A new precast pile sinking and grouting construction method

Abstract

This invention relates to a novel method for grouting precast pile driving, belonging to the technical field of building construction. The technical solution is as follows: First, drill and lift the drill to inject some reinforcing grout, forming a hollow section; then, drive the precast pile to expand the hollow section, the expanded borehole wall soil forms a foundation seal with the outer surface of the precast pile it surrounds, sealing the reinforcing grout inside the borehole; then, continue driving the pile, squeezing the reinforcing grout inside the borehole, expanding the borehole wall soil to form a saturated expanded borehole wall soil, which forms a reinforced seal with the outer surface of the precast pile it surrounds. As the precast pile gradually sinks, the pressure of the reinforcing grout inside the borehole gradually increases, the depth and amount of grout entering the borehole wall soil gradually increase, and the sealing performance between the bottom outer surface of the precast pile and the expanded borehole wall gradually improves, until the pile reaches the designed depth. This invention results in a large area of ​​soil around the pile reinforced by grout, high overall strength, and good overall stability, leading to a pile with high bearing capacity and good bearing stability.

Description

TECHNICAL FIELD

[0001] The present application relates to a new type of precast pile sinking and grouting construction method, belonging to the technical field of building construction. BACKGROUND

[0002] In the existing precast pile grouting construction process, the precast pile is first sunk to the designed depth, and then the surrounding soil at the bottom of the pile is grouted through the grouting pipe to reinforce the strength of the surrounding soil at the bottom of the pile, so as to improve the bearing capacity of the precast pile. The disadvantages are: first, during the sinking process, the precast pile squeezes and compacts the surrounding soil, especially the soil at the bottom of the pile. The compacted soil body increases the difficulty of the grout entering the soil, greatly reduces the amount and depth of the grout entering the soil; second, the number of grouting pipes is limited, the position is fixed, and the grouting outlet is fixed, which belongs to fixed-point grouting. The uniformity of the strength of the soil around the pile after grouting is poor, and the overall stability is not good; third, the inconsistency of the grouting pressure and the amount of grouting of each pile caused by human factors is very easy to cause insufficient bearing capacity of the pile. In order to solve the above-mentioned shortcomings, a new type of precast pile sinking and grouting construction method is proposed, which meets the requirements of more amount, greater depth and better uniformity of the reinforcing grout pressure into the surrounding soil of the pile. The reinforced soil around the pile has large area, high overall strength and good overall stability, and the formed pile has high bearing capacity and good bearing stability. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a precast pile sinking and grouting construction method. The precast pile sinking and grouting construction method uses the precast pile to pressurize the reinforcing grout in the drill hole, increases the internal pressure of the grout, forces more grout to enter the adjacent soil, and the adjacent soil body presents a saturated or even supersaturated state, forming a larger-diameter grouting soil body around the pile. After cementation and solidification, the bearing capacity of the formed pile is improved.

[0004] To solve the above problems, the specific technical scheme of the present application is as follows: a new type of precast pile sinking and grouting construction method, comprising the following steps: 1) Drilling and grouting soil around the pile: using a spiral drill, a down-the-hole drill or a rotary drilling rig, drilling a hole to the designed depth at the pile position by a drill, forming a pilot hole, then lifting the drill to the pilot hole, and pouring reinforcing grout into the pilot hole. The majority of the depth of the pilot hole is filled with reinforcing grout, and the near-surface section of the pilot hole is an air hole section with air inside. The drill is lifted to the ground surface and moved away from the pilot hole position; wherein the diameter of the pilot hole is smaller than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile cross section; the reinforcing grout is a functional mixed liquid with the functions of cementing soil and improving the mechanical strength of the foundation soil; 2) Pile driving and air compression in the hollow section: The precast pile with a plug at the bottom is aligned with the pilot hole using a pile driving equipment. The precast pile is driven downward, and the bottom end of the precast pile expands the hole wall of the hollow section. At the same time, the air sealed in the hollow section is compressed. The compressed air is discharged to the outside through the air release device on the plug at the bottom end of the precast pile; or the plug at the bottom end of the precast pile does not have an air release device, and the compressed air enters the soil of the hole wall. The pile driving, the expansion of the hole wall, and the air compression in the hollow section are all carried out until the bottom end of the precast pile enters the surface of the reinforcing grout in the pilot hole. The exhaust channel of the air release device on the plug is closed. The expanded hole wall soil and the outer surface of the precast pile in contact with it form a foundation seal, sealing the reinforcing grout in the pilot hole. 3) Pile Driving and Grouting: As the pile continues to drive, the bottom end of the precast pile expands the pilot hole, simultaneously squeezing out some of the reinforcing grout sealed within the pilot hole into the surrounding soil. The grout is forced into the expanded hole wall, reaching a dense and saturated state, forming a reinforced seal with the outer surface of the precast pile. As the precast pile gradually sinks, the pressure within the reinforcing grout sealed in the pilot hole gradually increases, the depth and amount of grout entering the surrounding soil gradually increase, and the saturation of the soil around the pilot hole gradually improves. The sealing performance of the reinforced seal between the bottom outer surface of the precast pile and the expanded hole wall also gradually improves. The pile is driven to the designed depth, meeting the top elevation requirements of the precast pile. The precast pile is one of the following: a prestressed concrete pile with an internal through hole, a steel pile, or a composite pile of concrete and steel hooks. The outer diameter of the plug at the bottom of the precast pile is not greater than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section.

