Better prediction of the geotechnical challenges of tunnelling through Chalk has been gained through improved definition and understanding of its stratigraphy.
“Over the last 30 years we have gone from just defining Chalk as Upper or Middle to identifying individual stratigraphies and flint beds, which is essential to understand the engineering behaviour,” said Chalk Rock director Rory Mortimore speaking at the opening day of the Chalk 2018 conference yesterday.
Mortimore’s keynote speech explored how the sector has developed since the last Chalk conference in 1989 and said that this greater understanding has benefitted both Crossrail and Tideway. “It will also benefit HS2 and the Stonehenge tunnel,” he said.
Mortimore stressed that accurate core logging is vital to identify the stratigraphy and identify marker beds and flint bands for borehole correlation.
Improvements in classification of micro-textures, analysis of stress and diagenic history and detailed understanding of cementing and bonding since the 1989 conference were also presented by Mortimore.
Nonetheless, he said that further research was needed. “At what point does cementing become more important than bonding? That is a key engineering question,” said Mortimore.
“There is also a long way to go to fully integrate properties, texture, laboratory tests and field scale tests into ground models.”