Pile group construction method for stiff composite piles

Abstract

The invention discloses a pile group construction method of a stiff composite pile, which comprises the following steps of: performing combined construction of long and short piles arranged in a grillage manner, concentrating single pile stress bubbles at pile ends, and performing post-patching on weak parts of side resistance and end resistance according to the difference of weak parts of side resistance and end resistance caused by soil layer difference and construction sequence after the post-stress redistribution of the pile group. Short core piles are complementarily piled at side resistance weak parts, and long core piles are complementarily piled at end resistance weak parts, so that the bearing capacity, strength and modulus of the parts and the uniformity and stability of the whole foundation are improved, and the soil arching effect of a soil body and a cement soil body is formed. The method can effectively reinforce weak parts of end resistance or side resistance and improve the bearing capacity of the pile foundation.

Description

Technical Field

[0001] The invention relates to a pile group construction method of a rigid composite pile. Background Art

[0002] When constructing a group of rigid composite piles, there are often areas with weak end resistance or side resistance. How to strengthen these weak areas has been a long-standing research topic in this field. Summary of the invention

[0003] The object of the present invention is to provide a method for constructing a group of rigid composite piles which can effectively strengthen the weak end resistance or side resistance and improve the bearing capacity of the pile foundation.

[0004] The technical solution of the present invention is: A method for constructing a group of rigid composite piles, which carries out grid-arranged long and short pile combination construction, and is characterized in that: stress bubbles of a single pile are concentrated at the pile end, and after the later stress redistribution of the pile group, piles are added at the weak parts of the side resistance and end resistance according to the difference in the weak parts of the side resistance and end resistance caused by the difference in soil layers and the construction sequence, short core piles are added at the weak parts of the side resistance, and long core piles are added at the weak parts of the end resistance, so as to improve the bearing capacity, strength, modulus and uniformity and stability of the overall foundation of the part, and form a soil arch effect of the soil and cement soil.

[0005] During the construction of supplementary piles: ① During construction, the predetermined pile length of the long core pile does not reach the bearing layer, and the pile end resistance is too small. It is necessary to continue to exceed the elevation and send the pile within 2m. If it still does not enter the bearing layer, the length of the core pile needs to be increased; ② During construction, the cement soil of the short core pile is mixed to a certain depth in the bearing layer to determine the pile length required for the core pile to enter the bearing layer; ③ If the length of a single core pile cannot reach the natural bearing layer, it is necessary to first spray, stir, counter-press, and squeeze and expand the range from 2m above the core pile end elevation to 3-5m below the bearing layer to form an artificial bearing layer under the pile end, and then carry out core pile construction, and at the same time verify that the pile end resistance meets the requirement of 2 / 3 of the final pressure value.

[0006] In methods ② and ③, when the stirring current reaches 400-500A or above, it indicates that the lower hard and dense sand layer bearing layer has been stirred. The soft soil layer within the range of 1-3m above the bearing layer elevation and the dense sand layer within the range of 1-8m below the bearing layer elevation are sprayed and stirred again to increase the cement content, and the back pressure is used to compact and expand the diameter to form an artificial dry and hard sand-containing cement soil bearing layer at the pile end; the single-section pipe pile is pressed into and enters a certain depth of the above-mentioned bearing layer before the cement soil is hardened, and overload and pressure stabilization construction is carried out. Stress concentration is used to promote the irreversible densification of the cement soil at the pile end and the soil of the bearing layer, and pre-pressing and settling are carried out to avoid deformation after construction. The final pressure value of the pressure stabilization meets the design limit value, and matches the limit value of the single-section pipe pile material, the pile side, and the pile end soil to jointly form the bearing capacity, forming a high strain rate in the plastic state, and late settlement hardening, completing pre-detection, pre-settlement, and pre-diagenesis.

[0007] When constructing a combination of long and short piles in a grid-like arrangement, the parameters of the long and short core composite piles are adjusted: construction interval time, core pile length, final pressure range value at a certain depth of different bearing layers, number of stable pressure and re-pressure times and duration, so that the area from 3m above the pile end to 8m below the pile end is the most important, critical and sensitive part for settlement and bearing capacity. Active pressurization induces plastic strain at the pile end, and the constitutive relationship of cement soil and soil is reshaped through "pressure-induced phase change". While improving the end resistance, the requirements for properties, strength and stiffness of different types of cement soil piles in the overall foundation during overlap construction are met.

[0008] The present invention can effectively strengthen the weak parts of the end resistance or the side resistance and improve the bearing capacity of the pile foundation.

[0009] The present invention will be further described below in conjunction with the embodiments. DETAILED DESCRIPTION

[0010] A method for constructing a group of rigid composite piles, which comprises the following steps: carrying out grid-arranged long and short pile combination construction, concentrating stress bubbles of a single pile at the pile end, and after the later stress redistribution of the pile group, according to the difference in weak parts of side resistance and end resistance caused by differences in soil layers and construction sequence, post-pile reinforcement is carried out at the weak parts of side resistance and end resistance, reinforcing the weak parts of side resistance with short core piles (i.e., rigid composite piles with a core pile less than or equal to the number of peripheral piles), reinforcing the weak parts of end resistance with long core piles (i.e., rigid composite piles with a core pile greater than the number of peripheral piles), thereby improving the bearing capacity, strength, modulus and uniformity and stability of the overall foundation at the part, and forming a soil arch effect of soil and cement soil.

