Ground launching method for large-section long-distance pipe-jacking tunnel

Abstract

The invention discloses a ground launching method for a large-section long-distance pipe-jacking tunnel. The ground launching method comprises the steps that a horizontal bearing pile is constructed on a stratum below a pipe-jacking well; the shallow soft stratum in front of the horizontal bearing piles is reinforced; a shallow foundation pit of the pipe jacking well is excavated, and a slope of the foundation pit is supported; a bearing platform of the horizontal bearing pile is constructed, during construction, the bearing platform is rigidly connected with pile body steel bars, vertical steel bars are reserved, and the periphery of the bearing platform is backfilled with gravel and cement backfill materials after construction is completed; a cast-in-place reinforced concrete pipe-jacking well with a reinforced structure is constructed, the pipe-jacking well is in rigid connection with the reserved vertical steel bars of the bearing platform during construction, and the shallow foundation pit is backfilled with plain soil backfill materials after construction is completed; and after equipment is installed and adjusted on the pipe jacking well, jacking construction of the pipe jacking tunnel is conducted. According to the method, a horizontal bearing pile is arranged, the strength and rigidity of a soil body in front of the horizontal bearing pile are enhanced, the horizontal bearing force under the pile foundation top consolidation condition is utilized, huge and reliable horizontal jacking force is provided for pipe jacking construction, and therefore pipe jacking tunnel ground launching is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of pipe jacking construction, and in particular to a method for starting a large-section and long-distance pipe jacking tunnel from the ground. Background Art

[0002] Pipe jacking is a type of trenchless construction for underground pipelines. Its characteristic is that the pipeline laying is changed from open excavation to underground excavation. It is very important in urban areas with busy traffic, dense population, many ground buildings, and complex underground structures and pipelines. It is becoming increasingly difficult to lay new underground pipelines and underground passages such as gas, heat, electricity, water supply, and drainage by the traditional trenching method. In order to reduce interference with traffic and normal activities of citizens, reduce unnecessary demolition, and reduce the impact on the city appearance and environmental sanitation, pipe jacking has become the best choice in municipal infrastructure projects.

[0003] For large-diameter jacking tunnels, the friction resistance between the outer wall of the pipe and the soil layer and the head-on resistance of the excavation surface should be overcome during the jacking construction. In order to ensure the normal construction of long-distance large-diameter jacking tunnels, it is usually necessary to provide a huge jacking force for the jacking construction. The jacking force is balanced by the passive earth pressure behind the working shaft.

[0004] Usually, the pipe jacking is an underground tunnel, the working shaft is located below the ground, and the soil behind the working shaft can resist the jacking force of the construction. In some special cases, such as when the pipe jacking tunnel passes through the embankment, the pipe jacking working shaft is located near the ground, the soil behind the working shaft is shallow, or even there is no soil behind the working shaft. At this time, how to balance the huge jacking force becomes the key technology for the ground initiation and construction of the pipe jacking tunnel.

[0005] Similar domestic projects use back piles on the back wall of the jacking working shaft to use the horizontal bearing capacity of the cantilever pile foundation to resist the jacking force of the jacking construction. This method has the following problems: the part of the back pile below the ground is a pile foundation constructed by machinery, and the part above the ground is a cast-in-place reinforced concrete column, and the construction process is complicated. There is no strong constraint on the top of the back pile, and it is free to deform, resulting in large internal forces and large deformations. When the strength of the soil inserted at the bottom of the back pile has not taken a significant effect, the back pile has already produced a large displacement, resulting in the failure of the bearing capacity of the conventional diameter back pile, and it cannot provide the huge jacking force of the jacking construction, unless a larger diameter back pile is used. Using back piles to bear the jacking force of the ground jacking construction has a poor force system, and a large-scale back pile force system needs to be set up, and the related engineering costs are high. Summary of the invention

[0006] The purpose of the present invention is to solve the problem of how to realize the ground start of a jacking tunnel in the case where a jacking tunnel passes through an embankment and the jacking working shaft is located near the ground and the soil behind the working shaft is shallow or even non-existent. A method for ground start of a jacking tunnel with a large cross-section and a long distance is provided. The method evenly arranges horizontal bearing piles under the bottom plate of the jacking shaft after structural reinforcement to strengthen the strength and rigidity of the soil in front of the horizontal bearing piles and utilizes the horizontal bearing capacity under the consolidation condition of the top of the pile foundation, thereby providing a huge and reliable horizontal jacking force for jacking construction.

