Experimental Study On Engineering Characteristics Of Inclined Piles Composite Foundation Under Vertical Repeated Loading And Unloading

Improper construction or side loading and excavation often lead to the inclination of pile body,which makes it difficult to upgrade.However,the lack of understanding of deformation characteristics of inclined pile composite foundation may lead to new engineering diseases.The model box and loading device are designed to study the deformation law of inclined pile composite foundation under repeated vertical loading and unloading.The results show that:(1)During cyclic loading,the settlement and lateral displacement of inclined pile top and its composite foundation increase with the increase of load,and the growth rate increases with the increase of load and decreases with the increase of loading times;during unloading,the settlement and lateral displacement of inclined pile top and its composite foundation do not change significantly at the initial stage of unloading,and elastic deformation occurs only at the last stage of 1-2 low pressure.(2)Under the same load,the settlement of pile top increases with the increase of inclination angle.There is a "critical inclination angle of settlement" for inclined piles(the first three loading and unloading cycles in this test are 6 degrees),which decreases with the increase of soil compactness.When the inclination angle is less than the critical value,the influence of the inclination on the settlement of piles is small.When the inclination angle is larger than the critical value,the settlement of pile top increases rapidly with the increase of the inclination angle.There is a "critical slope angle of lateral displacement" for inclined piles(9 degrees in this test),which corresponds to the peak value of lateral displacement.When the inclination angle is less than the critical value,the lateral displacement of pile top increases with the increase of inclination angle;when the inclination angle is greater than the critical value,the lateral displacement of pile top decreases with the increase of inclination angle.The "critical inclination angle of lateral displacement" is larger than the"critical inclination angle of settlement".(3)Under the same load,the settlement of composite foundation with inclined piles is larger than that of inclined piles,while the lateral displacement of composite foundation with inclined piles is larger than that of 6 degrees piles and smaller than that of 12 degrees piles.When the pile body is inclined,the lateral displacement of inclined pile and composite foundation is much smaller than its settlement,but the lateral displacement is more sensitive than the settlement.In engineering,the inclination of pile body and the settlement and lateral displacement of inclined pile and its composite foundation should be reduced as far as possible.(4)During the first cyclic loading,the soil pressure at the top of pile increases with the increase of load,and when the load is maximum,the corresponding soil stress increases with the decrease of degree,and the soil stress between piles is minimum.As the degree decreases,the load-sharing ratio between piles and soil increases correspondingly,and the load-sharing ratio between piles is the largest.The load-sharing ratio of the soil between piles decreases with the increase of load,and the pile gradually exerts the role of the pile.During the unloading process,the change of soil pressure at the top of the pile is not obvious at the beginning of unloading,but elastic deformation occurs only at the last level of 1-2 low pressure.The vertical pile still bears the load,the load ratio of inclined pile decreases,and the load ratio of vertical pile to soil increases to a certain value.(5)During the five loading cycles,the axial force of the pile body decreases gradually from the top to the bottom of the pile.With the increase of the load,the rate of the reduction of the axial force increases gradually.Axis force of inclined piles has a peak value,and the fluctuation of axial force of inclined piles is more obvious than that of vertical piles,and with the increase of angle,the fluctuation range of axial force of inclined piles is larger.(6)During the first cyclic loading,the bending moments of inclined and vertical piles increase gradually with the increase of depth,reach the peak value and then decrease gradually.The trajectory of inclined and vertical piles is like "crescent".During the loading process,the relative position of the peak moment away from the pile top will deepen with the increase of the angle.