EVALUATION AND MAPPING OF ENGINEERING BEHAVIOUR OF SOILS (THE CASE OF GIMBICHU TOWN)

Abstract

Soil is the ultimate foundation material which supports the structure. The proper functioning of the structure will, therefore, depend on the engineering properties of the underlying soil. The objective of this research is to evaluate the engineering properties of soils found in Gimbichu town by conducting different types of laboratory tests and to prepare soil map using ArcGIS software of Gimbichu town. Ten test pits were selected based on variation of the soil of the town and the current distribution of the residences to the municipality of Gimbichu town. The soil samples were collected from pits by direct manual excavation. From collected soil samples both laboratory and field tests were conducted. From laboratory tests both index and engineering properties were carried out and all laboratory tests were conducted by ASTM standards. Laboratory tests carried out on disturbed and undisturbed samples revealed that the natural moisture content ranges from 17.51 to 24.45%, specific gravity of the soils ranges from 2.64 to 2.85. Results of Atterberg limits tests shows that of soils of Gimbichu town have liquid limits ranging from 29.2 to 66.9%, plastic limit ranges from 21.54 to 42.88% and plastic index from 3.97 to 24.08%. These values indicate that the plasticity of the soils of the study area ranges from low to high plastic. The grain size distribution indicates that most of the soil samples have clay material more than 50%. Therefore, clay type of soil is dominantly located in the study area. The free swell test result indicates that soils of the study area are non-expansive which means degree of swell of the soils is non-swelling. The degrees of activity of all of the study area soils are inactive with values of Activity less than 0.75. Soils of the study area are classified according to USCS and AASHTO.USCS indicates main type of soils, which is highly plastic clay soil (MH) and some of the silty soils have low plasticity. According to AASHTO classification soils of the study area is A-7-5, which means clay soil with poor quality as a subgrade material. The Compaction test results showed that maximum dry density (MDD) of the study area ranges from 1.28 to 1.73gm/cm3 and the optimum moisture content (OMC) ranges 20 to 40%. The unconfined compressive strength test result and liquidity index indicates the soil consistency of the study area ranges from medium to very stiff. The silty sand soil has angle of internal friction ranges from 30.1 to 32.60 and cohesion ranges from 8 to 10 in kN/m.2 The consolidation test results shows that the soil exists naturally in a condition of over consolidated, which has O.C.R >1, therefore the soil had been subjected to a pressure in excess of the present pressure. Finally, from the grain size distribution and unconfined compressive test results the soil mapping was done by Archaist software which gives more information about the soil.