Integrated optimization of landslide alert systems

The use of differential Synthetic Aperture Radar Interferometry (dInSAR) for the detection and monitoring of earth surface processes is meanwhile an established method. However, this approach has only success if the observed area fulfils specific requests, like sufficient backscattering, flat slope gradients or very slow growth of vegetation. In this European Union funded project OASYS -integrated optimisation of landslide alert systems plays the early identification of endangered areas the main important role. For the recognition of surface movements we have decided to investigate the capability of dInSAR. The approach consists of several levels of SAR data processing. In the beginning of the processing levels we use the recorded data of the European Remote Sensing (ERS) satellites, flown in the ERS1/2 tandem mission for the determination of a Digital Elevation Model (DEM) of the area of investigation. This DEM serves on the one hand as a necessary processing level for the further SAR processing and on the other hand as an important data source for the GIS in the alert system, e.g. for the derivation of slope parameters. The further processing levels are based on the 3-pass interferometry approach using one or more additional ERS 1 and 2 radar scenes in relation to the ERS1/2-tandem data set for the final interferogram calculation. Within the framework of this project five test sites in China, Greece, Germany, Hungary and Rumania were investigated and their results concerning the detection of landslides and possible earth surface movements were presented.

The results of OASYS give an increase of competence in the conception and evaluation of monitoring systems for geodynamic processes. The knowledge, which was gained during the project, can be used for similar tasks, so OASYS serves as a reference project for monitoring of landslides.

Remote sensing technology embedded in a GIS database are used as a complementary tool for landslide hazard studies. This method offers an independent and complementary research approach. Using Earth observation data it is possible to detect traces of past and even recent mass movements, which might be sources for future landslides. LANDSAT ETM, SRTM, ERS and ENVISAT ASAR imageries and aerial photographs serve as base in a GIS to create maps as contribution to an "Landslide Hazard Information System" in order to perform user-defined computations of hazard maps. The detailed lineament analysis based on LANDSAT ETM and radar imageries contributes to an improved knowledge of the tectonic setting in the different investigation areas and of potential take-off domains.

The Laboratory of Geodesy and Geomatics has a deep involvement in monitoring of deformation of technical works and ground movements due to landslides. Numerous research projects help the academic and technical staff to improve and further develop the teaching items and procedures in this very important field. The staff of the Laboratory is responsible for teaching the course Engineering Surveying in the Department of Civil Engineering (8th semester). Improving the educational material and procedures on landslide monitoring contributes to higher quality of education for students (and staff). The participation of the Laboratory in OASYS project was of great benefit in this sense resulting into the preparation of teaching material (texts and presentations) and the re-organization of the course's structure. All this material could also be of benefit for other similar institutions and professionals.

In civil engineering piezo-electric accelerometers are successfully used for sensitive measurements of the structures response to dynamic seismic loads. Static inclinometers based on mass-spring technology enable the high precision detection of changes in its inclination. The transfer functions of the sensors are well known and there exists long-time experience concerning the adaptation to buildings. There exists very poor experience adapting these sensors directly to the soil to observe soil-mechanic events. Especially the difficult environment (adaptation problems in loose material) and the significant detection of extreme slow rates of motion represent high challenges. The instrumentation part of OASYS provides the opportunity to investigate the potential of the sensors in this non-standard scenario. With regard to further research activities (and other possible non-standard applications) the main goals are to get practical experiences with the sensors integration and referencing within the instrumentation network, to study its long-term characteristics and disturbance influences and to handle the expected enormous amount of collected data. The realization of these tasks requires the sensors integration into geotechnical models and the investigation of its properties using parametric and non-parametric calibration methods. It is also planned to develop special filter strategies for time-series with very bad signal-noise ratios and establish an event-based data logging.

Georobot is an innovation of the traditional surveying instruments and methods. A main frame of the landslides monitoring software system based on Georobot is designed. A special method which can effectively improve the monitoring precision of the system is applied in the software data processing. The whole Georobot landslides monitoring system is consist of base station (Georobot station), reference points, target points, computer and software. The communication between Georobot and computer is by radio or cable interfaced via GeoCOM command. The aim of the software is focusing on: Automatic measuring according to measurement schedule, Artificial intellectual function to deal with bad environment, Special data processing method to realize high precision, Manipulation of huge quantity of raw measurements, Rich format of out put data, Auto-alarming for danger, Friend interface for easy operation. The software done in VB environment mainly comprises the following functional modules: project managing, system initializing, learning measure, data querying, data processing and results outputting. The Georobot landslides monitoring system has several advantages, such as, high efficiency, high automation, real-time, high precision etc.

