SOIL RETENTION TESTS FOR DETERMINING DISPERSION OF CLAYEY SOILS.

The essential nature of dispersive clays was first noticed by U.S. Dams' soil scientists and agricultural engineers. Highway embankments and natural formations of high sodium dispersive clay were recorded as severely damaged by internal (tunnel) erosion of water flowing in the form of concentrated leaks within cracks. These dispersive clays, which cannot be differentiated from ordinary erosion-resistant clays by the routine civil engineering tests, erode rapidly in slow-moving (or even quiet) water by individual colloidal particles going into suspension. In Iraq, few studies were interested in such types of soils; that's why the present study takes into consideration dispersion of Baghdad clayey soil brought from three different Zones in Baghdad; the first soil is brought from Al. Kazaliyah district Zone (A), This Soil is classified as (CH) according to the Unified Soil Classification System (USCS). The second soil is brought from Al. Qadisiya District Zone (B) is classified as (CH), while the third Soil is Al. Dora region Zone (C) is classified as (CL). The conventional testing and interpretation are found to be inapplicable to analyze and identify the Dispersion soils due to the existence of Na+. The effect of water content was studied in two different tests for each soil; the pinhole test and soil retention test. The behavior of dispersive soil is not affected by water content, but water content may change the time to failure. This fact gives a good and new indicator of the maximum time to failure. [ABSTRACT FROM AUTHOR]