Pre-splitting type TBM tunnel construction method

Abstract

The invention relates to the technical field of tunnel engineering, and discloses a pre-splitting type TBM tunnel construction method. The problems that in the prior art, high-strength rocks are harden by means of cutters, but the cutter consumption is increased sharply, and the tunneling speed is low are solved; the surrounding rock in front of a tunnel face is weakened through small-diameter drilling charge blasting, however, resonance damage of TBM equipment is likely to be caused by blasting vibration, rock blocks in the high-stress surrounding rock after blasting are scattered and possibly block a cutterhead, and potential safety hazards exist. The technical problems that high-pressure water jet or chemical reagents are used for softening rocks, but the high-strength rocks are poor in permeability, the softening effect is limited, and the groundwater environment is possibly polluted are solved. The method comprises the following steps: (1) geological investigation and presplitting area positioning; (2) drilling a horizontal well; (3) perforation fracturing operation; (4) forming a weakening zone; and (5) normal tunneling of the TBM. According to the method, through accurate positioning of the horizontal well and the perforation, the pre-splitting action range is strictly limited to a high-strength rock section in front of a TBM cutterhead, and excessive disturbance to a non-target area is avoided.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, and in particular to a pre-splitting TBM tunnel construction method. Background Technology

[0002] As a core piece of equipment in modern tunnel construction, TBMs are widely used in hard rock tunnel projects in railways, water conservancy, and mining due to their continuous excavation, high degree of automation, and excellent forming quality. However, under geological conditions with high surrounding rock integrity (such as high-strength rocks like granite and basalt) and uniaxial compressive strength exceeding 150 MPa, TBM cutters are prone to abnormal wear or even breakage due to concentrated impact loads, significantly reducing the efficiency of cutter rock breaking (more than 50% lower than conventional medium-hard rock excavation speed). At the same time, the strong self-stability of the surrounding rock makes it difficult to implement traditional advanced blasting or loosening pre-splitting methods (blasting may cause excessive fragmentation of the surrounding rock or the risk of TBM jamming).

[0003] Existing solutions mainly include: 1. Conventional TBM direct tunneling: Relying on the cutterhead to withstand high-strength rock, but cutter consumption increases dramatically (the cost of replacing cutterheads per kilometer can reach several million yuan), and the tunneling speed is slow (monthly advance is often less than 100 meters); 2. Pre-drilling + loosening blasting: Weakening the surrounding rock in front of the tunnel face by blasting with explosives through small-diameter boreholes, but blasting vibrations can easily cause resonance damage to the TBM equipment, and the flying rock fragments after blasting in high-stress surrounding rock may clog the cutterhead, posing a safety hazard; 3. Hydraulic fracturing or chemical softening: Softening the rock using high-pressure water jets or chemical reagents, but limited by the poor permeability of high-strength rocks (e.g., the permeability coefficient of granite is usually less than 10⁻). 6 (cm / s), with limited softening effect and potential pollution of groundwater environment.

[0004] Chinese patent document 202410984419.9 discloses a decision-making method and computer equipment for TBM tunneling parameters based on advanced drilling. This invention is based on the principle that advanced drilling data and TBM parameters are consistent. It integrates and analyzes advanced drilling data with TBM tunneling parameters, using tunnel rock mass parameters as a link, to establish an advanced prediction model for TBM tunneling parameters near the tunnel face based on advanced drilling data. This enables advanced decision-making of TBM operating parameters during near-face construction, improving the safety of TBM tunneling in fractured zones, jammed strata, and other challenging terrains.

[0005] However, the above-mentioned solutions have at least the following technical problems during implementation: relying on cutting tools to withstand high-strength rock results in a surge in tool consumption and slow tunneling speed; weakening the surrounding rock in front of the tunnel face through small-diameter borehole blasting is problematic because blasting vibrations can easily cause resonance damage to the TBM equipment, and the flying rock fragments after blasting in high-stress surrounding rock may clog the cutterhead, posing a safety hazard; using high-pressure water jets or chemical reagents to soften the rock is limited by the poor permeability of high-strength rock, resulting in limited softening effects and potential groundwater pollution. Therefore, there is an urgent need to propose a pre-splitting TBM tunnel construction method. Summary of the Invention

