A NEW ground improvement technique has been used to strengthen the walls of the historic Whalers Tunnel in Perth.
The Calcite Insitu Precipitation System (CIPS) was developed by two Australian research scientists, Dr Edward Kucharski and Dr Graham Price.
Inspired by the need to improve the capacity of offshore foundations in calcareous sand using natural processes, the simple technique involves combining two water-based solutions which on mixing react to produce calcite or calcium carbonate, replacing the cement that originally bound sand grains together.
The Whalers Tunnel was built in 1837 by the Fremantle Whaling Company through a natural limestone calcarenite outcrop and left unlined. Over the past 160 years, water seepage has washed the calcite cement out of the limestone, leaving the walls weak and friable in places.
Safety concerns and the risk of collapse led to closure of the tunnel in 1996.A remediation project was launched by the City of Fremantle, with support from the state government, to strengthen the tunnel to meet safety standards and restore public access, while preserving the structure for future generations.
The environmentally friendly solutions were sprayed on to the tunnel walls and the formation of calcite crystals bound the sand particles and larger fragments of limestone together. Reaction time is extremely fast, achieving in days what natural geological processes took millions of years to produce.
The £400,000 remediation project involved installing steel arches, held in place by a system of 52 ground anchors, and transparent polycarbonate infill panels to protect against rock falls.
In contrast, CIPS is practically invisible, preserving the tunnel's complex eroded texture, and cost only £8,000.The method also left the limestone porous, allowing the pore water pressure regime behind the tunnel walls to remain unaltered, a major advantage in terms of tunnel design and environmental considerations.Two thousand litres of solution were sprayed over 100m 2in three passes along the tunnel, with each treatment taking a day.
Tests conducted by project engineer Ove Arup & Partners and geotechnical designer Dr Derek Pennington showed the CIPS treatment greatly increased the surface strength of the tunnel walls, making them more resistant to wind and water erosion.
The developers say the method can also be used to protect masonry, as well as being used in many civil engineering and mining applications such as the stabilisation of slopes and excavations, enhancing building foundations, coastal protection, repairing highway bases and strengthening railway embankments.
Australian universities have been quick to harness the novel technique in a wide range of applications, while research by Imperial College and Geotechnical Consulting Group (GCG) for London Underground has examined the CIPS stabilisation of ash embankments.
Awards from the Royal Academy of Engineering and Institution of Civil Engineers allowed Dr Fiona Chow of GCG to undertake research at the University of Western Australia to investigate improvements in the behaviour of pile foundations.