Abstract:
Geotechnical investigations are made to determine those geologic, seismologic, and soils
conditions that affect the safety, cost effectiveness, design, and execution of a proposed
engineering project. The objective of this thesis is to investigate the engineering properties of soil
found in Shewa Robit town.
The methodology used for this thesis was basically includes visual identification, sampling,
laboratory tests, and analysis of results. Samples are collected both from 1.5m and 3m in order to
determine the results of index properties, particle size distribution, compaction characteristics,
consolidation, free swell, and shear strength parameters. And appropriate laboratory tests was
performed according to AASHTO and ASTM standards. But since the study area soil is found to
be in tropical region, modified classification methods must be used additionally. At two test pits
the depth of 3m for taking soil samples is not reached because of the reason that a fractured rock
is encountered, for the study area the variation of NMC is due to the difference in vegetation cover
of the ground surface. Specific gravity of soil for the study area is found to be in similar range of
Gs values for silt and clay soils.
According to AASHTO classification, the study area soil is clay, it is fair to poor range to be used
as a subgrade material for highways. According to USCS the soil in the study area is found to be
CH and MH. Relatively higher values of LL, PL, and PI shows that the soil is cohesive by its
nature. UCS test results shows that the study area soil undrained shear strength and undrained
cohesion values are the values expected for fine grain soils.
Compaction test result shows that the OMC value is the value expected for cohesive soils of high
plasticity. MDD values also shows that for fine grain soils a less value of density is expected.
Since OCR for the soil is greater than one, the soil is over consolidated. This shows that the current
overburden pressure is not maximum load that the soil experienced. Since the k value of the soil
is less, the soil is almost impermeable. The Atterberg limit value of the study area shows that the
soil is fine grain soil which includes both silt and clay.
