Headrace Tunnel Research Articles

Analysis of the failure of Gilgel Gibe II hydropower head race tunnel using numerical approach

Analysis of the failure of Gilgel Gibe II hydropower head race tunnel using numerical approach

Tunneling in Weak Rock Mass - an Evaluation on Stability Condition of Headrace Tunnel of Setikhola Hydropower Project, 22MW

Tunneling in Weak Rock Mass - an Evaluation on Stability Condition of Headrace Tunnel of Setikhola Hydropower Project, 22MW

Implementation and Evaluation of a Complex Pumped-Storage Hydropower Plant with Four Units, Common Penstock, and Surge Tank in a Real-Time Digital Simulator

The demand for energy storage systems is rising together with the proportion of renewable energy sources (RES) in power systems. The highest capacity among the various energy storage systems in power systems is provided by pumped-storage hydropower (PSH). In this paper, the ability of the real-time digital simulator (RTDS), e.g., dSpace–SCALEXIO, to emulate a complex pumped-storage hydropower plant with four units, two common penstocks, a surge tank, and a long headrace tunnel is investigated. The RTDS is the smart brain of an advanced lab setup called power hardware in the loop (PHIL), which is an extremely safe and useful lab system for electrical power system research and testing hardware and methods under various conditions. In this research, the capability of an RTDS to emulate the behavior of a pumped-storage hydropower plant including four Francis pump-turbines, four short penstocks, two common penstocks, a surge tank, and a long headrace tunnel is evaluated. Francis pump-turbines are modelled based on the hill chart-based interpolation and waterways including penstocks and headrace tunnel are modelled based on the polynomial approximation of a hyperbolic function. Finally, the results from the RTDS are presented and discussed. According to the results of the paper, we confirm that the RTDS can accurately emulate the hydraulic, mechanical, and electrical transients of a pumped-storage hydropower plant with a complex configuration.

Design of a Self-Supporting Liner for the Renovation of a Headrace Tunnel at Chivor Hydropower Project

Ensuring access to affordable, reliable, sustainable, and modern energy, as declared in the United Nations’ Agenda 2030, requires both the inclusion of new renewable energy sources, and the renovation of existing hydropower infrastructure, since this resource is considered a key strategy to support flexibility in electric grids with high penetrations of variable generation. This paper addresses the design of a self-supporting lining for the renovation of a headrace tunnel, that has been affected by a buckling event, in order to extend the operating life of the Chivor Hydropower Project, located in Colombia. Studies performed by AES Corporation about the buckling events that affected the headrace tunnel and the condition assessment are first described. Then, the design alternatives to renovate this important part of the hydropower plant’s infrastructure are presented in a general way. The detailed design and construction planning for the selected alternative are then illustrated by showing some calculations used in hydropower design. Such a renovation project is one of the first of its class in Colombia and goes from studies of the buckling events to the design of a modern lining that will be constructed while keeping the 1000-MW (6% of Colombia’s demand) hydropower plant in operation conditions, in order to extend its life for 50 more years, which represents an example for managers and practitioners of large-scale hydraulic engineering projects.

Correlation Analysis of Machine Performance Parameters and Rock Mass Properties during Tunnel Boring Machine Excavation Process: A Case Study in Yin-song Headrace Tunnel, China

Abstract A rock breaking process during the tunnel boring machine (TBM) excavation sequence involves a complicated interaction between the disc cutters and the tunnel face, and the excavation process is influenced both by the rock mass properties and the TBM performance. Hence, in achieving a highly efficient TBM excavation, a mutual feedback analysis of rock mass properties and machine parameters is important. In this study, a correlation analysis of rock mass properties and TBM parameters is conducted based on the field data obtained from the Yin-song headrace tunnel in Jilin Province, China. Firstly, the correlation between the rock mass properties (i.e., uniaxial compression strength and rock quality designation index) and the machine parameters (i.e., thrust force, cutterhead torque, rotational speed, penetration depth, and penetration rate) obtained during the stable operation stage of TBM is extensively investigated. The variation in the TBM penetration rate as a function of rock mass properties and machine operation parameters is studied. A statistical prediction model that defines the effects of rock mass properties on the TBM penetration rate is established by multivariate linear regression analysis. The validity of the prediction model is verified by using the in situ monitoring data obtained from two different chainages of the project. This study can help rationalize the TBM machine parameters in order to obtain a highly efficient TBM excavation and a low life-cycle cost for the machine.

