Mresis ng divided by the overturning momentrnmine from the hydraulic pressure of the water in the reservoir movertursins note that the. Thus, it can be concluded that for gravity dam considered over here in study reflects that the dam was stable against overturning, sliding and shearing in. The dam shall be safe against overturning at any plane within the dam, at the base, or at any plane below the base. Ppt gravity dam powerpoint presentation free to view.
For the former it is usual to design the dam so that the resultant of all forces intersects the base within its middle third. Here are the basic steps to building a gravity dam the most common type of dam that we build. The overturning moment of an object is the moment of energy capable of upsetting the object. A gravity dam is a dam constructed from concrete or stone masonry and designed to hold back water by primarily using the weight of the material alone to resist the horizontal pressure of water pushing against it. To withstand the stability of concrete gravity dam, the dam has to be safe with the overturning force on dam, sliding force, compression and tension. To resist this, resisting moments are generated by the selfweight of the dam. Archgravity dams are the types of dams that use combined engineering methods of arch dams and gravity dams. The dam will not overturn provided that the moment around the turning point, caused by the water pressure, is smaller than the moment caused by the weight of. Gravity dam is so proportioned that its own weight resists the forces acting upon it. Safe against overturning at any horizontal plane within the dam. Definition of factor of safety of sliding and overturning.
Later gravity dams used a trapezoidal cross section. Pdf sliding and overturning safety factors of concrete. Sliding and overturning safety factors of concrete gravity dam under the influence of drainage specifications conference paper pdf available september 2015 with 3,953 reads how we. For the love of physics walter lewin may 16, 2011 duration. Design and construction of concrete gravity dams nptel. Ensuring of the proper functioning of concrete dams is one of the most challenging issues of todays engineering world. Stability analysis of concrete gravity dam an overview. Curved gravity dams designed for arch action and other types of concrete gravity dams are not covered in this manual. Gravity dams three major potential modes of failure of gravity dams include. This cross section eventually evolved into the common triangular cross section design of todays gravity dams. Gravity dams are constructed from masonry or concrete. It is primarily the weight of a gravity dam which prevents it from being overturned when subjected to the thrust of impounded water.
Storage dam diversion dam coffer dam power generation dam concrete gravity dam. Gravity dam is designed for various forces especially for the overturning moment and for the sliding forces. This factor of safety is defined asthe ratio of the resisting moment. Concrete dam engineering 1 0401544 hydraulic structures university of sharjah dept. Gravity dam stability analysis failure of gravity dam occurs due to overturning, sliding, tension and compression. As solid gravity dams resist the overturning moments due to all external forces such as water pressure, slit pressure etc by its own weight only, these are known as solid gravity dams. Check dam is a small dam designed to reduce flow velocity and control soil erosion diversion dam is a type of dam that diverts all or a portion of the flow of a river from its natural course masonry dam is a type of dam constructed with masonry. A gravity dam is designed in such a way that it resists all external forces acting on the dam like water pressure, wind pressure, wave pressure, ice pressure, uplift pressure by its own selfweight. The pressure due to this seepage is commonly called hydrostatic uplift and will reduce the stability of the dam against sliding and against overturning. Comparison of design and analysis of concrete gravity dam. Load combination g combination e, but with extreme uplift drains inoperative. The weight of gravity dam will cause a moment opposite to the overturning moment and the friction on the base will prevent the dam from sliding. Introduction concrete gravity dam is a solid structure built of mass concrete material.
Determination of various forces which acts on the structure is the first step in the design of dams. Conventional concrete and roller compacted concrete are both addressed. The calculations of the safety factor against overturning considering. Gravity dam modes of failure and criteria for structural stability of gravity dams a gravity dam may fail in the following ways. Failure of gravity dams causes and its failure modes. As solid gravity dams resist the overturning moments due to all external forces such as water pressure, slit pressure etc by its own weight only, these are known. Failure of dam notes word gravity dam stability analysis. It is made watertight by pointing the joints with cement. Factor of safety against overturning is expressed using the formula.
Gravity dams are solid concrete structures that maintain their stability against design loads from the geometric shape and the mass and strength of the concrete. Common retaining walls buttress toe heel gravity or semigravity retaining wall toe heel cantilever retaining wall stem footing toe heel buttress retaining wall stem. A drainage gallery is generally provided in order to relieve the uplift pressure exerted by the seeping water. Stability analysis of gravity dam using staad pro youtube. The purpose of this manual is to provide technical criteria and guidance for the planning and design of concrete gravity dams for civil works projects. This manual applies to all hqusace elements, major subordinate commands. Previous ferc gravity dam guidance dealt with nappe forces by ignoring. If the actual cross section of the dam is known, or if a cross section of the proposed dam be assumed, the stability against overturning may be determined graphically by either of the two following in fig. European commission joint research centre institute for the protection and security of the citizen contact information address. Requirements for stability following are the modes of failure of a gravity dam.
