Sand and clay interbed geology differentiation grouting pile planting construction method and system

Abstract

The application discloses a sand and clay interbedded stratum differential grouting pile planting construction method and system, and relates to the technical field of pile foundation construction. In view of the technical problems that the sand and clay interbeded stratum preformed hole pile planting is prone to hole collapse, grouting material performance is single, group pile stress is uneven, and geological analysis and design construction are disconnected, the method first carries out soil quality test and prepares two types of composite grouting materials with complementary performance, the first type is characterized by high fluidity and strong diffusion and is used for center piles, and the second type is characterized by high bonding strength, high curing strength and anti-loss and is used for side piles and corner piles; then, based on the group pile effect, the pile foundation under the pile cap is divided into a center pile area, a side pile area and a corner pile area and differential grouting is carried out, the center pile area is preferentially constructed, the temporary side wall of the side pile area and the corner pile area is formed by means of slurry diffusion, and then the pile is sunk by penetration control hammering. The application can realize variable stiffness leveling, reduce the differential settlement of the pile cap, improve the group pile bearing capacity and reduce the hole collapse rate.

Description

Technical Field

[0001] This invention belongs to the field of pile foundation construction technology, specifically relating to a method and system for differential grouting and pile planting in sand-clay interbedded geology. Background Technology

[0002] In the field of building pile foundation engineering, precast piles are widely used due to their advantages such as high construction efficiency, strong quality control, and significant environmental benefits. However, when driving piles in sand-clay interbedded strata, the high density of sand easily forms iron-plate sand after pile compaction, leading to temporary hardening of the soil at the pile tip and generating huge bond forces on the pile side; the poor permeability of clay causes instantaneous negative pore water pressure after the soil at the pile tip is compressed, creating an suction effect on the pile body and further increasing the penetration resistance; false limit phenomena frequently occur during the pile driving process in sand-clay interbedded strata. The above factors together lead to high penetration resistance, difficulty in pile driving, high damage rate of pile top or pile body, easy pile displacement, and significant dispersion of pile foundation bearing capacity after pile completion.

[0003] To overcome the aforementioned difficulties of direct pile driving, the pre-drilled pile driving method has emerged. This method involves first drilling a pilot hole, then filling the hole with filler material, and finally driving in precast pipe piles. This effectively solves problems such as pile damage, pile misalignment, and soil squeezing effects. Simultaneously, the filler material in the hole can improve the vertical bearing capacity of a single pile, making it highly applicable. However, under complex geological conditions where sand and clay layers alternate, the pre-drilled pile driving method still faces severe challenges: sand layers have high permeability and poor self-stabilization, while clay layers, due to their high clay content, are prone to softening when exposed to water. When drilling or pre-drilling in strata where water-bearing sand and clay layers frequently alternate, the sand layer is highly susceptible to accidents such as hole collapse and sand inrush caused by drill bit disturbance. The mechanism is as follows: the effective stress between sand grains in aquifers depends on the balance of pore water pressure. Drill bit disturbance causes the sand near the borehole wall to lose lateral restraint, and the pore water cannot drain out in time before the sand grains collapse into the borehole, resulting in borehole collapse. In clay layers, the clay particles absorb water and expand, softening the borehole wall and causing a sharp drop in borehole wall strength, which also makes it difficult to guarantee the quality of borehole formation. These factors significantly increase the difficulty of drilling and borehole wall stability control.

[0004] Meanwhile, existing grouting fillers have significant performance defects and are prone to material waste and environmental pollution. Currently used fillers such as fine aggregate concrete, cement grout, or cement mortar suffer from poor homogeneity, easy segregation and bleeding, and volume shrinkage after hardening. These drawbacks lead to micro-gaps between the grout layer and the pile hole wall, weakening side friction and discontinuous force transmission paths, thus affecting the interaction between the pile and soil. Furthermore, the strength of the grout is lower than that of high-strength precast pipe piles, creating an unfavorable situation of strong pile and weak shell. To ensure the full utilization of side friction along the pile length, over-grouting is often used. However, the grout is easily lost and overflows in large quantities due to the seepage of water-bearing sand layers, resulting not only in serious material waste and increased costs but also in environmental pollution and difficulties in subsequent earthwork excavation.

[0005] Furthermore, under the same rigid pile cap, due to the pile group effect, the actual stress distribution of each pile is not uniform, with the corner piles exhibiting the greatest reaction force, followed by the edge piles, and the central piles the least. Traditional pile driving methods typically employ uniform grouting material formulas and construction parameters, failing to take differentiated measures for the actual stress differences in different parts of the pile foundation. This one-size-fits-all grouting method does not conform to the design concept of variable stiffness leveling, resulting in material waste. In severe cases, it leads to insufficient safety reserves of bearing capacity in corner and edge piles, while the bearing potential of the central pile is not fully utilized, thus causing overall differential settlement of the pile cap. Simultaneously, the current technical system also suffers from a disconnect between geology, design, and construction. Summary of the Invention

[0006] To address the technical problems in existing technologies regarding pre-drilled pile driving under sand-clay interbedded geological conditions, such as easy collapse of pilot holes, single performance of grouting fillers, uneven stress distribution among pile groups, and disconnect between geological analysis and design / construction, this invention provides a differentiated grouting pile driving method and system for sand-clay interbedded geological conditions. By preparing two types of composite grouting materials with complementary properties, the pile foundation under the pile cap is differentiated into zones based on the pile group effect, and the geological analysis, structural design, and construction control are linked by grouting the central pile first to form a temporary retaining wall.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for differential grouting and pile installation in sand-clay interbedded geological formations, comprising the following steps: S1. Soil Testing and Analysis: Soil testing and analysis are conducted at the construction site to obtain the physical and mechanical parameters of each stratum. These parameters include the distribution depth, thickness, permeability coefficient, moisture content, and SPT blow count of each stratum. Indoor grouting simulation tests are used to verify the diffusion performance, setting time, and solidification strength of grouting materials with different proportions in the corresponding soil layers, providing a basis for the selection and proportioning of grouting materials. Since the permeability coefficient determines the diffusion capacity of the grout in the soil layer, the setting time determines the time window for pile driving, and the solidification strength determines the bearing capacity after pile formation, the test results in step S1 directly determine the subsequent material proportions and construction parameters.

