A construction method for pouring pile foundation in soft geology

Abstract

The invention relates to a construction method for pouring pile foundation in soft geology. The technical solution adopts a rotary grouting method to form a main and auxiliary pile foundation structure with a common cap, the auxiliary piles form a surrounding oblique support for the main piles, the upper ends of the pile columns are connected by the top cap, and the bottoms are connected by the bottom cap, and a plurality of pile columns form a whole. The bearing capacity is dispersed on the plurality of pile columns, so that the load of a single pile column is avoided to be too large. At the same time, due to the connection limit of the caps at both ends, the displacement and deflection of a single pile column can be avoided, and the stability of the pile foundation is improved. Due to the existence of the common bottom platform, the actual bearing area of ​​the bottom of the pile foundation is greatly increased, which can greatly improve the bearing capacity of the pile foundation in soft geology, and only pile holes need to be drilled, without excavation of earth, support of pile column templates and backfilling of earth, so the construction period is relatively short and the construction cost is relatively small.

Description

Technical Field

[0001] The invention relates to the field of building construction, in particular to a method for pouring a soft geological pile foundation. Background Art

[0002] As the bearing foundation of a building, the bearing capacity and stability of the pile foundation are of vital importance. Soft geology has a great negative impact on the stability and bearing capacity of the pile foundation, so targeted treatment of the geology or pile foundation structure is required.

[0003] There are two main methods for geological treatment. One is the compaction pile method, such as the invention patent with application number: CN201710888780.1. It densely drills holes in the soil and then tamps the holes with ash soil to form piles. The piles squeeze and compact the surrounding soil to improve the soft soil. The second is the rotary jet grouting method, such as the invention patent with application number: CN202210198712.3. It uses high pressure to spray the prepared slurry into the soil, which is fully mixed with the soil to form a consolidated body to improve the soft soil. The above two geological treatment methods have significantly improved the lateral stability of the pile foundation, but simply treating the geology is difficult to meet the requirements of bearing capacity and stability in many cases.

[0004] For pile foundations, if the requirements cannot be met by increasing the density and depth of the pile foundation, the bearing area will be increased by pouring a cap at the bottom of the pile foundation. There are two ways to pour the cap: one is to completely excavate the soil above and then pour it. This method requires complete excavation of the earth, which increases the construction volume. In addition, since the excavation of the earth cannot form a pile hole, additional formwork needs to be supported when pouring the pile column. After the pile column is formed, the earth needs to be backfilled and compacted, which significantly increases the construction period and construction cost.

[0005] Another method is to form a cap at the bottom of the pile column by means of rotary jet grouting, such as the invention patent with application number: CN201210334334.3. This method can only form a cap at the lower end of a single pile column, so the pile columns after forming are independent of each other, and the bearing capacity between the pile columns cannot be dispersed, which easily leads to the situation that individual pile columns are overloaded and damaged. Moreover, even if the geology is processed, the pile columns are still prone to deflection and displacement in earthquakes and shaking of superstructures because there is no mutual connection limit at the lower ends of the pile columns.

[0006] If a foundation structure is to be formed in which the bottoms of multiple piles are supported and connected by a common pedestal, the existing method can only be achieved by completely excavating the earth, supporting the formwork and pouring it, and then backfilling it. This is because there are two major difficulties in forming a common pedestal by increasing the range of the bottom rotary grouting. The first is how to clearly determine whether the range of the rotary grouting pedestal is connected to the bottom of each pile foundation. The second is that the range of the rotary grouting is too large, the geology is relatively soft, and the rotary grouting process disturbs the surrounding soil. How to avoid the collapse of the upper soil and the pile holes during the rotary grouting process? The purpose of the present invention is to solve the above two difficulties and form a foundation structure with a common pedestal by using rotary grouting. Summary of the invention

[0007] In order to solve the problems of poor stability and bearing capacity of soft geological pile foundations, long construction period and high construction cost, the present invention provides a soft geological pile foundation casting construction method.

