Hydraulic Structures-I Tutorial PDF

Hydraulic structures-I Tutorial class Contents:  Design the stability of dams, check and appreciate safety of dams  Design of dam appurtenant and their outlet structures  Analyze dam safety, instrumentation, monitoring and surveillance  Lay out, types and c...

Hydraulic structures-I Tutorial class Contents:  Design the stability of dams, check and appreciate safety of dams  Design of dam appurtenant and their outlet structures  Analyze dam safety, instrumentation, monitoring and surveillance  Lay out, types and components of Hydropower  Design the various energy dissipation Structures.  Applications of software in dam design and stability analysis ,dam breach, hydropower modeling, and reservoir sediment rate modeling. 1 Design the stability of dams, check and appreciate safety of dams  Concrete arch dam is considerable upstream curvature, structurally resisting the imposed loads by arch and cantilever action.  It transfer the major portion of the water load to the abutments or valley sides  Arch dam obtains its stability by both the self-weight and to a great extent by transiting the imposed loads by arch action into the valley walls.  Narrow gorges provide the most natural solution for an arch dam construction. Design Methods of Massive Arch Dams Commonly used methods of design of arch dams are 1) Thin cylinder theory 2) Thick cylinder theory 3) Elastic arch theory 4) Trial load analysis(most accurate) 5) Finite element method The best design of an arch dam is when: the load is divided between the arches and cantilevers. 2 Constant angle arch dam-for V- shaped valley Constant radius arch dam- For wider U- shaped valley What are different stability conditions of dam under which dam may fail?  A gravity dam may fail in following modes: I. Overturning of dam about the toe II. Sliding – shear failure of gravity dam The most common failure mode III. Compression – by crushing of the gravity dam IV. Tension-development of tensile forces w/c results in the crack in gravity dam. Q1. Which type of dam usually has a triangular profile and can resist the forces by its own weight? Q2. Type of dam where the forces acting on the dam are transmitted onto the abutment rocks is_________. 3 Q3. Which failure occurs when the net horizontal force above any plane in the dam or at the base of the dam exceeds the frictional resistance developed at that level?  A. Overturning B. Crushing C. Sliding D. Tension  Overturning- It happens when the resultant force fall out of the base or any horizontal sections. FSO 1.5 -2.5 it is safe of over turning. Righting moments about the toe to the overturning moments about the toe.  Crushing- It is a failure due to the failure of the dam material where the compression stress produced may exceed the allowable stress and the dam material may get crushed. 4  Sliding failures- It happens when sum of resisting horizontal force is less than sum of horizontal force tend to slide.  the recommended value of shear friction factor against sliding.  Shear Friction Factor is given by(SFF) = sliding factor (SF) + B.q / ∑Ph  where B = width of joint or section area = B x 1, q is the shear strength of the joint, and Ph is the sum of horizontal force causing sliding.  SF must be greater than 1 and SFF must be greater than 3 to 5. This analysis is carried out for a full reservoir case as well as an empty case.  The maximum compressive stresses occur at toe when the reservoir is _____ a) Empty. b) Full. c) Half. d) None of above.  Ans. when the reservoir is full, highest pressure will apply on toe. 5  Tension: When eccentricity is greater than B/6 (eccentricity falls outside the middle third), tension may develop. When tension prevails, cracks develop near the heel and uplift pressure distribution increases reducing the net salinizing force. This crack by itself does not fail the structure but it leads to failure of the structure by producing excessive compressive stresses.  The vertical stress at the toe was found to be 3.44 MPa at the base of the gravity dam section. If the downstream face of the dam has a slope of 0.617 horizontal: 1 vertical, the maximum principal stress at the toe of the dam when there is no tail water is _______________ Explanation: The principal stress at the toe is given by Pat toe= Pv. secΦ2 (with out considering the tail water). If there is tail water  where Pv= 3.44 MPa and  tan Φ = 0.617/1 i.e. Φ = 31.67°  Pat toe= 3.44 x sec(31.67°)2= 4.74 MPa 6  Height a dam  A concrete gravity dam having a maximum reservoir level at 200 m and the RL of the bottom of the dam 100 m. The maximum allowable compressive stress in concrete is 3000 KN/m2 and the specific gravity of concrete is 2.4.  Calculate the height of the dam and check whether it is a high dam or low dam.  H = 90 m High gravity dam(200-100=100m> 90m)  What is the formula for limiting height of a gravity dam?  