Case studies

Soil slopes

Rock slopes


Hollin Hill

Hollin Hill is a complex of landslides in North Yorkshire. The landslides occupy a hillside used for grazing sheep and the farmer has allowed the site to be instrumented to study the landslides.

Active waveguides with Slope ALARMS sensors, inclinometer casings and ShapeAccelArrays (SAAs) have been installed through lobes of landslide material that move most winters on shear surfaces approximately 1.5 metres below ground level. These instruments have been read since early 2010.

SAAs installed at Hollin Hill have allowed the comparison of continuous AE with continuous subsurface deformation measurements. A series of slope movements occurred in response to periods of rainfall in January 2014 (Figure below). These comparisons confirm that: AE rates generated by the system are directly proportional to the rate of deformation; AE monitoring of active waveguides can provide continuous information on slope displacements and displacement rates; and the technique is sensitive to small displacements, displacement rates (i.e. less than

An additional part of the study at this site is conversion of an inclinometer casing into an active waveguide. A small diameter steel tube has been installed in the casing and surrounded by sand backfill. A slope ALARMS sensor has been attached to this waveguide and monitoring commenced in January 2011 and is continuing. The aim is to compare performance of the inclinometer retro fitted and the standard waveguide designs. To date, the systems show comparable performance and this creates an opportunity to convert inclinometer casings that are currently read at time intervals into real-time continuously monitored instruments using Slope ALARMS (see Smith et al. 2014).

Further information can be found in:

Smith A (2015) Quantification of slope deformation behaviour using acoustic emission monitoring. PhD Thesis, School of Civil and Building Engineering, Loughborough University, UK. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/18593

Uhlemann S, Smith A, Chambers J, Dixon N, Meldrum P, Dijkstra T, Haslam E, Merritt A and Gunn D (2015) Assessment of ground-based monitoring techniques applied to landslide investigations. Geomorphology. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/19643

Dixon N, Spriggs MP, Smith A, Meldrum P and Haslam E (2015) Quantification of reactivated landslide behaviour using acoustic emission monitoring. Landslides 12 (3), 549-560. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/14573

Smith A, Dixon N, Meldrum P, Haslam E and Chambers J (2014) Acoustic emission monitoring of a soil slope: Comparisons with continuous deformation measurements. Géotechnique Letters 4 (4), 255-261. Awarded the Institution of Civil Engineers Thomas Telford Premium (Prize for Best Paper in Journal). At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/16094

Smith A, Dixon N, Meldrum P and Haslam E (2014) Inclinometer casings retrofitted with acoustic real-time monitoring systems. Ground Engineering Magazine, October Issue. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/16095

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Players Crescent

A landslide in a 12 metre deep rail cutting located near Southampton is being monitored by Network Rail. The tree lined slope is formed in Barton Clay Formation. Movements occur following prolonged periods of rainfall and these are measured using periodic surveys of inclinometer casings installed through the landslide.

Two active waveguides and Slope ALARMS systems were installed in February 2011 adjacent to an inclinometer casing (at the head of the slope) and a ShapeAccelArray (SAA) (at the toe of the slope – provided by project partner Geotechnical Observations Ltd).

The results from the field trial at Players Crescent demonstrate the performance of the Slope ALARMS system to provide continuous information on slope displacement rates with high temporal resolution (through comparisons with the SAA continuous deformation measurements). The study confirmed the ability of the Slope ALARMS system to detect slope movements of slow rate and small magnitude, and communicate warnings by way of an SMS message, based on trigger levels indicative of slope displacement rates. The messages can be used to initiate relevant action such as sending an engineer to inspect the site or controlling train access to the section of track. The field trial has demonstrated the capability of Slope ALARMS to provide real-time information that could be used by operators to make decisions on traffic safety.

Further information can be found in:

Dixon N, Smith A, Spriggs MP, Ridley A, Meldrum P and Haslam E (2015) Stability monitoring of a rail slope using acoustic emission. Proceedings of the Institution of Civil Engineers – Geotechnical Engineering 168 (5), 373-384. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/17487

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Flat Cliffs

On the Yorkshire coast, a community of approximately 30 houses is located on a landslide that moves periodically. The houses are not in danger of being destroyed but small movements of the landslide can cause the access road, water supply and sewage pipes to become distressed.

