Study of cracks and fissures phenomenon in Central Saudi Arabia by applying geotechnical and geophysical techniques

Abstract

This paper presents an approach to investigate the phenomenon of faults and cracks that appeared in the earth’s crust surface in Al-Qassim region, Saudi Arabia. Geophysical and geotechnical methods were used together in order to evaluate these cracks and identify the reasons that led to the emergence of such phenomenon. This type of faults and cracks can normally occur due to a geological or physical event or due to the nature and properties of the subsurface material. It was intended to use two different techniques at a time, compare, and integrate the outcome of the results. The geotechnical works included advancing rotary boreholes to depths of 25 to 31 m with sampling and testing. The geophysical method used included performing 2D electrical resistivity lines. The results of geophysical and geotechnical tests showed good agreement. The use of 2D electrical resistivity was found useful to establish the layer thicknesses of shale and highly plastic clay. This cannot be determined without deep and expensive direct boring investigation or other sophisticated methods. The results showed that the ground cracks and faults were mainly caused due to the nature of the soil in the area, which is considered as a high-risk soil type and classified within expansive soil groups. The subsurface formation contained excessive fines with high percentage of highly plastic clay materials. The volume changes due to humidity variations can result in either swelling or shrinking. These changes can have significant impact on engineering structures such as light buildings and roads. The possible mechanism of cracks formation is explained.