[0008] S2. Grouting Material Preparation: Based on the soil test analysis results of step S1, at least two composite grouting materials with different properties are prepared. The first type of grouting material, characterized by high fluidity and strong diffusivity, is used for grouting reinforcement of the central pile. It can penetrate into the pores of the water-bearing sand layer under low pressure and cement loose sand particles. The second type of grouting material, characterized by high bond strength, high cured strength, and anti-loss properties, is used for grouting reinforcement of the side piles and corner piles. After curing, it has high bond strength with both the pile body and the soil, and its viscosity is moderate, effectively preventing significant grout loss in the water-bearing sand layer. The performance differences between the two types of materials determine the basis for the subsequent differentiated grouting scheme: the first type of material achieves sand layer penetration reinforcement through its strong diffusivity, while the second type of material achieves pile side reinforcement and grout conservation through its high bond strength and anti-loss properties.

[0009] S3. Determination of Pile Location Zoning and Differentiated Grouting Scheme: Based on the planar dimensions of the rigid pile cap and the pile layout scheme, the pile locations below the pile cap are divided into a central pile zone, an edge pile zone, and a corner pile zone. The piles in the central pile zone are designated as central piles, the piles in the edge pile zone are designated as edge piles, and the piles in the corner pile zone are designated as corner piles. All central, edge, and corner piles are precast piles. Based on the theory of pile group effect analysis, the stress characteristics of the pile foundation in each zone are determined. The corner piles exhibit the largest pile top reaction force, followed by the edge piles, and the central piles exhibit the smallest. Based on this, a differentiated grouting scheme was formulated: For the pile positions within the central pile area, the first type of grouting material was used for grouting to fully penetrate the water-bearing sand layer using its liquefiable sand layer and strong diffusivity, increasing the effective penetration depth of the central pile driven by hammering, transferring the pile end load of the central pile to a deeper bearing layer, and improving the bearing stiffness of the central pile; for the pile positions within the side pile area and corner pile area, the second type of grouting material was used for grouting to enhance the side friction resistance of the side piles and prevent grout loss; for the pile positions located within the corner pile area, the second type of grouting material was used for grouting, and the grouting volume was greater than that in the side pile area, to maximize the bearing capacity and pull-out resistance of the corner piles.

[0010] S4. Prioritize pre-drilling, grouting, and driving the piles within the central pile area. Lower the grouting pipe to the bottom of the hole and grout in sections from bottom to top, using a low-pressure, slow-injection method to ensure the grout fully penetrates into the pores of the water-bearing sand layer. Avoid high-pressure grouting to prevent damage to the hole wall or grout loss. After grouting, allow it to stand for a period of time to allow the grout to fully penetrate and diffuse in the water-bearing sand layer and cement the surrounding sand particles. Within the time window before the grout initially sets, hoist the precast piles into position and drive them to the design elevation using a hammer. Control the pile driving termination condition by the penetration depth. Monitor the penetration depth in real time during the pile driving process. Stop driving the pile when the penetration depth reaches the design final hammer standard to avoid over-driving and damaging the pile body.

[0011] S5. After the grouting material in the central pile area has diffused in the soil, pre-drilling, grouting, and pile driving are carried out on the pile positions in the side pile area and the corner pile area. The pre-drilling, grouting, and pile driving process in the side pile area and the corner pile area is the same as in step S4. Since the first type of grouting material has penetrated and diffused in the water-bearing sand layer and formed a cementing reinforcement on the surrounding soil, it is equivalent to forming a temporary protective wall around the hole positions of the side piles and corner piles, thereby significantly reducing the collapse rate during the hole formation process of the side piles and corner piles. According to the differentiated grouting scheme determined in step S3, the corresponding type of grouting material is injected into each pre-drilled hole, and the second type of grouting material is used for the pile positions in the side pile area and the corner pile area. After grouting is completed, within the time window before the grout initially sets, the precast piles are hoisted into place and driven to the design elevation by hammering. The penetration is monitored in real time during the pile driving process, and pile driving is stopped when the penetration reaches the design final hammer standard.

[0012] S6. After construction is completed and the grouting material reaches the design strength, the pile foundation bearing capacity will be tested. This will verify the actual effect of differentiated grouting and guide subsequent pile foundation acceptance based on the test results.

[0013] Furthermore, in step S4, the drilling depth and single-hole grouting volume of the piles in the central pile area are both greater than those in the side pile area and the corner pile area; in step S5, the single-hole grouting volume of the piles in the corner pile area is greater than that of the piles in the side pile area. The beneficial effects of this further scheme are: it enables the central pile to form a deeper and stronger pile end reinforcement, transferring the pile end load to a deeper bearing layer, compensating for the insufficient bearing potential of the central pile due to the smaller reaction force caused by the group pile effect; the grouting volume in the corner pile area is greater than that in the side pile area, matching the stress characteristics of the corner pile with the largest pile top reaction force, enhancing the bearing capacity and pull-out resistance of the corner piles, thereby reducing differential settlement of the pile cap.

