports of the four-way connector are respectively connected to three independently controlled A grout pipe, B grout pipe and water pipe. [3] Sealing operation; [4] Grouting: Slurry A and slurry B are injected simultaneously in a 1:1 ratio. Slurry A is an isocyanate aqueous solution with a density of 1.05±0.05 g / cm3, and slurry B is a combined polyether aqueous solution with a density of 1.23±0.05 g / cm3. The solidification time of the mixed slurry is 15 to 20 seconds, the expansion ratio is 22 to 25 times, and the bonding strength is ≥3.0 MPa. The grouting process is as follows: first grout the short holes, then grout the long holes. When grouting each hole, start from the left and then the right, alternating between left and right. Finally, grout the middle hole. Limited grouting is used for each hole. The grouting process is an intermittent grouting method, and the pumping pressure is kept constant.

[0007] The special feature of the above-mentioned advanced chemical grouting reinforcement method for the tunnel face of extremely broken soft rock is that: in step [1], the long grouting pipe is a Φ42~Φ50 small pipe with a length of 5~6m, which is drilled first and then installed.

[0008] The special feature of the above-mentioned advanced chemical grouting reinforcement method for the tunnel face of extremely broken soft rock is that: in step [1], the length of the short grouting pipe is 3~4m, and Φ32~Φ40 hollow grouting anchor rods are used, and the installation is completed by self-drilling installation process; or Φ42~Φ50 small pipes are used, and holes are drilled first and then installed.

[0009] The special feature of the above-mentioned advanced chemical grouting reinforcement method for the tunnel face of extremely broken soft rock is that: in step [4], the grouting volume of each long hole is about 250~300kg, and the pumping pressure is controlled at 7.5-8.5MPa; the grouting method is to start the pump for 3 minutes and stop the pump for 25 seconds each time, and then repeat the cycle.

[0010] The special feature of the above-mentioned advanced chemical grouting reinforcement method for the tunnel face of extremely broken soft rock is that: in step [4], the grouting volume of each short hole is about 50~70kg, and the pumping pressure is controlled at 7.5-8.5MPa; the grouting method is to start the pump for 3 minutes and stop the pump for 25 seconds each time, and then repeat the operation.

[0011] The above-mentioned method for advanced chemical grouting reinforcement of tunnel face in extremely fractured soft rock is characterized by the following: in step [1], the hole positions of the short grouting pipe are taken from the reserved holes of the steel frame arch near the tunnel face as the holes for advanced grouting. The number of holes is 6, and they are evenly distributed in a circumferential manner.

[0012] The above-mentioned method for advanced chemical grouting reinforcement of tunnel face in extremely fractured soft rock is characterized by the following: in step [1], the holes of the long grouting pipe are obtained by using the reserved holes of the steel frame arch near the tunnel face as the holes for advanced grouting. The number of holes is 7, and they are evenly distributed in a circumferential manner.

[0013] The special feature of the above-mentioned advanced chemical grouting reinforcement method for the face of extremely broken soft rock tunnels is that the drilling and installation requirements of the grouting guide pipe in step [1] are as follows: the external insertion angle of the short grouting guide pipe hole is 25-30°, and the external insertion angle of the short grouting guide pipe hole is 15-20°; an overflow hole is drilled at the front end of the guide pipe 3m, and no hole is drilled in the remaining part of the tail end.

[0014] The special feature of the above-mentioned advanced chemical grouting reinforcement method for the tunnel face of extremely broken soft rock is that: during the sealing operation in step [3], sprayed grout, cement grout or grout is used to seal the cracks around the grouting hole to avoid leakage of grout during the grouting process.

[0015] The beneficial technical effects of the present invention are as follows: (1) The present invention achieves effective coverage of reinforcement depth and range. By adopting the strategy of staggered arrangement of 3~4m and 5~6m advanced grouting pipes, a reinforcement technology system combining long and short pipes and large and small angles is formed, which effectively overcomes the defects of limited reinforcement effect and easy generation of reinforcement blind spots of traditional single-length grouting pipes.