[0005] A novel method for grouting precast pile driving includes the following steps: 1) Drilling pilot holes and grouting around the pile: Using a auger, down-the-hole drill, or rotary drilling rig with an enlarging device, drill a hole at the pile location. Within the designed drilling depth, first retract the enlarging device of the drill bit and drill down to form a pilot hole. Then, open the enlarging device and drill down to form a large-diameter hole until the designed drilling depth is reached. Then, retract the enlarging device, lift the drill bit, and grout the reinforcing grout. Grout the large-diameter hole and part of the pilot hole. The section of the pilot hole near the ground surface is an air-filled section. Lift the drill bit to the ground surface and move the pilot hole position away. The diameter of the pilot hole is smaller than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section. The reinforcing grout is a functional mixed liquid that can bind soil and improve the mechanical strength of the foundation soil. 2) Pile driving and air compression in the hollow section: The precast pile with the plug at the bottom is aligned with the center of the pilot hole using the pile driving equipment. The precast pile is driven downward, and the bottom end of the precast pile expands the hole wall of the hollow section. At the same time, the air sealed in the hollow section is compressed. The compressed air is discharged to the outside through the air release device on the plug at the bottom end of the precast pile; or the plug at the bottom end of the precast pile does not have an air release device, and the compressed air enters the soil of the hole wall. The pile driving, the expansion of the hole wall, and the air compression in the hollow section are all carried out until the bottom end of the precast pile enters the reinforcing grout in the pilot hole. The exhaust channel of the air release device on the plug is closed. The expanded hole wall soil and the outer surface of the precast pile in contact with it form a foundation seal, sealing the reinforcing grout in the pilot hole and the large-diameter hole. 3) Pile Driving and Grouting: As the pile continues to drive, the bottom end of the precast pile expands the pilot hole, simultaneously squeezing some of the reinforcing grout sealed within the pilot hole and the main borehole into the surrounding soil. The grout is forced into the expanded pilot hole wall, reaching a dense and saturated state, forming a reinforced seal with the outer surface of the precast pile. As the precast pile gradually sinks, the pressure within the reinforcing grout sealed in the pilot hole and main borehole gradually increases, leading to a deeper penetration, a larger volume of grout into the surrounding soil, and a higher saturation of the soil in the pilot hole and main borehole walls. This also gradually improves the sealing performance between the bottom outer surface of the precast pile and the expanded pilot hole wall. The bottom end of the sinking precast pile is squeezed through the pilot hole and into the top of the main borehole, continuing pile driving. For main boreholes with a diameter smaller than the outer diameter of the precast pile... When the diameter of the precast pile is not less than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section, the bottom end of the precast pile is squeezed to enlarge the diameter hole, and the reinforcing grout in the large diameter hole is squeezed into the surrounding soil. The soil on the wall of the enlarged diameter hole is saturated and forms a reinforced seal with the outer surface of the precast pile it wraps around. When the diameter of the large diameter hole is not less than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section, part of the reinforcing grout in the large diameter hole is squeezed into the surrounding soil. The gap between the outer surface of the precast pile and the wall of the large diameter hole is filled with reinforcing grout, and the pile is driven to the design depth to meet the top elevation of the precast pile. The precast pile is one of the following: a prestressed concrete pile with an internal through hole, a steel pile, or a composite pile of concrete and steel hooks. The outer diameter of the plug at the bottom end of the precast pile is not greater than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section.

[0006] The venting device in step 2) is a normally open one-way valve structure. The bottom end of the movable valve core of the venting device is located at the lower end of the plug. During the pile driving process in the empty hole section, the venting hole of the venting device is in the open state. The pressurized air in the empty hole section is discharged into the atmosphere through the venting hole of the venting device and the cavity inside the precast pile. When the bottom end of the precast pile enters the surface of the reinforcing grout in the pilot hole, the bottom end of the movable valve core of the venting device is subjected to the upward force of the reinforcing grout, which pushes the movable valve core to move upward, closes the venting hole, and seals the reinforcing grout inside the hole.

[0007] The venting device in step 2) consists of a vertical through-hole inside the plug body, a long pipe connected to the upper end of the through-hole and penetrating the inner hole of the precast pile, a flexible hose connected to the upper end of the long pipe, and a switch valve connected to the other end of the flexible hose and placed on the ground. During the pile driving process, the switch valve is first opened, and the pressurized air in the empty hole section is discharged into the atmosphere through the through-hole inside the plug body, the long pipe, the flexible hose, and the switch valve. When the reinforcing grout flows out of the outlet of the switch valve, the switch valve is closed to seal the reinforcing grout in the hole. After the pile driving is completed, the connection between the long pipe and the through-hole of the plug body is disconnected, and the long pipe is lifted out of the inner hole of the precast pile.

[0008] In step 2), during pile driving and air extrusion in the hollow section, the air trapped in the hollow section is released sequentially through the plug, long pipe, flexible hose, and switch valve. When the bottom end of the precast pile enters the reinforcing grout in the pilot hole, the switch valve is closed to seal the reinforcing grout within the hole. In step 3), during pile driving and grouting, if a sharp drop in pile driving pressure occurs (except for changes in the surrounding soil layer and / or a sharp drop occurring when the precast pile passes through a large-diameter hole), pile driving is stopped. A high-pressure grouting pump is used, with the pump outlet connected to the switch valve outlet. The switch valve is opened, and the grouting pump is started. Reinforcing grout is added to the hole through the venting device to meet the continuously increasing pile driving pressure during the driving process. When the pile driving pressure approaches the allowable pressure value of the precast pile, pile driving is stopped, the switch valve is opened, and part of the high-pressure reinforcing grout in the hole flows back to the grout pool through the venting device. The switch valve is then closed to meet the safe pile driving pressure.

[0009] The precast pile bottom plug in step 2) has an air release device. The air release device does not release the air in the empty hole section. During the pile driving process, the air in the empty hole section is pressurized and enters the soil in the hole wall.

