K. N. OGHOYAFEDO

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.

The project titled “The effect of admixtures on properties of concrete: case study of sugar cane shaft ash, cow bone ash, groundnut shell ash,” will be carried out with the aim of knowing the effect the of the various types of admixtures used on the properties of concrete, in term of the workability of concrete, durability of concrete and the concrete strength. The material used are cow bone ash, groundnut shell ash, sugar cane shaft ash. The cow bone will be sourced along new Benin market, Edo state and the groundnut shell will be sourced from uselu market. The cow bone will be sun dried after careful separation from flesh, tissues and fats, the ash will be carried out by incinerating the bone at a temperature of 900⁰C in a furnace. Also, the groundnut shell ash will be obtained by burning groundnut shell on an iron sheet in the open air under normal temperature while sugar cane shaft ash. The method adopted will be; batching of concrete materials, mixing of concrete materials, production of cubes, curing of cubes (for 7days, 14days and 28days) while the test carried out during and after the concrete cubes are produced or casted are; sieve analysis test, slump test and compressive strength test. From the sieve analysis test carried out on both fine and coarse aggregates, it will be discovered that the coefficient of uniformity (Cu) obtained are less than 4, hence they are both “well-graded” aggregates. The slump test shows that there is increase in the slump value from sugar cane shaft ash-concrete, GSA-concrete, CBA-concrete and LP-concrete, likewise the compressive strength test increases from sugar cane shaft ash-concrete, GSA-concrete, CBA-concrete and LP-concrete. From the findings, it is evident that the combination of the three admixtures resulted in the highest percentage increase in compressive strength. Additionally, the average maximum strength was achieved when the fine aggregate was replaced by 15% with the admixture. Despite variations in replacement percentages, all samples exhibited compressive strengths that align with the expected design characteristics of concrete, particularly around the target value of 20 KN/mm². The sieve analysis further revealed a well-graded particle size distribution in the fine aggregate samples, indicating suitability for achieving optimal concrete mix designs.