The Human Impact on Stability of slopes
Decreasing stability of slope
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Urbanisation
Deforestation
Mining and extraction(undercutting) and excavation
Overloading the slope - waste dumping
Recreation
Farming(ploughing)
Transport construction
Acid rain
Decreasing amounts of interception adding weight to the slope
Lack of transpiration means that there is more water in the soil adding stress
Tree roots hold the soil together so without them it is more unstable
65% of deforestation in the amazon is for cattle ranching
Many cities expand onto hillsides and marginal land - Lima, Rio de Janeiro and Hong Kong
rio de Janeiro
Many favelas and other homes are being built n the hillsides adding weight - slope loading
6.7 million live there and 65% of growth is rural-urban migration
Hot and wet climate = fast chemical weathering = bedrock is quickly broken into a deep regolith. The frequent heavy rains saturate the regolith so it flows over underlying rock
2011 - 1,000 left homeless and 257 killed after torrential rain called floods and landslides/mudslides in mountain towns near Rio
floods and landslides kill 95 in Rio slums after 9 inches of rain in 24 hours
Hong Kong
7.5 million people live in Hong Kong and growing. All the flat land has been used so any further growth is on reclaimed land.
1972 Po Shan Road landslide. Built large concrete buildings on hillsides and undercut the slopes for the foundation causing a deadly landslide. 156 dead
Transport to and from mines results in deforestation, more surface runoff and the heavy machinery needed can creating vibrations
Flooding - releasing material into local streams and the use of water in mingin is also important
Undercutting -reducing the internal stability of slopes through tunnels and shafts
Heavy machinery needed can cause large vibrations
Affects the shape of slopes and steepen them - excavation - open cast mining in West Virginia USA where they blast the top of the mountain for low sulphur coal. They try to terrace (grade them) the sides to increase stability.
The material from mining which is excavated are often dumped onto a spoil tip which are artificial slopes made up of loose, unconsolidated material e.g. Aberfan
Aberfan - 1966 - a spoil tip collapsed over a coal mining village due to high amounts of rainfall and the steep slopes of the spoil tips. Now spoil tips have a lot of regulations.
Slopes were over 25 degrees and over 200m above the town on steep valley sides and on a line of springs which lubricated the underside
Occurred after a night of heavy rainfall created a mudflow with 100,000 cubic m of material
Engulfed a school at 9am. Killed 147, 116 were children and 5 teachers.
Most common on coastal slopes as resorts are built as close to the sea as possible
Holbeck Hall Hotel - 1993 - Scarborough
Was a particularly wet summer and the top layer of the cliff became saturated and moved slowly downhill. Tourism affects slope instability
Terracing can be used to stabilise slopes if done effectively. However generally farming and ploughing and terracing weakens the slope by creating steeper sections and removing the larger plants which bind the soil together.
Increased acidification of rain water have increased chemical weathering which weakens rocks and increases rock instability. Most pronounced in populated areas and with a lot of industrial activity such as Beijing or New Delhi
Carbonation
Minimising mass movements
Identifying potential landslides
Remote sensing (the recording of data from the earths surface via satellite, aeroplane or drone)
Can create slop stability analysis (SSA) using the remotely sensed data
Topographic map
Historic data
Landslide hazard map created from the identification
Application of geological and engineering knowledge before any hillside development
Hard engineering
Soft Engineering
Grading code from least stable to most stable
Pinning
Wire nets (or sometimes concerete blocks) are attached to a rock face or slope so that shear strength is increased, but also reducing the risk of rockfalls and erosion
Netting
May help collect fragments of scree which can be safely removed at a later data. This is often used in areas where tourism is important and where the risk of rockfall is high
Grading
Refers to the re-profiling of the slopes so that they become more stable. The overall effect is to reduce the gradient of these slopes, decreasing shear stress. Afforestation can be used to strength the new slopes.
Afforestation - the three benefits (interception, roots, transpiration)
Retaining walls
Surface drainage reduces the shear stress of excess water or internal drains
Geo materials - mix between hard and soft engineering - sustainable method of increasing slope stability
Using hard organic materials such as bamboo
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