UNDRAINED SHEAR BEHAVIOR OF SOILS OCCURRING WITHIN NNAMDI AZIKIWE UNIVERSITY, AWKA

ABSTRACT

During this research work, namely; the undrained shear behavior of soils within Nnamdi Azikiwe University, five different samples within the university compound were analyzed. Some laboratory test was carried out for classification and identification of their engineering properties, these tests include particle size distribution, Atterberg limit test, specific gravity, and free swell tests. Also, shear strength test (UU triaxial test) at different cell pressures and one-dimensional consolidation test, were carried out for the determination of some necessary parameters in an undrained condition. Disturbed and undisturbed samples were collected from five different locations, at a depth of not less than 0.6m, and taken to the university civil engineering laboratory for soil analysis, where classification test was perfomed on the disturbed samples while txiaxial UU test and consolidation test were performed using undisturbed samples trimmed to the required shape. PSD test showed that SM1 and SM3 are U.G and N.W.G, with less drainage characteristics, while SM2, SM4 and SM5 have higher drainage characteristics and that also, all the Samples belong to (A-6) or clayey soil group except SM5. Also, using the ASTM source and I.S chart for identification and classification, Atterberg limit test indicated that SM1, SM2 and SM4 are lean clay with a medium to high dry strength, while SM3 is silty-clay and SM5 is silty-sand, with none to slight dry strength. Virtually all the samples contained feldspar and are koaline soil type, as revealed by specific gravity test. The degree of expansiveness was also ascertained in free swell and linear shrinkage test, which stipulates that SM1 and SM3 are moderate, SM2 and SM4 are high and SM5 is low. The undrained shear strength parameters (Cu) and (Ø) of the triaxial UU test followed an increasing order of SM5, SM4, SM2, SM1 and SM3 from the highest to the lowest, and also using Terzaghi’s bearing capacity formulae, the bearing capacity of the samples followed the same order of increase, and judging with some presumed values of bearing capacities, in accordance to B.S (8004) 1986, SM4 and SM5 are very stiff boulder or/and hard clay, SM2 is stiff clay and SM1 and SM3 are hard clay. One-dimentional consolidation test showed that the rate of expulsion of water due to lateral loads is higher in SM2 and SM4 and lesser in SM1, SM3 and SM5, which corresponds to the drainage characteristics observed in PSD test stated earlier on. The values of settlement were computed, which showed an increasing order of settlement of SM5, SM4, SM3, SM1 and SM2, from highest to lowest, even if SM5 happens to have the highest value of (Cu).These parameters gave this work a reasonable conclusion stating that the entire samples contain some level of clay, which is considered an expansive soil and possess less or no resistance strength to shearing and in application of vertical loads, water dissipates slowly from the interstices of the soil, which indicated that settlement of structures on such soils are bound, and thus cannot be trusted to erect structures without proper geotechnical consultations. All this per this research presents multiple behaviors of these samples irrespective of their various locations.