[0007] The present invention is achieved through the following technical solutions:

[0008] The present invention provides a method for starting from the ground of a large-section and long-distance pipe jacking tunnel, comprising the following steps:

[0009] S1. Horizontal bearing piles are constructed in the stratum below the location of the pipe jacking well;

[0010] S2. Strengthen the shallow soft stratum in front of the horizontal bearing piles;

[0011] S3. Use natural slope to excavate shallow foundation pit for pipe jacking well and support the slope of foundation pit;

[0012] S4. A cap for horizontal bearing piles is constructed in the foundation pit. During construction, the cap is rigidly connected to the pile reinforcement and vertical reinforcement is reserved. After completion, the cap is backfilled with crushed stone cement backfill around it.

[0013] S5, the cast-in-place reinforced concrete jacking well with structural reinforcement is constructed. During construction, the jacking well is rigidly connected with the reserved vertical steel bars of the cap. After completion, the shallow foundation pit is backfilled with plain soil backfill material;

[0014] S6. After installing and adjusting the equipment in the pipe jacking well, carry out the pipe jacking tunnel jacking construction.

[0015] As a preferred embodiment of the present invention, in step S1, according to the pile position layout, mechanical drilling is used to construct the horizontal bearing piles, and the pile top is overfilled with at least 80 cm of concrete.

[0016] As a preferred solution of the present invention, in step S1, the verticality of the horizontal bearing pile should not be greater than 1 / 200, and the settlement of the pile top should not be greater than 100 mm.

[0017] As a preferred embodiment of the present invention, in step S2, clay and silt are reinforced by high-pressure rotary spraying, and sand is reinforced by grouting. The unconfined compressive strength of the reinforced stratum at 28d age is not less than 1.0MPa.

[0018] As a preferred embodiment of the present invention, in step S3, the foundation pit of the jacking pipe shaft is excavated in layers, the earthwork is excavated vertically, and the earthwork excavation is carried out by manual excavation and mechanical excavation.

[0019] As a preferred embodiment of the present invention, when the foundation pit depth in step S3 is less than 2.0 m, a natural slope excavation method is adopted, and mesh sprayed concrete is used to support the slope.

[0020] As a preferred solution of the present invention, when the foundation pit depth in step S3 is greater than 2.0 m, a natural slope excavation method is adopted, and a soil nail wall is used to support the slope.

[0021] As a preferred solution of the present invention, in the step S4, before constructing the foundation, the over-concrete of the horizontal bearing pile is firstly broken, and the reinforcement of the pile body is protected during the breaking.

[0022] As a preferred embodiment of the present invention, when constructing the jacking shaft in step S5, the top of the pedestal should be embedded in the bottom plate of the jacking shaft by at least 100 mm, and the vertical steel bars reserved in the pedestal should extend into the bottom plate of the jacking shaft to meet the anchoring length requirement.

[0023] As a preferred embodiment of the present invention, during the pipe jacking construction in step S6, paraffin wax needs to be applied on the outer wall of the pipe for lubrication according to the specific soil conditions.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1. In the construction of the present invention, horizontal bearing piles are first constructed, and the pile foundation is rigidly connected with the cap and the bottom plate of the jacking well. Relying on the integrity of the jacking well, the huge jacking force is sequentially transmitted from the back wall to the bottom plate and the horizontal bearing piles. The force transmission system is clear and reasonable, reliable and efficient, and provides a guarantee for the long-distance construction of large-diameter jacking tunnels starting from the ground;

[0026] 2. The present invention strengthens the strength and rigidity of the soil in front of the horizontal bearing pile through ground reinforcement measures, which is equivalent to moving the top fixed end of the horizontal bearing pile downward to a good soil in the deep layer;

