Study On The Pile Shaft Friction Reduction During Pile Driving

The vibrations is inevitable during the pile driving,it will weaken the soil strength around the pile,and lend to the reduction of the pile shaft friction.Because of this reason,the pile driving become more difficult and the accident more frequent.In order to reduce economic loss,ensure the pile driving safety,prediction of pile drivability is an essential link before pile installation,the pile shaft friction will be determined through the pile drivability.In this paper,the number model of dynamic pile driving will be built at first,and using this model for numerical simulation analysis by the MATLAB.The pile segments vibrations peak velocity for various depth is obtained,also getting the peak velocity of soil vibrations.Then calculating the soil stress and strain by the peak velocity,analyzing the influence on shear modulus.Using above results to calculate the external load energy imposed on various depth soil during pile driving with blow counts.The pile shaft friction reduction model is be built based on the energy method in this paper,and calculating the ratio between external load energy imposed on the soil during pile driving and ultimate resistance capacity of soil,determining the degradation degree of pile shaft friction.In this paper,analyzing the initial vertical effective stress,blow counts and classification of soil(e.g.loose,medium,dense)influence on the pile shaft friction.From the result show that,with the increasing of initial vertical effective stress,the degradation degree of pile side friction decreases,the probability of soil liquidation around the pile become smaller.But with the increasing of blow counts,the degradation of the shaft friction becomes more serious,and the soil capacity reduces,the soil around pile is more likely liquefaction.When the classification of soil becomes dense from medium,the loading impact on the soil is also increasing,but the ultimate resistance capacity of soil is invariant,so the classification of soil increasing will lead to the degradation degree of pile side friction more serious.At last of this paper,combining with engineering project to build the numerical model,and compared the result with field recorded data to verify the correctness of this model.