[0016] (2) This invention uses a combined polyether polyol chemical grout, which has low viscosity and strong permeability, and can be effectively injected into the micro-cracks in extremely broken soft rock. Not only is the gelation time controllable, but it also has sufficient long-term strength and durability after curing, which can provide a lasting reinforcement effect for the surrounding rock and meet the safety requirements of the tunnel throughout its entire life cycle. During grouting, the isocyanate and combined polyether materials are transported to the end of the small guide pipe or the hollow grouting anchor rod through independent pipelines for mixing, and then pumped into the pipeline under pressure. The materials fill the gaps in the surrounding rock through the foaming of the mixture, and form a whole by good cementing of the loose rock mass, thereby improving the stability of the tunnel face. During the grouting process, an intermittent limited injection method (pump start for 3 minutes, pump stop for 25 seconds) is used in conjunction with precise pumping pressure control (about 8MPa), which fundamentally solves the common problems of grout leakage, grout runoff and pressure runaway in the traditional cement-based grouting process, ensuring the grouting quality and the uniformity of the stone body. Attached Figure Description

[0017] Figure 1 This is a diagram showing the distribution of pre-grouting holes at the tunnel face in an example of the present invention. Figure 2 This is a schematic diagram of the insertion angle of the pre-grouting guide pipe at the tunnel face in an example of the present invention; Figure 3 This is a schematic diagram of the assembly of the sleeve valve pipe and the grouting conduit in an example of the present invention; Figure 4 This is a schematic diagram of the connection of the four-way joint during tunnel pre-grouting in an example of the present invention; Figure 5 These are photos of the tunnel face sealing and drilling site in an example of the present invention; Figure 6 These are photos of the tunnel face grouting site in an example of the present invention; Figure 7 These are photos showing the on-site consolidation effect of advanced chemical grouting at the tunnel face in an example of this invention. Figure 8 This is a comparison diagram of convergence deformation in a typical area of ​​the present invention, showing the difference between chemical grouting reinforcement and no grouting reinforcement. Figure 9 This is a comparison diagram of the strength of specimens obtained in a typical region of the present invention and specimens in an unreinforced region.

[0018] Attached reference numerals: 1-Short guide pipe hole position; 2-Long guide pipe hole position; 3-Short grouting guide pipe; 4-Long grouting guide pipe; 5-Steel arch frame; 6-Sleeve valve pipe; 7-Quick connector for sleeve valve pipe; 8-Connecting sleeve; 9-A Grout pipe; 10-B Grout pipe; 11-Water pipe; 12-Four-way connector. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0020] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0021] This invention provides a method for pre-treatment chemical grouting reinforcement of the tunnel face in extremely fractured soft rock, the specific steps of which are as follows: 【1】Installation of grouting conduit: After tunnel excavation, the tunnel face is sealed with shotcrete. The locations of the pre-grouting holes are marked on the face, and holes are drilled using a staggered arrangement of long and short grouting guide pipes. Long grouting guide pipes (5-6m in length, Φ42-Φ50) are drilled first and then installed. Short grouting guide pipes (3-4m in length) are installed using Φ32-Φ40 hollow grouting anchors via a self-drilling process; alternatively, Φ42-Φ50 guide pipes are drilled first and then installed. The external insertion angle of the short grouting guide pipe holes is 25-30°, and that of the short grouting guide pipe holes is 15-20°. Overflow holes are drilled 3m from the front end of the guide pipes, and no holes are drilled in the remaining tail section.

[0022] [2] Grouting pipe connection: The exposed end of the grouting conduit is sealed and connected to the output port of the four-way connector. The three input ports of the four-way connector 12 are respectively connected to three independently controlled A grout pipe 9, B grout pipe 10 and water pipe 11. 【3】Sealing operation: All cracks around the grouting hole must be sealed to prevent material leakage during the grouting process; the sealing method can be sprayed grout, cement grout, or chemical grouting. [4] Grouting: Slurry A and slurry B are injected simultaneously in a 1:1 ratio. Slurry A is an isocyanate aqueous solution with a density of 1.05±0.05 g / cm3, and slurry B is a combined polyether aqueous solution with a density of 1.23±0.05 g / cm3. The solidification time of the mixed slurry is 15 to 20 seconds, the expansion ratio is 22 to 25 times, and the bonding strength is ≥3.0 MPa. The grouting process is as follows: first grout the short holes, then the long holes, alternating between left and right sides, and finally grouting the middle holes. Limited grouting is used per hole, and the grouting process is intermittent, with the pumping pressure kept constant. When grouting long holes, the total grouting volume per hole is approximately 250-300 kg, and the pumping pressure is controlled at 7.5-8.5 MPa. The grouting method involves starting the pump for 3 minutes and stopping it for 25 seconds, repeating this cycle. When grouting short holes, the total grouting volume per hole is approximately 50-70 kg, and the pumping pressure is controlled at 7.5-8.5 MPa. The grouting method also involves starting the pump for 3 minutes and stopping it for 25 seconds, repeating this cycle.

