Correlations of Strength and Elastic Modulus of Cohesive Soil with SPT in Bakrajo Region-Kurdistan of Iraq

Reasonably estimating the uniaxial compressive strength (UCS) and elastic modulus (E) of cohesive soil is crucial in the routine design of structures built on such soils. However, there is no reasonable relationship that could be utilized to estimate (UCS) and (E) of cohesive soils in the Kurdistan region of Iraq using the field test of Standard Penetration Test (SPT). This research aims to fill this knowledge gap. Seventeen (17) high-quality undisturbed samples were collected and tested in the laboratory, and the results were then used to develop predictive models using simple regression analysis and multi-linear regression analysis. Also, the SPT for each sample was measured in the field. It was found that the UCS is correlated with reasonable accuracy with dry density and SPT of the soil with a coefficient of correlation (R) of 0.62 and 0.58, respectively. Furthermore, a poor correlation is found between the UCS and liquid limit (LL) and the plasticity index (PI). In addition, it has been noticed that using multi-linear regression improves the accuracy as it increases R to 0.84. The developed correlations could be used in estimating the UCS for cases where it is impossible to get a high-quality undisturbed sample for the UCS test.