The modes of failure of gravity dam are :-
- OverTurning or Rotation about toe :- When resultant force acting at any section if it passes outside the toe, the dam shall rotate or overturn about toe. In other words, it means that if horizontal forces dominate over vertical forces the dam will definately rotates. At such condition we mainly use factor of safety , it is the ratio of righting moments(anticlockwise) about toe to the overturning moments(clockwise) about toe. The factor of safety should not be less than 1.5.
- Crushing :- It generally happens when the compressive stress exceeds the allowable stress of the material of dam, hence the dam may fail. The total normal stress = Direct stress + Bending stress Pmax will be produced on the end which is near to the resultant force, if Pmin is negative then tension is produced at that end.
- Sliding or also called shear failure :- When horizontal forces responsible for sliding dominate frictional resistance of dam at that level. To prevent sliding the horizontal forces(∑H) should be less than shear resistance(μ∑V). i.e. ∑H <μ∑V
The explanation is for 1st year students, as the word shows ‘seasoning’ means removal of water in presence of proper air circulation under controlled conditions and while seasoning, water does not exceed 15% of its dry weight.
Following benefits are:-
- to make it durable against cracks, warp and sharp.
- to make it fit for receiving treatments of paints, varnishes, preservatives, etc.
- to make it workable for various operations while construction work.
- to increase strength, hardness and stiffness against rough use.
- increase electrical resistance power.
- to make it suitable for joining with other types of timber.
- to make it suitable for burning as a fuel.
If through investigation we found that the shallow soil is unstable and weak( means the bearing capacity of soil is not satisfactory) then pile foundation is considered. And also the pile foundation is cheaper than any other ground improvement cost. Piles are also give better results in jetties or bridge piers. Hence piles are specifically applicable:
- for multistory buildings, subjected to heavy loads and vibrations.
- for resisting lateral loads like in overhead tanks and transmission towers.
- for industrial building which are subjected to large moments(about the base of the crane) due to movement of cranes.
Pile foundation are generally used when poor soil conditions extend to large depth and applied load is quite heavy and also suitable when grillage( a cross framework of timber and metal beams) and raft ( a fully spread concrete slab which supports columns and walls) foundation are expensive.
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Gradient shows the meeting of elevation points at one end with respect to depression points at other end.
Sometimes 1st year or 2nd year students got confused when they hear about 1 in 100. Here 1 represents vertical distance and 100 represents horizontal distance in mm or cm or foot or inch or meter or KM as per requirement.
Types of gradients generally used in railway are:-
- Ruling gradient:- the grade at which a single locomotive can easily pass out train without any additional efforts.
- pusher gradient:- the gradient at which more than one locomotives are used to push the train.
- Momentum gradient:- the gradient at which momentum is provided to locomotive at down grade to overcome steeper gradient.
- Station yard gradient:- these gradients are provided to drain out water.
Such gradients are provided only to haul the train.
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