Abstract：Research purposes： Aiming at the compactness requirement of the 200 km/h railway line for mixed passenger and freight traffic，the improvement program and quality inspection method are proposed in this paper through doing indoor experiment on the different filling materials for expansive soil, for the purpose of meeting the requirement of subgrade.
Research methods：Through studying the information and doing site experiment on filling, the researches are doing on the construction technique , quality inspection method and quality evaluation standard for subgrade compact of 200 km/h railway line for mixed passenger and freight traffic. The rational construction parameters and evaluation standard are presented through doing research on the construction techniques, including the techniques of smashing, mixing and compacting rending improved soil.
Research results：The improvement program is given for meeting the requirement of construction of the subgrade, the construction technique is presented for smashing, mixing and compacting improved expansive soil and the suitable quality inspection method is proposed for filling subgrade through making experiment, design and discussion on suitable structural mode for subgrade and prevention mode for side slope.
Research conclusions： Compared with the expansive soil, the plastic index of improved expansive soil with lime is better, the liquid-limit water content remains no change basically，the plastics-limit water content is increased and the plastic index is lowered. The best water content is increased and the max. dry density is lowered after mixing lime.
2007, Vol. 24 
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