[0010] The precast pile bottom plug has an air release device, which consists of a long pipe, a flexible hose, and a switch valve placed on the ground connected in sequence. The lower end of the long pipe is connected to a vertical through hole in the plug. During the precast pile sinking process in step 2), the switch valve is closed, and the air sealed in the empty hole section is pressurized and enters the soil in the hole wall. During the pile driving and grouting in step 3), when the pile driving pressure drops sharply, except for changes in the soil layer around the pile and / or the sharp drop that occurs when the precast pile passes through a large-diameter hole, the pile driving is stopped. A high-pressure grouting pump is used, and the pump outlet is connected to the outlet of the switch valve. The switch valve is opened, the grouting pump is started, and reinforcement grout is added to the hole through the air release device to meet the requirements of the pile driving pressure continuously increasing during the pile driving process. When the pile driving pressure approaches the allowable pressure value of the precast pile, the pile driving is stopped, the switch valve is opened, and part of the high-pressure reinforcement grout in the hole flows back to the grout pool through the air release device. Then the switch valve is closed to meet the safe pile driving pressure.

[0011] The plug at the bottom of the precast pile is shaped like a cone or frustum, with a smaller bottom and a larger top.

[0012] The drilling depth of the drill bit shall not exceed the length of the precast pile; the final driving pressure of the precast pile shall meet the design requirements.

[0013] The reinforcing grout is a granular grout and / or a chemical grout; wherein the granular grout includes one or more of cement grout, cement mortar, clay grout or cement-clay grout, and the chemical grout includes one or more of silicates, calcium chloride, epoxy resin, acrylate, acrylamide, acrylate or pulp-based grout.

[0014] The precast pile driving and grouting construction method described in this application, which employs the above-mentioned method, has the following advantages: 1. In the precast pile driving grouting construction method of this application, the soil reinforcement grout around the pile is injected into the pilot hole or pilot hole and the large-diameter hole before pile driving. The pilot hole and the large-diameter hole below the pilot hole are formed by auger drilling, rotary drilling or down-the-hole drilling. The soil on the hole wall and the soil at the bottom of the hole are conducive to the entry of grout. During the pile driving process, the reinforcement grout sealed in the pilot hole or pilot hole and the large-diameter hole is squeezed by the downward-moving bottom end face of the precast pile, and the internal pressure of the grout increases. The high-pressure and high-flow-rate grout forces more grout into the adjacent soil and into the soil deeper. The soil is saturated or even oversaturated. The precast piles, as they move downwards, expand the diameter of the grout inlet wall, further squeezing the grout inside the expanded hole wall to expand outwards, forming a monolithic grouted soil body with a larger outer diameter. After cementation and solidification, the overall strength is high. It can be seen that the grouting of the soil around the pile is completed during the pile driving process, and the grout is injected into the soil in its original state. Compared with the existing construction process of driving the pile first and then grouting, the grout in the reinforced soil is easier to enter, enters in larger quantities, and enters to a deeper depth, which is more conducive to improving the bearing capacity of the pile.

[0015] 2. In the precast pile driving and grouting construction method of this application, no reinforcing grout is injected into the empty section above the pilot hole. Instead, the precast pile is driven down to expand the empty section. The expanded hole forms a foundation sealing fit with the outer surface of the precast pile it encloses, sealing the pilot hole or the pilot hole and the large-diameter hole with reinforcing grout. As the pile continues to drive, the internal pressure of the grout in the hole gradually increases, and some grout is forced into the soil of the adjacent hole wall. At the same time, the bottom end of the moving precast pile expands into the pilot hole wall with grout, forming a dense and saturated state, and then... A reinforced sealing mating pair is formed between the outer surfaces of the precast pile and the surrounding soil. As the precast pile sinks, the internal pressure of the grout in the pilot hole or pilot hole and the large-diameter hole increases, and the amount and depth of grout entering the soil of adjacent hole walls increase. The density and saturation of the enlarged hole wall formed by the expansion of the pilot hole at the bottom of the precast pile increases, and the sealing performance of the reinforced sealing mating pair between the enlarged hole wall and the outer surface of the precast pile also increases. Therefore, foundation sealing is fundamental; it is crucial when the grout is squeezed out during pile driving. The process involves sealing a highly fluid grout with a certain internal pressure in the pilot hole or pilot hole and large-diameter hole, forming a reinforced seal with a sealing performance higher than the foundation seal. Continued pile driving expands the pilot hole and compresses the grout within, further enhancing the seal performance. This process continues until a high-performance reinforced seal is achieved. Without a foundation seal, the low-compressibility, highly fluid grout will flow out of the pilot hole filled with grout at the bottom of the precast pile, creating a grout outflow channel within the hole wall soil, making it impossible to seal the grout within the pilot hole. In this application, the combination of a foundation seal and a reinforced seal with gradually increasing sealing performance from top to bottom satisfies the requirement that as the precast pile sinks, the internal pressure of the grout in the pilot hole or pilot hole and large-diameter hole gradually increases, the amount of grout entering the soil gradually increases, and the depth of entry gradually increases. This results in a large amount of grout entering the pile bottom and bearing layer soil, a deep depth, a large solid volume, and high strength, which is beneficial for significantly improving the bearing capacity of the formed pile. Large-diameter holes are generally located at the bottom of the pile, increasing the storage capacity of the reinforcing grout. When the diameter of the large-diameter hole is smaller than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section, the bottom end of the precast pile is squeezed to enlarge the diameter hole, forcing the reinforcing grout inside the large-diameter hole into the surrounding soil. The soil on the wall of the enlarged large-diameter hole is saturated and forms a reinforced seal with the outer surface of the precast pile it encloses. When the diameter of the large-diameter hole is not smaller than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section, part of the reinforcing grout inside the large-diameter hole is squeezed into the surrounding soil. The gap between the outer surface of the precast pile and the wall of the large-diameter hole is filled with reinforcing grout, resulting in high grout strength, which is beneficial to improving the pile's bearing capacity. Typically, the pilot hole is left unfilled with reinforcing grout within a 2-8m length near the ground surface to form a foundation seal. Let the diameter of the pilot hole be d, and the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section be D, where Dd = (50-260) mm. For foundation soil layers with low compressibility, take the smaller value; for foundation soil layers with small D values, take the smaller value.

