A foundation pit support structure and construction method thereof

Abstract

The present invention discloses a foundation pit support structure and a construction method thereof, which belongs to the technical field of construction engineering support, and includes retaining piles, a cable-stayed system, an anchor pile, a support rod, a waist beam, a bidirectional oil cylinder, a steel wire rope, a crown beam, a slider, and a limit beam; the cable-stayed system includes an inclined composite pile and an anchor rod, and the specific construction steps of the technical scheme are: construction preparation, construction of retaining piles, construction of a cable-stayed system, construction of a crown beam, construction of anchor piles, foundation pit excavation, trench excavation, construction of a slider, a waist beam, a limit beam and a support rod, continued excavation and dynamic adjustment of the support structure, and construction completion. The present invention realizes dynamic adjustment of the support strength as the foundation pit is gradually excavated, so that the force of the retaining piles is more reasonable, and the support depth is deepened, and most structures can be recycled and reused, thereby saving costs.

Description

Technical Field

[0001] The invention relates to the technical field of building engineering support, and in particular to a foundation pit support structure and a construction method thereof. Background Art

[0002] For foundation pit projects within the excavation depth of 5m in soft soil areas, the retaining structure forms used in the current existing support technologies generally adopt cement-soil gravity retaining walls, steel-cement-soil mixing walls, slope excavation, inclined support and other technologies.

[0003] The characteristic of cement-soil gravity retaining wall is that the retaining structure is composed of multiple rows of continuously overlapped "grid-shaped" cement-soil piles in vertical and horizontal directions. Generally, there is no support in the pit, which is convenient for rapid excavation. It has the dual functions of retaining soil and stopping water. However, the displacement control ability is weak, the construction quality is difficult to control, and the economy is average.

[0004] The steel-cement soil mixing wall is a composite retaining and water-proof structure formed by inserting steel into the continuously overlapped triaxial cement soil piles. It has the advantages of being applicable to a wide range of soil types, having little impact on the surrounding environment, having good anti-seepage performance, and being applicable to a wide range of soil layers. However, for foundation pits within 5m, the cost per meter is high, the construction requirements are high, and the quality of cement soil piles is difficult to control.

[0005] Slope excavation is a foundation pit excavation method that uses an inclined soil slope. It has the advantages of shorter construction period and low cost. The disadvantage is that the slope ratio requirement is large, and both the slope stability requirements and the upper width requirements must be met at the same time, and it has a greater impact on the surrounding environment.

[0006] The inclined cast-beam support is to set up a central island at the bottom of the foundation pit, and use steel pipes, steel sections and other rods to connect the cap beam and the central island. During the excavation process, the soil under the rod is temporarily not excavated. It has the characteristics of low cost and little impact on the surrounding environment. However, the reserved soil affects the construction, and the central island affects the pouring of the bottom plate.

[0007] To sum up, the support method of shallow foundation pit is still not perfect enough, and most buildings currently build two-story basements, which basically exceeds the scope of shallow foundation. The above scheme is no longer applicable. However, the support method commonly used in deep foundation pits is not only expensive, but also has a great impact on the surrounding environment. Therefore, on this basis, the present invention proposes a inclined pile support system for foundation pits to solve the above problems. Summary of the invention

[0008] In view of the above technical problems existing in the prior art, the present invention proposes a foundation pit support structure and a construction method thereof, which overcomes the shortcomings of the prior art. By respectively setting anchor piles and a diagonal system inside and outside the foundation pit, the entire support system is made more stable, and a slider and a two-way oil cylinder are provided, so that the support strength can be dynamically adjusted as the foundation pit is gradually excavated, and the inner support rod of the foundation pit is supported in the middle part of the retaining pile, which reduces the length of the diagonal support rod, that is, increases the stability of the diagonal support rod. In addition, through the support of the diagonal support rod, the deflection of the retaining pile is significantly reduced, making the force of the retaining pile more reasonable. The foundation pit retaining structure of the present invention can deepen the support depth, and most structures can be recycled and reused, saving costs.

