High ground stress carbonaceous slate tunnel grading support method

Abstract

The invention discloses a high crustal stress carbonaceous slate tunnel grading support method which comprises the following steps: S1, constructing crustal stress release holes in a tunnel face to predict a large deformation grade, and determining a reserved deformation amount; s2, an advanced small guide pipe is constructed on the tunnel face arch wall part for advanced pre-reinforcement; s3, a tunnel is excavated; s4, primary support is constructed, and system anchor rods and steel arches are constructed according to the large deformation grade; s5, when the deformation of the primary support is 1 / 3-1 / 2 of the actual reserved amount, a second layer of primary support is constructed; and S6, secondary lining is constructed according to the large deformation grade. The method is suitable for supporting systems with different deformation grades, the problems of deformation limit invasion, arch replacement and rock falling are solved, the construction progress is accelerated, and the personal safety of constructors is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel structures, and in particular to a hierarchical support method for a high-in-situ stress carbonaceous slate tunnel. Background Art

[0002] Carbonaceous slate is a metamorphic rock formed by low-temperature and low-pressure metamorphism of mud or silt sedimentary rocks rich in organic matter. At the microscopic level, it is composed of numerous flakes arranged and combined to form a fissure layered structure. It is easy to break and easily breaks along the parallel bedding direction. It has low strength and poor mechanical properties. It is widely distributed in the western region of my country. At the same time, due to the interaction between the Pacific Plate and the Indian Plate in the western region, high tectonic stress is stored in the process of terrain formation, so that carbonaceous slate tunnels usually face serious large deformation problems caused by high ground stress during construction, resulting in a series of problems such as steel frame distortion, steel frame fracture, primary support cracking, and secondary lining cracking.

[0003] For high-in-situ stress carbonaceous slate large deformation tunnels, the current support methods basically control tunnel deformation through the "yield support" or "strong support" method, lacking a support system suitable for different deformation levels, resulting in large deformation problems. Therefore, it is necessary to take targeted support measures for different deformation levels of carbonaceous slate tunnels under high in-situ stress. Summary of the invention

[0004] The purpose of the present invention is to provide a graded support method for high-ground stress carbonaceous slate tunnels to solve the technical problems in the prior art of lacking a support system suitable for different deformation levels, frequent occurrence of large deformation diseases, resulting in serious delays in tunnel construction schedules, and threats to the safety of construction workers.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a hierarchical support method for a high-in-situ stress carbonaceous slate tunnel, comprising the following steps:

[0007] S1. Construct ground stress relief holes on the tunnel face to predict the large deformation level and determine the reserved deformation amount;

[0008] S2. Pre-reinforce the arch wall of the face with an advance small conduit;

[0009] S3, tunnel excavation;

[0010] S4. Carry out initial support, and construct system anchors and steel arch frames according to the large deformation level;

[0011] S5. When the initial support deformation is 1 / 3 to 1 / 2 of the actual reserved amount, the second layer of initial support is applied;

[0012] S6. Construct secondary lining according to the maximum deformation level.

[0013] Furthermore, the large deformation levels are level I, level II, and level III, and the corresponding reserved deformation amounts are 20 cm, 40 cm, and 50 cm, respectively.

[0014] Furthermore, in order to accurately predict the deformation during tunnel construction, the geological conditions along the tunnel are carefully surveyed through advanced geological drilling and advanced geological forecasting to obtain accurate geological conditions. Combined with the survey results, the ground stress conditions, rock mechanical properties and other information are analyzed to accurately predict the large deformation level of the tunnel.

[0015] Furthermore, the advance small duct is arranged within the tunnel arch wall and is a hot-rolled seamless steel pipe with a diameter of 42 mm and a length of 4 m. The grouting hole diameter of the advance small duct is 6 to 8 mm, the outward inclination angle α=5° to 10°, and the overlap length is not less than 1 m.

[0016] Furthermore, the S3 adopts a step method to excavate the tunnel, and locking anchor rods are arranged on both sides of the bottom of the step.

[0017] Furthermore, the locking foot anchor rod is a self-advancing locking foot anchor rod, which is 4 meters long and has eight rods in total per frame.

