A soft soil foundation existing highway widening pile net reinforced retaining wall structure and construction method

Abstract

The application provides a soft soil foundation existing road widening pile net reinforced retaining wall structure and construction method, relates to the field of soft soil foundation, and the structure comprises an existing road foundation stepped connection area, which is excavated with multiple steps; a widening area soft soil foundation excavation and flattening area, which is arranged at the soft soil foundation outside the existing road foundation; a pile bearing type foundation treatment structure, which is located at the widening area soft soil foundation excavation and flattening area; an upper part widening road foundation reinforced filling body, which is engaged with the existing road foundation stepped connection area, interface geogrid is arranged at the steps, and the interface geogrid is wrapped with fillers layer by layer to form a reverse package type reinforced structure; an outside block type wall surface, which is arranged at the outer edge of the upper part widening road foundation reinforced filling body; a wall top pressing component, which is arranged at the top of the outside block type wall surface; a tension type geogrid, which is connected with the outside block type wall surface; a connecting and coordinating component, which is assembled between the tension type geogrid and the outside block type wall surface; and a composite waterproof and drainage system. The application has the effect of improving the bearing capacity of the soft soil foundation.

Description

Technical Field

[0001] This application relates to the field of soft soil foundation technology, and in particular to a reinforced retaining wall structure and construction method for widening existing highways on soft soil foundations. Background Technology

[0002] The widening and reconstruction of existing expressways and ordinary national and provincial trunk roads has become an important engineering measure to improve the traffic capacity of the road network, enhance road service levels, and extend the service life of infrastructure. Compared with building new highways, widening and reconstruction of existing highways can make full use of the original roadbed, pavement, and traffic corridor resources, reduce new construction land and engineering disturbances, and has advantages such as resource conservation, low carbon emission reduction, and engineering economy.

[0003] However, widening and reconstructing existing highways is not simply a matter of widening the roadbed. The key lies in achieving coordinated stress distribution and deformation between the newly constructed widened roadbed and the existing roadbed. The existing roadbed bears traffic loads over a long period and undergoes natural consolidation, resulting in significant differences in density, stiffness, settlement state, and stress history compared to the newly constructed widened roadbed. Conversely, the newly constructed widened roadbed is still in the stress adjustment and compaction deformation stage during construction and the initial service period, making it prone to additional settlement and lateral deformation. Therefore, the junction between the old and new roadbeds often experiences abrupt changes in stiffness, inconsistent settlement, shear slippage, and stress concentration, which in turn induces longitudinal cracks, changes in cross slope, shoulder cracking, misalignment at the junction, and reduced overall embankment stability, affecting the driving comfort, safety, and long-term durability of the widened highway.

[0004] Currently, existing highway widening projects often employ measures such as slope cutting and excavation, stepping treatment, layered filling and compaction, laying geogrids, and constructing retaining walls or reinforced soil retaining walls to enhance the connection between the old and new roadbeds and control differential settlement. Among these, stepping treatment can improve the interlocking effect at the interface between the old and new roadbeds; geogrids can improve the overall integrity of the fill through a reinforcing effect; and retaining walls or reinforced soil retaining walls can, to some extent, address the issues of insufficient widening space and external support. While these measures are effective under conventional widening conditions, they still have shortcomings in complex situations such as construction with continuous traffic flow, widening on slopes in mountainous areas, large fill heights, or limited external space.

[0005] On the one hand, traditional methods of widening roadbeds and reinforcing them mainly rely on laying geogrids. This reinforcement primarily depends on the interfacial friction and tensile stiffness between the geogrid and the fill material, offering limited constraint on lateral deformation of the fill. When the widened fill is subjected to vehicle loads, filling loads, and rainwater infiltration, the reinforced structure struggles to effectively contain and constrain the fill material, easily leading to lateral bulging deformation on the outer side of the widened roadbed and further exacerbating vertical settlement and deformation inconsistencies at the junction of the old and new roadbeds. On the other hand, existing roadbed widening projects are often constrained by road boundaries, adjacent structures, slope topography, and traffic organization conditions, making it difficult to employ large-slope or large-scale excavation methods. While traditional rigid retaining structures offer strong lateral support, their high rigidity makes them prone to abrupt deformations between the rigid wall and the flexible fill, hindering long-term coordinated deformation between the old and new roadbeds. Furthermore, rigid retaining walls typically require large foundation excavation spaces, resulting in significant construction disturbances that fail to meet the requirements of low-disturbance, rapid, and safe construction for existing highways. Conversely, conventional reinforced soil retaining wall structures suffer from insufficient overall synergy between the wall surface, the reinforced structure, and the existing roadbed. Under loads on the top of the wall, traffic loads, and rainwater infiltration, problems such as wall bulging, top cracking, concentrated localized deformation of the reinforced structure, and persistent differential settlement of the roadbed may still occur.

