Assembled support system without internal bracings in large-area foundation pit and construction method therefor

Abstract

An assembled support system without internal bracings in a large-area foundation pit and a construction method therefor. The assembled support system comprises: a foundation pit retaining structure member (1); a capping beam (12) and a waler beam (13) provided at the top and the waist of the foundation pit retaining structure member (1); and assembled prestressed anchoring members (2) provided on the outer side of the foundation pit, and inclined supporting members (3) provided on the inner side of the foundation pit. The inclined supporting members (3) and a retaining structure (11) are arranged at an included angle and the top portions thereof are connected. The inclined supporting members (3) are arranged right opposite to the assembled prestressed anchoring members (2). Beam string structure members (4) are provided at the positions of the capping beam (12) and the waler beam (13) between adjacent inclined supporting members (3). The assembled support system can effectively control foundation pit deformation without the need to use a large number of internal bracings, thus allowing foundation pits to have wide excavation working faces, and further can be disassembled and reused.

Description

An assembled support system without internal support in a large-area foundation pit and its construction method Technical Field

[0001] The present invention relates to an assembled support system without internal support in a large-area foundation pit and a construction method thereof, belonging to the technical field of foundation pit support, and is applicable to the design and construction of construction projects, municipal projects, tunnel projects and other buildings (structures). Background Art

[0002] In the design and construction of construction projects, municipal engineering projects, tunnel projects, and other buildings (structures), foundation pit support often requires the installation of an internal support system. When the foundation pit excavation depth is deep, the internal support system usually needs to be increased to ensure the structural stability of the support system. However, in large foundation pits, adding support will result in a large amount of temporary structural material waste, which will inevitably increase the project cost. At the same time, adding internal support will also block the excavation working surface to a certain extent, affecting the efficiency of foundation pit excavation.

[0003] Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings of the related art, the present invention provides an assembled support system without internal support in a large-area foundation pit and a construction method thereof, which can effectively control the deformation of the foundation pit and avoid the use of a large number of internal support rods in the foundation pit, thereby ensuring a larger excavation space in the foundation pit, and also has the advantages of being completely detachable and reusable.

[0005] A technical solution adopted by the present invention to solve its technical problem is:

[0006] An assembled support system without internal support in a large-area foundation pit, comprising:

[0007] A foundation pit retaining structure, wherein the top and waist of the foundation pit retaining structure are respectively provided with a crown beam and a surrounding purlin beam, and an assembled prestressed anchor is provided on the outside of the foundation pit;

[0008] An inclined support member, the inclined support member is arranged inside the foundation pit of the enclosure structure, the inclined support member is arranged at an angle to the enclosure structure and is connected at the top;

[0009] The inclined support members are arranged opposite to the assembled prestressed anchor members, and the crown beam and the surrounding purlin beam are respectively provided with tensioned beam structure members at positions between adjacent inclined support members.

[0010] As a further optional design of the present technical solution, the foundation pit retaining structure includes a retaining structure in the form of a retaining wall or a retaining pile, and one of the crown beams and several of the purlin beams are fixedly connected to the retaining structure in sequence from top to bottom; the retaining wall adopts an assembled underground continuous wall, and the retaining piles adopt steel sheet piles or precast concrete piles.

[0011] As a further optional design of the present technical solution, the assembled prestressed anchor comprises a plurality of recyclable prestressed tie rods uniformly distributed along the length and depth directions of the foundation pit. One end of the detachable prestressed anchor rod is fixed in the rock and soil through an anchoring steel pipe, and the other end is locked on the purlin beam through an anchor head.

[0012] As a further optional design of the present technical solution, the anchoring steel pipe includes a steel pipe body and a slot and a disassembly locking key arranged on the steel pipe body. The end of the recyclable prestressed pull rod is rotatably provided with a clamping plate, and the clamping plate passes through the slot and constrains relative displacement inside the steel pipe body through the disassembly locking key.

[0013] As a further optional design of the present technical solution, the slot extends parallel to the length direction of the steel pipe body, the length of the connectable plate is less than the length of the slot, the disassembly locking key is fixed on the inner wall of the steel pipe body and extends perpendicular to its length direction, the two disassembly locking keys are arranged at intervals along the length direction of the slot and staggered in the width direction, and at the same time, the two disassembly locking keys partially overlap with the horizontally placed clamping plate.

