Reinforcing method for defects of bored pile body in geological sand layer

Abstract

The application discloses a reinforcing method for pile body defects in geological sand layers, which is characterized by the following steps: precise positioning of the position, type and size of the pile body defects by means of pile top drilling and coring combined with low-strain reflection wave method or acoustic wave transmission method; radial injection of cement slurry along the pile body at the position of the pile body defects through the drilling and coring hole to form a sand layer solidification protection ring around the pile body; placement of a high-pressure jetting device along the drilling and coring hole to the position of the pile body defects, cleaning of the position of the pile body defects by means of high-pressure water jet, and discharge of the waste slag generated in the cleaning process out of the pile by means of compressed air; and pressure injection of self-compacting micro-expansion concrete into the position of the pile body defects by means of a grouting pump through a grouting pipe to realize the reinforcement of the position of the pile body defects. The method is characterized by the fine operation of solidifying the sand layer in a specific area around the pile and then locally cleaning the sand layer, which realizes efficient and thorough cleaning of the sediment in the sand layer and high-strength reinforcement of the sand layer, improves the operation efficiency, reduces the cost, and reduces the disturbance to the sand layer around the pile foundation.

Description

Technical Field

[0001] This invention relates to the field of pile foundation technology, and in particular to a method for reinforcing cast-in-place piles with defects in the pile body located in geological sand layers. Background Technology

[0002] Cast-in-place piles are a widely used type of pile foundation in building foundation engineering. During the construction of bored cast-in-place piles, a certain amount of sediment or loose particles inevitably remain in the pile body or at the pile bottom. These defects significantly reduce the structural integrity and end bearing capacity of the pile, affecting the overall stability of the pile foundation. Currently, for pile foundations with sediment at the pile bottom or defects in the pile body, post-grouting technology is often used for reinforcement. This involves drilling to locate the defects, cleaning debris, and injecting grout to repair the pile body and improve its bearing capacity. However, when the pile body is located in a geological sand layer, traditional reinforcement methods face significant challenges. Specifically, when using high-pressure water or grout for flushing and cleaning, loose sand, sand particles, or gravel around the pile continuously flow into the cleaning area, making it impossible to completely remove sediment, mud, and other debris. At the same time, continuous scouring causes a large amount of sand to be lost from the pile side, forming increasingly larger cavities, and even endangering the stability of the pile body and the safety of the surrounding soil.

[0003] To address the aforementioned problems, existing technologies typically employ the "curtain grouting" method. This involves first injecting high-pressure grout around the pile to be reinforced, forming a closed, water-stopping curtain to prevent the outward flow of sand and soil. Then, cleaning and reinforcing grouting are performed inside the curtain. While effective, this method suffers from significant drawbacks, including a long construction period, large quantities of grouting material, and high costs.

[0004] In existing technologies, some methods attempt to address such defects through grouting reinforcement. For example, Chinese patent document CN103174135A discloses a repair method for substandard post-grouting cast-in-place piles, which involves drilling pilot holes outside the pile, adding grouting pipes, and performing post-grouting to improve the pile's bearing capacity in response to defects such as sediment. However, this method involves wide-area grouting and does not optimize for the dynamic problem of sand particles intruding into the sand layer, resulting in incomplete cleaning and high costs. Chinese patent document CN103541359B discloses a remedial method for quality defects in cast-in-place piles, which improves bearing capacity by drilling, cleaning cracks or mud inclusions, and grouting repair, but does not specifically address the intrusion of sand particles into the sand layer. Chinese patent document CN111608174A discloses a method for treating karst caves in karst areas based on bored cast-in-place piles, including site compaction, construction of cofferdams, and grouting for water stoppage, to treat defects in loose soil layers and improve the bearing capacity of the pile ends. It uses a full-circumference water stop curtain, resulting in a long construction period.

