Modern Reconnaissance Methods For Geohazard Detection And Monitoring In Site Investigation

One element of a site investigation often involves the location of any geohazards that may cause increased costs during construction. Thus, there is a need for rapid indirect methods to carry out a reconnaissance survey of the ground surface to identify any anomalous areas that may be associated with the presence of a geohazard.

Geophysical surveying methods operated above the ground surface and from the air, and remote sensing methods operated from space, have been developed over the last decade as suitable methods for fulfilling this reconnaissance role. Increased computer power and improved software have improved the processing of data and enhanced resolution of the target zones is being achieved as a result of the higher quality information available from an increasing range of satellites. Some of these improved methods have particular relevance to the detection and monitoring of geohazards.

The paper describes the physical and chemical characteristics of a wide range of geological hazards, which particularly affect Britain, and that enable them to be observed using indirect methods. The geohazards can be classified in terms of those showing density contrasts that enables the identification of voids and infillings, ground movement that facilitates the detection of many active geohazards and chemical variations in the soil that allow the movement of natural and anthropogenic contamination to be observed.

Recent development of indirect investigation methods are discussed and illustrated with reference to the observation of sinkholes in chalk beneath a building using cross-hole seismic tomography, the detection of mine entrances using airborne thermal detectors, the identification of contamination plumes draining from mine spoil tips using high resolution airborne electromagnetic measurements (HiRes) and the monitoring of the consolidation of alluvial deposits beneath an industrial development using permanent scatterer radar interferometry (PSInSAR).

• Introduction

• Geological hazards in civil engineering

• Use of geophysical techniques for the assessment of geological hazards

• Characterization of solution features – cross-hole seismic tomography

• Location of mine entrances – thermal imaging

• Detection of contaminant plumes – high-resolution airborne geophysics

• Digital terrain models and ground movement monitoring – LIDAR and PSInSAR

• Conclusions

• Acknowledgements

• References

• Figures