Soil Mechanics, Lab Testing & Analysis

Question 1

Organic Soils

Answer 1

Able to retain water –> higher compressibility –> more settlement potential and higher corrosion potential

Question 2

Type of Strength for (1) coarse grained soils and (2) fine grained soils

Answer 2

Coarse Grained Soils
-derive strength from friction b/w particles

Fine Grained Soils
-Derive strength from electro-chemical attraction b/w particles (cohesion)

Question 3

Undrained Shear Strength

Answer 3

Shear strength of clay is fixed value = apparent cohesion
Undrained shear strength increases with increasing PI

Measured in field with pocket pen or torvane
Can be estimated from indirect measurements (CPT, SPT, etc) but MUST be correlated with lab test results

Question 4

Sample Disturbance

Answer 4

Reduces Su
Increase strain required to achieve peak shear stress
reduce soil stiffness
eliminate strain softening
Less of an issue for CU and DSS

Question 5

Soils with medium toughness and very low dilatancy

Answer 5

Describes clay (not silt)

Question 6

What is soil resistivity?

Answer 6

Used for measuring volume of soils to determine conductivity of soil

Question 7

Cohesion vs Undrained Shear Strength vs Shear Stress

Answer 7

Cohesion = undrained shear strength (cu or su) = 1/2 shear strength (tau)

Question 8

Compression Index Correlations

Answer 8

Use LL over void ratio if…. soil is NC and highly plastic

Void ratio is applicable to all clays with wider range of plasticity