Experimental Study On The Bearing Capacity Behavior Of Pipe-pile With Holes Under Vertical Load

Pre-stressed pipe-pile has been applied in China since the mid-1980 s with a history of more than thirty years. They are considerable economic benefits have been brought in at the same time for their high quality, less noise, high speed of construction.Nonetheless, during the course of static sinking, the excess hydrostatic pore water pressures generated hereby would result in rather negative impacts on their surroundings and cause severe engineering accidents as well as big loss in economy and security under very sever circumstances. Therefore, to reduce the negative effects caused by static sinking pipe-pile, a new kind of technique regarding pipe-piles proposed by the introduction of pipe-piles with hole, which has made it possible to effectively accelerate the dissipation of excess hydrostatic pore water pressures in progress, reducing the unfavorable impacts of squeezing effect on surrounding buildings.In spite of the advantages mentioned above, but open holes on pipe-piles can also weaken the ultimate bearing capacity, and has some impact on the bearing capacity behavior of those vertically loaded pipe-piles, stress concentration caused by opening holes on pipe-pile reduces the bearing capacity of pipe-pile are still unknown at present.According to above discussion, this paper study and analyze the working properties of pipe-piles with hole under vertical load by combining the indoor model test with numerical stimulation method. Main content are as follows.(1) Based on the indoor model test of pipe-piles with hole during static-sinking,the change of excess hydrostatic pore water pressure is mainly divided into the acceleration rise generation phase and the slow decline dissipation phase. The size of excess hydrostatic pore water pressure increases with the increment of the depth H and the rate of dissipation is smaller and smaller when the radial distance R keeps invariant.Moreover, it decreases with the increases of the radial distance R and the rate of dissipation is also smaller and smaller when the depth H remains unchanged.(2) The optimal hole distribution of pipe-pile with hole design is star-shaped hole distribution, which was verified from the analyze of the dissipating cases of the excess hydrostatic pore water pressure and the change of excess hydrostatic pore water pressure ratio in the different position after 58 hours of rest. Analysis on the influence of the section opening porosity of pipe to the change of excess hydrostatic pore water, it was verified that excess hydrostatic pore water pressure caused by static-sinking can be effectively reduced and the influence area of squeezing effect can be also weakened by means of increasing the section opening porosity properly.(3) Indoor model test and FLAC3 D numerical simulation method were usedrespectively so as to study single pile static sinking test and the Q-s curves, axial force distributions, and side friction distributions can be illustrated. Its correctness and reliability of it are verified when the results of two tests are basically consistent.(4) By comparing and analyzing, it can be concluded that open holes on pipe-piles can effectively reduce the water content in the soil, increase the shear strength of the soil, increase the friction of the pile side, and reduce the settlement of the pile. However,the bearing capacity of pipe-pile will be reduced to some extent. It is inferred that axial force reduction ratio of pile of star-shaped pipe-pile with hole is minimum and it is some influence that the amount of opening holes on the pile wall has some influence on the distribution of side friction of pile. In conclusion, that the best hole distribution of pipe-pile with hole design is star-shaped hole distribution is verified again.