Green construction method for improving overall performance of arch bridge pile foundation under complex unloading environment

Abstract

This invention relates to a green construction method for improving the overall performance of arch bridge pile foundations under complex unloading environments. It utilizes a combination of anchored static pressure piles and horizontal piles to reinforce the pile foundations of deformation-sensitive arch bridges. Anchored static pressure piles enhance the vertical bearing capacity of the pile foundation and control the vertical settlement of the arch foot. The connecting rods formed by the horizontal piles significantly improve the horizontal bearing capacity of the pile foundation and limit the horizontal displacement of the arch foot under the influence of the unloading environment, ensuring the safety of the arch bridge under unloading conditions. Furthermore, by backfilling the excavated area with modified excavated soil, zero-waste construction is achieved. This method is a low-disturbance construction method combining new and old piles, suitable for arch bridges or other deformation-sensitive bridge or building structures. In complex unloading environments with low headroom and high disturbance, it can conveniently, quickly, and effectively improve pile foundation performance and control foundation deformation, offering advantages such as being environmentally friendly, convenient, low-disturbance, and low-cost.

Description

Technical Field

[0001] This invention relates to a green construction method for improving the overall performance of arch bridge pile foundations under complex unloading environments, belonging to the field of civil engineering construction technology. Background Technology

[0002] With the development and utilization of urban underground space, there are increasingly more cases of underground engineering projects located near bridges, such as foundation pit excavation and tunnel excavation near arch bridges. In soft soil areas, the excavation and unloading of underground projects are often accompanied by significant soil disturbance, which can affect the nearby bridge pile foundations and thus the safety of the superstructure. As a deformation-sensitive structure, arch bridges (especially through-arch bridges) will inevitably threaten their normal use if the arch feet undergo significant displacement under unloading conditions.

[0003] Most existing arch bridges are quite old, some even being protected historical structures, which places higher demands on deformation control. Traditional pile foundation replacement construction itself causes significant disturbance to the arch bridge foundation. For some ancient arch bridges with durability issues, the disturbance outweighs the protective effect. Other bridge foundation reinforcement measures, such as bored piles, cannot be implemented normally due to the low clearance of arch bridges. These traditional reinforcement methods cannot effectively utilize existing piles, generate significant construction waste and carbon emissions, and suffer from high costs and environmental pollution. Therefore, this invention, as a green technology and construction method for improving the overall performance of arch bridge pile foundations under complex unloading environments, solves the aforementioned problems. Summary of the Invention

[0004] To address the shortcomings and problems in existing construction techniques, a technology and construction method for improving the overall performance of arch bridge pile foundations under complex unloading environments is proposed. This method can minimize the adverse effects of underground construction disturbances on arch bridges, enhance the bearing capacity of arch bridge pile foundations, and control uneven settlement and horizontal displacement of the arch abutments under unloading conditions. This ensures the structural safety of the arch bridge even under surrounding construction influences, significantly improving its seismic performance and disturbance resistance. It achieves zero-waste construction and is characterized by its green, low-carbon, high-efficiency, and energy-saving features.

[0005] To solve the above-mentioned technical problems, the present invention provides a technology and construction method for improving the overall performance of arch bridge pile foundations under complex unloading conditions, characterized by the following steps:

[0006] First, the bridge pier cap is reinforced to provide a larger ground contact area after reinforcement and widening. Jacks are then installed under the cap as temporary supports. Excavation is carried out inside the existing pile foundation beneath the cap, a concrete layer is poured, anchor bolts are installed, and pile holes are pre-drilled. Static pressure piles are then driven in using the reaction forces provided by the existing pile foundation and the new cap. A small foundation pit is excavated directly below the arch, where anchor bolt static pressure piles are also installed. Finally, the new cap is connected to the existing foundation using horizontal piles, forming a unified structure and achieving pile foundation reinforcement and settlement control. A concrete pad is constructed below the jacks for support; I-beams and bearing plates are installed above the jacks. The jacks serve as temporary supports for the bridge pier cap, and part of the widened abutment remains in contact with the existing soil, providing sufficient support during the excavation of the working platform beneath the cap.

