Construction method for improving bearing capacity of drilling prefabricated composite pile

Abstract

The invention discloses a construction method for improving the bearing capacity of a drilled prefabricated composite pile, belongs to the technical field of cast-in-place pile planting construction, and aims to meet the requirement for high bearing capacity of a cast-in-place pile foundation. The method is characterized by comprising the following steps: drilling: controlling a spiral drill rod to slowly descend and drill to form a pile hole; when a drill bit at the lower end of the spiral drill rod is 2-5 m away from the designed elevation of the pile bottom, cement paste starts to be injected through a grouting pipe; when the drill bit drills to the designed elevation of the pile bottom, the drill bit hovers and rotates for 1-3 min, and at the moment, the spiral drill rod and the drill bit do not descend any more, so that it is guaranteed that loose soil generated at the pile end and injected cement paste are fully stirred; drilling tool lifting: controlling the lifting speed of the drill bit to be lower than the ascending speed of the injected slurry, re-drilling to the bottom of the hole when the drill bit is lifted to the position 2-5m away from the pile bottom, continuing grouting and lifting, and stopping grouting until the drill bit is completely lifted to the outside of the pile hole; and hole bottom tamping is conducted, specifically, a prefabricated concrete pile is implanted into the pile hole, and tamping operation is conducted on the pile end to improve the bearing capacity of the pile end.

Description

Technical Field

[0001] The invention belongs to the technical field of cast-in-place pile construction, in particular to a construction technology for the bearing capacity of a bored prefabricated composite pile. Background Art

[0002] Concrete cast-in-place piles are a type of pile foundation formed by pouring concrete into a drilled hole on the ground or underwater. The structure of this type of pile consists of a concrete column, the diameter of which is usually between 30 cm and 120 cm. The length can be determined according to specific project requirements, generally reaching tens of meters or even hundreds of meters. The main function of cast-in-place piles is to enhance the bearing capacity and stability of the foundation through the bearing capacity of the concrete combined with the foundation soil after hardening. It is suitable for different types of soil and geological conditions. Its construction process usually includes drilling, drilling tool lifting, pouring, pile top treatment, etc.

[0003] However, the above technology often has the following defects: when constructing the central pressure cast-in-place pile, due to the specific structure of the auger head of the drilling rig (the end cover of the auger head needs a certain operating space to be opened, such as Fig.13 As shown in the figure, some loose soil will remain at the bottom of the pile hole, resulting in a loss of resistance at the pile end. Even if post-grouting measures are taken to compensate for it, it is difficult to make the injected cement slurry completely combine with the loose soil, resulting in uneven distribution between the loose soil and the cement slurry, which affects the bearing capacity of the pile end after solidification. Therefore, the existing construction technology is currently unable to meet the high bearing capacity requirements of cast-in-place pile foundations.

[0004] The existing authorized patent proposes a method for drilling prefabricated composite piles (the inventors of CN200510009711.6 are Wang Changqing and Zou Yanhui). The inventor of the method for drilling prefabricated composite piles proposed a construction method for drilling rammed bottom grouting piles on June 5, 2018 (document number CN108677936A), which improves the pile end bearing capacity to a certain extent, but still cannot fully meet the requirements of high pile end bearing capacity.

[0005] In recent years, the pre-drilled grouting pile method has been widely used, but the pressure grouting and pile value process are rough construction, and the control of key construction nodes has not been taken seriously, resulting in the loss of single pile bearing capacity and waste. After actual measurement, the pile end bearing capacity loss reached 100% (grouting method affects about 50%, and no effective compaction loss is about 50%. For specific data, please refer to the table 5.35-2 on page 21 of the industry standard JGJ94-2008 of the People's Republic of China). The above data is also verified in the actual measurement process. After years of pile foundation construction research and pile foundation construction experience accumulation, the inventor now provides a method for greatly increasing the bearing capacity of the pile end of the pre-drilled grouting pile (a method for improving the bearing capacity of the pile end of the pre-drilled grouting pile) to meet the requirements of higher bearing capacity of the cast-in-place pile foundation. Summary of the invention

[0006] In order to make up for the deficiencies of the prior art and solve the technical problems raised in the background technology, a method for improving the bearing capacity of the pile end of the pre-formed hole grouting pile is proposed to meet the requirement of higher bearing capacity of the cast-in-place pile foundation.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a method for improving the bearing capacity of the pile end of a pre-grouted pile comprises the following steps:

[0008] S1. Drilling: Connect the auger rod to the drilling rig, control the auger rod to slowly descend and drill to form a pile hole;

[0009] S2, primary grouting: when the drill bit at the lower end of the spiral drill rod is 2 to 5 meters away from the designed elevation of the pile bottom, cement slurry is injected through the grouting pipe (drilling with slurry in advance can reduce the generation of loose soil at the pile end), and the cement slurry injection pressure is controlled to be 6 to 10 MPa;

[0010] S3. When the drill bit drills to the designed elevation of the pile bottom (a stop sensor is set at the hole bottom elevation to prevent the drill bit from continuing to move downward. Note: over-drilling will affect the compaction effect of the hole bottom), grouting is performed and the drill bit is suspended and rotated for 1 to 3 minutes. At this time, the auger rod and the drill bit do not move downward any more to ensure that the loose soil generated at the pile end is fully mixed with the injected cement slurry to form cement soil or cement mortar.