The landslide in glacial deposits has been instrumented by CH2M (previously Halcrow) with a range of traditional geotechnical instruments such as inclinometers and piezometers to help understand the geometry of the landslide and the factors that result in movements.

An active waveguide with Slope ALARMS sensor has been installed through the landslide and continuous monitoring of acoustic emission is taking place. Real-time messages are generated if slope movements occur. The rates of acoustic emission generated over time are being compared with measurements of deformation made using an adjacent inclinometer. A period of movement that occurred after the 2013/2014 winter revealed the shear surface to be at approximately 14 metres below ground level. This period of movement was also detected by the Slope ALARMS system.

Further information can be found in:

Dixon N, Moore R, Spriggs MP, Smith A, Meldrum P and Siddle R (2014) Performance of an acoustic emission monitoring system to detect subsurface ground movement at Flat Cliffs, North Yorkshire, UK. IAEG XII Congress, 2, 117-120, Turin. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/16096

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Scarborough

Cliff instability along the Scarborough coastline triggered Scarborough Borough Council to commission ground investigations, which were interpreted by CH2M; to facilitate stability analysis and inform on-going risk assessments. As part of a monitoring programme an array of instruments were installed across the cliffs, and an active waveguide was installed at Scarborough in November 2012.

A section of cliff behind the Scarborough Spa, South Bay, Scarborough, was identified to have marginal stability, and could potentially develop a first-time failure. This slope threatens a road and a historical building.

A conventional inclinometer adjacent to the active waveguides provides deformation measurements for comparison with the AE measurements. Monitoring to date has not detected ground movements.

Further information can be found in:

Smith A (2015) Quantification of slope deformation behaviour using acoustic emission monitoring. PhD Thesis, School of Civil and Building Engineering, Loughborough University, UK. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/18593

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Peace River

A landslide occurred during May 2013 that severely damaged a significant section of highway 744 in Peace River, Alberta, Canada (see figure below). This rotational slide was triggered by excessive rainfall. After the initial remediation attempt further movement has resulted in an additional drop of ground level by 2-3m in places.

Two active waveguides and associated Slope ALARMS sensors have been installed in another active landslide further up-slope of this recent major landslide. There is concern that a major event may occur at this location, which would cut the important highway. The installation is part of a collaborative monitoring program with Thurber Engineering and Queen’s University, Kingston, Canada.

The slope sits on the crest of the hill, and Heart River and Peace River lie down-slope on either side. The landslide has a history of annual movement, and stabilisation has been attempted through installation of a pile wall. The latest version of the Slope ALARMS sensors (MKII) was installed in this monitoring program. Continuous real-time monitoring of acoustic emission is taking place with text warning messages generated when slope movements occur. Comparisons with SAA continuous deformation measurements are being made.

Further information can be found in:

Smith A, Dixon N, Berg N, Take A and Proudfoot D (2014) Listening for Landslides: Method, Measurements and the Peace River Case Study. Geohazards 6. Ontario, 1-10. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/16113

 


Ripley

The Ripley landslide (British Columbia, Canada) is a small slow moving translational failure that is known to have been active since 1951. It poses a risk to the onsite infrastructure since both the Canadian National and Canadian Pacific rail tracks run adjacent to each other along the entire breadth of the landslide.

In response to this threat, an extensive suite of monitoring technology is now being applied that includes: monitoring using GPS stations and piezometers; linear fibre optic sensing; ShapeAccelArray (SAA); satellite based interferometry; and ground-based SAR and LiDAR.

An active waveguide and Slope ALARMS system was also installed at the site in November 2015.

 


Ruthlin

A landslide triggered by the period of wet weather in winter 2014 caused damage to a minor rural road near Ruthlin Mill, Wales. Surface drainage was constructed as part of the remediation effort and Monmouthshire County Council enlisted Parsons Brinckerhoff to perform a monitoring programme to inform on-going risk assessments for the site. As part of this monitoring programme two active waveguides were retrofitted inside existing standpipe casings in January 2015 to convert the periodically read instruments to real-time continuous deformation monitoring systems. The Slope ALARMS systems send SMS messages to Monmouthshire County Council and Parsons Brinckerhoff if movement occurs.

 


Duffryn

The wet weather in winter 2014 also triggered a landslide that caused damage to a rural road near Duffryn Cottages, Wales. As for Ruthlin, Monmouthshire County Council enlisted Parsons Brinckerhoff to perform a monitoring programme to inform on-going risk assessments for the site. As part of this monitoring programme an active waveguide was retrofitted inside an existing standpipe casing in January 2015 to convert the periodically read instrument to a real-time continuous deformation monitoring system. The Slope ALARMS system sends SMS messages to Monmouthshire County Council and Parsons Brinckerhoff if movement occurs.

