CFG pile construction method for gravel miscellaneous fill stratum

Abstract

The invention discloses a gravel miscellaneous fill stratum CFG pile construction method which comprises the following steps that an undesirable soil layer is excavated, and graded gravel is adopted for layered backfill replacement; a CFG pile is constructed on the graded broken stone, and the pile bottom end of the CFG pile is embedded into the strongly weathered mudstone; laying lower-layer graded sand gravels on the upper layer of the graded broken stones, laying a steel-plastic geogrid on the upper layer of the lower-layer graded sand gravels, and laying upper-layer graded sand gravels on the steel-plastic geogrid; and inspecting the composite foundation. Municipal road engineering soft foundation replacement filling and gravel miscellaneous fill stratum CFG pile construction are combined, and the problems that the gravel miscellaneous fill stratum CFG pile hole forming quality is poor, formed holes are prone to collapsing, the over-irrigation coefficient is too large, detection is complex, and the top two-way geogrid construction quality is poor are solved from the source; and working procedures can be effectively interspersed, the construction efficiency is improved, the labor cost is saved, the construction period is shortened, the construction process is adjustable, the construction quality is improved, and certain economic benefits are achieved.

Description

Technical Field

[0001] This application belongs to the field of municipal road construction technology, specifically relating to a CFG pile construction method for gravel and mixed fill soil strata, which is applicable to the use of CFG piles for soft soil foundation treatment in gravel and mixed fill soil strata. Background Technology

[0002] With the advancement of urbanization and the continuous increase in the mileage of highways and urban roads, CFG piles, as an effective method for soft soil foundation treatment, have played an important role in this process. CFG piles, or cement-fly ash-gravel piles, are high-bond-strength piles formed by mixing cement, fly ash, gravel, stone chips, or sand with water. They are widely used in the construction of industrial and civil buildings, ports and docks, highways, and urban roads, and are particularly suitable for treating soft soil foundations with characteristics such as high water content, high compressibility, poor permeability, high sensitivity, low strength, and uneven thickness.

[0003] In highway and urban road construction, the application of CFG piles is mainly reflected in the following aspects.

[0004] I. Enhancing Foundation Bearing Capacity: CFG piles can significantly improve the bearing capacity of the foundation, meeting the strength requirements of highways and urban roads. Through CFG pile composite foundation treatment, the load can be effectively distributed to deeper soil layers, thereby reducing foundation settlement and differential settlement.

[0005] II. Controlling Foundation Deformation: CFG piles possess excellent rigidity and integrity, effectively controlling foundation deformation. In highway and urban road expansion projects, the CFG pile composite foundation treatment method can significantly reduce differential settlement between new and old roadbeds and horizontal surface displacement, ensuring the smoothness and stability of the road.

[0006] Third, shortened construction period: The construction process of CFG piles is relatively simple, using a drilling and pressure grouting pile forming process that is pollution-free, vibration-free, and noise-free, making it particularly suitable for urban construction. At the same time, the construction speed of CFG piles is relatively fast, which can greatly shorten the construction period of highways and urban roads.

[0007] IV. Significant Environmental Benefits: CFG piles utilize a large amount of industrial waste such as fly ash in their pile materials, achieving the rational utilization of industrial waste. This not only reduces industrial waste pollution but also conserves resources, demonstrating significant environmental benefits.

[0008] In conclusion, with the advancement of urbanization and the continuous increase in the mileage of highways and urban roads, CFG piles, as an effective method for soft soil foundation treatment, will play an increasingly important role in future urban construction. Summary of the Invention

[0009] The purpose of this application is to provide a construction method for CFG piles in gravel-fill soil strata. Based on the characteristics of CFG piles in gravel-fill soil strata, this method combines soft soil replacement in municipal road engineering with the construction of CFG piles in these strata. By controlling the quality of soft soil replacement, CFG pile drilling, CFG pile testing, and the construction quality of the geogrid on top of the CFG piles, this method fundamentally solves the problems of poor drilling quality, easy hole collapse, excessive over-grouting coefficient, complex testing, and poor construction quality of the top bidirectional geogrid in gravel-fill soil strata. Simultaneously, it allows for effective interleaving of construction processes, improving construction efficiency, saving labor costs, shortening the construction period, allowing for adjustment of the construction process, and improving construction quality, thus offering certain economic benefits.