[0006] Furthermore, drainage and deformation control are also prominent issues in existing roadbed widening projects. The outer side of the widened roadbed is usually a newly filled area, and the compaction quality of the fill material, interface drainage conditions, and rainwater infiltration paths significantly affect its long-term stability. If the drainage system is inadequate, rainwater can easily seep in along the interface between the old and new roadbeds or the back wall area, leading to reduced fill material strength, decreased interfacial friction of the geogrid, and accumulation of pore water pressure, thereby weakening the anti-slip capacity and overall stability of the widened roadbed. Existing widening measures often design reinforcement, support, drainage, and construction auxiliary measures separately, lacking an integrated structural system that addresses the coordinated stress distribution between the old and new roadbeds, differential settlement control, and lateral stabilization support. Summary of the Invention

[0007] In order to overcome the technical problems described in the prior art, this application provides a reinforced retaining wall structure with pile network for widening existing highways on soft soil foundations and a construction method thereof.

[0008] Firstly, this application provides a reinforced retaining wall structure with pile mesh for widening existing highways on soft soil foundations, which adopts the following technical solution: A pile-mesh reinforced retaining wall structure for widening existing highways on soft soil foundations, including... In the existing stepped connection zone of the roadbed, multiple steps are excavated to construct a composite connection interface between the old and new roadbeds with interlocking steps. The soft soil foundation excavation and leveling area in the widening zone is located on the soft soil foundation outside the existing roadbed. The pile-supported foundation treatment structure is located in the soft soil foundation excavation and leveling area of ​​the widening zone. It is composed of pile body, pile cap, geogrid near the pile cap, and inter-pile cushion layer to form a pile-net composite bearing system, which transfers the upper load to the deep stable soil layer. The upper widening roadbed reinforced fill is located above the soft soil foundation excavation and leveling area of ​​the widening area, and is connected to the existing roadbed stepped connection area through steps. Interface geogrids are laid at the steps, and the interface geogrids are folded back layer by layer to wrap the fill material to form a reverse wrapping reinforcement structure to restrain lateral deformation. The outer segmented wall is located at the outer edge of the upper widened roadbed reinforced fill to provide lateral support; The top capping component is located at the top of the outer segmented wall surface; Multiple tension geogrids are installed, all located within the upper widened roadbed reinforced fill. Their two ends are connected to the outer segmented walls on both sides, forming a transverse tension limiting system. Connecting and coordinating components are assembled between the tensioned geogrid and the outer segmented wall surface to adjust the tension of the tensioned geogrid. The composite drainage and waterproofing system is arranged on the top of the reinforced fill of the widened roadbed, on the back of the outer segmented wall, and above the pile-net composite load-bearing system.

[0009] Furthermore, the pile body is one of the following: precast pile, pipe pile, cement-soil mixing pile, concrete cast-in-place pile, plain concrete pile. Multiple pile bodies are arranged in a rectangular or quincunx pattern, and the outer side of the segmented wall and the transition area between the old and new roadbeds are densely arranged. Geogrids near the pile caps are continuously laid across adjacent pile caps.

[0010] Furthermore, the pile-intercalation cushion layer is filled with graded crushed stone, gravel, or permeable sand, and laid on top of the pile cap and the geogrid near the pile cap. The pile-intercalation cushion layer is connected to the bottom drainage channel of the composite drainage system located above the pile-net composite bearing system.

[0011] Furthermore, the reverse-wrapping reinforcement structure is made of geogrid and composite reinforcement strips laid in layers. Each layer of composite reinforcement strips is folded back and compacted to the outer side of the segmented wall to form a continuous wrapped reinforcement body.

[0012] Furthermore, the outer segmented wall is composed of multiple prefabricated wall panels assembled longitudinally and vertically along the road, with adjacent prefabricated wall panels connected by connecting pins, insertion slots, or back connecting rings.

