A composite treatment method for high water content clayey soil deep filling foundation

Abstract

The present application belongs to the technical field of geotechnical engineering foundation treatment, and particularly relates to a composite treatment method for high-water-content clay deep filling foundation. The method comprises the following steps: pre-drilling a hole at the designed pile position by dry drilling process to form a pile hole; sinking a pipe into the pile hole to the designed depth, pouring gravel into the pipe, and vibrating and compacting the gravel while pulling out the pipe to form a gravel pile; and carrying out overall dynamic compaction on the site after the construction of the gravel pile is completed. The present application changes the sinking pipe from soil extrusion penetration to in-hole positioning through pre-drilling, solves the problem of pipe sticking and pipe holding in the conventional extrusion sinking pipe in high-water-content clay, and realizes deep-shallow integrated reinforcement through the synergistic effect of deep gravel pile reinforcement and shallow dynamic compaction compaction, which is suitable for high filling foundation treatment of highway, municipal, civil engineering and the like.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering foundation treatment technology, specifically relating to a composite treatment method for deep fill foundations of high-moisture-content cohesive soil. Background Technology

[0002] High-moisture-content cohesive soil refers to fine-grained soil with a natural moisture content significantly higher than its optimum moisture content. It is characterized by high moisture content, low permeability, high compressibility, and poor water stability. According to current relevant technical specifications, high-moisture-content cohesive soil is not suitable for direct use as roadbed or foundation filling material. It generally requires improvement treatment such as sun-drying and mixing with lime before use, or it should be discarded.

[0003] However, in the construction of mountain roads, municipal works, and site leveling projects, the amount of excavation and filling work is enormous, with numerous "excavating mountains and filling gullies" scenarios. Due to factors such as tight schedules and cost control, the high-moisture-content cohesive soil excavated is often directly backfilled without effective treatment, forming large areas of deep fill foundations with high-moisture-content cohesive soil. Such fill foundations generally have the following problems: First, the high-moisture-content cohesive soil has high plasticity, making it difficult to fully break up and evenly spread the soil blocks during compaction. This results in numerous weak interlayers, concentrated areas of hard lumps, and areas of varying moisture content within the fill, leading to poor backfill uniformity. Second, the soil strength index is low, and the foundation bearing capacity generally fails to meet design requirements. Third, the compressibility of the fill varies significantly, leading to substantial differential settlement after construction, which can easily cause road surface cracking, structural tilting, and other defects.

[0004] For deep fill foundations, dynamic compaction is a commonly used treatment method, which uses the impact of a falling hammer to compact the soil. However, dynamic compaction has significant limitations when applied to fill foundations with high water content cohesive soil: high water content cohesive soil has extremely low permeability, and the excess pore water pressure generated by dynamic compaction is difficult to dissipate in time, easily leading to the "rubber soil" phenomenon; at the same time, the effective reinforcement depth of dynamic compaction is limited, and the reinforcement effect on the lower part of the soil in deep fills is minimal, and the reinforcement effect varies significantly for non-uniform fills.

[0005] Crushed stone piles are another commonly used method for treating soft foundations, improving the bearing capacity of the foundation by forming vertical reinforcements and drainage channels within the foundation. However, conventional crushed stone pile construction often employs a compaction-driven pipe method, where soil is squeezed into the pile hole by a driven pipe before the pile is formed. In high-moisture-content cohesive soils, the adhesion force between the soil and the outer wall of the pile pipe is extremely high, resulting in excessive resistance during pipe penetration and extraction. This can lead to equipment overload, or even pipe adhesion, entanglement, or breakage accidents, resulting in a very low pile success rate. Furthermore, soil squeezing and vibration can damage the soil structure between piles, reducing its strength. Therefore, the conventional compaction-driven crushed stone pile method is difficult to implement in high-moisture-content cohesive fill foundations.

[0006] Although the existing technology has developed a combined treatment approach of "crushed stone piles + dynamic compaction," which involves constructing crushed stone piles first and then performing dynamic compaction, this approach still has shortcomings: First, the construction of crushed stone piles still relies on conventional driven pipe technology, and the feasibility of crushed stone pile construction in high moisture content cohesive soil has not been addressed; second, the process arrangement and parameters are mainly designed for general cohesive soil or collapsible loess, and have not been adapted to the characteristics of uneven backfilling and low bearing capacity of high moisture content cohesive soil foundations.

