A foundation pit support structure and construction method for a restricted terrain near an old bridge

Abstract

This invention provides a foundation pit support structure for restricted terrain near an existing bridge, comprising a longitudinal support structure, a transverse support structure, and a cover concrete. The longitudinal support structure consists of several rows of piles that decrease in height along the length of the bridge, corresponding to the existing bridge bottom slope. The transverse support structure extends from the end of the longitudinal support structure away from the river towards a direction perpendicular to the bridge. The cover concrete is used to cover the longitudinal and transverse support structures. This invention also provides a construction method for a foundation pit support structure for restricted terrain near an existing bridge, including the following steps: pre-construction preparation, construction of the support structure, and cover treatment. This invention can replace anchor cables with internal bracing in the support structure, thereby reducing structural displacement of the support structure, minimizing its impact on the existing structure, and improving durability.

Description

[Technical Field]

[0001] This invention relates to the field of bridge construction technology, specifically to a foundation pit support structure and construction method for confined terrain near an old bridge. [Background Technology]

[0002] When large foundation pits need to be excavated near existing buildings, and the deeper the pit and the more complex the surrounding environment, it is necessary to support the existing buildings, i.e., the perimeter walls of the foundation pit. For example, when constructing a double-track bridge, it is often built adjacent to an existing bridge. When excavating the foundation pit for the new double-track bridge, the existing bridge's slope needs to be encroached upon. In this case, the slope needs to be demolished. After the slope is demolished, the abutments and slopes that originally provided support through the slope lose their supporting structure. Since the excavation depth is large when excavating a foundation pit near an existing bridge, it is considered a deep foundation pit project. Therefore, before excavating the foundation pit for a new double-track bridge under the aforementioned restricted terrain, the abutments and slopes of the existing bridge need to be protected before the slope is demolished. In existing technologies, a pile and anchor cable structure system is often used to support old bridges. The anchor rods of this structure need to penetrate the existing bridge and road to complete the support, thus damaging the existing bridge and road structures.

[0003] Chinese utility model patent CN216948316U discloses "an anchor cable support system for pile bank support," which includes an anchor cable assembly and a support pile bank. The anchor cable assembly includes an anchor cable anchorage section, an anchor cable free section, and an anchor. The anchor cable anchorage section extends into a stable layer deep in the soil to form an anchor body. The free section includes two steel cables extending from the anchor cable anchorage section, which pass around the support pile bank and are locked by the anchor. The anchor includes an anchor body, and the interior of the anchor body is configured with a first through hole and a second through hole. The first through hole and the second through hole are staggered, so that the free section of the anchor cable is fixed to the support pile bank through the first through hole and the second through hole. This design ensures that each anchor cable assembly is directly and tightly connected to the support pile, resulting in uniform stress on each support pile and improving the stability of the foundation pit. Furthermore, existing technologies also use various similar anchor cable structures in conjunction with pile bank support to support bridge abutments. However, in actual construction, the following problems exist:

[0004] To better support the existing bridge abutments and the road slope behind them, multiple rows of piles of equal length need to be poured along the bridge's length. Additionally, anchor cable structures need to be constructed between the piles. The construction of these anchor cable structures is complex, and because the anchor cables penetrate into the existing road structure, this penetration can damage the existing road structure. Furthermore, the anchor cable support system experiences significant deformation, impacting traffic safety on the existing road. Therefore, the primary challenge is to develop a more durable support structure that minimizes structural displacement and impacts the existing structure. [Summary of the Invention]

[0005] The present invention aims to solve at least one of the above-mentioned technical problems and provide a foundation pit support structure and construction method for restricted terrain near old bridges. It can replace the anchor cable support structure with internal bracing, thereby achieving the purpose of reducing the structural displacement of the support structure, reducing the impact of the support structure on the existing structure, and making it more durable.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A foundation pit support structure for a restricted terrain adjacent to an old bridge includes a longitudinal support structure, a transverse support structure, and a cover concrete. The longitudinal support structure consists of several rows of piles arranged along the length of the bridge, with the height of the piles decreasing as the height of the existing bridge bottom slope decreases. The transverse support structure extends from the end of the longitudinal support structure away from the river towards the length of the bridge, corresponding to the existing slope and providing slope support. The cover concrete is used to cover the longitudinal and transverse support structures.

