Field Response of High Speed Rail Box Tunnel During Horizontal Grouting

The construction of two bored tunnels passing underneath an existing high speed rail (HSR) box tunnel needed to traverse obliquely through the diaphragm wall originally used for excavation and lateral support during construction of the HSR box tunnel. An access lift shaft was constructed adjacent to the HSR box tunnel diaphragm wall to provide access for the horizontal grouting equipment used to modify the surrounding soil to have sufficient water tightness and shear strength for safe tunnel eye creation and removal of steel H-beams left within the soil mixing wall. The grout block behind the tunnel eye was constructed first, followed by a long distance (up to 52 m) horizontal grouting (LDHG) program to form the other grout block around the steel H-beams. Since the grouted area was confined by a box tunnel on top and diaphragm walls on both sides, inappropriate grouting pressure could cause significant vertical movement of the HSR box tunnel above and potentially endanger the safety of the HSR service within. The grouting program was adjusted in accordance to real time box tunnel motion as detected by electronic beam sensors along the side walls of the box tunnel. Our strategies for overcoming the challenges associated with long distance horizontal wash boring through diaphragm walls, scattered with steel H-beams, and accompanying grouting strategy will be presented in this paper. The vertical movement of the HSR box tunnel during the LDHG program was well controlled to less than 4 mm, while the maximum lateral displacement of the shaft diaphragm wall was maintained below 9 mm.