Method for processing string-shaped boulders in subsurface tunnel based on cross-hole CT (Computed Tomography) accurate detection

Abstract

The invention discloses a subsurface tunnel string-shaped boulder treatment method based on cross-hole CT accurate detection, through combination of geological accurate detection and static controllable crushing, the stability of a tunnel face and a vault when a tunnel passes through a boulder development stratum is ensured, and through an advanced detection-static crushing-encrypted support three-in-one technology in a complex construction environment, the construction efficiency is improved. The requirement for safe and efficient treatment of string-shaped boulder groups of different scales is met, the inherent problem of safety of a vault and a tunnel face in the boulder treatment process is solved by adopting the cross-hole CT scanning, static crushing and dense small guide pipe supporting technology, and the safety of the vault and the tunnel face is guaranteed by adopting the three technical measures of geological transparent pretreatment, static silent crushing and active reinforcing and supporting. The problems of low construction efficiency, serious noise pollution and large surrounding rock disturbance existing in a traditional method are effectively solved. The method has the advantages of being safe in construction, efficient in treatment, economical, reasonable and the like, and plays a positive and important role in improving the urban underground excavation tunnel construction progress, guaranteeing the project quality and reducing the construction cost.

Description

Technical Field

[0001] This invention relates to the field of municipal underground space construction technology, specifically to a method for handling isolated boulders in mined tunnels based on precise cross-hole CT detection. Background Technology

[0002] With the rapid development of above-ground transportation and construction in China, above-ground space is approaching saturation. The number of underground space projects such as urban subways, underground stations, and water conservancy tunnels continues to increase. The cut-and-cover method has been widely used due to its many advantages, such as strong geological adaptability, flexible cross-sectional shape, high space utilization, and controllable disturbance to the surrounding environment. However, for the geological conditions of cut-and-cover tunnels, which are "unpredictable ahead," especially the high-strength string of isolated boulders hidden in soft and uneven strata such as granite residual layers, the traditional passive treatment mode of "excavation-revealing-pause-blasting-secondary decomposition-external disposal" is not only inefficient and causes serious delays, but also the strong mechanical vibration and smooth blasting are more likely to cause noise and air pollution, damage the soil structure, and lead to tunnel deformation and face instability. In cities, this can easily cause the risk of ground and building settlement. Solving these problems has become one of the most intractable technical challenges in the field of municipal underground space construction.

[0003] For example, Chinese invention patent application number CN201410704377.5 discloses a method for refined detection of isolated boulders in subway shield tunnel sections based on resistivity cross-hole CT, including: designing a scientific and reasonable borehole layout scheme in the unexcavated section ahead of the tunnel face; laying a resistivity cross-hole CT survey network, and adopting a detection scheme that combines two-dimensional general survey and three-dimensional detailed survey; using a new combined observation mode for data acquisition to obtain more effective information about isolated boulder anomalies; constructing a three-dimensional resistivity inversion objective function and inversion equation carrying a distance weighting function, and using a parallel analytical fast solution algorithm for the partial derivative matrix; forming a resistivity imaging result map of isolated boulder anomalies within the survey area, and combining it with existing geological analysis to infer the size, spatial distribution, and other information of the isolated boulders.

[0004] For example, Chinese invention patent application number CN202411216967.3 discloses a tunnel construction method applicable to urban underground boulder areas, which includes: step one, full-section grouting reinforcement of the soil at the tunnel face; step two, setting up advanced pipe roof support at the tunnel portal; and step three, horizontal drilling with down-the-hole hammer to remove the boulder.

[0005] For example, Chinese invention patent application number CN202510315318.7 discloses a method for detecting underground continuous walls in boulder strata by seismic wave cross-hole tomography and construction, including the following steps: boulder detection, blasting pre-decomposition and drilling of beaded boulder strata, depressurization and gas release and covering of the top of the blasting hole, and cleaning the wall and groove with a square hammer.

