Three-dimensional analysis of basal heave for excavations with diaphragm walls

Plane Strain (two-dimensional) analysis is regularly used by engineers to design braced excavation system as three dimensional analysis is very computational expensive and time consuming. However, the results from plane strain analysis can be excessively conservative when the length of the excavation is small. Both plane strain (2D) and three-dimensional (3D) finite element analyses were carried out in this study. The main aim of this study was to determine the influence of the embedment wall depth (D), excavation length (L) and wall thickness (d) on the performance of a braced diaphragm wall system. The results are compared in terms of compressive strut force, lateral wall movements and basal heave factor of safety. The Plane strain ratio (PSR) which is defined as the maximum wall deflection from 3D analysis divided by the maximum wall deflection from 2D analysis is used to compare the wall performance for a number of different excavation and wall geometries. The finite element analyses indicate that the basal heave factor of safety is proportional to the embedment wall depth and wall thickness, but inversely proportional to the excavation length. The increase in wall embedment depth had a more significant influence on the lateral wall deflection, strut force and basal heave factor of safety for a 1.0 m thick diaphragm wall compared with a 0.6 m thick diaphragm wall. In general, the two dimensional analysis gives the most conservative results compared with the three-dimensional analysis, particularly when the length of the excavation is small.Bachelor of Engineering (Civil