[0009] In order to achieve the above object, the present invention adopts the following technical solution:

[0010] A foundation pit support structure, characterized in that it includes retaining piles, a cable-stayed system, anchor piles, support rods, waist beams, bidirectional oil cylinders, steel wire ropes, crown beams, sliders, and limit beams; the cable-stayed system includes inclined composite piles and anchor rods, a crown beam is cast on the top of the retaining piles, a cable-stayed system is constructed in the soil outside the foundation pit, the ends of the anchor rods in the cable-stayed system are connected to the steel bars in the crown beam, the sliders are stuck on the surface of the retaining piles, and the sliders move on the surface of the retaining piles, and a waist beam is arranged on the side of the retaining piles close to the foundation pit The waist beam connects the sliders on the surfaces of adjacent retaining piles, the sliders are connected to the waist beam by welding, a two-way oil cylinder is connected to the waist beam by bolts, the limit beam is anchored on the side of the retaining pile close to the foundation pit, and is located on the upper part of the waist beam, anchor piles are constructed in the soil inside the foundation pit, the support rods are connected to the waist beam and the anchor piles by hinges, one end of the steel wire rope is anchored at the end of the retaining pile, and the other end is connected to the two-way oil cylinder, an axial force sensor is installed on the support rod, and tension and compression sensors are installed on the steel wire rope and the anchor rod.

[0011] Preferably, the composite piles in the cable-stayed system are a composite of cement soil piles and prestressed concrete piles, basalt fibers are added to the cement soil piles, the prestressed concrete piles are any one of pipe piles, hollow square piles, and bamboo piles, the upper and lower ends of the prestressed concrete piles are blocked with steel plates, anchor holes are reserved on the steel plates, the cavity of the prestressed concrete piles is filled with one of concrete, mortar, and cement slurry, the anchor rod is anchored in the prestressed concrete cavity, the anchoring length of the anchor rod is 2 / 3 to 3 / 4 of the length of the prestressed concrete pile, and the portion outside the anchoring section of the anchor rod is wrapped with an isolation layer, which is any one of waterproof tape, butter, PVC pipe, and soft rubber pipe.

[0012] Preferably, the retaining piles are prefabricated concrete components, and the retaining piles are any one of pipe piles and hollow square piles.

[0013] Preferably, the anchor pile is a composite pile, the outer core of the composite pile is a cement soil pile, and the inner core is a prestressed concrete pile, and the prestressed concrete pile is any one of a pipe pile, a hollow square pile, and a bamboo pile; a pulley or an arc-shaped steel plate is arranged at the cross-section of the end of the retaining pile, and the steel wire rope passes around the pulley or the arc-shaped steel plate at the anchoring position and is connected to the two-way oil cylinder.

[0014] Preferably, the support rod is one or a combination of double I-beams, H-beams, steel pipes, and reinforced concrete.

[0015] Preferably, the slider is a semi-circular tube type or a channel steel type, and the selection of the slider corresponds to the selection of the retaining pile. If the retaining pile is a pipe pile, the slider is a semi-circular tube type; if the retaining pile is a hollow square pile, the slider is a channel steel type.

[0016] A construction method of a foundation pit support structure, characterized in that a foundation pit support structure is used for construction, and the specific construction steps are as follows:

[0017] Step 1: Construction preparation

[0018] Before construction, prepare two circular iron plates with the same diameter as the prestressed concrete piles in the cable-stayed system, weld one end of the anchor rod to the center of the circular iron plate, and set an isolation layer on the part outside the anchoring section of the anchor rod. Insert the end of the anchor rod that is not welded with the circular iron plate and pass through the cavity of the prestressed concrete pile to ensure that the central axis of the anchor rod coincides with the central axis of the prestressed concrete pile. The lower end of the prestressed concrete pile is sealed with a circular iron plate welded with an anchor rod, and grouting is performed with one of concrete, mortar, and cement slurry. After the filling material in the cavity is initially solidified, grouting is performed, and then the upper end of the prestressed concrete pile is sealed with a circular iron plate; anchor the steel wire rope at the end of the retaining pile, and install the axial force sensor and the tension and compression sensor on the corresponding components respectively;

[0019] Step 2: Construction of retaining piles

[0020] Use static pressure or hammering method to implant the retaining piles into the designed position, ensure that the wire rope is on one side of the foundation pit, put the steel cage into the retaining piles, and pour concrete, leaving room for structural reinforcement connected to the crown beam;

