Top arch collapse cavity treatment method for tuffaceous volcanic ash stratum

Abstract

The invention relates to the technical field of open-type TBM construction, in particular to a tuffaceous volcanic ash stratum top arch collapse cavity treatment method. The collapse cavity of the top arch is grouted through three grouting procedures, and specific grouting liquid is used in each procedure; the grouting range of the first-time shallow grouting sealing is 0-3 m outside the outline of the tunnel vault, the surface layer of the collapse cavity is sealed after grouting, and it is guaranteed that follow-up grouting slurry is not lost; the grouting ranges of the subsequent two procedures are 3-4.5 m and 4.5-6 m outside the outline of the vault of the tunnel, and the damage rate of the tuffaceous volcanic ash stratum is reduced through the three-time grouting procedure; the method not only can reduce the change rate of the convergence value of the section, but also can reduce the loss of the grouting liquid, and is suitable for implementation of large-scale construction projects.

Description

Technical Field

[0001] The present invention relates to the technical field of open TBM construction, and in particular to a method for treating the crown cavity collapse in tuffaceous volcanic ash strata. Background Art

[0002] A full-face tunnel boring machine (Tunnel Boring Machine, TBM) is a large comprehensive construction equipment that utilizes the reaction force of the rock wall to achieve the thrust and torque required for the tunneling function, and realizes the functions of one-time tunneling, initial support, and muck transportation of the tunnel under normal temperature and pressure. It integrates machinery, electricity, hydraulics, and pneumatics to achieve the automation and factoryization of tunnel construction. If the excavation operation of a large open TBM can be carried out continuously, the entire construction speed will be accelerated and the construction period will be significantly shortened, especially when constructing over a long distance in stable surrounding rocks, this feature is particularly obvious.

[0003] However, during the conception and implementation of the present application, the inventor found that: during the tunneling process of a large open TBM in poor geological conditions of tuffaceous volcanic ash in class V special surrounding rocks, after the poor formation is pulled out of the tail shield, it is still necessary to re-reinforce the cavity collapse to minimize the construction risks of the TBM, accelerate the project construction, ensure the construction quality, avoid safety accidents caused by continuous collapse of the cavity, reduce the occurrence of initial support deformation of the tunnel, and ensure the smooth tunneling of the open TBM. Generally speaking, the traditional method for cavity collapse reinforcement is to backfill and grout the concrete at one time with small ducts after establishing the initial support. However, in the construction of tuffaceous volcanic ash strata, the formation is loose and cannot form holes directly, and the small ducts cannot be pre-buried. The tuffaceous volcanic ash strata have the characteristics of porosity and low cementation. The porosity of the honeycomb structure formed by its volcanic clastic materials (albite, orthoclase, etc.) can reach 30% - 50%. Shallow cavities (<6m) are more susceptible to the influence of surface water infiltration. The single concrete grouting liquid has coarser particles and higher viscosity, and it is difficult to effectively penetrate into the tiny cracks of the honeycomb structure of volcanic clasts, resulting in an increase in the tunnel section convergence value (convergence value: based on the section diameter, or based on the distances from the section vertex to the left and right ends respectively, the difference between the initial tunnel section and the tunnel section at a certain moment).

[0004] Therefore, in view of the geological characteristics of high section deformation rate during the grouting backfill of the cavity collapse in tuffaceous volcanic ash strata, it is necessary to propose a method for treating the crown cavity collapse in tuffaceous volcanic ash strata to reduce the change rate of the section convergence value.

[0005] The above content is only used to assist in understanding the technical solution of the present invention, and does not represent an admission that the above content is prior art. Summary of the Invention

[0006] The main object of the present invention is to provide a method for treating the crown cavity collapse in tuffaceous volcanic ash strata, aiming at the geological characteristics of high cross-section deformation rate during grouting backfill of the cavity in tuffaceous volcanic ash strata, and solving the problem of how to reduce the change rate of the cross-section convergence value.

