Anti-Liquefaction Analysis Of Deep Mixing Cement Pile's Composite Foundation

The newly-build Kunming-Hekou railway of total length 380km,from Kunming, Yunnan Province to Hekou of the Sino-Vietnam frontier, is the trunk railway that connect China and Vietnam. It is significant to build Kun-He railway, which can alleviate the serious nervous situation for a long time of transportation of the existing narrow gauge track railway of our country, form the network planning of the medium and long-term railway, and promote economic and social development of our country. There is large-area saturated silty-fine sand ground along the Kunming-Hekou railway. Most of these areas are located in 8 degree earthquake region, and the ground is liquefiable with the acting of earthquake load. The liquefaction,the lateral flow of the liquefiable ground,and the embankment settlement generated by embankment damage are the main reason for the damage railway. So we must clearly know the earthquake liquefaction mechanism of saturated silty-fine sand ground; and we can quantitative assessment the influence of earthquake liquefaction for the railway subgrade. And building one or more economic and appropriate earthquake-resistance reinforcement method is very necessary and urgent.The deep mixing pile is the mixture of the soil and the curing agent (such as cement or cement powder, lime powder, adding a certain amount of admixture agent), which is mixed by using deep mixer in suit, along the depth direction. The composite foundation reinforced by the deep mixing pile can improve the bearing capacity of the foundation, ameliorate the properties of the foundation's settlement, reduce the settlement and the uneven settlement caused by the loads. The curing agents of the deep mixing pile have many kinds, including cement, lime, flyash, asphaltum, slurry, chemical materials, and so on. But cement is usually used, because of the facilitate of getting, the wide scope of the soil formers, the higher intensity and the better stability after being reinforced, and so on.The passage is in the background of liquefaction of saturated sand in Kunming-Hekou railway. According to the Kun-He Railway DK25+800 working section, the model of consolidating liquefied sand with deep mixing pile is build on FLAC3D software. Numerical results with and without deep mixing pile improvement were then compared to illustrate the improvement effect of deep mixing pile on high liquefaction potential sandy atratum.The analysis was conducted incorporated with dynamic pore pressure and effective stress calculation and fluid flow modeling. The development rule of pore pressure, the settlement and the lateral displacement of the ground were discussed in different seismic accelerations. Numerical results with and without deep mixing pile improvement were then compared to illustrate the improvement effect of deep mixing pile on high liquefaction potential sandy soil layer.