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Development and Application of a New-Type Apparatus for K0 Test of Soil

Most of the existing methods that are used to measure the coefficient of earth pressure at rest (K0) are not suitable for coarse granular soil because of the rubber membrane; therefore, an apparatus to measure the K0 of coarse-grained soil should be developed. The aim of this article is to introduce a new-type apparatus for measuring the K0 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 K0 oedometer, tests on a dry sand using both the new apparatus and the conventional K0 oedometer were performed. Results proved that the newly developed apparatus is more accurate than the water-bag type K0 oedometer. Of importance, some tests of coarse granular soils were taken for application of the apparatus. The results show that the K0 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 K0 changing with the overconsolidation ratio during unloading. The K0 of coarse granular soil decreases when the density increases, and the influence of the gradation on K0 is evident.