DAMS.
Dams
arc required for the purpose of impounding water in reservoirs, for
diverting it from streams, or for storing in the canons or elsewhere
the debris coming from the mines.
Foundation.—-The
first object sought in selecting a site is a foundation sufficiently
solid and impervious to prevent settling of the dam, leakage under its
base, and wear in front by water running over its top. Where possible
the entire foundation should be in solid rock.
A
hard, level, compact rock always affords the best foundation, but where
that cannot be obtained any thick, impermeable stratum strong enough to
sustain the pressure will suffice. Gravel soil is better than earth,
but requires sheet piling to prevent sipage beneath the base of the
dam. No reliance can be placed on vegetable soil. In India, where it is
impracticable to go down to the bed-rock, stone wells filled with
concrete and connected by rows of piles have been used.
In
preparing the foundation the soil and all porous material, sand and
gravel, is stripped off, and when the solid ground is reached it should
be carefully and thoroughly tested by shafts or borings. Where the
rock is fissured all loose material should be removed; some engineers
recommend covering the foundation with a layer of pud-