[0006] In view of the above technical problems, this disclosure provides a pre-splitting TBM tunnel construction method, which solves the problems of existing technologies that rely on cutting tools to withstand high-strength rock, but the consumption of cutting tools increases sharply and the tunneling speed is slow; using small-diameter boreholes to charge explosives to weaken the surrounding rock in front of the tunnel face, but the blasting vibration can easily cause resonance damage to the TBM equipment, and the scattering of rock fragments after blasting in high-stress surrounding rock may block the cutterhead, posing a safety hazard; using high-pressure water jets or chemical reagents to soften the rock, but the softening effect is limited by the poor permeability of high-strength rock, and may pollute the groundwater environment.

[0007] According to one aspect of this disclosure, a method for constructing a pre-splitting TBM tunnel is provided, comprising the following steps: (1) Geological exploration and pre-splitting area location: Explore the surrounding rock in front of the tunnel axis, identify and locate the high-strength rock area with a uniaxial compressive strength of not less than 120MPa; (2) Drilling of horizontal wells: Drill at least one horizontal well along the tunnel axis, the trajectory of which passes through the high-strength rock area described in step (1); (3) Perforation and fracturing operation: Perforate the high-strength rock area in step (1) in the horizontal well described in step (2) and inject fracturing fluid into the perforation channel to generate a fracture network in the high-strength rock area; (4) Formation of weakened zone: After the crack network in step (3) has expanded and stabilized, a filler is injected into the crack network. After the filler solidifies, it forms a weak connection zone with a strength lower than that of the original rock, in order to reduce the direct rigid contact stress between the TBM cutterhead and the surrounding rock. (5) TBM normal tunneling: After completing the construction of the weak connection zone structure in step (4), the TBM advances through the rock mass containing the weak connection zone.

[0008] In some embodiments of this disclosure, in step (1) geological exploration and positioning, the high-strength rock area identified and located is a continuous rock segment with a length of not less than 5 meters or a local hard rock protrusion.

[0009] In some embodiments of this disclosure, in step (2) horizontal well drilling, the horizontal well is drilled from the surface above or to the side of the tunnel design axis or directly from the TBM face.

[0010] In some embodiments of this disclosure, in step (2) of horizontal well drilling, directional drilling is used, and the diameter of the horizontal well is 100 mm to 200 mm.

[0011] In some embodiments of this disclosure, in step (3) perforation fracturing operation, the perforation positions are evenly distributed along the circumference of the horizontal well, the perforation spacing is 0.5 meters to 1 meter, the diameter of the formed perforation channel is 5 meters to 10 meters, and the depth of the perforation channel is 1 meter to 3 meters to penetrate the well wall and enter the surrounding rock.

[0012] In some embodiments of this disclosure, in step (4) weakening zone formation, the filler is a low elastic modulus material, including bentonite cement slurry mixture, resin-based binder, or foamed concrete slurry.

[0013] The beneficial effects of this invention are as follows: This invention infers the changes and development trends of internal external loads based on changes in rock mass velocity; This invention can directly obtain the changes and trends of local rock mass velocity, which is more scientific than manual judgment and does not rely on experience. This invention can effectively prevent the collapse of the surrounding rock at the support shoe location and improve tunneling efficiency.

[0014] Directional pre-fracture control: Through precise positioning of horizontal wells and perforations, the pre-fracture range is strictly limited to the high-strength rock section in front of the TBM cutterhead, avoiding excessive disturbance to non-target areas (such as weak interlayers or weakened surrounding rock); Filler compatibility: The filler selection takes into account both "weakening effect" and "long-term stability" - low elastic modulus ensures reduced contact stress, while having a certain strength (to prevent excessive collapse of the pre-cracked zone and blockage of the cutter head gap). Advanced pre-splitting coordination: The advanced layout of horizontal wells (50~100m ahead of the tunnel face) is matched with the TBM tunneling speed to achieve a continuous operation mode of "pre-splitting while tunneling" and ensure construction efficiency.

