LANDSLIDE MONITORING SYSTEMS & TECHNIQUES

MANEEB MASOODM.Tech.Part-1(15152010)

Introduction•Landslides are downslope movements of

rock, debris or earth under the influence of gravity.

•Landslides are one of the most significant hazards in terms of socio-economic costs, threatening infrastructures and human settlements.

•The monitoring of their surface displacement is thus crucial for the prevention and forecast of landslides.

Systems and Techniques for Landslide Monitoring

•1. Remote sensing or satellite techniques with space-derived information.

•2. Photogrammetric techniques •3. Ground-based conventional surveying

techniques•4. GPS techniques•5. Geotechnical techniques

Remote sensing techniques•SAR(Synthetic Aperture Radar) Imagery•InSAR(Interferometric Synthetic Aperture

Radar) techniquesFor landslides,

Ground based;Satellite based.

• RADAR (Radio Detection and Ranging)Satellite sends a pulse of electromagnetic energy into spacethat reflects upon encountering the Earth surface.(A radar transmits radio waves or microwaves that reflect from any object in their path. A receive radar, which is typically the same system as the transmit radar, receives and proesses these reflected waves to determine properties of the objects)

• SAR (Synthetic Aperture RADAR)Larger antenna = better resolution -> SAR uses the spacecraftmotion to simulate an extremely long antenna.

• InterferometricDifference 2 phase images of the same area at different times to detect ground motion = interferogram.Combine many interferograms to produce amean velocity map in which the color shows the speed at which the ground is moving.InSAR (Interferometric Synthetic Aperture RADAR)

Berkeley slow moving landslides InSAR

InSAR at the scale of country

Photogrammetric techniques forlandslide monitoring

•The interpretation of aerial photography has proven to be an effective technique for recognizing and delineating landslides.

•It is an effective technique for recognizing and delineating 3D overview of the terrain from which the interrelations of photography, drainage, surface cover, geology materials, and human activities on the landscape can be viewed and evaluated.

Ground-based conventional surveying techniques for landslide monitoring

•Triangulation•Levelling•Monitoring by Total Stations

Using Global Positioning System techniques in landslide monitoring

• GPS provides specially coded satellite signals that can be processed with a GPS receiver, enabling the receiver to compute position, velocity and time.

• A minimum of four GPS satellite signals are required to compute positions in three dimensions and the time offset in the receiver clock.

• Accuracy and precision of data increases with more satellites.

GPS TrilaterationWith signals from two satellites, the receiver can narrow down its location to just two points on the earths surface.Were the two circles intersect.

GPS Trilateration--cont.• Knowing its distance from

three satellites, the receiver can determine its location because there is only two possible combinations and one of them is out in space.

• In this example, the receiver is located at b.

• The more satellite that are used, the greater the potential accuracy of the position location.

GPS Techniques(a)fast-static(FS)(b)real time kinematics(RTK)

Special considerations for monitoring• The selected targets must reflect the mean

behaviour of the surrounding area.• Tree canopy, buildings and other obstacles that

could restrict the reception of the satellite signalshould be avoided.

• To mark the station points, it is advisable to use sturdy stations.

• It is convenient to include within the control network several fixed points outside the landslide area.

• To strengthen the results, it will also be helpful to use different methods and repeat the observations.

Geotechnical techniques for landslidemonitoring

•Geotechnical sensors are used extensively in themonitoring of structures.

•The main geotechnical sensors used for deformation monitoring include; extensometers, inclinometers, piezometers, strain meters, pressure cells, geophones, tilt meters and crack meters.

•InclinometersThey are instruments installed in

boreholes drilled within the landslide mass.

They measure the curvature of initially straight boreholes, thus detecting any change in inclination of the borehole casing.

• ExtensometersMeasure the axial displacement between a

number of reference points in the same measurements axis. They can be installed within a borehole or on the slope surface.

The wire extensometer is widely used typically measuring baselines of up to 80 m in length with a accuracy of ± 0.3 mm per 30 m.

The actual accuracy depends on the temperature corrections and on the quality of the installation of the extensometer.

Maintaining a constant tension throughout the use of the wire extensometer is very important.

•PiezometersMany landslides are triggered by slope

saturationfollowing heavy rainfall.

Measurement of pore water pressures and piezometric levels form an important part of slope stability analysis.

Threshold levels can be defined to provide early warning of conditions that may lead to catastrophic failure.

•GeophonesThey are devices that can measure

vibration associated with movement.They can detect landslides on the basis of

frequency composition, amplitude, and duration of the vibration signal.

References• Using Global Positioning System techniquesin landslide monitoring

Josep A. Gili a,b,*, Jordi Corominas a, Joan Rius a Department of Geotechnical Engineering and Geosciences, Technical University of Catalonia, Jordi Girona 1–3,Edifici D-2, 08034 Barcelona, Spainb Institute of Geomatics, Barcelona, SpainReceived 24 November 1998; accepted for publication 8 July 1999

• Traditional and Innovative Techniques for Landslide Monitoring:dissertation on design criteria Paolo Mazzanti1, Giorgio Pezzetti21NHAZCA S.r.l. & Department of Earth Sciences, Università di Roma “Sapienza”, Rome, Italy2FIELD S.r.l. Bergamo, Italy

• Landslide monitoring with InSARE. Chaussard, R. Burgmann,J. Cohen-Waeber, B. Delbridge (University of California Berkeley)

• Landslide deformation monitoring with ALOS/PALSAR imagery: A D-InSAR geomorphological interpretation method Romy Schlögel ⁎, Cécile Doubre, Jean-Philippe Malet, Frédéric Masson Institut de Physique du Globe de Strasbourg, CNRS UMR 7516, Université de Strasbourg/EOST, 5 rue Descartes, 67084 Strasbourg, Cedex, France

• Landslide monitoring by combining of CR-InSAR and GPS techniquesWu Zhu a,c,⇑, Qin Zhang a,b, XiaoLi Ding c, Chaoying Zhao a,b, Chengsheng Yang a,b,Feifei Qu a, Wei Qu a,ba College of Geology Engineering and Geomatics, Chang’an University, No. 126 Yanta Road, Xi’an 710054, China. bKey Laboratory of Western China’s Mineral Resources and Geological Engineering, Ministry of Education, No. 126 Yanta Road, Xi’an 710054, Chinac Department of Land Surveying and Geo-Informatics, Hong Kong Polytechnic University, Hong Kong, ChinaReceived 19 November 2012; received in revised form 21 November 2013; accepted 3 December 2013Available online 10 December 2013