Developing correlation between undrained shear strength and index properties of cohesive soils found in Waliso Town

Abstract

In developing countries including Ethiopia, infrastructures are currently constructing in fast rate. Accurate determination of the soil shear strength parameters is a major concern in the design of these different geotechnical structures. However, experimental determination of the strength parameters is extensive, cumbersome and costly. And also, the laboratory equipment's and field instruments are not available in all areas to get these parameters. In order to cope with such problems, developing correlation is a crucial one to get shear strength parameters. Therefore, this study was conducted to develop correlation between undrained shear strength and Index properties of cohesive soils found in Waliso Town. Index properties and undrained shear strength behavior of these soils was studied by conducting laboratory tests. For this study, undisturbed and disturbed soil samples from twenty test pits at 3m depths were taken. And also, ten secondary data was used. Totally, thirty soil samples were used. For test procedures American Society for Testing & Material (ASTM) standards was used. For analysis and developing correlation Microsoft Excel (MS-Excel) and Computer program aided Software (SPSS 20) were used. Combining selected variables, single linear regression and multiple linear regression models were developed for the prediction of undrained shear strength parameter. The study shows that undrained shear strength parameter (Cu) was significantly correlated with plastic limit(PL), liquid limit(LL),bulk density(γb), dry density(γd) and natural moisture content (NMC) whereas it was not significantly correlated with plasticity index (PI), specific gravity(Gs) and liquidity index (LI) of study area soil. From the study, the best Model is obtained from multiple linear regression (MLR) analysis and given by: Cu = 90.939*γd – 0.804*LL – 1.311*PL + 37.044; coefficient of determination (R2 ) = 0.843, Adj. R2= 0.825 and P value =0.00 < 0.05. Using the developed model, undrained shear strength parameter can be computed as well as it is expected to have wide application in the construction to minimize the cost, effort, and time for laboratory tests of undrained shear strength of the study area.