State of Practice: Excavations in Soft Soils

This paper examines the state of practice of the design and construction of excavations in soft soils. The review is based primarily on the author's experience, published case histories, and discussions with colleagues involved in the design and construction of excavations in soft soils. It is not a survey of current practices, because such a survey would not be practicable, or even useful, because of many variations in local practices. The paper examines major milestones in the development of the design and construction of excavations in soft soils, and reviews recent developments and trends in design and construction practices. Traditionally, the design and construction of excavations is handled contractually as a design-build contract, with the responsibility for the design and construction of the shoring system delegated to the contractor. However, new developments in analytical design tools and construction methods, as well as wider recognition of the potential legal consequences of the impacts of excavation-induced deformations on existing structures, and the need to address these issues in advance of construction, is leading to new approaches in the design and construction of excavations in general, and for soft soils in particular. Recent innovations in construction methods, such as the introduction of deep-soil mixing and jet grouting, are providing greater flexibility in the design and construction of excavations for deformation control. This paper reviews these developments and summarizes data from case histories to illustrate practical application of these new methodologies and construction techniques for the design and construction of excavations in soft soils.