Week 6: E.G.1 and E.G.2

Question 1

What is the purpose of Engineering Geology?

Answer 1

Assuring that the geological factors affecting location/design/construction/operation and maintenance are recognised and provided for. (For engineering works)

Question 2

What are the 7 ideal stages of Site Investigation?

Answer 2

Pre-feasibility - Desk study & site walkover.
Feasibility - Comprehensive desk study and limited intrusive investigations.
Tender design - Geophysics, test pits, trial holes & limited boreholes.
Detailed design - Intrusive testing & lab testing.
Construction - Monitoring & additional testing.
Post-construction - Monitoring.
Remedial - Forensic investigations.

Question 3

What are the 3 extents of investigations?

Answer 3

Lateral extent - Limited to site boundaries.
Shallow footings - Investigate to a depth 2x the expected width below the base of foundations.
Deep foundations (piles) - Investigate to a depth 3x the diameter of the pile tip below founding depth.

Question 4

What does TSF mean?

Answer 4

Tailings Storage Facilities.

Question 5

Why must we study Geology?

Answer 5

All our work will be involved with using the material of the Earth or placing structures on certain materials.

Question 6

Does the TSF investigation just require 1 limit of the extent of investigation?

Answer 6

No. TSF investigations may require different limits for different aspects.
Geotechnical - To the base of potential failure horizons.
Geohydrological - To understand aquifers at great depths.

Question 7

What is the biggest rule when thinking about the extent of the investigation?

Answer 7

Do not stop at the first competent horizon. It could be resting on a soft material.

Question 8

What are the 2 components of investigation?

Answer 8

Desk studies (non-intrusive).
Site investigation: Remote sensing (non-intrusive) and digging or drilling (intrusive).

Question 9

Remote sensing involves Geophysical techniques: Gravity surveys, resistivity surveys, magnetic surveys, seismic surveys.
What is the purpose of doing this? What is still missing, flaw?

Answer 9

To create maps with zones of different geological/geotechnical properties. The map often can’t define the properties.

Question 10

What is a term for Invasive techniques?

Answer 10

Ground truthing.

Question 11

What are the 3 main ground truthing methods?

Answer 11

Test pitting. Drilling. Penetrometers.

Question 12

What machinery is used in test pitting? (2 main ones)

Answer 12

TLB (Tractor loaded backhoe).
Excavator.

Question 13

What are the 3 main types of drills?

Answer 13

Auger, percussion, rotary cored.

Question 14

Give some names of penetrometers.

Answer 14

DCP, DPSH, SPT, CPTu, Cone.

Question 15

What are the pros and cons of test pitting and auger drilling?
Take note the CONS especially!

Answer 15

Pros: Easy access to soil. Disturbed & undisturbed samples of soil.
Cons: Dangerous, collapsing sidewalls. Limited by water table.

Question 16

What are the pros and cons of percussion drilling?
Take note the CONS especially!

Answer 16

Pros: Depths of 100m. Faster & cheaper than core drilling. Can do geophysical tests down hole. Install piezometers or stand pipes.
Cons: Samples are broken soil & rock. Poorer horizons are often lost. Difficulty drilling when: Loose/porous ground & cavities and below water table.

Question 17

What are the pros and cons of core drilling?
Take note of CONS especially!

Answer 17

Pros: Depths over 1000m. Can do in-situ tests. Retrieve samples from below water table.
Cons: Expensive & slow. Poorer horizons are often lost, it’s washed out. All samples are disturbed. Sample not as good as test pitting.

Question 18

What are the pros and cons of penetrometers?

Answer 18

Pros: Quick & cheap. Small intrusion (hole). Good correlation with certain geotechnical parameters.
Cons: Poor/no sample. Limited by a hard horizon. Difficult/complex to interpret sample.

Question 19

What is the hierarchy of techniques?

Answer 19

1. Direct examination & testing: Auger holes & test pits.
2. Methods that retrieve undisturbed samples & can conduct in-situ tests: Rotary cored-drilling & continuous SPTs.
3. ‘Blind’ methods, don’t retrieve samples but geotechnical parameters: DPSH, DCP, CSW & seismics.
4. Methods used only to extrapolate info: Percussion drilling, gravity & resistivity.

Question 20

What does the process involve to map the callibrated model?

Answer 20

It’s an iterative process.

Question 21

What are the following 3 statements a part of?
1. (SANS 1936) Any new development on dolomitic land must have a dolomite hazard investigation.
2. (SANS 634) A new residential township must be registered with NHBRC and requires a geotechnical investigation.
3. (NHBRC) New residences need a foundation investigation.

Answer 21

The regulatory environment.

Question 22

What does nearly all geotechnical problems arise from?

Answer 22

A change in moisture.

Question 23

What are some of the ways water impacts the environment?

Answer 23

It shapes the landscape, affects structures and influences geological processes.

Question 24

How does water shape the landscape?

Answer 24

Erosion is dependent on the water velocity & volume.
Deposition is dependent on loss of velocity & volume.

Question 25

How does water affect structures?

Answer 25

Floods: Poor stormwater/river control. Landslides: When steep terrain is undercut by rivers/saturated ground. Sinkholes: When river collect and dissolves limestones collapsing the land surface.

Question 26

How does water affect geological environment?

Answer 26

Leaching: Removal/addition of compounds/clays. (Uranium oxide) Aquifers: Water storage & pollution.

Question 27

What is the water table referred to as?

Answer 27

Phreatic surface. - Where pore water pressure equals atmospheric pressure. - The boundary between the saturated and unsaturated zones. - The upper surface of the zone of ground water saturation.

Question 28

What is the definition of the following terms? Aquifers, Aquicludes and Aquitards.

Answer 28

Aquifers: A body of porous rock/sediment saturated with ground water. Aquicludes: A formation that is impermeable to the flow of water. [Very rare] Aquitards: A formation that has low-permeability that stores ground water and transmit it slowly from one aquifer to another. [Most frequent]

Question 29

What is a perched water table?

Answer 29

A localised zone of saturated soil held above the main water table by an impermeable layer. This creates a separate, elevated water body.

Question 30

How does water flow? What are the 2 factors that affect this flow?

Answer 30

Water moves slowly through spaces/voids and in fissures in the rock and soil. The movement of water is influenced by gravity and pressure. The 2 factors are permeability (flow of water) and porosity (storage of water).

Question 31

What is a Vadose zone?

Answer 31

An unsaturated zone.

Question 32

How are aquifers recharged?

Answer 32

Precipitation.

Question 33

Give an example of a confined layer, a confining layer and an unconfined layer?

Answer 33

An unconfined layer: An Aquifer that doesn't have a confining layer on both sides. Confined layer: An Aquifer that is between two confining layers. Confining layer: An Aquitard with very low permeability and porosity.