[0011] S4, drilling tool lifting: control the drill bit lifting speed to be lower than the injection slurry rising speed. When the drill bit is lifted to 2-5m from the pile bottom, drill to the bottom of the hole again (the stop drilling sensor will be triggered again) and continue grouting and lifting the drill until the drill bit is fully lifted out of the pile hole and then stop grouting;

[0012] S5. Hole bottom tamping: insert precast concrete piles into the pile hole and use the precast concrete piles as the medium to tamp the pile end to improve the bearing capacity of the pile end.

[0013] Preferably, the water-cement ratio of the cement slurry is controlled in the range of 0.6 to 0.8, and the diameter of the pile hole is controlled in the range of 300 to 1000 mm.

[0014] Preferably, the length of the precast concrete pile is consistent with the designed pile length, and the distance between the outer edge of the precast concrete pile and the inner wall of the pile hole is 10 to 100 mm.

[0015] Preferably, a hammer device or a high-frequency vibration device is used during tamping, and the precast concrete pile is used as a medium to compact the pile bottom before final setting, and a sleeve-extended guide rod is used as an auxiliary part, the lower end of the sleeve-extended guide rod is sleeved on the upper end of the precast concrete pile, and the upper end of the sleeve-extended guide rod is connected to the hammer device, or the upper end of the sleeve-extended guide rod is connected to the high-frequency vibration device through a jaw clamp.

[0016] Preferably, after the bottom of the hole is compacted, a steel pipe is inserted into the gap between the pile hole and the precast concrete pile, and the gap is filled with cement slurry. The grouting pressure of the cement slurry is controlled to be 6 to 10 MPa, and the water-cement ratio of the cement slurry is controlled to be in the range of 0.6 to 0.8, so that the cement slurry is wrapped around the precast concrete pile, and finally a bored and rammed bottom grouting pile is formed as a whole that bears pressure together.

[0017] During the grouting process, a one-way structure is provided at the slurry outlet at the lower end of the auger rod, so that the cement slurry in the auger rod can only flow out into the pile hole, but not vice versa. The one-way structure is two opposing semicircular pieces, and a lap structure is provided at the joint of the two opposing semicircular pieces. After the joint, a round cover for blocking the slurry outlet is formed, and each semicircular piece is connected to the end of the slurry outlet through a connecting piece (hinge or torsion spring). Alternatively, the one-way structure is: when grouting is being injected, under the action of the cement slurry pressure, the sliding block in the lower part of the auger rod descends to expose the slurry outlet, and the cement slurry flows out into the pile hole. When there is no grouting, the sliding block returns to a natural state, and the slurry outlet is hidden in the inner cavity of the auger rod.

[0018] During the grouting process, a support is fixedly connected, provided or installed at the lower end of the drill bit. The bottom of the support is designed to be sharp, and there is a hollowed-out part on the support. The support provides space for the slurry outlet of the drill bit to ensure that the slurry outlet of the drill bit is not blocked and can divert the slurry. The support is a triangular plate, and a hollowed-out groove is provided at the corresponding position of the slurry outlet; or the support is composed of multiple plates connected in a star shape, and a hollowed-out groove is provided at the corresponding position of the slurry outlet to form a space to protect the slurry outlet from being blocked and to divert the slurry.

[0019] An autonomous cement slurry disturber is provided in the grouting channel to automatically stir the cement slurry injected downward with a certain pressure.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. The construction method for improving the bearing capacity of the bored prefabricated composite pile described in the present invention is as follows: when the drill bit reaches the bottom of the pile, the spiral drill rod and the drill bit are controlled to rotate while grouting, so as to fully stir the mixture of cement slurry and loose soil, so that the cement slurry and the loose soil are evenly dispersed to form cement soil or cement mortar to improve the bearing capacity of the pile end, and in the process of lifting the drill tool, the drill is repeatedly drilled downward and grouting is performed to lift the drill to break up and decompose the blocky soil and reduce the pores between the soil. After that, the pile end is compacted with the prefabricated concrete pile as the medium to discharge the air in the slurry, improve the density of the slurry, further improve the bearing capacity of the pile end, and enhance the supporting effect on the building or engineering structure.

[0022] 2. In order to improve the bearing capacity of the precast composite pile, the method of the present invention has made great efforts in the operation details. The present invention sets a limit sensor at the relevant position of the guide rod of the main tower of the drilling rig to control the process of stopping drilling, suspending and rotating for 1 to 3 minutes when the drill bit descends to the design elevation of the pile bottom. The limit sensor (stop sensor) is set at the elevation of the bottom of the hole to prevent the drill bit from continuing to descend. Over-drilling will affect the tamping effect of the bottom of the hole. It must be operated according to the design elevation and ensure the misoperation of artificial over-drilling. When the pile hole is over-drilled, that is, drilled deeper than the design, when the precast concrete pile is inserted into the pile hole, it will be misjudged that the bottom end face of the precast concrete pile has contacted the pile bottom, affecting the subsequent tamping operation using hammer equipment or high-frequency vibration equipment. The inventor found during the construction operation that over-drilling seriously damaged the bearing capacity of the precast composite pile. This problem has not been raised in the art.

