| The high speed running train needs a smooth and stable foundation.The subgrade which is the foundation of track system mus maintain the designing parameters of track within a standard under the operating condition. It is prescribed definitely in《Design Code for Passenger Dedicated Railway Line Of Ballastless Track》:The value of the post-construction settlement of the subgrade is no more than 3cm. The total length of the soft soil in Tianjin line is about 60km, and there is still 15km of soft soil subgrade if bridges are adopted in many sections.Thereby, the prediction and effective control of settlement is the key point of designing and construction of high speed railway subgrade.Based on on-site test of soft soil foundation reinforced by rigid pile on jing-jin high speed railway, the compression test, triaxial test, isotropic compression test of 12 layers of on-site soil under typical section is done.The settlement development of typical section is analysed by ABAQUS, and according to modulus of compressibility Es and e-p curves, the ultimate settlement of ground is predicted using the methods of equivalent layerwise summation, Mindlin and modulus of composite foundation.According to the results of nonlinear finite element analysis, the post-construction settlement of foundation of high speed railway that the composite-foundation of rigid pile and surcharge preloading is used is satisfied with《Design Code》.Based on the three types of connection between cap(foundation) and pile top,i.e.the first type is pile top being in contact with cap,the second is the pile top being separated from foundation by a layer sand or gravel cushion, and the third is the cushion block between foundation and pile top.At last, a discussion is made on the effect of thickness and modulous of cushion block between pile cap and pile on the development of settlement and pore pressure solution, stress ratio of pile and soil, penetration deformation of pile end behivour.
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