Water Diversion Tunnel Research Articles

The Stability Analysis of Lining Structure of Water Diversion Tunnel of Hydropower in Strong Earthquake Area

To obtain dynamic stability of lining structure of water diversion tunnel under the 100 years beyond 1% probability earthquake condition, the three-dimensional dynamic analysis for water diversion tunnel of large hydropower station was conducted by the dynamic time history method. The distribution of plastic zone and response characteristics of the stress and the displacement and acceleration of each key position of water diversion tunnel under earthquake was obtained. It is shown that the lining structure of the diversion tunnel was subjected to forced vibration according to the excitation ground vibration. The greater the peak of ground vibration was, the greater the dynamic displacement and tensile and compressive stress of the lining structure was. The tensile and compressive stress of the upper horizontal section at the entrance among the lining of diversion tunnel was the largest. The maximum tensile stress of the lining at the entrance is 1.3 MPa. The stress of tunnel lining was asymmetry in the horizontal direction. Each tunnel was close to the side of the other tunnel, the stress value was larger, and the stress value was smaller away from the side of the other tunnel. The farther the plastic zone of the diversion tunnel was from the entrance and exit of the tunnel, the smaller the plastic zone was. The plastic area of the surrounding rock between the eight water diversion tunnels did not occur through. After the earthquake, the plastic zone was through only in the export position of eight diversion tunnels. The local position in the diversion tunnel was damage under the 100 years beyond 1% probability earthquake condition, but the whole tunnels were safe and stable.

The Impact of Temperatures on the Stability of Rocks Surrounding a Single Fracture

Research on the influence of temperature and the accompanying stress on the stability of the rocks surrounding an underground tunnel has become ever more important. This paper constructs a geometric model of a single-fracture tunnel by combining a high-temperature underground tunnel as the object of study with an example that uses a high-temperature tunnel segment in the water diversion tunnel of a hydropower station in Xinjiang. Based on the relevant theoretical analysis, with the consideration of different working conditions, a numerical experimental analysis was conducted to determine the two-dimensional transient temperature field distribution of the tunnel rock mass by using a numerical analysis software. The experimental data was consistent with the measured data. The calculated results show the following: a. when the temperature difference is greater, the stress concentration is higher near the fracture of the surrounding rock; b. the degree of the stress concentration in the crack tip region is not positively correlated to the distance, and there is a sensitive region where the stress varies.

Research and Construction Control Points of Vertical Jacking Technology of Water Diversion Tunnel

Taking the circulating water diversion tunnel project of a large power plant as an example, a new type of underground excavation technology, namely vertical jacking construction technology was studied. The reaction force of the bottom of the tunnel was calculated accurately by establishing the calculation model, and the countermeasures to overcome the reaction force were put forward. At the same time, the vertical jacking process, control points and monitoring content were discussed. Through the above research and analysis, it can provide reference and help for the construction of similar projects, and promote the further development of the technology.

Risk Assessment of Water Inrush in Tunnel through Water-Rich Fault

A fuzzy comprehensive evaluation method based on gray theory is proposed to assess the risk of water inrush in tunnels through water-rich fault. The Grey-Fuzzy method consists of two parts: one is the single factor evaluation matrix which is created by evaluation index and the risk grade membership function, the other one is the weight of each evaluation index set by using the norm gray correlation degree. Five influence factors (fault dip, groundwater level, RMR, permeability and strata inclination) are selected as evaluation indices from the aspects of stratum lithology, geological structure and hydrogeological condition. The orthogonal numerical simulation test is applied to obtain the quantitative evaluation index of geological structure. Finally, the established risk evaluation method of water inrush was applied to the water diversion tunnel project of Longjinxi. The evaluation results can match the reality situation in tunnel construction.