Geodesy offers a variety of tools capable of being used for instrumenting a slope for purposes of monitoring its stability. The tools can be employed at various stages of the monitoring process, called multi scale observation process. During the initial stages where bigger regions are to be monitored GPS, InSAR, and Airbornelaser scanning may be used. GPS, Total stations and Terrestrial laser scanning become useful at an intermediary stage for smaller zones. The ultimate monitoring phase would require automatic, continuous, and frequent measurement tools, where continuous GPS and motorized total stations may be employed.

Multidisciplinary projects give the opportunity to build up a European network of knowledge on a specific subject. For OASYS, a network consisting of 12 partners was established, which broadens the scientific horizon of all of them. This network enhanced the knowledge concerning e.g. deformation measurements, sensors, and knowledge-based systems, geodynamic processes. This network of experts can lead to fruitful cooperations for further projects and for the exchange of PhD students.

During the stage of organizing the monitoring procedures to be used at the 'Prinotopa' Greek test site, a survey was made about the use of different (geodetic) sensors. The sensors under investigation were mainly the Global Positioning System, GPS, Total Stations and Robotic (motorized) Total Stations, as well as classical geodetic measurement techniques (geodetic levelling). Their adequacy was examined both according to the accuracy of each method and, also, the suitability of each method to be included into an automated alert system. As a result, report and guidelines have been prepared.

We have developed with Geodev company a Movement Monitoring System (MMS) includes GPS receiver and Laser distance meter, we will applied this system together with Georobot Monitoring System for Landslide Monitoring. Now we have made some tests in university campus, and will develop correspondence software.

One of the most important fields of activity of the Laboratory of Geodesy and Geomatics, Aristotle University of Thessalonica, is Engineering Surveying. A major part of research and research projects is dedicated to the measurement, monitoring, evaluation, estimation and presentation of possible deformations of structures (buildings, bridges, dams etc.) and ground movements that are caused either by landslides (as in the case of the OASYS project) or geotectonic activity. In order to support the abilities of the Laboratory in this field, a robotic Total Station was used for the measurement of the control network at the Greek test site "Prinotopa" and special software was designed and applied for the collection, statistical evaluation, and adjustment of observations, deformation estimation and preparation of relevant databases. The SYSDeform software was developed by a PhD student with the support of the academic staff of the Laboratory. This software has been used for OASYS computations and is now at beta-testing procedures. It has different modules (measurement, adjustment of geodetic networks, deformation of structures, tunnels and ground etc.).

GEODATA has developed together with the TU Wien a multi sensor system as an advanced evaluation tool for landslide monitoring. It consists of 1 piezometer, 1 inclinometer, 1surface extensometer, 3 tilt meters and 6 accelerometers. For this multi sensor system an appropriate installation location has been found in the opencast mine Hambach/Cologne. The object of the accelerometer data analysis was to find a possible relation between slope deformation processes and accelerometer signals in time and quantity (amplitude, frequency, phase, signal structure)

Processing of data acquired from different measurement techniques at the Greek test site "Prinotopa" was done following the appropriate computation and adjustment methodologies. Then, the resulting data (movements, deformation, etc.) from the geodetic monitoring network implemented at Prinotopa site (consisting of 20 monitoring points and 3 control points, GPS campaigns, motorized Total Station campaigns) were obtained, evaluated and reported. Also, the resulting data from the geotechnical monitoring network (consisting of 43 inclinometers, 27 piezometers and a rain gauge) were obtained, evaluated and reported. All the above-mentioned data have been made available to the research partners in the project.

The Greek test site "Prinotopa" was selected for monitoring because of its importance to the Egnatia Odos S.A. as an end-user in this project. The monitoring network was designed on the basis of the available geological data. The geodetic monitoring network implemented at Prinotopa site consists of twenty (20) monitoring points and three (3)control points. Four (4) GPS campaigns have been carried out so far as well as six (6) motorized total station measurements. These measurements are to be used for the testing and validation of an automatic geodetic monitoring system. The geotechnical monitoring network consists of forty three (43) inclinometers, twenty seven (27) piezometers and a rain gauge that were gradually installed over the period 2002-2004. These are manually measured every 2 months. The results of monitoring are to be used in conjunction with the geodetic results in the integrated automatic monitoring system. All these data have been made available to the research partners in the project.

