Precast pile implantation grouting stirring base expanding construction method

Abstract

The construction method comprises the following steps that S1, a long spiral drill rod downwards rotates rightwards and forwards to drill to a specified depth, and part of loose soil is upwards returned; s2, when drilling to the designed depth, cement paste is injected into the lower end of the pile for ground expansion stirring, and the thickness of a bearing layer at the pile end is reserved; s3, cement paste and sandy soil are stirred in the soil layer on the upper portion of the bearing stratum through a mechanical stirring bottom-expanding drill bit device to form a bottom-expanding large-head pile; s4, the long spiral drill rod is lifted to the ground; and S6, a precast pile is implanted downwards. According to the method, the pile end bearing capacity is improved, the precast pile length is reduced, an existing long spiral drilling machine is adopted, the use cost is low, the construction speed is high, application and popularization are easy, and the pile end bearing capacity is improved.

Description

Technical Field

[0001] The invention relates to the technical field of grouting for implanting prefabricated piles, and in particular to a grouting, stirring and bottom expansion method for implanting prefabricated piles. Background Art

[0002] The method of implanting precast piles with grouting and mixing to expand the bottom is aimed at the current domestic construction precast pile foundation market, which is to increase the pile length infinitely in order to meet the design bearing capacity requirements and control the stable settlement of the building under long-term load, resulting in a substantial increase in the cost of pile foundation engineering. The present invention is to increase the bearing capacity of the pile end to reduce the length of the precast pile.

[0003] In a method of drilling prefabricated composite piles with patent number CN200510009711.6, the process flow is: after drilling the entire pile length and injecting cement slurry to protect the wall, the prefabricated pipe piles are installed to form the piles. The main problem with this method is that although the length of the pile can be controlled, it has the disadvantages of complicated construction procedures, high process requirements, long construction period, and high cost. It is difficult to operate and has many faults in the market, and it is not easy to be mastered by more practitioners, so it is not easy to promote.

[0004] In a spiral drill rod center pump concrete grouting bottom expansion device with patent number ZL01211476.6, when the spiral drill rod drills to the designed depth, cement slurry is injected to reinforce the loose soil at the bottom of the hole, and the loose soil at the bottom of the hole is solidified into cement soil through cement slurry. It has no bottom expansion effect at all, so it has not been promoted.

[0005] Therefore, we proposed a method of implanting precast piles and grouting and mixing to expand the bottom to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for implanting prefabricated piles by grouting, stirring and bottom expansion.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A method for implanting prefabricated piles by grouting, stirring and bottom expansion comprises the following steps: S1, the long spiral drill rod rotates right and forward to drill to the specified depth, and returns some loose soil upward; S2. When drilling to the designed depth, inject cement slurry into the soil layer at the end of the precast pile, leaving the upper end of the bearing layer thickness at the end of the pile; S3, using a mechanical stirring bottom expansion drill bit device to stir cement slurry and sand in the soil layer at the end of the prefabricated pile, in the upper end of the reserved pile end bearing layer thickness to form a bottom expansion big head pile; S4, the long spiral drill rod rotates counterclockwise to return the loose soil on the drill rod to the hole for compaction and wall protection; S5, the long auger rod is lifted to the ground; S6. Insert the precast pile downward.

[0008] Preferably, as described in step S1, the long spiral drill rod rotates forward to drill to the designed depth.

[0009] Preferably, when drilling to the designed depth as described in step S2, inject cement slurry at the upper end of the reserved thickness of the pile tip bearing stratum in the soil layer at the pile tip of the precast pile. Preferably, as described in step S3, the mechanical stirring under-reaming bit device rotates while injecting cement slurry and lifts the drilling tool to form an under-reamed large head.

[0010] Preferably, as described in step S6, the depth of the reserved bearing stratum at the pile tip is not less than 1.0 m.

[0011] Preferably, as described in step S1, the Beidou positioning system (accuracy ±2 cm) is linked with the ground penetrating radar to adjust the drilling parameters in real time, where the rotational speed is 50 - 120 rpm and the drilling pressure is 5 - 20 MPa.

[0012] Preferably, as described in step S3, during grouting, a smart joint control system for grouting pressure and flow rate is adopted, and the pumping parameters are dynamically adjusted through the PID algorithm to ensure the slurry filling coefficient.

