Classification of slope movement

Question 1

Valley rebound

Answer 1

Happens with the release of strain energy in U shaped valleys formed due to glacial movements, due to glaciers melting and leads to slope distortion

Question 2

Cambering

Answer 2

-plastic deformations due to preglacial conditions
-down slope movement of capstone and superficail mudstone

Question 3

Bulging

Answer 3

-plastic deformations due to preglacial conditions
-upslope movement of deformable strata @ the valley floor

Question 4

Creep

Answer 4

Seasonal
- due to change in temperature or freeze thawing
- change in volume and theefore movements

True
- continuous displacement under constant stress
-can precede flow or failure

Leads to
-curvature of trees and retaining walls
-slope of fences and poles

Question 5

Subsidence

Answer 5

Natural due to solutions in the internal strata or freeze thaw

Manmade due to pumping of oil or water

Question 6

Landslides

Answer 6

-Imposed stress is greater than the resistance
-Large movements are a combination of falls, slides and flows

Falls can be caused by
- Shear surface under gravity therefore initial sliding
-Overhang due to the undermining of the slope from erosion or seepage
-change in temp causes change in vol and therefore movements
- water in tension cracks cause PWP and ice forces

Slides
- distinct failure surface
- can be translational rotational or compound
* Translational usually in rock and not that deep. composed of 1 unit or numerously closely related units. can lead to spreading failure
* Rotational happens in soft soils that allow shear failure through intact materials but pure rotation is only in homogenous soils
* Compound failures are deep with cureved and translational failure planes. happens in non homogenous soils. Corners in the slip surface lead to breaks @ GL

Flows
-slide with internal deformations leading to high velocity and large reach
- happens in clays above the liquid limit but sands dont need high wc since they form due to particle movements
- can form from falls or slides if there is large fluid entrainment therefore increased PWP

Question 7

Peak vs residual strength

Answer 7

Dips from peak to residual since there is entrainment and therefore increased WC (dilatancy) also particle are reoriented to be // to the shear plane

Residual is reached after large deformation and often governs slope stability
* just under peak for low plasticity since theres no reorientation due to rolling resistance
* for high plasticity its is much below the peak

Strength generally governed by
- Natural arragement of particles
- Bonds (minerology and fabric)
- Fluids (water and air pressure)

Question 8

First time slide

Answer 8

Happens in unsheared soils and at least part of the failure occurs at the peak strength
- For low plasticity tau remains at the peak and there are unifrom deformations along the surface
- For high plasticity there is progressive failure

Progressive failure
- the shear force exceeds the strength in a certain zone + passes on the stress leading to failure in a brittle material defined by

Ib = (tau_p - tau_r)/tau_p, Brittleness index

-The avergae mobilised strength lies between the
peak and the residual
- Residual –> Peak –> Prepeak fom toe to top of slope

Question 9

Slides in pre-existing shears

Answer 9

Existing failure surface therefore residual strength, examples
- Existing landslides
-Shear surface induced by tectonics

Question 10

Pore water conditions

Answer 10

Shorterm
- undrained for a low permeability soil with sufficiently long drainage paths or granular soils after shock loading
- U is now a function of change in total stress

delta U = delta U as a function of sigma +