Field Performance of High-Speed Rail Box Tunnel during Horizontal Grouting

The new twin bored tunnels passing under an existing high-speed rail (HSR) box tunnel need to break through a diaphragm wall retaining earth pressures during the construction of box tunnel. In addition, along the alignment there are steel beams that might affect the tunnel boring machine (TBM) advance. To resume TBM advance, surrounding soil is improved to achieve required water tightness and shear resistance using the long distance horizontal grouting (LDHG) up to 75 m from nearby access shafts. Because the grouted area is confined by box tunnel at top and diaphragm walls at both sides, any improper grouting programs can cause significant heave to the box tunnel and rail above and endanger the safety of the high -speed rail service. Electronic beam sensors installed along two side walls in the box tunnel provide the real-time elevation changes of the box tunnel to soothe public concerns and adjust the grouting program accordingly. The countermeasures to resolve the challenges in the long distance horizontal boring operations and grouting works will be discussed in this paper. The maximum elevation variation of the HSR tunnel in the LDHG program is well controlled less than 4 mm. The maximum deflection of the shaft diaphragm wall is less than 6 mm for the breakout block grouting and below 10 mm for the LDHG program.