Journal of Jilin University(Earth Science Edition) ›› 2023, Vol. 53 ›› Issue (4): 1163-1163.doi: 10.13278/j.cnki.jjuese.20220011

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Characteristics and Mechanism of Shear Strength Variation with Time of Cohesive Soil Layers in Chongming Dongtan Reclamation Area

Wang Qing1, Lü Zuojun1, Yao Meng1, Dong Jiaqi1, Xia Weitong1, Yang Tianliang2, Niu Cencen1   

  1. 1. College of Construction Engineering, Jilin University, Changchun 130026, China
    2. Shanghai Institute of Geological Survey/Key Laboratory of Land Subsidence Monitoring and Prevention, Ministry of Natural 
    Resources, Shanghai 200072, China
  • Received:2022-01-08 Online:2023-07-26 Published:2023-08-10
  • Supported by:
    the National Natural Science Foundation of China (41820104001), the Entrusted Project of Key Laboratory of Land Subsidence Monitoring and Prevention of the Ministry of Natural Resources (2020(D)-011(F)-03，2021(D)-004(F)-01) and the International Geoscience Program (IGCP663)

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Abstract: Abstract： To carry out engineering geological evaluation of hydraulic reclamation areas such as Chongming Dongtan, this paper aims at the change in shear strength of the underlying clayey soil layers in Chongming Dongtan. Considering different reclamation times, soil samples from boreholes in five different reclamation areas (within the 1949 cofferdam, 1949-1964, 1964-1976, 1976-1990, and 1990-1998) were selected for direct shear tests, and the variation of shear strength of soils in different periods and layers were analyzed.  Moreover, the microstructure of the soil samples was observed by scanning electron microscopy, and the change in shear strength was analyzed qualitatively and quantitatively from a microscopic perspective. The results revealed that: 1) The shear strength of the clayey layer varied as， the clay layer in the 1949-1964 reclamation zone had the largestshear strength, and the peak shear stress at 50, 100, 200, and 300 kPa is 33.31, 46.68, 102.10 and 147.15 kPa, respectively. Little difference in shear strength between boreholes in silty clay layer was observed under various levels of vertical pressure. From west to east, the shear strength indexes of the clay layer showed an opposite trend to that of the silty clay layer, in relation to the trend in natural water content. 2) From west to east, significant changes in the microstructure of the soil samples were observed. The soil microstructure in clay layer changed from a flocculent/aggregate to a matrix structure， and the soil microstructure in silty clay layer gradually transitioned from a skeletal/aggregate structure to a matrix structure and to a flocculent/aggregate structure. 3)  The average pore diameter of the particle was negatively related to the cohesion and positively related to internal friction angle. In addition, the average shape coefficient of the particle was positively related to the cohesion and negatively related to internal friction angle. This indicated that average pore diameter  and the average shape coefficient of the particles were directly related to the shear strength indexes of the soil.

Key words: Chongming Dongtan, reclamation area, cohesive soil, shear strength, mechanism analysis

CLC Number: 

  • P642.13
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