Ground deformations caused by the construction of the Rio Piedras underground station using the stacked drift tunneling method

A geotechnical monitoring program has provided valuable information of surface and subsurface ground movements associated to the excavation of the Rio Piedras station of the Tren Urbano Project using the stacked drift tunneling method. The stacked drift tunnel was constructed with fifteen approximate 3 x 3 m square concrete-filled drifts or small tunnels and was excavated through highly overconsolidated silty clays, sandy clays and sands known as the Hato Rey formation (Older Alluvium). Compensation grouting was undertaken between the tunnel and overlying structures to compensate for ground losses associated to the tunnel. Additionally, consolidation grouting was injected in the lower drifts area to improve underground conditions during tunneling.; The monitoring data was compiled, analyzed and summarized in an attempt to relate the measured ground movements to construction activities and to compare the measurements with the settlement predictions. The monitoring data of most of the instruments at the tunnel are graphically presented in this report.; The ground movements associated to the excavation of the stacked drift tunnel were larger than predicted. Much of the observed surface and subsurface settlements developed after the drift tunnel heading passed the locations of the instruments and is therefore associated to the ground loss around the temporary tunnel bracing. The use of compensation grouting proved to be useful in minimizing the settlements.