[0007] Furthermore, the jacks are positioned transversely along the outer side of the old pile foundation, beneath the widened pile cap. No jacks are placed at either end of the pile cap longitudinally, leaving space for excavation beneath the pile cap. This excavation is for the construction of the new pile cap. The location of the maximum pile deflection under unloading can be calculated using the deflection differential equation. Placing the new pile cap at this location minimizes pile deflection caused by unloading. The new pile cap, combined with the old piles, provides reaction force for the anchored static pressure piles and connects the old and new piles. It can also connect with the horizontal piles longitudinally, further enhancing the bearing capacity of the pile foundation.

[0008] Furthermore, a small foundation pit is excavated directly beneath the arch, where a concrete foundation is poured to serve as the foundation for the new piles. Anchor joints and pile driving holes are pre-installed, and static pressure piles are constructed. While the static pressure piles are in place, horizontal piles are constructed towards the piers on both sides, connecting them to the new foundation under the piers to form a unified structure. After the horizontal piles are completed, the small foundation pit under the arch can be backfilled with excavated topsoil mixed with cement. The number of horizontal piles can be determined based on traffic conditions and clearance under the bridge. If necessary, a foundation beam can be constructed in the shallow ground layer to connect with the old foundation, thus forming a double-layer connection and reinforcement between the old and new piles and the old and new foundations.

[0009] After the anchor static pressure piles under the pier cap are installed, the jacks can be removed and the locations where the jacks were placed should be backfilled with concrete. The working space of the anchor static pressure piles also needs to be backfilled after construction. The backfill material can be miscellaneous fill soil excavated on site, which is crushed and mixed with cement to form high-strength concrete.

[0010] The small pit under the arch can be used as a working space to drive steel pipe piles as horizontal piles using hydraulic jacks. The steel pipe piles are driven into the soil layer to a predetermined depth by a segmented driving method. After driving is completed, the soil in the steel pipe is replaced with concrete.

[0011] The newly added static pressure piles and horizontal piles are circular, while the foundation beams connecting the pile caps constructed on the ground surface are rectangular. The spacing between any two adjacent newly added static pressure piles is 2 to 5 times the pile diameter.

[0012] Compared to existing technologies, the advantages of this invention are as follows: Addressing the engineering problem of arch bridge pile foundations and abutments being disturbed under complex unloading environments, this invention proposes a simple, efficient, and convenient on-site construction method combining anchored static pressure piles and horizontal piles. The vertical anchored static pressure piles enhance the vertical bearing capacity of the existing pile foundation, control the settlement and deformation of the abutment, and maintain a fixed connection between the new abutment and the old pile foundation, limiting the lateral movement of the old pile foundation. The horizontal piles combine the new and old vertical piles into a unified structure, significantly improving the horizontal bearing capacity of the bridge pile foundation and enhancing the bending resistance of the existing pile foundation. Under lateral unloading conditions, the lateral deformation of the arch bridge pile foundation and abutment can be better controlled, thereby reducing the horizontal displacement and angular displacement of the arch foot abutment. Simultaneously, the combination of vertical static pressure piles and horizontal piles forms a stable underground support, changing the original load transfer mode and deformation mechanism, and improving the overall integrity of the old arch bridge, which greatly improves resistance to construction disturbances and seismic damage. Backfilling with improved excavated soil achieves zero-waste construction. This construction method boasts advantages such as minimal disturbance, excellent protection, strong adaptability, speed and convenience, safety and stability, and environmental friendliness. It can solve various problems in arch bridges, including insufficient bearing capacity of existing piles, excessive deformation due to construction, and poor overall structural integrity. This application is not limited to arch bridges but is also applicable to any pile-foundation bridge with limited clearance and strict control over foundation deformation. Attached Figure Description

[0013] Figure 1 This is a front view of the reinforcement effect after the completion of the construction of this invention;

[0014] Figure 2 This is a schematic diagram of the construction of the pier cap widening and vertical anchor static pressure piles in this invention;

[0015] Figure 3 This is a top view of the reinforced foundation for the combination of old and new piles in this invention;

[0016] Figure 4 for Figure 3 Schematic diagram of horizontal piles in section AA;

[0017] Figure 5 This is a schematic diagram of the horizontal pile construction in this invention.