[0006] Existing technologies suffer from problems such as low efficiency, high safety risks, and large disturbances at the tunnel face due to traditional mechanical crushing methods. Based on the above-mentioned technical problems in existing technologies, this invention provides a method for handling string boulders in mined tunnels based on cross-hole CT precise detection. Summary of the Invention

[0007] To address the aforementioned technical problems in existing technologies, this invention provides a method for handling isolated boulders in mined tunnels based on precise cross-hole CT detection.

[0008] The present invention adopts the following technical solution: This invention provides a method for handling isolated boulders in mined tunnels based on precise cross-hole CT detection, comprising: Step 1: In front of the tunnel excavation face, parallel detection holes are set up on both sides of the tunnel axis at 20m intervals to form multiple cross-hole detection profiles; high-density scanning of the rock and soil within 30m in front of the tunnel is carried out using seismic wave CT and electromagnetic wave CT combined detection technology to generate a three-dimensional geological model and accurately identify the spatial location, size, shape and distribution density of the string of isolated boulders. Step 2: Based on the three-dimensional geological model obtained in Step 1, a borehole network is laid out for the boulder body. The borehole diameter is 50mm, the borehole spacing is controlled at 300~500mm according to the strength and volume of the boulder, the row spacing is 300mm, and the arrangement is quincunx. The borehole depth is not less than 300mm of the boulder thickness. Step 3: Drill precisely according to the design in Step 1. Select calcium oxide-based static expansion agent. Mix the agent and water at a ratio of 1:0.24 to form a paste. Pour the paste into the hole to 100mm inside within 10 minutes. Use a tamping rod to compact the paste and avoid gaps. Set up a warning zone after pouring. Allow the reaction time to 2-7 hours to allow the inside of the boulder to expand and crack. Step 4: Clear broken rock blocks until the flatness error of the excavation surface is ≤3cm; in the section where boulders are treated, install 300mm intervals in a staggered pattern along the tunnel arch, and install Φ42mm×3.5m advanced small guide pipes with an external insertion angle of 5°~8°. Inject cement grout with a water-cement ratio of 1:1, and grout in sections using a grouting pump at a grouting pressure of 0.5~1.0MPa for 5 minutes to form a reinforced arch shell; then, under the protection of the support, use short-foot excavation and promptly construct steel frames and shotcrete initial support; Step 5: Repeat steps 1 to 4 to form a detection-breaking-support cycle operation until the entire string of isolated boulders is safely traversed.

[0009] Furthermore, in step 1, the combined seismic wave CT and electromagnetic wave CT detection technology adopts a high-precision dual-wave field detection system. The seismic wave CT resolution is ≤0.1m, and the electromagnetic wave CT has a discrimination degree of ≥95% between boulders and soil. The detection data is processed by a weighted fusion algorithm to eliminate the ambiguity of single-wave field detection. The three-dimensional geological model intuitively displays the spatial stacking relationship of boulders and the angle with the tunnel axis.

[0010] Furthermore, in step 1, a two-dimensional cross-hole CT scan is used to conduct a preliminary survey and delineate the suspected isolated rock areas; within the suspected isolated rock areas, a three-dimensional cross-hole CT scan is used for a detailed survey to achieve precise three-dimensional spatial positioning and morphological identification of the isolated rock.

[0011] Furthermore, in step 1, the detection holes are arranged in a main hole and verification hole pattern, with a main hole spacing of 20m and a verification hole arranged between every 3 main holes. The detection results of the verification hole and the main hole do not deviate by more than 5%, thus achieving full coverage of the detection of string of isolated rocks.

[0012] Furthermore, in step 2, the drilling network layout is simulated and optimized using BIM technology. The drilling angle is adjusted according to the spatial shape of the boulder. For irregular boulders, additional denser holes are added at protruding parts with a spacing of 200mm to ensure that the expansion pressure is evenly applied to the entire area of ​​the boulder.

[0013] Furthermore, in step 3, 0.5% to 1% of a composite retarder is added to the calcium oxide-based static expansion agent, and the reaction time is adjusted to 3 to 12 hours according to construction requirements. In water-rich strata, 2% to 3% of a waterproof accelerator is added to prevent the slurry from being diluted by water, so as to stabilize the expansion pressure.

