Early warning of geotechnical limit states: Slope ALARMS (a slope displacement rate sensor)

Size: px

Start display at page:

Download "Early warning of geotechnical limit states: Slope ALARMS (a slope displacement rate sensor)"

Neal Augustus Lloyd
6 years ago
Views:

1 Early warning of geotechnical limit states: Slope ALARMS (a slope displacement rate sensor) Professor Neil Dixon School of Civil and Building Engineering Loughborough University

2 Outline of presentation Monitoring geotechnical limit states Known unknowns What, where and when? Continuous, real-time and robust Trigger levels and who to share the data with Slope ALARMS: Displacement rate sensor Acoustic emission (AE) monitoring Case studies, including comparisons with traditional techniques Summary: The benefits

3 Specification for an early warning system Sufficient warning to enable action to be taken (implement emergency plan) No false alarms (undermines confidence) Provide information on rates and magnitude of movement (assess likelihood and significance) Identify mode of failure (assess significance and inform action)

4 Geotechnical limit states Ultimate limit states Complete loss of stability (e.g. shear failure) First-time failures fast moving & large displacements Reactivated slow moving & often (but not always) small displacements Serviceability limit states Loss of function (e.g. track alignment, debris on track) Both are a function of deformations (i.e. magnitude and distribution)

5 How difficult can it be? Can complex mechanisms be identified by a simple trigger level from a measured value? Complex relationships and processes: Site specific behaviour such as weather, vegetation, geometry, material, history, engineering interventions, time Causes: Rainfall pore water pressures & moisture content leading to reduced strength (possibly increased destabilising forces), and through shearing processes these result in.. Effects: Deformations (when, where, how fast, magnitude)? Time frame: Rate of stability decrease from initiation to collapse? It is not easy and there is no magic wand

6 What, where and when? Known unknowns Every instrument on a project should be selected and placed to assist with answering a specific question, if there is no question then their should be no instrumentation Dunnicliff (1988) Do you know what you don t know (i.e. what question do you need to answer)?

7 Deep shear surface

8 Shallow shear surface

9 Wash out/fall

10 Wash out

11 Must haves Reliable measurements (robust with no false alarms) Low/little maintenance High confidence levels Tried and tested ( but how do you achieve this for new ideas?) Measurements that are: Relevant, accurate, reliable, affordable, accessible Continuous and real-time? Verification Other instruments, cameras, site visit?

12 Trigger levels so what? Alarms (information) who should it be sent to? If interpretation is needed, send to expert Geotechnical Engineer to turn the data into useful information! If a clear/simple response can be made (no interpretation required), send to central control (but how to minimise/deal with false alarms?) Simple trigger levels must be reviewed and revised over time based on experience (engineering judgement needed) What does real-time monitoring mean? Arguably, real-time requires processing on the instrument so output (trigger) can be actioned immediately

13 Slope ALARMS: AE monitoring technique AE are relatively high-frequency stress waves which propagate through materials surrounding the generation source (10s of khz) The AE monitoring technique is well established in other industries In soil, AE is generated by inter-particle friction and hence the detection of AE is an indication of deformation Research over a 50 year period has shown that AE can be used to detect deforming soil bodies (slopes)

14 Monitoring approach: Active waveguide

15 Active waveguide Assessment of Amplitude (V) Transducer Landslides using Acoustic Threshold level (V) ALARMS sensor node WSN Real-time Monitoring Time Ring-down counts (RDC) If RDC > Trigger value, send warning Systems GSM ALARMS communication node WSN A slope displacement rate sensor

Slope ALARMS Collaboration between Loughborough University and British Geological Survey Unitary battery device Piezoelectric transducer detects AE Sensor measures AE ring-down counts

16 Slope ALARMS Collaboration between Loughborough University and British Geological Survey Unitary battery device Piezoelectric transducer detects AE Sensor measures AE ring-down counts (RDC) and logs number for a set time period (e.g. 15, 30, 60 minutes) Automatic SMS messages sent when thresholds are exceeded Trials are underway at sites in UK, Austria, Canada and Italy

17 UK trial sites BIONICS, Newcastle Spa, Scarborough Hollin Hill Flat Cliffs, Filey Ruthlin/Dyffryn Players Crescent

18 Hollin Hill trial

19 Instrumentation Source: Smith A, Dixon N, Meldrum P & Haslam E (2014) Inclinometer casings retrofitted with acoustic real-time monitoring systems. Ground Engineering, October Issue.

