Study Of Penetration Mechanism And Construction Effect Of The Sleeve For Lager Diameter Cast-in-place Piles Installation Using High-Frequency Vibratory Hammers

With the development of the construction technique of cast-in-place pile with sleeve driven by high-frequency vibratory hammers,the cast-in-place piles have been widely used in construction engineering.However,the researches on the high-frequency vibratory penetration mechanism of the cast-in-place pile sleeve,particularly the construction effect due to sleeve driving,are still incomplete.In light of this,the high-frequency vibratory penetration mechanism and construction effect of the large-diameter sleeve driving are studied by the model test,analytical and numerical methods.The main original works and innovative achievements are as following:1.The model test is carried out to investigate the excess pore pressure,extruding stresses,the degree of soil plug and penetration speed during the vibratory driving of sleeve for the cast-in-place pile into the sand foundation.2.The finite element model is introduced,by using the commercial code ABAQUS,to simulate whole driving process of the sleeve from the ground surface to the desired depth by applying vibratory hammers.The comparison between the model test and numerical simulation verifies the feasibility of using the finite-infinite coupling model to simulate the high-frequency vibratory driving process of the sleeve for cast-in-place pile.3.The environmental effect during the high-frequency vibratory sleeve driving into the clay foundation is investigated by setting up the three-dimensional model.The influences of the vibratory frequency,dynamics load amplitude,interface frictional coefficient,and soil modulus on the safety distance of the construction are compared.The influences of isolation trench’s filling material,depth,width,shape and position on the damping effect are investigated.4.The soil plugging effect during high-frequency sleeve driving into clay foundation is studied by setting up the three-dimensional model.The change law of the void ratio of the soil plug,the distribution of the shaft resistance inside and outside the sleeve,the degree of the soil plug and the arching effect during the high-frequency sleeve driving are also analyzed.The influences of the vibration frequency,sleeve diameter,and the soil layer property on soil plugging effect are discussed.A simplified formula is obtained to calculate the soil plug resistance.5.The squeezing effect during the high-frequency vibratory sleeve driving into clay foundation is investigated by setting up the three-dimensional model.The change rule of squeezing displacement and excess pore water pressure during high-frequency vibratory sleeve driving into the clay foundation are analyzed.The influences of the soil modulus,possion ratio,frictional coefficient,vibratory frequency and sleeve diameter on the squeezing displacement are discussed.6.The pore water pressure analytical model of the sand foundation is established,and the distribution and change law of the excess pore water pressure incurred by the high-frequency vibratory sleeve driving into the sand foundation are studied.7.Taking the soil plugging effect during vibratory sleeve driving into account,the shear between the soil elements outside the sleeve and the vertical stress at the sleeve bottom are calculated by using the Gudehus-Bauer hypoplasticity constitutive model,and then the penetration speed is obtained by modelling of the high-frequency vibratory driving of the cast-in-place pile sleeve into sand.In order to validate the calculation model,the penetration speed obtained by the calculation model is compared with those by the experiment and the finite element simulation.The calculation model provides a reliable way for practical engineering to quickly and accurately predict the penetration speed of sleeve.