Lovat has signed a contract to supply a refurbished earth pressure balance TBM for two tunnel bores entirely below groundwater levels, with heads of up to 60m, in Istanbul by the end of the year.
The 3.6m diameter EPBM will be used by local contractor Oztas to drive the Gurpinar and Firuzkoy tunnels, which are 5,227m and 3.770m long, respectively.
After the RME136SE Series 19500 machine has been refurbished in Toronto, it will be launched to drive the longer of the two tunnels through strata consisting of hard to stiff over-consolidated plastic clay containing some weak sandstone, siltstone, claystone and tuff.
In terms of groundwater flow difficulties, greater inflow is expected at an anticipated fault zone. Elsewhere, saturated sand layers are on the alignment where the bore passes through a ‘formless landslide complex’, Lovat said. On this bore the maximum head above the invert is 60m.
The shorter drive, for the Tahtakale-Ambarh wastewater tunnel in Firuzkoy, will pass through three different geological formations and experience groundwater levels varying to result in heads of 1m-48m, the company added. The strata along the route will vary from similar ground to the first drive to enter very soft to firm sandy-silty clay as well as a zone of limestone with marl fragments and clay layers.
