A backfill soil composite foundation structure

Abstract

This utility model provides a backfill soil composite foundation structure, relating to the field of foundation treatment technology. It includes an array of bored piles, with the pile tips penetrating deep into a stable bearing layer. Grouting reinforcement zones are provided between and around the piles via grouting holes. A cushion layer is laid on top of the bored piles and the grouting reinforcement zones, and a concrete cushion layer is laid on top of the cushion layer. A retaining wall is poured on top of the concrete cushion layer, and backfill is provided behind the retaining wall. Vertically spaced clay waterproofing layers are provided in the backfill. By setting up the bored piles and grouting reinforcement zones, the bored pile tips penetrate deep into the stable bearing layer, providing the main vertical bearing capacity and resistance to horizontal thrust. The grouting reinforcement zones strengthen the soil between and around the piles, allowing the piles and soil to share the load, effectively improving the integrity and bearing capacity of the foundation and solving the problem of poor bearing capacity in backfill soil foundations.

Description

Technical Field

[0001] This utility model relates to the technical field of foundation treatment, specifically to a backfill soil composite foundation structure. Background Technology

[0002] After mining operations are completed, high retaining walls are often built on the backfill soil of the mining area to meet site usage requirements. However, the composition of the backfill soil is complex and the bearing capacity is poor, which cannot meet the requirements of the high retaining wall. Therefore, it is necessary to treat the backfill soil of the site for foundation treatment.

[0003] Conventional foundation treatment methods, such as replacement layer and dynamic compaction, have limited effectiveness in reinforcing deep soft soil foundations. Furthermore, uneven energy transfer can lead to uneven settlement of the retaining wall, resulting in instability and cracking, posing significant safety hazards. Existing composite foundation treatment technologies also have limitations when used alone, failing to guarantee effective foundation deformation control and sufficient shear strength. For example, grouting cannot ensure uniform foundation reinforcement, and bored piles can result in weak overall shear resistance of the foundation.

[0004] Therefore, this utility model provides a backfill soil composite foundation structure. Utility Model Content

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a backfilled soil composite foundation structure.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a backfill soil composite foundation structure, comprising drilled cast-in-place piles arranged in an array, wherein the pile ends of the drilled cast-in-place piles penetrate into the stable bearing layer, and grouting reinforcement zones are provided between the piles and around the piles through grouting holes.

[0007] A mattress layer is laid on top of the bored pile and the grouting reinforcement area, a concrete cushion layer is laid on top of the mattress layer, and a retaining wall is poured on top of the concrete cushion layer;

[0008] Behind the retaining wall, there is backfill soil, and in the backfill soil, there are clay waterproof layers arranged at vertical intervals.

[0009] Drilled cast-in-place piles, with their ends penetrating deep into the bearing stratum, directly transfer the superstructure load to a deeper, stable stratum compared to traditional foundations relying solely on loose backfill. This completely avoids foundation settlement and tilting issues caused by backfill compression deformation, significantly increasing the overall load-bearing capacity of the structure. By setting up grouting reinforcement zones between and around the piles, the originally loose backfill soil is consolidated into a high-strength cement-soil mixture. This fills the strength difference between the soil between the piles and the cast-in-place piles, preventing pile damage caused by localized stress concentration. The piles and the reinforced soil between them form a composite load-bearing system, jointly bearing the superstructure load and improving the overall stiffness and deformation resistance of the foundation. The top cushion layer and concrete pad form a double buffer and transfer layer, further balancing the stress differences between the piles and the soil, reducing localized impacts during load transfer. The concrete pad protects the cushion layer from subsequent construction damage and evenly distributes the retaining wall load to the composite foundation, preventing uneven stress caused by localized damage to the pad. Setting up vertically spaced clay waterproofing layers in the backfill behind the wall can specifically block the path of groundwater vertical infiltration along the backfill, reduce the soaking of the backfill by groundwater, prevent the backfill from softening and reducing its strength, and at the same time reduce the lateral thrust of groundwater pressure on the back of the retaining wall, protect the stability of the retaining wall structure, and extend the overall service life of the foundation.