Editorial: Special Issue on Smart and Green Infrastructures with Optimum Life Cycle Solutions

Editorial: Special Issue on Smart and Green Infrastructures with Optimum Life Cycle Solutions

New Perspectives on Excavation Disturbance Zones: Main Driving Forces

The support theory of the excavation disturbance zone (EDZ) cannot provide an accurate physical explanation or theoretical description of the time-dependent properties required for the development of an EDZ. Therefore, the primary factors that cause the formation of an EDZ should be determined to further improve the support theory of the EDZ and grasp the principle underlying the control of the long-term stability of rock masses. Considering the headrace tunnel and nuclear waste repository as the research background, this study aimed to understand the deformation damage evolution process of the surrounding rock after tunnel excavation under different working conditions using the self-developed realistic failure process analysis (RFPA2D) code. The simulation revealed the following. First, an EDZ is formed, although the deformation damage to the surrounding rock is relatively small under the action of environmental factors. Second, under the action of stress in the abovementioned case, the deformation speed, damage degree, and scope of the surrounding rock significantly increase, accelerating the formation and development of the EDZ. Therefore, the boundary of the EDZ expands significantly. Third, when environmental factors are blocked, the range of the EDZ is small due to the small deformation damage to the surrounding rock. Thus, the main factors responsible for the formation of the EDZ are environmental factors, whereas stress is only an auxiliary factor. A numerical simulation method that considers environmental factors can more accurately reproduce the formation of an EDZ. Therefore, a study of the internal mechanism of the EDZ phenomenon can provide a more in-depth understanding of the essential characteristics of an EDZ at the macro level. Furthermore, it can provide a scientific basis and method for the construction and support designs of underground excavation projects and widen the possibilities for further improving the support theory of the EDZ.

Transient analysis of a hydropower plant with a super-long headrace tunnel during load acceptance: Instability mechanism and measurement verification

The current development trend of China's hydropower is moving toward ultra-high heads, complex geological scenarios, ultra-large capacities, and the Tibetan region. The construction of hydropower stations with super-long headrace tunnels is conducive to overcoming the constraints of complex geological conditions and making full use of hydropower resources. However, these stations have unique technical problems that limit their commercial development, including pressure fluctuations during load rejection and the operational stability of the power-frequency regulation. In this study, a potential problem in hydropower stations with super-long headrace tunnels, the instability during load acceptance, is studied by combining prototype experiments with 1D transient numerical simulations. First, according to a test case using a prototype hydropower station, the instability phenomenon occurring during a simultaneous load acceptance of two Francis turbines in a hydropower station with a 20-km headrace tunnel is described. Next, using 1D steady-state and transient simulations, the factors leading to the instability are analyzed in detail. Finally, countermeasures for the safe operation of hydropower stations are proposed based on numerical simulations and supplementary prototype experiments. Hydropower stations with super-long headrace tunnels exhibit a characteristic where the net head decreases sharply with an increase in the flow rate. Therefore, prior to load acceptance, the maximum output achievable by the multiple units under the operating net head has to be carefully determined to avoid over-adjustment of the guide vane opening and detrimental phenomena such as operational instability and extremely low pressure in the draft tube.

