Australian-based TBM manufacturer, TERRATEC, celebrated the delivery of two hard rock tunnel boring machines (TBMs) for the second phase of tunneling on the Royal Irrigation Department’s Mae Tang-Mae Ngad water diversion project, in northern Thailand, following successful factory acceptance tests last month.
The robust 4.74-m diameter TERRATEC Double Shield machines will be deployed by Thai contractors Right Tunnelling Co. Ltd. and Siamphan Enterprise PCL on two contracts – totaling over 15 km of TBM driven tunnel – for the 25km-long Phase 2 tunneling works, which traverse the challenging mountainous terrain north of Chiang Mai city.
These TBMs have been designed to confront the highly complex and variable geology of the region, which ranges from granite, gneiss, quartzite and schist, to sandstone, siltstone, shale, slate, mudstone and claystone, and varies from massive to highly fractured and weathered rock masses (with a UCS range of 8 MPa to 220 MPa), including numerous fault and fracture zones and the potential for high groundwater inflows.
In order to handle these challenging conditions, the tough yet versatile TERRATEC cutterheads have each been equipped with heavy-duty 17-in. disc cutters and feature large bucket openings, as well as anti-wear plates and lubrication systems for the injection of foams and polymers to assist with wear prevention and dust suppression. The 1,500-kW Electric Variable Frequency Main Drives (VFDs) will allow the cutterheads to cut efficiently in harder rock zones at a maximum speed of 9 rpm and deliver 2,896 kNm of torque of to cope with more fractured zones of the alignment.
In addition, the machines are fitted with state-of-the-art probe drilling systems, located behind ring gear style segment erectors, that provide 360-degree coverage for probing and grouting of the ground ahead of the TBMs; as well as dewatering pumps that have the capacity to manage groundwater inflows of up to 100 L/sec.
“We are delighted to be working with TERRATEC as our partner on this landmark water tunnel,” said Teerapon Wangmontri, President of Siamphan Enterprise PCL. “Due to the complex geology expected on the project, we wanted to choose a tried and tested manufacturer of hard rock machines such as TERRATEC, whose double shield TBM experience is exceptional.”
As the two machines progress along their respective alignments, they will install precast concrete segmental lining rings consisting of four x 1,400-mm wide honeycomb style segments, with an inner diameter of 4 m, which will be backfilled with pea-gravel and grouted in place. Excavated muck and supplies will be conveyed via rail-bound systems.
The Mae Tang-Mae Ngad water diversion tunnel is located about 55 km north of Chiang Mai, in northern Thailand, and is designed to convey 28 cubic m per second of raw water from the Mae Tang River to Mae Ngad and Mae Kuang reservoirs. The project aims to augment the current water supply to the Chiang Mai and Lampun Provinces involving over 50 km of tunnel that is being built in two phases.
When the overall project is complete, in 2021, a savings of more than 160 million cubic m of water will be seen each year. The extra water will help support a range of industries and sectors, such as the consumer sector, agriculture and tourism.