[0010] In a preferred embodiment, the retaining wall is a reinforced concrete structure, and the retaining wall has drainage holes arranged in a quincunx pattern, with a filter bag installed on each drainage hole.

[0011] The technical advantages of adopting the above-mentioned further solutions are as follows: The retaining wall is a reinforced concrete structure. Compared with ordinary plain concrete retaining walls, reinforced concrete can effectively resist the load transmitted by the composite foundation and the lateral pressure of the backfill soil behind the wall, reducing the risk of cracking and overturning of the retaining wall due to excessive stress. The quincunx-shaped arrangement of drainage holes can form multi-point decentralized drainage, quickly draining the water accumulated in the backfill soil behind the wall due to rainfall and groundwater infiltration, avoiding the superposition of lateral water pressure and backfill pressure caused by water accumulation, which could lead to displacement and deformation of the retaining wall; at the same time, the drainage of accumulated water can prevent the backfill soil from softening due to long-term soaking, ensuring the strength stability of the backfill soil behind the wall. The filter bags installed on the drainage holes can play a filtering role, preventing fine soil particles in the backfill soil from entering the drainage holes with the water flow, avoiding blockage of the holes and drainage failure, solving the problem that traditional drainage holes are prone to losing their drainage function due to soil particle accumulation, and ensuring the long-term stable operation of the retaining wall drainage system.

[0012] In a preferred embodiment, a permeable sand and gravel layer with a thickness of 1m is provided between the retaining wall and the backfill.

[0013] The technical advantages of adopting the above-mentioned further solution are as follows: The 1m thick permeable gravel layer has the characteristics of large pores and high permeability, which can serve as a concentrated water-conducting layer for water accumulation behind the wall. Water in the backfill soil behind the wall can quickly permeate into the permeable gravel layer and then be discharged through the drainage holes. Compared with relying solely on drainage holes to directly absorb water from the backfill soil, the drainage speed is greatly improved, reducing the time that water stays behind the wall. The permeable gravel layer can form a continuous and uniform permeable space along the back of the retaining wall, allowing water accumulation in different locations behind the wall to be collected through the permeable layer and discharged through the drainage holes. This avoids local water accumulation dead zones caused by uneven permeability of the backfill soil, further reducing the impact of local water pressure on the retaining wall and ensuring uniform stress on the retaining wall.

[0014] In one preferred embodiment, the mattress layer is composed of graded sand and gravel material with a thickness of 300-600 mm. The crushed stone particle size of the graded sand and gravel material is 5-20 mm, and the sand is medium to coarse sand.

[0015] The technical advantages of adopting the above-mentioned further solutions are as follows: the graded sand and gravel can provide load-bearing capacity through the interlocking of particles, while also possessing moderate flexibility, allowing for slight deformation under load. This balances the settlement difference between the bored pile and the reinforced soil between the piles, avoiding stress concentration caused by rigid contact and protecting the pile body and the cushion layer itself. The thickness range of 300-600mm can be flexibly adjusted according to the actual upper load of the project. A smaller thickness is selected for smaller loads, and a larger thickness is selected for larger loads, enhancing the buffering and stress balance capabilities and avoiding the problems of insufficient buffering due to an excessively thin cushion layer and reduced load transfer efficiency due to an excessively thick layer.

[0016] In a preferred embodiment, the stabilizing bearing layer is a weathered rock layer or a dense sand and gravel layer.

[0017] The technical advantages of adopting the above-mentioned further solutions are as follows: Weathered rock layers and dense sand and gravel layers can prevent the misidentification of loose soil layers and weak interlayers as bearing layers during construction, which could lead to excessive settlement at the pile tips and overall instability of the foundation, thus ensuring the stability and reliability of the borehole pile bearing foundation. Compared to loose soil layers, weathered rock layers and dense sand and gravel layers have high compression modulus and minimal settlement. After the borehole piles penetrate into these strata, the subsequent settlement at the pile tips can be significantly reduced, thereby controlling the total settlement of the entire composite foundation, preventing retaining wall cracking and displacement due to foundation settlement, and ensuring the long-term performance of the structure.

