Exam 1 Review Flashcards
What forces create/contribute to a soil’s consistence
Cohesion and adhesion; attraction between soil particles and pore water, attraction of soil particles to each other
What is soil consistence?
Degree to which a soil resists deformation or rupture due to external mechanical stressors
5 ways water affects soil consistence
- Strength; decreases as water increases
- Soils swell
- Liquefaction in fine textured soils
- Water content reduced, soils become plastic
- Soils can become semi solid at certain point of water reduction
What are the atterberg limits?
The point where water becomes liquid, LL
Point where no volume change in reduction of water, shrinkage limit SL
Point where soil behaves like plastic, PL
Four states of soil by atterberg are:
- Solid
- Semisolid
- Plastic
- Liquid
What is the plasticity index
The difference between a soils plastic limit and liquid limit. The greater the difference the greater its plasticity.
What is a non plastic soil
A soil with a plasticity index of zero. It is cohesionless.
What do we use the plasticity index for?
Classifying fine textured soils, mostly.
How is a soils firmness measured?
By the amount of pressure it can withstand before it falls apart.
Okay. Name qualitative degrees of firmness and how it is measured.
Very soft, soft, stiff, very stiff, hard.
Resistance to penetration by a blunt object.
Cohesion and adhesion. Go.
Cohesion: the force of attraction between water molecules
Adhesion: the force of attraction between water molecules and other particles (soil)
Name all the qualitative categories for describing soil’s consistency and qualifications therein.
Consistence (the dirty one)
Dry classes (loose to extremely hard)
Comparative dry and wet to stress put on specimen
Firmes classes (loose…friable…extremely firm)
Stickiness classes (non, slightly, moderately, or very sticky)
Plasticity classes (non, slightly, moderately or very sticky) measured by 4cm long wire width
What factors influence structure formation?
Pm type Environmental conditions such as local climate Amount and type of clay present Organic materials Recent site management history
What are the classifications of a soils structure?
Based on grade, form and size of particles. Structureless Weak Moderate Strong
How are peds separated
By lines of weakness
How are SL and LL determined? PL?
SL and LL as a function of % moisture content. PL is determined I. A mechanical (physical) process.
What are six signs of soil instability?
- Slope
- Shape of slope
- Moisture status
- Soil texture (eg. Fine textured more at risk)
- Surfical indications (vegetation or creep)
- Bedrock type and strike
What’s entropy?
The intention of mass to achieve the lowest point of energy possible, aka everything’s desire to end up in the ocean.
What is strike?
The angle at which the bedrock lies
What can a forest manager do to mitigate risk in an inherently high risk area?
Leave vegetation on roadsides
Retain natural angle of repose
In special cases, one must practice end hauling
Patch cutting (limiting size of blocks)
Variable retention (keeping standing trees for water interception)
Stay out
Retain natural drainage (subsurface as well)
Harvesting methods (aka appropriate machinery and hauling)
Two biggest factors that affect at risk areas
Texture (fine) and moisture
How much does water weigh?
1kg/litre at 0 elevation
Aka. 1g/cc
So…. 1000kg/m3
How does water effect mass wasting?
Lubricate particles Adds weight Reduces cohesion Can infiltrate and dissolve salts in certain clays, realigning sheets to parallel Reduces shear strength
Types of geomorphological areas prone to mass wasting?
Sedimentary and metamorpho-sedimentary formations
Stable ones are igneous and metamorphic
What is a bedding plane?
The bedrock boundary with the materials on top (eg. Sedimentary rock with basal till on top)
An unstable bedding place is when there is really nothing interlocking the bedding place with materials on top.
What rocks are prone to exfoliation? And what is it?
Exfoliation is when rock cracks and pieces break off to form colluvium. Igneous and schistostic metamorphic rock are prone when exposed to intense heating and cooling.
What is shear strength?
The force resisting downward movement of mass - frictional resistance.
What is safety factor? (Fs)
A quantitative analysis of riskiness of an area.
Equal to shear stress/shear strength
Would be 1 when both are equal.
What part to friction and tension play?
Friction is the shear strength holding particles to a surface. Tension is the force pulling materials downward. Friction is a function of how sticky the material is to the slope, and is influenced by forces of cohesion as well.
Three things many areas with lots of mass wasting have in common?
- Volcanic activity
- Heavy precipitation
- Fine textured soils
Five common triggers for mass wasting?
Plate tectonics Earthquakes Volcanism High precip and flooding Isostatic rebound
How is strength of material judged?
By the greatest stress it can sustain, aka consistence.
What happens when Fs is >1?
Failure can be expected.
In what case might mass wasting occur without water?
In earthquakes.
What is geological discontinuity and how does it play a part in instability?
When bedding places differences in structure and makeup exist such as with sedimentary rock, and especially if this runs parallel to the slope.
Three types of material involved in landslides?
Rock - hard mass
Debris - soil material with a range of sizes
Earth - soil material with mostly small particles
The size types of landslide movement?
- Topples
- Flows
- Slides (rotational, translational debris, block)
- Falls
- Spreads
- Complex (combo of of above)
