ABSTRACT
The design method based on reliability was introduced and has been gradually used for construction of civil engineering structures, including design of foundations. However, there are a lot of problems in this method when applying it to geotechnical engineering. For example, soil properties are different from those of other civil engineering materials, such as concrete and steel. Because the ground is naturally deposited except for compacted or improved soils, variability in soil properties is completely different from artificially manufactured materials whose properties are strictly controlled. In addition to this inherent difference, human errors at measurement of soil parameters should be taken account. Sample disturbance is one of key issues to obtain reliable soil parameters at laboratory test. Although in situ tests do not need to consider the sample disturbance, measured values are strongly influenced by the drilling method and/or the testing method. In Standard Penetration Test (SPT), for example, the method for dropping the hammer affects the N value.
