Expandable loess tunnel supporting method based on bottom vertical steel anchor rods

Abstract

The invention discloses an expansive loess tunnel supporting method based on bottom vertical steel anchor rods, and relates to the technical field of tunnel supporting. Comprising the following steps that S1, before a tunnel is excavated, supporting operation is conducted on a surrounding rock section of the expansive loess tunnel through a base vertical steel anchor rod supporting method; s2, a tunnel is excavated, a step method and an equal-division excavation method are adopted for excavation of a tunnel body, and a shotcrete-anchor supporting method is adopted for the tunnel body; s3, radial anchor rods are constructed and concrete is sprayed in time after excavation, and bottom anchor rods are constructed in time after the inverted arch is excavated; s4, according to the surrounding rock condition and the maximum excavation span, 5-10 vertical steel anchor rods are constructed in time after the surrounding rock at the bottom of the tunnel is excavated; the supporting method that the vertical steel anchor rods are constructed at the bottom in time after the expansive loess tunnel is excavated is adopted, steel has the high tensile strength and can play the tensile function in time, construction is conducted in time after foundation construction excavation, surrounding rock upheaval deformation is effectively controlled, and the safety of the expansive loess tunnel in the construction and operation whole life period is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel support, in particular to an expansive loess tunnel support method based on bottom vertical steel anchor rods. Background Art

[0002] With the progress of science and technology and the process of urban modernization in my country, more and more people are pouring into urban life and development. This requires that my country's transportation network must be more and more developed to meet the requirements of urbanization in my country. The development of underground space will be the focus of my country's urban development. Rail transit shuttling between cities is also an important part of my country's transportation network. my country is a mountainous country, which will inevitably require the development of mountain tunneling projects. In some cities in my country's loess distribution areas, it has become a major problem to build mountain tunnels and underground subway projects. After the excavation of the expansive loess tunnel, the initial ground stress release speed of the surrounding rock is fast and the deformation is large, resulting in large deformation of the sprayed anchor support structure and the invert structure, which is easy to crack and damage. Usually, the initial support of the expansive loess tunnel construction adopts radial anchor rods, steel arch frames and sprayed concrete combined support measures, and the base is reinforced with cement-based piles such as rotary jet piles and root piles.

[0003] Cement-based piles require on-site drilling before pouring or spraying for their strength. It takes nearly a month for the strength to develop to reach the designed strength. One hour or one day after the pile foundation is constructed, its tensile strength is very low or even close to 0. The deformation rate of the surrounding rock after excavation of the expansive loess tunnel is fast. Without support measures, the bottom surrounding rock can be uplifted and deformed by more than 10 cm after one hour. If cement-based piles such as jet grouting piles and root piles are used for reinforcement, the base uplift deformation can be reduced under the premise that the tensile strength is large enough without fracture. However, as mentioned above, due to the slow strength development of cement-based piles, its tensile strength is basically 0 after one hour of pouring, which is completely unable to play the role of reinforcing the base surrounding rock. On the contrary, the pile body will be broken due to the uplift deformation of the surrounding rock, losing its design function and application value.

[0004] After excavation of expansive loess tunnels, the deformation rate of the surrounding rock is fast and the deformation value is large. The tunnel body sprayed anchor support and the base arch structure have large convergence and uplift deformation and are prone to cracking. The conventional tunnel body radial anchor rods and base cement foundation piles cannot exert their tensile bearing capacity in time due to their slow strength development. Under the action of rapid uplift deformation of the base surrounding rock, the pile body is easily broken and loses its design function and application value, and the construction and operation safety cannot be guaranteed. Therefore, a support method for expansive loess tunnels based on bottom vertical steel anchor rods is proposed to solve the above problems. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides an expansive loess tunnel support method based on bottom vertical steel anchors to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for supporting an expansive loess tunnel based on a bottom vertical steel anchor, characterized in that it comprises the following steps: S1. Before tunnel excavation, the base vertical steel anchor support method is used to support the surrounding rock section of the expansive loess tunnel; S2. Excavate the tunnel. The tunnel body is excavated by using the step method and other partial excavation methods, and the tunnel body is supported by spray anchor; S3. Apply radial anchors and shotcrete promptly after excavation, and apply bottom anchors promptly after invert excavation; S4. According to the surrounding rock conditions and the maximum excavation span, 5-10 vertical steel anchors shall be installed in time after the surrounding rock is excavated at the bottom of the tunnel; S5. Arrange one anchor rod on each side at the junction of the tunnel arch wall foot and the invert arch. The anchor rod material and longitudinal spacing are the same as the vertical steel anchor rods at the base. S6. The vertical anchor rods of the base and arch wall foot are made of steel pipes, and the anchor rod body is made of steel, arranged in a plum blossom or triangle cross pattern; S7. Drill holes at the bottom ends of the vertical anchor rods at the base and the arch wall footings. The bottom ends are in a pointed cone shape to achieve support operations for the expansive loess tunnel.

