Construction method for hole shrinkage aftertreatment of cast-in-situ bored pile

Abstract

The invention provides a construction method for hole shrinkage aftertreatment of a cast-in-situ bored pile, and relates to the technical field of cast-in-situ pile construction. A jet grouting pile position is calibrated on the periphery of the reducing pile, a geological drilling rig / jet grouting drilling rig is adopted to penetrate through a soft soil layer to a hard soil layer, and an annular reinforcing system is constructed; a high-pressure jet grouting machine is used for injecting curing agent slurry, an annular jet grouting pile body connected in an engaged mode is formed, the inner edge of the annular jet grouting pile body completely covers the hole shrinkage area, and curing reconstruction of the hole wall unstable soil body is achieved; secondary refilling is conducted on the pile top pit, and the load transmission continuity is ensured; and the repairing effect is quantitatively evaluated through side resistance checking calculation, and construction quality closed-loop control is formed. Through the synergistic effect of the jet grouting piles and the reducing piles, the compression bearing capacity of the foundation piles is remarkably improved, the problem that deep defect repairing cannot be achieved through a traditional construction method is solved, and the beneficial effects of being flexible in construction, high in adaptability, high in economical efficiency, environmentally friendly, free of pollution and the like are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of cast-in-place pile construction, and more specifically, to a construction method for post-treatment of necking of bored cast-in-place piles. Background Art

[0002] As an important deep foundation form in civil engineering, a pile foundation consists of a pile body penetrating into the rock and soil layers and a bearing platform at its top, and can efficiently transfer the upper load to a stable stratum. Among them, bored cast-in-place piles are widely used in various engineering fields due to their flexible construction and strong adaptability. However, the necking phenomenon that easily occurs during the construction of bored cast-in-place piles has become a key problem restricting the project quality and safety.

[0003] The occurrence of the necking phenomenon has the characteristics of multi-factor coupling: on the one hand, in soft soil, silt, plastic soil or alternating soft and hard strata, improper control of drilling parameters (such as too fast drilling speed and too large drilling pressure) easily leads to the instability of the hole wall; on the other hand, if the concrete is not poured in time after the hole is formed, the soil around the hole will plastically flow into the hole under the imbalance of mud pressure, causing local reduction of the hole diameter. Necking will not only make it difficult to lower the steel reinforcement cage, but also cause a sudden change in the cross-section of the pile body, significantly reducing the compressive bearing capacity of the foundation pile, and even leading to the failure of the engineering structure in severe cases.

[0004] The remedial measure for necking in the related technology is to drive additional cast-in-place piles around, but the rotary drilling rig is limited by the internal support system in the foundation pit and is difficult to operate in the deep part. Although the percussion cast-in-place pile can adapt to complex strata, its work efficiency is low, the economic cost is high, and problems such as bottom sediment and mud pollution are easily generated during the construction process. In recent years, the newly developed construction methods such as large-diameter down-the-hole hammers and full casing construction can improve the stability of the hole wall, but mainly focus on drilling in special strata or environmental protection requirements, and do not directly solve the problem of repairing the pile body defects after necking. Summary of the Invention

[0005] The problem to be solved by the present invention is: how to repair the bearing capacity loss caused by the necking of bored cast-in-place piles in complex strata restricted by the internal support system in the foundation pit.

[0006] To solve the above problem, the present invention provides a construction method for post-treatment of necking of bored cast-in-place piles, including S1. Detecting and determining necking: comparing the theoretical volume of concrete required for the designed cast-in-place pile with the actual concrete consumption after the concrete pouring is completed. If the theoretical volume of concrete required for the designed cast-in-place pile is greater than the actual concrete consumption, it is determined that the cast-in-place pile has necked in the soft soil layer;

[0007] S2. Drilling: Mark the position of the jet grouting pile around the periphery of the necked cast-in-place pile, and use a geological drilling rig or a jet grouting rig to drill to the designed depth at the marked position of the jet grouting pile. The bottom of the pile penetrates through the soft soil layer and enters the lower hard soil layer to form a plurality of drilled holes arranged around the cast-in-place pile and communicating with each other;

[0008] S3. Jet grouting: Use a high-pressure jet grouting machine to inject the curing agent slurry into the borehole to form a jet grouted pile. The pile top is located at the top surface of the soft soil layer, and the pile bottom penetrates through the soft soil layer and enters the hard soil layer. The projections of multiple jet grouted piles on the horizontal plane are connected in a circular overlapping manner, and the inner edge covers the area where the cast-in-place pile has a reduced diameter.

