MASS MOVEMENT

SUBMITTED BY

NASEER AHMAD KHANSUBMITTED TO :

DR SUNITA SINGH

MASS MOVEMENT:-Mass Movement is defined as the down slope movement of rock and regolith near the Earth's surface mainly due to the force of gravity. Mass movements are an important part of the erosion process, as it moves material from higher elevations to lower elevations where transporting agents like streams and glaciers can then pick up the material and move it to even lower elevations.

Mass movement processes are occurring continuously on all slopes; some act very slowly, others occur very suddenly, often with disastrous results.

Any perceptible down slope movement of rock or regolith is often referred to in general terms as a landslide.

Landslides, however, can be classified in a much more detailed way that reflects the mechanisms responsible for the movement and the velocity at which the movement occurs.

Mass Wasting 

What is mass wasting? Mass wasting refers to several processes that have the following

in common:1. Downslope movement of rock or weathered material 2. Movement is due to pull of gravity 3. There is no flowing medium (water, air or ice) that carries the

material  Why is mass wasting important?1. Processes represent a significant hazard to property and

people 2. Need to identify where and under what conditions these

processes occur 3. Avoid construction in areas prone to mass wasting or attempt

to prevent mass wasting  *Generally, mass wasting occurs when gravitational forces exceed

frictional or shear forces (strength) of material. 

Shear stress is the downslope pulling causing mass movement related to the mass of the material and the angle of the slope.

 

Shear strength is the counteraction of the force of shear stress (i.e., friction).

 

If stress is greater than strength, then mass movement occurs.

Possibly triggered by:

1.  Earthquake

2. Construction work (blasting)

3. Flooding

 Driving force behind Mass Wasting:

1. Downslope pull of gravity

2. Depends on weight (amount) of material on slope.

3. Increasing amount of material can lead to mass wasting.

4. Depends on steepness of slope.

5. Over steepening slopes can lead to mass wasting.

 

Clays provide cohesion to unconsolidated materials.

Mineral cements hold rock together

 

Role of Water in Mass Wasting

1. Small amount of water can increase strength.

2. Surface tension of water helps hold material together.

3. Saturation with water weakens material.

4. Hydrostatic pressure can act to push grains apart.

 

Role of Vegetation in Mass Wasting

1. Roots add strength to material by binding loose material together.

2. In semi-arid and arid regions, forest fires can remove vegetation from hill slopes, leaving surface materials vulnerable to mass wasting.  

 

Planes of Weakness in Material Planes of weakness in the material can facilitate mass wasting if the

planes are oriented parallel to the slope. Planes of weakness include bedding planes in sedimentary rocks and

foliation planes in metamorphic rocks.

 

Mass Wasting Processes

Processes can be classified based on

1. Type of material that moves

2. Nature of movement (flow or slide)

3. How fast material moves; e.g. rock falls/slides, slump, debris flows/earth flows/mud flows, creep

 

Slope Stability is influenced by:1.      Steepness2.     Angle of repose3.     Fluid effects4.     Expansive clays presence5.     Vegetation present6.     Earthquakes7.     Quick clays presence Types of mass movement:1.  Fall -- rocks fall from great distances as a result of gravity2. Slide -- mostly coherent unit slides on a slope or bedding plane3. Slump -- rock unit falling a short distance due to rotation4. Flow -- landslides involving an unconsolidated mass that moves in

a chaotic fashion5. Solifluction -- soil component moving over permafrost layers,

analogous to a hockey puck sliding on ice6. Creep -- extremely slow movement due to gravity

Slumps

Movement of coherent block of material along a curved surface.

More likely to occur when slope is undercut from below, material is saturated.

Common on river banks where stream erosion over steepens banks.

  Example of slump

CreepExtremely slow movements downslope Rates of creep are 1-10 mm/year Bent tree trunks, fence posts, and utility poles; gravestones tilted

downslope indicate that creep has occurred. Creep damages buildings, roads

Debris flows, earth flows, mud flowsFlows are movements in which the material deforms chaotically as it

moves. Debris flows -- contains large boulders, gravels Earth flows -- sandy materialMudflow -- mud with considerable water

Most common mass wasting types

Avalanche Slump

Creep Flow Rockslide

Fall Avalanche Slide Flow Slump Creep

Deposits of Mass Wasting

Mass wasting produces sediment deposits.

These deposits commonly contain a wide range of sizes of particles (they are "unsorted").

The deposits do not show layering (they are "unstratified")

 

How do we prevent landslides and mass wasting? This is NOT possible.

A better question is “how do we lessen the effects” of mass wasting? 1.      Remove weight from slope 2.     Engineering controls 3.     Vegetation and GeofabricTM

4.     Cables and anchoring systems 5.     Tunnels built over highways thus reducing weight

THANK YOU

NASEER AHMAD KHAN