[0008] A construction method for a foundation pit support structure in a restricted terrain near an old bridge, used for constructing the aforementioned foundation pit support structure in such a restricted terrain near an old bridge, includes the following steps:

[0009] Pre-construction preparations include clearing the construction site, preparing construction equipment and materials;

[0010] Construction support structure: The longitudinal support structure is constructed along the length of the bridge corresponding to the outer side of the abutment; the transverse support structure is constructed along the width of the bridge, and the transverse support structure is perpendicular to the longitudinal support structure.

[0011] Concrete covering treatment: Concrete covering treatment is performed on the transverse support structure and the longitudinal support structure respectively.

[0012] Furthermore, when the abutment is a lightweight abutment and the existing conical slope needs to be removed, the longitudinal support structure is located on both sides of the lightweight abutment and is constructed along the edge of the conical slope in the direction of the bridge's length, resulting in a number of pile supports that gradually decrease in length along the extension direction of the lightweight abutment; the transverse support structure is constructed from the highest point of the longitudinal support structure and is constructed in the direction perpendicular to the bridge along the rear slope of the lightweight abutment.

[0013] Furthermore, the pile support includes primary longitudinal support, secondary longitudinal support and tertiary longitudinal support. The total height of the primary longitudinal support, the secondary longitudinal support and the tertiary longitudinal support decreases step by step according to the height of the existing bridge bottom cone slope. The secondary longitudinal support is located between the primary longitudinal support and the tertiary longitudinal support. The transverse support structure is connected to the side of the primary longitudinal support away from the river.

[0014] Furthermore, when the pile length range H of the longitudinal support structure and / or the transverse support structure is ≥10m, after obtaining the transverse support structure, an inner support template for pouring an inner support is built on a construction plane at a preset height. The inner support template is connected to both the longitudinal support structure and the transverse support structure. Concrete is then poured into the inner support template to obtain the inner support.

[0015] The internal support includes a longitudinal wainscoting, a transverse wainscoting, and a connecting arm. The longitudinal wainscoting extends along the length of the bridge and connects to the piles of the longitudinal support structure. The transverse wainscoting extends along the width of the bridge and connects to the piles of the transverse support structure. The two ends of the connecting arm connect the longitudinal wainscoting and the transverse wainscoting.

[0016] Furthermore, the internal support includes a first internal support and a second internal support with identical structures. The longitudinal lateral beam of the first internal support connects to the longitudinal support structure, and the transverse lateral beam of the first internal support connects to the top of the transverse support structure. The second internal support is located on the side of the first internal support facing the pre-excavated pit and connects the piles of the longitudinal support structure and the transverse support structure.

[0017] Furthermore, the method for determining the length of the pile is as follows: taking the bottom surface of the pre-excavated foundation pit as the reference surface, the distance from the reference surface to the top surface of the pile is the length of the pile.

[0018] Furthermore, the construction support structure includes the following steps:

[0019] Step S1: On a first construction plane, construct the support structure on both sides of the lightweight bridge abutment along the length of the bridge to obtain the first-level longitudinal support. The first-level longitudinal support includes several first piles and a first cap beam. The length of the first piles is H≥17m. The several first piles are spaced apart along the length of the bridge and extend inwards towards the ground. The first cap beam connects the ends of the several first piles located outside the ground.

[0020] Step S2: Excavate from the first construction plane perpendicular to it. After excavating to a preset height, a second construction plane lower than the first construction plane is obtained. On the second construction plane, a support structure is constructed to obtain the transverse support structure. The transverse support structure includes several transverse piles and a transverse cap beam. The length of the transverse piles is 10m < H < 17m. Several transverse piles are spaced apart along the width of the bridge and extend inward toward the ground. The transverse cap beam connects one end of several transverse piles located outside the ground.

[0021] Step S3: The second construction plane extends to the river side, and a support structure is constructed on the second construction plane to obtain the secondary longitudinal support. The secondary longitudinal support includes several second piles and a second cap beam. The length of the second piles is 10m < H < 17m. Several second piles are spaced apart along the length of the bridge and extend inward toward the ground. The second cap beam connects one end of several second piles located outside the ground.

