Roughness evaluation in shotcrete-lined water tunnels with invert concrete based on cases from Nepal

Most of the existing roughness estimation methods for water tunnels are related to either unlined or concrete/steel-lined tunnels. With the improvement in shotcrete technology, advancement in tunneling equipment and cost and time effectiveness, future water tunnels built for hydropower projects will consist of rock support with the extensive use of shotcrete lining in combination with systematic bolting and concrete lining in the tunnel invert. However, very little research has been performed to find out tunnel surface roughness for shotcrete-lined tunnels with invert concrete, which is important in calculating overall head loss along the waterway system to achieve an optimum and economic hydropower plant design. Hence, the main aim of this article is to review prevailing methods available to calculate tunnel wall roughness, and to use existing methods of head loss calculation to back-calculate roughness of the shotcrete-lined tunnels with invert concrete by exploiting measured head loss and actual cross-sectional profiles of two headrace tunnels from Nepal. Furthermore, the article aims to establish a link between the Manning coefficient and the physical roughness of the shotcrete-lined tunnel with invert concrete and to establish a link between over-break thickness and physical roughness. Attempts are also made to find a correlation between over-break thickness and rock mass quality described by Q-system and discussions are conducted on the potential cost savings that can be made if concrete lining is replaced by shotcrete lining with invert concrete.

Application of Particle Image Velocimetry Technology in Water Tunnel

A display and analysis system for hermetical flow field in water tunnel is developed based on the particle image velocimetry(PIV)technology.It consists of some subsystems,such as lamp-house,imaging,image processing and analyzing,control and particles putting.Taking the flow fields around a sphere and a cylinder model as an example under higher Renolds number 5.8×105 in water tunnel,we inquired into the application of the system to water tunnel experiment by cross correlation algorithm.The measure error is less than 2%.The test results show that the developed system can measure and display the flow field accurately in complex flow field without touching and disturbing.The research work indicates that PIV has lots of potential applications in the underwater flow field measurement.

Fiber optic sensing and performance evaluation of a water conveyance tunnel with composite linings under super-high internal pressures

For long-distance water conveyance shield tunnels in operation,the high internal water pressure may cause excessive deformation of composite linings,affecting their structural integrity and serviceability.However,the deformation and failure characteristics of lining structures under internal water pressure are not well investigated in the literature,particularly for three-layer composite linings.This study presents an in situ experimental investigation on the response of two types of composite linings(i.e.separated and combined lining structures)subjected to internal pressures,in which a fiber optic nerve system(FONS)equipped with distributed strain and displacement sensing nerves was employed to monitor the performance of the two composite linings during testing.The experimental results clearly show that the damage of the tunnel lining under different internal pressures was mainly located in the self-compaction concrete layer.The separated lining structure responded more aggressively to the variations in internal pressures than the combined one.Moreover,two evaluation indices,i.e.radial displacement and effective stiffness coefficient,are proposed for describing the changes in the structural bearing performance.The effective stiffness coefficients of the two types of lining structures were reduced by 39.4%and 29.5%,respectively.Considering the convenience of field monitoring,it is suggested that the average strains at different layers can be used as characteristic parameters for estimating the health conditions of lining structures in service.The analysis results provide a practical reference for the design and health evaluation of water conveyance shield tunnels with composite linings.

WATER TUNNEL EXPERIMENTAL INVESTIGATION ON THE DRAG REDUCTION CHARACTERISTICS OF THE TRAVELING WAVY WALL

Drag reduction experiment of the traveling wavy wall at high Reynolds number is conducted.A suit of traveling wavy wall device is developed.The drag forces of the traveling wavy wall with various wave speeds（c）are measured under different water speeds（U）in the K15 cavitation water tunnel and are compared with that of the flat plate.The results show that the mean drag force of the traveling wavy wall have decreased and then increased with oscillation frequency increasing at the same flow speed.Under different flow speeds,when traveling wave wall reached to the minimum of drag force,the corresponding the ratio of the wall motion phase speed c to flow speed U,c /U is slightly different.Within the parameters of the experiment,whenc /U reaches a certain value,the drag force of the traveling wavy wall can be less than that of the flat plate.The drag reduction can be up to 42%.Furthermore,as the value ofc /U increases,the traveling wavy wall can restrain the separation and improve the quality of flow field.

