Abstract

Traditionally the temporary support of deep excavations in gravely soils consists of non-secant piles anchored at multiple levels. The standard practice for its design is the use of simplified methods and limit equilibrium principles, such as Terzagui’s method or the FHWA 99 guidelines, despite the fact that these procedures were originally developed for sheet piles or anchored walls on relatively shallow excavations supporting a medium dense soil. The present study draws on the applicability of such simplified tools to model the static response of deep excavations in stiff gravelly soils and their implications for the design. For that purpose, the static response of an excavation supported with anchored piles was evaluated with a detailed finite element model of a case study and the results compared with the simplified hand-calculation procedures. The study unit was the excavation for the Beauchef Poniente building located in the fluvial deposits of the Mapocho River in Santiago, which has a 6200 m2 plan area and a depth of 28 m. The excavation was supported with reinforced concrete piles of 1 m in diameter and anchored at three levels. A plain strain finite element model was developed in PLAXIS 2D using the Hardening Soil constitutive relation to capture the shear-deformation response of the gravel. The soil parameters were calibrated against large scale triaxial tests on Santiago gravel and the displacement profiles measured with inclinometers. The analysis showed that the static earth pressures on the pile and anchors tension computed from the 2-D non-linear finite elements model are in excellent agreement with the simplified design procedures such FHWA guidelines or simple elastic beam approximations.