1. Baldi G., Bellotti R., Ghionna V., Jamiolkowski M. and Pasqualini E. (1982), Design Parameters for Sands from CPT. Procr. 2nd Eur. Sym. On Penetration Test. A.A. Balkema, Rotterdam, The Netherlands, Vol. 2 pp. 425–432
2. Dimillio A.F., Briaud J.L., O’Neill M.W. and Geo-Resources Consultants (1987), Pile Group Prediction Symposium: Summary Vol. 1, Sandy Soil. Rep. No. FHwA-ts-87–221, Fed. Hwy Admin, Washington D.C.
3. Gibbens R. and Briaud J. L. (1994). Data and Prediction Request for the Spread Footing Prediction Event. Predicted and Measured Behavior of Five Spread Footing on Sand. ASCE Geotech. Spec. Publ. No. 41 ASCE N.Y. pp 11–85.
4. Juang C. H., Huang X. H., Holtz R. D. and Chen J. W. (1996), Determining Relative Density of Sands from CPT Using Fuzzy Sets. J. of Geo. Eng. Vol. 122, pp. 1–5.
5. Klir G. J. and Yuan B. (1995). Fuzzy Set and Fuzzy Logic. Theory and Application, Prentice Hall PTR, Upper Saddle River, N.Y.