[0009] S4: Supplementary grouting: After the grouting is completed, use the curing agent slurry to fill the concave holes that appear at the top of the jet grouted pile.

[0010] S5: Acceptance: Confirm the bearing capacity compensation effect of the jet grouted pile on the reduced diameter of the cast-in-place pile through a static load test.

[0011] Optionally, in the above S3, determine the circular equivalent diameter D' of the jet grouted pile according to a preset relationship. The equivalent diameter D' needs to satisfy:

[0012] πD′l 软土 q sk旋喷桩-软土 +πD′l 硬土 q sk旋喷桩-硬土 ≥πDl 软土 q sk灌注桩-软土 +πDl 硬土 q sk灌注桩-硬土

[0013] Wherein, D is the design diameter of the cast-in-place pile; D' is the circular equivalent diameter of the jet grouted pile; l 软土 is the length of the jet grouted pile in the soft soil layer; l 硬土 is the length of the jet grouted pile in the hard soil layer; q sk旋喷桩-软土 is the standard value of the ultimate lateral friction resistance between the jet grouted pile and the soft soil layer, which can be obtained from the single-pile static load compression test of the jet grouted pile; q sk旋喷桩-硬土 is the standard value of the ultimate lateral friction resistance between the jet grouted pile and the hard soil layer, which can be obtained from the single-pile static load compression test of the jet grouted pile; q sk灌注桩-软土 is the standard value of the ultimate lateral friction resistance between the cast-in-place pile and the soft soil layer, obtained according to the exploration report; q sk灌注桩-硬土 is the standard value of the total ultimate lateral resistance between the cast-in-place pile and the hard soil section, obtained according to the exploration report.

[0014] Optionally, the preset relationship is:

[0015]

[0016] Wherein, D2 is the diameter of the jet grouted pile;

[0017] b is the overlapping thickness of two adjacent jet grouted piles;

[0018] D1 is the diameter of the circle formed by the centers of the jet grouted piles.

[0019] Optionally, in the above S3, the length of the jet grouted pile in the hard soil layer is 1 - 2m.

[0020] Optionally, in the above S3, the curing agent slurry includes a fixing agent powder and water, and the mass percentage of the fixing agent powder and water is 0.8 - 1.2. The fixing agent powder includes, by mass percentage, 25 - 45% P.O.42.5R cement, 30 - 55% ground granulated blast-furnace slag powder, 25 - 35% fly ash, 25 - 35% silica fume, 3 - 5% anhydrous sodium sulfate, and 1 - 3% polyacrylamide.

[0021] Optionally, in the above S3, the grouting pressure of the curing agent slurry is greater than 20 Mpa, the flow rate is greater than 30 L / min, the lifting speed is 0.1 - 0.2 m / min, and the air flow pressure is greater than 0.7 MPa.

[0022] Optionally, in the above S3, after the slurry spraying pipe of the high-pressure jet grouting machine sinks to the designed depth, stop drilling, keep rotating, increase the pressure of the high-pressure mud pump of the high-pressure jet grouting machine to 20 - 40 MPa, spray slurry at the pile bottom for no less than 30 s, and spray slurry while rotating.

[0023] Optionally, in the above S3, when the jet grouting pipe of the high-pressure jet grouting machine approaches the pile top, start slow lifting and jet grouting from 1.0 m below the pile top, jet grout for several seconds, then slowly lift upward by 0.5 m until reaching the slurry stop surface at the pile top.

[0024] Optionally, in the above S3, the jet grouting piles are constructed in three sequences, skipping two holes, and the next sequence of jet grouting piles is constructed after the previous sequence of jet grouting piles has finally set.

[0025] Optionally, in the above S4, the curing agent slurry includes a fixing agent powder and water, and the mass percentage of the fixing agent powder and water is 1.0 - 1.2.

