ULTIMATE BEARING CAPACITY OF
UNDERREAMED PILE -FINITE ELEMENT METHOD Dr Neha Jain Nikhil Bhatia Sr Lecturer Student/Research
scholar Jaypee Institute of Engineering and Technology, Guna Madhya Pradesh ABSTRACT
Underreamed piles having one or more bulb at specified locations along their depths have been extensively used in India to support wide variety of structures in almost all types of soil strata. The present investigation makes use of Finite element analysis to calculate the ultimate bearing load for singly bulb underreamed pile in group. The content of this paper is limited to 2-D axisymmetric elastic analysis for axially loaded pile with unit cell idealization to analyze a single pile in group. The Ultimate bearing load of the pile for different stem and bulb
diameter in five types of soil viz. ‘soft clay’, ‘stiff clay’, ‘dense sand’ ,‘Loose sand’ and ‘silt’ have been determined. On the material side Young modulus and Poisson’s ratio of soil and pile has been kept constant with depth. Effect of body forces is also taken constant with depth. Ultimate load is calculated for stem diameter ranges from 0.2 to 0.5m, length ranges from 3.5 to 9m and all values elastic modulus range is taken for respective soil while poisons ratio, depth of rock bed and the Ratio of bulb diameter by pile diameter is kept constant to ease the complexity of calculation. The output of the present research is the formulae that is suggested for each type of soil as specified above and the variables as stem diameter, length and elastic modulus in terms of their multiplication factor which is obtained by observing their respective trend with the increase in length of pile, diameter of pile stem and elastic modulus, which further increases the scope of work and its flexibility to calculate the bearing load for any value by simply using the multiplication factor corresponding to that value. Load deflection criteria are assumed to calculate the ultimate bearing load. The ultimate load corresponding to 25mm Elastic settlement is assumed, for example as similar criteria is taken by CBRI for their calculation in which 25mm of total settlement is considered. The results have been verified by four different method which thereby creating the reliable data base for designing of these foundations.