Cost-Benefit Analysis of Combined Retaining Walls Construction

Abstract

Stability of slopes can be improved by using soil nailing as one of in situ soil reinforcements. In the case when the soil nailing system alone is not feasible, then other types of retaining walls can be used together. Therefore, this paper aimed to assess combination soil nailing and crib wall in terms of cost benefits. Analysis of cost comparison from cost-benefit analysis (CBA) was carried out between soil nailing and crib wall as a reference. Common problems of soil nailing such as rebar encroaching to neighbouring land were solved by using a crib wall because it can be constructed on a small space. This type of combination is known as a combined system retaining structure. Design and construction data have been collected from a project under construction in Selangor. The results of CBA proved that the construction should proceed with the combined system when the benefit-cost ratio (BCR) is greater than 1 and the net present value (NPV) is greater than 0. When NPV and BCR are used to determine the CBA, there is an economic validation to further the project if NPV and BCR are equal to 0 that shows the breakeven point (less certain outcome). However, if BCR is less than 0, then the project should not proceed with the selected method. The findings suggest that a comparison of the cost estimation could verify the future feasibility of the proposed method.