[0013] Preferably, as described in step S6, a distributed fiber optic sensor is adopted during the implanting stage to monitor the stress distribution of the pile body in real time and generate a bearing capacity cloud map.

[0014] Before inserting the precast pile in the present invention, after the long spiral drill hole reaches the designed pile length plus the pile tip bearing stratum, cement slurry is injected and the stirring broad knife is extended. While injecting cement slurry, it rotates and lifts the drill to form a cement soil or cement mortar under-reamed large head, increasing the end resistance area and achieving the purpose of improving the bearing capacity of a single pile. It solves the prominent problems that the bearing capacity of a single pile in soft soil areas is low and cannot reach the design value and saves the length of precast piles. According to the "Technical Code for Building Pile Foundations" JGJ94 - 2008, the standard value of the vertical ultimate bearing capacity of a single pile Quk = Qsk + Qpk (skin friction plus end resistance). Taking sandy soil as an example, when calculating with equal area, the calculated result shows that the pile tip Qpk is more than ten times higher than the pile side Qsk. Therefore, an effective way to improve the bearing capacity of a single pile is to increase the pile tip area, which has an obvious effect. The main purpose of the grouting and stirring under-reaming method for inserting precast piles is to increase the local diameter of the pile tip, expand the end resistance area, give full play to the bearing capacity of the pile tip foundation, improve the bearing capacity of a single pile, reduce the number of piles used or the total number of piles, reduce the project cost, and save resources.

[0015] The pile hole drilled in the present invention is smaller than the designed diameter, which complies with the technical requirements of the "Technical Code for Building Pile Foundations" JGJ94 - 2008. It does not disturb the original soil layer on the inner wall of the pile hole and reduces the soil strength. Moreover, the specific gravity of the loose soil is greater than that of the slurry for slurry-supported piles, meeting the requirements of shaft protection and there is no problem of reducing the skin friction of a single pile. This process of grouting and under-reaming greatly improves the bearing capacity of a single pile.

[0016] The present invention can improve the bearing capacity of the pile tip, greatly reduce the project cost, solve the problem of infinitely increasing the pile length to meet the design bearing capacity requirements, adopt the existing long spiral drill, with low use cost, fast construction speed, easy to promote and use, and has a remarkable effect on improving the bearing capacity of the pile tip. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of the present invention; Figure 2 It is a schematic structural diagram of the positive drilling of the present invention to the designed pile length; Figure 3 is a schematic diagram of grouting and stirring to expand the bottom in the present invention; Figure 4 is a schematic diagram of the reverse rotation and lifting of the soil to protect the wall of the expanded bottom pile in the present invention; Figure 5 is a schematic diagram of the installation of a precast pile to form a pile in the present invention. Detailed Embodiment

[0018] Next, the technical solutions in the embodiments of the invention will be clearly and completely described in conjunction with the drawings in the embodiments of the invention. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all of the embodiments.

[0019] Refer to Figure 1 -5, a grouting and stirring method for expanding the bottom of an implanted precast pile, and its detailed method steps include: 1. The long spiral drill rod rotates clockwise and downwards to the specified depth, and part of the loose soil is returned upwards. The diameter of the clockwise rotating long spiral drill rod is smaller than the designed pile diameter. The Beidou positioning system with an accuracy of ±2 cm is linked with the ground penetrating radar to adjust the drilling parameters in real time, where the rotation speed is 50 - 120 rpm and the drilling pressure is 5 - 20 MPa; 2. When drilling to the designed depth, cement slurry is injected at the upper end of the reserved pile tip bearing layer thickness in the soil layer at the pile tip of the precast pile, the soil layer at the pile tip of the precast pile; 3. Use the mechanical stirring and bottom expanding drill bit device to stir the cement slurry and sand in the bearing layer to form an expanded bottom large head pile. The mechanical stirring and bottom expanding drill bit device rotates, injects cement slurry and lifts the drill tool to form an expanded bottom large head. When grouting, a grouting pressure and flow intelligent control system is adopted, and the pumping parameters are dynamically adjusted through the PID algorithm to ensure the slurry filling coefficient; 4. The long spiral drill rod is lifted to the ground; 5. The precast pile is implanted downwards, and the depth of the pile tip entering the bearing layer is not less than 1.0 m. During the implantation stage, a distributed optical fiber sensor is adopted to monitor the stress distribution of the pile body in real time and generate a bearing capacity cloud map.