[0014] Furthermore, in step 4, the segmented grouting is divided into two steps: initial grouting and re-grouting. The initial grouting pressure is 0.3~0.5MPa to fill large pores, and the re-grouting pressure is 0.8~1.0MPa to penetrate small cracks. After grouting, the core drilling method is used to test the strength of the solidified body so that the compressive strength is above 2.5MPa.

[0015] Furthermore, in step 4, the advanced small-diameter pipe reinforcement system must ensure a longitudinal overlap length ≥1.0m, an increase in stiffness of the reinforced arch shell formed after grouting ≥50%, and a water-stopping performance permeability coefficient ≤1×10⁻⁶. -6 cm / s; short advances are adopted, with each cycle advance ≤1m, to reduce disturbance.

[0016] Furthermore, in step 4, for water-rich string-like isolated rock formations, a cement-water glass double-liquid grout pretreatment step is added before grouting. The volume ratio of the double-liquid grout is 1:0.5, and the grouting pressure is 0.3~0.5MPa, forming a temporary water-stop curtain to prevent grout loss and groundwater inrush during the grouting process.

[0017] Furthermore, the method for handling isolated boulders in a mined tunnel based on cross-hole CT precision detection also includes a dynamic monitoring step during construction. Settlement observation points and convergence observation points are set up on the tunnel arch and both sides, and monitored every 2 hours. When the settlement exceeds 3mm / d or the convergence exceeds 2mm / d, excavation is suspended, the spacing of the small guide pipes is increased to 250mm, and the grouting pressure is increased to 1.0~1.2MPa. Construction is resumed after the deformation stabilizes.

[0018] Compared with the prior art, the superior effects of the present invention are as follows: 1. The present invention describes a method for handling a series of isolated boulders in a mined tunnel based on cross-hole CT precision detection. This method involves pre-construction detection and cross-hole CT scanning technology, which fundamentally transforms the handling of isolated boulders from passive treatment after encounter to proactive, predictive treatment. 2. The method for handling isolated boulders in mined tunnels based on cross-hole CT precision detection described in this invention uses static blasting technology that produces no vibration, no shock waves, and no flying rocks, causing minimal disturbance to the surrounding rock. It is particularly suitable for vibration-sensitive urban environments, and also produces low noise and no dust pollution. 3. The method for treating isolated boulders in mined tunnels based on cross-hole CT precision detection described in this invention greatly enhances the integrity and stability of the tunnel face and effectively controls deformation through small-diameter pipe reinforcement and grouting measures. 4. The method for handling isolated boulders in a mined tunnel based on cross-hole CT precision detection described in this invention is a complete set of methods with a short construction period, low cost, and high safety. Through static crushing, it not only has good environmental protection effects, but also causes minimal disturbance to the surrounding strata and important structures of the mined tunnel, thus ensuring environmental safety. Attached Figure Description

[0019] Figure 1 This is a longitudinal section image of a boulder detected by cross-hole CT scanning in an embodiment of the present invention; Figure 2 This is a planar view of a boulder detected by cross-hole CT scanning in an embodiment of the present invention; Figure 3 This is a longitudinal section view of the treatment of isolated boulders during tunnel excavation in an embodiment of the present invention; Figure 4 This is a cross-sectional view of the treatment of isolated boulders during tunnel excavation in an embodiment of the present invention; Figure label: 1. Cross-hole CT scanning borehole; 2. String of boulders; 3. Pre-excavation small guide pipe; 4. I-beam arch frame; 5. Initial shot concrete; 6. CT scanning receiver; 7. Static blasting borehole; 8. Excavation face; 9. Completely weathered granite; 10. Tunnel axis. Detailed Implementation

