Headrace Tunnel Research Articles

A novel numerical model for evaluating the high-frequency vibration intensity of the headrace tunnel in pumped storage power station

High-frequency pressure pulsation induced by the rotor-stator interaction is a frequently observed phenomenon in pumped storage power stations. The propagation of the pulsation can induce severe problems associated with the vibration and noise in the headrace tunnel. Considering this engineering problem, we aimed to develop a numerical model for predicting the vibration identity of the headrace tunnel and to provide boundary condition for investigating the environmental vibrations. In the proposed numerical model, the interactions in the fluid-pipe-surrounding medium system were considered. And the effect of the surrounding medium was decoupled based on the propagation characteristics of P- and S-waves. The established numerical model avoids the need to solve for the dynamics of the entire surrounding medium. The results derived from the proposed time-domain model were compared with those obtained from the frequency-domain model and 3D FSI simulation, which validated the correctness of the proposed numerical model. Simulation results for an actual pumped storage power station revealed that, considering the influence of surrounding rock, the vibration amplitude of the pipe wall was on the order of 10−7m. This amplitude was reduced by over tenfold, indicating that the surrounding rock significantly dampened the vibration intensity of the headrace tunnel.

Hydraulic impact of pressure transients from water conveyance tunnel on the complex hydrogeological system: A case study HPP Pirot, Serbia

Hydraulic tunnels, integral components of hydropower plant (HPP) systems, traversing diverse rock masses, pose challenges for long-term operation. The study’s main goal was to investigate how hydraulic transients originating from the headrace tunnel transfer through the concrete lining and manifest in surrounding aquifer systems. In this experimental study at the water pressure tunnel of HPP Pirot (Serbia), a novel monitoring approach was employed. The internal piezometers with highly sensitive probes are distributed strategically along the tunnel in different geological environments. This approach involved monitoring of water pressure in the surrounding rock masses and observing the impact of hydraulic transients generated by HPP operation. A comprehensive analysis of monitoring data, incorporating ordinal and partial correlations and considering geological features, provides a profound understanding of groundwater dynamics, pressure transient phenomena, and hydrogeological characterization during HPP operation. The study highlights the complex and spatially diverse hydrogeological environment, emphasizing the varying reactivity of pore pressure during HPP operation, particularly concerning Water Mass Oscillations (WMO). Reactive piezometers near the surge tank demonstrate significant pressure variations, while those located further away display synchronous pressure changes with reduced amplitudes. Schematic hydrogeological models have been created based on the hydraulic impacts of HPPs in different geological environments along the tunnel route. The water pressure response enabled aquifer characterization of (1) a thin-layered, low-fissured aquifer closely related to the reservoir, with low influence on WMO transients; (2) a low-fissured, compartment aquifer or non-aquifer with minimal to no influence on WMO transients; (3) a well-structured karst aquifer system influenced by WMO transients; (4) a fault-controlled zone of deep hypogene karst aquifer discharge highly influenced by WMO transients; and (5) an aquifer with a dominant development of the karst conduit system highly influenced by WMO transients. The study highlights the significance of monitoring water pressure within the rock mass as a fundamental element in analyzing the interaction between water pressure tunnels and the hydrogeological environment. Applying the presented instrumentation and methodology facilitates effective monitoring in research areas where pressure tunnels are constructed.

Optimization of governor parameters for transient process of hydropower system with two turbine units sharing a super long headrace tunnel

