Response of Soft Soil Mixing with Recycled Gypsum (Plasterboard) as Stabilized Agent for Soil underneath oil tank as a case study

Abstract

Soil stability plays a vital rule in projects’ infrastructure such as embankment, retaining walls dams and highway. Structure built on soft soil may experience uncontrollable settlement and critical bearing capacity. This may not meet the design requirements for the geotechnical engineers. Soil stabilization is a process to change such undesirable properties in order to meet the requirements. The main objective of this study is to evaluate the use of recycled gypsum, which is derived from gypsum waste plasterboard, as a stabilized agent for soft clay. Twenty eight experimental tests have been conducted to improve a soil brought from a site in Basra (Garma Ali/south of Iraq) using four different recycled gypsum percentage varying from 0 to 15%. The properties which have been studied are grain size distribution, Atterberg limits, unconfined compressive strength, and compressibility. The results indicate that as the gypsum contents increase, the liquid limit decreases up to gypsum content of 3% and then increases. The plastic limit has been decrease up to 7 % of the gypsum content and then increases. Furthermore, the maximum dry density decreases while the optimum moisture content is increased as the percentage of gypsum content has increased. The compression index (Cc) has increased as the gypsum content increases while the swelling index has increased up to 5% then it has decreased. The unconfined compressive strength has increased by adding recycled gypsum up to 5% while it is reduced as the percentages of gypsum has increased beyond 5%. Adding 5% of recycled gypsum raise the bearing capacity to approximately 167% compared with the bearing capacity of untreated one.