A method for treating silt soft soil foundation based on a synergistic reinforcement mechanism

Abstract

The present application relates to the technical field of silt soft soil foundation treatment, and discloses a silt soft soil foundation treatment method based on a synergistic reinforcement mechanism, which comprises three main construction procedures of rigid core area construction, pile-surrounding transition area construction and surface layer reinforcement area construction; the pile-surrounding transition area construction is started after the concrete of the cast-in-place pile reaches 1MPa in the initial setting stage and is completed before the final setting of the concrete of the cast-in-place pile. Through the innovative structural design and the accurate process timing, the present application realizes the deep synergy between the cast-in-place pile and the high-pressure jet grouting, and significantly improves the overall rigidity, bearing capacity and anti-uniform settlement capacity of the foundation.

Description

Technical Field

[0001] This invention relates to the field of silty soft soil foundation treatment technology, specifically, to a silty soft soil foundation treatment method based on a synergistic enhancement mechanism. Background Technology

[0002] Silt-rich soft soil foundations have fine particles and a high porosity, making them prone to significant settlement and deformation under external loads. This can lead to uneven foundation settlement and structural cracking. Furthermore, water is difficult to drain, resulting in a slow consolidation process. Improper handling during construction can lead to prolonged instability, impacting project progress and safety. Under load or over time, the soil is susceptible to creep, causing later-stage settlement to exceed design expectations and affecting structural durability. Existing foundation treatment technologies often employ single reinforcement methods, making it difficult to simultaneously improve strength and control deformation, leading to stress concentration or uneven reinforcement.

[0003] Cast-in-place piles are a common method for treating this type of foundation, but when used alone, they suffer from low side friction resistance in the soft soil surrounding the pile and are prone to problems such as necking and borehole collapse. Existing technologies attempt to improve foundation performance through combined processes.

[0004] Chinese invention patent CN105064331A discloses a method for first performing high-pressure jet grouting in peat soil to form a solidified body, and then constructing cast-in-place piles, aiming to improve the quality of hole formation and control the concrete filling coefficient. However, this method involves sequential grouting and pile formation, resulting in insufficient synergy in their mechanical properties, and it does not optimize the pile body itself.

[0005] Chinese invention patent CN106836204A discloses a device and method for grouting and reinforcing the soil around a pile using a rotatable three-way nozzle to improve the pile's side friction. However, the grouting is completed before pile formation, failing to take advantage of the optimal bonding time during the hydration process of the pile concrete, and the bonding strength between the reinforced area and the pile needs to be improved.

[0006] Chinese invention patent CN115305905A discloses a method for reinforcing soft interlayers in foundations in conjunction with pile foundation construction, employing post-grouting technology to treat deep soft interlayers. However, the grouting operation is carried out after the pile body is fully formed, making it difficult for the grout to form an effective interlocking and bonding with the pile body, and the process is complex and time-consuming.

[0007] In summary, existing technologies have failed to effectively address the synergistic effect of cast-in-place piles and high-pressure grouting reinforcement in time and space, making it difficult to achieve a smooth transition from rigid piles to soft soil. Consequently, there is still considerable room for improvement in the integrity, bearing capacity, and settlement resistance of composite foundations. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a silty soft soil foundation treatment method based on a synergistic enhancement mechanism. Through innovative structural design and precise process timing, it achieves deep synergy between cast-in-place piles and high-pressure jet grouting, significantly improving the overall stiffness, bearing capacity and resistance to uneven settlement of the foundation.

[0009] This invention provides a method for treating silty soft soil foundation based on a synergistic enhancement mechanism, which includes three main construction procedures: rigid core zone construction, pile perimeter transition zone construction, and surface reinforcement zone construction.

[0010] During the construction of the rigid core area, the drilling and grouting process is used to drill grouting holes 21 in the soft soil, install steel casings, put in steel cages, and pour concrete to form cast-in-place piles; the construction of the pile perimeter transition zone is started at the initial setting stage of the cast-in-place pile concrete and after the cast-in-place pile strength reaches 1MPa, and is completed before the final setting of the cast-in-place pile concrete.

[0011] During the construction of the pile perimeter transition zone, high-pressure jet grouting technology is used to drill jet grouting holes 31 around the cast-in-place pile and perform high-pressure jet grouting to form a composite pile on the cast-in-place pile foundation; after the composite pile has solidified, the surface reinforcement zone construction is carried out.

[0012] During the construction of the surface reinforcement zone, a plain concrete cushion layer incorporating basalt fiber mesh is laid on the soft soil surface.

[0013] To better realize the present invention, further, when constructing the rigid core area, the steel cage placed into the grouting hole 21 is a variable cross-section steel cage with an enlarged end at the bottom; the diameter of the enlarged end is 1.1 to 1.25 times the diameter of the upper part of the steel cage.

[0014] To better realize the present invention, the height of the enlarged end is not less than 5 times the enlarged diameter value and does not exceed 1 / 4 of the total height of the steel cage.

[0015] To better realize the present invention, the rigid core area is further constructed by using concrete with a water-cement ratio of 0.5 to 0.6 for grouting. The construction of the pile perimeter transition area is started 4 to 6 hours after the grouting is completed.

[0016] To better realize the present invention, the steel casing is further provided to be 300-500mm above the soft soil surface.

[0017] To better realize the present invention, further, during the construction of the pile perimeter transition zone, a set of circumferentially distributed jet grouting holes 31 are drilled around each cast-in-place pile using a drilling rig, and after the grouting pipe is inserted, the high-pressure equipment is started to perform high-pressure jet grouting.

[0018] Let: the diameter of injection hole 21 be D1, the diameter of jet nozzle 31 be D2, the distance between the central injection hole 21 and the outer jet nozzle 31 be L1, the distance between two adjacent jet nozzles 31 in the same group be L2, and the distance between two adjacent injection holes 21 be L3; let: the safety margin be S; satisfy: D1>D2, L2=(1.1~1.3)D2, L3=(2.5~6)L1, L1=D1 / 2+D2 / 2+S and S=50~200mm.

[0019] To better realize the present invention, further, during high-pressure jet grouting, the grouting pipe is controlled to rotate and rise from the bottom to the top edge of the jet grouting hole 31 while the grouting pressure decreases, so that the cement grout forms a distribution characteristic of being thick at the bottom and thin at the top.

[0020] To better realize the present invention, further, during high-pressure rotary jet grouting, the grouting pressure decreases linearly from 40MPa to 20MPa.

[0021] To better realize the present invention, further, during high-pressure rotary jet grouting, the lifting speed of the grouting pipe is 10~25cm / min and the rotation speed is 10~20r / min.

[0022] To better realize the present invention, further, when constructing the surface reinforcement zone, the thickness of the plain concrete cushion layer is 100~300mm, in which a micro pressure box (1) is pre-embedded, and the amount of basalt fiber is 0.8~1.0kg / m³.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects.

[0024] (1) The present invention discloses a method for treating silty soft soil foundation based on a synergistic enhancement mechanism. The silty soft soil foundation is divided into zones for construction. Through the synergistic effect of the pile bearing zone, the pile perimeter transition zone and the surface reinforcement zone, the vertical stiffness gradient distribution and horizontal continuous enhancement are achieved, which effectively improves the stress transmission path and suppresses differential settlement.

[0025] (2) The present invention discloses a method for treating silty soft soil foundation based on a synergistic enhancement mechanism. The construction of the pile bearing zone and the pile transition zone adopts a combined grouting and spraying process. The uneven settlement is suppressed by the grouting piles, and the soil compressibility is improved by the high-pressure jet grouting reinforcement zone, thereby reducing soil creep and effectively controlling foundation settlement.

