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P.V. Jayakrishnan, Marwan Halasa, Moreno Scotto, Pietro Pezzano
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Innovative and cost-effective method of road embankment foundation design using basal reinforcement technique for Duqm roads project in Oman (Paper 925)

The Duqm area in the Central Eastern Oman is located 600km south west of Muscat, the capital city of Sultanate of Oman. Extensive developmental projects like sea port, airport, dry dock, oil refinery, crude oil storage terminals, infrastructure like roads, railway, bridges, factories, buildings and residential villas etc. are under construction or on the anvil. The Duqm area is marked by the extensive presence of ‘soft sabkha’ soil which drastically influences the construction of foundations for civil engineering structures in that area.

Generally, soil having low undrained shear strength is often referred as ‘soft soil’.  Construction of embankments on soft soil can be critical because they have low strength and high compressibility. Since such soils have low permeability, the failure happens at an undrained condition within a short period after the embankment construction. ‘Sabkha’ is an Arabic expression to describe a type of soft soil with high salt content and are characterized by low bearing capacity and low SPT values. Sabkha soils are widely distributed in the Arabian Peninsula. Generally, for sabkha soil having SPT value less than 5 in muddy conditions, the first and foremost conventional solution of ground improvement adopted by designers for road projects in the Middle East region is provision of stone columns below the road embankment for total depth of soft soil.  

High strength geosynthetic layers can be used as basal reinforcement for the construction of embankments over soft soils, satisfying the stability criteria laid by the international standards like BS 8006: 2016. Unidirectional high tensile strength geogrids like Paralink™ is well suited for basal reinforcement applications in Sabkha soil. Depending on the type and magnitude of expected settlement of foundation sabkha soil, this technique can be adopted replacing the conventional deep ground improvement solutions, for majority of the cases.

            Through the case reference of basal reinforcement technique application for Duqm roads project in Oman, this paper briefly outlines the problems associated with the design and construction of embankments over soft sabkha soil commonly found in the Arabian Peninsula and the application of geosynthetic materials as basal reinforcement for stabilizing such embankments, avoiding time consuming and expensive deep ground improvement techniques generally adopted by the road designers.

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