Stability analysis of divergence tunnel of storage dam by finite and boundary element method. Case study: Ardak dam (Mashhad)

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1 Stability analysis of divergence tunnel of storage dam by finite and boundary element method Case study: Ardak dam (Mashhad) SH. Taheri 1, H. Saghi 2 1- Ms.c Rock mechanic engineering and academic member of azad university of Mashhad 2-PhD Student of Hydraulics, Department of Civil Engineering, Ferdowsi University, Mashhad, Iran and designer of TOOSAB consulting engineering company Shahab.Taheri@gmail.com Abstract The purpose of this research is study of stability of water diversion tunnel of Ardak dam of Mashhad and analyzing it through the experimental and numerical methods and finally providing different methods and controlling stability of tunnel housing based on regional strategic situation. For this purpose, at first the condition of regional geology determined thorough ground experiments and cross-drilled bore tunnels and exploration, and then suitable options identified to determine location and depth of the tunnel. Then specific parameters for designing tunnel were determined and designing the covert tunnel is accomplished by using various soft wares (including software and UNWEDGE and PHASE2) which are based on Finite element methods, and wedge method. Finally, the achieved results were validated through experimental analysis (RMR and Q methods) and providing the amount required for increasing the stability of tunnel maintenance has been proposed through natural sustainability of land. Keywords: Ardak dam, Finite element, Boundary element, stability of tunnel 1.Introduction Considering that the most important issue of all countries, especially in arid and semi-arid areas is water shortage crisis in the near future, so lack of water and appearing gradually the real and vital value of water makes people and the countries to take maximum utilization of available water in the lodge. In mean while one of the methods of exploitation of groundwater is the implementation of dams. In making the body of dam and to keep the environment dry, diversion condition of river flow should be examined and during this review diversion tunnel is one of the appropriate options e. In this article, stability of water diversion tunnel of Ardak has been reviewed and different stages of design will be provided as follows: Plan Introduction Geological studies of diversion tunnel Diversion tunnel stability analysis through the experimental method Diversion tunnel stability analysis through numerical methods Diversion tunnel stability analysis through wedge method Conclusions and providing suggestions and related solutions ١

2. Specification of Ardak dam Ardak Dam is 69 kilometers away from North West of Mashhad and it is located in geographical coordinate's o o 36 46 Northern latitude and 59 26 Eastern longitude.

2 2. Specification of Ardak dam Ardak Dam is 69 kilometers away from North West of Mashhad and it is located in geographical coordinate's o o Northern latitude and Eastern longitude. This dam is under Construction on Ardak River. Earthy type of this dam is clay core with the height of 55.5 m from the river bed, crest length 410 m and the reservoir volume 30 million cubic meters (the normal level). This dam has been designed for the purpose of agriculture and supplying drinking water in Mashhad. Diversion tunnel project with 245 meters in length, and circular cross section with 4 meters in diameter has been built in the right side of dam body.figures 1 shows area of diversion tunnel of Ardak dam. Divergence tunnel Figure 1: area of diversion tunnel of Ardak dam. 3. Geological studies of diversion tunnel area: Water diversion tunnel has been designed in the right side of dam.the 243 meter long tunnel started in the 1259 balance at point C along with N2 1E and continues to point C1 in 1245 meter balance through changing direction and equal to 30 the West.formative stone of its Path, like those formative stones of right side of Ardak dam are consisting of marl, calcareous marl and limestone. Special quality of these stones is excellent and the RMR value of them is at least 60 based on different obtained parameters and the horseshoe shape tunnel with 4 meter in diameter is designed and it is stable for one month based on tunnel stability diagram bug (seeing BinaVoosky, 1948). Tunnel drilling areas in which there is considerable thickness of marl layers, it should be more careful about capability of inflation and erosion especially because of lower geomechanic parameters and necessary arrangements should be considered [1]. Despite the band of different joints and layered levels upon the objective theory of lack of EP and JP intersection caused by discontinuous levels and levels of cross drilling, evanescent Mountain Pyramids are in the roof and sides of tunnel and also they likely will slip, so the necessary arrangements should be taken into consideration during drilling to prevent the fall upon stone blocks. ٢