[0018] In a preferred embodiment, the clay waterproof layer is a rammed clay waterproof layer, which is set at vertical intervals of 4m, has a thickness of 0.6m, and extends to the top of the reinforced concrete retaining wall.

[0019] The technical advantages of adopting the above-mentioned further solutions are as follows: After compaction, the rammed clay has low porosity and extremely poor permeability, significantly improving its water-tightening effect compared to ordinary loose clay. This effectively blocks vertical groundwater seepage and prevents water-tightening failure caused by loose clay. A 4m vertical interval ensures that groundwater is frequently blocked during seepage, preventing the formation of long, continuous seepage paths. A 0.6m thickness reduces clay usage and lowers project costs while maintaining water-tightness, avoiding seepage leaks due to excessive intervals and resource waste due to excessive thickness. The clay water-tight layer extends to the top of the retaining wall, covering the entire height of the backfill behind the wall, forming a full-height vertical seepage barrier. This prevents top seepage due to the water-tight layer not reaching the top, blocks vertical seepage paths in the backfill behind the wall, and protects the stability of the entire structure behind the wall.

[0020] In a preferred embodiment, the grouting reinforcement zone covers the area of ​​the bored pile group in the horizontal direction, and the grouting reinforcement zone covers the area below the top of the bored pile in the depth direction. The grouting holes in the grouting reinforcement zone are arranged in an isosceles triangular quincunx pattern with a spacing of 2m, and the hole depth is 13m.

[0021] The technical advantages of adopting the above-mentioned further scheme are as follows: the grouting reinforcement zone horizontally covers the area of ​​the cast-in-place pile group and deeply covers the area below the pile top, ensuring that the soil between all cast-in-place piles and around the piles is reinforced, avoiding unreinforced areas due to insufficient reinforcement range, and ensuring uniform overall foundation stiffness. The isosceles triangular quincunx arrangement allows the grouting holes to be evenly distributed on the horizontal plane, enabling the cement grout to diffuse more evenly into the soil between the piles during grouting, avoiding local soil areas not being penetrated by grout due to uneven hole placement, ensuring consistent strength of the reinforced soil between the piles, and reducing the risk of uneven stress. The 2m hole spacing ensures that the grout diffusion range overlaps, avoiding unreinforced areas; the 13m hole depth ensures that the reinforcement depth covers the main stress-bearing soil layer below the pile top, improving the strength of deep soil, avoiding compression deformation of the lower soil due to insufficient reinforcement depth, and further ensuring the overall stability of the composite foundation.

[0022] This utility model provides a backfill soil composite foundation structure. It has the following beneficial effects:

[0023] This utility model sets up bored cast-in-place piles and grouting reinforcement zones. The pile ends of the bored cast-in-place piles penetrate deep into the stable bearing layer, providing the main vertical bearing capacity and resistance to horizontal thrust. The grouting reinforcement zone strengthens the soil between and around the piles, so that the piles and soil share the load, effectively improving the integrity and bearing capacity of the foundation and solving the problem of poor bearing capacity of backfilled soil foundations.

[0024] The installation of the cushion layer and concrete pad layer can regulate the stress in the pile and soil, evenly transfer the load, prevent stress concentration in the pile, avoid cracking of the retaining wall foundation, and effectively control foundation deformation. The clay waterproof layer, drainage holes, and sand and gravel permeable layer behind the retaining wall work together to prevent groundwater infiltration, quickly drain water accumulated behind the wall, reduce the impact of water pressure on the retaining wall, and further ensure the stability of the retaining wall.

[0025] Therefore, it is suitable for the construction of ultra-high retaining walls on deep soft soil foundations such as mine backfill soil, with high reliability and good application prospects. Attached Figure Description

[0026] Figure 1 A structural schematic diagram of a backfill soil composite foundation structure provided by this utility model;

[0027] Figure 2 This is a top view of a backfilled soil composite foundation structure provided by this utility model.