INTERFERENCE OF SIDE STRUT WITH THE NATURAL CAVITATING FLOWS AROUND A SUBMERGED VEHICLE IN WATER TUNNEL EXPERIMENTS

To apply the measurements of model experiment in water tunnel to the actual sailing condition, it is necessary to know accurately the strut effect and its rule. In the present work, the corresponding interferences of one-side strut and two-side strut on the natural cavitating flows around a submerged vehicle in water tunnel were investigated numerically, using the homogeneous equilibrium two-phase model coupled with a natural cavitation model. The numerical simulation results show that the strut types have distinct effects on the hydrodynamic properties. For the same given upstream velocity and downstream pressure, the existence of the strut leads to an increment of natural cavitation number, reduces the low-pressure region and depresses the pressure on the vehicle surface near the sides of strut. In the case of given cavitaiton number, the influences of the two-side strut on the drag and lift coefficients are both enhanced along with the increment of attack angle, however the influence of the one-side strut gradually gets stronger on the drag coefficient but weaker on the lift coefficient contrarily. In addition, based on the present numerical results, a correction method by introducing the sigmoidal logistic function is proposed to eliminate the interference from the foil-shaped strut.

IWHR HIGH SPEED WATER TUNNEL FOR CAVITATION RESEARCH

The paper concerns with the design philosophy,feasibility study,as well as some peculiar features of IWHR water tunnel for cavitation research.The highlights worth-mentioning are the maximum velocity of 35m/s and Reynolds number of 1×10~7 as well as the provision of a specially designed air resorber.

Risk assessment model of tunnel water inrush based on improved attribute mathematical theory

Tunnel water inrush is one of the common geological disasters in the underground engineering construction.In order to effectively evaluate and control the occurrence of water inrush,the risk assessment model of tunnel water inrush was proposed based on improved attribute mathematical theory.The trigonometric functions were adopted to optimize the attribute mathematical theory,avoiding the influence of mutation points and linear variation zones in traditional linear measurement functions on the accuracy of the model.Based on comprehensive analysis of various factors,five parameters were selected as the evaluation indicators for the model,including tunnel head pressure,permeability coefficient of surrounding rock,crushing degree of surrounding rock,relative angle of joint plane and tunnel section size,under the principle of dimension rationality,independence,directness and quantification.The indicator classifications were determined.The links among measured data were analyzed in detail,and the objective weight of each indicator was determined by using similar weight method.Thereby the tunnel water inrush risk assessment model is established and applied in four target segments of two different tunnels in engineering.The evaluation results and the actual excavation data agree well,which indicates that the model is of high credibility and feasibility.

3D Finite Element Simulation of Tunnel Boring Machine Construction Processes in Deep Water Conveyance Tunnel

Applying stiffness migration method,a 3D finite element mechanical model is established to simulate the excavation and advance processes.By using 3D nonlinear finite element method,the tunnel boring machine(TBM) excavation process is dynamically simulated to analyze the stress and strain field status of surrounding rock and segment.The maximum tensile stress of segment ring caused by tunnel construction mainly lies in arch bottom and presents zonal distribution.The stress increases slightly and limitedly in the course of excavation.The maximum and minimum displacements of segment,manifesting as zonal distribution,distribute in arch bottom and vault respectively.The displacements slightly increase with the advance of TBM and gradually tend to stability.