[0022] Step S4: Excavate from the vertical second construction plane to obtain a third construction plane lower than the second construction plane. The third construction plane is flush with the waist beam of the first longitudinal support. On the third construction plane, construct an inner support formwork for pouring the first inner support. The inner support formwork includes a longitudinal waist beam formwork, a transverse waist beam formwork, and a connecting beam formwork. The longitudinal waist beam formwork extends along the length of the bridge and is connected to the piles of the longitudinal support structure. The transverse waist beam formwork is connected to the piles of the transverse support structure. The two ends of the connecting beam formwork are connected to the longitudinal waist beam formwork and the transverse waist beam formwork. Pour concrete into the inner support formwork to obtain the first inner support.

[0023] Step S5: Excavate from the vertical third construction plane to a preset height to obtain a fourth light construction plane that is lower than the third construction plane. Construct a support structure on the fourth light construction plane to obtain the third-level longitudinal support. The third-level longitudinal support includes several fourth piles and a fourth cap beam. The length of the fourth piles is H < 10m. Several fourth piles are spaced apart along the length of the bridge and extend inwards. The fourth cap beam connects one end of several fourth piles located outside the ground.

[0024] Step S6: Excavate from the vertical fourth light construction plane to a preset height to obtain a fifth light construction plane that is lower than the fourth light construction plane. Construct the second inner support on the fifth light construction plane. After the construction of the second inner support is completed, the deep foundation pit can be formally excavated on the side of the fifth light construction plane facing the river.

[0025] By adopting the above technical solution, the present invention has the following beneficial effects:

[0026] The above-mentioned foundation pit support structure and construction method are adopted to simultaneously support the slopes of the bridge abutments and the road behind them. Compared with the existing technology of supporting the slopes of the bridge abutments and roads by using pile support combined with anchor cable structure, the internal support replaces the anchor cables, thus protecting the existing bridge abutments and the road behind them. Compared with the existing technology of constructing piles and anchor cables along the entire length of the bridge and adding concrete cover treatment between the piles, the internal support in this scheme is a rigid structure. Compared with the flexible structure of the anchor cables, it can reduce the displacement of the support structure, and also solve the impact of the anchor cables penetrating into the existing road on the existing road. Finally, the concrete cover between the piles also makes the overall support structure more aesthetically pleasing. [Attached Image Description]

[0027] Figure 1 This is a schematic diagram of the foundation pit support structure in this invention.

[0028] Figure 2 for Figure 1 A schematic diagram of the construction steps for the foundation pit support structure.

[0029] Figure 3 Figure 2 Top view of step S2.

[0030] Figure 4 Figure 2 Top view of step S3.

[0031] Table 1 shows a comparison of the effects of primary longitudinal support and existing technical solutions.

[0032] In the attached diagram, 100 - Lightweight abutment, 11 - Primary longitudinal support, 101 - First construction plane, 102 - First pile, 103 - First capping beam, 12 - Secondary longitudinal support, 121 - Secondary pile, 122 - Secondary capping beam, 13 - Tertiary longitudinal support, 130 - Fourth lightweight construction plane, 131 - Fourth pile, 132 - Fourth capping beam, 14 - Transverse support structure, 140 - Second construction plane, 141 - Transverse pile, 142 - Transverse capping beam, 15 - Internal support, 150-Internal support formwork, 151-Longitudinal bridge girders formwork, 152-Transverse bridge girders formwork, 153-Connecting beam formwork, 154-Longitudinal bridge girders, 155-Transverse bridge girders, 156-Connecting arm, 157-Third construction plane, 161-First internal support, 162-Second internal support, 301-Rotary drilling rig, 302-Excavator, 303-Existing bridge bottom cone slope, 304-Pre-excavated foundation pit, 305-Slope, 306-Bridge body, 307-River. [Specific implementation method]

