APPLICATION OF GIS-GPS FOR MAPPING SOIL INDEX PROPERTIES

IGC 2009, Guntur, INDIA Application of GIS-GPS for Mapping Soil Index Properties APPLICATION OF GIS-GPS FOR MAPPING SOIL INDEX PROPERTIES Sumedh Yamaji Mhaske Ph.D. Student, Department of Civil Engineering, Indian Institute of Technology (IIT) Bombay, Powai, Mumbai 400 076, India. E-mail: z7404801@iitb.ac.in Deepankar Choudhury Associate Professor, Department of Civil Engineering, Indian Institute of Technology (IIT) Bombay, Powai, Mumbai 400 076, India. E-mail: dc@civil.iitb.ac.in ABSTRACT: Index properties of soil such as specific gravity, moisture content, dry density, wet density etc. are the important parameters in geotechnical engineering and they are changing from place to place both along the depth and width of the stratum.it is important for the geotechnical engineers to know about variation of the index properties of soil before carrying out design and construction of any geotechnical structure. Any field or laboratory soil testing will provide result which is too specific for a particular location to generalize over an extended area. In this paper, an attempt is made to develop a methodology to map the important index properties of soil by using Geographic Information System (GIS) and Global Positioning System (GPS) using existing soil exploration reports. The method suggested in this paper will help all the soil exploration agencies and practising geotechnical engineers for immediate decision making process about soil suitability as foundation materials. 1. INTRODUCTION Soil is a natural material having variety of physical properties, most of which are not constant and it is varying from place to place. Index properties of soils are those properties which are mainly used in the identification and classification of soils and help the geotechnical Engineer in predicting the suitability of soils as foundation/construction material (Ramamurthy & Sitharam 2005). Specific gravity of soil particles, particle size distribution, Consistency limits and moisture content etc are the index properties of soil. Apart from that permeability, compressibility and shear strength are the engineering properties of soil. Moisture content of soil is one of the important factor depending upon which the shear strength of soil will change. Geographic Information System (GIS) is a computer based information system capable of capturing, storing, analyzing, and displaying geographically referenced information, i.e. the data identified according to a particular location/region. And Global Positioning System (GPS) is a satellite-based navigation and surveying system for determination of precise position and time, using radio signals received from the satellites, in real-time or in post-processing mode. (Kulkarni 2003). The use of GIS, which is capable to analyze regional areas based on spatial distribution, is well known. As more and more data become available in a digitized format it is possible to develop software routines that can perform identification of Index soil properties and preparation of thematic maps of soil type, moisture content, ground water depth, SPT value etc in conjunction with a GIS. Traditional methods of mapping soil index properties by using any other information system fail to provide information pertaining to the spatial aspects in geotechnical Engineering. The application of geographic information system in geotechnical will be new in the Indian Construction industry. GIS will allow soil investigators and different people involved in project with different backgrounds to get the information about soil properties on a single click. The integration of GIS, GPS and database of index properties of soil will be very helpful to the soil investigators and contractors working in Mumbai region for understanding the soil strata and deciding the correct soil strata for resting the foundation of structure. 2. BASICS OF GIS, GPS AND PROPERTIES OF SOIL 2.1 Geographic Information System (GIS) Geographic Information System provides efficient tools for inputting data into database, retrieval of selected data items for further processing and software modules which can analyze or manipulate the retrieved data in order to generate desired information on specific form. The components of a GIS are pictorially represented in Figure 1. GIS stores spatial and non spatial data in two different databases. The geocoded spatial data defines an object that has an orientation and relationship with other objects in two (2D) or three dimensional (3D) space. GIS uses three types of data to represent a map or any geo-referenced data, namely, point type, line type, and area or polygon type. It can work with both the vector and the raster geographic models. The vector model is generally used for describing the discrete features, while the raster model does it for the continuous features. One of the major advantages of the GIS is that it incorporate all type of relevant data either available in aerial photographic data, 35