[0020] To better understand the above-mentioned objectives, features and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0021] This invention first employs cross-hole CT scanning technology to accurately determine the three-dimensional distribution of the string of isolated boulders 2 ahead, ensuring targeted subsequent processing. Then, based on the detection results, static blasting is designed and implemented for silent and safe breaking. Next, the rock mass is cleared to create a working face for support. As the tunnel continues to advance, the stability of the excavation face is ensured by relying on the advanced small guide pipe 3 for intensified grouting and advanced support. Through the cyclical operation mode of "detection-breaking-support", the construction safety, processing efficiency, economy, and environmental protection are greatly improved. This invention solves the problems of slow construction progress and insufficient safety in tunnel excavation through string of isolated boulders, and introduces a new measure for safe and efficient excavation of tunnels under complex geological conditions. Example

[0022] The method for handling isolated boulders in mined tunnels based on precise cross-hole CT detection includes: Step 1: In front of the tunnel excavation face, parallel detection holes are set up on both sides of the tunnel axis 10 at a spacing of 20m to form multiple cross-hole detection profiles; high-density scanning of the rock and soil within 30m in front of the tunnel is carried out using the combined detection technology of seismic wave CT and electromagnetic wave CT to generate a three-dimensional geological model and identify the spatial location, size, shape and distribution density of the string of isolated boulders 2. Step 2: Based on the three-dimensional geological model obtained in Step 1, a borehole network is laid out for the boulder body. The borehole diameter is 50mm, the borehole spacing is controlled at 300~500mm according to the strength and volume of the boulder, the row spacing is 300mm, and the arrangement is quincunx. The borehole depth is greater than or equal to the thickness of the boulder by 300mm. Step 3: Drill precisely according to the design in Step 1. Select calcium oxide-based static expansion agent. Mix the agent and water at a ratio of 1:0.24 to form a paste. Pour the paste into the hole to 100mm inside within 10 minutes. Use a tamping rod to compact the paste and avoid gaps. Set up a warning zone after pouring. Allow the reaction time to 2-7 hours to allow the inside of the boulder to expand and crack. Step 4: Clear the broken rock blocks until the flatness error of the excavation surface is ≤3cm; in the section where boulders are treated, install 3 Φ42mm×3.5m advanced small guide pipes with an external insertion angle of 5°~8° along the tunnel arch in a staggered pattern with a spacing of 300mm, and inject cement grout with a water-cement ratio of 1:1. Grout in sections using a special grouting pump, with a grouting pressure of 0.5~1.0MPa and a holding pressure of 5 minutes to form a reinforced arch shell; then, under the protection of the support, use short-foot excavation and construct steel frame and shotcrete initial support; Step 5: Repeat steps 1 to 4 to form a detection-breaking-support cycle operation until the entire string of isolated boulders is safely traversed.

[0023] In some specific embodiments, cross-hole CT scanning is performed in front of the tunnel excavation face. Detection holes are laid out at 20m intervals on both sides of the tunnel axis 10. Seismic CT and / or electromagnetic CT technologies are used to conduct three-dimensional geological exploration within a 30m range ahead, identifying the spatial distribution, size, and shape of the string of boulders 2. Based on the detection results, a static blasting design is developed. The borehole diameter is 50mm, the borehole spacing is controlled between 300-500mm according to the strength and volume of the boulders, the row spacing is set to 300mm, and a staggered arrangement is used. The borehole depth is determined according to the thickness of the boulders, and is 300mm or more. Static blasting is then carried out. After precise drilling according to the design, calcium oxide-based static fracturing agent slurry is applied. The grouting was completed within 10 minutes and compacted with tamperes. After grouting, a warning zone was set up, and the boulders were allowed to fully fracture within 2-7 hours. The fractured rock mass was manually cleared, and the flatness error of the excavation face was no more than 3cm. Advanced support was reinforced with pre-insertion guide pipes 3. In the boulder treatment section, 42mm diameter and 3.5m long pre-insertion guide pipes 3 were laid at 300mm intervals with an external insertion angle of 5°-8°. Then, cement grout with a water-cement ratio of 1:1 was injected at a grouting pressure of 0.5~1.0MPa. Tunnel excavation was carried out under the protection of the formed support system, using a short advance and low-disturbance excavation method. Initial support was applied, and the above steps were repeated to form a work cycle until the boulder area was completely traversed.