[0013] Furthermore, the composite waterproofing and drainage system includes a top waterproof layer for preventing rainwater infiltration, a drainage board for draining seepage, a filter layer for preventing the loss of fine particles from the filler, a bottom drainage ditch, and wall drainage components.

[0014] Secondly, this application provides a construction method for a pile-mesh reinforced retaining wall structure for widening existing highways on soft soil foundations. Based on the aforementioned pile-mesh reinforced retaining wall structure for widening existing highways on soft soil foundations, the method includes the following steps. S1. Surveying and setting out: Delineate the excavation range of the expanded soft soil, pile positions, control lines for the outer segmented wall and composite waterproofing and drainage system; S2. Soft soil excavation and leveling: Clear the surface soft soil of the widened area, replace and compact it to form the soft soil foundation excavation and leveling area of ​​the widened area. S3. Pile construction: Construct piles according to the design spacing, verify the pile positions and complete the pretreatment of the pile tops; S4. Construction of pile-net composite bearing system: Install pile caps on the pile tops, continuously lay geogrids near the pile caps, fill the inter-pile cushion layer in layers, and form a pile-net composite bearing system. S5. Excavation of existing roadbed steps: The existing roadbed is excavated in stages to form multiple steps on the widening side. Interface geogrids are laid on the step surface and extended to the widening area to form a transition connection section. S6. Layered reinforced filling: The subgrade fill material is layered on top of the pile-net composite bearing system. The outer edge of each layer is compacted towards the wall side by interface geogrid and reinforcement material to form a reverse-wrapped reinforced structure. S7. Segmented wall installation: The outer segmented wall is hoisted and assembled step by step as the filling height increases, and the wall alignment and verticality are corrected. S8. Construction of the tension system: Lay tension geogrid and fix it to the outer segmented wall surface by connecting and coordinating components; S9. Composite waterproofing and drainage construction: Lay a waterproof layer on the top of the roadbed, install drainage boards and filter layers, and lay bottom drainage blind ditches and drainage outlets. S10. Finishing and shaping: Cast the top capping components of the wall, cast and shape the top surface of the roadbed, connect with the original road surface, and remove temporary construction components.

[0015] Furthermore, in step S4, the geogrid near the pile cap is continuously laid across adjacent pile caps, and the inter-pile cushion layer is rolled and fixed in layers to form a continuous tensile network. The tensile membrane effect is used to redistribute the pile-soil load and reduce the differential settlement between piles.

[0016] Furthermore, in step S8, an initial preload is applied to the tension geogrid. When the new and old roadbeds experience differential settlement during the highway operation phase, the connecting and coordinating components release the node constraints, allowing the tension geogrid to slip slightly and adaptively adjust the tension, continuously constraining the lateral deformation of the wall.

[0017] Furthermore, in step S9, the top waterproof layer is laid in line with the road surface drainage cross slope, and the drainage board and bottom drainage blind ditch are interconnected to form a complete drainage channel, reducing the adverse effects of water infiltration on the soft soil foundation and the strength of the reinforced grid interface.

[0018] In summary, this application includes at least one of the following beneficial technical effects: 1. This invention forms a pile-net composite bearing system by widening the soft soil foundation excavation and leveling area, pile body, pile cap, geogrid near the pile cap, and pile cushion layer. This allows the upper load to be transferred to the deep stable soil layer through the diffusion of the pile cushion layer, the tensile transfer of the geogrid near the pile cap, and the combined bearing of the pile body. This effectively improves the bearing capacity of the soft soil foundation, reduces the settlement of the soil between piles, and reduces the uneven support at the bottom of the widened roadbed. 2. This invention uses the existing roadbed stepped connection zone and interface geogrid to form a composite connection interface between the original treatment zone of the existing roadbed and the newly built pile-net composite treatment zone, which combines the effects of stepped interlocking, interface friction and geogrid ties, thereby improving the stress transmission path at the junction of the old and new roadbeds and reducing the risk of differential settlement, shear slip and longitudinal cracking of the pavement. 3. This invention uses a reverse-wrapping reinforcement structure to wrap and constrain the backfill material layer by layer, so that the widened backfill has continuous connection, lateral constraint and deformation adaptability, which can reduce the lateral bulging of the backfill material and the concentration of soil pressure on the back of the wall, and improve the adaptability of the upper backfill to uneven settlement of soft soil foundation. 4. This invention combines the outer segmented wall surface, the top capping component, the tension geogrid, and the connecting and coordinating components into a synergistic force-bearing system that restricts the outward tilt of the wall top, the outward bulging of the wall surface, and the lateral expansion of the roadbed top, while allowing for coordinated local deformation and avoiding node damage and stress concentration caused by rigid connections.