AbstractThe governor parameters affect the stability and regulation quality of hydropower system with two turbine units sharing a super long headrace tunnel (SLHT). To improve the transient process of hydropower system, this study investigates the optimization of governor parameters. First, the model of hydropower system with two turbine units sharing an SLHT is established. Second, the optimization scheme of governor parameters for transient process of hydropower system is designed by genetic algorithm. The mathematical formulation of genetic algorithm is illuminated. The implementation procedure of genetic algorithm is illustrated. Then, the optimization results of governor parameters by genetic algorithm are analyzed by illustrating the regulation quality of hydropower system under two operating conditions. Finally, the effect of asymmetrical factors on optimal governor parameters is revealed. The asymmetrical layout of bifurcated penstocks, asymmetrical layout of turbine units, and asymmetrical load disturbances are considered. The results indicate that the objective function of hydropower system is composed of the dynamic indexes for frequency oscillations of two turbine units and water level oscillation in surge tank. The fitness function evolves in the direction that makes the regulation quality of hydropower system become better. Under the symmetrical or asymmetrical bifurcated penstocks, turbine units, and load disturbances, the optimal parameters of governors are asymmetrical. The regulation quality of hydropower system under the governor parameters of genetic algorithm is obviously better than that under the governor parameters of Stein formula. The optimal governor parameters are directly affected by the asymmetrical factors of hydropower system. With the increase of the flow inertia of one bifurcated penstock, the optimal parameters of the other governor become greater.

Optimization of hydraulic parameters for pipeline system of hydropower station with super long headrace tunnel based on mayfly algorithm considering operational scenarios

AbstractThis paper studies the optimization of hydraulic parameters for pipeline system of hydropower station with super long headrace tunnel (HSSLHT) based on mayfly algorithm considering operational scenarios. Firstly, the state equation of HSSLHT under load disturbance is derived. The optimization design of hydraulic parameters for pipeline system based on mayfly algorithm is proposed. Then, the optimization of hydraulic parameters is conducted and analyzed. Finally, the effects of pipeline diameters and transfer coefficients of turbines on the optimization of hydraulic parameters for pipeline systems are revealed. The results show that the optimization of hydraulic parameters for pipeline system is a multiobjective problem, and the several objective functions exhibit significant conflicts. Compared to the firefly algorithm and genetic algorithm, the objective function under mayfly algorithm is improved by 14.7% and 5.1%, respectively. The mayfly algorithm can make the hydraulic parameters for the pipeline system reach the Pareto optimal solution under both load decrease condition and load increase condition. The diameter of penstock has an obvious influence on the robustness of dynamic performance of HSSLHT. When the diameter of penstock increases by 30%, the robustness of HSSLHT becomes worse and the robustness index deteriorates by 57%. The reason is that the flow inertia of penstock becomes smaller with the increase of diameter, and the flow inertia of penstock is favorable for resisting disturbance of HSSLHT. The coefficient of throttled orifice head loss and the lengths and head losses of headrace tunnel and penstock are the key hydraulic parameters for matching the operation of HSSLHT.

Evaluation on the Squeezing and Design of Support system in Headrace Tunnel of Middle Modi Hydroelectic Project

Tunneling through a weak rock possess a great challenge. These challenges depends upon type of rock, excavation method, stress and deformation behavior of the rock etc. Squeezing is one of the major problem which is likely to occur during excavation of tunnel through weak rock. A reliable prediction of the extent of squeezing is essential so that a strategy can be established regarding stabilizing measures and for optimizing the support well in advance. In this paper, Middle Modi Hydroelectric Project located in the Kaski District has been taken as the case study. In this project, huge squeezing problem occurred at about chainage 1+140m At this section deformation has been recorded well over 65cm Hence, this paper basically deals with squeezing analysis using different approaches. Rock types along the headrace tunnel alignment are sheared phyllite and fractured quartzite. Mostly, intercalation of phyllite and quartzite has been found in the squeezed section Rockmass quality found in the squeezed section is extremely poor to exceptionally poor. Four main methods have been used to evaluate the squeezing phenomenon viz empirical methods such as Singh (1992) and Goel (2000), semi-empirical such as Hoek and Marinos (2000), analytical method such as (Convergence Confinement Method, 2000) and mumerical program Phase2. The main factors that control the squeezing phenomenon are the rock mass parameters and rock stresses. The uniaxial unconfined compressive strength of intact rock has been back calculated from measured deformations using phase2 program and found to be in the range of 10 to 15Mpa in the squeezed section Deformation was calculated using CCM and Compared with phase2 result. Due to excessive deformation temporary supports were provided at several locations, steel ribs are buckled and shotcrete lining is also cracked. All these have to be removed before application of final lining Finally two different approaches have been studied using phase program to address the existing problems in squeezed section of headrace tunnel ie. design of support system considering either circular shape with final lining (shotcrete and steel rib) or reshaping existing D-shaped tunnel into horseshoe shaped and providing final concrete lining.