[0007] To achieve the above object, a method for treating the crown cavity collapse in tuffaceous volcanic ash strata provided by the present invention performs grouting treatment on the crown cavity through three grouting procedures;

[0008] The three grouting procedures include: the first shallow grouting closure, the second middle grouting backfill, and the third deep grouting backfill;

[0009] The grouting fluid for the first shallow grouting closure is HCH-II type chemical grout, and the grouting area is within 120° of the tunnel crown and 0 - 3m outside the tunnel crown contour, that is, grouting layer I;

[0010] The grouting fluid for the second middle grouting backfill is cement slurry or cement double-fluid slurry, and the grouting area is within 120° of the tunnel crown and 3 - 4.5m outside the tunnel crown contour, that is, grouting layer II;

[0011] The grouting fluid for the third deep grouting backfill is cement slurry or cement double-fluid slurry, and the grouting area is within 120° of the tunnel crown and 4.5 - 6m outside the tunnel crown contour, that is, grouting layer III;

[0012] The cement double-fluid slurry is cement slurry - water glass double-fluid slurry.

[0013] Optionally, the method specifically includes,

[0014] S1, the first shallow grouting closure: Five grouting holes are evenly opened at the bottom of the cross-section of grouting layer I, and the self-advancing hollow anchor rod is drilled through the grouting holes to a position 2.5m outside the tunnel crown contour. The HCH-II type chemical grout is pumped into grouting layer I through the self-advancing hollow anchor rod by using a special chemical grouting pump;

[0015] Along the tunnel extension direction, the first shallow grouting closure is carried out every 1.5m;

[0016] S2, the second middle grouting backfill: Along the tunnel extension direction, five backfill holes 1 are evenly opened at the bottom 0.5m away from the cross-section of grouting layer I, and the self-advancing hollow anchor rod is drilled through the backfill holes 1 to a position 4.5m outside the tunnel crown contour. The cement slurry or cement double-fluid slurry is pumped into grouting layer II through the self-advancing hollow anchor rod by using a grouting pump;

[0017] Along the tunnel extension direction, the second middle grouting backfill is carried out every 1.5m;

[0018] S3. Third deep grouting and backfilling: Along the extension direction of the tunnel, five backfilling holes 2 are evenly opened at the bottom 1 m away from the cross-section of Grouting Layer I. The self-advancing hollow anchor rod is drilled through the backfilling hole 2 to a position 6 m outside the contour of the tunnel arch crown, and the cement slurry or cement double-fluid slurry is pumped into Grouting Layer III through the self-advancing hollow anchor rod by using a grouting pump.

[0019] Along the extension direction of the tunnel, the third deep grouting and backfilling is carried out every 1.5 m;

[0020] Optionally, the water-cement volume ratio of the cement slurry is 0.5:1; in the cement double-fluid slurry, the volume ratio of the cement slurry to the water glass slurry is 1:1.

[0021] Optionally, the grouting holes, backfilling holes 1 and backfilling holes 2 in S1, S2 and S3 are arranged staggeredly.

[0022] Optionally, the 5 grouting holes in S1 are evenly distributed on the fan-shaped arc at the upper end of the primary grouting section; the 5 backfilling holes in S3 are evenly distributed on the fan-shaped arc at the upper end of the secondary grouting section; the 5 backfilling holes in S5 are evenly distributed on the fan-shaped arc at the upper end of the tertiary grouting section.

[0023] Optionally, the grouting pressure of the special chemical grouting pump in S1 is 0.3 - 0.5 MPa; the grouting pressure of the grouting pump in S2 is 0.5 - 1 MPa; the grouting pressure of the grouting pump in S3 is 0.5 - 1.5 MPa.

[0024] Optionally, the method further includes the following steps:

[0025] S0. Establish initial support.

[0026] Optionally, the method further includes the following steps:

[0027] S4. After the grouting is completed, monitoring points are set in the tunnel.

[0028] Optionally, the monitoring points in S4 are located at the top and the left and right ends of the tunnel cross-section. Three monitoring points form a set of detection surfaces, and the detection surfaces are evenly distributed along the tunneling direction. The distance between adjacent two detection surfaces is 3 - 5 m.

[0029] Optionally, a total station is set on the detection surface, which can collect the convergence data of the monitoring points.

