Module 5 : Advanced Soil Characterization

Lecture 44 & 45 : Introduction to Geotechnical Centrifuge Modelling

5.6.3 Scale factor for body forces or geostatic forces

F = Mg

5.22

5.23

 

5.24

5.6.4 Potential of geotechnical centrifuge for geoenvironmental project
          Geotechnical centrifuge has potential application in geoenvironmental problems such as fluid and contaminant transport that is mostly governed by seepage forces. The permeability of high compacted liners is very low. Therefore, determination of permeability and contaminant transport parameters (advective-dispersive) is extremely time consuming with normal 1-g modelling. For establishing advective-dispersive contaminant transport parameters, it is essential that the contaminant solution flows through the soil column as discussed in module 3. This is time intensive even for a small soil column. Using geotechnical centrifuge for simulating seepage can considerably reduce the time required for experimentation as discussed below.

Seepage force (SF)

5.25

v is the discharge velocity, k is the permeability, is the unit weight of water and W is the weight of seepage water.

5.26

 

5.27

t is the time.
The hydraulic conductivity of the soil, k can be represented by Eq. 5.26.

5.28

where ρw is the fluid density, m is the dynamic viscosity of the fluid, and K is the intrinsic permeability. If the same pore fluid and the soil are used in the model and prototype, then Eq. 5.26 can be written as:

5.29

 

 

5.30

5.31

Substituting Eqs. 5.25, 5.28 and 5.29 in Eq. 5.24, and considering seepage force as a body force with scale factor represented by Eq. 5.22, we get

5.32

 

5.33

          The above derivation clearly indicates that the seepage phenomenon is accelerated at N-g due to increase in velocity of flow. The time for seepage in model is reduced by 1/N2. Therefore, permeability of compacted liner can be determined in short interval of time with the help of geotechnical centrifuge model and the prototype permeability can be obtained by using the scale factor derived above. The advective-dispersive transport parameters can also be established in relatively short duration due to accelerated seepage in geotechnical centrifuge.