[0021] Step 3: Construction of the cable-stayed system

[0022] A drilling rig is used to construct a cement soil pile, and during the construction of the cement soil pile, basalt fiber is evenly mixed, and the prestressed concrete pile and anchor rod combination prepared in step 1 is implanted into the cement soil pile;

[0023] Step 4: Construction of crown beam

[0024] Connect the top of the anchor rod to the structural reinforcement of the retaining pile, fix the crown beam template, tie the reinforcement, and pour concrete in the template to form the crown beam;

[0025] Step 5: Construction of anchor piles

[0026] A pile driver is used to form a cement soil pile at the designed position, and a static pressure pile driver is used to implant the prestressed concrete pile into the cement soil pile;

[0027] Step 6: Excavation of foundation pit

[0028] When the anchor rods, anchor piles and cap beams reach the designed strength, start pre-tensioning the anchor rods. The pre-tensioning force is 20%-60% of the designed tension of the anchor rods. Then, start excavation. The tension of the anchor rods is monitored by the tension and compression sensors on the anchor rods. When the monitoring value of the tension and compression sensors reaches 70% of the designed value of the anchor rod tension, stop excavation.

[0029] Step 7: Digging the trench

[0030] A triangular trench is formed by using slotting equipment. The deepest part of the trench reaches the designed bottom of the foundation pit. The depth of the trench gradually decreases from the anchor pile to the retaining pile. The part of the anchor pile above the bottom of the trench is broken and the prestressed concrete pile is recovered. The anchor pile is exposed 0.3~0.5m from the bottom of the trench.

[0031] Step 8: Construction of sliders, waist beams, limit beams and support rods

[0032] Select a slider according to the retaining pile, weld the slider to the waist beam, install a two-way oil cylinder on the crown beam, and connect the two-way oil cylinder with a steel wire rope; anchor a limited beam on the side of the retaining pile close to the foundation pit, and the limited beam is located on the upper part of the slider; install hinged supports on the waist beam and the prestressed concrete piles in the anchor pile, respectively, connect the support rod to the two hinged supports, clamp the slider on the retaining pile, and use a two-way oil cylinder to tension the steel wire rope, so that the retaining pile, slider, waist beam, support rod, and anchor pile form a whole;

[0033] Step 9: Continue excavation and dynamically adjust the support structure

[0034] As excavation continues to the bottom of the foundation pit, the soil pressure on the retaining piles will gradually increase. The steel wire rope is tensioned by a bidirectional oil cylinder. During the tensioning process, the tension sensor on the steel wire rope is monitored to ensure that the monitoring value of the tension sensor is less than the ultimate bearing capacity of the steel wire rope. The method for dynamically adjusting the support structure is as follows:

[0035] (1) After the support rod is installed, the wire rope is tensioned by the bidirectional oil cylinder, which drives the slider to move, thereby increasing the axial force of the support rod. When the monitoring value of the support rod axial force sensor reaches 60% of the support rod, the bidirectional oil cylinder is locked to keep the slider in place;

[0036] (2) When the monitoring value of the tension and compression sensor on the anchor rod reaches 80% of the design value of the anchor rod tension, the bidirectional oil cylinder is started. When the monitoring value of the axial force sensor reaches 80% of the support rod, the bidirectional oil cylinder is locked to keep the position of the slider stationary.

[0037] (3) When the monitoring value of the tension and compression sensor on the anchor rod reaches 90% of the design value of the anchor rod tension, the bidirectional cylinder is started. When the monitoring value of the axial force sensor reaches 95% of the support rod, the bidirectional cylinder is locked to keep the position of the slider stationary.

[0038] Step 10: Construction completed

[0039] With the dynamic adjustment of the support structure, the foundation pit is gradually excavated to the designed depth.

[0040] Preferably, the cable-stayed system in step three is constructed at an angle, the angle between the center axis of the anchor rod and the vertical direction is in the range of 65° to 80°, and the distance between the center axes of adjacent anchor rods is 1 to 5 times the distance between the center axes of adjacent retaining piles.

[0041] Preferably, in step eight, the waist beam is a segmented structure, the length of each waist beam is 1 to 5 times the distance between the center axes of adjacent retaining piles, and the ratio of the length of each waist beam to the distance between the center axes of adjacent retaining piles is equal to the number of sliding blocks on the waist beam.