[0019] 5. This invention forms a composite waterproofing and drainage system through a top waterproof layer, drainage board, filter layer, bottom drainage channel and drainage outlet. It can reduce water infiltration, promptly drain water accumulated on the back of the wall and above the pile-net composite bearing system, and reduce the adverse effects of moisture content changes and pore water pressure accumulation on the strength of soft soil foundation, reinforced interface performance and long-term stability of widened roadbed.

[0020] 6. This invention controls the pile position, pile cap elevation, geogrid laying path, reverse wrapping position, wall installation line shape, and layered filling thickness through construction auxiliary components, enabling soft soil foundation treatment, pile-grid composite structure construction, upper reinforced filling, outer wall installation, and top tie construction to be connected in stages, gradually formed, and synergistically stressed, thereby improving construction quality, construction efficiency, and project controllability. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the widening of an existing soft soil roadbed in an embodiment of this application.

[0023] Figure 2 This is a schematic diagram of the pile foundation in the embodiments of this application.

[0024] Figure 3 This is a schematic diagram of the reverse-enclosed reinforced structure, the outer segmented wall, and the upper widened roadbed reinforced fill body in the embodiments of this application.

[0025] Figure 4 This is a schematic diagram of the outer segmented wall, the top capping component, the tie-type geogrid, and the connecting and coordinating components in the embodiments of this application.

[0026] Attached reference numerals: 1. Existing roadbed stepped connection zone; 2. Soft soil foundation excavation and leveling zone in the widened area; 3. Pile-supported foundation treatment structure; 31. Pile body; 32. Pile cap; 33. Geogrid near the pile cap; 34. Pile cushion layer; 4. Upper widened roadbed reinforced fill; 5. Reinforced structure with reverse wrapping; 6. Outer segmented wall; 7. Top capping component; 8. Tie-type geogrid; 9. Connecting and coordinating components; 91. Clamping steel plate; 92. Turnbuckle; 93. Rotary joint; 94. Elastic buffer layer; 10. Composite drainage system; 11. Anchor. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] This application discloses a pile-mesh reinforced retaining wall structure and construction method for widening existing highways on soft soil foundations. (Refer to...) Figure 1 , Figure 2 , Figure 3 and Figure 4A reinforced retaining wall structure for widening existing highways on soft soil foundations includes: a stepped connection zone 1 for the existing roadbed; an excavation and leveling zone 2 for the widened soft soil foundation; a pile-supported foundation treatment structure 3; a reinforced upper widened roadbed fill 4; an outer segmented wall 6; a capping component 7; a tension geogrid 8; connecting and coordinating components 9; and a composite drainage system 10. The surface of the excavation and leveling zone 2 for the widened soft soil foundation is composed of silt, miscellaneous fill, and other weak and unfavorable soil. During construction, the excavation is carried out in sections to remove the silt, and the excavation boundary overlaps with the existing foundation treatment area of ​​the roadbed. After excavation, a gravel replacement layer is laid and compacted in layers to form a flat, uniformly bearing pile foundation surface.

