A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geotechnical and Geoenvironmental Engineering, School of Engineering and Technology

Thesis (M.Sc.) - Asian Institute of Technology, 2009

Unforeseen of rock mass conditions exists in mountainous tunneling. Traditional investigation methods such as the borehole data are not adequate to give clear information on rock mass condition. Therefore a geostatistical treatment of the investigation data may be helpful in modeling the prediction. Rock mass conditions of Lam Ta Khung Pumped storage project and Klong Tha Dan dam project were evaluated by means of Geomechanics Classification (RMR). Initially, RMR values were determined from the borehole data. Statistics analysis was basically performed to check the distribution of data and sampling error. Then, the geostatistics analysis including variogram and kriging were conducted to estimate RMR values and to draw RMR contour map data in the rock mass. The ordinary kriging or the best linear unbiased estimation was used to estimate the RMR value along tunnels in Lam Tha Khong Pumped storage project and Klong Ta Dan dam project. Finally, reliability of the estimated values was verified by comparing with RMR obtained from the tunnel face mapping. Moreover, the uncertainty of kriged estimation could be evaluated in form of standard deviation of kriging. The results show the most likelihood of estimation met at Lam Tha Khong project but not at Klong Tha Dan project. The study shows that the reliability of the geostatistical prediction depends a great deal on the geological characteristics of the site