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] It should be noted that when a component is described as "fixed to" another component, it can be directly on the other component or it may be centered within another component. When a component is described as "set to" another component, it can be directly set on the other component or it may be centered within another component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this article are for illustrative purposes only.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] like Figures 1 to 4 As shown, a preferred embodiment of the present invention provides a foundation pit support structure for confined terrain near an existing bridge, which is suitable for protecting the edge of a deep foundation pit when excavating a deep foundation pit near an existing structure. It includes a longitudinal support structure, a transverse support structure 14, and a cover concrete. The longitudinal support structure consists of several rows of piles that decrease in height along the length of the bridge, corresponding to the existing bridge bottom slope 303. The height of the piles decreases as the existing bridge bottom slope 303 decreases. The transverse support structure 14 extends from the end of the longitudinal support structure away from the river 307 towards a direction perpendicular to the bridge. The transverse support structure 14 corresponds to the existing slope 305 and provides support for the slope 305. Specifically, the transverse support structure 14 abuts against the edge of the existing slope 305. The cover concrete is used to cover the longitudinal support structure and the transverse support structure 14.

[0037] This embodiment also provides a construction method for a foundation pit support structure under restricted terrain near an old bridge, which is used to construct the aforementioned foundation pit support structure and includes the following steps:

[0038] Pre-construction preparations include clearing the construction site, preparing construction equipment and materials. The prepared construction equipment includes rotary drilling rig 301 and excavator 302.

[0039] Construction support structure: The longitudinal support structure is constructed along the length of the bridge corresponding to the outer side of the abutment; the transverse support structure 14 is constructed along the width of the bridge. The transverse support structure 14 is perpendicular to the longitudinal support structure.

[0040] Concrete cover treatment: Concrete cover treatment is performed on the transverse support structure 14 and the longitudinal support structure respectively. The cover treatment is well known to those skilled in the art and will not be described in detail here.

[0041] In this embodiment, when the abutment is a lightweight abutment 100 and the existing conical slope needs to be removed, the longitudinal support structure is located on both sides of the lightweight abutment 100 and constructed along the edge of the conical slope along the length of the bridge. Specifically, it is constructed from the end of the lightweight abutment 100 away from the river 307 along the edge of the conical slope along the length of the bridge; resulting in a plurality of pile supports that gradually decrease along the length extension direction of the lightweight abutment 100. Specifically, the height of the plurality of pile supports increases from the end of the lightweight abutment 100 away from the river 307 towards... The height of the pile supports decreases sequentially along the direction of river 307, meaning that the height of several pile supports decreases step by step according to the existing cone slope height. Specifically, the pile supports include primary longitudinal support 11, secondary longitudinal support 12, and tertiary longitudinal support 13. The heights of primary longitudinal support 11, secondary longitudinal support 12, and tertiary longitudinal support 13 decrease sequentially from the end of the lightweight bridge abutment 100 away from river 307 towards river 307, with secondary longitudinal support 12 located between primary longitudinal support 11 and tertiary longitudinal support 13. The transverse support structure 14 is constructed starting from the end of primary longitudinal support 11 away from river 307, and is constructed perpendicular to the bridge along the rear slope of the lightweight bridge abutment 100, so that the transverse support structure 14 is perpendicular to primary longitudinal support 11, secondary longitudinal support 12, and tertiary longitudinal support 13.

[0042] The main support location of the longitudinal support piles is the existing bridge bottom cone slope. Since the edge of the bridge bottom cone slope slopes downward from the end of the lightweight abutment 100 away from the river 307 towards the river 307, the longitudinal support piles are also constructed in a step-by-step manner. Only by starting construction from the end of the lightweight abutment 100 away from the river 307 can the excess cone slope be gradually broken down towards the lower edge while using the longitudinal support structure to support the cone slope with greater stress, so as to ensure the stability and safety of construction.