[0028] Legend:

[0029] 1. Drilled pile; 2. Grouting hole; 3. Cushion layer; 4. Concrete cushion layer; 5. Retaining wall; 6. Grouting reinforcement zone; 7. Clay waterproof layer; 8. Sand and gravel permeable layer; 9. Drainage hole. Detailed Implementation

[0030] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0031] This embodiment provides a construction and application of an ultra-high retaining wall composite foundation structure for backfill areas in mines. Through the synergistic effect of bored piles 1, grouting reinforcement zone 2, cushion layer 3, concrete cushion layer 4, and retaining wall 5, the problem of poor bearing capacity and large deformation of backfill foundation is solved, providing stable support for the high retaining wall 5.

[0032] like Figure 1As shown, this embodiment provides a technical solution: a backfill soil composite foundation structure, including multiple bored piles 1 arranged in a rectangular array and grouting reinforcement zones 6 formed between and around the piles through grouting holes 2. A cushion layer 3, composed of graded sand and gravel, is laid on top of the bored piles 1 and the grouting reinforcement zones 6. A concrete cushion layer 4 is laid on top of the cushion layer 3, and a retaining wall 5, a reinforced concrete structure, is poured on top of the concrete cushion layer 4. The wall is filled with backfill soil; the pile tip of the bored pile 1 is inserted into the stable bearing layer (weathered rock layer or dense sand and gravel layer); the grouting reinforcement zone 6 is formed between and around the bored pile 1 through the grouting hole 2, which is used to strengthen the soil strength between and around the pile; a clay water-proof layer 7 is set vertically at intervals in the backfill soil behind the wall. The clay water-proof layer 7 is a rammed clay water-proof layer, and drainage holes 9 are arranged in a plum blossom pattern on the retaining wall 5. The drainage holes 9 are equipped with filter bags. A sand and gravel permeable layer 8 is set between the retaining wall 5 and the backfill soil behind the wall.

[0033] The above construction method is as follows: Figure 1-2 As shown: Drilled piles 1 are arranged in a rectangular array. The piles within the retaining wall heel slab area are located directly below each buttress, with a pile spacing of 2-3 times the pile diameter. Ensure the pile tip of each drilled pile 1 penetrates at least 2m into the underlying stable bearing layer. Reinforcement is continuous along the pile length. The pile diameter is 800mm below the buttress and increases to 1000mm near the wall panel to accommodate different stress conditions. Grouting holes 2 are arranged in an isosceles triangular quincunx pattern between and around the drilled piles 1, with a spacing of 2m and a depth of approximately 13m. The stress is greater below the retaining wall panel and toe slab, so the grouting holes 2 are more densely spaced at 1.5m intervals. Ordinary Portland cement of grade 32.5 or higher is used, with a water-cement ratio of 0.5-1.0. Initially, a grout with a water-cement ratio of 1.0 is used, which can be adjusted according to site conditions. If necessary, a cement and water glass dual-slurry should be used. The water glass should have a Baume degree of 35-40 Be and a modulus of 2.8-3.2. The volume ratio of cement slurry to water glass should be 1:0.5-1. The grouting pressure should be 1.0-7.0 MPa. When using a cement-water glass dual-liquid fast-setting grout, the grouting pressure should not exceed 1.0 MPa. The pressure should be controlled to avoid ground heave. If necessary, dispersed grouting can be adopted. A drilling, single-pipe forward-advancing segmented method should be adopted, advancing layer by layer and row by row from top to bottom and from outside to inside. The drilling diameter is 75 mm, the opening diameter is 110 mm, and the borehole pipe with a diameter of 89 mm and a length of 1.2 m is installed. The grouting pipe diameter is 42 mm, and the allowable deviation of verticality is ±1%. The grouting reinforcement zone 6 formed after grouting covers the group area of ​​the drilled piles 1 in the horizontal direction and covers a certain depth below the pile top in the depth direction, so that the loose fill between and around the piles is consolidated into a high-strength cement-soil body.

