Investigation on the Effect of Cyclic Moisture Change on Rock Swelling in Hydropower Water Tunnels

This manuscript investigates the interaction between cyclic wetting and drying, material composition/structure and swelling potential of weathered rocks. Laboratory tests were performed at the Norwegian University of Sciences and Technology (NTNU) and the Karlsruhe Institute of Technology (KIT). The rocks tested are of sedimentary and volcanic origin and were sampled from the headrace tunnels of two different hydropower projects located in Albania and the Philippines. Both headrace tunnels will experience a medium static water head of about 60 m at a base load of operation. However, hydropower plants of modern age are seldom operated to their base load due to power demand in the market, which causes fluctuation in the operation regime of the power plants. To determine the effect of moisture fluctuations on the swelling behavior of weathered rocks surrounding water tunnels, repeated wetting and drying cycles of swelling tests were performed on intact rock samples. The effect of unloading and thus allowing stagewise deformation to occur, as is the case in rock mass of shotcrete supported water tunnels, was comprehended in the testing procedure. Maximum swelling pressure tests on both pulverized and intact rock samples were included in the testing program. A comparison of the swelling test results is presented and correlated to the compositional and structural characteristics of each sample obtained by XRD and thin-section analyses. Finally, the effect of cyclic moisture change on the rock swelling is discussed in the context of long-term stability and support assessment of hydropower water tunnels

Norwegian Design Principle for High Pressure Tunnels and Shafts: Its Applicability in the Himalaya

Cost effective, safe and long term sustainable hydropower development is a key for the lasting economic growth in the Himalayan region. Increasing pressure towards the use of renewal and environmentally friendly energy for industrial growth and daily household use will force Himalayan region to exploit hydropower energy more extensively. The tradi-tionally used design approach of fully lined underground waterway system is costly, finan-cially unfeasible and is an obstacle to attract investment in hydropower sector in the Hima-laya. Hence, more innovative solutions are needed to make hydro generated energy more cost effective and long-term sustainable energy solution. This paper briefly describes geo-logical set-up of the Scandinavia, history of Norwegian Hydropower and reviews the de-sign principle used to develop underground waterway system in Norway. Brief comments are also made on the applicability of these principles in the Himalayan region. It is planned that more discussions will be made in the future on the geo-tectonic environment of the Himalaya and suitability of Norwegian design principle in the Himalayan region

Methods Applied in the Prediction of Brittle Failure in Tunnels and Underground Caverns

Tunnels and underground caverns located at greater depth (high rock cover or overburden) are subjected to high in-situ stress environment. Those rock mass that are relatively unjointed and massive are exposed to the brittle failure, which is famously known as rock spalling/ rock bursting phenomenon. Establishing state of the stress and evaluating stress-induced instability in tunnels passing through such rock mass at relatively greater depth is therefore a challenge. The aim of this manuscript is to describes existing brittle failure (rock burst) prediction methods that are being practiced worldwide and propose necessary editions so that quality of assessment is enhanced. The methods described are very practical and the author is confident that professional engineers will use them to evaluate and predict potential rock burst/ rock spalling scenario in the tunnels during planning, design and construction phases. Each method of prediction is explained, applicability extent is highlighted and comparisons between the methods are made

Turnkey Contract - A Management Challenge under Himalayan Geological Condition

Himalayan geology poses special attention and tunnelling challenges, which are associated to the engineering geological conditions in the rock mass. Completing tunnelling project within scheduled contractual time is an issue to be carefully brainstormed and planned by a very competent project management team. This team work is especially a key demand for the projects built under turnkey contract having fixed performance guarantees, completion milestones and contract sum. This is because, delay in construction completion will bring huge contractual penalties and extra cost to the contractor and is, therefore, a management headache to the project team. Hydropower projects consisting long underground waterways system passing through varying geological ground conditions may hinder achieving targeted milestones due to uncertainty associated to the geological risks. This paper present Khimti I Hydropower Project (60 MW) that has 10 km long underground waterway system, one km long access tunnel, many construction Adits and an underground powerhouse. The project was constructed under a turnkey contract called KC2 contracts with main civil contractor responsible for both design and construction implementation of the project. The construction quality was guaranteed through several contractual performance tests listed under the KC2 contract. This article attempts to review on the way the geological ground condition has influenced in the completion milestone of the project and highlights on what are the key issues that must be carefully accessed before accepting a turnkey contract for hydropower project with long underground waterway systems

Predicting Tunnel Squeezing: A Discussion based on Two Tunnel Projects

Tunnel squeezing is a phenomenon, which is frequently confronted while tunneling through Himalayan rock mass. Weak and schistose rocks like mudstone, shale, slate, phyllite, schist, highly schistose mica gneiss and the rock mass of the tectonic fault zones are incapable of sustaining high stresses. A reliable and trustworthy prediction on the extent of squeezing is therefore essential. The reliable prediction results help to make strategy regarding stabilizing measures and optimization of tunnel rock support well in advance. This paper is mainly focused in analyzing the tunnel squeezing that took place in connection with the two tunnel cases; i.e. Kali Gandaki 'A' and Middle Marsyangdi headrace tunnels. The main focus is given to look on the applicability of squeezing analysis using Hoek and Marinos approach in combination with the equation proposed by Panthi for the estimation of rock mass strength for highly schistose rocks of the Himalaya. The measured tunnel convergence (squeezing) and lab tested mechanical properties of the rocks from these two headrace tunnels have been used to verify the applicability of the proposed methods and also the uncertainty analysis approach on squeezing introduced by Panthi

