- Nefco, TreviIcos JV
- Rhode Island, USA
- PBA 928
To prevent pollution due to sewer overflow into the Narragansett Bay, the commission decided for two 70 m deep, 9 m diameter and 3 miles long storage tunnels with drop- and ventilation shafts.
Seven pairs of shafts are drilled of which three pairs with the Wirth top drill rig. The other four shafts for research purposes with 3 different kinds of drill methods.
The job was executed with the hydraulically driven 280 kNm PBA 928. The rig performed well for excavating both the overburden as the rock. Two flat bottom drill bit bodies with effective hole cutting diameters 1210mm and 2130mm are used. Both with a compressed air chamber for reversed air lift drilling.