ABSTRACT
Almost any major geotechnical project requires in-situ testing and performance monitoring to be carried out as part of the geotechnical design. With the increase in size and complexity of our soil and rock structures both in-situ testing and performance monitoring are of over-proportionally increased importance.
Over the last few years there has been a recognizeable revival in the demand of the market for in-situ testing. This includes tests carried out in boreholes as well as large-scale tests at accessible surfaces. Within this paper a thorough review is given on the various borehole testing methods and equipment such as pressuremeters, dilatometers and borehole jacks. In particular, it is shown that the common borehole jacks (e.g. Goodman Jack) can influence the test results considerably. Against this background a new borehole jack has been developed which is particularly designed for use in soft rock and soil providing in-depth information on the relevant deformation moduli of the ground.
Mention is made on a number of new large in-situ testing equipment such as an 8 MN Plate Load testing equipment and Extra Large Flat Jacks which have been employed in some major dam projects.
In the area of in-situ rock stress measurements the trend is clearly away from the overcoring methods (too delicate; too costly; poor cost/benefit ratio). On the increase are hydraulic fracturing and borehole slotting, both of the methods which allow high-definition measurements to be carried out at reasonable costs. Examples are provided with most recent test results.
The trend for high-definition measurements is also recognizeable in performance monitoring. Of particular importance is linewise observation of boreholes or pipes. A combination of mobile probes (mobile inclinometer and mobile extensometer) can provide the full 3-D deformation stage of the ground. Examples are presented for an underground mine and a foundation in collapsing ground.
Finally, an example from inner-city tunnelling is given which highlights the trend for real-time monitoring and computer processing of the measurement data.
