COMPRESSION CHARACTERISTICS OF DOUBLE-LAYER SOFT CLAY FOUNDATION UNDER DIFFERENT LOADING MODES

The upper soft and lower hard double-layer soft clay foundation in reclamation land of costal area in Tianjin has complicated physical properties and engineering characteristics. Its deformation characteristics are different under different loading modes. This phenomenon can result in large post-construction settlement and uneven settlement in engineering practice. It can further lead to many engineering problems such as economic losses and even casualties. At present,most of the recent studies focus on the upper hard and lower soft double-layer soft clay foundation under constant loading mode. However,non-negligible settlement can happen due to some foundation under repeated loading. So far,the consolidation deformation mechanism of the double-layer soft clay foundation under different loading modes is deficient. The theoretical research lags far behind the engineering practice,which restricts the development of economic construction in relevant area. Therefore,it is particularly significant to study the deformation characteristics of double-layer soft clay foundation. This paper conducts one-dimensional consolidation test and Scanning Electron Microscope(SEM)test on the double-layer soft clay foundation in reclamation land,and then obtained compression characteristics and microcosmic mechanism of the soil sample. Applying one-dimensional consolidation test,this paper studies the deformation differences of double-layer soft clay foundation under repeated loading mode and constant loading mode. Furthermore,it discusses the micro-deformation mechanism of double-layer soft clay foundation under different loading modes based on the SEM test. The experimental results provide theoretical basis to establish deformation model and predict long-term settlement of the double-layer soft clay foundation. The results show the follows:(1)Under repeated loading mode,the compression coefficient and consolidation coefficient of double-layer soft clay foundation decrease obviously at the initial stage and then slowly decrease until stable. (2)Under different loading modes,the variation tendencies of compression coefficient and consolidation coefficient of the soil sample are different. (3)Compared with repeated loading mode,the initial value of compression coefficient is higher while the value of consolidation coefficient is lower under constant loading mode,and the variable quantity ranges from 30% to 45%. (4)When the loading grade is invariable,the settlement of double-layer soft clay foundation caused by repeated loading exceeds 30% to 45% than that caused by constant loading. (5)Moreover,increasing loading grades squeezes and reduces soil internal macropore,and can improve the roundness,orientation and the degree of homogenization of pores. Comparably,the repeated loading mode has the same effect on soil internal pores' roundness,orientation,and internal structure,which has relatively poor orderliness.