TUNNELLING IMPACTS | TECHNICAL


Left, figure 8: Initial pipeline profile


Calculation of longitudinal radius of curvature based on three consecutive flexural displacement data points


Flexural displacement profile


build almost all structures without significant vibration impact. In order to mitigate this risk, it is common for major asset owners (e.g. Transport for London (TfL), Thames Water Utilities Limited (TWUL)) to require an exclusion zone around their assets and this is typically 15m from a vibratory source which is usually piling or vibratory compaction. Even at greater ranges, some piling works can present


difficulties but modern ‘city rigs’ and pre-augured vibratory methods can often meet the requirements


of third-party asset owners in restricting PPVs (peak particle velocities) to acceptable levels. Straightforward predictive guidance is given in British Standard BS5228- 2:2009 for piling and tunnelling works and the Highways Agency (Transport Research Laboratory TRL) has published detailed predictive methods for a range of vibratory sources caused by mechanised construction works (Hiller & Crabb, 2000). Threshold values relating damage to transient and continuous vibration levels for various structural


Material capable of sustaining tension under bending (e.g. cast iron, ductile iron, steel) Bending (compression) D


y = D/2 Left, figure 9: Bending (tension) Neutral axis D y = D


Development of flexural tensile strains for pipe material either capable or incapable of sustaining tension under bending


Material incapable of sustaining tension under bending (e.g. masonry, vitrified clay, unreinforced concrete) Bending (tension)


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