ABSTRACT In order to evaluate soil parameters free from regional variations both in soil behaviour and technical quality, a new procedure to determine the shear strength for design use, τ f (mob) as well as consolidation yielding stress, σ'y is proposed. Various methods to determine τ f (mob) in current practice are first reviewed and it is then revealed that regional difference in technical quality is significant. It is indicated that cone penetrometer, sheathed field vane and direct shear tests are recommended as the tests to minimize the effect of quality difference together with that the direct shear strength offsets the strength anisotropy and be uniquely related to τ f (mob). Results of investigations with the proposed method consisting of three tests described above are presented for three marine clays. Point resistance, field vane, direct shear and unconfined compression strengths were investigated and the correction factor to determine τ f (mob) from these strengths are shown together with those proposed in various methods. It is demonstrated that σy' can be obtained from the shear strengths both in the field and in the normally consolidated state, and τ f (mob) can uniquely be related to σ'y irrespective of clay properties. Further, it is also shown that τ f (mob) and σ'y can be predicted without undisturbed samples when vane shear and direct shear strengths in the normally consolidated state are obtained.