[0014] Further, in step S2, the first type of grouting material is mainly composed of inorganic cementitious materials, with a water-cement ratio controlled within the range of 0.6 to 0.7, and contains 0.5% to 1.0% water-reducing agent and 0.1% to 0.3% retarder by weight of cement; the second type of grouting material is a cement-inorganic composite material, mainly composed of cement, with a water-cement ratio controlled within the range of 0.5 to 0.55, and contains 6% to 8% micro-expansion agent, 5% to 8% silica fume and 10% to 15% slag powder by weight of cement. The beneficial effects of the above-mentioned further solutions are as follows: a higher water-cement ratio combined with a water-reducing agent gives the first type of grouting material excellent fluidity, enabling it to penetrate into the pores of the water-bearing sand layer under low pressure; the retarder extends the grouting time, ensuring that the grout fully diffuses and binds loose sand particles before initial setting; a lower water-cement ratio combined with a micro-expansion agent enables the second type of grouting material to have high bonding strength with both the pile body and the soil after curing; the micro-expansion agent generates moderate expansion during the curing process to tightly fill the voids at the pile-soil interface; active admixtures such as silica fume and slag powder further improve the bonding strength and impermeability of the grout, and the moderate viscosity can effectively prevent the grout from being lost in large quantities in the water-bearing sand layer.

[0015] Further, in step S3, the central pile area refers to the pile positions located at the geometric center of the foundation plane, the side pile area refers to the pile positions located in the middle sections of each side of the foundation, and the corner pile area refers to the pile positions located at each corner of the foundation. The beneficial effect of this further scheme is that, based on the force distribution pattern under the pile group effect—with the corner piles exhibiting the greatest reaction force, followed by the side piles, and the central piles exhibiting the least—the differentiated grouting scheme is matched to the actual stress characteristics of the pile foundation in each area.

[0016] Further, in step S3, when the number of piles in the pier cap is greater than 9 and arranged in a row-column pattern, the corner pile area includes piles located at the four corners of the pier cap, the side pile area includes piles located at the middle positions of the four sides of the pier cap, and the central pile area includes piles located at the center of the pier cap and the remaining piles within the central area of ​​the pier cap; when the number of piles in the pier cap is no more than 9, the side pile area includes piles located at the middle sections of each side of the pier cap, the corner pile area includes piles located at each corner of the pier cap, and the central pile area includes the remaining piles. The beneficial effect of the above further scheme is that different zoning rules are adopted for different pile sizes, so that the zoning matches the stress distribution of the pile group effect, improving the targeting of differentiated grouting.

[0017] Further, in step S4, the driving depth of the central pile is greater than the depth of its pre-drilled hole; in step S5, the driving depth of the side piles and the corner piles is greater than the depth of their pre-drilled holes, so that the pile ends of the central pile, the side piles, and the corner piles enter the soil below the pre-drilled hole and form a composite pile with the grouting material. The central pile, with the help of the liquefaction effect of the first type of grouting material on the pile end sand layer, increases the effective penetration depth of the central pile during hammer driving, transferring the pile end load of the central pile to a deeper bearing layer, thereby improving the support stiffness of the central pile; the side piles and corner piles, with the help of the high bonding strength of the second type of grouting material, increase the pile side friction resistance of the side piles and corner piles, and utilize the moderate expansion generated during the curing process of the micro-expansion agent to tightly fill the voids at the pile-soil interface, improving the pile side friction resistance and pull-out bearing capacity of the side piles and corner piles. The beneficial effects of the above further scheme are: matching the actual support stiffness of each pile with the distribution of the upper load, realizing variable stiffness leveling design, and reducing differential settlement of the pile cap.

[0018] Secondly, the present invention provides a differential grouting and pile driving construction system for sand-clay interbedded geological layers, comprising: The soil testing and analysis unit is used to conduct soil tests and analyses on the construction site, obtain the physical and mechanical parameters of each stratum, and verify the diffusion performance, setting time and solidification strength of grouting materials with different proportions in the corresponding soil layers through indoor grouting simulation tests. The grouting material preparation unit is used to prepare at least two composite grouting materials with different properties based on the test and analysis results of the soil test and analysis unit. The first type of grouting material is characterized by high fluidity and strong diffusivity and is used for grouting reinforcement of central piles. The second type of grouting material is characterized by high bond strength, high curing strength and anti-loss properties and is used for grouting reinforcement of side piles and corner piles. The pile location zoning and grouting scheme determination unit is used to divide the pile locations below the pile cap into a central pile area, a side pile area, and a corner pile area based on the pile group effect and the planar dimensions and pile layout of the rigid pile cap. It determines the stress characteristics of the pile foundation in each area and formulates a differentiated grouting scheme. The differentiated grouting scheme is as follows: the pile locations in the central pile area are grouted using the first type of grouting material, while the pile locations in the side pile area and the corner pile area are grouted using the second type of grouting material. The piles corresponding to the pile locations in the central pile area are central piles, the pile locations corresponding to the pile locations in the side pile area are side piles, and the pile locations corresponding to the pile locations in the corner pile area are corner piles. All central piles, side piles, and corner piles are precast piles. The central pile construction unit is used to prioritize the pre-drilling, grouting and pile driving of the pile positions within the central pile area. After the grouting is completed, the precast pile is hoisted into place before the grout initially sets, and the pile is driven by hammering. The pile driving termination condition is controlled by the penetration degree. The corner pile construction unit is used to pre-drill holes, grout, and drive piles in the side pile area and the corner pile area after the grouting material in the central pile area has diffused in the soil. The pre-drilling, grouting, and pile driving process in the side pile area and the corner pile area is the same as the construction process of the central pile construction unit. The quality inspection unit is used to test the bearing capacity of the pile foundation after construction is completed and the grouting material has reached the design strength.