3D Finite Element Analysis of TBM Water Diversion Tunnel Segment Coupled with Seepage Field

In most studies of tunnel boring machine(TBM)tunnelling, the groundwater pressure was not considered, or was simplified and exerted on the boundary of lining structure. Meanwhile, the leakage, which mainly occurs in the segment joints, was often ignored in the relevant studies of TBM tunnelling. Additionally, the geological models in these studies were simplified to different extents, and mostly were simplified as homogenous bodies. Considering the deficiencies above, a 3D refined model of the surrounding rock of a tunnel is firstly established using NURBS-TIN-BRe P hybrid data structure in this paper. Then the seepage field of the surrounding rock considering the leakage in the segment joints is simulated. Finally, the stability of TBM water diversion tunnel is studied coupled with the seepage simulation, to analyze the stress-strain conditions, the axial force and the bending moment of tunnel segment considering the leakage in the segment joints. The results illustrate that the maximum radial displacement, the minimum principal stress, the maximum principal stress and the axial force of segment lining considering the seepage effect are all larger than those disregarding the seepage effect.

Protection against water or mud inrush in tunnels by grouting:A review

Grouting is a major method used to prevent water and mud inrush in tunnels and underground engineering. In this paper, the current situation of control and prevention of water and mud inrush is summarized and recent advances in relevant theories, grout/equipment, and critical techniques are introduced. The time-variant equations of grout viscosity at different volumetric ratios were obtained based on the constitutive relation of typical fast curing grouts. A large-scale dynamic grouting model testing system （4000 mm × 2000 mm × 5 mm） was developed, and the diffusions of cement and fast curing grouts in dynamic water grouting were investigated. The results reveal that the diffusions of cement grouts and fast curing grouts are U-shaped and asymmetric elliptical, respectively. A multi-parameter real-time monitoring system （＆#981; = 1.5 m, h = 1.2 m） was developed for the grouting process to study the diffusion and reinforcement mechanism of grouting in water-rich faulted zone. A high early strength cream-type reinforcing/plugging grout, a high permeability nano-scale silica gel grout, and a high-expansion filling grout were proposed for the control of water hazards in weak water-rich faulted zone rocks, water inrush in karst passages, and micro-crack water inrush, respectively. Complement technologies and equipment for industrial applications were also proposed. Additionally, a novel full-life periodic dynamic water grouting with the critical grouting borehole as the core was proposed. The key techniques for the control of water inrush in water-rich faulted zone, jointed fissures and karst passages, and micro-crack water inrush were developed.

Prevention and treatment technologies of railway tunnel water inrush and mud gushing in China

Water inrush and mud gushing are one of the biggest hazards in tunnel construction. Unfavorable geological sections can be observed in almost all railway tunnels under construction or to be constructed, and vary in extent. Furthermore, due to the different heights of mountains and the lengths of tunnels, the locations of the unfavorable geological sections cannot be fully determined before construction, which increases the risk of water inrush and mud gushing. Based on numerous cases of water inrush and mud gushing in railway tunnels, the paper tries to classify water inrush and mud gushing in railway tunnels in view of the conditions of the surrounding rocks and meteorological factors associated with tunnel excavation. In addition, the causes of water inrush and mud gushing in combination of macroand micromechanisms are summarized, and site-specifc treatment method is put forward. The treatment methods include choosing a method of advance geological forecast according to risk degrees of different sections in the tunnel, determining the items of predictions, and choosing the appropriate methods, i.e. draining-oriented method, blocking-oriented method or draining-and-blocking method. The treatment technologies of railway water inrush and mud gushing are also summarized, including energy relief and pressure relief technology, advance grouting technology, and advance jet grouting technology associated with their key technical features and applicable conditions. The results in terms of treatment methods can provide reference to the prevention and treatment of tunnel water inrush and mud gushing.

Formation mechanisms of water inrush and mud burst in a migmatite tunnel：a case study in China

This paper presents a case study of water inrush and mud burst occurring in a migmatite tunnel to study its formation mechanisms. The geological investigation and mineralogical analysis showed that water inrush and mud burst in the migmatite was closely related to the component of the host rock. High content of soluble minerals,e.g.,calcite and dolomite,would make the migmatite rock prone to be fragmentized,isintegrated and eventually form different sorts of connected or semi-connected veins. The field exploration revealed most cavities in the magmatite tunnel were eroded by groundwater and formed large interconnected networks. The two faults and the dike in the magmatite tunnel became the preferred paths and provided great convenience for plenty of precipitation and mud slurry. Due to high water pressure and blast disturbance,the cavities can soon connect each other as well as all sorts of veins,forming a complex ground channel for water inrush and mud burst. To estimate the potential occurrenceof water inrush and mud burst,the water bursting coefficient was employed. The results showed the water bursting coefficient of the magmatite tunnel was much bigger than the threshold values and it can be used to explain the accident of water inrush and mud burst occurring in the magmatite tunnel.