[0010] The objective of this application is achieved through the following technical solution: A method for constructing CFG piles in gravelly fill soil strata includes the following steps: Step S01, soft soil replacement: excavate the unsuitable soil layer and replace it with graded crushed stone in layers; Step S02, pile foundation construction: CFG piles are constructed on graded crushed stone, with the bottom end of the CFG pile embedded in strongly weathered mudstone. Step S03, geogrid construction: lay a lower layer of graded gravel on top of the graded crushed stone, lay a steel-plastic geogrid on top of the lower layer of graded gravel, and then lay an upper layer of graded gravel on top of the steel-plastic geogrid. Step S04: Inspect the composite foundation.

[0011] Furthermore, in step S01, an excavator is used to remove the undesirable soil layer within a replacement depth of 3m, and the excavated waste soil is transported to the waste disposal site. When the excavator is 20cm away from the design elevation, manual cleaning is required.

[0012] Furthermore, in step S01, the natural crushed stone used for graded crushed stone has a particle size of 5~40mm, a crushing value ≤30%, a liquid limit value <25%, and a mud content ≤5%. The loose thickness of the graded crushed stone during paving is no more than 30cm. It is compacted using a vibratory roller, with compaction carried out in layers from low to high, and from the edges to the middle. The overlap between rows is 0.3~0.5m, and the overlap between compaction sections is more than 2m. The roller travel speed is no more than 4km / h, and the compaction density is ≥93%.

[0013] Furthermore, in step S02, when drilling begins, the drill bit valve is closed, the drill rod is moved downwards until the drill bit touches the ground, and then the motor is started to drill; if the drill rod is found to be shaking or difficult to drill, the advance is slowed down; during the drilling process, the pile driver's automatic control system strictly controls the descent speed and rotation speed of the drill rod to match the two; when an obstacle is encountered, drilling is stopped immediately, the obstacle is cleared, and then drilling resumes; drilling mud is removed at any time during the drilling process, and the remaining drilling mud is removed after the drilling rig is moved; the drilling rig adopts a skip-hole operation, and after the mixture at the adjacent position has solidified, the adjacent pile position is drilled.

[0014] Furthermore, in step S02, after the hole reaches the design elevation, drilling is stopped and concrete pumping begins. When the drill core tube is filled with concrete, the tube is pulled out while pumping continues, requiring continuous pumping. The slump of the concrete upon arrival is controlled at 160-200mm. When the main aggregate is crushed stone with a particle size of 5-15mm, fly ash, retarder, and pumping agent are added to the concrete, and the retarding time is controlled at more than 6 hours.

[0015] Furthermore, in step S02, when pumping concrete, the drill rod lifting speed shall be controlled within 3.0 m / min, and it is strictly forbidden to lift the drill rod before pumping material; if continuous grouting is not possible during construction, the fine sand and backfill soil layers shall be avoided according to the survey report and the geological conditions, and the machine shall not be stopped in the fine sand and backfill soil layers; during construction, the ratio of the actual grouting volume to the theoretical volume of each pile, i.e., the filling coefficient of the concrete, shall be maintained at least 1.15, and the over-grouting height of the concrete shall not be less than 0.5 m.

[0016] Furthermore, in step S02, after the CFG piles have been naturally cured for 7 days, earthwork excavation is organized according to the principle of excavating first and then driving. The excavation boundary is marked with lime, and the excavation depth is accurately measured to avoid over-excavation or secondary excavation. When 30cm remains, manual excavation is carried out in conjunction with a small excavator. Mechanical excavation is carried out to the top elevation of the pile and the earthwork is leveled.

[0017] Furthermore, in step S02, after the soil between the piles is cleaned, the cutting position is marked along the pile head with an ink line or red paint. The cutting position is 2cm higher than the designed pile top elevation. A disc cutter is used to make a circumferential cut along the marked line, cutting in place in one go. At least 10% of the total number of piles are sampled for pile integrity testing.

