A large underground structure constructed by underground excavation in saturated soft soil and a construction method thereof

Abstract

The present application belongs to the technical field of underground structure excavation construction, and discloses a large underground structure constructed by excavation in saturated soft soil and a construction method thereof. The method for constructing the large underground structure by excavation in saturated soft soil comprises the following steps: setting up longitudinal pipe roofs along the periphery of the outer contour of the underground structure, reinforcing the soil longitudinally and excavating in sections, arranging vertical steel supports in the intermediate holes, arranging vertical steel beams in the side holes, backfilling the gaps in the holes, excavating the soil in layers, tightly pressing the two ends of the horizontal steel supports against the vertical steel beams on both sides, and excavating to the position of the last support until the excavation is completed; longitudinally excavating the bottom soil in sections, welding the short steel beams into horizontal steel beams after each excavation; sequentially constructing the structure in layers from bottom to top, and removing the horizontal steel supports. The present application overcomes the problems of the current pipe roof method in saturated soft soil, such as the need for compartmentalization, large surface subsidence, large reinforcement range, high construction cost, long construction period, and difficulty in constructing multi-layer structures.

Description

Technical Field

[0001] This invention belongs to the field of underground structure excavation and construction technology, and particularly relates to a large-scale underground structure and its construction method that is excavated and constructed in saturated soft soil. Background Technology

[0002] With the progress of urbanization, the surrounding environment of underground projects is becoming increasingly complex. Due to the constraints of the surrounding environment, sometimes it is necessary to use the cut-and-cover method in urban centers. However, due to a series of problems such as complex technology, high engineering risks, and large surface settlement, the traditional cut-and-cover method has only been used a few times in the construction of large underground structures in soil strata. It is almost impossible to construct large underground structures in saturated soft soil areas, and the construction of multi-story large underground structures is completely unexplored.

[0003] In order to solve the problem of tunneling in saturated soft soil areas and improve the applicability of tunneling methods, relevant engineering and technical personnel in China have made some attempts at tunneling technology in saturated soft soil areas. In China, the construction methods of pipe jacking + box culvert jacking or pipe jacking + excavation and support have been adopted in Shanghai, Beijing and Taiwan for underground engineering construction in soft soil areas such as road crossings, river crossings and airport crossings. However, these construction methods have obvious defects: (1) The working face of this type of construction method needs to be reinforced with a large-scale full-section stratum reinforcement measures and excavated in sections or steps. Otherwise, the working face will be exposed, the longitudinal stability of the soil will be poor, there will be a large construction risk, and the settlement deformation will be large. It is generally only suitable for single-layer underground structure construction with small structural height and it is difficult to carry out multi-layer underground structure construction; (2) The box culvert jacking method has very high requirements for jacking construction accuracy. Otherwise, the surface settlement control will not be ideal. The surface settlement of the Shanghai Middle Ring Road project that used this method to cross the West Suburbs Hotel and Hongqiao Road once reached 26cm; (3) The box culvert fabrication and jacking site requirements are large. In the case of increasingly tight land use in the urban center, the applicability is relatively poor; (4) The excavation and support scheme has problems such as dense support and many construction joints, which affect the overall structural quality and waterproofing. Although the Gongbei Tunnel of Hong Kong-Zhuhai-Macau Bridge successfully implemented a double-layer underground structure in saturated soft soil by supplementing the pipe jacking and excavation-as-you-go method with the pipe freezing method, the project has a small span and the long-distance freezing process is costly, so it does not have universal application value.