[0023] The present invention also proposes controlling the drill bit lifting speed to be lower than the injection slurry rising speed. When the drill bit is lifted to a position 2 to 5 m from the pile bottom and then re-drilled to the hole bottom elevation, the limit sensor will be triggered again, and grouting and drilling will continue until the drill bit is completely lifted outside the pile hole and grouting is stopped to ensure the grouting effect.

[0024] 3. During the construction process, the grouting holes are often blocked and difficult to clean. The present invention proposes that during the grouting process, a one-way structure is provided at the grout outlet at the lower end of the auger rod 1, so that the cement slurry in the auger rod 1 can only flow out into the pile hole, but not vice versa.

[0025] Under normal circumstances, the slider of the grouting hole is completely retracted to the bottom of the grouting hole and seals the grouting hole, so that soil will not enter the grouting hole and block it during drilling. During grouting, cement slurry enters the grouting hole through the grouting pipe, so that the pressure inside the grouting hole gradually increases, and then the slider moves downward under the action of pressure and stretches the spring downward. After the flow channel protrudes from the lower end surface of the drill bit, the cement slurry inside the grouting hole flows out through the grooves and multiple flow channels, so that the grouting operation proceeds normally. After the grouting is stopped, the spring pulls the slider upward to return to the inside of the grouting hole and seals it again.

[0026] After repeated verification, the bearing capacity (pile end bearing capacity) of the bored prefabricated composite pile obtained by the method of the present invention is increased by 2 to 3 times compared with the prior art (CN108677936A). BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] Figure 1 It is a schematic diagram of the construction method of the present invention;

[0029] Figure 2 It is a schematic diagram of the connection between the precast concrete pile and the sleeve extension guide rod in the present invention;

[0030] Figure 3 It is a schematic diagram of the structure of the spiral drill rod and the drill bit in the present invention;

[0031] Figure 4 is a cross-sectional view of the drill bit of the present invention;

[0032] Figure 5 yes Figure 4 A partial enlarged view of the middle part;

[0033] Figure 6 It is a structural schematic diagram of the slider in the present invention;

[0034] Figure 7 It is a schematic diagram of the structure of the mounting ring in the present invention;

[0035] Figure 8 It is a structural schematic diagram of one form of the support assembly in the present invention;

[0036] Fig. 9 It is a structural schematic diagram of another form of the support assembly in the present invention;

[0037] Fig.10 It is a form of unidirectional structure proposed by the present invention; Fig.11 The material outlet blocking structure in the prior art is not composed of two semicircular pieces but is equivalent to a circular baffle hinged to the side wall of the material outlet. The baffle 25 in the prior art is an integrated structure, and the slurry outlet is easily blocked.

[0038] Fig.12 A photo of the present invention in which the end cover is changed into a one-way valve or a unit structure (this is an improved process diagram, in which the two semicircular baffles are not installed);

[0039] Fig.13 Take a photo of the existing end cap;

[0040] Fig.14 The present invention provides a set of on-site photos of relevant tests on the bored prefabricated composite piles obtained based on the method of the present invention.

[0041] In the figure: auger rod 1, drill bit 2, connecting column 3, grouting hole 4, grouting pipe 5, step 6, slider 7, groove 8, flow channel 9, spring 10, limit cylinder 11, limit rod 12, block 13, support 14, hollowed groove 15, mounting ring 16, support 17, turntable 18, blade 19, blade 20, drainage sheet 21, precast concrete pile 22, sleeve extension guide rod 23. Support 24, semicircular sheet (semicircular baffle) 25, semicircular sheet 25 is rotatably connected to 24 through a torsion spring, and blocks the discharge port. DETAILED DESCRIPTION

[0042] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0043] Specific implementation method 1: Figure 1 to Figure 2 As shown, the construction method for improving the bearing capacity of the bored prefabricated composite pile (the method for improving the bearing capacity of the pile end of the pre-hole grouting pile method) of the present invention comprises the following steps:

[0044] S1, drilling: connecting the auger rod 1 to the drilling rig, controlling the auger rod 1 to slowly descend and drill to form a pile hole;

[0045] S2, primary grouting: when the drill bit (2) at the lower end of the spiral drill rod (1) is 3m away from the designed elevation of the pile bottom, cement slurry is injected through the grouting pipe (5), and the grouting is carried out in advance to reduce the generation of loose soil at the pile end, and the cement slurry grouting pressure is controlled to be 8 MPa;

[0046] S3, when the drill bit (2) drills to the designed elevation of the pile bottom, it is suspended and rotated for 2 minutes, and at this time the spiral drill rod (1) and the drill bit (2) no longer move downward to ensure that the loose soil generated at the pile end is fully mixed with the injected cement slurry to form cement soil or cement mortar;

