A case study of the behaviour of a vertical seawall

Abstract

Reclamation is a major construction activity in Singapore, and this often entails the construction of a vertical sea-wall to contain the reclamation. In Singapore a frequently used technique is the use of L-Blocks. However, there are concerns about the movement and tilt of such relatively light blocks. An ongoing reclamation in the northeast of Singapore makes use of nearly 5.6 km of such wall. As a requirement, prior to commencement of construction, a finite element study was carried out to analyze the possible movement and tilting of the blocks as well as the long-term settlement of the seabed. Instrumentation clusters were then installed to provide valuable data to validate the accuracy of the design and also allow lessons to be learned from the difference between prediction and measurement. This paper is a report of the comparison between prediction and performance that was carried out at this site. As is the case in many actual constructions projects, the effect of certain activities unanticipated in the design caused the measured value to differ significantly from prediction. When these are factored out, it is evident that the finite element analysis can produce reasonable trend, though not the magnitude. However, the results thus far suggest that two simple steps can greatly improve performance, namely a more accurate soil profiling and accounting for the higher stiffness of stiffer strata due to non-linearity at small strain.