[0019] Furthermore, during the construction of the central pile construction unit, the drilling depth and single-hole grouting volume of the pile positions in the central pile area are greater than those in the side pile area and the corner pile area, and the single-hole grouting volume of the pile positions in the corner pile area is greater than that of the pile positions in the side pile area; the central pile construction unit includes a long spiral drilling rig, grouting pipe, hoisting equipment, and a pile driver.

[0020] Furthermore, the pile location zoning and grouting scheme determination unit determines the stress characteristics of each zone of the pile foundation based on the finite element analysis results of the pile group effect.

[0021] Furthermore, after the grouting of the central pile construction unit is completed, the first type of grouting material is allowed to penetrate and diffuse in the water-bearing sand layer before pre-drilling is carried out on the pile positions in the side pile area and the corner pile area. The diffusion property of the first type of grouting material is used to form a temporary protective wall for the surrounding soil. During the hammer driving process, the penetration degree is monitored in real time, and the pile driving is stopped when the penetration degree reaches the design final hammer standard.

[0022] The beneficial effects of this invention are: The first type of grouting material is injected slowly under low pressure into the pores of the water-bearing sand layer, cementing the loose sand particles to form a protective wall layer with a certain strength, providing stable hole wall support for the subsequent pre-drilling of edge and corner piles. This solves the problem of difficult hole drilling in water-bearing sand-clay interbedded layers. Utilizing the temporary protective wall effect formed by the initial grouting of the first type of grouting material in the center pile effectively reinforces the water-bearing sand layer, significantly reducing the hole collapse rate during the pre-drilling process of edge and corner piles, and ensuring the quality of hole formation and construction safety.

[0023] The edge and corner piles use high-viscosity, loss-resistant grouting materials. Their high viscosity and micro-expansion properties effectively overcome the problem of grout loss in water-bearing sand layers, preventing large amounts of grout from spreading beyond the pile cap area. The mechanism is as follows: the second type of grouting material has a low water-cement ratio and high viscosity, limiting its penetration distance in water-bearing sand layers. The grout forms a controlled, limited diffusion zone around the borehole rather than flowing away over long distances along seepage channels. The micro-expansion agent generates micro-expansion during grout setting, sealing the seepage channels between the grout and the borehole wall, further preventing grout loss. This saves on grouting material usage and reduces the impact on the surrounding environment.

[0024] The first type of grouting material for the central piles fully penetrates and diffuses in the water-bearing sand layer, cementing the loose sand particles into a whole and effectively improving the mechanical properties of the bearing stratum at the pile tip. The micro-expansion agent added to the second type of grouting material for the side and corner piles undergoes moderate expansion during the curing process, tightly filling the voids at the pile-soil interface and significantly improving the pile side friction and pull-out bearing capacity. The mechanism is as follows: after the grout in the central pile penetrates and cements the sand particles, the density and deformation modulus of the bearing stratum at the pile tip increase, and the pile tip resistance increases accordingly. The micro-expansion agent in the side and corner piles generates expansive products such as ettringite during cement hydration, producing approximately 0.05% to 0.1% confined expansion, which compresses and compacts the micro-cracks at the pile-soil interface, transforming the pile side friction from pile-soil contact friction into effective bonding between the pile, grout, and soil, thereby significantly improving the overall bearing capacity and pull-out performance of the pile group.

[0025] By implementing differentiated grouting based on the different stress characteristics of the center pile, side pile, and corner pile, the center pile can increase its effective pile length and improve its support stiffness with the help of highly diffusive grout, while the side piles and corner piles can enhance their side resistance with the help of high-bonding-strength grout. This allows the actual support stiffness of each pile to match the distribution of the superstructure load, realizing the variable stiffness leveling design concept. This can reduce the differential settlement of the pile cap and reduce the internal force of the pile cap.

[0026] The performance of grouting materials was verified through indoor grouting simulation tests. The test data guided the design of grouting parameters, and the design results guided differentiated construction on site. By combining geological analysis, structural design and on-site construction, the disconnect between various links in traditional construction was changed, and the transformation from experience-based construction to analysis-based decision-making construction was realized. Attached Figure Description

[0027] Figure 1 This is a schematic flowchart of the differential grouting and pile planting construction method for sand-clay interbedded geology provided in an embodiment of the present invention; Figure 2 This is a schematic diagram showing the distribution of the rectangular pile cap and each pile in an embodiment of the present invention. Figure 3 This is a schematic diagram of the pile position zoning under the pier cap provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the cross-sectional profile of the grouting material for the central pile provided in an embodiment of the present invention; Figure 5 This is a schematic cross-sectional view of the corner pile grouting material provided in an embodiment of the present invention.

[0028] In the diagram: 1-Pile; 2-Pile location zoning diagram; 21-Central pile area; 22-Side / corner pile area; 31-Central pile; 32-First type of grouting material diffusion area; 33-Soil layer on the side of the central pile; 34-Soil layer at the end of the central pile; 41-Side / corner pile; 42-Second type of grouting material diffusion area; 43-Soil layer on the side of the side / corner pile; 44-Soil layer at the end of the side / corner pile. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1: Pile foundation project of a high-rise building.

[0031] This embodiment uses the pile foundation construction of a high-rise residential building in a coastal city as an example. The geological conditions of this project are typical water-bearing sandy clay interbedded layers. From top to bottom, the strata are distributed as follows: fill layer, approximately 2.0m thick; clay layer, approximately 4.0m thick; water-bearing silty fine sand layer, approximately 6.0m thick, with a permeability coefficient of 5.2×10⁻⁶. -3 cm / s; clay layer, approximately 3.0 m thick; medium-coarse sand layer, i.e., confined aquifer, approximately 8.0 m thick, with a permeability coefficient of 8.7 × 10⁻⁶ cm / s; -3 cm / s; stiff plastic clay layer, not drilled through.

