Abstract:
In this study 24 sites in Khartoum City were analyzed using ADINA program to find the ultimate vertical capacity for the piles with different lengths and diameters. The analysis process depended on information derived from previous soil investigations for the sites considered in the thesis. In each site the average value for each soil parameter was estimated from all boreholes in that site. Also the average thickness of each soil layer had been calculated. In this study the piles and soil were modeled by solid 2-dimensional rectangular isoparametric 8 or 9-node elements. The elements of the pile were assumed to remain elastic at all times, and the soil was idealized as either a linear elastic material or a Mohr-Coulomb elastoplastic material.
The analysis process started with applying loads to piles incrementally until a failure was encountered. The analysis results coupled with the coordinates of the sites, were loaded into a 3D Field Pro Beta v0.76 program for mapping contour lines for them. From these contour maps it had been found that pile load capacities in the north-western region of Central Khartoum are larger than those in the south-eastern region. Also pile load capacity for Khartoum Airport site and the surrounding area was small at all depths, this indicated generally the low strength of the soil in this area.
From analysis results it had been found that pile axial capacity increased with the increase in the pile diameter and length. But the settlement of pile decreased with the increase of pile length and diameter. Besides that pile load capacity and pile settlement are affected by soil type around it.
Also it had been found that the shear stress on the pile surface and in the soil near it are affected by pile load value, pile diameter and soil type around it, and the effect of soil plasticity on the axial response of a single pile is significant at high loads.
When the pile is loaded, the distribution of vertical stress along pile decreases with the increase in pile diameter. The highest vertical stress is on the top of the pile and decreases gradually towards it’s bottom. But the stresses on the soil are low (compared to the pile) and they decrease gradually towards the top of the pile and away from it. The highest strain is in the soil surrounding the bottom of the pile, and it decreases gradually also towards the top and away from pile. But the strain in the pile is small. The highest vertical displacement is in the vicinity of the pile. The settlement of the soil around the pile will be less according to its distance away from it. The horizontal strain is tension at the bottom of the pile and compression at the top of the pile.
