A Soil-Water Coupled Finite Element Analysis of Open-Cut Excavation for Soft Clay Deposit by an Elasto-Viscoplasctic Model

Abstract

A case study of open-cut excavation in soft clay deposit has been performed by a soil-water coupled finite element analysis with an elasto-viscoplastic model. As a part of the construction of the new subway line called Nakanoshima line in Osaka, large and deep excavation has been carried out by the open-cut excavation method with earth retaining wall through the thick alluvial Nakanoshima clay deposit Nakanoshima clay is soft and sensitive and the thickness is about 10 meters. Since the construction site is located at the center of Osaka city and is surrounded by many civil structures, it was necessary to minimize the deformation of ground behind the earth retaining walls. One of the earth retaining wall is very close to the big buildings and the other is also very close to the revetment of river. The excavation has been successfully performed. In the present study, a case history of the excavation in the construction of subway station mentioned above is numerically back analyzed. In the analysis, a finite element method based on a Biot's type of two phase mixture theory [1] is adopted and an elasto-viscoplastic model considering structural changes [2] is used. Comparison between numerical analysis results and the measured results shows that the simulations method can well reproduce the deformation of earth retaining wall by incorporating the proposed compensation method of measurement data. In addition, it is confirmed that the construction has been successfully executed without significant damage of earth retaining wall and the alluvial clay deposit. Furthermore, the effect of time-dependent behaviors of clay during the excavation such as creep and consolidation are discussed.