[0027] 3. In the present invention, since the upper part of the horizontal bearing pile is located in the longitudinally reinforced stratum and the lower part of the pile foundation is located in the stratum with good original state, the pile foundation has large horizontal constraints, the pile foundation is less deformed under the horizontal jacking force, and the horizontal bearing pile has high bearing capacity, which is conducive to reducing related engineering costs;

[0028] 4. In the present invention, the horizontal bearing piles are located at the lower part of the jacking shaft, which reduces the floor space occupied by the jacking starting structure. The horizontal bearing piles are constructed by mechanical drilling, which speeds up the construction time of the jacking starting structure, and has significant energy-saving and environmental protection benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0030] Figure 1 It is a schematic diagram after the horizontal bearing pile is constructed in the present invention;

[0031] Figure 2 It is a schematic diagram of the reinforcement of the shallow soft stratum in front of the horizontal bearing pile in the present invention;

[0032] Figure 3 It is a schematic diagram after excavating a shallow foundation pit for a jacking well in the present invention;

[0033] Figure 4 It is a schematic diagram of the horizontal bearing pile cap in the present invention;

[0034] Figure 5 It is a schematic diagram after the pipe jacking well is constructed in the present invention;

[0035] Figure 6 It is a schematic diagram of the jacking construction of the pipe jacking tunnel in the present invention;

[0036] Figure 7 The present invention is a flow chart of the method for starting from the ground in a large-section and long-distance pipe-jacking tunnel.

[0037] Marks and corresponding parts names in the attached drawings:

[0038] 1-existing embankment slope, 2-existing ground, 3-horizontal bearing piles, 4-over-concrete on top of piles, 5-reinforced stratum in front of piles, 6-slope of foundation pit, 7-capping platform, 8-vertical reinforcement, 9-crushed stone cement backfill, 10-jacking well, 11-plain soil backfill, 12-jacking tunnel. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0041] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0042] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0043] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0044] In the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width and other dimensions of various components in the embodiments of the present application shown in the drawings, as well as the overall thickness, length, width and other dimensions of the integrated device are only exemplary descriptions and should not constitute any limitation to the present application.

[0045] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces), unless otherwise clearly and specifically defined.

[0046] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0047] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like 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 or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0048] Pipe jacking is a pipeline burial construction technology with no excavation or less excavation. It mainly uses the jacking force generated by the jacking equipment in the working pit to overcome the friction between the pipeline and the surrounding soil, push the pipeline into the soil according to the designed slope, and transport the soil away. After one section of the pipe is pushed into the soil layer, the second section of the pipe is pushed in. The principle is to use the thrust of the main jacking cylinder and the pipeline room, relay room, etc. to push the tool pipe or tunnel boring machine from the working pit through the soil layer to the receiving pit and lift it. The pipeline follows the tool pipe or tunnel boring machine and is buried between the two pits.

[0049] In general, pipe jacking is an underground tunnel, the working shaft is located below the ground, and the soil behind the working shaft can resist the jacking force of the construction. However, in some special cases, such as when the pipe jacking tunnel passes through the embankment, the pipe jacking working shaft is located near the ground, the soil behind the working shaft is shallow, or even there is no soil behind the working shaft. At this time, how to balance the huge jacking force becomes the key technology for the ground launch and construction of the pipe jacking tunnel.

[0050] Based on this, the applicant has conducted in-depth research and invented a method for the ground start of a large-section and long-distance jacking tunnel. This method evenly arranges horizontal bearing piles under the bottom plate of the jacking shaft after structural reinforcement, and strengthens the strength and stiffness of the soil in front of the horizontal bearing piles. The horizontal bearing capacity under the consolidation conditions of the top of the pile foundation is utilized to provide a huge and reliable horizontal jacking force for the jacking construction, thereby realizing the ground start of the jacking tunnel.

