Jet Grouting Applications for Large-Scale Basement Construction in Soft Clay

This paper describes innovative applications of jet grouting to solve complex design problems for a large-scale basement construction in soft clay. Because the site was located adjacent to an existing mass rapid transit station and viaduct, very stringent criteria were imposed on the permissible displacements caused by site construction activities. A system of jet grout slab and block configuration, in conjunction with diaphragm walls and temporary steel struts, was adopted to provide lateral bracing for the main basement excavation. Ground treatment for a narrow excavation at a long vehicular ramp included a combination of jet grout slabs and vertical jet grout walls. The excavation of three large stair core openings was supported using vertical jet grout walls. A self-stabilized jet grout retaining structure, with terraced slopes on the front and back, was formed across the width of the basement to retain a temporary excavation 12m deep. This allowed simultaneous excavation for the basement to proceed, while foundation works were still in progress at the ground surface on the retained side of the jet grout structure. The triple fluid jetting technique was adopted to minimize disturbance to the existing ground during jet grouting operations. Excavation for the basement was successfully executed with inward wall deflections limited to 11.2mm where a jet grout block was used and 38.4mm generally.