[0024] In some specific embodiments, the static blasting borehole 7 is designed with a diameter of 50mm. The spacing of the static blasting borehole 7 is dynamically adjusted according to the specific strength characteristics and volume of the boulder, and is reasonably controlled within the range of 300~500mm. At the same time, the row spacing is uniformly set to 300mm. The mixing ratio of the static fracturing agent needs to be selected according to the construction conditions. Under the condition of an ambient temperature of 25℃, a water-cement ratio of 1:0.24 is adopted to enable the static fracturing agent to generate the best expansion pressure and ideal reaction speed, effectively shortening the overall construction time and accelerating the project progress.

[0025] In some specific embodiments, static blasting is specifically used for tunnel excavation. This method effectively breaks up the target rock mass through the chemical action of a static expanding agent. The entire process generates no shock waves, vibrations, or dust pollution, thus eliminating the air pollution problems caused by traditional blasting methods at the source. In addition, this process completely avoids the severe vibration and impact effects caused by blasting or large-scale mechanical demolition operations, protecting the integrity of the tunnel surrounding rock and initial support structure, and reducing the impact on the safety performance of adjacent buildings. While ensuring construction efficiency, it also improves the overall environmental friendliness and safety of the project.

[0026] In some specific embodiments, for the fractured zone of the isolated boulder in the tunnel, a densely packed advanced small-diameter pipe 3-support system is adopted: Φ42mm×3.5mm seamless steel pipes are laid in a quincunx pattern at 300mm intervals along the circumference of the arch, with a longitudinal overlap length of not less than 1.0m and an external insertion angle precisely controlled at 5°-8°. Pure cement grout with a water-cement ratio of 1:1 is injected through a grouting pump, and the grouting pressure is steadily increased to 0.5-1.0MPa and held for 5 minutes. The grout quickly penetrates and consolidates the loose zone formed after the isolated boulder is fractured and the surrounding soft soil, forming a complete, continuous "reinforced arch shell" with certain rigidity and water-stopping performance. At the same time, following the principles of "advanced pipe, strict grouting, short excavation, and strong support", a short excavation method is adopted, and anchor spraying initial support is applied in a timely manner during cyclic construction to effectively suppress the deformation of the surrounding rock. The advanced small-diameter pipe 3-support system is safely constructed to prevent the deformation of the surrounding rock and ensure construction safety and controllability.