[0023] The specific solution of the present invention will be described below with reference to the accompanying drawings and embodiments, taking the Munjino Brdo Tunnel in Serbia as an example.

[0024] The construction steps for the advanced chemical grouting reinforcement of the tunnel face are as follows: 【1】Installation of grouting conduit: like Figure 1As shown, the reserved holes of the steel arch frame 5 near the working face are used as the sampling points for the advanced drilling and grouting holes. There are 6 holes at the 4m short guide pipe hole position 1, which are evenly distributed in a circumferential direction with a hole spacing of about 1.71m. There are 7 holes at the 6m long guide pipe hole position 2, which are evenly distributed in a circumferential direction with a hole spacing of about 1.71m. like Figure 2 As shown, a rock drilling rig was used for drilling. The short grouting guide pipe 3 is a Φ32 hollow grouting anchor rod, which was installed using a self-drilling installation process. The long grouting guide pipe 4 is a Φ42 grouting guide pipe, which was installed using a Φ57 drill bit to drill holes first and then install them. The short grouting guide pipe 3 has an external insertion angle of 30°, and the long grouting guide pipe 4 has an external insertion angle of 20°. The front 3m of both the short grouting guide pipe 3 and the long grouting guide pipe 4 are drilled with overflow holes according to the small guide pipe hole layout requirements, and the remaining tail section is not drilled.

[0025] Once the rock drilling platform is ready, the self-drilling installation of the grouting pipes can begin one hole at a time, proceeding from bottom to top. First, the drilling of the Φ32 hollow grouting anchor rod 3 in hole 1 (4m) is completed. Then, the anchor rod remains in place until the grouting of hole 1 (4m) is finished. After that, the drilling of the Φ42 grouting guide pipe 4 in hole 2 (6m) begins.

[0026] The external insertion angle of the 4m hole is 25-30°, and the external insertion angle of the 6m hole is 15-20°; an overflow hole is drilled at the front 3m of the guide pipe, and no hole is drilled at the rear; after the rock platform vehicle is ready, the drilling and installation of the grouting pipe can be started one hole at a time in the order from bottom to top. First, the drilling of the 3-4m grouting guide pipe is completed, and then it stands still. After the installation of the 3-4m grouting guide pipe is completed, the drilling of the 5-6m grouting guide pipe begins. If pipe blockage or grout leakage occurs during the process, the corresponding grouting guide pipe must be reinstalled; the exposed length of the pre-grouting guide pipe after installation should not be less than 10cm to facilitate the installation and welding of the sleeve valve pipe 6. If obstacles such as steel frames are encountered during drilling, the drilling position can be adjusted appropriately and the hole can be re-drilled; [2] Grouting pipe connection: like Figure 3 As shown, the quick connector 7 of the Φ12 sleeve valve pipe 6 is welded to the connecting sleeve 8 of the Φ32 hollow grouting anchor rod 3, and the internal space of the Φ32 hollow grouting anchor rod 3 is used as the grouting channel. After the connecting sleeve 8 is installed on the Φ32 hollow grouting anchor rod 3, the gap is sealed tightly by welding. The requirements for the assembly and welding of the sleeve valve pipe are as follows: the quick connector of the Φ12 sleeve valve pipe is connected to the connecting sleeve 8 of the grouting conduit by welding, and the internal space of the grouting conduit is used as the grouting channel; after the connecting sleeve 8 is installed on the grouting conduit, the gap is sealed tightly by welding.

