Different shapes of cross-section of tunnels

The shapes of tunnels mainly depends upon the purpose (they follow in future) and  second to resist  internal and external pressures.

tunnel-circular-and-horse-shoeegg-shaped-and-segmental-tunnel elliptical-and-poly-centric-tunnelThese are most common Cross-sections widely used by construction companies. The Circular section offers greater resistance to external pressure and highly suitable for unstable ground such as sand or soft clay. They are not used as traffic tunnels because they require more filling to make flat base, hence used for carrying water and sewage under pressure.

In the next section we will explain about them.

Modes of failure of Gravity dam

The modes of failure of gravity dam are :-

  1. 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.
  2. 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 stressformula                                                        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.
  3. 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
  4. Tension

Why to perform Seasoning of Timber?

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.

Application of under Reamed pile

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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