An already fragile slope above the SH7b, the road only access into the resort town of Hanmer Springs, was further affected from the 2016 7.8 magnitude Kaikoura Earthquake and resultant aftershocks with frequent low energy rockfall and debris onto the state highway.
Initially the entire slope which was around 300m long and up to 40m high was designed to be covered with a low energy mesh drape to contain the small debris and rockfall to the road edge which would have been quick and easy to construct.
After commencing we found further tension cracks and localized movements to the slope to the North of the existing area that required stabilisation. Rockfall sources were also found to be coming from further up the slope and bouncing, so the design changed to include a 100m long rockfall attenuator through the middle section with the additional slip area treated with 700m2 of actively stabilised G65/3mm TECCO mesh anchored with 30/11 into broken ground with grout flush.
To construct the concrete plinths high up the slope for the attenuator a significant amount of tree felling was completed with a helicopter used to fly material and the concrete to the post foundations along the slope. The initial G80/2mm DELTAX drape was still completed as designed to the southern end of the face.