[0005] Therefore, when dealing with defects in loose soil layers or similar sand layers, existing technologies often employ full-circumference water-stop curtain grouting. This involves high-pressure grouting around the pile to be reinforced, forming a closed curtain to prevent the inflow of surrounding sand, followed by internal cleaning and reinforcement grouting. While this method effectively prevents sand inflow and soil loss, it suffers from drawbacks such as large grout material consumption, wide construction area, long cycle (usually requiring a long curing time), and high cost. Furthermore, it significantly disturbs the surrounding sand layers, potentially leading to borehole collapse or pile deformation. Therefore, existing methods for reinforcing cast-in-place piles struggle to simultaneously achieve efficient cleaning, effective prevention of sand inflow, and improved pile bearing capacity and durability in geological sand layers, while also controlling costs and minimizing disturbance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for reinforcing cast-in-place piles with defects in the geological sand layer. This method overcomes the defects of traditional cast-in-place pile reinforcement operations. By performing a fine operation of first solidifying and then locally cleaning the sand layer in a specific area around the pile, it can efficiently and thoroughly clean the sediment in the sand layer and carry out high-strength reinforcement, thereby improving construction efficiency, reducing construction costs, and reducing disturbance to the sand layer around the pile foundation.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for reinforcing cast-in-place piles with defects located in geological sand layers, comprising the following steps: Step 1: Drill core samples at the top of the cast-in-place pile and use the low-strain reflection wave method or sonic transmission method to accurately locate the position, type and size of defects in the pile body. Step 2: Using the core drilling holes, a high-pressure jetting device is used to spray cement grout radially along the pile body at the defect location, ensuring that the cement grout is fully mixed with the sand layer to form a solidified protective ring around the pile body. Step 3: After the sand layer has solidified and formed a protective ring, place the high-pressure jetting device along the core drilling hole into the defect area of ​​the pile body. Use high-pressure water jet to cut the loose concrete, mud, and rusted steel bars on the surface of the defect area of ​​the pile body. At the same time, use compressed air to discharge the waste generated during cleaning out of the pile until the flushing water becomes clear, indicating that the loose material, mud, sand and other debris in the defect area of ​​the pile body has been cleaned. Step 4: Use a grouting pump to inject self-compacting micro-expansion concrete into the defect area of ​​the pile body through the grouting pipe. Insert the grouting pipe to the bottom of the defect in the pile body, and use a bottom-up, layered filling method to ensure that the concrete fully fills the gaps and holes in the defect in the pile body until the concrete overflows from the top of the defect in the pile body. If the overflowing concrete has no air bubbles or segregation, it indicates that the defect in the pile body has been completely filled.

[0008] Furthermore, the location of the pile defect includes the depth and radial range of the defect, the type of pile defect includes cracks, holes or mud inclusions, and the size of the pile defect includes length, width or volume.

[0009] Furthermore, in step two, the diameter of the radially sprayed cement slurry is 0.5 to 1 meter beyond the pile diameter, and the cement slurry is ordinary silicate cement slurry.

[0010] Furthermore, the ordinary silicate cement slurry is of low grade and high water-cement ratio, and the spraying speed is controlled to ensure that the cement slurry is fully mixed with the sand layer. Furthermore, in step two, the curing time of the sand layer solidification protective ring is no less than 48 to 72 hours, forming a stable protective ring to prevent sand particles, gravel, or sand from flowing into the protective ring.

[0011] Furthermore, in step four, the grade of the self-compacting micro-expansion concrete is higher than that of the concrete in the cast-in-place pile body.

[0012] Furthermore, in step three, the high-pressure water jet pressure is 20-25 MPa and the compressed air pressure is 0.6-0.8 MPa, which achieves the cleaning of the defective area of ​​the pile body and the discharge of waste residue, ensuring that the defective area of ​​the pile body is filled densely. The present invention's method for reinforcing pile defects located in geological sand layers employs the aforementioned technical solution. Specifically, this method uses core drilling at the pile top combined with low-strain reflection wave or sonic logging to precisely locate the position, type, and size of the pile defects. Using the core drilling holes, cement grout is radially injected along the pile shaft at the defect location, forming a solidified protective ring around the pile. A high-pressure jetting device is placed along the core drilling holes in the defect area, and high-pressure water jets clean the defect area. Compressed air is used to remove the waste generated during cleaning. Finally, a grouting pump injects self-compacting micro-expansion concrete into the defect area through a grouting pipe, achieving reinforcement of the pile defects. This method overcomes the shortcomings of traditional pile reinforcement operations by performing a precise operation of first solidifying and then locally cleaning the sand layer in a specific area around the pile. This achieves efficient and thorough removal of sediment from the sand layer and high-strength reinforcement, improving construction efficiency, reducing construction costs, and minimizing disturbance to the surrounding sand layer. Attached Figure Description