[0007] In summary, for deep fill foundations in cohesive soil with high water content, there is an urgent need for a foundation treatment method that can reliably form crushed stone piles in cohesive soil with high water content, and can achieve synergistic reinforcement of deep strengthening and shallow compaction. Summary of the Invention

[0008] To address the aforementioned problems, this application discloses a composite treatment method for deep fill foundations of cohesive soil with high water content, comprising the following steps:

[0009] S1. Dry pre-drilling: Pre-drilling is carried out at the designed pile location using dry drilling technology to form pile holes;

[0010] S2. Non-compacted driven pipe pile formation: The driven pipe is driven into the pile hole to the design depth, crushed stone filler is put into the driven pipe, and the pipe is pulled out while vibrating to compact it, forming a crushed stone pile.

[0011] S3. Overall dynamic compaction: After the crushed stone pile construction is completed, the site is subjected to overall dynamic compaction.

[0012] Furthermore, the pile positions of the crushed stone piles are arranged in a quincunx or rectangular array.

[0013] Furthermore, in step S1, the diameter of the pile hole is 0.7 to 0.9 times the designed pile diameter of the crushed stone pile.

[0014] Furthermore, in step S1, the drilling rate of the pre-drilled hole is 0.8 to 1.2 m / min, and the verticality deviation of the hole is no more than 1%.

[0015] Furthermore, in step S2, the particle size of the crushed stone filler is 5-25 mm, the mud content is no more than 3%, and the tube pulling speed is 0.5-0.8 m / min.

[0016] Furthermore, in step S3, the overall dynamic compaction adopts a graded process of first spot compaction and then full compaction. The overlap width of the compaction points in the full compaction is not less than 1 / 3 of the hammer diameter, and the impact energy of the full compaction is 1 / 3 to 1 / 2 of the impact energy of the spot compaction.

[0017] Furthermore, the tamping energy of the point tamping is 2000-6000 kN·m, and the tamping is carried out 2-3 times. The tamping points are arranged in a quincunx pattern, and the average settlement of the last two tamping blows is no more than 5 cm as the standard for stopping the hammering.

[0018] Furthermore, step S3 includes a subbase construction step: a sand and gravel mixture subbase is laid on the surface of the site after dynamic compaction, and then leveled by full compaction and final compaction.

[0019] Furthermore, the thickness of the sand and gravel mixture subbase is 30–50 cm.

[0020] Furthermore, it also includes the step of zoning according to the requirements of the superstructure load: for high load-bearing areas, steps S1 to S3 and the subbase construction steps are executed in sequence; for ordinary areas, crushed stone pile construction is not carried out, only the overall dynamic compaction and subbase construction steps are executed.

[0021] Beneficial effects

[0022] (1) This invention specifically addresses the issues of uniformity and insufficient bearing capacity in backfill foundations with high moisture content cohesive soil. Through the synergistic effect of crushed stone piles and dynamic compaction, the crushed stone piles form a vertical reinforcement skeleton at a deep depth, thereby improving the overall bearing capacity through pile replacement. At the same time, the crushed stone piles, acting as vertical drainage channels, can accelerate the dissipation of excess pore water pressure generated by dynamic compaction, effectively preventing the "rubber soil" phenomenon in high moisture content cohesive soil during dynamic compaction. On the other hand, the dynamic compaction impact deeply compacts the fill, enabling the originally loose and uneven fill to achieve a relatively consistent density at different depths, thus significantly reducing the variability of the mechanical properties of the fill and fundamentally solving the inherent problems of poor uniformity and low bearing capacity in high moisture content cohesive soil backfill foundations.

[0023] (2) This invention breaks through the construction taboo of conventional driven stone piles in high-moisture cohesive soil from the perspective of technological principle. The invention creatively adopts the stone pile construction technology of "dry operation pre-drilling + non-compacting driven pipe", which forms the pile hole channel in advance by pre-drilling holes, so that the subsequent driven pipe operation is changed from "soil squeezing penetration" to "positioning along the hole", which completely avoids the problem of pipe sticking and entanglement caused by the high adhesion of high-moisture cohesive soil. This makes the application of stone pile technology in high-moisture cohesive soil change from "infeasible" to "feasible", filling the technical gap of stone pile construction under this soil condition.