[0016] 3. In the precast pile driving and grouting construction method of this application, no reinforcing grout is injected into the near-surface pilot hole section, forming a hollow section. During the construction process of expanding the hollow section during pile driving, the air in the hollow section is released using the venting device on the plug, preventing air from entering the grout. This is beneficial to improving the quality of the grout-reinforced soil around the pile, especially when the pilot hole wall soil in this section is a dense, low-compressibility soil layer, such as dense sand or saturated soil. When the pilot hole wall soil in this section contains a non-dense soil layer, which is usually a soil layer with a void ratio e≥0.6 and low water content, such as an under-consolidated fill layer or a slightly dense silt layer, the plug is not equipped with a venting device, or the plug is equipped with a venting device but the venting channel is not opened. During the pile driving process, the air in the hollow section is forced into the non-dense soil layer, reducing the permeability of the expanded hole wall soil and improving the sealing performance of the foundation.

[0017] 4. The precast pile driving and grouting construction method of this application, for complex foundation soil conditions, can replenish grout through an air release device during pile driving to meet the insufficient reinforcement grout. For example, in soil layers with large grout absorption such as cracks around the pile, the pile driving pressure will decrease significantly. Replenishing grout ensures the quality of soil reinforcement. Alternatively, excess grout in the pilot hole or pilot hole and large-diameter hole can be flowed back to the grout pool through the air release device. For example, in bearing layers with low compressibility, the pile driving pressure is close to the allowable pressure value of the precast pile. Releasing grout ensures safe construction and reduces grout waste. The plug body has a conical or frustum-shaped structure, which is beneficial for expanding the pilot hole during pile driving, improving the sealing of the foundation and enhancing the sealing performance.

[0018] 5. In the precast pile driving and grouting construction method of this application, the drilling depth of the drill bit is not greater than the length of the precast pile, ensuring that most or even almost all of the reinforcing grout in the hole enters into the adjacent soil, thereby reinforcing the soil. This is especially true for soils with high compressibility and low strength, such as the loose soil at the bottom of the hole and the slightly dense soil layer on the borehole wall, where the amount of grout entering is even greater. It can be seen that the method of driving and grouting the pile with reinforcing grout in this application has a large area of ​​soil reinforcement, good integrity, and can significantly improve the overall strength of the reinforced soil. It also has good uniformity and stability, which can make up for the deficiency of low strength of the original soil around the pile and the adverse effect of the loose soil at the bottom of the hole on the bearing capacity of the pile. When the bottom of the pile is a large-diameter hole, and the diameter of the large-diameter hole D1 is greater than the outer diameter D of the precast pile, the space between the outer surface of the precast pile and the wall of the large-diameter hole is filled with grout; a small amount of grout will also remain between the outer surface of the precast pile and the wall of the enlarged hole, forming a thin layer of grout, which is beneficial for pile driving and sealing; the high-strength grout remaining on the outer surface of the precast pile can improve the bonding force between the outer surface of the precast pile and the surrounding soil-grout mixture.

[0019] 6. The precast pile driving and grouting construction method of this application uses a drilling tool with an enlarging device to form a hole. For soil layers with low compressibility around the pile, such as gravelly soil layers or dense coarse sand layers, enlarging drilling can be adopted, which is beneficial to pile driving construction.

[0020] 7. In the precast pile driving and grouting construction method of this application, the final driving pressure of the precast pile is determined based on the test pile test and design, and is usually not less than the final pressure value of the existing post-grouting prestressed pipe pile driving construction, so as to ensure the safety of the completed pile. Attached Figure Description

[0021] Figure 1 This is a construction process diagram for Example 1.

[0022] Figure 2 This is a construction process diagram for Example 2.

[0023] Figure 3 for Figure 1 A magnified view of part A.

[0024] Figure 4 for Figure 1 A magnified view of section B.

[0025] Figure 5 This is a schematic diagram of the connection of the venting devices in Examples 3, 4, and 5.

[0026] Figure 6 for Figure 2 A magnified view of a portion of point C.

[0027] In the diagram, 1-auger drill bit, 11-auger drill bit, 12-auger drill rod, 13-auger drill bit with expansion device, 2-pilot hole, 3-reinforcing grout, 4-precast pile, 5-air, 6-plug, 7-venting device with one-way valve structure, 71-movable valve core, 72-vent hole, 8-venting device with combined valve structure, 81-through hole, 82-long pipe, 83-hose, 84-switch valve, 9-reinforcing soil, 10-large diameter hole. Detailed Implementation Example 1

