Effect of Nondurable Material on Settlement of Embankments

Sedimentary rock fragments are used to build embankments. The fragments are made of durable and nondurable rocks. Durable rocks are defined as those that do not slake in the presence of water. In embankments, nondurable rock fragments are subjected to (a) compressive contact forces induced by other fragments and (b) slaking when they come into contact with water. These two processes convert the nondurable rock fragments into soil that moves into the space between the durable rock fragments, causing the settlement of the embankment. The goal of the present study was to calculate the amount of settlement experienced by a mixture of nondurable shale and durable limestone fragments when it is subjected to embankment loads. To this end, mixtures of the shale and limestone were placed in a metallic cylinder and subjected to three constant pressures. The settlement of the mixtures was measured at pressures equal to 345, 690, and 1,380 kPa. The settlements were measured first when the mixtures were dry. Then the mixtures were flooded with water, and the new settlements were recorded. The amount of settlement varied with the percentage by weight of the shale in the mixtures. The greatest settlements were recorded in the mixtures made of 100% shale. Small settlements were recorded when the mixtures were dry. Settlement was the result of the crushing and slaking of the shale fragments.