COMPARATIVE STUDY OF SOIL SHEAR STRENGTH USING STANDARD AND EXTENDED CELL PRESSURE

The fundamental geotechnical parameter for stability of all Civil Engineering structures, such as foundations and slopes, is soil shear strength, shear strength is governed by Mohr- Coulomb failure criterion. Current standard geotechnical practice often uses a limited and a conventional range of 100KN/m2, 205KN/m2 and 310KN/m2, Extrapolating the failure envelope obtained from this narrow, limited range to low or high in-situ stresses can introduce significant error into geotechnical design, leading to unsafe structure. This study investigates the shear strength characteristics of soil samples collected from Ogbowo, Ekosodin village, Edo State, Nigeria, through a comparative analysis of standard and extended cell pressure applications. Soil specimens were prepared from five different samples to get the accurate values of Angles of internal friction and cohesion by drawing the Mohr circle using the standard and extended cell pressure, to evaluate how extended cell pressure configurations influence the determination of soil shear strength compared to convention testing method. The analytical results reveal that the soil at the study site is predominantly fine-grained, characterized by critically low angles of internal friction, which indicates minimal frictional resistance and a reliance on cohesive bonding for shear strength. Comparative analysis consistently demonstrates that cohesion values derived from the standard triaxial testing approach (15,13,12,28 and 19kN/m2 respectively) are significantly higher than those obtained through the extended nine-cell pressure range (2,5,6.4,8,12kN/m2 respectively). While the extended pressure testing resulted in an increases in the angle of internal friction. for the standard cell pressure (0.57º, 4.15º,4.29º,1.43º,1º and those of the extended cell pressure 2.43º, 3.89º, 4.41º, 5.71º, 2.63º respectively). it simultaneously caused a substantial reduction in cohesive strength. Consequently, this research concludes that the standard geotechnical engineering cell pressure range provides a more reliable and higher estimation of soil shear strength for the studied site. The findings suggest that the use of extended cell pressures may underestimate the short-term stability of the soil, making the conventional standard triaxial method more appropriate for site-specific geotechnical design and analysis.