Experimental Study On Settlement Control Of Expansive Soil Subgrade Of High-speed Railway

Expansive soil expands when encountering water, shrinks and crazes when losing water, it performances badly on the engineering property and will seriously affect subgrade settlement. The speed of train is high, to ensure regularity of the upper track and reduce maintenance workload, the requirements of settlement after construction of subgrade are extremely stringent. To meet the requirements, road embankment or subgrade of expansive soil needs to be improved. In order to reach this goal, a series of experimental studies and calculation have been processed:1. Laboratory experiments have been done on representative samples from expansive soil region of He-ning Hige-speed Railway in this thesis. Physical and swelling property parameters such as mineral composition, liquid limit, plastic limit, frees welling ratio, cation exchange capacity are obtained. When lime is used as stabilized agent to improved the properties of expansive soil, compare physical and swelling property of expansive soil with reformative soil's, it can be seen that physical property of modified expansive soil is greatly improved, swelling property is prodigiously restrained.2. In-situ swelling force tests of subgrade have been done on the basis of different structures of roadbed and different swelling properties of subsoil. Expansion characteristic of expansive soil subgrade such as swelling force, swelling capacity are understanded, which provides gist for principle of subgrade treatment, cut replacement depth and least roadbed height.3. Methods for settlement calculation such as layerwise summation method, empirical calculation method are introduced. Final settlement can be calculated by adopting method of exponent or Asaoka, according as settlement-time curve. Settlement after construction is calculated, which includes three portions: settlement of road embankment under trainload, settlement of subgrade under trainload, residual settlement of subgrade under road embankment load. The front portions is calculated by layerwise summation method, the last portion is calculated by final settlement, the result satisfies requirement.