Hmax low gravity dam = f / (Sc + 1) γw where f = allowable compressive stress of the dam material, Sc = Specific gravity of concrete and γw = unit weight of water.  Height of low dam< f / (Sc + 1) γw  This limiting height draws a dividing line between a low and a high gravity dam.  The criteria to classify a dam as a large dam is __________ Ans. Capacity of the reservoir not less than 1 million cubic meters Base width of the dam 7 Elementary and practical Profile of a gravity dam  An elementary profile of a gravity dam is the theoretical shape of its cross- section when it is subjected to only three main forces, viz. self weight, water pressure, and uplift pressure.  It has zero top width and no free board. Earth dam failures can be grouped into three general categories:  overtopping failures,  seepage failures, and  structural failures. Criteria For Design Of Earth Dams  Sufficient spillway capacity and freeboard are provided so that there is no danger of overtopping of the dam.  Seepage flow through the embankment is controlled. 8 1. What is the recommended formula for top width of a very low dam? T= 0.2H + 3 2‐Which of the following zone in Zoned type embankment prevents piping through cracks? a) Central core b) Transition zone c) Outer zone d) Core wall 3. Which of the following earth dam is suitable only on impervious foundation? a) Zoned embankment type b) Homogenous embankment type c) Non‐homogenous type d) Diaphragm type 2. Which is the most widely used method of slope stability analysis of earth dam? The Swedish Method of Slices. Five factors influence slope stability of an embankment: 1) Shear strength of the soil; 2) Unit weight; 3) Embankment height; 4) Slope steepness; and 5) Pore pressure within the soil. 9 How to Analyze the Stability of concrete Gravity Dams? 1. Gravity Method: This method of stability analysis is also sometimes known as two dimensional methods. (a) Graphical Method (b) Analytical Method 2. Trial Load Twist Method-In this method of analysis, the entire dam is divided into a number of vertical cantilevers and horizontal beams. 3. Slab Analogy Method: In this method the analysis is made by dividing the analogous slab into horizontal and vertical beams. 4. 3D finite element method (FEM) 5. Experimental Methods: Experimental methods may be direct method and indirect method. Direct method is also known as three dimensional, model analyses, whereas indirect method as photo elastic model analysis. Three methods are widely used to evaluate dam foundation stability:  model test, limit equilibrium, and finite element (FEM) or finite difference method (FDM). 10 Design of dam appurtenant and their outlet structures  APPURTENANT STRUCTURES - Refers to ancillary(additional) features of a dam, such as the outlet, spillway, outlet conduit, tunnels, intake structures and others.  A spillway is essentially a safety valve for the dam and must be properly designed.  The spillway can be best built independently of the dam where there is a deep narrow gorge with steep banks separated from a flank by a hillock.  A concrete or an earthen dam can be constructed across the main valley and a spillway can be constructed independently into the saddle under such circumstances.  An un-gated spillway(retarding reservoir) starts functioning as soon as the water level in the reservoir crosses the __________________ a) maximum reservoir level b) minimum reservoir level c) maximum conservation level d) full Supply level 11  Maximum conservation level =normal pool level which is the maximum elevation to which the reservoir water surface will rise during normal operating conditions.  This is equivalent to the elevation of the spillway crest or the top of the spillway gates,  An ogee spillway is mostly suitable for concrete gravity dams especially when the spillway is located within the dam body in the same valley.  The trough spillway or chute spillway is the simplest type of a spillway which can be easily provided independently and at low costs} earthen dams  Straight drop spillways are most suitable for thin arch dams.  Energy dissipaters is a device designed to protect downstream areas from erosion by minimizing the flow velocity up to an acceptable limit. NB: Read more about energy dissipators and dam appurtenant structures, please! 12  Dam Safety: Instrumentation, Monitoring & Surveillance  Instrumentation of dams is the use of devices to measure safety parameters of such dams which together with visual inspections and other measurements made at the site provide powerful tools to evaluate the performance and discover early signs of abnormal behavior.  Dam safety concerns do not stop at site selection, or the design and construction stages of a dam, but continue throughout its whole life.  Dam monitoring is one part of a surveillance program that includes visual inspections and testing. Instrumentation has a key role in dam monitoring.  