[0014] As a further optional design of this technical solution, the steel pipe body also includes a plurality of stiffening plates arranged inside the steel pipe body. The stiffening plates are fixedly connected to the inner wall of the steel pipe body provided with the slot and are symmetrically distributed on both sides along the length direction of the slot.

[0015] As a further optional design of the present technical solution, the inclined support member includes a plurality of inclined piles evenly distributed along the length direction of the foundation pit, and the inclined piles are prefabricated reinforced concrete structures or steel structures.

[0016] As a further optional design of the present technical solution, the inclined support members and the enclosure structure are fixedly connected by a combination of embedded connectors and poured concrete, or are fixed together by welding / bolt connections; the inclined support members are connected to each other by abutment members.

[0017] As a further optional design of the present technical solution, the tensioned beam structure includes a chord rod, a steel web and a chord rod axial force adjustment device, the rear end of the steel web is hinged to the crown beam or the surrounding purlin beam, the chord rod axial force adjustment device is fixedly connected to the front end of the steel web, the chord rod is connected to the front end of the chord rod axial force adjustment device and its two ends are respectively hinged to the crown beam or the surrounding purlin beam located on both sides of the steel web.

[0018] With the help of the above technical solution, the prefabricated support system without internal support in a large-area foundation pit of the present invention can achieve at least the following technical advantages:

[0019] The prefabricated support system of the present invention achieves the goal of reducing the need for mechanical supports by installing a beam-string structure. Inclined supports are then used to transmit the horizontal forces of the crown beam and surrounding purlin to the bottom of the foundation pit. Recyclable prestressed tie rods and anchor steel pipes are also provided to further prevent deformation of the retaining structure. This solution avoids the need for internal supports within the foundation pit, ensuring a relatively open excavation working surface, minimizing deformation of the retaining structure, and ensuring the safety of the foundation pit. Furthermore, the system is fully removable and reusable, saving on the consumption of temporary facility materials.

[0020] Another technical solution adopted by the present invention to solve its technical problem is:

[0021] A construction method for an assembled support system without internal supports in a large-area foundation pit comprises the following steps:

[0022] (1) Preparatory work: slope the soil above the crown beam, use sprayed concrete to protect the slope, construct inclined piles, retaining structures, and anchor steel pipes, and assemble and reinforce them;

[0023] (2) Start earth excavation construction;

[0024] (3) When the excavation reaches the preset elevation of the crown beam, the crown beam is constructed on the foundation pit retaining structure corresponding to the preset elevation, and the chord beam structure is installed and pre-tensioned;

[0025] (4) When the excavation reaches the preset elevation of the purlin beam, the purlin beam is constructed on the retaining structure corresponding to the preset elevation, and abutments are installed between the corresponding purlin beam and the inclined pile, the string beam structure is installed again and prestressed, and then a recyclable prestressed tie rod is directional driven toward the anchor steel pipe. After the two are firmly connected, prestress is applied and the anchor head is locked to the purlin beam;

[0026] (5) Continue excavation until the design elevation of the foundation pit bottom is reached, which means that the earthwork excavation and support operations are completed;

[0027] (6) After the underground construction is completed, the following items will be dismantled and recycled: recyclable prestressed tie rods, beam string components, purlins, crown beams, inclined supports, foundation pit retaining structures, and anchoring steel pipes.

[0028] As a further optional design of the present technical solution, in the steps (3) and (4), the chord beam structure is installed and pre-tensioned, specifically including: setting up and installing the chord rod, the steel web, and the chord rod axial force adjustment device, and pre-tightening the chord rod according to the design tension; wherein the design tension of the chord rod is determined according to the following formula:

[0029] Where F is the tension of the chord rod (in N), L is the effective length of the steel web (in m), q is the support reaction of the foundation pit retaining structure at the corresponding position (in N / m), β1 and β2 are the angles between the web and the left and right chord rods, respectively, and k is the safety factor.

