Soft rock tunnel yielding filling supporting structure and construction method

Abstract

The invention relates to the technical field of soft rock tunnel supporting, in particular to a soft rock tunnel yielding filling supporting structure and a construction method. The structure is constructed by the method. The method comprises the steps of obtaining crustal stress data, rock stratum mechanics data and surrounding rock deformation data; when the surrounding rock deformation data exceed a deformation threshold value, the surrounding rock deformation area and the expanding excavation amount are locked through model simulation; the length of the corresponding step is increased according to the expanding excavation amount, and the height of the corresponding step is reduced; anchor rods are installed, and the surrounding rock surface is sealed; laying a steel arch; an injection hole is reserved in the top of the surrounding rock deformation area, a filling material is injected, and a yielding filling layer is formed; and concrete is sprayed on the surrounding rock contour surface corresponding to each step again to form a primary support structure. The construction and operation safety of the tunnel can be guaranteed when the deformation of the soft rock tunnel is large and the duration time is long, and the construction cost and workload are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of soft rock tunnel support, and particularly relates to a yielding and filling support structure for soft rock tunnels and a construction method therefor. Background Technique

[0002] During the construction and excavation of high in-situ stress stratified soft rock tunnels, under the action of strong extrusion stress of the weak surrounding rock, soft rock tunnels are characterized by large deformation, high deformation rate and long deformation time. As a result, asymmetric extrusion large deformation disasters often occur in the surrounding rock of the excavated soft rock tunnels, which will cause waste of human and material resources for minor repairs at least.

[0003] At present, for high in-situ stress soft rock tunnels, conventional three-step excavation is generally adopted to control the deformation of the surrounding rock during the construction process. Further, on the basis of the conventional three-step excavation, the industry has also put forward the support concept of "combination of yielding and resistance" for soft rock tunnels, and derived support structures such as yielding steel arches, flexible filling layers and constant resistance bolts. The combination of these support structures and the conventional three-step excavation can only have good support effects when the deformation of the surrounding rock is small; when the deformation of the soft rock tunnel is large and lasts for a long time, the combination of these support structures and the conventional three-step excavation cannot well ensure the construction and operation safety of the tunnel; in addition, most of these support structures are full-section support structures, which greatly increase the construction cost.

[0004] Considering that asymmetric extrusion deformation usually occurs in tunnels in stratified soft rock strata, and the deformation part often concentrates on a certain part of the surrounding rock of the soft rock tunnel. If a full-section support structure is adopted, such as filling flexible materials in the full section, it will increase a large amount of construction economic cost and workload.

[0005] To sum up, it is necessary to develop a yielding and filling support structure for soft rock tunnels and a construction method therefor. On the one hand, it solves the problem that the combination of the existing full-section support structure and the conventional three-step excavation cannot ensure the construction and operation safety of the tunnel when the deformation of the soft rock tunnel is large and lasts for a long time. On the other hand, it solves the problem that the adoption of a full-section support structure leads to an increase in construction cost and workload when deformation occurs in a certain part of the surrounding rock of the soft rock tunnel. Summary of the Invention

