Abstract
The author describes the construction of a 660 metre tunnel through the Penmaenbach headland, forming part of the A55 improvement scheme. The headland is formed of intrusive rhyolite rock of Ordovician age, and is known to be highly fissured. A non electrical low vibration blasting technique (nonel) was utilized (see IRRD 261321). At the end of the tunnel a short length of soft ground and mixed faced working was driven by multiple headings using a labour intensive arch supported system. The construction of the two tunnel portals is compared. The West portal is formed square into a steep rock face exposed after removal of an extensive talus slope. Drilling was carried out using a holman voltac tracked drill rig and rock was cleared after blasting using a hydraulic backactor. The East portal formed at a shallow skew angle required supported open cut excavation designed to retain the hillside. (TRRL)
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