Extreme water level of surge chamber in hydropower plant under combined operating conditions

The design height of surge chambers is determined by the lowest and highest water levels under combined operating conditions. We considered four typical combined operating conditions: successive-load-rejection operating condition (SLROC), successive-load-acceptance operating condition (SLAOC), load-acceptance-then-rejection operating condition (LATROC), and load-rejection-then-acceptance operating condition (LRTAOC). A theoretical formula was derived to determine the worst superposition moment of extreme water levels using the implicit function theorem. An actual hydropower plant was used to analyse extreme water levels. The results showed that the tangential point for the headrace tunnel discharge-water level relationship curve of initial and superposed operating conditions was the worst superposition moment. The highest water level at the worst superposition moment was higher than that at the superposition moment of maximum flow into the surge chamber; similarly, the lowest water level at the worst superposition moment was lower than that at the superposition moment of maximum flow out of the surge chamber. When the cross-sectional area of impedance hole was small, the highest and lowest water levels occurred in SLROC and SLAOC, respectively. Conversely, when the cross-sectional area was large, the highest and lowest water levels occurred in LATROC and LRTAOC, respectively. The proposed formula avoids repeated trial calculations to determine extreme water levels, providing important theoretical significance and engineering application value.

Comparison of Tunnel Construction Cycle with NTNU Model for the Headrace Tunnel of Seti Khola Hydropower Project

Achieving smooth and efficient blasting of tunnel walls is a challenging task. Tunneling performance and advancement can best be performed with proper and effective blasting techniques in drill and blast techniques. In this manuscript, the Seti Khola hydropower project's headrace tunnel's real-time statistics are used to compare the overall performance of tunnel excavation for the widely used blasting approach. The headrace tunnel's 663 meters of observed and recorded length comprises rocks with weak to medium blastibility. According to the Q-system, this tunnel section's rock mass quality class ranges from good to bad. The rock type found has a monotonous sequence of metasandstone and phyllite with quartz partings and discontinuities filled with clay to silt. A variation in the excavation cycle is observed in relation to the presence of different rock mass classes. Ultimately, the NTNU model is compared and analysis is done on the drilling patterns and cycles of tunnel building. It was discovered that using the NTNU model for tunnel excavation presents a significant opportunity to enhance performance.

Hydraulic Transient Impact on Surrounding Rock Mass of Unlined Pressure Tunnels

The frequent pressure pulsations due to hydraulic transients in hydropower plants induce cyclic loading on the rock mass that may contribute to increased instances of block falls and increased risk of tunnel collapse over the power plant lifetime. This study focuses on understanding the effect of frequent start and stop sequences of hydropower in unlined pressure tunnels. For this purpose, data from a pore water pressure monitoring system is utilized, which was installed at the downstream end of the headrace tunnel at the 50 MW Roskrepp hydropower plant in southern Norway. The objective of this study is to analyze the recorded data and quantify the impact of the hydraulic transient on the surrounding rock mass in the unlined pressure tunnel. The monitoring of pressure data over several years clearly shows that frequent load changes could cause a considerable effect on the rock mass and constituent joint system. A delayed response of the pressure in boreholes in the rock mass compared with inside the tunnel is seen in all start and stop sequences and is considered to be the main reason for instability caused by transients. The response of pore pressure in boreholes is greatly influenced by the characteristics of joints. The results show that the start sequence and shorter shutdown duration exert a greater impact on rock mass as compared to the stop sequence and longer shutdown duration. Therefore, it is recommended to increase the shutdown duration so that the impact can be minimized to increase the tunnel lifetime. This study recommends implementing a more conservative design approach in tunnels with weak rock masses in projects that involve frequent load changes.

Mitigating loose rock fall and cavity formation in Adit-2 tunnel of Rammam III hydroelectric project in Himalayas, India: Challenges and Solutions.

