Reliability based predictive model for estimating shear strength values of locust bean waste ash compacted black cotton soil

Abstract

A cheap and eco-friendly method of soil improvement is vital in achieving a reduction in the negative effect of climate change and cost of construction. Black cotton soil (BCS)–locust bean waste ash (LBWA) blend was evaluated via laboratory test, thereafter subjected the results to computer base program. Soil was treated with 0, 2, 4, 6, 8 and 10% LBWA by dry weight and compacted with different energies. A regression equation was developed from the laboratory measured values to serve as a limit state equation and integrated into a FORTRAN program, to generate safety index (SI) for shear strength values in the range of coefficient of variation (COV) of 10–100%. Results of statistical analysis show strong interaction between the shear strength values and the soil parameters (Locust bean waste ash, LBWA; Cohesion, CO; Friction angle, FA; Plasticity index, PI; Maximum dry density, MDD; Optimum moisture content, OMC; Percentage fine, PF; Cation exchange capacity, CEC; Specific gravity,Gs and Compactive effort, CE).Results show that for the laboratory model, safety indices are sensitive to changes in all the parameters considered. Results showed that among the entire variables, MDD, PI and OMC have major effect denoted by wide variations in their safety indices, seriously influenced by the COV. Safety indices for the effect of LBWA changed from −0.263 to −0.256, −0.134 to −0.13 and 0.00253 to −0.00246 for BSL,WAS and BSH, in that order. Aslo, values for untreated soil changed from −1.19 to −1.17, −1.08 to −1.06 and −0.973 to −0.954 for BSL, WAS and BSH, in that order. Similar pattern was recorded for other variables. Results obtained fell to meet up with the minimum regulatory value of 1.0 as stated by the Nordic Committee on Build Regulations at 10–100% COV as expected. The recorded safety indices for all the independent variables considered shows higher values when compared to that of the untreated soil. A more effective additive such as cement or lime blended with LBWA is commended to model shear strength values of the modified soil for dams or embankment applications.