[0032] like Figure 1 As shown, the construction method includes the following steps: Step S1: Foundation soil testing and analysis.

[0033] Detailed geological surveys and indoor geotechnical tests were conducted before construction to obtain the physical and mechanical parameters of the aforementioned strata, with a focus on determining the permeability, porosity, and particle size distribution of the third and fifth sand layers. The permeability coefficient is a key parameter determining the diffusion capacity of the grout; a higher permeability coefficient in a sand layer allows for easier grout penetration and diffusion, but also increases the risk of loss. Therefore, it is essential to rationally select the grout mix ratio and grouting pressure based on the permeability coefficient. Based on the test data, indoor grouting simulation tests were conducted to determine the diffusion radius and appropriate grouting volume for different grout mix ratios in each sand layer. Empirical values ​​for the permeability coefficient of common strata are shown in Table 1.

[0034] Table 1. Empirical values ​​for permeability coefficients in common formations.

[0035] Step S2: Preparation of grouting materials.

[0036] The first type of grouting material, namely the grouting material for center piles, is mainly composed of inorganic cementitious materials. In this embodiment, P·O 42.5 silicate cement is selected as the inorganic cementitious material, with the following proportions: 100 parts by weight of silicate cement, 65 parts by weight of water (water-cement ratio 0.65), 0.8 parts by weight of polycarboxylate superplasticizer, 0.4 parts by weight of thickener (hydroxypropyl methylcellulose), and 0.2 parts by weight of retarder. During preparation, the cement and superplasticizer are first dry-mixed evenly, then water is added and stirred for at least 2 minutes. The grout is then filtered through a 16-mesh sieve before use. The high water-cement ratio combined with the superplasticizer gives the grout excellent fluidity, while the retarder extends the initial setting time to approximately 6 hours, providing a sufficient time window for pile driving and ensuring that the grout can fully penetrate and diffuse in the water-bearing sand layer. The measured diffusion radius of this grout in the water-bearing sand layer reaches 0.8–1.2 m, and the initial setting time is approximately 6 hours.

[0037] The second type of grouting material, namely grouting material for edge piles and corner piles, is a cement-inorganic composite material with cement as the main component and active admixtures added. In this embodiment, P·O 42.5 silicate cement is selected as the main cement, with the following proportions: 100 parts by weight of silicate cement, 52 parts by weight of water (water-cement ratio 0.52), 7 parts by weight of UEA-type micro-expansion agent, 6 parts by weight of silica fume, 12 parts by weight of S95 grade slag powder, 2 parts by weight of defoamer (modified organosilicon), and 1.0 part by weight of polycarboxylate superplasticizer. During preparation, the cement, micro-expansion agent, defoamer, silica fume, and slag powder are first dry-mixed evenly, and then water and superplasticizer are added and stirred for at least 3 minutes. The low water-cement ratio ensures high strength of the grout after curing. The micro-expansion agent undergoes moderate volume expansion during curing, which can tightly fill the voids at the pile-soil interface and eliminate micro-gaps between the grouting layer and the borehole wall. Active admixtures such as silica fume and slag powder further improve the bonding strength and impermeability of the grout. The grout achieves a compressive strength of 58 MPa after 7 days of curing and a bond strength of 1.8 MPa with the pile concrete; after 28 days, its compressive strength reaches 70 MPa and its bond strength with the pile concrete reaches 2.5 MPa. Performance indicators for both types of grouting materials are shown in Table 2.

[0038] Table 2 Comparison of the performance of the two types of grouting materials

[0039] Step S3: Determine the pile location zoning and differentiated grouting scheme.

[0040] The rigid foundation of this project measures 12.0m × 12.0m, and the design uses φ600mm prestressed concrete pipe piles, with a total of 13 piles installed. (For example...) Figure 2 and Figure 3As shown, the pile positions employ a 3×3 row and column arrangement of 9 piles, with one pile placed at the center of every four adjacent arrays, for a total of 13 piles. The 4 piles located at the four corners of the pile cap constitute the corner pile area, and the 4 piles located in the middle sections of each side of the pile cap constitute the edge pile area. Both the corner pile area and the edge pile area use Class II grouting material. In this embodiment... Figure 3 In the diagram, the corner pile area and the edge pile area are uniformly drawn as edge / corner pile area 22, and the five piles located in the center area of ​​the pile cap are designated as center pile area 21. For example... Figure 3 As shown, the central pile area 21 is distributed inside the rectangular frame-shaped side / corner pile area 22. For ease of description, the side piles and corner piles are sometimes collectively referred to as side / corner piles, or the side / corner pile area is described as side / corner pile area 22.

[0041] Based on the finite element analysis results, without considering differentiated reinforcement, the reaction force at the top of the corner piles is approximately 1.25 times the average, the side piles are approximately 1.05 times, and the center piles are approximately 0.75 times. This indicates that the corner piles bear the greatest reaction force under the pile group effect and require stronger reinforcement; the center pile 31 has the smallest reaction force, but its bearing potential has not yet been fully realized. Based on this, a differentiated grouting scheme was formulated: the center pile area 21 uses Class I grouting material, with a single-hole grouting volume of 0.6 times the borehole volume; the side pile area uses Class II grouting material, with a single-hole grouting volume of 0.5 times the borehole volume; and the corner pile area uses Class II grouting material, with a single-hole grouting volume of 0.55 times the borehole volume. That is, the single-hole grouting volume in the corner pile area is greater than that in the side pile area. See Table 3 for the differentiated grouting scheme.

