The Shaking Table Experimental Study On Liquefiable Sand Soil Improved By Pile

Liquefaction of saturated sand soil during earthquake is an important subject in geotechnical engineering. Sand-gravel pile has been widely used in liquefiable ground due to its effectiveness and adaptability. At present, some knowledge about anti-liquefaction mechanism of sand-gravel pile has been acquired, but it is quite limited. The design and anti-liquefaction judgement in practical engineering mainly focus on the effect of densification, either it is too conservative or the risk of liquefaction still exists. Research related is lack of experimental data. Cement-soil pile has been widely used in soft-soil foundation. Cement-soil pile is carried out consolidating on liquefiable ground by a few practical engineering, but the design, construction and anti-liquefaction judgement of cement-soil pile has not been approved commonly. And there is little study on cement-soil pile to consolidate liquefiable ground.In this view, under the support of National Science Fund Project "The experimental study on mechanism of piles improving liquefiable soil" (No.50578104), by comparing the difference of excess pore water pressure and bearing plate settlement in non-improved soil and the soil improved with sand-gravel pile, cement-soil pile, and the two kinds of piles uniting, shaking table tests were designed and carried out to analyze the effectiveness of sand-gravel pile and cement-soil pile. The results are as follows:1. In non-improved soil, the excess pore water pressure ratio reached nearly the same value of 1.3 in all the three layers, so the entire layer liquefied. However, the excess pore water pressure ratio in the deeper layer was a little smaller than in the middle and shallow layers. Among the liquefaction levels of the three layers, the deep layer was the highest. The time of excess pore water pressure reached peak in the deeper layer was longest, so the liquefaction region firstly appeared in shallow layer, then penetrated to the deeper. At last, the entire layer liquefied.2. In the soil improved with sand-gravel pile, the excess pore water pressure in shallow layer is biggest. The excess pore water pressure ratio reached peak at 1.2,0.82 and 0.73 separately in shallow,middle and deeper layer. So the shallow layer liquefied completely, the middle layer local liquefied, the deeper layer liquefied a little. So the anti-liquefaction capacity of soil improved with sand-gravel pile had improved. Sand-gravel pile improved the dissipation of pore water in the deeper soil.3. In the soil improved with cement-soil pile, the excess pore water pressure increased with the depth of the soil. The excess pore water pressure ratio reached peak at 0.72, 0.82 and 1.03 separately in shallow,middle and deeper layer. So the shallow layer liquefied a little, the middle layer local liquefied, the deeper layer liquefied completely. The cement-soil pile improved the anti-liquefaction capacity of the middle and shallow layer a lot.4. In the soil improved with the two kinds of piles uniting, the excess pore water pressure increased with the depth of the soil. The excess pore water pressure ratio reached peak at 0.86, 0.94 and 0.89 separately in shallow,middle and deeper layer. So the entire layers liquefied, but not completely. Both the two kinds of piles played a certain role in improving the anti-liquefaction capacity of the soil.5. Judging from macroscopic view phenomenon, soil improved with sand-gravel pile had the best result. Judging from settlement amounts, soil improved with cement-soil pile had the best result.6. The cement-soil pile location had moved a bit, but the sand-gravel pile location had not moved. Just judging from the pile location, soil improved with sand-gravel pile had the best result, soil improved with two kinds of piles unite takes second place, soil improved with cement-soil pile had the worst result.7. The excess pore water pressure ratio in the soil improved with sand-gravel pile had reached 1 at the shallow layer. The excess pore water pressure ratio in the soil improved with cement-soil pile had reached 1 at the deeper layer. The excess pore water pressure ratio in the soil improved with the two kinds of piles uniting had not reached 1 at all the layer, and the settling amount of soil improved with two kinds of piles uniting takes second place. So cement-soil pile foundation is one kind of effective method to consolidate liquefaction ground.