[0047] A limit sensor is arranged at a position related to the guide rod of the main tower of the drilling rig, and is used to control the process of stopping drilling, suspending and rotating for 2 minutes when the drill bit (2) descends to the designed elevation of the pile bottom; a limit sensor (stop sensor) is arranged at the elevation of the bottom of the hole to prevent the drill bit from continuing to descend, and over-drilling will affect the compaction effect of the bottom of the hole;

[0048] S4, drilling tool lifting: the lifting speed of the drill bit (2) is controlled to be lower than the rising speed of the injected slurry. When the drill bit (2) is lifted to a position 3 m from the pile bottom and the drill is re-drilled to the hole bottom elevation, the limit sensor is triggered again, and grouting and drilling are continued until the drill bit (2) is completely lifted outside the pile hole and the grouting is stopped;

[0049] S5. Hole bottom tamping: insert the precast concrete pile 22 into the pile hole (cement slurry in the hole is in liquid state), use the precast concrete pile 22 as a medium to tamp the pile end to improve the pile end bearing capacity, and tamp the pile bottom before final setting. The bearing capacity can be increased by 2 to 3 times.

[0050] During the grouting process, a one-way structure is provided at the grout outlet at the lower end of the spiral drill rod (1), so that the cement grout in the spiral drill rod (1) can only flow out into the pile hole, but not vice versa.

[0051] The water-cement ratio of cement slurry is controlled within the range of 0.7 and the pile hole diameter is 800mm.

[0052] The length of the precast concrete pile (22) is consistent with the designed pile length, and the distance between the outer edge of the precast concrete pile (22) and the inner wall of the pile hole is 50 mm.

[0053] During tamping, a hammer device or a high-frequency vibration device is used, and a sleeve-lengthened guide rod (23) is used as an auxiliary component. The lower end of the sleeve-lengthened guide rod (23) is sleeved on the upper end of the precast concrete pile (22), and the upper end of the sleeve-lengthened guide rod (23) is connected to the hammer device, or the upper end of the sleeve-lengthened guide rod (23) is connected to the high-frequency vibration device through a jaw clamp.

[0054] After the bottom of the hole is compacted, a steel pipe is inserted into the gap between the pile hole and the precast concrete pile (22), and the gap is filled with cement slurry. The cement slurry injection pressure is controlled to be 8 MPa, and the water-cement ratio of the cement slurry is controlled to be within a range of 0.7, so that the cement slurry is wrapped around the precast concrete pile (22), and finally a drilled hole compacted grouting pile that is integral and jointly bears pressure is formed.

[0055] Specific implementation method 2: Fig.10 As shown, during the grouting process, a one-way structure is provided at the slurry outlet at the lower end of the auger rod 1, so that the cement slurry in the auger rod 1 can only flow out into the pile hole, but not vice versa. The one-way structure can be two opposing semicircular pieces, and a lap joint structure is provided at the butt joint of the two opposing semicircular pieces, and a round cover for blocking the slurry outlet is formed after the butt joint, and each semicircular piece is connected to the end of the slurry outlet through a connector (the connector is a hinge or a torsion spring). The rest is the same as the first embodiment.

[0056] Specific embodiment three: The one-way structure can also be: when grouting, under the action of cement slurry pressure, the sliding block in the lower part of the auger rod (1) moves downward to expose the slurry outlet hole, and the cement slurry flows out into the pile hole. When there is no grouting, the sliding block returns to the natural state, and the slurry outlet hole is hidden in the inner cavity of the auger rod 1. The rest is the same as the specific embodiment one.

[0057] Specific implementation method four: Figure 8 As shown, during the grouting process, a support member 14 is fixedly connected, provided or installed at the lower end of the drill bit 2. The bottom of the support member 14 is designed to be sharp, and there is a hollowed-out part on the support member 14. The support member 14 provides space for the slurry outlet of the drill bit 2 to ensure that the slurry outlet of the drill bit 2 is not blocked and can divert the slurry.

[0058] like Fig.10 As shown, the support member 14 is a triangular plate, and a hollowed-out groove 15 is provided at a position corresponding to the pulp outlet; or the support member 14 is composed of multiple plates connected together in a star shape, and a hollowed-out groove 15 is provided at a position corresponding to the pulp outlet, so as to form a space to protect the pulp outlet from being blocked and to divert the pulp. Others are the same as the first, second or third embodiments.

[0059] Specific implementation method 5: An autonomous cement slurry disturber is provided in the grouting channel to automatically stir the cement slurry injected downward with a certain pressure. The rest is the same as specific implementation methods 1, 2, 3 or 4.

[0060] Embodiment 1: For specific implementations three, four, and five, the following specific structures can be used to implement them, and of course other structures can also be used to implement them. The protection of the present invention is not limited. It can be cleaved as a special equipment used in the construction method for improving the bearing capacity of the prefabricated composite piles, and further improves the spiral drill rod 1 and the drill bit 2 at the lower end of the base. The lower end of the spiral drill rod 1 is equipped with a drill bit 2 (the drill bit 2 is provided with a protective device to ensure that the grouting port is not blocked during the drilling process, and to prevent the grouting from being completed due to the blockage of mud and sand during the drilling process). The top of the drill bit 2 is provided with a connecting column 3 for connecting with the spiral drill rod 1; the drill bit 2 and the connecting column 3 are both provided with a grouting hole 4; the top of the grouting hole 4 is connected to a grouting pipe 5, and the bottom of the grouting hole 4 is provided with a step portion 6; the bottom of the grouting hole 4 is slidably connected to a slider 7; the upper side of the slider 7 is provided with a groove 8; the side of the slider 7 is evenly distributed with a group of flow channels 9, and the flow channels 9 are connected to the groove 8; a group of springs 10 are evenly distributed between the upper side of the slider (7) and the step portion 6. After the cement slurry enters the grouting hole 4 , it presses the slider 7 downward, so that the flow channel 9 extends out of the lower end of the drill bit 2 , and the cement slurry flows out through the flow channel 9 .

