A method for tunnel side cavity excavation

Abstract

The application discloses a kind of tunnel side part solution cavity's partial excavation construction method, its specific steps are: ① after discovering solution cavity, timely adjustment design parameter, arch part is carried out ahead of time support;② excavation and support uncovered solution cavity part, and reserve core soil;③ solution cavity part is installed drainage pipe and grouting pipe, carries out drainage and grouting operation, uncovered solution cavity part continues to forward construction at this time;④ after solution cavity internal grouting is completed, excavate solution cavity bottom, and carry out solution cavity bottom initial support, so that it is connected with uncovered solution cavity part initial support;⑤ after ensuring that initial support is stable, excavate core soil.The application solves the problem that when solution cavity appears in tunnel side part, stress of surrounding rock is uneven, deformation is difficult to control, construction stagnates and the like, prevents solution cavity collapse and rock block from happening, while ensuring tunnel construction progress and structural safety.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering construction and can be used when karst cavities appear on the side of a tunnel. Specifically, it is a method for sectional excavation of karst cavities on the side of a tunnel. Background Technology

[0002] When constructing tunnels in karst areas, geological phenomena such as water-bearing caves, karst cavities, and underground rivers are frequently encountered. If these phenomena are not properly handled during construction, they may cause disasters such as mudslides, water inrushes, karst cavity collapses, and tunnel collapses, thereby affecting the progress of the project and the safety of personnel.

[0003] When encountering karst caves during tunnel construction, the traditional solution is to halt work, perform grouting and filling, and then resume excavation. The drawbacks of this method are the unknown workload of karst cave treatment, significant impact on construction progress, and the inability to guarantee the safety and reliability of the grouting structure, easily leading to secondary work stoppages. For example, ZL202010295693.7 proposes a tunnel construction method for a deep, large karst cave section with no filling across the side; ZL202010294929.5 proposes a tunnel construction method for a narrow, shallow karst cave section with no filling across the side; and ZL202122834938.1 proposes a karst cave sealing structure on the outer side of a water-rich tunnel. All these methods require work stoppage for treatment, with excavation only resuming after grouting and the construction of the support structure. Furthermore, if the karst cavity is too large or the sealing structure lacks stability, it will severely affect construction progress and efficiency, thereby increasing project costs. Summary of the Invention

[0004] To address the problems of delayed construction progress and difficulty in ensuring structural safety in existing methods, this invention proposes a sectional excavation method for karst cavities on the side of tunnels. By dividing the tunnel into two parts, an uncovered karst cavity and a covered karst cavity, and carrying out sectional excavation and construction, this method solves problems such as uneven stress on the surrounding rock, difficulty in controlling deformation, and delayed construction progress, thereby improving construction quality and efficiency.

[0005] The technical solution of the present invention is as follows:

[0006] A method for sectional excavation of a karst cavity on the side of a tunnel includes the following steps:

[0007] S1: After discovering the lateral cavities during tunnel excavation, the initial support of the tunnel face was reinforced, and advanced support was installed at the tunnel arch.

[0008] S2: Excavate the rock mass of the uncovered karst cavity area, apply initial support to the uncovered karst cavity area, install anchor bolts and sprayed concrete, and reserve core soil;

[0009] S3: Drill holes on the side of the side cavity to install drainage pipes and grouting pipes for drainage and grouting operations;

[0010] S4: After the grouting inside the side cavity is completed, excavate the rock mass at the bottom of the cavity and construct the initial support covering the cavity, connecting it with the initial support of the uncovered cavity, and install anchor bolts and shotcrete.

[0011] S5: Monitor the deformation parameters of the initial support of the covered cavity area, and excavate the core soil after ensuring that the initial support of the covered cavity area is stable.

[0012] S6: Repeat steps S2, S3, S4 and S5 until the initial support of the uncovered cavity section and the initial support of the covered cavity section are on the same excavation section.

[0013] In the above-mentioned method for the sectional excavation of the karst cavity on the side of the tunnel, in step S1, the advance support uses perforated steel pipes with a length of 3.0 to 4.5 meters and a diameter of φ42 mm, arranged in a quincunx pattern; the arrangement density of the rock mass in the uncovered karst cavity area is 40 cm circumferentially and 300 cm longitudinally; the arrangement density of the karst cavity area on the side should be 20 cm circumferentially and 180 cm longitudinally.

[0014] In the above-mentioned method for sectional excavation of the cavities on the side of the tunnel, the initial support reinforcement measures in step S1 include reducing the spacing between steel frames, increasing the strength of the steel frames, increasing the number of steel mesh layers, and increasing the thickness of shotcrete.

[0015] In the above-mentioned method for sectional excavation of the karst cavity on the side of the tunnel, the drainage pipe and the grouting pipe are located on the upper part of the core soil and on the side of the karst cavity, and are installed by drilling using a pneumatic drilling rig.