Instability can occur by either overturning or sliding along the foundation contact or along horizontal cracks or even construction lift lines. The horizontal distance from the toe of the dam to the resultantbase intersection point is. This method of stability analysis is also sometimes known as two dimensional methods. A gravity dam must be designed to safeguard against overturning and sliding. Analysis of gravity dam fluid mechanics and hydraulics. Gravity dams are a type of dam which is secured by making it of such a size and shape that it will resist overturning, sliding or crushing at the toe.
In a gravity dam, stability is secured by making it of such a size and shape that it will resist overturning, sliding and crushing at the toe. Gravitydam stability gravity dam part 2 stability analysis load combinations gravity dam design should be based on the most adverse load combination a. In monolithic curved gravity and arch dams, some proportions of the loads may be carried by tangential shear and twist effects, as well as by the more usually considered arch and cantilever actions. Written by civil engineers, dam safety officials, dam owners, geologists, hydraulic engineers, and risk analysts, this handbook is the first cooperative attempt to provide practical solutions to dam problems within the financial constraints faced by dam owners. Forces acting on a dam structure and calculations different types of forces acts on a dam structure such as water pressure, self weight, wave pressure etc. The upstream face may be kept throughout vertical or partly slanting for some of its length. The weight of the wall will have moment resisting the overturn. The foundation for a gravity dam is most important sound rock is best, but smaller dams have performed well on soft foundations. The surface of the concrete is subjected to very high water velocities as well as abrasion, and therefore must be steelplated.
Gravity dams depend on their own weight for structural stability. The weight of gravity dam will cause a moment opposite to the overturning moment and the friction. Gravity dam design united states army corps of engineers. Of these, the most comprehensive is the 1983 volume by jansen 1 published by the u. Evaluation of failure modes for concrete dams diva. Such a dam is very strong and rigid and requires least maintenance.
Over flow dam non over flow dam concrete gravity dam. Factor of safety against overturning consider force acting on the gravity retaining wall with the lever arm as shown below. Building a dam is a complex, multistep process that requires huge amounts of manpower, raw materials, and investment. Learning outcome after this lecture, students should be able to 1. Gravity dams, concrete, design criteria, ridas, eurocode, limit turn ing iii. The following are the various methods which can be adopted for carrying out the stability analysis of gravity dams. Dam awareness may 2018 introduction responsibility and.
Chapter 6 concrete dam engineering with examples 1. To withstand the stability of conc rete gravity dam, the dam has to be safe with the overturning force on dam, sliding force, compression and tension. Failure of gravity dam occurs due to overturning, sliding, tension and compression. Gravity walls, generally, are trapezoidal in shape, but also may be built with broken backs. The different components of concrete gravity dams and their layouts. These are more suitable in steep valleys where earth dams may tend to slip. The resultant of the normal force at the base of footing must be within. The base and other dimensions should be such that the resultant falls within the middle onethird of the base. Concrete gravity dam has the many load combinations such structures has to maintain its stability when the dam having the different. Gravity dams are designed so that each section of the. Pdf multiple step method of design of gravity dam and. Proper design is also required to safeguard against piping which is a severe problem in the design of earthen dam.
Consider 1 unit length 1 m length of dam perpendicular to the cross section. Multiple step method of design of gravity dam and comparison with cadam software conference paper pdf available september 2016 with 6,492 reads how we measure reads. There have been several studies of dam failures published in the last 30 years. Pdf sliding and overturning safety factors of concrete gravity. The dam may also be prevented from sliding by keying its base into the bedrock.
The most common failure mode for gravity dams is sliding or overturning along or beneath the damfoundation interface. Load combination f combination c, but with extreme uplift drains inoperative. This will provide a factor of safety in excess of 2. Concrete and masonry dams the national academies press. Gravity dam design challenge 1 the factor of safety of the dam against overturning fs must be larger than 2 design requirements. The behaviour of a spillway, discharge part, and intake part of the dam is similar to concrete gravity dams, thus the geometry and loading conditions may be more complicated westberg and hassanzadeh,2007. The moment about toe is induced from the lateral soil pressure causing it to overturn. A concrete gravity dam has a triangular cross section with the base much wider than the crest. This oversight was only discovered after the dam had experienced significant downstream movement. That study listed and discussed dam failures that have occurred over. For structures consisting of a section of concrete gravity dam within an embankment dam, the concrete section will be designed in accordance with this manual.
The calculations of the safety factor against overturning considering the. Comparison of design and analysis of concrete gravity dam 19. The dam is configured to provide enough mass and a sufficiently wide base to resist sliding and overturning in response to the force of water pushing against it. A gravity dam may collapse in one or more sections which have been. Study set 912 static of fluids center of pressuresubmerged surfaces. The thesis is focused on high concrete gravity dams and the longtan. Sliding and overturning safety factors of concrete gravity dam under the influence of drainage specifications.