Soil Testing Flashcards
Wet Sieving
- Seperate fine from coarse grains by washing soil on sieves
Dry sieving
- Shake through sieves of descending size
- Retained on sieves is weighed and recorded
Hydrometer Analysis
- Different grain sizes fall through liquids at different velocities
- Grain reaches terminal velocity by stocks law
Compaction
- Densification of soils by removing air
- Increate strength, stability and reduce frost damage by water removal
Variables of compaction
1 - Dry density/weight
2- Water content
3 - Compactive effort
4 - Soil type
Standard Proctor Test
- 2.4kg hammer method
- 300mm drop
- 27 blows/layer
- 3 layers
Elevation head (he)
Height of a point above a reference point level
Total head (h)
Water pressure in height of column of water above datum level
Coefficient of permeability (k)
Discharge velocity of water flow in soil under action of a unit hydraulic gradiant (m/s)
Discharge velocity (v)
Mean velocity of flow of water related to the cross-sectional area which it flows
Hydraulic gradient (i)
- Ratio of the difference in total head on either side of a soil layer
- To thickness of layer measured in direction of flow
Shear Strength of Soil
- When max strength is reach soil fails
- Particles either roll along each other (up and down along the direction) or slide flat along the top
Importance of Shear Strength
- When building upon it need to know limitations
Factors Affecting Shear Strength
- Frictions and cohesion (interlocking and bonding)
- Soil compaction
- Inital state
- Structure
Shear Strength Testing
- Direct shear test
- Triaxial test
Direct Shear (shear box) Test
- Soil put in metal shear box
- Box is split into two halves horizontally
- Normal force applied at top of box
- Shear foce applied by moving one half of the box relative to other to cause failure in soil
- Pros: quick, simple, easy to prepare, easy to analyse
- Cons: fails from chosen plain not weakest, failure may not always be horizontal
Pressure Head
Height of which the water rises in the piezometer above the point.
Max dry density (Pd max)
Max density a soil can reach using compaction
Optimum water content (W opt)
Water content needed to allow soil to reach max dry unit weight following compaction
