Evaluation of Bearing Capacity of Ground in Transition Zone

The determination of ultimate bearing capacity in transition zone by classical theory is not clearly explained (IS: 6403-1981: Code of Practice for the Determination of Bearing Capacity of Shallow Foundation, first revision, New Delhi, 1981 [1]) (Murthy in Soil Mechanics and Foundation Engineering. Marcel Dekker Inc. New York [2]; Punmia and Jain in Soil Mechanics and Foundations, 17th edn. Laxmi Publications, New Delhi, India [3]). Most of them including IS: 6403-1981 suggest a linear interpolation between general and local shear failure in transition zone with no further explanation. Practicing engineers do not have consistency in calculation of bearing capacity in the transition zone. More often, they are likely to encounter the situation of the angle of internal friction lying between 28° and 36°. Many a times, it is felt that the baring capacity is overestimated. Therefore, an attempt is made in this paper to determine the ultimate bearing capacity by different methods in the transition zone and to give more precise calculation procedure for the determination of bearing capacity in the transition zone. For this purpose, Terzaghi’s bearing capacity factors are used in the analysis. An attempt is made to present bearing capacity factors as a function of angle of internal friction of soil considering local shear zone, transition zone and general shear zone. Three methods to determine the ultimate bearing capacity of soil in transition zone are discussed, and their relative conveniences are brought out.