[0042] Table 3 Differentiated Grouting Schemes

[0043] Step S4: Pre-drilling the center pile hole, grouting, and planting the pile.

[0044] like Figure 4 As shown, a long spiral drilling rig is used for pre-drilling. First, holes are drilled at the pile positions within the central pile area 21. After drilling to the designed depth, the first type of grouting material is injected through the grouting pipe, with the grouting volume being 0.5 to 0.7 times the borehole volume. The drilling depth and grouting volume of the pile positions within the central pile area 21 are greater than those in the side / corner pile areas. The purpose is to form a deeper and stronger pile end reinforcement, allowing the pile end of the central pile 31 to penetrate the water-bearing sand layer and enter a deeper bearing layer, namely the central pile end soil layer 34. After grouting, the pile is left to stand for approximately 30 minutes to allow the first type of grouting material to fully penetrate and diffuse in the water-bearing sand layer, forming a first type of grouting material diffusion area 32 on both sides of the pile end. Grout is replenished promptly if it is lost. The purpose of standing is to give the grout sufficient time to penetrate and diffuse, allowing it to fully cement the surrounding sand particles, i.e., the central pile side soil layer 33, forming the temporary protective wall required for subsequent side / corner pile construction.

[0045] The grouting pipe is lowered to 0.3m from the bottom of the hole, and grouting is carried out in sections from bottom to top. Low-pressure, slow grouting is used for the piles within the central pile area 21, with the grouting pressure maintained between 0.5 and 1.0 MPa. The purpose of low-pressure, slow grouting is twofold: firstly, to avoid high-pressure grouting damaging the hole wall stability or causing grout to suddenly flow out along cracks; secondly, to ensure that the grout evenly fills the sand layer pores through penetration, forming a continuous and reliable solidified body.

[0046] Approximately 0.5 hours after grouting, pile driving was carried out using a diesel-powered pile driver. Penetration was recorded in real-time during the driving process. For the central pile 31, due to the effective penetration and reinforcement of the fifth layer of medium-coarse sand by the first type of grouting material, the resistance during hammering through this layer was significantly reduced, and the pile tip successfully entered the sixth layer of stiff plastic clay, increasing the effective pile length by approximately 1.5m compared to conventional construction. Penetration was used as the final hammer control standard during pile driving; driving was stopped when the penetration reached the designed final hammer standard to avoid blindly pursuing pile length and damaging the pile body. Since the initial setting time of the first type of grouting material is adjustable within the range of 4–10 hours, this embodiment scheduled the hammer driving to be completed within 2–4 hours after grouting to fully utilize the lubrication and resistance reduction effect of the grout during its flow state.

[0047] Step S5: Pre-drill holes for side piles and corner piles, grout, and install piles.

[0048] like Figure 5 As shown, after the construction of the central pile area 21 is completed, the pre-drilling of pile positions in the side pile area and corner pile area is carried out. At this time, the first type of grouting material of the central pile 31 has penetrated and diffused in the water-bearing sand layer, cementing the loose sand particles around the hole, i.e., the soil layer 33 on the side of the central pile, to form a temporary protective wall, providing stable hole wall support for the pre-drilling of the side and corner piles 41. The pre-drilling is also carried out using a long spiral drilling rig. According to the scheme determined in step S3, the corresponding type of grouting material is injected into each pre-drilled hole. The grouting pipe is lowered to 0.3m from the bottom of the hole, and grouting is carried out in sections from bottom to top. Gravity grouting is used for the pile positions in the side pile area and corner pile area, relying on the natural flow of the grout to fill the space inside the hole. The second type of grouting material forms an annular grout shell on both sides of the pile body, i.e., the diffusion area 42 of the second type of grouting material, to avoid the second type of grout from diffusing and being lost outside the hole due to high-pressure grouting.

[0049] Construction records show that after adopting this method, the collapse rate during the drilling process of the side piles and corner piles (or side and corner piles 41) was reduced from 18% in conventional construction to below 4%. After grouting, pile driving was carried out using a diesel-powered pile driver. The pile driving process of the side and corner piles 41 was smooth, and the verticality of the piles was controlled within 0.8%. The pile driving of the side piles and corner piles was scheduled to be completed within 1 to 3 hours after grouting to match the shorter setting time of the second type of grouting material.

[0050] Step S6: Quality inspection.

[0051] Seven days later, a static load test was conducted, and the main results are as follows: the ultimate bearing capacity of the pile group after differentiated grouting was 28,600 kN, which was about 18.2% higher than that of the control group using uniform grouting material (24,200 kN); the maximum differential settlement between the edge and center of the pile cap was 4.2 mm, which was about 50.6% lower than that of the control group (8.5 mm); the unevenness coefficient of the pile top reaction force between the corner piles and the center pile 31 decreased from 1.58 in the control group to 1.22, and the stress distribution of the pile body was significantly improved.

[0052] Example 2: Pile foundation project of a multi-story frame building.

[0053] This embodiment takes the pile foundation construction of a multi-story frame building as an example. The foundation size of this project is 8.0m×8.0m, and the design adopts φ500mm prestressed concrete pipe piles, with a total of 9 piles arranged in a 3×3 row and column pattern, with a pile spacing of 2.6m. According to the pile group effect analysis results, the pile positions under the foundation are divided into: the central pile area 21, which is one pile position located in the center of the foundation; the side pile area, which is four pile positions located in the middle of the four sides of the foundation; and the corner pile area, which is four pile positions located in the four corners of the foundation. Since the number of piles is no more than 9, this embodiment does not set a transition zone. When the number of pile positions is small, the pile group effect is relatively mild, and zonal grouting can meet the requirements for variable stiffness leveling.

