Junior Recital: Alister Smith, Guitar

Kemp Recital Hall Saturday Evening April 29, 1995 9:30p.m

Acoustic emission behaviour of dense sands

Interpretation of acoustic emission (AE) generated by particulate materials has to date been qualitative. The objective of this study was to move the discipline towards quantitative interpretation of AE to: enable early warning of serviceability and ultimate limit state failures in the field, and enhance the instrumentation of element and physical model tests in the laboratory. Results from a programme of drained triaxial tests on dense sands show that: AE generation is proportional to the imposed stress level, imposed strain rate, fabric coordination number and boundary work done; there are two types of AE response at the transition from contractive to dilative behaviour, which was governed by the mean particle size; and AE activity in particulate materials is negligible until the current stress conditions (compression and/or shear) exceed the maximum that has been experienced in the past. Relationships have been quantified between AE and boundary work (i.e. AE generated per Joule) for a unit volume of sand under isotropic compression and shear, and between AE and shear strain rate. An example interpretation framework demonstrates how AE measurements could be used to identify the transition from contractive to dilative behaviour, mobilisation of peak shear strength and quantify accelerating deformation behaviour that typically accompanies shear zone development

Quantification of landslide velocity from active waveguide generated acoustic emission

Acoustic emission (AE) has become an established approach to monitor stability of soil slopes. However, the challenge has been to develop strategies to interpret and quantify deformation behaviour from the measured AE. AE monitoring of soil slopes commonly utilises an active waveguide which is installed in a borehole through the slope and comprises a metal waveguide rod or tube with a granular backfill surround. When the host slope deforms, the column of granular backfill also deforms and this generates AE that can propagate along the waveguide. Presented in the paper are results from the commissioning of dynamic shear apparatus used to subject full scale active waveguide models to simulated slope movements. The results confirm that AE rates generated are proportional to the rate of deformation, and the coefficient of proportionality that defines the relationship has been quantified (e.g. 4.4 x 105 for the angular gravel examined). The authors demonstrate that slope velocities can be quantified continuously in real-time through monitoring active waveguide generated AE during a slope failure simulation. The results show that the technique can quantify landslide velocity to better than an order of magnitude (i.e. consistent with standard landslide movement classification) and can therefore be used to provide an early warning of slope instability through detecting and quantifying accelerations of slope movement

Acoustic emission monitoring of active waveguides to quantify slope stability

The active waveguide is installed in a borehole that penetrates stable stratum below any shear surface or potential shear surface that may form beneath a slope. It comprises a metal waveguide rod or tube that provides a low resistance path for acoustic emission to travel from the source at the shear surface to the sensor at the ground surface. The annulus surrounding the waveguide is backfilled with granular soil. When the host slope deforms, the column of granular soil also deforms and this induces inter-particle friction and releases relatively high levels of acoustic emission that can propagate along the waveguide. Field trials and laboratory experiments reported by the authors have demonstrated that acoustic emission rates generated by active waveguides are proportional to the velocity of slope movement. This summary describes the operation of the active waveguide and Slope ALARMS acoustic emission sensor for use in slope stability monitoring. An on-going research project aiming to develop an algorithm that can quantify slope displacement rates through monitoring active waveguide generated acoustic emission is introduced

Acoustic emission generated by glass beads in compression and shearing

Acoustic emission (AE) monitoring offers the potential to sense particle-scale interactions that lead to macro-scale responses of granular materials. This paper presents results from a programme of drained triaxial tests performed on densely packed glass beads to establish quantitative interpretation of AE during isotropic compression, shearing and associated stick–slip events. Relationships have been quantified between: AE and boundary work (i.e. AE generated per Joule) for a unit volume of glass beads under isotropic compression and shear; AE and shear displacement rate; and the amplitude of deviator stress cycles and AE activity during stick–slip events. In shear, AE generation increased with shear strain and reached peak values that were maintained from volume minimum (i.e. the transition from contractive to dilative behaviour) to peak dilatancy, whereupon AE generation gradually reduced and then remained around a constant mean value with further increments of shear strain. In each stick–slip event, AE activity increased during shear strength mobilisation, particle climbing and dilation, and then reduced with the subsequent deviator stress drop during particle sliding and contraction. The amplitude of these cycles in AE activity were governed by the amplitude of deviator stress cycles during stick–slip events, which were also proportional to the imposed stress level and inversely proportional to particle size

