Engineering geology of Kankai Hydroelectric tunnel alignment

This paper describes the engineering geological characteristics of rock mass in the headrace tunnel, powerhouse, and intake portal of the Kankai Hydroelectric Project. The project area lies in the Lower Siwaliks of east Nepal and consists of alternating sandstone and mudstone beds with frequent siltstone intercalations. The rock mass of the project area was classified according to rock mass rating (RMR) and rock mass quality index (Q) systems. It is of very poor, poor, to fair quality (categories V, IV, and III) in the headrace tunnel; of very poor quality (category V) in the powerhouse; and of fair quality (category III) in the intake portal. The stability analysis of irregularly jointed and fractured rocks of the area was carried out using SWEDGE and UNWEDGE. The analysis gave the safety factor of 0.45, 0.64, and 0.45, respectively for the powerhouse, intake portal, and headrace tunnel. The final safety factors obtained after the installation of support for powerhouse, intake portal, and headrace tunnel were 1.14, 3.33, and 4.53, respectively.

Engineering geological study of the Kali Gandaki 'A' hydroelectric project area, western Nepal Lesser Himalaya

The Kali Gandaki 'A' hydroelectric project area lies in the Lesser Himalayan Zone of the Syangja district of western Nepal. The rocks are characterised by highly deformed, thick sequences of the elastic rocks belonging to the Andhi Khola Formation and the carbonates of Darsing Dolomite, both belonging to the Kali Gandaki Supergroup. The dark bluish grey, brecciated and highly fractured dolomite is exposed on the abutments of the proposed diversion dam site area. It also forms steep cliffs to the north of the dam site. The contact between the dolomite and the overlying phyllite is a tectonized zone. This contact exposed along the exploratory audit and test trenches gives evidence of a fault dipping steeply towards the east. The phyllites exposed along the proposed headrace tunnel alignment and in the powerhouse site are variable in composition and rock strength. At the powerhouse area thin bands of limestone are intercalated in phyllites with sheared contacts. The headrace tunnel alignment makes acute angle with the foliation along most of the length and some sections passes parallel to the foliation. An inferred fault at about 1 km chainage, shear zones with varying thickness and a syncline at about 4 km from the intake portal are the main geological structures along the tunnel alignment which have to be carefully dealt with during the design and construction phase of the project.

Stability and stress analyses of headrace tunnel, Upper Seti Storage Hydroelectric Project, Western Nepal

The Upper Seti (Damauli) Storage Hydroelectric Project has a capacity of 128 MW, the storage type scheme, and includes 1000 m long horse shoe headrace tunnel, 140 m high concrete gravity dam, two diversion tunnels of lengths 712 m and 881 m and an underground powerhouse. The study was carried out to identify stability and stress conditions for the headrace tunnel to suggest the required tunnel support. The project area extensively covers dolomite and minorly covers slate. The rock mass classification showed fair to good quality of dolomite and poor to fair quality of slate. The surface wedges would form in intake portal and powerhouse site. In the headrace tunnel, structural wedges would be formed due to underground excavation and would be stabilized with the help of shotcrete and rock bolting. doi: 10.3126/bdg.v10i0.1419 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 45-54