Construction Case of Ground Improvement Work Using V-JET Method in Subway Station Renewal Work-Paper

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The report describes use of the V-JET high-pressure grouting method to improve ground beneath Minamisunamachi Station during a widening project on Tokyo Metro’s Tozai Line. Ground improvement was required before excavation to stabilize the underground structure and excavation base, while limiting settlement and track movement. Working beneath an operating station presented strict constraints: equipment had to fit within the station, weigh less than one tonne, and be movable through narrow spaces without disrupting train service.<br /><br />The construction team developed a compact machine, 1.7 m high and 0.9 tonnes, which could be transported on an electric trolley and moved manually. Work was conducted during limited overnight periods. Spoil viscosity was also reduced to prevent material from obstructing guide holes, creating uplift, or raising the track.<br /><br />Ground improvement caused settlement of the existing structure, attributed mainly to a temporary reduction in bearing capacity after soil cutting and before the improved ground hardened. Automated monitoring tracked structural movement. Construction locations and sequencing were adjusted, and work was paused when settlement increased. Although movement continued, relative displacement remained within the established control limits, and the work was completed without track deformation or disruption to subway operations.<br /><br />Full-length core sampling and uniaxial compression tests confirmed that the improved ground met the project’s required performance criteria. The measured strength variability was comparable to that of conventional deep-mixing methods. The case demonstrates that compact equipment, careful spoil management, staged construction, and continuous deformation monitoring can enable jet-grouting work in confined, operational railway environments.

Keywords

V-JET grouting

high-pressure grouting

ground improvement

Tokyo Metro Tozai Line

Minamisunamachi Station

settlement monitoring

compact construction equipment

operational railway environment

deep mixing comparison

excavation support