[0007] To further optimize the technical solution, the base vertical steel anchor support method in step S1 is suitable for expansive loess tunnels in grade V and VI surrounding rock areas.

[0008] To further optimize the technical solution, in step S5, one anchor rod is arranged on each side, and the angle with the vertical is 10-20°.

[0009] To further optimize the technical solution, in step S6, the vertical anchor rods of the base and the arch wall foot are made of steel pipes with a diameter of 42-108 mm and a wall thickness of 4-6 mm, and the anchor rod body is made of steel not less than HRB400 and has a length of 4-8 m.

[0010] To further optimize the technical solution, in step S6, the horizontal and vertical spacings of the anchor rod bodies are 1-1.2 m.

[0011] To further optimize the technical solution, in step S7, holes are drilled vertically in the base and within 0.5-1.0m of the bottom end of the anchor rod of the arch wall foot, with a hole diameter of 2-5mm, a longitudinal hole spacing of 10-15cm, and 2-3 holes evenly distributed in the annular direction.

[0012] To further optimize the technical solution, the anchor rod body in step S6 is an anchor rod steel pipe, and threaded pipes are respectively provided at both ends of the anchor rod steel pipe.

[0013] To further optimize the technical solution, a plurality of steel strands are arranged inside the anchor steel pipe, the plurality of steel strands are distributed in a ring at equal intervals, and both ends of the steel strands are anchored at the threaded pipes at both ends of the anchor steel pipe.

[0014] To further optimize the technical solution, in step S7, when the loess surrounding rock contains more water, cement slurry or cement-water-glass slurry is injected into the vertical steel anchor rod to fill the gap between the tunnel wall and the loess surrounding rock.

[0015] To further optimize the technical solution, grouting holes are provided at the bottom end of the vertical steel anchor rod in step S7, and the grouting holes are evenly distributed.

[0016] Compared with the prior art, the present invention provides an expansive loess tunnel support method based on bottom vertical steel anchor rods, which has the following beneficial effects: 1. The support method for the expansive loess tunnel based on the bottom vertical steel anchor rods, the present invention proposes a support method of promptly applying vertical steel anchor rods at the bottom after the expansive loess tunnel is excavated, utilizing the property of steel having high tensile strength and being able to promptly exert its tensile function, and promptly applying the anchor rods after the base construction and excavation, so as to effectively control the uplift and deformation of the surrounding rock in time, and the pile body will not break, thereby ensuring the safety and reliability of the construction and operation of the expansive loess tunnel throughout its life cycle.

[0017] 2. The support method for the expansive loess tunnel based on the bottom vertical steel anchor rods adopts a support method in which, in addition to the radial anchor rods used for the tunnel body after the excavation of the expansive loess tunnel, vertical steel anchor rods are promptly applied at the bottom. The steel has a high tensile strength and is used to effectively control the uplift and deformation of the surrounding rock in a timely manner, so that the pile body will not break. At the same time, compared with cement foundation piles, the base vertical steel anchor rods have the significant advantages of small construction space, convenient operation, high work efficiency and easy to ensure construction quality. Therefore, the present invention has significant innovation and engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A support arrangement diagram of vertical steel anchor rods at the bottom of an expansive loess tunnel according to an expansive loess tunnel support method based on bottom vertical steel anchor rods proposed by the present invention; Figure 2 The tunnel structure section and tunnel body support design drawing of a method for supporting an expansive loess tunnel based on bottom vertical steel anchors proposed by the present invention; Figure 3 This is a numerical calculation model diagram of a method for supporting an expansive loess tunnel based on bottom vertical steel anchors proposed by the present invention; Figure 4 This is a measurement point arrangement diagram of the calculation results of a method for supporting an expansive loess tunnel based on bottom vertical steel anchors proposed by the present invention; Figure 5 The present invention is a schematic flow chart of a method for supporting an expansive loess tunnel based on bottom vertical steel anchor rods. DETAILED DESCRIPTION