[0006] The purpose of the present invention is to provide a yielding and filling support structure for soft rock tunnels and a construction method therefor. The specific technical solutions are as follows: A construction method for a yielding and filling support structure of a soft rock tunnel. During the tunneling process of the soft rock tunnel, a three-step structure is excavated. The three-step structure includes an upper step, a middle step and a lower step. The construction method includes: Step S1: During the tunneling process of the soft rock tunnel, conduct in-situ stress tests, rock mechanics experiments and surrounding rock deformation monitoring on the excavated on-site surrounding rock in real time, and obtain in-situ stress data, rock mechanics data and surrounding rock deformation data respectively; Step S2: When the surrounding rock deformation data abnormally increases and exceeds the deformation threshold, use discrete element numerical calculation software to process the in-situ stress data, the rock stratum mechanical data, and the surrounding rock deformation data at this time, and establish a numerical model of the soft rock tunnel; use the model to simulate the on-site tunnel excavation process, and then analyze and obtain the surrounding rock deformation characteristics, and lock the surrounding rock deformation area and the amount of excavation enlargement; the deformation threshold is that the deformation amount corresponding to the surrounding rock deformation data is less than or equal to 80 cm. Step S3: When the surrounding rock deformation area is locked in the surrounding rock corresponding to the upper bench, during tunneling, reduce the height of the upper bench according to the amount of excavation enlargement, and increase the length of the upper bench. When the surrounding rock deformation area is locked in the surrounding rock corresponding to the lower part of the upper bench and the upper part of the middle bench, during tunneling, reduce the height of the middle bench according to the amount of excavation enlargement, and increase the length of the middle bench. When the surrounding rock deformation area is locked in the surrounding rock corresponding to the lower part of the middle bench and the upper part of the lower bench, during tunneling, reduce the height of the lower bench according to the amount of excavation enlargement, and increase the length of the lower bench. Step S4: Install bolts on the surrounding rock after tunneling; subsequently, spray concrete on the surrounding rock profile surfaces corresponding to the upper bench, the middle bench, and the lower bench respectively to seal the surrounding rock surface. Step S5: Lay steel arch frames at intervals along the tunneling direction of the soft rock tunnel; sequentially arrange steel wire meshes and geotextiles between two adjacent steel arch frames in the surrounding rock deformation area; reserve injection holes at the top of the surrounding rock deformation area, inject filling materials to form a pressure-relieving filling layer; subsequently, spray concrete on the surrounding rock profile surfaces corresponding to the upper bench, the middle bench, and the lower bench respectively to form an initial support structure.

[0007] Optionally, the construction method further includes step S6 of fabricating an invert support structure; specifically, during the tunneling process of the soft rock tunnel, it also includes excavating the bottom of the tunnel to form an invert, and sequentially installing bolts and laying segments on the invert to form an invert structure; subsequently, spraying concrete on the invert structure to obtain an invert support structure.

[0008] Optionally, the construction method further includes step S7 of constructing a secondary lining; specifically, construct a secondary lining on the initial support structure and the invert support structure respectively.

[0009] Optionally, the discrete element numerical calculation software includes 3DEC discrete element numerical calculation software or PFC discrete element numerical calculation software.

[0010] Optionally, the length of the upper bench is 5 - 7 m, and the height is 3 - 4 m; the length of the middle bench is 20 - 25 m, and the height is 2 - 3 m; the length of the lower bench is 8 - 10 m, and the height is 3 - 4 m.

[0011] Optionally, a core soil is reserved at the joint of the upper bench and the middle bench; a core soil is reserved at the joint of the middle bench and the lower bench.

[0012] Optionally, the in-situ stress data includes horizontal principal stress data and vertical principal stress data.

[0013] Optionally, the rock mass mechanical data includes rock mass compressive strength, elastic modulus, Poisson's ratio, cohesion, internal friction angle, joint normal stiffness, and normal shear stiffness.

[0014] Optionally, the aperture of the injection hole is 50 - 100 cm; the filling material includes dry sand, ceramsite, and foam concrete.

[0015] In a second aspect, the present invention provides a yielding filling support structure for a soft rock tunnel, which is constructed by using the construction method of the yielding filling support structure for a soft rock tunnel.

[0016] Applying the technical solution of the present invention has at least the following beneficial effects: The construction method of the yielding filling support structure for a soft rock tunnel provided by the present invention, when the surrounding rock deformation data becomes abnormally large and exceeds the deformation threshold, uses discrete element numerical calculation software to process the in-situ stress data, rock mass mechanical data, and surrounding rock deformation data at this time, and establishes a numerical model of the soft rock tunnel; uses this model to simulate the on-site tunnel excavation process, and then analyzes and obtains the surrounding rock deformation characteristics, and locks the surrounding rock deformation area and the amount of overexcavation; increases the length of the corresponding bench according to the amount of overexcavation, and reduces the height of the corresponding bench, changing the conventional three-bench structure. Among them, increasing the length of the corresponding bench facilitates the slow release of stress in the surrounding rock deformation area, and reducing the height of the corresponding bench facilitates the overexcavation treatment of the surrounding rock deformation area; an injection hole is reserved at the top of the surrounding rock deformation area, and a filling material is injected to form a yielding filling layer, which can better release the surrounding rock pressure and absorb the energy released by the surrounding rock deformation. Therefore, the present invention adopts local overexcavation filling of the surrounding rock deformation area combined with the initial support structure, which can jointly inhibit the surrounding rock deformation and solve the problems of increased construction cost and workload caused by using a full-section support structure when a part of the surrounding rock of a soft rock tunnel deforms; in addition, the present invention adopts local overexcavation filling of the surrounding rock deformation area combined with the changed three-bench structure, which can ensure the safety of tunnel construction and operation when the deformation of the soft rock tunnel is large and lasts for a long time.