[0030] Principle of the invention:

[0031] After the initial support is established, five grouting holes are evenly drilled at the bottom of the cross-section of Grouting Layer Ⅰ. The self-advancing hollow anchor rod is drilled through the grouting holes to a position 2.5 m outside the contour of the tunnel crown. The HCH-Ⅱ chemical grout is pumped into Grouting Layer Ⅰ through the self-advancing hollow anchor rod by using a special chemical grouting pump; five backfill holes 1 are evenly drilled at the bottom of the cross-section of Grouting Layer Ⅱ. The self-advancing hollow anchor rod is drilled through the backfill holes 1 to a position 4.5 m outside the contour of the tunnel crown. The cement slurry or cement double-fluid slurry is pumped into Grouting Layer Ⅱ through the self-advancing hollow anchor rod by using a grouting pump; five backfill holes 2 are evenly drilled at the bottom of the cross-section of Grouting Layer Ⅲ. The self-advancing hollow anchor rod is drilled through the backfill holes 2 to a position 6 m outside the contour of the tunnel crown. The cement slurry or cement double-fluid slurry is pumped into Grouting Layer Ⅲ through the self-advancing hollow anchor rod by using a grouting pump, finally filling the cavity and the cracks in the rock and soil mass, bonding the anchor rod body with the surrounding rock and soil mass to form an anchor solid, thereby realizing the support and reinforcement of the surrounding rock.

[0032] The embodiment of the present invention provides a method for treating the top arch cavity collapse in tuffaceous volcanic ash strata, which at least has the following beneficial effects:

[0033] 1. For the method for treating the top arch cavity collapse in tuffaceous volcanic ash strata provided in this application, the top arch cavity is grouted through three grouting processes, and specific grouting fluids are used in each process; the grouting range of the first shallow grouting closure is within 120° of the tunnel crown and 0 - 3 m outside the contour of the tunnel crown. After grouting, the surface of the cavity is sealed, and the grouting slurry does not flow out. The grouting ranges of the subsequent two processes are 3 - 4.5 m and 4.5 - 6 m outside the contour of the tunnel crown. The three grouting processes reduce the damage rate to the tuffaceous volcanic ash strata; this method can not only reduce the change rate of the cross-section convergence value, but also reduce the loss of the grouting fluid.

[0034] 2. The grouting fluid is transported through the self-advancing hollow anchor rod, integrating functions of drilling, grouting, and anchoring, greatly shortening the construction time, improving the construction efficiency, and being applicable to the implementation of large-scale construction projects.

[0035] 3. When grouting through the self-advancing hollow anchor rod, the slurry can fully fill the cracks in the rock and soil mass under high pressure, solidifying the anchor rod body and the surrounding rock and soil mass into one body, improving the anchoring force and uplift resistance of the anchor rod, and ensuring the anchoring effect.

[0036] 4. By adopting three grouting processes, the grouting pressure of the first grouting process is 0.3 - 0.5 MPa, the grouting pressure of the second grouting process is 0.5 - 1 MPa, and the grouting pressure of the third grouting process is 0.5 - 1.5 MPa. Compared with traditional grouting, the slurry is injected from the inside out through the slurry outlet holes of the drill bit, which can make the slurry fully fill the cracks in the rock and soil mass, consolidate the rock mass and soil layer, and has a suitable grouting diffusion radius and good anchoring quality. Description of the Drawings

[0037] Figure 1 This is the construction schematic diagram of the present invention.

[0038] Figure 2 This is the statistical chart of the cross-section convergence value data.

[0039] Figure 3 This is the statistical chart of the cross-section convergence value data.

[0040] Figure 4 This is the statistical chart of the cross-section convergence value data.

[0041] Figure 5 This is the statistical chart of the cross-section convergence value data.

[0042] Reference numerals: 1 surrounding rock, 2 tunnel, 3 TBM, 4 self-advancing hollow anchor, 5 grouting layer I, 6 grouting layer II, 7 grouting layer III, 8 monitoring point.

[0043] The realization, functional features and advantages of the object of the present invention will be further described with reference to the embodiments and the accompanying drawings. Detailed Embodiments

[0044] In order to better understand the above technical solution, the exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art.