[0018] Furthermore, in step S03, after the 10cm layer of graded gravel on top of the graded crushed stone is laid and compacted, a layer of steel-plastic geogrid is laid. The longitudinal and transverse ultimate tensile strength of the steel-plastic geogrid is >50kN / m, the elongation is <3%, the ultimate peel force at the rib intersection is >300N, the unit area mass is not less than 780g / ㎡, the longitudinal overlap length of the steel-plastic geogrid is greater than 20cm, the transverse overlap length is greater than 15cm, and it is fixed with U-shaped nails. The U-shaped nails are made of Φ8mm HPB300 steel bars, 9cm long and 10cm high, and the U-shaped nails are spaced 100×100cm in a staggered pattern. After the steel-plastic geogrid is laid, another 10cm layer of graded gravel is laid. The graded gravel particle size is 1~30mm, the saturated compressive strength of the stone is >30MPa, and the compaction density is ≥95%.

[0019] Furthermore, in step S04, in order to verify the effect of CFG pile treatment on the gravel and mixed fill soil layer, the bearing capacity of the treated composite foundation is tested. The number of composite foundation bearing capacity tests should not be less than 1% of the total number of piles, and should not be less than 3 points.

[0020] Beneficial effects of this application: 1. Effectively ensure the construction quality of CFG piles in gravelly and mixed fill soil strata, and avoid poor hole formation quality, easy hole collapse, and excessive over-grouting coefficient of CFG piles in gravelly and mixed fill soil strata.

[0021] 2. Effectively improve the quality and efficiency of CFG pile head cutting in gravelly fill soil strata, improve the efficiency of CFG pile body integrity detection in gravelly fill soil strata, and provide a basis for the construction quality of CFG pile body in gravelly fill soil strata.

[0022] 3. Effectively ensure the quality of steel-plastic geogrid laying on top of CFG piles in gravelly and miscellaneous fill soil layers, improve the construction quality and efficiency of steel-plastic geogrid, and ensure that the bearing capacity of the composite foundation meets the requirements.

[0023] 4. Effectively ensure that the CFG pile composite bearing capacity of the crushed stone and miscellaneous fill soil layer meets the design document requirements, avoid insufficient foundation bearing capacity due to various factors, thereby avoiding quality problems and effectively ensuring the use function and effect of municipal roads.

[0024] 5. Further ensure the construction quality of CFG piles in gravelly and mixed fill soil strata, reduce costs, improve quality, and provide guidance and direction for efficient and high-quality foundation treatment construction.

[0025] The aforementioned main solution and its various further alternatives can be freely combined to form multiple solutions, all of which are solutions that can be adopted and are claimed in this application; furthermore, the (non-conflicting alternatives) can also be freely combined with each other and with other alternatives. Those skilled in the art, after understanding the solution of this application, will realize from the prior art and common general knowledge that there are many combinations, all of which are technical solutions to be protected by this application, and will not be exhaustively listed here. Attached Figure Description

[0026] Figure 1 This is a schematic cross-sectional view of the strata in this application.

[0027] Figure 2 This is a schematic diagram of the floor plan of this application.

[0028] Figure 3 This is a schematic diagram of the transverse overlap of the bidirectional geogrid in this application.

[0029] Figure 4 This is a schematic diagram of the longitudinal overlap of the bidirectional geogrid in this application.

[0030] In the diagram: 1-Strongly weathered mudstone, 2-Miscellaneous fill, 3-CFG pile, 4-Graded crushed stone, 5-Lower layer graded gravel, 6-Steel-plastic geogrid, 7-Upper layer graded gravel, 8-U-shaped nail. Detailed Implementation

[0031] The following non-limiting embodiments are used to illustrate this application.

[0032] Example 1 refer to Figures 1-4 As shown, a method for constructing CFG piles in a gravel-filled soil stratum combines soft soil replacement with graded gravel and CFG pile engineering, including the following steps: Step S01, soft soil replacement: excavate the unfavorable soil layer on top of the fill soil 2, and replace it with graded gravel 4 in layers, specifying the soft soil replacement depth as 3m, and the compaction degree of the graded gravel is ≥93%.

