Deep excavation in under-consolidated clayey deposit

In this study, a deep excavation in an under-consolidated deposit in Zhuhai, China, was reported and investigated via plane strain finite element analysis (FEA). First, the project was simulated via FEA (under-consolidated deposit), and a reasonable agreement between the lateral displacement of the measured and simulated retaining wall was obtained. Another FEA was then conducted under the assumption that the deposit was in a normally consolidated state. The numerical results indicate that the under-consolidated case resulted in a 25% increase in maximum lateral displacement of the contiguous pile-formed retaining wall, a 32% increase in bending moment in the wall, and approximately twice the maximum surface settlement behind the wall, when compared with those of the normally consolidated case. The main reasons for this are as follows: (1) the under-consolidated deposit was weaker, and (2) the ongoing consolidation of the under-consolidated deposit induced green-field settlement (approximately 4 mm) during the project period, thereby enhancing the bending deformation of the wall. Therefore, when designing deep excavation in an under-consolidated deposit, not only its weaker strength but also the negative effect of green-field settlement during the project period should be considered.