Sigra News August 2015

August 2015

Here is an update from Sigra Australia:

International Conference Presentations & Melbourne Geotechnical Investigation


Sydney & Hong Kong Conference Presentations

This spring will be an exciting time for engineers in the civil engineering industry with two international conferences in September:

The Ninth International Symposium on Field Measurements in Geomechanics (FMGM), hosted by the Australian Centre for Geomechanics, in Sydney, Australia, 9th-11th September 2015,


The Underground Design and Construction Conference 2015, hosted by the Institute of Minerals and Mining, Hong Kong Branch, in Hong Kong, 11th and 12th September 2015.

Sigra will be presenting at both these conferences and will have a booth in Hong Kong.

At the Sydney Conference Dr Ian Gray has the pleasure of presenting a Kenote Address on the topic of “The measurement and interpretation process to determine the state of stress in rock including the effects of fluid pressure” which looks at what effective stress really is in fractured rock mass. In the paper on “The measurement of fluid pressure in rock and soil”  cement displacement pressure transducer installation technology will be presented. This system replaces the conventional piezometer as it is both of lower cost to install and provides a verifiable connection to fluid in the ground and a test against leakage along the borehole. It is suitable for simple civil engineering operations or for complex deep multi-point pressure sensing applications in aquifers or gas wells.

In Hong Kong the paper being presented is entitled the “Investigation needs for underground excavations” which will be of particular interest given the extent of tunnelling work proposed in Hong Kong, the rest of South East Asia and indeed Australia. Its draws on civil, mining and petroleum engineering experience to provide a new look at how exploration/site investigations can be efficiently conducted for underground space using the best of available technology.

We look forward to meeting visitors and discussing how to meet project needs at both these conferences.


Geotechnical Investigation for Melbourne Tunnelling

Insitu stress testing by Sigra lays the foundation for detailed design of future Melbourne city tunnels.

In what may be a first for Melbourne, local exploration testing of the city siltstones by Sigra under the Yarra River has measured the insitu stress regime.


Sigra has completed a set of bi-axial insitu stress measurements by overcoring, using our proprietary insitu stress measurement tool.  The measurements are carried out concurrently with exploration coring using a HQ wireline coring system.  Details of this system are eloquently demonstrated in this video.

The stress testing was achieved in the siltstone of varying competency from sound to highly fractured zones indicative of some stress relief.  The data from these tests provides measurement of the change in strain of a pilot hole drilled into the strata, during overcoring as well as compass bearing of the principal stress.

The information on loads through a formation is best characterised by the state of tectonic strain.  This is the calculated strain which would generate the stress levels that are measured.  Rock stress is thus calculated on the elastic properties of the rock.

The Sigra stress testing is part of a suite of testing services for the civil and mining industry that include overcoring of surface strain gauge devices, 3D borehole stress measurements using Sigra’s stress measurement tool with an axial strain device, hydraulic fracturing for biaxial measurement, fracture reopening for determining stress perpendicular to a fracture, and borehole breakout analysis.

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