[0042] Preferably, the limiting beam in step eight is a segmented structure, and the length of each segment of the limiting beam is 3 to 7 times the distance between the center axes of adjacent retaining piles.

[0043] Beneficial technical effects brought by the present invention:

[0044] By arranging anchor piles and inclined-stayed systems inside and outside the foundation pit respectively, the entire support system is made more stable, and a sliding block and a two-way oil cylinder are provided, so that the support strength can be dynamically adjusted as the foundation pit is gradually excavated, and the inner support rods of the foundation pit are supported in the middle part of the retaining piles, which reduces the length of the inclined support rods, that is, increases the stability of the inclined support rods. In addition, through the support of the inclined support rods, the deflection of the retaining piles is significantly reduced, so that the force on the retaining piles is more reasonable. The foundation pit retaining structure of the present invention can deepen the support depth, and most structures can be recycled and reused, saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The present invention is a schematic structural diagram of a foundation pit support structure and a construction method thereof.

[0046] Figure 2 The present invention is a structural top view of a foundation pit support structure and a construction method thereof.

[0047] Figure 3It is a structural cross-sectional view after trench excavation in a foundation pit support structure and a construction method thereof of the present invention.

[0048] Figure 4 It is a structural cross-sectional view of a foundation pit support structure and a construction method thereof after excavation to the bottom of the foundation pit in the present invention.

[0049] Figure 5 The present invention is a schematic structural diagram of a sliding block and a waist beam in a foundation pit supporting structure and a construction method thereof.

[0050] Among them, 1- guard piles, 2- anchor rods, 3- anchor piles, 4- support rods, 5- waist beams, 6- two-way cylinders, 7- wire ropes, 8- crown beams, 9- slide blocks, and 10- limiting beams. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0052] Embodiment 1:

[0053] like Figures 1 to 5 As shown, a foundation pit support structure is characterized in that it includes a retaining pile 1, a cable-stayed system, an anchor pile 3, a support rod 4, a waist beam 5, a two-way oil cylinder 6, a steel wire rope 7, a crown beam 8, a slider 9, and a limit beam 10; the cable-stayed system includes an inclined composite pile and an anchor rod 2, a crown beam 8 is cast on the top of the retaining pile 1, a cable-stayed system is constructed in the soil outside the foundation pit, the end of the anchor rod 2 in the cable-stayed system is connected to the steel bar in the crown beam 8, the slider 9 is stuck on the surface of the retaining pile 1, and the slider 9 moves on the surface of the retaining pile 1, and a waist beam is arranged on the side of the retaining pile 1 near the foundation pit Beam 5, waist beam 5 connects sliders 9 on the surface of adjacent retaining piles 1, sliders 9 and waist beam 5 are connected by welding, bidirectional oil cylinder 6 is connected to waist beam 5 by bolts, the limit beam 10 is anchored on the side of retaining pile 1 close to foundation pit, and is located on the upper part of waist beam 5, anchor piles 3 are constructed in the soil inside the foundation pit, support rods 4 are connected to waist beam 5 and anchor piles 3 by hinges, one end of steel wire rope 7 is anchored at the end of retaining pile 1, and the other end is connected to bidirectional oil cylinder 6, an axial force sensor is installed on support rod 4, and tension and compression sensors are installed on steel wire rope 7 and anchor rod 2.

[0054] Preferably, the composite piles in the cable-stayed system are a composite of cement soil piles and prestressed concrete piles, basalt fibers are added to the cement soil piles, the prestressed concrete piles are any one of pipe piles, hollow square piles, and bamboo piles, the upper and lower ends of the prestressed concrete piles are sealed with steel plates, two anchor holes are reserved on the steel plates, the cavity of the prestressed concrete piles is filled with one of concrete, mortar, and cement slurry, the anchor rod 2 is anchored in the prestressed concrete cavity, the anchoring length of the anchor rod 2 is 2 / 3 to 3 / 4 of the length of the prestressed concrete pile, and the portion outside the anchoring section of the anchor rod 2 is wrapped with an isolation layer, and the isolation layer is any one of waterproof tape, butter, PVC pipe, and soft rubber pipe.

[0055] Preferably, the retaining pile 1 is a prefabricated concrete component, and the retaining pile 1 is any one of a pipe pile and a hollow square pile.

