Preloading for reduction of compressibility characteristics of sabkha soil profiles

Abstract

Sabkha soils are coastal and inland salt flat deposits of arid climates, which invariably contain an appreciable amount of organic materials. They are, therefore, characterized by being highly compressible with a significant part of the settlement taking place as secondary compressions. In this study, the applicability of a preloading technique in improving the compressibility characteristics of sabkha sediments was investigated through construction of an instrumented test embankment on a typical sabkha formation from the southwest coast of Saudi Arabia. Settlement and pore pressure measurements were taken for an observation period lasting 1 year. Compressibility parameters were determined in the laboratory from extensive standard and long-term consolidation tests on undisturbed samples taken from the site before and after the preloading process. The laboratory test results substantiated by the relatively large settlements measured under the test embankment indicate that the precompression method is an effective technique that can eliminate the primary consolidation settlements and reduce the secondary compressions of sabkha sediments. The field behavior was predicted utilizing the conventional theory of consolidation and the finite element method. Using laboratory-determined compressibility parameters, the one-dimensional theory of consolidation highly overestimated the measured settlements and significantly underestimated the observed settlement-time behavior. However, close agreement between observed and predicted behavior was obtained when field parameters were used in the analyses. Although substantially overestimating the time required for completion of primary settlements, the finite element predictions of the magnitude and the rate of settlements are considered satisfactory.