Gary John Fowmes

Monitoring buried pipe deformation using acoustic emission : quantification of attenuation

Deformation of soil bodies and soil-structure systems generates acoustic emission (AE), which are high-frequency stress waves. Listening to this AE by coupling sensors to structural elements can provide information on asset condition and early warning of accelerating deformation behaviour. There is a need for experimentation to model the propagation of AE in buried pipe systems to enhance understanding of real behaviour. Analytical solutions are often based on many assumptions (e.g. homogeneity, isotropy, boundary conditions and material properties) and cannot exactly represent the behaviour of the in situ system. This paper details a series of experiments conducted on buried pipes to investigate AE attenuation in pipes due to couplings and soil surround. The attenuation coefficients reported provide guidance to engineers for designing sensor spacing along buried pipes for monitoring ground deformations, and active waveguide installation depths for slope deformation monitoring. Attenuation coefficients have been quantified for both air–pipe–air and air–pipe–soil trilayer systems for the frequency range of 20–30 kHz.

Strategies for rock slope failure early warning using acoustic emission monitoring

Research over the last two decades has led to development of a system for soil slopes monitoring based on the concept of measuring Acoustic Emission (AE). A feature of the system is the use of waveguides installed within unstable soil slopes. It has been demonstrated that the AE measured through this technique are proportional to soil displacement rate. Attention has now been focused on the prospect of using the system within rock materials. The different nature of the slope material to be monitored and its setting means that different acoustic trends are measured, and development of new approaches for their interpretation are required. A total of six sensors have been installed in two pilot sites, firstly in Italy, for monitoring of a stratified limestone slope which can threaten a nationally important road, and secondly in Austria, for monitoring of a conglomerate slope that can endanger a section of the local railway. In this paper an outline of the two trial sites is given and AE data collected are compared with other physical measurements (i.e. rainfall and temperature) and traditional geotechnical instrumentation, to give an overview of recurring AE trends. These include clear AE signatures generated by stress changes linked to increased ground water levels and high energy events generated by freeze-thaw of the rock mass.

Sustainability aspects of using geotextiles

The sustainability of materials and processes is commonly assessed by calculating the carbon emissions (CO2) generated. This is a simplification, but the ease of calculation encourages the comparison of solutions; it makes the output of assessments accessible, transparent and repeatable; and CO2 savings can readily be counted towards industry and national and international targets. This chapter describes a framework for calculating embodied carbon of construction solutions that incorporate geotextiles. It outlines techniques for determining the carbon footprint and common definitions, presents examples of embodied carbon for geotextile materials, defines life cycle boundaries and presents sample calculations for common construction case studies: protection, a working platform and landfill capping. All three examples demonstrate significant CO2 savings that can result from employing geotextiles. These savings are realised by reducing the amount of imported fill material used, which minimises transport-related carbon emissions. The approach that is introduced can be used to undertake site-specific calculations to inform decisions regarding the selection of approaches to construction that contribute to sustainable practice.