[0029] Reference Figure 1 , Figure 2 , Figure 3 and Figure 4 The pile-supported foundation treatment structure 3 is located in the soft soil foundation excavation and leveling area 2 of the widening zone. The pile-supported foundation treatment structure 3 is composed of piles 31, pile caps 32, geogrids 33 near the pile caps, and a cushion layer 34 between piles to form a pile-net composite bearing system. The piles 31 are one of the following: precast piles, pipe piles, cement-soil mixing piles, cast-in-place concrete piles, and plain concrete piles. In this embodiment, the piles 31 are precast prestressed pipe piles, which penetrate the surface soft soil and embed into the underlying stable silty clay layer. Multiple piles 31 are arranged in a rectangular or quincunx pattern, with equal spacing in conventional areas and denser arrangement close to the back of the outer segmented wall 6 and in the transition area between the old and new roadbeds. The pile caps 32 are cast-in-place reinforced concrete, which increase the bearing area at the pile top and alleviate stress concentration at the pile top. A geogrid 33 is continuously laid on top of the pile cap 32, spanning adjacent pile caps 32 without interruption. The geogrid 33 utilizes the tensile membrane effect to transfer the load from the soil between piles to the pile cap 32 and the pile body 31. A pile cushion layer 34 is constructed on top of the pile cap 32 and the geogrid 33. The pile cushion layer 34 is constructed by layering and compacting graded crushed stone, gravel, or permeable sand. A connecting channel is reserved at the bottom of the pile cushion layer 34, connecting to the bottom drainage ditch of the composite drainage system 10. This allows for timely drainage of water accumulated above the pile-net composite bearing system, preventing water from softening the underlying soft soil foundation.

[0030] Reference Figure 1 , Figure 2 , Figure 3 and Figure 4The existing roadbed is widened by graded excavation of the side slopes to form a multi-stage stepped structure. The upper widened roadbed reinforced fill 4 is located above the soft soil foundation excavation and leveling area 2 in the widened area, and is connected to the existing roadbed stepped connection area 1 through step interlocking. A composite connection interface is formed by step interlocking, interface friction, and grid bonding. The steps are slightly inclined to the inside of the roadbed to facilitate the compaction of the fill. The outer segmented wall 6 is set on the outer edge of the upper widened roadbed reinforced fill 4 to provide lateral support. Each step surface is covered with a layer of interface geogrid. Part of the interface geogrid is embedded and anchored inside the existing roadbed steps, and the other part extends outward into the upper widened roadbed reinforced fill 4 and folds back to the outer segmented wall 6 to wrap and compact the fill, forming a reverse-wrapped reinforced structure 5. The reverse-wrapped reinforced structure 5 is formed by laying geogrid and composite reinforcement strips. Each layer of reinforcement material is reserved for folding back on the outer segmented wall 6. After the fill material of this layer is laid and compacted, the reinforcement material is folded back upwards to wrap the fill material, and then the next layer of fill material is laid to cover the reverse-wrapped reinforcement material. This process is repeated layer by layer to form an integral wrapped reinforced body. Anchors 11 are vertically spaced on the outer segmented wall 6 to anchor the reverse-wrapped reinforced structure 5, so that the lateral expansion of the fill material is restrained by the friction of the compacted fill material, reducing the concentration of soil pressure on the back of the wall. A transition filling section is set between the step and the pile-net composite bearing system. The transition section is layered with multiple layers of interface geogrid to smooth the difference in stiffness between the old and new foundations and reduce abrupt settlement.

[0031] Reference Figure 1 , Figure 2 , Figure 3 and Figure 4 The outer segmented wall 6 is composed of multiple precast wall panels assembled longitudinally and vertically along the road. Adjacent precast wall panels are connected by connecting pins, interlocking slots, or back connecting rings. The segmented structure allows the wall to undergo slight vertical settlement and small rotation during soft soil settlement, avoiding cracking, misalignment, and stress concentration in the overall rigid wall due to differential settlement.

[0032] Reference Figure 1 , Figure 2 , Figure 3 and Figure 4 The top capping component 7 is a cast-in-place reinforced concrete capping beam, which is cast along the longitudinal length of the road on the top of all the outer segmented wall surfaces 6, connecting the dispersed wall blocks into a whole, and at the same time serving as the stress-dispersing base of the tension geogrid 8.