3 4. Stability analysis of Diversion tunnel through experimental method: Experimental methods for diversion tunnel stability analysis, includes various methods such as Q and RMR methods. theses methods are established based on experimental results obtained from analysis of large numbers of Projects implemented throughout the world.using experimental methods, quality stone will be classified within the implementation of diversion tunnel. Using the results of such classifications, we can estimate inherent nature of stones and understand that how such stone acts in different engineering conditions Stability analysis of diversion tunnel through RMR method : System RMR (geomechanical category) was proposed by Bynavsky in At this method six parameters such as single axial resistance, RQD, distance between the discontinuity, the discontinuity condition, the status of underground water and the direction of discontinuities has a noticeable role. In this way, each of theses six parameters has been valued in order to geomechanical classification of rock mass and then is classified to very good stone cairn, good, average, poor and very poor based on directions of discontinuity. Finally, stable condition of stone within the diversion tunnel can be specified based on the tables provided and the classifications accomplished. For example, classification of stone within the diversion tunnel of Ardak dam as well as the above method is as a good stone with a firm average time of 7 months for 8 meter entrance adhesion to the rock mass about o Kp And friction angle about In this research, sustainability of restricted area of Ardak Dam diversion tunnel run has been shown through RMR method and the results tables (1) and (2). Table 1: Input data using RMR method Input data for classification of rock Rock Quality Designation: 95 Spacing :500 mm Condition of discontinuities : Separation between discontinuities : 0.5 Condition of joint surface: slightly Rough Discontinuties persistance : 2 Thickness of the joiut infilling : 1mm Weathering condition of rock: slightly weatherd General ground water condition : Damp Orientation of discontiniuty: fair Estimation of rock weatherability: Intermediate resistance Rating ٣

4 Table 2: Results of RMR method The results of classification Value of Basic RMR Value of Adjusted RMR Value of RMR for dry condition Cohesion (Kpa) Internal friction Angle Span or Height Maximum Unsupported span Equivalent dimension Basic Rock Mass Strengh The design Rock Mass Strengh In- Situ deformation modulus Q classification Value Description Rating Range Class No Description Rating Mpa 38.4Degrees 8.5m 7.1m 5.3m 34.7 Mpa 22.6 Mpa 23.6 Gpa Fair Good rock Average stand-up time 1 yr for 10-m span 4.2. Stability analysis diversion tunnel by Q method Barton and his colleagues of Geomechanics Institute of Norway (1976has issued Index Q to determine the rock mass quality of place which this tunnel; is being drilled [2]. RQD Jr Jw Q = * * (١) Jn Ja SRF In this relation RQD is as coefficient of the rock mass quality, Jn As number of non-continuity series, Jr as roughness of the most unfavorable non-linkage, Ja as grade of changes or filling along the weak layer, Jw as a reduction factor of joint water and SRF is as tension reduction factor. Value of Q can change from to 1000 on a logarithmic scale of rock mass quality. for relating the quality index Q to the behavior of underground factor and retaining amount required, Barton and his colleagues have defined another parameter as "equivalent after: drilling (De) which is obtained of crater ration, diameter, or height of drilling as well as amount which called "retaining important factor". Retaining important factor is dependant of type of underground space user and degree of instability of related factor. ESR is similar to the reverse of "safety factor" which is used in designing of stone gable roofs. In this research, stability of restricted area of performing diversion tunnel of Ardak Dam is shown through Q method and the results in tables (3) and (4). ٤

