University of Khartoum

Guidelines for the Design of Piles in Expansive Soils

Guidelines for the Design of Piles in Expansive Soils

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Title: Guidelines for the Design of Piles in Expansive Soils
Author: Ahmed, Elfatih Osman
Abstract: The use of pile foundation to support light to moderate weight buildings is now increasing rapidly; this necessitates a good design that gives a consideration to the changing environment and supporting soil conditions. This research is mainly dealing with the design and performance of small diameter short piles since this type is used to support light to moderate weight structures in expansive soils. The research is composed of series of laboratory and field investigations. Tests were carried out on model piles to investigate the effect of moisture content increase on bearing capacity, and the uplift forces exerted on piles. The percentage of the swelling pressure that is transferred to the piles (uplift factor) was found to be 18%. Full scale pile load tests were carried out to study the effect of wetting on the bearing capacity of piles fully embedded in expansive soils. The field tests on piles in addition to the laboratory investigations were used to draw guidelines for the design of piles in expansive soils. The guidelines for the design are given for the values of adhesion factor and end bearing capacity factor. Both factors are used to design for bearing capacity, while the uplift coefficient value was used for design for uplift resistance. It is recommended to use an adhesion factor of 0.45 for moisture content less or equal to the plastic limit of the soil. The adhesion factor increases linearly with increase of moisture content for moisture contents greater than the plastic limit. The recommended end bearing capacity factor is 7.0 for fissured clay and 9.0 for very stiff to hard expansive clay. The recommended uplift coefficient is equal to 20%. The factor of safety was suggested to be 3.5 depending on results of field tests. It is interesting to note that field investigations on piles showed that the bearing capacity of piles is reduced by 60% due to wetting of the surrounded soils. This decrease is mainly due to the decrease in the shear strength of the soil due to wetting.
URI: http://khartoumspace.uofk.edu/handle/123456789/10828
Date: 2015-05-14


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