[0033] In step S01, for the area requiring replacement, an excavator is used to remove the unsuitable soil layer within a 3m replacement depth. The excavated excavated soil is then transported by a loader to a more compacted section, and dump trucks are used to transport it to the designated spoil disposal site. When the excavator excavates to a depth of 20cm from the design elevation, manual cleaning of the bottom is required.

[0034] In step S01, the natural crushed stone used for graded crushed stone has a particle size of 5~40mm, a crushing value ≤30%, a liquid limit value <25%, and a mud content ≤5%. When paving the graded crushed stone, the loose thickness should not exceed 30cm. A vibratory roller should be used for compaction, proceeding in layers from low to high, and from the edges to the center. The overlap between rows (transverse) should be 0.3~0.5m, and the overlap between compaction sections (longitudinal) should be more than 2m. The roller's travel speed should not exceed 4km / h, and the compaction density should be ≥93%.

[0035] Step S02, pile foundation construction: CFG piles 3 are constructed on graded crushed stone 4. The bottom end of the CFG piles 3 is embedded in the strongly weathered mudstone 1. The pile diameter is 42cm, the spacing is 120×120cm, and they are arranged in an equilateral triangle. The pile end is embedded 50cm into the strongly weathered mudstone.

[0036] In step S02, at the start of drilling, the drill bit valve is closed, and the drill rod is moved downwards until the drill bit touches the ground. Then, the motor is started to drill. Generally, the speed is increased gradually from slow to fast. This reduces drill rod swaying and makes it easier to check for drilling deviations so that they can be corrected in time. During the drilling process, if the drill rod is found to be swaying or difficult to drill, the advance should be slowed down. Otherwise, it may easily lead to borehole deviation, displacement, or even damage to the drill rod and drilling tools.

[0037] During drilling, the pile driver's automatic control system strictly controls the drill rod's descent speed and rotation speed to ensure they are matched. Drilling is stopped immediately upon encountering an obstacle, and resumed only after the obstacle is cleared. Drill mud is removed continuously during drilling, and any remaining mud is removed after the drill rig is moved. The drill rig employs a skip-hole operation, drilling adjacent pile positions only after the mixture at adjacent locations has solidified.

[0038] In step S02, after the borehole reaches the design elevation, drilling is stopped, and concrete pumping begins. Once the drill core is filled with concrete, the core is pulled out while pumping continues, requiring continuous pumping. The slump of the concrete delivered to the site should be controlled between 160-200mm (this can be adjusted appropriately based on slump loss during transport from the mixing plant to the construction site, and determined based on on-site pile testing). If the main aggregate is crushed stone, it should not be too large, with a particle size of 5-15mm (this should meet the relevant provisions of the "Technical Specification for Concrete Pumping Construction" (JGJ / T 10-95)). Fly ash, a retarder, and a pumping agent are added to the concrete, with a retarding time controlled to be at least 6 hours, ensuring good workability.

[0039] In step S02, when pumping concrete, the drill rod lifting speed should be controlled within 3.0 m / min, and it is strictly forbidden to lift the drill rod before pumping material. If continuous grouting cannot be carried out due to other reasons during construction, the drilling should be stopped in fine sand and backfill soil layers, avoiding these areas, based on the survey report and the geological conditions. During construction, the ratio of the actual grouting volume to the theoretical volume of each pile, i.e., the concrete filling coefficient, should be maintained at least 1.15, and the over-pouring height should not be less than 0.5 m. Construction records should be kept during the drilling and grouting process.

[0040] In step S02, after the CFG piles have been naturally cured for 7 days, earthwork excavation is organized according to the principle of "first excavation, first demolition". The excavation boundary line is marked with lime, and the excavation depth is accurately measured to avoid over-excavation or secondary excavation. When 30cm remains, manual excavation is carried out in conjunction with a small excavator, and mechanical excavation is carried out to the top elevation of the pile and the earthwork is leveled.

[0041] In step S02, after the soil between the piles is cleaned, the cutting position is marked along the pile head with an ink line or red paint. The cutting position is 2cm higher than the designed pile top elevation. A circular cutter is used to make a circumferential cut along the marked line, cutting to the desired depth in one go. At least 10% of the total number of piles are sampled for pile integrity testing (according to the requirements of "JGJ79-2012 Technical Specification for Building Foundation Treatment" and "Sichuan Provincial Construction Engineering Quality On-site Testing Manual").