[0027] like Figure 1 and Figure 2 As shown, multiple cross-hole CT scanning boreholes 1 are arranged parallel to each other on both sides of the tunnel's design axis at specific intervals, forming a detection network covering a predetermined area in front of the tunnel. The transmitter and CT receiver 6 move between or within different boreholes, forming densely intersecting ray profiles. The cross-hole CT scanning boreholes 1 provide channels for the transmission and reception of seismic waves or electromagnetic waves. By collecting wave velocity or electromagnetic field intensity data penetrating different geological bodies, the internal geological structure can be inferred, such as... Figure 2 The planar layout allows for comprehensive detection without blind spots, enabling the surrounding of the isolated rock in three-dimensional space. The string-like boulders 2 are irregularly arranged in a string-like form, i.e., discrete and clustered, embedded in the weak surrounding rocks such as completely weathered granite 9. The physical and mechanical properties of the two are vastly different. Figure 1 The random distribution of the string of boulders 2 in the longitudinal and vertical directions is clearly shown. The string of boulders 2 is the target body to be processed. Its spatial position, size and shape are the core output information of the detection. Accurately drawing its boundary is the basis for all subsequent designs. The detection system, consisting of cross-hole CT scanning borehole 1 and CT scanning receiver 6, acquires massive amounts of data. After processing by professional software, a high-resolution three-dimensional geological model is generated. This model can not only clearly distinguish the boundary between the string of isolated boulders 2 and the completely weathered granite 9, but also accurately mark the three-dimensional coordinates, volume and orientation of each isolated boulder, providing direct and accurate input for the next step of static blasting borehole 7 and the advanced small guide pipe 3 in the support scheme. like Figure 3 and Figure 4 As shown, an advanced support system is first implemented before excavating to the isolated rock area: The advanced small guide pipe 3 is driven into the rock mass at a small outward angle outside the tunnel arch outline. Its tail end is welded or reliably connected to the subsequently erected I-beam arch frame 4. Its front end extends into the stable rock layer in front of the unexcavated boulder influence zone, forming an umbrella-shaped or arch-shaped pre-support bearing structure. Grout is injected into the surrounding rock mass through the guide pipe. After the grout solidifies, it can bond the loose, completely weathered granite 9 and the potential fracture zone into a whole, significantly improving the self-supporting capacity of the surrounding rock and creating a stable external environment for safe static blasting of boulders. The I-beam arch frame 4 is erected close to the rock wall behind the excavation face and is the main skeleton of the initial support. The initial shotcrete 5 is sprayed and covered on the I-beam arch frame 4 and the excavated rock surface in a timely manner, which tightly bonds the steel frame and the surrounding rock into an integral load-bearing structure. The I-beam arch frame 4 provides strong radial support force to inhibit the deformation of the surrounding rock. The initial shotcrete 5 can seal the rock surface to prevent weathering and spalling, and works together with the I-beam arch frame 4 to make the support structure bear the load as a whole. Together with the advanced guide 3, they form a complete support system in depth and three-dimensional circumferential direction, namely, a reinforced arch shell. Under the protection of the reinforced arch shell, static blasting boreholes 7 were drilled on the excavation face 8 according to the borehole network parameters designed by the detection model. These static blasting boreholes 7 directly impacted the interior of the string of isolated boulders 2. Figure 4 As shown, the static blasting borehole 7 is the channel for injecting static fracturing agent. The expanding agent undergoes a chemical reaction inside the hole, generating huge expansion pressure, which slowly and silently expands and cracks the hard string of isolated rocks 2 from the inside, avoiding violent vibration and impact on the surrounding completely weathered granite 9 and the constructed support structure.

[0028] Tunnel axis 10 is the baseline that runs through all design and construction. The layout of cross-hole CT scanning borehole 1, the orientation of the advance guide pipe 3, the installation of the I-beam arch frame 4, and the excavation progress are all controlled based on tunnel axis 10 to ensure that the entire treatment process is carried out accurately along the design line and to prevent the tunnel axis from shifting due to the treatment of isolated rocks.

[0029] Furthermore, in step 1, the combined seismic wave CT and electromagnetic wave CT detection technology adopts a high-precision dual-wave field detection system. The seismic wave CT resolution is ≤0.1m, and the electromagnetic wave CT has a discrimination degree of ≥95% between boulders and soil. The detection data is processed by a weighted fusion algorithm to effectively eliminate the ambiguity of single-wave field detection. The three-dimensional geological model intuitively displays the spatial stacking relationship of boulders and the angle with the tunnel axis.

[0030] In some specific embodiments, the cross-hole CT scan uses a high-precision and high-resolution seismic CT system, which can effectively detect underground geological structures. The spacing between the detection holes is 20m, which enables a comprehensive understanding of the geological conditions ahead of the construction site. Through professional data processing and imaging software, a detailed three-dimensional geological model can be generated. The three-dimensional geological model not only clearly shows the distribution of various strata structures, but also accurately displays the specific spatial location and morphological characteristics of isolated boulders, providing important geological basis and technical support for tunnel construction.

[0031] Furthermore, in step 1, a two-dimensional cross-hole CT scan is used to conduct a preliminary survey and delineate the suspected isolated rock occurrence area; within the suspected isolated rock occurrence area, a three-dimensional cross-hole CT scan is used for a detailed survey to achieve precise three-dimensional spatial positioning and morphological identification of the isolated rock.