Soil pressure and pore pressure for seismic design of tunnels revisited: considering water-saturated, poroelastic half-space

This paper describes a systematic study on the fundamental features of seismic soil pressure on underground tunnels, in terms of its magnitude and distribution, and further identifi es the dominant factors that signifi cantly infl uence the seismic soil pressure. A tunnel embedded in water-saturated poroelastic half-space is considered, with a large variety of model and excitation parameters. The primary features of both the total soil pressure and the pore pressure are investigated. Taking a circular tunnel as an example, the results are presented using a fi nite element-indirect boundary element(FE-IBE) method, which can account for dynamic soil-tunnel interaction and solid frame-pore water coupling. The effects of tunnel stiffness, tunnel buried depth and input motions on the seismic soil pressure and pore pressure are also examined. It is shown that the most crucial factors that dominate the magnitude and distribution of the soil pressure are the tunnel stiffness and dynamic soil-tunnel interaction. Moreover, the solid frame-pore water coupling has a prominent infl uence on the magnitude of the pore pressure. The fi ndings are benefi cial to obtain insight into the seismic soil pressure on underground tunnels, thus facilitating more accurate estimation of the seismic soil pressure.

Predictive analysis of stress regime and possible squeezing deformation for super-long water conveyance tunnels in Pakistan

The prediction of the stress field of deep-buried tunnels is a fundamental problem for scientists and engineers. In this study, the authors put forward a systematic solution for this problem. Databases from the World Stress Map and the Crustal Stress of China, and previous research findings can offer prediction of stress orientations in an engineering area. At the same time, the Andersonian theory can be used to analyze the possible stress orientation of a region. With limited in-situ stress measurements, the Hock-Brown Criterion can be used to estimate the strength of rock mass in an area of interest by utilizing the geotechnical investigation data, and the modified Sheorey＇s model can subsequently be employed to predict the areas＇ stress profile, without stress data, by taking the existing in-situ stress measurements as input parameters. In this paper, a case study was used to demonstrate the application of this systematic solution. The planned Kohala hydropower plant is located on the western edge of Qinghai-Tibet Plateau. Three hydro-fracturing stress measurement campaigns indicated that the stress state of the area is SH - Sh 〉 Sv or SH 〉Sv 〉 Sh. The measured orientation of Sn is NEE （N70.3°-89°E）, and the regional orientation of SH from WSM is NE, which implies that the stress orientation of shallow crust may be affected by landforms. The modified Sheorey model was utilized to predict the stress profile along the water sewage tunnel for the plant. Prediction results show that the maximum and minimum horizontal principal stres- ses of the points with the greatest burial depth were up to 56.70 and 40.14 MPa, respectively, and the stresses of areas with a burial depth of greater than 500 m were higher. Based on the predicted stress data, large deformations of the rock mass surrounding water conveyance tunnels were analyzed. Results showed that the large deformations will occur when the burial depth exceeds 300 m. When the burial depth is beyond 800 m, serious squeezing deformations will occur in the surrounding rock masses, thus requiring more attention in the design and construction. Based on the application efficiency in this case study, this prediction method proposed in this paper functions accurately.

Treatment of tunnel wash waters-experiments with organic sorbent materials.PartⅠ:Removal of polycyclic aromatic hydrocarbons and nonpolar oil

Tunnel wash waters characterize all waters that run off after washing procedures of tunnels are performed.These waters represent a wide spectrum of organic and inorganic pollutants,such as polycyclic aromatic hydrocarbons(PAHs)and toxic metals.Removal of such contaminants from water runoff was investigated using laboratory tests after washing procedure was performed on two road tunnels in eastern Norway(Hanekleiv and Bragernes).Due to diverse character of both,treatment media and treated wash waters, the wh...