5 The details of the classification system mentioned above, are shown that theses two systems instead on the importance of Joint Profiles, and considered index RQD as underground water conditions. So it is no surprise if these two systems are connected to each other. Therefore, analyzing more than 117 historical samples, Bnyavasky presented equation RMR = 9 lnq + 44 for the expression of these two systems. In this study, according to the results of field tests, this obtained equation confirms somewhat the validity of the equation which Bnyavsky proposed [3,4, 5]. Table 3: Input data using Q method Input data for classification of rock Rock Quality Designation : 95 Joint number set : one joint set Joint Roughness : Rough undulating Joint Alteration : Slightly altered Water Inflow Condition : Dry Excavation or mirror inflow Stress Reduction : swelling Rock (Mild) Rating Table 4: the results of classification of rock using Q method The results of classification In- situ deformation modulus Maximum Unsupported span : Permanent Support Pressure Span or height Equivalent Dimension Q RMR Description Rating 27/4 Gpa 7/7 m 0/1516 Mpa 9/3 m 5/8m 8/ /7 Good Rock 5. Stability analysis of Diversion tunnel through numerical methods Diversion tunnel design requires collection of basic that includes status of tension in virgin rock, geometric specifications of space dug, tension distribution in the rock mass including drilled space and general status of geology of area. In this research, field information of the areas of drilling diversion tunnel of Ardak Dam collected and then this analysis was performed using the software Phase2 based on Finite element method and border element. This software has an extensive capability for analyzing of tensions around the underground excavation area and estimating their stability. Using software PHASE2 Included preparation of relevant scale underground space model, figuration of considered environment to smaller components, setting the desired range to determine tensions (which is the same as radius 5R in this study(r is the tunnel radius) to determine tension levels), to determine the status of ٥

6 Geology, boundary layer, existing joint within the area, and defining materials contain privacy of tunnel based on failure criterion. Finally, obtained information from this software, includes minimum and maximum stress, perpendicular stress to the tunnel layer, safety factor, points surrendered (on the materials that are plastic case) and transports e in different directions [10,11]. In this study in order to analyzing diversion tunnel of Ardak Dam using software Phase 2 relevant calculations have been performed for each tunnel section of the tunnel regarding to the material of layers and their physical and mechanical properties height of slag rock and ratio of horizontal to vertical tensions which is obtained based on the Poisson ratio. Table (5) shows Physical and mechanical parameters and parameters of failure criteria of different rock units. Also as the tunnel span is 4 meters, there is no plastic case and it is as complete elastic based on the rock properties. Figure (2) shows results of analysis within the dam diversion tunnel of Ardak dam by the software. Regarding to the calculations and analysis in different sections, all have more than one safety factor and such thing indicates that stone can be static without maintaining. Of course, parts that have a topical collapse or junction joint layers with tunnel, appropriate maintenance attempt should be accomplished. In other words, suitable maintainer is used in order to establishing stability and preventing weathering of stones of ceiling, floor and walls of tunnel tunnels. It is used shot Crete 10 cm thickness and injected rock bolts with 2.8 meters with 25 mm in diameter with spacing 1*1 meter in this project. 6. Stability analysis of Diversion tunnel through wedge method: One of the major issues in the design of diversion tunnel is to determine the appropriate path for the tunnel is such a way that with regard to slope and along the major discontinuities of region, the lowest collapse (structure control) may have. During excavation of Diversion tunnel at the restricted area that has several discontinuity categories, you may encounter with stone wedge that have different sizes at different levels. Transporting Potential blocks which are most critical in establishing, could weaken, slip or fall the adjacent blocks and thus it is threat to the desire space. Therefore, in designing such tunnel active or disable maintenance systems should be used in order to keep sustainability of drilled space. For example, rock bolts are the samples of active maintenance systems and shot Crete and various types of steel frames are the examples of disable maintenance systems. On the other hand, displacement of unstable blocks causes significant tensions in the maintenance system and system should be designed based on the incoming power. Please note that the unstable rock block (stone wedge) is resulting from the intersection with of discontinuities to the level of drilled space and can be moved to one of the cases such as fall, slip and rotation. Therefore, for analyzing the stability of such spaces slope and the direction of average slope of main systems of rock mass of region should be estimated and those potential wedges with the potential of slip of fall from the ceiling or walls should be diagnosed. Finally, safety factor for the wedges are calculated according to the method of their abandonment and the balance of maintenance required for making coefficient confidence of the single wedges to the level acceptable [12]. Stereo graph methods to understand controlled split by structural complications and evaluate individual chocks are useful in underground structures. But the above methods for designing large tunnels are very time consuming using computer methods to analyze the effects of unstable structure is recommended. Therefore, in this study, software unwedge has been used to analyze the existing wedge within diversion tunnel of Ardak dam. In this software as software PHASE2, accurate design of diversion tunnel should be defined. By entering the required information, software reviews the effect of joints to the stability of the water diversion tunnel and considers how the wedges form and ultimately regarding to the most dangerous formed wedge threads (if any), the best maintenance system is suggested [13,14]. After consideration the condition of diversion tunnel of Ardak Dam, it is noticed that the number of six wedges are formed during the tunnel and only one wedge has a confidence coefficient less than 1.Although this wedge has not significant weight and it's much gap. So the maintenance system was only designed to slice 1. ٦