[0013] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram illustrating the location of pile defects in this method; Figure 2 This is a schematic diagram of the sand layer curing protective ring setup in this method; Figure 3 This is a schematic diagram of the cleaning of defective parts of the pile body in this method; Figure 4 This is a schematic diagram of reinforcing the defective areas of the pile body with self-compacting micro-expansion concrete using this method. Detailed Implementation

[0014] Implementation, for example Figures 1 to 4 As shown, the reinforcement method for cast-in-place piles with defects located in geological sand layers according to the present invention includes the following steps: Step 1: Drill a core sample at the top of pile 1 and use the low-strain reflection wave method or sonic transmission method to accurately locate the position, type and size of pile defect 11. Step 2: Using the core drilling hole 2, a high-pressure jetting device is used to radially spray cement grout along the pile body at the location of pile defect 11, ensuring that the cement grout is fully mixed with the sand layer to form a solidified protective ring 3 around the pile body. This overcomes the problems of the existing technology, which has a wide curing range around the entire perimeter and causes great disturbance to the sand layer. It only targets the local area around the defect for curing, which greatly reduces the amount of grouting material used. At the same time, it effectively prevents sand, gravel or sand from flowing into the cleaning area, ensuring that subsequent cleaning operations can be carried out without interference. Step 3: After the sand layer solidifies and the protective ring 3 is formed, the high-pressure jetting device is placed along the core drilling hole 2 into the area of ​​pile defect 11. The high-pressure water jet cuts the loose concrete, mud, and rusted steel reinforcement surface attachments at the pile defect 11. At the same time, compressed air is used to discharge the waste generated during cleaning out of the pile until the flushing water becomes clear, indicating that the loose material, mud, sand and other debris at the pile defect 11 have been cleaned. This cleaning process avoids sand loss and hole enlargement. Combined with the protective effect of the solidified protective ring, it achieves thorough cleaning without causing the formation of new holes, thus improving the reliability of the reinforcement effect. Step 4: Using a grouting pump, self-compacting micro-expansion concrete is pressurized into the pile defect 11 area through grouting pipe 4. Grouting pipe 4 is inserted to the bottom of pile defect 11. A bottom-up, layered filling method is used to ensure the concrete fully fills the gaps and cavities in pile defect 11 until concrete overflows from the top of pile defect 11. The overflowing concrete shows no air bubbles or segregation, indicating that pile defect 11 is completely filled. This method overcomes the problems of insufficient grouting and limited load-bearing capacity improvement in existing technologies. Through the micro-expansion characteristics of high-strength concrete, it ensures complete filling of pile defect gaps and cavities, thereby significantly improving the pile's load-bearing capacity and durability.

[0015] Preferably, the location of the pile defect includes the depth and radial range of the defect, the type of pile defect includes cracks, holes or mud inclusions, and the size of the pile defect includes length, width or volume.

[0016] Preferably, in step two, the diameter of the radially sprayed cement slurry is 0.5 to 1 meter beyond the pile diameter, and the cement slurry is ordinary silicate cement slurry.

[0017] Preferably, the ordinary silicate cement slurry is of low grade and high water-cement ratio, and the spraying speed is controlled to ensure that the cement slurry is fully mixed with the sand layer. Preferably, in step two, the curing time of the sand layer solidification protective ring is not less than 48 to 72 hours, forming a stable protective ring to prevent sand particles, gravel or sand from flowing into the protective ring.

[0018] Preferably, in step four, the grade of the self-compacting micro-expansion concrete is higher than the grade of the concrete in the cast-in-place pile body.

