Model Test And Analysis Of The Engineering Characteristics Of The Pile Composite Foundation Under The Condition Of Lateral Unloading

As a new form of foundation, relying on its advantages and characteristics, composite foundation is more and more widely used in the modern engineering construction.Composite foundation share the load by the piles and the soil between piles, this makes the bearing and deformation capacity of composite foundation has a natural advantage.The study of composite foundation is mostly about vertical work character under the condition of no buried deep.So the design of combined pile composite foundation is just based on the vertical work character, and do not consider of lateral impact for excavation of foundation pit in the future.But in the construction of modern city, more and more engineering need to excavate foundation pits near the existing buildings.In this paper, through the indoor model test, Studying the properties of the combined pile group composite foundation's work under the condition of vertical load and lateral unloading. Granite residual soil as model soil and with cement mortar made of two kinds of length square pile.The dial indicator is measured to the vertical displacement and horizontal displacement of the foundation;Pasting strain gauge in the pile body grooves for measuring the points of strain values of pile body, to calculate the axial force and bending moment of pile.The main conclusions are as follows:(1) In the process of lateral unloading of composite foundation, pile and soil will produce vertical displacement.When the excavation to the short pile bottom, the displacement is larger.(2)In the process of lateral unloading of composite foundation, pile body will occur horizontal displacement in the direction of foundation pit, and with the foundation pit excavation, horizontal displacement will increase. Short pile top displacement is greater than the displacement of long pile top, and the horizontal displacement of pile in the front row is larger than the pile in the back row.When the excavation to the short pile bottom, the horizontal displacement value added is great.(3)When excavation to short pile bottom, deformation of the foundation is very large.It indicates that the foundation has been damaged at this point.Soil can be considered as the destructive first, then case the pile body damage.Finally it would lead to the foundation damage in an all-round way.(4)With the lateral unloading, the vertical stress of piles and soil for the composite foundation changes,and the internal force of the pile body changes,the bending moment of the pile occur.