The turbulent geological history of “The Himalayas” arguably poses the most challenging ground conditions than anywhere in the world for underground excavations works. Cavity formation, loose fall, rock busting, high ingress of water and squeezing ground conditions are common phenomenon that encountered along tunnel profile in Himalayas. The Rammam III Hydroelectric Project, situated in Sikkim Himalayan belt lies in Main Crystalline Thrust zone (MCT) and is facing its fair share of Geological challenges during the underground excavation process.The primary objective of the Rammam Stage-III Hydro Electric Project is to generate 120 MW power through 8.2 km of HRT (Head Race Tunnel).Excavation of the Adit-2 to HRT has been challenging because of its proximity to the Jhepi Khola, a fault-incised stream. The tunnel’s progress was impeded by various obstructions of small and large magnitude caused by several sympathetic shears along joints and other geological complexities.This paper will focus on the challenges faced in mitigating loose rock falls, cavity formation in Adit-2 from RD 312.0m to 320.0 m. To address the issue, an effective excavation philosophy known as DRESS (Drainage-Reinforcement-Excavation-Support-Solution) was adopted. The solution proposed is highly effective in addressing water-bearing issues in the Himalayas.The treatment method adopted not only achieved the desired level of safety and smooth construction progress, but also provides a valuable reference for future similar cases of loose fall and cavity formations.

Propagation characteristics analysis of high-frequency vibration in pumped storage power station based on a 1D fluid-solid coupling model

High-frequency pressure fluctuation is a common hydraulic phenomenon in pumped storage power station (PSPS), which is caused by the rotor-stator interaction in the pumped turbine. The propagation of the high-frequency vibration (HFV) could transmit the vibration energy to the upstream headrace tunnel, inducing severe environmental vibration and noise pollution. This study aims to establish an applicable numerical model to investigate the propagation characteristics of HFV, and evaluate the vibration magnitude of both solid and fluid in the headrace tunnel of the PSPS. In this study, a one-dimensional (1D) numerical model is established for the fluid solid interaction (FSI) behavior of the pipe, where the equations of solid and fluid are solved intuitively in the time domain by the Finite Difference Method (FDM) and Method of Characteristics (MOC), respectively. Detailed discretization schemes and solution procedures are deduced and presented in this study. Four validation cases are carried out to examine the established model. The results demonstrate that the established mode is applicable for predicting the vibration in the fluid-filled pipe (FFP). The non-reflect boundary conditions are proposed to eliminate the influence of the reflected wave from the boundary. The propagation characteristics of the high-frequency vibration (HFV) in FFP are comprehensively analyzed and summarized based on a real PSPS. And magnitude distributions of the pressure fluctuation, axial and radial vibration along the pipeline axis are presented and discussed.

Study of the inhibitory effect of a soft cushion on the propagation of pressure pulsation in pumped storage power stations

AbstractHigh‐frequency pressure pulsations are hydraulic phenomena that are frequently observed in pumped storage power stations. These pulsations can propagate through the steel pipes, concrete lining, and the surrounding rock system, which in turn may have detrimental effects on the environment, such as noise pollution, and relocation of the local residents. This paper proposes a vibration‐damping concept that involves wrapping a local soft cushion layer outside the buried steel pipe; this layer could partially eliminate the pressure fluctuations in the headrace tunnel, thereby reducing the ground vibrations caused by the pressure pulsations. In this study, the finite element method was used to model the propagation of vibrations in the surrounding rock and fluid‐filled pipes, including static simulation of the structure, and dynamic simulation of the surrounding rock. The simulation results suggest that adding an appropriate local soft bedding layer can effectively reduce the ground vibrations by more than 60% and the possible surface noise within the standard vertical vibration norms. The inhibitory effect of the soft cushion on the propagation of vibrations is determined by the wrapping angle, thickness, and material of the bedding layer. This effect increases with increasing wrapping angle and thickness of the bedding layer, and decreases with increasing elastic modulus of the material. After the addition of the bedding layer between the steel pipe and concrete lining, the pressure in the inner pipe is primarily borne by the steel lining rather than the coupling of the steel lining, concrete lining, and the surrounding rock. Hence, the thickness of the part of the steel liner in contact with the soft bedding layer should be increased. In addition, the thickness variations in the steel pipe joints should be smooth to avoid stress concentration.