[0019] Preferably, in step three, the high-pressure water jet pressure is 20-25 MPa and the compressed air pressure is 0.6-0.8 MPa, which realizes the cleaning of the defective area of ​​the pile body and the discharge of waste residue, and ensures that the defective area of ​​the pile body is filled densely.

[0020] Example 1 This embodiment addresses reinforcement measures for defects in cast-in-place piles located in sand layers. First, core drilling equipment is used to drill and extract core samples from the pile body. By combining the core sample holes with low-strain dynamics and sonic logging methods, the location of the defect in the pile body is accurately determined. It is identified as a crack defect with a length of approximately 0.5 meters, a width of approximately 0.1 meters, and a depth of 5-6 meters in the middle of the pile body.

[0021] Subsequently, a high-pressure jetting device was delivered to the defect location on the pile body through the orifice, and low-grade (PO 32.5) and high water-cement ratio (1:2) ordinary silicate cement grout was sprayed radially along the pile body, with the spraying diameter extending 0.5 meters beyond the pile diameter. The spraying lifting speed was controlled at 0.2 meters per minute to ensure that the cement grout was fully mixed with the sand layer, forming a solidified sand layer zone surrounding the pile body. The solidification time was 48 hours, forming a stable protective ring that prevented the inflow of surrounding sand, gravel, and sand particles.

[0022] After solidification, the high-pressure jetting device is placed at the defect location of the pile body through the hole. High-pressure water jet (pressure of 20MPa) is used to cut loose concrete, mud inclusions and rusted steel bars attached to the surface. At the same time, compressed air (pressure of 0.6MPa) is used to discharge the waste residue until the flushing water becomes clear, forming a high-pressure flushing zone.

[0023] Finally, a grouting pump is used to inject self-compacting micro-expansion concrete (C35), one grade higher than the pile's design grade (C30), into the high-pressure flushing zone through a grouting pipe. The grouting pipe is inserted to the bottom of the defect, and a bottom-up, layered filling method is used, with each layer 0.2 meters high, until the concrete overflows from the top of the defect without air bubbles or segregation, forming a fine-aggregate concrete reinforcement zone. After reinforcement in this embodiment, the pile's bearing capacity is increased by approximately 20%, durability is significantly improved, the construction period is 72 hours, and the total cost is reduced by 30% compared to traditional curtain grouting.

[0024] Example 2 This embodiment is an optimization based on Embodiment 1, targeting larger-sized hole defects. The pile body is inspected, and the location of the defect is located by drilling. The defect is a hole with a volume of approximately 0.1 cubic meters, located in the sand layer 8-9 meters below the pile body.

[0025] During the formation of the sand layer solidification zone, the spraying diameter was extended to 1 meter beyond the pile diameter, using ordinary silicate cement grout with a high water-cement ratio (1:2.5), and the spraying lifting speed was 0.15 meters / minute to accommodate the risk of sand layer flow over a wider area. The curing time was extended to 72 hours to ensure the strength of the protective ring.

[0026] The high-pressure water jet pressure is adjusted to 25MPa, and the compressed air pressure is 0.8MPa to thoroughly remove mud and loose particles, forming a high-pressure flushing zone.

[0027] C40 self-compacting micro-expansion concrete is injected through grouting pipes, filling in layers of 0.15 meters each to ensure compaction. This embodiment is suitable for severe defects, increasing the load-bearing capacity by approximately 25% after reinforcement, minimizing disturbance to the sand layer, and reducing costs by 25% compared to existing technologies, demonstrating the adaptability of this method to different defect scales.

[0028] Example 3 This embodiment further optimizes embodiments 1 and 2, addressing the composite defect of mud-bearing cracks. The pile body is inspected, and the defect is located as a 1-meter-long crack containing mud, with a depth of 6-7 meters.

[0029] The spray diameter for the sand layer curing zone is 0.75 meters, using PO 42.5 cement slurry (water-cement ratio 1:2), with a lifting speed of 0.18 meters / minute, and curing time of 48 hours.