高应力条件下岩体钻孔变形与地应力关系研究

锦屏二级水电站引水隧洞上覆岩体一般埋深1500~2000 m，最大埋深约为2525 m，具有埋深大、洞线长、洞径大的特点，为超深埋长隧洞特大型地下水电工程。最大地应力可达到70 MPa以上，在隧洞开挖过程中，由于存在超高的地应力，局部岩体出现了强烈的岩爆和变形。地应力测试钻孔中经常出现岩饼现象，孔壁则会出现变形甚至塌落，给地应力测试造成很大的困难。通过孔壁周围应力状态的理论分析、钻孔孔内电视摄像、岩石单轴抗压试验成果分析和多种岩体地应力测试方法等研究，证明钻孔变形对地应力测试的影响，及其与岩体地应力之间的关系，找到了消除和减少影响的解决办法，得到在高应力条件下的可靠的岩体原始地应力测试成果。 The general burial depth of water diversion tunnel of Jinping II Hydropower Station is about 1500 - 2000 m and the maximum depth is about 2525 m. It has the characteristics of large depth, long hole line length and wide diameter which is an extra large underground hydropower project. The maximum in-situ stresses can reach more than 70 MPa. In the tunnel excavation process, due to the existence of high ground stress, local rock body appeared strong rockburst and deformation. It often occurs rock cake and hole wall deformed or even collapsed in stress testing, which put great difficulties to the test. Based on the theoretical analysis of the stress state around the hole wall, the television camera in the borehole hole, analysis of the uniaxial compressive test results of the rock, and various test methods of the rock stress, the influence of the borehole deformation on the geostress test and the relationship between the stress of the rock mass are proved. Then solutions are made to eliminate and reduce the impact, and obtain the reliable original rock stress test results under high stress conditions.

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-BReP 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.

Underground Excavation Behaviour of the Queenston Formation: Tunnel Back Analysis for Application to Shaft Damage Dimension Prediction

The Niagara Tunnel Project (NTP) is a 10.1 km long water-diversion tunnel in Niagara Falls, Ontario, which was excavated by a 7.2 m radius tunnel boring machine. Approximately half the tunnel length was excavated through the Queenston Formation, which locally is a shale to mudstone. Typical overbreak depths ranged between 2 and 4 m with a maximum of 6 m observed. Three modelling approaches were used to back analyse the brittle failure process at the NTP: damage initiation and spalling limit, laminated anisotropy modelling, and ubiquitous joint approaches. Analyses were conducted for three tunnel chainages: 3 + 000, 3 + 250, and 3 + 500 m because the overbreak depth increased from 2 to 4 m. All approaches produced similar geometries to those measured. The laminated anisotropy modelling approach was able to produced chord closures closest to those measured, using a joint normal to shear stiffness ratio between 1 and 2. This understanding was applied to a shaft excavation model in the Queenston Formation at the proposed Deep Geological Repository (DGR) site for low and intermediate level nuclear waste storage in Canada. The maximum damage depth was 1.9 m; with an average of 1.0 m. Important differences are discussed between the tunnel and shaft orientation with respect to bedding. The models show that the observed normalized depth of failure at the NTP would over-predict the depth of damage expected in the Queenston Formation at the DGR.

Geological and geotechnical observations from the Niagara Tunnel Project

The Niagara Tunnel Project is a water diversion tunnel that was constructed in Niagara Falls, ON, Canada. The tunnel was excavated by a 14.4-m-diameter tunnel boring machine that passed through 11 geological formations. The rock types included limestone, sandstone, siltstone, shale, and mudstone. The overbreak was divided into four zones, evaluated by observations as the tunnel excavation progressed. Overbreak within the Rochester, Neagha, and Grimsby Formations was <0.6 m deep typically, measured perpendicular to the designed excavation perimeter. The Power Glen Formation had overbreak as deep as 2.7 m. The deepest overbreak was measured in the Queenston Formation, where 3–4 m was typical and associated with the tunnel alignment. Maximum overbreak occurred when the tunnel was aligned perpendicular to the maximum horizontal stress. The overbreak was focused in the crown and inverted, with only minor volumes of sidewall overbreak occurring. The deep overbreak within the Queenston was overcome by utilizing spiles and adjusting the tunnel alignment to minimize the duration of excavation in the Queenston Formation. The tunnel went into operation in March, 2013.