[0056] Preferably, the anchor pile 3 is a composite pile, the outer core of the composite pile is a cement soil pile, and the inner core is a prestressed concrete pile, and the prestressed concrete pile is any one of a pipe pile, a hollow square pile, and a bamboo pile; a pulley or an arc-shaped steel plate is arranged at the cross-section of the end of the retaining pile 1, and the steel wire rope 7 passes around the pulley or the arc-shaped steel plate at the anchoring position and is connected to the two-way oil cylinder 6.

[0057] Preferably, the support rod 4 is one or a combination of double I-beams, H-beams, steel pipes, and reinforced concrete.

[0058] Preferably, the slider 9 is a semi-circular tube type or a channel steel type, and the selection of the slider 9 corresponds to the selection of the retaining pile 1. If the retaining pile 1 is a pipe pile, the slider 9 is a semi-circular tube type; if the retaining pile 1 is a hollow square pile, the slider 9 is a channel steel type.

[0059] Embodiment 2:

[0060] like Figures 1 to 5 As shown, the following construction is carried out using a foundation pit support structure and a construction method thereof described in the present invention:

[0061] Step 1: Construction preparation

[0062] Before construction, prepare two circular iron plates with the same diameter as the prestressed concrete piles in the cable-stayed system, weld one end of the anchor rod 2 to the center of the circular iron plate, and set an isolation layer on the part outside the anchoring section of the anchor rod 2. Insert the end of the anchor rod 2 that is not welded with the circular iron plate and pass it through the cavity of the prestressed concrete pile to ensure that the central axis of the anchor rod 2 coincides with the central axis of the prestressed concrete pile. The lower end of the prestressed concrete pile is sealed with a circular iron plate welded with the anchor rod 2, and grouting is performed with one of concrete, mortar, and cement slurry. After the filling material in the cavity is initially solidified, grouting is performed, and then the upper end of the prestressed concrete pile is sealed with a circular iron plate; anchor the steel wire rope 7 to the pile end of the retaining pile 1, and install the axial force sensor and the tension and compression sensor on the corresponding components respectively;

[0063] Step 2: Construction retaining pile 1

[0064] Use static pressure or hammering to implant the retaining pile 1 into the designed position, ensure that the steel wire rope 7 is on one side of the foundation pit, put a steel cage into the retaining pile 1, and pour concrete, leaving room for structural reinforcement connected to the crown beam 8;

[0065] Step 3: Construction of the cable-stayed system

[0066] A drilling rig is used to construct a cement soil pile, and basalt fiber is evenly mixed into the cement soil pile during the construction, and the prestressed concrete pile and anchor rod 2 combination prepared in step 1 is implanted into the cement soil pile;

[0067] Step 4: Construction of crown beam 8

[0068] Connect the top of the anchor rod 2 to the structural reinforcement of the retaining pile 1, fix the template of the crown beam 8, tie the steel bars, and pour concrete in the template to form the crown beam 8;

[0069] Step 5: Construction of anchor piles 3

[0070] A pile driver is used to form a cement soil pile at the designed position, and a static pressure pile driver is used to implant the prestressed concrete pile into the cement soil pile;

[0071] Step 6: Excavation of foundation pit

[0072] When the anchor rod 2, the anchor pile 3 and the cap beam 8 reach the design strength, start pre-tensioning the anchor rod, the pre-tensioning force is 20%-60% of the design tension of the anchor rod, then start excavation, monitor the tension of the anchor rod 2 through the tension and compression sensor on the anchor rod 2, and stop excavation when the monitoring value of the tension and compression sensor reaches 70% of the design value of the tension of the anchor rod 2;

[0073] Step 7: Digging the trench

[0074] A triangular trench is formed by using a slotting device. The deepest part of the trench reaches the designed bottom surface of the foundation pit. The trench depth gradually decreases from the anchor pile 3 to the retaining pile 1. The part of the anchor pile 3 above the bottom of the trench is broken, and the prestressed concrete pile is recovered. The anchor pile 3 is exposed 0.3~0.5m from the bottom surface of the trench.

