A thesis submitted in partial fulfillment of the requirements for t h e degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1989

In this study the failure of a canal cut slope and the stability of non-improved trial cut slope proposed by JICA, at Charoenraj Pumping Station of RID located at Samut Prakan Province, were investigated. The in situ undrained shear strengths of the clay from various test methods and their correlations were obtained. The undrained shear strength and shear strength parameters of post excavation condition of the clay were determined in the laboratory by Recompression Technique of CKoU-TC and CKoU-TE tests and then were applied in the stability analysis. Simplified Bis hop Method was used for stability analysis. For short-term condition three approaches of undrained shear strength determination were used, i.e. empirical correlation approach similar to LADD's USA method, BJERRUM's correction approach, and AAS's correction approach. While for long-term condition two analytical methods, i.e. effective stress analysis (ESA) and undrained strength analysis (USA) were used. The long-term factor of safety of cut slope in the clay obtained from ESA method is considerably too high compared to that from USA method. A factor of safety obtained from AAS's correction approach is lower than factors of safety obtained from ESA and USA methods. The construction record and the analysis indicated that the failure of the canal slope was due to surcharge near the slope. The USA method yields a factor of safety for the condition at failure equal to 1.02. For the proposed non-improved trial slopes, (a) for the 1:4 proposed slope the AAS's correction approach and BJERRUM's correction approach suggest that the slope fails in short- term condition and (b) for the 1:6 proposed slope the USA method suggests a stable long-term condition with factor of safety of only 1.14, while the AAS's correction approach suggests failure condition in long-term.