In practice, i.e. for tasks in land development and spatial planning, information on the landslide susceptibility is needed for large areas. Therefore the focus in OASYS was on the regional assessment of the landslide susceptibility. These premises in scale and level of detail required an assessment approach that is independent from detailed local data, like detailed terrain data or hydrological models. Therefore a statistical approach was applied, taking into account a variety of factors contributing to landslides that can be applied in small-scale investigations. In particular slopes where no information is available on past landslides should be assessed. The landslide susceptibility could be quantified by the derived probabilities. It was possible to identify those from the available factors, which have the highest relative importance as landslide indicators. The model therefore provides information about causative relations in the system of slope stability and instability in its spatial scope.

The deeper geochemical and sedimentological examination of the different deposits (loesses, palaeosols, clay and sand layers) which are built up the high banks can provide new informations to the question of landslide formation and collapsing. It may be hypothesized that the geochemical conditions and petrophysical properties of the sediments are changed by backwaters of ground- and pressure waters and their flow. So, for example the backwater of ground waters has an effect on the carbonate-cementation of the grains in the loess, it leaches the carbonates, besides this the flowing water take away the most fine particles, so it cause suffosion (solution) and leads to collapsing. Also the petrophysical properties (angle of friction, cohesion or value of consistency, porosity) and in this manner the durability or stability of the high banks can be also affected by the change of mineral composition (e.g. formation of clay minerals which have different water absorbing and swelling capacity) of the sediments during these processes and it can lead to formation of a sliding plane or a shear surface. Investigations have already been carried out that were made in order to disclose the sedimentological and geochemical conditions of loess-paleosol sequences in South-Hungary.

With regard to further research activities (and other possible non-standard applications) one goal is to get practical experiences with the sensors integration and referencing within the instrumentation network, to study its long-term characteristics and disturbance influences and to handle the expected enormous amount of collected data. So the new sensors and instruments give experience in data acquisition and processing of the data. The theoretical strategies considered for OASYS result in software developments, which can be used in further projects and in teaching.

The aim of these developments was to find such dynamic phenomena or signals, which can be used to forecast the impending landslide with a higher reliability than the static geodetic deformation measurements. The loess walls show no movements detectable by geodetic methods. For monitoring micro-deformation processes, since their sub-microscopic realm, dynamic measuring methods can be applied. Such kind of real-time systems give information about the evolution of the internal state of the slope and therefore a reliable event precursor could be obtained. The concept is the measurement and analysis of ambient vibrations on the loess wall to investigate the changes of the geotechnical parameters of the soil.

New results gained in projects should always be transferred to the students, so that they can profit from actual research topics. Multidisciplinary projects like OASYS are even more interesting to students; it helps them being more creative in their own actual and future work. So a knowledge transfer of innovative trends in measurement and evaluation techniques but also a transfer of practical experience takes place. In this case, the methodology, practical examples and results of the project are used in the courses on Engineering Geodesy at the Vienna University of Technology and technical University of Braunschweig.

In many cases it is for various reasons not possible to follow an ideal approach when dealing with (possible) landslides. Due to the many restrictions that may exist, observation concepts are implemented that cover only very limited aspects of the complex interactions determining the slope behaviour. The findings of the OASYS project will help us to apply a much better methodology by transferring these results and the related knowledge directly into projects. In addition, we will be able to provide better consulting services to our customers based on an integrated approach utilizing the findings of OASYS.

Based on the results of OASYS we will implement an information system for landslide monitoring projects. Currently, we are providing instrumentation and monitoring equipment/services. Results are published mainly in tabular and graphic formats. The findings of OASYS allow us to develop more comprehensive GIS based information systems providing additional information like aerial/ satellite images, geological and geotechnical information as well as warning and alerting features.

The full roving GPS observation strategy - which was developed for the investigation of antenna mean phase centre offsets using the observations of micro scale networks (1-10 m) - was generalized for the deformation investigation of local scale networks (1-2 km). Because this method estimates the mean antenna offsets referring to the mean elevation angel of the actual observations, it can be used to cancel the phase biases of the individual antennas. It proved to be an optimal strategy for those campaign receivers, which are not used continuously. The changes of the antenna characteristics can be recognized and cancelled during the deformation measurements. The method was successfully applied in the horizontal monitoring of the high loess wall on riverbanks.

The results of OASYS and especially the findings from instrumentation and monitoring at the test sites like Hambach will provide direct input in major improvements and further developments of innovative sensor systems. Thus, future users will have the benefit of better suitable and more reliable instruments.