Kraftwerk Witznau, Verpressversuche zur Ertüchtigung des Druckstollens

AbstractIn response to spalling of concrete parts, the headrace tunnel was to be strengthened section by section and made fit for the years to come. Since little information was available on the condition of the tunnel and the cause of the spalling, possible damage patterns and causes were analyzed and grouting in combination with concrete rehabilitation were defined as strengthening measures. During a break in operation of approx. 2 months in June 2020, cement injections were tested in grouting trials in different variants to determine their suitability and optimize the parameters and the work to be carried out. The tests and the investigations carried out revealed interesting findings about the condition of the tunnel. The grouting was carried out at low pressure, at different distances and drilling depths, testing important parameters for the subsequent execution and enabling optimization. The porosity of the lining was significantly reduced by grouting, thus improving the quality of the shell. A before‐and‐after measurement with georadar investigation demonstrated the improvement of the lining due to the grouting.A remarkable finding is the combination of the relatively poor quality of the lining concrete, which is due to the construction during World War II, with the practically uncracked and relatively tight lining. It is a testimony to a high level of construction skill that it was possible to create such durable structures with the means available at the time.

Challenges in Tunneling in the Himalayas: A Survey of Several Prominent Excavation Projects in the Himalayan Mountain Range of South Asia

The Himalayas are one of the most unstable regions in the world. Underground excavations are very challenging in this region due to the fragile geology, tectonic activities and complex geological structures. In the present study, three hydropower head race tunnel projects from Nepal, as well as six additional tunnel projects from Bhutan, India and Pakistan located at different parts of the Himalayas, are reviewed with a focus on the common problems encountered during the tunneling and their possible causes and remedies. It is found that rock bursts often occurred around the overburden of 1000 m or higher, while tunnel squeezing problems were commonly observed in a wide range of overburden. Most of the rock failures occurred in sheared zones, thrusts and heavily weathered rock mass. The geological conditions around these projects are often characterized by significant presence of folds, faults, joints and interbedding of different types of rock strata; they are so complex and diverse that it is often difficult to accurately predict the field condition from conventional geotechnical site investigation. In many cases, the presence of shear zones, thrusts and tectonic activities has a strong influence on the in situ stress. Review of these prominent projects suggests that the complicated dynamics between a wide range of geological and geotechnical factors play a critical role in the tunneling in the Himalayas.

Nonlinear hydraulic coupling characteristics and energy conversion mechanism of pipeline - surge tank system of hydropower station with super long headrace tunnel

This paper aims to study the nonlinear hydraulic coupling characteristics and energy conversion mechanism of pipeline - surge tank system of hydropower station with super long headrace tunnel. Firstly, the model of hydropower station considering nonlinear hydraulic coupling of pipeline - surge tank system is established. Then, the dynamic behaviors are evaluated, and the effects of nonlinear head losses of pipeline - surge tank system on dynamic behaviors are analyzed. Finally, the energy conversion mechanism of pipeline - surge tank system is revealed. The results indicate that both the nonlinear head loss term of super long headrace tunnel and linear head loss term of penstock are unfavorable for stability. The nonlinear throttling orifice head loss of surge tank has a remarkable impact on dynamic response processes. The nonlinear head losses of pipeline - surge tank system mainly affect the kinetic energy of flow in pipeline. A part of the kinetic energy of flow in pipeline interconverts with the kinetic energy of flow in surge tank.

Application of Optical Fiber Sensing Technology in Permeability Test of Three-Dimensional Physical Model of Medium and Long-Distance Diversion Tunnel