[0061] A group of telescopic components are evenly distributed between the upper side of the slider 7 and the step portion 6; the telescopic component includes a limit cylinder 11 and a limit rod 12, and one end of the limit rod 12 is slidably connected to the inside of the limit cylinder 11; a group of blocks 13 are evenly distributed at the bottom of the grouting hole 4 above the slider 7.

[0062] A mounting ring 16 is fixedly connected inside the grouting hole 4; a support 17 is fixedly connected inside the mounting ring 16 through a bracket; a turntable 18 is rotatably connected on the upper side of the support 17; a group of blades 19 are evenly distributed on the side of the turntable 18; a group of blades 20 are evenly distributed on the upper side of the turntable 18.

[0063] Embodiment 2:

[0064] The construction method for improving the bearing capacity of the bored prefabricated composite piles of the present invention comprises the following steps:

[0065] S1, drilling: connecting the auger rod 1 to the drilling rig, controlling the auger rod 1 to slowly descend and drill to form a pile hole;

[0066] S2, primary grouting: when the drill bit (2) at the lower end of the spiral drill rod (1) is 3m away from the designed elevation of the pile bottom, cement slurry is injected through the grouting pipe (5), and the grouting is carried out in advance to reduce the generation of loose soil at the pile end, and the cement slurry grouting pressure is controlled to be 8 MPa;

[0067] S3, when the drill bit 2 drills to the designed elevation of the pile bottom (the end face of the pile bottom), grouting is performed and the auger rod 1 and the drill bit 2 are suspended and rotated for 1 to 3 minutes, and at this time, the spiral drill rod 1 and the drill bit 2 no longer descend to ensure that the virtual soil generated at the pile end is fully mixed with the injected cement slurry to form cement soil or cement mortar. The formed cement soil or cement mortar can enhance the bearing capacity of the pile end after solidification. Without this operation, the virtual soil at the pile end will seriously affect the bearing capacity of the pile end. The bearing capacity without the virtual soil at the pile end is about twice that of the virtual soil at the pile end.

[0068] S4, drilling tool lifting: control the drill bit 2 lifting speed to be lower than the injection slurry rising speed, and when the drill bit 2 is lifted to 2-5m from the pile bottom, drill to the bottom of the hole and continue grouting and lifting the drill until the drill bit 2 is completely lifted out of the pile hole and then stop grouting. In this step, ensure that the cement slurry level in the hole is higher than the drill bit 2 before stopping grouting, and the wall protection hole and primary grouting are completed;

[0069] S5. Hole bottom tamping: insert the precast concrete pile 22 into the pile hole (cement slurry in the hole is in liquid state), and use the precast concrete pile 22 as a medium to tamp the pile end to improve the pile end bearing capacity, which can be increased by about 2 to 3 times.

[0070] In the prior art, when constructing cast-in-place pile foundations, due to the specific structure of the head of the drilling rig's spiral drill rod 1, a portion of loose soil will remain at the bottom of the pile hole, resulting in a loss of resistance at the pile end, and the loose soil is difficult to mix with the cement slurry in time during grouting, resulting in an uneven distribution between the loose soil and the cement slurry, which affects the bearing capacity of the pile end after solidification. Therefore, the existing construction technology is currently difficult to meet the high bearing capacity requirements of cast-in-place pile foundations.

[0071] When the drill bit 2 reaches the bottom of the pile, the present invention controls the spiral drill rod 1 and the drill bit 2 to rotate while grouting, so as to fully stir the mixture of cement slurry and loose soil, so that the cement slurry and the loose soil are evenly dispersed to form cement soil or cement mortar, so as to improve the bearing capacity of the pile end, and in the process of lifting the drill tool, the drilling is repeated downward for many times and the grouting and drilling are performed to break up the blocky soil and reduce the pores between the soil. After that, the pile end is compacted with the precast concrete pile 22 as the medium to discharge the air in the slurry, improve the density of the slurry, further improve the bearing capacity of the pile end, and enhance the supporting effect on the building or engineering structure.

[0072] The water-cement ratio of cement slurry is controlled in the range of 0.6 to 0.8, and the pile hole diameter ranges from 300 to 1000 mm.

[0073] The length of the precast concrete pile 22 (precast high-strength concrete member) is consistent with the designed pile length, and the distance between the outer edge of the precast concrete pile 22 and the inner wall of the pile hole is 10 to 100 mm.