[0075] Step 8: Construction of slider 9, waist beam 5, limit beam 10 and support rod 4

[0076] According to the retaining pile 1, a slider 9 is selected, the slider 9 is welded to the waist beam 5, and a two-way oil cylinder 6 is installed on the crown beam 8, and the two-way oil cylinder 6 is connected to the wire rope 7; a limited position beam 10 is anchored on the side of the retaining pile 1 close to the foundation pit, and the limited position beam 10 is located on the upper part of the slider 9; hinged supports are respectively installed on the waist beam 5 and the prestressed concrete piles in the anchor pile 3, and the support rod 4 is connected to the two hinged supports, and the slider 9 is clamped on the retaining pile 1, and the two-way oil cylinder 6 is used to tension the wire rope 7, so that the retaining pile 1, the slider 9, the waist beam 5, the support rod 4, and the anchor pile 3 form a whole;

[0077] Step 9: Continue excavation and dynamically adjust the support structure

[0078] As excavation continues to the bottom of the foundation pit, the soil pressure on the retaining pile 1 will gradually increase. The steel wire rope 7 is tensioned by the bidirectional oil cylinder 6. During the tensioning process, the tension sensor on the steel wire rope 7 is monitored to ensure that the monitoring value of the tension sensor is less than the ultimate bearing capacity of the steel wire rope 7. The method for dynamically adjusting the support structure is as follows:

[0079] (1) After the support rod 4 is installed, the wire rope 7 is tensioned by the bidirectional oil cylinder 6, thereby driving the slider 9 to move, so that the axial force of the support rod 4 increases. When the monitoring value of the axial force sensor of the support rod 4 reaches 60% of the support rod 4, the bidirectional oil cylinder 6 is locked to keep the position of the slider 9 unchanged;

[0080] (2) When the monitoring value of the tension and compression sensor on the anchor rod 2 reaches 80% of the design value of the tension of the anchor rod 2, the bidirectional oil cylinder 6 is started. When the monitoring value of the axial force sensor reaches 80% of the support rod 4, the bidirectional oil cylinder 6 is locked to keep the position of the slider 9 unchanged.

[0081] (3) When the monitoring value of the tension and compression sensor on the anchor rod 2 reaches 90% of the design value of the tension of the anchor rod 2, the bidirectional oil cylinder 6 is started. When the monitoring value of the axial force sensor reaches 95% of the support rod 4, the bidirectional oil cylinder 6 is locked to keep the position of the slider 9 unchanged.

[0082] Step 10: Construction completed

[0083] With the dynamic adjustment of the support structure, the foundation pit is gradually excavated to the designed depth.

[0084] Preferably, the cable-stayed system in step three is constructed at an angle, the angle between the center axis of the anchor rod 2 and the vertical direction is in the range of 65° to 80°, and the distance between the center axes of adjacent anchor rods 2 is 1 to 5 times the distance between the center axes of adjacent retaining piles 1.

[0085] Preferably, in step eight, the waist beam 5 is a segmented structure, and the length of each waist beam 5 is 1 to 5 times the distance between the center axes of adjacent retaining piles 1, and the ratio of the length of each waist beam 5 to the distance between the center axes of adjacent retaining piles 1 is equal to the number of sliding blocks 9 on the waist beam 5.

[0086] Preferably, in step eight, the limiting beam 10 is a segmented structure, and the length of each segment of the limiting beam 10 is 3 to 7 times the distance between the center axes of adjacent retaining piles 1 .

[0087] The present invention relates to a foundation pit support structure and a construction method thereof. Anchor piles and a diagonal tension system are respectively arranged inside and outside the foundation pit, so that the entire support system is more stable. A sliding block and a bidirectional oil cylinder are provided, so that the support strength can be dynamically adjusted as the foundation pit is gradually excavated. The inner support rods of the foundation pit are supported at the middle part of the retaining piles, which reduces the length of the diagonal support rods, that is, increases the stability of the diagonal support rods. In addition, the deflection of the retaining piles is significantly reduced through the support of the diagonal support rods, so that the force on the retaining piles is more reasonable. The foundation pit retaining structure of the present invention can deepen the support depth, and most structures can be recycled and reused, saving costs.

[0088] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention also fall within the protection scope of the present invention.