[0030] As a further optional design of this technical solution, the cross-sectional model of the chord rod is determined according to the following formula:

[0031] Where A1 is the cross-sectional area of ​​the chord rod (in m2), L is the effective length of the steel web (in m), q is the support reaction of the foundation pit retaining structure at the corresponding position (in N / m), β1 and β2 are the angles between the web and the left and right chord rods, respectively, and f is the maximum effective length of the steel web (in m). Q1 is the yield strength of the material used (in Pa), and k is the safety factor.

[0032] As a further optional design of this technical solution, the cross-sectional model of the steel web is determined according to the following formula:

[0033] Where A2 is the cross-sectional area of ​​the vertical steel web (in m2), L is the effective length of the steel web (in m), q is the support reaction force of the foundation pit retaining structure at the corresponding position (in N / m), and f Q2 is the yield strength of the material used (unit: Pa), and k is the safety factor.

[0034] Compared with the related technologies, the construction method of the present invention is based on an assembled support system without internal support in a large-area foundation pit. First, it adopts an assembled support system without internal support in a large-area foundation pit, so it must have the technical advantages of the above-mentioned assembled support system; secondly, the construction method of the present invention integrates the construction process of the assembled support system with the foundation pit excavation process, and optimizes the design process of the pre-stressed string beam structure, which ensures the safety and efficiency of deep foundation pit construction to the greatest extent, and also has the advantages of overall detachability and reusability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described below with reference to the accompanying drawings and examples.

[0036] FIG1 is a schematic top view of the structure of an assembled support system according to an embodiment of the present invention.

[0037] FIG2 is an enlarged view of the structure at point A in FIG1 , which is mainly used to show the detailed structure of the beam string structure.

[0038] FIG3 is a side view of the structure of the prefabricated support system according to an embodiment of the present invention, in which the beam string structure is omitted and the assembly relationship between the foundation pit retaining structure, the prefabricated prestressed anchor and the inclined support is mainly shown.

[0039] FIG4 is an enlarged view of the structure at point B in FIG3 , which is mainly used to show the internal structure of the anchor steel pipe and its connection method with the recyclable prestressed tie rod.

[0040] 5 and 6 are cross-sectional views at CC and DD in FIG. 4 , respectively.

[0041] Explanation of the meaning of the reference numerals in the figure: 1- foundation pit retaining structure; 11- retaining structure; 12- crown beam; 13- purlin beam; 131- steel beam body; 132- stiffening rib; 2- assembled prestressed anchor; 21- recyclable prestressed tie rod; 211- clamping plate; 22- anchoring steel pipe; 221- steel pipe body; 221-1- slot; 222- disassembly locking key; 223- stiffening plate; 3- inclined support member; 31- inclined pile; 32- abutment member; 4- beam-string structure; 41- chord rod; 42- steel web member; 421- central steel web member; 422- steel web members on both sides; 43- chord rod axial force adjustment device; 441- first connecting plate; 442- second connecting plate. DETAILED DESCRIPTION

[0042] To further clarify the objectives, technical solutions, and advantages of the embodiments of the present invention, the following will provide a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. It should be understood that the described embodiments are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0043] Example 1:

[0044] FIG1 to FIG6 are schematic structural diagrams of a preferred embodiment 1 of the present invention, in which an assembled support system without internal support in a large-area foundation pit is shown, comprising:

[0045] The foundation pit retaining structure 1 has a crown beam 12 and a purlin beam 13 at its top and waist, and an assembled prestressed anchor 2 at its outer side.

[0046] The inclined support member 3 is arranged on the inner side of the foundation pit of the enclosure structure 11. The inclined support member 3 is arranged at an angle to the enclosure structure 11 and is connected at the top;

[0047] The inclined support members 3 are arranged opposite to the assembled prestressed anchor members 2 , and the crown beam 12 and the surrounding purlin beam 13 are respectively provided with beam string structures 4 at positions between adjacent inclined support members 3 .

[0048] When the prefabricated support system of the first embodiment of the present invention is used in a large-scale deep foundation pit of a building, the foundation pit retaining structure 1 is based on the foundation pit retaining structure 1. The foundation pit retaining structure 11 itself uses the provided crown beam 12 and the surrounding purlin beam 13 to form a reinforced integrated retaining pile wall, wherein the surrounding purlin beam 13 is a steel beam body 131 provided with stiffening ribs 132. The inclined support members + tension string structure members 4 are used on both sides to further enhance the strain and deformation capacity of the entire retaining pile wall. The tension string structure members 4 can also transmit the internal support force in the horizontal direction to achieve the function of supporting the retaining pile wall, thereby being able to resist the deformation or overturning of the retaining pile wall into the foundation pit.