Stability analysis and evaluation of rock support in headrace tunnel of Khimti-2 Hydroelectric Project

Stability analysis and evaluation of rock support in headrace tunnel of Khimti-2 Hydroelectric Project

Corrosion Damage Detection in Headrace Tunnel Using YOLOv7 with Continuous Wall Images

Infrastructure that was constructed during the high economic growth period of Japan is starting to deteriorate; thus, there is a need for the maintenance and management of these structures. The basis of maintenance and management is the inspection process, which involves finding and recording damage. However, in headrace tunnels, the water supply is interrupted during inspection; thus, it is desirable to comprehensively photograph and record the tunnel wall and detect damage using the captured images to significantly reduce the water supply interruption time. Given this background, the aim of this study is to establish an investigation and assessment system for deformation points in the inner walls of headrace tunnels and to perform efficient maintenance and management of the tunnels. First, we develop a mobile headrace photography device that photographs the walls of the headrace tunnel with a charge-coupled device line camera. Next, we develop a method using YOLOv7 for detecting chalk marks at the damage locations made during cleaning of the tunnel walls that were photographed by the imaging system, and these results are used as a basis to develop a system that automatically accumulates and plots damage locations and distributions. For chalking detection using continuous wall surface images, a high accuracy of 99.02% is achieved. Furthermore, the system can evaluate the total number and distribution of deteriorated areas, which can be used to identify the causes of change over time and the occurrence of deterioration phenomena. The developed system can significantly reduce the duration and cost of inspections and surveys, and the results can be used to select priority repair areas and to predict deterioration through data accumulation, contributing to appropriate management of headrace tunnels.

Application of Cross-hole Seismic Tomography to Inferred Cavities Condition.

The construction of the Rajamandala hydroelectric power plant civil works has experienced critical problems that arise in the implementation process, with the occurrence of cracks cavities conditions in the headrace tunnel locations. We applied the cross-hole seismic tomography to detect important heterogeneities and mechanical proprieties of the formations between two boreholes in this case inferred cracks cavities condition. The seismic source is inside the borehole “a sparker” and the receivers “hydrophones” are in an adjacent one, the sparker is lowered into the borehole one step at the time. Seismic waves, propagating in the tunnel wall rock, spread widely, and are reflected and refracted when encountering interfaces between rocks with different acoustic impedances. Reflected waves returning to the receivers are recorded. After the processing of the first arrivals of the P waves we obtain a cross section of the seismic velocities in between the two wellbores. With the cross-hole seismic tomography, the basis could be provided to the tunnel construction and parameter adjustments to guarantee the construction safety. Our result shown that there is a weak zone above the tunnel with low Vp zone (~1.2 km/s) may be related to weak zone (may be fracture, unconsolidated rock, and fluid-filled rock or landslide caving). Checker-board resolution test is also conducted to determine the tomogram areas that are reliable to be interpreted. Our challenges are we have poor resolution due to not enough raypath. The Cross-hole seismic tomography can effectively and safely guide the excavation of the tunnel section working surface in combination with reconstructed images and excavation technology.

Theoretical analysis of the attenuation characteristics of high-frequency pressure vibration in pumped storage power station

High-frequency vibration is a common hydraulic phenomenon in pumped storage power station. In this study, a theoretical model for analyzing the high-frequency vibration in fluid-pipe-surrounding support coupling system is established. The discontinuity characteristics between the pipe wall and surrounding medium are modeled by the linear spring model, where axial and radial spring constants represent the bounding degree of the pipe and surrounding support. The relation between the wave speed and attenuation characteristics of the high-frequency vibration could be derived from the established theoretical model. And a strategy for estimating the attenuation rate of the high-frequency vibration is proposed. According to the theoretical analysis results, the connection and transition of the vibration energy through the pipe and surrounding support mainly rely on radial bounding. With decreasing in the compressibility of the pipe wall and the surrounding medium, the attenuation rate of high-frequency decreases. One of the reasons why the high-frequency pressure vibration could propagate over long distances in the pumped storage power station may be attributed to the little compressibility of the solid structures in the headrace tunnel.

