Comparison of analyses of soil nailed and anchored support systems in deep excavations

Deep excavations play an important role in the modern civil engineering practices in big cities. Civil engineers have to keep the ground in balance during deep excavations to provide for the development of high storey buildings, and realize the constructions such as subways and tunnels. It is aimed within the context of this thesis to compare the deep excavation support systems comprising soil nail systems soil anchors. The Plaxis 7.2 program utilizing the finite elements method is being widely used for the numeric analysis of the geotechnical engineering problems. In this study its used to analyse the behavior of soil nailed and anchored excavation support systems which are initially designed by classical methods. Typical excavation in four different soil models of for different heights (8, 10, 12 and 15 m) have been analysed. The stability of the excavations is also analysed with the computer code Talren, which is a limiting equilibrium slope stability analysis program. The computed factor of safety values are compared with the results of Plaxis analysis and observed to be close to each other. Finite elements analysis also yield deformations to be expected in both excavation support system which are also compared. Cost comparisons are also made for the excavation support systems that have been studied, and it is noticed. That in clayey soils, for excavations depths up to 10 m soil nail systems are more economical, beyond which anchored systems become more economical. Anchored systems are found to be more economical in sandy soils for all excavation depths studied. The choice of excavation support system willl also depend on site and soil conditions, including the existence of neighbouring structures which might be adversely attected from soil displacements. Keywords : Deep excavation, Soil nail, Anchor, Effective stress, Displacements, Plaxis 7.2, Talren 4.