[0008] The technical solution includes the following steps:

[0009] Step 1, drilling pile holes: drilling holes according to the designed hole positions, the pile holes include a main hole and multiple auxiliary holes, the multiple auxiliary holes are evenly distributed around the main hole, the main hole is vertically downward, the lower ends of the auxiliary holes are inclined away from the main hole, and the bottom of the main hole is lower than the bottom of the auxiliary holes;

[0010] Step 2, pouring mud into the hole and closing the hole opening: pouring wall protection mud into the main hole and the auxiliary hole, and covering the hole openings of the main hole and the auxiliary hole with sealing plugs, each of which is plugged with a pressure sensor, and the sealing plug on the main hole is plugged with a rotary spray pipe, a water injection pipe and a water extraction pipe, and the lower end of the rotary spray pipe is equipped with a rotary spray head;

[0011] Step 3: Hole bottom jetting: The lower end of the jetting pipe of the main hole is extended to the bottom of the main hole for jetting. The jetting medium is water. The jetting pipe is gradually lifted up during jetting to form a jetting cavity filled with mud at the bottom of the hole. Until the jetting cavity is connected with the auxiliary hole, the value of the pressure sensor at the orifice of the auxiliary hole will fluctuate and increase significantly.

[0012] Step 4: Replace the slurry in the hole with water and lower the steel cage: After the construction of the jet grouting cavity is completed, remove the jet grouting pipe, pump out the slurry from the bottom of the jet grouting cavity with a water pump, and inject water from the hole with a water injection pipe. Continue to inject water and pump out for a period of time until the liquid discharged from the pumping pipe is clear; then hang the prefabricated steel cage in the main hole and the auxiliary hole;

[0013] Step 5: Casting the bottom cap: insert a grouting pipe into the main hole, inject concrete slurry from the bottom of the jet-jet cavity and gradually lift the grouting pipe upwards, so that the water in the jet-jet cavity is gradually replaced by the concrete slurry, and the bottom cap is formed after the concrete solidifies;

[0014] Step six, grouting in the hole: grouting in the main hole and the auxiliary hole and forming the main pile and auxiliary pile after solidification.

[0015] In step six, the main hole and the auxiliary hole are grouted one by one using the displacement grouting method. After the concrete solidifies, the pile column is formed, with the main hole containing the main pile and the auxiliary hole containing the auxiliary pile.

[0016] In step six, after the water in the hole is pumped out, grouting is performed using conventional methods. After the concrete solidifies, the pile column is formed, with the main pile in the main hole and the auxiliary pile in the auxiliary hole.

[0017] In step 4, the upper end of the steel cage is higher than the hole mouth. In step 6, after the main piles and auxiliary piles are solidified, a formwork is set on the top of each pile column, and concrete is poured and solidified to form a top cap, which is connected to all the main piles and auxiliary piles.

[0018] After the construction of step one is completed and before the construction of step two, cement rings are poured at the openings of the main hole and the auxiliary hole.

[0019] In step 1, the bottom of the main hole is at least 50 cm lower than the bottom of the auxiliary hole.

[0020] The inner wall of the cement ring is a conical surface that is larger at the top and smaller at the bottom, and the outer wall of the sealing plug is a conical surface that is consistent with the inner wall of the cement ring.

[0021] In step 3, after the jet cavity is connected to the auxiliary hole, the jet pipe is further lifted up by 20 to 30 centimeters.

[0022] In step three, after the jet nozzle is lifted to the final height, if there is a secondary hole that is not connected to the jet nozzle cavity, the jet nozzle direction is adjusted and the jet nozzle pressure is increased to perform additional spraying on the secondary hole until the secondary hole is connected to the jet nozzle cavity.

[0023] In step five, mortar fibers are mixed into the concrete mortar.

[0024] The pouring construction method of the present invention is improved from the perspective of pile foundation structure, and can be used in conjunction with geological treatment methods such as compaction pile method or rotary jet grouting method, and can further improve the stability and bearing capacity of the pile foundation on the basis of geological treatment;

[0025] The present invention adopts the rotary grouting method to form the main and auxiliary pile foundation structure with a common cap. Due to the existence of the common bottom platform, the actual bearing area of ​​the bottom of the pile foundation is greatly increased, which can greatly improve the bearing capacity of the pile foundation in soft geology. In addition, only pile holes need to be drilled, and no earth excavation, support of pile column templates and backfilling of earth are required. The construction period is relatively short and the construction cost is relatively small.

