Study On The Shaking Table Test Of Liquefiable Sand Foundation Reinforced By Composite Pile Under Vertical Load

Sand liquefaction reinforced is an issue that geotechnical of world countries have been not stop exploring. Because frequent occurrence of earthquakes caused by the soil liquefaction, not only arised in unreinforced soil, but also soil liquefaction reinforced frequently produces problems, causing tremendous damage to property, so study on the sand liquefaction reinforcement is particularly important. Gravel pile reinforcing liquefiable sand soil can eliminate liquefaction, steel pile reinforcing liquefiable sand soil in order to improve the bearing capacity of foundation, has been done a lot of research. However, research in steel pipe and gravel pile composite reinforcement liquefiable sand soil, especially the vertical load applied to study the characteristics of steel pipe and gravel pile composite foundation reinforcement has little, which need do a lot of in-depth researches. Therefore, further exploring the effects of soil liquefaction and liquefaction features by composite piles reinforcement under vertical loads and pile settlement have some practical significance. The thesis is supported by National Natural Science Foundation of China (No.50578104)"The experimental study on mechanism of piles improving liquefiable soil" and Shanxi Province Key Laboratory projects of Loess area highway construction and maintenance technology transport sector (Contract Number KLTLR-Y13-3)"The experimental study on pile foundation of liquefied soil", mainly study on shaking table tests of steel pipe pile and gravel pile composite reinforcement model under different vertical loads, observating macroscopic phenomena of composite pile foundation under appling Okg,0.5kg,1kg,1.5kg,2kg and2.5kg load,recording experimental data, drawing time-history curves of excess pore water pressure and earth pressure in different depths and the pile settlement, synthetically analyzing the peak of excess pore water pressure and soil pressure and the change trend of differential settlement and obtaining the following conclusions:(1) Macroscopic phenomena of steel pipe and gravel pile composite foundation reinforcement under different loads shows that after the end of vibration, the surface of the soil model box gather a lot of water, indicating that gravel pile plays a role in drainage significantly, and as the water is discharged, pore water pressure is dissipated. The trends of excess pore water pressure in different depths rise rapidly firstly, then slowly decline after reaching a peak, Analysis on different decreases show that pore water pressure is dissipated beginning from shallow, gradually spread downward, and as the increase of the depth, soil liquefaction is becoming difficult. (2) The parabolic curve along the depth of the earth pressure of composite pile reinforced soil under different loads shows a variation of the opening to the left, and the earth pressure value in the middle is greater than that in the shallow and in the deep. The middle of pile is prone to damage and break. Therefore, it reminds people should pay special attention to protecting the middle of composite foundation pile of buildings.(3) The time-history curve of settlement of the pile shows the greater load and the larger settlement, and applied load from0.5kg to1kg, settlement produces mutation. As the load continues to increase, the settlement increases rapidly, and at this time, the constraints of soil on the pile has not been obvious.(4) Comparing excess pore water pressure with subsidence curve, before excess pore water pressure is not reach the peak, the soil has not yet been liquefaction, subsidence curve rise gently, and the bearing capacity of piles is still apparent; after the peak, the soil locally emergences liquefaction, the constraints of soil on the pile decrease, the settlement increase quickly, the pile subsides suddenly, and the bearing capacity has ceased to exist.In summary, the change of excess pore water pressure of steel pipe piles and gravel pile composite foundation reinforcement model under vibration loads can determine the extent of liquefaction of sand; earth pressure variations along the depth can be judged the part of the pile damage; settlement, as an important indicator of building design can be used to control ranges of the allowable bearing capacity, so study on the three indicators that pore water pressure and soil pressure and the settlement have far-reaching significance in determining different liquefaction foundation site and controlling the bearing capacity of buildings in different loads in actual projects.