scholarly journals Engineering Geological Design of Underground Works for Upper Madi Hydroelectric Project

2012 ◽  
Vol 9 ◽  
pp. 27-34
Author(s):  
Prem Krishna K.C. ◽  
Krishna Kanta Panthi
Keyword(s):  
Rock Mass ◽  
Complex Geometry ◽  
Empirical Method ◽  
Underground Structures ◽  
Hydroelectric Project ◽  
Headrace Tunnel ◽  
Himalayan Geology ◽  
Rock Mass Condition ◽  
Complex Geology ◽  
Actual Rock

Himalayan geology is termed as one of the youngest tectonic formations in the world. Tunneling in this region is hence complex in nature. The very complex geology in the region offers challenges in stability of even the best located underground structures. Tunneling in weak rock is more challenging in terms of stability and application of support. Moreover, in many occasion, prediction of the rock mass has been done optimistically in most of the underground projects in Nepal. In this paper, predicted versus actual rock mass condition has been compared for two already completed projects. Based on this needed support is calculated by empirical method for the project under investigation and later on verified by numerical analysis using the software Phase2. Stability analysis is also done for both high pressure headrace tunnel and underground surge shaft. Numerical method of analysis has an added advantage over empirical and analytical methods, particularly in complex geometry. The Phase2 code and the Hoek-Brown Failure criterion have been used to determine the state of stress, strength factor and deformations around the periphery and in the tunnel walls.DOI: http://dx.doi.org/10.3126/hn.v9i0.7069 Hydro Nepal Vol.9 July 2011 27-34

scholarly journals Comparison between Predicted Rock Mass Classes and Actual Rock Mass Classes in Headrace Tunnel of Upper Mai Hydroelectric Project, Nepal

2018 ◽  
Vol 22 ◽  
pp. 41-44
Author(s):  
Kanchan Chaulagai
Keyword(s):  
Rock Mass ◽  
Design Stage ◽  
Design Phase ◽  
Mica Schist ◽  
Construction Time ◽  
Hydroelectric Project ◽  
Actual Observation ◽  
Headrace Tunnel ◽  
Actual Rock ◽  
Q System

This study involves comparison of predicted rock mass classes in design stage with actual rock mass classes of headrace tunnel of Upper Mai Hydroelectric Project. The total length of headrace tunnel is 2070.52 m. The lithology of the study area consists of gneiss, schistose gneiss and mica schist. The rock mass classifications, Q-system were used to predict rock mass classes during the design phase as well as for classify rock mass during excavation of headrace tunnel. The applicability and validity of proposed classification has been checked by comparing the prediction with actual observation after completion of excavation. It was found that the predicted classes does not exactly matches with the actual rock masses as a results effecting in construction time as well as in cost and economy of the project. HYDRO Nepal JournalJournal of Water Energy and EnvironmentIssue No: 22Page: 41-44Uploaded date: January 14, 2018

scholarly journals The Use of Self Supporting Capacity of Rock Mass for Sustainable Hydropower: An Analysis of the Middle Marsyangdi Headrace Tunnel, Nepal

1970 ◽  
Vol 6 ◽  
pp. 18-26
Author(s):  
Kiran K. Shrestha ◽  
Krishna K Panthi
Keyword(s):  
Rock Mass ◽  
Stability Analysis ◽  
Concrete Lining ◽  
Rock Support ◽  
Hydroelectric Project ◽  
Tunnel Section ◽  
Geological Conditions ◽  
Headrace Tunnel ◽  
Support Principle

The history of hydropower development in the Himalaya indicates that many tunnels have suffered from cost over- runs and delays. These issues are directly dependent on the quality of rock mass and the permanent rock support applied in underground excavation. Right judgment and proper evaluation of the self supporting capability of the rock mass and the use of optimum rock support systems help considerably in reducing construction cost and delays. This paper examines such issues as geological conditions in the Himalayas and varying approaches and costs in tunnel construction. An assessment is made regarding the exclusion of permanent concrete lining in the headrace tunnel of the 72MW Middle Marsyangdi Hydroelectric Project in Nepal. The project has 5.2 km fully concrete lined headrace tunnel that passes through fair to poor rock mass. The evaluation is based on the use of actually recorded rock mass quality of the headrace tunnel during construction and rock support principle used at the comparable Khimti Hydro Project headrace tunnel. The evaluation includes calculation of equivalent tunnel section for similar headloss, stability analysis, assessment of possible water leakage, and required injection grouting measures. We conclude that the headrace tunnel without permanent concrete lining was possible and would have been equally stable, at considerable fnancial savings.Key words: Equivalent tunnel section; Squeezing; Tunnel lining; Stability analysis; Leakage control; Hydropower; NepalDOI: 10.3126/hn.v6i0.4188Hydro Nepal Vol 6, January 2010Page : 18-26Uploaded Date: 23 January, 2011

scholarly journals Engineering geological study of the Mai Khola Hyroelectric Project, Ilam, eastern Nepal

