An Alternative Method for Internal Stability Prediction of Gravelly Soil

Abstract

Experimental observations have shown that geometric characteristics of the soil have significant impact on the internal stability. Due to the diversity of grain composition, the degree of correlation between geometric control variables and internal stability for different types of soil may not be the same. Based on the statistical information of 140 different soils collected from the literature, an alternative method is proposed to assess the internal stability of gravelly soil with the maximum grain size reaching 60 mm. According to the values of d90, all the 140 soils are first classified into three clusters through hierarchical clustering method. Average values of d90 for cluster I, II and III are 8.16 mm, 58.66 mm and 152.33 mm, respectively. Then, the experimental results are taken as dichotomous variable (0 refers to internally unstable and 1 refers to internally stable). Point-biserial correlation coefficient is introduced to measure the correlation between geometric control variables and internal stability of the soils. The results show that Cu (coefficient of uniformity) and (d15c/d85f)max of cluster II present the highest degree of correlation with internal stability of soils among the three clusters. Therefore, an assessing method is suggested which unites two control variables (Cu and (d15c/d85f)max) to identify the internal stability of gravelly soil, and the boundary of the method is proposed as well. At last, laboratory tests are carried out to assess the internal stability of 8 gravelly soil samples which were gathered locally. The proposed method, together with five commonly used criteria, is used for the prediction of internal stability. By comparing the predictive results with the test results, the reliability of the suggested method is verified.