[0015] Improved tunneling efficiency: By pre-splitting and weakening high-strength surrounding rock, the rock-breaking load of the TBM cutter is significantly reduced, and the tunneling speed is increased by 30% to 100% (depending on the strength of the surrounding rock). Extended equipment lifespan: The risk of abnormal tool wear and breakage is significantly reduced, and the maintenance cycle is extended (the number of tool replacements per kilometer is reduced by more than 50%). Enhanced safety: Avoids the vibration damage and rock fragment scattering risks of traditional blasting pre-splitting, and is suitable for stable construction of high-stress, deep-buried tunnels; Wide adaptability: The fracturing parameters and filler type can be adjusted for different strengths of surrounding rock (120~300MPa), and it is compatible with various TBM models (open type, double shield, etc.).

[0016] This invention solves the industry problems of high tool wear and low tunneling efficiency in hard rock TBM construction through the innovative approach of "advanced pre-splitting + precise weakening", and has significant engineering application value and promotion prospects.

[0017] This invention breaks through the limitations of traditional TBMs that passively deal with hard rock. By conducting advanced geological surveys, it accurately locates high-strength rock strata and actively pre-splitting and weakens them, transforming the uncertainty of construction into controllability.

[0018] By creating an artificial weak connection zone in front of the cutterhead, the peak load and vibration impact during TBM rock breaking are greatly reduced, thus effectively protecting the expensive cutterheads, reducing the number of cutter replacements and downtime, and significantly improving the overall tunneling efficiency.

[0019] Pre-splitting treatment makes the rock fragments more uniform in size, effectively avoiding problems such as cutter jamming, chamber jamming, and blockage of the conveying system caused by oversized rock masses, ensuring the smooth operation of the slag removal system, and further stabilizing the tunneling pace.

[0020] Although the pre-treatment process is added, the resulting increase in tunneling speed, decrease in tooling costs, and shortened construction period lead to comprehensive economic benefits that far outweigh the investment. This method is particularly suitable for long-distance, deep-buried, high-strength rock tunnel projects. Attached Figure Description

[0021] Figure 1 This is a flowchart of the construction method for pre-splitting TBM tunnels; Detailed Implementation

[0022] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention. Example 1

[0023] This example discloses a pre-splitting TBM tunnel construction method. (See also...) Figure 1 , Includes the following steps: (1) Geological exploration and pre-splitting area location: Explore the surrounding rock in front of the tunnel axis, identify and locate the high-strength rock area with a uniaxial compressive strength of not less than 120MPa; (2) Drilling of horizontal wells: Drill at least one horizontal well along the tunnel axis, with the trajectory of the horizontal well passing through the high-strength rock area in step (1); (3) Perforation and fracturing operation: In step (2), perforation is performed in the horizontal well targeting the high-strength rock area in step (1), and fracturing fluid is injected into the perforation channel to generate a fracture network in the high-strength rock area; (4) Formation of weakened zone: After the crack network in step (3) has expanded and stabilized, filler is injected into the crack network. After the filler solidifies, a weak connection zone with a strength lower than that of the original rock is formed to reduce the direct rigid contact stress between the TBM cutterhead and the surrounding rock. (5) TBM normal tunneling: After completing the construction of the weak connection zone structure in step (4), the TBM advances through the rock mass containing the weak connection zone.

[0024] In step (1) geological exploration and positioning, the high-strength rock area identified and located is a continuous rock segment with a length of not less than 5 meters or a local hard rock protrusion.

[0025] In step (2) horizontal well drilling, the horizontal well is drilled from the surface above or to the side of the tunnel design axis or directly from the TBM face.

[0026] In step (2), directional drilling is used in the horizontal well drilling, and the diameter of the horizontal well is 100 mm to 200 mm.

[0027] In step (3) of the perforation fracturing operation, the perforation positions are evenly distributed along the circumference of the horizontal well, the perforation spacing is 0.5 meters to 1 meter, the diameter of the formed perforation channel is 5 meters to 10 meters, and the depth of the perforation channel is 1 meter to 3 meters to penetrate the well wall and enter the surrounding rock.

[0028] In step (4) the formation of the weakened zone, the filler is a low elastic modulus material, including bentonite cement slurry mixture, resin-based binder, or foamed concrete slurry.

[0029] Taking a highway tunnel project as an example (tunnel diameter 8m, traversing granite strata, uniaxial compressive strength 180~220MPa, local continuous hard rock section length 8~12m), the specific implementation steps are as follows: Step 1: Geological Survey Based on the results of core drilling and geophysical exploration before the TBM starts, it was determined that there are three continuous high-strength granite sections (10m, 8m and 12m in length, respectively) within 50-100m in front of the tunnel face, with a uniaxial compressive strength of 190MPa. The predicted cutter consumption for conventional TBM tunneling is ≥20 pieces / km, and the monthly advance is ≤80m.