Review on the prevailing methods for the prediction of potential rock burst / rock spalling in tunnels

Rock burst / rock spalling is among the prevailing stability challenges, which can be met while tunneling through hard rock mass. Especially, this is very relevant for the mountainous country like Norway where hard rock is dominating and many road, railway and hydropower tunnels have to be aligned deep into the mountain with steep valley slope topography. Tunnels passing beneath deep rock cover (overburden), in general, are subjected to high in-situ stresses. If the rock mass is relatively unjointed and massive, which is the most likely case in Norway, a brittle failure may occur in the tunnel periphery, which is known as rock spalling / rock bursting. Establishing state of the stress and evaluating stress induced instability in tunnels passing through brittle rock mass at relatively greater depth is of course a challenge. This manuscript reviews and describes the existing rock burst prediction methods that are being practiced worldwide so that these can be used by professional engineers as base for the evaluation and predict potential rock burst / rock spalling scenario in the tunnels under planning and design. The manuscript describes each method itself, highlights extent of applicability and compares with other prediction methods

Analysis of Engineering Geological Uncertainties Related to Tunnelling in Himalayan Rock Mass Conditions

The need for tunnelling in Nepal, as in the Himalayan region in general, is enormous, particularly for hydropower development. Due to active tectonic movement and dynamic monsoon, the rock mass in the Himalaya is relatively weak and highly deformed, schistose, weathered and altered. Predicting rock mass quality, analyzing stress induced problems, in particular tunnel squeezing, and predicting inflow and leakage often have been found extremely difficult during planning stage. Considerable discrepancies have been found between predicted and actual rock mass conditions, resulting in significant cost and time overrun for most of the tunnelling projects. Finding innovative solutions for quantifying geological uncertainties and assessing risk are therefore key factors for cost effective and optimum future tunnelling through Himalayan rock mass. In this thesis, a probabilistic approach of uncertainty analyses has been introduced to deal with the most important geological uncertainties reflecting Himalayan rock mass conditions. A geological uncertainty analysis model concept based on the software program @Risk has been applied for this purpose. The analyses presented in this thesis are based mainly on four headrace tunnel cases from Nepal; 1) 60 MW Khimti I hydropower project, 2) 144 MW Kaligandaki “A” hydroelectric project, 3) 14 MW Modi Khola hydroelectric project, and 4) 69 MW Middle Marsyangdi hydroelectric project. The first three projects have been completed recently and the fourth one is under construction. The thesis identifies the most crucial aspects of tunnel stability problems (geological uncertainties) by reviewing the engineering geological conditions of the respective cases and the Himalayan geology. It also evaluates the theoretical aspects of the main factors influencing on tunnel stability, reviews the engineering geological conditions, the extent of pre-construction phase engineering geological investigations, evaluates the deviation between predicted and actual rock mass conditions, and describes the laboratory testing that has been carried out for the respective cases. Probabilistic approaches that have been applied in the field of engineering geology in past and the basic theory on statistical analyses are briefly discussed. Main emphasis is then placed on the descriptions of useful probability distribution functions (pdf), the @Risk statistical analysis tool, the applied uncertainty analysis model concept and @Risk analysis for the respective tunnel cases. The uncertainty analyses include rock mass quality evaluation based on the Q-system of rock mass classification for Khimti and Modi Khola headrace tunnels, tunnel squeezing based on Hoek and Marinos approach for Kaligandaki and Middle Marsyangdi headrace tunnels, and finally analysis of water leakage from the Khimti headrace tunnel. The degree of correlation between simulated results achieved by the @Risk model and values actually measured in the tunnel is discussed and the sensitiveness and effect of variations in the value of each input parameter and sensitivity of equations and methods used to analyze geological uncertainties are evaluated. It is concluded that the proposed uncertainty analysis approach gives very promising results and has a great potential for analyzing tunnel projects in the Himalayan rock mass conditions, but more cases are needed for conforming the reliability of the methodology

Assessment on the 2014 Jure Landslide in Nepal – a disaster of extreme tragedy

The landslides kill many people every year in Nepal and in the Himalayan region, which devastates society in the local area. A famous living memory of an example of landslide induced devastation was the landslide at Tinau river that took place in early September 1981 damming the river completely, which breached after few days causing huge flood downstream. The flood swept away concrete tower of the Tinau Hydropower Project, two suspension bridges, one concrete bridge at Butwal, part of Butwal city was completely damaged and many hundred people lost their life. Similarly, on the night of 2nd August 2014 (02:30 AM), a huge landslide, famously known as “Jure Slide”, took place along Sunkoshi River valley on Araniko Highway that connects Kathmandu with Tibet. The landslide killed 156 people who were on sleep in their houses, savaged 120 houses, partially damaged 37 more, dammed Sunkoshi river creating an artificial dam of approximately 50 m high and an approximately 3 km long reservoir was formed. A huge flood occurred after partial breach of the dam damaging barrage structures of the Sunkoshi Hydropower Project located about one kilometer downstream from the slide area. It took over two months to drain artificially created reservoir. The main aim of this manuscript is to describe and evaluate Jure landslide. Critical aspects on the causes of landslide will be highlighted giving emphasis on topography, geology, rock mass, monsoon, and earthquake