Bearing Capacity Assessment for Building Foundations Using Different Approaches –a Comparative Study at Addis Ababa, Central Ethiopia
No Thumbnail Available
Date
2014-05-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Bearing capacity failure is one of the main foundation design criteria for the safety and serviceability of engineering structures. Such type of failure generally occurs due to under-estimating or inadequate geological understanding of a construction site. This study was conducted in Addis Ababa, Central Ethiopia. The main objective of the study was to characterize and assess the bearing capacity of foundation materials.
For the purpose of foundation materials characterization, a large quantity of drilling and laboratory testing data, both from preexisting and ongoing projects, have been collected, filtered and finally a geotechnical database has been developed in GIS environment. Besides, a comparative bearing capacity assessment was made for the most common soil types in the study area. From the study, it was found that light to dark grey clays and saturated tuff deposits possess inferior mechanical and engineering properties. On the other hand, paleosols and red clays were found to have better mechanical and engineering properties as far as foundation engineering is concerned. Besides, considerably thick saturated tuff deposits were encountered in some localities, which may pose liquefaction related foundation failures. From the present study, it was also found that the swelling pressure of light to dark grey clays is high for light weight structures.
In order to estimate the bearing capacity of common soil types in the study area, a comparative assessment through Analytical, Empirical and Ethiopian Building Code Standard approaches were used. From the analysis it was observed that variable ranges of bearing capacity values were obtained, mainly due to differences in the term used in the estimation techniques. The difference is high especially for larger footings (mats). Besides, the influence of the mechanical and engineering properties of foundation materials in the study area were found to be clearly reflected on the bearing capacity. As a result, light to dark grey clays and saturated tuff deposits are found to have low bearing capacities than the red clays and paleosols. Further, for larger depths and widths, a very high bearing capacity has been resulted in paleosols and red clays. It is on the order of magnitude greater than the bearing pressure produced by the heaviest structures. This indicates that there is virtually no risk of a bearing capacity failure. So the design of large footings in these soils would be governed by settlement, not bearing capacity. However, for the mat foundations on expansive clays and saturated tuff, much smaller values were obtained and bearing capacity is a concern.
Finally, based on the general findings of the study, suitable recommendations have been forwarded.
Description
Keywords
Bearing Capacity, Assessment, Building Foundations, Comparative Study, Addis Ababa, Central Ethiopia