[0026] The beneficial effects of the construction method for post-treatment of necking of bored cast-in-place piles in the present invention are as follows: By comparing the designed theoretical concrete volume with the actual pouring volume, if the actual consumption is significantly less than the theoretical value, it indicates that the effective cross-sectional area of the pile body decreases due to soil body retraction or hole wall collapse in the soft soil layer. This method indirectly determines necking using construction data, without the need for complex detection equipment, with low cost and convenient operation. Jet grouting piles are arranged around the outer edge of the necked pile to ensure that the bored hole penetrates through the soft soil layer to the hard soil layer, so that the jet grouting piles form a "miniature pile group", transferring the load to the stable stratum. At the same time, the deformation of the soft soil is restricted through the interaction between the piles. The high-pressure jetting of the curing agent slurry forms a circularly interlocked jet grouting pile body, and the slurry penetrates and consolidates the soft soil, improving the soil stiffness and shear strength. The circular pile group forms a "confining effect", restricting the plastic flow of the soil around the necked pile, and the jet grouting piles and the necked pile jointly bear the upper load to compensate for the loss of their cross-sectional area. For the pile top cavity caused by slurry shrinkage or soil settlement, replenish the curing agent slurry to ensure the pile top is dense, avoid stress concentration, and ensure the coordinated working of the pile and soil. The bearing capacity compensation of the original pile by the jet grouting pile is accepted through static load tests to ensure that the overall bearing capacity after reinforcement meets the design requirements.

[0027] The construction method for post-treatment of necking of bored cast-in-place piles in the present invention directly covers the necking area with a ring-shaped overlapping jet grouting pile group, solidifies the soil body to increase the side friction area of the original pile side wall, effectively enhances the side resistance of the cast-in-place pile, and further effectively improves the bearing capacity of the pile body. The jet grouting pile penetrates into the hard soil layer to provide additional end bearing capacity, and the ring structure of the jet grouting pile inhibits further deformation of the soil body and prevents secondary necking. The jet grouting rig in the present invention is small in volume and does not require large-scale equipment, and can operate in the limited space of the support system in the foundation pit, overcoming the equipment limitations of the traditional pile supplement method. Moreover, compared with the cast-in-place pile or impact hole pile to be supplemented, the jet grouting material consumption is less, the construction period is short, and there is no mud pollution, meeting the trend of green construction. Description of the Drawings

[0028] Figure 1 It is a plan view of the treatment of a cast-in-place pile with necking by jet grouting piles according to an embodiment of the present invention;

[0029] Figure 2 It is a sectional view of the treatment of a cast-in-place pile with necking by jet grouting piles according to an embodiment of the present invention;

[0030] Figure 3 It is a schematic diagram for calculating the equivalent diameter of the jet grouting pile according to an embodiment of the present invention;

[0031] Figure 4 For Figure 3 It is an enlarged structural schematic diagram of part A in

[0032] Figure 5 It is a schematic diagram of the construction sequence of the jet grouting pile according to an embodiment of the present invention.

[0033] Description of the Reference Numerals:

[0034] 1, cast-in-place pile; 2, jet grouting pile; 3, soft soil layer; 4, hard soil layer. Detailed Embodiments

[0035] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given with reference to the drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments described herein. On the contrary, these embodiments are provided to more thoroughly and completely understand the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not used to limit the protection scope of the present invention.

[0036] As used herein, the term "comprising" and its variants are open-ended, i.e., "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiment". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts such as "first" and "second" mentioned in the present invention are only used to distinguish different devices, modules or units, and are not used to limit the order or interdependence of the functions performed by these devices, modules or units.

[0037] It should be noted that the modifications of "one" and "multiple" mentioned in the present invention are illustrative rather than restrictive. Those skilled in the art should understand that, unless otherwise clearly specified in the context, it should be understood as "one or more".

[0038] As Figure 1 、 Figure 2 shown, a construction method for post-treatment of the necking of bored cast-in-place piles provided by an embodiment of the present invention includes:

[0039] S1. Detect and determine necking: Compare the theoretical volume of concrete required for the designed cast-in-place pile 1 with the actual concrete consumption after the concrete pouring is completed. If the theoretical volume of concrete required for the designed cast-in-place pile 1 is greater than the actual concrete consumption, it is determined that the cast-in-place pile has necked in the soft soil layer.

[0040] S2. Drilling: Mark the positions of the jet grouting piles 2 around the periphery of the necked cast-in-place pile 1. Use a geological drill or a jet grouting drill to drill to the designed depth at the marked positions of the jet grouting piles. The bottom of the pile penetrates through the soft soil layer 3 and enters the lower hard soil layer 4 to form a plurality of drilled holes arranged around the cast-in-place pile and communicating with each other.

