To enable dredging in front of a 350m long quay wall at the Southampton Container Terminal, strengthening works were undertaken using jet grouting. During the course of these works the 26.5m deep sheet pile wall experienced a sudden and unexpected seaward movement.
GCG was commissioned to provide technical expertise in relation to the cause of the sudden movement of the sheet pile wall, and also to ascertain whether the strengthening works were fit for their intended purpose of enabling the berth do be deepened by an additional 3.2m.
We carried a series of two dimensional finite element analyses of the wall at Berth 205. Three basic analyses were carried out which covered the construction of the existing sheet pile wall, installation of the grout wall and dredging in front of the wall. The validity of the soil models and model parameters used in the analyses was checked by a comparison with the available laboratory data. The effects of key variables including the initial horizontal stresses in the ground, effectiveness of the relieving platform and its piles, tidal variations in water level in front of and behind the quay wall, different dredging levels, and fluid grout pressures acting during the formation of the grout wall were considered in the analyses.
Although some uncertainties existed, particularly in relation to loads that might have been imposed on the sheet pile wall during ‘original’ construction and subsequent jet grouted wall installation, the finite element predictions fitted the actual behaviour of the soil and quay walls at the Southampton Terminals very well. Because the state-of-the-art numerical analyses used to model the soil behaviour and construction sequence were regarded as producing high quality predictions that could be relied upon, they played a key role in the resolution of the associated legal proceedings.