[0004] CN111485575A discloses a construction method for steel frame support of ultra-large cross-section pipe jacking tunnels in saturated soft soil areas. The ultra-large cross-section pipe jacking tunnel is formed by pipe jacking distributed around its perimeter. This method uses compartmentalized pipes to divide the ultra-large cross-section pipe jacking tunnel into multiple compartments horizontally. Each compartment is further divided into multiple soil layers vertically. Each compartment is excavated in a top-to-bottom sequence. Steel frame supports for supporting the soil are installed simultaneously in the excavated areas. The steel frame supports include a bottom beam, two side columns, and a top beam. The bottom beam in the upper soil layer serves as the top beam in the lower soil layer. Pre-tensioning is applied to the steel frame supports. Although this method can be applied to underground excavation projects in saturated soft soil and has been used in the Shanghai Metro Line 14 Guiqiao Road Station underpass project in Caojiagou, it still has significant limitations. This method adds intermediate compartment pipes, and the bottom and side pipe curtains have larger diameters, significantly increasing investment in the pipe curtain alone. The upper compartment bottom beam rests on the soil, where the soft soil foundation has low bearing capacity. Furthermore, during the excavation of the lower compartments, the upper compartment supports within the fracture surface area are in a loose state, posing a significant risk of settlement. Therefore, grouting reinforcement is required for almost the entire excavation section to improve its foundation bearing capacity and longitudinal excavation stability. This soil reinforcement investment is also very high. There are numerous compartment working faces, and each compartment needs to be excavated at a staggered distance. Support must be installed after each excavation step before proceeding to the next step, resulting in cumbersome procedures, low efficiency, and a long construction period. The structure is covered with densely packed horizontal and vertical supports, which significantly impacts structural construction and waterproofing quality. For these reasons, this method is primarily used for single-story underground structures; it is neither economical nor safe for multi-story structures.

[0005] Based on the above analysis, the existing technologies have the following problems and shortcomings: Existing underground excavation methods in saturated soft soil areas suffer from poor deformation control, high investment costs, complex and cumbersome construction, and long construction periods. This is because these methods essentially still rely on the support principles of traditional underground excavation methods, dividing the large excavation section into several smaller sections and supporting them as they are excavated. This approach is not very suitable for constructing large underground structures such as underground railway stations in saturated soft soil, and is basically unsuitable for building multi-story structures. To address the shortcomings of existing underground excavation methods in saturated soft soil areas, especially for large-span multi-story underground structures, it is necessary to propose new ideas and technical solutions. Summary of the Invention

[0006] To overcome the problems existing in related technologies, the present invention discloses an embodiment of a large-scale underground structure constructed by tunneling in saturated soft soil and a method thereof. Specifically, it relates to a method for constructing underground stations, long-span tunnels, and similar long-span underground projects by tunneling in saturated soft soil.

[0007] The technical solution is as follows: A method for constructing large underground structures by tunneling in saturated soft soil, comprising the following steps:

[0008] S1, the pipe jacking is carried out longitudinally along the outer contour of the station. The pipe jacks are connected by interlocking. The groundwater within the pipe jack enclosure is drained, and the soil inside the upper pipe jack is horizontally reinforced.

[0009] S2, longitudinally excavate and reinforce the soil in sections. After each section is excavated, vertical holes are excavated. Vertical steel supports are installed in the middle holes, and vertical steel beams are installed in the side holes. Short steel beams are installed at the bottom of both the vertical steel supports and the steel beams. The gaps in the holes are backfilled. A transverse steel beam is installed on top of the steel supports. The jacks on the steel supports are used to apply pre-stress to make the transverse steel beam tightly against the upper pipe curtain. The two ends of the transverse steel beam are tightly welded to the vertical steel beam.

[0010] S3, excavate to the position of the first horizontal steel support, erect the first horizontal steel support, and pre-apply axial force by using jacks set on the horizontal steel support to tighten the two ends of the horizontal steel support with the vertical steel beam;

[0011] S4, excavate layer by layer to the position of the lowest horizontal steel support, erect the lowest horizontal steel support, and pre-apply axial force by using jacks set on the horizontal steel support to tighten the two ends of the horizontal steel support with the vertical steel beam;

[0012] S5, longitudinally segmented excavation of the bottom soil, after each segment is excavated to the bottom, the short steel beams are connected to form a transverse steel beam;

[0013] S6, Lay the waterproof layer on the base plate, construct the structural base plate, and remove the lowest horizontal steel support;

[0014] S7, the station structure is constructed layer by layer to form a closed structure, and grouting is performed behind the structure for backfilling;

[0015] S8, remove the vertical steel supports to complete the station construction.

[0016] In one embodiment, in step S1, the internal soil 4m below the upper pipe curtain is horizontally reinforced; grease-based water-stopping filling material is injected into the locking mechanism.

[0017] In one embodiment, in step S1, the horizontal reinforcement is carried out using horizontal high-pressure jet grouting, horizontal deep-hole grouting, or segmented horizontal reinforcement.