[0027] 【3】Sealing operation: All cracks around the grouting hole must be completely sealed to prevent material leakage during the grouting process; sealing methods include spraying grout, cement grout, and chemical grouting. [4] Grouting: The grouting material is a combination of polyether polyols, which is a mixture of isocyanate (A grout) and combination polyether (B grout) in a 1:1 volume ratio. The grout densities of the two grouts are (1.05±0.05) g / cm3 for component A and (1.23±0.05) g / cm3 for component B. The curing time of the A / B grout mixture is 15 to 20 seconds, the expansion ratio of the A / B grout is 22 to 25 times, and the bonding strength is ≥3.0 MPa.

[0028] Before using the chemical irrigation pump, it must be carefully inspected to ensure that it is intact, fully functional, bolts are tightened, all slurry inlet and outlet pipes are unobstructed, the slurry outlet cylinder is sealed and leak-free, there are no residual impurities in the slurry outlet working cylinder, the lubricating oil cup is filled with machine oil or hydraulic oil, and gear oil must not be added. Check whether the air filter element in the pneumatic three-piece set is contaminated. If it is contaminated or blocked, clean it repeatedly with canned rust remover. Before starting the air compressor, carefully check whether the air compressor is operating normally and whether the pressure meets the working pressure requirements of the grouting pump. Before connecting the power air source pipeline, open the valve first, blow out the debris from the pipeline, and then connect the air pipe, tie it tightly, and slowly open the air valve of the chemical grouting pump. Observe the dripping oil situation at the transparent display on the top of the oiler. Adjust it to about 15-20 drops per minute. During grouting, replenish the oil in a timely manner according to the oil level. The chemical grouting pump should not be run without oil for a long time. like Figure 4 As shown, the connecting pipes of the equipment should avoid being mixed. All isocyanate pipes 9 should be identified by wrapping both ends and the connected cylinders with red insulating tape. All polyether pipes 10 should be identified by wrapping both ends and the connected cylinders with several turns of white insulating tape. After the commissioning is completed, lead the three grouting pipes (isocyanate, polyether and water pipes 11) of the grouting pump to the quick connector. Connect the three feed pipes to the mixing valve of the four-way connector 12. Connect the discharge port to the Φ12 sleeve valve pipe 6 through the quick connector. During the grouting process, the water pipe 11 only needs to be connected and kept sealed.

[0029] Before assembly, all threaded connections and Φ12 sleeve valve quick connectors 7 of the slurry discharge system must be coated with grease for easy disassembly. All quick connectors must be equipped with O-ring seals. After connecting all pipes, close the isocyanate and polyether valves at the pump outlet, open the pressure relief valves of the isocyanate and polyether, insert the pressure relief pipes into the tanks according to the markings, open the air supply valve, and run the chemical injection pump to completely expel the air from the slurry inlet pipe and the tank. Use visual inspection or container measurement to check whether the slurry discharge rates of the isocyanate and polyether groups are consistent. Under normal circumstances, the slurry discharge piston should discharge the same amount of slurry when moving up and down. If any inconsistency occurs, the cause should be identified and the fault eliminated immediately until normal slurry discharge is achieved. After commissioning, the three grouting pipes (isocyanate, polyether, and water pipes) of the grouting pump are led to the quick connector. The three feed pipes are connected to the mixing valve of the four-way connector. The discharge port is connected to the sleeve valve pipe through the quick connector. The main function of the water pipe is to clean the pipe. During the grouting process, it is only necessary to connect the pipe and keep it sealed. The water does not participate in the entire grouting process. After the grouting pump is debugged, the two materials, isocyanate and polyether, are transported to the end of the small guide pipe or hollow grouting anchor through independent pipelines for mixing. The mixture is then pumped into the pipeline. The mixed foam fills the gaps in the surrounding rock, effectively cementing the loose rock mass into a whole and improving the stability of the working face. During grouting, first grout the 4m hole 1, alternating between left and right, and finally grout the middle hole. A limited amount of grout is used per hole, with a total grouting volume of approximately 66.6KG per hole. When grouting the 6m hole 2, alternate between left and right, and finally grout the middle hole. A limited amount of grout is used per hole, with a total grouting volume of approximately 300KG per hole. During the grouting process, the two materials are transported through independent pipelines to the end of the Φ32 hollow grouting anchor rod 3 or the Φ42 grouting conduit 4 for mixing, and then pumped into the pipeline under pressure. When there is no significant change in grouting pressure and flow rate, based on field experimental data, pause for approximately 25 seconds, then resume pumping for 5 minutes. When there is still no significant change in grouting pressure and flow rate, pause again and resume pumping. Repeat this process multiple times until the set pressure is reached and the process ends.

