Bypass Tunnel Research Articles

Investigating supercritical flow characteristics and movement of sediment particles in a narrow channel bend using PTV and video footage

This experimental study investigates the cause of nonuniform invert abrasion observed at sediment bypass tunnel (SBT) bends by examining the variations in velocity distributions, turbulence properties, bed shear stress, and bulk sediment movements under three supercritical bend flow conditions, detailed investigation of such flow is scarce. Using a laboratory-scaled model (1:22) of the downstream bend at Solis SBT, Switzerland, the research utilized particle tracking velocimetry and high-speed cameras with spherical sandstones and glass spheres representing sediments. The results indicate that as the secondary currents develop in the flow direction, the flow properties and sediments redistribute across the channel: the high-momentum fluids are directed toward the outer wall, the bed shear stress increases toward the outer wall, and the sediments are pushed toward the inner wall, which then follow this path downstream, even in straight sections, despite lower bed shear stress. This distribution of sediments, driven by secondary currents, leads to deeper invert abrasions toward the inner wall at SBT bends and downstream sections. Thus, these abrasions are primarily influenced by sediment movement rather than the bed shear stress alone. The study's findings are also valuable for validating future numerical simulations.

Modeling the morphological response of gravel–bed rivers subject to repeated sediment bypass tunnel operations

Introduction: Sediment bypass tunnels (SBTs) are operated during floods to re-establish sediment continuity past dams with the ultimate goal of decreasing accumulation in reservoirs. Depending on the location of the intake structure and operational conditions, SBTs may release either bed load-laden or bed load-free flows in the form of sudden floods (pulses). When evaluating the impacts of SBTs, the traditional approach has been to monitor channel changes in the years following project completion. However, by the time these impacts become evident, mitigation is challenging.Methods: This research adopts a forward-thinking methodology, emphasizing the prediction of potential impacts during the project’s early planning stages. We use a one-dimensional morphodynamic model to forecast the potential morphological response of a gravel-bed river with an idealized geometry to a series of SBT operations characteristic of projects in the Swiss Alps.Results: The morphological response of the downstream reach over the medium to long term is influenced by the alternating pattern of bed load-laden and bed load-free flow releases. This pattern is instrumental in forming a transition region near the SBT outlet hydrograph boundary layer (HBL).Discussion: Within the (HBL), fluctuations in bed elevation and slope are localized, while variations in grain-size distribution persist throughout the downstream region.

3D Numerical Model Validation Using Experimental Test Data for Patrind Hydropower Project

Whilst numerical modelling is commonly used for simulation to check the design of water conveyance, sluicing and spillway structure design, the numerical modelling has rarely been compared with the physical model tests. The objective of this research presented in this paper was to examine the validity and suitability of the numerical computational fluid dynamics (CFD) modeling method within an ANSYS Fluent/CFD R 18.2 software and compare its results with a fully instrumented and well-run physical model test at the 1:45 scale, carried out for Patrind Hydropower Project located in Pakistan. The physical model test was conducted for confirmation and optimization of a natural de-sanding basin, and diversion of suspended sediment-rich flood waters using a bypass tunnel. The numerical simulation was able to reproduce physical model test results and data gathered over a 7-year project operation to an acceptable level of accuracy. A detailed explanation of the approach used in numerical modelling together with analysis of simulation diagrams of ANSYS Fluent/CFD is also presented. The research shows that a 3D numerical model with accurate boundary conditions and mesh size can replace the need for physical model tests.

