| Summary: | 碩士 === 中原大學 === 土木工程研究所 === 101 === Soft soil has high water content, high compressibility, low strength, and poor permeability, if soft soil is not improvement, building load will produce a subsidence hazard. Surcharging methods are often used to improve the soft clay layer, and it can avoid uneven settlement. Previous research is mainly about pure unloading. However, in reality it include repeating loading and unloading.
To explore the effects of different stress history on secondary compression of soft soil, in this study, six soil samples were re-mixed and poured into a medium-sized one-dimensional consolidation cell to produce homogeneous soil specimens. Three different surcharging operations with surcharge ratios of 0.125 and 0.25 where designed. The three surcharging operation included removing surcharge only, removing surcharge to 27.4kPa and then reloading back to final pressure, and unloading without surcharge 27.4kPa and then reloading back to final pressure. The slope of secondary compression curve, strain rate, change of void ratio are analyzed.
According the test results, the slope of secondary compression curve from the test of removing surcharge only is about 0.001~ 0.121mm and the void ratio change amount of tp-10tp is about 0.001~0.023, this is the lowest among these three operations. The results of the other two operations with unloading to 27.4kPa, the slope of secondary compression curve with surcharge is about 0.017~0.168mm and the void ratio change amount of tp-10tp is about 0.001~0.023, and the slope of secondary compression curve without surcharge is about 0.028~0.223mm and the void ratio change amount of tp-10tp is about 0.002~0.046. The slope of the secondary compression curve of traditional one-dimensional consolidation test is about 0.029~0.283mm and is greater than those from the other three operations, means that surcharging with different loading history can effectively reduce the magnitude of secondary compression settlement amount.
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