INVESTIGATION ON ENGINEERING PROPERTIES OF WET SOILS FOR ON-SHORE CONSTRUCTION NEAR LAKE HAWASSA

Abstract

There are different types of onshore constructions that are constructed for different activities in the world, such as recreational, lodge, residences and port. In Ethiopia mostly onshore constructions are done for recreation purposes, like hotels and lodges. Hawassa town which is the capital city of SNNPR is one of the fastest growing towns in Ethiopia. From the structural land use plan, the future expansion of the town is towards the west of Lake Hawassa. So, for onshore construction and generally for all constructions it is necessary to identify the engineering property of the soil. Thus, the main objective of this study is to investigate engineering properties of wet soils nearby Lake Hawassa, towards the town expansion. The engineering properties of soil are one of the basic soil parameter used to design foundations, retaining walls and soil design and construction etc. in the study area. To such end, the research addresses the lack of engineering data for design and construction of the civil engineering structures foundation. During investigation of the soil in the study area, preliminary site observations, field testing such as natural moisture contents and field density are performed on 16 samples from 5 test pits. The engineering and index properties of soils are determined from laboratory tests based on ASTM and AASHTO soil testing standard. Engineering properties such as shear strength, consolidation parameters and index properties such as Atterberg limits, specific gravity, and particle size distributions are determined by their own corresponding common tests. The particle size analysis testing results showed that the dominant proportion of soil particles in the research area is silt, which has clay size content ranges from 3.4 – 60.6%, silt fraction 24.7- 83.0%, sand fraction 3 - 61.6% and gravel content from 0.1 – 3.3%. Atterberg limit test showed that 8 samples are non-plastic soil in nature. For the rest samples the liquid limit ranges from 46 – 70.4%, plastic limit ranges from 13.93 – 40.06% and plastic index from 10.1 –56.49%. The specific gravity test results ranges from 1.65 to 2.52. The standard proctor compaction test maximum dry density ranges from 0.906 to1.3 gm/cm3 and the optimum moisture content ranges 9 to 38 %. Based on the Prakash Modified Unified Soil Classification System, the plastic soils in the study area are categorized as inorganic silt and clay soil with medium and high plasticity. These plastic soils are classified under MI,MH and CH soil group. The non - plastic soils are classified under inorganic medium silt, fine silt and clay sized fractions (MIN-MHN), inorganic coarse and medium silt sized fractions (MLN-MIN) and silty sands (SMN) soil group. The one-dimensional consolidation test result shows that the soil compression index ranges from 0.273-0.421, recompression index ranging from 0.049-0.098. According to the undrained shear box test result the cohesion value ranges from 0.02 – 8.38 kpa and angle of internal friction ranges from 21.10 – 320. The pH and Electro Conductivity test revealed that the ph value of the soil ranges from 7.5 to 10.42 and electro conductivity ranges from 0.1 to 8.4 Deci Siemens per meter. The organic content value of the study area ranges from 0.15% - 2.04%.