[0028] like Figure 1 As shown, a novel precast pile driving and grouting construction method includes the following steps: 1) Drilling pilot holes and grouting for soil reinforcement around cast-in-place piles: such as Figure 1Steps (a) to (c) involve using a drilling tool consisting of a auger bit and a auger drill rod to drill a hole at the pile location to the designed depth using an auger drilling machine, forming a pilot hole. The drilling tool is then lifted, and reinforcing grout is injected into the pilot hole. The pilot hole is filled with reinforcing grout for most of its depth. The section of the pilot hole near the ground surface is an empty section containing air. The drilling tool is then lifted to the ground surface, and the pilot hole is removed. The diameter of the pilot hole is smaller than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section. The reinforcing grout is a granular grout and / or a chemical grout. The granular grout includes one or more of the following: cement grout, cement mortar, clay grout, or cement-clay grout. The chemical grout includes one or more of the following: silicate, calcium chloride, epoxy resin, acrylate, acrylamide, acrylate, or a pulp-based grout. The reinforcing grout bonds with the soil, improving the mechanical strength of the soil around the pile. 2) Piling and squeezing air in the void section: such as Figure 1 In steps (d) and (e), the precast pile with a plug at its bottom is aligned with the pilot hole using a pile-setting device, and the precast pile is driven downwards. The bottom of the precast pile expands the pilot hole, and simultaneously, the air trapped within the hollow section is released through a venting device on the plug at the bottom of the precast pile. Figure 3 As shown, the venting device is a normally open one-way valve structure. The bottom end of the movable valve core of the venting device is located at the lower end of the plug. During the pile driving process in the hollow section, the venting port of the venting device is open, and the pressurized air in the hollow section is discharged into the atmosphere through the venting port of the venting device and the inner cavity of the precast pile; as Figure 4 As shown, when the lower end of the precast pile enters the surface of the reinforcing grout in the pilot hole, the bottom end of the movable valve core of the venting device is subjected to the upward force of the reinforcing grout, which pushes the movable valve core upward, closes the vent hole, and seals the reinforcing grout inside the pilot hole; the expanded pilot hole wall soil and the outer surface of the precast pile in contact with it form a foundation seal. 3) Pile driving and grouting: such as Figure 1 As shown in steps (f) and (g), the pile driving continues. The bottom end of the precast pile is expanded by the extrusion and expansion of the pilot hole. At the same time, part of the reinforcing grout sealed in the pilot hole is squeezed into the surrounding soil. The grout is pressed into the expanded pilot hole wall, presenting a dense and saturated state, forming a reinforced seal with the outer surface of the precast pile. As the precast pile gradually sinks, the pressure in the reinforcing grout sealed in the pilot hole gradually increases. The depth of the reinforcing grout entering the surrounding soil gradually increases, the amount of grout entering gradually increases, and the saturation of the pilot hole wall soil gradually increases. The sealing performance of the reinforced seal between the bottom outer surface of the precast pile and the expanded pilot hole wall also gradually improves. The pile is driven to the design depth to meet the top elevation of the precast pile.

[0029] The precast pile is one of the following: a prestressed concrete pile with an internal through hole, a steel pile, or a composite pile of concrete and steel hooks; the outer diameter of the plug at the bottom of the precast pile is not greater than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the positive section of the precast pile, and the plug has a frustum-shaped structure with a smaller bottom and a larger top; the length of the precast pile is not less than the depth of the borehole; the final driving pressure of the precast pile is determined based on the test pile detection and design.

[0030] In this embodiment, the drilling tool for the pilot hole is a auger drill, but down-the-hole drill or rotary drilling tool can also be used to construct the pilot hole.

[0031] In step 2) of this embodiment, when driving the pile and squeezing out the air in the hollow section, if the soil on the hole wall contains a non-dense soil layer with a void ratio e ≥ 0.6 and low water content, such as an under-consolidated fill layer or a slightly dense silt layer, the precast pile bottom plug may not have an air release device. Instead, a plug with a conical structure can be used. Figure 5 As shown, the air in the hollow section is squeezed into the non-dense soil layer, which reduces the permeability of the soil in the hole wall after the expansion and improves the sealing performance of the foundation. Example 2

[0032] like Figure 2 As shown, a novel precast pile driving and grouting construction method includes the following steps: 1) Drilling pilot holes and grouting for soil reinforcement around cast-in-place piles: such as Figure 2 Steps (a) to (f) involve using a drilling tool consisting of a auger bit with an expanding device and a auger rod to drill at the pile location using a drilling rig. Within the designed drilling depth, the expanding device of the drill bit is first retracted and lowered to form a pilot hole. Then, the expanding device is opened and the drill bit is lowered to form a large-diameter hole, continuing until the designed drilling depth is reached. The expanding device is then retracted, and the drilling tool is raised to inject reinforcing grout. Reinforcing grout is injected into the large-diameter hole and part of the pilot hole. The section of the pilot hole near the ground surface is an air-filled section. The drilling tool is then raised to the ground surface, and... Remove the pilot hole location; wherein the diameter of the pilot hole is smaller than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section; the reinforcing grout is a granular grout and / or a chemical grout; wherein the granular grout includes one or more of cement grout, cement mortar, clay grout or cement-clay grout, and the chemical grout includes one or more of silicates, calcium chloride, epoxy resin, acrylate, acrylamide, acrylate or pulp-based grout; the reinforcing grout bonds with the soil to improve the mechanical strength of the soil around the pile; 2) Pile driving and air compression within the hollow section: When the soil in the hollow section contains non-dense soil layers with a void ratio e≥0.6 and low water content, such as under-consolidated fill layers or slightly dense silt layers, the pile driving construction should proceed as follows: Figure 2In steps (g) and (h), the precast pile with a plug at its bottom is aligned with the pilot hole using a pile-setting device, and the precast pile is driven downwards. This causes the hole wall of the hollow section at the bottom of the precast pile to expand, simultaneously compressing the air trapped within the hollow section. No venting device is provided on the plug at the bottom of the precast pile. Figure 6 As shown, the compressed air enters the soil of the borehole wall. The pile driving, the expansion of the borehole wall, and the squeezing of the air in the empty section of the borehole to the bottom end of the precast pile enter the surface of the reinforcing grout in the pilot hole. The expanded soil of the borehole wall in the empty section forms a foundation seal with the outer surface of the precast pile in contact with it, sealing the reinforcing grout in the pilot hole and the large-diameter hole. The air in the empty section is forced into the non-compacted soil layer, which reduces the permeability of the expanded borehole wall soil and improves the sealing performance of the foundation seal. 3) Pile driving and grouting: such as Figure 2 In steps (i) and (j), pile driving continues. The bottom end of the sinking precast pile expands the pilot hole, simultaneously squeezing some of the reinforcing grout sealed within the pilot hole and the large-diameter hole into the surrounding soil. The grout is forced into the expanded pilot hole wall, reaching a dense and saturated state, forming a reinforced seal with the outer surface of the precast pile. As the precast pile gradually sinks, the pressure within the reinforcing grout sealed in the pilot hole and the large-diameter hole gradually increases, leading to a deeper penetration and a larger volume of grout into the surrounding soil. As the saturation of the soil around the large-diameter borehole gradually increases, the sealing performance between the outer surface of the precast pile bottom and the wall of the expansion pilot hole also gradually improves. The bottom end of the sinking precast pile is squeezed through the pilot hole and enters the top of the large-diameter borehole. Since the diameter D1 of the large-diameter borehole is larger than the outer diameter D of the precast pile, the pile continues to be driven. The precast pile enters the cavity of the large-diameter borehole, squeezing some of the reinforcing grout in the large-diameter borehole into the surrounding soil. The reinforcing grout remaining in the large-diameter borehole fills the gap between the outer surface of the precast pile and the wall of the large-diameter borehole. The pile is driven to the design depth to meet the top elevation of the precast pile.

