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  • 1. Proceedings of Indian Geotechnical Conference December 15-17, 2011, Kochi (Paper No. M-253) DEVELOPMENT OF SOIL SUITABILITY MAP FOR GEOTECHNICAL APPLICATIONS USING GIS APPROACHS.Sakunthala Devi, ME Student, Anna university- Chennai, sakugopiram@gmail.comV.K Stalin, Professor of Civil Engineering, Anna University-Chennai, staliniisc@yahoo.co.in.ABSTRACT: The preliminary geotechnical site investigation aims to develop a working site model that is used to analyzethe site and to plan site activities.GIS is a versatile tool that can be used to aid preliminary geotechnical site evaluations andit is time saving.The use of the GIS database allows the engineers to easily and rapidly manage large volumes of data whilealso being able to examine it in detail .Hence in this study the geotechnical database and soil suitability map were createdfor South Chennai.Various interpolation technique were used to create the spatial continuity and variability of the importantgeotechnical parameters and the database was created from available bore log data.These database and the thematic mapserves as a basic tool in effective planning and execution of the site investigation work by providing guidance on spatialcontinuity of geotechnical properties in the south Chennai.INTRODUCTION statistical techniques, geotechnical engineers can quantifyWith the introduction of GIS, missing spatial data & the degree of spatial variation of soil properties and obtaincorresponding attribute information could be generated. more meaningful estimates at unsampled locations andGIS systems are time saving, cost economical, useful for provide input to reliability analyses.Regression analysis is aStructural Engineers, Geotechnical Engineers, urban statistical tool for the investigation of relationshipsPlanners and even the local inhabitant for any future between variables. The uncertainty in the estimation of soildevelopmental activities in the area concerned. Many properties are described in terms of standard deviation,geotechnical database and suitability maps were created all coefficient of variation and confidence interval. Fromover the world. In model study [1] Geotechnical database statistical results, the mean, median and ranges of 95%for Bangkok city (GeSEP) was created to manage and confidence intervals for each property are established.interpret the soil data’s obtained from more than 20000 Those ranges can help structural and foundation engineersboreholes and GIS software GRASS 5.0 was used to during the process of foundation analysis.visualize soil profiles. The model study [2] involvesmultiple regression equation, chi-square test and k-nearestneighbour classification to create, Soil CharacteristicsPrediction Model (SCPM) for Coimbatore city and GIS wasused to manage the database and to develop thematic maps.In model study [3] by using the GIS tools in conjunctionwith the ACCESS database, GeoCovilha XXI database wascreated and the data of different tests were visualised.Model study [4] deals with the generation of thegeotechnical database using the program ArcView/GIS 9.0.for city of Mayagüez and this was used to identify areas ofliquefaction potential or seismic hazards..North Seageotechnical database was created from collectedgeotechnical reports in quadrant K and L North Sea usingGIS and statistical approach in model study [5]. In thiswork geotechnical database and various geotechnical mapswere created for South Chennai.METHODOLOGYThe flowchart used to create the database and themetic mapwas shown in Fig. 1.GIS is a specific information system Fig. 1 Flow chart for creating map and databaseapplied to geographical data and is mainly referred to assystem of hardware, software and procedures designed to Geotechnical Databasesupport the capture, management, manipulation, analysis, Paper maps are used traditionally as both storage andmodeling and displaying of spatially referenced data for display medium. They work well when the amount of datasolving complex planning and management problems.Using is small, the rate of data changing is slow but when the data 797
  • 2. S.Sakunthala Devi & V.K.Stalinset becomes larger, it is necessary to prepare several special maps to avoid confusion and to facilitate reading. In thatsituation, the traditional maps or plans show someshortcomings. Those problems can be avoided by GISwhich can handle essentially unlimited data and provide asecure and easily updated database to generate maps for anyspecialist use to extract useful information hidden inside alarge data collection, the data should be well organised..Meanwhile, databases show their flexibility. To managesubsurface data collected from borings, the geotechnicaldatabase management system was designed. Thegeotechnical information in this database is classified intoseveral tables. The database is implemented using aMicrosoft Access software package. The advantages oforganising geotechnical data into a relational database areto handle an enormous amount of data, to shareinformation, to update data quickly, to derive thematicmaps easily. Furthermore, incorporating geotechnicaldatabase with GIS and geostatistics packages can enable topredict the spatial variation of variables, to visualisegeological features or to locate the potentially hazardousareas. Those advantages help the engineers, designers andthe authorities to make the decisions effectively.Study Area Fig. 2 N-value map @ 8.5m depthThe study area was divided into two zones and the detailsare shown in Table 1. Ground Water Table Map for Various Zones of Study AreaTable 1 Study area details containing various zones The GWT map for the zone I and zone II were created by Topo to Raster interpolation technique. The GWT map for Zone Village the zone I & II were shown in Fig. 3.From the map it is I Kotturpuram,Adyar,Besant Nagar,Perungudi inferred that, for Zone I the GWT varies 0.6m to 4.4m and in Zone II the GWT varies 1 to 3.1m. II Egatur, Navalur, Keelambakam,Siruseri, Padur,ThoraipakkamRESULTS AND DISCUSSIONGround Water Table, Bearing Capacity of soil (Computedfrom ‘N’ value) maps were developed for the study areaand these maps are used in the design of geotechnicalstructures.Further the consideration were also given withrespect to statistical analysis of various geotechnicalparameter and the regression equation for variousdependent geotechnical parameter were developed from thebore log data. The geotechnical database was created usingaccess. The above sequence of work was discussedelaborately in the following sub section.Geotechnical Map for Various Zones in the Study Areaon Various Depths Using GIS The variations of geotechnical parameters (N-value, -value, WT, QU) with respect to depth for two differentzones were analyzed.N-value map for various zones of study areaThe N-value map for Zone I & Zone II were created byKriging and IDW method .The N-value maps at 8.5m depth Fig. 3 Ground Water Table map for zone I and Zone IIwas shown in Fig. 2. 798
