GIS-BASED APPROACH TO IDENTIFY THE SUITABLE LOCATIONS FOR SOIL SAMPLING IN SINGAPORE

Shallow slope failures due to rainfall commonly occur in residual soil, especially in tropical areas like Singapore. Therefore, it is critical to understand the distribution of residual soil properties throughout Singapore Island. Proper procedures are required for selection of appropriate locations of soil sampling to obtain the representative soil properties. The aim of this study is to establish the necessary procedures and methods which are applicable to select suitable locations for soil sampling in Singapore. In this study, the Geographical Information System (GIS) with the incorporation of three layers: digital elevation model (DEM), slope angle, and the soil sampling locations from past studies were used to generate suitability map for determination of soil sampling locations in Singapore. Five suitability classes were implemented in each layer: very low, low, medium, high, and very high. Four types of spatial analyses such as "Analysis by weights", "Inference matrix method", "Fuzzy Overlay Gamma method", and "per-cell statistic maximum method (PCSM)" were assessed to identify the appropriate method for determination of the suitable locations for soil sampling in Singapore. These analyses were carried out using Spatial Analyst Tools in ArcGIS environment. The results of this study indicated that the spatial analysis by weights and Fuzzy Overlay Gamma are suitable for determination of soil sampling locations up to 100 data points. The spatial analysis using the inference matrix is suitable for determination of limited number of soil sampling locations. The spatial analysis using the PCSM method is suitable for determination of large number of soil sampling locations. The findings from this study will benefit the practical engineers in surveying as well as other related researchers for determination of suitable locations of soil sampling.