[0049] In a further optional implementation of Example 1 of the present invention, the foundation pit retaining structure 1 includes a retaining structure 11 in the form of a supporting wall or a supporting pile, a crown beam 12 and a plurality of purlin beams 13 are fixedly connected to the retaining structure 11 in sequence from top to bottom; the supporting wall adopts an assembled underground continuous wall, and the supporting piles adopt steel sheet piles or precast concrete piles.

[0050] In a further optional implementation of Example 1 of the present invention, referring to Figure 1, the assembled prestressed anchor 2 includes a plurality of recyclable prestressed pull rods 21 that are evenly distributed along the length and depth directions of the foundation pit. One end of the detachable prestressed anchor rod is fixed in the rock and soil through an anchoring steel pipe 22, and the other end is locked on the surrounding purlin beam 13.

[0051] More specifically, referring to Figures 3 and 6 , the two ends of the recyclable prestressed tie rod 21 are respectively provided with an anchor head and a clamping plate 211. The clamping plate 211 can be fixedly connected to the end of the recyclable prestressed tie rod 21 via a sleeve. One end of the recyclable prestressed tie rod 21 is then locked to the anchor steel pipe 22 via the clamping plate 211, thereby being fixed in the rock and soil, while the other end is supported on the foundation pit retaining structure 1 via the anchor head.

[0052] In a further optional implementation of Example 1 of the present invention, referring to Figures 4-6, the anchoring steel pipe 22 includes a steel pipe body 221 and a slot 221-1 and a disassembly locking key 222 arranged on the steel pipe body 221. The end of the recyclable prestressed rod 21 is rotatably provided with a clamping plate 211. The clamping plate 211 passes through the slot 221-1 and constrains the relative displacement inside the steel pipe body 221 by the disassembly locking key 222, so that the clamping plate 211 of the recyclable prestressed rod 21 can be locked inside the anchoring steel pipe 22.

[0053] In a further optional implementation of Example 1 of the present invention, referring to Figures 4 and 6, the slot 221-1 extends parallel to the length direction of the steel pipe body 221, the length of the connectable plate is less than the length of the slot 221-1, and the disassembly locking key 222 is fixed on the inner wall of the steel pipe body 221 and extends perpendicular to its length direction. The two disassembly locking keys 222 are arranged at intervals along the length direction of the slot 221-1 and staggered in the width direction. At the same time, the two disassembly locking keys 222 partially overlap with the horizontally placed clamping plate 211.

[0054] In a further optional implementation of Example 1 of the present invention, referring to Figures 4-6, the steel pipe body 221 also includes a plurality of stiffening plates 223 arranged inside the steel pipe body 221. The stiffening plates 223 are fixedly connected to the inner wall of the steel pipe body 221 provided with the slot 221-1, and are symmetrically distributed on both sides along the length direction of the slot 221-1.

[0055] In a further optional implementation of Example 1 of the present invention, the inclined support member 3 includes a plurality of inclined piles 31 evenly distributed along the length direction of the foundation pit, and the inclined piles 31 are prefabricated reinforced concrete structures or steel structures.

[0056] In a further optional implementation of Example 1 of the present invention, the inclined support members 3 and the enclosing structure are fixedly connected by a combination of embedded connectors and cast-in-situ concrete, or are fixed together by welding / bolt connection; the inclined support members 3 are connected to each other by abutment members 32.

[0057] It can be understood that the abutment member 32 described in the first embodiment can firmly connect the inclined pile 31 and the surrounding structure, ensuring reliable force transmission at the connection node.

[0058] It should be noted that, in a specific implementation, the abutment 32 described in the first embodiment may include a first clamping member and a second clamping member that are detachably fixedly connected to the inclined pile 31 and the surrounding purlin beam 13, respectively, and may also include a steel connection member that integrates the first clamping member and the second clamping member. More specifically, according to the shape of the inclined pile 31 and the surrounding purlin beam 13, the first clamping member may be set as an open ring type pipe clamp, and the second clamping member may be set as a square groove type clamp.

