Pile sinking method of prefabricated square pile in sandy soil

Abstract

The invention discloses a pile sinking method of a prefabricated square pile in sandy soil, which comprises the following steps of: (1) surveying and setting out at a construction site, determining a guide hole position, (2) carrying out field excavation at the guide hole position, and building a bearing platform, (3) selecting a high-pressure jet grouting machine to carry out guide hole grouting, (4) adopting a static pressure walking type pile press, hoisting a first section of prefabricated pipe pile in place, re-checking and adjusting the pile position, and carrying out pile sinking on the first section of prefabricated pipe pile. (5) when the distance between the pile top of the first section of the prefabricated pipe pile and the ground is 0.5-1.0 m, hoisting the second section of the prefabricated pipe pile, carrying out pile splicing operation, continuously sinking the pile, and carrying out primary pressurization on the pile top of the first section of the prefabricated pipe pile until the distance between the pile top of the first section of the prefabricated pipe pile and the ground is 0.5-1.0 m; and (6) pile sinking operation of other sections of prefabricated pipe piles is carried out according to the step (5) until the piles are formed. According to the method, the pile forming resistance is effectively reduced, the pile end can smoothly reach an expected supporting layer, safety and reliability are achieved, and compared with a traditional pile sinking method, the method is more economical and effective.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pile construction, in particular to a method for sinking prefabricated square piles in sand. Background Art

[0002] Prefabricated pipe piles have the advantages of high bearing capacity, good bending resistance, reliable pile quality, short construction period, and good economic benefits. They have reasonable product structure, complete varieties and specifications, and a wide range of design options. They are now widely used in pile foundation construction. In construction, static pressure method and hammer method are usually used. However, when there is a thick and dense sand layer or a hard clay layer in the stratum, it is often difficult to sink the pile. Once forced construction is carried out, the pile body will be damaged, and the pile top elevation will not meet the design requirements, which will not only waste materials but also have adverse effects on the construction of the next process. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a method for sinking prefabricated square piles in sandy soil, which can specifically adopt the following technical solutions: The method for sinking prefabricated square piles in sandy soil of the present invention comprises the following steps: The first step is to measure and lay out the lines at the construction site to determine the location of the lead hole; The second step is to conduct on-site excavation at the location of the lead hole and build the cap; The third step is to select a high-pressure jet jet machine for drilling and grouting; The fourth step is to use a static pressure walking pile driver to hoist the first section of prefabricated pipe pile into place. After checking and adjusting the pile position, the pile end is put into the soil and initially pressurized. At the same time, the verticality of the pile body is checked and corrected, and then the pile sinking operation is officially started. During this process, the verticality of the pile body is always observed and corrected; Step 5: When the top of the first section of prefabricated pipe pile is 0.5-1.0m away from the ground, lift the second section of prefabricated pipe pile to connect the piles, and then continue to sink the piles, and keep a record of the pressure value during this process; The sixth step is to carry out the pile sinking operation of other segments of prefabricated pipe piles according to step five until the piles are completed.

[0004] Preferably, after the last section of prefabricated pipe pile driving is completed, the static pressure walking pile driver is used for re-pressing, and the number of re-pressing times is at least three times. The settlement amount of the last re-pressing is controlled within 20 mm, and a detailed and accurate record is made of the termination pile driving force.

[0005] Preferably, a BW water stop strip with a bottom at the same height as the pile top elevation is provided in the guide hole of the cap.

[0006] Preferably, the grouting material used in the drilling is a mixture of cement and bentonite.

[0007] Preferably, when the hole diameter of the guide hole is 900 mm, the cement grouting amount per meter of hole is 70-120 kg, wherein the water-cement ratio is between 1:0.7-1:1, and the weight of bentonite does not exceed 33% of the weight of cement.

[0008] The method for sinking prefabricated square piles in sandy soil provided by the present invention aims to solve the difficult problem of sinking traditional square piles in dense sandy soil or hard clay layers. The method adopts a pile sinking scheme of first dredging holes and grouting and then statically pressing the square piles, which effectively reduces the pile resistance and enables the pile end to smoothly reach the expected bearing layer. The method is safe, reliable and easy to construct. Compared with traditional pile sinking methods, it is more economical and effective and can be widely promoted in actual construction.

[0009] Compared with the prior art, the advantages of the present invention are as follows: 1) The present invention effectively ensures the lateral friction of the pile foundation by optimizing the ratio of grouting materials, so that pile formation can be achieved even when dense coarse sand or the measured standard penetration number N63.5 is above 25 hits; 2) Compared with the traditional scheme of setting up a raft foundation on a natural foundation and setting up a raft / independent foundation after filling, the present invention improves the bearing capacity of a single pile and reduces the area of ​​the cap (a water retaining plate can be set between the caps), thereby reducing the construction cost by 10-50%; 3) The present invention reasonably controls the weight of the hammer head and the static pressure tonnage, effectively avoiding the pile body crack phenomenon caused by the damage of the pile head and / or the sudden breakage of the pile body during pile delivery in the traditional construction process, thereby ensuring the construction quality and construction safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a construction flow chart of the present invention.

