A method for stabilizing settlement of pile foundation / composite foundation reinforcement

Abstract

This invention discloses a method for stabilizing settlement of pile foundations / composite foundation reinforcements, belonging to the field of building pile foundation construction technology. This method divides various construction conditions according to pile type, soil displacement characteristics, geological conditions, and design requirements. After pile formation, soil rest and pile strength testing are completed first, followed by static pressure piling machine or hammering equipment to apply additional pressure to the single pile. To address the problem of obstructed pile driving for long piles and large-diameter piles, grouting processes at the pile end and pile side are used to reduce pile-soil resistance. After the pile settles to a preset range, the load is maintained and stabilized until settlement is stable. This invention integrates defect repair, pre-settlement, full-coverage performance testing, and bearing capacity reinforcement, effectively solving engineering problems such as sediment and mud skin in bored cast-in-place piles, floating of soil displacement piles, excessive settlement of various pile types, and difficulty in driving large-diameter long piles. It features safe construction, wide applicability, and excellent quality control, and can be widely applied to various pile foundations and composite foundation reinforcement projects, including bored cast-in-place piles, precast pipe piles, CFG piles, carrier piles, long spiral piles, and ultra-high strength cement-soil piles.

Description

Technical Field

[0001] This invention belongs to the field of construction technology of building pile foundations and composite foundations, specifically relating to a method for stabilizing settlement of pile foundations / composite foundation reinforcements. It is applicable to the pre-treatment, pre-inspection and defect reinforcement construction of various pile foundations and composite foundation reinforcements in industrial and civil buildings and municipal engineering. Background Technology

[0002] In current construction engineering, pile foundations and composite foundation reinforcements are widely used, but different pile types have various common quality problems: 1. During the drilling and pile formation process of bored cast-in-place piles, sediment is easily formed at the bottom of the hole and mud cake is easily attached to the hole wall. Both of these factors will significantly reduce the pile end resistance and pile side friction resistance, ultimately causing the pile foundation settlement to exceed the standard and the actual bearing capacity to fail to meet the design requirements. Conventional post-grouting technology is constrained by factors such as geological conditions, construction technology, and human operation, and the defect treatment effect is unstable.

[0003] 2. For soil displacement piles such as precast piles, vibratory driven concrete piles, CFG piles, and carrier piles, the driving process will generate a strong soil displacement effect, which can easily cause the pile to float (the carrier pile itself and the adjacent piles will float during the bottom filling process), and the accumulation of excess pore water pressure in the soil, which will lead to abnormal stress on the pile, reduced bearing capacity, and continuous increase in settlement in the later stage.

[0004] 3. Although non-displacement piles such as long spiral soil extraction piles and ultra-high strength cement-soil piles do not have a significant soil displacement effect, they generally suffer from uneven stress at the pile tip and excessive settlement at the pile tip.

[0005] 4. Large-diameter, ultra-long pile foundations have high self-weight and soil friction resistance. Even when conventional pile driving equipment is operating at full load, it is still difficult to make the pile body settle effectively, which makes construction and quality control difficult.

[0006] 5. Traditional pile foundation acceptance often adopts a sampling inspection mode, which cannot conduct a full-coverage inspection of all piles on site, and potential engineering problems are easily left unresolved; conventional preloading processes such as surcharge preloading and vacuum preloading are only suitable for large-scale soft soil foundation reinforcement and cannot be used for precise pretreatment and performance verification of individual piles.

[0007] In summary, existing construction and testing technologies cannot simultaneously achieve multiple objectives such as defect remediation, pre-settlement, full-coverage testing, and bearing capacity reinforcement, resulting in shortcomings in project quality control. Therefore, there is an urgent need for a widely applicable and comprehensive pile foundation stabilization and settlement construction method. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing a method for stabilizing settlement in pile foundations / composite foundation reinforcements. This method allows for differentiated construction based on pile type, geological conditions, and design requirements. After pile formation, provided the soil has settled and the pile strength meets standards, it utilizes static pressure / hammer loading, load stabilization, and grouting to achieve pile defect repair, pre-settlement, and bearing capacity pre-testing in one step. This effectively solves problems such as sediment and mud skin, pile uplift, excessive settlement, and difficulties in driving long / large diameter piles, comprehensively improving the construction quality and long-term stability of pile foundation engineering.

