Monday, December 30, 2013

GATE, PSUs - Hydraulics, Irrigation, water resource Engg. notes - part 3

Hello there,
How have you been? Are you preparing yourself for some Engineering exam such as GATE or for PSUs?
  • A multipurpose reservoir is the one which is planned and constructed to serve various purposes.
  • The useful storage is the volume of water stored in the reservoir between minimum pool level and normal pool level.
  • The water stored in the reservoir below the the minimum pool level is called dead storage.
  • For a flood control reservoir, the effective storage is equal to Useful Storage+ Surcharge Storage - Valley Storage.
  • Trap efficiency of a reservoir is a function of capacity/inflow ratio.
  • The forces which are considered for the analysis of the elementary profile of gravity dam under empty reservoir condition is self weight.
  • The uplift pressure on a dam can be controlled by :
  1. constructing cutoff under upstream face
  2. constructing drainage channels between the dam and its foundations
  3. by pressure grouting in foundation
  • The uplift pressure on the face of a drainage gallery in a dam is taken as two third of hydro-static pressure at toe plus one-third of hydro-static pressure at heel.
  • Horizontal acceleration due to earth-quake results in hydro-dynamic pressure and inertia force into the body of the dam.
  • Hydro-dynamic pressure due to earthquake acts at a height of 4H/3.pi.  above the base.
  • The major resisting force in a gravity dam is self weight.
  • Total force due to wave action on a gravity dam acts at a height of 3/8(hw) above the reservoir surface.
  • When the reservoir is full, maximum compressive force in a gravity dam is produced at the toe.
  • The maximum permissible eccentricity for no tension at the base of a gravity dam is B/6.
  • Presence of tail water in a gravity dam decreases the principal stress and shear stress.
  • The elementary profile of a dam is a right angled triangle.
  • In the empty condition of reservoir and with the elementary profile of a dam, the vertical stress at heel and toe respectively are given by 2W/B and 0.

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