[0042] Step S03, Geogrid Installation: A 10cm layer of graded gravel 5 is laid on top of the graded crushed stone 4, with a compaction density ≥95%. A steel-plastic geogrid 6 is then laid on top of the lower layer of graded gravel 5. The steel-plastic geogrid 6 has a longitudinal and transverse ultimate tensile strength >50kN / m, elongation <3%, ultimate peel force at rib intersections >300N, and a unit area mass not less than 780g / ㎡. It is fixed using U-shaped nails 8, made of Φ8mm HPB300 steel bars, 9cm long and 10cm high, with a spacing of 100×100cm in a staggered pattern. Finally, a 10cm layer of graded gravel 7 is laid on top of the steel-plastic geogrid 6, with a compaction density ≥95%, effectively ensuring a composite foundation bearing capacity ≥250Kpa.

[0043] In step S03, after the 10cm layer of graded gravel on top of the graded crushed stone is laid and compacted, a layer of steel-plastic geogrid is laid. The longitudinal and transverse ultimate tensile strength of the steel-plastic geogrid is >50kN / m, elongation <3%, ultimate peel force at the rib intersection is >300N, and the unit area mass is not less than 780g / ㎡. The longitudinal overlap length of the steel-plastic geogrid is greater than 20cm, and the transverse overlap length is greater than 15cm. It is fixed with U-shaped nails. The U-shaped nails are made of Φ8mm HPB300 steel bars, 9cm long and 10cm high, with a spacing of 100×100cm and a staggered pattern. After the steel-plastic geogrid is laid, another 10cm layer of graded gravel is laid. The graded gravel particle size is 1~30mm, the saturated compressive strength of the stone is >30MPa, and the compaction density is ≥95%.

[0044] Step S04, inspect the composite foundation: According to the design documents, the characteristic value of the bearing capacity of the treated composite foundation should be ≥250KPa. In order to verify the effect of CFG pile treatment on the gravel and miscellaneous fill soil layer, the bearing capacity of the treated composite foundation should be tested. The number of composite foundation bearing capacity tests should not be less than 1% of the total number of piles, and should not be less than 3 points (according to the requirements of "JGJ79-2012 Technical Specification for Building Foundation Treatment" and "Sichuan Provincial Construction Engineering Quality On-site Testing Manual").

[0045] The foregoing basic examples and their further alternative examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed in this application. In the scheme of this application, each alternative example can be arbitrarily combined with any other basic example and alternative example.

[0046] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for constructing CFG piles in gravelly fill soil strata, characterized in that, Includes the following steps: Step S01, soft soil replacement: excavate the unfavorable soil layer and replace it with graded crushed stone (4) in layers; Step S02, pile foundation construction: CFG piles (3) are constructed on graded crushed stone (4), and the bottom end of the CFG piles (3) is embedded in strongly weathered mudstone (1); Step S03, geogrid construction: lay a lower layer of graded gravel (5) on top of graded crushed stone (4), lay a steel-plastic geogrid (6) on top of the lower layer of graded gravel (5), and then lay an upper layer of graded gravel (7) on top of the steel-plastic geogrid (6). Step S04: Inspect the composite foundation.

2. The method for constructing CFG piles in gravelly fill soil strata according to claim 1, characterized in that: In step S01, an excavator is used to remove undesirable soil layers within a 3m depth of the replacement layer. The excavated soil is transported to the spoil disposal site. When the excavator is 20cm away from the design elevation, manual cleaning is required.

3. The method for constructing CFG piles in gravelly fill soil strata according to claim 1 or 2, characterized in that: In step S01, the natural crushed stone used for graded crushed stone has a particle size of 5~40mm, a crushing value of ≤30%, a liquid limit value of <25%, and a mud content of ≤5%. The loose thickness of the graded crushed stone during paving is no more than 30cm. It is compacted using a vibratory roller, with compaction carried out in layers from low to high, and from the edges to the middle. The overlap between rows is 0.3~0.5m, and the overlap between compaction sections is more than 2m. The roller travel speed is no more than 4km / h, and the compaction density is ≥93%.

