1. WE PUT YOU ON SOLID GROUND
The use of Non-Invasive Geophysical Techniques to build 3-Dimensional ground models and reduce the cost and risk of site investigation
Sam Setchell, Muhammad Azrief bin Azahar, Qusanssori Noor bin Rusli and Nick Lowe
WE PUT YOU ON SOLID GROUND
19th Southeast Asian Geotechnical Conference & 2nd AGSSEA Conference (19SEAGC & 2AGSSEA) Kuala Lumpur 31 May – 3 June 2016

2. Presentation Outline Site Investigations Geophysical Techniques
Towards 3D models
Case Studies
Langat Sewer, KL
Meru Landfill, Western Australia
Cominco Phosphate Project, Republic of the Congo

3. Site Investigations Geotechnical Hazards present a major project risk.
Site Investigation – Relies on expensive drilling to gain information on ground conditions
‘Point’ data means a conservative approach much be taken
More Data = Better geotechnical model = Lower Risk
Non-Invasive techniques – to reduce risk

4. Geophysical Site Investigation
Geophysics - ideally suited to geotechnical site investigations
Provides Engineering Parameters without the need for drilling
Quickly and cheaply maps variability – allows refined and reduced drilling
Can be converted into 3D ground models

5. Geophysical Techniques pt. 1
Multi Channel Analysis of Surface Waves – MASW
Measures 2D profile of compressibility / strength of soils and rocks
Continuous analysis of surface waves – CSWS
Measures 1D profile of compressibility in high resolution
Ground Penetrating Radar – GPR
High resolution 2D scans that quickly highlight depth to features as well as voids.

6. Geophysical Techniques pt. 2
Gravity Techniques
geological features, man- made structures and voids
Electrical Resistivity Tomography (ERT)
Measures 2D profile of resistivity of sub surface materials
Ground Conductivity – EM
Magnetics

7. MASW Technique
The MASW Technique utilises surface waves elastic condition (stiffness) of the ground for geotechnical engineering purposes.
A 2D Map of ground stiffness – in terms of sear-wave velocity (Vs) is created

8. 3D models of ground conditions can be created by non invasive techniques

9. Multiple lines used to create a 3D survey

10. Development of Geotechnical Model
No firm identification or logo allowed on any sheet except the cover sheet (slide 1 of this template).
Authors may choose either the horizontal or vertical format for their presentation.

11. Calibrating the Model
SPT N-Values from subsequent drilling investigation
Compressibility
High Medium Low
Compressible layers lead to rapid reduction in SPT n
No firm identification or logo allowed on any sheet except the cover sheet (slide 1 of this template).
Authors may choose either the horizontal or vertical format for their presentation.
Some lag, but otherwise good agreement between MASW and SPTn

12. Depth to Bedrock
Use of CSWS technique allowed identification of variable depth to bedrock under residential development in Fremantle.
Surface represents inferred top of bedrock. This was then verified with just 1 borehole

13. Detailed Case Study – Langat Sewer
Study to measure the depth to bedrock along the alignment of a proposed sewer
Directional drilling to be undertaken → strength of soil very important
CSWS and SASW used to fill in gaps from pre-existing bore hole data.
With the controlled surface wave system it is the element of control that is the main advance from sasw. An industrial vibrator that can be controlled in frequency to 0.1 Hz resolution.

14. Langat Sewer Advantages of CSWS/SASW over drilling:
Data could be collected from the actual pipeline alignment – drilling had been taking place up to 50m away.
10 tests a day – much greater coverage of data
Little disturbance to traffic
Cheaper for the client

15. Example Profile
With the controlled surface wave system it is the element of control that is the main advance from sasw. An industrial vibrator that can be controlled in frequency to 0.1 Hz resolution.

16. Example Report Output Profile
Location of tests in 2D plan view (red line shows profile)
Location of tests on aerial photo
With the controlled surface wave system it is the element of control that is the main advance from sasw. An industrial vibrator that can be controlled in frequency to 0.1 Hz resolution.

17. Detailed Case Study – Langat Sewer
Profiles were produced for the whole sewer alignment
Amount of data collected allowed client to make decisions and reroute some areas of pipeline
Over all a successful application of a geophysical method!
With the controlled surface wave system it is the element of control that is the main advance from sasw. An industrial vibrator that can be controlled in frequency to 0.1 Hz resolution.

18. Meru Landfill – Using geophysics to plan location
Limestone outcrops had been found on the site of proposed landfill development
The previous landfill cell encountered unforeseen rock at shallow levels, resulting in a significant cost overrun (for excavation)
A 4 month drilling campaign was proposed to identify the extent of this limestone with an estimated budget of A$650, (~2 million ringgit) - almost 3 times what was allowed.
The critical aspect was to get complete (or close to complete) 3D coverage across the site.
The MASW technique (Multi Channel Analyses of Surface Waves) was chosen by Infra Tech.
Completed within a budget of A$75, (~232, ringgit)

19. Detailed MASW Survey – 13 lines

20. 2D MASW output
Evidence of some rock material (known to be limestone) shown in Black/Red

21. 2D to 3D conversion
Fence diagram shows clear band of rock material

22. 3D Block Model
Blocks representing ‘limestone’ can be isolated and an estimation of volume of limestone material can be made – all before drilling!

23. Presentation Conclusions
Inadequate site investigations can lead to project failure (or worse)
Geophysical techniques provide a cheep and quick way to gather information
Add value by:
Reducing Risk – better site understanding
Reducing drilling cost
Creating more accurate ground models

24. WE PUT YOU ON SOLID GROUND FASTER, STRONGER, CHEAPER, SAFER, GREENER
THANK YOU
WE PUT YOU ON SOLID GROUND FASTER, STRONGER, CHEAPER, SAFER, GREENER