Experimental Study Of Engineering Characteristics Of Adjacent Inclined Pile With Both Ends Constrained Under Vertical Loading And Unloading

In industrial factory buildings,port wharfs,bridge foundations and other projects,soil subsidence and lateral displacement are often caused by surcharge and overload,resulting in excessive bending moment and deflection of piles adjacent to pile foundations under lateral displacement of soil,resulting in offset or even fracture.In this paper,the horizontal displacement variation and engineering characteristics of inclined double-row piles with adjacent two-end restraint under three vertical cyclic loading and unloading are studied by indoor model tests.The results show that:(1)Settlement of load plate and horizontal displacement of pile body are larger at initial loading stage,then the growth rate slowed down,when the second load exceeds the maximum load of the first load,the loading curve develops along the extension line of the first load curve,which has memory,the three unloading curves are similar,and the elastic deformation is obvious when unloading to 0 kN,the rebound of the top and bottom of the pile is less than that of the middle pile body,which indicates that the horizontal displacement is restrained by the tied beam at the top of the pile and the restrained embedding at the bottom of the pile.(2)During loading and unloading,the horizontal displacement of pile top and pile body decreases with the increase of inclination angle when the lateral load of foundation is constant in the range of 0～9.Under the same load,the lateral displacement of the top of inclined piles is smaller than that of vertical piles.In the same row of piles,the larger the inclination angle,the smaller the displacement.In practical engineering,inclined piles with rock-socketed bottom and connecting beams at top are used for slope foot piles,which is more advantageous to resist sliding.(3)The values of axial force and bending moment of each pile are similar,and all decrease with the increase of inclination angle.,in the same row of piles,the increase of inclination angle will cause a great difference in bending moment values.The inclination angle of the back row piles is larger than that of the front row piles,and the bending moment value is much smaller than that of the front row piles,besides the influence of the inclination angle,the shielding effect of the front row piles on the back row piles also enlarges the difference of the bending moment values.(4)During the loading process,the frictional resistance of each pile changes alternately along the pile depth.,the frictional resistance of each pile decreases with the increase of the inclined pile angle,in the same row of piles,the increase of the inclined pile angle will cause a great difference in the frictional resistance value.,in the unloading process,the change of friction resistance at 0 kN is obviously larger than that at the previous stages.(5)During the loading process,the lateral earth pressure of each pile increases with the increase of the load,and the growth rate of the central earth pressure of the pile body is larger,which indicates that the central earth pressure of the lateral double-ended confined inclined pile is very sensitive to the loading.Under the action of load,the peak value of lateral earth pressure of each pile appears at 0.37 H-0.56H,the upper and middle parts of the pile body with side-restrained inclined double-row piles are the key points of quality control.(6)The soil pressure on pile side decreases slowly before and during unloading.When unloading to 0 kN,the soil pressure on pile side decreases obviously.The value of earth pressure is not 0 when unloading to 0 kN,and the peak earth pressure is about 0.34-0.69 times of the peak earth pressure of the maximum load series,this shows that the main deformation of soil besides elastic deformation is plastic deformation,in practical engineering,surcharge should be controlled to prevent excessive plastic deformation of soil.