[0016] In the above-mentioned method for sectional excavation of the karst cavity on the side of the tunnel, the drainage pipe is a φ100mm corrugated pipe with a longitudinal spacing of 50cm, and the end of the corrugated pipe is wrapped with geotextile.

[0017] In the above-mentioned method for sectional excavation of the cavities on the side of the tunnel, the grouting pipe is a φ42mm hot-rolled seamless steel pipe with a length of 0.7m. The pipe is arranged in a quincunx pattern with a circumferential spacing of 50cm and a longitudinal spacing of 150cm. The grouting material is silicate cement slurry with a water-cement weight ratio of 0.5:1. The grouting pressure is controlled within 0.1MPa.

[0018] In the above-mentioned method for sectional excavation of the karst cavity on the side of the tunnel, the excavation cycle length of the rock mass in the uncovered karst cavity area is 1.2 to 1.8 m, and the excavation cycle length of the rock mass in the covered karst cavity area is 1.8 to 3.0 m.

[0019] In the above-mentioned method for sectional excavation of the karst cavity on the side of the tunnel, in steps S2 and S4, the bottom of the initial support for the uncovered karst cavity and the initial support for the covered karst cavity are equipped with locking anchor bolts. The locking anchor bolts are located 30cm above the bottom of the initial support steel frame and are welded and fixed to the steel frame.

[0020] In the above-mentioned method for the partial excavation of the karst cavity on the side of the tunnel, in step S5, the initial support stability is determined by monitoring and measuring with a total station. When the monitored displacement rate is less than 1 mm / d, the core soil is excavated.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] 1. This invention divides the tunnel into two parts: an uncovered karst cavity and a covered karst cavity, and excavates and constructs them in sections. By reserving core soil and surrounding rock in the karst cavity area, the original stress field near the karst cavity is protected, avoiding stress concentration and large deformation in the surrounding rock near the karst cavity. This also prevents the karst cavity from collapsing and rock fragments from falling during tunnel construction.

[0023] 2. This invention divides the tunnel into two parts: an uncovered karst cavity and a covered karst cavity, allowing for sectional excavation and construction. By excavating and constructing the uncovered karst cavity section, the construction progress and efficiency are ensured, avoiding the shortcomings of traditional methods such as work stoppages for treatment and delays in construction when the volume of the karst cavity is unknown. Simultaneously, it optimizes the problem of limited working space and restricted areas for grouting, support, and drainage in traditional karst cavity treatment, improving the efficiency and quality of karst cavity treatment.

[0024] 3. This invention reinforces the surrounding rock and initial support by strengthening the arch pre-support and setting arch foot anchor bolts, thereby enhancing the self-stabilizing ability of the surrounding rock and ensuring the safety and reliability of the support structure. At the same time, the monitoring and measurement method ensures the stability of the initial support in the cavity area, avoiding problems such as weak sealing structure and easy secondary collapse, thus ensuring construction quality and structural safety. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the construction principle of the rock mass in the cavity section of this invention.

[0026] Figure 2 This is a three-dimensional schematic diagram illustrating the arrangement principle of construction equipment for rock mass in the solution cavity area according to the present invention.

[0027] Figure 3 This is a partial schematic diagram of the construction of the cavity section in this invention.

[0028] The attached diagram is labeled as follows: 1-lateral cavity, 2-rock mass not covered by the cavity, 3-core soil, 4-initial support for the uncovered cavity, 41-advanced support, 42-grouting pipe, 43-drainage pipe, 44-anchor bolt, 5-rock mass covered by the cavity, 6-initial support for the covered cavity. Detailed Implementation

[0029] like Figure 1-3 As shown, this invention discloses a method for sectional excavation of karst cavities on the side of a tunnel. The tunnel is divided into two parts: an uncovered karst cavity and a covered karst cavity, which are excavated and constructed in sections. The excavation of the tunnel face and the treatment of the karst cave are carried out simultaneously. By adopting methods such as strengthening the arch support in advance, setting the arch foot anchor bolts, and reserving core soil and surrounding rock in the karst cavity area, the self-stabilizing ability of the surrounding rock and the safety and reliability of the support structure are protected, and the problems of work stoppage and construction delays in traditional methods are solved.

[0030] Specifically, the following steps are included:

[0031] S1: Initial support reinforcement and advanced support layout:

[0032] During tunnel construction, after discovering the karst cavity 1 on the side of the tunnel, the initial support of the tunnel face was promptly reinforced, and advance support 41 was installed in the arch. The advance support 41 should be densely arranged around the karst cavity 1 on the side.