Claims

1. A foundation pit support structure, characterized in that: It includes retaining piles, a cable-stayed system, anchor piles, support rods, waist beams, two-way oil cylinders, wire ropes, crown beams, sliders and limit beams; the cable-stayed system includes inclined composite piles and anchor rods, a crown beam is cast on the top of the retaining piles, a cable-stayed system is constructed in the soil outside the foundation pit, the end of the anchor rod in the cable-stayed system is connected to the steel bar in the crown beam, the slider is stuck in the surface of the retaining pile, and the slider can move on the surface of the retaining pile, a waist beam is arranged on the side of the retaining pile close to the foundation pit, the waist beam connects the sliders on the surfaces of adjacent retaining piles, the slider and the waist beam are connected by welding, a two-way oil cylinder is connected to the waist beam by bolts, the limit beam is anchored on the side of the retaining pile close to the foundation pit and is located on the upper part of the waist beam, an anchor pile is constructed in the soil inside the foundation pit, the support rods are connected to the waist beam and the anchor piles by hinges, one end of the wire rope is anchored at the end of the retaining pile, and the other end is connected to the two-way oil cylinder, an axial force sensor is installed on the support rod, and tension and compression sensors are installed on the wire rope and the anchor rod.

2. A foundation pit support structure according to claim 1, characterized in that: The composite piles in the cable-stayed system are a composite of cement soil piles and prestressed concrete piles, wherein basalt fibers are mixed into the cement soil piles, and the prestressed concrete piles are any one of pipe piles, hollow square piles, and bamboo piles. The upper and lower ends of the prestressed concrete piles are blocked with steel plates, and anchor holes are reserved on the steel plates. The cavity of the prestressed concrete piles is filled with one of concrete, mortar, and cement slurry. The anchor rods are anchored in the prestressed concrete cavity, and the anchoring length of the anchor rods is 2 / 3 to 3 / 4 of the length of the prestressed concrete piles. The portion outside the anchoring section of the anchor rod is wrapped with an isolation layer, and the isolation layer is any one of waterproof tape, butter, PVC pipe, and soft rubber pipe.

3. A foundation pit support structure according to claim 1, characterized in that: The retaining piles are prefabricated concrete components, and are any one of pipe piles and hollow square piles; a pulley or an arc-shaped steel plate is arranged at the cross section of the end of the retaining pile, and the steel wire rope passes around the pulley or the arc-shaped steel plate from the anchoring position and is connected to the bidirectional oil cylinder.

4. A foundation pit support structure according to claim 1, characterized in that: The anchor pile is a composite pile, the outer core of the composite pile is a cement soil pile, and the inner core is a prestressed concrete pile. The prestressed concrete pile is any one of a pipe pile, a hollow square pile, and a bamboo pile.

5. The foundation pit support structure according to claim 1, characterized in that: The support rod is one or a combination of double I-beams, H-beams, steel pipes, and reinforced concrete.

6. A foundation pit support structure according to claim 1, characterized in that: The slider is a semi-circular tube type or a channel steel type. The selection of the slider corresponds to the selection of the retaining pile. If the retaining pile is a pipe pile, the slider is a semi-circular tube type. If the retaining pile is a hollow square pile, the slider is a channel steel type.