[0074] During compaction, a hammering device (such as a hydraulic vibrating hammer, a diesel hammer) or a high-frequency vibration device is used to compact the pile bottom before final setting using the precast concrete pile 22 as a medium, and a sleeve-extended guide rod 23 is used as an auxiliary component (the top pile end of the precast concrete pile 22 is above or below the ground), the lower end of the sleeve-extended guide rod 23 is sleeved on the upper end of the precast concrete pile 22, and the upper end of the sleeve-extended guide rod 23 is connected to the hammering device, or the upper end of the sleeve-extended guide rod 23 is connected to the high-frequency vibration device through a jaw clamp.

[0075] After the bottom of the hole is compacted, a steel pipe is inserted into the gap between the pile hole and the precast concrete pile 22, and the gap is filled with cement slurry. The grouting pressure of the cement slurry is controlled to be 6-10 MPa, and the water-cement ratio of the cement slurry is controlled to be in the range of 0.6-0.8, so that the cement slurry is wrapped around the precast concrete pile 22, and finally a bored and rammed bottom grouting pile is formed as a whole and jointly bears pressure, so as to further improve the bearing capacity of the pile body.

[0076] like Figures 3 to 9 As shown, a specific example of a device for improving the bearing capacity of the pile end of the pre-hole grouting pile driving method is given, which does not constitute a specific limitation to the present invention. The device is suitable for the above-mentioned construction method for improving the bearing capacity of the pile end of the bored prefabricated composite pile, including a spiral drill rod 1; a drill bit 2 is installed at the lower end of the spiral drill rod 1; a connecting column 3 is arranged on the top of the drill bit 2 for connecting with the spiral drill rod 1; grouting holes 4 are opened inside the drill bit 2 and the connecting column 3; a grouting pipe 5 is connected to the top of the grouting hole 4, and a step portion 6 is arranged at the bottom of the grouting hole 4; a slider 7 is slidably connected to the bottom of the grouting hole 4; a groove 8 is opened on the upper side of the slider 7; a group of flow channels 9 are evenly distributed on the side of the slider 7, and the flow channels 9 are connected to the groove 8; a group of elastic Spring 10; under normal circumstances, the slider 7 is completely retracted to the bottom of the grouting hole 4 and blocks the grouting hole 4, so that soil will not enter the grouting hole 4 and block it during drilling. During grouting, cement slurry enters the grouting hole 4 through the grouting pipe 5, so that the pressure inside the grouting hole 4 gradually increases, and then the slider 7 moves downward under the action of pressure and stretches the spring 10 downward. After the flow channel 9 protrudes from the lower end surface of the drill bit 2, the cement slurry inside the grouting hole 4 flows out through the groove 8 and multiple flow channels 9, so that the grouting operation proceeds normally. After the grouting is stopped, the spring 10 pulls the slider 7 upward to return to the inside of the grouting hole 4 and re-seals it.

[0077] A group of telescopic components are evenly distributed between the upper side of the slider 7 and the step portion 6; the telescopic component includes a limit tube 11 and a limit rod 12, and one end of the limit rod 12 is slidably connected to the inside of the limit tube 11; a group of blocks 13 are evenly distributed at the bottom of the grouting hole 4 above the slider 7; by setting the telescopic component, the movement state of the slider 7 can be limited by the limit tube 11 and the limit rod 12 during the process of the slider 7 sliding up and down inside the grouting hole 4, so that the end face of the slider 7 is always kept perpendicular to the axis of the grouting hole 4, thereby improving the blocking efficiency of the slider 7 on the grouting hole 4, and by setting the block 13 to block the upper side of the slider 7, the slider 7 will not move upward due to the pressure of the soil below during the drilling process.

[0078] As a preferred embodiment of the present invention, a support member 14 is fixedly connected to the lower end of the drill bit 2; the support member 14 is composed of a group of inclined plates; the bottom of the support member 14 is designed to be sharp; the support member 14 is provided with a hollowed-out groove 15 at the corresponding position of the slider 7; by providing the sharp support member 14, it is convenient for the drill bit 2 to drill downward, and the support member 14 is used to shield the slider 7 to prevent the soil or stone from directly impacting the slider 7 and causing damage to it during drilling. The hollowed-out groove 15 is provided to avoid the support member 14 blocking the downward movement of the slider 7, so that the bottom of the slider 7 can enter the hollowed-out groove 15 during grouting, and prevent the soil under the drill bit 2 from pressing on the surface of the slider 7 and causing the slider 7 to be difficult to move down smoothly, so as to ensure that the flow channel 9 extends smoothly out of the lower end of the drill bit 2. On the other hand, a plurality of inclined plates are used to divide the lower side of the drill bit 2 into a plurality of areas, and the cement slurry can be dispersed by the inclined plates when it flows out through the flow channel 9, and flows outward through each area respectively, which can further improve the uniformity of grouting and make the cement slurry evenly distributed inside the pile hole.

[0079] In this embodiment, the support member 14 may be composed of four evenly distributed inclined plates, such as Figure 8 As shown; it can also be composed of two evenly distributed inclined plates, such as Fig. 9 shown.

