A MODIFIED COLLAPSE TEST FOR GYPSEOUS SOILS

Abstract

Gypseous soil is one of soils which presents a risk for engineering structures, specially with high contamination of gypsum, because of the problem of collapse of soil under the footings, during soaking of these soils with water from any source.  There is another problem causes by leaching process and the continuous dissolution of the residual undissolved gypsum inside the soil skeleton (A. Awn 2004), which creates cavities below hydraulic structures and irrigation channels and reduce the bearing capacity of soil below these heavy structures.  It arises during the last two decades, the need for more practical and easier method to measure the collapsibility in the laboratory and field, since more than 10% of the total Iraqi area was gypseous soil and contain 15% to 70% gypsum.

During the last two decades the need was appear for constructing a new practical device to measure the collapsibility during the soaking or leaching test, which is easier than the conventional single or double odometer test (Jennings, J.E. and Knight, K. 1957), (Knight K. 1963).  This modified device which is designed and constructed locally, was effective to measuring the collapsibility at field and laboratory in addition to the ability to measure the compressibility at long time leaching for these types of problematic soil.

A model test includes a cylindrical plastic container with 45cm diameter and 500cm height open from top to fix a water control system for fixing the head of water.  An artificial gypseferous soil was prepared with (70%, 60%, 50%, 40% and 30% gypsum) was placed inside the container with 17.3kN/m3 density.  A standards circular shaft applied 100kPa stress was applied at all stages of tests.

The results of model tests and the new device used in this study shows a simple, high activity in measuring the collapsibility, in addition to the ability to measure the compressibility of such soil at leaching process, at the same time