Experimental study with hydraulic modeling of a reservoir desilting operation using a sediment bypass tunnel

Experimental study with hydraulic modeling of a reservoir desilting operation using a sediment bypass tunnel

Long-term trajectory of the macroinvertebrate community in the downstream channel of a hydropower dam after the operation of a sediment bypass tunnel

A sediment bypass tunnel (SBT) is a dam facility used to mitigate reservoir sedimentation and is expected to contribute to river ecosystem restoration by delivering sediment to the degraded downstream channel. We analyzed past monitoring data of benthic invertebrates sampled downstream of the Asahi Dam in Nara Prefecture Japan to understand the long-term changes in the invertebrate community after the installation of the SBT. Before the SBT installation, the reaches upstream of the dam (one Up site) and downstream of the dam (two Down sites) showed different invertebrate communities, dominated by invertebrates that preferred clean cobble beds, sand and gravel layers, or run habitats in the former and invertebrates that preferred stable or porous beds or pool habitats in the latter. A significant increase in the Up–Down site community similarity within a few years after the SBT installation indicated a rapid recovery of the invertebrate community at the Down sites. During the 16 years of the after-SBT period, the total density and taxon richness at the Down sites increased in the early half, while they decreased in the latter half due to bed changes associated with the continuous accumulation of sediments. The change in dominant invertebrates from taxa of the large sizes to those of the small sizes and the increase in the interhabitat community similarity suggest that the bed of the Down sites became finer and flatter by sand and gravel that filled interstitial spaces of cobbles in the late stage. While the invertebrate community at the Down sites recovered dramatically by the sediment supply through the SBT, additional actions (e.g., cobble augmentation, installation of flow guiding structures) to maintain a balanced sediment size distribution and developed pool-riffle structures would be necessary to maintain the potential habitat heterogeneity and biodiversity in the long term. Our study also demonstrated that invertebrates responded to the sediment supply according to their habitat preferences, which suggests that the classifications of invertebrates by habitat-related traits (e.g., bed-residence types and pool-riffle types in this study) would help to properly understand the sediment and bed status of river reaches under channel degradation or aggradation.

The Validation of a Look-Ahead Geophysical System at the Rondout West-Branch Bypass Tunnel

The Validation of a Look-Ahead Geophysical System at the Rondout West-Branch Bypass Tunnel

An efficient and economic desilitation strategy for reservoir sustainable development under the threat of extreme flooding threaten

Abstract Severe sediment disaster has already been observed locally and worldwide, and serious disasters will happen increasingly in the future due to climate change. Hence, developing a proper reservoir desilitation strategy is an urgent priority to ensure sustainable water resources development worldwide. This study aims to investigate the release efficiency of the bypass tunnel in the reservoir. Firstly, a 2D numerical model was adapted to reproduce the most severe sedimentation disaster due to Typhoon Aere and obtain a reliable result compared with the measured data. Then, the concept of climate change was embedded to understand the release capability of the bypass tunnel under slight to worst scenarios. Finally, the bypass tunnel is demonstrated to be effective in releasing sediment during typhoon periods and prolonging the reservoir lifespan. In conclusion, this study proposes a proper solution to reservoir sedimentation during extreme flooding events. The optimization of water resources and economic benefits can help reservoir management achieve the goal of sustainable development. The presented research can be promoted in the worldwide reservoir to face the possibly severe sediment disaster under the threat of climate change.

Study on the Koshibu Dam sediment bypass tunnel operation based on sediment transport monitoring in upstream reaches

SBTs (sediment bypass tunnels) are a leading technique to mitigate reservoir sedimentation. SBTs consist of a tunnel connecting the upstream and downstream reaches of a dam and diverts sediment-laden flood directly during flood events. A difficulty in operating SBTs is to reduce sediment inflow into the reservoir effectively, and simultaneously sustaining dam functions such as flood mitigation and hydropower generation. To optimize the problem in controlling the timings required in opening and closing the gates in the SBTs, which are governed by the hydrograph and inflow sediment data. Despite many studies on SBT operations considering hydrograph, there are few of those on the temporal change of sediment inflow. Ultimately, this study aims at improving SBT operations by understanding sediment inflow from upstream reaches using an indirect bedload monitoring system called an impact sensor. For this study, the Koshibu River basin was chosen because impact sensors are already placed in several locations around the basin including inside of the SBT. This observation has revealed the amount of transported sediment during each season in a year, are shown with relations between hydrograph and sediment inflow, and the spatial transient of sediment transport peak levels. According to these observations, desirable rules for SBT operations are suggested.