[0018] In one embodiment, after the groundwater is drained in step S1, there is no need for continuous precipitation.

[0019] In one embodiment, the drilling in step S2 is performed by mechanical drilling or by manual drilling.

[0020] In one embodiment, before placing the vertical support and steel beam in step S2, the sediment at the bottom of the hole is cleaned, a layer of concrete is poured at the bottom of the hole to level it, and a grouting pipe is buried at the bottom for grouting reinforcement.

[0021] In one embodiment, in step S2, the voids in the excavated hole are backfilled with sand and gravel, supplemented by grouting; when the bearing capacity or stiffness of the foundation of the bottom pipe curtain is insufficient, concrete is poured into the voids in the excavated hole or the soil at the bottom of the lower pipe curtain is horizontally reinforced.

[0022] In one embodiment, in steps S1 to S8, the vertical steel support, the horizontal and vertical steel beams are all connected as a whole by connecting rods or scissor braces along the longitudinal direction.

[0023] In one embodiment, in steps S1 to S8, the jacks on the vertical and horizontal steel supports can be equipped with an automatic axial force compensation system. During the construction process, based on deformation monitoring, the axial force pre-applied to each jack is adjusted appropriately through the hydraulic pump station and control station to further control settlement and horizontal displacement.

[0024] Another objective of this invention is to provide a large underground structure constructed by tunneling in saturated soft soil, comprising: pipe jacks, vertical steel supports, vertical steel beams, horizontal steel beams, horizontal steel supports, short steel beams, a base plate, and jacks;

[0025] The pipe curtain is jacked longitudinally along the outer contour of the station. The pipe curtains are connected by interlocking. The groundwater within the pipe curtain enclosure is drained, and the soil inside the upper pipe curtain is horizontally reinforced.

[0026] The soil is reinforced by longitudinal excavation in sections. After each section is excavated, vertical holes are dug, and vertical steel supports are installed in the middle holes.

[0027] Vertical steel beams are installed at the side holes, and short steel beams are installed at the bottom of both the vertical steel supports and the vertical steel beams. The gaps in the holes are backfilled. A horizontal steel beam is installed at the top of the vertical steel supports. A preload is applied using jacks on the vertical steel supports to make the horizontal steel beam tightly against the upper pipe curtain. The two ends of the horizontal steel beam are tightly welded to the vertical steel beam.

[0028] Excavation reaches the position of the first horizontal steel support, the first horizontal steel support is erected, and axial force is pre-applied by jacks set on the horizontal steel support, so that the two ends of the horizontal steel support are tightly pressed against the vertical steel beam;

[0029] The bottom soil is excavated longitudinally in sections, and after each section is excavated to the bottom, the short steel beams are connected to form a transverse steel beam.

[0030] Lay the waterproof layer on the base slab, construct the structural base slab, and remove the lowest horizontal steel support.

[0031] Combining all the above technical solutions, the advantages and positive effects of this invention are as follows:

[0032] First, in view of the technical problems existing in the prior art and the difficulty of solving these problems, and closely combining the technical solution to be protected by this invention with the results and data during the research and development process, this paper analyzes in detail how the technical solution of this invention solves the technical problems, and the inventive technical effects brought about after solving the problems, as described in detail below:

[0033] This invention makes full use of the longitudinal stiffness of the pipe curtain, and the pipe curtain diameter is generally small; there is no need to pre-reinforce the soil within the excavation area; the steel beams and supports adopt the support types commonly used in foundation pits, which can be reused; therefore, the engineering investment of this method is greatly reduced.

[0034] This invention constructs a segmented vertical support system for the pipe curtain within a 4m height space below the top pipe curtain, ensuring the longitudinal stability of the soil at this excavation height. The vertical support feet are directly supported on the upper and lower high-rigidity pipe curtains and are equipped with a pre-applied axial force system, which facilitates the control of vertical deformation. There is no force transfer during the excavation process, and the vertical deformation is independent of the structural layer height. Therefore, this invention can be used for the construction of multi-story underground structures.