[0059] In a further optional implementation of Example 1 of the present invention, the tensioned beam structure 4 includes a chord rod 41, a steel web 42 and a chord rod axial force adjustment device 43, the rear end of the steel web 42 is hinged to the crown beam 12 or the surrounding purlin beam 13, the chord rod 41 axial force adjustment device 43 is fixedly connected to the front end of the steel web 42, the chord rod 41 is connected to the front end of the chord rod axial force adjustment device 43 and its two ends are respectively hinged to the crown beam 12 or the surrounding purlin beam 13 on both sides of the steel web 42.

[0060] More specifically, the rear end of the steel web 42 is hinged to the crown beam 12 or the surrounding purlin 13 through a first connecting plate 441 , and both ends of the chord rod 41 are hinged to the crown beam 12 or the surrounding purlin 13 located on both sides of the steel web 42 through second connecting plates 442 .

[0061] It should be noted that, in specific implementation, the steel web 42 described in the first embodiment may also include a central steel web 421 and two side steel webs 422 symmetrically arranged on the sides of the central steel web 421. More specifically, a chord tension rod axial force adjustment device 43 is provided at the end of the central steel web 411 to connect to the chord tension rod 41 and withstand the force transmitted by the tension rod. The specific structure of the central steel web 421 or the two side steel webs 422 may include a web body and ribs arranged on both sides of the web body. The ribs are used to connect to the crown beam 12 or the surrounding purlin beam 13, thereby ensuring the firmness of the fixation of the steel web 42, and thus optimizing the stress strength of the central steel web 421 or the two side steel webs 422.

[0062] The foundation pit support system in related technologies uses a retaining structure + internal support method to support the foundation pit. For large-area foundation pits, this will inevitably result in a large amount of temporary structural material waste, which will inevitably increase the project cost and will also block the excavation working surface to a certain extent, affecting the efficiency of the foundation pit excavation work.

[0063] In view of this, the first embodiment of the present invention aims to provide an assembled support system without internal supports in a large-area foundation pit, which can promote the significant technical effect of fundamentally solving the above-mentioned problems in a multi-dimensional collaborative manner, as follows:

[0064] In the first dimension, the prefabricated support system of embodiment 1 of the present invention can lengthen the spacing of the mechanical supports of the foundation pit retaining structure by installing the tensioned beam structure 4 on the purlin beam 13 and the crown beam 12 of the foundation pit retaining structure 1, while reducing the deformation of the retaining structure 11 when the span is large, thereby achieving the purpose of reducing the number of mechanical supports.

[0065] In the second dimension, the first embodiment of the present invention, building on the beneficial effects of the first dimension, eliminates the internal support structure typically installed inside the foundation pit as a mechanical support. Instead, the top of the inclined support member 3 is used to withstand horizontal forces near the ground, and transmits these forces to the bottom of the foundation pit via the inclined piles 31. This not only avoids the need for internal supports within the foundation pit, ensuring a relatively open excavation working surface, but also reduces deformation of the retaining structure 11, ensuring the safety of the foundation pit.

[0066] In the third dimension, the first embodiment of the present invention builds on the beneficial effects of the first dimension by utilizing the abutment members 32 to withstand the horizontal force transmitted from the perimeter purlin beam 13. The abutment members 32 then transmit the horizontal force to the corresponding position at the waist of the tilting pile 31, forming a stable force-bearing system in which the perimeter purlin beam 13, the abutment members 32, and the tilting pile 31 jointly withstand the horizontal force. This not only avoids the need for internal supports within the foundation pit, ensuring a relatively open excavation working surface, but also reduces deformation of the retaining structure 11, ensuring the safety of the foundation pit.

[0067] In the fourth dimension, the embodiment of the present invention can, on the basis of the beneficial effects in the above three dimensions, set recyclable prestressed tie rods 21 at specific positions of the foundation pit retaining structure 1, and combine with the anchoring steel pipe 22 to reduce the deformation of the foundation pit retaining structure 1 and further ensure the safety of the foundation pit.

