Box Jacking Method Implementation in Rock for Mesaimeer Pedestrian Underpass Structure in Qatar
الملخص
Mesaimeer pedestrian underpass is proposed under the live traffic of Sabah Al Ahmad Road, Doha, Qatar which consists of a four dual lane carriageway, in addition to diverge lanes, service road lanes and right turn lanes by box jacking/pushing method for a total distance of 80.6 m. Due to the necessity of maintaining undisturbed traffic and to avoid disruption of the existing utilities crossing over the underpass alignment, the use of conventional Cut and Cover method is not feasible. Accordingly, trenchless construction method by box jacking/pushing is to be implemented in weathered limestone rock overlaid by fill soil. The method of construction of box jacking includes constructing shaft as launching pit for jacking operation, aligning the precast concrete box into position, excavating the soil/rock at the face of the precast concrete box, then pushing the box into the excavated length, and repeating the process. This paper includes overview of the project and its challenges intending to bring greater familiarity with the box jacking process in rock formation. The design and anticipated construction challenges are discussed from both structural and geotechnical perspectives. The challenges faced include box segment protection details, waterproofing details, construction and expansion joint details, high jacking loads due to rock formation, excavation advancement rate, necessity of grouting at box over-head and impact on existing utilities. Both structural and geotechnical analysis/design are assessed by numerical finite element modelling (FEM). Further, instrumentation and monitoring measures are planned to monitor various utilities and assess the impact during construction.