[0033] The precast pile is one of the following: a prestressed concrete pile with an internal through hole, a steel pile, or a composite pile of concrete and steel hooks; the outer diameter of the plug at the bottom of the precast pile is not greater than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the positive section of the precast pile, and the plug has a conical structure with a smaller bottom and a larger top; the length of the precast pile is not less than the depth of the borehole; the final driving pressure of the precast pile is determined based on the test pile detection and design.

[0034] In this embodiment, the drilling tool for the pilot hole is a auger drill with an enlarging device. Alternatively, a down-the-hole drill with an enlarging device or a rotary drilling tool with an enlarging device can be used to construct the pilot hole and large-diameter hole.

[0035] In step 2) of this embodiment, the air in the hollow section is squeezed out by driving the pile. The precast pile bottom plug can be equipped with a normally open one-way valve structure for releasing air, such as... Figure 3 , 4As shown, the construction process of driving piles, squeezing out the empty hole section, releasing the air in the empty hole section, forming a foundation seal, and sealing the reinforcement grout in the hole is the same as in Example 1.

[0036] In this embodiment, the diameter D1 of the large-diameter hole can also be smaller than the outer diameter D of the precast pile. In step 3), after the bottom end of the precast pile is squeezed through the pilot hole, the pile continues to be driven. The bottom end of the precast pile squeezes the soil of the large-diameter hole wall, and at the same time, the grout in the large-diameter hole is squeezed into the soil of the hole wall. The soil of the large-diameter hole wall that has been squeezed into the hole wall becomes dense and saturated, forming a reinforced seal with the outer surface of the precast pile. As the precast pile gradually sinks, the pressure in the reinforcing grout sealed in the large-diameter hole gradually increases, the depth of the reinforcing grout entering the surrounding soil gradually increases, the amount of grout entering gradually increases, the saturation of the soil of the large-diameter hole wall gradually increases, and the sealing performance of the reinforced seal formed between the outer surface of the bottom of the precast pile and the wall of the squeezed large-diameter hole gradually improves. The pile is driven to the design depth to meet the top elevation of the precast pile. Example 3

[0037] A novel precast pile driving and grouting construction method, step 2) involves driving the pile and squeezing out the air in the hollow section. The air release device is a combined valve structure, consisting of a long pipe, a flexible hose, and a switch valve placed on the ground connected in sequence. The lower end of the long pipe is connected to a vertical through hole in the plug body. The plug body has a frustum-shaped structure. Figure 5 As shown; during the pile driving process, the switch valve is first opened, and the pressurized air in the empty hole section is discharged into the atmosphere through the through hole in the plug body, the long pipe, the hose, and the switch valve. When the reinforcing grout flows out of the outlet of the switch valve, the switch valve is closed to seal the reinforcing grout in the hole. After the pile driving is completed, the connection between the long pipe and the through hole of the plug body is disconnected, and the long pipe is lifted out of the precast pile hole.

[0038] The remaining construction steps are the same as in Example 1 or Example 2. Example 4

[0039] A novel precast pile driving and grouting construction method, in step 3), when the pile driving pressure drops sharply (excluding changes in the compressibility of the soil around the pile and / or the sharp drop that occurs when the precast pile passes through a large-diameter hole), pile driving is stopped. A high-pressure grouting pump is used, with the pump outlet connected to the outlet of a switch valve. The switch valve is opened, the grouting pump is started, and reinforcing grout is added to the hole through the venting device to meet the continuously increasing pile driving pressure during the driving process. When the pile driving pressure approaches the allowable pressure value of the precast pile, pile driving is stopped, the switch valve is opened, and part of the high-pressure reinforcing grout in the hole flows back to the grout pool through the venting device. Then the switch valve is closed to meet the safe pile driving pressure.

[0040] The sharp drop in pile driving pressure is related to the interaction force between the expanded soil layer and the soil around the pile, as well as the pressure of the grout inside the hole. For the same hole diameter, the lower the compressibility of the expanded soil layer, the greater the pile driving pressure. For the same compressible soil layer, the larger the borehole diameter, the lower the pile driving pressure. When the borehole diameter is larger than the outer diameter of the precast pile, the soil on the borehole wall has no direct effect on the pile driving pressure, and it can only be transmitted through the grout inside the hole. The higher the grout pressure inside the hole, the greater the pile driving pressure.