[0026] The pile foundation structure cast by the casting process of the present invention is composed of a plurality of pile columns, the auxiliary piles form a surrounding diagonal brace for the main piles, the upper ends of the pile columns are connected by the top cap, and the bottoms are connected by the bottom cap. The plurality of pile columns form a whole, and the bearing capacity is dispersed on the plurality of pile columns, thereby avoiding excessive load on a single pile column. At the same time, due to the connection limit of the caps at both ends, the displacement and deflection of a single pile column can be avoided, thereby improving the stability of the pile foundation;

[0027] The present invention seals and injects mud into the main and auxiliary holes and the rotary jet cavity and maintains positive pressure in the hole cavity during the rotary jet process. The increase in pressure in the auxiliary hole can clearly determine that the auxiliary hole is connected to the rotary jet cavity. At the same time, the sealed positive pressure can prevent soil and pile hole collapse. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of step one.

[0029] Figure 2 This is a schematic diagram of step 2.

[0030] Figure 3 This is a schematic diagram of step three.

[0031] Figure 4 This is a schematic diagram of step four.

[0032] Figure 5 This is a schematic diagram of step five.

[0033] Figure 6 This is a schematic diagram of step six.

[0034] Figure 7 Schematic diagram of pouring cement ring.

[0035] Figure 8 Schematic diagram of pouring the top cap.

[0036] Fig. 9 for Figure 7 Enlarged view of position A in the middle.

[0037] Fig.10 for Figure 2 Enlarged view of position B in the middle.

[0038] Fig.11 for Figure 2 Enlarged view of position C in the middle. DETAILED DESCRIPTION

[0039] In conjunction with the accompanying drawings, the present invention includes the following steps:

[0040] Step 1: Drill pile holes, such as Figure 1As shown: according to the designed hole position, the pile hole includes a main hole 1 and multiple auxiliary holes 2. The multiple auxiliary holes 2 are evenly distributed around the main hole 1. The main hole 1 is vertically downward, and the lower ends of the auxiliary holes 2 are inclined away from the main hole 1. The bottom of the main hole 1 is lower than the bottom of the auxiliary holes 2. The multiple auxiliary holes 2 are distributed in a conical shape with a larger bottom and a smaller top, which is in a diagonal support shape for the main hole 1.

[0041] Step 2: Fill the hole with mud and seal the hole. Figure 2 , Fig.10 and Fig.11 As shown: wall protection slurry is poured into the main hole 1 and the auxiliary hole 2 to prevent the hole wall from collapsing during the subsequent construction process, and sealing plugs 5 are added to the orifices of the main hole 1 and the auxiliary hole 2. A pressure sensor 6 is inserted on each sealing plug 5 to monitor the pressure in the hole. A rotary spray pipe 7, a water injection pipe 8 and a water extraction pipe 9 are inserted on the sealing plug 5 on the main hole 1. A rotary spray head 10 is installed at the lower end of the rotary spray pipe 7;

[0042] Step 3: Hole bottom spraying, such as Figure 3 As shown: the lower end of the rotary spraying pipe 7 of the main hole 1 extends to the bottom of the main hole 1, and the upper end of the rotary spraying pipe 7 is connected to the rotary spraying equipment. The rotary spraying pipe 7 performs rotary spraying, and the spraying medium is water. The water is mixed with the soil around the bottom of the main hole 1 to form mud. The lower end of the water pumping pipe 9 extends to the bottom of the hole. While rotary spraying, the mud is pumped out. The pumping speed is controlled by the pressure sensor 6 on the sealing plug 5 at the orifice of the main hole 1 to keep the positive pressure in the hole. The rotary spraying pipe 7 is gradually lifted during rotary spraying, and the soil at the bottom of the hole is continuously mixed into mud and pumped out, forming a rotary spraying cavity 11 filled with mud at the bottom of the hole. The mud in the hole can support the hole wall and the rotary spray cavity 11 during rotary spraying to avoid soil collapse; pay attention to lifting the water extraction pipe 9 synchronously when lifting the rotary spray pipe 7, so that the lower end of the water extraction pipe 9 is always higher than the rotary spray head 10 to avoid interference with the rotary spray liquid. When the rotary spray pipe 7 is raised to the height of the bottom of the auxiliary hole 2, the rotary spray cavity 11 is connected with the auxiliary hole 2. Since the main hole 1 and the rotary spray cavity 11 are positive pressure, the value of the pressure sensor 6 at the orifice of the auxiliary hole 2 will fluctuate and increase significantly after the connection. Through the pressure sensor 6, it can be known whether the rotary spray cavity 11 is connected with the auxiliary hole 2.