In order to accurately simulate the dynamic change law of seepage field during construction, this paper proposes the application of optical fiber sensing technology in the permeability test of three-dimensional physical model of medium and long-distance headrace tunnel. This paper introduces the principle of optical fiber sensing, analyzes and compares the application advantages of optical fiber and general electrical signal sensing in the safety monitoring of long-distance diversion tunnel. Taking the safety monitoring of a 16# long tunnel of a diversion project as an example, the selection of monitoring sections, monitoring items, and the layout and networking of monitoring instruments are studied. In addition, combined with the tunnel project, the physical simulation of the construction process of the deep buried headrace tunnel under high seepage pressure is carried out, and the water pressure automatic control water supply system and the discrete flower tube seepage generation system are designed and manufactured to realize the high simulation of the seepage field. The seepage and evolution law in the surrounding rock of headrace tunnel during dynamic construction are calculated and analyzed. The test results show that the maximum external water pressure of the headrace tunnel is 15 MPa, which is equivalent to 1500 m head pressure, and the similar scale of head pressure is 100. Therefore, taking 15 m constant head water supply pressure for simulation calculation, the excavation of the tunnel is 120 cm, and the two-dimensional seepage of the vertical section of Z = 91 cm . The seepage flow of the two sides of the tunnel is large, and the contour of the hydraulic gradient is dense. The coordinates are 0.7 m, 2.090 m, and 0.9 m. This point in the original rock mass is located at the same elevation point of the four headrace tunnels and directly below the model exploratory tunnel. The head pressure is 1.40 m, and the corresponding prototype point pressure head is 140 M. During construction, such a high external water pressure is a great safety hazard. Conclusion. The test conclusion provides a theoretical basis for the seepage prevention construction technology design of the headrace tunnel and is of great significance to the long-term stability, safety evaluation, and prediction of the headrace tunnel.

Contribution for the roadmap of hydraulic short circuit implementation: Case of Grand-Maison pumped storage power plant

The objectives of the 2050 energy policy based on the decarbonization of the electric power networks generate drastic changes for grid balancing with a massive integration of non-dispatchable Renewable Energy Sources. Hydroelectric power plants already significantly support electricity power system flexibility with innovative solutions such as variable speed units, fast frequency control, fast generating to pumping modes transition, high ramping rate, inertia emulation, etc.For pumped storage power plants (PSP), a quick solution to increase the flexibility without large investment is to operate the power plant in hydraulic short circuit (HSC) mode. This technological solution is simple to implement, but requires an in-depth study of various technical aspects among which the hydraulic transients of the new operating modes is of high importance from the installation’s safety perspective. In the framework of XFLEX HYDRO H2020 European research project, the exploitation of this solution is under implementation at Grand-Maison PSP. Located in the French Alps, Grand-Maison PSP is equipped with 8 reversible multi-stage Francis pump-turbines and 4 Pelton turbines, for a total installed capacity of 1800MW, thus being the largest PSP in Europe and one of the major PSP in the world. The waterway includes a headrace tunnel, a headrace surge tank, 3 parallel penstocks feeding the 12 units operated under a maximum gross head of 955mWC.In this paper, after a description of the general HSC considerations, the 1D model of the Grand Maison PSP and the related validation are presented. Finally, the most critical load cases in HSC operation are described to identify the potential hydraulic transient issues, such as extreme water levels in the upstream surge tank, maximum static pressure along the pressure shaft and minimum static pressure along the tunnels. The analysis performed for Grand Maison PSP is a contribution to the roadmap for the implementation of HSC operation in pumped storage power plant and will be made available as a public deliverable of the XFLEX HYDRO H2020 European research project.

Rock mass characterization and support analysis of pressurized headrace tunnel of the Upper Balephi “A” Hydroelectric Project, Nepal

Detailed geological, engineering geological and geotechnical assessment are prerequisites for any design works in underground excavation. Due to complex geology in young Himalayan, it is mandatory. Any misjudgment in support design may results huge losses of cost and time of the project. This paper encompasses detailed analysis carried out for examining the rock mass properties for optimum support along a pressurized headrace tunnel of Upper Balephi “A” Hydroelectric Project, Nepal. Empirical, analytical and numerical methods were applied for safe tunnel design. The rock mass quality and support in these areas were estimated using the rock mass rating (RMR), geological strength index (GSI) and rock mass quality (Q) systems. The detailed rock engineering assessment indicated that there are some critical locations along the headrace tunnel alignment. Rock mass quality values derived from different methods were used for calculating modulus of deformation, Hoek-Brown constants, strength of rock mass, in situ stresses, squeezing and support pressure using available empirical equations. The support determined from the empirical methods were evaluated for the overall stability of the required excavation by using finite element method. The analysis showed that the support pressure and deformation can be predicted very well and magnitude of the displacements and extent of the plastic zones can be reduced significantly by application of the support installation. The numerical modelling reveals that the support suggested by empirical methods are appropriate. Both empirical and numerical approaches are necessary for the confirmation of reliable support design of underground structure.

