Productivity Study of Box Jacking for Culvert Installations

Box jacking (BJ) is an open-face, trenchless, construction technique used for installing underground precast concrete segments having box or rectangular cross-sections. In this method, culverts and drainage structures, which are box or rectangular in shape, are installed through the ground from an entry shaft to an exit shaft. Box Jacking projects often face schedule delays or loss of productivity due to inherent uncertainties in identifying unknown underground conditions, change of soil, and groundwater level on culvert alignment. This leads to imprecision in cost estimates; thus, bidding prices for box jacking projects are usually kept on a higher side. In this paper, a need to document major productivity factors in BJ process is highlighted. This study identifies and ranks productivity-related factors in BJ process, and develops an analytic hierarchy model (AHP) to understand the relative interdependency among various factors that contractors and engineers consider to avoid delays and improve productivity. Ranking of these factors is expected to improve the productivity by planning and executing BJ projects in a more efficient manner. A total of 27 productivity factors are considered of which six factors - type of soil, shaft design, use of intermediate jacking stations, crew and operator experience, obstructions, or unexpected soil conditions and drive length - are identified to be critical.