| SUI-YU-Railway is an important part of speedy-railway-network. Its span is 144 kilometers and it is a convenient speedy-channel between Chengdu and Chongqing. SUI-YU-Railway is a new line and it is the first time to build such a spaning-space-interval-seamless railway. The railway is used both for passenger-transportation and freight-transportation. The velocity of passenger-transportation-train and freight- transportation-train is 200 kilometers per hour and 120 kilometers per hour respectively. The foundation of SUI-YU-Railway is soft red-layer. The distinct property of red-layer is high compressibility, low bearing capacity and very small permeability. The sedimentation rate of red-layer foundation is small and the settlement is very large. In order to satisfied with the subgrade's design-criterion of the 200-kilometers-per-hour-railway some reinforcement should be done to the soft clay foundation. The DJM-pile composite foundation reinforced with geogrid is used to stabilize the clay foundation therefore. In order to study the settlement variation law of DJM-pile composite foundation, in-site measuring are done and the 3D numerical foundation model is established according to the DK10 working section of SUI-YU-Railway. All of the results is used to assess the feasibility and reliability of the stabilized technology of DJM-pile with geogrid composite foundation in red-layer area.Field observation in DK10 working section lasted one and a half years, the observation after construction is one year. The settlement of clay foundation, settlement of embankment bedding, horizontal displacement of side-slope-corner in different depths, pressures of pile-cap and soil, pore-water pressures of different depths and stress of geogrid had been measured. The beyond construction settlement after one year is 0.033～0.048m. The overall settlement is 0.051～0.053m. The designing criterion of 200-kilometers-per-hour-railroad request that settlement after construction should less than or equal to 0.15m, settlement velocity after construction should less than or equal to 4 centimeters per year. It is shown that the settlement is satisfied with the designing criterion. The stress ratio of pile to soil is 3.75. The maximum value of geogrid stress is 48.72 kilonewton per meter, which is closed to the geogrid limited tensile strength. It is feasible to use DJM-pile composite foundation to stabilize soft clay foundation.The 3D DJM-pile composite foundation model is established using FLAC3D software. The pile-soil contact surface and geogrid is taken into acount. The embankment building process and consolidation process were simulated so as to approach what is actually happening. Analysis and data contrast is done between original foundation and stabilized foundation.Data contrast is done between numerical simulation numeration results and field observation results. The foundation surface settlement distribution tendency of numerical simulation numeration results and site-monitoring results is identical. The settlement after construction of numerical simulation numeration results is very close to the site-monitoring data. According to the conclusion the 3D numerical simulation method can be used to indicate the settlement of railway foundation after construction. It can supply some references to similar projects.
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