[0017] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The present invention will be further described in detail below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 is a schematic flow chart of a construction method of a yielding filling support structure for a soft rock tunnel in an embodiment; Figure 2 is the simulation result of the in-situ surrounding rock by a numerical model of a soft rock tunnel (the dotted arrow outside the layered soft rock indicates the direction of the vertical principal stress, and the solid arrow outside the layered soft rock indicates the direction of the horizontal principal stress); Figure 3 is a schematic structural diagram of the surrounding rock deformation area; Figure 4 is a perspective view of a three-step structure adjusted according to the excavation amount; Figure 5 is Figure 4 the front view of; Figure 6 is a schematic structural diagram of a yielding filling support structure for a soft rock tunnel; Among them, 1, layered soft rock; 2, upper bench; 3, middle bench; 4, lower bench; 5, surrounding rock deformation area; 5.1, injection hole; 5.2, yielding filling layer; 6, bolt; 7, primary support structure; 8, invert support structure; 9, secondary lining; 10, core soil. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention. Embodiment

[0020] Refer to Figure 1 , a construction method of a yielding filling support structure for a soft rock tunnel. During the tunneling process of a soft rock (the soft rock is layered soft rock 1 with a rock stratum dip angle of 40° and a high in-situ stress environment with a lateral pressure coefficient of 2) tunnel, a three-step structure is excavated. The three-step structure includes an upper bench 2, a middle bench 3, and a lower bench 4. The construction method includes: Step S1: During the excavation of a soft rock tunnel, conduct in-situ stress tests, rock mechanics experiments, and surrounding rock deformation monitoring on the excavated in-situ surrounding rock in real time to obtain in-situ stress data, rock mechanics data, and surrounding rock deformation data respectively; Step S2: When the surrounding rock deformation data abnormally increases and exceeds the deformation threshold, use discrete element numerical calculation software to process the in-situ stress data, the rock mechanics data, and the surrounding rock deformation data at this time, and establish a numerical model of the soft rock tunnel; use the model to simulate the on-site tunnel excavation process, and then analyze and obtain the surrounding rock deformation characteristics, and lock the surrounding rock deformation area 5 (that is, determine the area corresponding to the surrounding rock deformation area 5) and the amount of overexcavation; for specific simulation results, see Figure 2 ; the deformation threshold is that the deformation amount corresponding to the surrounding rock deformation data is less than or equal to 80 cm; Step S3: The surrounding rock deformation area 5 is locked in the surrounding rock corresponding to the lower part of the upper bench 2 and the upper part of the middle bench 3, see the left arch waist in Figure 3 . During tunneling, reduce the height of the middle bench 3 according to the amount of overexcavation, and increase the length of the middle bench 3; specifically, see Figures 4 to 5 . The overexcavation depth corresponding to the amount of overexcavation is 80 cm; the length of the middle bench 3 is 22 m, and the height is 2.4 m; the length of the upper bench 2 is 6 m, and the height is 3.7 m; the length of the lower bench 4 is 8 m, and the height is 3.7 m; Step S4: See Figure 6 . After tunneling, install bolts 6 on the surrounding rock (the bolts 6 are specifically mortar bolts 6 with a diameter of Φ22 mm, and the length of the bolts 6 is 7 m, and the spacing between adjacent bolts 6 is 1.2 m). Specifically, during the excavation of the soft rock tunnel, the three benches are advanced synchronously. After each bench and the invert have advanced a distance of two sets of steel arch frames (not more than two sets), install bolts 6; subsequently, spray concrete on the surrounding rock profile surfaces corresponding to the upper bench 2, the middle bench 3, and the lower bench 4 respectively to seal the surrounding rock surface; among them, the excavated surrounding rock surface is relatively rough, and when spraying concrete, in order to spray the surrounding rock surface relatively flat, it is necessary to control the thickness of the sprayed concrete to be 6 - 8 cm; Step S5: Lay steel arch frames (specifically I22b steel arch frames) at intervals along the tunneling direction of the soft rock tunnel; arrange steel mesh and geotextile between two adjacent steel arch frames in the surrounding rock deformation area 5 in sequence; reserve injection holes 5.1 at the top of the surrounding rock deformation area 5, inject filling materials to form a pressure-relieving filling layer 5.2; subsequently, spray concrete on the surrounding rock profile surfaces corresponding to the upper bench 2, the middle bench 3, and the lower bench 4 again to form an initial support structure 7.

