From a flow net which of the following information can be obtained?
1. Rate of flow
2. Pore water pressure
3. Exit gradient
Select the correct answer using the codes given below:
Seepage pressures, uplift pressures, exit gradient and pore-water pressure can be obtained from a flownet.
Which one of the following soil types is most likely to be subjected to liquefaction under seismic forces?
A flownet of a coffer dam foundation has 6 flow channels and 18 equipotential drops. The head of water lost during seepage is 6 m. If the coefficient of permeability of foundation is 4 x 10-5 m/min, then the seepage loss per metre length of dam will be
Seepage loss per metre length,
Given, k = 4 x 10-5 m/min
= 4 x 10-5 x 24 x 60 m/day
= 0.0576 m/day
= 0.1152 m3/day
= 11.52 x 10-2 m3/day
Nf is number of flow channels = 6.0
Nd is number of equipotential drops = 18
Capillary rise is maximum for
For fine grained soils effective size ‘d’ is smaller so it will experience more capillary rise.
Water is flowing in an upward direction through a stratum of sand, 4 m thick, under a total head difference of 2 m. The sand has a specific gr. of 2.65 and void ratio of 0.065. The factor of safety against quick sand condition would be
For design of filter the criteria usually adopted is
The constant of proportionality between seepage velocity and hydraulic gradient is called
Vs = kpi
Where, Vs = seepage velocity
kp = coeff. of percolation
Seepage Velocity = Coefficient of Percolation x Hydraulic Gradient
In an earthen dam the phreatic line is
The critical hydraulic gradient of a soil ic is given by
where G = specific gravity, e = void ratio
Critical hydraulic gradient
If the permeability of soil does not depend on its mineral content but depends on orientation of particles then the void space is known as
Micropores, often found between and within soil aggregates, are so small that surface tension holds water in place. It does not depend on mineral content rather depends on orientation of the particles. Instead of draining away, water moves through micropores only when suction is created by thirsty roots.