Quiz
Geotechnical Engineering 2 Permeability
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Questions in this quiz (22)
1The flow of water in soils normally occurs at very low velocities and hence is essentially a laminar flow regime.
- ATrue
- BFalse
2If high velocity flow occurs through a soil what will happen?
- ASoil erosion
- BNothing
- CThe worms will come to the surface
3Laminar flow is the result of the application of a pressure gradient
- ATrue
- BFalse
4What are two ways a pressure gradient can occur?
- AThe existence of a difference in ground water level from one side of a soil mass to the other
- BThe application of pressure (e.g. the weight of a building or an embankment) which increases pore water pressure above its static value and causes flow.
- CRain fall seeping into the ground
- AThe existence of a difference in ground water level from one side of a soil mass to the other
5What is a Typical value of coefficient of permeability for Gravel?
- A10^3 -10 Permeable
- B10 - 10^-2 Permeable
- C10^-2 - 10^-5 Slightly permeable
- Dless than 10^-5 Impermeable
6What is the typical value of coefficient of permeability for Sand
- A10^3 - 10 Permeable
- B10 - 10^-2 Permeable
- C10^-2 - 10^-5 slightly permeable
- Dless than 10^-5
7What is the typical coefficient of permeability for silt?
- A10^3 - 10 Permeable
- B10 - 10^-2 Permeable
- C10^-2 - 10^-5 slightly permeable
- Dless than 10^5 Impermeable
8What is the typical coefficient of permeability for clay?
- A10^ 3 - 10 Permeable
- B10 - 10^-2 Permeable
- C10^-2 - !0^-5 slightly permeable
- Dless than 10^-5
9Why do the Values of Co-efficient of Permeability k vary?
- ASoil porosity
- BShape and size of soil grains
- CThe void spaces between the grains and the density of the soil.
10What are the three major factors which affect the relationship between values of co-efficient of permeability k measured in the laboratory and those achieved in the field.
- A1. Condition of soil tested in lab must be the same as exists in field ie same density same orientation of sample. Orientation of sample is important because soils will often have a different k value for vertical flow and horizontal flow (anisotropy)
- B2. Layering of soil and direction of flow - permeability of a series of layers with flow parallel to layers is analogous to electrical current through resistors in parallel, while permeability with flow at right angles to layering is analagous to current in resistors in series.
- C3. A difference in hydraulic conditions between lab and field. Because of these factors where a k value is important to a design is important that values measured in the lab are confirmed by large scale field tests.
- A1. Condition of soil tested in lab must be the same as exists in field ie same density same orientation of sample. Orientation of sample is important because soils will often have a different k value for vertical flow and horizontal flow (anisotropy)
11What is the constant head permeameter test for?
- AGravels and coarse sands
- BFine sands
- Cloose uniform filtered sands with well rounded grains
12What is soil does the falling head permeameter test?
- AGravels and coarse sands
- Bfine sands
- Cloose uniformly filtered sands with well rounded grains
13The Hazen's Formula is an alternative method of determining Co-efficient of Permeability that applies only to loose uniform filter sands with well rounded grains
- ATrue
- BFalse
14When is the falling head permeameter test used?
- Acoarse gravels
- Bcoarse sands
- Cfine sands where the flow rate through the soils becomes too small to measure accurately
15What is the procedure for the falling head permeameter?
- A1. Allow water to flow through sample until a steady flow is achieved.
- B2. Record the time t required for water level to drop from initial water level h1
to final water level h2. - CRepeat measurement three times.
- A1. Allow water to flow through sample until a steady flow is achieved.
16The formula to use when finding the coefficient of permeability for the falling head permeameter is k = a. L .loge (h1/ h2)/ A.T
- ATrue
- BFalse
17Consolidation Test ( for silts and clays where permeability is very low) Data determined in the Consolidation test is used to determine k as follows :
- Ak = Mv. Cv.w .g
- Bk=QL/thA
18What is the arrange
- AThe general arrangement for pump tests requires the drilling of a central well large enough in diameter to allow the installation of a submersible pump if depth is greater than 6 metres or of suction hose if less than six metres.
- BThis bore should penetrate through the water bearing layer into impermeable material below.
- CThis is followed by the drilling of a series of observation wells which can be much smaller diameter as they are only used for measuring water level as the test proceeds.
- DThese observation wells are arranged on a series of radial lines with at least two bores per line.
- EOnce drilling is complete the bores should be left until ground water level returns to its normal static level before testing is carried out.
- FWhen testing is being carried out it is important that water pumped out of the bore is conveyed a sufficient distance away from the test area that it cannot flow back and re-charge the reservoir.
19What are Soakage tests
- AIn these tests which are usually performed for design of drainage fields, relatively shallow 100mm diameter postholes are frequently used, particularly for effluent soakage fields which need to be close to the surface to maintain aerobic conditions for the soil bacteria in the drainage field.
- BAnaerobic conditions lead to bad odours, are caused when insufficient oxygen is available. The standard conditions used for Septic Tank Effluent field testing to NZS 4610:1982 requires that the hole be kept full for 24 hours prior to testing to simulate saturated conditions.
- CThe walls of the borehole should also be scratched to break up any disturbance due to the drilling process.The hole is filled to the surface and the water level measured, topping up hole as needed.
- DThe rate of drop of water level at the end of the test sequence ie after 4 hours observation is used to determine which of 5 categories the site falls into.
20A flow net s used to study the flow of water through a permeable medium.
- ATrue
- BFalse
21What is a flow net?
- AA graphical construction showing the path of water flow and consist of flow lines and equipotential lines
- Bpath of water through the soil
- Clines joining points of equal hydraulic pressure (contours)
22Equipotential lines are joining points of equal hydraulic pressure (contours of hydraulic pressure)
- ATrue
- BFalse
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- Diploma Geotechnical Engineering 2 Quiz on Geotechnical Engineering 2 Permeability, created by Pauline Leota on 14/05/2015.
- Author
- Pauline Leota
- Language
- English
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