Continuous surface wave testing as a new addition to the holistic approach of treating abandoned chalk mines and collapse features in chalk

Collapses in areas of chalk from either abandoned historical mines or natural dissolution features has been affecting domestic housing and infrastructure with increased frequency in the south of England. Recently, an holistic approach has been deployed on a number of remediation projects to combat this growing issue (Milne and O’Donovan, 2015). However, this approach relies heavily on extensive intrusive investigation techniques pre, post and during works, which causes severe disruption, time and cost issues. This paper summarises an extension to the holistic approach and describes the introduction of stiffness profiling by means of Continuous Surface Wave testing as an additional tool to monitor the treatment and investigation of collapse features and other weaknesses within chalk. Rapidly generated ‘simple inversion’ stiffness-depth profiles and advanced layered inversion stiffness-depth profiles, can be generated both pre and post treatment works and used as part of the holistic approach for investigation and validation purposes for all types of chalk remediation projects. As part of this approach Continuous Surface Wave testing can be used to locate and verify areas of uncertainty, allowing targeting of the the more expensive intrusive ground investigation techniques. This paper uses a case study of first-hand experienced of Continuous Surface Wave testing for remediation of a collapse in chalk in Hertfordshire. It focuses on both the results of this project trial and the appropriate application of Continuous Surface Wave testing alongside the wider holistic approach and describes the key benefits and limitations to the stakeholder, remediation contractor and designer. The paper provides a discussion of the opportunities for the use Continuous Surface Wave stiffness profiling as a rapid, and cost-effective way of obtaining real time non-intrusive data for control and management of chalk mine and collapse treatment schemes.