[0021] The construction method further includes step S6 of fabricating an invert support structure 8; specifically, during the excavation of a soft rock tunnel, it also includes excavating the bottom of the tunnel to form an invert, and successively installing bolts 6 (the bolts 6 are specifically mortar bolts 6 with a diameter of Φ22, a length of 7 m, and a spacing of 1.2 m between adjacent bolts 6) on the invert and laying segments to form an invert structure; subsequently, spraying concrete on the invert structure to obtain the invert support structure 8.

[0022] See Figure 6 , the construction method further includes step S7 of constructing a secondary lining 9 (specifically a waterproof lining); specifically, the secondary lining 9 is constructed on the primary support structure 7 and the invert support structure 8 respectively.

[0023] The discrete element numerical calculation software is 3DEC discrete element numerical calculation software.

[0024] A core soil 10 is reserved at the connection of the upper bench 2 and the middle bench 3 to facilitate providing a support force and improving the stability of the surrounding rock of the excavation face; a core soil 10 is reserved at the connection of the middle bench 3 and the lower bench 4 to facilitate providing a support force and improving the stability of the surrounding rock of the excavation face.

[0025] The in-situ stress data includes horizontal principal stress data and vertical principal stress data.

[0026] The rock mass mechanical data includes rock mass compressive strength, elastic modulus, Poisson's ratio, cohesion, internal friction angle, joint normal stiffness, and normal shear stiffness.

[0027] The aperture of the injection hole 5.1 is 50 - 100 cm (specifically 60 cm); the filling material is ceramsite.

[0028] The yieldable filling support structure of the soft rock tunnel constructed by the construction method increases the length of the corresponding bench according to the excavation amount and reduces the height of the corresponding bench, changing the conventional three-bench structure. Among them, increasing the length of the corresponding bench facilitates the slow release of the stress in the surrounding rock deformation area 5, and reducing the height of the corresponding bench facilitates the excavation of the surrounding rock deformation area 5 to the excavation amount; an injection hole 5.1 is reserved at the top of the surrounding rock deformation area 5, and a filling material is injected to form a yieldable filling layer 5.2, which can better release the surrounding rock pressure and absorb the energy released by the surrounding rock deformation. Therefore, adopting local excavation and filling of the surrounding rock deformation area 5 combined with the primary support structure 7 can not only jointly restrain the surrounding rock deformation, but also reduce the workload and construction cost; in addition, adopting local excavation and filling of the surrounding rock deformation area 5 combined with the changed three-bench structure can ensure the safety of tunnel construction and operation when the deformation of the soft rock tunnel is large and lasts for a long time.