[0009] To achieve the above objectives, the present invention adopts the following complete technical solution: A method for stabilizing settlement of pile foundations / composite foundation reinforcements is applicable to the pre-treatment of defects, pre-testing of performance, and reinforcement of bearing capacity after pile formation in various types of pile foundations and composite foundation reinforcements. It addresses engineering problems such as insufficient pile bearing capacity, excessive settlement, soil displacement and uplift, pile bottom sediment, pile side mud skin, and difficulties in driving long / large diameter piles. After the pile material strength meets requirements, a static pressure pile driver or hammer is used to apply pressure to a single pile. Once the pile settles to the preset settlement range, the pressure is maintained until the pile settlement converges and reaches a stable standard. Through pre-loading, pre-testing, and integrated pre-treatment, the pile foundation bearing capacity and settlement deformation indicators fully meet design and specification requirements. Specific construction methods are as follows: (1) For bored piles and conventional composite foundation reinforcement: After the strength of the pile material reaches 75% of the design strength, use pressure lower than the ultimate strength of the pile material to carry out overload preloading and settlement pre-testing, use compressive stress to squeeze and compact the pile bottom sediment, weaken the adverse effect of the pile side mud skin, and eliminate excessive settlement of the pile body after construction. (2) For piles that exhibit soil squeezing effects and are prone to pile body uplift, including precast piles, vibratory driven concrete piles, carrier piles, and CFG piles: ① Non-precast displacement piles: After the strength of the pile material reaches 75% of the design strength, overload preloading and settlement pre-testing are carried out using pressure lower than the ultimate strength of the pile material to eliminate the problem of pile floating caused by soil displacement (cast-in-place concrete carrier piles, when the bottom is compacted and filled with carrier, will cause the pile itself and adjacent piles to float), and at the same time check the hidden danger of insufficient bearing capacity caused by soil displacement. ② Precast piles (pipe pile carrier piles, when the bottom is compacted and filled with carrier, the pile and adjacent piles float up): After construction, use pressure lower than the ultimate strength of the pile material and 90% of the design ultimate bearing capacity of a single pile for overload preloading and settlement pre-testing to completely eliminate the problem of excessive settlement caused by soil displacement and floating. (3) For non-displacement piles other than bored piles, including ultra-high strength cement-soil piles and long spiral soil extraction piles: after the strength of the pile material reaches the design strength, use pressure lower than the ultimate strength of the pile material to carry out overload preloading and settlement pre-detection, optimize the stress state of the pile end, and control abnormal settlement of the pile end. (4) For pile foundations with high bearing capacity and strict settlement control requirements: Select construction equipment that matches the strength of the pile body, operate with the maximum rated pile driving force of the equipment, and use grouting softening measures to reduce the side friction and end resistance of the pile; after the pile body is pressed to the preset settlement range, maintain the maximum pressure throughout the process until the settlement converges and reaches the design stability standard. (5) For long piles and large-diameter piles, where the maximum pile driving force of the equipment cannot cause effective settlement of the pile body: first, grout the pile bottom and pile side separately or simultaneously to reduce the contact resistance between the pile and the soil; after the concrete strength of the pile body is ≥ 75% of the design strength, use a pile driving force greater than the design value of the single pile bearing capacity for pre-loading (or hammer energy to promote the settlement and convergence of the pile body) to the preset range and then hold the load and stabilize the pressure until the settlement reaches the stable standard.

[0010] Furthermore, for piles with a large length-to-diameter ratio and a large pile diameter, grouting at the pile tip and grouting on the pile side are carried out simultaneously.

[0011] Furthermore, grouting pipes are pre-embedded inside the pile body, and directional grouting operations are carried out in the soil area below the pile tip based on the pre-embedded grouting pipes.

[0012] Furthermore, the preset settlement range is determined by comprehensive calculation based on pile length, site stratum distribution, geotechnical parameters, and design settlement limit.

[0013] Furthermore, the pressure stabilization time is uniformly controlled between 1 and 30 minutes; the entire pressure stabilization process is synchronously collected and recorded, including the measured strength of the pile body, the stabilization pressure, the maximum output pressure of the equipment, the total number of hammer blows, the ten blows per round in the last three rounds, the single-shot penetration, and the stabilization value after grouting, among other complete construction parameters.

[0014] Furthermore, the grout used for grouting is a cement-based lubricating grout, which is made by using cement as the main material and compounding it with nano-silica powder or water glass.

[0015] Furthermore, displacement piles employ a multi-stage, gradient-increasing pressure method, with each subsequent stage of pressure building upon the previous one, resulting in a gradual decrease in pile settlement and achieving stable settlement convergence. After grouting is completed, acoustic wave detection, electromagnetic detection, and geophysical engineering methods are used to assess the grouting reinforcement and pile-soil bonding effectiveness. This replaces the previously time-consuming and labor-intensive multi-stage testing methods, such as bearing capacity testing, high-strain testing, low-strain testing, and material strength testing. Beneficial effects

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. Comprehensive testing coverage with zero omissions of potential hazards: Abandoning the traditional sampling testing model, we achieve 100% pre-stress testing of all pile foundations on site, comprehensively investigate individual pile quality defects, and significantly improve the acceptance rate of pile foundations.

