Landslide and slope stability Flashcards
Definition of a landslide?
a downslope movement of rock or soil as a more or less coherent mass known as mass wasting or movement
What is a rotation slide?
downslope movement of a coherent block of earth material along a curved slip plane, develops unconsolidated material, can be rapid or slow and exposes a headwall, spreads out at the bottom example: Holbeck Hall June 1993
what is a translational slide?
the is a mass movement occurring along a planar slip plane example 2009 highway 64
what is a flow?
downslope movement in form of a fluid material is saturated - debris flow >50% coarser than sand, often boulders size of houses rapid.
earth and mudflows >50% particles smaller than sand example 2010 maierato S Italy, distinct upside down funnel shape
what is a fall?
on a cliff or steep slope, rock forms an overhang where already been eroded example pennington point devon 2009
what are causes of landslides?
they occur when driving forces pulling the soil are equal to or exceed the resisting forces
what is the factor of safety?
ratio of resisting forces to driving forces F= shear strength/shear stress, so if F is less than or equal to 1 the slope will fail
what are the driving forces?
they are either the weight acting parallel to the slope or its seismic shaking perpendicular to gravity holding soil, parallel component of gravity pulls soil downslope
what are resisting forces?
it is the strength of the material, strength added by roots, butterising supports lower part of slope. shear strength of materials = cohesion + internal friction
what is internal friction?
caused due to grains rubbing together, depends on how slick the grains are and how much force acting upon them
what are the factors causing landslides?
2 categories either increasing driving forces or factors reducing resisting forces, humans activities affect both
how are the driving forces increased?
by steepening the slope, humans/ nature can modify slope so its not at angle of repose, adding weight or earthquakes etc can cause return to this angle
how would you decrease the resisting forces?
adding water, fills pore spaces reduces internal friction, can cause liquefaction, sediment can be oversaturated, water alters angle of repose.
steeping slope - reduces normal stress reduces internal friction
slip plane, surface of weakness, weak materials (deeply weathered materials, undercutting reduces buttressing of lower slope, removing vegetation