[0043] In this embodiment, when the pile length H of the longitudinal support structure and / or the transverse support structure 14 is ≥10m, in the construction support structure, after obtaining the transverse support structure 14, an inner support template 150 for pouring an inner support 15 is erected on a construction plane at a preset height. The inner support template 150 is connected to both the longitudinal support structure and the transverse support structure 14. Concrete is then poured into the inner support template 150 to obtain the inner support 15. The inner support 15 includes a longitudinal lateral beam 154, a transverse lateral beam 155, and a connecting arm 156. The longitudinal lateral beam 154 extends along the length of the bridge and connects to the piles of the longitudinal support structure. The transverse lateral beam 155 extends along the width of the bridge and connects to the piles of the transverse support structure 14. The two ends of the connecting arm 156 connect the longitudinal lateral beam 154 and the transverse lateral beam 155. The method for determining the length of the pile is as follows: taking the bottom surface of the pre-excavated foundation pit 304 as the reference surface, the distance from the reference surface to the top surface of the pile is the length of the pile. Specifically, the pile includes an internal section inserted into the soil layer and an exposed section exposed outside the soil layer. The method for determining the internal section and the exposed section is well known to those skilled in the art and will not be elaborated here. In this embodiment, the "length of the pile" refers to the length of the exposed section, that is, the distance from the reference surface to the top surface of the exposed section. With the existing road slope and cone slope being supported, since the transverse support structure 14 is perpendicular to the primary longitudinal support 11, the secondary longitudinal support 12, and the tertiary longitudinal support 13, the lateral pressure on the transverse support structure 14 from the existing slope and the lateral pressure on the longitudinal support structure from the cone slope can be mutually offset by the internal support 15. This allows the longitudinal support structure and the transverse support structure 14 to be connected by the internal support 15 to share the load, which not only improves the stability of the entire structure but also enhances the support effect on the existing road slope and cone slope. It also eliminates the need for reinforcement by pulling the longitudinal support structure or the transverse support structure 14 with anchor cables, thereby reducing the construction of anchor cables. The rigid internal support structure replaces the flexible anchor cable structure, reducing the displacement of the support structure and avoiding the impact caused by the anchor cables penetrating deep into the existing road slope structure.

[0044] In this embodiment, the inner support 15 includes a first inner support 161 and a second inner support 162 with identical structures. The longitudinal lateral beam 154 of the first inner support 161 is connected to the longitudinal support structure, and the transverse lateral beam 155 of the first inner support 161 is connected to the top of the transverse support structure 14. The second inner support 162 is located on the side of the first inner support 161 facing the pre-excavated pit 304 and is connected to the piles of the longitudinal support structure and the transverse support structure 14.

[0045] like Figure 2 As shown, in this embodiment, when protecting the lightweight bridge abutment 100, the construction support structure includes the following steps:

[0046] Step S1: Construction is carried out on a first construction plane 101, specifically, the first construction plane 101 is the bridge deck; support structures are constructed on opposite sides of the lightweight abutment 100 along the length of the bridge to obtain the primary longitudinal support 11. The drilling and pouring of the support piles and the pouring of the cap beam of the primary longitudinal support 11 are existing technologies; the primary longitudinal support 11 includes four first piles 102 and one first cap beam 103. The length of the first piles 102 is H≥17m. The four first piles 102 are arranged in parallel at intervals along the length of the bridge and extend inwards towards the ground. The first cap beam 103 connects the tops of several first piles 102. The construction method of the first cap beam 103 is as follows: the pile top reinforcement of the support piles and the cap beam reinforcement are welded to the top surface of the four first piles 102 on the first construction plane 101. After the reinforcement is constructed, a pouring form is arranged, a reinforcement cage is placed in the pouring form, and concrete is poured in the reinforcement cage to form the first cap beam 103.

[0047] Step S2: Excavate from the first vertical construction plane 101 to a preset height, resulting in a second construction plane 140 lower than the first construction plane 101. Specifically, during the excavation from the first vertical construction plane 101, only the soil within the support range of the primary longitudinal support 11 is excavated. The method for determining this range is well-known to those skilled in the art and will not be elaborated here. Concrete surface treatment is applied to the primary longitudinal support 11 on the second construction plane 140. This surface treatment is well-known to those skilled in the art and will not be elaborated here. The support structure is constructed on the second construction plane 140, resulting in a transverse support structure 14. The transverse support structure 14 includes several transverse piles 141 and a transverse capping beam 142. The length of the transverse piles 141 ranges from 10m < H < 17m. Several transverse piles 141 are arranged parallel and spaced along the width of the bridge, with their bottom ends extending inwards towards the ground. The transverse capping beam 142 connects the tops of several transverse piles 141.