[0043] Step 4: Replace the mud in the hole with water and lower the steel cage 12. Figure 4 As shown: after the construction of the rotary spray cavity 11 is completed, the rotary spray pipe 7 is removed, the lower end of the water pumping pipe 9 extends downward to the bottom of the rotary spray cavity 11, the lower end of the water injection pipe 8 is located at the orifice of the main hole 1, the water injection pipe 8 injects water from the orifice, and the water pumping pipe 9 pumps mud from the bottom. Due to the large specific gravity of the mud, the mud in the hole and the rotary spray cavity 11 will be gradually replaced by water, and the water injection and pumping are continued for a period of time until the liquid discharged from the water pumping pipe 9 is clear; then the prefabricated steel cage 12 is suspended in the main hole 1 and the auxiliary hole 2, and the lower end of the steel cage 12 extends to the bottom of the rotary spray cavity 11;

[0044] Step 5: pour the bottom cap 13, such as Figure 5As shown: a grouting pipe is lowered into the main hole 1, and the lower end of the grouting pipe extends to the bottom of the rotary jet cavity 11, and concrete slurry is injected and the grouting pipe is gradually lifted up. Due to the large specific gravity of the concrete slurry, the water in the rotary jet cavity 11 is gradually replaced by the concrete slurry, and the water overflows and is discharged from the orifice. The total lifting height of the grouting pipe is equal to the height of the rotary jet cavity 11. When the concrete solidifies, a bottom cap 13 is formed. The bottom cap 13 bears the bottom of all piles, disperses the load of a single pile, and connects and limits the bottom of the pile to prevent the pile from shifting.

[0045] Step 6: grouting in the hole, such as Figure 6 As shown: the main pile 14 and the auxiliary pile 15 are formed after grouting in the main hole 1 and the auxiliary hole 2 and solidification.

[0046] In step six, the main hole 1 and the auxiliary hole 2 are grouted one by one using the displacement grouting method. After the concrete solidifies, the pile column is formed, with the main hole 1 containing the main pile 14 and the auxiliary hole 2 containing the auxiliary pile 15.

[0047] In step six, after the water in the hole is pumped out, grouting is performed using a conventional method. After the concrete solidifies, the pile column is formed, with the main hole 1 containing the main pile 14 and the auxiliary hole 2 containing the auxiliary pile 15 .

[0048] Which method to use depends on whether the geological conditions can keep the pile hole from collapsing after drainage. If so, conventional casting is used; if not, replacement casting is used. The quality of piles cast by conventional casting is better than that by replacement casting. Therefore, conventional casting is given priority when geological conditions permit.

[0049] Cast the top cap 16, such as Figure 8 As shown, in step 4, the upper end of the steel cage 12 is higher than the hole mouth. In step 6, after the main piles 14 and the auxiliary piles 15 are solidified, a template is set on the top of each pile column, and concrete is poured and solidified to form a top cap 16. The top cap 16 is connected to all the main piles 14 and the auxiliary piles 15; the top cap 16 is jointly supported by all the piles, and the part of the steel cage 12 that is higher than the hole mouth is the connecting steel bar between the pile column and the top cap 16, and the top cap 16 serves as the foundation of the superstructure.

[0050] After the construction of step 1 is completed and before the construction of step 2, cement ring 4 is poured at the openings of the main hole 1 and the auxiliary hole 2. Figure 7 and Fig. 9 As shown: the orifices of the main hole 1 and the auxiliary hole 2 are expanded to form a countersunk hole 3 at the orifice, a template is set up in the countersunk hole 3, the template and the side wall of the countersunk hole 3 surround an annular space, concrete is poured in the annular space, and a cement ring 4 is formed after the concrete solidifies. The inner hole of the cement ring 4 needs to be larger than the diameter of the orifice to ensure that the cement ring 4 does not interfere with the position of the steel cage 12 in the hole to avoid affecting the lowering of the steel cage 12; in step 2, the outer wall of the sealing plug 5 cooperates with the inner wall of the cement ring 4 to form a seal.

