Q1. Discuss the variables affecting the hydraulic conductivity of sands. Q2. If

Question

Q1. Discuss the variables affecting the hydraulic conductivity of sands.

Q2. If the hydraulic conductivity of a natural clay is too high, discuss two strategies to lower the hydraulic conductivity.

Q3. A deposit of soil having a hydraulic conductivity of 10-6 m/s is 16m deep and overlies another impenetrable stratum of soil. A sheet pile wall is driven to a depth of 12 m in the deposit, after which the soil is excavated on one side of the sheet pile wall. At steady-state flow, the difference in water level between the two sides of the sheet pile is 4 meters. Redraw this system to scale on a full sheet of paper, and determine the quantity of seepage under the sheet pile into the excavation using a flow net. (NOTE: It is required to use a STRAIGHT EDGE to redraw the boundaries below)

Q4. Calculate the equivalent hydraulic conductivity value of a horizontally layered system in the vertical direction kEQ,V (assume Layer 1 has k1 and Layer 2 has k2). Follow the same logic of the derivation given in class for the equivalent hydraulic conductivity of a layered system in the horizontal direction. If k1 = 100 k2, which layer will control the flow through the system?

Q5. Draw the flow net for seepage under the structure shown on the next page (you don’t need to redraw this one – just print this page and draw the flow net onto it in pencil).
a)Determine the total seepage rate under dam if the soil has a hydraulic conductivity of 5x10-5 m/s.
b)What is the uplift force on the base of the structure (hint: find the area under the plot of pressure versus distance under the dam)?
c)Use the flow net that you drew in part c to calculate the exit gradient in the element nearest to the downstream toe of the dam.
   Assuming that the total unit weight of the soil is equal to 16 kN/m3, define the critical gradient and check to see if the exit gradient is
   acceptable.

Explanation / Answer

1 ANSWER:

1) Factor that affect soil permeability and hydraulic conductivity :

1. Grain-size

2. Void ratio

3. Composition

4. Fabric or structural arrangement of particles

5. Degree of saturation

6. Presence of entrapped air and other foreign matter.

Permeability vary with the square of particle diameter. It is a logical that the smaller the grain-size, the smaller the voids and lower the permeability

A link flanked by permeability and grain-size is added suitable in case of stroke down and silts that in case of additional soils because the grain are additional equidimensional in addition to its fabric change which are not vital

This suggest a easy method for the opinion of permeability of a earth at any annulled ratio at come again? time values of permeability are recognized at the two or more canceled ratios.

Once the line is drawn, permeability at any void ratio can be read in a straight line.

power of soil work of painting on permeability is usually a little meaning in case of the gravels, sands, and silts, if not mica and also organic matters are present. However, this is a major significance in case of clays.

Montmorillonite has the smallest amount permeability with sodium as the negotiable ion (less than the 10–7 cm/s, even at a very high void ratio of 15).

sodium montmorillonite is wear by the engineers as an additive to further soils to make them opposed to. Kaolinite is hundred period more porous than the montmorillonite.

material or the structural collection of particles is an essential soil which point influence the permeability, particularly fine-grained soils.

At the identical void ratio, it is a logical to wait for that the soil in the most flocculated situation will have a high permeability and the one in the nearly everyone separate situation will have the lowest permeability

Higher the quantity of the dispersion, higher permeability. In case of a sure sand permeability may enhance the three-fold when the scale of infiltration increase starting 80% to 100%.

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