[0017] 2. Comprehensive solution for multiple problems: It addresses issues such as sediment and mud cake in bored piles, floating and excessive pore water pressure in displacement piles, obstruction of driving long / large diameter piles, and excessive settlement of various pile types. It is applicable to a wide range of pile types.

[0018] 3. Significant pre-settlement effect: The settlement of the piles is completed in advance during the construction phase, which greatly reduces the settlement in the later stage of building operation and improves the long-term safety of the structure.

[0019] 4. Construction safety is controllable: The pre-loading and re-loading pressures are strictly lower than the ultimate strength of the pile material, so that structural damage such as cracking or breakage of the pile will not be caused during reinforcement and testing.

[0020] 5. The grouting process has a dual function: in the early stage, the grout acts as a lubricant and reduces resistance, ensuring the smooth progress of pile driving; in the later stage, the grout hardens and can strengthen the soil around the pile, further improving the pile side friction and overall bearing capacity.

[0021] 6. Strong process integration: The process is simple and the procedures are continuous, which can be seamlessly integrated with the existing pile foundation construction, maintenance and acceptance procedures without the need for major adjustments to the on-site construction organization, resulting in high construction efficiency. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0023] Example 1: Drilled cast-in-place pile (thick sediment and thick mud cake condition) A civil building project uses bored cast-in-place piles with a diameter of 800 mm, a length of 15 m, a concrete design strength of C30, and a single pile design ultimate bearing capacity of 4000 kN. The main strata of the site are silty clay. After the piles were completed, the thickness of the sediment at the bottom of the hole was 8 cm, and the thickness of the mud skin on the pile side exceeded the standard.

[0024] 1. Grouting construction: 10 days after the pile body concrete is poured, cement-water glass double liquid grout is injected using the grouting pipes pre-embedded in the reinforcing cage on the pile side and pile end; the grouting pressure is controlled at 1.5~2.0 MPa, and the total grouting volume for a single pile is 50 L.

[0025] 2. Strength verification: The concrete strength of the test blocks cured under the same conditions reached 22.5 MPa, which is 75% of the design strength, thus meeting the pre-construction conditions.

[0026] 3. Preloading: Apply 3000 kN pressure (75% of the design ultimate bearing capacity) using a static pile driver, and control the pile driving speed at 10 mm / min.

[0027] 4. Holding and stabilizing the load: Stop increasing the pressure when the cumulative settlement at the top of the pile reaches the preset value of 25 mm, and hold the load and stabilize the pressure for 1 to 5 minutes; if the settlement at the top of the pile does not continue to increase, the settlement is considered stable.

[0028] 5. Subsequent testing: Seven days after the completion of preloading construction, a static load test was conducted on a single pile. Under the action of an ultimate load of 4000 kN, the total settlement at the top of the pile was 18.6 mm, which was less than the limit specified in the code and the design limit. The pile was deemed to be qualified.

[0029] Example 2: Large-diameter PHC static pressure pipe pile (pile driving obstructed condition) A municipal engineering project uses PHC precast pipe piles with a diameter of 700 mm, a length of 30 m, and a single pile design ultimate bearing capacity of 9000 kN. A 1260 type static pressure pile driver is used for construction, with a maximum output pile driving force of 8600 kN. When the pile is driven to the design elevation, it cannot be driven any further.

[0030] 1. Pre-embedded structure: During the prefabrication stage of the pipe pile, two Φ25 mm grouting pipes are pre-embedded along the inner wall of the pile body, with the bottom end of the grouting pipes extending to below the pile end plate.

[0031] 2. Grouting to reduce drag: Cement-based grout is injected through pre-embedded grouting pipes at a pressure ≥1.0 MPa and a grouting volume of 30 L per pile to soften the soil at the pile tip and along the pile side.

[0032] 3. Loading and stabilizing pressure: After grouting is completed, apply 7000 kN pressure to continue driving the pile to the design elevation; after the pile top settlement reaches the preset value of 20 mm, hold the load and stabilize the pressure for 3 minutes, and end the operation after the settlement stabilizes.

[0033] 4. Effect verification: Subsequent static load tests on single piles showed that the pile bearing capacity met the design requirements, and the final settlement was only 15 mm.

[0034] Example 3: Carrier pile (soil displacement and floating condition) A residential building project used piles with a diameter of 600 mm and a length of 16 m. The design ultimate bearing capacity of a single pile was 7000 kN. The site strata were mainly silty clay. After the piles were completed, significant pile uplift occurred due to the soil squeezing effect. A static pressure pile driver was used to preload the piles in multiple stages with gradient pressure increases, gradually increasing the pressure and controlling settlement convergence. Once the piles settled to a preset level, the load was held and stabilized until the settlement was completely stable. After construction, a follow-up test showed that the pile uplift problem had been completely eliminated, and the bearing capacity and settlement indicators met the design and specification requirements.

