A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Level One (Core FAQs)
Part I: Slope
1. Is force and moment equilibrium satisfied by Janbu’s method,
Bishop’s method and Morgenstern-Price method? (S1)
Janbu’s method and Morgenstern-Price method are non-circular analytical
method and they are frequently used for soil slopes while Bishop’s method
is circular analytical method. Bishop’s Simplified method and Janbu’s
Simplified method assume that the inter-slice forces are horizontal and
inter-slice shear forces are neglected.
Equilibrium Method Moment
Equilibrium
291
Force Equilibrium
Horizontal Vertical
Janbu’s Simplified No Yes Yes
Bishop’s Simplified Yes No Yes
Morgenstern-Price Yes Yes Yes
2. Why are fill slopes compacted to dense state instead of loose state?
(S2)
In rainstorm, the runoff from rainfall infiltrate into the top layer of fill slopes.
It may result in saturation of this layer of fills leading to the decrease in soil
suction. Consequently shallow slope failure may occur.
If the fill slope is in a loose state, the soils would tend to decrease in
volume during deformation. As a result this induces a rise in pore-water
pressure which triggers slope failure in form of mud-avalanche.
If the fill slope is in a dense state, the soils would tend in increase in
volume during deformation and it only fails like a mud slump.
3. Other than liquefaction, what are the possible causes of failure of
loose fill slopes? (S3)
Other than static liquefaction, slow-moving slips driven by transient pore
water pressure leading to high speed landslide are the other possible
cause of failure of loose fill slopes.
For loose fill lying on low permeability soil layers, there is potential storage