[0011] Figure 2 It is a cross-sectional view of the square pile and the lead hole in the present invention. DETAILED DESCRIPTION

[0012] The following is a detailed description of an embodiment of the present invention in conjunction with the accompanying drawings. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific construction process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0013] like Figure 1 , 2 As shown, the method for sinking prefabricated square piles in sandy soil according to the present invention comprises the following steps: The first step is to measure and lay out the lines at the construction site to determine the location of the lead hole; The second step is to conduct on-site excavation at the location of the lead hole and build the cap; The third step is to select a high-pressure jet jet machine for drilling and grouting; Among them, a BW water stop strip with a bottom equal to the pile top elevation is arranged in the lead hole of the cap to play a waterproof role. The grouting material used in the lead hole is a mixture of cement and bentonite.

[0014] Since bentonite has a long setting time and low strength, while cement has a short setting time and high strength, the ratio of grouting materials has a great influence on the grouting effect. Reasonable ratio of grouting materials can provide time guarantee for piling, thereby ensuring the grouting quality. In the present invention, for the pile body, especially the pile bottom, which is medium-coarse sand, when the hole diameter is 900mm, the cement grouting amount per meter is 70-120kg, wherein the water-cement ratio is between 1:0.7-1:1, and the weight of bentonite does not exceed 33% of the weight of cement. In the specific implementation, specific adjustments are made according to the actual geological conditions.

[0015] The fourth step is to use a static pressure walking pile driver to hoist the first section of the prefabricated pipe pile into place. After checking and adjusting the pile position, the pile end is put into the soil and initially pressurized. At the same time, the verticality of the pile body is checked and corrected, and then the pile sinking operation is officially started. During this process, the verticality of the pile body is always observed and corrected. In addition, since the static pressure walking pile driver moves slowly, the time interval between piling cannot be too short, generally maintained at 1-6 hours; Step 5: When the top of the first section of prefabricated pipe pile is 0.5-1.0m away from the ground, lift the second section of prefabricated pipe pile to connect the piles, and then continue to sink the piles, and keep a record of the pressure value during this process; Step 6: Follow step 5 to sink no more than 3 sections of prefabricated pipe piles until the piles are formed. For the last section of prefabricated pipe piles, after the sinking operation is completed, a static pressure walking pile driver shall be used for re-pressing at least three times. The settlement of the last re-pressing shall be controlled within 20mm, and a detailed and accurate record shall be made of the termination pile driving force.

[0016] Among them, 1.0 The initial stage of grouting in the lead hole played a role of lubricant, solving the problem of pile sinking difficulty in medium-coarse sand. 2.0 The later stage of grouting in the lead hole played a role of post-grouting, improving the bearing capacity of the pipe pile.

[0017] After the prefabricated pipe pile is formed, the static pressure walking pile driver should be moved to the next station and the next prefabricated pipe pile should be driven according to the above steps. For dense pile groups, the pile driving sequence should be adopted according to the actual situation on site, such as skip driving every other pile or driving the middle pile first and then the surrounding piles. It should be pointed out that the hammer equipment, construction technology and process parameters (including pile driving force) of the engineering pile should be the same as those of the test pile.

[0018] It should be noted that, in the description of the present invention, terms indicating orientation or positional relationships, such as "front", "rear", "left", "right", "vertical", "horizontal", "inside", "outside", etc., are based on the orientation or positional relationships shown in the 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 should not be understood as a limitation on the present invention.

Claims

1. A method for sinking prefabricated square piles in sandy soil, characterized in that: The steps include: The first step is to measure and lay out the lines at the construction site to determine the location of the lead hole; The second step is to conduct on-site excavation at the location of the lead hole and build the cap; The third step is to select a high-pressure jet jet machine for drilling and grouting; The fourth step is to use a static pressure walking pile driver to hoist the first section of prefabricated pipe pile into place. After checking and adjusting the pile position, the pile end is put into the soil and initially pressurized. At the same time, the verticality of the pile body is checked and corrected, and then the pile sinking operation is officially started. During this process, the verticality of the pile body is always observed and corrected; Step 5: When the top of the first section of prefabricated pipe pile is 0.5-1.0m away from the ground, lift the second section of prefabricated pipe pile to connect the piles, and then continue to sink the piles, and keep a record of the pressure value during this process; The sixth step is to carry out the pile sinking operation of other segments of prefabricated pipe piles according to step five until the piles are completed.

2. The method for sinking prefabricated square piles in sandy soil according to claim 1, characterized in that: After the last section of prefabricated pipe piles are driven, the static pressure walking pile driver is used for re-driving. The number of re-driving is at least three times. The settlement of the last re-driving is controlled within 20 mm, and a detailed and accurate record is made of the termination pile driving force.

3. The method for sinking prefabricated square piles in sandy soil according to claim 1, characterized in that: A BW water stop strip with a bottom at the same height as the pile top elevation is arranged in the lead hole of the cap.

4. The method for sinking prefabricated square piles in sandy soil according to claim 1, characterized in that: The grouting material used when drilling the hole is a mixture of cement and bentonite.

5. The method for sinking prefabricated square piles in sandy soil according to claim 4, characterized in that: When the hole diameter of the guide hole is 900 mm, the cement grouting amount per meter of the hole is 70-120 kg, wherein the water-cement ratio is between 1:0.7 and 1:1, and the weight of the bentonite does not exceed 33% of the weight of the cement.

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