[0018] In the diagram, 1-the superstructure of the arch bridge, 2-the foundation, 3-the widened portion of the foundation, 4-the existing old pile, 5-the working space of the static pressure pile, 6-the static pressure pile, 7-the steel-concrete crossbeam, 8-the cushion layer, 9-the I-beam, 10-the jack, 11-the steel-concrete cushion layer, 12-the pile driver, 13-the anchor rod, 14-the pile hole, 15-the horizontal static pressure pile, 16-the diaphragm wall, 17-the foundation pit, 18-the lateral reinforcement area of ​​the old pile, 19-the hydraulic jack, 20-the support slide bar, 21-the fixing device, 22-the new foundation A, 23-the new foundation B. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The embodiments described in this patent are only some embodiments of the present invention, not all embodiments, and can be adjusted and replaced with appropriate devices according to the actual situation on site.

[0020] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance. Similarly, terms such as "upper," "lower," "left," "right," "front," "back," "horizontal," and "vertical" mentioned in this patent description are all relative positional relationships and have no specific meaning, and should not be construed as limiting this invention.

[0021] Example 1: See Figures 1 to 4 , Figure 1 This is a schematic diagram illustrating the reinforcement effect after the construction of this invention is completed. Figure 2 This is a schematic diagram illustrating the construction of the widened foundation and newly added vertical anchor static pressure piles in this invention. Figure 3 This is a top view of the reinforced foundation for the combination of old and new piles in this invention. Figure 4 This is a cross-sectional schematic diagram of the newly added foundation in this invention. Figure 5 This is a schematic diagram of the horizontal pile construction in this invention.

[0022] The following detailed description, in conjunction with the accompanying drawings, further illustrates the construction method described in the patent: a green construction method for improving the overall performance of arch bridge pile foundations under complex unloading environments, specifically including the following construction steps:

[0023] (1) Leveling the arch bridge abutment and the construction area under the arch bridge;

[0024] (2) Clear the surface soil near the bridge pier and dig down about 10cm.

[0025] (3) Enlarge the foundation construction: Tie steel cages (steel bars pass through the foundation) around the foundation 2 and on the lower surface, pour concrete, and widen and reinforce the pier. The widened width is twice the diameter of the old pile, and the height of the widened reinforcement should be the same as the height of the original foundation. The completed reinforcement body 3.

[0026] (4) Jack placement: Excavation is carried out below the pile cap and outside the existing pile foundation (see...). Figure 1 At location 18 (of the middle component), the excavation depth is 1m. After excavation, a 20cm thick concrete pad is poured as the bearing layer for the jack. Between the jack and the foundation, a pad 8 and an I-beam 9 are sequentially installed from top to bottom. The pad 8 is in contact with the widened reinforcement 3, and the I-beam 9 is located at the lower part of the pad 8 and in contact with the jack (e.g., ...). Figure 2 (As shown). When the bottom surface of the pier cap is flat and the width and rigidity are sufficient, I-beams are not required. Jacks are arranged along the outer side of the old pile foundation in the transverse direction of the bridge, and no jacks are arranged on both sides of the pier cap in the longitudinal direction of the bridge.

[0027] (5) Excavation of the working space for static pressure piles: After the jacks are installed, excavation can be carried out inside the old piles. The location of the maximum pile deflection (Z) under the influence of unloading (shallow tunnel or foundation pit excavation, etc.) can be calculated using the deflection differential equation. y,max The excavation depth is set at Z. y,max At a depth of 0.2m below, but sufficient space should be provided to accommodate the normal operation of the anchor-mounted static pressure pile driver. The excavation depth generally does not exceed 3m. If the maximum deflection of the old pile foundation occurs at location (Z... y,max If the depth exceeds 3m, then the excavation depth is taken as 3m. The calculation method for pile deformation and internal forces under the influence of unloading using the flexural differential equation is as follows:

[0028]

[0029] In the formula: EI is the bending stiffness of the pile; y is the deflection of the pile; z is the calculated depth; m is the proportional coefficient of the horizontal resistance coefficient of the foundation; D is the diameter of the pile; u is the friction coefficient of the pile-soil contact surface; b0 is the calculated width of the pile, which is taken according to the "Technical Specification for Building Pile Foundations" (JGJ94-2008). When the pile has a circular cross section, if the pile diameter D≥1, b0=0.9(D+1); if the pile diameter D<1, then b0=0.9(1.5D+0.5).

