ASSESSMENT OF SETTLEMENT FOR RAFT FOUNDATION UNDER ECCENTRIC LOADING NEARBY SANDY SLOPE USING FINITE ELEMENT METHOD

Abstract

Abstract Communication Towers may be found in areas outside cities, where sloping lands and hills, a self-supporting tower with four legs and a height of 50 meters with raft foundation is the typical tower adopted in this study. The communication tower represents a lightweight structure compared to other structures and at the same time exposed to eccentric load represented by the overturning moment resulting from the wind load, this load depend on the basic wind speed, and the prevailing speeds in Iraq (33, 38, 42, and 44) m/sec are the speeds which adopted to obtain the values of eccentricity. The study examines the behavior of tower foundation near sandy slope under the influence of parameters: eccentricity ratio (e/B) at values (0.08, 0.11, 0.14, and 0.15), relative density (loose, medium, dense), angle of slope at values ) with constant height of the slope (10) m and embedment depth of the foundation (Df/B) at values (0 and 0.125), using Finite Element Method in Plaxis 3D program, these parameters investigate with two constitutive models: Hardening Soil Model (HSM) and Mohr Coulomb Model (MCM). After finding a method of representing the projected moment on raft foundation by Finite Element Method in Plaxis 3D program, results of angle of rotation for all models of the study are compared with the permissible value of (1/600), one of the most important findings of this study is that the ultimate bearing capacity of the foundation was not reached, and the failure mechanism IV is the overturning of the structure, and its determinants are differential settlement and angle of rotation of the foundation. The results of soil representation with (HSM) are close to that of (MCM) for both dense and medium-dense soils, while the results of (HSM) exceed significantly (MCM) in loose soils. The results also indicate that the acceptable distance of the tower foundation from the crest of the slope is equal to half the width of the .5), which cancels out the effect of the slope and the foundation behaves as if it were on flat ground, which is also the recommended distance for the construction of the tower safely and for the two soils dense and medium-dense density, while avoiding the construction of the tower on loose soils, depending on the permissible value of the angle of rotation. Increasing the ratio of the embedment depth for the foundation reduces the maximum settlement below foundation by a rate ranging from (31.18-47.25) %.