This dissertation is on the geotechnical aspects of the completed Bangkok MRT Blue Line Project and its extension which is currently under design. There were 18 cut and cover subway stations and nearly 22 km of tunnels constructed by the use of earth pressure balanced shield tunnel boring machines. The soil profile model up to depths of 60 to 65 m consists of seven layers: Weathered Crust and Backfill Material; Very Soft to Soft Bangkok Clay; Medium Stiff Clay; Stiff to Hard Clay; Medium Dense to Very Dense Sand; Very Stiff to Hard Clay; and Very Dense Sand. The strength and deformation characteristics of the Bangkok subsoils are determined from laboratory tests (mainly oedometer and triaxial tests) and in-situ field tests (such as vane tests and pressuremeter tests). Additionally, the small strain behaviour is also investigated using Bender element tests in the laboratory and cross hole seismic tests in the field. The soil parameters needed for the deformation analyses are determined for the Mohr Coulomb Model, Soft Soil Model, Hardening Soil Model, and the Hardening Soil Model with Small Strain Stiffness.