[0068] Example 2:

[0069] In another embodiment 2 of the present invention, a construction method for an assembled support system without internal supports in a large-area foundation pit is provided, with reference to Figures 1-6, comprising the following steps:

[0070] (1) Preparatory work: the soil above the crown beam 12 is sloped, the slope surface is protected by sprayed concrete, and inclined piles 31, retaining structures 11, and anchoring steel pipes 22 are constructed, assembled, and reinforced;

[0071] (2) Start earth excavation construction;

[0072] (3) When the excavation reaches the preset elevation of the crown beam 12, the crown beam 12 is constructed on the retaining structure 11 of the foundation pit corresponding to the preset elevation, and the chord beam structure 4 is installed and pre-tensioned;

[0073] (4) When the excavation reaches the preset elevation of the purlin beam 13, the purlin beam 13 is constructed on the foundation pit retaining structure 1 corresponding to the preset elevation, and the abutment member 32 is installed between the corresponding purlin beam 13 and the inclined pile 31, and the string beam structure 4 is installed and prestressed again, and then the recyclable prestressed tie rod 21 is directional driven toward the anchor steel pipe 22. After the two are firmly connected, prestress is applied and the anchor head is locked to the purlin beam 13;

[0074] (5) Continue excavation until the design elevation of the foundation pit bottom is reached, which means that the earthwork excavation and support operations are completed;

[0075] (6) After the construction of the underground part is completed, the following parts are dismantled and recycled: the prestressed tie rods 21, the beam string structure 4, the purlin beams 13, the crown beams 12, the inclined supports 3, the enclosure structure 11, and the anchoring steel pipes 22.

[0076] The second embodiment of the present invention is a construction method for a prefabricated support system without internal supports in a large-scale foundation pit. The technical contribution and results made in addressing the shortcomings of the existing technology are directly reflected in the beneficial effects of the prefabricated support system used. On the other hand, it is also reflected as follows: the components used in this construction method, such as the purlin beam 13, the tensioned beam string structure 4, the detachable prestressed anchor rod 21, the inclined pile 31, the enclosure structure 11, etc., are assembled and constructed using a factory prefabrication and on-site assembly model. This assembly construction method can ensure project quality while reducing construction waste. In addition, this method integrates the construction process of the prefabricated support system with the foundation pit excavation process and optimizes the design process of the prestressed beam string structure 4.

[0077] It can be understood that the "reinforcement" method of step (1) described in the second embodiment can be grouting reinforcement to ensure the reliability of the bearing performance. Specifically, the inclined support member 3 needs to withstand the transmitted force, which is completed using grouting holes. Specifically, the inclined pile 31 can use various types of piles such as prestressed concrete pipe piles, steel pipe piles, and steel piles. Grouting pipes and reserved grouting holes should be set for them during the material preparation stage. The meaning of grouting here: post-grouting refers to injecting slurry into the surrounding rock and soil through the grouting holes reserved in the pile body. Its function is to inject cement slurry and penetrate into the rock and soil to harden, thereby increasing the friction between the pile surface and the rock and soil, and thus improving the bearing capacity of the pile.

[0078] It should be noted that, in the specific implementation, the prerequisite of step (1) may also include: first leveling the construction site, positioning and laying out the foundation pit and retaining structure, and installing the machinery on site; and then implementing step (1) at the determined retaining structure positioning point.

[0079] It can be understood that step (4) described in the second embodiment is used to ensure that the horizontal force of the retaining structure 11 can be continuously transmitted to the inclined piles 31 and then to the passive zone soil.

[0080] In a further optional implementation of the second embodiment of the present invention, in step (3) and step (4), the chord beam structure 4 is installed and pre-tensioned, specifically including: setting up and installing the chord rod 41, the steel web 42, and the chord rod axial force adjustment device 43, and pre-tightening the chord rod 41 according to the design tension; wherein the design tension of the chord rod 41 is determined according to the following formula:

[0081] Where F is the tension of the chord rod (in N), L is the effective length of the steel web (in m), q is the support reaction of the foundation pit retaining structure at the corresponding position (in N / m), β1 and β2 are the angles between the web and the left and right chord rods, respectively, and k is the safety factor.

[0082] In a further optional implementation of the second embodiment of the present invention, the cross-sectional model of the chord rod 41 is determined according to the following formula:

[0083] Where A1 is the cross-sectional area of ​​the chord rod (in m2), L is the effective length of the steel web member 42 (in m), q is the support reaction force of the foundation pit retaining structure at the corresponding position (in N / m), β1 and β2 are the angles between the web member and the left and right chord rods, respectively, and f is the maximum effective length of the steel web member 42 (in m). Q1 is the yield strength of the material used (in Pa), and k is the safety factor.