Observed ground and pile group responses due to tunneling in Bangkok stiff clay

A 5.15 m diameter water diversion tunnel was driven into Bangkok stiff clay using an earth pressure balance shield. The tunnel was driven within a clear distance of 2 m from the closest pile of a 3 × 4 pile group supporting an expressway. During construction, tunnel driving parameters as well as induced ground and pile group responses were recorded. To avoid cutting the piles supporting the expressway, the alignment of the tunnel was adjusted and curved. As a result of this change in tunnel alignment, the tunnel advancing rate was reduced from an average 17 m/day for a straight drive to an average of only 6 m/day for the curved alignment, and the ratio between the tunnel face pressure and overburden pressure was changed from 0.5 to 0.4, accordingly. Due to the reduction of the tunnel face pressure, up to a 280% larger inward ground movement towards the tunnel was observed. As the shield penetration rate decreased, the torque required for tunnel driving was reduced by 33%, while the ratio between shield penetration rate and soil extraction was almost constant throughout the tunnel route. A transverse influence zone due to tunnel driving was identified to extend up to a distance that was twice the tunnel diameter radially from the longitudinal tunnel axis. The maximum tilting of the expressway pier and deduced differential settlement of the pile located within the influence zone were up to 1:2600 and 2.0 mm, respectively. Tilting of all the piers was mainly caused by long-term subsurface settlement having the tilting direction towards the tunnel. This long-term subsurface settlement was up to about 80% of the total.

Study on Rockburst Intensity Prediction Based on Efficacy Coefficient Method

Based on the basic principle of the efficacy coefficient method, a model of rockburst intensity prediction was established. Considering the key affecting factors of rockburst, three factors were selected as evaluation indexes including the ratio of maximum tangential stress and rock uniaxial compressive strength, the ratio of compressive and tensile strength of rock and elastic energy index. Finally, the model was applied to the rockburst prediction of water diversion tunnel of Jiangbian hydropower station and the results show that the method is reliable, and it provids a new idea to predict rockburst.

Researches on the Stability of Deeply-Buried Water Diversion Tunnel Based on Strength Reduction Method

In view of the complexity of the deeply-buried water diversion tunnel and adopting the advantage of slope strength reduction method, this research takes advantage of strength reduction method to study the stability of diversion tunnel. Based on the instance of Jinping II hydropower, this paper analyzes Yantang Formation III surrounding rocks buried 2500m deep below the ground, adopts the Mohr-Coulomb criterion, takes the cavern displacements or relative displacement as buckling critical criterion, and finally concludes that the safety factor is 1.5 in this instance, not far from 1.2 in the norm. It is thus reasonable to use strength reduction method to study the stability of the deeply-buried water diversion tunnel. The method can get safety factor easily and objectively and can provide scientific basis for evaluating the deeply-buried water diversion tunnel and the design for the supporting structure.

Geological Model of Mae Tang-Mae Ngad Diversion Tunnel Project, Northern Thailand

Most of infrastructure projects around the world have to focus on a clear understanding of geological model which may be determined from various sources of information. The limitation in geotechnical data and budget affects the accuracy of the geological model, particularly for projects of long and deep tunnel of which accessibility to the excavation points is difficult and far reaching. Therefore, an approach adopted for interpretation plays an important role in the level of uncertainty of the derived geological model. This paper focuses on the determination of the geological models at the site of a long water diversion tunnel project in a complex geologic setting in northern Thailand from an approach to understand the relationship between regional tectonic setting and local tectonic condition so that geological structures and rock mass conditions along the tunnel alignment can be assessed for a better planning of tunnel design and construction. The paper describes tectonic settings at regional scale (Northern Thailand and Eastern Myanmar), tectonic features and geologic condition in project area, geotechnical investigation and data along tunnel alignment and predicted tunnel ground behavior.

Research on Generating Mechanism and Treatment Measures of Concrete Bubbles

Concrete bubble is a common phenomenon in the concrete construction process. Generation and existence of concrete air bubble not only influence the concrete appearance, but also affects concrete service life. Especially for concrete surface with high requirements just as water diversion tunnel, concrete bubble gradually raises concern of engineering construction parties. Engineering technical personnel take a number of measures to eliminate concrete surface bubble in project practice. Based on analysis of many bubble elimination methods, generating mechanism and treatment measures of concrete bubble are discussed, providing reference for eliminating concrete bubbles.

