Landslide is a typical natural disaster around the world. Factors such as slope material, intensity and duration of rainfall, earthquakes and loadings, infiltration and seepage conditions strongly influence the stability of slope because of the decrease in resistance forces or the increase of driving force. A lot of methods for increasing slope stability are already developed nowadays. This research using C-RHA columns for slope strengthening. C-RHA mortar was made of cement, sand and microsilica from fine rice husk ash (RHA). Replacement 10 % of the weight of cement by RHA would increase the strength of the column.
The effect of C-RHA columns on slope stability simulated by a series of centrifuge modeling tests which were conducted at the Experimental Center of Civil Engineering, Department of Civil Engineering, National Central University. The slope is prepared by moist tamping method at optimum water content about 12 % with a mixture material consist of 20 % of the fine content (kaolinite) and 80 % of quartz sand. The C-RHA columns were penetrated perpendicular to the slope surface. During the test, the acceleration was gradually increased until the slope failed. The process of the failure was recorded through cameras during centrifuge spinning. Cameras and laser displacement scanner record the failure process, slope deformation and ground surface change.
The decreasing spacing of C-RHA column increases the safety factor of the slope. The test results show that when the spacing between the C-RHA columns is reduced, the timing of the cracks at the top of the slope can be delayed, and the location of the cracks will be far away from the top of the slope, which will delay the timing of the slope failure. In this case delay means reaching higher g level. The first crack of the slope without column occurs at 40 g, the crack depth is about 0.33h, the second crack occurs at 45 g, and the damage occurs at the 50 g. When the spacing of the slope is 6.7d, 5d and 4d, the first crack of the slope occurs at 40 g, 45 g and 55 g, respectively, and the crack depth is 0.30h, 0.33h times and 0.56h. The second crack occurred at 43 g, 49 g, and 65 g, and fail at 48 g, 55 g, and 65 g. From the side view of the slope, the decreasing number of C-RHA column spacing will decrease the depletion mass of slope, which is the volume of displaced soil that overlies the failure surface but underlies the original ground surface. The depletions mass normalized by the volume of theoretical planar failure wedge with failure angle of θ=(β+?)/2 are 67.0 %, 64.5 %, 59.3 % and 48.6 %, respectively.
Keywords: C-RHA, Centrifuge modeling, Slope Stability
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