Cover Picture: Geomechanics and Tunnelling 3/2021

AbstractRing line no.15 is one of four new metro lines of the Grand Paris Express mega‐project. The construction lot T2C in the southeast of Paris with a length of approx. 7 km is a key part of the new line. It consists of a 4.7 km long tunnel between Noisy‐Champs and Champigny, a 2.2 km long bypass tunnel with a maintenance station, a large‐scale underground junction cavern, and intermediate access shafts. Difficult ground conditions, limited space for construction, and the requirement for minimization of settlements in an urban environment determine the ground control systems for this tunnel project. Among others, the AT – 139 pipe umbrella system with press connection and a wall thickness of 8 mm, foot piles from the DSI hollow bar system as well as GRP face anchors were used. (photo: DSI Underground)

Underwater 3D Rigid Object Tracking and 6-DOF Estimation: A Case Study of Giant Steel Pipe Scale Model Underwater Installation

The Zengwen desilting tunnel project installed an Elephant Trunk Steel Pipe (ETSP) at the bottom of the reservoir that is designed to connect the new bypass tunnel and reach downward to the sediment surface. Since ETSP is huge and its underwater installation is an unprecedented construction method, there are several uncertainties in its dynamic motion changes during installation. To assure construction safety, a 1:20 ETSP scale model was built to simulate the underwater installation procedure, and its six-degrees-of-freedom (6-DOF) motion parameters were monitored by offline underwater 3D rigid object tracking and photogrammetry. Three cameras were used to form a multicamera system, and several auxiliary devices—such as waterproof housing, tripods, and a waterproof LED—were adopted to protect the cameras and to obtain clear images in the underwater environment. However, since it is difficult for the divers to position the camera and ensure the camera field of view overlap, each camera can only observe the head, middle, and tail parts of ETSP, respectively, leading to a small overlap area among all images. Therefore, it is not possible to perform a traditional method via multiple images forward intersection, where the camera’s positions and orientations have to be calibrated and fixed in advance. Instead, by tracking the 3D coordinates of ETSP and obtaining the camera orientation information via space resection, we propose a multicamera coordinate transformation and adopted a single-camera relative orientation transformation to calculate the 6-DOF motion parameters. The offline procedure is to first acquire the 3D coordinates of ETSP by taking multiposition images with a precalibrated camera in the air and then use the 3D coordinates as control points to perform the space resection of the calibrated underwater cameras. Finally, we calculated the 6-DOF of ETSP by using the camera orientation information through both multi- and single-camera approaches. In this study, we show the results of camera calibration in the air and underwater environment, present the 6-DOF motion parameters of ETSP underwater installation and the reconstructed 4D animation, and compare the differences between the multi- and single-camera approaches.

Study on the influence of bypass tunnel angle on gas shunting efficiency of urban road tunnels

In order to analyze the feasibility of setting bypass tunnel in urban highway tunnel for pollutant purification and dust removal, a physical model including main tunnel and bypass tunnel is established based on ICEM and Fluent numerical simulation software. The purpose of this paper is to analyze the influence of the angle between the bypass tunnel and the main tunnel on the velocity field, pressure distribution and the efficiency of air flow from main tunnel to bypass tunnel. The results show that low-speed and low-pressure areas are generated in the main tunnel which is corresponding to the bypass tunnel entrance (short passageway), and vortices are formed. After the tunnel is opened to traffic, this area will become a pollutant accumulation zone. The bypass tunnel shunting efficiency will increase as the angle decreases. In engineering design, under conditions that meet the safety and economics of the project construction, the included angle can be set to the minimum but not less than 30° to achieve the maximum efficiency.