[0018] Furthermore, when the maximum deformation level in S4 is level III, prestressed anchor rods are also required; the system anchor rods include 4-meter mortar anchor rods, 8-meter mortar anchor rods, and 10-meter mortar anchor rods.

[0019] Furthermore, the secondary linings corresponding to the large deformation levels I, II and III in S6 are 55 cm, 55 cm and 60 cm respectively.

[0020] The small pipe is injected into the unexcavated soil in front of the face, and becomes a whole with the surrounding rock through grouting, giving full play to the bearing capacity of the surrounding rock, forming an active support structure with longitudinal continuous beams and transverse reinforcement arches, improving the passive force distribution of the support system, and enhancing the overall stability of the tunnel; on the other hand, the physical and mechanical parameters of the surrounding rock and soil are improved through high-pressure grouting, forming a reinforced area with greater rigidity in the unexcavated rock and soil, reducing the degree of release of the disturbed surrounding rock load, and also playing a waterproof role. Through these two aspects, the stability of the rock and soil is improved, and when the tunnel is excavated, the plastic zone area can be reduced and the time for the appearance of the plastic zone can be delayed.

[0021] Based on the above technical solution, the embodiments of the present invention can at least produce the following technical effects:

[0022] (1) The hierarchical support method for high-in-situ stress carbonaceous slate tunnels provided by the present invention selects reasonable reserved deformation amount, support parameters and excavation methods according to the deformation grade. The tunnel deformation is effectively controlled, the monthly construction progress is improved by 32.45%, and the project cost is reduced by 27.1%.

[0023] (2) The hierarchical support method for high-ground stress carbonaceous slate tunnels provided by the present invention is applicable to support systems with different deformation levels, and solves the problems of deformation limit intrusion, arch replacement, and rock block falling, which not only speeds up the construction progress, but also ensures the personal safety of construction workers.

[0024] (3) Advance support is an important means to maintain the stability of the tunnel face and ensure construction safety. In conventional design, advance support is arranged within the 120° range of the arch. In the large deformation section, not only is the stability of the tunnel face top poor and the block falling is serious, but the stability of the side wall is also extremely poor, and a large amount of spalling will occur after excavation. This tunnel is an auxiliary tunnel with a small cross-section. According to the treatment principle of "fast excavation and fast support, early closure of initial support", the two-step with inverted arch excavation method is selected, and a small advance guide tube is applied to the arch wall. This not only ensures the stability of the side wall in the initial excavation, but also has a good effect on the subsequent deformation control. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0026] Figure 1 This is a cross-sectional view of a level I large deformation support according to an embodiment of the present invention;

[0027] Figure 2 It is a cross-sectional view of a level II large deformation support according to an embodiment of the present invention;

[0028] Figure 3 It is a cross-sectional view of a level III large deformation support according to an embodiment of the present invention;

[0029] In the figure: 1. 4-meter mortar anchor, 2. 8-meter mortar anchor, 3. 10-meter mortar anchor, 4. 10-meter prestressed anchor, 5. First layer initial support, 6. Second layer initial support, 7. Secondary lining, 8. Locking foot anchor. DETAILED DESCRIPTION

[0030] The following will combine the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0031] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application; the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance; in addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0032] The present invention provides a hierarchical support method for a high-in-situ stress carbonaceous slate tunnel, comprising the following steps:

[0033] S1. Construct ground stress relief holes on the tunnel face to predict the large deformation level and determine the reserved deformation amount;

[0034] S2. Pre-reinforce the arch wall of the tunnel face with an advance small conduit; the advance small conduit is laid within the tunnel arch wall, and is a hot-rolled seamless steel pipe with a diameter of 42mm and a length of 4m. The diameter of the grouting hole 8 of the advance small conduit is 6-8mm, the outward inclination angle α=5°~10°, and the overlap length is not less than 1m. The grouting slurry can be silicate cement slurry, the grouting pressure is between 1 and 2MPa, the initial setting time is about 1h, the 3h strength is not less than 2MPa, and the final setting strength is between 6 and 8MPa.

[0035] S3, tunnel excavation: The tunnel excavation adopts the step method, and the locking anchors are arranged on both sides of the bottom of the step. The locking anchors are self-propelled locking anchors, 4m long, and 2 at each location.