[0041] S3. Jet grouting: Use a high-pressure jet grouting machine to inject the curing agent slurry into the drilled holes to form jet grouting piles. The top of the pile is located at the top surface of the soft soil layer, and the bottom of the pile penetrates through the soft soil layer 3 and enters the hard soil layer 4. The projections of the plurality of jet grouting piles 2 on the horizontal plane are annularly and occlusively connected, and the inner edge covers the necked area of the cast-in-place pile 1.

[0042] S4: Supplementary grouting: After the grouting is completed, the concave cavities appearing at the top of the jet grouting piles are filled with the curing agent slurry.

[0043] S5: Acceptance: Confirm the bearing capacity compensation effect of the jet grouting piles on the necking of the cast-in-place pile 1 through a static load test.

[0044] Specifically, in step S1, necking is determined by the difference in concrete usage (theoretical volume > actual usage). Its essence is based on the physical relationship that necking causes the pore diameter to shrink and the actual filling volume of concrete to decrease. This detection logic can avoid the adaptability limitations of traditional detection methods (such as ultrasonic method) for complex strata and achieve real-time quality monitoring during the construction process. Through steps S2 and S3, a group of jet grouting piles are formed in a circular interlocking pattern around the necked pile. Referring to Figure 1 and Figure 3 shown, the inner edge of the jet grouting pile group covers the necked area to construct a "sleeve effect" to restrain the lateral deformation of the soil. The bottom of the jet grouting pile penetrates through the soft soil layer and anchors into the hard soil layer to block the plastic flow path of the soft soil layer. The curing agent slurry generates splitting penetration and compaction effects during the spraying process to reshape the soil structure around the necked area and restore the integrity of the pile-soil contact surface. The pile top stress concentration is eliminated by supplementary grouting, and the load sharing ratio of the jet grouting pile to the original pile is verified by the static load test to ensure that the reinforcement system meets the bearing capacity redundancy requirements.

[0045] Compared with the traditional pile replacement method that requires large-scale rotary drilling equipment, in this embodiment, a modular combination of a geological drill / jet grouting drill is used, which is especially suitable for narrow spaces restricted by the foundation pit support system, solving the problem of accessibility of deep operation equipment. The diameter of the jet grouting pile is much smaller than that of the replacement cast-in-place pile, reducing the amount of concrete used, shortening the construction time, and improving the construction efficiency. The solidified body of the jet grouting pile increases the cohesion and internal friction angle values of the soil around the necked area, as well as increases the shear strength of the pile-soil interface. Moreover, the jet grouting pile group transfers part of the load to the lower hard soil layer, and the vertical load is shared through the combined action of the pile and the soil. And the circular interlocking structure forms a "stiffening rib" effect to inhibit the bending deformation of the pile body and improve the horizontal bearing capacity. This embodiment also introduces a static load test to ensure the compensation effect of the bearing capacity. Through the systematic detection-reinforcement-verification process, this embodiment realizes the technical leap from "passive remedy" to "active enhancement" for the repair of necking defects, with significant engineering practical value.

[0046] Optionally, as Figure 1 shown, in the above S3, the circular equivalent diameter D' of the jet grouting pile is determined according to a preset relationship, and the equivalent diameter D' needs to satisfy:

[0047] πD′l 软土 q sk旋喷桩-软土 +πD′l 硬土 q sk旋喷桩-硬土 ≥πDl 软土 q sk灌注桩-软土 +πDl 硬土 q sk灌注桩-硬土

[0048] where, D is the design diameter of the cast-in-place pile; D' is the circular equivalent diameter of the jet grouting pile; l 软土 is the length of the jet grouting pile in the soft soil layer; l 硬土is the length of the jet grouting pile in the hard soil layer; q sk旋喷桩-软土 is the standard value of the ultimate lateral friction resistance between the jet grouting pile and the soft soil layer, which can be obtained from the static load compression test of a single jet grouting pile; q sk旋喷桩-硬土 is the standard value of the ultimate lateral friction resistance between the jet grouting pile and the hard soil layer, which can be obtained from the static load compression test of a single jet grouting pile; q sk灌注桩-软土 is the standard value of the ultimate lateral friction resistance between the cast-in-place pile and the soft soil layer, which is obtained according to the exploration report; q sk灌注桩-硬土 is the total standard value of the ultimate lateral resistance between the cast-in-place pile and the hard soil section, which is obtained according to the exploration report.