20 Cumulative AE: Cluster 2

21 Cumulative AE RDC

22 Typical AE response to reactivated slope movements (Hollin Hill) Peak velocity Source: Dixon N, Spriggs MP, Smith A, Meldrum P & Haslam E (2014) Quantification After Dixon of et al. (2014) reactivated landslide behaviour using acoustic emission monitoring. Landslides, DOI: /s z

23 Quantification of velocity and displacement from AE (Hollin Hill) Cumulative displacement derived from AE Source: Dixon N, Spriggs MP, Smith A, Meldrum P & Haslam E (2014) Quantification of reactivated landslide behaviour using acoustic emission monitoring. Landslides, DOI: /s z

Hollin Hill landslide, UK: Comparison of continuous AE and SAA measurements Source: Smith A, Dixon N, Meldrum P, Haslam E & Chambers J (2014) Acoustic emission

24 Hollin Hill landslide, UK: Comparison of continuous AE and SAA measurements Source: Smith A, Dixon N, Meldrum P, Haslam E & Chambers J (2014) Acoustic emission monitoring of a soil slope: Comparisons with continuous deformation measurements. Géotechnique Letters 4(4), OPEN ACCESS DOI: /geolett

25 Retrofitted inclinometer casing

26 Retrofitted inclinometer waveguide vs SAA Source: Smith A, Dixon N, Meldrum P & Haslam E (2014) Inclinometer casings retrofitted with acoustic real-time monitoring systems. Ground Engineering, October Issue.

27 Monmouthshire: Retrofitted standpipes

28 Players Crescent rail cutting

29 AE and inclinometers: Installed Feb Source: Dixon N, Smith A, Spriggs MP, Ridley A, Meldrum P & Haslam E (2014) Stability monitoring of a rail slope using acoustic emission (Accepted for publication).

30 Displacements and sensors

31 Slope deformations (April/May 2012) SAA - Geotechnical Observations Ltd

32 Displacement (mm), Hourly rainfall/10 (mm) RDC rate (per hour) Displacement (mm), Hourly rainfall/10 (mm) Cumulative RDC Cumulative AE vs deformations Players Crescent - Deformation event - 19/04/2012 to 05/05/2012, 1.2mm over 2 weeks (~ 0.09mm/day), SAA and AEWG /03/ :02 27/03/ :02 06/04/ :02 16/04/ :02 26/04/ :02 06/05/ :02 Time (days) Cumulative slope displacement (mm) Hurn hourly rainfall (mm) Cumulative RDC Players Crescent - Deformation event - 19/04/2012 to 05/05/2012, 1.2mm over 2 weeks (~ 0.09mm/day), SAA and AEWG /03/ :02 27/03/ :02 06/04/ :02 16/04/ :02 26/04/ :02 06/05/ :02 Time (days) Cumulative slope displacement (mm) RDC rate (per hour)

33 Events sequence for movements at bottom and top of slip

34 Triggering rainfall event

35 International Trial Sites Peace River, Canada Grossreifling, Austria Ripley, Canada Passo della Morte, Italy

36 Passo della Morte, Italian Alps Boreholes Instruments installed from tunnel

37 AEWG2 event, November 2011

38 AEWG2 event, November 2011 RDC response to rainfall

39 AE response to changing water level

40 Trial for the Austrian Railways SART Sentinel for Alpine Rail Traffic In partnership with German Company INGLAS Combined system of monitored debris catch fence for immediate warning of threat to line and Slope ALARMS for early warning for inspection/ remedial action System linked to OeBB Operation Control Centre Ongoing extended trial in progress

41 Weak conglomerate Instrumented fence Vertical waveguide Horizontal waveguides

2014 16:07:23 SW1 1 13 3,62 11 0-74 46 62 31 31 0 1.031 31.05.

42 Event example Timestamp Type Domain Device Voltage [V] Temp. [ C] Pull Out max. dyn. accelertion [1/1000 g] static acceleration [1/1000 g] RSSI [dbm] Status Ax Ay Az Tx Ty Tz :07:23 SW , :08:19 SW , :13:47 SW , :14:18 SW ,

43 Slope ALARMS: Benefits AE monitoring provides an early warning of slope failure Information on slope displacement rates is instantaneous, continuous and in real-time AE rates are proportional to slope displacement rates over many orders of magnitude AE rates can detect very slow displacement rates and continue to operate at large displacements (>>500mm) Inclinometer casings can be converted into continuous and real-time displacement rate sensors

44 Acknowledgements Funders: EPSRC, FFG and stakeholders Partners: Sensor electronics and operation developed with British Geological Survey Collaborators: Geotechnical Observations Ltd; INGLAS, Germany; CNR-IRPI, Italy; Queen s University, Canada; University of Alberta, Canada, Newcastle University; CH2M; Thurber Engineering; Parsons Brinckerhoff Stakeholders: Network Rail, OeBB (Austrian Railway),, Alberta Transportation, Scarborough Borough Council, Monmouthshire County Council, Canadian Pacific Railway, Canadian National Railway

An acoustic emission slope displacement rate sensor case studies

FMGM 2015 PM Dight (ed.) 2015 Australian Centre for Geomechanics, Perth, ISBN 978-0-9924810-2-5 https://papers.acg.uwa.edu.au/p/1508_54_dixon/ An acoustic emission slope displacement rate sensor case studies