[0030] During grouting, holes of two different depths are grouted sequentially. If cross-grouting occurs between adjacent holes during the grouting process, the grouting volume of the current grouting hole should be increased appropriately, but not more than twice the rated volume. The grouting effect is evaluated by comprehensively analyzing factors such as cross-grouting, leakage, grouting volume, and grouting pressure. If necessary, holes are drilled again for supplementary grouting until the expected purpose is achieved.

[0031] like Figures 5-7As shown, the above-described embodiment of the present invention has been applied to the T3 tunnel of the E76 highway in Serbia. The present invention achieves effective coverage of reinforcement depth and range. By employing a strategy of alternating long and short grouting conduits (3-4m and 5-6m), a reinforcement technology system combining long and short sections and large and small angles is formed, effectively overcoming the shortcomings of traditional single-length grouting conduits, such as limited reinforcement effect and the tendency to create reinforcement blind spots. The combined polyether polyol (foaming type) chemical grout used in this invention has low viscosity and strong permeability, which can effectively inject into the micro-fractures in extremely broken soft rock. Not only is the gelation time controllable, but it also has sufficient long-term strength and durability after curing, providing a lasting reinforcement effect for the surrounding rock and meeting the safety requirements of the tunnel throughout its entire life cycle. At the same time, by pre-inserting foaming material at the orifice for sealing and using an intermittent limited injection method (3 minutes of pump start-up, 25 seconds of pump stop-up) combined with precise pumping pressure control (approximately 8MPa), the problems of grout leakage, grout runoff, and pressure runaway commonly encountered in traditional cement-based grouting processes are fundamentally solved, ensuring grouting quality and the uniformity of the stone body.

[0032] In the Munijo Brdo tunnel in Serbia, loose deposits randomly exist at the top of the tunnel face. Even with a "bowl-sized" open face during excavation, these loose deposits can slide downwards, sometimes even dragging the core soil along with them. The surrounding rock is thin-layered, with thicknesses measured in millimeters, and the interlayer contact surfaces are smooth and unbonded. When an open face appears during excavation, the surrounding rock peels off layer by layer. If not sealed in time, this can easily cause the tunnel face to collapse, posing significant challenges to excavation and initial support construction.

[0033] This patented advanced chemical grouting reinforcement technology has been fully applied in the construction of a fractured soft rock section hundreds of meters long at the exit of the Munijo Brdo tunnel. Figure 5-7 (As shown). Field application and test results show that: I. Chemical grouting uses isocyanate (BASF brand from Germany) and polyether in a 1:1 ratio to generate polyether polyol. This material has a fast reaction speed, good permeability, and certain bonding strength, and is particularly suitable for cementing and reinforcing fault fracture zones in tunnels.

[0034] Second, the use of advanced polyurethane chemical grouting effectively suppressed extrusion deformation and collapse instability at the tunnel face, providing a safe and stable working environment for excavation and support operations. Statistics show that the success rate of tunnel excavation cycles (referring to cycles where no significant collapse occurs at the tunnel face and excavation and support advance is successfully achieved) has steadily increased from less than 80% under traditional support to over 98%.

[0035] III. After chemical grouting pre-reinforcement, the tunnel convergence deformation rate decreases rapidly, and the stabilization time is shortened. Figure 8The cumulative convergence deformation was successfully controlled within 85% of the design-reserved deformation value, effectively preventing the initial support structure from being encroached upon or damaged due to excessive deformation, and meeting the strict requirements of EU tunnel construction specifications for deformation control.

[0036] IV. The average compressive strength of the polyurethane-rock composite consolidated specimens obtained from on-site core sampling reached 12.8 MPa (n=5, standard deviation ±1.2 MPa), which is far higher than the strength of undisturbed fractured shale (usually <2 MPa). Figure 9 This demonstrates its significant advantages and potential in forming a high-strength surrounding rock "bearing ring".