[0035] The present invention has large vertical and horizontal support stiffness and large support spacing. The pipe jacking support system of the present invention can be constructed quickly. After the vertical support system is constructed, large-scale earthwork excavation can be carried out as if it were an open excavation pit, which greatly improves construction efficiency and can significantly reduce the construction period. At the same time, the construction structure and waterproofing are carried out in a large space, and the construction quality is guaranteed.

[0036] Secondly, considering the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by this invention are specifically described as follows:

[0037] This invention provides a method for constructing a large underground structure by tunnel excavation in saturated soft soil. A longitudinal pipe curtain is installed around the outer contour of the underground structure, and the soil within a 4-meter range below the top pipe curtain is horizontally reinforced. The reinforced soil is excavated longitudinally in sections, with vertical holes dug immediately after each section. Vertical steel supports are installed in the middle holes, and vertical steel beams are installed in the side holes. Short steel beams are installed at the bottom of both the vertical steel supports and the steel beams. The gaps in the holes are backfilled and compacted. A transverse steel beam is installed at the top of the steel supports, tightly abutting against the pipe curtain. The soil is excavated in layers, and horizontal steel supports are erected promptly. The ends of the horizontal steel supports are tightly abutted against the vertical steel beams on both sides until the lowest support is reached. The bottom layer of soil is excavated longitudinally in sections, and the short steel beams are welded into transverse steel beams after each section is excavated. The structure is constructed layer by layer from bottom to top, and the horizontal steel supports are removed. After the structure is enclosed into a ring, grout is injected behind the structure, and the vertical steel supports are removed. This method overcomes the problems of current pipe-jacking construction methods in saturated soft soil, such as the need for compartmentalization, large surface settlement, large reinforcement range, high construction cost, long construction period, and difficulty in constructing multi-story structures. It makes it possible to widely adopt the cut-and-cover method to construct large underground structures in saturated soft soil. Attached Figure Description

[0038] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0039] Figure 1 This is a schematic diagram of a large underground structure constructed by tunneling in saturated soft soil, provided by an embodiment of the present invention.

[0040] Figure 2 This is a flowchart of a method for constructing a large underground structure by tunneling in saturated soft soil, provided by an embodiment of the present invention.

[0041] Figure 3 This is a cross-sectional schematic diagram of step S101 in a method for constructing a large underground structure by tunneling in saturated soft soil according to an embodiment of the present invention.

[0042] Figure 4 This is a cross-sectional schematic diagram of step S102 in a method for constructing a large underground structure by tunneling in saturated soft soil according to an embodiment of the present invention.

[0043] Figure 5 This is a longitudinal cross-sectional schematic diagram of step S102 in a method for constructing a large underground structure by tunneling in saturated soft soil according to an embodiment of the present invention.

[0044] Figure 6 This is a cross-sectional schematic diagram of step S103 in a method for constructing a large underground structure by tunneling in saturated soft soil according to an embodiment of the present invention.

[0045] Figure 7 This is a cross-sectional schematic diagram of step S104 in a method for constructing a large underground structure by tunneling in saturated soft soil according to an embodiment of the present invention.

[0046] Figure 8 This is a cross-sectional schematic diagram of step S105 in a method for constructing a large underground structure by tunneling in saturated soft soil according to an embodiment of the present invention.

[0047] Figure 9 This is a cross-sectional schematic diagram of step S106 in a method for constructing a large underground structure by tunneling in saturated soft soil according to an embodiment of the present invention.

[0048] Figure 10 This is a cross-sectional schematic diagram of step S107 in a method for constructing a large underground structure by tunneling in saturated soft soil according to an embodiment of the present invention.

[0049] Figure 11 This is a cross-sectional schematic diagram of step S108 in the method for constructing a large underground structure by tunneling in saturated soft soil according to an embodiment of the present invention:

[0050] In the diagram: 1. Pipe curtain; 2. Vertical steel support; 3. Vertical steel beam; 4. Horizontal steel beam; 5. Horizontal steel support; 6. Short steel beam; 7. Base plate; 8. Jack. Detailed Implementation

[0051] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0052] Example 1

[0053] like Figure 1 As shown, an embodiment of the present invention provides a large underground structure constructed by tunneling in saturated soft soil, comprising: a pipe curtain 1, vertical steel supports, vertical steel beams 3, horizontal steel beams 4, horizontal steel supports 5, short steel beams 6, a base plate 7, and jacks 8.