[0084] In a further optional implementation of the second embodiment of the present invention, the cross-sectional model of the steel web member 42 can be determined according to the following formula:

[0085] Where A2 is the cross-sectional area of ​​the vertical steel web (in m2), L is the effective length of the steel web 42 (in m), q is the support reaction force of the foundation pit retaining structure at the corresponding position (in N / m), and f Q2 is the yield strength of the material used (unit: Pa), and k is the safety factor.

[0086] The construction method of the prefabricated support system of the first embodiment of the present invention and the prefabricated support system of the second embodiment of the present invention both utilize the foundation pit enclosure structure 1, the inclined support member 3, the prefabricated prestressed anchor member 2, and the prestressed string beam structure member 4 to form a support system without internal support in the foundation pit, thereby avoiding the use of a large number of internal support rods in the foundation pit, saving the materials used for the foundation pit support, and ensuring that the foundation pit has a sufficient excavation surface. At the same time, the deformation of the foundation pit can be effectively controlled. In addition, the construction method of the prefabricated support system of the second embodiment of the present invention can also reduce construction costs, and the support structure in the foundation pit can be recycled after the construction is completed, further reducing the consumption of engineering materials.

[0087] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modifications and equivalent changes made to the above embodiment based on the technical essence of the present invention fall within the scope of protection of the present invention.

Claims

1. An assembled support system without internal bracing in a large - area foundation pit, characterized in that, Comprising: A foundation pit retaining structure member, with a capping beam and a waling beam respectively provided at the top and waist of the foundation pit retaining structure member, and an assembled prestressed anchor is provided on the outer side of the foundation pit; An inclined support member, which is arranged on the inner side of the foundation pit of the retaining structure, and the inclined support member is arranged at an angle with the retaining structure and connected at the top; The inclined support member and the assembled prestressed anchor are arranged opposite to each other, and a beam string structure member is respectively provided on the capping beam and the waling beam at the position between adjacent inclined support members.

2. The assembled support system without internal bracing in a large - area foundation pit according to claim 1, characterized in that, The foundation pit retaining structure member includes a retaining structure in the form of a retaining wall or a retaining pile. One capping beam and several waling beams are fixedly connected to the retaining structure in sequence from top to bottom; the retaining wall adopts an assembled diaphragm wall, and the retaining pile adopts a steel sheet pile or a precast concrete pile.

3. The assembled support system without internal bracing in a large - area foundation pit according to claim 2, characterized in that, The assembled prestressed anchor includes a plurality of recoverable prestressed tie rods evenly arranged simultaneously in the length direction and the depth direction of the foundation pit. One end of the detachable prestressed anchor rod is fixed in the rock and soil body through an anchoring steel pipe, and the other end is locked on the waling beam through an anchor head.

4. The assembled support system without internal bracing in a large - area foundation pit according to claim 3, characterized in that, The anchoring steel pipe includes a steel pipe main body and a slotted opening and a disassembly locking key arranged on the steel pipe main body. A clamping plate is rotatably arranged at the end of the recoverable prestressed tie rod. The clamping plate passes through the slotted opening and is restricted from relative displacement inside the steel pipe main body through the disassembly locking key.

5. The assembled support system without internal bracing in a large - area foundation pit according to claim 4, characterized in that, The slotted opening extends parallel to the length direction of the steel pipe main body. The length of the connectable plate is less than the length of the slotted opening. The disassembly locking key is fixed on the inner wall of the steel pipe main body and extends perpendicular to its length direction. The two disassembly locking keys are arranged at intervals along the length direction of the slotted opening and are staggered in the width direction. At the same time, both of the two disassembly locking keys partially overlap with the horizontally placed clamping plate.

6. The assembled support system without internal bracing in a large - area foundation pit according to claim 5, characterized in that, The steel pipe main body further includes a plurality of stiffening plates arranged inside the steel pipe main body. The stiffening plates are fixedly connected to the inner wall of the steel pipe main body provided with the slotted opening and are symmetrically distributed on both sides along the length direction of the slotted opening.