[0033] Reference Figure 1 , Figure 2 , Figure 3 and Figure 4Multiple tension geogrids 8 are provided, and these tension geogrids 8 are arranged at intervals along the roadbed height within the upper widened roadbed reinforced fill 4. The tension geogrids 8 transversely penetrate the entire widened roadbed, extending to the back of the outer segmented wall 6 at both ends, forming a transverse tension limiting system to restrict the outward tilting of the wall top and the outward bulging deformation of the wall surface. The connecting and coordinating components 9 are assembled at the connection nodes between the tension geogrids 8 and the outer segmented wall 6, including clamping steel plates 91, turnbuckles 92, swivel joints 93, and elastic buffer pads 94. The clamping steel plates 91 are fixedly installed on the outer segmented wall 6 by bolts, and the elastic buffer pads 94 are pressed between the clamping steel plates 91 and the outer segmented wall 6. The elastic buffer pads can be damping pads, rubber pads, etc. One end of the turnbuckles 92 is welded and fixed to the clamping steel plates 91, and the other end is fixedly connected to the tension geogrids 8 through the swivel joints 93. During the construction phase, pre-tension force can be applied to the pull-type geogrid 8 using turnbuckles 92 and the position can be locked. During the highway operation phase, differential settlement occurs between the old and new roadbeds. When the differential settlement causes tension on the pull-type geogrid 8, the clamping steel plate 91 will squeeze and locally push the outer segmented wall 6. The elastic buffer layer 94 is compressible. At the pressure position of the clamping steel plate 91, the elastic buffer layer 94 undergoes elastic compression deformation, increasing the contact area between the clamping steel plate 91 and the outer segmented wall 6, dispersing local concentrated compressive stress, and preventing local pressure cracking of the outer segmented wall 6. After the load disappears, the elastic buffer layer 94 rebounds and returns to the initial clamping state. The differential settlement between the old and new roadbeds will cause the tension geogrid 8 to slip laterally / longitudinally, leading to slight misalignment of the clamping steel plate 91 relative to the outer segmented wall 6. The elastic buffer layer 94 can undergo shear deformation, allowing the clamping steel plate 91 to slip slightly, thus offsetting the additional shear force transmitted from the tension geogrid 8 and preventing the shear force from acting directly on the wall bolts and concrete surface. Repeated vehicle loads and long-term slow settlement of the roadbed result in cyclical alternating stress at the nodes. The polymer materials inside the damping pads and rubber pads have internal friction. When the clamping steel plate 91 repeatedly squeezes and misaligns the pad, the pad converts the additional stress generated by settlement and vehicle vibration into heat energy dissipation through internal material friction, avoiding continuous stress accumulation and preventing stress fatigue damage to the wall, geogrid, and turnbuckle 92 connection parts.

[0034] Reference Figure 1 , Figure 2 , Figure 3 and Figure 4The composite drainage system 10 is arranged on the top of the reinforced fill body 4 of the widened roadbed, on the back of the outer segmented wall 6, and above the pile-net composite bearing system. The composite drainage system 10 includes a top waterproof layer, drainage board, filter layer, bottom drainage ditch, and wall drainage components. A seepage-proof and waterproof layer is laid on the top of the roadbed and is laid along the cross slope of the road surface to block the vertical infiltration of rainwater; the back of the outer segmented wall 6 is fully covered with drainage board, and the outside of the drainage board is wrapped with filter geotextile to prevent fine particles of filler from blocking the drainage channel and quickly drain the seepage water behind the wall; a bottom drainage ditch is set along the bottom of the pile mattress layer 34 to collect the seepage water above the pile-net composite bearing system; drainage holes are reserved at the bottom of the precast wall and are connected to the drainage board. The accumulated water is discharged through the drainage holes to the side ditch on the outside of the roadbed, continuously reducing the pore water pressure inside the fill body and soft soil.

