DETAIL INVETIGATION OF GEOTECHNICAL PROPERTIES OF TROPICAL SOILS OF GATO TOWN

Abstract

Residual weathering in tropical climates is the main factor for the in situ formation of residual tropical soils. The formation process gives them characteristics which are quite different from those of transported soils. Therefore, the conventional concept of soil mechanics (which is based on the properties of transported soils) is not applicable to many tropical residual soils as they might consist of aggregates or crystals of weathered mineral matter that break down and become progressively finer under continuous manipulation. The overall aim of this study is to come up with reliable results for some of the engineering and index properties of soils found in Gato town in order to understand clearly the nature of the soils and for better design and construction of civil engineering structures in the town. To achieve this objective around 15 Disturbed and 8 undisturbed soil samples are collected from four systematically selected test pits at 1.5m, 3m and 5m depths. The undisturbed samples were taken from the test pits manually by cutting a rectangular block of soil and trimming into a proposed test specimen and covering with plastics to prevent the loss of moisture. In this project work both index and engineering properties of tropical residual soil have been investigated on the soil specimen by the test procedures recommended for tropical residual soils. Generally it was found that sample pre-test treatment alters the result of Gato town soil when compared to a commonly used soil test procedures for temperate soils. Moisture content determination, using oven temperatures of l05°c and 50°c were carried out on the soil samples to investigate the presence of structural water and from the test result it has been observed that the soil from study area have structural water. Atterberg Limits were investigated for oven dry and air dry pretest treatment and for 5 min and 30 min mixing time. From the test results, the soil under investigation has been affected by pretest treatment and duration of mixing time. Specific Gravity Test was conducted at three different test temperatures (as received moisture, air- dried and oven dried at a temperature of 105°c). Particle size distribution, atterberg limit and proctor tests were conducted at air dried and oven dried pretest treatment and from test result the clay content of the particle increases with increasing temperature. From proctor test result it was observed that oven dried sample has maximum dry density and less optimum moisture content relative to air dried sample. Proctor test was also conducted for using fresh sample and same sample for each trial. For shear strength parameters determination undisturbed soil samples were collected from four test pits and unconsolidated undrained test was conducted by direct shear apparatus.