Influences of material dilatancy and pore water pressure on stability factor of shallow tunnels

Explicit finite difference code was used to calculate the stability factors of shallow tunnels without internal support in limit state. The proposed method was formulated within the nonassociative plasticity. For the shallow tunnels in soft clay, without considering the influences of pore water pressure and dilatancy, numerical results were compared with the previously published solutions. From the comparisons, it is found that the present solutions agree well with the previous solutions. The accuracy of the strength reduction technique was demonstrated through the comparisons. The influence of the pore water pressure was discussed. For the shallow tunnels in dilatant cohesive-frictional soils, the dilatant analysis was carried out.

Key technologies for construction of Jinping traffic tunnel with an extremely deep overburden and a high water pressure

Jinping traffic tunnel is one of the deepest traffic tunnels in the world with a maximum overburden of 2 375 m and the overburden over 73% of its total length is larger than 1 500 m. The tunnel is 17.5 km long and designed to provide a shortcut road between two hydropower stations： Jinping I and Jinping II of the Jinping Hydropower Project, located on Yalong River, Liangshan State, Sichuan Province, China. The tunnel is so deep that building any shafts is impossible. The construction starts from both ends （east and west ends）, and the construction length from the west end is 10 km with a blind heading. This paper deals with an overview of this project and analysis of the engineering features, as well as key technologies developed and applied during the construction, including geological prediction, rock burst prevention under a super high in-situ stress, sealing of groundwater with a high pressure and big flow rate, ventilation for a blind heading of 10 km, wet spraying of shotcrete at zones of rock burst and rich water, etc. The application of the new technologies to the construction achieved a high quality tunnel within the contract period.

高速水洞中超空泡稳定性与通气率定量试验研究

超空泡航行体通气规律对空泡形态控制具有重要意义。本文描述了在高速水洞中建立水下航行体通气率对超空泡形态及稳定性影响的一种试验研究方法。基于不同空化器和模型攻角条件下的空泡形态及通气率测量试验结果,总结得到无量纲通气率计算的经验表达式。通过对有、无尾翼条件下的通气率试验进行比较,初步获得尾翼对超空泡泄气的影响规律。研究结果表明,通气率需要保持在一定范围内方可获得形状稳定、边界清晰的通气超空泡。依据试验结果给出了超空泡稳定性的判别方法。

Water inflow forecasting for tunnel considering nonlinear variation of permeability coefficient

To assess the water inflow which is more suitable to the actual conditions of tunnel,an empirical correlation about the permeability coefficient changing with depth is introduced.Supposing that the surrounding rock is heterogeneous isotropy,the formula for calculating water inflow of tunnel with the nonlinear variation of permeability coefficient is deduced.By the contrast analysis with the existing formulas,the presented method has the similar value to them;moreover,the presented method has more simple form and easy to use.Due to parameter analysis,the water inflow decreases after considering the nonlinear variation of permeability coefficient.When the attenuation coefficient a>0,the water inflow increases first till reaches the maximum at a certain depth,then decreases and is close to 0 finally if deep enough.Thus,it is better to keep away from the certain depth where it is with the maximum water inflow for safe operation and economical construction,and reduce the water damage.Based on the analysis,the radius of tunnel has less impact on the amount of water inflow,and the water inflow just increases by 6.7% when the radius of tunnel increases by 1 m.

大型空泡水洞试验设施结构有限元分析

大型空泡水洞试验设施是目前中国规模最大的水洞系统,为评估其整体结构强度和抗震设计安全性,对空泡水洞结构进行三维有限元数值分析,考虑正常工作工况和地震载荷作用极限工况下的结构刚强度,基于振型分解反应谱法计算了地震惯性加速度载荷,并对结构地震位移响应进行校核。结果表明:空泡水洞的结构变形在正常工作工况主要表现为水洞内壁的膨胀变形,在极限工况下主要表现为由地震载荷引起的水洞顶部水平位移;空泡水洞高应力区域主要位于结构角隅处的筒壁和加强筋。这对中国自主研发大型空泡水洞具有重要的借鉴意义。