Numerical Analysis And Parametric Study Of Granular Anchor Pile On Expansive Soil Using Finite Element Method: Case Of Addis Ababa, Bole Sub-City

Abstract

A wide range of heaving problems of expansive soil in Addis Ababa become a major difficulty for the construction of low rising buildings by causing different damages in the building. Hence an attractive and economical design solution may be required for such type of problem. Since Granular Anchor Pile is one of the recent ground improvement technique which devised for resisting pull out forces. In a Granular Anchor Pile, the footing is anchored to a mild steel plate placed at the bottom of the granular pile through a reinforcing rod or a cable. Therefore, this research paper is done for the objective of numerical analysis on the performance of Granular Anchor Pile under the heave of expansive soil using PLAXIS 3D program by studying the effect of pile length, diameter and pile spacing and examining the suitability of Granular Anchor Pile as an alternative solution for heave problems of expansive soils for low rising building found in Addis Ababa city especially in Bole Sub-City. According to the result, the pile can have an uplift capacity of a minimum of 510 kN and a maximum of 4,477 kN under the analysis for a pile dimension of L=1m, d=0.4m, and s=3d and L=6m, d=0.4m and s=1.5d respectively. Also, the percentage increase in uplift capacity of the pile is 109, 58, and 39% when the pile length increased from 1 to 3m, 3 to 4m, and 4 to 6m respectively. This is due to an increase in the self-weight of the pile and friction mobilized between the pile and soil interface. Additionally, the uplift capacity of the pile reduced by 5.5, 17.1, and 32% when the diameter of the pile increased from 0.2 to 0.3m, 0.3 to 0.4m, and 0.4 to 0.6m respectively. The pile capacity also reduced by 12 and 10% when pile spacing increased from 1.5d to 2d and 2d to 3d respectively. These are due to the reduction of the number of piles in the group and soil confinement. According to the suitability analysis, the construction of the pile can spend about 2800 Ethiopian birr for simple G+1 building per footing. Generally, it is observed that Granular Anchor Pile has high performance in resisting uplift loads coming from the heaving of expansive soil and variables that considered in the analysis (pile length, diameter, and spacing) have a significant influence on the performance of the pile and the pile is feasible to apply for the actual problem of Expansive soil in a low rising building constructed in the country because of its convenience for all considerations.