[0041] The remaining construction steps are the same as in Example 3. Example 5

[0042] A novel precast pile driving and grouting construction method, step 2) involves driving the pile and squeezing out the air in the hollow section. The air release device is a combined valve structure, consisting of a long pipe, a flexible hose, and a switch valve placed on the ground connected in sequence. The lower end of the long pipe is connected to a vertical through hole in the plug body. Figure 5 As shown; when the borehole wall soil of the empty section contains non-dense soil layers with a void ratio e≥0.6 and low water content, such as under-consolidated fill layers or slightly dense silt layers, during the pile driving process, when the switch valve is closed, the air trapped in the empty section will be forced into the non-dense soil of the borehole wall by the pressure of the bottom surface of the precast pile. The air forced into the expanded borehole wall soil reduces the permeability of the borehole wall soil and improves the sealing performance between the expanded borehole wall and the outer surface of the precast pile, which in turn improves the sealing performance of the foundation.

[0043] The remaining construction steps are the same as in Example 4.

Claims

1. A novel method for grouting precast pile driving, characterized in that... Includes the following steps: 1) Drilling a pilot hole and injecting reinforcing grout around the pile: Using a auger, down-the-hole drill, or rotary drilling rig, a hole is drilled to the designed depth at the pile location to form a pilot hole. The drill string is then raised, and reinforcing grout is injected into the pilot hole. Most of the depth of the pilot hole is filled with reinforcing grout, and the section near the ground surface of the pilot hole is an air-filled section. The drill string is then raised to the ground surface, and the pilot hole is moved away. The diameter of the pilot hole is smaller than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section. The reinforcing grout is a functional mixed liquid that binds the soil and improves the mechanical strength of the foundation soil. 2) Pile driving and air compression in the hollow section: The precast pile with a plug at the bottom is aligned with the pilot hole using a pile driving equipment. The precast pile is driven downward, and the bottom end of the precast pile expands the hole wall of the hollow section. At the same time, the air sealed in the hollow section is compressed. The compressed air is discharged to the outside through the air release device on the plug at the bottom end of the precast pile; or the plug at the bottom end of the precast pile does not have an air release device, and the compressed air enters the soil of the hole wall. The pile driving, the expansion of the hole wall, and the air compression in the hollow section are all carried out until the bottom end of the precast pile enters the surface of the reinforcing grout in the pilot hole. The exhaust channel of the air release device on the plug is closed. The expanded hole wall soil and the outer surface of the precast pile in contact with it form a foundation seal, sealing the reinforcing grout in the pilot hole. 3) Pile Driving and Grouting: As the pile continues to drive, the bottom end of the precast pile expands the pilot hole, simultaneously squeezing out some of the reinforcing grout sealed within the pilot hole into the surrounding soil. The grout is forced into the expanded hole wall, reaching a dense and saturated state, forming a reinforced seal with the outer surface of the precast pile. As the precast pile gradually sinks, the pressure within the reinforcing grout sealed in the pilot hole gradually increases, the depth and amount of grout entering the surrounding soil gradually increase, and the saturation of the soil around the pilot hole gradually improves. The sealing performance of the reinforced seal between the bottom outer surface of the precast pile and the expanded hole wall also gradually improves. The pile is driven to the designed depth, meeting the top elevation requirements of the precast pile. The precast pile is one of the following: a prestressed concrete pile with an internal through hole, a steel pile, or a composite pile of concrete and steel hooks. The outer diameter of the plug at the bottom of the precast pile is not greater than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section.

2. A novel method for grouting precast pile driving, characterized in that... Includes the following steps: 1) Drilling pilot holes and grouting around the pile: Using a auger, down-the-hole drill, or rotary drilling rig with an enlarging device, drill a hole at the pile location. Within the designed drilling depth, first retract the enlarging device of the drill bit and drill down to form a pilot hole. Then, open the enlarging device and drill down to form a large-diameter hole until the designed drilling depth is reached. Then, retract the enlarging device, lift the drill bit, and grout the reinforcing grout. Grout the large-diameter hole and part of the pilot hole. The section of the pilot hole near the ground surface is an air-filled section. Lift the drill bit to the ground surface and move the pilot hole position away. The diameter of the pilot hole is smaller than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section. The reinforcing grout is a functional mixed liquid that can bind soil and improve the mechanical strength of the foundation soil. 2) Pile driving and air compression in the hollow section: The precast pile with the plug at the bottom is aligned with the center of the pilot hole using the pile driving equipment. The precast pile is driven downward, and the bottom end of the precast pile expands the hole wall of the hollow section. At the same time, the air sealed in the hollow section is compressed. The compressed air is discharged to the outside through the air release device on the plug at the bottom end of the precast pile; or the plug at the bottom end of the precast pile does not have an air release device, and the compressed air enters the soil of the hole wall. The pile driving, the expansion of the hole wall, and the air compression in the hollow section are all carried out until the bottom end of the precast pile enters the reinforcing grout in the pilot hole. The exhaust channel of the air release device on the plug is closed. The expanded hole wall soil and the outer surface of the precast pile in contact with it form a foundation seal, sealing the reinforcing grout in the pilot hole and the large-diameter hole. 3) Pile Driving and Grouting: As the pile continues to drive, the bottom end of the precast pile expands the pilot hole, simultaneously squeezing some of the reinforcing grout sealed within the pilot hole and the main borehole into the surrounding soil. The grout is forced into the expanded pilot hole wall, reaching a dense and saturated state, forming a reinforced seal with the outer surface of the precast pile. As the precast pile gradually sinks, the pressure within the reinforcing grout sealed in the pilot hole and main borehole gradually increases, leading to a deeper penetration, a larger volume of grout into the surrounding soil, and a higher saturation of the soil in the pilot hole and main borehole walls. This also gradually improves the sealing performance between the bottom outer surface of the precast pile and the expanded pilot hole wall. The bottom end of the sinking precast pile is squeezed through the pilot hole and into the top of the main borehole, continuing pile driving. For main boreholes with a diameter smaller than the outer diameter of the precast pile... When the diameter of the precast pile is not less than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section, the bottom end of the precast pile is squeezed to enlarge the diameter hole, and the reinforcing grout in the large diameter hole is squeezed into the surrounding soil. The soil on the wall of the enlarged diameter hole is saturated and forms a reinforced seal with the outer surface of the precast pile it wraps around. When the diameter of the large diameter hole is not less than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section, part of the reinforcing grout in the large diameter hole is squeezed into the surrounding soil. The gap between the outer surface of the precast pile and the wall of the large diameter hole is filled with reinforcing grout, and the pile is driven to the design depth to meet the top elevation of the precast pile. The precast pile is one of the following: a prestressed concrete pile with an internal through hole, a steel pile, or a composite pile of concrete and steel hooks. The outer diameter of the plug at the bottom end of the precast pile is not greater than the outer diameter of the precast pile or the diameter of the inscribed circle of the outer contour of the precast pile's cross-section.