[0054] Based on the finite element analysis results, the pile top reaction force of the corner piles is approximately 1.15 times the average value, that of the edge piles is approximately 1.03 times, and that of the central pile 31 is approximately 0.82 times. Accordingly, a differentiated grouting scheme was formulated: For piles within the central pile area 21, Class I grouting material was used, with a single-hole grouting volume of 0.6 times the borehole volume; for piles within the edge pile area, Class II grouting material was used, with a single-hole grouting volume of 0.5 times the borehole volume; and for piles within the corner pile area, Class II grouting material was used, with a single-hole grouting volume of 0.55 times the borehole volume.

[0055] During construction, the central pile area 21 was constructed first. After the grout in the central pile 31 had diffused, the pre-drilled holes in the side pile area and corner pile area were then constructed. The test results showed that the ultimate bearing capacity of the pile group in this embodiment was increased by about 15% compared with the control group with uniform grouting, the maximum differential settlement of the pile cap was reduced by about 45%, and the non-uniformity coefficient of the pile top reaction force between the corner piles and the central pile 31 was reduced from 1.42 to 1.18.

[0056] This embodiment also provides a differential grouting and pile driving construction system for sand-clay interbedded geological layers, including: The soil testing and analysis unit is used to conduct soil tests and analyses on the construction site, obtain the physical and mechanical parameters of each stratum, and verify the diffusion performance, setting time and solidification strength of grouting materials with different proportions in the corresponding soil layers through indoor grouting simulation tests. The grouting material preparation unit is used to prepare the first type of grouting material and the second type of grouting material based on the test and analysis results of the soil test and analysis unit. The pile location zoning and grouting scheme determination unit is used to divide the pile locations under the rigid pile cap into the central pile area 21, the side pile area and the corner pile area according to the planar dimensions of the rigid pile cap and the pile layout scheme. Based on the group pile effect, the stress characteristics of the pile foundation in each area are determined and a differentiated grouting scheme is formulated. The central pile construction unit is used to prioritize the pre-drilling, grouting and pile driving of pile positions within the central pile area 21, including a long spiral drilling rig, grouting pipe, hoisting equipment and pile driver. The corner pile construction unit is used to pre-drill holes, grout and drive piles in the side pile area and corner pile area after the grouting of the central pile area 21 is completed and the grout has spread. The quality inspection unit is used to test the bearing capacity of the pile foundation after construction is completed and the grouting material has reached the design strength.

[0057] Other implementation methods: When the number of piles in the pile cap is large (e.g., 25 piles arranged in a 5×5 row and column pattern), a transition zone can be set between the central pile area 21, the side pile area, and the corner pile area. The pile positions in the transition zone are located in the middle ring area of ​​the pile cap plane. The grouting scheme is as follows: the pile positions in the transition zone are grouted with a mixed grout of the first type of grouting material and the second type of grouting material at a volume ratio of 1:1. The grouting volume per hole is 0.5 to 0.6 times the borehole volume. As the distance between the pile position and the central pile area 21 increases, the proportion of the second type of grouting material in the mixed grout is gradually increased to achieve a smooth transition of grouting parameters from the central pile area 21 to the side pile area and the corner pile area. In addition to the row and column pile arrangement, the pile position zoning method described in this invention is also applicable to other pile arrangement forms such as quincunx and staggered arrangement. The first type of grouting material can also be other inorganic cementitious material systems, and the micro-expansion agent in the second type of grouting material can also be a sulfoaluminate or calcium oxide expansion agent. The hammer-driven pile driving method can also be replaced by static pressure method. The differentiated grouting scheme can also be dynamically adjusted based on the measured pile top reaction force data. All of these fall within the protection scope of this invention.

[0058] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for differential grouting and pile planting in sand-clay interbedded geological formations, characterized in that, Includes the following steps: S1. Conduct soil tests and analyses on the construction site to obtain the physical and mechanical parameters of each stratum, and verify the diffusion performance, setting time and solidification strength of grouting materials with different proportions in the corresponding soil layers through indoor grouting simulation tests. S2. Based on the experimental analysis results of step S1, prepare at least two composite grouting materials with different properties: a first type of grouting material and a second type of grouting material; the first type of grouting material is mainly composed of inorganic cementitious materials, with a water-cement ratio controlled in the range of 0.6 to 0.7, and contains 0.5% to 1.0% water-reducing agent and 0.1% to 0.3% retarder by weight of cement; the second type of grouting material is a cement-inorganic composite material, mainly composed of cement, with a water-cement ratio controlled in the range of 0.5 to 0.55, and contains 6% to 8% micro-expansion agent, 5% to 8% silica fume and 10% to 15% slag powder by weight of cement; S3. Based on the planar dimensions of the rigid pile cap and the pile layout scheme, the pile positions below the pile cap are divided into a central pile area, a side pile area, and a corner pile area. The piles corresponding to the pile positions in the central pile area are central piles, the piles corresponding to the pile positions in the side pile area are side piles, and the piles corresponding to the pile positions in the corner pile area are corner piles. All central, side, and corner piles are precast piles. Based on the pile group effect, the stress characteristics of the pile foundation in each area are determined, and a differentiated grouting scheme is formulated. The differentiated grouting scheme is as follows: the pile positions in the central pile area are grouted using the first type of grouting material, while the pile positions in the side pile area and the corner pile area are grouted using the second type of grouting material. S4. Prioritize pre-drilling, grouting and driving the piles in the central pile area. After grouting is completed, hoist the precast piles into place before the grout sets. Drive the piles by hammering and control the pile driving termination conditions by penetration. S5. After the grouting material in the central pile area has diffused in the soil, pre-drilling, grouting and pile driving are carried out on the pile positions in the side pile area and the corner pile area. The pre-drilling, grouting and pile driving process in the side pile area and the corner pile area is the same as step S4. S6. After construction is completed, once the grouting material reaches the design strength, the pile foundation bearing capacity test will be conducted.