[0020] After entering the construction site and starting drilling, adjust the pile diameter by comparing with the geological exploration report. Control the pile length. During construction, the drilling depth and borehole diameter should be adjusted in a timely manner according to different geological conditions. When drilling near the pile tip, reserve the thickness of the bearing stratum. According to the current regulation "Technical Code for Building Pile Foundations" JGJ94 - 2008: For general cohesive soil, it should be not less than 2d (d is the pile diameter); for sandy soil, it should be not less than 1.5d; for gravelly soil, it should be not less than 1d, and do not disturb the pile tip bearing stratum.

[0021] Before implanting the precast pile in the present invention, long - spiral drill to the designed pile length. For the soil layer at the pile tip of the precast pile, reserve the thickness of the pile tip bearing stratum. Inject cement slurry at the upper end and extend the mixing cutter. While injecting cement slurry, rotate and lift the drill to form a cement - soil or cement - mortar enlarged bottom head, increasing the end - bearing area and achieving the purpose of improving the bearing capacity of a single pile. Solve the prominent problems that the bearing capacity of a single pile in soft soil areas is relatively low and cannot reach the design value and save the length of precast piles. According to "Technical Code for Building Pile Foundations" JGJ94 - 2008, the standard value of the vertical ultimate bearing capacity of a single pile Quk = Qsk + Qpk (skin friction plus end - bearing resistance). Taking sandy soil as an example, when calculating with equal area, the calculated result shows that the pile tip Qpk is about ten times higher than the pile side Qsk. Therefore, an effective way to improve the bearing capacity of a single pile is to increase the pile tip area, which has obvious effects. The main purpose of the grouting and mixing enlarged bottom method for implanting precast piles is to increase the local diameter of the pile tip, expand the end - bearing area, give full play to the bearing capacity of the pile tip foundation, improve the bearing capacity of a single pile, reduce the number of piles used or the total number of piles, reduce the project cost, and save resources.

[0022] The drilled pile hole in the present invention is smaller than the designed diameter, complying with the technical requirements of "Technical Code for Building Pile Foundations" JGJ94 - 2008. It does not disturb the original soil layer on the inner wall of the pile hole and reduces the soil strength. Moreover, the specific gravity of the loose soil is greater than that of the slurry in the slurry - supported pile, meeting the requirements of shaft protection and there is no problem of reducing the skin friction of a single pile. During the process of grouting and enlarged bottom, the soil strength of the pile body is also reduced, achieving the goals of precast piles, that is, "control" the precast pile to reach the designed pile length and "control" the driving or pressing of the precast pile to reach the designed penetration and final pressure value, greatly improving the bearing capacity of a single pile.

[0023] The method of the present invention is as follows: Drilling and soil discharge Rotate the long - spiral drill pipe downward in a right - hand rotation and forward rotation, drill to the specified depth. During drilling, part of the loose soil will return upward. The diameter of the long - spiral forward - rotating drill pipe is smaller than the designed pile diameter to reduce the disturbance to the soil layer on the hole wall and ensure the original state of the hole wall.

[0024] Inject cement slurry When drilling to the designed depth, inject cement slurry at the upper end of the soil layer at the pile tip of the precast pile, reserving the thickness of the pile tip bearing stratum. The injection of cement slurry creates conditions for the subsequent formation of an enlarged bottom pile, and at the same time helps to improve the strength and stability of the pile tip soil.

[0025] Mixing and under-reaming Use a mechanical mixing and under-reaming bit device to work in the bearing stratum. While the device rotates, inject cement slurry and lift the drill string, so that the cement slurry and sand are fully stirred to form an under-reamed large-head pile. The formation of the under-reamed large head can increase the bearing area at the pile end and significantly improve the bearing capacity of a single pile.

[0026] Lifting of drill pipe Lift the long spiral drill pipe to the ground to prepare for the subsequent implantation of precast piles.

[0027] Implantation of precast piles Implant the precast pile downward to ensure that the depth of the bearing stratum at the pile end is not less than 1.0 m, so that the precast pile can fully play its bearing role.