[0026] (3) The present invention discloses a method for treating silty soft soil foundation based on a synergistic enhancement mechanism, which forms a "pile-soil-cement body" composite structure through a combination process, effectively controlling foundation settlement and improving the side friction resistance of the soil around the pile.

[0027] (4) The present invention discloses a method for treating silty soft soil foundation based on a synergistic enhancement mechanism, which matches the jet grouting parameters with the structural dimensions to ensure that the composite foundation forms an integral load-bearing structure, thereby significantly improving the foundation stability and long-term durability.

[0028] (5) The present invention discloses a method for treating silty soft soil foundation based on a synergistic enhancement mechanism. Using the method for treating silty soft soil foundation based on a synergistic enhancement mechanism disclosed in the present invention can reduce the safety and maintenance costs of construction operations and improve construction efficiency. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the main process of a silty soft soil foundation treatment method based on a synergistic enhancement mechanism in Example 2.

[0030] Figure 2 Hole position arrangement Figure 1 A typical design drawing.

[0031] Figure 3 This is a frontal schematic diagram of the first typical structure of composite piles.

[0032] Figure 4 This is a frontal schematic diagram of the second typical structure of composite piles.

[0033] Figure 5 This is a schematic diagram showing the installation of a steel casing and the insertion of a variable cross-section steel cage in the grouting hole 21 during the construction of the rigid core area of ​​this invention.

[0034] Figure 6 This is a schematic diagram showing the state of cast-in-place piles formed after rigid core zone construction on a silty soft soil foundation.

[0035] Figure 7 To construct a rigid core zone and a pile-perimeter transition zone for the silty soft soil foundation. Figure 3 The diagram shows the state of the composite pile.

[0036] Figure 8 This is a schematic diagram showing the surface reinforcement zone after the construction of the silty soft soil foundation.

[0037] Figure 9 This is a schematic diagram of a variable cross-section steel cage.

[0038] Figure 10 This is a typical schematic diagram of an open drainage ditch.

[0039] Figure 11 This is a displacement cloud diagram of the cast-in-place pile in the first group of schemes in Example 6.

[0040] Figure 12 The results show the settlement monitoring of the foundation surface monitoring points in the first group of schemes in Example 6.

[0041] Figure 13 This is a displacement cloud diagram of the cast-in-place pile in the second group of schemes in Example 6.

[0042] Figure 14 The results show the settlement monitoring of the foundation surface monitoring points in the second group of schemes in Example 6.

[0043] Figure 15 This is a displacement cloud diagram of the cast-in-place pile in the third group of schemes in Example 6.

[0044] Figure 16 The results show the settlement monitoring of the foundation surface monitoring points in the third group of schemes in Example 6.

[0045] Figure 17 This is a displacement cloud diagram of the cast-in-place pile in the fourth group of schemes in Example 6.

[0046] Figure 18 The results show the settlement monitoring of the foundation surface monitoring points in the fourth group of schemes in Example 6.

[0047] Among them: 100, soft soil; 200, composite pile; 300, plain concrete cushion layer;

[0048] 1. Miniature pressure box; 2. Cast-in-place pile; 21. Grouting hole 21; 22. Steel casing; 23. Variable cross-section steel cage; 3. Jet grouting pile; 31. Jet grouting hole 31; 4. Basalt fiber mesh. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0050] Example 1:

[0051] In view of the characteristics of silty soft soil, this embodiment provides a silty soft soil foundation treatment method based on synergistic enhancement mechanism, including three main construction procedures: rigid core zone construction, pile perimeter transition zone construction, and surface reinforcement zone construction.

[0052] During the construction of the rigid core area, the drilling and grouting process is used to drill grouting holes 21 in the soft soil, install steel casing 22, put in the steel cage, and pour concrete to form grouting pile 2; the construction of the pile perimeter transition zone is started at the initial setting stage of the concrete of grouting pile 2 and after the strength of grouting pile 2 reaches 1MPa, and is completed before the final setting of the concrete of grouting pile 2.

[0053] During the construction of the pile perimeter transition zone, high-pressure jet grouting technology is used to drill jet grouting holes 31 around the cast-in-place pile 2 and perform high-pressure jet grouting to form a composite pile 200 on the basis of the cast-in-place pile 2; after the composite pile 200 has solidified, the surface reinforcement zone construction is carried out.

[0054] During the construction of the surface reinforcement zone, a plain concrete cushion layer of 300 mm incorporating basalt fiber mesh 4 is laid on the soft soil surface.

[0055] The silty soft soil foundation treatment method described in this embodiment firstly involves constructing a rigid core zone to form cast-in-place piles 2, which bear the vertical load of the superstructure and transfer it to the deep stable soil layer, thereby suppressing uneven settlement. Secondly, a composite pile 200 is formed by high-pressure jet grouting between the cast-in-place piles 2 and the surrounding soft soil 100 through the construction of the pile perimeter transition zone, which provides auxiliary reinforcement to the cast-in-place piles 2, improves the compressibility of the soil layer, and alleviates soil creep. After the construction of the rigid core zone and the pile perimeter transition zone are completed, a "pile-soil-cement" composite structure is formed, where "soil" refers to soft soil, "pile" specifically refers to bored cast-in-place piles, and "cement" specifically refers to the cement-soil consolidation body formed by high-pressure jet grouting, i.e., the jet grouting piles and their diffusion zone. Then, basalt fiber mesh 4 is implanted into the plain concrete cushion layer 300 through the construction of the surface reinforcement zone, using the bridging effect of the fibers to suppress cracking of the cushion layer. The above treatment method not only solves the foundation settlement problem of silty soft soil foundation, but also improves the surface strength and feasibility, and is especially suitable for high-rise buildings, bridges and other projects with high requirements for settlement control.

[0056] The silty soft soil foundation treatment method described in this embodiment is based on the technical concept of a combined grouting and jet grouting process, achieving a synergistic effect between cast-in-place piles 2 and jet grouting in time and space. Temporally, the construction of the pile perimeter transition zone begins during the initial setting stage of the cast-in-place pile 2 concrete, after the pile 2 reaches a strength of 1 MPa, and is completed before the final setting of the cast-in-place pile 2 concrete; after the pile construction is completed, the surface reinforcement zone construction is carried out. Spatially, the rigid core zone is located in the deep foundation layer, the pile perimeter transition zone surrounds the rigid core zone in a ring shape, forming a composite pile 200 that bears the overall load, and the surface reinforcement zone covers the shallow soft soil 100 of the foundation, forming an integral rigid support layer; the three work synergistically to achieve the step-by-step transfer and diffusion of vertical loads, effectively improving the foundation bearing capacity and controlling post-construction settlement. This synergistic enhancement mechanism significantly improves the overall stability of the foundation through the temporal and spatial coupling of the rigid core zone, the pile perimeter transition zone, and the surface reinforcement zone. On-site monitoring data shows that after the composite pile 200 is formed, the pile-soil stress ratio tends to be uniform, the basalt fiber mesh 4 effectively limits the expansion of surface cracks, and the post-construction settlement is reduced by about 40% compared with the traditional process.

[0057] Compared with existing technologies, the silty soft soil foundation treatment method disclosed in this embodiment is an optimization of the pile-perimeter jet grouting combined reinforcement method. It utilizes cast-in-place pile technology to solve the problems of deep bearing capacity and structural stability, and employs high-pressure jet grouting technology to address the issues of low strength of the soft soil between and around the piles, as well as insufficient surface flatness and bearing capacity, thereby improving the lateral friction resistance of the soil around the piles. In particular, the use of high-pressure jet grouting fundamentally improves the engineering properties of the soil around the piles, transforming weak silt into high-strength cement-soil, and improving the surrounding soil through compaction. This not only changes the object and mode of friction but also increases the effective radius of the pile, and ensures the coordinated work of the pile and the reinforced body through mechanical interlocking and chemical bonding. Ultimately, the traditional, inefficient "pile-soft soil" friction system is upgraded to a highly efficient composite friction system composed of "pile-high-strength cement-soil-compacted reinforced soil," thus significantly improving the lateral friction resistance of the soil around the piles.