3. The novel precast pile driving and grouting construction method according to claim 1 or 2, characterized in that: The venting device in step 2) is a normally open one-way valve structure. The bottom end of the movable valve core of the venting device is located at the lower end of the plug. During the pile driving process in the empty hole section, the venting hole of the venting device is in the open state. The pressurized air in the empty hole section is discharged into the atmosphere through the venting hole of the venting device and the cavity inside the precast pile. When the bottom end of the precast pile enters the surface of the reinforcing grout in the pilot hole, the bottom end of the movable valve core of the venting device is subjected to the upward force of the reinforcing grout, which pushes the movable valve core to move upward, closes the venting hole, and seals the reinforcing grout inside the hole.

4. The novel precast pile driving and grouting construction method according to claim 1 or 2, characterized in that: The venting device in step 2) consists of a vertical through-hole inside the plug body, a long pipe connected to the upper end of the through-hole and penetrating the inner hole of the precast pile, a flexible hose connected to the upper end of the long pipe, and a switch valve connected to the other end of the flexible hose and placed on the ground. During the pile driving process, the switch valve is first opened, and the pressurized air in the empty hole section is discharged into the atmosphere through the through-hole inside the plug body, the long pipe, the flexible hose, and the switch valve. When the reinforcing grout flows out of the outlet of the switch valve, the switch valve is closed to seal the reinforcing grout in the hole. After the pile driving is completed, the connection between the long pipe and the through-hole of the plug body is disconnected, and the long pipe is lifted out of the inner hole of the precast pile.

5. The novel precast pile driving and grouting construction method according to claim 4, characterized in that: In step 2), during pile driving and air extrusion in the hollow section, the air trapped in the hollow section is released sequentially through the plug, long pipe, flexible hose, and switch valve. When the bottom end of the precast pile enters the reinforcing grout in the pilot hole, the switch valve is closed to seal the reinforcing grout within the hole. In step 3), during pile driving and grouting, if a sharp drop in pile driving pressure occurs (except for changes in the surrounding soil layer and / or a sharp drop occurring when the precast pile passes through a large-diameter hole), pile driving is stopped. A high-pressure grouting pump is used, with the pump outlet connected to the switch valve outlet. The switch valve is opened, and the grouting pump is started. Reinforcing grout is added to the hole through the venting device to meet the continuously increasing pile driving pressure during the driving process. When the pile driving pressure approaches the allowable pressure value of the precast pile, pile driving is stopped, the switch valve is opened, and part of the high-pressure reinforcing grout in the hole flows back to the grout pool through the venting device. The switch valve is then closed to meet the safe pile driving pressure.

6. The novel precast pile driving and grouting construction method according to claim 1 or 2, characterized in that: The precast pile bottom plug in step 2) has an air release device. The air release device does not release the air in the empty hole section. During the pile driving process, the air in the empty hole section is pressurized and enters the soil in the hole wall.

7. The novel precast pile driving and grouting construction method according to claim 6, characterized in that: The precast pile bottom plug has an air release device, which consists of a long pipe, a flexible hose, and a switch valve placed on the ground connected in sequence. The lower end of the long pipe is connected to a vertical through hole in the plug. During the precast pile sinking process in step 2), the switch valve is closed, and the air sealed in the empty hole section is pressurized and enters the soil in the hole wall. During the pile driving and grouting in step 3), when the pile driving pressure drops sharply, except for changes in the soil layer around the pile and / or the sharp drop that occurs when the precast pile passes through a large-diameter hole, the pile driving is stopped. A high-pressure grouting pump is used, and the pump outlet is connected to the outlet of the switch valve. The switch valve is opened, the grouting pump is started, and reinforcement grout is added to the hole through the air release device to meet the requirements of the pile driving pressure continuously increasing during the pile driving process. When the pile driving pressure approaches the allowable pressure value of the precast pile, the pile driving is stopped, the switch valve is opened, and part of the high-pressure reinforcement grout in the hole flows back to the grout pool through the air release device. Then the switch valve is closed to meet the safe pile driving pressure.

8. The novel precast pile driving and grouting construction method according to any one of claims 1 to 7, characterized in that: The plug at the bottom of the precast pile is shaped like a cone or frustum, with a smaller bottom and a larger top.

9. The novel precast pile driving and grouting construction method according to any one of claims 1 to 7, characterized in that: The drilling depth of the drill bit shall not exceed the length of the precast pile; the final driving pressure of the precast pile shall meet the design requirements.

10. The novel precast pile driving and grouting construction method according to claim 1 or 2, characterized in that: The reinforcing grout is a granular grout and / or a chemical grout; wherein the granular grout includes one or more of cement grout, cement mortar, clay grout or cement-clay grout, and the chemical grout includes one or more of silicates, calcium chloride, epoxy resin, acrylate, acrylamide, acrylate or pulp-based grout.

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