Investigation of Effects of Excavations on Adjacent Foundations using Finite Element Modeling

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Addis Ababa University


Deformations caused by excavations are important to determine because for the past decade, deep excavations are becoming more common in Addis Ababa. Due to congestion of places, most of these excavations are near adjacent buildings. Numerous high rise buildings are erected and the effect of these on the adjacent grounds which in turn on adjacent foundations have not been studied very thoroughly. The purpose of this master’s thesis is to first determine the effects of foundation loads at different levels on a red clay soil and to see the effect on adjacent excavations as a result of vertical and horizontal displacements. Four foundation levels are used by differentiating between the numbers of their respective building basements: no basement, one basement, two basements and three basements foundation levels. For the same foundation level, the distance from the edge of excavation was also varied from 0m to 3.5m and to 7m. The variations of vertical and horizontal displacements were plotted against the distance from the face of excavation. The results showed that at 3.5m from the face of excavation and beyond that, the displacements decreased to a minimum value. Similar trends are shown in the decrease of the vertical and horizontal displacements for those cases with the same number of strut levels showing that the strut level will affect the value of the deformation in spite of the vertical excavation level. The second purpose is to determine the vertical and horizontal displacements of the ground and wall under different cases by changing soil, wall and excavation properties by means of parametric study. PLAXIS 3D Foundation V.1 was used as a tool to carry out all the analysis. The parameters are varied for three levels of excavations i.e. 4.9m, 10.35m and 15m Final excavation. The modulus of elasticity and the excavation depth showed prominent effect on the results. The allowable deformation values from EBCS 7 and other literature have been compared with the cases with the most critical deformation values. The result of the comparison is that those cases with low stiffness modulus values resulted with high deformation exceeding the allowable values from previous literatures. Key words: Deformations, secant pile wall, PLAXIS, allowable values



Deformations;secant pile wall;PLAXIS; allowable values