7. A construction method for a foundation pit support structure, characterized in that: The foundation pit support structure described in claim 1 is used for construction, and the specific construction steps are as follows: Step 1: Construction preparation Before construction, prepare two circular iron plates with the same diameter as the prestressed concrete piles in the cable-stayed system, weld one end of the anchor rod to the center of the circular iron plate, and set an isolation layer on the part outside the anchoring section of the anchor rod. Insert the end of the anchor rod that is not welded with the circular iron plate and pass through the cavity of the prestressed concrete pile to ensure that the central axis of the anchor rod coincides with the central axis of the prestressed concrete pile. The lower end of the prestressed concrete pile is sealed with a circular iron plate welded with an anchor rod, and grouting is performed with one of concrete, mortar, and cement slurry. After the filling material in the cavity is initially solidified, grouting is performed, and then the upper end of the prestressed concrete pile is sealed with a circular iron plate; anchor the steel wire rope at the end of the retaining pile, and install the axial force sensor and the tension and compression sensor on the corresponding components respectively; Step 2: Construction of retaining piles Use static pressure or hammering method to implant the retaining piles into the designed position, ensure that the wire rope is on one side of the foundation pit, put the steel cage into the retaining piles, and pour concrete, leaving room for structural reinforcement connected to the crown beam; Step 3: Construction of the cable-stayed system A drilling rig is used to construct a cement soil pile, and during the construction of the cement soil pile, basalt fiber is evenly mixed, and the prestressed concrete pile and anchor rod combination prepared in step 1 is implanted into the cement soil pile; Step 4: Construction of crown beam Connect the top of the anchor rod to the structural reinforcement of the retaining pile, fix the crown beam template, tie the reinforcement, and pour concrete in the template to form the crown beam; Step 5: Construction of anchor piles A pile driver is used to form a cement soil pile at the designed position, and a static pressure pile driver is used to implant the prestressed concrete pile into the cement soil pile; Step 6: Excavation of foundation pit When the anchor rods, anchor piles and cap beams reach the designed strength, start pre-tensioning the anchor rods. The pre-tensioning force is 20%-60% of the designed tension of the anchor rods. Then, start excavation. The tension of the anchor rods is monitored by the tension and compression sensors on the anchor rods. When the monitoring value of the tension and compression sensors reaches 70% of the designed value of the anchor rod tension, stop excavation. Step 7: Digging the trench A triangular trench is formed by using slotting equipment. The deepest part of the trench reaches the designed bottom of the foundation pit. The depth of the trench gradually decreases from the anchor pile to the retaining pile. The part of the anchor pile above the bottom of the trench is broken and the prestressed concrete pile is recovered. The anchor pile is exposed 0.3~0.5m from the bottom of the trench. Step 8: Construction of sliders, waist beams, limit beams and support rods Select a slider according to the retaining pile, weld the slider to the waist beam, install a two-way oil cylinder on the crown beam, and connect the two-way oil cylinder with a steel wire rope; anchor a limited beam on the side of the retaining pile close to the foundation pit, and the limited beam is located on the upper part of the slider; install hinged supports on the waist beam and the prestressed concrete piles in the anchor pile, respectively, connect the support rod to the two hinged supports, clamp the slider on the retaining pile, and use a two-way oil cylinder to tension the steel wire rope, so that the retaining pile, slider, waist beam, support rod, and anchor pile form a whole; Step 9: Continue excavation and dynamically adjust the support structure As excavation continues to the bottom of the foundation pit, the soil pressure on the retaining piles will gradually increase. The steel wire rope is tensioned by a bidirectional oil cylinder. During the tensioning process, the tension sensor on the steel wire rope is monitored to ensure that the monitoring value of the tension sensor is less than the ultimate bearing capacity of the steel wire rope. The method for dynamically adjusting the support structure is as follows: (1) After the support rod is installed, the wire rope is tensioned by the bidirectional oil cylinder, which drives the slider to move, thereby increasing the axial force of the support rod. When the monitoring value of the support rod axial force sensor reaches 60% of the support rod, the bidirectional oil cylinder is locked to keep the slider in place; (2) When the monitoring value of the tension and compression sensor on the anchor rod reaches 80% of the design value of the anchor rod tension, the bidirectional oil cylinder is started. When the monitoring value of the axial force sensor reaches 80% of the support rod, the bidirectional oil cylinder is locked to keep the position of the slider stationary. (3) When the monitoring value of the tension and compression sensor on the anchor rod reaches 90% of the design value of the anchor rod tension, the bidirectional cylinder is started. When the monitoring value of the axial force sensor reaches 95% of the support rod, the bidirectional cylinder is locked to keep the position of the slider stationary. Step 10: Construction completed With the dynamic adjustment of the support structure, the foundation pit is gradually excavated to the designed depth.

8. The construction method of a foundation pit support structure according to claim 7, characterized in that: The cable-stayed system in step three is constructed at an angle, the angle between the center axis of the anchor rod and the vertical direction is in the range of 65° to 80°, and the distance between the center axes of adjacent anchor rods is 1 to 5 times the distance between the center axes of adjacent retaining piles.

9. The construction method of a foundation pit support structure according to claim 7, characterized in that: In step eight, the waist beam is a segmented structure, and the length of each waist beam is 1 to 5 times the distance between the center axes of adjacent retaining piles. The ratio of the length of each waist beam to the distance between the center axes of adjacent retaining piles is equal to the number of sliding blocks on the waist beam.

10. The construction method of a foundation pit support structure according to claim 7, characterized in that: In step eight, the limiting beam is a segmented structure, and the length of each segment of the limiting beam is 3 to 7 times the distance between the center axes of adjacent retaining piles.

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