7. The assembled support system without internal bracing in a large - area foundation pit according to any one of claims 3 to 6, characterized in that, The inclined support member includes a plurality of inclined piles evenly arranged along the length direction of the foundation pit. The inclined piles adopt a precast reinforced concrete structure or a steel structure.

8. The assembled support system without internal bracing in a large - area foundation pit according to claim 7, characterized in that, The inclined support member and the retaining structure are fixedly connected by a combination method of embedded connecting pieces + cast-in-place concrete, or are fixed together by welding / bolt connection methods; the inclined support members are connected to each other through abutting members.

9. The assembled support system without internal bracing in a large - area foundation pit according to claim 8, characterized in that, The beam string structure member includes a chord tie rod, a profiled steel web member and a chord tie rod axial force adjusting device. The rear end of the profiled steel web member is hinged on the capping beam or the waling beam. The chord tie rod axial force adjusting device is fixedly connected to the front end of the profiled steel web member. The chord tie rod is connected to the front end of the chord tie rod axial force adjusting device, and both ends of the chord tie rod are respectively hinged on the capping beam or the waling beam located on both sides of the profiled steel web member.

10. A construction method of an assembled support system without internal bracing in a large - area foundation pit based on any one of claims 1 to 9, characterized in that, Including the following steps: (1) Carry out preparatory work: Slope the soil above the capping beam, spray concrete on the slope surface for protection, respectively construct inclined piles, retaining structures, and anchoring steel pipes, and assemble and reinforce them; (2) Start the earth excavation construction; (3) When excavating to the preset elevation position of the capping beam, construct the capping beam on the foundation pit retaining structure corresponding to the preset elevation position, and install and pre-tension the cable-beam structure member; (4) When excavating to the preset elevation position of the collar beam, construct the collar beam on the retaining structure corresponding to the preset elevation position, install a contact member between the corresponding collar beam and the inclined pile, install and pre-tension the cable-beam structure member again, then drive the recoverable prestressed tie rod in the direction of the anchor steel pipe, apply prestress after they are firmly connected and lock the anchor head to the collar beam; (5) Continue the excavation until the designed elevation of the bottom of the foundation pit is reached, that is, complete the earth excavation and support operations; (6) After the construction of the underground part is completed, successively remove and recycle: the recoverable prestressed tie rod, the cable-beam structure member, the collar beam, the capping beam, the inclined support member, the foundation pit retaining structure member, the anchor steel pipe.

11. The construction method of an assembled support system without internal bracing in a large - area foundation pit according to claim 10, characterized in that, In the steps (3) and (4), the chord beam structure member is installed and pre-tensioned, specifically including: erecting and installing the chord tie rod, the profiled steel web member, and the chord tie rod axial force adjusting device, and pre-tightening the chord tie rod according to the designed tension; wherein, the designed tension of the chord tie rod is determined according to the following formula: Wherein, F is the tension of the chord tie rod (unit: N), L is the effective action length of the steel web member (unit: m), q is the reaction force of the foundation pit retaining structure at the corresponding position (unit: N / m), β1 and β2 are the angles between the web member and the chord tie rods on the left and right sides respectively, and k is the safety factor. ​ 12. A construction method of an assembled support system without internal bracing in a large-area foundation pit according to claim 11, characterized in that The cross-section model of the chord tie rod is determined according to the following formula: In the formula, A1 is the cross-sectional area of the chord tie rod (unit: ㎡), L is the effective action length of the steel web member (unit: m), q is the reaction force of the foundation pit retaining structure at the corresponding position (unit: N / m), β1 and β2 are the angles between the web member and the chord tie rods on the left and right sides respectively, and f Q1 is the yield strength of the material used (unit: Pa), and k is the safety factor.

13. A construction method of an assembled support system without internal bracing in a large-area foundation pit according to claim 12, characterized in that The section model of the profiled steel web member is determined according to the following formula: Wherein, A2 is the cross-sectional area of the vertical steel web member (unit: ㎡), L is the effective action length of the steel web member (unit: m), q is the reaction force of the foundation pit retaining structure at the corresponding position (unit: N / m), f Q2 is the yield strength of the material used (unit: Pa), and k is the safety factor.

Images