[0019] In order to be able to understand the features and technical contents of the embodiments of the present disclosure in more detail, the implementation of the embodiments of the present disclosure is described in detail below in conjunction with the accompanying drawings. The attached drawings are for reference only and are not used to limit the embodiments of the present disclosure. In the following technical description, for the convenience of explanation, a full understanding of the disclosed embodiments is provided through multiple details. However, one or more embodiments can still be implemented without these details. In other cases, to simplify the drawings, well-known structures and devices can be simplified for display.

[0020] The terms "first", "second", etc. in the specification and claims of the embodiments of the present disclosure and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged where appropriate, so that the embodiments of the embodiments of the present disclosure described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0021] In the embodiments of the present disclosure, the terms "upper", "lower", "inside", "middle", "outside", "front", "back" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. These terms are mainly intended to better describe the embodiments of the present disclosure and their embodiments, and are not intended to limit the indicated devices, elements or components to have a specific direction, or to be constructed and operated in a specific direction. Moreover, in addition to being used to indicate directions or positional relationships, some of the above terms may also be used to indicate other meanings. For example, the term "upper" may also be used to indicate a certain dependency or connection relationship in certain circumstances. For those of ordinary skill in the art, the specific meanings of these terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0022] In addition, the terms "disposed", "connected", and "fixed" should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, elements, or components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0023] Unless otherwise stated, the term "plurality" means two or more.

[0024] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure may be combined with each other.

[0025] Example: Please refer to Figure 1-5 As shown, the present invention discloses a method for supporting an expansive loess tunnel based on a bottom vertical steel anchor rod, comprising the following steps: S1. Before tunnel excavation, a base vertical steel anchor support method is used to support the surrounding rock section of the expansive loess tunnel. The base vertical steel anchor support method in step S1 is applicable to the surrounding rock sections of the expansive loess tunnel of grade V and VI; S2. Excavate the tunnel. The tunnel body is excavated by using the step method and other partial excavation methods, and the tunnel body is supported by spray anchor; S3. Apply radial anchors and shotcrete promptly after excavation, and apply bottom anchors promptly after invert excavation; S4. According to the surrounding rock conditions and the maximum excavation span, 5-10 vertical steel anchors shall be installed in time after the surrounding rock is excavated at the bottom of the tunnel; S5, at the junction of the tunnel arch wall foot and the inverted arch, one anchor rod is arranged on each side, and the anchor rod material and longitudinal spacing are the same as the base vertical steel anchor rod. In step S5, one anchor rod is arranged on each side, and the angle with the vertical is 10-20°; S6, the base vertical and arch wall foot anchor rods are made of steel pipes, the anchor rod bodies are made of steel, and are arranged in a plum blossom or triangle cross pattern. In step S6, the base vertical and arch wall foot anchor rods are made of steel pipes with a diameter of 42-108mm and a wall thickness of 4-6mm. The anchor rod bodies are made of steel not less than HRB400 and have a length of 4-8m. In step S6, the horizontal and vertical spacings of the anchor rod bodies are 1-1.2m. The anchor rod bodies in step S6 are anchor steel pipes, and threaded pipes are respectively provided at both ends of the anchor steel pipe. A plurality of steel strands are provided inside the anchor steel pipe, and the plurality of steel strands are distributed in a ring at equal intervals. The two ends of the steel strands are respectively anchored at the threaded pipes at both ends of the anchor steel pipe. S7, drilling holes at the bottom ends of the base vertical and arch wall foot anchor rods, the bottom ends are pointed cone-shaped, to achieve support operation of the expansive loess tunnel, in step S7, drilling holes within the range of 0.5-1.0m at the bottom ends of the base vertical and arch wall foot anchor rods, the hole diameter is 2-5mm, the longitudinal hole spacing is 10-15cm, and 2-3 holes are evenly distributed in the annular direction, in step S7, when the loess surrounding rock contains more water, cement slurry or cement-water corrugated glass slurry is injected into the vertical steel anchor rod to fill the gap between the tunnel wall and the loess surrounding rock, in step S7 The bottom end of the vertical steel anchor rod is provided with grouting holes, and the grouting holes are evenly arranged. The technical solution of the present invention adopts a support method of vertical steel anchor rods at the bottom in a timely manner in addition to radial anchor rods for support in the tunnel body after the expansive loess tunnel is excavated. The steel has a high tensile strength and can effectively control the uplift and deformation of the surrounding rock in a timely manner, so that the pile body will not break. At the same time, compared with cement foundation piles, the base vertical steel anchor rod has the significant advantages of small construction space, convenient operation, high work efficiency and easy to ensure construction quality.

