Abstract
A section of the Deep Tunnel Sewerage system (DTSS) in Singapore is aligned under the Singapore Central Expressway (CTE) and Pan Island Expressway (PIE) and crosses the Kallang River at three locations. At a particular section of the DTSS adjacent to the PIE, the tunnel crosses the Kallang River in a section known as Woodsville. The Singapore Land Transport Authority (LTA) is constructing a major cut and cover highway tunnel, known as the Kallang and Paya Lebar Expressway (KPE) which follows part of the Kallang River and intercepts the PIE at Woodsville. At the latter location, the KPE crosses over the DTSS tunnel. To control the excavation-induced heave of DTSS tunnel that would be caused by the excavation of the expressway tunnel above it was necessary to improve the ground condition at the DTSS tunnel horizon. Jet grouting, using a triple tube method, was selected as the most suitable means of ground improvement. Jet grouting parameters including the lifting rate, water pressure, water flow rate, grout pressure, grout flow rate, air pressure and rotation measurements can be used to verify the jet grout column diameter and the quality of each column. Target jetting parameters were defined at start of operation in representative ground conditions and were verified by coring and compressive strength tests prior to installation of the production columns. An extensive field and laboratory test programme was under taken to investigate whether the performance criteria for the jet grouting work had been achieved. In this study, the grout energy plots of about 300 columns were analysed and compared with the field and laboratory test results. The pressure meter modulus values presented in this study were obtained from the loading curves. It was observed that the integrity of grout core is interrelated with the grout energy input. Based on detailed numerical analysis, it was established that the strength and the stiffness of the grout columns should be greater than 600 kPa and 150 MPa to maintain the tunnel heave within acceptable design limits. A detailed post construction testing programme carried out at this site confirmed that a grouting energy of over 75 MJ/m is adequate to achieve about 1.6 m diameter grout columns with the above specified strength and stiffness parameters. Based on pre and post construction field and laboratory testing programme a reliable correlation is established between SPT 'N' value and the design modulus value for jet grouted material as: design = 8N MPa. In addition, the grouted material depicted predominantly brittle behaviour with occasional strain softening effect. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.
Published Version
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