[0024] (3) The process is well coordinated, and the "pile first, then tamping" method achieves double reinforcement. The present invention adopts the construction sequence of "first crushed stone piles, then dynamic tamping", but it is different from the traditional combined construction method in that: through the optimization of pre-drilling and non-compacting driven pipes, the construction quality of crushed stone piles is guaranteed; while the subsequent dynamic tamping reinforces the shallow non-uniform fill, its impact force acts on the crushed stone pile head, which expands the diameter of the pile head and compacts the soil between the piles, further improving the pile-soil synergistic performance and achieving a synergistic effect of 1+1>2.

[0025] (4) Deep and shallow layers are considered together for integrated reinforcement. Crushed stone piles provide deep vertical reinforcement, penetrating the entire deep fill layer; dynamic compaction provides overall compaction of the shallow layer (3-8m below the surface). The two complement each other in depth and form a synergistic system of "deep bearing capacity + shallow homogenization" in function, which solves the inherent contradiction of "taking the deep layer into account and the shallow layer into account" in deep fill foundations.

[0026] (5) Differentiated design by zone, taking into account both technology and economy. The present invention can carry out differentiated design by zone according to the requirements of the superstructure load. The high load-bearing area adopts pile-ramming combined treatment, while the ordinary area only adopts dynamic ramming treatment, thus achieving the optimization of project cost while ensuring technical reliability. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart of the construction process of the present invention.

[0029] Figure 2 This is a schematic diagram of the plum blossom-shaped layout of the crushed stone pile positions according to the present invention.

[0030] Figure 3 This is a schematic diagram of the rectangular array layout of the crushed stone pile positions according to the present invention.

[0031] Figure 4 This is a schematic diagram of the dynamic compaction point arrangement of the present invention.

[0032] Figure 5 This is a schematic cross-sectional view of the foundation structure after the processing according to the present invention.

[0033] The markings in the diagram are as follows: 1—stone pile; 2—dynamic compaction point. Detailed Implementation

[0034] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0035] (I) Overall Implementation Method

[0036] like Figure 1 As shown, the composite treatment method for deep fill foundations of high-moisture-content cohesive soil provided by the present invention includes the following steps: S1, dry pre-drilling; S2, non-compacting pipe pile driving; S3, integral dynamic compaction. The technical terms, process details, and alternative solutions involved in each step are explained below.

[0037] In this invention, "high moisture content cohesive soil" refers to fine-grained soil with a natural moisture content significantly higher than the optimum moisture content.

[0038] The term "deep fill foundation" refers to a backfill foundation with a fill thickness of more than 10 meters.

[0039] Step S1: Dry pre-drilling

[0040] Dry drilling technology is used to pre-drill holes at the designed pile locations to form pile holes.

[0041] The term "dry drilling" refers to a drilling method that does not use mud or water for wall protection during the drilling process. Specifically, it can employ conventional dry drilling techniques such as long spiral drilling rig drilling or rotary drilling rig dry drilling.

[0042] The pre-drilled holes serve two purposes: first, they pre-form the pile hole channel, allowing subsequent pipe sinking operations to change from soil squeezing into the existing pile hole to placement along the existing pile hole, thus avoiding the high adhesion resistance of the high-moisture-content cohesive soil to the pipe wall; second, during the drilling process, the soil conditions at the hole opening can be used to determine whether there are hidden obstacles such as large-diameter hard lumps at the pile location, thus preventing the pipe sinking from being obstructed.

[0043] As a preferred option, the diameter of the pre-drilled hole is 0.7 to 0.9 times the designed diameter of the crushed stone pile. If the diameter of the pre-drilled hole is too small, the driven pipe may still scrape and squeeze the hole wall during penetration, failing to fully utilize the function of the pre-drilled hole; if the diameter of the pre-drilled hole is too large, the amount of crushed stone filling material increases, reducing economic efficiency, and weakening the constraint effect of the pile body on the soil between the piles. This ratio range takes into account both the feasibility of driven pipe and the quality of pile formation.

[0044] As a preferred option, the drilling rate should be controlled at 0.8–1.2 m / min, and the verticality deviation of the borehole should not exceed 1%. Excessive drilling speed can easily lead to borehole wall collapse and irregular borehole shape; excessive verticality deviation can cause misalignment of the driven pipe and tilting of the pile. The pilot hole depth should be slightly greater than the designed pile length (e.g., 0.3–0.5 m beyond the design depth) to ensure the driven pipe is in place.