[0036] S4, construct the first layer of initial support 5, and construct system anchors and steel arch frames according to the large deformation level;

[0037] S5. When the initial support deformation is 1 / 3 to 1 / 2 of the actual reserved amount, the second layer of initial support 6 is applied;

[0038] S6. Apply secondary lining 7 according to the large deformation level.

[0039] When the maximum deformation level in S4 is level III, prestressed anchor rods 4 are also required; the system anchor rods include 4-meter mortar anchor rods 1, 8-meter mortar anchor rods 2, and 10-meter mortar anchor rods 3.

[0040] The large deformation level and construction parameters are shown in Table 1. The large deformation level support cross-section diagram is shown in Figure 1-3 As shown,

[0041] Table 1

[0042]

[0043]

[0044] A certain tunnel section H2DK1+278.6~H2DK1+218.6 showed large deformations of varying degrees, and the support intrusion section totaled 60m. Twenty-four tunnel sections were inspected, of which six had deformation rates exceeding 30mm / d, and ten had deformation rates between 10mm / d and 30mm / d. The total deformation of some tunnels was close to the meter level. Combining the inspection data of the 24 sections, the large deformation level showed random and disordered characteristics. The support system of the present invention was adopted after the H2DK1+218.6 section, and the reasonable reserved deformation amount, support parameters and excavation methods were selected according to the deformation level, so that the deformation of the tunnel was effectively controlled. The monthly construction progress increased from 20.4m to 30.2m, an increase of 32.45%. In addition, the project cost was reduced from 170,000 / linear meter to 124,000 / linear meter, a reduction of 27.1%.

[0045] The structures, functions and connection forms disclosed in this article can be implemented in other ways. For example, the embodiments described above are only exemplary, for example, multiple components can be combined or integrated into another component; in addition, each functional component in each embodiment of this article can be integrated into one functional component, or each functional component can exist physically separately, or two or more functional components can be integrated into one functional component.

[0046] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, which all fall within the protection scope of the present invention.

Claims

1. A hierarchical support method for high-in-situ stress carbonaceous slate tunnels, characterized in that: The following steps are involved: S1. Construct ground stress relief holes on the tunnel face to predict the large deformation level and determine the reserved deformation amount; S2. Pre-reinforce the arch wall of the face with a small advance conduit; S3, tunnel excavation; S4. Carry out initial support, and construct system anchors and steel arch frames according to the large deformation level; S5. When the initial support deformation is 1 / 3 to 1 / 2 of the actual reserved amount, the second layer of initial support is applied; S6. Construct secondary lining according to the maximum deformation level.

2. The hierarchical support method for high-in-situ stress carbonaceous slate tunnel according to claim 1 is characterized in that: The large deformation levels are Level I, Level II, and Level III, and the corresponding reserved deformation amounts are 20 cm, 40 cm, and 50 cm, respectively.

3. The hierarchical support method for high ground stress carbonaceous slate tunnel according to claim 1 is characterized in that: The advance small duct is arranged within the tunnel arch wall. It is a hot-rolled seamless steel pipe with a diameter of 42mm and a length of 4m. The grouting hole diameter of the advance small duct is 6-8mm, the outward inclination angle α=5°~10°, and the overlap length is not less than 1m.

4. The hierarchical support method for high ground stress carbonaceous slate tunnel according to claim 1 is characterized in that: The S3 tunnel is excavated using a step method, and locking anchor rods are arranged on both sides of the bottom of the step.

5. The hierarchical support method for high-in-situ stress carbonaceous slate tunnel according to claim 4 is characterized in that: The locking foot anchor rod is a self-advancing locking foot anchor rod, 4 meters long, with a total of eight rods per frame.

6. The hierarchical support method for high-in-situ stress carbonaceous slate tunnel according to claim 1 is characterized in that: When the maximum deformation level in S4 is level III, prestressed anchor rods are also required; the system anchor rods include 4-meter mortar anchor rods, 8-meter mortar anchor rods, and 10-meter mortar anchor rods.

7. The hierarchical support method for high ground stress carbonaceous slate tunnel according to claim 1 is characterized in that: The secondary linings corresponding to the large deformation levels I, II and III in S6 are 55cm, 55cm and 60cm respectively.

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