Model Test Of Hammering PHC Pipe Pile In Soft Soil Region Of Northern Anhui

PHC pipe pile is a new type of pile foundation that is widely used in various types of foundation reinforcement projects.It has the advantages of simple and rapid construction,mass production,energy saving and environmental protection,and suitable for various geological conditions.However,in the engineering practice,PHC pipe piles often have problems such as pile damage,skewed piles,and sinking difficulties,which have a great impact on the progress and quality of the project.Therefore,by studying the mechanism of pile-soil interaction for hammering PHC pipe pile,it can provide references for the construction and design of PHC pile under similar engineering geological conditions.In order to investigate the squeezing effect and soil plug effect of hammering PHC pipe piles,ascertaining the mechanism of pile-soil interaction of hammered PHC pipe piles,and using the model test method to simulate the PHC pipe pile hammering pile-sinking process.The FBG sensor on the model pile,and the pore water pressure sensor,earth pressure gauge and acceleration sensor embedded in the model box filling,are used to monitor the open model pile and the model with pile tip pile under the hammer load of the pile top,finding the variation range and change law of the pile strain,pore pressure and earth pressure in soil around the pile,analyzed and summarized the variation of each data in the model test.The following conclusions were obtained:(1)The number of hammers required for pile driving is higher than that with pile shoe.When the depth of pile sinking reaches 80%of the pile length,the number of hammers required for the model pile with pile shoes is significantly less than that of the open model pile.It can be concluded that the pile shoes have a significant effect on reducing the soil plug effect during pile driving;(2)The IFR is about 14%when the depth of the open model pile sinks to 40cm,the IFR is about 15%when it reaches 80cm,the IFR is about 14%when it reaches 120cm,and the IFR is about 8.5%after the pile is completed.The IFR value is stable when the depth of entry is 120cm,and the IFR value decreases when the depth of the model pile is between 120cm and 150cm.The IFR value decreases from relatively stable to decreasing,indicating that the plug effect of model pile-soil plug increases steadily and gradually,and the soil entering the model pile gradually decreases.The extrusion effect of the model pile on the surrounding soil is gradually obvious;(3)During the process of hammering and sinking of two model piles,the strain change curve of each FBG sensor will obviously fluctuate up and down according to the hammering frequency.The FBG sensor entering the soil body will show compressive strain and the strain will fluctuate little,and will not enter.The FBG sensor outside the soil shows tensile strain and the strain fluctuation is significantly larger.Compared with open model piles,the strain of piles with piled piles is significantly smaller than that of open model piles;(4)The pore water pressure will generate small fluctuations with the hammering frequency when the two model piles sink.When the model pile sinking depth reaches the pore pressure gauge U4-U6,U7-U9 buried in the saturated sand layer,the pore water pressure increases big.Among them,U4 and U7 are nearest to the model pile,and the pore water pressure increases more than U5,U6 and U8 and U9 far from the model pile,and the excess pore water pressure at the monitoring point near the model pile dissipates fastest.The excess pore water pressure dissipation at the monitoring points farther from the model pile is relatively slow;(5)The soil pressure around the pile increases with the increase of the buried depth of the soil pressure gauge when the two model piles are piled,which is shared with the soil around the pile with more hammering load as the pile depth increases.In the body,the T1-T6 data fluctuation for monitoring the lateral earth pressure is obviously less than the T7 and T8 for monitoring the vertical earth pressure;(6)When two model piles hammer the pile,the accelerometer G1 is embedded in the unsaturated silty clay layer with the shallowest depth,the minimum acceleration is measured,and the accelerometer G2 is buried in the saturated silt layer and sand layer contact surface.The acceleration measured is the largest,and the accelerometer G3 is embedded in a saturated sand layer with the deepest depth and the measured acceleration is at the median value.The acceleration of the soil around the pile during the process of pile sinking of the two model piles will fluctuate up and down with the hammering frequency,but the range of change is not large.