Rock Squeezing Analysis in Young Mountains: A Case Study of Headrace Tunnel of Supermadi Hydroelectric Project in Nepal

The tunnel stability was assessed by analysing stress in the opening. Squeezing is the major problem faced while excavation a tunnel alignment in Himalayan region. This research was done in Super Madi hydroelectric project of 44 MW, in which main focus on the rock mass section of headrace tunnel of Inverted D shaped. The prediction of squeezing is done using various empirical, semi empirical, semi analytical and numerical modeling for the three different rock class. Finite element analysis was done using Rock science Phase2 software and output was verified by site investigation. The main lithologies of the area along the tunnel axis are banded gneiss. Based on the site condition, this study recommend the accurate method of predicting rock squeezing in the lesser Himalayan region with similar site conditions. It is found that the higher deformation occurs in high tunnel depth with low Q value.

Operational Stability of Hydropower Plant with Upstream and Downstream Surge Chambers during Small Load Disturbance

A surge chamber is a common pressure reduction facility in a hydropower plant. Owing to large flow inertia in the upstream headrace tunnel and downstream tailrace tunnel, a hydropower plant with upstream and downstream surge chambers (HPUDSC) was adopted. This paper aimed to investigate the operational stability and nonlinear dynamic behavior of a HPUDSC. Firstly, a nonlinear dynamic model of the HPUDSC system was built. Subsequently, the operational stability and nonlinear dynamic behavior of the HPUDSC system were studied based on Hopf bifurcation theory and numerical simulation. Finally, the influencing factors of stability of the HPUDSC system were investigated. The results indicated the nonlinear HPUDSC system occurred at subcritical Hopf bifurcation, and the stability domain was located above the bifurcation curve, which provided a basis for the tuning of the governor parameters during operation. The dominant factors of stability and dynamic behavior of the HPUDSC system were flow inertia and head loss of the headrace tunnel and the area of the upstream surge chamber. Either increasing the head loss of the headrace tunnel and area of the upstream surge chamber or decreasing the flow inertia of the headrace tunnel could improve the operational stability of the HPUDSC. The proposed conclusions are of crucial engineering value for the stable operation of a HPUDSC.

Optimization of Rockburst Risk Control Measures for Deeply Buried TBM Tunnels: A Case Study

Choosing reasonable control measures for different intensity rockburst risks not only effectively prevents and mitigates rockburst risks but also reduces time and engineering investment costs. Due to the limitations of the tunnel boring machine’s structure and working conditions, tunnels excavated by TBMs are highly susceptible to rockbursts. What is even worse is that there are very few measures to control the rockburst risk in these tunnels. Implementing reasonable control measures from the limited mitigation measures to control and mitigate rockburst in TBM tunnels is an urgent problem that warrants a solution. In this paper, a large number of on-site rockburst risk control cases and a large amount of MS monitoring data (the total mileage of MS monitoring is approximately 7 km, lasting for 482 days) are used to derive a reasonable scheme to control the rockburst risk of different intensities in twin TBM tunnels. First, the rockburst early warning effect of the two headrace tunnels of the Neelum–Jhelum hydropower station based on microseismic monitoring is analyzed. Second, based on highly accurate rockburst warning results, 94 rockburst risk control cases are applied to analyze the control effect of different control measures at different intensities of rockburst risk. Then, by combining factors such as the time cost and expense cost of different control measures, more reasonable control measures for different intensity rockburst risks are proposed: for slight rockburst risk, normal excavation is preferred; for moderate rockburst risk, horizontal destress boreholes are preferred; and for intense rockburst risk, a combination of measures of shortening daily advance and horizontal destress boreholes is preferred. The research results can provide a reference for other TBM excavation projects to carry out rockburst risk prevention and mitigation.

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