Project

A 670m long bored tunnel was constructed for cables and utilities in Pandan, Singapore. The tunnel was constructed 16m below ground and runs below the Sungei Pandan rivermouth. Three shafts were built for the tunneling operations.

Jet grouting works were performed for the construction of lateral intermediate and base slabs for shaft excavation support and groundwater control. In addition, jet grout blocks were formed at tunnel break in/break out locations and to provide additional support for the thrust block. The jet grouting works were carried out in soft marine clay, silty clay and peaty clay.

The jet grout slabs were designed to be between 1.5m and 2.9m thick. The target unconfined compressive strength of the jet grout material was 1.0 MPa.

Quality control measures included the control of the grout mix, online monitoring of drilling and grouting parameters during execution, sampling of the grout-soil backflow as well as post construction testing via coring tests.

In total, about 1,900 m3 of jet grout slab was formed.