[0045] It should be noted that before the dry drilling, the site is usually pre-treated, such as ① site pre-treatment: clearing and leveling the site to be treated to form a construction working surface; ② layout of crushed stone pile positions: laying out the crushed stone pile positions on the pre-treated site according to the design drawings, etc.

[0046] In a further embodiment, the pile positions can be arranged in a quincunx or rectangular array, as shown in the schematic diagram below. Figure 2 As shown in (plum blossom shape) and (rectangular shape). The pile diameter is generally 0.4-0.6 m, the pile spacing is generally 1.0-2.5 m, and the pile length should penetrate the main fill layer and enter the lower relatively stable bearing layer by at least 1.0 m. The above pretreatment parameters can be generally set by those skilled in the art based on the design bearing capacity, fill thickness, and soil conditions.

[0047] Step S2: Non-compacted pipe pile driving

[0048] The pipe is driven into the pile hole to the designed depth, and crushed stone filler is put into the pipe. The pipe is pulled out while being vibrated to compact it, forming a crushed stone pile.

[0049] The term "non-compaction pipe sinking" refers to a pipe sinking method in which the pipe is driven into the pile hole formed by the pre-drilled hole, and the driving process does not produce a significant soil squeezing effect on the surrounding soil. In essence, the pipe sinking mainly overcomes the frictional resistance between the pipe wall and the hole wall, rather than the soil compaction resistance. Therefore, the difficulty of pipe sinking is greatly reduced, and the structural disturbance to the soil between the piles is minimal, which is conducive to protecting the strength of the soil between the piles.

[0050] The term "simultaneous pipe pulling and vibration compaction" refers to the continuous vibration of the pipe during the pipe pulling process, which causes the crushed stone filling inside the pipe to be compacted during the fall, forming a dense and continuous pile body.

[0051] As a preferred option, the crushed stone filler particle size is 5–25 mm, the mud content is no more than 3%, and the pipe extraction rate is 0.5–0.8 m / min. If the filler particle size is too large, it can easily become stuck inside the pipe, causing pile breakage; if it is too small, the pile strength will be insufficient. Excessive mud content will reduce the drainage performance and strength of the pile. Too fast a pipe extraction rate can easily lead to pile diameter reduction or pile breakage, while too slow a rate will affect work efficiency. The filler should be added in batches, with the pipe extracted to a corresponding height after each batch to ensure continuous and uniform pile construction.

[0052] In this step, since the pipe is positioned along the existing pile hole, the problems of pipe sticking and entanglement caused by the high adhesion of cohesive soil with high water content are completely avoided, and the pile formation process is continuous and controllable. Non-compaction penetration causes little disturbance to the soil between piles, and the structural strength of the soil between piles is preserved, laying the foundation for subsequent pile-soil co-bearing.

[0053] Step S3: Overall dynamic compaction

[0054] After the crushed stone piles are constructed, the site is subjected to overall dynamic compaction.

[0055] As a preferred option, the overall dynamic compaction adopts a staged process of first spot compaction and then full compaction: such as Figure 4 As shown, in the spot compaction stage, the site is compacted multiple times according to the design compaction energy; in the full compaction stage, a low-energy full compaction is used to comprehensively reinforce the site. The overlap width of the full compaction points is not less than 1 / 3 of the hammer diameter, and the full compaction energy is 1 / 3 to 1 / 2 of the spot compaction energy. Insufficient overlap of compaction points will leave uncompacted areas, resulting in uneven density of the shallow layer; excessively high full compaction energy may disturb the already compacted shallow structure.

[0056] As a preferred method, the tamping energy is 2000–6000 kN·m, with 2–3 passes, and 4–8 blows per tamping point per pass. The tamping points are arranged in a quincunx pattern, with the spacing between adjacent tamping points generally being 1.5–2.5 times the diameter of the tamping hammer. The standard for stopping the hammering is that the average settlement of the last two blows should not exceed 5 cm. Those skilled in the art can adjust the tamping energy and number of passes according to the designed reinforcement depth and load-bearing requirements, and alternative forms such as a square tamping point arrangement can also be used.