[0033] During tunnel construction, when encountering a lateral karst cavity 1 during face excavation, to prevent surrounding rock instability and ensure structural safety and stability, initial support parameters and advanced support should be promptly strengthened to complete this cycle of construction. Specific initial support strengthening measures include: reducing steel frame spacing, increasing steel frame strength, increasing the number of steel mesh layers, and increasing shotcrete thickness. Simultaneously, 3.0 to 4.5-meter long, φ42mm perforated steel pipes are used for advanced rock support 41. The arrangement is quincunx-shaped, with a circumferential spacing of 40cm and a longitudinal spacing of 300cm for the rock mass 2 not covered by the karst cavity; the perimeter spacing for the lateral karst cavity 1 should be 20cm circumferentially and 180cm longitudinally.

[0034] S2: Proceed to the next cycle of construction, excavating the uncovered rock mass in the solution cavity 2:

[0035] S2.1 Adjustment Design: When encountering a side cavity 1 during construction, the size of the side cavity 1 should be observed and measured first. The tunnel should be divided into rock mass 2 with uncovered cavity and rock mass 5 with covered cavity. Based on the divided area, the steel frame lengths of the initial support 4 with uncovered cavity and the initial support 6 with covered cavity should be determined.

[0036] S2.2 Excavation operation: Excavate the rock mass 2 of the uncovered karst cavity, with an excavation cycle length of 1.2 to 1.8 m; at the same time, retain the core soil 3 and the rock mass 5 covering the karst cavity to protect the original stress field near the karst cavity and prevent the karst cavity from collapsing and rock falling during tunnel construction.

[0037] S2.3 Steel frame installation: Perform initial support 4 for the uncovered cavity area, that is, add steel frame, install longitudinal connecting bars and steel mesh. The specific initial support parameters are the same as in step S1.

[0038] S2.4 Anchor Bolt Installation: Install arch foot locking anchor bolts 44 and arch pre-support 41 to enhance the self-stabilizing ability of the surrounding rock and ensure the safety and reliability of the support structure. Among them, the arch foot locking anchor bolts 44 should be located 30cm above the arch feet on both sides of the initial support 4 steel frame and welded to the steel frame; the arch pre-support 41 is the same as in step S1.

[0039] S2.5 Shotcrete: After the steel frame, longitudinal connecting bars, steel mesh, anchor bolts 44 and pre-support 41 of the rock mass 2 not covered by the karst cavity are completed, shotcrete operation is carried out to complete the initial support 4 of the uncovered karst cavity, and to seal and stabilize the surrounding rock.

[0040] S3: Treatment of side cavity 1:

[0041] S3.1 Drainage Operation: After the excavation of the rock mass 2 in the uncovered cavity area and the initial support 4 are completed, drainage pipes are drilled on the upper part of the core soil 3 and the side of the cavity 1 using a pneumatic down-the-hole drill. The diameter of the holes is 100mm and the longitudinal spacing is 50cm. After drilling, φ100mm corrugated pipes are installed as drainage pipes 43. The ends of the corrugated pipes are wrapped with geotextile to prevent sand and gravel from blocking the drainage channels.

[0042] S3.2 Grouting Operation: When the drainage volume is small, a pneumatic drilling rig is used to drill holes for grouting pipes on the upper part of the core soil 3 and the side of the side cavity 1. The diameter of the holes is 45mm, and the arrangement density is 50cm in the circumferential direction and 150cm in the longitudinal direction, in a staggered pattern. After drilling, a φ42mm hot-rolled seamless steel pipe is installed as grouting pipe 42, with a length of 0.7m. After installation, grouting operation is carried out. The grouting material is silicate cement slurry with a water-cement ratio of 0.5:1 by weight, and the grouting pressure is controlled within 0.1MPa.

[0043] S3.3 Simultaneous construction of uncovered cavities: When grouting is in progress, excavation of the uncovered cavities 2 rock mass and initial support 4 are carried out simultaneously, that is, repeating step S2. The excavation cycle length is 1.2 to 1.8m to ensure construction progress and efficiency.

[0044] S3.4 Further drainage and grouting: When step S2 is repeated and the side cavity 1 has not been grouted, the side of the newly constructed uncovered cavity can be initially supported 4. Drilling can continue to install drainage pipes and grouting pipes to increase the drainage and grouting area. That is, repeat steps S3.1 and S3.2 to improve the treatment efficiency of the side cavity 1.

[0045] S3.5: Repeat the construction work for the uncovered cavity area in S3.3 and the drainage and grouting work in S3.4 until the grouting of the side cavity 1 is completed.

[0046] S4: Excavation of the rock mass covering the karst cavity 5:

[0047] S4.1 Excavation Operation: After the grouting of the side cavity 1 is completed, excavate the bottom of the rock mass 5 covering the cavity, while retaining the core soil 3. The excavation cycle length is 1.8-3.0m. The purpose of retaining the core soil is to create a counter-pressure effect, avoiding stress concentration and large deformation in the surrounding rock near the cavity, and ensuring the safety and stability of the cavity.