Acoustic emission sensing of pipe-soil interaction: Full-scale pipelines subjected to differential ground movements

This paper presents the first full-scale demonstration of the potential use of pipe/soil interaction-generated acoustic emission (AE) for early detection of buried pipe deformation. Full-scale tests were performed at the buried infrastructure research facility at Queen's University, Canada, using a split-box apparatus to impose differential ground motion on a steel pipe buried in dry sand, and to investigate the influence of stress level and patterns of deformation on AE generation. The pipe was instrumented with AE sensors, strain gauges, fibre optic strain sensing and linear potentiometers, and surface deformation was measured using an automatic total station. AE measurements were used to interpret the evolution of the pipe/soil interaction behaviour. AE activity correlated strongly (R2 from 0.83 to 0.99) with both the rate and magnitude of pipe deformation at different burial depths, and quantified relationships are presented that enable interpretation of pipe/soil interaction behavior from AE measurements

Early detection of seepage-induced internal erosion using acoustic emission monitoring

Techniques for monitoring water-retaining earth structures are currently limited in their capacity to detect seepage-induced internal erosion (e.g. suffusion) in its early stages, or before serious damage has occurred. Acoustic emission (AE) is widely used in many industries for non-destructive assessment of materials and systems, but despite its advantages it is seldom used in geotechnical engineering as the AE generated by particulate materials is highly complex and difficult to measure and interpret. This project aims to develop the interpretation of AE generated by seepage-induced internal instability phenomena. A continuous, real-time AE early warning system for detecting seepage erosion mechanisms and processes will enable safety-critical decisions to be made. Laboratory testing with a large permeameter apparatus is being used to characterise and quantify the AE generated by the hydromechanical behaviour of a range of internally unstable soils. Initial results show that key processes such as the internal movement of particles can be measured and interpreted using AE

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

Inclinometer casings retrofitted with acoustic real-time monitoring systems

The paper details the concept of retrofitting inclinometer casings with active waveguides in order to provide subsurface instrumentation that can monitor the stability of slopes continuously and in real-time. The operation of the active waveguide, the unitary battery operated Slope ALARMS acoustic emission sensor and warning communication system are described. A field trial previously reported by the authors demonstrates that acoustic emission rates generated by active waveguides are proportional to the velocity of slope displacements, and can therefore be used to detect changes in rates of movement (i.e. accelerations and decelerations) in response to destabilising (e.g. rainfall) and stabilising (e.g. remediation) effects. The paper presents the results of a field trial of the acoustic monitoring system retrofitted inside an inclinometer casing in a reactivated landslide at Hollin Hill, North Yorkshire, UK. The study demonstrates that this approach can provide continuous information on slope movements with high temporal resolution. Converting manually and periodically read inclinometer casings into continuously monitored active waveguides using Slope ALARMS sensors is a cost effective solution to provide real-time information that could be used in the protection of people and infrastructure

Stability monitoring of a rail slope using acoustic emission

The paper details the use of acoustic emission generated by active waveguide subsurface instrumentation to monitor the stability of a rail soil cutting slope failure. Operation of the active waveguide, unitary battery-operated acoustic emission sensor and warning communication system are described. Previous field trials reported by the authors demonstrate that acoustic emission rates generated by active waveguides are proportional to the velocity of slope movement, and can therefore be used to detect changes in rates of movement in response to destabilising and stabilising effects, such as rainfall and remediation, respectively. The paper presents a field trial of the acoustic emission monitoring system at a reactivated rail-cutting slope failure at Players Crescent, Totton, Southampton, UK. The results of the monitoring are compared with both periodic and continuous deformation measurements. The study demonstrated that acoustic emission monitoring can provide continuous information on displacement rates, with high temporal resolution. The ability of the monitoring system to detect slope movements and disseminate warnings by way of text messages is presented. The monitoring approach is shown to provide real-time information that could be used by operators to make decisions on traffic safety