[0051] In step 1, the bottom of the main hole 1 is at least 50 centimeters lower than the bottom of the auxiliary hole 2. The height difference is the height of the jet-jet cavity 11, that is, the bottom support 13.

[0052] The inner wall of the cement ring 4 is a conical surface that is larger at the top and smaller at the bottom, and the outer wall of the sealing plug 5 is a conical surface that is consistent with the inner wall of the cement ring 4. After the sealing plug 5 is pressed into the cement ring 4, the cooperation of the conical surfaces can more effectively ensure the sealing effect.

[0053] In step three, after the jet cavity 11 is connected with the auxiliary hole 2 , the jet pipe 7 is further lifted up by 20 to 30 centimeters to ensure that the bottom of the auxiliary hole 2 is completely connected with the jet cavity 11 .

[0054] In step three, after the jet grouting pipe 7 is lifted to the final height, if a certain secondary hole 2 is not connected with the jet grouting cavity 11 due to the difference in soil hardness at the positions of the secondary holes 2, the jet grouting direction is adjusted and the jet grouting pressure is increased to perform additional spraying at the position of the secondary hole 2 until the secondary hole 2 is connected with the jet grouting cavity 11.

[0055] In step five, since a steel skeleton cannot be implanted in the bottom pedestal 13 , mortar fibers are mixed into the concrete mortar. The mortar fibers are usually polypropylene fibers, which improve the crack resistance, impermeability and integrity of the bottom pedestal 13 .

[0056] The pouring construction method of the present invention improves the pile foundation structure and can be used in conjunction with geological treatment methods such as compaction pile method or rotary jet grouting method. On the basis of geological treatment, the stability and bearing capacity of the pile foundation can be further improved.

[0057] The present invention adopts the rotary grouting method to form the main and auxiliary piles 15 foundation structure with a common foundation. Due to the existence of the common bottom platform, the actual bearing area of ​​the bottom of the pile foundation is greatly increased, which can greatly improve the bearing capacity of the pile foundation in soft geology. Moreover, only pile holes need to be drilled, and there is no need to excavate earth, support pile column templates and backfill earth. The construction period is relatively short and the construction cost is relatively small.

[0058] The pile foundation structure cast by the casting process of the present invention is composed of a plurality of pile columns, wherein the auxiliary piles 15 form a surrounding diagonal brace for the main piles 14, and the upper ends of the pile columns are connected by the top pedestals 16, and the bottoms are connected by the bottom pedestals 13. The plurality of pile columns form a whole, and the bearing capacity is dispersed on the plurality of pile columns, thereby avoiding excessive load on a single pile column. At the same time, due to the connection limit of the pedestals at both ends, displacement and deflection of a single pile column can be avoided, thereby improving the stability of the pile foundation.

[0059] The present invention seals and injects mud into the main and auxiliary holes 2 and the rotary jet cavity 11 and maintains positive pressure in the hole cavity during the rotary jet process. The increase in pressure in the auxiliary hole 2 can clearly determine that the auxiliary hole 2 is connected to the rotary jet cavity 11. At the same time, the sealed positive pressure can prevent soil and pile hole collapse.