[0048] Step S3: The second construction plane 140 extends to the side of the river 307. The support structure is constructed on the second construction plane 140 to obtain the secondary longitudinal support 12. The secondary longitudinal support 12 includes several second piles 121 and a second cap beam 122. The length of the second piles 121 is 10m < H < 17m. Several second piles 121 are arranged in parallel at intervals along the length of the bridge and their bottom ends extend inward toward the ground. The second cap beam 122 connects the top ends of several second piles 121.

[0049] Step S4: Excavate from the vertical second construction plane 140 to obtain a third construction plane 157 that is lower than the second construction plane 140. The third construction plane 157 is flush with the waist beam of the first-level longitudinal support 11. On the third construction plane 157, an inner support formwork 150 is erected for pouring the first inner support 161. Specifically, during construction, reinforcing bars are pre-embedded at the top of the second pile 121 and at the height position of the first pile 102 corresponding to the top of the second pile 121. When excavation reaches the aforementioned height, the corresponding positions of the second pile 121 and the first pile 102 are broken to expose the pre-embedded reinforcing bars. A longitudinal beam formwork 151 is tied with reinforcing bars at the aforementioned position on the third construction plane 157. The longitudinal beam formwork 151 extends along the length of the bridge, and the reinforcing bars of the longitudinal beam formwork 151 are welded to the pre-embedded reinforcing bars. During construction of the top of the transverse pile 141, reinforcing bars are pre-embedded. When the inner support formwork 150 is erected, the position of the transverse pile 141 corresponding to the pre-embedded reinforcing bars is broken to expose the pre-embedded reinforcing bars. A longitudinal beam formwork 151 is tied with reinforcing bars at the aforementioned position on the third construction plane 157. A transverse bridge waist beam formwork 152 is tied to the top of 141 with steel bars. The transverse bridge waist beam formwork 152 extends along the width of the bridge, and the steel bars of the transverse bridge waist beam formwork 152 are welded to the pre-embedded steel bars. Two connecting beam formworks 153 are tied on the third construction plane 157. One end of one connecting beam formwork 153 is connected to the middle of the longitudinal bridge waist beam formwork 151, and the other end of the connecting beam formwork 153 is connected to the end of the transverse bridge waist beam formwork 152 away from the bridge body 306. One end of the other connecting beam formwork 153 is connected to the end of the longitudinal bridge waist beam formwork 151 facing the transverse bridge waist beam formwork 152, and the other end of the connecting beam formwork 153 is connected to the end of the transverse bridge waist beam formwork 152 facing the longitudinal bridge waist beam formwork 151. The formwork is supported at the longitudinal bridge waist beam formwork 151, the transverse bridge waist beam formwork 152 and the two connecting beam formworks 153, and the inner support formwork 150 is completed. Concrete is poured into the corresponding template to obtain the first internal support 161.

[0050] Step S5: Excavate from the vertical third construction plane 157 to a preset height to obtain a fourth light construction plane 130 lower than the third construction plane 157. Construct a support structure on the fourth light construction plane 130 to obtain a three-level longitudinal support 13. The three-level longitudinal support 13 includes several fourth piles 131 and a fourth cap beam 132. The length of the fourth piles 131 is H < 10m. The several fourth piles 131 are spaced apart along the length of the bridge and extend inwards towards the ground. The fourth cap beam 132 connects the ends of the several fourth piles 131 located outside the ground.

[0051] Step S6: Construction begins on the fourth light construction plane 130. After excavating to the preset height, a fifth light construction plane lower than the fourth light construction plane 130 is obtained. The second internal support 162 is constructed on the fifth light construction plane. The construction method for the second internal support 162 is the same as that for the first internal support 161 in step S4, and will not be repeated here. After the construction of the second internal support 162 is completed, the formal excavation of the deep foundation pit can begin on the side of the fifth light construction plane facing the river 307.

[0052] In this construction support structure, the pile lengths of the primary longitudinal support 11, secondary longitudinal support 12, and transverse support structure 14 are all greater than 10m. In existing technologies, anchor cable structures are often used to reinforce piles of this length when constructing them. However, since the support structure in this scheme supports the existing bridge abutment and the slope 305 of the road behind the abutment, the impact of anchor cable embedding into the existing road needs to be considered when constructing the anchor cable structure. That is, if the inner road of slope 305 is affected by the embedding of the anchor cable, it will affect the traffic flow of the existing bridge structure. By using the inner support 15 in this case to reinforce the primary longitudinal support 11, secondary longitudinal support 12, and transverse support structure 14, the entire support structure can be stressed collaboratively, making the entire pile support structure more stable and eliminating the need for anchor cable construction. In addition, since the inner support 15 is a triangular brace, the edge of the triangular brace, as a rigid structure, is smaller than that of the flexible anchor cable structure, thereby reducing the displacement of the support structure and reducing the impact of the support structure on the existing road.

