3D Modelling For Geotechnical Investigation

Abstract

Soil has very important functions such as to support buildings, railway lines, pipelines, dams and roads. However, good site characterisation or accurate geotechnical investigations will enhance a good design of the foundation to support the structure. Sound geotechnical investigation requires reliable soil data in the area of interest so as to achieve accurate information about the site. A combination of in-situ testing, site description, use of ancillary data (such as aerial photographs, remote sensing images, geologic maps, etc) , soil and rock sampling for further laboratory tests is used during investigations. In order to understand and interpret the soil properties of the site before any design is made, a 3D view is essential. This is because it enhances visualization of geotechnical properties in three dimensions and facilitates interpretation of the underground information. The major problem in geotechnical presentation is uncertainties due to prediction of soil properties in un-sampled areas. Field observations are usually spaced to minimize cost of drilling boreholes at each and every meter, hence; interpolation between these widely-spaced data points is done. In this research, geostatistics with R computing software was used in spatial interpolation of soil properties in un-sampled areas. A three-dimensional model for geotechnical investigation was developed using observations from seven boreholes drilled to a depth of 14m in the study area. The soil properties were obtained from both in-situ and laboratory tests. R code was developed during the study where regression and Kriging methods (hybrid interpolation technique) were used to determine spatial variation of geotechnical soil properties such as plasticity index, SPT blow counts etc. The nugget, sill and range of the experimental varioqrarn model were determined at 0.0037, 0.0218 and 2000m respectively for plasticity index. The spatial interpolation model for discrete geotechnical investigations with the computer R code were used to produce 3D visualization of soil properties in the boreholes. The SPT blow counts predicted in the entire study area varied from 0-50 N values with high resistance as from 7m deep. Soil types encountered were mainly marls, clayish sandy deposits. The developed 3D model can be used to improve geotechnical investigations where the distribution of the measured soil properties for example SPT (N) counts within the area of interest is visualized. This will greatly intensify fairly accurate and economical geotechnical design since the cost of data collection, analysis and mapping will be reduced by increasing the spacing of the boreholes.