[0058] The silt-laden soft soil foundation treatment method described in this embodiment is applicable to silt-laden soft soil foundation treatment scenarios such as coastal alluvial plains and river and lake tidal flats, and has significant advantages, especially for infrastructure projects with high settlement control requirements and tight construction schedules. By optimizing the construction sequence and material ratio, the foundation bearing capacity can be increased by more than 50% without significantly increasing costs, providing a reliable technical approach for engineering construction under complex geological conditions.

[0059] Example 2:

[0060] This embodiment is a further optimized scheme based on Embodiment 1.

[0061] A method for treating silty soft soil foundations based on a synergistic enhancement mechanism, such as Figure 1 As shown, it includes the following steps:

[0062] Step S1: Site pretreatment, and marking the center of injection hole 21 and the center of jet nozzle 31 according to the hole layout diagram;

[0063] Step S2, pile construction; including: rigid core zone construction and pile perimeter transition zone construction;

[0064] Step S3, surface construction; including: surface reinforcement zone construction;

[0065] Step S4, finishing touches complete.

[0066] Before construction, based on the shape and size of the foundation construction area, the diameter and position of the grouting holes 21 and jet grouting holes 31 need to be scientifically designed, and a precise hole layout diagram needs to be drawn, such as: Figure 2A schematic diagram of the borehole layout is provided. The design adheres to the following constraints: the grouting holes 21 are arranged in a quincunx pattern, with 6-12 jet grouting holes 31 evenly distributed around each grouting hole 21. The borehole layout design satisfies: D1 > D2, L2 = (1.1~1.3)D2, L3 = (2.5~6)L1, L1 = D1 / 2 + D2 / 2 + S, and S = 50~200 mm; where D1 is the diameter of the grouting hole 21, D2 is the diameter of the jet grouting hole 31, L1 is the distance between the central grouting hole 21 and the surrounding jet grouting holes 31, L2 is the distance between two adjacent jet grouting holes 31 in the same group, L3 is the distance between two adjacent grouting holes 21, and S is the safety margin. The length of the cast-in-place pile 2 is determined based on the geological survey report, ensuring penetration of the soft soil layer and anchorage in the stable bearing layer.

[0067] The safety margin is determined by considering the following factors: First, drill rod deviation, measurement errors, and formation inhomogeneity mean that the jet grouting hole 31 and the grouting hole 21 cannot be in close contact. Second, the jet grouting flow causes the cement slurry to diffuse around the hole, forming a transition zone. In this embodiment, this transition zone is needed to effectively connect the cast-in-place pile 2 with the jet grouting reinforced body to form an integral load-bearing structure. Therefore, the distance between the jet grouting hole 31 and the grouting hole 21 cannot be too large. Third, in this embodiment, the construction of the transition zone around the pile needs to be completed within the optimal window period after the construction of the rigid core zone to ensure that the cement slurry in the transition zone effectively overlaps and fuses with the concrete of the cast-in-place pile 2. During the initial setting stage, the strength of the cast-in-place pile 2 is relatively low, and it is necessary to prevent high-pressure jetting from disturbing and damaging the cast-in-place pile 2. Therefore, the distance between the jet grouting hole 31 and the grouting hole 21 cannot be too small. In summary, the safety margin needs to comprehensively consider the coupled effects of multiple factors such as pile structure, construction parameters, construction accuracy, formation response, and structural connection strength.

[0068] The central cast-in-place pile 2 is surrounded by six jet grouting piles 3. The diameter of the cast-in-place pile 2 is approximately 600 mm, and the diameter of the jet grouting piles 3 is approximately 500 mm. The safety margin is set at 150 mm. The high-pressure jet grouting cement slurry penetrates into the soil around the piles and diffuses, with the diffusion amount being equivalent to the safety margin. The resulting composite pile 200 structure is as follows: Figure 3 As shown.

[0069] The central cast-in-place pile 2 is surrounded by six jet grouting piles 3. The diameter of the cast-in-place pile 2 is approximately 600 mm, and the diameter of the jet grouting piles 3 is approximately 500 mm. A safety margin of 50 mm is set. The high-pressure jet grouting cement slurry penetrates into the soil around the piles and diffuses. The diffusion exceeds the safety margin, causing them to merge. The resulting composite pile 200 structure is as follows: Figure 4 As shown.

[0070] The site pretreatment in step S1 specifically includes: clearing and leveling the site, and setting up drainage ditches around the perimeter of the piles. The drainage ditches are usually open ditches used to divert surface water into a collection well.

[0071] After marking the center of the grouting hole 21 and the center of the jet grouting hole 31, cast-in-place piles 2 are placed in the silty soft soil foundation using the rigid core zone construction method, and jet grouting piles 3 are placed around each cast-in-place pile 2 using the pile perimeter transition zone construction method. The central cast-in-place pile 2 and the multiple peripheral jet grouting piles 3 together form a set of composite piles 200. It should be noted that the construction of the jet grouting piles 3 starts during the initial setting stage of the cast-in-place pile 2 concrete and after the cast-in-place pile 2 reaches a strength of 1 MPa, and is completed before the final setting stage of the cast-in-place pile 2 concrete. Due to the special timing of the construction of cast-in-place piles 2 and jet grouting piles 3, a concentrated construction method of a set of composite piles 200 is usually adopted to ensure construction quality. Therefore, in the entire silty soft soil foundation treatment method, the rigid core zone construction and the pile perimeter transition zone construction are usually carried out alternately.

[0072] The construction of the rigid core area specifically includes the following steps.

[0073] Step SA1, Drilling the injection hole 21; specifically, this involves selecting a suitable drill bit according to the diameter of the injection hole 21, drilling the hole using a drilling rig according to the designed hole position, adjusting the verticality using a spirit level and plumb bob to ensure that the drilling inclination does not exceed 1%, and drilling to the designed bearing layer depth. A brick drilling rig can be used.

[0074] Step SA2 involves installing a steel casing 22. Specifically, after drilling is completed, a steel casing 22 is installed to prevent the borehole opening from collapsing. Generally, the steel casing 22 extends 300-500mm above the soft soil surface.

[0075] Step SA3, initial hole cleaning; specifically, this refers to cleaning the soil and debris inside the hole to prepare for the subsequent hoisting of the reinforcing cage and pouring of concrete.

[0076] Step SA4, lowering the reinforcing cage; specifically, this refers to lowering the prefabricated variable cross-section reinforcing cage 23 into the hole. The lowering should be stable and accurate, avoiding collision with the hole wall. Figure 10 As shown, the bottom of the variable cross-section steel cage 23 is an enlarged end, and the diameter of the enlarged end is 1.1 to 1.25 times the diameter of the middle part of the steel cage. Preferably, the bottom diameter of the enlarged end is 15% to 20% larger than the top diameter.

[0077] Step SA5, secondary hole cleaning; specifically, after the reinforcement cage is hoisted, a guide pipe is lowered to perform secondary hole cleaning, further cleaning the debris and sediment in the hole to ensure that the cleanliness of the bottom of the hole meets the requirements for concrete pouring.

[0078] Step SA6, concrete pouring; specifically, this refers to pouring underwater concrete into the hole. During the pouring process, the flow rate and pressure of the concrete must be controlled to ensure that the concrete can fill the hole evenly and densely, forming a high-quality cast-in-place pile 2.

[0079] The state after drilling grouting hole 21 in soft soil mass 100, embedding steel casing 22, and hoisting variable cross-section steel cage 23 is as follows: Figure 5 As shown. The state of the cast-in-place pile 2 after concrete pouring is as follows. Figure 6 As shown.