ANALYSIS OF EFFICIENCY OF METHODS DRYING OF THE METRO POLYETH AIR WITH THE EQUIPMENT IN THE BYPASS WAY

Ensuring the normalized parameters of the microclimate of tunnel air of service connecting branches (SCB) of the deep underground utility company “Kiev Metro” with a length of 1400 m is a priority, through avoiding damage to the insulating materials of the contact flights, which can cause a short circuit. The location of ventilation equipment or drainage or heating installations in a single-track tunnel of the connecting branch is impossible due to limited space, therefore the only place where such equipment can be located is a bypass tunnel. With the optimized operation of the mechanical tunnel ventilation system in energy-saving modes, in 2019, for technical reasons, the soil layer around the tunnels was cooled, resulting in a decrease in the temperature of the tunnel air and an increase in relative humidity above the normal level, which sometimes reached 95 %.The value of the relative humidity of the tunnel air in underground tunnels of deep underground utility company “Kiev Metro” depends on the temperature and absolute humidity of the tunnel air, the temperature of the rim of the walls of the tunnels and the presence of possible additional sources of moisture in the tunnels.The decrease in the relative humidity of the tunnel air during the implementation of the assimilation method by increasing the air exchange SCB-1 in the line to the station. m. Khreschatyk with a length of 1400 m due to the installation of an additional ventilation unit in the bypass tunnel (in the area of PK09 + 40) and means of directing the air flow into the tunnel can lead to an increase in the flow rate of tunnel air to 30 and 26 kg/s, respectively, while the relative humidity will decrease by 5 %. To implement this method, it is necessary to expend an electric power of 40 kW.When implementing the method of drying tunnel air with an additional air drying machine located in the bypass tunnel, it is possible to reduce the relative humidity by (12...14) % and to ensure compliance with the standard humidity of 75 %. However, the implementation of this method is energy-intensive in comparison with the implementation of the assimilation method (increase in air exchange), since the necessary expenditure of electric power for drainage is about 212 kW.According to the results of the study for utility company “Kiev Metro”, a method of heating tunnel air with an additional heat gun installed in the bypass tunnel with a 40 kW heater based on electric heating elements is recommended, which will lead to heating of the tunnel air with a simultaneous decrease in relative humidity by (7...11) % warming the soil layer around the tunnel and avoiding its cooling in the future. The practical implementation of the method for heating tunnel air requires an electric power cost of about 60 kW.

Preliminary assessment of the impacts of sediment sluicing events on stream insects in the Mimi River, Japan

Dam sedimentation is a crucial issue that interferes with flood control and electric power generation. To address this, sediment dredging, bypass tunnel, flushing, and sluicing have been applied. Despite the potential impacts of these operations on stream environments, few studies have explored the environmental/ecological consequences of such regime shifts in sediment dynamics. Specifically, impacts of sediment sluicing on stream fauna have never been reported. This study assessed primary impacts of sediment sluicing events operated with the two cascade dams (the Saigo and Ouchibaru Dams) on stream insects in the lower Mimi River, Japan. The sediment sluicing, accompanied by a major flooding event in the river, was first operated in September 2017. Stream insect data downstream of the four cascade dams, including the two sluicing dams and a reference river, were collected yearly or biyearly in winter and summer from 2010 to 2018. Following the initiation of retrofitting the Saigo Dam for optimizing sediment sluicing, a downstream reach of the dam experienced marked perturbations in terms of both individual density and species richness. The density and richness dramatically decreased and the community significantly differed in winter 2017 from pre-impact conditions. The density, richness, and community composition subsequently recovered in winter 2018, even after the sediment sluicing impact, suggesting that the anticipated negative ecological impacts of the sluicing are limited. Non-metric multidimensional scaling and permutational multivariate analysis of variance revealed distinct differences in communities between summer and winter samples at non-regulated sites or sites farther downstream of the dam that are characterized by fewer Simuliidae in summer and relatively abundant Heptageniidae. This could serve as a reference for assessments of ecological consequences of sediment sluicing in the region.