remote sensing images data, tabular data etc. These and other information are viewed as individual coverage that may be simultaneously overlaid depending on the desired detail of the analysis. Data integration is the linking of information in different forms through a GIS is shown in Figure 2. Fig. 1: Basic Components of a Geographic Information System (GIS) (Source: www.gisdevelopment.com) Fig. 2: Data Integration is the Linking of Information in Different Forms through a GIS (Source: http://erg.usgs.gov/isb/pubs/gis_poster/index.html, 2005) 2.2 Global Positioning System (GPS) The Global Positioning System is being used all over the world for numerous navigational and positioning applications, including navigation on land, in air and on sea, determining the precise coordinates of important geographical features as an essential input to mapping and Geographical Information System (GIS), along with its use for precise cadastral surveys, vehicle guidance in cities and on highways using GPS-GIS integrated systems, earthquake and landslide monitoring, etc. The Navigation Satellite Timing and Ranging Global Positioning System (NAVSTAR GPS) developed by the U.S. Department of Defense (DOD) to replace the TRANSIT Navy Navigation Satellite System (NNSS) by mid-90 s, is an all-weather high accuracy radio navigation and positioning system which has revolutionised the fields of modern surveying, navigation and mapping. The GPS, which consists of 24 satellites in near circular orbits at about 20,200 km altitude, now provides full coverage with signals from minimum 4 satellites available to the user, at any place on the Earth. By receiving signals transmitted by minimum 4 satellites simultaneously, the observer can determine his geometric position (latitude, longitude and height), Coordinated Universal Time (UTC) and velocity vectors with higher accuracy, economy and in less time compared to any other technique available today ( Kulkarni 2003). GPS is primarily a navigation system for real-time positioning. However, with the transformation from the ground-to-ground survey measurements to ground-to-space measurements made possibly by GPS, this technique overcomes the numerous limitations of terrestrial surveying methods, like the requirement of intervisibility of survey stations, dependability on weather, difficulties in night observations, etc. These advantages over the conventional techniques and the economy of operations make GPS the most promising surveying technique of the future. With the well-established high accuracy achievable with GPS in positioning of points separated by few hundreds meters to hundreds of km, this unique surveying technique has found important applications in diverse fields. 2.3 Properties of Soils The properties of soil can be divided as Index properties and Engineering properties. The main Engineering properties are permeability, compressibility and shear strength. The brief description of few engineering and index properties of soil are given below (Jumikis 1965, Phadake & Jain 1998): Permeability indicates the ease with which the water can flow through soils. Compressibility is related with the deformations which soil undergoes when subjected to compressive loads. The Shear strength helps in determining stability of slopes, bearing capacity of soils and the earth pressures on retaining structures. The specific gravity of soil solids is the ratio of the density of a given volume of soil solids to the greatest density (at +4 C) of an equal volume of pure water. The principal soil grain properties are the size and shape of grains and the mineralogical character of the finer fractions. The most significant aggregate property of cohesionless soils is the relative density, whereas that of cohesive soils is the consistency. Moisture content is that amount of water which is contained in the voids of the soil. It is one of the important factor depending upon which the shear strength of soil will change. Consistency is the property of materials which shows its resistance to flow. When referred to soil, it means, the degree of resistance offered by fine grained soil to 36

deformation. The water content at which the soil changes from one state to another state termed as consistency limits. Dry density of soil mass is the ratio of mass of soil solids to the volume of soil mass. Therefore the properties of soil such as specific gravity, moisture content, dry density, wet density and consistency limits such as liquid limit, plastic limits and shrinkage limits are the essential for determination of engineering properties of soil, which will help to geotechnical engineer for decision making process of suitability of soil as foundation materials or construction materials. If the properties of soil are properly studied and the results of soil exploration correctly understood and intelligently applied to the design and construction of earthworks and structural foundations, failures usually can be avoided. 2.4 Relationship between Various Soil Properties The following relationship between various soil properties can be useful for determination of other missing properties of soil (Jumikis 1965). For example, if specific gravity (G) and dry unit weight (γ d ) of soil are known then saturated unit weight (γ sat ), moisture content (ω), porosity (n) and void ratio (e) can be determined by using the following relations (Jumikis 1965): Saturated unit weight, 1 γ = 1 γ +γ G sat d w where, γ w = unit weight of water. Moisture content, 1 1 ω= γw γd Gγ w Porosity, γ d n = 1 G γ w (3) Void ratio, Gγ w e = γ d 1 (4) 3. NEED OF STUDY It is traditional practice in civil engineering for construction of new civil projects to carry out soil exploration by taking number boreholes in a given plot. It is seen that the a reference sketch of bore holes drilled in the plot is prepared on a paper by giving their location by taking reference of local permanent points such as corner of any exiting building or any other point. Then the geotechnical Engineers will work out the safe bearing capacity of soil at foundation level of entire building plot from borehole data and laboratories soil test results. Many (1) (2) times the previous experience regarding a local soil profile of a typical area and laboratories soil test result will help to the geotechnical engineers regarding taking decision about the soil suitability as a foundation material. The latitude, longitude of boreholes data are many time missing. In this paper an attempt is made to use Global Positioning System (GPS) receivers to map the exact location of boreholes which can be used as input data in GIS and GRAM++ software is used to run the queries to know various properties of soil. Figure 3 shows the location of boreholes in GIS map of Mumbai city. Fig. 3: Borehole Locations on GIS Map of Mumbai City 4. STUDY AREA Mumbai City and its suburban is taken as a study area. Mumbai is situated from a latitude of 18 53'N to 19 15'N and Longitude of 72 48'E. to 73 00'E. The city covers an area of 437 square km. Total 300 numbers of borehole data, undisturbed soil test report and rock core test report were collected from various government engineering institutes and professionals working in geotechnical engineering field. A database of soil properties such as specific gravity, dry density, wet density, ground water depth, moisture content etc. are created in Microsoft access 2003. GIS software GRAM++, ver. 1.4 (Venkatachalam 2006) is used for creation of GIS map of Mumbai City by digitizing the scanned paper map of Mumbai City. Point layers are created for location of borehole and city name. Similarly polygon layers are created for inner boundaries and outer boundaries of city. Features and line layer is created for internal roads of Mumbai City. After cleaning the digitized map for errors such as silver polygon, overshoot and undershoot it is linked with database generated for soil properties. Some missing properties of soils are worked out by using the relationship given in equation (1) to equation (4). By using Vector Analysis, a module of GRAM++ various queries were run and thematic 37