Landslide Classification mainly based on the schemes of U.S A and Italy. %l1. The U.S.A scheme can be summarized as below: -Type of Movement: Falls, Topples, Slides (Rotational/Translational, Few Units/Many Units), Lateral Spreads, Flows, Complex -Type of Material: Bedrock: Rock fall, rock topple, rock slump, rock block slide/rock slide, rock spread, rock flow (deep creep), combination of two or more principal types of movement -Engineering Soils: Predominantly coarse: Debris fall, debris topple, debris slump, debris block slide/debris slide, debris spread, debris flow, soil creep, combination of two or more principal types of movement -Predominantly fine: Earth fall, earth topple, earth slump, earth block slide/earth slide, earth spread, earth flow, soil creep, combination of two or more principal types of movement 2.Italys scheme has been described by Dr.Alessandro Ghinoi 3.Below is proposed by Cui Zhengquan: 1.Landslides and its Results -Landslide Deposits(delQ); 2.Collapse and its Results -Collapse Deposits(colQ); 3.Slide and Collapse(Mixing type) and its Results -Slide-Collapse -Deposits(csQ); 4.Fall-slip and its Results -Fall-slip Deposits(fsQ)(a new concept); 5.Fall-down and its Results -Fall-down Deposits(fdQ) 6.Tipping-crash and its Results -Tipping-crash Deposits(tpQ)(a new concept); 7.Deformable Body or Deformable Realm ,include Creep(dfQ); 8.Slip-flow and its Deposits -Slip-flow Deposits(sfQ)(a new concept); 9.Debris-laden Flow and its Results -Debris-laden Flow Deposits(dlfQ). The OASYSs classification scheme to be produced by the combination of those three schemes as mentioned above.

Subsequent research projects at the Vienna University of Technology and Technical University of Braunschweig can benefit from: - the instruments and sensors used in the OASYS project - the new experience with the sensors - the increase in knowledge in the field of landslide monitoring gained in the project - the monitoring data collected during the project at the test sites - the contacts with international reasearch partners (networking)

Reliable and in time alarming of landslides requires the development of an alert system. In this project standard investigation and interpretation methods (i.e. observations with geodetic and geotechnical sensors, geometrical and geophysical slide-models etc.) shall be significantly improved using knowledge-based systems as new key technology. Originally coming from artificial intelligence, knowledge-based systems are suitable to combine hybrid sources of quantitative and qualitative expert knowledge using rule-based inference components. Automated decision processes can be established supporting the user to handle the often enormous amount of information in the right way. In geodetic and geotechnical applications the typical combination of incoming measurement data and its interpretation provides a very high potential for knowledge-based applications. The operational use is still at the beginning and offers a rich field for research activities. The main goals linked with this project can be focussed on: 1. Creation of methods and tools for geodetic and geotechnical knowledge acquisition. 2. Represen-tation and merging of complex knowledge in computer models. 3. Integration of knowledge-based systems in engineering processes.

The new results obtained from the project were built into the material used for teaching of students for environmental engineering and environmental sciences at the West-Hungarian University. Both new measuring techniques and evaluation methods are transferred to the students. In this way the students can profit directly from the newest research results.

The GIS technology is an attractive device to support landslide monitoring and makes possible to understand the interaction of the different processes. The results of geodetic deformation measurements are the attributes of different geometric elements. They can be used to investigate the recent landslide activity looking for the alarm signals of the potential risk. The geometric arrangement of the developed basic GIS system is a 8 km; 12 km central area covered by four topographic map segments (scale: 1:10 000) that are given in the national grid. This is the base layer of the system in raster data format, which allows the geometric interpretation of the different objects. Other involved maps were scanned, scaled and rotated to the same system using raster data format. The precision of the objects orientation is better than 1 cm.

A multidisciplinary project like OASYS gives a deep insight to various fields of knowledge and research, which broadens the scientific horizon of the partners. Dealing with the OASYS field of research, many new ideas and questions arise which are not part of the OASYS project and which should be investigated in new projects.

By means of the method can be checked if the high loess wall has any relation to a deeper geological formation, which may couple the landslide to e.g. tectonic movements. The second possible application of the method is the detection of gravity change due to vertical and horizontal displacement (redistribution) of topographic masses. Although this is a rather theoretical possibility because of the expected low deformation rate prior to a landslide event, the variation of water table monitored by gravity measurements may be an important indicator in the prediction of possible surface movements.

Livrables

Partager cette page

Télécharger