[0057] In this step, on the one hand, dynamic compaction compacts the shallow, non-uniform fill, reducing the variability of the fill's mechanical properties; on the other hand, the impact of the compaction on the pile heads causes the pile heads to expand in diameter and the crushed stone to be squeezed into the soil between the piles, resulting in a displacement and compaction effect on the soil between the piles, which improves the pile-soil synergy. Finally, the crushed stone piles act as vertical drainage channels, accelerating the dissipation of excess pore water pressure generated by dynamic compaction, effectively preventing the "rubber soil" phenomenon in high-moisture-content cohesive soils during dynamic compaction. Thus, the crushed stone piles provide deep vertical reinforcement, while dynamic compaction provides shallow (generally 3–8 m below the surface) overall compaction. The two complement each other in depth, forming an integrated reinforcement system of "deep bearing capacity + shallow homogenization".

[0058] After the overall dynamic compaction is completed, as a preferred option, a sand and gravel mixture subbase can be laid on the site surface and then leveled by full compaction. The preferred thickness of the subbase is 30–50 cm, and the subbase material can be graded sand and gravel with a sand-to-gravel ratio of approximately 3:7 and a maximum particle size of no more than 5 cm. The function of the subbase is to form a flat and dense bearing layer and to coordinate the distribution of pile-soil loads.

[0059] As a preferred solution, the site can be divided into zones based on the requirements of the superstructure load: For high-load-bearing areas (such as directly below embankments, heavy equipment foundation areas, and tall structure areas), steps S1 to S3 and the subbase construction steps are executed sequentially. The high load-bearing requirements are met through the synergistic effect of deep reinforcement by crushed stone piles and shallow compaction by dynamic tamping. For ordinary areas (such as general road areas, green areas, and light-load areas), where the requirements for bearing capacity and foundation modulus are not high, crushed stone pile construction can be omitted, and only the overall dynamic tamping and subbase construction steps are performed. This zoning scheme can significantly reduce the project cost while meeting the load-bearing requirements of each area.

[0060] It should be noted that the numerical ranges of the pilot hole diameter ratio, drilling rate, filler parameters, tamping energy, and bedding layer thickness mentioned above are all preferred embodiments. Conventional adjustments and equivalent substitutions made by those skilled in the art under the concept of this invention (such as changes in drilling equipment and tamping point arrangement) should all fall within the protection scope of this invention.

[0061] The embodiments and technical effects of the present invention are described below with reference to the accompanying drawings and specific engineering examples, but the embodiments of the present invention are not limited thereto.

[0062] Example 1

[0063] The backfill foundation of a newly built factory building has a backfilling period of 7-8 years, a fill thickness of 6-20m, and the fill material is high-moisture-content red clay with a natural moisture content of 38%-46% and a liquid limit of w. L =53%~60%, plasticity index I P =24~29. The compression coefficient α was determined by indoor geotechnical testing. 1-2 =0.42~0.68MPa⁻¹, the characteristic value of the foundation bearing capacity is only 105~125kPa. The design requirements are that the bearing capacity of the treated composite foundation is ≥200kPa, the post-construction settlement is ≤25cm, and the differential settlement is ≤0.5%.

[0064] The specific steps for foundation treatment using the method of this invention are as follows:

[0065] S1. Site Pre-treatment: Remove debris, vegetation, and loose soil from the surface of the fill site. Use bulldozers to level the site and create a smooth working surface. Fill and smooth any uneven areas.

[0066] S2. Crushed stone pile layout: Lay out the pile locations according to the design drawings (crushed stone piles will be placed at the locations of the independent column foundations of the factory building; no piles will be placed at the locations of factory roads and ground levels), using a quincunx pattern (see attached). Figure 2 As shown), the pile spacing is 1.5m, the pile diameter is 0.5m, and the pile length is 10m (penetrating the high water content cohesive soil fill layer into the lower relatively dense silty clay bearing layer for no less than 1.0m).

[0067] S3. Dry Pre-drilling: A long spiral drilling rig is used for dry drilling. The pre-drilling diameter is 0.4m, the drilling rate is controlled at 1.0m / min, the verticality deviation of the drilling is ≤1%, and the pre-drilling depth is 10.5m (0.5m extra depth to ensure the pipe is in place). During drilling, the soil coming out of the hole is observed and recorded for any abnormalities such as large-diameter hard lumps.