maps of soil properties such as moisture content, specific gravity, liquid limit, plastic limit were prepared. 5. THEMATIC MAPS OF MUMBAI CITY The thematic maps of soil properties such as moisture content, specific gravity, liquid limit, plastic limit etc were generated by using Vector analysis module of GRAM++ software. These will be very helpful to know the variation of soil profile from place to place and in varying depth to depth. Geotechnical engineers can very easily locate the suitable soil strata for laying foundation of structures. Some of the typical thematic maps are given in Figures 4 and 5. Figures 4 and 5 show the thematic maps of specific gravity, liquid limit for typical Mumbai city soil respectively. 6. RESULTS Typical index properties of Mumbai city soil are given in Table 1 for four different locations. It is observed that there are the fluctuations in ground water table from 0.5 m to 3.5 m below ground level, due to the tidal effect of sea. The brownish medium stiff clay, bluish grey silty clay are available at a depth ranging from 2 m to 3 m, and upto 20 m at some places like Chembur, Kurla and Wadala respectively. The places such as Bandra, Tilaknagar and Dharavi, black marine clay is available at a depth of 1.8 m to 6.3 m. 7. CONCLUSIONS Geotechnical engineers can run more queries of various combinations regarding the various properties of soil which will help in decision making process. This paper will benefit to Geotechnical Engineers, Consultants, Investigators and Clients in the following manner: Updated information can be maintained regarding soil index properties Reduces time for decision making as all information is in one system Various maps can be generated in vector Analysis module which will depict the updated soil characteristics. Helps to the contractors in knowing about the soil profile beforehand about the start of their work GPS can be used for mapping positioning of boreholes during night shift or any weather condition. Fig. 4: Thematic Map for Specific Gravity of Typical Soil of Mumbai City 38

Station Chembur Tilaknagar Fig. 5: Thematic Map for Liquid Limit of Typical Soil of Mumbai City Soil type Table 1: Index Properties of Soil of Mumbai City Depth range (m) Ground water table (m) Dry unit weight (kn/m 3 ) Moisture content % Liquid limit % Specific gravity Brownish medium stiff clay 2.0 3.0 3.5 13.7 21.9 46 2.59 Blackish soft marine clay 1.8 6.3 0.7 16.4 28 66 2.63 Kurla Bluish grey silty clay 2.2 7.9 0.5 8.3 82 108 2.64 Wadala Bluish grey silty clay 4.0 20.0 1.1 9.8 69 103 2.77 REFERENCES Jumikis, A.R. (1965). Soil Mechanics, An East-West Edition, D. Van Nostrand Company. Kulkarni, M.N. (2003). Global Positioning System and its Application, CEP Training Course, IIT Bombay, pp. 1 15. Phadake, V.R. and Jain, R.K. (1998). Geotechnical Engineering, Nirali Prakashan. Ramamurthy, T.N. and Sitharam, T.G. (2005). Geotechnical Engineering [Soil Mechanics], S. Chand. Venkatachalam, P. (2006). DST-NRDMS Sponsored Training Programme: Geospatial Technologies and Applications: Principle of GIS, GRAM++ GIS Package Development and Applications, CSRE, IIT Bombay, Mumbai. 39