[0054] The pipe jacking 1 is longitudinally advanced along the outer contour of the station. The pipe jacks are connected by interlocking mechanisms. Groundwater within the pipe jack enclosure is drained, and the internal soil approximately 4 meters below the upper pipe jack is horizontally reinforced. Figure 3 .

[0055] The soil is reinforced by longitudinal excavation in sections. After each section is excavated, vertical holes are dug, and vertical steel supports are installed in the middle holes.

[0056] A vertical steel beam 3 is installed at the side hole, and short steel beams 6 are installed at the bottom of both the vertical steel support 2 and the vertical steel beam 3. The gaps in the hole are backfilled. A horizontal steel beam 4 is installed at the top of the vertical steel support 2. A preload is applied using jacks 8 on the vertical steel support 2 to tighten the horizontal steel beam 4 against the upper pipe curtain 1. The two ends of the horizontal steel beam 4 are then tightly welded to the vertical steel beam 2. Figures 4-5 .

[0057] Excavation proceeds to the position of the first horizontal steel support 5. The first horizontal steel support is then erected, and axial force is pre-applied using jacks 8 mounted on it. The two ends of the horizontal steel support 5 are then firmly anchored to the vertical steel beam 2. (Example:) Figure 6 As shown.

[0058] The bottom soil is excavated longitudinally in sections. After each section reaches the bottom, the short steel beams 6 are connected to form a transverse steel beam. For example... Figure 8 As shown.

[0059] Lay the waterproof layer on the base slab, construct the structural base slab 7, and remove the lowest horizontal steel support 5. (For example...) Figure 9 As shown.

[0060] like Figure 2 The embodiment of the present invention provides a method for constructing a large underground structure by tunneling in saturated soft soil, comprising the following steps:

[0061] S101 involves longitudinally jacking a pipe jack along the outer contour of the station, with interlocking connections between the pipe jacks. Groundwater within the pipe jack enclosure is drained, and the internal soil approximately 4 meters below the upper pipe jack is horizontally reinforced. For example... Figure 3 As shown.

[0062] S102 involves longitudinal, segmented excavation to reinforce the soil. After each segment is excavated, vertical holes are drilled. Vertical steel supports are installed in the middle holes, and vertical steel beams are installed in the side holes. Short steel beams are installed at the bottom of both the vertical steel supports and the steel beams. The gaps inside the holes are backfilled. Horizontal steel beams are installed on top of the steel supports. Pre-stress is applied using jacks on the steel supports to ensure the horizontal steel beams are tightly fitted to the upper pipe curtain. The two ends of the horizontal steel beams are then welded securely to the vertical steel beams. Figures 4-5 As shown.

[0063] S103, excavation reaches the position of the first horizontal steel support, the first horizontal steel support is erected, and axial force is pre-applied by jacks set on the horizontal steel support, the two ends of the horizontal steel support are tightly pressed against the vertical steel beam. For example... Figure 6 As shown.

[0064] S104, excavate layer by layer to the position of the lowest horizontal steel support, erect the lowest horizontal steel support, and pre-apply axial force using jacks set on the horizontal steel support to tighten the two ends of the horizontal steel support against the vertical steel beam. For example... Figure 7 As shown.

[0065] S105 involves longitudinally excavating the bottom soil in segments, and connecting short steel beams into transverse steel beams after each segment has been excavated to the bottom. For example... Figure 8 As shown.

[0066] S106, Lay the waterproof layer on the base slab, construct the structural base slab, and remove the lowest horizontal steel support. (Example) Figure 9 As shown.

[0067] S107, the station structure is constructed layer by layer to form a closed structure, and grouting and backfilling are carried out behind the structure in a timely manner to ensure that the filling between the structure and the pipe curtain is dense. For example... Figure 10 As shown.

[0068] S108, remove the vertical steel supports to complete station construction. (For example...) Figure 11 As shown.

[0069] Example 2

[0070] Based on the method for constructing large underground structures by tunneling in saturated soft soil provided in Embodiment 1 of the present invention, further, in step S101, the locking mechanism is filled with water-stopping filling materials such as grease.

