Research On Working Behavior Of Slightly Inclined Pile Under Vertical Load And Of Vertical Pile Under Inclined Load

Piles may incline due to the movement of soil into the pit during pit excavation or incorrect driven sequence and hole digging sequence during pile installation. Most inclinations of piles are beyond the limitation imposed by the Technical Code for Building Pile Foundations. It is a tough problem to determine the bearing capacity of slightly inclined pile in practice.Field load-tests on inclined piles with different degrees of inclination (0.7%~ 2.4%) are performed. Based on modeling one of the load-test results, the required characteristics of soil for FEM analysis are obtained to conduct numerical analysis. Bearing capacities of totally inclined piles with different degrees of inclination (within 10%) in different soil conditions are studied. What's more, bearing capacities of partially inclined piles, inclined pile-groups and partially inclined piles due to pit excavation are also studied based on the parameters from the back analysis. The effects of dissipation of excess pore pressure on the bearing capacity of inclined piles are also considered.From the results of tests and FEM, it can be concluded that bearing capacity of slightly inclined pile does not necessarily decrease. Under the same vertical load, the settlements of inclined piles with the degree of inclination no more than 4% are even smaller than that of a plumb pile, but comparatively large bending moments will be produced. Under the same vertical load, settlements of partially inclined piles with the degree of inclination within 5% are smaller than that of plumb pile. For partially inclined pile, axial load transferred to the lower part of the partially inclined pile will produce a lateral force on it, which would lead to large contra-flexure deformation and moment in the lower part especially when the joining point is below the point of contra-flexure. As a result, inclined piles often fail due to excessive flexural deformation. Under the same procedure of consolidation, increaments of settlement and lateral displacement at pile top increase with the degree of inclination. Although the degree of inclination of pile inclined due to excavation is small (the degree of inclination 0.15%), settlement of inclined pile is larger than that of plumb pile under the same vertical load. Little increment in the degree of inclination (form 0.07% to 0.15%) will cause a large increment in the lateral displacement at pile top under the same vertical load. Large initial moment is produced in pile due to pit excavation, which is unfavorable to the bearing capacity of inclined pile.Bearing capacities of vertical piles under inclined load are also studied herein. As far as the condition concerned in this paper, there is a critical vertical load, under which the lateral deformation is reduced mostly when vertical load is applied before the lateral one. Benefits of vertical loads on reducing lateral moment at pile top mainly apprear at the late stage of lateral loading period. The weaker the soil, the greater the effect of vertical load on the lateral displacement at pile top.