Slope Failure

What are the two most important agents controlling the movement of Earth's materials?

Gravity and running water

What is the fundamental cause of slope failure?

The pull of gravity overcoming cohesive and frictional forces

List the four main facilitators of slope failure mentioned in the text

Excess water, ground vibration, over-steeping, and vegetation removal

Slope failure occurs when the slope stability factor (Fs) is less than what value?

One

What is the formula for the slope stability factor (Fs)?

Fs = resisting force / driving force

How does the driving force (Fdr​) for a potential landslide change as the slope angle increases?

The driving force increases with the slope

What two components make up the resisting force against slope failure?

The normal force (FN​) and sediment properties like cohesion and internal friction

At approximately what angle of slope does loose, dry sediment typically fail?

Greater than about 35 degrees

How do small amounts of water affect the cohesion of sediment grains?

They hold grains together via surface tension

What is the effect of free water (saturation) on sediment grains, and what property does it increase?

It lubricates the grains and increases pore pressure, reducing resistance

The strength of a rock mass is primarily controlled by what features?

Localized weaknesses

What are some examples of localized weaknesses that control rock strength?

Joints, faults, bedding, and foliation

A rapid, vertical or near-vertical drop of earth material is known as what type of movement?

A fall

Besides the direct impact, what additional damaging effect can a rockfall generate?

A shock wave

What type of mass movement involves a coherent unit slipping along a failure surface without a rotational component?

A slide (or translational slide)

What is the term for a rotational slide that moves along a concave shear surface?

A slump 

During a slump, the moving block of material typically remains in what condition?

Relatively undisturbed

An increase in _____ pressure is a common trigger for a slump

water 

During which season are slumps particularly common?

During the spring thaw

What term describes a mass movement with a chaotic and turbulent internal structure?

Sediment flow

In a sediment flow, what role do mixed-in fluids like water and air play?

They lubricate the flow

A sediment flow with less than 20% water is classified as a _____ flow

granular

A sediment flow containing 20% to 40% water is classified as a _____ flow

slurry

What does a mass movement with greater than 40% water grade into?

Stream flow

What is the specific name for a flow that contains a substantial amount of 'different' material (e.g., logs, boulders, human-made objects)?

Debris flow 

What is 'runout' in the context of slope failure?

The horizontal distance a mass movement travels

What phenomenon can allow for unexpectedly long runout distances from a landslide or fall?

A cushion of air and pulverized material

What type of slow slope movement is described as a general viscous soil flow?

Creep

What type of slow slope movement is specifically related to freeze-thaw cycles?

Solifluction

What are the primary threats to people and objects from sediment flows?

They can trap or bury objects, posing a threat of trauma, asphyxiation, and hypothermia

How do landslides typically cause structural damage to objects?

They dislocate objects 

What mitigation strategy involves removing material from the head of a slope to prevent failure?

Balancing moments 

What is the purpose of installing drains as a slope failure mitigation technique?

To remove water from earth materials, reducing pore pressure

Besides drains, what is another water-related mitigation strategy focused on the top of a slope?

Reducing infiltration at the slope head

What type of engineered structure can be built at the base of a slope to help prevent failure?

Retaining walls

What mitigation technique involves anchoring unstable rock masses to more stable rock underneath?

Rock bolts 

What is one indicator of increasing risk mentioned in the case study notes, related to a reservoir?

The basin was nearly full shortly before failure