[0049] Specifically, through inequality constraints, it is ensured that the total ultimate lateral friction resistance of the jet grouting pile in the soft soil and hard soil layers is not lower than that of the original cast-in-place pile. That is, the annular jet grouting pile needs to provide sufficient lateral friction resistance to compensate for the loss of the lateral resistance of the cast-in-place pile caused by diameter reduction, while maintaining the continuity of the load transfer of the pile-soil system. D' is not the actual geometric dimension, but a virtual diameter obtained through equivalent transformation by a preset relationship. The lateral resistance compensation requirements are calculated separately for the soft soil and hard soil layers, reflecting a differential compensation strategy for the mechanical properties of different soil layers. The soft soil layer focuses on controlling plastic deformation, and the hard soil layer ensures effective load transfer.

[0050] In this alternative embodiment, the limitation of estimating the parameters of the jet grouting pile by the traditional empirical method is broken through. By accurately calculating D' through a formula, the lateral friction resistance after reinforcement is made greater than the original design value, avoiding over-design or insufficient reinforcement, and realizing precise bearing capacity compensation. This embodiment elevates the jet grouting pile reinforcement design from empirical judgment to the level of quantitative calculation by establishing a strict mathematical equivalent model, which not only ensures the reliability of the reinforcement effect but also significantly reduces the engineering cost, representing an important technological progress in the field of treating the diameter reduction of bored cast-in-place piles.

[0051] Optionally, as Figure 3 、 Figure 4 shown, the preset relationship is:

[0052]

[0053] wherein, D2 is the diameter of the jet grouting pile;

[0054] b is the overlapping thickness of two adjacent jet grouting piles;

[0055] D1 is the diameter of the circle formed by the centers of the jet grouting piles.

[0056] Specifically, D2 is generally 500 - 800 mm, D1 is taken as the diameter of the cast-in-place pile plus 100 - 200 mm, is the angle between the line connecting the center of the circle formed by the centers of multiple jet grouting piles (i.e., the center O of the cast-in-place pile) and any jet grouting center and the line connecting this jet grouting center and the adjacent jet grouting center, It is the included angle between the line connecting the center of any jet grouting pile and the center of its adjacent jet grouting pile and the line connecting the overlapping point of the jet grouting pile and its adjacent jet grouting pile.

[0057] In this alternative embodiment, by establishing an accurate mathematical relationship between geometric parameters and the equivalent diameter, the design of the annular overlapping reinforcement of jet grouting piles is upgraded from empirical judgment to a calculable and verifiable engineering technology, which greatly improves the construction economy on the premise of ensuring the reinforcement effect. It is an important methodological innovation in the field of pile foundation defect repair.

[0058] Optionally, in the above S3, the length of the jet grouting pile in the hard soil layer is 1 - 2 m.

[0059] Specifically, after the bottom of the jet grouting pile is embedded in the hard soil layer, the end resistance of the pile is effectively excited and jointly bears the load with the side friction resistance. As a relatively incompressible layer, the hard soil layer prevents the continuous plastic deformation of the soft soil layer from being transmitted to the pile body and inhibits the recurrence of necking.

[0060] In this alternative embodiment, by scientifically defining the length of the hard soil section, multi-objective optimization is achieved in aspects such as bearing capacity improvement, construction cost control, and risk prevention and control, forming key technical parameters with both mechanical rationality and engineering economy, providing a precise design benchmark for the repair of necking of bored cast-in-place piles.

[0061] Optionally, in the above S3, the curing agent slurry includes a fixing agent powder and water, the mass percentage of the fixing agent powder and water is 0.8 - 1.2, and the fixing agent powder includes 25 - 45% P.O.42.5R cement, 30 - 55% blast furnace slag micro-powder, 25 - 35% fly ash, 25 - 35% silica fume, 3 - 5% anhydrous sodium sulfate, and 1 - 3% polyacrylamide by mass percentage.

[0062] Specifically, P.O.42.5R cement, where P.O. represents Portland Ordinary Cement; 42.5 indicates the strength grade of the cement, that is, the compressive strength of this cement under standard curing conditions (28 days) is not less than 42.5 megapascals (MPa); R represents Rapid Hardening, indicating that the early strength of this cement develops relatively fast. The clinker strength of the cement is not less than 42.5 MPa, and the specific surface area is ≥450 m2 / kg; the mineral powder is granulated blast furnace slag powder, in powder form, with a specific surface area of ≥500 m2 / kg and an activity index of not less than 95% at 28 days; the fly ash is in powder form, with a specific surface area of ≥400 m2 / kg; the silica fume is in powder form, with a specific surface area of ≥400 m2 / kg; the anhydrous sodium sulfate is in powder form, with a mass fraction of Na2SO4 ≥99%, a moisture content of ≤0.5%, a chloride ion content of ≤0.06%, and a calcium and magnesium ion content of ≤0.0005%; the polyacrylamide is in light yellow granular form, with an anionic molecular structure, a water content of ≤10%, and a dissolution time of ≤10 min.

