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

PPT Presentation

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The report describes the use of the V-JET ground-improvement method during subway-station renewal beneath an existing structure founded on very soft ground. The improvement was intended to stabilize a primary beam and excavation base, and to limit settlement during construction. It was designed to cover 50% of the track’s longitudinal area, with a thickness of 2.0–3.8 m.<br /><br />Because the existing structure had no soil cover, blocked grout spoil could generate uplift. The construction plan was therefore changed to work from inside the station, retaining the weight of the overlying structure. To reduce disruption and avoid daily installation and removal of track scaffolding, the team also revised the temporary storage arrangement. Materials were transported by trolley for distances of up to 250 m.<br /><br />A compact construction machine was developed for the confined site. Its height was reduced from 2.5 m to 1.7 m, and its weight from 1.7 to 0.9 tonnes by separating the machine body from the hydraulic unit.<br /><br />The improved ground was silt with an SPT N-value of 0–1. Potential causes of settlement—including bleeding, grout-induced excess water pressure, temporary loss of bearing capacity, and a gap beneath the existing concrete—were considered. Water-filled settlement gauges were installed at structural joints, and the work was sequenced to disperse the effects of construction. Final settlement was about 90% of the primary control value.<br /><br />Full-length cores were tested for unconfined compressive strength. Results ranged from 0.95 to 3.52 MN/m², with an average of 2.06 MN/m² against a design strength of 1.00 MN/m². The work met the specified performance, remained within deformation limits, caused no track deviation, and was completed without disrupting train operations.

Keywords

V-JET

ground improvement

subway station renewal

soft ground

settlement control

grout injection

excavation base stabilization

confined construction

unconfined compressive strength

track operations