[0032] Furthermore, in step 1, the detection holes are arranged in a main hole and verification hole pattern, with a main hole spacing of 20m and a verification hole arranged between every 3 main holes. The detection results of the verification hole and the main hole do not deviate by more than 5%, so as to achieve no omission in the detection of isolated rocks.

[0033] Furthermore, in step 2, the drilling network layout is simulated and optimized using BIM technology. The drilling angle is adjusted according to the spatial shape of the boulder. For irregular boulders, additional denser holes are added at protruding parts with a spacing of 200mm to ensure that the expansion pressure is evenly applied to the entire area of ​​the boulder.

[0034] Furthermore, in step 3, 0.5% to 1% of a composite retarder is added to the calcium oxide-based static expansion agent, and the reaction time is adjusted to 3 to 12 hours according to construction requirements. In water-rich strata, 2% to 3% of a waterproof accelerator is added to prevent the slurry from being diluted by water, so as to stabilize the expansion pressure.

[0035] Furthermore, in step 4, the segmented grouting process is divided into two steps: initial grouting and re-grouting. The initial grouting pressure is 0.3~0.5MPa to fill large pores, and the re-grouting pressure is 0.8~1.0MPa to penetrate small cracks. After grouting, the strength of the solidified body is tested by core drilling, and the compressive strength is above 2.5MPa.

[0036] Furthermore, in step 4, the advanced small-diameter pipe reinforcement system must ensure a longitudinal overlap length ≥1.0m, an increase in stiffness of the reinforced arch shell formed after grouting ≥50%, and a water-stopping performance permeability coefficient ≤1×10⁻⁶. -6 cm / s; short advances are adopted, with each cycle advance ≤1m, to reduce disturbance.

[0037] Furthermore, in step 4, for water-rich string-like isolated rock formations, a cement-water glass double-liquid grout pretreatment step is added before grouting. The volume ratio of the double-liquid grout is 1:0.5, and the grouting pressure is 0.3~0.5MPa, forming a temporary water-stop curtain to prevent grout loss and groundwater inrush during the grouting process.

[0038] Furthermore, the method for handling isolated boulders in a mined tunnel based on cross-hole CT precision detection also includes a dynamic monitoring step during construction. Settlement observation points and convergence observation points are set up on the tunnel arch and both sides, and monitored every 2 hours. When the settlement exceeds 3mm / d or the convergence exceeds 2mm / d, the excavation is suspended, the spacing of the small guide pipes is increased to 250mm, and the grouting pressure is increased to 1.0~1.2MPa. Construction is resumed after the deformation stabilizes.

[0039] This invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims.

Claims

1. A method for treating string-shaped boulders in a tunnel excavated by dark mining based on cross-hole CT precision detection, characterized in that, The method comprises the following steps: Step 1, in front of the tunneling face, a plurality of detection holes are arranged in parallel along the two sides of the tunnel axis at an interval of 20 m, forming a plurality of cross-hole detection profiles; Step 2, based on the three-dimensional geological model obtained in step 1, a drilling network is arranged for the isolated rock mass, the drilling diameter is 50 mm, the drilling interval is controlled to be 300-500 mm according to the strength and volume of the isolated rock mass, the row spacing is 300 mm, the drilling is arranged in a quincunx shape, and the drilling depth is not less than 300 mm of the thickness of the isolated rock mass; Step 3, accurate drilling is performed according to the design in step 1, a calcium oxide-based static expanding agent is selected, the agent is mixed with water at a ratio of 1:0.24 to form a paste, the paste is poured into the hole to a position 100 mm inward from the hole opening within 10 minutes, a tamping rod is used to tamp the paste to avoid voids, a warning area is set after pouring, and the isolated rock mass is expanded and cracked after 2-7 hours of reaction; Step 4, the broken rock mass is cleaned to a flatness error of the excavation face of less than or equal to 3 cm; in the isolated rock mass treatment section, a quincunx shape is formed along the tunnel arch at an interval of 300 mm, a Φ42 mm*3.5 m advance small guide pipe is arranged, an external insertion angle is 5°-8°, a cement single slurry with a water-cement ratio of 1:1 is injected, the slurry is injected by a grouting pump in stages, the grouting pressure is 0.5-1.0 MPa and the pressure is maintained for 5 minutes, and a reinforced arch is formed; then, short footage tunneling is performed under the protection of support, and a steel frame and a shotcrete primary support are timely constructed; Step 5, steps 1 to 4 are repeated to form a detection-breaking-support cycle until the entire isolated rock mass area is safely passed through. In step 1, the seismic wave CT and electromagnetic wave CT joint detection technology adopts a high-precision dual-wave field detection system, the seismic wave CT resolution is less than or equal to 0.1 m, the electromagnetic wave CT resolution is greater than or equal to 95% for the isolated rock mass and the soil body, the detection data is processed by a weighted fusion algorithm to eliminate the multi-solution of single-wave field detection, and the three-dimensional geological model directly displays the spatial superposition relationship of the isolated rock mass and the angle between the isolated rock mass and the tunnel axis.

