Efficient Solutions to Reinforce Weak Soil Strata

Abstract

Abstract Site selection for Industrial / Oil & Gas plants is a complex process requiring careful consideration of numerous factors to render it technologically and economically viable. Any error committed during selection of plot will have short- and long-term ramifications in terms of cost, safety, operability etc. This paper presents the issues faced in development of pre-finalized project plots and improvements that are carried out in most effective and economical way for safe functioning of the plant. Geotechnical investigations were conducted to obtain soil characteristics at different depths of predefined bore hole locations at each of the project plot. Also ground water levels were measured at each of the bore hole location to establish the ground water level to identify the measures to be considered during design and construction. In some project plots / unit plot areas, liquefaction risks were anticipated due to presence of loose silty sand layers in the event of earthquake. This may result in differential settlement of structures and equipment supported and the same will affect the operation and long-term integrity of that unit / plant. In some other unit plots, allowable bearing pressure at proposed founding level is not adequate to support the heavy loads from equipment. Removal of these silty sand layers at varying depths (5 to 7.0m) and replacing with compacted engineering fill is one of the options, however not pursued due to time and cost. Project / unit plots were finalized based on soil properties, type of structures and anticipated loads etc., and cost benefit analysis was performed for different geotechnical solutions to identify optimal soil reinforcement solution. Due to presence of weak soil in large storage areas with liquefaction potential, soil improvement using ‘vibro-replacement’ technique was finalized to prevent excessive / differential settlement and to improve allowable bearing pressure. State-of-the-art soil stabilization technique using geo-synthetics to increase the stiffness of weak soil was employed in other project / unit areas intended to support moderately loaded facilities. Removal of loose topsoil and replacement by ‘Engineering Fill’ supplemented with adequate compaction was deemed sufficient in certain areas bearing lightly loaded facilities. By tailoring different geotechnical solutions that suits the unit / plot soil conditions, expensive soil improvements & large/raft foundation solutions were eliminated. As a result, foundation footprint and concrete quantities were optimized which resulted in substantial savings in construction cost and improvement in project schedule due to elimination of laborious activities.