A Case Study of Assessing the Accuracy of Secondary Consolidation Prediction Using Qualitative Approach

Abstract

Infrastructure constructed, especially over soft organic soil layers, can be subjected to excessive settlement within its life cycle due to the complex behaviour of the soft soil with time. However, with necessary actions prior to construction, the impacts from such soil layers can be mitigated to some extent. The case under consideration is a leisure resort in Matara, a 15-storey hotel resting on a raft foundation near the southern coastal line of Sri Lanka. With time, some cracks have formed within the building, and an investigation was done to identify the cause for the crack formation. It has been determined that cracks have appeared due to the excessive settlement of the subsurface. Furthermore, ground investigation results suggest that a peat layer is beneath the building within a depth of 15-24m. As per the survey report on the settlement of the building, secondary consolidation of the soft soil significantly impacts the excessive settlement. Therefore, three methods were used to predict the secondary consolidation settlement of the peat layer beneath the building. The methods are prediction using empirical correlations, laboratory experiment results that will follow the constant coefficient of secondary consolidation throughout time and the qualitative method, which assumes that the secondary consolidation coefficient varies with time. Based on the above techniques, predictions were made, and results suggest that the qualitative method has a significant accuracy compared to the actual settlements of the building. These observations provide some proof that the coefficient of secondary consolidation varies with time according to the qualitative approach and does not remain constant throughout the lifespan of the building as suggested by conventional methods. KEYWORDS: Coefficient of secondary consolidation, Crack formation, Settlement, Soft soil, Time-dependent settlement