Claims

1. A soft geological pile foundation pouring construction method, characterized in that: The steps include: Step 1, drilling a pile hole: drilling a hole according to a designed hole position, the pile hole comprising a main hole (1) and a plurality of auxiliary holes (2), the plurality of auxiliary holes (2) being evenly distributed around the main hole (1), the main hole (1) being vertically downward, the lower ends of the auxiliary holes (2) being inclined away from the main hole (1), and the bottom of the main hole (1) being lower than the bottom of the auxiliary holes (2); Step 2, injecting mud into the hole and sealing the hole opening: injecting wall protection mud into the main hole (1) and the auxiliary hole (2), and covering the hole openings of the main hole (1) and the auxiliary hole (2) with sealing plugs (5), each of which is plugged with a pressure sensor (6), and the sealing plug (5) on the main hole (1) is plugged with a rotary spray pipe (7), a water injection pipe (8) and a water extraction pipe (9), and the lower end of the rotary spray pipe (7) is equipped with a rotary spray head (10); Step 3, bottom jetting: the lower end of the jetting pipe (7) of the main hole (1) is extended to the bottom of the main hole (1) for jetting, the jetting medium is water, the lower end of the water extraction pipe (9) is extended to the bottom of the hole, and the mud is pumped out while jetting, and the pumping speed is controlled by the pressure sensor (6) on the sealing plug (5) at the orifice of the main hole (1) to keep the positive pressure in the hole, and the jetting pipe (7) is gradually lifted up during the jetting to form a jetting cavity (11) filled with mud at the bottom of the hole until the jetting cavity (11) is connected with the auxiliary hole (2); because the main hole (1) and the jetting cavity (11) are at positive pressure, the value of the pressure sensor (6) at the orifice of the auxiliary hole (2) will fluctuate and increase significantly after the connection, and it can be known through the pressure sensor (6) whether the jetting cavity (11) is connected with the auxiliary hole (2); Step 4, replacing the slurry in the hole with water and lowering the steel cage (12): after the construction of the jet grouting cavity (11) is completed, the jet grouting pipe (7) is removed, the pumping pipe (9) pumps out the slurry from the bottom of the jet grouting cavity (11), and the water injection pipe (8) injects water from the hole mouth, and continues to inject water and pump out for a period of time until the liquid discharged from the pumping pipe (9) is clear; then, the prefabricated steel cage (12) is suspended in the main hole (1) and the auxiliary hole (2); Step 5, pouring the bottom cap (13): inserting a grouting pipe into the main hole (1), injecting concrete slurry from the bottom of the jet-jet cavity (11) and gradually lifting the grouting pipe, so that the water in the jet-jet cavity (11) is gradually replaced by the concrete slurry, and the bottom cap (13) is formed after the concrete solidifies; Step six, grouting in the hole: grouting is injected into the main hole (1) and the auxiliary hole (2) and solidified to form a main pile (14) and an auxiliary pile (15).

2. A soft geological pile foundation pouring construction method according to claim 1, characterized in that: In step six, the main hole (1) and the auxiliary hole (2) are grouted one by one using a displacement grouting method. After the concrete solidifies, the pile column is formed, with the main hole (1) containing the main pile (14) and the auxiliary hole (2) containing the auxiliary pile (15).

3. A soft geological pile foundation pouring construction method according to claim 1, characterized in that: In step six, after the water in the hole is pumped out, grouting is performed using a conventional method, and after the concrete solidifies, the pile column is formed, with the main hole (1) containing the main pile (14) and the auxiliary hole (2) containing the auxiliary pile (15).

4. A soft geological pile foundation pouring construction method according to claim 1, characterized in that: In step 4, the upper end of the steel cage (12) is higher than the hole opening. In step 6, after the main piles (14) and the auxiliary piles (15) are solidified, a template is set on the top of each pile column, and concrete is poured and solidified to form a top cap (16). The top cap (16) is connected to all the main piles (14) and the auxiliary piles (15).

5. The method for pouring pile foundation in soft geology according to claim 1, characterized in that: After step one is completed and before step two is completed, cement rings (4) are poured at the openings of the main hole (1) and the auxiliary hole (2).

6. The method for pouring pile foundation in soft geology according to claim 1, characterized in that: In step 1, the bottom of the main hole (1) is at least 50 centimeters lower than the bottom of the auxiliary hole (2).

7. The method for pouring pile foundation in soft geology according to claim 5, characterized in that: The inner wall of the cement ring (4) is a conical surface that is larger at the top and smaller at the bottom, and the outer wall of the sealing plug (5) is a conical surface that is consistent with the inner wall of the cement ring (4).

8. The method for pouring pile foundation in soft geology according to claim 1, characterized in that: In step three, after the jet cavity (11) is connected to the auxiliary hole (2), the jet pipe (7) is further lifted up by 20 to 30 centimeters.

9. The method for pouring pile foundation in soft geology according to claim 1, characterized in that: In step three, after the jet spraying tube (7) is lifted to the final height, if a certain auxiliary hole (2) is not connected to the jet spraying cavity (11), the jet spraying direction is adjusted and the jet spraying pressure is increased to perform additional spraying on the auxiliary hole (2) until the auxiliary hole (2) is connected to the jet spraying cavity (11).

10. The method for pouring pile foundation in soft geology according to claim 1, characterized in that: In step five, mortar fibers are mixed into the concrete mortar.

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