[0026] Judgment criteria: The comparative effect analysis of the embodiment of the present invention and other support methods is conducted through a comprehensive analysis of four aspects: calculation conditions, calculation conditions, calculation model and calculation results.

[0027] 1. Calculation conditions: The surrounding rock of the expansive loess tunnel is V grade, the burial depth is 40m, the maximum span of the tunnel excavation is 7.87m, the height is 11.45m, the lining adopts a composite lining, the initial support C25 shotcrete is 23cm thick, the secondary lining C35 concrete is 40mm thick, the longitudinal spacing of the steel arch frame I16 steel is 0.8m, the side wall is equipped with a 3m long Φ25 ordinary hollow anchor rod, the locking foot anchor pipe Φ42mm wall thickness 5mm hot-rolled seamless steel pipe, the invert C35 concrete, the invert backfill C20 concrete, see the present invention Figure 2 Tunnel structure section and tunnel support design drawings.

[0028] 2. Calculation conditions: The comparative calculation conditions are shown in Table 1.

[0029] Table 1 is as follows: 3. Computational model: Numerical calculation model such as Figure 3 As shown; the calculation results are as follows Figure 4 shown.

[0030] 4. Calculation results: The calculation results and comparison are shown in Table 2.

[0031] Table 2 is as follows: Note: Safety factor in the table = tensile strength / maximum tensile stress From Table 2, we can see that: The present invention (working condition 2) can reduce the uplift deformation of the base surrounding rock from 408 mm to 48 mm, which is within the allowable range of construction safety. Under the three cement-based pile reinforcement methods, the uplift value can be controlled within the safe range without breaking the pile body. However, since the pile body is subjected to large tensile stress in the early stage of construction and breaks, the function of controlling deformation cannot be achieved.

[0032] It can be seen from Table 2 that after one day of construction, only the tensile safety factor of the base reinforcement component in Condition 2 of the present invention is greater than 1, and the safety factors of other cement-based pile components are all less than 1, indicating that tensile failure has occurred. The data in Table 2 show that the support method of the present invention is also significantly better than other methods for the deformation of the initial support structure. In summary, the support method for the construction of loess tunnels based on vertical steel anchor rods proposed in the present invention has excellent bearing capacity and can ensure the safety of tunnel construction and the reliability of the structure.

[0033] The beneficial effects of the present invention are as follows: the support method for the expansive loess tunnel based on the bottom vertical steel anchor rod, the support method for the expansive loess tunnel based on the bottom vertical steel anchor rod, the present invention proposes a support method of promptly applying the vertical steel anchor rod at the bottom after the expansive loess tunnel is excavated, utilizing the property that the steel has a high tensile strength and can promptly exert the tensile function, promptly applying the vertical steel anchor rod after the base construction excavation, promptly controlling the uplift deformation of the surrounding rock, and preventing the pile body from breaking, thereby ensuring the safety and reliability of the construction and operation of the expansive loess tunnel throughout its life cycle; the support method of promptly applying the vertical steel anchor rod at the bottom in addition to the radial anchor rod support in the tunnel body after the excavation of the expansive loess tunnel, utilizing the property that the steel has a high tensile strength, promptly controlling the uplift deformation of the surrounding rock, and preventing the pile body from breaking, and at the same time, the base vertical steel anchor rod has the significant advantages of small construction space, convenient operation, high work efficiency and easy guarantee of construction quality compared with cement foundation piles, therefore, the present invention has significant innovation and engineering application value.

