Causes of mass movements and prevention Flashcards
(Increased shear stress) Removal of lateral support through…
undercutting or slope steepening e.g. erosion by the river
(Increased shear stress) Removal of underlying…
support e.g. undercutting by rivers
(Increased shear stress) Loading of the slope such as…
weight of water, vegetation and accumulation of debris.
(Increased shear stress) Lateral pressure when…
water in cracks, freezing in cracks, pressure release.
(Increased shear stress) Transient stress caused by…
earthquakes, movement of trees in wind.
(Reduced shear strength) Weathering effects such as…
the disintegration of granular rocks, hydration of clay, dissolution of cementing materials.
(Reduced shear strength) Changes in pore-water…
pressure such as saturation, softening of a material.
(Reduced shear strength) Organic effects such as…
burrowing of animals, the decay of tree roots.
Weathering on slopes may reduce…
cohesion and resistance.
Water reduces the cohesion of particles by…
saturation. Water pressure in saturated soils decreases the frictional strength of the solid material.
Friction can be easily overcome even on…
gentle slopes(3 degrees) if water is present. E.g. solifluction
Cohesive forces act to…
bind the particles together. However, if saturation is too high, the material may liquify which reduces its cohesive strength.
Pivoting occurs in…
the debris layers which contain material embedded in the slope.
Vegetation binds the soil so…
it is stabilised. However, vegetation may allow soil moisture to build up and make landslide more likely.
Cut-and-fill technique is…
a small level terrace with an over-steepened slope on both ends.
Cut-and-fill technique is used to…
provide horizontal base plus reasonable access.
The steep slopes created by the cut-and-fill technique are…
potentially much less stable than former natural slope and in time of intense rainfall, vulnerable to small but damaging landslides.
Strategies to prevent falls:
- flattening of the slope
- reinforcement of the rock walls by grouting with cement
- benching the slope(creating terraces)
Strategies to prevent slides and flows:
- drainage of the surface water
- sealing surface cracks to prevent infiltration
- subsurface drainage
- retaining walls at the foot
Pinning is used to…
attach nets to a rock face or slope at risk of rock falls
Netting may help to…
collect fragments, which can be safely removed later. Used in areas of high tourism.
Grading refers to…
reprofiling of slopes so that they become more stable.
Afforestation is planning…
of new forests in upper parts of a catchment to increase interception and reduce overland flow.