Probabilistic Time Estimation of Tunneling Projects: The Uri Headrace Tunnel

Probabilistic time estimation is an essential part of proper risk management in tunneling projects. In recent decades, several models have been developed for this purpose, one of which was developed by Isaksson and Stille (Rock Mech Rock Eng 38:373–398, 2005). In this paper, Isaksson and Stille’s probabilistic time and cost estimation model was improved and then applied to estimate the total tunneling time of the headrace tunnel in the Uri hydropower project in India. The improvements allow the user to more accurately account for different types of geological features and disruptive events. The result of the estimation is a distribution of tunneling time. The outcome illustrates how a proper understanding of the geological setting of the project and its effect on construction performance can contribute to effective risk management.

Effect of the nonlinearity of head loss on stability and dynamic performance for hydropower plant with surge tank during small load disturbance

The nonlinearity of the head loss in hydropower plants is normally neglected in the stability analysis during small load disturbance. However, for the hydropower plant with the super long headrace tunnel, the head loss is large and its nonlinearity would affect the regulation stability. This paper investigates the stability and dynamic performance for hydropower plant with surge tank (HPST) considering the nonlinearity of headrace tunnel head loss (HTHL) and penstock head loss (PHL) during small load disturbance. Firstly, the mathematical model of HPST considering the nonlinearity of HTHL and PHL is established. The stability analysis is conducted based on Hopf bifurcation theory and stable region, and verified by numerical simulation. Then, the influence mechanism of the nonlinearity of HTHL and PHL is revealed. Finally, the formula for the critical stable cross-sectional area (CSCA) of the surge tank considering the nonlinearity of HTHL and PHL is proposed and analyzed. The results indicate that, for the stability and dynamic performance, the nonlinearity of HTHL has obvious influence, while the nonlinearity of PHL has little influence. During load decrease disturbance (LDD), the nonlinearity of HTHL is adverse to stability of HPST and can rise the CSCA of the surge tank, while the nonlinearity of PHL is conductive to stability of HPST and can reduce the CSCA of the surge tank. During load increase disturbance (LID), the rules are inverse. In addition, the step load variation value has a noticeable impact on the stability of HPST and the CSCA of the surge tank. Therefore, the step load variation value must be considered in the design of surge tank. The proposed formula for the CSCA of the surge tank is feasible for actual application and has a higher precision than classical Thoma criterion.

Failure behavior of horseshoe-shaped tunnel in hard rock under high stress: Phenomenon and mechanisms

A particle flow code (PFC) was first applied to examining the mechanical response of a horseshoe-shaped opening in prismatic rock models under biaxial compression. Next, an improved complex variable method was proposed to derive the stress distribution around the opening. Lastly, a case study of tunnel failure caused by rock burst in Jinping II Hydropower Station was further analyzed and discussed. The results manifest that a total of four types of cracks occur around the opening under low lateral confining stress, namely, the primary-tensile cracks on the roof-floor, sidewall cracks on the sidewalls, secondary-tensile cracks on the corners and shear cracks along the diagonals. As the confining stress increases, the tensile cracks gradually disappear whilst the spalling failure becomes severe. Overall, the failure phenomenon of the modelled tunnel agrees well with that of the practical headrace tunnel, and the crack initiation mechanisms can be clearly clarified by the analytical stress distribution.