[0071] Example 3

[0072] Based on the method for constructing large underground structures in saturated soft soil by tunneling provided in Embodiment 1 of the present invention, the horizontal reinforcement in step S101 can be carried out by horizontal high-pressure jet grouting or horizontal deep hole grouting. When the reinforcement length is long and the grouting quality cannot be guaranteed, the horizontal reinforcement is carried out in segments together with step S102.

[0073] Example 4

[0074] Based on the method for constructing large underground structures by tunneling in saturated soft soil provided in Embodiment 1 of the present invention, further, after the groundwater in step S101 is drained, there is no need for continuous precipitation.

[0075] Example 5

[0076] Based on the method for constructing large underground structures in saturated soft soil by tunneling provided in Embodiment 1 of the present invention, the excavation in step S102 is generally carried out by mechanical drilling, but manual excavation can also be used when geological conditions permit.

[0077] Example 6

[0078] Based on the method for constructing a large underground structure by tunneling in saturated soft soil provided in Embodiment 1 of the present invention, further, in step S102, before placing the vertical support and steel beam, the sediment at the bottom of the hole must be cleaned, and a layer of concrete must be poured at the bottom of the hole to level it. If necessary, grouting pipes are buried at the bottom for grouting reinforcement.

[0079] Example 7

[0080] Based on the method for constructing a large underground structure in saturated soft soil by tunneling provided in Embodiment 1 of the present invention, in step S102, the backfilling of the voids in the excavation hole is carried out with sand and gravel, and grouting measures are preferred; when the bearing capacity or stiffness of the bottom pipe curtain foundation is insufficient, the voids in the excavation hole can also be filled with concrete or the soil at the bottom of the lower pipe curtain can be horizontally reinforced.

[0081] Example 8

[0082] Based on the method for constructing a large underground structure by tunneling in saturated soft soil provided in Embodiment 1 of the present invention, further, in steps S101-S108, the vertical steel supports, horizontal and vertical steel beams are all connected into a whole by connecting rods or scissor braces along the longitudinal direction.

[0083] Example 9

[0084] Based on the method for constructing large underground structures in saturated soft soil by tunneling provided in Embodiment 1 of the present invention, the jacks on the vertical and horizontal steel supports in steps S101-S108 can be equipped with an automatic axial force compensation system. During the construction process, based on the deformation monitoring, the axial force pre-applied to each jack can be adjusted appropriately through the hydraulic pump station and control station to further control settlement and horizontal displacement.

[0085] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0086] The construction method described in the above embodiments is a typical example. These embodiments are only used to further illustrate the details and effects of the method of the present invention and do not constitute a limitation on the present invention. Those skilled in the art can make corresponding modifications based on the external environmental conditions of the project, combined with engineering geological and hydrogeological conditions, during engineering implementation. For example, the method of the present invention is not limited to large underground structures in saturated soft soil areas; it can also be used in unsaturated soil or hard soil layers, and is equally applicable to small underground structures.

[0087] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention and within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for constructing large underground structures by tunneling in saturated soft soil, characterized in that, The method includes the following steps: S1, the pipe jacking is carried out longitudinally along the outer contour of the station. The pipe jacks are connected by interlocking. The groundwater within the pipe jack enclosure is drained, and the soil inside the upper pipe jack is horizontally reinforced. S2, longitudinally excavate and reinforce the soil in sections. After each section is excavated, vertical holes are excavated. Vertical steel supports are installed in the middle holes, and vertical steel beams are installed in the side holes. Short steel beams are installed at the bottom of both the vertical steel supports and the steel beams. The gaps in the holes are backfilled. A transverse steel beam is installed on top of the steel supports. The jacks on the steel supports are used to apply pre-stress to make the transverse steel beam tightly against the upper pipe curtain. The two ends of the transverse steel beam are tightly welded to the vertical steel beam. S3, excavate to the position of the first horizontal steel support, erect the first horizontal steel support, and pre-apply axial force by using jacks set on the horizontal steel support to tighten the two ends of the horizontal steel support with the vertical steel beam; S4, excavate layer by layer to the position of the lowest horizontal steel support, erect the lowest horizontal steel support, and pre-apply axial force by using jacks set on the horizontal steel support to tighten the two ends of the horizontal steel support with the vertical steel beam; S5, longitudinally segmented excavation of the bottom soil, after each segment is excavated to the bottom, the short steel beams are connected to form a transverse steel beam; S6, Lay the waterproof layer on the base plate, construct the structural base plate, and remove the lowest horizontal steel support; S7, the station structure is constructed layer by layer to form a closed structure, and grouting is performed behind the structure for backfilling; S8, remove the vertical steel supports to complete the station construction.