[0080] Construction of the pile perimeter transition zone is carried out around each cast-in-place pile 2, and the construction of the pile perimeter transition zone around each cast-in-place pile 2 must be completed during the initial setting stage of the concrete of that cast-in-place pile 2.

[0081] The construction of the transition zone around the piles specifically includes the following steps.

[0082] Step SB1, Drilling the jet grouting hole 31; specifically, this involves selecting a suitable drill bit based on the diameter of the jet grouting hole 31, drilling according to the designed hole position, moving the drilling rig to the work point, adjusting the base to be level, ensuring the drill rod is vertically aligned with the marked hole position, and drilling to the designed grouting bottom elevation. Typically, the depth of the jet grouting hole 31 is the same as or slightly shallower than the depth of the grouting hole 21.

[0083] When drilling the jet grouting hole 31, in order to prevent the drill bit from accidentally approaching the pile body of the cast-in-place pile 2 at a deep depth and causing damage, it is necessary to use the verticality control system built into the drilling rig to ensure that the verticality deviation of the drill rod is strictly controlled within 1%. If necessary, mud wall protection technology can also be used.

[0084] Step SB2, high-pressure jet grouting; specifically, it refers to starting the high-pressure equipment, using pressure gradient control to rotate and lift the grouting pipe to achieve bottom-up jetting operation. Cement slurry, water, and air form a high-speed jet through the nozzle, ensuring that the jet stream fully cuts the soil. Simultaneously, the drill rod is lifted to force the cement slurry to mix with the damaged soil.

[0085] exist Figure 6 Based on the state shown, jet grouting holes 31 are drilled and high-pressure jet grouting is performed to form jet grouting piles 3 and a transition zone that penetrates into the soil around the piles, as shown in the diagram. Figure 7 As shown.

[0086] Furthermore, PI 42.5 cement and a cement grout with a water-cement ratio of 0.8:1 to 1:1 are used. The grouting pipe is controlled to rotate and rise at a uniform speed from bottom to top, and the grouting pressure is controlled to decrease with the lifting height. The lifting speed of the grouting pipe is generally 10-25 cm / min, the rotation speed is generally 10-20 r / min, and the grouting pressure decreases linearly from 40 MPa to 20 MPa from the bottom to the top of the hole.

[0087] Experiments revealed that when using PI 42.5 cement and a cement grout with a water-cement ratio of 0.8:1 to 1:1 for jet grouting, the final setting strength is 15MPa to 25MPa at a grouting pressure of 40MPa, and 10MPa to 18MPa at a grouting pressure of 20MPa. Considering factors such as the vertical stress difference in soft soil, the final setting strength of the jet grouting pile, the impact of grouting pressure on soil disturbance, and the diffusion range of the cement grout in the soil, this embodiment strictly implements a pressure gradient control strategy during jet grouting. This strategy involves using sensors and a control system built into the grouting pipe to linearly decrease the grouting pressure from 40MPa at the bottom of the hole (deep layer) to 20MPa at the surface (shallow layer).

[0088] For high-pressure jet grouting, PI 42.5 cement can be used, mixed with a water-cement ratio of 1:1 to prepare the cement slurry. After thorough mixing, the slurry should be filtered through a sieve to prevent nozzle clogging. This formula produces a slurry with good fluidity, effectively spraying and filling soil pores under grouting pressures of 20-40 MPa to achieve diffusion. This balances reinforcement effectiveness with minimizing disturbance to adjacent piles, resulting in a cement-soil consolidation body of moderate strength. If necessary, a small amount of water-reducing agent can be added to optimize performance.

[0089] During high-pressure jet grouting, the cement slurry diffuses around the hole to form a transition zone. This transition zone effectively improves the compactness and integrity of the soil, and its diffusion radius can also be described as the thickness of the transition zone.

[0090] First, let's discuss the three individual jet grouting piles. Under the same geological conditions, the thickness of the transition zone decreases with decreasing grouting pressure, exhibiting a frustum-shaped distribution that is smaller at the top and larger at the bottom. This conforms to the pile formation pattern of high-pressure jet grouting piles in the "Foundation Treatment Handbook." This shape is beneficial for the pile to withstand higher loads at depth, enhancing its vertical bearing capacity, reducing lateral stress concentration, avoiding excessive disturbance to adjacent structures, and ensuring the continuity and stability of the reinforced body in soft soil layers. However, the soil composition of silty soft soil foundations varies significantly with depth. Deeper soil layers typically have a stronger structure and relatively higher density, thus increasing the resistance to grout diffusion. This leads to a relatively smaller transition zone thickness, resulting in a deviation from the ideal frustum-shaped distribution of the three jet grouting piles. Specifically, the difference in thickness between the bottom and top transition zones narrows, meaning the final shape is more cylindrical.

[0091] Secondly, it should be noted that the transition zone performance is the result of the combined effects of mechanical construction and material reaction during pile construction. During high-pressure jet grouting, the thickness of the transition zone is affected by the injection parameters: higher grouting pressure and slower lifting speed result in a larger cutting range of the cement grout on the surrounding soil, leading to a thicker transition zone; conversely, insufficient grouting pressure or excessively rapid lifting will result in a smaller transition zone thickness. In addition, the transition zone thickness is also related to the grout material parameters: a lower water-cement ratio results in relatively poor grout fluidity but a more concentrated penetration range into the soil, leading to a more stable transition zone thickness; if the water-cement ratio is too high, the grout is prone to excessive diffusion, potentially resulting in a larger thickness but insufficient strength.

[0092] In this embodiment, high-pressure jet grouting forms high-strength jet grouting piles 3 in the jet grouting borehole 31, while simultaneously penetrating into the surrounding soil to form a transition zone. This transition zone merges almost directly with the cast-in-place piles 2, forming a pile structure with composite characteristics in the silty soft soil foundation, denoted as composite pile 200. Composite pile 200, in conjunction with the in-situ characteristics of the soil, achieves stress coordination, enabling the pile to effectively provide support at different depths. This ensures both deep bearing capacity and reduces shallow stress abrupt changes, reflecting a dynamic balance between artificial intervention and natural geological response.

[0093] After completing the construction of all rigid core areas and pile perimeter transition areas according to the borehole layout diagram, the surface reinforcement zone is constructed on the surface of the silty soft soil foundation.

[0094] The construction of the surface reinforcement zone specifically includes the following steps.

[0095] Step S31, laying basalt fiber mesh 4; specifically, this means calculating the amount of basalt fiber mesh 4 according to the designed admixture and laying basalt fiber mesh 4.

[0096] Step S32, pouring the foundation layer; specifically, this involves mixing cement, sand, gravel, and water in a specific ratio, with a mixing time of no less than 2 minutes to ensure uniform mixing; after transportation to the site, compacting with an immersion vibrator to ensure no missed areas or over-vibration, smoothing immediately after pouring, ensuring the surface of the plain concrete foundation layer 300mm is flat and the elevation meets design requirements. For example: the plain concrete foundation layer 300mm uses C15 plain concrete, with a mass ratio of cement:water:sand:crushed stone = 1:0.52:2.07:4.02. The cement used is 32.5 grade ordinary Portland cement, the water is clean tap water, the sand is medium sand, and the gravel is 5~31.5mm continuously graded crushed stone.

[0097] Step S33, curing; specifically, after pouring, cover with plastic film in a timely manner for curing, and the curing time shall not be less than 7 days.

[0098] exist Figure 7Based on the above, basalt fiber mesh 4 is laid on the surface of the soft soil 100mm above the pile foundation. The state after pouring the cushion layer is as shown. Figure 8 As shown. The state of the silty soft soil foundation after pile foundation construction and surface construction is as follows. Figure 9 As shown.