4. The method for constructing CFG piles in gravelly fill soil strata according to claim 1, characterized in that: In step S02, when drilling begins, the drill bit valve is closed, the drill rod is moved downwards until the drill bit touches the ground, and the motor is started to drill. If the drill rod is found to be shaking or difficult to drill, the drilling speed is slowed down. During the drilling process, the pile driver's automatic control system strictly controls the descent speed and rotation speed of the drill rod to match the two. When an obstacle is encountered, drilling is stopped immediately, the obstacle is cleared, and drilling resumes. Drill mud is removed at any time during the drilling process, and the remaining drill mud is removed after the drilling rig is moved. The drilling rig adopts a skip-hole operation, and after the mixture at the adjacent position has solidified, the adjacent pile position is drilled.

5. The method for constructing CFG piles in gravelly fill soil strata according to claim 4, characterized in that: In step S02, after the hole reaches the design elevation, drilling is stopped and concrete pumping begins. When the drill core tube is filled with concrete, the tube is pulled out while pumping continues, requiring continuous pumping. The slump of the concrete upon arrival is controlled at 160-200mm. When the main aggregate is crushed stone with a particle size of 5-15mm, fly ash, retarder, and pumping agent are added to the concrete, and the retarding time is controlled at more than 6 hours.

6. The method for constructing CFG piles in gravelly fill soil strata according to claim 5, characterized in that: In step S02, when pumping concrete, the drill rod lifting speed shall be controlled within 3.0 m / min, and it is strictly forbidden to lift the drill rod before pumping material. If continuous grouting is not possible during construction, the fine sand and backfill soil layers shall be avoided according to the survey report and the geological conditions. The machine shall not be stopped in the fine sand and backfill soil layers. During construction, the ratio of the actual grouting volume to the theoretical volume of each pile, i.e., the filling coefficient of the concrete, shall be maintained at least 1.15, and the over-grouting height of the concrete shall not be less than 0.5 m.

7. The method for constructing CFG piles in gravelly fill soil strata according to claim 1, characterized in that: In step S02, after the CFG piles have been naturally cured for 7 days, earthwork excavation is organized according to the principle of first excavation and first demolition. The excavation boundary is marked with lime, and the excavation depth is accurately measured to avoid over-excavation or secondary excavation. When 30cm remains, manual excavation is carried out in conjunction with a small excavator. Mechanical excavation is carried out to the top elevation of the pile and the earthwork is leveled.

8. The method for constructing CFG piles in gravelly fill soil strata according to claim 1 or 7, characterized in that: In step S02, after the soil between the piles is cleaned, the cutting position is marked along the pile head with an ink line or red paint. The cutting position is 2cm higher than the designed pile top elevation. A disc cutter is used to make a circumferential cut along the marked line, cutting in place in one go. At least 10% of the total number of piles are sampled for pile integrity testing.

9. The method for constructing CFG piles in gravelly fill soil strata according to claim 1, characterized in that: In step S03, after the 10cm layer of graded gravel on top of the graded crushed stone is laid and compacted, a layer of steel-plastic geogrid is laid. The longitudinal and transverse ultimate tensile strength of the steel-plastic geogrid is >50kN / m, the elongation is <3%, the ultimate peel force at the rib intersection is >300N, the unit area mass is not less than 780g / ㎡, the longitudinal overlap length of the steel-plastic geogrid is greater than 20cm, the transverse overlap length is greater than 15cm, and it is fixed with U-shaped nails (8). The U-shaped nails are made of Φ8mm HPB300 steel bars, with a length of 9cm and a height of 10cm. The spacing of the U-shaped nails is 100×100cm, and they are arranged in a quincunx pattern. After the steel-plastic geogrid is laid, another 10cm layer of graded gravel is laid. The particle size of the graded gravel is 1~30mm, the saturated compressive strength of the stone is >30MPa, and the compaction density is ≥95%.

10. The method for constructing CFG piles in gravelly fill soil strata according to claim 1, characterized in that: In step S04, to verify the effect of CFG pile treatment on the gravelly fill soil layer, the bearing capacity of the treated composite foundation is tested. The number of composite foundation bearing capacity tests should not be less than 1% of the total number of piles, and should not be less than 3 points.

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