2. The method for constructing large underground structures by tunneling in saturated soft soil according to claim 1, characterized in that, In step S1, the soil 4m below the upper pipe curtain is horizontally reinforced; grease-based water-stopping filling material is injected into the locking mechanism.

3. The method for constructing large underground structures by tunneling in saturated soft soil according to claim 1, characterized in that, In step S1, horizontal reinforcement is carried out using horizontal high-pressure jet grouting, horizontal deep hole grouting, or segmented horizontal reinforcement.

4. The method for constructing large underground structures by tunneling in saturated soft soil according to claim 1, characterized in that, In step S1, after the groundwater is drained, there is no need for continuous precipitation.

5. The method for constructing large underground structures by tunneling in saturated soft soil according to claim 1, characterized in that, The drilling in step S2 can be done mechanically or manually.

6. The method for constructing large underground structures by tunneling in saturated soft soil according to claim 1, characterized in that, Before placing the vertical support and steel beam in step S2, the sediment at the bottom of the hole is cleaned, a layer of concrete is poured at the bottom of the hole to level it, and a grouting pipe is buried at the bottom for grouting reinforcement.

7. The method for constructing large underground structures by tunneling in saturated soft soil according to claim 1, characterized in that, In step S2, the voids in the excavated hole are backfilled with sand and gravel, supplemented by grouting. When the bearing capacity or stiffness of the foundation of the bottom pipe curtain is insufficient, concrete is poured into the voids in the excavated hole or the soil at the bottom of the lower pipe curtain is horizontally reinforced.

8. The method for constructing large underground structures by tunneling in saturated soft soil according to claim 1, characterized in that, In steps S1-S8, the vertical steel support, the horizontal and vertical steel beams are all connected as a whole by connecting rods or scissor braces along the longitudinal direction.

9. The method for constructing large underground structures by tunneling in saturated soft soil according to claim 1, characterized in that, In steps S1-S8, the jacks on the vertical and horizontal steel supports can be equipped with an automatic axial force compensation system. During the construction process, based on the deformation monitoring, the axial force of each jack can be adjusted appropriately in a timely manner through the hydraulic pump station and control station to further control settlement and horizontal displacement.

10. A method for constructing a large underground structure in saturated soft soil by tunneling according to any one of claims 1-9, characterized in that... The large underground structure constructed by tunneling in saturated soft soil includes: pipe curtain (1), vertical steel support (2), vertical steel beam (3), horizontal steel beam (4), horizontal steel support (5), short steel beam (6), bottom plate (7), and jacks (8). The pipe curtain (1) is pushed longitudinally along the outer contour of the station. The pipe curtain 1 is connected by a locking mechanism. The groundwater within the pipe curtain enclosure is drained, and the soil inside the upper pipe curtain is horizontally reinforced. The soil is reinforced by longitudinal excavation in sections. After each section is excavated, vertical holes are dug, and vertical steel supports are installed in the middle holes (2). A vertical steel beam (3) is set at the side hole. A short steel beam (6) is set at the bottom of both the vertical steel support (2) and the vertical steel beam (3). The gap in the hole is backfilled. A horizontal steel beam (4) is set at the top of the vertical steel support (2). A preload is applied by the jack (8) on the vertical steel support (2) so that the horizontal steel beam (4) is pressed tightly against the upper pipe curtain (1). The two ends of the horizontal steel beam (4) are tightly welded to the vertical steel beam (2). Excavate to the position of the first horizontal steel support (5), erect the first horizontal steel support, and pre-apply axial force by using jacks (8) set on the horizontal steel support (5) to tighten the two ends of the horizontal steel support (5) against the vertical steel beam (2); The bottom soil is excavated longitudinally in sections, and after each section is excavated to the bottom, the short steel beams (6) are connected to form a transverse steel beam. Lay the waterproof layer on the base plate, construct the structural base plate (7), and remove the lowest horizontal steel support (5).

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