Study on Some of the Engineering Properties of Soils Found in Gilgel-Beles Town

Abstract

In civil engineering works, "soil" is used in any kind of civil engineering structure, either as foundation material to support the load exerted by structures, or as construction materials. From this point of view, the geotechnical engineers are mainly interested in the engineering behaviour of soils and classify the soils on the basis of their properties. The construction of civil engineering structures is developing fast in Gilgel-Beles Town like other main towns of Ethiopia. In the construction industry, engineering characteristics of soils play a significant task as input data in preliminary design, designing and construction. However, engineering properties such as index properties and consolidation characteristics of the Gilgel-Beles soil is not studied well yet. Therefore, investigating the engineering properties and identifying the characteristic of the soil is very important for construction works as well as for further studies in the future as an input. The objective of this research was to investigate some of engineering properties of soils found in Gilgel-Beles town. To achieve the objective, disturbed and undisturbed samples from different parts of the city were collected. To determine the properties of soil the test was conducted by using ASTM standard test procedure. Based on the laboratory test results the properties of soils of the study area were specific gravities range from 2.6 to 2.72, clay fraction 23-54.6%, silt fraction 14.9-50.5%, sand fraction 20.82-39.1% and gravel fraction 0-1.4%, liquid limit 30 – 52.5%, plastic limit, 24.9 – 40.5% and plastic index 5 – 19.5%. According to USCS classification system of plasticity chart, most of the soil of the study area falls below A-Line in ML region, and TP-3, TP-5 and TP-7 in MH region, which have high plasticity (LL>50%) and the classification soils found in Gilgel-Beles town were ML, MH and CL. And also, according to AASTHO soil classification, the study area soils were dominantly categorized in A-7-5 and A-7-6 which is poor for sub-grade materials. Based on the compaction test, maximum dry density (MDD) ranges from1.57 to 1.81 g/cm3 with optimum moisture content from 17 to 35.38 %. Unconfined compressive strength of the soil at the study area ranges from 85.28 to 179kN/m2 and un-drained shear strength 42.64 to 89.5kN/m2 According to the relation between consistency and unconfined compression strength of clays, the unconfined compressive strength of the study area is included in medium consistency. From the one dimensional consolidation test result, the over-consolidation ratios of the soils are more than one, so the soil in the study area is over consolidated in the past with maximum effective stress.