Claims

1. A method for stabilizing settlement of pile foundations / composite foundation reinforcements, characterized in that, When the strength of the pile material meets the requirements, a static pressure pile driver or hammering equipment is used to apply load to the single pile. After the pile settles to the preset settlement range, the pressure is maintained and stabilized until the pile settlement converges and reaches a stable standard. Through preloading, pre-testing, and integrated pretreatment, the pile foundation bearing capacity and settlement deformation indicators fully meet the design and specification requirements. Specific construction methods are as follows: (1) For bored piles and conventional composite foundation reinforcement: After the strength of the pile material reaches 75% of the design strength, use pressure lower than the ultimate strength of the pile material to carry out overload preloading and settlement pre-testing, use compressive stress to squeeze and compact the pile bottom sediment, weaken the adverse effect of the pile side mud skin, and eliminate excessive settlement of the pile body after construction. (2) For piles that exhibit soil squeezing effects and are prone to pile body uplift, including precast piles, vibratory driven concrete piles, carrier piles, and CFG piles: ① Non-precast displacement piles: After the strength of the pile material reaches 75% of the design strength, overload preloading and settlement pre-testing are carried out using pressure lower than the ultimate strength of the pile material to eliminate the problem of pile floating caused by soil displacement and simultaneously investigate the hidden danger of insufficient bearing capacity caused by soil displacement. ② Precast piles: After construction, surcharge preloading and settlement pre-testing are carried out using pressure lower than the ultimate strength of the pile material and 90% of the design ultimate bearing capacity of a single pile to completely eliminate the problem of excessive settlement caused by soil displacement and floating. (3) For non-displacement piles other than bored piles, including ultra-high strength cement-soil piles and long spiral soil extraction piles: after the strength of the pile material reaches the design strength, use pressure lower than the ultimate strength of the pile material to carry out overload preloading and settlement pre-detection, optimize the stress state of the pile end, and control abnormal settlement of the pile end. (4) For pile foundations with high bearing capacity and strict settlement control requirements: Select construction equipment that matches the strength of the pile body, operate with the maximum rated pile driving force of the equipment, and use grouting softening measures to reduce the side friction and end resistance of the pile; after the pile body is pressed to the preset settlement range, maintain the maximum pressure throughout the process until the settlement converges and reaches the design stability standard. (5) For long piles and large-diameter piles, where the maximum pile driving force of the equipment cannot cause effective settlement of the pile body: first, grout the pile bottom and pile side separately or simultaneously to reduce the contact resistance between the pile and the soil; after the concrete strength of the pile body is ≥ 75% of the design strength, use a pile driving force greater than the design value of the single pile bearing capacity for pre-loading or hammer energy to promote the settlement of the pile body and convergence penetration. After reaching the preset amplitude, hold the load and stabilize the pressure until the settlement reaches the stable standard.

2. The method for stabilizing settlement of pile foundation / composite foundation reinforcement according to claim 1, characterized in that: For piles with a large length-to-diameter ratio and a large pile diameter, grouting at the pile tip and grouting on the pile side should be carried out simultaneously.

3. The method for stabilizing settlement of pile foundation / composite foundation reinforcement according to claim 1 or 2, characterized in that: Grouting pipes are pre-embedded inside the pile body, and directional grouting operations are carried out in the soil area below the pile end based on the pre-embedded grouting pipes.

4. The method for stabilizing settlement of pile foundation / composite foundation reinforcement according to claim 1, characterized in that: The preset settlement range is determined by comprehensive calculation based on pile length, site stratum distribution, geotechnical parameters, and design settlement limit.

5. The method for stabilizing settlement of pile foundation / composite foundation reinforcement according to claim 1, characterized in that: The pressure stabilization time is uniformly controlled between 1 and 30 minutes; the entire pressure stabilization process is synchronously collected and recorded, including the measured strength of the pile body, the stabilizing pressure, the maximum output pressure of the equipment, the total number of hammer blows, the ten blows per of the last three rounds and the single-shot penetration, and the stabilizing pressure value after grouting.

6. The method for stabilizing settlement of pile foundation / composite foundation reinforcement according to claim 1 or 2, characterized in that: The grout used for grouting is a cement-based lubricating grout, which is made of cement as the main material and compounded with nano-silica powder or water glass.

7. The method for stabilizing settlement of pile foundations / composite foundation reinforcements according to claim 1, characterized in that: In method (2), the displacement piles are driven by a multi-level gradient increasing pressure method. The pressure of each level is gradually increased on the basis of the pressure of the previous level, and the settlement of the pile body decreases step by step to achieve stable settlement convergence. After the grouting construction is completed, the grouting reinforcement and pile-soil bonding effect are detected by sonic detection, electromagnetic detection and engineering geophysical exploration.