Surge wave characteristics for hydropower plant with upstream double surge tanks connected in series under small load disturbance

The surge tanks play a crucial role in moderating the oscillation in hydropower plants after load disturbance. Due to the immense flow inertia in extra-long headrace tunnels, hydropower plants with upstream double surge tanks connected in series (UDSTS) are put forward. This paper aims to study surge wave characteristics in surge tanks, which is of great significance for safe operation. Firstly, the mathematic model of UDSTS system coupled with turbine-governor-penstock (TGP) system is established. Then, the analytical formulas for the frequencies of surge waves are derived, and their rationality is verified as well. The generation mechanism and influencing factors of surge waves are investigated. Finally, the guiding suggestions for actual design are proposed. The results indicate that the formulas have great accuracy. The surge waves in double surge tanks are the superposition of two subwaves (i.e. fundamental wave and interharmonic). The fundamental wave is mainly affected by the long headrace tunnel, cross-sectional areas of both surge tanks. The dominant factors of the interharmonic are the short headrace tunnel length, the cross-sectional area of the surge tank near the turbine. The proposed conclusions for surge wave characteristics can provide theoretical reference for practical applications.

Long-term modelling of the Arkun multipurpose reservoir

The Arkun hydropower and dam project is located on the Coruh River in the North-west of Turkey. The project was completed in 2014. The reservoir is mainly used for energy generation. For this purpose, a main powerhouse with 225 MW and an environmental powerhouse with 12 MW were constructed. Additionally, the reservoir and operation scheme shall contribute to mitigate floods. A minimum ecological flow is mandatory in the Coruh River between the river section reaching from the eco powerhouse which is located downstream of the CFSGD dam and the main powerhouse which is connected to the reservoir via a 14 km headrace tunnel. During the feasibility stage the hydropower projects in Turkey frequently applied simplified methods for the estimation of the energy generation potential. This approach led to an overestimation of the energy general in many cases. Therefore, a reservoir operation model was created which considered monthly runoff data from 1963 to 2005. This model considered the operation of the two powerhouses, evaporation, potential irrigation uses, and spilling. In order to provide a reliable annual generation prognosis, the future development status was considered by the adaptation of the run-off time series. The results of this modelling confirm both the estimated power production during feasibility stage and the actual power production during the operation period.

Study on Mutual Feedback Mechanism and Stability Control of Toppling Slope and Tunnels with High Excavation Rate

During the construction of large-scale hydropower projects in deep mountain gorge areas of the Western China, the difficulties, such as uncontrollable large deformation, great deformation caused by small disturbance, are often encountered in the process of implementation. In particular, due to the limitation of topography, geological conditions and the layout of structures, the slope and dense tunnel group with large section need to be excavated simultaneously in the toppling rock mass. The feedback action mechanism between slope and tunnel excavation is complicated and the deformation control of toppling rock is difficult, which leads to great challenges to engineering construction. In MW hydropower project in west of China, the intake slope, the spillway channel slope, four headrace tunnels, and the sand flushing tunnel, as well as the construction traffic tunnel are arranged in Huishi Ridge on the left bank, where two high slopes and six lager cross-section tunnels are simultaneously excavated and the excavation rate in the toppling deformation rock mass is over 50%, moreover, the lateral coverage thickness of tunnel body is less than the diameter of the tunnel, which leads to the great difficulty of stability control. The excavation stability and safe of the thin mountain ridge is the vital issue to the success of the whole project. Based on the study of the physical and mechanical parameters of toppling rock mass of MW HPP, the mutual feedback mechanism of toppling slope and tunnel group is revealed, an excavation method involving horizontal partitioning, vertical layering, reserving rock plug and reasonable skipping warehouse is proposed. Monitoring results shows that the slope and surrounding rock of the tunnels are stable during the operation period. The research of this paper based on the MW HPP can provide reference for other similar projects.