[0030] Step 2: Horizontal Well Drilling A directional drilling rig is used to drill a horizontal well with a diameter of 150mm and a depth of 100m in front of the tunnel face on the ground surface directly above the tunnel design axis (buried at a depth of about 50m).

[0031] Step 3: Perforation fracturing For each high-strength rock section, perforations were carried out at corresponding locations on the horizontal wellbore (located using drilling survey data): four perforations were evenly distributed per meter of well section (0.5m spacing), with a diameter of 8mm and a depth of 2m (entering the surrounding rock). A water-based fracturing fluid was injected using a high-pressure pump set, and the pressure was gradually increased to 22MPa until the surrounding rock fractured, forming a radial microfracture network (fracture aperture 0.1~0.3mm, extension length 1~3m).

[0032] Step 4: Filler Injection After fracturing, a bentonite-cement mixture grout (bentonite:cement:water = 1:2:3, elastic modulus approximately 8 GPa, compressive strength 3 MPa) is injected. Pressure is controlled (0.5~1 MPa) to ensure the grout fully fills the cracks. After curing, a continuous weakly connected zone is formed (its strength is only 1 / 20 to 1 / 10 of the original rock).

[0033] Step 5: TBM Excavation After pre-splitting was completed, the TBM began tunneling. Actual measurement data showed that the average rock-breaking load of the cutters decreased from 1200kN under normal working conditions to 700kN (a decrease of 42%), the cutter wear rate decreased by 60% (the tunneling distance of a single cutter increased from 800m to 1300m), the monthly footage increased to 150m (an increase of 87.5% compared to normal working conditions), and there were no instances of cutter jamming or excessive fracturing of the surrounding rock.

[0034] Although some preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0035] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this application and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A pre-splitting TBM tunneling method, characterized by, The method comprises the following steps: (1) Geological survey and pre-splitting area positioning: survey the surrounding rock in front of the tunnel axis, identify and locate the high-strength rock area with uniaxial compressive strength not less than 120 MPa; (2) Drilling of horizontal well: drill at least one horizontal well along the direction of the tunnel axis, and the trajectory of the horizontal well passes through the high-strength rock area in step (1); (3) Perforation and fracturing operation: perforate the high-strength rock area in step (1) in the horizontal well in step (2), and inject fracturing fluid into the perforation hole to form a fracture network in the high-strength rock area; (4) Formation of weakening zone: after the fracture network in step (3) is stable, a filling agent is injected into the fracture network, and the filling agent forms a weak connection zone with lower strength than the original rock after solidification, so as to reduce the direct rigid contact stress between the TBM cutterhead and the surrounding rock; (5) Normal TBM tunneling: after the construction of the weak connection zone in step (4) is completed, the TBM advances through the rock mass containing the weak connection zone.

2. The presplitting TBM tunneling method of claim 1, wherein: In the step (1) of geological survey and positioning, the identified and located high-strength rock area is a rock section with a continuous length not less than 5 meters or a local hard rock protrusion.

3. The presplitting TBM tunneling method of claim 1, wherein: In the step (2) of drilling of horizontal well, the horizontal well is drilled from the ground surface above the tunnel design axis or above the side or directly drilled horizontally from the TBM working face.

4. The presplitting TBM tunneling method of claim 1, wherein: In the step (2) of drilling of horizontal well, directional drilling is used, and the diameter of the horizontal well is 100-200 mm.

5. The presplitting TBM tunneling method of claim 1, wherein: In the step (3) of perforation and fracturing operation, the perforation positions are uniformly distributed along the circumference of the horizontal well, the perforation interval is 0.5-1 m, the perforation hole diameter is 5-10 m, and the perforation hole depth is 1-3 m penetrating the well wall and entering the surrounding rock.

6. The presplitting TBM tunneling method of claim 1, wherein: In the step (4) of formation of weakening zone, the filling agent is a low elastic modulus material, including bentonite cement slurry mixture or resin-based cementing agent or foam concrete slurry.

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