Monitoring of a Deep Excavation Supported by Anchored Retaining Walls

Contiguous bored piles 80 cm in diameter with ground anchors were designed as retaining wall for a deep excavation. Inclinometers were utilized to monitor displacements. The maximum depth of excavation is 25 m, and the subsoils are composed of stiff clays with high plasticity. Design calculations were made by the two-dimensional finite element program Plaxis. The bored pile walls showed a fairly good displacement performance, being on the safe side under ordinary design conditions in which the ground anchors are perpendicular to the retaining walls. Diagonally positioned ground anchors were designed at a convex corner of the project to prevent the ground anchors from intersecting. Designing these diagonal ground anchors at the convex corner prevented stiff wall behaviour in this case. The deformation modulus is the key parameter for accurately predicting displacements. Back analyses of the retaining walls were executed based on measured displacements, and new deformation modulus values were found by using the actual displacements in Plaxis. These findings were compared with the deformation modulus values calculated by using some correlations based on the undrained shear strength given in the literature. Thus, correlations using the measured displacements of a deep excavation project are recommended for highly plastic clays.