VISUALIZATION OF GEOINFORMATION IN DAM DEFORMATION MONITORING

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1 VISUALIZATION OF GEOINFORMATION IN DAM DEFORMATION MONITORING Gergana Antova Abstract This paper introduces laser scanning as an instrument which may be applicable to the field of dam deformation monitoring. The advantages of this technique for modeling and providing a much more valid representation of the actual surface shape are represented. An opportunity for visualization of dam deformation processes based on periodically determined geodetic measurements is discussed. A method for dam deformation investigation, based on the deformations-theory and on the finite elements method, is proposed. The main priorities of using such geodetic determinations in comparison with the mass applied in the practice coordinate differences are shown. The practical application of the method for a real object Ognianovo dam is shown. Different ways of visualization of geoinformation describing deformation process are shown. Assistant professor Gergana Antova University of Architecture, Civil Engineering and Geodesy Bulgaria, Sofia, bul. Hristo Smirnenski 1 Tel.: (439), fax: , antova_fgs@uacg.bg Keywords: dam deformation monitoring, geometrical modeling, 3D laser scanners ITRODUCTION Monitoring the structural behavior of large dams has always been a topic of great importance, due to the impact these structures have on the whole landmark where they are built up. In particular in the last two decades the evolution of computing techniques has introduced the possibility of very accurate mathematical modeling of static and dynamic problems concerning dams. Confirmative practice in Bulgaria is to determine displacements in dam construction by geodetic methods that measure horizontal displacements and vertical subsidence. Analyzing the results consists of composing diagrams of displacements in the shape of d=f(t), where displacement d is presented as a function of time T. However, it is interesting for us to determine deformations and their presentation as function of space and time. This will allow us analyze more precisely deformation state of the dam and better visualize received geoinformation. That s why it is more advisable to determine and analyze components of deformation [1], which gives more information than coordinate changes. Their visualization gives more detailed presentation of deformation process in the whole body of the dam, not only in several discrete points of it. Thus, the role of deformation monitoring surveys becomes much broader than just the conventional determination of the geometrical status of the deformable object. CALCULATION OF DEFORMATION COMPONENTS Finite Element Method is used as a base of calculations. Well known formula from the deformation theory [] gives a connection between components of the symmetric tensor of deformation and linear deformation in one direction in a deformable body. A possible solution to the established problem could be found via plane version of the relation: cos e cos e cos e cos cos cos cos cos cos, (1) xx yy zz xy xz zy namely cos e cos e cos cos, () xx yy xy

2 where is a relative linear deformation of a segment : 3 rd INTERNATIONAL CONFERENCE ON CARTOGRAPHY AND GIS o L o L L L, (3) L L o and L are the lengths of segment for different measuring moments L o initial length of segment ; L actual length of segment ; e xx, e yy, xy, are the components of the symmetric tensor of deformation, where e xx, e yy - are relative linear deformations; xy - is relative angular deformations; is direction angles of the segment according to a orthogonal coordinate system axes Oxyz. Area and angle deformations as well as principle axes of deformations related to the center of gravity of each finite element are calculated. As it can be observed, in this case the unknown quantities are three. To define their simple values it is necessary to have disposal of relative linear deformations of three segments. That s the reason for triangular shape of finite elements. DESCRIPTION OF THE OBJECT Ognianovo earthen dam is situated at 40 kilometers eastern from Sofia. It is built up in 80 featuring 600 m of length and 45 m of height in its highest part. Geodetic monitoring system includes 15 control points (BHT), 5 benchmarks (HP), 6 ground benchmarks and 0 piezometers, situated on the dam crest and on 3 berms two on the downstream surface and one on the upstream surface. Figure 1. In the nearby of the dam a geodetic network is established during the dam construction. It consists of 8 control points and 16 leveling control points. Local coordinate frame is defined with axis Y in the crest direction and axis X perpendicular to it and positive in downstream direction.

3 Dam deformation measurements are realized in October 1991, May 199, November 1994, March 1997, May 1999 and September 000. Horizontal displacements of the control points on the crest according to direction ОВС1-ОВС are measured. Heights of all leveling points are determined by precise leveling. VISUALIZATION OF GEOINFORMATION From geodetic measurements Vertical subsides on downstream dam surface determined by observations in October 1991 and May Two types of visualization are presented with contours and colored. Figure. Vertical subsides on downstream surface visualization with contours Figure 3. Vertical subsides on downstream surface - visualization in color From calculated deformation parameters The elements of deformation tensor via linear deformations of segments are calculated using own software. As we have coordinate measurements only in 1 points on the crest and first berm upstream, we can calculate deformation parameters for this part of the dam forming 10 triangle finite elements as it s shown on Fig. 4. Obtained results from applied method for period October May 1999 are shown in Table 1. Maps of deformations visualize relative linear deformations, angle deformations and principle axes of deformations.