[0051] like Figure 7The flowchart of the method for starting a pipe jacking tunnel from the ground in the present application is shown. The method for starting a pipe jacking tunnel from the ground with a large cross section and a long distance provided in the embodiment of the present application comprises the following steps:

[0052] S1, constructing horizontal bearing piles 3 in the stratum below the location of the jacking well 10;

[0053] S2, strengthening the shallow soft stratum in front of the horizontal bearing pile 3;

[0054] S3, excavate a 10-shallow foundation pit for the jacking well in the form of natural slope, and support the slope of the foundation pit;

[0055] S4, construct a cap 7 for the horizontal bearing pile 3 in the foundation pit. During construction, the cap 7 is rigidly connected to the pile body reinforcement, and vertical reinforcement 8 is reserved. After completion, the surrounding area of ​​the cap 7 is backfilled with crushed stone cement backfill 9;

[0056] S5, constructing a cast-in-place reinforced concrete jacking well 10 with a reinforced structure. During construction, the jacking well 10 is rigidly connected to the cap 7 with reserved vertical steel bars 8. After completion, the shallow foundation pit is backfilled with plain soil backfill material 11;

[0057] S6. After installing and adjusting the equipment in the pipe jacking shaft 10, the pipe jacking tunnel 12 is jacked in.

[0058] In the present application, horizontal bearing piles 3 are first constructed in the stratum below the location of the jacking pipe well 10, and then the shallow soft stratum in front of the horizontal bearing piles 3 is reinforced, and then a shallow foundation pit of the jacking pipe well 10 is excavated in the form of natural slope, and then a cap 7 of the horizontal bearing piles 3 is constructed in the foundation pit. After completion, the surrounding area of ​​the cap 7 is backfilled with crushed stone cement backfill 9, and then the cast-in-place reinforced concrete jacking pipe well 10 with structural reinforcement is constructed. After completion, the shallow foundation pit is backfilled with plain soil backfill 11, and finally the jacking pipe well 10 is equipped with equipment for jacking pipe tunnel 12. This method provides a huge and reliable horizontal jacking force for jacking construction by setting horizontal bearing piles 3 and strengthening the strength and rigidity of the soil in front of the horizontal bearing piles 3, and utilizes the horizontal bearing capacity under the consolidation condition of the top of the pile foundation, thereby realizing the ground start of the jacking pipe tunnel.

[0059] In this application, since the horizontal bearing piles 3, the cap 7, and the bottom plate of the jacking well 10 are rigidly connected in sequence, the huge jacking force is transmitted from the back wall to the bottom plate of the jacking well 10 and the horizontal bearing piles 3 in sequence by relying on the integrity of the jacking well 10. The force transmission system is clear and reasonable, and it is reliable and efficient to provide long-distance construction guarantee for large-diameter jacking tunnels starting from the ground. At the same time, since the horizontal bearing piles 3 are located at the bottom of the jacking well 10, the area occupied by the jacking starting structure is reduced.

[0060] According to some embodiments of the present application, after the on-site construction preparation in step S1 is completed, mechanical drilling is used to construct the horizontal bearing pile 3 according to the pile position setting. Since the horizontal bearing pile 3 is constructed by mechanical drilling, the construction time of the jacking starting structure is accelerated, and the energy-saving and environmental protection benefits are very significant.

[0061] According to the bottom plate area of ​​the jacking well 10, the horizontal bearing piles 3 are evenly distributed in the stratum below the location. In order to ensure that the concrete on the top of the horizontal bearing piles 3 is dense and free of floating slurry, the top of the horizontal bearing piles 3 is overcasted with concrete, and the height of the overcast concrete 4 on the top of the pile is at least 80cm. Figure 1 As shown in the figure, the existing embankment slope 1 is located in front of the construction area of ​​the horizontal bearing pile 3, and the horizontal bearing pile 3 is constructed by drilling holes starting from the existing ground 2.

[0062] According to some embodiments of the present application, in step S1, the verticality of the horizontal bearing pile 3 should not be greater than 1 / 200, and the settlement of the pile top should not be greater than 100 mm. Since the verticality deviation of the pile foundation is directly related to the stability and bearing capacity of the pile foundation, the requirements for the verticality of the pile foundation are of great significance. By requiring the verticality of the horizontal bearing pile 3 and the settlement of the pile top to meet the above requirements, it is helpful to ensure the construction quality of the horizontal bearing pile 3.

