Optimization of cost-effectiveness for soil-nailed system in retaining wall

Abstract

Soil nailing is one of in situ soil reinforcement method to improve stabilization of slopes, retaining system, and excavation works. Soil nailing designs are optimized to be cost-effective in construction management. This dissertation aims to analyze the optimization of the soil nailing with three different parameters: inclination, spacing, and length of the nail. All optimizations must meet the factor of safety (FOS) permissible limit. The case data was collected from three selected sites in Selangor. The slope with soil nailing was reanalyzed using SLOPE/W software program based on the limit equilibrium method (LEM) and also Morgenstern and Price Method (M­P) to optimize the design and compute the FOS. During reanalysis, all three nail parameters were separately optimized based on the case conditions and FOS requirements. The results of the reanalysis showed that reducing nail length can reduce the FOS, meanwhile reducing the nail inclination and nail spacing can increase the FOS. The reanalysis results proved that increased nail inclination does not increase the cost, but the cost decreases by the reduced nail length. Cost reduction is mainly affected by reducing nail length, and the number of nails. In addition, the problems of soil nailing such as rebar encroaching on neighbouring land can be solved by using a crib wall because it can be constructed on a small space. The combination of soil nailing and crib wall systems complement the drawback with each other'.)s advantages and made the retaining system ideal to strengthen the hillside. When a cutting slope occurs in a narrow area bordering neighbouring land, combining these two systems is necessary for reducing construction costs. The construction costs of soil nailing and crib wall were compared and merged to prove the effectiveness of the combination system. The cost-benefit analysis results of the combined system is a good option when the benefit-cost ratio is greater than one and the net present value is greater than zero. The results indicated that the cost savings of the combined system are acceptable. Therefore, the optimization of the soil nailing and the combined systems contribute to cost-effective construction management.