[0030] The solution to the flexure differential equation is as follows:

[0031] Equation (1) is a fourth-order differential equation with variable coefficients, and it also contains a composite function integral term. Directly solving this equation yields no analytical solution. This application developed a Matlab program to solve it. The program uses the Euler method to solve the differential equation and the Newton iteration method to solve for the integral coefficients. Here, boundary conditions for solving the equation are also introduced. For flexible long piles, the effective embedment depth L at the pile tip... e The displacement and rotation at the pile top are negligible and approximately zero. The pile top is simplified to a free state. Under the condition of a horizontal force H0 and a bending moment M0 acting at the pile top, the entire boundary condition is written as:

[0032]

[0033] Combining the boundary condition equation (2), the program only needs to input 8 parameters (EI, m, D, u, M0, H0, L, L). e By inputting the parameters sequentially, the program can calculate the internal forces and deformation values ​​of the pile and plot the curves. The location of the maximum pile deflection (Z) can then be identified from the curves. y,max ).

[0034] (6) Concrete is poured at the bottom of the excavated space, with anchor bolt holes and pile driving holes 14 pre-reserved. This concrete cushion layer can serve as a new foundation beneath the old foundation. For example... Figure 1 As shown, the new foundation A ( Figure 1 Component 22) needs to be cast together with the existing old pile 4, and also needs to be connected with the horizontal piles (components 7 and 15) to be constructed later.

[0035] (7) Static pressure pile construction: Install anchor bolts and arrange pile drivers 12. After the pile drivers are arranged, start driving the anchor bolt static pressure piles 6. The diameter of the static pressure pile is generally selected to be 0.5D to 1.0D of the old pile diameter. The number of new piles can be adjusted appropriately according to the spacing of the old piles.

[0036] (8) A skip-pile construction method is adopted. To avoid the influence of adjacent static pressure pile construction on the strength of the old piles, a skip-pile construction method is adopted. That is, the first, third, fifth, etc., are driven in first, and the second, fourth, etc., are driven in after the soil and the old piles have stabilized, until the construction of all piles is completed. If the site conditions are complex, hollow steel pipe piles can also be selected to reduce the disturbance to the old piles during static pressure pile construction. After the steel pipe piles are driven in, concrete is filled into the piles.

[0037] (9) Excavate a foundation pit with the same depth as the static pressure pile working space 5 and the same length as the old arch bridge pier below the arch. Construct a diaphragm wall 16 on the transverse sidewall of the foundation pit, and pour a concrete cushion layer at the bottom as the new pier B. Figure 1(23) In the middle component, anchor bolt holes and pile driving holes 14 are reserved for static pile construction. (10) Horizontal pile driving: Horizontal piles 15 are driven into the side wall of the foundation pit 17, such as Figure 4 As shown. The specific horizontal pile driving process is shown in [the image / document]. Figure 5 The steel pipe piles are fixed in the fixing device 21. The four corners of the fixing device 21 are supported by sliding rods 20 on the diaphragm wall 16. Then, a hydraulic jack 19 is used to press the steel pipe piles horizontally into place through the fixing device. After the first section of the steel pipe pile is pressed in, a 0.1m gap is left for welding the next pile section. The same method is used until the horizontal pile is pushed into the contact position with the old pile foundation. The other side of the horizontal pile is constructed in the same way.

[0038] (11) Construction of the crossbeam: such as Figure 5 As shown, a trench with a depth and width of 1D (the diameter of the pile) is excavated in the ground, a reinforcing cage is placed below, and a horizontal beam is constructed. The cross-sectional dimension of the horizontal beam is approximately 0.9D, extending from the diaphragm wall 16 until it connects with the existing pile foundation. The layout of the horizontal beam and horizontal piles can be found in [reference needed]. Figure 3 .