2. The method according to claim 1, wherein, In step 1, two-dimensional cross-hole CT detection is used for general investigation to preliminarily delineate the suspected isolated rock mass occurrence area; three-dimensional cross-hole CT detection is used for detailed investigation in the suspected isolated rock mass occurrence area to realize accurate three-dimensional spatial positioning and shape identification of the isolated rock mass.

3. The method according to claim 1, wherein, In step 1, the detection hole arrangement adopts a main hole and a check hole mode, the main hole interval is 20 m, and one check hole is arranged between every three main holes, the detection result deviation of the check hole and the main hole is not more than 5%, and the isolated rock mass detection is fully covered.

4. The method according to claim 1, wherein, In step 2, the drilling network arrangement adopts BIM technology simulation optimization, the drilling angle is adjusted according to the spatial shape of the isolated rock mass, and for irregular isolated rock mass, an encryption hole is additionally arranged at a protruding position, the interval is 200 mm, and the expansion pressure is uniformly applied to the whole isolated rock mass.

5. The method according to claim 1, wherein, ​ 6. The method according to claim 1, wherein, In step 3, the calcium oxide-based static expansion agent is added with 0.5%-1% of a composite retarder, the reaction time is adjusted to 3-12 hours according to the construction requirements, and 2%-3% of a waterproof accelerator is added in the water-rich stratum to prevent the slurry from being diluted by water and to stabilize the expansion pressure.

7. The method according to claim 1, wherein, In step 4, the segmented grouting process is divided into two steps of initial injection and re-injection, the initial injection pressure is 0.3-0.5 MPa to fill large pores, the re-injection pressure is 0.8-1.0 MPa to penetrate small cracks, and the core drilling method is used to detect the strength of the consolidated body after grouting to make the compressive strength above 2.5 MPa.

8. The method according to claim 1, wherein, In step 4, the advanced small catheter encryption support system needs to ensure that the longitudinal lap length is greater than or equal to 1.0 m, the stiffness of the reinforced arch shell formed after grouting is increased by more than 50%, the water stopping performance permeability coefficient is less than or equal to 1x10 -6 cm / s; short footage excavation is adopted, and each cycle footage is less than or equal to 1m to reduce disturbance.

9. The method according to claim 1, wherein, In step 4, for the water-rich string-shaped boulder stratum, a cement-silicate double-liquid slurry pretreatment step is added before grouting, the volume ratio of the double-liquid slurry is 1:0.5, the grouting pressure is 0.3-0.5 MPa, a temporary water stop curtain is formed to prevent slurry loss and groundwater gushing during grouting.

10. The method according to claim 1, wherein, Further comprising a dynamic monitoring step during construction, settlement observation points and convergence observation points are arranged at the tunnel vault and both sides, monitoring is performed every 2 hours, when the settlement exceeds 3 mm / d or the convergence exceeds 2 mm / d, the tunneling is temporarily stopped, the small duct layout interval is encrypted to 250 mm, and the grouting pressure is increased to 1.0-1.2 MPa, and the construction is resumed after the deformation is stabilized.

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