2018 ◽  
Vol 56 (1) ◽  
pp. 55-63
Author(s):  
Pusker Raj Joshi ◽  
Kamal Kant Acharya ◽  
Rabindra Dhakal
Keyword(s):  
Rock Mass ◽  
Surge Tank ◽  
Surface Mapping ◽  
Concrete Dam ◽  
Hydroelectric Project ◽  
Hill Slope ◽  
Headrace Tunnel ◽  
Middle Siwalik ◽  
The Hill ◽  
Poor Relation

The Mai Khola Hydroelectric Project, a run-of-river scheme, has a capacity 15.6 MW. It has design discharge of 16 m3/s, design net head of 112.71 m and includes 2192 m long inverted-D shaped headrace tunnel with 4.3 m diameter, concrete dam of 10.6 m height and semi-surface powerhouse. The project area consists of rocks of the Middle Siwalik Subgroup, comprising of sandstone, siltstone and mudstone, inter bedded frequently. Sandstone is predominant in head works area, headrace tunnel and is completely absent in a surge tank, and penstock alignment. Siltstone alternating with thin layer of mudstone is predominant in powerhouse area. The headrace tunnel outlet portal and surge shaft lie on the hill slope characterized by colluvial deposits. The penstock alignment passes through highly weathered siltstone and mudstone. The semi-surface powerhouse and the tailrace canal lie on the lower alluvial terrace. The Main Boundary Thrust (MBT) is the major structure observed at about 90 m upstream from the weir axis. The average Q-value of rock mass along the headrace tunnel surface mapping was 0.062–1.33 and after excavation the value was 0.004–0.23. An extremely poor to poor relation was observed between the rock mass class on surface mapping and exceptionally poor to very poor on excavation. Analysing the results of the surface and underground study of the rock mass, the excess support is required during construction.  

scholarly journals Engineering geology of Kankai Hydroelectric tunnel alignment

2006 ◽  
Vol 31 ◽  
pp. 67-74
Author(s):  
Sunil Kumar Dwivedi ◽  
Prakash Chandra Adhikary
Keyword(s):  
Rock Mass ◽  
Poor Quality ◽  
Project Area ◽  
Hydroelectric Project ◽  
Headrace Tunnel ◽  
Quality Category ◽  
Tunnel Alignment ◽  
The Stability ◽  
Quality Categories ◽  
Intake Portal

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.

scholarly journals Analysis of Squeezing Phenomenon in the Headrace Tunnel of Chameliya Project, Nepal

2014 ◽  
Vol 13 ◽  
pp. 44-51 ◽  
Author(s):  
Pawan Kumar Shrestha ◽  
Krishna Kanta Panthi ◽  
Chhatra Bahadur Basnet
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Cross Section ◽  
Support Pressure ◽  
Rock Mass Properties ◽  
Tunnel Wall ◽  
Hydroelectric Project ◽  
Mass Properties ◽  
Headrace Tunnel ◽  
Tunnel Cross Section

The headrace tunnel of Chameliya Hydroelectric Project, Nepal has faced severe squeezing problems from chainage 3+100m to 3+900m. Due to the severe squeezing and deformation, the tunnel cross section has narrowed considerably along this 800m long tunnel stretch. The tunnel wall closure (deformation) is mostly well over 1 m and the maximum recorded closure exceeds 2m. This paper assesses the squeezing phenomenon along this tunnel stretch through evaluation of rock mass properties and support pressure. Three different methods (two analytical and one 2D finite element numerical modeling program) are used in this analysis. The finding is that it is possible to predict extent of squeezing in tunnel if more than one method is used to verify rock mass mechanical properties. DOI: http://dx.doi.org/10.3126/hn.v13i0.10039HYDRO NEPAL Journal of Water, Energy and EnvironmentIssue No. 13, July 2013Page: 44-51Uploaded date: 3/13/2014

scholarly journals Back calculation of in-situ rock stresses for a tunnel project in Himachal, India

2011 ◽  
Vol 42 ◽  
pp. 117-124
Author(s):  
Krishna Kanta Panthi
Keyword(s):  
Rock Mass ◽  
Element Model ◽  
The State ◽  
Stability Assessment ◽  
Rock Support ◽  
Hydroelectric Project ◽  
State Of Stress ◽  
Headrace Tunnel ◽  
Tunnel Instability

Determination of in-situ stresses in the rock mass is necessary for stability assessment and proper design of underground openings. It is important to know the state of stress surrounding the opening so that right and optimum rock support is assigned as preliminary and permanent rock support. However, the majority of long tunnels with high rock cove r face severe tunnel instability problems related to rock stresses. The headrace tunnel of Parbati II hydroelectric project is one of such tunnels, especially the tunnel segment passing through Manikaran quartzite. It is known fact that the extent and type of stress induced instability vary greatly upon rock type, deformability properties, jointing and inter-bedding characteristics in the rock mass. This paper back calculates the state of stress using Phase 2  finite element model  in a TBM  bored segment of  the tunnel and  also briefly reviews mechanical properties of the  intact rock that may have direct link on the  nature of stress induced  instability. It is believed that back calculated stress magnitude may be useful for the stability assessment in other segment of headrace tunnel.