Study on Sediment Management Strategy of Sandy River Reservoir

The establishment and operation of one hydropower complex will change the movement law of water flow and sediment of the river way, and sediment deposition is difficult to avoid. Due to the characteristics of “high utilized water head, small reservoir storage, high sediment content and particle hardness” of proposed Upper Arun Hydroelectric Project, this paper applies one-dimensional hydrodynamic & sediment model to studying the movement law of flow and sediment of 3 different sediment management strategy, then finding the rational one which can not only maintain a sustainable live storage of the reservoir by sediment flushing, but also reduce sediment abrasion to turbines. The results show that, when the proposed fully open of all low-level outlets for sediment flushing being implemented during high flow periods, the difference of sedimentation is relatively minor, which all 3 options can effectively maintain the live storage of the reservoir thereby minimizing deposition of sediment at the places that will affect project operation. Therefore, the selection of sediment management strategy should depends on the comprehensive technical and economic comparison. Due to the advantages of relatively short outage periods, conventional technology of construction and the largest Net Present Value, the appropriate sediment desilting operation mode is applying a sediment bypass tunnel with its intake located in the middle of reservoir, and meanwhile utilizing the reservoir’s sedimentation effect, to reduce sediment content transported through the turbines.

The Glendoe Tunnel Collapse in Scotland

For Glendoe hydro-electric scheme in Scotland, the tunnelling contract was design–build. After a year, the tunnel collapsed, blocking a 71-m length, which necessitated construction of a by-pass tunnel. The responsibility for the collapse was examined in court and the findings were later appealed by a further three judges. The judge of the first case found that the cause of the failure was “erodible rock” and the other three judges agreed, but, it is argued, that there is evidence for a complex wedge failure at a scale larger than the geological mapping. It is considered that the Owner of the tunnel, Scottish Southern Electricity took on the risk by agreeing to a TBM-constructed, mostly unlined tunnel rather than a drill and blasted, fully lined tunnel as had been postulated at tender. The Contractor, Hochtief, constructed the tunnel and lined it in accordance with a Rock Excavation Classification design sheet that was agreed by all parties and approved by the Engineer. A clause, ‘Option M’ limited the responsibility of the Contractor “for defects in the works due to his design so far as he proves that he used reasonable skill and care to ensure that it complied with the works information”. The question is posed as to whether or not the current judicial process may be an impediment to valid decision-making on responsibility for dealing with complex geotechnical problems. This paper suggests that these issues require a technical assessment and engineering judgement decision, rather than a legal opinion, adjudicated on the basis of opined contractual responsibility. Perhaps, an erudite technical panel deliberation rather than a judicial process should be given the final authority in such cases.

Oxygen control mechanism in non-ventilation excavation based on the simultaneous mining of coal and gas

A new type of non-ventilation excavation system model, which is based on the theory of simultaneously exploiting coal resources and gas from high-gas coal seams in a closed space, is established, consisting of a central ventilation tunnel and a non-ventilated excavating roadway. The respiration and comfort of the mining personnel, as well as gas control, are investigated. The nitrogen curtain is activated prior to opening the air door to replace the gas in the air perturbation space with nitrogen. The nitrogen curtain is simultaneously activated in the barotropic zone to prevent the flow of oxygen into the excavating roadway. The gas pressure relationship between different zones is studied when the air door is closed. The gas pressure only allows nitrogen to flow from the barotropic zone to the central tunnel zone, which ensures that the oxygen is effectively controlled under the closed air door condition. The proposed mechanism for blocking oxygen in the bypass tunnel is validated via the building analogy simulation and numerical simulation model. The presented non-ventilation excavation design efficiently blocks oxygen via simultaneous control of the air door and nitrogen curtain. This study provides a theoretical foundation for the application of non-ventilation excavation processing.

Void detection in two-component annulus grout behind a pre-cast segmental tunnel liner using Ground Penetrating Radar

Ground Penetrating Radar (GPR) is being considered as a potential non-destructive technique for ensuring complete annulus grout backfill behind pre-cast segmental tunnel liners. Current methods for ensuring grout backfill involve drilled verification holes through the waterproof liner. The Rondout bypass tunnel, in Newburgh, NY, where void formation behind the tunnel liner is possible due to high groundwater pressures, provided an example project to evaluate GPR capabilities. While the application of GPR for void detection in one component grouts behind tunnel liners has been well-documented, site specific calibration of the GPR equipment and the application to two-component grouts is necessary. Experiments were conducted on actual tunnel segments to determine the most appropriate antenna frequency that can penetrate through the steel-reinforced segments and produce the best resolution. Mock air and water voids were embedded within areas of complete grout behind the segment to demonstrate the GPR signatures. Steel reflectors buried within the grout provided indirect measurements of the electromagnetic (EM) properties of the two-component grout. All field results were compared against analytical evaluation and numerical models to validate void detection. The findings of this research allow for direct implementation of the GPR technique for detection of voids behind segmental tunnel liners with two-component grout backfill.