2. The method for differential grouting and pile planting in sand-clay interbedded geological formations according to claim 1, characterized in that, In step S4, the drilling depth and single-hole grouting volume of the piles in the central pile area are both greater than those in the side pile area and the corner pile area; in step S5, the single-hole grouting volume of the piles in the corner pile area is greater than that of the piles in the side pile area.

3. The method for differential grouting and pile planting in sand-clay interbedded geological formations according to claim 1, characterized in that, In step S3, the central pile area refers to the pile positions located in the geometric center area of ​​the foundation plane, the side pile area refers to the pile positions located in the middle section area of ​​each side of the foundation, and the corner pile area refers to the pile positions located at each corner of the foundation.

4. The method for differential grouting and pile planting in sand-clay interbedded geological formations according to claim 3, characterized in that, In step S3, when the number of piles in the pier cap is greater than 9 and arranged in rows and columns, the corner pile area includes piles located at the four corners of the pier cap, the side pile area includes piles located at the middle of the four sides of the pier cap, and the central pile area includes piles located at the center of the pier cap and the remaining piles located within the central area of ​​the pier cap; when the number of piles in the pier cap is not greater than 9, the side pile area includes piles located at the middle of each side of the pier cap, the corner pile area includes piles located at each corner of the pier cap, and the central pile area includes the remaining piles.

5. The method for differential grouting and pile planting in sand-clay interbedded geological formations according to claim 1, characterized in that, In step S4, the driving depth of the central pile is greater than the depth of its pre-drilled hole; in step S5, the driving depth of the side piles and the corner piles is greater than the depth of their pre-drilled holes, so that the pile ends of the central pile, the side piles and the corner piles enter the soil below the pre-drilled hole and form a composite pile with the grouting material.

6. A differentiated grouting and pile driving system for sand-clay interbedded geology, characterized in that, include: The soil testing and analysis unit is used to conduct soil tests and analyses on the construction site, obtain the physical and mechanical parameters of each stratum, and verify the diffusion performance, setting time and solidification strength of grouting materials with different proportions in the corresponding soil layers through indoor grouting simulation tests. The grouting material preparation unit is used to prepare at least two composite grouting materials with different properties based on the test and analysis results of the soil test and analysis unit: a first type of grouting material and a second type of grouting material; the first type of grouting material is mainly composed of inorganic cementitious materials, with a water-cement ratio controlled in the range of 0.6 to 0.7, and contains 0.5% to 1.0% water-reducing agent and 0.1% to 0.3% retarder by weight of cement; the second type of grouting material is a cement-inorganic composite material, mainly composed of cement, with a water-cement ratio controlled in the range of 0.5 to 0.55, and contains 6% to 8% micro-expansion agent, 5% to 8% silica fume and 10% to 15% slag powder by weight of cement; The pile location zoning and grouting scheme determination unit is used to divide the pile locations below the pile cap into a central pile area, a side pile area, and a corner pile area based on the pile group effect and the planar dimensions and pile layout of the rigid pile cap. It determines the stress characteristics of the pile foundation in each area and formulates a differentiated grouting scheme. The differentiated grouting scheme is as follows: the pile locations in the central pile area are grouted using the first type of grouting material, while the pile locations in the side pile area and the corner pile area are grouted using the second type of grouting material. The piles corresponding to the pile locations in the central pile area are central piles, the pile locations corresponding to the pile locations in the side pile area are side piles, and the pile locations corresponding to the pile locations in the corner pile area are corner piles. All central piles, side piles, and corner piles are precast piles. The central pile construction unit is used to prioritize the pre-drilling, grouting and pile driving of the pile positions within the central pile area. After the grouting is completed, the precast pile is hoisted into place before the grout initially sets, and the pile is driven by hammering. The pile driving termination condition is controlled by the penetration degree. The corner pile construction unit is used to pre-drill holes, grout, and drive piles in the side pile area and the corner pile area after the grouting material in the central pile area has diffused in the soil. The pre-drilling, grouting, and pile driving process in the side pile area and the corner pile area is the same as the construction process of the central pile construction unit. The quality inspection unit is used to test the bearing capacity of the pile foundation after construction is completed and the grouting material has reached the design strength.

7. The differential grouting and pile planting construction system for sand-clay interbedded geology according to claim 6, characterized in that, During the construction of the central pile construction unit, the drilling depth and single-hole grouting volume of the pile positions in the central pile area are greater than those in the side pile area and the corner pile area. The single-hole grouting volume of the pile positions in the corner pile area is greater than that of the pile positions in the side pile area. The central pile construction unit includes a long spiral drilling rig, grouting pipe, hoisting equipment, and a pile driver.

8. The differential grouting and pile planting construction system for sand-clay interbedded geology according to claim 6, characterized in that, The pile location zoning and grouting scheme determination unit determines the stress characteristics of each zone of the pile foundation based on the finite element analysis results of the pile group effect.

9. The differential grouting and pile planting construction system for sand-clay interbedded geology according to claim 6, characterized in that, After the grouting of the central pile construction unit is completed, the first type of grouting material is allowed to penetrate and diffuse in the water-bearing sand layer before pre-drilling is carried out on the pile positions in the side pile area and the corner pile area. The diffusion property of the first type of grouting material is used to form a temporary protective wall for the surrounding soil. During the hammer driving process, the penetration degree is monitored in real time, and the pile driving is stopped when the penetration degree reaches the design final hammer standard.

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