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| Shear strength of the medium-high liquid limit clay in the Yellow River Flooded Areas considering the subgrade equilibrium moisture condition |
| JIANG Hongguang1，CAO Rang1，MA Xiaoyan2，ZHAO Qing1，4，YAO Zhanyong1，ZHU Shichao3，CHEN Luchuan3 |
(1. School of Qilu Transportation，Shandong University，Jinan，Shandong 250061，China；2. Road Bureau，Shandong Provincial Department of Transport，Jinan，Shandong 250002，China；3. Qilu Transportation Development Group Co.，Ltd.，Jinan，
Shandong 250101，Shandong，China；4. Shandong Provincial Communications Planning and Design Institute，
Jinan，Shandong 250031，China) |
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Abstract In order to provide a guide for design and construction of clayey soil subgrades in the Yellow River Alluvial Plain，the physical and mechanical properties of the medium-high liquid limit clay subgrade including the shear strength，the equilibrium moisture content and the long-term stability were studied. Direct shear tests under 24 conditions were performed. The relationships between the shear strength indices and compaction conditions were discussed，and the empirical formulae of the soil cohesion and the friction angle were established as functions of the moisture content and the compaction degree. Based on the 84 groups filter tests，the relationships between the saturation degree and the matric suction were obtained at different initial compaction states，and the empirical parameters of the soil-water characteristic curve equations were given according to MEPDG method and Frendlund & Xing model. The equations of the equilibrium moisture content and the corresponding shear strength of the medium-high liquid limit clay subgrade were deduced，and the critical subgrade height was proposed considering the safety factor and the equilibrium moisture content. Results show that，for the medium-high liquid limit clay mainly composed of silt particle with higher roundness in the Yellow River flooded areas，the shear strength indices is markedly influenced by the soil moisture content but that the friction angle is independent on the compaction degree. The high soil air-entry value(more than 199 kPa)，ascending with increasing the compaction degree，indicates that the soil with a high compaction degree has great water retaining capacity at high saturation state. The equilibrium moisture content is bigger by 4%–8% than the optimum moisture content，which results in a larger reduction of the shear strength. For the typical bi directional and four lane highway in the Yellow River flooded areas，the critical subgrade heights at the construction and equilibrium moisture contents are 20 m and 8 m respectively.
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2018, Vol. 37 
