Abstract
In order to study the effects of the microstructure parameters of cement modified subgrade silty soil (CMSS) in a frozen area under freeze-thaw (F-T) cycles on the macroscopic mechanical properties, the static triaxial test, scanning electron microscopy (SEM), and grey relation analysis (GRA) were implemented on silty soil modified with 0% and 2% cement at optimum moisture content from the northwest in Jilin Province in China. The results showed that the shear strength, the cohesion of 0% and 2% CMSS, decreased with the increase of F-T cycles, while the internal friction angle was not obviously changed. The shear strength and its parameters of 2% CMSS doubled compared to that of 0% CMSS. The micro-parameters, representing the particle morphological characteristics, particle arrangement, and pore characteristics of CMSS, changed differently under F-T cycles. If the cement was not added, the cohesion and the internal friction angle were most sensitive to the average particle diameter (Dp) and the average particle abundance (C), respectively. When the cement content was 2%, the cohesion was chiefly affected by the particle size fractal dimension (Dps), while the internal friction angle was mainly related to the average pore diameter (Dh). The main principle of cement improvement was to decrease Dh of soil under F-T cycles.
Highlights
The area of the Chinese territory covered by frozen soil is the third largest in the world, of which the seasonally frozen area is 5.137 × 106 km2, accounting for 53.5% of the country’s land area [1,2], widely distributed in the northeast and northwest
The subgrade material in the seasonally frozen area filled with silty soil has the problems of large settlement deformation and difficult compaction, so it is necessary to modify it before using as the subgrade material [5,6,7,8,9]
The macroscopic mechanical properties of unmodified and cement modified silty soil under F-T were studied by a static triaxial test; the microstructure images of those under the same conditions were obtained by scanning electron microscopy (SEM)
Summary
The area of the Chinese territory covered by frozen soil is the third largest in the world, of which the seasonally frozen area is 5.137 × 106 km , accounting for 53.5% of the country’s land area [1,2], widely distributed in the northeast and northwest. The silty soil as a widely distributed subgrade material in the northeast of China is exposed to at least one freeze-thaw (F-T) cycle each year Because it has low natural moisture content, a small plasticity index, and weak shear strength, these make it sensitive to frost heave and water stabilities [3,4]. A laboratory study about the behavior of Brasilia subgrade lateritic soil showed that the pore size distribution was a bimodal curve and changed with the compression, which indicated that the microstructure was strongly related to the mechanical behavior [23]. The macroscopic mechanical properties of unmodified and cement modified silty soil under F-T were studied by a static triaxial test; the microstructure images of those under the same conditions were obtained by SEM. The microscopic mechanism of the macroscopic mechanical properties of the cement modified silty soil was revealed with the grey relation analysis (GRA), which would provide reliable reference data for cement modified subgrade silty soil (CMSS) in seasonally frozen areas
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