Projection of joints from surface to tunnel level — a Case Study

A joint-study of a granitic batholith recorded orientations and spacings of joint-sets at outcrop and at three separate sections of a water diversion tunnel. A second joint-survey in the tunnel determined the average joint spacing along the spring lines. Joint-set spacing studies show a 40–50% reduction of joint-set spacing underground, compared to those at the surface. Individual equal-area plots of surface joints for the two major facies of the granitic rock showed different maxima. But when the joints in the two facies were combined into one equal-area plot, the predominent facies, which represented 73% of the joints plotted, masked the prominent sets of the second facies. Hence, joint surveys for individual rock facies are warranted. Comparison of equal-area plots of surface and tunnel joints in the same rock facies reveals a striking similarity in joint-set maxima.

Spoil disposal from the planned Northfield to Quabbin tunnel, western Massachusetts

Excavation of a 16-km water diversion tunnel from Northfield Mountain to Quabbin Reservoir in western Massachusetts may be undertaken from at least three shafts in addition to the outlet adit. This account is concerned with the disposal of spoil from the aqueduct. The rock formations are mainly gneiss and schist, with minor quartzite and amphibolite. Structurally the area is part of the Pelham dome and folds on its east side. The greatest impact on the environment would be dumping of the rock spoil in piles. The total volume would be about 215,000 m3. An underground power house, if decided upon, would add another 43,000 m3 of spoil. Some of the material could be used in the project itself, for instance as riprap along the spillway. None of the piles would be deeper than 6 m, their combined extent not exceeding 14 h. The smallest impact would result if off-site contractors were to take the material as fill or aggregate. The broken rock out of one shaft might be utilized in the realignment of a nearby highway. The sites are in hilly, rural woodland. Two are close to water and one overlooks an upland bog. Adverse effects of spoil disposal can be minimized by selecting areas that avoid slope instability and interference with natural drainage, as well as undue ecologic change. Special problems involve a site that is underlain by clay and a shaft likely to yield bedrock with sulfide minerals.

Geology of the Harold D. Roberts Tunnel, Colorado: Station 468+49 to East Portal

The Harold D. Roberts Tunnel is a 23.3-mile water-diversion tunnel that extends through the western part of the Front Range between Grant and Dillon, Colorado. This report concerns the geology of the southeastern segment of the tunnel, which is partly in the Montezuma stock—a Laramide quartz monzonite pluton—but is mainly in Precambrian basement rocks. The Precambrian metamorphic rocks consist of relatively thick, complexly folded units of amphibolite, migmatite, microcline gneiss, and biotite gneiss. These rocks were invaded by plutons of Boulder Creek Granite and Silver Plume Granite, regarded as syntectonic and late tectonic, respectively, in relation to Precambrian deformation and metamorphism. Most of the basement rocks are distinctly foliated. Laramide deformation resulted in elevation of the core of the Front Range along northward-trending marginal upthrusts and in development of the Front Range mineral belt, a broad northeast-trending zone of strike-slip faults, veins, and igneous intrusions that extends diagonally across the range. The Montezuma stock was emplaced approximately at the junction of the mineral belt with the western margin of the range relatively late in the deformation. The stock is massive and shows little indication of flow fabric. Analysis of fault data obtained in the tunnel indicates two complementary sets of strike-slip faults, trending northeast and northwest, apparently related to wrench-fault movement along the mineral belt. Minor faults are randomly oriented but tend to be concentrated in north-trending dip-slip sets approximately parallel to the marginal upthrusts. The fracture pattern in the Montezuma stock conforms to the regional fault pattern. The major joint sets and fault sets are parallel to one another and probably formed concurrently. The fracture pattern in the Precambrian rocks is unlike that in the Montezuma stock. Minor faulting was controlled largely by the rock fabric. Joints bear no obvious relation to the faults or rock fabric and are believed to have formed mainly later than the faults. The anomalous rupture pattern in the foliated basement rocks is attributed to their anisotropy and to a probable transition from pseudoductile to brittle behavior as the core of the range was uplifted.