[0063] In this alternative embodiment, a curing agent slurry is used to reinforce the soft soil layer around the pile. Compared with ordinary cement, the particles of the curing agent are finer, and the strength and durability of the curing agent slurry reinforcement are better than those of cement, and it can better reinforce and fill the surrounding soil. The curing agent undergoes physical and chemical reactions with the soft soil layer, expanding the shear slip surface and increasing the standard value of the ultimate side friction resistance.

[0064] Optionally, in the above S3, the grouting pressure of the curing agent slurry is greater than 20 Mpa, the flow rate is greater than 30 L / min, the lifting speed is 0.1 - 0.2 m / min, and the air flow pressure is greater than 0.7 MPa.

[0065] Optionally, by precisely controlling four core parameters: grouting pressure, flow rate, lifting speed, and air flow pressure, fine-tuning control of the injection process of the curing agent slurry is achieved. The grouting pressure > 20 MPa to overcome the initial formation resistance, enabling the slurry to penetrate deeply into microfractures and pores. The high pressure causes the slurry to generate turbulence, enhancing the cutting ability of the soil structure and forming a reticular solidification zone. The flow rate > 30 L / min, and the lifting speed is 0.1 - 0.2 m / min. The large flow rate ensures sufficient slurry to fill the pores per unit time, avoiding the slurry suction empty window period. The air flow pressure > 0.7 MPa, and the high-pressure air flow breaks the slurry into micron-sized droplets, increasing the specific surface area and improving the penetration efficiency. In the process of this embodiment's grouting, the slurry supply should be continuous, and the slurry mixing should be ensured to be uniform. If the slurry supply stops due to reasons, the slurry mixer should be lowered to no less than 0.5 m below the slurry stop surface, and then spraying and lifting should be carried out after the slurry supply is restored. To ensure the continuity of the slurry supply, in this embodiment, the slurry needs to be stirred for 10 - 20 min, then filtered, pumped into the second filter screen through a mud pump, and after the second filtration, it flows into the slurry bucket for standby. Before grouting in this embodiment, to prevent the slurry from flowing around and polluting the entire working surface, a slurry drainage ditch needs to be set at the drilled hole of the jet grouting pile, so that the upward-cascading slurry can flow through the drainage ditch to the slurry return pond for concentration, and it can be recycled for secondary use if necessary. In this embodiment, after grouting is completed, an appropriate amount of clean water is injected into the slurry tank, the high-pressure pump is started, and the residual slurry in all pipelines is cleaned until it is clean.

[0066] In this optional embodiment, through the fine-tuning parameter control system, the formation repair level of the high-pressure jet grouting process is improved, achieving multi-dimensional breakthroughs in aspects such as pile-forming quality, construction efficiency, and environmental compatibility, providing a standardized solution for industrial implementation in the treatment of pile diameter reduction of cast-in-place piles.

[0067] Optionally, in the above S3, when the grouting pipe of the high-pressure jet grouting machine sinks to the designed depth, stop drilling, keep rotating, increase the pressure of the high-pressure mud pump of the high-pressure jet grouting machine to 20 - 40 MPa, spray grout at the pile bottom for no less than 30 s, and spray grout while rotating.

[0068] Specifically, the 20 - 40 MPa ultra-high-pressure slurry impacts the soil at the pile bottom, forming a reinforcement zone with a diameter enlarged by 1.5 - 2 times, and the bearing area increases to 2.25 - 4 times of the original design. With a 30 s dwell spraying time, the continuous high pressure causes cumulative plastic deformation of the soil at the pile bottom, and the compression modulus increases to 3 - 5 times of the initial value.

[0069] In this optional embodiment, through the precise control of the pile bottom strengthening process parameters, targeted repair of the bearing capacity at the bottom of the pile with reduced diameter and strengthening of the end bearing capacity are achieved.