[0011] When carrying out the subsequent pile construction: ① During the construction, the predetermined pile length of the long core pile does not reach the bearing layer, and the pile end resistance is too small. It is necessary to continue to exceed the elevation and send the pile within 2m. If it still does not enter the bearing layer, the length of the core pile needs to be increased; ② During the construction, the cement soil of the short core pile is mixed to a certain depth in the bearing layer to determine the pile length required for the core pile to enter the bearing layer; ③ If the length of the single-section core pile (generally 15m) cannot reach the natural bearing layer, it is necessary to first spray, stir, counter-press, and squeeze and expand in the range from 2m above the core pile end elevation to 3-5m below the bearing layer to form an artificial bearing layer under the pile end, and then carry out the core pile construction, and at the same time verify that the pile end resistance meets the requirement of 2 / 3 of the final pressure value.

[0012] In methods ② and ③, when the stirring current reaches 400-500A or above, it indicates that the lower hard and dense sand layer bearing layer has been stirred. The soft soil layer within the range of 1-3m above the bearing layer elevation and the dense sand layer within the range of 1-8m below the bearing layer elevation are sprayed and stirred again to increase the cement content, and the back pressure is used to compact and expand the diameter to form an artificial dry and hard sand-containing cement soil bearing layer at the pile end; the single-section pipe pile is pressed into and enters a certain depth of the above-mentioned bearing layer before the cement soil is hardened, and overload and pressure stabilization construction is carried out. Stress concentration is used to promote the irreversible densification of the cement soil at the pile end and the soil of the bearing layer, and pre-pressing and settling are carried out to avoid deformation after construction. The final pressure value of the pressure stabilization meets the design limit value, and matches the limit value of the single-section pipe pile material, the pile side, and the pile end soil to jointly form the bearing capacity, forming a high strain rate in the plastic state, and late settlement hardening, completing pre-detection, pre-settlement, and pre-diagenesis.

[0013] When constructing a combination of long and short piles in a grid-like arrangement, the parameters of the long and short core composite piles are adjusted: construction interval time, core pile length, final pressure range value at a certain depth of different bearing layers, number of stable pressure and re-pressure times and duration, so that the area from 3m above the pile end to 8m below the pile end is the most important, critical and sensitive part for settlement and bearing capacity. Active pressurization induces plastic strain at the pile end, and the constitutive relationship of cement soil and soil is reshaped through "pressure-induced phase change". While improving the end resistance, the requirements for properties, strength and stiffness of different types of cement soil piles in the overall foundation during overlap construction are met.

[0014] The present invention utilizes stress history (construction preloading) and path control (pile-soil stiffness gradient) to achieve stress diffusion and redistribution of loads, breaking through the bottleneck of the curtain effect of traditional pile groups.

Claims

1. A method for constructing a group of rigid composite piles, which comprises grid-arranged long and short piles for combined construction, and is characterized by: The stress bubbles of a single pile are concentrated at the pile end. After the stress of the pile group is redistributed in the later stage, according to the differences in the weak parts of the side resistance and end resistance caused by the differences in soil layers and the construction sequence, post-pile reinforcement is carried out in the weak parts of the side resistance and end resistance. Short core piles are added to the weak parts of the side resistance, and long core piles are added to the weak parts of the end resistance to improve the bearing capacity, strength, modulus and uniformity and stability of the overall foundation, forming a soil arch effect of soil and cement soil.

2. The method for constructing a group of rigid composite piles according to claim 1, characterized in that: During the construction of supplementary piles: ① During construction, the predetermined pile length of the long core pile does not reach the bearing layer, and the pile end resistance is too small. It is necessary to continue to exceed the elevation and send the pile within 2m. If it still does not enter the bearing layer, the length of the core pile needs to be increased; ② During construction, the cement soil of the short core pile is mixed to a certain depth in the bearing layer to determine the pile length required for the core pile to enter the bearing layer; ③ If the length of a single core pile cannot reach the natural bearing layer, it is necessary to first spray, stir, counter-press, and squeeze and expand the range from 2m above the core pile end elevation to 3-5m below the bearing layer to form an artificial bearing layer under the pile end, and then carry out core pile construction, and at the same time verify that the pile end resistance meets the requirement of 2 / 3 of the final pressure value.

3. The method for constructing a group of rigid composite piles according to claim 2, characterized in that: In methods ② and ③, when the stirring current reaches 400-500A or above, it indicates that the lower hard and dense sand layer bearing layer has been stirred. The soft soil layer within the range of 1-3m above the bearing layer elevation and the dense sand layer within the range of 1-8m below the bearing layer elevation are sprayed and stirred again to increase the cement content, and the back pressure is used to compact and expand the diameter to form an artificial dry and hard sand-containing cement soil bearing layer at the pile end; the single-section pipe pile is pressed into and enters a certain depth of the above-mentioned bearing layer before the cement soil is hardened, and overload and pressure stabilization construction is carried out. Stress concentration is used to promote the irreversible densification of the cement soil at the pile end and the soil of the bearing layer, and pre-pressing and settling are carried out to avoid deformation after construction. The final pressure value of the pressure stabilization meets the design limit value, and matches the limit value of the single-section pipe pile material, the pile side, and the pile end soil to jointly form the bearing capacity, forming a high strain rate in the plastic state, and late settlement hardening, completing pre-detection, pre-settlement, and pre-diagenesis.

4. The method for constructing a group of rigid composite piles according to claim 1, 2 or 3, characterized in that: When constructing a combination of long and short piles in a grid arrangement, the parameters of the long and short core composite piles are adjusted: construction interval time, core pile length, final pressure range value at a certain depth of different bearing layers, number of stable pressure and re-pressure and duration, so that 3m above the pile end to 8m below the pile end are the most important, critical and sensitive parts for settlement and bearing capacity. Active pressurization induces plastic strain at the pile end, and reshapes the constitutive relationship of cement soil and soil through "pressure-induced phase change". While improving the end resistance, the requirements for properties, strength and stiffness of different types of cement soil piles in the overall foundation during overlap construction are met.