 


Passo della Morte

At Passo della Morte in the Italian Eastern Alps a geomorphological survey has identified potential instability of the valley side slope that could result in a debris/rock avalanche, which would threaten the Tagliamento River. A nationally important road passes through a tunnel 130 m long behind the potentially unstable slope.

The stratum comprises a sequence of Limestone layers, dipping in the slope direction towards the river. Although currently there is no clear evidence of movement, the geological setting indicates a predisposition to instability that could involve a large landslide and extremely fast deformations can be foreseen.

To appraise the physical characteristics of the rock mass and to provide an early warning of instability, monitoring instrumentation has been installed and monitored since late 2010 by the Italian Research Institute for Hydro-Geological Hazard Protection. Extensometers, MEMS, TDR cables, a vertical inclinometer and a seismic station to monitor Limestone rock mass deformation generated micro-tremors. Slope ALARMS sensors have been installed on three steel waveguides that have been grouted in horizontal boreholes that penetrate the steeply dipping limestone layers.

In this application, deformation of the rock mass and grout surround to the waveguide generate acoustic emission that can be used to identify periods of slope deformation and indicate relative stability. Monitoring has been continuous since December 2010. The measured AE response is being compared with direct deformation measurements and detected micro-tremor trends. Initial results indicate a strong response of the acoustic sensors to rainfall events, increases in the phreatic surface in the rock mass and snow loading on the slope. No significant rock mass deformations have been detected at depth within the slope to date. It is planned to continue monitoring for the foreseeable future.

In addition to the above, two active waveguides (i.e. with gravel backfill surround to the steel tube) have been installed to monitor an active large landslide, which is located adjacent to the above rock slope. An in-place inclinometer is located adjacent to one of the waveguides and this enables direct comparison of performance. In addition, a local wireless network has been established for the three sensors in the rock mass at the Passo della Morte site to enable real-time messages to be generated if slope movements occur and acoustic emission trigger thresholds are exceeded.

Further information can be found in:

Dixon N, Codeglia D, Smith A, Fowmes G, Meldrum P and Haslam E (2015) An acoustic emission slope displacement rate sensor: Case studies. 9th International Symposium on Field Measurements in Geomechanics. Sydney, Australia (in press). At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/19021

Codeglia D, Dixon N, Fowmes GJ and Marcato G (2015) Strategies for rock slope failure early warning using acoustic emission monitoring. In IOP Conference Series: Earth and Environmental Science (Vol. 26, No. 1, p. 012028). IOP Publishing. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/19402

Dixon N, Spriggs MP, Marcato G and Pasuto A (2012) Landslide hazard evaluation by means of several monitoring techniques, including an acoustic emission sensor. Proceedings of the 11th International and 2nd North American Symposium on Landslides and Engineered Slopes. Landslides and Engineered Slopes: Protecting Society through Improved Understanding. CRC Press, 2, 1405-1411. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/10238

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Grossreifling

The Grossreifling trial site (Styria, Austria) consists of a steep conglomerate slope that threatens a section of railway line. The trial site was set up with project partners INGLAS in April 2014 as a complementary component of the Sentinel for Alpine Railway Traffic (SART) project, which is jointly funded by the Austrian Railway (OeBB) and the Austrian Research Council. The system takes advantage of a dual approach: early warning of imminent rockfalls, given by acoustic emission generated within the rock slope, and detection of rock fall occurrence, provided by a light static catch fence instrumented with movement sensors that give information about the debris that detaches from the slope and impacts the fence. The AE monitoring system comprises three waveguides grouted into the rock slope, two horizontal and one vertical. A strong response to ground water flow linked to rainfall has been established. The critical time for slope stability is in the spring following snow melt, however, there were no slope failures in spring 2015 due to the mild winter. Monitoring will continue through spring 2016.

Further information can be found in:

Codeglia D, Dixon N, Fowmes GJ and Marcato G (2015) Strategies for rock slope failure early warning using acoustic emission monitoring. In IOP Conference Series: Earth and Environmental Science (Vol. 26, No. 1, p. 012028). IOP Publishing. At: https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/19402

 


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