Dartmouth Shopping Centre — Rock Anchors

A commercial redevelopment in Dartmouth needed its rock walls held in place while the excavation went down beside them. The design called for 152 grouted rock anchors, 8 and 10 metres long, drilled into the face at a downward angle and plated against the rock.

The engineer’s sequence set the pace: one row at a time, with every hole grouted within 48 hours of being drilled. Each bearing plate sits on a formed grout block, so the load goes into sound rock however rough the face is behind it.

Along one section the anchors as specified were never going to work. Most of what came out of those 26 holes was crusher dust, and an open hole would not have held its shape long enough to place a bar and grout it. We proposed hollow-bar anchors instead: the bar drills its own hole and stays in it, and the grout is pumped down through the bar to fill the hole from the bottom up. The engineer approved the change, and all 26 were drilled and installed in two days.