Test Research Of Composite Pile Foundation Bearing Capacity And Performance In Q₂Lishi Loess Area

With the rapid development of social economy,more and more high buildings and ultra-high buildings have sprung up from the motherland, but at the same time, the foundation has always acted as the root. Pile foundation,with high bearing capacity and small differential settlement, have been widely applied in high-speed railway, highway, large bridge, the construction of the foundation of civil buildings and ultra-high buildings. The basic solution has always been a difficulty in the construction of super-high buildings in Longdong large thickness of loess. Therefore, the author combined the super-high building projects in the south circle of Gansu province Qingyang city xifeng district.According to the engineering geological conditions in the region and the research results of the super-tall buildings form of the basis all over the world, the author puts forward the long composite friction pile foundation as the foundation in Q2lishi large thickness loess region. At the same time, the author used a series of capacity tests to proof his thought.The capacity tests contain a lot,such as natural foundation loading plate test, the bearing capacity of single pile vertical compressive test and the composite pile vertical compressive bearing capacity. At the same time, the author arranged a lot of concrete strain gauges and reinforcement stress meters in the body of the pile and the soil pressure boxes in the pile bottom and the bottom of the pile caps within the test. Through the data measured by these sensors,the author studied the feasibility of the foundation scheme and made certain discussion of the behaviors of single pile under vertical load. The capacity characteristic of the large diameter long friction pile and the composite pile foundation, their axial force of pile and pile side friction distribution are also studied in the test.Through the contrast analysis of single pile and single pile-cap’s vertical compressive bearing capacity and the Q-s curve,the author found that there is a transition load in the single pile and single pile-caps test.Through the constrast of the pile side friction’s distribution form along the pile in the tests of the single pile and composite pile test,the author concluded that the pile side friction values measured in the experiment is bigger than standard value, and under the action of a single pile caps, the shaft friction peak points in the distribution of the pile side friction are more than in the single pile test and the maximum peak point along the pile shaft down. At the same time,through some research on the develop degree of the pile side friction, the author think that with the increase of load, the pile side friction in the same section decreases. Through the pressure box under the bottom of the pile caps,the author analysed the stress distribution along the pile center distance form and drew coefficient variation curve of pile caps with the change of the vertical load in the experiment, analysed the differences in range and relevant specification. The conclusion of the test can provide theoretical basis for the pile foundation design in the similar loess areas in the future.