4 Figure 4. Finite elements on the downstream dam surface with principle axes of deformations Table 1. Components of deformation in plane XY Relative deformations Principle axes of deformations Finite Area element e xx e yy xy deformation Direction Angle of Emax Emin Emax, [*E-04] [*E-04] [*E-04] [*E-04] [*E-04] [*E-04] [g]. 1*3* *3* *3* *106* *106* *106* *106* *11* *11* *11* Figure 5. Map of relative linear deformations Figure 6. Map of relative angular deformations

5 3D LASER SCANNING FOR DAM DEFORMATION MONITOROING 3 rd INTERNATIONAL CONFERENCE ON CARTOGRAPHY AND GIS Now imagine not 10 but finite elements describing dam surface. Yes, it is possible by using 3D laser scanning systems that capture millions of points per second. The dam of Cancano Lake described in [1] Geometric Modeling of a Large Dam by Terrestrial Laser Scanning by Alba, M., Giussani, A., Roncoroni, F., Scaioni, M., Valgoi, P., presents an arc gravity structure featuring 136 m of height and 381 m of length at the crest. In Fig. 7 some color maps showing deformations on the portion of the dam scanned from station 8000 according to different comparisons are shown. The evaluated deformations in the middle point of the dam crest correspond to values measured by total station. Moreover, surface deformations in the remaining portion of the downstream face are according to the expected structural behavior of the dam. Figure 7. Maps of deformations evaluated by comparing different kinds of surfaces in Oct 005 and May mesh from (Oct 005) vs resampled point-cloud (May 006);. polynomial surface (Oct 005) vs resampled pointcloud (May 006); CONCLUSION Visualization of geoinformation describing dam deformation processes depends of the type of geodetic measurements. Very often changes in heights of target points on the dam surface, which are results of precise leveling, give information about vertical displacements of the dam. Suitable way of presentation of that geoinformation is surface view with contours and colored which gives more detailed presentation of deformation process in the whole body of the dam, not only in several discrete points of it. Dam deformation method described and applied above determines and analyzes components of deformation, which gives more information than coordinate changes. Because of the type of geodetic measurements, deformation analysis can be applied only in that part of the dam situated between crest and first berm. More representative results could be received from geodetic measurements which ensure 3D coordinates of the whole dam surface. That will provide as with data for entire geometrical modeling and better visualization of the deformation surface and the body of the dam. Advantages of 3D laser scaning over conventional geodetic methods for gathering spatial data an visualization are shown below: Fast data acquisition (eg. 3 days for TLS and days for geodetic network establishement and measurements) and high quality of gathered data would improve the study of the statical behaviour of large dams. Data derived from laser scanning are very accurate and dense, so that they could be used for even more refined analysis. That techniques provides geometric data for finite-element modelling (FEM) of the structure by spatial filtering of the original point cloud, obtaining a regularized point ensity along X, Y and Z axes. Different models could be produced, according to a step of 0, 50, 100 and 00 cm in all directions. Different data sets would allow the selection of the most suitable geometric model for mathematical modelling purposes.

6 Reference: [1] Antova G., Dam Deformation investigation Based On Periodically Determined Spatial Chord Length, SGEM, Albena, Bg, 005 [] Varbanov Hr., Tepawicharov A., Ganev T., Applied Theory Of Elasticity, Sofia, 199 [3] Alba, M., Giussani, A., Roncoroni, F., Scaioni, M., Valgoi, P., 006. Geometric Modelling of a Large Dam by Terrestrial Laser Scanning. In Proc. of FIG Mondial Congress, Munich, Germany, Oct. 8-13, pp. 15, unpaginated CDROM. Biography notes Gergana Boyanova Antova is an assistant professor at the Department of Surveying and Geoinformatics, Faculty of Geodesy, University of Architecture, Civil Engineering and Geodesy, Sofia, Bulgaria since 001, where she lectures in basic and advanced courses in surveying, mathematical post processing of geodetic measurements, CAD systems and Geoinformatics. She studied Geodesy and achieved her MSc. degree in 000 in the same university. Her research interests and fields of publication are based on New technologies for dam deformation monitoring.