[0029] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A construction method for a pressure-yielding filling support structure of a soft rock tunnel, wherein a three-step structure is excavated during the excavation of the soft rock tunnel, wherein the three-step structure comprises an upper step (2), a middle step (3) and a lower step (4); wherein: The construction method comprises: Step S1: During the excavation of a soft rock tunnel, in-situ stress testing, rock stratum mechanics experiments and surrounding rock deformation monitoring are carried out on the excavated surrounding rock in real time to obtain in-situ stress data, rock stratum mechanics data and surrounding rock deformation data respectively; Step S2, when the surrounding rock deformation data becomes abnormally large and exceeds the deformation threshold, the ground stress data, the rock stratum mechanical data and the surrounding rock deformation data are processed by discrete element numerical calculation software to establish a soft rock tunnel numerical model; the model is used to simulate the on-site tunnel excavation process, and then the surrounding rock deformation characteristics are analyzed and the surrounding rock deformation area (5) and the excavation amount are locked; the deformation threshold is that the deformation amount corresponding to the surrounding rock deformation data is less than or equal to 80 cm; Step S3, when the surrounding rock deformation area (5) is locked to the corresponding surrounding rock above the upper step (2), the height of the upper step (2) is lowered according to the excavation amount during excavation, and the length of the upper step (2) is increased; When the surrounding rock deformation area (5) is locked to the corresponding surrounding rock below the upper step (2) and above the middle step (3), the height of the middle step (3) is lowered according to the excavation volume during excavation, and the length of the middle step (3) is increased; When the surrounding rock deformation area (5) is locked to the corresponding surrounding rock below the middle step (3) and above the lower step (4), the height of the lower step (4) is lowered according to the excavation volume during excavation, and the length of the lower step (4) is increased; Step S4, after excavation, anchor rods (6) are installed on the surrounding rock; subsequently, concrete is sprayed on the surrounding rock contour surfaces corresponding to the upper step (2), the middle step (3) and the lower step (4) to seal the surrounding rock surface; Step S5, laying steel arch frames at intervals in sequence along the excavation direction of the soft rock tunnel; placing steel mesh and geotextile in sequence between the steel arch frames in the surrounding rock deformation area (5); reserving injection holes (5.1) at the top of the surrounding rock deformation area (5), injecting filling materials to form a pressure-releasing filling layer (5.2); and then spraying concrete again on the surrounding rock contour surfaces corresponding to the upper step (2), the middle step (3) and the lower step (4) to form an initial support structure (7).

2. The construction method of the soft rock tunnel pressure-yielding filling support structure according to claim 1 is characterized in that: The method further comprises step S6 of manufacturing an inverted arch support structure (8); specifically, during the excavation of a soft rock tunnel, the method further comprises excavating the bottom of the tunnel to form an inverted arch, and sequentially installing anchor rods (6) on the inverted arch and laying pipe segments to form an inverted arch structure; and then spraying concrete on the inverted arch structure to obtain the inverted arch support structure (8).

3. The construction method of the soft rock tunnel pressure-yielding filling support structure according to claim 2 is characterized in that: The method further comprises step S7 of applying a secondary lining (9); specifically, the secondary lining (9) is applied respectively on the initial support structure (7) and the invert support structure (8).

4. The construction method of the soft rock tunnel pressure-yielding filling support structure according to claim 1 is characterized in that: The discrete element numerical calculation software includes 3DEC discrete element numerical calculation software or PFC discrete element numerical calculation software.

5. The construction method of the soft rock tunnel pressure-yielding filling support structure according to claim 1 is characterized in that: The length of the upper step (2) is 5-7 m and the height is 3-4 m; the length of the middle step (3) is 20-25 m and the height is 2-3 m; the length of the lower step (4) is 8-10 m and the height is 3-4 m.

6. The construction method of the soft rock tunnel pressure-yielding filling support structure according to claim 1 is characterized in that: Core soil is reserved at the connection between the upper step (2) and the middle step (3); and core soil is reserved at the connection between the middle step (3) and the lower step (4).

7. The construction method of the soft rock tunnel pressure-yielding filling support structure according to claim 1 is characterized in that: The geostress data includes horizontal principal stress data and vertical principal stress data.

8. The construction method of the soft rock tunnel pressure-yielding filling support structure according to claim 1 is characterized in that: The rock formation mechanics data include rock mass compressive strength, elastic modulus, Poisson's ratio, cohesion, internal friction angle, joint normal stiffness and normal shear stiffness.

9. The construction method of the soft rock tunnel pressure-yielding filling support structure according to claim 1 is characterized in that: The diameter of the injection hole (5.1) is 50-100 cm; the filling material includes dry sand, ceramsite and foam concrete.

10. A soft rock tunnel pressure-yielding filling support structure, characterized in that: The structure is constructed by using the construction method of the soft rock tunnel pressure-yielding filling support structure as described in any one of claims 1 to 9.

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