Influence of the boring and sampling methods on the unconfined compression strength of a clay is inbestigated. In the boring works, an ordinary core-tube method and the drill-pipe method are employed. In the sampling process, the effect of twisting the sample tube, to cut off the soil along the lower end of the tube, is investigated. Results of the investigation are summarised as follows;
1) As far as the influence on the unconfined compression strength is concerned, no appreciable difference between the core-tube and drill-pipe methods is found out. However, the drill-pipe method seems to be advantageous from the view point of practical operation.
2) The effect of twisting the sample tube is hardly observed. If the boring rod is bent, however, the twisting will cause the set up of an unequal pressure on the surface of the tube.