Dam surveillance is a key risk mitigation tool, providing a means of early hazard identification to reduce the probability of undesirable events that could lead to dam failure occurring. What is the purpose of instrumentation and monitoring?  Avoid catastrophic(breach) site incident( Reservoirs constitute a potential hazard to downstream life and property)  Provides information about the performance of the dam  Giving an early warning in case of any issue that may arise Rehabilitation, and repair 13 What factors do you need to check to ensure the safety of the dam? water level(Sounders/Electric water level meters) and storage, seepage and infiltration, deformation and displacement, pore water pressure(Vibrating Wire Piezometers) and weather and seismic activity. Dam Safety Overview and the Federal Role in the United States Periodic inspections are required at least once per year, with detailed inspections every 5 -7 years, extraordinary inspections during and after abnormal events (i.e. large floods), and a thorough dam safety assessment every 15 – 20 years. Report results every 2 years for High Hazard Potential dams, every 5 years for Significant Hazard Potential dams and every 10 years for Low Hazard Potential dams. The primary purpose of the dam safety inspection program is to enhance the safety of dams and appurtenant structures for the protection of downstream life and property. Dam Surveillance programmers & instrumentations are intended to detect and, where possible, to identify symptoms of distress at the earliest possible stage.  National Dam Safety Program (NDSP)- operated by Federal Emergency Management Agency (FEMA)  National Institute of Standards and Technology (NIST)-implementation of guideline  Interagency Committee on Dam Safety (ICODS)- policies and guidelines to enhance dam safety and security.  The U.S. Army Corps of Engineers’ (USACE)- responsible for maintaining the safety of federally owned dams. 14 Typical instrumentations and monitoring used in evaluating causes of common problems/concerns in the dam. Time-domain reflectometry (TDR)  Measuring the pore water pressure is a direct method to monitor the uplift pressure in gravity dams. 15. 16. 17  Layout, types and components of Hydropower  Hydropower engineering refers to the most common renewable energy technology involved in converting the potential energy and kinetic energy of water into more easily used electrical energy.  Hydropower generation is the production of electrical energy from running water through turbines without reducing its quantity.  The prime mover in the case of hydropower is hydraulic turbine which transforms the energy of the water into mechanical energy.  Specific speed: defined as the speed of a turbine which is identical in shape, geometrical dimensions, blade angles, gate opening etc., with the actual turbine but of such a size that it will produce unit power when working under unit head.  Primary or 'firm', power is the power which is always available(continuously available) from a plant corresponds to the minimum stream flow without consideration of storage without any break on a guaranteed basis.  Secondary, or surplus, power is the remainder and is not available all the time. Q1.The maximum quantity of water that is estimated to remain available in a storage reservoir for supply; even during worst dry periods, is known as its:  (a) firm yield (b) design yield (c) reservoir yield (d) primary yield 18 Calculation of specific speed, power generated, discharge and number of turbine 1. In a hydropower station, water is available at a rate of 175 m3/s under a head of 18 m. The turbines run at a speed of 150 rpm(N) with overall efficiency of 82%. Find the number of turbines required if they have the maximum specific speed of 460. N P  150P  Specific speed of the turbine: 0.5 0.5 Ns    460 H 1.25 181.25  Power generated by a turbine, P  12927.5kw Flow required by a turbine P 12927.5 Q   89.281 m 3 / s h 0.82  9.8118 175 No. of turbines   1.96 say 2 turbines 89.281 19  Principal Components of Hydroelectric Scheme What is Hydropower Plant? Hydropower plant uses hydraulic energy of water to produce electricity.  The power obtained from this plant is termed as hydroelectric power. Main components of hydroelectric power plant including i.e., (1) Storage Reservoir and dam (2) Forebay and Intake Structures, (3) Head Race or Intake Conduits, (4) Surge Tank, (5) Turbines and Generators, (6) Power House, and (7) Tail Race and Draft Tube. Note: Read their function 20  Principal Components of Hydroelectric Scheme. Intake as integral part of the Dam Gate Bellmouth Trashrack Draft Tube 21 Cont…. 22 Cont’d…. 