[0053]

[0054] Table 1

[0055] In addition, referring to Table 1, Table 1 lists a comparison between the support method of this embodiment and the existing method of using piles and anchor cables at the first longitudinal support 11 of the lightweight bridge abutment 100. The comparison results show that when the support method of this embodiment is used at the first longitudinal support 11, the construction is more convenient, the overall displacement of the support structure is small, there is no impact on the existing road, the support effect is good, and the cost is not much different from that of using piles and anchor cables.

[0056] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A construction method for a foundation pit support structure in a restricted terrain adjacent to an old bridge, characterized in that, The construction method for the foundation pit support structure used in restricted terrain near an existing bridge includes the following steps: Pre-construction preparations include clearing the construction site, preparing construction equipment and materials; Construction support structure: The foundation pit support structure under the restricted terrain near the old bridge includes a longitudinal support structure, a transverse support structure (14), and a cover concrete. The longitudinal support structure consists of several rows of pile supports set along the length of the bridge. The height of the pile supports decreases as the height of the existing bridge bottom cone slope (303) decreases. The transverse support structure (14) extends from the end of the longitudinal support structure away from the river (307) towards the length of the bridge. The transverse support structure (14) corresponds to the existing slope (305) and can support the slope (305). The cover concrete is used to cover the longitudinal support structure and the transverse support structure (14). During construction, along the The longitudinal support structure is constructed on the outer side of the abutment along the length of the bridge to obtain the longitudinal support structure; the transverse support structure (14) is constructed along the width of the bridge to obtain the transverse support structure (14), which is perpendicular to the longitudinal support structure; when the pile length range H of the longitudinal support structure and / or the transverse support structure (14) is ≥10m, after obtaining the transverse support structure (14), an inner support template (150) for pouring an inner support (15) is built on a construction plane at a preset height. The inner support template (150) is connected to both the longitudinal support structure and the transverse support structure (14), and concrete is poured into the inner support template (150) to obtain the inner support (15). The inner support (15) includes a longitudinal wainscoting (154), a transverse wainscoting (155), and a connecting arm (156). The longitudinal wainscoting (154) extends along the length of the bridge and connects to the piles of the longitudinal support structure. The transverse wainscoting (155) extends along the width of the bridge and connects to the piles of the transverse support structure (14). The two ends of the connecting arm (156) connect the longitudinal wainscoting (154) and the transverse wainscoting (155). Concrete covering treatment: Concrete covering treatment is performed on the transverse support structure (14) and the longitudinal support structure respectively.

2. The construction method for a foundation pit support structure under restricted terrain near an old bridge as described in claim 1, characterized in that, When the abutment is a lightweight abutment (100) and the existing bridge bottom cone slope (303) needs to be removed, the longitudinal support structure is located on both sides of the lightweight abutment (100) and construction begins along the edge of the cone slope (303) in the direction of the bridge length, resulting in a number of pile supports that gradually decrease along the length extension direction of the lightweight abutment (100); the transverse support structure (14) is constructed from the end of the highest position of the longitudinal support structure and in the direction perpendicular to the bridge along the rear slope of the lightweight abutment (100).

3. The construction method for a foundation pit support structure under restricted terrain near an old bridge as described in claim 2, characterized in that: The pile support includes a primary longitudinal support (11), a secondary longitudinal support (12) and a tertiary longitudinal support (13). The total height of the primary longitudinal support (11), the secondary longitudinal support (12) and the tertiary longitudinal support (13) decreases step by step according to the height of the existing bridge bottom cone slope (303). The secondary longitudinal support (12) is located between the primary longitudinal support (11) and the tertiary longitudinal support (13). The transverse support structure (14) is connected to the side of the primary longitudinal support (11) away from the river (307).

