The Santa Rosa Tunnel: AT – Pipe Umbrella Support System permits Continuation of Excavation following Tunnel Collapse

In Lima, a Tunneling project is currently under construction that will efficiently connect the northern suburb of San Juan de Lurigancho with the suburb of Rímac located further towards the South-West. The project includes two parallel, 300m long road tunnels – the San Martín and Santa Rosa tunnels that will lead through the Santa Rosa Hill. The tunnel tubes are 8m high and 14.2m wide and accommodate two 3.5m wide lanes per direction.

Excavation of the Santa Rosa Tunnel had to be interrupted in February 2011 when a part of the tunnel collapsed as work was progressing. Following the collapse, a new technical study was carried out that would ensure that the tunnel could be advanced safely. In contrast to the first design, the tunnel will now be lined with reinforced concrete instead of conventional concrete nearly along its total length. The new design requires approx. 10 x as much reinforcing steel as originally planned.

For the technically demanding task of excavating the collapsed part of the tunnel a second time, DSI Peru supplied the Type AT – 139/NC Pipe Umbrella Support System with Threaded Nipple Couplings. This system is a special development of DSI: Additional steel nipples with a threaded connection are pressed into and welded onto both ends of the extension tubes. This threaded nipple connection provides an elastic design load over the entire pipe umbrella length which is equal to the one of a standard pipe. Thereby, the AT – Pipe Umbrella Support System increases the stability in the working area by transferring loads in the longitudinal direction and decreasing excavation induced deformations.

Thanks to the high stability and safety provided by the AT – Pipe Umbrella Support System in unstable ground conditions, work could be continued quickly and efficiently. DSI also provided design-related and on-site support during the entire construction phase.