[0063] According to some embodiments of the present application, in step S2, clay and silt are reinforced by high-pressure jet grouting, and sand is reinforced by grouting, and the unconfined compressive strength of the reinforced stratum at 28 days is not less than 1.0 MPa. Different reinforcement treatment methods can be used for different strata below the jacking shaft 10. By reinforcing the shallow soft stratum in front of the pile foundation, the top of the horizontal bearing pile 3 forms a whole rigid body. After the stratum in front of the horizontal bearing pile is reinforced, Figure 2 shown.

[0064] Since the reinforced stratum 5 in front of the pile strengthens the strength and rigidity of the soil in front of the horizontal bearing pile 3, it is equivalent to moving the top fixed end of the horizontal bearing pile 3 downward to a deeper and better soil; and the upper part of the horizontal bearing pile 3 is located in the longitudinally reinforced stratum, while the lower part of the pile foundation is located in the original and better stratum, the pile foundation has a large horizontal constraint, the pile foundation is less deformed under the action of the horizontal jacking force, and the horizontal bearing pile 3 has a high bearing capacity, which is beneficial to reducing related engineering costs.

[0065] According to some embodiments of the present application, in step S3, the foundation pit of the jacking well 10 is excavated in layers, the earthwork is excavated vertically, and the earthwork excavation is carried out by manual excavation and mechanical excavation. After the foundation pit is excavated, a natural slope is used to form a foundation pit slope 6, and the foundation pit slope 6 is supported according to the depth of the foundation pit.

[0066] According to some embodiments of the present application, when the foundation pit depth in step S3 is less than 2.0m, a natural slope excavation method is adopted, and mesh sprayed concrete is used to support the slope. C25 concrete is sprayed with a thickness of 150mm, and a double-layer steel mesh is used for foundation pit slope support. Steel bars.

[0067] According to some embodiments of the present application, when the foundation pit depth in step S3 is greater than 2.0 m, a natural slope excavation method is adopted, and a soil nail wall is used to support the slope. The soil nail wall setting parameters are determined according to calculations.

[0068] According to some embodiments of the present application, when the foundation pit of the jacking well 10 is excavated in step S3, soil is reserved in the area between the front and rear rows of horizontal bearing piles 3 along the jacking direction, and a corresponding foundation pit slope 6 is formed, so that after excavation, the reserved soil can bear a certain horizontal bearing capacity, and at the same time, the backfill volume around the cap 7 can be reduced in the later stage, which is conducive to reducing related engineering costs. Figure 3 shown.

[0069] According to some embodiments of the present application, in the step S4, the over-poured concrete 4 on the top of the horizontal bearing pile 3 is manually removed before constructing the cap 7, and effective measures should be taken to protect the reinforcement of the pile body during the removal. When constructing the cap 7 of the horizontal bearing pile 3, the cap 7 is rigidly connected to the reinforcement of the pile body, and the cap 7 should reserve vertical reinforcement 8 to be rigidly connected to the jacking well 10 later. After completion, the cap 7 is backfilled with crushed stone cement backfill 9 around it to increase the horizontal load-bearing area of ​​the cap 7 and improve the horizontal bearing capacity of the structure. The backfill material can be crushed stone + 8% cement. After the construction of the horizontal bearing pile cap, Figure 4 shown.

[0070] According to some embodiments of the present application, when constructing the jacking well 10 in step S5, the top of the cap 7 should be embedded in the bottom plate of the jacking well 10 by at least 100 mm to better transmit the horizontal jacking force, and the cap 7 reserves vertical steel bars 8 extending into the bottom plate of the jacking well 10 to meet the anchoring length requirements. After the top of the cap 7 is embedded in the bottom plate of the jacking well 10, it is more conducive to the transmission of the jacking force.

