Correct Answer - Option 2 : Gravity dam
Out of the above options, in the case of gravity dam uplift pressure at the base is minimum as in gravity dam we provide drainage path or cutoff valve to reduce uplift pressure at the base.
(i) Uplift is an active force that exists within both the foundation and the concrete structure itself.
(ii) This pressure is present in cracks, pores, and joints of the concrete within a dam, at the interface between the dam and the foundation, and in cracks, pores, and seams within the foundation rock.
(iii) Large uplift pressures can compromise the structural adequacy of concrete gravity dams and serve as the principal cause of failure.
(iv) Because uplift pressures can greatly impact the stability of concrete gravity dams, they must be analyzed and accounted for during the design and evaluation of such structures.
(v) Direct reduction of uplift pressures can be accomplished by the incorporation of a drain curtain, also known as drainage or relief wells.
(vi) These internal drainage systems consist of a series of vertical or vertically-inclined wells or boreholes that facilitate the draining of the foundation and abutments in order to relieve the uplift pressure caused by impounded water.
(vii) Effectiveness in reducing uplift pressures through drainage systems is dependent upon drain hole size, depth, spacing, and maintenance as well as the character of the foundation.
(viii) In addition, a grout curtain positioned upstream of a drain curtain within the dam’s base can also facilitate the reduction of uplift pressures by eliminating or decreasing the number of seepage paths.