(a) An impervious concrete gravity dam of length 50 m and width 18 m is to be constructed on a uniform soil deposit of depth 15 m which overlies impermeable rock. The dam is to be provided with a 8 m deep cut-off wall at the position shown on Figure 3. If the water depth at the upstream face is 9 m and the soil has a permeability of 1 x 10-7 m/sec:
i. Sketch the flow net.
ii. Estimate the seepage quantity in cubic metres per day.
iii. Estimate the pore water pressure at points A to E on Figure 3.

(b) For each of the following scenarios, would the seepage quantity calculated in 2a) increase or decrease (no calculation required)? Provide a brief explanation for each answer.
i. The soil is more permeable than has been assumed.
ii. The level of water within the dam increases.
iii. The depth of the cut-off wall is increased.

Transcribed Image Text:

Upstream water level Dam 9 m Downstream 18 m water level A B D E 6 m 8 m Top of soil layer 15 m Cut-off wall Impermeable rock Upstream water level Dam 9 m Downstream 18 m water level A B D E 6 m 8 m Top of soil layer 15 m Cut-off wall Impermeable rock