[0034] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0035] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for supporting an expansive loess tunnel based on bottom vertical steel anchors, characterized in that: The following steps are involved: S1. Before tunnel excavation, the base vertical steel anchor support method is used to support the surrounding rock section of the expansive loess tunnel; S2. Excavate the tunnel. The tunnel body is excavated by using the step method and other partial excavation methods, and the tunnel body is supported by spray anchor; S3. Apply radial anchors and shotcrete promptly after excavation, and apply bottom anchors promptly after invert excavation; S4. According to the surrounding rock conditions and the maximum excavation span, 5-10 vertical steel anchors shall be installed in time after the surrounding rock is excavated at the bottom of the tunnel; S5. Arrange one anchor rod on each side at the junction of the tunnel arch wall foot and the invert arch. The anchor rod material and longitudinal spacing are the same as the vertical steel anchor rods at the base. S6. The vertical anchor rods of the base and arch wall foot are made of steel pipes, and the anchor rod body is made of steel, arranged in a plum blossom or triangle cross pattern; S7. Drill holes at the bottom ends of the vertical anchor rods at the base and the arch wall footings. The bottom ends are in a pointed cone shape to achieve support operations for the expansive loess tunnel.

2. The method for supporting an expansive loess tunnel based on bottom vertical steel anchors according to claim 1, characterized in that: The base vertical steel anchor support method in step S1 is suitable for expansive loess tunnels in grade V and VI surrounding rock areas.

3. The method for supporting an expansive loess tunnel based on bottom vertical steel anchors according to claim 1, characterized in that: In step S5, one anchor rod is arranged on each side, with an angle of 10-20° with the vertical.

4. The method for supporting an expansive loess tunnel based on bottom vertical steel anchors according to claim 1, characterized in that: In step S6, the vertical anchor rods of the base and the arch wall foot are made of steel pipes with a diameter of 42-108 mm and a wall thickness of 4-6 mm, and the anchor rod body is made of steel material not less than HRB400 and has a length of 4-8 m.

5. The method for supporting an expansive loess tunnel based on bottom vertical steel anchors according to claim 1, characterized in that: In step S6, the horizontal and vertical spacings of the anchor rod bodies are 1-1.2 m.

6. A method for supporting an expansive loess tunnel based on bottom vertical steel anchors according to claim 1, characterized in that: In the step S7, holes are drilled vertically in the base and within 0.5-1.0m of the bottom end of the anchor rod of the arch wall foot, with a hole diameter of 2-5mm, a longitudinal hole spacing of 10-15cm, and 2-3 holes evenly distributed in the annular direction.

7. A method for supporting an expansive loess tunnel based on bottom vertical steel anchors according to claim 1, characterized in that: The anchor rod body in step S6 is an anchor rod steel pipe, and threaded pipes are respectively provided at both ends of the anchor rod steel pipe.

8. A method for supporting an expansive loess tunnel based on bottom vertical steel anchors according to claim 7, characterized in that: A plurality of steel strands are arranged inside the anchor steel pipe, and the plurality of steel strands are distributed in a ring at equal intervals, and both ends of the steel strands are anchored at the threaded pipes at both ends of the anchor steel pipe.

9. The method for supporting an expansive loess tunnel based on bottom vertical steel anchors according to claim 1, characterized in that: In step S7, when the loess surrounding rock contains more water, cement slurry or cement-water-glass slurry is injected into the vertical steel anchor rod to fill the gap between the tunnel wall and the loess surrounding rock.

10. The method for supporting an expansive loess tunnel based on bottom vertical steel anchors according to claim 1, characterized in that: In step S7, grouting holes are opened at the bottom end of the vertical steel anchor rod, and the grouting holes are evenly distributed.

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