Design, construction, and monitored behavior of two large-diameter cylindrical diaphragm walls on an offshore reclamation island

Abstract

Two semi-underground liquefied natural gas (LNG) storage tanks with an excavation depth of 25.6 m were constructed on an offshore reclamation island in Dapeng Bay, Shenzhen, China. Two cylindrical retaining diaphragm walls with a diameter of 100 m were adopted for the deep excavation. This paperpresents detailed information on the design and construction of these two cylindrical retaining diaphragm walls. As the elevation changes in the soil and rock layers were very severe, the non-axisymmetric distribution of the lateral pressure was significant. Diaphragm walls with different embedded depths were designed to cut off the seepage paths inside and outside the retaining structure. The strength of the rock was extremely high; therefore, a combination of predrilling using a rotary excavator and grooving using a milling machine was adopted in the trenching construction of the diaphragm wall. The monitored soil and rock pressures acting on the diaphragm wall are discussed. The lateral deformation of the diaphragm wall was described, and the hoop force and vertical bending moment of the retaining diaphragm wall were analyzed, which could be a reference for similar projects.