Determining stress limits to prevent soil compaction, it is important to know the mechanical properties of soils. One important parameter is the precompression stress which is often used as a criterion for soil susceptibility to compaction. The objectives of this study were to 1) compare precompression stresses derived from plate sinkage test (PST) and confined compression test (CCT) and relate these values to soil shear strength obtained from shear box and 2) design a torsional shear box for determining the shear strength of the topsoil. In this research, a series of pre and main tests were done on a sandy loam soil. The objectives of pre-tests were to make uniform soil samples and to obtain suitable pre-loading method. In main tests, the effects of two moisture contents (17 and 19%db) and six pre-loading stresses (0, 25, 50, 100, 150 and 200 kPa) on pre-compaction stress using a factorial experiment in a completely randomized design with three replication were studied. Compressive loading types consisted of plate sinkage test (PST) and confined compression test (CCT). The initial soil conditions for PST, CCT and direct shear tests were similar. The results showed that, although a positive and significant (R 2 =0.71) correlation between the pre-compaction stress was obtained with both loading types, the redicted with PST was accurate, whereas the value, obtained with CCT were 4.5 (17 %db) and 8.5 (19 %db) times higher the applied pre- loadings. The relationships between the pre- compaction stress and the corresponding shear strength (for both PST and CCT) were linear (R 2 =0.95) and significant ( P 0.01). The pre- compaction stress values depend on the compressive loading tests, however, the corresponding shear strength had positive and linear relationship w