Monitoring buried pipe deformation using acoustic emission: quantification of attenuation

Abstract

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 tri-layer systems for the frequency range of 20 to 30 kHz.Keywords: acoustic emission; attenuation; buried pipes; deformation; field instrumentation; landslides; monitoring; non-destructive testing; slopes IntroductionAcoustic emission (AE) monitoring of slopes uses active waveguides (Figure 1), which are installed in boreholes, or retrofitted inside existing inclinometer or standpipe casings. They are installed to intersect existing or anticipated shear surfaces beneath the slope, and they comprise the composite system of a steel tube, connected in lengths using screw threaded couplings, with a granular backfill surround (i.e. a type of buried pipe). As the host slope deforms, the active waveguide deforms, and this causes particle-particle and particle-waveguide interactions to take place, which generate the AE. The predominant zone of AE generation is at the shear surface. Generated AE rates are proportional to applied displacement rates, where the coefficient of proportionality Smith et al. Monitoring Buried Pipe Deformation Using AE: Quantification of Attenuation 17/08/2016 3 is dependent on the depth to the shear surface and the distance AE propagates along the waveguide to the ground surface where it is measured. Quantifying this magnitude of attenuation for each installation is essential to deriving slope displacement rates from measured AE rates, which can be used to warn users of accelerating slope deformation behaviour to enable evacuation of vulnerable people and timely repair and maintenance of critical infrastructure (Koerner et al., 1981;Nakajima et al., 1991;Smith et al., 2014a;Smith et al., 2014b;Dixon et al., 2015a;Dixon et al., 2015b;Smith, 2015;Smith & Dixon, 2015;Smith et al., 2016).[Insert Figure 1 here] Developments in AE monitoring of pipe networks (e.g. Alleyne & Cawley, 1992;Alleyne & Cawley, 1997) for the detection and location of defects (e.g. Lowe et al., 1998) and leaks (e.g. Mostafapour & Davoudi, 2013;Anastasopoulos et a...

An acoustic emission landslide early warning system for communities in low-income and middle-income countries

“…These types of pipes with a range of geometries have been employed in all previous field installations of the Slope ALARMS system for both technical and practical reasons (Dixon et al 2015a). The wall thickness of the tube is selected to optimise the propagation of AE long distances with minimum attenuation, hence enabling AE generated at depth within a slope to be transmitted to the sensor at ground level (Smith et al 2017b). In addition, the 3-mm tube thickness facilitates threading of the tube to allow use of screw couplings between lengths, which aids rapid installation and also minimises attenuation of AE at the connections (Smith et al 2017b).…”

Acoustic Emission Sensing of Pipe–Soil Interaction: Full-Scale Pipelines Subjected to Differential Ground Movements

“…The backfill used in the experiments was synthetic olivine sand (used in commercial sand blasting), which has higher particle density than conventional silica sands, enabling reuse in multiple tests as it is resilient to crushing and degradation (Ni et al 2017). The properties of olivine sand are shown in Table 2. A steel pipe was selected for this study for two key reasons: (1) steel pipelines are the most common choice for transporting water, oil and gas across large geographic areas and hence are likely to intersect a range of geohazards; and (2) AE propagates long distances in steel with minimal attenuation (<0.2 dB/m) (Smith et al 2017b).…”

“…Nascent technologies, such as fibre optics, are beginning to provide valuable pipe asset health monitoring information; however, retrofitting hundreds of thousands of kilometres of assets with these sensors would be prohibitively intrusive and expensive. The advantage of the AE approach is that sensors could be installed at discrete locations, for example at spacings of hundreds of metres (Smith et al 2017b), to provide high spatial and temporal resolution information for use in early warning of adverse deformation behaviour.…”

Photographic feature: Acoustic emission monitoring of coastal slopes in NE England, UK

“…The AE monitoring approach employs an active waveguide (Figure 1), which is a subsurface instrument installed inside a borehole that intersects existing or potential shear surfaces beneath the slope (Smith et al, 2014a;Dixon et al, 2015a;Dixon et al, 2015b;Smith & Dixon, 2015;Smith et al, 2016a;Smith et al, 2016b;Smethurst et al, 2017). It can also be retrofitted inside existing inclinometer (e.g.…”