[0030] The cleaning process combines high-pressure water jet (22MPa) and compressed air (0.7MPa) to focus on removing rust and other deposits, creating a high-pressure flushing zone.

[0031] C35 concrete was used for filling, and the grouting was carried out in layers of 0.18 meters each through grouting pipes. This embodiment provides reliable reinforcement, increases load-bearing capacity by 22%, offers high construction safety, is environmentally friendly, and is suitable for complex sandy environments.

[0032] This method employs core drilling equipment to inspect the pile body. Through core sampling and low-strain analysis, the location, type, and size of pile defects are determined. The defects are then treated by delivering a high-pressure jetting pipe to the defect location and radially spraying ordinary silicate cement grout into the defect area. The spray diameter extends 0.5–1 meter beyond the pile diameter, forming a sand-solidified zone. After the sand-solidified zone has cured for at least 48 hours, the high-pressure jetting pipe is again delivered to the defect location through drilling. High-pressure water jets cut away loose concrete, mud inclusions, and rusted steel reinforcement surface deposits at the defect location. Simultaneously, compressed air is used to remove waste from the pile until the flushing water becomes clear, forming a high-pressure flushing zone. Finally, self-compacting micro-expansion concrete is delivered to the high-pressure flushing zone through a grouting pipe via drilling, forming a self-compacting micro-expansion concrete reinforcement zone.

[0033] In this method, the pile body is the core load-bearing foundation of the reinforcement project. The material is mostly concrete with an internal steel reinforcement skeleton. It needs to work together with the sand layer to bear the upper load. Its original integrity is the key foundation for the reinforcement effect.

[0034] Core drilling, formed by the core drilling process, is a channel for operating equipment to enter the defect area of ​​the pile body. It requires precise positioning and the hole diameter must match the equipment size, while ensuring the stability of the hole wall to prevent the sand layer from collapsing and blocking it.

[0035] The location of the pile defects is the target area for reinforcement, including defects such as cracks, holes, and mud inclusions. It is necessary to determine their depth, range, and size by core drilling combined with low strain method and sonic logging method to provide a basis for subsequent construction. The sand layer solidification zone is located outside the defect area of ​​the pile body. It forms a ring-shaped protective ring by high-pressure injection of low-grade / high water-cement ratio ordinary silicate cement grout. The radial range is 0.5 to 1 meter outside the pile diameter. The solidification time is not less than 48 to 72 hours, which can prevent sand particles from flowing in and sand from being lost.

[0036] The high-pressure flushing zone is located within the solidified sand layer and at the pile defect. High-pressure water jets are used to clean the loose concrete, mud, and other debris in the defect area, and compressed air is used to remove slag until the flushing water is clear, creating a clean interface for filling and reinforcement.

[0037] The reinforcement zone is filled with self-compacting micro-expansion concrete of a grade one grade higher than that of the pile body concrete. The filling method is adopted from bottom to top and in layers to ensure that there are no voids, air bubbles and segregation, thereby restoring and improving the bearing capacity of the pile body.

[0038] Grouting pipes are specialized pipelines for transporting reinforcing concrete. They must have sufficient strength and pressure resistance, and be inserted to the bottom of the pile defect. The density of the concrete filling is ensured by controlling the lifting speed.

[0039] This method is highly targeted and reliable. It creatively proposes the idea of ​​"solidifying the periphery first, then cleaning the interior". By using ordinary silicate cement grout (low grade / high water-cement ratio type) to form a "sand layer solidification protective ring" within a range of 0.5 to 1 meter around the defect, a stable protective shell is first formed around the pile. Then, the slag removal operation is carried out inside the shell without interference. This fundamentally solves the problems of incomplete slag removal and hole enlargement caused by sand layer flow. The reinforcement effect is significant and reliable.

[0040] Highly efficient and low-cost, this method only hardens the perimeter of the localized area requiring slag removal, significantly reducing the amount of cement grout used and the construction scope compared to the traditional full-circumference curtain grouting method. Furthermore, by closely integrating the hardening and slag removal steps, the overall construction cycle is shortened, effectively reducing construction costs.