scholarly journals Fluid Flow and Leakage Assessment Through an Unlined/Shotcrete Lined Pressure Tunnel: A Case from Nepal Himalaya

2021 ◽  
Author(s):  
Krishna Kanta Panthi ◽  
Chhatra Bahadur Basnet
Keyword(s):  
Fluid Flow ◽  
Rock Mass ◽  
Cost Effective ◽  
Hydropower Plant ◽  
Water Leakage ◽  
Hydroelectric Project ◽  
Water Head ◽  
Headrace Tunnel ◽  
Hydraulic Jacking ◽  
Leakage Assessment

AbstractThe use of unlined/shotcrete lined pressure tunnels and shafts are cost-effective solutions for a hydropower project and are being implemented worldwide. To implement this concept, the ground conditions at the area of concern should be favorable regarding minimum principal stress magnitude, which should be higher than hydrostatic water head acting on the tunnel periphery. In addition, the rock mass should be relatively unjointed or joints in the rock mass should be relatively tight. Among the most important issues in the design of unlined/shotcrete lined pressure tunnels is the extent of hydraulic jacking and water leakage out of the tunnel during operation. This manuscript first presents fluid flow and potential hydraulic jacking assessment of two selected locations of the headrace tunnel of Upper Tamakoshi Hydroelectric Project (UTHP) in Nepal using the UDEC. It is noted here that the 7960 m long headrace tunnel will experience a hydrostatic water head that will vary from 2.9 to 11.5 bars (0.29–1.15 MPa). The headrace tunnel is supported by sprayed concrete (shotcrete) in combination with systematic rock bolts in the tunnel walls and crown. The invert of the tunnel and few hundred meters downstream end (at surge shaft area) of the headrace tunnel is being concrete lined after the completion of all other works. The qualitative fluid flow assessment carried out using UDEC indicated considerable pressure built-up in the joint systems suggesting potential hydraulic jacking. This was especially the case at the downstream segment (downstream from chainage 7100 m) of the headrace tunnel. The manuscript further presents the quantitative results of water leakage estimation from the headrace tunnel carried out using Panthi (Panthi KK (2006) Analysis of engineering geological uncertainties related to tunnelling in Himalayan rock mass conditions. PhD Thesis, NTNU, Trondheim, Norway;Panthi, Note on estimating specific leakage using Panthi’s approach, NTNU, Trondheim, 2010;) approach. The leakage assessment carried out indicated an average specific leakage of about 2.5 l/min/m tunnel, which may result in over 210 l/s leakage from the headrace tunnel. The evaluation also indicated that the outer reach (860 m downstream segment) of the headrace tunnel after chainage 7100 m seems extremely vulnerable and over 80 l/s water leakage may occur only from this headrace tunnel segment during operation of the hydropower plant.

scholarly journals Evaluation on the Potential Use of Shotcrete Lined High Pressure Tunnel at Upper Tamakoshi Hydroelectric Project

2012 ◽  
Vol 10 ◽  
pp. 73-80 ◽  
Author(s):  
Bibek Neupane ◽  
Krishna Kanta Panthi
Keyword(s):  
High Pressure ◽  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Pressure Head ◽  
Economic Loss ◽  
Hydroelectric Project ◽  
Headrace Tunnel ◽  
Key Factor ◽  
Input Variables ◽  
Pressure Tunnels And Shafts

Optimization of rock support is a key factor for successful use of underground space for hydropower development in the Himalaya. Therefore, finding innovative, optimum and economic solution will be the only way to guarantee such optimization. A main issue is to determine the extent of hydraulic fracturing and assess the water leakage possibility during the operation of such tunnels. The leaked water not only causes economic loss but also may severely affect the stability of tunnel, valley side slopes and the environment.The use of fully concrete/steel lined pressure tunnels against hydraulic fracturing in the rock mass is a costly alternative. Hence, it is advantageous to explore possibilities of minimizing the length of the concrete or steel lining in high pressure tunnels and shafts. A proper assessment of hydraulic fracturing of the rock mass plays an important role in this endeavor.This paper evaluates whether or not hydraulic fracturing (splitting) will occur at the 4,746m long shotcrete-lined high pressure headrace tunnel of 456 MW Upper Tamakoshi Hydroelectric Project (UTKHEP). The Upper Tamakoshi HEP is a high head project (gross head 822m) and the proposed shotcrete lined high pressure headrace tunnel will experience maximum hydrostatic pressure head of 40 bar (400m water column) at normal plant operation. To check the possibility of hydraulic fracturing, both deterministic and two dimensional numerical modeling techniques have been used. In addition, the paper also highlights the importance and challenges to be faced while estimating representative input variables needed for both deterministic and numerical modeling.DOI: http://dx.doi.org/10.3126/hn.v10i0.7118 Hydro Nepal Vol.10 January 2012 73-80

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