Pre-reading - soil mechanics Flashcards
What are soils in an engineering sense and how are they distinguished from rocks?
Soils are either man made or naturally occurring and unlike rock the individual particles are not sufficiently bonded
What are some examples of soil as a waste material from construction, industry and domestic?
Construction - excavation spoil
Industry - ash, slag, pulversied fuel ash
Domestic - landfill sites
What are selected soil materials?
These are materials that do not have the negative associated to waste i.e. pollution
What are selected soil materials like?
might be spread in thin layers, well compacted may be called engineered fill
Why are selected soil materials used in engineering (with examples)?
High shear strength and low compressibility providing adequate stability and ensure volume changes are small (highway embankments and earth dams)
What are the general problems associated with contaminated soils?
contaminants could comprise of metals such as mercury or lead which could cause harm to plant, animal and human health and could also be dmamging to building mterials embedded in the soil
What 2 groups of naturally occuring soils are there?
In-situ - formed at that location
and those
transported to their current location
What 2 catergories of in-situ soil are there?
Weathered rocks and peat
How might transported soils be moved?
Water
Wind
Ice
Volcanics
Gravity
WHat does weathering produce?
Decomposition and desintergration of rocks
What is the process that causes disintergration of rock?
Mechanical weathering
Where is mechanical weatrhing most intense and what does this lead to?
Cold environments resulting in the fragmentation of the rock and its mineral grains
What causes decomposition and what does this lead to?
Chemical alteration and thus decomposition turning the hard rock into softer clay
Where is chemical weathering/ decomposition most intense?
Hot, wet climates like the tropics
What are peats?
Almost entierly organic matter being composed of partly decmoposed and fragmented plant remains
How much of earths land surface is peat?
5 to 8%
What can glacial drifts (glacial deposits) be divided into?
Soil deposited directly by ice
Soils deposited by melt waters
What is soil depsosited by galciers called?
Till
How is lodgement clay formed and what is often reffered to as?
At the glaciers base and often boulder clay
How was ablation till formed?
Debris on the ice surface which is lowered as ice melts
What is the typical composition of ablation tills?
Sands, gravels, cobbles and bouldrers
What might soils deposited by outwash plains be reffered to as?
outwash deposits
Where is wind blown soil production most prevalent?
dry areas where there is little moisture to hold
What is the name of wind blown soils?
Aeolian deposits
What are some examples of areas where you can find aeolian deposits?
deserts, coastlines and periglacial regions
What are the 2 forms of wind blown deposits?
Dunes
Loess
What are dunes?
mounds of sand with different shapes and sizes
How much will sand dunes migrate in a year?
Over 10m/yr
What are loess deposits?
they cover a large area mostly in the NH where silt are mixed with sand and clay particles
What is the minerology of soil particles determined by?
original rock and degree of alteration
What are the different types of groundwater recharge with an example?
Artificial - irrigation losses
Natural - excess rainfall
Indirect - aquitard leakage
What is hydrogeology?
study of the movement, occurence, distribution and geological interaction of water with earths crust
What is porosity?
fraction of given volume which is void or interstices