4. The construction method for a foundation pit support structure under restricted terrain near an old bridge as described in claim 3, characterized in that: The inner support (15) includes a first inner support (161) and a second inner support (162) with the same structure. The longitudinal wainscoting (154) of the first inner support (161) is connected to the longitudinal support structure, and the transverse wainscoting (155) of the first inner support (161) is connected to the top of the transverse support structure (14). The second inner support (162) is located on the side of the first inner support (161) facing the pre-excavated pit (304) and is connected to the piles of the longitudinal support structure and the transverse support structure (14).

5. The construction method for a foundation pit support structure under restricted terrain near an old bridge as described in claim 1, characterized in that, The method for determining the length of the pile is as follows: the bottom surface of the pre-excavated foundation pit (304) is taken as the reference surface, and the distance from the reference surface to the top surface of the pile is the length of the pile.

6. The construction method of a foundation pit support structure under restricted terrain near an old bridge as described in claim 4, characterized in that: The construction support structure includes the following steps: Step S1: Construction is carried out on a first construction plane (101). Support structures are constructed on both sides of the lightweight bridge abutment (100) along the length direction of the bridge to obtain the first-level longitudinal support (11). The first-level longitudinal support (11) includes several first piles (102) and a first cap beam (103). The length of the first piles (102) is H≥17m. Several first piles (102) are spaced apart along the length direction of the bridge and extend inward toward the ground. The first cap beam (103) connects the ends of several first piles (102) located outside the ground. Step S2: Excavate from the first construction plane (101) perpendicular to the ground plane. After excavating to a preset height, a second construction plane (140) lower than the first construction plane (101) is obtained. A support structure is constructed on the second construction plane (140) to obtain the transverse support structure (14). The transverse support structure (14) includes several transverse piles (141) and a transverse cap beam (142). The length of the transverse piles (141) is 10m < H < 17m. Several transverse piles (141) are spaced apart along the width direction of the bridge and extend into the ground. The transverse cap beam (142) connects the ends of several transverse piles (141) located outside the ground. Step S3: The second construction plane (140) extends to the river (307) side. A support structure is constructed on the second construction plane (140) to obtain the secondary longitudinal support (12). The secondary longitudinal support (12) includes several second piles (121) and a second cap beam (122). The length of the second piles (121) is 10m < H < 17m. Several second piles (121) are spaced apart along the length of the bridge and extend into the ground. The second cap beam (122) connects one end of several second piles (121) located outside the ground. Step S4: Excavate from the vertical second construction plane (140) to obtain a third construction plane (157) lower than the second construction plane (140). The third construction plane (157) is flush with the waist beam of the first-level longitudinal support (11). On the third construction plane (157), construct an inner support formwork (150) for casting the first inner support (161). The inner support formwork (150) includes a longitudinal waist beam formwork (151), a transverse waist beam formwork (152), and a connecting beam. The formwork (153) consists of a longitudinal waist beam formwork (151) extending along the length of the bridge and connected to the piles of the longitudinal support structure, a transverse waist beam formwork (152) connected to the piles of the transverse support structure (14), and a connecting beam formwork (153) whose opposite ends are connected to the longitudinal waist beam formwork (151) and the transverse waist beam formwork (152); concrete is poured into the inner support formwork (150) to obtain the first inner support (161). Step S5: Excavate from the vertical third construction plane (157) to a preset height to obtain a fourth light construction plane (130) lower than the third construction plane (157). Construct a support structure on the fourth light construction plane (130) to obtain the third-level longitudinal support (13). The third-level longitudinal support (13) includes several fourth piles (131) and a fourth cap beam (132). The length of the fourth piles (131) is H < 10m. Several fourth piles (131) are spaced apart along the length of the bridge and extend into the ground. The fourth cap beam (132) connects the ends of several fourth piles (131) located outside the ground. Step S6: Excavate from the vertical fourth light construction plane (130) to a preset height to obtain a fifth light construction plane that is lower than the fourth light construction plane (130). The second inner support (162) is constructed on the fifth light construction plane. After the construction of the second inner support (162) is completed, the deep foundation pit can be formally excavated on the side of the fifth light construction plane facing the river (307).

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