Reliability Evaluation of Compacted Tropical Red Soil Admixed with Waste Wood Ash for Use as Road Construction Material

Abstract

A first-order reliability program (FORM) was applied to evaluate the potential of Tropical Red Soil (lateritic soil) admixed with waste wood ash (WWA) and compacted with British Standard Light (BSL) energy for use as road construction material. Regression models were developed from laboratory data using Mini-tab R15 software which served as limit state equations for the reliability analysis. Using the developed models for compaction characteristics, and a well-known distributions for the related soil parameters, safety indices were calculated considering compaction characteristics (maximum dry density, MDD and optimum moisture content, OMC) as dependent variables and the soil parameters (content of WWA, content of clay, content of silt, content of sand and specific gravity as independent variables). The results revealed that safety index is influenced by alteration in the soil parameters. Results shows that content of clay, content of silt, content of sand and specific gravity are significantly affected by the change in coefficient of variation (COV) and for that reason must be firmly controlled in lateritic soil-waste wood ash (WWA) mixtures compacted with BSL energy for use in road pavement as sub-base material. It was evident from the safety index that WWA content has little effect as its value almost continued unchanged at all COV values used. Stochastically, the BSL energy used did not yield satisfactory safety index value of 1.0 as recommended by the Nordic Committee on Building Regulation. Hence, higher energy level with better additives having higher potency such as cement, lime or bitumen is suggested to model compaction characteristics of lateritic soil-waste wood ash (WWA) mixtures for road pavement purpose as sub-base material for 10-100% variation in COV.