[0045] Generally speaking, the traditional treatment for cavity collapse reinforcement is to backfill and grout the concrete at one time using small ducts after the primary support is established. However, during the construction in tuffaceous volcanic ash strata, the strata are loose and direct hole drilling cannot be carried out. Small ducts cannot be pre-buried, and with the grouting method using small ducts, the grout is prone to loss, which not only causes material waste but also cannot be accurately injected into the cavity for effective backfill. In addition, after the inventor detected the cavity in the tuffaceous volcanic ash strata, it was found that the tuffaceous volcanic ash strata have the characteristics of porosity and low cementation. The porosity of the honeycomb structure formed by its volcanic clastic materials (such as albite and orthoclase) can reach 30% - 50%. Shallow cavities (<6m) are more susceptible to the influence of surface water infiltration. If the method of multiple grouting (the number of grouting times is greater than three) is used, due to the loose structure of the tuffaceous volcanic ash strata, the grout will diffuse unevenly, resulting in local blockage. The subsequent required grouting pressure gradually increases, even damaging the strata. Moreover, the method of grouting once every 1m during multiple grouting not only has a long construction period but also is likely to cause secondary damage to the honeycomb structure formed by volcanic clastic materials. In addition, the single concrete grouting liquid has coarser particles and higher viscosity, making it difficult to effectively penetrate into the tiny cracks of the volcanic clastic honeycomb structure, and the cross-section convergence value increases.

[0046] Based on the above description, an embodiment of a method for treating the crown cavity in tuffaceous volcanic ash strata of the present invention is proposed.

[0047] The first embodiment

[0048] The first step is to establish grouting layer Ⅰ. The grouting area is within 120° of the tunnel crown and 0 - 3m outside the tunnel crown contour. First, use a YT28 hand-held pneumatic drill to drill grouting holes for grouting layer Ⅰ, and evenly open five grouting holes at the bottom of the cross-section of grouting layer Ⅰ.

[0049] The second step is to grout using a special chemical grouting pump. The chemical material is HCH-Ⅱ type chemical grout, and the mixing ratio is A:B = 1:1 (volume ratio). The grouting area is within 120° of the tunnel crown and 0 - 3m outside the tunnel contour. The main purpose is to seal the surface of this area. The grouting pressure is 0.3 - 0.5MPa. Drill the self-advancing hollow anchor through the grouting hole to a position 2.5m outside the tunnel crown contour, and use the grouting pump to pump the HCH-Ⅱ type chemical grout into grouting layer Ⅰ through the self-advancing hollow anchor. The self-advancing hollow anchor is φ32×6mm, made of Q420 material, and the length is 2.5m.

[0050] The third step is to establish grouting layer Ⅱ. The grouting area is within 120° of the tunnel crown and 3 - 4.5m outside the tunnel crown contour. First, use a YT28 hand-held pneumatic drill to drill backfill holes 1 for grouting layer Ⅱ, and evenly open five backfill holes 1 at the bottom of the cross-section of grouting layer Ⅱ.

[0051] Step 4: Grout with cement slurry or cement double-fluid slurry. The cement slurry (water-cement ratio of the cement slurry is 0.5:1), and the double-fluid slurry (cement slurry-sodium silicate double-fluid slurry, volume ratio of 1:1). The grouting range is 0 - 3 m outside the tunnel contour of 120° at the crown. Mainly conduct surface sealing in this range. The grouting pressure is 0.5 - 1 MPa. Drill the self-advancing hollow anchor through the backfill hole 1 to a position 4.5 m outside the tunnel crown contour. Use the grouting pump to pump the cement slurry or cement double-fluid slurry into Grouting Layer II through the self-advancing hollow anchor. The self-advancing hollow anchor is φ32×6 mm, made of Q420 material, and has a length of 4.5 m.

[0052] Step 5: Establish Grouting Layer III. The grouting area is within 120° of the tunnel crown and 4.5 - 6 m outside the tunnel crown contour. First, use a YT28 hand-held pneumatic drill to drill backfill holes 2 in Grouting Layer I. Uniformly open five backfill holes 2 at the bottom of the cross-section of Grouting Layer III.

