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 www.infratecheng.com 19th Southeast Asian Geotechnical Conference & 2nd AGSSEA Conference (19SEAGC & 2AGSSEA) Kuala Lumpur 31 May – 3 June 2016

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

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

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

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.

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

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

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

Multiple lines used to create a 3D survey

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.

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

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

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.

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

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.

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.

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.

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$650,000.00 (~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$75,000.00. (~232,000.00 ringgit)

Detailed MASW Survey – 13 lines

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

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

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

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

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