1. Danfors, B., 1974. Compaction in the subsoil. Swedish Institute of Agricultural Engineering, Uppsala, Report No. S24, p. 91.
2. Freitag, D.R., 1971. Methods of measuring soil compaction. In: Barnes, K.K., et al. (Eds.), Compaction of Agriculture Soils, ASAE Monograph, St. Joseph, MI, pp. 47–103.
3. Gupta, S.C., Hadas, A., Voorhees, W.B., Wolf, D., Larson, W.E., Sharma, P.P., 1990. Development of guides on the susceptibility of soils to excessive compaction, University of Minnesota BARD Report. St. Paul.
4. Swedish experiments on subsoil compaction by vehicles with high axle load;Hakansson;Soil Use and Management,1985
5. Effect of high axle load traffic on subsoil compaction and crop yield in humid regions with annual freezing;Hakansson;Soil and Tillage Res.,1987