[0053] Step 6: Grout with cement slurry or cement double-fluid slurry. The grouting range is 0 - 3 m outside the tunnel contour of 120° at the crown. Mainly conduct surface sealing in this range. The grouting pressure is 0.5 - 1.5 MPa. Drill the self-advancing hollow anchor through the backfill hole 2 to a position 6 m outside the tunnel crown contour. Use the grouting pump to pump the cement slurry or cement double-fluid slurry into Grouting Layer III through the self-advancing hollow anchor. The self-advancing hollow anchor is φ32×6 mm, made of Q420 material, and has a length of 6 m.

[0054] Step 7: After grouting, install three monitoring points at the top and left and right ends of the tunnel cross-section according to the monitoring plan. During the construction process, strengthen the monitoring frequency of the tunnel convergence after passing through, analyze the data in a timely manner, and understand and control the tunnel settlement and convergence conditions through the analyzed data, so as to take corresponding measures in a timely manner to ensure the safety of the tunnel after the TBM passes through.

[0055] Second Embodiment

[0056] First, establish the initial support: After the tunnel is excavated, install the fabricated steel arch on the surface of the tunnel surrounding rock, and then combine the steel arch with the surrounding rock by spraying concrete to form a combined support structure.

[0057] Step 1: Establish Grouting Layer I. The grouting area is within 120° of the tunnel crown and 0 - 3 m outside the tunnel crown contour. First, use a YT28 hand-held pneumatic drill to drill grouting holes in Grouting Layer I. Uniformly open five grouting holes at the bottom of the cross-section of Grouting Layer I.

[0058] In the second step, a special chemical grouting pump is used for grouting. The chemical material is HCH-II type chemical slurry, and the mixing ratio is A:B = 1:1 (volume ratio). The grouting range is 0 - 3m outside the 120° tunnel contour of the crown. The main purpose is to seal the surface of this range. The grouting pressure is 0.3 - 0.5MPa. The self-advancing hollow anchor rod is drilled through the grouting hole to a position 2.5m outside the tunnel crown contour. The HCH-II type chemical slurry is pumped into Grouting Layer I through the self-advancing hollow anchor rod by using the grouting pump. The self-advancing hollow anchor rod is φ32×6mm, made of Q420 material, and the length is 2.5m;

[0059] In the third step, Grouting Layer II is established. The grouting area is within the 120° range of the tunnel crown and 3 - 4.5m outside the tunnel crown contour. First, use a YT28 hand-held pneumatic drill to drill backfill holes 1 for Grouting Layer II. Five backfill holes 1 are evenly opened at the bottom of the cross-section of Grouting Layer II;

[0060] In the fourth step, cement slurry or cement double-fluid slurry is used for grouting. The cement slurry (the water-cement ratio of the cement slurry is 0.5:1), and the double-fluid slurry (cement slurry-sodium silicate double-fluid slurry, volume ratio is 1:1). The grouting range is 0 - 3m outside the 120° tunnel contour of the crown. The main purpose is to seal the surface of this range. The grouting pressure is 0.5 - 1MPa. The self-advancing hollow anchor rod is drilled through backfill hole 1 to a position 4.5m outside the tunnel crown contour. The cement slurry or cement double-fluid slurry is pumped into Grouting Layer II through the self-advancing hollow anchor rod by using the grouting pump. The self-advancing hollow anchor rod is φ32×6mm, made of Q420 material, and the length is 4.5m;

[0061] In the fifth step, Grouting Layer III is established. The grouting area is within the 120° range of the tunnel crown and 4.5 - 6m outside the tunnel crown contour. First, use a YT28 hand-held pneumatic drill to drill backfill holes 2 for Grouting Layer III. Five backfill holes 2 are evenly opened at the bottom of the cross-section of Grouting Layer III;

[0062] In the sixth step, cement slurry or cement double-fluid slurry is used for grouting. The grouting range is 0 - 3m outside the 120° tunnel contour of the crown. The main purpose is to seal the surface of this range. The grouting pressure is 0.5 - 1.5MPa. The self-advancing hollow anchor rod is drilled through backfill hole 2 to a position 6m outside the tunnel crown contour. The cement slurry or cement double-fluid slurry is pumped into Grouting Layer III through the self-advancing hollow anchor rod by using the grouting pump. The self-advancing hollow anchor rod is φ32×6mm, made of Q420 material, and the length is 6m;