For designing the maintenance system regarding to the

maintenance system including 6-meter rock bolts used to

These rock bolts are preferably in types of resin or

Because these two factors, are more effective than

The section of tunnel with anchorage The section of

with anchorage The deflection curves of tunnel without

7 For designing the maintenance system regarding to the weight and specifications of the wedge, a proper maintenance system including 6-meter rock bolts used to achieve appropriate confidence coefficient. These rock bolts are preferably in types of resin or grout ones. Because these two factors, are more effective than mechanical rock bolts [15]. The section of tunnel with anchorage The section of tunnel without anchorage The deflection curves of tunnel with anchorage The deflection curves of tunnel without anchorage Stress distribution out of plane with anchorage Safety factor distribution without anchorage Figure2: analysis results of Ardak dam divergence tunnel using PHASE2 software ٧

$mechanical characteristics fracture$ criteria of rock Density(gr/cm3) Poisson

001 20 Marly line stone 2.6 0.25 25000 0.

1 3D view of tunnel Front view of tunnel

8 Type of rock Table5: Physical and mechanical characteristics fracture criteria of rock Density(gr/cm3) Poisson coff. Module elasticity Fracture criteria of Hook and Brown Uniaxial compressive strength (Mpa) M s Marl Marly line stone Wedge contribution on domain Input data of joints Support Data of stability analysis Dimensions of wedge no. 1 3D view of tunnel Front view of tunnel Figure3: analysis results of ardak dam divergence tunnel using UUWEDGE software ٨