[0068] S4. Non-compacted driven pipe forming of crushed stone pile body: The vibratory driven pipe is driven to the design depth (pile bottom elevation) along the pre-drilled hole channel. During the driving process, the driving speed is uniform and there is no obvious jamming phenomenon. After reaching the design depth, graded crushed stone filler (particle size 5-25mm, mud content 1.8%) is added in batches. The pipe pulling rate is controlled at 0.6m / min, and vibration compaction is carried out while pulling the pipe, finally forming the crushed stone pile body. After the pile is completed, random inspection shows that the pile body is continuous and intact, and no broken piles or diameter reduction are found.

[0069] S5. Overall Dynamic Compaction Reinforcement: After the crushed stone piles are completed and pass inspection, overall dynamic compaction is carried out. Point compaction uses an energy level of 5000 kN·m, with two passes. The first pass has a point spacing of 5.0m, and the second pass is interleaved. Each point in each pass receives 5-7 blows (the standard for stopping the hammer is that the average settlement of the last two blows is ≤5cm). Full compaction uses an energy level of 1000 kN·m, with one pass and 3 blows per point. The overlap width of the compaction points is not less than 1 / 3 of the hammer diameter (hammer diameter 2.5m).

[0070] During construction, the excess pore water pressure caused by dynamic compaction dissipated well, and no "rubber soil" phenomenon occurred, indicating that the pre-drilled stone piles formed an effective vertical drainage channel.

[0071] S6. Final compaction and leveling of the subbase: Lay a 40cm thick sand and gravel mixture subbase (sand-gravel ratio 3:7, maximum particle size ≤5cm), and perform final compaction and leveling using a 1000kN·m energy level compactor. The resulting schematic diagram of the final foundation structure cross-section is shown below. Figure 5 As shown.

[0072] Effect detection:

[0073] After treatment, static load tests on the composite foundation using single piles showed that the characteristic value of the composite foundation's bearing capacity reached 228 kPa, meeting the design requirements (≥200 kPa). Dynamic penetration testing and wave velocity testing of the deep soil layers revealed a significant improvement in the compaction of the lower and middle sections of the fill, and a marked improvement in the uniformity of the fill. Post-construction settlement monitoring for 18 months showed a cumulative settlement of 21.3 cm and a differential settlement of 0.32%, both meeting the design control standards.

[0074] Example 2

[0075] A fill site in an industrial park has a fill thickness of 8-15m. The fill material is high-moisture-content cohesive soil (natural moisture content 32%-44%, liquid limit w). L=51%~58%). The plant area is divided into a heavy equipment area (high load-bearing area, with a design load-bearing capacity ≥280kPa) and a general road area (general area, with a design load-bearing capacity ≥150kPa).

[0076] The partitioning differentiation design scheme of this invention is adopted:

[0077] Heavy equipment area (approximately 12,000 m²): A combined pile-ramming treatment process was adopted. Crushed stone piles were spaced 1.6 m apart, arranged in a staggered pattern, with a pile diameter of 0.5 m and a pile length of 8 m (penetrating the fill layer); dynamic compaction was performed using 5000 kN·m level point compaction (3 passes) + 1500 kN·m level full compaction; the foundation layer thickness was 50 cm. After treatment, testing showed that the characteristic value of the composite foundation bearing capacity reached 296 kPa, meeting the design requirements for heavy equipment foundations.

[0078] Ordinary road area (approximately 28,000 m²): only dynamic compaction was used, without crushed stone piles. Dynamic compaction employed 3000 kN·m energy level point compaction (2 passes) + 1000 kN·m energy level full compaction; the foundation layer thickness was 30 cm. Post-treatment testing showed that the characteristic value of the foundation bearing capacity reached 172 kPa, meeting the road design requirements.

[0079] Economic benefits: According to comparative calculations, the total cost of adopting the zoned differentiated design scheme is about 62% of that of adopting the pile-ramming combined treatment scheme for all areas, saving about 38% of the project cost, and achieving significant economic benefits while ensuring the load-bearing requirements of each area.

[0080] Example 3

[0081] A municipal high embankment site has an embankment height of 10-12m. The fill material is high-moisture cohesive soil (natural water content 40%-45%, liquid limit w) generated from the excavation of surrounding foundation pits. L =52%~55%). The groundwater level within the site area is low (depth > 15m), and there is no groundwater influence. The design requires the foundation bearing capacity after treatment to be ≥160kPa and the compaction degree to be ≥93%.

