ENGINEERING GEOLOGICAL PROPERTIES AND MICRO-MECHANISM OF RESIDUAL SOILS DERIVED FROM MUDSTONE IN HARARE, ZIMBABWE

From a geotechnical perspective, residual soil derived from the mudstone in Zimbabwe is often viewed as a regional problematic soil, indicating that their behavior can deviate from traditional rules of soil behavior. Thus it appears especially important to accurately assess its engineering characteristics, which can provide theoretical guidance to engineering investigation and construction. In this study, a laboratory study is conducted to investigate the physical and mechanical properties of the soils, and then the special characteristics in mechanics are explained from the aspects of mineral composition, chemical components, and microstructures. The results show that this residual soil is termed hard clayey soil with low expansibility and compaction. For undisturbed soil, it is unsaturated and possessed the high strength because of structural strength inherited from parent rock. The soil shows an aggregate structure which contains a highly orientated kaolin aggregation and many fissures according to the result of SEM. In addition, the ferrous cementing effect can result in a high strength between the aggregations, which is monitored. Because of strong water sensitivity and disintegration, the cohesion can be remarkably reduced after soaking and the internal friction angle can also be reduced under wetting and drying cycle. The high collapsible deformation is not founded. Therefore, geotechnical engineers should pay close attention to engineering disasters due to meteoric water.