Geotechnical map is commonly used to support projects, especially civil engineering projects and land use planning. It can provide engineers with information regarding soil types and their bearing capacity. Therefore, geotechnical map helps to figure out the best location for specific building and the best type of foundation to be used in order to avoid problems that can be caused by soil such as swelling, excessive settlement, landsliding, etc.

In this paper Geographic Information System (GIS) was employed to construct a knowledge base for geotechnical experts. The procedure based on employing the ArcGIS software and its extensions: Geo-statistical and Spatial Analyst in applying interpolation methods and representing results. Soil data for more than 100 boreholes logs distributed within city of Nablus were manipulated through ArcGIS software to test its capability for spatially modeling its types all over the city.

The interpolation procedures were implemented to display the soil type information for any point of the whole area. Kriging, Inverse Distance Weighting (IDW) and Thiessen polygon interpolation procedures were used to predict soil type’s distribution. The qualitative description of the soil was turned into quantitative figures that could be interpolated by means of coding. The results of the study showed non realistic distribution for soil types at some places when using IDW and kriging methods, the minimum average error in predicated soil type was achieved when using the Thiessen polygon method.

It can be concluded that GIS techniques through ArcGIS and its extensions could be considered as a good base for developing an expert system for geotechnical investigation for soil types.