Development and Application of a New-Type Apparatus for Ko Test of Soil

Most of the existing methods that are used to measure the coefficient of earth pressure at rest (K-o) are not suitable for coarse granular soil because of the rubber membrane; therefore, an apparatus to measure the K-o of coarse-grained soil should be developed. The aim of this article is to introduce a new-type apparatus for measuring the K-o of coarse granular soil. A method for correcting the effect of the side wall friction is proposed to ensure test accuracy. To compare it with the conventional water-bag type K-o oedometer, tests on a dry sand using both the new apparatus and the conventional K-o oedometer were performed. Results proved that the newly developed apparatus is more accurate than the water-bag type K-o oedometer. Of importance, some tests of coarse granular soils were taken for application of the apparatus. The results show that the K-o of the coarse granular soil is almost a constant value during the loading steps but changes greatly during the unloading steps. In addition, an equation is proposed to predict K-o changing with the overconsolidation ratio during unloading. The K-o of coarse granular soil decreases when the density increases, and the influence of the gradation on K-o is evident.