[0063] In the seventh step, after the grouting is completed, three monitoring points are buried at the top and the left and right ends of the tunnel section according to the monitoring plan. The monitoring points are located at the top and the left and right ends of the tunnel section. The three monitoring points form a set of detection surfaces. The detection surfaces are evenly distributed along the tunneling direction. The distance between adjacent two detection surfaces is 3 - 5m. Total stations are set on the detection surfaces, which can collect the convergence data of the monitoring points.

[0064] Third Embodiment

[0065] Based on the second embodiment, real-time monitoring and data analysis were carried out on four consecutive sections (section interval of 3 m) using a total station:

[0066] The four sections are located at the positions of pile numbers DLI18 + 628, DLI18 + 631, DLI18 + 634, and DLI18 + 637. The grouting backfill was completed on February 8, 2025. Subsequently, continuous convergence monitoring was carried out on this section of the tunnel, and the tunnel was in a stable state. The convergence monitoring points of the tunnel section were arranged at the top and waist to comprehensively evaluate the safety and stability of the tunnel and to meet different monitoring method and technical requirements. (In the section pile number DLI18 + 628, DLI represents the project name or line code; the mileage number (18) represents the whole kilometer number of this section from the project starting point, that is, at 18 kilometers; the offset (+628) indicates the position 628 meters further forward based on the 18-kilometer reference point. Therefore, this section is actually located at 18.628 kilometers from the starting point.)

[0067] The monitoring points at the top and the left and right ends of the tunnel section can better reflect the overall deformation characteristics of the tunnel. The settlement monitoring at the top of the section (point A) can reveal the subsidence of the vault, while the convergence monitoring at the left and right ends (points B and C) can capture the changes in the cross-section of the tunnel.

[0068] In summary, from the cross-section convergence values Figure 2 of the test results, when using this method to treat the crown cavity collapse, the change amount of the convergence value of the tunnel section is 0.31 - 0.52 mm, and the change rate of the convergence value is 0.09 - 0.16 mm / d; from the cross-section convergence values Figure 3 of the test results, when using this method to treat the crown cavity collapse, the change amount of the convergence value of the tunnel section is -0.36 - 0.24 mm, and the change rate of the convergence value is -0.11 - 0.07 mm / d; from the cross-section convergence values Figure 4 of the test results, when using this method to treat the crown cavity collapse, the change amount of the convergence value of the tunnel section is 0.11 - 0.26 mm, and the change rate of the convergence value is 0.03 - 0.08 mm / d; from the cross-section convergence values Figure 5 of the test results, when using this method to treat the crown cavity collapse, the change amount of the convergence value of the tunnel section is 0.19 - 0.32 mm, and the change rate of the convergence value is 0.06 - 0.10 mm / d;

[0069] According to the "Monitoring Report on Tunnel Engineering in the Kyushu Region (2023 Revised Edition)" released by the Ministry of Land, Infrastructure, Transport and Tourism of Japan, the convergence rate of the tuff formation shows the following pattern: in the initial deformation stage (0 - 7 days after excavation), the maximum daily change rate in the unlined state reaches 2.8 - 3.5 mm / d, and the typical monitoring curve shows that the first 3 days account for more than 60% of the total; in the stable control stage (7 - 30 days after support), after using prestressed anchor rods + shotcrete support, it drops to 0.5 - 1.2 mm / d, and locally reaches 1.8 mm / d in special fractured zones (requiring supplementary grouting reinforcement). Due to its good cementation, tuff has high strength and low deformation, while the tuffaceous volcanic ash formation has weak cementation or is unconsolidated, resulting in low strength, easy deformation, and higher convergence values. Therefore, the geological characteristics of the tuffaceous volcanic ash formation make the cross-section have a higher deformation rate during the collapse cavity grouting backfill compared to the tuff formation.

