The effect of orientation and shape distribution of gravel on slope angles in central Taiwan

Abstract

We compare gravel orientation and slope angle distribution to highlight their possible relationship with various gravel shapes in the Ninety-Nine Peaks area in central Taiwan. In the study area, four gravel shapes—disk, equant, bladed, and roller—are collected and studied. Disk and equant shapes comprise more than 65% of the gravel. Eighty-five percent weight of gravel particles is composed of quartz sandstone. Sand particles only make up 14% of the matrix. The matrix strength ranges from 100 to 250 kg/cm 2. The slope angle ranges from 60° to 70°, and more than 50% of the study area consists of such slopes. Linear regression analysis shows that when the proportion of disk, bladed, and roller shapes in the gravel increases, the slope angle increases, although the linear relationship remains indistinct. An important inverse relationship is that as the proportion of equant shapes in the gravel increases, the slope angle clearly performs differently by decreasing. The results of the investigation also show that the slope angle is lower when the imbrication direction of the gravel is parallel to the slope surface.