[0028] Precautions Drilling and parameter control Before construction, carefully compare the geological exploration report and adjust the drilling depth and borehole diameter in a timely manner according to different geological conditions. When drilling close to the pile end, reserve an appropriate thickness of the bearing stratum and follow the provisions of the Technical Code for Building Pile Foundations JGJ94 - 2008. Generally, for cohesive soil, it is not less than 2d (d is the pile diameter), for sandy soil, it is not less than 1.5d, and for gravel soil, it is not less than 1d to avoid disturbing the bearing stratum at the pile end.

[0029] Under-reaming and drill pipe lifting operation When lifting the drill for under-reaming the large head, strictly control the reverse rotation speed and the timing of lifting the drill to ensure that the loose soil can effectively return to the hole and be compacted. Closely monitor the compaction of the loose soil in the hole and the change of the reaction force to avoid blindly lifting the drill and affecting the retaining wall effect and the quality of the pile body.

[0030] Injection of cement slurry Accurately control the injection volume, injection position and injection pressure of the cement slurry to ensure that the cement slurry and sand are fully stirred and evenly mixed to form a stable and reliable under-reamed structure. At the same time, pay attention to the quality and mix ratio of the cement slurry to ensure that its performance meets the engineering requirements.

[0031] Implantation of precast piles During the implantation of the precast pile, keep the pile body vertical to avoid excessive deviation and affecting the bearing performance of the pile. Ensure that the depth of the pile end entering the bearing stratum meets the design requirements. In case of any abnormal situation, take timely measures for treatment.

[0032] Environmental protection measures During the construction process, classify and collect and treat solid wastes such as waste cement slurry and drill cuttings to avoid random disposal and environmental pollution. Give priority to choosing environmentally friendly cement and other materials to reduce the negative impact on the environment. Reasonably arrange the construction time to avoid high-noise operations during the rest time of residents and reduce the interference of construction noise on the surrounding environment and residents' lives.

[0033] As described above, it is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, shall be covered by the protection scope of the present invention.

Claims

1. A method for implanting prefabricated piles by grouting, stirring and bottom expansion, characterized in that: The following steps are involved: S1, the long spiral drill rod rotates right and forward to drill to the specified depth, and returns some loose soil upward; S2. When drilling to the designed depth, inject cement slurry into the soil layer above the thickness of the bearing layer at the reserved pile end; S3, using a mechanical stirring bottom expansion drill bit device to mix cement slurry and sand in the soil layer at the end of the prefabricated pile to form a bottom expansion large head pile; S4, the long spiral drill rod rotates counterclockwise to return the loose soil on the drill rod to the hole for compaction and wall protection; S5, the long auger rod is lifted to the ground; S6. Insert the precast pile downwards.

2. The method of implanting prefabricated piles by grouting, stirring and bottom expansion according to claim 1, characterized in that: According to step S1, the long spiral forward-rotating drill pipe is drilled to the designed length.

3. The method of implanting prefabricated piles by grouting, stirring and bottom expansion according to claim 1, characterized in that: According to step S3, the mechanical stirring bottom enlargement drill bit device rotates, injects cement slurry, and lifts the drill tool to form a bottom enlarged big head.

4. The method of implanting prefabricated piles by grouting, stirring and bottom expansion according to claim 1, characterized in that: According to step S6, the depth of the bearing layer reserved at the pile end is not less than 1.0 m.

5. The method of implanting prefabricated piles by grouting, stirring and bottom expansion according to claim 1, characterized in that: According to step S1, the Beidou positioning system (accuracy ±2cm) is used in conjunction with the geological radar to adjust the drilling parameters in real time, wherein the rotation speed is 50-120rpm and the drilling pressure is 5-20MPa.

6. The method of implanting prefabricated piles by grouting, stirring and bottom expansion according to claim 1, characterized in that: According to step S3, during grouting, an intelligent joint control system for grouting pressure and flow is used to dynamically adjust pumping parameters through a PID algorithm to ensure the slurry filling coefficient.

7. The method of implanting prefabricated piles by grouting, stirring and bottom expansion according to claim 1, characterized in that: According to step S6, during the implantation phase, a distributed optical fiber sensor is used to monitor the stress distribution of the pile body in real time and generate a bearing capacity cloud map.

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