[0035] This application provides a construction method for a pile-mesh reinforced retaining wall structure for widening existing highways on soft soil foundations, employing the following technical solution: S1. Surveying and setting out: Using surveying equipment, delineate the excavation range of the soft soil, pile positions, outer segmented wall 6 and composite waterproofing and drainage system 10, set up control lines, set up elevation control piles, and simultaneously install pile positions, grid laying, and wall positioning construction auxiliary components. S2. Soft soil foundation excavation and leveling: Sectional excavation and cleaning of the surface silt, miscellaneous fill and other soft soil in the widening area, replacement with permeable granular material and compaction in layers to form the soft soil foundation excavation and leveling area 2 in the widening area. S3, Pile 31 Construction: Construct pile 31 according to the design points. After construction, verify the pile position, test the pile quality, and perform leveling pretreatment on the pile top. S4. Construction of the pile-net composite bearing system: A pile cap 32 is cast in place at the top of each pile. A geogrid 33 is continuously laid on the top surface of the pile cap 32 near the pile cap. The inter-pile cushion layer 34 is filled in layers and compacted to form a continuous tension network. The pile-soil load is redistributed by the tensile membrane effect to reduce the differential settlement between piles. S5. Excavation of existing roadbed steps: The existing roadbed is excavated in stages to widen the side slope and form multiple steps. After the loose soil on the step surface is cleared, an interface geogrid is laid. The interface geogrid extends outward to the widened area to form a transition connection section. S6. Layered reinforced filling: The subgrade fill material is laid in layers above the pile-net composite bearing system. Reinforcing material is laid on the outer edge of each layer and folded back and compacted on the outer side of the block wall 6. Layer by layer construction forms a continuous reverse-wrap reinforced structure 5. S7. Installation of the outer segmented wall panel 6: The precast wall blocks are hoisted in stages according to the height of the roadbed filling. The outer segmented wall panel 6 is assembled by connecting pins and interlocking slots to correct the longitudinal alignment and verticality of the wall. S8. Construction of the tie-bar system: Lay tie-bar geogrid 8 according to the designed floor height. The two ends of the tie-bar geogrid 8 are clamped and fixed to the back of the outer segmented wall 6 by connecting and coordinating components 9. After applying the initial pretension by rotating the turnbuckle 92, lock it. When the new and old roadbeds experience differential settlement during the operation phase, the connecting and coordinating components 9 release the node constraints, allowing the tie-bar geogrid 8 to slip slightly and adaptively adjust the tension, continuously constraining the lateral deformation of the wall. S9. Composite waterproofing and drainage construction: A top waterproof layer is laid on the top surface of the roadbed, and drainage boards are pasted on the back of the outer segmented wall 6 and wrapped with a filter layer. Bottom drainage blind ditch is laid at the bottom of the mattress layer, and drainage holes are reserved on the outer segmented wall 6 to connect with the drainage channel. The top waterproof layer is arranged to fit the cross slope of the road drainage. The drainage boards and bottom drainage blind ditch are interconnected to form a complete drainage channel, reducing the adverse effects of water infiltration on the soft soil foundation and the strength of the reinforced grid interface. S10. Finishing and shaping: Cast the top capping component 7 on site, cast and shape the top surface of the roadbed, connect with the existing road structure layer, remove temporary supports, positioning components and other construction auxiliary components to complete the overall construction.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A pile-mesh reinforced retaining wall structure for widening existing highways on soft soil foundations, characterized in that, include In the existing stepped connection zone of the roadbed, multiple steps are excavated to construct a composite connection interface between the old and new roadbeds with interlocking steps. The soft soil foundation excavation and leveling area in the widening zone is located on the soft soil foundation outside the existing roadbed. The pile-supported foundation treatment structure is located in the soft soil foundation excavation and leveling area of ​​the widening zone. It is composed of pile body, pile cap, geogrid near the pile cap, and inter-pile cushion layer to form a pile-net composite bearing system, which transfers the upper load to the deep stable soil layer. The upper widening roadbed reinforced fill is located above the soft soil foundation excavation and leveling area of ​​the widening area, and is connected to the existing roadbed stepped connection area through steps. Interface geogrids are laid at the steps, and the interface geogrids are folded back layer by layer to wrap the fill material to form a reverse wrapping reinforcement structure to restrain lateral deformation. The outer segmented wall is located at the outer edge of the upper widened roadbed reinforced fill to provide lateral support; The top capping component is located at the top of the outer segmented wall surface; Multiple tension geogrids are installed, all located within the upper widened roadbed reinforced fill. Their two ends are connected to the outer segmented walls on both sides, forming a transverse tension limiting system. Connecting and coordinating components are assembled between the tensioned geogrid and the outer segmented wall surface to adjust the tension of the tensioned geogrid. The composite drainage and waterproofing system is arranged on the top of the reinforced fill of the widened roadbed, on the back of the outer segmented wall, and above the pile-net composite load-bearing system.

2. The pile-mesh reinforced retaining wall structure for widening existing highways on soft soil foundations according to claim 1, characterized in that, The pile body is one of the following: precast pile, pipe pile, cement-soil mixing pile, concrete cast-in-place pile, plain concrete pile. Multiple pile bodies are arranged in a rectangular or quincunx pattern, and the outer side of the block-type wall and the transition area between the old and new roadbeds are densely arranged. The geogrid near the pile cap is continuously laid across the adjacent pile cap.

