ABSTRACT
During the past decade, jet grouting has become a common method of ground improvement to facilitate microtunneling, tunneling and deep excavations in marginal to difficult ground conditions, particularly on the Island of Oahu, Hawaii due to a combination of unique geology and environmental protection requirements. Design considerations, construction issues and performance of jet grouted soils and variable uncemented and cemented ground for horizontal directional drilling (HDD), microtunneling and shafts construction are summarized and evaluated for seven recent major trenchless pipeline installation projects (US$ 20 to 40 million each) in urban Honolulu, under Honolulu Harbor and in the Pacific Ocean. Jet grouting was performed for pipeline and manhole support, shaft perimeter support, and groundwater control in complex geologic conditions where jet grouting served both temporary and permanent roles. One case history involved an emergency design/built microtunneling project and FEM analysis was found to be a very useful tool in making important modification to 15m deep jacking shaft groundwater control design and to persuade the project team to accept the recommendations. Also included in the evaluation is a forensic evaluation of jet grouting related contract problems and claims ended in legal dispute.
Design considerations include geotechnical baseline conditions and specification requirements. Construction issues include jet grout column size and strength variations due to subsurface conditions, missing grout zones, shafts performance with jet grouted bottom plug for ground water control, ground heave and subsidence associated with jet grouting and shaft excavation perimeter support constructed using jet grouted columns. Deeper excavation depths ranged from 6m to 14m below sea level and jet grouting depths ranged from 1m to 40m below sea level.
Keywords: Jet grouting; construction claims; shaft; microtunneling.