[0034] After pile driving and grouting are completed, the laitance at the top of the bored pile 1 is removed, and the soil between the piles at the pile top elevation is excavated to the design elevation to form a working surface. Then, a 300mm thick cushion layer 3 is laid. The cushion layer is composed of graded sand and gravel material, with crushed stone with a particle size of 5-20mm and medium-coarse sand. The cushion layer extends 400mm beyond the subsequent concrete cushion layer on each side to ensure that the pile and soil share the load and prevent stress concentration in the pile.

[0035] A 100mm thick concrete pad 4 is laid on top of the mattress layer 3, extending 100mm beyond the bottom slab of the retaining wall 5 on each side. This serves to protect the mattress layer 3 and evenly distribute the load. The retaining wall 5 is a reinforced concrete structure, with a reinforced concrete raft foundation located on top of the concrete pad 4. It is constructed according to the design drawings on the reinforced foundation. Drainage holes 9, with a diameter of 100mm, are arranged in a staggered pattern at 2m x 2m intervals on the retaining wall 5, starting 0.5m from the ground and extending to the top. A filter bag is installed behind the drainage holes to prevent soil particles from clogging them.

[0036] A 1m thick permeable sand and gravel layer 8 is installed at the top of the retaining wall 5 to quickly drain the water behind the wall; a 0.6m thick compacted clay waterproof layer 7 is installed vertically at 4m intervals behind the retaining wall up to the top to prevent groundwater infiltration; and permeable materials are used on the back of the wall.

[0037] Expansion joints are provided every 15m along the retaining wall 5, located at 1 / 3 of the distance between the two buttresses to accommodate temperature changes and minor foundation deformations.

[0038] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. It will be apparent to those skilled in the art that this utility model is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or basic characteristics of this utility model. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of this utility model is defined by the appended claims rather than the foregoing description, and thus all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this utility model. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0039] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A backfilled soil composite foundation structure, comprising an array of bored cast-in-place piles (1), characterized in that, The pile tip of the bored pile (1) is inserted into the stable bearing layer, and the piles of the bored pile (1) are provided with grouting reinforcement zones (6) through grouting holes (2). A mattress layer (3) is laid on top of the bored pile (1) and the grouting reinforcement area (6), a concrete mattress layer (4) is laid on top of the mattress layer (3), and a retaining wall (5) is poured on top of the concrete mattress layer (4). Behind the retaining wall (5) is backfill soil, and in the backfill soil are vertically spaced clay waterproof layers (7).

2. The backfill soil composite foundation structure according to claim 1, characterized in that: The retaining wall (5) is a reinforced concrete structure, and the retaining wall (5) is provided with drainage holes (9) arranged in a plum blossom pattern, and the drainage holes (9) are provided with filter bags.

3. The backfill soil composite foundation structure according to claim 2, characterized in that: A permeable sand and gravel layer (8) is provided between the retaining wall (5) and the backfill soil, and the thickness of the permeable sand and gravel layer (8) is 1m.

4. The backfill soil composite foundation structure according to claim 1, characterized in that: The mattress layer (3) is composed of graded sand and gravel material with a thickness of 300-600 mm. The crushed stone particle size of the graded sand and gravel material is 5-20 mm, and the sand is medium-coarse sand.

5. The backfill soil composite foundation structure according to claim 1, characterized in that: The stable bearing layer is a weathered rock layer or a dense sand and gravel layer.

6. The backfilled soil composite foundation structure according to claim 1, characterized in that: The clay waterproof layer (7) is a rammed clay waterproof layer. The vertical spacing of the clay waterproof layer (7) is set to 4m, the thickness is 0.6m, and it extends to the top of the retaining wall (5).

7. The backfill soil composite foundation structure according to claim 1, characterized in that: The grouting reinforcement zone (6) covers the area of ​​the bored pile (1) group in the horizontal direction, and the grouting reinforcement zone (6) covers the area below the top of the bored pile (1) in the depth direction. The grouting holes (2) of the grouting reinforcement zone (6) are arranged in an isosceles triangular quincunx pattern with a spacing of 2m and a hole depth of 13m.

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