[0070] Optionally, in the above S3, when the jet grouting pipe of the high-pressure jet grouting machine approaches the pile top, starting from 1.0 m below the pile top, slowly lift and rotate the jet grouting for several seconds, and then slowly lift upward by 0.5 m until reaching the slurry stop surface at the pile top.

[0071] Specifically, in this embodiment, slow lifting is started 1.0m below the pile top to reduce the slurry pressure gradient and prevent the escape of bubbles caused by a sudden pressure drop. A top pressure compensation chamber is formed through 3-5 seconds of static spraying, and the radial diffusion of the slurry increases by 30-50%. After each 0.5m lifting, the lifting is paused, and the slurry is allowed to sink by its own weight to fill the blind area of the previous spraying, forming an interlayer bite zone with a thickness of ≥0.3m. The slurry stopping surface is 0.3-0.5m higher than the designed pile top to compensate for the consolidation shrinkage of the slurry, and the flatness of the pile top is ensured through subsequent finishing.

[0072] In this optional embodiment, the problem of insufficient density and shrinkage depression that are prone to occur at the top of the jet grouting pile is solved through the design of a refined grouting process for the pile top.

[0073] Alternatively, as Figure 5 As shown, in the above S3, the jet grouting piles are divided into three sequences and the construction is skipped two holes. After the jet grouting piles of each sequence are finally set, the next sequence of jet grouting piles is constructed.

[0074] Specifically, in this embodiment, the skip hole construction is divided into three sequences, and the construction order is I1→I2→II1→I3→II2→III1→II3→III2→III3. The annular rotary jet grouting piles are divided into three construction batches (sequence I, sequence II, sequence III), and the interval time of each sequence is greater than the final setting time of the slurry to ensure that the subsequent piles are constructed after the adjacent pile bodies form initial strength. The spacing between piles in each sequence is 3 times the pile diameter, and the superimposed disturbance of continuous construction is avoided by spatial jumping. The stratum stress increment caused by the construction of sequence I piles is dissipated through the skip hole area. By the time of sequence II construction, the stratum stress recovers to 85%-90% of the initial value. The sequence I piles after final setting serve as micro retaining structures to limit the radial displacement of sequence II piles during grouting. The micro cracks formed by the solidification and shrinkage of sequence I piles become slurry infiltration channels for sequence II piles, thereby increasing the slurry vein density in the bite zone.

[0075] In this optional embodiment, the construction of the jet grouting pile group is transformed from "disorderly disturbance" to "orderly coordination" through the sequence of step-by-step skip-hole construction, thereby maximizing the coordinated reinforcement effect of the jet grouting pile group and minimizing the ground disturbance.

[0076] Optionally, in the above S4, the curing agent slurry includes fixing agent powder and water, and the mass percentage of the fixing agent powder and water is 1.0 to 1.2.

[0077] Specifically, after the jet grouting is completed, due to the water separation effect of the slurry, there is generally varying degrees of shrinkage, and a cavity appears on the top of the consolidated body. In this embodiment, the mass percentage of the curing agent powder and water is 1.0-1.2, and the curing agent powder is the same as above.

[0078] In this alternative embodiment, by precisely controlling the ratio of the fixing agent powder to water, an optimal balance is achieved between the fluidity and strength of the supplementary grouting fluid, ensuring both the collaborative working performance between the restoration and the original pile and significantly improving the construction efficiency and economy.

[0079] Although the present invention is disclosed as above, the scope of protection of the present invention is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will all fall within the scope of protection of the present invention.

Claims

1. A construction method for post-treatment of necking of bored cast-in-place piles, characterized in that, Including: S1. Detecting and determining necking: Comparing the theoretical volume of concrete required for the designed cast-in-place pile with the actual amount of concrete used after the concrete pouring is completed. If the theoretical volume of concrete required for the designed cast-in-place pile is greater than the actual amount of concrete used, it is determined that necking occurs in the soft soil layer of the cast-in-place pile. S2. Drilling: Marking the position of the jet grouting pile around the periphery of the necked cast-in-place pile, and using a geological drill or a jet grouting drill to drill to the designed depth at the marked position of the jet grouting pile. The bottom of the pile penetrates through the soft soil layer and enters the lower hard soil layer to form multiple interconnected drilled holes arranged around the cast-in-place pile. S3. Jet grouting: Using a high-pressure jet grouting machine to inject the curing agent slurry into the drilled holes to form jet grouting piles. The top of the pile is located at the top surface of the soft soil layer, and the bottom of the pile penetrates through the soft soil layer and enters the hard soil layer. The projections of multiple jet grouting piles on the horizontal plane are annularly interlocked, and the inner edge covers the necked area of the cast-in-place pile. S4: Supplementary grouting: After the grouting is completed, the concave cavity appearing at the top of the jet grouting pile is filled with the curing agent slurry. S5: Acceptance: Confirming the bearing capacity compensation effect of the jet grouting pile on the necking of the cast-in-place pile through a static load test.

