Lessons Learned from Construction of Two LNG Cryogenic Sumps

At a liquefied natural gas facility in Trinidad it was necessary to construct two cryogenic sumps. The excavations were approximately 9m x 9m and 7.5m deep and 16m x 16m and 9.9m deep. The design of each sump was to drive sheet piling through the upper soft marine deposits into the hard old marine sediments. As the excavation of the smaller sump was nearing completion excessive wall movement occurred. Work was stopped and movement of the walls was monitored for two weeks until it was concluded that work could be safely resumed. The second sump was then redesigned using internal bracing to prevent similar movement. The bracing system was uniquely designed on site using scrap pieces of beams for the wales and steel pipe piles for the struts. During installation of the sheeting for the second sump, sheet piles were driven extremely easy with a vibratory hammer for the full depth whereas the initial sump required an impact hammer to drive the sheets full length. As a result, additional sheet piling was imported, cut into 2 meter sections, welded onto the existing sheeting and each sheet was redriven. The excavation and construction of the sump was then successfully completed.