Lecture 2 - Factual and Interpretive Reporting

Question 1

What does BS5930: 1999 indicate?

Answer 1

Basic principles of how rocks should be described

Particular order

Question 2

What three decisions must be made for soil descriptions? (NOTE: Opposite from order or words)

Answer 2

Principal soil type
Secondary and minor fractions
Other features

Question 3

How do you distinguish silt from clay using the dry strength technique?

Answer 3

Roll a moistened sample into a thread/ribbon
Air dry
Crumble
SILT will crumble easily, CLAY will not

Question 4

How do you distinguish silt from clay using the dilatancy technique?

Answer 4

Place sample in one hand, palm up
Add water to form a putty
With empty hand, pat sample hand for 5-10 secs
If water rises to surface = SILT

Question 5

what two types of laboratory tests are undertaken and what do they test for?

Answer 5

Geotechnical - classification, shear/compressive strength

Environmental - sulphate, pH, metals

Question 6

How is moisture content worked out? What happens to sample before test?

Answer 6

Sample dried in oven

p=(W-D)/D

p = fraction of total evaporable moisture content of sample, W = mass of original sample,
D = mass of dried sample

Question 7

How is particle size distribution carried out?

Answer 7

Sieve analysis

Question 8

What are Atterberg limits?

Answer 8

Depending on water content, soil is solid, semi-solid, plastic or liquid

Question 9

What is meant by plastic and liquid limit?

Answer 9

Plastic limit = where soil becomes plastic

Liquid Limit = where soil becomes liquid

Question 10

What is the plasticity index? How is it worked out?

Answer 10

Measure of plasticity

Its difference between Liquid limit and Plastic limit

Question 11

Give an example of a chemical classification?

Answer 11

pH

Question 12

How is the California bearing ratio calculated? What does it measure?

Answer 12

Measures compaction

Pressure to penetrate soil sample with standard plunger, divided by pressure to penetrate a standard crushed rock

Question 13

How is shear strength calculated?

Answer 13

Unconfined compressive strength

Question 14

How does uniaxial shearing occur? What does it measure?

Answer 14

Soil sample cylinder compressed between two plates

Measures maximum load at failure

Question 15

How is shear strength of soil tested under controlled drainage conditions?

Answer 15

Triaxial test

Question 16

During a triaxial test what is the specimen subjected to?

Answer 16

Confining fluid/air pressure

Loaded axially to failure

Question 17

Why is it called triaxial test?

Answer 17

3 principal stresses known and controlled

Question 18

What is major principal stress (o1) the sum of?

Answer 18

Applied axial stress (^o = P/A) + chamber (confining) pressure (o3)

Question 19

What is the intermediate and minor principal stresses? How are they similar?

Answer 19

o2 and o3

They have identical values

Question 20

How are soil, groundwater and soil leachate collected for chemical testing?

Answer 20

Soil - disturbed samples
Groundwater - directly collected
Soil leachate - subject to leaching in lab