[0037] V. Due to the unique advantages of polyurethane grout, such as short curing time and no need for maintenance, excavation can be organized immediately after grouting, achieving "zero waiting time." Compared with the curing waiting time of more than 12 hours required for traditional cement grouting, the average single-cycle operation time (including support) is shortened by about 40% (Table 1). This significantly increases the average monthly progress and fundamentally alleviates the pressure on the construction schedule.

[0038] Table 1. Comparison of single-cycle man-hours for tunnels using new and old grouting materials and processes. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for pre-treatment chemical grouting reinforcement of the tunnel face in extremely fractured soft rock, characterized in that, Includes the following steps: 【1】Installation of grouting conduit: After the tunnel excavation is completed, the tunnel face is sealed with shotcrete; the positions of the advanced grouting holes are marked on the tunnel face, and holes are drilled in a staggered arrangement of long and short grouting pipes, and long and short grouting pipes are installed. [2] Grouting pipe connection: The exposed end of the grouting conduit is sealed and connected to the output port of the four-way connector. The three input ports of the four-way connector are respectively connected to three independently controlled A grout pipe, B grout pipe and water pipe. [3] Sealing operation; [4] Grouting: Slurry A and slurry B are injected simultaneously in a 1:1 ratio. Slurry A is an isocyanate aqueous solution with a density of 1.05±0.05 g / cm3, and slurry B is a combined polyether aqueous solution with a density of 1.23±0.05 g / cm3. The solidification time of the mixed slurry is 15 to 20 seconds, the expansion ratio is 22 to 25 times, and the bonding strength is ≥3.0 MPa. The grouting process is as follows: first grout the short holes, then grout the long holes. When grouting each hole, start from the left and then the right, alternating between left and right. Finally, grout the middle hole. Limited grouting is used for each hole. The grouting process is an intermittent grouting method, and the pumping pressure is kept constant.

2. The method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock according to claim 1, characterized in that: Step [1] For medium-length grouting pipes with a length of 5~6m, drill holes first and then install them.

3. The method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock according to claim 1, characterized in that: In step [1], the length of the short grouting pipe is 3~4m. Φ32~Φ40 hollow grouting anchor rods are used and the installation is completed by self-drilling installation process; or Φ42~Φ50 small pipes are used, and holes are drilled first and then installed.

4. The method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock according to claim 1, characterized in that: In step [4], the total injection volume per hole is approximately 250-300 kg, and the pumping pressure is controlled at 7.5-8.5 MPa. The injection method is to start the pump for 3 minutes and stop the pump for 25 seconds each time, and repeat the cycle.

5. The method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock according to claim 1, characterized in that: In step [4], when grouting the short holes, the total grouting volume per hole is about 50~70kg, and the pumping pressure is controlled at 7.5-8.5MPa; the grouting method is to start the pump for 3 minutes and stop the pump for 25 seconds each time, and then repeat the cycle.

6. The method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock according to claim 1, characterized in that: In step [1], the holes of the short grouting pipe are obtained by using the reserved holes of the steel frame arch near the working face as the holes for the advanced grouting holes. The number of holes is 6, and they are evenly distributed in a circumferential manner.

7. The method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock according to claim 1, characterized in that: In step [1], the holes of the medium-length grouting pipe are obtained by using the reserved holes of the steel frame arch near the working face as the holes for the advance grouting holes. The number of holes is 7, and they are evenly distributed in a circumferential manner.

8. The method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock according to claim 1, characterized in that: The requirements for drilling and installing the grouting conduit in step [1] are as follows: the external insertion angle of the short grouting conduit hole is 25-30°, and the external insertion angle of the short grouting conduit hole is 15-20°; an overflow hole is drilled at the front end of the conduit for 3m, and no hole is drilled in the remaining part of the tail end.

9. The method for advanced chemical grouting reinforcement of the tunnel face in extremely fractured soft rock according to claim 1, characterized in that: Step [3] During the sealing operation, use sprayed grout, cement grout or grout to seal the cracks around the grouting hole to prevent grout leakage during the grouting process.

Images