Intrinsic properties such as texture and dynamic properties such as water content, wetting and drying cycles and external loads are recognized as being important factors influencing soil compactibility. Soil compaction in fields usually occurs due to flood irrigations during intensive crop production as well as mechanized harvesting operations by using heavy machinery in wet soils. Soil strength is measured in terms of the maximum stress that can be applied before the occurrence of the substantial increase in soil compression. Estimating the soil stress at its compaction threshold (i.e. precompaction stress, ? pc ) and the soil sensitivity to excess compaction (compression index, C c ) when the applied stresses due to the field traffic exceed the ? pc , can be useful to prevent soil compaction. The soil strength is termed precompaction stress (? pc ) at which the soil deformation changes from reversible behavior (elastic) to the irreversible behavior (plastic). On the other hand, due to soil is not an elastic and resilient matter, at each loading and unloading cycles a permanent deformation occurred in soil. By limiting the load below ? pc , the risk of additional soil compaction can be minimized. One of the natural characteristics of the soils in arid and semi-arid regions is having high calcium carbonate (lime) content. There is little information on the effect of lime and soil hardening under wetting and drying cycles on compaction strength of calcareous soils in Iran. Therefore, the objectives of this research were to study the effects of lime percentage under wetting and drying cycles on soil load bearing capacity (precompaction stress) and shear strength and to determine the relationship between these two soil strength values. In this research, a silty loam soil with very low carbonate content was used. Then, soils with different carbonate percentages (10, 30 and 50) were prepared. In order to the soils to regain their natural structure; first the soils were kept at field capacity for two months and then kept in laboratory conditions for ten months. Then, each pot was sliced through into two parts. The top part was used for samples without wetting and drying cycles; and the bottom part was used for samples with wetting and drying cycles. Then, the soil was wetted to desirable water content (0.7PL, 0.9PL and 1.1PL). In samples without wetting and drying process and without any preload, the half-pot was used directly for loading; whereas for the samples with preload (200 kPa), the soil from the half-pot was transferred to metal cylinder with minimum disturbance. Stress-sinkage and stress-strain curves were drawn for plate sinkage test (PST) and confined compression test (CCT), respectively. For each curve, three different methods were considered to determine the ? pc . These methods were: (1) Casagrande method, (2) maximum curvature and (3) intersection of virgin compression line (VCL) and x-axis. Soil shear strength parameters (cohesion, c and Internal friction angle, ? ) were measured by using a direct shear box test. The effects of carbonate, wetting and drying cycles, water content and preload on precompaction stress and shear strength were studied using a factorial experiment in a randomized complete block design with three replications. Results showed that in PST, the maximum and minimum values of ? pc were obtained with Casagrande and maximum curvature methods, respectively. In CCT, the maximum values of ? pc were obtained with Casagrande method and the minimum values of ? pc were obtained with intersection of VCL and x-axis. By increasing the carbonate, water content, preload and with 6 cycles of wetting and drying, the ? pc increased. Also ? pc in both PST and CCT increased by increasing the carbonate content, preload and with wetting and drying proce and by decreasing the water content. Increasing the carbonate content at low (10%) and high (50%) levels led to increasing and decreasing C C , respectively. Also, wetting and drying process and preload led to decreasing and increasing, respectively, sensitivity to soil compaction. Whereas the increase in water content resulted in an increase in soil sensitivity to compaction. The soil cohesion was decreased with an increase in the carbonate content . it was increased with increase in water content or preload and with inducing wetting and drying. With Increasing the carbonate content the angle of internal friction was increased and this parameter was decreased with increasing the water content, preload or inducing wetting and drying. In both PST and CCT, the correlation between precompaction stress and shear strength was high significant.