Keywords: Breaking up from heading in soft ground (Walker 1888).jpg Breaking up from heading in soft ground Severn tunnel construction Original Thomas A Walker 1888 The Severn Tunnel Facing page 82 <br>Scan Internet Archive http //www archive org/details/severntunnelits01walkgoog 1888 Thomas A Walker PD-old-100 Scans from Walker 1888 the Severn Tunnel Tunnelling |