[0082] The main construction parameters for processing using the method of this invention are:

[0083] Crushed stone piles: pile spacing 2.2m (rectangular array layout), pile diameter 0.4m, pile length 6m;

[0084] Pre-drilling: Drilling rate 0.9 m / min, verticality deviation ≤1%;

[0085] Crushed stone filler: particle size 5-20mm, mud content 2.5%, tube pulling speed 0.7m / min;

[0086] Dynamic compaction: point compaction energy level 2500kN·m (2 passes, 5 blows per point), full compaction energy level 800kN·m (1 pass, 2 blows per point), compaction point overlap width 1 / 3 of the hammer diameter;

[0087] Subbase: 35cm thick, graded sand and gravel.

[0088] Post-treatment test results: The characteristic value of the composite foundation bearing capacity is 185 kPa, and the compaction degree is 94.2%–96.5%, meeting the design requirements. No pipe adhesion or entanglement occurred during the construction of the crushed stone piles, and the pile completion qualification rate was 100%, verifying the effectiveness and reliability of the method of this invention in high-moisture-content cohesive soil fill foundations.

[0089] The method of this invention is reasonable in process, simple to operate, and has controllable construction quality. The core equipment (auger drilling rig, vibratory pipe driving machine, and dynamic compaction machine) are all conventional equipment in the field of geotechnical engineering, requiring no special equipment and having good applicability. This invention can be widely applied to the reinforcement treatment of deep fill foundations with high moisture content cohesive soil in highway, municipal, and civil engineering fields. It is particularly suitable for engineering scenarios with large fill thickness, poor backfill uniformity, and high bearing capacity requirements, and has significant technical and economic benefits.

[0090] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A composite treatment method for deep fill foundations of high-moisture-content cohesive soil, characterized in that, Includes the following steps: S1. Dry pre-drilling: Pre-drilling is carried out at the designed pile location using dry drilling technology to form pile holes; S2. Non-compacted driven pipe pile formation: The driven pipe is driven into the pile hole to the design depth, crushed stone filler is put into the driven pipe, and the pipe is pulled out while vibrating to compact it, forming a crushed stone pile. S3. Overall dynamic compaction: After the crushed stone pile construction is completed, the site is subjected to overall dynamic compaction.

2. The processing method according to claim 1, characterized in that: The crushed stone piles are arranged in a quincunx or rectangular array.

3. The processing method according to claim 1, characterized in that: In step S1, the diameter of the pile hole is 0.7 to 0.9 times the designed pile diameter of the crushed stone pile.

4. The processing method according to claim 1, characterized in that: In step S1, the drilling rate of the pre-drilled hole is 0.8 to 1.2 m / min, and the verticality deviation of the hole is no more than 1%.

5. The processing method according to claim 1, characterized in that: In step S2, the particle size of the crushed stone filler is 5-25 mm, the mud content is no more than 3%, and the tube pulling speed is 0.5-0.8 m / min.

6. The processing method according to claim 1, characterized in that: In step S3, the overall dynamic compaction adopts a graded process of first spot compaction and then full compaction. The overlap width of the compaction points in the full compaction is not less than 1 / 3 of the diameter of the hammer, and the impact energy of the full compaction is 1 / 3 to 1 / 2 of the impact energy of the spot compaction.

7. The processing method according to claim 6, characterized in that: The tamping energy of the tamping is 2000-6000 kN·m, and the tamping is carried out 2-3 times. The tamping points are arranged in a quincunx pattern, and the average settlement of the last two tamping blows is no more than 5 cm as the standard for stopping the hammering.

8. The processing method according to claim 1, characterized in that: Step S3 is followed by a subbase construction step: a sand and gravel mixture subbase is laid on the surface of the site after dynamic compaction, and then leveled by full compaction and final compaction.

9. The processing method according to claim 8, characterized in that: The thickness of the sand and gravel mixture subbase is 30–50 cm.

10. The processing method according to claim 8, characterized in that: It also includes the step of zoning according to the requirements of the superstructure load: for high load-bearing areas, steps S1 to S3 and the subbase construction steps are executed in sequence; for ordinary areas, no crushed stone pile construction is carried out, only the overall dynamic compaction and subbase construction steps are executed.

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