3. The pile-mesh reinforced retaining wall structure for widening existing highways on soft soil foundations according to claim 1, characterized in that, The pile-interlocking cushion layer is constructed using graded crushed stone, gravel, or permeable sand, and is laid on top of the pile cap and the geogrid near the pile cap. The pile-interlocking cushion layer is connected to the bottom drainage channel of the composite drainage system located above the pile-net composite bearing system.

4. The pile-mesh reinforced retaining wall structure for widening existing highways on soft soil foundations according to claim 1, characterized in that, The reverse-wrapping reinforcement structure is made of geogrid and composite reinforcement strips laid in layers. Each layer of composite reinforcement strips is folded back and compacted to the outer side of the segmented wall to form a continuous wrapped reinforcement body.

5. A reinforced retaining wall structure with pile mesh for widening existing highways on soft soil foundations according to claim 1, characterized in that, The outer segmented wall is composed of multiple prefabricated wall panels assembled longitudinally and vertically along the road. Adjacent prefabricated wall panels are connected by connecting pins, insertion slots, or back connecting rings.

6. A reinforced retaining wall structure with pile mesh for widening existing highways on soft soil foundations according to claim 1, characterized in that, The composite waterproofing and drainage system includes a top waterproof layer to prevent rainwater infiltration, a drainage board to guide and drain seepage, a filter layer to prevent the loss of fine particles from the filler, a bottom drainage ditch, and wall drainage components.

7. A construction method for a pile-mesh reinforced retaining wall structure for widening an existing highway on soft soil foundation, based on any one of claims 1-6, characterized in that, Includes the following steps, S1. Surveying and setting out: Delineate the excavation range of the expanded soft soil, pile positions, control lines for the outer segmented wall and composite waterproofing and drainage system; S2. Soft soil excavation and leveling: Clear the surface soft soil of the widened area, replace and compact it to form the soft soil foundation excavation and leveling area of ​​the widened area. S3. Pile construction: Construct piles according to the design spacing, verify the pile positions and complete the pretreatment of the pile tops; S4. Construction of pile-net composite bearing system: Install pile caps on the pile tops, continuously lay geogrids near the pile caps, fill the inter-pile cushion layer in layers, and form a pile-net composite bearing system. S5. Excavation of existing roadbed steps: The existing roadbed is excavated in stages to form multiple steps on the widening side. Interface geogrids are laid on the step surface and extended to the widening area to form a transition connection section. S6. Layered reinforced filling: The subgrade fill material is layered on top of the pile-net composite bearing system. The outer edge of each layer is compacted towards the wall side by interface geogrid and reinforcement material to form a reverse-wrapped reinforced structure. S7. Segmented wall installation: The outer segmented wall is hoisted and assembled step by step as the filling height increases, and the wall alignment and verticality are corrected. S8. Construction of the tension system: Lay tension geogrid and fix it to the outer segmented wall surface by connecting and coordinating components; S9. Composite waterproofing and drainage construction: Lay a waterproof layer on the top of the roadbed, install drainage boards and filter layers, and lay bottom drainage blind ditches and drainage outlets. S10. Finishing and shaping: Cast the top capping components of the wall, cast and shape the top surface of the roadbed, connect with the original road surface, and remove temporary construction components.

8. A reinforced retaining wall structure for widening existing highways on soft soil foundations according to claim 7, characterized in that, In step S4, the geogrid near the pile cap is continuously laid across adjacent pile caps, and the inter-pile cushion layer is rolled and fixed to the geogrid in layers to form a continuous tension network. The pile-soil load is redistributed by the tensile membrane effect, reducing the differential settlement between piles.

9. A reinforced retaining wall structure with pile mesh for widening existing highways on soft soil foundation as described in claim 7, characterized in that, In step S8, an initial preload is applied to the tension geogrid. When the new and old roadbeds experience differential settlement during the highway operation phase, the connecting and coordinating components release the node constraints, allowing the tension geogrid to slip slightly and adaptively adjust the tension, continuously constraining the lateral deformation of the wall.

10. A reinforced retaining wall structure for widening existing highways on soft soil foundations according to claim 7, characterized in that, In step S9, the top waterproof layer is laid in line with the road surface drainage cross slope, and the drainage board and bottom drainage blind ditch are interconnected to form a complete drainage channel, reducing the adverse effects of water infiltration on the soft soil foundation and the interface strength of the reinforced grid.

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