GEOLOGICAL HAZARDS AND SOIL STABILIZATION OF WESTERN SAUDI SABKHA SOILS

Abstract

Sabkha is one of the most problematic soils along the western and eastem coasts of Saudi Arabia. Problems such as corrosion of reinforcing steel, deterioration and disintegration of concrete, low soil strength which is further reduced by wetting and some other problems associated with highways have been noticed in some locations of sabkha terrains. Therefore, it became necessary to investigate the hazards of sabkha soil and to assess the best ways and means for its improvement. -. A site reconnaissance study was conducted along the western coast of Saudi Arabia. Three diiferent types of sabkha, namely Al-Thunaib, Al-Rayyis, and Al- Qunfudhah (in the vicinity of Rabigh, Yanbu and Al-Qunfudhah cities, respectively) were selected to have clayey, sandy and silty soil types, respectively, and to represent the sabkhas in the westem region of Saudi Arabia. These three sabkhas were geomorphologically and engineering geologically investigated and mapped. The mineralogical composition of their bulk soil samples and clay fiactions were identified by X-Ray difi'raction method. The sabkha brines were chemically analyzed for their major and minor ionic constituents, electrical conductivity and the pH values. In addition, subsurface geological cross-sections, contour maps showing the variation of the groundwater table and the distribution of the prevailing ions in the sabkha brines were drawn. The potential geological hazards of the sabkha were described by considering the effect of salt concentration, depth to groundwater table and soil type on the engineering behavior of the sabkha soil. Three hazardous grade maps were prepared for the three sabkhas delineating the distribution of hazardous zones within the studied areas. _ The three types of sabkha were subjected to a soil stabilization program using Portland cement, hydrated lime and a natural pozzolan. As expected, the natural pozzolan did not improve neither soil strength nor consistency. However, Portland cement was the best stabilizer for sabkha soil improvement, while the hydrated lime gave good results only with clayey soil of Sabkhat Al-Thunaib.