23  Types of Hydropower Plant with Layout According to the availability of head 1. Low head power plants < 15 m 2. Medium head power plants 15 – 50 m 3. High head power plants 50-250 m 4. Very high power head plants > 250 m According to the nature of the load 1. Base load plants- always available power 2. Peak load plants- available during excess flow According to the availability of water 1. Runoff river plant with or without pondage(small water storage)-no need of dam/reservoir 2. Storage type plants 3. Pump storage plants 4. Diversion canal plant 5. Mini and micro-hydel plants. 24 25. Pump storage plants 26 Plant capacity: Usually this type of classification is arbitrary(random): for example: Micro hydro < 100 kW Mini hydro < 1000 kW Small to Medium < 60 MW Large Hydro > 60 MW Purpose 1.Single-purpose developments: The water is used only for the purpose of producing electricity. 2.Multipurpose developments: used for many purposes for example, irrigation, flood control, navigation, municipal, and industrial water supply. Basis of Operation: Power/electric generation through two different power supply systems, 1. Off-grid (isolated) (SCS) plant operating independently. self- contained system is the decentralized system responsible for most rural electrification. 2. In a grid system (ICS): Plant operating as part of the interconnected grid system. 27  Working principle of hydroelectric power plant Potential energy kinetic energy hydraulic turbine mechanical work electric generator electric power What is the principle of hydropower? In simple words, falling water spins the water turbine. The turbine drives the alternator coupled with it and converts mechanical energy into electrical energy. This is the basic “working principle of hydroelectric power plant.” 28 Cont… Fig. Pictorial representation of working principle of hydroelectric power 29  Dam Engineering software(application software for design and analysis) The stability and safety are very important issues for the dam structure which are built in seismic regions. 1. RS-DAM is a computer program to evaluate the transient response of a completely cracked concrete dam section subjected to seismic loads. structural behavior and safety of concrete dams. based on rigid body dynamic equilibrium. sliding analysis of a cracked dam 2. TADAM (Thermal Analysis of concrete DAMs) -technique to solve the 1D thermal transfer problem, allowing the calculation of temperature 3. CADAM2D (Computer Analysis of DAMs)- It performs stability analyzes for hydro- static loads and seismic loads. 3D stability analysis software for hydraulic structures 4. GEOSTASEST-2D limit equilibrium slope stability analysis software program 30  Cont’d… 5. Geo-Studio software  Is an integrated geotechnical analysis software suite for analyzing slope stability, groundwater flow, and heat and mass transfer in soil and rock.  Best used for seismic analysis of an earthen dam based on finite element method Stress-strain, seepage, slope stability, dynamic analysis. SEEP/W and SLOPE/W are sub programs of GEOSTUDIO which can simulate the movement and pore-water pressure distribution within. SLOPE/W is the leading slope stability software for soil and rock slopes, analyzing both simple and complex problems for a variety of slip surface shapes, pore-water pressure conditions, soil properties, and loading conditions. Slope Stability Analysis of embankment dam By Geo5 6. ANSYS software -simulates the effect of an earthquake on a dam. Dam break/breach simulations and shape of concrete gravity dams 31  Cont’d… 7. HYDRA or SOLIDWORKS- determine capacity of hydropower that utilizes the discharge.  Used to model 3D of Turbine component model. HYDRA- to calculates the optimal design parameters of hydropower plants. 8. Staad Pro V8i Software  Used for Gravity Dam design and stability analysis. It is one of the most widely used structural analysis of dam. 3D modeling and analysis of gravity dam of solid element 9. HEC-RAS model -U.S. Army Corps of Engineers’ HEC-RAS model features a movable boundary sediment transport calculation module that was recently used to simulate sedimentation processes resulting from hydropower development. The model estimates the rate amount of sediment load yield (tons) and runoff (m3/s) in the sub-basin.  Sedimentation can affect hydropower production due to loss of reservoir storage and/or damage to the facility's mechanical components. HEC-HMS computes watershed sediment yield using the Modified Universal Soil Loss eq. The silt / sand particles entering the water conductor system is to be removed by providing desilting basins. 32 10. GeoSIG- Seismic Instrumentation and Monitoring systems not only help reducing risks and costs, but also help avoiding disaster by its notifications which allows to initiate early damage detection and therefore helps saving lives as well as assets.  The system allows to rapidly evaluate the structural response thus provides a highly useful measure for decision making whether to allow normal operation or to initiate a more comprehensive inspection before doing so. 11.DAMSAT- harnesses satellite technology to remotely monitor water and tailings dams. 33 Any Questions? 34