[0070] For the method for treating the crown collapse cavity of the tuffaceous volcanic ash formation proposed in this application, both the change amount and the change rate of the convergence value of the tunnel cross-section are much lower than those of the tuff formation, and can significantly reduce the change rate of the convergence value of the tunnel cross-section in the tuffaceous volcanic ash formation.

[0071] It should be noted that although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. 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 present invention.

[0072] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and its equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for treating the roof arch collapse cavity of a tuffaceous volcanic ash formation, characterized in that, The method grouts the crown cavity through three grouting procedures; The three grouting procedures include: the first shallow grouting for sealing, the second middle grouting for backfilling, and the third deep grouting for backfilling; The grouting fluid for the first shallow grouting for sealing is HCH-II type chemical grout, and the grouting area is within 120° of the tunnel crown and 0 - 3m outside the tunnel crown contour, that is, grouting layer I; The grouting fluid for the second middle grouting for backfilling is cement slurry or cement double-fluid slurry, and the grouting area is within 120° of the tunnel crown and 3 - 4.5m outside the tunnel crown contour, that is, grouting layer II; The grouting fluid for the third deep grouting for backfilling is cement slurry or cement double-fluid slurry, and the grouting area is within 120° of the tunnel crown and 4.5 - 6m outside the tunnel crown contour, that is, grouting layer III; The cement double-fluid slurry is cement slurry - water glass double-fluid slurry.

2. The method according to claim 1, characterized in that, The method specifically includes the following steps, S1, the first shallow grouting for sealing: Uniformly open five grouting holes at the bottom of the cross-section of grouting layer I, drill the self-advancing hollow anchor through the grouting holes to a position 2.5m outside the tunnel crown contour, and use a special chemical grouting pump to pump the HCH-II type chemical grout into grouting layer I through the self-advancing hollow anchor; Along the tunnel extension direction, the first shallow grouting for sealing is carried out every 1.5m; S2, the second middle grouting for backfilling: Along the tunnel extension direction, uniformly open five backfilling holes 1 at the bottom 0.5m away from the cross-section of grouting layer I, drill the self-advancing hollow anchor through the backfilling holes 1 to a position 4.5m outside the tunnel crown contour, and use a grouting pump to pump the cement slurry or cement double-fluid slurry into grouting layer II through the self-advancing hollow anchor; Along the tunnel extension direction, the second middle grouting for backfilling is carried out every 1.5m; S3, the third deep grouting for backfilling: Along the tunnel extension direction, uniformly open five backfilling holes 2 at the bottom 1m away from the cross-section of grouting layer I, drill the self-advancing hollow anchor through the backfilling holes 2 to a position 6m outside the tunnel crown contour, and use a grouting pump to pump the cement slurry or cement double-fluid slurry into grouting layer III through the self-advancing hollow anchor. Along the tunnel extension direction, the third deep grouting for backfilling is carried out every 1.5m.

3. The method according to claim 1 or 2, characterized in that, The water-cement volume ratio in the cement slurry is 0.5:1; in the cement double-fluid slurry, the volume ratio of the cement slurry to the water glass slurry is 1:

1.

4. The method according to claim 2, wherein The grouting holes, backfilling holes 1 and backfilling holes 2 in S1, S2 and S3 are arranged staggeredly.

5. The method according to claim 2, wherein The grouting pressure of the special chemical grouting pump in S1 is 0.3 - 0.5MPa; the grouting pressure of the grouting pump in S2 is 0.5 - 1MPa; the grouting pressure of the grouting pump in S3 is 0.5 - 1.5MPa.

6. The method according to claim 2, wherein The method further includes the following steps: S0, establish the initial support.

7. The method according to claim 2, wherein The method further includes the following steps: S4, after the grouting is completed, set monitoring points in the tunnel.

8. The method according to claim 7, characterized in that In S4, the monitoring points are located at the top and the left and right ends of the tunnel cross-section. Three monitoring points form a detection surface, and the detection surfaces are evenly distributed along the tunneling direction. The distance between adjacent two detection surfaces is 3 - 5m.

9. The method according to claim 8, wherein Total stations are set on the detection surfaces, which can collect the convergence data of the monitoring points.

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