  • 3. Development Of soil Suitability Map for Geotechnical Application Using GIS ApproachAngle of Internal Friction ( ) Map for Various Zones of primary key (project ID of project table) to foreign keyStudy Area (project ID of other table).Once database was organized,The value was computed from the N value using the necessary information can be derived in the form of reports,Teng’s relationship.By using IDW interpolation method, forms (shown in Fig. 6)the variation in at various depth were obtained. Thevalue map was given in Fig. 4. Fig. 5 Qu map for zone I and Zone II @ 10 m depthFig. 4 map @ 0.75 and 1.5 m depthQu map for various zones of study areaThe bearing capacity of the pile was calculated from theMeyerhof equation from the SPT N value. The dia of pile( ) was 0.6m , length was 10m and the embedded lengthwas 8.5m. The ultimate bearing capacity (Qu) wascalculated for Zone I and Zone II .The Qu maps for zone I& II were created by IDW interpolation technique and wereshown in Fig. 5. In zone I, the mean value of Qu was3420KN .In zone II, mean value of Qu was 3953KN.Geotechnical database using ACCESSFrom the available bore log data the geotechnical databasewas created for Chennai with the help of application calledMS access. The set of data were stored inside the databasenamed as Chennai database. This database consists ofvarious tables which contains information such as groundwater levels, SPT results, borelogs and laboratory testresults and this table were interconnected by linking Fig. 6 Form 1(area wise project work) 799
  • 4. S.Sakunthala Devi & V.K.StalinStatistical Analysis of Various Geotechnical Properties CONCLUSIONSStatistical techniques were used to quantify the degree of The study area composed of two different zones and thespatial variation. The statistical approach for N-value and base map was created. The best interpolation techniquevalue was discussed. Descriptive statistics include the available for creating N value map was Kriging which wasmean, median, standard deviation, maximum, minimum validated based on cross interpolation technique .From SPTvalue i.e.) the statistical parameters. N values, the angle of internal friction of a zone at differentRelationship between N and Other Geotechnical depths were computed based on correlation between N-Parameters value and for granular soil(After Peck , Hanson and The SPT N of soil is one of the most important parameter Thomburn).The allowable bearing capacity map at 10m forused for geotechnical analysis .It can be obtained from the two zones were computed based on the Meyerhofstandard penetration test.SPT test were quite expensive and equation for the developed N-value map. Using theon the other hand grain size distribution test, water content computed average SPT N-values, bearing capacity for 0.6mwere obtained at low cost. The relationship is established dia pile of 10m length was found out. The geotechnicalbetween SPT N and grain size distribution .Firstly the linear database named Chennai Database was created to manageequation was examined large quantity of available data .The statistical analysis of The linear relationship was given by SPT N and was developed to quantify the degree of SPT N =constant+c1gravel+c2CS+ c3 MS+c4 FS + c5 silt spatial variation of these soil properties. There statisticsWhere C1, C2, C3, C4 and C5 were coefficient of the were made. The uncertainties present were represented inindependent variables and statics were given in Table 2. terms of SD, coefficient of variance ant the coincidence interval of 95%.The relation between SPT N and otherTable 2 Regression statistics for linear relationship geotechnical parameters were developed with help of the Regression Statistics regression analysis .Both linear and quadratic relationship were established . The developed graphs and the database Multiple R 0.627765 can be used by civil engineers, geotechnical engineers and R Square 0.394089 geologists for planning, designing, investigation, analysis Adjusted R Square 0.361791 and design of structures. Standard Error 28.52346 REFERENCES Observations 111 1. Panoot Suwanwiwattana.S,Karchoke Chantawarangul.K, Warakorn Mairaing.H, (2004),The R2 and R2adj (In table 4.3) were too low, the linear ‘The development of Geotechnical database of Bankokrelationship between the variables were not significant. So a subsoil using Geographic Resources Analysis Andquadratic relationship was established and the statics was Support System (GRASS) GIS’. Source fromshown in Table 3. www.gisdevelopment.net. 2. Gandhimathi (2010) “Spatial analysis of soil inTable 3 Regression statistics for quadratic relationship Coimbatore for Geotechnical engineering purposes “in Regression Statistics International Journal of Engineering Science and Multiple R 0.707279 Technology Vol. 2(7), 2010, 2982-2996. 3. Victor Manuel Cavaleiro, José Alcino Rodrigues- R Square 0.500244 Carvalho &Luis Ferreira Gomes (2006),’ Geotechnical Adjusted R Square 0.427362 mapping in the area of Covilhã, Portugal.A Standard Error 27.22039 methodology using GIS’, in IAEG2006 Paper number 211. Observations 111 4. Carmen Y. Lugo Cintrón (2007) ‘Development of a Geotechnical database for the city of Mayagüez,When the order of the relationship was increased from first Puerto Rico’.a post graduate thesis submitted to theorder (linear) to second order ( quadratic) ,the coefficient University of Puerto Rico, Mayagüez campusof determination R2 and R2adj increase remarkably from 5. Le Minh Son (2002),’Compiling Geotechnical data to39.4 % to 50 % and 36.14 % to 42.2% respectively and the determine the distribution and properties of Top sandP-value was lesser than 0.05 ( confidence significance). deposits in Quadrant K&L of the Dutch sector –North Sea”, A post graduate thesis submitted to International Institute for Geo-Information Science and Earth Observation(ITC). 800