Effect of Coconut Shell Ash on Pore Water Pressure Changes in Sand

Abstract

Previous studies showed that the addition of coconut shell ash (CSA) to soil improved the California Bearing Ratio, Maximum Dry Density, and Unconfined Compressive Strength. But the effect of CSA in decreasing soil susceptibility to static liquefaction has yet to be investigated. Static liquefaction is a major concern because it is defined as when soil loses its strength and behaves like a fluid. This causes settlements, damages buildings, and endangers lives. The loss in soil strength is attributed to the increase in pore water pressure. Pore water pressure buildup is more likely to happen in loose and saturated sands. This study hypothesizes that the particle size and the chemical property of CSA can reduce the liquefaction susceptibility of sands by decreasing pore water pressure buildup when the sand is subjected to vertical loads. For the experiment, the consolidated undrained (CU) triaxial test was conducted. The Cam-Clay model was used to analyze soil behavior between the control samples and the samples mixed with CSA. Results show that administering 5 % CSA expanded the soil's yield surface, improving soil's ability to respond elastically to deformations. Five percent CSA decreased pore water pressure buildup in the samples subjected to 50 kPa and 100 kPa consolidating pressures by 6.53 % and 5.55 %, respectively. However, for the sample subjected to 25 kPa consolidating pressure, 5 % CSA caused an adverse effect by increasing pore water pressure buildup by 10.73 %. The low consolidating pressure negates the effect of CSA and there should be a sufficiently high consolidating pressure to decrease pore water pressure buildup.