[0099] Plain concrete cushion layer 300 is a rigid layer that can restrain the lateral deformation of the soil, allowing the local soil to share the load with the surrounding soil when under stress, thus improving the integrity and deformation resistance of the foundation. Generally, the thickness of plain concrete cushion layer 300 is 100~300mm, and the dosage of basalt fiber mesh 4 is 0.8~1.0kg / m³.

[0100] The other parts of this embodiment are the same as those in Embodiment 2, and will not be described again.

[0101] Example 3:

[0102] This embodiment is a further optimization based on embodiment 1 or embodiment 2. The water content of the silt is measured by drilling and sampling. If the water content of the silt exceeds 60%, the triple-pipe jet grouting process is adopted to start the "water-air-slurry" triple jetting mode. High-pressure water, high-pressure air and cement slurry are delivered to the nozzles through the triple pipes respectively. The pressure and duration of the jet grouting are adjusted according to the actual situation.

[0103] Typical process parameters include: high-pressure water working pressure of 10±2 MPa, high-pressure air working pressure of 0.5~0.8 MPa, and cement grout injection pressure of 20~40 MPa. In the "water-air-grout" triple-jet mode, high-pressure water is mainly used for cutting and pre-crushing the soil, and the working pressure is usually controlled at 10±2 MPa to avoid excessive disturbance to extremely soft silt; high-pressure air is mainly used to assist water jetting and slag removal. Excessive working pressure can easily cause borehole wall instability and surface gas escape, while insufficient pressure cannot effectively assist water jetting and slag removal; cement grout is mainly used to form the solidified body, and the injection pressure is still maintained in a relatively high range of 20-40 MPa, and a linear decreasing control is implemented from the high pressure of 40 MPa at the bottom of the borehole to the low pressure of 20 MPa at the surface to ensure the strength and quality of the solidified body.

[0104] The DGZ-150 series multi-tube jet grouting drill rig from Shaanxi Xitan Geological Equipment Co., Ltd., and the XPL-50B anchoring jet grouting drill rig from Tianjin Juqiang High Pressure Pump Co., Ltd., can both achieve the "water-air-grout" triple jetting function. Choose the appropriate equipment based on your actual needs; further details are omitted.

[0105] The other parts of this embodiment are the same as those in Embodiment 1 or Embodiment 2, so they will not be described again.

[0106] Example 4:

[0107] This embodiment is a further optimization based on embodiment 1 or embodiment 2. During the construction of the surface reinforcement zone, a miniature pressure box 1 is pre-embedded in the plain concrete cushion layer 300 to monitor the stress.

[0108] Plain concrete cushion layer 300 does not contain steel bars or other reinforcing materials. After basalt fiber mesh 4 is implanted, the bridging effect of the fibers is used to inhibit the cracking of the cushion layer, enhance crack resistance and deformation resistance, reduce shrinkage cracks, and better adapt to special situations such as large loads or uneven foundation.

[0109] The pre-embedded miniature pressure cell 1 measures the contact pressure at the interface between the silty soft soil foundation and the plain concrete cushion layer 300 mm. Before laying the plain concrete cushion layer, the miniature earth pressure cell is placed on the surface of the foundation in the construction area where the concrete cushion layer has not yet been laid, with the measuring surface facing down. To protect the pressure cell from damage during the pouring process, a 1-2 cm thick layer of fine sand can be placed on top of it, and a plate vibrator can be used to gently compact the concrete, ensuring that the concrete is dense without damaging the pressure cell. For small-scale projects or short-term monitoring, wired transmission can be used, connecting the miniature pressure cell 1 directly to the field data acquisition instrument via a data cable to read data in real time. For large-scale projects or long-term monitoring, wireless transmission is often used. The miniature pressure cell 1 has a built-in wireless sensing module that wirelessly transmits the collected pressure data to the field receiving base station or cloud server, reducing wiring costs and interference with construction.

[0110] If abnormal test data is detected, first check if the miniature pressure box 1 is malfunctioning and if there is interference in the transmission, ruling out false anomalies caused by equipment or transmission problems. Technicians should immediately go to the site to verify whether the subgrade is cracked, whether the foundation has settled, bulged, or has localized deformation, and determine if there are problems such as uneven load distribution or foundation instability. If the anomaly is confirmed to be caused by excessive foundation stress or deformation, immediately suspend the construction of the superstructure to prevent the load from continuing to increase and escalating the danger.

[0111] Preferably, the miniature pressure box 1 is battery powered and wirelessly transmitted, making it easy to install without the need for additional cable laying, and it can adapt to complex underground environments without being affected by the risk of cable damage.

[0112] The other parts of this embodiment are the same as those in Embodiment 1 or Embodiment 2, so they will not be described again.

[0113] Example 5:

[0114] The underground parking garage project in a city's commercial district has a foundation primarily composed of silty soft soil. This soil layer is deep and of poor quality, exhibiting low bearing capacity and high compressibility, posing a significant challenge to the stability of the underground parking garage foundation. The construction area is located in the city center, surrounded by dense buildings and complex underground pipelines. The groundwater level is high and remains close to the surface year-round. The silty soft soil has a water content of approximately 70%, a large porosity, and is in a fluid plastic state, making foundation treatment extremely difficult.

[0115] For high-pressure jet grouting operations, a pre-drilled guide hole 31 is prepared. The hole diameter is usually slightly larger than the outer diameter of the nozzle, typically 100-150 mm. This diameter is sufficient for the nozzle to be lowered smoothly and is far less than the safety distance, posing no threat to the pile body. Through the high-pressure jet grouting process, a reinforced and consolidated body with a diameter much larger than the hole diameter can be formed around this guide hole, i.e., a jet grouting pile 3 with a designed pile diameter of D2.

[0116] Based on geological conditions and construction constraints, the borehole layout is designed as follows: Grouting holes 21 are arranged in a quincunx pattern, with six jet grouting holes 31 evenly distributed around each grouting hole 21, satisfying the following conditions: D1=600mm, D2=500mm, L1=650mm, L2=650mm, L3=1500mm, S=100mm; where D1 is the diameter of the grouting hole 21, D2 is the diameter of the jet grouting hole 31, L1 is the distance between the central grouting hole 21 and the outer jet grouting holes 31, L2 is the distance between two adjacent jet grouting holes 31 in the same group, L3 is the distance between two adjacent grouting holes 21, and S is the safety margin.

[0117] The safety margin S is a comprehensive quantitative value combining empirical and theoretical approaches. Determining its value requires comprehensive consideration of three main construction uncertainties: drill rod deviation, measurement error, and formation heterogeneity, while also taking into account engineering requirements such as high-pressure jet disturbance and construction operation safety. Based on engineering experience and statistical analysis of construction errors, the safety margin S is set at 50-200 mm, preferably 100 mm, to ensure effective avoidance of disturbance to the existing pile body under various construction uncertainty conditions. The safety margin S described in this embodiment ensures that even under the most unfavorable conditions, jet grouting pile construction will not cause structural damage to adjacent cast-in-place piles.

[0118] Construction was carried out according to the above-mentioned borehole layout diagram. Multiple sets of composite piles 200, arranged in a quincunx pattern, were installed in the silty soft soil foundation. Each set of composite piles 200 included one cast-in-place pile 2 at the center and six jet grouting piles 3 evenly distributed around it. The cast-in-place piles 2 had a diameter of 600mm, an average length of approximately 18m, and the bearing layer was a relatively hard silty clay layer. The spacing between the cast-in-place piles 2 was 1500mm. After the rigid core area was constructed, high-pressure jet grouting was used for reinforcement between the piles. The main body of each jet grouting pile 3 had a diameter of 500mm, and its length was similar to that of the cast-in-place piles 2. With a safety margin set at 100mm, the spacing between the outer jet grouting piles 3 and the central cast-in-place pile 2 in the same set of composite piles 200 was 650mm, thus determining the spacing between adjacent jet grouting piles 3 in the same set of composite piles 200 to be 650mm. This structure can improve the strength of the soil between piles and the overall stability of the foundation.