[0039] (12) After the construction of the vertical static pressure piles, horizontal piles and crossbeams is completed, remove the jacks 10; backfill the excavated area (static pressure pile working space 5, old pile side 18, foundation pit 17) with concrete. Backfilling at location 18 can provide lateral reinforcement of the old piles; steel cages are laid in working space 5 and foundation pit 17, and backfilling is carried out using improved excavated soil mixed with cement, which can connect the new and old vertical piles and deep horizontal piles and surface crossbeams; after the working space 5 is poured, it can reinforce the pile top, inner side and pile cap of the old pile foundation, and after the foundation pit 17 is poured, it can serve as a new pile cap, which can connect the new and old piles and control the deformation of the arch foot.

[0040] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention. Equivalent transformations or substitutions made based on the above technical solutions all fall within the scope of protection of the claims of the present invention.

Claims

1. A green construction method for improving the overall performance of arch bridge pile foundations under complex unloading conditions, characterized in that... The method includes the following steps: Step 1: First, reinforce the bridge pier cap so that the reinforced and widened cap has a larger ground contact area; Step 2: Install jacks under the foundation as temporary supports; Step 3: Excavate inside the old pile foundation below the pile cap, pour a concrete layer, install anchor rods, reserve pile holes, and use the support reaction force provided by the existing pile foundation and the new pile cap to implant static pressure piles. Step 4: Excavate a small foundation pit directly below the arch and install anchor static pressure piles in the same way; Step 5: Finally, connect the newly built pile cap with horizontal piles to form a whole with the original foundation, so as to achieve pile foundation reinforcement and settlement control. In step 2, a concrete pad is constructed at the bottom of the jack to provide support; I-beams and pads are sequentially installed on the top of the jack, and the jack is used as a temporary support for the bridge pier cap. At the same time, part of the widened abutment is still in contact with the original soil. In step 3, the excavation below the pile cap is for the purpose of pouring the new pile cap. The location of the maximum deflection of the pile foundation under the influence of unloading is calculated based on the deflection differential equation. The new pile cap is placed at this location to minimize the pile foundation deflection caused by unloading. The new pile cap overlaps with the old pile, providing reaction force for the anchor static pressure piles and simultaneously connecting the new and old piles. The expression for the pile deflection differential equation considering friction effects based on the m-method is as follows: (1) In the formula: EI is the bending stiffness of the pile; y is the deflection of the pile; z is the calculation depth; m is the proportional coefficient of the horizontal resistance coefficient of the foundation; D is the diameter of the pile; denoted as , where is the coefficient of friction between the pile and the soil; b0 is the calculated width of the pile. When the pile has a circular cross-section, if the pile diameter D ≥ 1, then b0 = 0.9(D + 1); if the pile diameter D < 1, then b0 = 0.9(1.5D + 0.5). In step 4, a small foundation pit is excavated directly below the arch, and a concrete foundation is poured to serve as the foundation for the new piles. Anchor joints and pile driving holes are reserved for the construction of static pressure piles. In step 5, when the static pressure piles are completed, horizontal piles are constructed towards the piers on both sides to connect the horizontal piles with the new pier caps under the piers to form a whole; after the horizontal piles are constructed, the excavated topsoil mixed with cement can be used to backfill the small foundation pit under the arch.

2. The green construction method for improving the overall performance of arch bridge pile foundations under complex unloading conditions as described in claim 1, characterized in that, The small pit under the arch serves as the working space. Steel pipe piles are driven into the soil at a predetermined depth using hydraulic jacks. After the piles are driven in sections, the soil inside the steel pipes is replaced with concrete.

3. The green construction method for improving the overall performance of arch bridge pile foundations under complex unloading conditions as described in claim 1, characterized in that, The newly added static pressure piles and horizontal piles are all circular, and the foundation beams for the connecting pile caps constructed on the ground surface are rectangular.

4. The green construction method for improving the overall performance of arch bridge pile foundations under complex unloading conditions as described in claim 1, characterized in that, The spacing between adjacent piles in the newly added static pressure piles is 2 to 5 times the pile diameter.

Images