9 7. Discussion and conclusion With reviewing obtained results the following conclusions can be achieved: In total, and for total restricted area diversion tunnel has a 10cm shot Crete with a square resistance of 200 tons together with stretching 2 meter rock bolts in length so that its cargo capacity is about 25 tons and resistance of holder cables is about 35 tons/meter and capacity of loading in the cargo is about 10 tons. the installation distances of rock bolts in the tunnel length and width are as 1 / 5 meters. establishing the maintenance system in tunnel is thus rock bolts are installed initially in order to prevent movement. In other words, the created wedge is fixed to the original rock mass to be controlled thereby. During a short time, after the installation of rock bolts, shot Crete are sprinkled on the walls and roof of tunnel. After applying maintenance systems within the tunnel, the safety factor reaches 3.32 which is appropriate for the tunnel with the congestion tension. Swelling of the marl causes the considerable reduction of shear resistance of rock masses and therefore parts of the rock mass are separated. Such frail increases by increasing depth through swelling and indisposition the stones of underground space, so strengthening operation of rock mass should be accomplished at the points which are more likely to taking place disruption and slip through swelling marls. Results of stability analysis using experimental methods show that quality of stones is good enough, in other words, results of rock mass classification through Q and RMR methods shows the close relation ship to each other. But it is not possible in the experimental methods that all effective factors on behavior of the tunnel and maintenance system could be in the classification of system.because theses classifications are based on experiment and a true result may not be obtained. Results of stability analysis through numerical methods using software PHASE2 shows this fact that, regarding to the specification of swelling rocks and whereas, the quality of the region is desirable, practically a simple maintenance system is sufficient for stability of the tunnel. For this purpose, shot Crete with 10cm thickness has been used in the parts of tunnel which can not be loaded. Injection rock bolts (unfolding) with 2.80 meter height and 25mm in diameter with 1*1 meter distance in the span of the tunnel entrance and parts of tunnel cage which were much feebler, have been used. In the stability analysis through wedge methods, software UNWEDGE has been used and based on the results, there was only one wedge with safety factor less than 1 it is so considerable. That wedge didn't have much weight and this fact indicated that such wedge is which has not so effect on the tunnel. In general this should be noted that the results are achieved by software, are relative and can not be completely relied on and this is due to the effects of unforeseen environmental factors on the rock mass and tunnel stability. Therefore, this software only has one viewpoint and ultimately designer himself should take the final decision. 8. REFERENCES [1] Singh, B., Viladkar, M.N. and Samadhiya, N.K.,(1995), "A semi-empirical method for the design of support system ", Tunnelling and Underground Space Technology, Volume 10, Issue 3, Pages [2] Hoek, E.,(1998), "Reliability of Hoek-Brown estimates of rock mass properties and their impact on design", International Journal of Rock Mechanics and Mining Sciences, Volume 35, Issue 1, Pages [3] Singh, B. and Goel, R.K.,(1999), "Geological strength index (GSI) rack mass classification", Rock Mass Classification, Pages [4] Beard, A.N.,(2010), "Tunnel safety, risk assessment and decision-making", Tunnelling and Underground Space Technology, Volume 25, Issue 1, Pages [5] Beard, A.N.,(2009), "Fire safety in tunnels Fire Safety Journal", Fire Safety Journal, Volume 44, Issue 2, Pages [6] Baykasoğlu, A., Çevik, A., Özbakır, L., and Kulluk, S.,(2009), " Generating prediction rules for liquefaction through data mining", Expert Systems with Applications, Volume 36, Issue 10, Pages ٩

10 [7] L. Zhang, J.A. Franklin.,(1993), '' Prediction of water flow into rock tunnels: an analytical solution assuming an hydraulic conductivity gradient'', International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, Volume 30, Issue 1, Pages [8] N. Coli, G. Pranzini, A. Alfi, V. Boerio.,(2008), '' Evaluation of rock-mass permeability tensor and prediction of tunnel inflows by means of geostructural surveys and finite element seepage analysis'', Engineering Geology, Volume 101, Issues 3-4, Pages [9] Mohammad H. Sadaghianiand Saleh Dadizadeh.,''Study on the effect of a new construction method for a large span metro underground station in Tabriz-Iran'', Department of Civil Engineering, Sharif University of Technology, Tehran, Iran. [10] Gurocak, Z., Solanki, P., Zaman M.M.,(2007), Empirical and numerical analyses of support requirement for a diversion tunnel at the Boztepe dam site, eastern Turkey", Engineering Geology, Volume 91, Issues 2-4, Pages [11] Leu, S.S.,(2001), " Data mining for tunnel support stability: neural network approach", Automation in Construction Volume 10, Issue 4, Pages [12] Osgoui, R. and Ünal, E., "An empirical method for design of grouted bolts in rock tunnels based on the Geological Strength Index (GSI)". [13] Kamrunnahar, M., and Macdonald, M.,(2009), " Prediction of corrosion behavior using neural network as a data mining tool". [14] Modic, J.,(2003), " Fire simulation in road tunnels Tunnelling and Underground Space Technology ", Tunnelling and Underground Space Technology, Volume 18, Issue 5, Pages [15] Harris Fabillah, J. Nishi.,(2006),'' Underground space use approach in Indonesia Jakarta mass rapid transit project case study'', Tunnelling and Underground Space Technology, Volume 21, Issues 3-4, Pages 466. ١٠

Underground Excavation Design Classification

Underground Excavation Design Underground Excavation Design Classification Alfred H. Zettler alfred.zettler@gmx.at Rock Quality Designation Measurement and calculation of RQD Rock Quality Designation index