Shallow Foundations in a Coastal Desert Setting: Problems, Challenges, and Arrival at Appropriate Recommendations

The near surface, highly weathered limestones of the state of Qatar have complex lithologies attributable, mainly, to post depositional changes that have altered some relatively hard rocks into soils and some carbonate soils into a rock matrix. The matrix, often clayey, sometimes cemented (with gypsum, anhydrite, and/or calcite grains) is not a rock nor could be considered as a soil per se. These "altered" deposits are: (i) difficult to sample in the undisturbed state, (ii) extremely variable in composition and properties, and (iii) are susceptible to degradation, particularly when wet. The paper presents typical geotechnical information from three selected sites where these deposits (diagenetic limestone) have been encountered. Plate load test data, carried out to predict settlements, are shown. Arrival at appropriate foundation geometries and allowable bearing capacity values, consistent with field conditions, are noted. For the present, design of shallow foundations in Qatar and nearby areas has remained largely empirical and dependent upon site-specific information aided by: judgment, local experience, and plate load test results.