[0119] Generally, the higher the pile density per unit area, the higher the overall foundation stiffness, the slower the settlement rate, and the smaller the settlement amount. The larger the diameter of a single pile, the slower the settlement rate, the smaller the final settlement, and the higher the shear and bending strength of the pile. The higher (longer) the pile height (length), the lower the settlement rate and the more stable the later settlement. On the one hand, increasing the pile height (length) can reduce the settlement rate and stabilize later settlement; this measure does not change the strength of the pile material itself, but the adverse effects of increased self-weight stress and increased construction deviation due to increased pile length must be considered. On the other hand, increasing the pile density per unit area can improve the overall foundation stiffness and slow down settlement; therefore, design changes do not increase the material strength of a single pile.

[0120] The cement grout used for injection is prepared by mixing ordinary Portland cement with a strength grade of not less than 42.5 at a water-cement ratio of 0.8:1 to 1:1. The cement grout used for high-pressure jet grouting is prepared by mixing PI 42.5 cement at a water-cement ratio of 0.8:1 to 1:1. When the high-pressure jet grouting pipe is lifted upwards: the rotation speed is controlled at 20–25 r / min, the lifting speed is controlled at 15–20 cm / min, and the grouting pressure is controlled to decrease gradually within the range of 40–20 MPa.

[0121] Example 6:

[0122] To verify the effectiveness of the silty soft soil foundation treatment method based on the synergistic enhancement mechanism described in any one of Examples 1 to 5, this example conducts a simulation analysis of four foundation construction schemes based on the specific scheme of Example 5: "pileless foundation", "cast-in-place pile 2 foundation", "cast-in-place pile 2 + jet grouting pile 3 foundation", and "cast-in-place pile 2 + upper thin and lower thick jet grouting pile 3 foundation".

[0123] The basic material parameters of each structure are shown in Table 1:

[0124] Table 1 Basic Material Parameters

[0125]

[0126] Group 1, the "pileless foundation" scheme, involves directly laying soil fill roadbed on the surface of silty soft soil foundation.

[0127] Group 2, “Ground-cast pile 2 foundation” scheme, is based on the specific scheme disclosed in Example 5, which only involves placing ground-cast pile 2 in the silty soft soil foundation, and then laying plain concrete cushion layer 300 on the surface of the silty soft soil foundation.

[0128] Group 3, “Ground-cast pile 2 + jet grouting pile 3 foundation” scheme, is based on the specific scheme disclosed in Example 5. Ground-cast pile 2 and jet grouting pile 3 are placed in the silty soft soil foundation, but the jet grouting pile 3 adopts equal pressure jet grouting, and the surface of the silty soft soil foundation is also covered with plain concrete cushion layer 300.

[0129] Group 4, “Ground-cast pile 2 + upper thin and lower thick jet grouting pile 3 foundation” scheme, is based on the specific scheme disclosed in Example 5. Ground-cast pile 2 and jet grouting pile 3 are placed in the silty soft soil foundation, and the jet grouting pile 3 adopts the variable pressure jet grouting with the lower large and the upper small. The surface of the silty soft soil foundation is also covered with plain concrete cushion layer 300.

[0130] The first group of "pileless foundation" schemes, through finite element simulation (settlement conditions), such as... Figure 11 , Figure 12 As shown, the results indicate that the impact range of the foundation displacement without piles is relatively wide, with the maximum displacement value being approximately 0.04975m. From the surface settlement curve, the maximum surface settlement is approximately 0.0489m, and the settlement gradually increases from the monitoring points on both sides towards the middle, indicating that the foundation settlement is widely distributed and the settlement amount is relatively large when there are no piles, and the surface deformation is quite significant.

[0131] The second group of "cast-in-place pile foundation 2" schemes, through finite element simulation (settlement conditions), such as... Figure 13 , Figure 14 As shown, the results indicate that the maximum displacement is approximately 0.04241 m, which is smaller than that of the pileless foundation; the maximum settlement of the surface settlement curve is approximately 0.0416 m, which is about 15.0% smaller than that of the pileless foundation. At the same time, the spatial distribution of the displacement influence is relatively more concentrated, indicating that the bored pile foundation has a certain control effect on the foundation settlement, can reduce the maximum settlement, and can constrain the spatial range of foundation deformation.

[0132] The third group of "2 cast-in-place piles + 3 jet grouting piles for the foundation" scheme, through finite element simulation (settlement conditions), such as... Figure 15 , Figure 16As shown, the results indicate that the maximum displacement further decreased to approximately 0.03154 m; the surface settlement curve shows that the maximum settlement was approximately 0.0311 m, which is about 25.2% less than the maximum settlement of the bored pile foundation. The slope of the settlement curve changed more significantly, indicating that adding jet grouting piles 3 to the bored pile foundation can effectively improve the overall stiffness of the foundation, further narrow the displacement influence range, and reduce the surface settlement.

[0133] The fourth group of "2 cast-in-place piles + 3 upper-dilute-lower-concentrate jet grouting piles for the foundation" scheme, through finite element simulation (settlement conditions), such as... Figure 17 , Figure 18 As shown, the results indicate that the maximum displacement is only about 0.01891m, the smallest among the four foundation types; the maximum settlement of the surface settlement curve is about 0.0187m, which is about 40.0% less than the maximum settlement of the three foundations with bored piles + jet grouting piles, and the settlement curve is the most gradual, indicating that this combination has the best control effect on foundation deformation. The "sparse at the top and dense at the bottom" distribution of the jet grouting piles better matches the characteristics of foundation stress transmission, significantly reducing foundation displacement and surface settlement, and making the displacement field distribution more uniform.

[0134] The displacement of the pileless foundation has a wide range, with a maximum displacement of 0.04975m and a maximum surface settlement of 0.0489m. The settlement is widespread and the deformation is significant. Although the bored pile foundation is an improvement over the pileless foundation, with the maximum displacement reduced to 0.04241m and the maximum surface settlement reduced by 15.0% to 0.0416m, and the displacement distribution is more concentrated, there is still room for optimization. After adding jet grouting piles 3 to the bored pile foundation, the maximum displacement is further reduced to 0. The maximum surface settlement was 0.03154m, which was 25.2% less than that of the bored pile foundation, to 0.0311m. The overall stiffness of the foundation was improved and the displacement influence range was narrowed. The bored pile + upper thin and lower thick jet grouting pile 3 foundation performed the best, with a maximum displacement of only 0.01891m, which was the smallest among the four types. The maximum surface settlement was reduced to 0.0187m, which was 40.0% less than that of the bored pile + jet grouting pile 3 foundation. Moreover, the settlement curve was gentle and the displacement field was evenly distributed.

[0135] By comparing displacement and surface settlement data for four different foundation types, the differences in deformation control capabilities among them are clearly evident. The effectiveness of the bored pile + upper-sparse-lower-dense jet grouting pile 3-type foundation is the most prominent. This advantage stems from the fact that the "upper-sparse, lower-dense" distribution of the jet grouting piles precisely matches the stress transfer characteristics of the foundation, fully utilizing the bearing capacity of the bored piles. From the rationality of the structural design to the actual deformation control effect, it demonstrates significant effectiveness, providing an efficient and reliable solution for foundation engineering.

[0136] The other parts of this embodiment are the same as any one of Embodiments 1-5, and will not be described again.

[0137] Example 7:

[0138] This embodiment describes in detail some of the key technical points of the silt and soft soil foundation treatment method based on Embodiments 1-6.

