Lecture 2 - Geotechnical Engineering

Question 1

What should be worn when dealing with contaminated soil?

Answer 1

Personal protective equipment (PPE)

Question 2

How is degree of contamination measured?

What two tests can be done? Why are they done?

Answer 2

Mean as not uniform contamination
Mean value test - identify 95% confidence levels of measured mean
Maximum value test - tests whether max value in sample set is outlier

Question 3

What is a common soil problem? What can be done?

Answer 3

Leactate

Can be diluted to acceptable levels

Question 4

How is the dilution factor calculated?

Answer 4

Dilution factor = Qc + (Qu/Qc)
Where Qu = water flow in surface water receptor
Qc = contaminated groundwater flow from site

Question 5

Name two remediation methods?

Answer 5

Removal of soil to landfill

Bioremediation

Question 6

How are bearing capacities of soil calculated?

Answer 6

SPT

Triaxial tests

Question 7

What kind of foundations are usually used?

Answer 7

Shallow foundations or piles

Question 8

What can happen during void collapse if mineral stability is poor?

Answer 8

Void can be filled by equal volume of overlying rock
(Rare due to bulking)
Usually void void migrates upward through strata until process no longer supported when collapse is absorbed

Question 9

What is the minimum cover rule in terms of void collapse?

Answer 9

Rock cover above seam : 5-10 times seam thickness required

Question 10

What can be done to assist mineral stability?

Answer 10

Grouting

Question 11

How can potential slope failures be addressed?

Answer 11

Input of concrete

Question 12

What are the three different types of shallow foundations?

Answer 12

Strip foundations, pile foundations or raft foundations

Question 13

Describe strip shallow foundations?

Answer 13

Narrow (width >1m still)
Concrete footing
Typically support walls

Question 14

Describe pad shallow foundations

Answer 14

Support columns , various types

Question 15

Describe raft/slab shallow foundations, why are they used?

Answer 15

Reinforced steel grid, pumped concrete

Spreads load, used for soft/loose soils

Question 16

What characterise deep foundations?

Answer 16

Piling (different types and methods)

Question 17

When would end bearing piles be used and when would friction piles be used?

Answer 17

End bearing - soft compressible soil on top of hard incompressible layer
Friction - soft soil gradually stiffening with depth

Question 18

Describe displacement piles

Answer 18

Soft displaced radially and vertically. Concrete, steel or combination
Typically drive

Question 19

How are driven piles made?

Answer 19

Drive steel tube into ground to form void

Void filled with concrete as tube removed

Question 20

How are non-displacement piles made?

Answer 20

Soil removed using massive rotary rig,
Filled with concrete
Pre-cast piles

Question 21

When are non-displacement piles useful?

Answer 21

Boulder clay and made ground

Question 22

What is meant by the term ‘bearing capacity’?

Answer 22

Capacity of soil to support loads applied to ground

Question 23

What is the ultimate bearing capacity?

Answer 23

Theoretical max. pressure without failure

Question 24

What is the allowable bearing capacity?

Answer 24

Maximum pressure which may be applied to soil
Adequate FOS against shear failure is ensured
Settlement should not cause damage to structure

Question 25

What is the total bearing capacity of a settlement?

Answer 25

Uniform settlement of entire structure, weight of structure and imposed loads

Question 26

What is the differential structure of a settlement?

Answer 26

Loads on structure are unevenly distributed, variations in soil properties, construction related variations

Question 27

What is used to fill in mined seams and voids?

Answer 27

Bulk in-fill Grouting/Ground stabilisation

Question 28

What is permeation grout?

Answer 28

Used for basement, shafts, dams, funnels

Requires groundwater control, liquid grout flows through soil, displaces water and gas

Question 29

How is dynamic compaction done? Where is it effective?

Answer 29

Repeated dropping of heavy weights (6 to 30 tonnes) onto ground from 10 to 30m
Effective for made ground

Question 30

What is the typical improvement depth of dynamic compaction and what kind of soil is it most effective on?

Answer 30

3-10m

Less than 25% fine soil

Question 31

What equation can be used to work out improvement depth from dynamic compaction?

Answer 31

D=0.5 * square root W*H
Where:
D = improvement depth, m
W = pounder weight in metric ton
H = drop height, m

Question 32

What is vibro compaction? How is it done? When is it most suitable?

Answer 32

Densifying granular soil

1. Torpedo shaped vibrating pole inserted into ground (3-5m long)
2. Penetrates to design depth under own weight and water jetting/lubricant
3. Backfilled

Question 33

How do soil-cement columns compact?

Answer 33

Mixing in-situ soil with cement

Produces soil-cement columns which are higher strength, lower compressibility and lower permeability