[0041] This method boasts high construction safety and environmental friendliness. The entire construction process requires no large excavation equipment. After defect location, the core-extracted holes serve as channels for subsequent solidification, cleaning, and filling operations, minimizing disturbance to the sand layer. During cleaning, compressed air is used to remove waste, and the protective effect of the sand layer solidification ring prevents sand loss and hole enlargement. The reinforcement process is completed through pressure grouting, minimizing disturbance to the surrounding sand layer and avoiding safety hazards such as hole collapse and pile deformation. Ordinary silicate cement grout is a commonly used environmentally friendly material in engineering, releasing no toxic or harmful substances and not polluting groundwater, meeting green construction requirements. This method is suitable for composite pile defects such as cracks, holes, or mud inclusions located in geological sand layers. The sand layer solidification protective ring, with a solidification time of no less than 48 hours, ensures the thoroughness of the cleaning process and construction safety, providing a foundation for concrete reinforcement.

Claims

1. A method for reinforcing cast-in-place piles with defects located in geological sand layers, characterized in that... Includes the following steps: Step 1: Drill core samples at the top of the cast-in-place pile and use the low-strain reflection wave method or sonic transmission method to accurately locate the position, type and size of defects in the pile body. Step 2: Using the core drilling holes, a high-pressure jetting device is used to spray cement grout radially along the pile body at the defect location, ensuring that the cement grout is fully mixed with the sand layer to form a solidified protective ring around the pile body. Step 3: After the sand layer has solidified and formed a protective ring, place the high-pressure jetting device along the core drilling hole into the defect area of ​​the pile body. Use high-pressure water jet to cut the loose concrete, mud, and rusted steel bars on the surface of the defect area of ​​the pile body. At the same time, use compressed air to discharge the waste generated during cleaning out of the pile until the flushing water becomes clear, indicating that the loose material, mud, sand and other debris in the defect area of ​​the pile body has been cleaned. Step 4: Use a grouting pump to inject self-compacting micro-expansion concrete into the defect area of ​​the pile body through the grouting pipe. Insert the grouting pipe to the bottom of the defect in the pile body, and use a bottom-up, layered filling method to ensure that the concrete fully fills the gaps and holes in the defect in the pile body until the concrete overflows from the top of the defect in the pile body. If the overflowing concrete has no air bubbles or segregation, it indicates that the defect in the pile body has been completely filled.

2. The method for reinforcing cast-in-place piles with defects located in geological sand layers according to claim 1, characterized in that: The location of the pile defect includes the depth and radial range of the defect; the type of pile defect includes cracks, holes or mud inclusions; and the size of the pile defect includes length, width or volume.

3. The method for reinforcing cast-in-place piles with defects located in geological sand layers according to claim 1, characterized in that: In step two, the diameter of the radially sprayed cement slurry is 0.5 to 1 meter beyond the pile diameter, and the cement slurry is ordinary silicate cement slurry.

4. The method for reinforcing cast-in-place piles with defects in geological sand layers according to claim 3, characterized in that: The ordinary silicate cement grout is of low grade and high water-cement ratio, and the spraying speed is controlled to ensure that the cement grout is fully mixed with the sand layer.

5. The method for reinforcing cast-in-place piles with defects located in geological sand layers according to claim 1, characterized in that: In step two, the curing time of the sand layer solidification protective ring shall not be less than 48 to 72 hours, so as to form a stable protective ring to prevent sand particles, gravel or sand from flowing into the protective ring.

6. The method for reinforcing cast-in-place piles with defects located in geological sand layers according to claim 1, characterized in that: In step four, the grade of the self-compacting micro-expansion concrete is higher than that of the concrete in the pile body.

7. The method for reinforcing cast-in-place piles with defects in geological sand layers according to claim 1, characterized in that: In step three, the high-pressure water jet pressure is 20-25 MPa and the compressed air pressure is 0.6-0.8 MPa, which achieves the cleaning of the defective area of ​​the pile body and the discharge of waste residue, ensuring that the defective area of ​​the pile body is filled densely.

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