[0048] S4.2 Support Operation: Construct the initial support 6 for the cavity area, connecting it to the initial support 4 for the uncovered cavity area. Specifically, this involves constructing a steel frame, longitudinal connecting bars, steel mesh, anchor bolts 44, and shotcrete. The anchor bolts 44 are located 30cm above the bottom of the initial support steel frame and are welded to it. The specific parameters for the steel frame, longitudinal connecting bars, steel mesh, and shotcrete are the same as in step S1.

[0049] S5: Monitoring and Measurement and Core Soil 3 Excavation:

[0050] The deformation of the initial support 6 in the cavity area was monitored in real time using a total station. When the deformation rate was less than 1 mm / d, it indicated that the initial support 6 had entered a stable state, and the core soil 3 could be excavated at this time.

[0051] S6 Cyclic Construction:

[0052] Repeat steps S2, S4 and S5 until the initial support 4 for the uncovered cavity and the initial support 6 for the covered cavity are on the same excavation section, that is, the initial support 6 for the cavity with an excavation cycle length of 1.8 to 3.0 m catches up with the initial support 4 for the uncovered cavity with an advance of 1.2 to 1.8 m in the previous cycle.

Claims

1. A method for sectional excavation of a cavitary cavity on the side of a tunnel, characterized in that, Includes the following steps: S1: After discovering the side cavity (1) during tunnel excavation, the initial support of the tunnel face was strengthened, and advanced support (41) was set in the tunnel arch. S2: Excavate the rock mass in the uncovered karst cavity area (2), construct the initial support for the uncovered karst cavity area (4), install anchor bolts and sprayed concrete, and reserve core soil (3); S3: Drill holes on the side of the side cavity (1) to install drainage pipe (43) and grouting pipe (42) for drainage and grouting operations; S4: After the grouting inside the side cavity (1) is completed, the rock mass (5) covering the cavity is excavated, and the initial support (6) covering the cavity is constructed to connect it with the initial support (4) of the uncovered cavity. Locking anchors and shotcrete are then installed. S5: Monitor the deformation parameters of the initial support (6) covering the cavity, and after ensuring the stability of the initial support (6) covering the cavity, excavate the core soil (3). S6: Repeat steps S2, S3, S4 and S5 until the initial support (4) of the uncovered cavity and the initial support (6) of the covered cavity are in the same excavation section. In step S1, the advanced support (41) uses perforated steel pipes with a length of 3.0 to 4.5 meters and a diameter of φ42 mm to be arranged in a quincunx pattern; the arrangement density of the rock mass (2) in the uncovered karst cavity area is 40 cm in circumferential spacing and 300 cm in longitudinal spacing; the arrangement density of the lateral karst cavity (1) area should be 20 cm in circumferential spacing and 180 cm in longitudinal spacing. In steps S2 and S4, the bottom of the uncovered cavity initial support (4) and the covered cavity initial support (6) are provided with locking anchor rods (44). The locking anchor rods (44) are located 30cm above the bottom of the initial support steel frame and are welded and fixed to the steel frame. In step S5, the stability of the initial support (6) covering the cavity is determined by monitoring and measuring with a total station. When the monitored displacement rate is less than 1 mm / d, the core soil (3) is excavated.

2. The method for sectional excavation of a tunnel side cavity according to claim 1, characterized in that: In step S1, the initial support reinforcement measures include reducing the spacing between steel frames, increasing the strength of the steel frames, increasing the number of steel mesh layers, and increasing the thickness of shotcrete.

3. The method for sectional excavation of a tunnel side cavity according to claim 1, characterized in that: The drainage pipe (43) and grouting pipe (42) are located on the upper part of the core soil (3) and the side of the side cavity (1), and are installed by drilling with a pneumatic drilling rig.

4. The method for sectional excavation of a tunnel side cavity according to claim 3, characterized in that: The drainage pipe (43) is a φ100mm corrugated pipe with a longitudinal spacing of 50cm, and the ends of the corrugated pipe are wrapped with geotextile.

5. The method for sectional excavation of a tunnel side cavity according to claim 4, characterized in that: The grouting pipe (42) is a φ42mm hot-rolled seamless steel pipe with a length of 0.7m. It is arranged in a plum blossom pattern with a circumferential spacing of 50cm and a longitudinal spacing of 150cm. The grouting material is silicate cement slurry with a water-cement weight ratio of 0.5:

1. The grouting pressure is controlled within 0.1MPa.

6. The method for sectional excavation of a tunnel side cavity according to claim 1, characterized in that: The excavation cycle length of the rock mass (2) without the karst cavity is 1.2 to 1.8 m, and the excavation cycle length of the rock mass (5) with the karst cavity is 1.8 to 3.0 m.

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