[0080] As a preferred embodiment of the present invention, a mounting ring 16 is fixedly connected inside the grouting hole 4; a support 17 is fixedly connected inside the mounting ring 16 through a bracket; a turntable 18 is rotatably connected to the upper side of the support 17; a group of blades 19 are evenly distributed on the side of the turntable 18; a group of blades 20 are evenly distributed on the upper side of the turntable 18; when the cement slurry flows inside the grouting hole 4, it can exert a force on the blades 19, pushing the blades 19 and the turntable 18 to rotate, and then using the rotating blades 19 to stir and disturb the cement slurry, promote uniform mixing of the components inside the cement slurry, and discharge the air inside it, and when the turntable 18 rotates, it drives multiple blades 20 to rotate synchronously, and the blades 20 can further break up, cut, and crush the block concrete that is not fully mixed, thereby reducing the quality defects of the concrete after molding.

[0081] Drilling grouting equipment usually needs to be cleaned after use to prevent the equipment from being blocked and difficult to clean after the concrete solidifies. After use, the present invention connects the grouting pipe 5 to a water pump, and injects clean water into the grouting pipe 5 through the water pump, thereby flushing the grouting pipe 5, the grouting hole 4 and the various components therein. At this time, the water flow can drive the blades 19 and the turntable 18 to rotate, and then the rotating blades 19 are used to disturb the water flow, forming a spiral water flow inside the grouting hole 4, improving the singleness of the water flow movement direction, thereby improving the cleaning efficiency of various components.

[0082] A group of upwardly curved drainage pieces 21 are evenly distributed on the inner side of the mounting ring 16; during the grouting process, the drainage pieces 21 can cooperate with the blades 19. When the cement slurry acts on the surface of the drainage pieces 21, it can flow further toward the blades 19 along the curved surface of the drainage pieces 21, impact and mix with the cement slurry broken up by the blades 19, further improve the disturbance effect, improve the uniformity of the cement slurry and discharge the air; during the cleaning process, the water flow moves upward along the surface of the drainage pieces 21 toward the blades 19, thereby flushing the lower side of the blades 19, so that both the upper and lower sides of the blades 19 can be cleaned, preventing the concrete from adhering to the surface of the blades 19 and affecting its rotation effect after hardening.

[0083] like Fig.14 As shown, the bored prefabricated composite piles using the method of the present invention were subjected to pile body verification tests. The bearing capacity (pile end bearing capacity) of the bored prefabricated composite piles obtained by the method of the present invention was increased by 2 to 3 times compared with the prior art (CN108677936A). Continuously improving the bearing capacity of bored prefabricated composite piles is the technical goal pursued by bored prefabricated composite pile construction technology.

[0084] During the drilling process, cement slurry is injected into the prefabricated composite pile through the grouting port of the drill bit, which has a comprehensive reinforcement effect on the foundation soil on the pile side and pile end without dead angles. The quality of the cement slurry wall hole must also be based on the premise that the prefabricated pipe piles can be placed in place. In order to ensure that the prefabricated pipe piles can be placed in place, during the construction process, neither false soil at the pile end can be generated nor over-drilling can be performed. Over-drilling means exceeding the designed pile hole depth. If the pile hole is deepened, after the prefabricated concrete pile 22 is inserted into the pile hole, it will affect the judgment of construction, the compaction operation, and the bearing capacity of the pile end. The present invention proposes and solves these problems.

[0085] After the prefabricated pipe piles are placed in place, grouting pipes need to be placed to solve the gaps in cement slurry penetration and precipitation after drilling, and to further enhance the bearing capacity of the foundation soil. Many experiments have verified that the construction method of the bored prefabricated composite piles proposed by the present invention has stable, reliable and comprehensive characteristics, and greatly improves the bearing capacity of the bored prefabricated composite piles.

[0086] The method of the present invention has been verified on construction sites for many times, as shown in Table 1 and Table 2. Before the application date, the method of the present invention was used in the actual construction of the following projects under the premise of taking technical confidentiality measures, and it was repeatedly verified that the method of the present invention increases the pile end bearing capacity by at least 2 to 3 times.

[0087] Table 1

[0088]

[0089] Table 2

[0090]

[0091] The above-mentioned front, back, left, right, top and bottom are all based on the figures in the specification. Figure 1 As a benchmark, and according to the person's observation angle as the standard, the side of the device facing the observer is defined as the front, the left side of the observer is defined as the left, and so on. In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present invention.