[0139] Technical point 1: During the construction of the rigid core area, the thickness of the sediment at the bottom of the hole should not be too high. Generally, it should not exceed 40mm.

[0140] Referring to the "foundation of 2 cast-in-place piles + 3 jet grouting piles with thinner top and thicker bottom" structure in Example 6, two sets of tests were designed: a "standard group" and a "sediment exceeding the standard group". The key test parameters in the "standard group" are: the sediment involved in steps SA3 and SA5 is 40mm, and the grouting pressure during the construction of jet grouting piles 3 is 22MPa; the key test parameters in the "sediment exceeding the standard group" are: sediment 100mm, and other parameters are the same as in the standard group.

[0141] Table 2 shows some parameters of settlement, strength of cast-in-place pile 2, and strength of jet grouting pile 3 after 30 days of monitoring:

[0142] Table 2 Comparison of Partial Test Results between the "Standard Group" and the "Sediment Exceeding Standard Group"

[0143]

[0144] Table 2 shows that a larger thickness of sediment at the bottom of the borehole leads to a higher settlement rate and a larger settlement amount; however, it has little impact on the strength of the pile itself. Excessive sediment thickness, such as 100 mm, significantly increases the total settlement and settlement rate of the foundation, but has little impact on the material strength of the cast-in-place piles and jet grouting piles. This indicates that the sediment thickness primarily weakens the bearing stiffness of the pile tip bearing layer and the pile-soil synergy, leading to increased overall foundation deformation, but under the conditions of this experiment, it did not have a significant adverse effect on the material strength of the pile concrete and cement-soil consolidation.

[0145] Technical Point 2: During the construction of the rigid core area, the reinforcing cage inserted into the grouting hole 21 is a variable cross-section reinforcing cage 23. Furthermore, the structural parameters of the enlarged bottom end of the variable cross-section reinforcing cage 23 need to be designed comprehensively considering the structural stress and construction operability.

[0146] The variable cross-section reinforcing cage 23 has consistent dimensions at the top and middle, with a larger enlarged end at the bottom. The variable cross-section reinforcing cage 23 enhances the bending stiffness of the lower part of the pile, improves stress distribution, and reduces pile bottom displacement. However, excessive enlargement can increase construction difficulty and material costs, and may lead to difficulties in lowering the reinforcing cage or uneven concrete pouring. The outer diameter of the enlarged end of the variable cross-section reinforcing cage 23 is typically 1.1 to 1.25 times the outer diameter of the top or middle section, i.e., an enlargement of 10% to 25%; in actual engineering, it is often designed to be an enlargement of 15% to 20%. Furthermore, the height of the enlarged end should not be less than 5 times the enlarged diameter and should not exceed 1 / 4 of the total height of the reinforcing cage. For example, if the outer diameter of the upper part of the reinforcing cage is 1m, and the enlarged end is calculated to be 1.2m with a 20% enlargement, then the height of the enlarged end should not be less than 1m. Simultaneously, the height of the enlarged end should not exceed 1 / 4 of the total height of the reinforcing cage to prevent imbalance during hoisting or shift of the center of gravity during pouring.

[0147] Technical Point 3: Optimal timing for construction of the pile perimeter transition zone: After each cast-in-place pile 2 is completed, the construction of the pile perimeter transition zone around the cast-in-place pile 2 should be started during the initial setting stage of the cast-in-place pile 2 concrete and after the strength of the cast-in-place pile 2 reaches 1MPa, and should be completed before the final setting of the cast-in-place pile 2 concrete.

[0148] After the concrete initially sets, the cement hydrates to form a gel, and the grout begins to lose its plasticity and harden initially. The pile body possesses low-strength integrity (generally ≥1MPa), which can resist slight lateral pressure and vibration during grouting. At this time, the pile body is not yet fully hardened (final setting is not complete), and the surrounding soft soil is still in a relatively "loose" state. The grout from high-pressure jet grouting can penetrate and mix the soil between the piles more smoothly, avoiding the limitation of grouting range or uneven grout diffusion caused by the increased soil pressure around the pile body after it has fully hardened.

[0149] During the initial setting stage of the concrete of cast-in-place pile 2, when the strength of cast-in-place pile 2 reaches 1MPa, it has the initial strength to resist lateral disturbance, while the soil around the pile has not been completely compacted, which is conducive to the penetration of grout during jet grouting, thereby realizing the integration of the "rigid core" and "pile perimeter transition" zones.

[0150] The initial setting time of the concrete in cast-in-place pile 2 is closely related to the concrete mix proportion. Low water-cement ratio concrete (≤0.5) can achieve a strength of 1-2 MPa after 4 hours of initial setting, meeting the lateral pressure resistance requirements during jet grouting. When using this type of low water-cement ratio concrete, the pile perimeter transition zone construction is generally carried out 4-6 hours after grouting. High water-cement ratio concrete (>0.6) may only achieve a strength of 0.5-1 MPa after 4 hours. Jet grouting should only be initiated after the strength reaches ≥1 MPa to prevent the pile body from being cracked by the grouting pressure. When using this type of high water-cement ratio concrete, the pile perimeter transition zone construction is generally carried out 5-7 hours after grouting.

[0151] Technical point 4: Grouting pressure range during the construction of the pile perimeter transition zone.

[0152] The analysis considers both the purpose of grouting and the pile structure. First, the jet grouting pile 3 formed by high-pressure jet grouting acts as a reinforcing body, directly strengthening the soil surrounding the cast-in-place pile 2. This significantly reduces the diameter of the cast-in-place pile 2 while maintaining the same bearing capacity. Second, the cement grout from the high-pressure jet grouting penetrates the soil layer around the jet grouting hole 31, forming a transition zone that enhances soil bonding. The integrated load-bearing structure formed by the jet grouting pile 3 and the cast-in-place pile 2 connected through this transition zone is the composite pile 200. Therefore, the grouting pressure needs to meet the requirements of the combined grouting and jet grouting process. To form a reinforcing body within a certain range, sufficient grout penetration radius is also required to ensure that the central cast-in-place pile 2 and the surrounding jet grouting pile 3 together form a composite pile 200.

[0153] The analysis focuses on the geological characteristics. For hard or poorly permeable strata such as dense sand and gravel layers, higher pressure is required to effectively diffuse the grout, fill pores, and compact the surrounding soil. In silty soils, which are softer, excessive pressure may lead to excessive disturbance; therefore, the grouting pressure must be appropriate for the stratum strength. Furthermore, under the same geological conditions, the influence of grouting pressure on construction performance was studied using the controlled variable method: as the grouting pressure decreases, the spray radius decreases, the settlement rate increases, the pile strength of the jet grouting pile 3 decreases, the cement content per unit volume of soil decreases, and the frequency of pipe blockage decreases. High-pressure grouting can more fully fill the voids around the pile and compact the soil, resulting in a tighter bond between the grout and the concrete of the cast-in-place pile 2 and the surrounding soil. This significantly increases the side friction of the pile, thereby effectively improving the overall bearing capacity and stability of the composite pile 200. Simultaneously, under high pressure, the grout can penetrate micro-cracks in the soil, forming a network reinforcement structure and enhancing the shear strength of the soil around the pile. However, it should be noted that excessive grouting pressure may cause cracks in the concrete of the cast-in-place pile 2 due to excessive impact from the cement grout, damaging the integrity of the pile body, reducing the strength of the single pile, and potentially causing disturbance to the soil structure. Conversely, reduced grouting pressure results in a smaller spray radius and weakened diffusion capacity of the cement grout.

