Study On The Stress And Deformation Mechanism Of Soil Nailing Under Pile Driving Vibration

Soil nailing is one of the most commonly used support forms in foundation pit support engineering in China.In the actual foundation pit project,vibration loads caused by pile driving in adjacent sites or transportation vehicles may significantly affect the stress and deformation of foundation pit support structure.This involves the influence of vibration load on mechanical properties of the soil and bearing capacity of nail-soil interface.At present,the research on bearing capacity of soil nail under different vibration loads is not deep enough.Therefore,the research on the influence of vibration load of pile driving on the stress and deformation of soil nailing in foundation pit has important engineering value and scientific significance.In this paper,the pull-out capacity of the soil nail and the influence of vibration on the nail-soil interface strength under different overburden pressure and water content were studied by model tests.By applying different tensile forces at the end of the model nail,the nail-soil interface generated a certain friction force to simulate the mechanical properties of different nail-soil interface in actual engineering,and the influence law of vibration load on the shear stress of the nail-soil interface under different stress levels was studied.Based on this,the numerical analysis model was established to simulate the behavior of stress and deformation of soil nailing under pile driving vibration load by two methods,i.e.the attenuation method of nail-soil interface strength and the direct application of vibration load.The influence law of pile driving vibration load on stress and deformation of soil nail support in foundation pit was studied and summarized,and the following research results were obtained:(1)Both overburden pressure and soil moisture content have significant effects on the pull-out capacity of the nail-soil interface.With the increase of overburden pressure,the pull-out capacity of the nail-soil interface increases significantly,and the pull-out displacement corresponding to the maximum shear stress increases accordingly.With the increase of soil moisture content,the interface shear stress between the soil and the nail decreases obviously,and the pull-out displacement corresponding to the maximum shear stress decreases correspondingly.(2)The vibration load of pile driving will lead to the attenuation of the nail-soil interface strength.The longer the vibration duration is,the more obvious the strength attenuation of the nail-soil interface is.The greater the soil moisture content is,the greater the attenuation degree of the nail-soil interface strength is.The greater the overburden pressure is,the smaller the attenuation degree of the nail-soil interface strength is.(3)In the soil nailing of foundation pit,the axial force of the soil nail in each layer is unevenly distributed along the length of the soil nail,showing the distribution law of "large in the middle and small at both ends".After the strength attenuation of the nail-soil interface,the variation law of the soil nail axial force in each layer is basically the same,and the maximum value of the soil nail axial force is at the position of the potential slide surface.With the attenuation of the nail-soil interface strength,the soil nail axial force continues to increase,and the pull-out capacity of each soil nail interface develops successively,but the maximum axial force of the soil nail is always at the potential slide surface.(4)In the soil nailing support of foundation pit,the shear stress of the nail-soil interface in each layer is not uniformly distributed along the length of the soil nailing,and the shear stress of the nail-soil interface is zero at the potential slide surface.With the attenuation of the nail-soil interface strength,the lateral displacement of the foundation pit wall becomes larger,which leads to the increase of the relative displacement between the nail-soil and the redistribution of the nail-soil interface shear stress.The nail-soil interface whose shear stress reaches the nail-soil interface strength decreases with the attenuation of the interfacial strength.In order to maintain the stability of the foundation pit,other nail-soil interfaces are used,and the shear stress increases with the increase of the relative displacement between the soil and the soil nail.