Endovascular bypass for salvage of vascular access in hemodialysis catheter-consigned patients.

This study was performed to retrospectively assess the efficacy of percutaneous creation of an intervascular bypass with or without stent graft deployment (endovascular bypass) for salvage of abandoned vascular access sites in hemodialysis catheter-consigned patients. Salvage of abandoned vascular access sites was attempted in 16 patients with hemodialysis catheters. These vascular access sites were salvaged using endovascular bypass techniques to redirect the access flow to a nonarterialized vein as a new outflow conduit or cannulation segment. The postintervention primary, assisted primary, and secondary patency rates of the access site and bypass were calculated using the Kaplan-Meier method. The procedural and clinical success rates were both 100%. The postintervention primary patency rate of the bypass and access site at 360 days was 75.7 ± 12.5% and 56.8 ± 14.9%, respectively. The mean follow-up period was 461.9 days (range: 121-900 days). No major complications were observed. One bare bypass tunnel rupture and one pseudoaneurysm were noted during the procedure. Salvage of abandoned vascular access sites for hemodialysis catheter-consigned patients can be technically feasible and clinically successful using endovascular bypass techniques in selected patients when surgical revision is not considered or is not possible.

A numerical modeling study of sediment bypass tunnels at shihmen reservoir, Taiwan

Many reservoirs in the world were built years ago and losing their storage capacities At Shihmen reservoir Taiwan topological geological and seismological factors greatly increased sediment delivery to the reservoir A large amount of fine sediments entered the reservoir in the form of turbidity current Due to limited desilting facilities majority of the sediments deposited near the dam leading to a significant loss of the storage capacity Moreover extreme typhoon events produced sufficiently high sediment concentrations that water supply was interrupted causing social and economic problems A number of sediment management projects have been planned for the reservoir in order to extend the reservoir life and maintain water supply but few tools are available to understand the effectiveness of the proposed projects In this study a two dimensional D layer averaged turbidity current numerical model is presented and used as a reservoir evaluation tool The sediment bypass tunnel is the study focus as it has been proposed as an important sediment removal measure The model is presented and then validated using the available physical model data Once validated the model is used to evaluate the effectiveness of two proposed sediment bypass plans Further the physical model scale effect is investigated using the numerical model which is often unknown This study serves as a further verification that the newly developed D turbidity current model is robust and useful for practical project applications

Mass hibernaculum of Pipistrellus pipistrellus in a bypass tunnel of the Slapy water reservoir, Czech Republic (Chiroptera: Vespertilionidae)

The bat hibernaculum, situated on the right bank of the Vltava river near Třebenice, approximately 300 metres under the dam of the Slapy water reservoir (49,82232913° N, 14,43661106° E), was discovered in 2010. The bats use a bypass tunnel quarried in 1949–1951 during the construction of the dam. The first check revealed a mass winter aggregation of the common pipistrelle (Pipistrellus pipistrellus), comprising almost 4000 individuals. Since the discovery till 2017, we recorded regular wintering of 2090–4251 individuals of this bat. Moreover, we obtained data on the hibernation of other eight species at this locality: Myotis myotis, M. daubentonii, M. nattereri, M. mystacinus, Barbastella barbastellus, Nyctalus noctula, Vespertilio murinus, and Plecotus auritus. The occurrence of the soprano pipistrelle (Pipistrellus pygmaeus) was confirmed only by detection of echolocation calls and netting at the entrance to the tunnel, but not in the winter aggregation.