[0154] Analysis shows that ultra-high pressure can fully cut, mix, and compact the soil, ensuring uniform mixing of cement grout and soil particles to form an extremely dense, low-porosity, high-strength cement-soil consolidation. However, excessive grouting pressure can lead to excessive disturbance of the soil layer; reduced grouting pressure weakens the soil breaking and compaction effect, decreases the uniformity and density of the grout-soil mixture, and correspondingly reduces the strength of the consolidated body; insufficient grouting pressure results in excessively low strength of the jet grout pile and affects the diffusion range of the cement grout into the soil.

[0155] Therefore, it is necessary to comprehensively consider the grouting purpose, pile structure, stratum characteristics, and other conditions to design an appropriate grouting pressure.

[0156] In engineering practice, the grouting pressure should be controlled between 20 and 40 MPa to ensure the effective diffusion radius and reinforcement effect, while avoiding adverse disturbance to the pile body and surrounding soil.

[0157] Based on the above "standard group", another test was designed: "insufficient pressure group". In the "insufficient pressure group", the grouting pressure during the jet grouting operation was 15MPa, and other aspects were the same as the standard group.

[0158] Table 3 shows some parameters of settlement, strength of cast-in-place pile 2, and strength of jet grouting pile 3 after 30 days of monitoring:

[0159] Table 3. Comparison of partial test results between the "Standard Group" and the "Insufficient Pressure Group"

[0160]

[0161] Table 3 shows that insufficient grouting pressure significantly weakens the overall stiffness and deformation resistance of the foundation, severely affects the quality of pile formation, and leads to a significant reduction in the strength of the cement-soil consolidation, resulting in increased settlement and continuous settlement development. Insufficient grouting pressure during jet grouting weakens the cutting, mixing, and compaction effect of the high-pressure jet on the soil around the pile, reducing the uniformity and density of the cement grout mixing with the soil, and thus lowering the strength of the jet grouting pile consolidation. This directly weakens the reinforcement effect of the "flexible transition zone," leading to poor pile-soil synergy, insufficient overall foundation stiffness, and consequently, increased settlement and continuous settlement development.

[0162] Therefore, based on the specific example in Example 5, the grouting pressure is not less than 20 MPa.

[0163] Technical Point 5: During the construction of the pile perimeter transition zone, the grouting pressure of the high-pressure jet grouting decreases as the lifting height increases. The grouting pressure of the high-pressure jet grouting decreases linearly along the depth direction from 40MPa to 20MPa, that is, the highest pressure (40MPa) is used at the bottom of the hole, and the pressure decreases linearly as the grouting pipe is lifted to the ground surface, dropping to the lowest pressure (20MPa) at the ground surface.

[0164] Technical point 6: Basalt fiber mesh 4 is incorporated into the plain concrete subbase 300. Specifically, 0.8~1.0 kg / m² of basalt fiber mesh is incorporated into the plain concrete subbase 300. 3 Basalt fibers.

[0165] Concrete itself is weak in tensile strength and brittle. The addition of basalt fiber mesh 4 helps it absorb some tensile stress through interfacial bonding, inhibiting crack propagation. Tensile strength increases with increasing dosage, stabilizing after reaching an optimal dosage. Simultaneously, an appropriate amount of basalt fiber mesh 4 can improve the internal porosity of the concrete, forming a three-dimensional network structure that provides lateral restraint, inhibiting axial deformation and thus improving compressive strength. Therefore, incorporating basalt fiber into plain concrete cushion layer 300 can significantly improve its crack resistance and overall toughness, effectively inhibiting crack propagation caused by stress concentration due to changes in grouting pressure. In actual construction, it is essential to ensure uniform fiber dispersion and avoid excessive aggregation to fully utilize its reinforcing effect.

[0166] The other parts of this embodiment are the same as those in the above embodiments, and will not be described again.

[0167] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for treating silty soft soil foundations based on a synergistic enhancement mechanism, characterized in that: It includes three main construction procedures: rigid core zone construction, pile perimeter transition zone construction, and surface reinforcement zone construction. During the construction of the rigid core area, the drilling and grouting process is used to drill grouting holes (21) in soft soil, install steel casing (22), put in steel cage, and pour concrete to form grouting piles (2). Construction of the pile transition zone was initiated during the initial setting stage of the concrete of the cast-in-place pile (2) and after the strength of the cast-in-place pile (2) reached 1MPa, and was completed before the final setting of the concrete of the cast-in-place pile (2). During the construction of the pile perimeter transition zone, high-pressure jet grouting technology is used to drill jet grouting holes (31) around the cast-in-place pile (2) and perform high-pressure jet grouting to form a composite pile (200) on the basis of the cast-in-place pile (2); after the composite pile (200) has solidified, the surface reinforcement zone construction is carried out. During the construction of the surface reinforcement zone, a plain concrete cushion layer (300) incorporating basalt fiber mesh (4) is laid on the soft soil surface.

2. The method for treating silty soft soil foundation based on a synergistic enhancement mechanism according to claim 1, characterized in that: During the construction of the rigid core area, the reinforcing cage placed in the grouting hole (21) is a variable cross-section reinforcing cage (23) with an enlarged end at the bottom; the diameter of the enlarged end is 1.1 to 1.25 times the diameter of the upper part of the reinforcing cage.

3. The method for treating silty soft soil foundation based on a synergistic enhancement mechanism according to claim 2, characterized in that: The height of the enlarged end shall not be less than 5 times the enlarged diameter and shall not exceed 1 / 4 of the total height of the steel cage.

4. The method for treating silty soft soil foundation based on a synergistic enhancement mechanism according to claim 1, characterized in that: During the construction of the rigid core area, concrete with a water-cement ratio of 0.5 to 0.6 is used for grouting. After grouting is completed for 4 to 6 hours, the construction of the pile perimeter transition area is started.

5. The method for treating silty soft soil foundation based on a synergistic enhancement mechanism according to claim 1, characterized in that: The steel casing (22) extends 300-500mm above the soft soil surface.

6. The method for treating silty soft soil foundation based on a synergistic enhancement mechanism according to claim 1, characterized in that: During the construction of the pile perimeter transition zone, a set of circumferentially distributed jet grouting holes (31) are drilled around each cast-in-place pile (2) by a drilling rig. After the grouting pipe is inserted, the high-pressure equipment is started to perform high-pressure jet grouting. Note: The diameter of the injection hole (21) is D1, the diameter of the jet nozzle (31) is D2, the hole distance between the central injection hole (21) and the outer peripheral jet nozzle (31) is L1, the hole distance between two adjacent jet nozzles (31) in the same group is L2, and the hole distance between two adjacent injection holes (21) is L3. set up The safety margin is S; satisfying: D1>D2, L2=(1.1~1.3)D2, L3=(2.5~6)L1, L1=D1 / 2+D2 / 2+S and S=50~200mm.

7. The method for treating silty soft soil foundation based on a synergistic enhancement mechanism according to claim 6, characterized in that: During high-pressure jet grouting, the grouting pipe is controlled to rotate and rise from the bottom to the top of the jet grouting hole (31) while the grouting pressure decreases, so that the cement grout forms a distribution characteristic of being thick at the bottom and thin at the top.

8. The method for treating silty soft soil foundation based on a synergistic enhancement mechanism according to claim 7, characterized in that: During high-pressure jet grouting, the grouting pressure decreases linearly from 40MPa to 20MPa as the lifting height changes.

9. A method for treating silty soft soil foundation based on a synergistic enhancement mechanism according to claim 7, characterized in that: During high-pressure jet grouting, the lifting speed of the grouting pipe is 10~25cm / min and the rotation speed is 10~20r / min.

10. The method for treating silty soft soil foundation based on a synergistic enhancement mechanism according to claim 1, characterized in that: During the construction of the surface reinforcement zone, the thickness of the plain concrete cushion layer (300) is 100~300mm, in which a micro pressure box (1) is pre-embedded, and the basalt fiber content is 0.8~1.0kg / m³.

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