[0092] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A construction method for improving the bearing capacity of bored prefabricated composite piles, characterized in that: The following steps are involved: S1, drilling: connecting the auger rod (1) to the drilling machine, and controlling the auger rod (1) to slowly descend and drill to form a pile hole; S2, primary grouting: when the drill bit (2) at the lower end of the spiral drill rod (1) is 2 to 5 m away from the designed elevation of the pile bottom, cement slurry is injected through the grouting pipe (5), and drilling is carried out in advance with slurry to reduce the generation of loose soil at the pile end, and the cement slurry grouting pressure is controlled to be 6 to 10 MPa; S3, when the drill bit (2) reaches the designed elevation of the pile bottom, it is suspended and rotated for 1 to 3 minutes, and at this time, the spiral drill rod (1) and the drill bit (2) no longer move downward, so as to ensure that the loose soil generated at the pile end is fully mixed with the injected cement slurry to form cement soil or cement mortar; A limit sensor is arranged at a position related to the guide rod of the main tower of the drilling rig, and is used to control the process of stopping drilling, suspending and rotating for 1 to 3 minutes when the drill bit (2) descends to the designed elevation of the pile bottom; a limit sensor (stop sensor) is arranged at the elevation of the bottom of the hole to prevent the drill bit from continuing to descend, and over-drilling will affect the compaction effect of the bottom of the hole; S4, drilling tool lifting: the lifting speed of the drill bit (2) is controlled to be lower than the rising speed of the injected slurry. When the drill bit (2) is lifted to a position 2 to 5 m from the pile bottom, the limit sensor will be triggered again after drilling to the hole bottom elevation, and the grouting and drilling will continue until the drill bit (2) is completely lifted outside the pile hole and the grouting is stopped; S5, tamping the hole bottom: inserting the precast concrete pile (22) into the pile hole, using the precast concrete pile (22) as a medium to tamping the pile end to improve the pile end bearing capacity, and tamping the pile bottom before final setting.

2. A construction method for improving the bearing capacity of bored prefabricated composite piles according to claim 1, characterized in that: During the grouting process, a one-way structure is provided at the grout outlet at the lower end of the spiral drill rod (1), so that the cement grout in the spiral drill rod (1) can only flow out into the pile hole, but not vice versa.

3. A construction method for improving the bearing capacity of bored prefabricated composite piles according to claim 2, characterized in that: The one-way structure is two opposing semicircular pieces, and an overlap structure is provided at the joint of the two opposing semicircular pieces. After the joint, a round cover for blocking the pulp outlet is formed. Each semicircular piece is connected to the end of the pulp outlet through a connecting piece (hinge or torsion spring). Alternatively, the one-way structure is as follows: when grouting is being injected, under the action of cement slurry pressure, the sliding block in the lower part of the auger rod (1) moves downward to expose the slurry outlet hole, and the cement slurry flows out into the pile hole; when grouting is not being injected, the sliding block returns to a natural state, and the slurry outlet hole is hidden in the inner cavity of the auger rod (1).

4. A construction method for improving the bearing capacity of bored prefabricated composite piles according to claim 1, 2 or 3, characterized in that: The water-cement ratio of cement slurry is controlled in the range of 0.6 to 0.8, and the pile hole diameter ranges from 300 to 1000 mm.

5. A construction method for improving the bearing capacity of bored prefabricated composite piles according to claim 4, characterized in that: The length of the precast concrete pile (22) is consistent with the designed pile length, and the distance between the outer edge of the precast concrete pile (22) and the inner wall of the pile hole is 10 to 100 mm.

6. A construction method for improving the bearing capacity of bored prefabricated composite piles according to claim 1, 2, 3 or 5, characterized in that: During tamping, a hammer device or a high-frequency vibration device is used, and a sleeve-lengthened guide rod (23) is used as an auxiliary component. The lower end of the sleeve-lengthened guide rod (23) is sleeved on the upper end of the precast concrete pile (22), and the upper end of the sleeve-lengthened guide rod (23) is connected to the hammer device, or the upper end of the sleeve-lengthened guide rod (23) is connected to the high-frequency vibration device through a jaw clamp.

7. A construction method for improving the bearing capacity of a bored prefabricated composite pile according to claim 1, 2, 3 or 5, characterized in that: After the bottom of the hole is compacted, a steel pipe is inserted into the gap between the pile hole and the precast concrete pile (22), and the gap is filled with cement slurry. The cement slurry injection pressure is controlled to be 6-10 MPa, and the water-cement ratio of the cement slurry is controlled to be in the range of 0.6-0.8, so that the cement slurry is wrapped around the precast concrete pile (22), and finally a drilled hole compacted bottom grouting pile is formed as a whole and jointly bears pressure.

8. A construction method for improving the bearing capacity of bored prefabricated composite piles according to claim 1, 2, 3 or 5, characterized in that: During the grouting process, a support member (14) is fixedly connected, provided or installed at the lower end of the drill bit (2); the bottom of the support member (14) is designed to be sharp, and the support member (14) has a hollowed-out portion. The support member (14) supports space for the grout outlet of the drill bit (2), ensuring that the grout outlet of the drill bit (2) is not blocked and that the grout can be diverted.

9. A construction method for improving the bearing capacity of bored prefabricated composite piles according to claim 8, characterized in that: The support member (14) is a triangular plate, and a hollow groove (15) is provided on the support member (14) at a position corresponding to the pulp outlet; or the support member (14) is composed of a plurality of plates connected together in a star shape, and a hollow groove (15) is provided at a position corresponding to the pulp outlet, so as to form a space for protecting the pulp outlet from being blocked and for diverting the pulp outflow.

10. A construction method for improving the bearing capacity of bored prefabricated composite piles according to claim 1, 2, 3, 5, or 9, characterized in that: An autonomous cement slurry disturber is provided in the grouting channel to automatically stir the cement slurry injected downward with a certain pressure.

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