Design of Cantilever Soldier Pile Retaining Walls in Stiff Clays and Claystones

The T-REX Project is a $1.67 billion project in the Denver Metropolitan area that consists of approximately 19 miles of a new Light Rail Transit (LRT) line, and improvements to approximately 17 miles of two interstate highways. Several miles of new retaining walls were required to provide for widened roadways and new light rail track. Because the right-of-way was restricted, tied-back walls were often infeasible, and so cantilever caisson walls with heights of over 30 feet and diameters up to 4 feet were employed. The caisson walls represented a considerable expense to the design-build team, and significant studies were performed to optimize the design. Foundation conditions along most of the alignment consisted primarily of stiff clays and relatively weak claystone, often with moderate to high swell potential. A study of design methods available for walls in these materials indicates that uncertainties exist in selecting the appropriate long-term loading, soil strength, and even the method of analysis for design of long-term soldier pile walls. This paper describes the evaluation of the uncertainty and selection of a design approach for the project.