[0071] The construction process of the main structure of the jacking well 10 is as follows: measurement and setting out → base treatment → cushion construction → reinforcement engineering → formwork engineering → concrete engineering. When constructing the main structure of the jacking well 10, the corresponding embedded parts for the jacking pipe construction should be pre-buried. After the main structure of the jacking well 10 is completed, the shallow foundation pit is backfilled with plain soil backfill material 11. Figure 5 shown.

[0072] According to some embodiments of the present application, the construction process of the pipe jacking tunnel in step S6 is as follows: equipment commissioning and trial operation → pipe laying → pipe placement → pipe jacking → calibration. According to the specific soil conditions, the pipe jacking tunnel 12 needs to apply paraffin wax lubrication on the outer wall of the pipe to ensure smooth jacking. Figure 6 shown.

[0073] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for starting a large-section long-distance pipe jacking tunnel from the ground, characterized in that: The following steps are involved: S1. Horizontal bearing piles are constructed on the stratum below the location of the jacking well; S2. Strengthen the shallow soft stratum in front of the horizontal bearing piles; S3. Use natural slope to excavate shallow foundation pit for pipe jacking well and support the slope of foundation pit; S4. A cap for horizontal bearing piles is constructed in the foundation pit. During construction, the cap is rigidly connected to the pile reinforcement and vertical reinforcement is reserved. After completion, the cap is backfilled with crushed stone cement backfill around it. S5, the cast-in-place reinforced concrete jacking well with structural reinforcement is constructed. During construction, the jacking well is rigidly connected with the cap with reserved vertical steel bars. After completion, the shallow foundation pit is backfilled with plain soil backfill material; S6. After installing and adjusting the equipment in the pipe jacking well, carry out the pipe jacking tunnel jacking construction.

2. The method for starting from the ground in a large-section long-distance pipe jacking tunnel according to claim 1, characterized in that: In step S1, according to the pile position layout, mechanical drilling is used to construct the horizontal bearing pile, and the pile top is overfilled with at least 80 cm of concrete.

3. The method for starting from the ground in a large-section long-distance pipe jacking tunnel according to claim 1, characterized in that: In step S1, the verticality of the horizontal bearing pile should not be greater than 1 / 200, and the settlement of the pile top should not be greater than 100 mm.

4. The method for starting from the ground in a large-section long-distance pipe jacking tunnel according to claim 1, characterized in that: In step S2, clay and silt are reinforced by high-pressure jet spraying, and sand is reinforced by grouting. The unconfined compressive strength of the reinforced stratum at 28 days is not less than 1.0 MPa.

5. The method for starting from the ground in a large-section long-distance pipe jacking tunnel according to claim 1, characterized in that: In step S3, the foundation pit of the jacking pipe shaft is excavated in layers, the earthwork is excavated vertically, and the earthwork excavation is carried out in two ways: manual excavation and mechanical excavation.

6. The method for starting from the ground for a large-section long-distance pipe jacking tunnel according to claim 1, characterized in that: When the foundation pit depth in step S3 is less than 2.0 m, a natural slope excavation method is adopted, and mesh sprayed concrete is used to support the slope.

7. The method for starting from the ground for a large-section long-distance pipe jacking tunnel according to claim 1, characterized in that: When the foundation pit depth in step S3 is greater than 2.0 m, a natural slope excavation method is adopted, and a soil nail wall is used to support the slope.

8. The method for starting from the ground for a large-section long-distance pipe jacking tunnel according to claim 1, characterized in that: In the step S4, before constructing the foundation, the over-filled concrete of the horizontal bearing pile is firstly removed, and the reinforcement of the pile body is protected during the removal.

9. The method for starting from the ground in a large-section long-distance pipe jacking tunnel according to claim 1, characterized in that: When constructing the jacking well in step S5, the top of the cap should be embedded in the bottom plate of the jacking well by at least 100 mm, and the vertical steel bars reserved in the cap should extend into the bottom plate of the jacking well to meet the anchoring length requirements.

10. The method for starting from the ground for a large-section long-distance pipe jacking tunnel according to claim 1, characterized in that: During the pipe jacking construction in step S6, paraffin wax needs to be applied on the outer wall of the pipe for lubrication according to the specific soil conditions.

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