2. The construction method for post-treatment of necking of bored cast-in-place piles according to claim 1, characterized in that, In the above S3, the annular equivalent diameter D' of the jet grouting pile is determined according to a preset relationship, and the equivalent diameter D' needs to satisfy: πD′l 软土 q sk旋喷桩-软土 +πD′l 硬土 q sk旋喷桩-硬土 ≥πDl 软土 q sk灌注桩-软土 +πDl 硬土 q sk灌注桩-硬土 Among them, D is the designed diameter of the cast-in-place pile; D' is the equivalent circular diameter of the jet grouting pile; l 软土 is the length of the jet grouting pile in the soft soil layer; l 硬土 is the length of the jet grouting pile in the hard soil layer; q sk旋喷桩-软土 is the standard value of the ultimate lateral frictional resistance between the jet grouting pile and the soft soil layer; q sk旋喷桩-硬土 is the standard value of the ultimate lateral frictional resistance between the jet grouting pile and the hard soil layer; q sk灌注桩-软土 is the standard value of the ultimate lateral frictional resistance between the cast-in-place pile and the soft soil layer; q sk灌注桩-硬土 is the standard value of the total ultimate lateral resistance between the cast-in-place pile and the hard soil section.

3. The construction method for post-treatment of the necking of bored cast-in-place piles according to claim 2, characterized in that, The preset relationship is: where D2 is the diameter of the jet grouting pile; b is the overlapping thickness of two adjacent jet grouting piles; D1 is the diameter of the circle formed by the centers of the jet grouting piles.

4. The construction method for post-treatment of necking of bored cast-in-place piles according to claim 2, characterized in that, In the above S3, the length of the jet grouting pile in the hard soil layer is 1 - 2m.

5. The construction method for post-treatment of the necking of bored cast-in-place piles according to claim 1, characterized in that, In the above S3, the curing agent slurry includes a curing agent powder and water, and the mass percentage of the curing agent powder and water is 0.8 - 1.

2. The curing agent powder includes 25 - 45% P.O.42.5R cement, 30 - 55% blast furnace slag micro-powder, 25 - 35% fly ash, 25 - 35% silica fume, 3 - 5% anhydrous sodium sulfate, and 1 - 3% polyacrylamide by mass percentage.

6. The construction method for post-treatment of the necking of bored cast-in-place piles according to claim 1, characterized in that, In the above S3, the grouting pressure of the curing agent slurry is greater than 20 Mpa, the flow rate is greater than 30 L / min, the lifting speed is 0.1 - 0.2 m / min, and the air pressure is greater than 0.7 MPa.

7. The construction method for post-treatment of necking of bored cast-in-place piles according to claim 1, characterized in that, In the above S3, when the grouting pipe of the high-pressure jet grouting machine sinks to the designed depth, stop drilling, keep rotating, increase the pressure of the high-pressure mud pump of the high-pressure jet grouting machine to 20 - 40 MPa, and spray grout at the bottom of the pile for no less than 30 s, while spraying grout and rotating.

8. The construction method for post-treatment of the necking of bored cast-in-place piles according to claim 1, characterized in that, In the above S3, when the jet grouting pipe of the high-pressure jet grouting machine is lifted close to the top of the pile, start from 1.0 m below the top of the pile, slowly lift and jet grout, jet grout for several seconds, and then slowly lift 0.5 m upward until the stop grouting surface at the top of the pile.

9. The construction method for post-treatment of the necking of bored cast-in-place piles according to claim 1, characterized in that, In the above S3, the jet grouting piles are constructed in three sequences, skipping two holes, and the next sequence of jet grouting piles is constructed after the previous sequence of jet grouting piles has finally set.

10. The construction method for post-treatment of necking of bored cast-in-place piles according to any one of claims 1-9, characterized in that, In the above S4, the curing agent slurry includes a curing agent powder and water, and the mass percentage of the curing agent powder and water is 1.0 - 1.2.

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