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A pre-design guide for cantilever retaining walls and a detail parametric study of such walls is presented here. Mathematical models based on statistical methods were improved for calculating safety factors of sliding, overturning, and slope stability of those walls. The harmony search algorithm (HSA)-a metaheuristic method-was employed to realize reasonable results of the pre-design guide from all distinct cases. Through the design algorithm, the optimal design was determined for varied soil types differently from suggestions of design codes. Thus, an optimal pre-design guide for safe and economic wall design was realized in a shorter time compared to the conventional method.

In this paper, discrete design optimization of a cantilever retaining wall has been submitted associated with a detailed parametric study of the wall. In optimal design, the minimum wall weight is treated as the objective function. Through design algorithm, the optimal design variables (base width, toe width, thickness of base slab and angle of front face) yielded minimum structural weight of the wall and satisfied stability conditions have been determined for different soil parameter values. At the end, a detail parametric study searching the effect of change of soil parameters on the retaining wall design has been conducted with 120 optimized wall designs for different values; eight values of the angle of internal friction, three values of the unit volume weight and five values of wall heights. The obtained results from optimization analyses indicate that change of the angle of internal friction more effective than change of the unit volume weight on the optimal wall weight. Economic wall design with optimization analysis is achieved in a shorter time than the traditional method.

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It is a well-known fact that water content has a significant effect on the engineering properties of fine-grained soils. There is a close relationship between consistency limits and geotechnical parameters of fine-grained soils. This experimental study was performed to investigate the effect of randomly distributed polypropylene fibers (PP) and some additive materials [e.g., Borogypsum (BG), Fly Ash (FA) and Cement (C)] on consistency limits and plasticity index of a fine-grained soil. The Taguchi method was applied to the experiments and standard L9 Orthogonal Array (OA) with four factors and three levels were chosen. A series of consistency limits were conducted on each specimen. 0-20% BG, 0-20% FA, 0-0.25% PP and 0-3% of C by total dry weight of mixture were used in the preparation of specimens. In the tests, distilled water (DW), DW + 0.05% Air-Entrainer (AE) and DW + 0.15% AE were used as mixture liquid. Experimental results showed that the most effective material for decreasing the liquid limit and plasticity index of the samples were fly ash, polypropylene fiber respectively. The plasticity index decreased with increasing of AE. The values of plasticity index for distilled water, distilled water + 0.05% air-entrainer and distilled water + 0.15% air-entrainer in optimum conditions were 16%, 14% and 8%, respectively.

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