The aim of the research, the results of which are set forth in this article, is to supplement the scientific description of the properties of the weakly bearing swampy surfaces of forest machinery movement. In the course of the experiments, the following tasks were set: to reveal the interrelationships of the physical and mechanical properties of weak soil; to test the possibility of expressing the specific cohesion, the angle of internal friction and the shear modulus through its modulus of deformation; to investigate the relationship between the cone index and physical and mechanical properties of weak soil. The experiments were carried out on the territory, leased by the LLC "Kupechesky Dom" (Pskov) in summer and autumn of 2016. To determine the angle of internal friction, specific adhesion, modulus of de-formation, shear modulus and cone index, methods that were regulated by the relevant standards were used. The article presents the main statistical data on the properties of samples of weak soil and information on the correlation of values of properties of weak ground. Based on the results of the study, close bonds of specific adhesion, the angle of internal friction, shear modulus and cone index with the modulus of deformation of weak soil were revealed. Based on the results of experimental data processing and values of the coefficients of determination of the formulas obtained for the properties of weak soil, it was confirmed that the values of specific adhesion, angle of internal friction, shear modulus and cone index are in practice expressed in terms of the deformation modulus with satisfactory accuracy. The calculated values of the conic index are compared with the previously known theoretical formulas and the experimental values measured during the experiments. It is shown that the results of the comparison make it possible to insist on the satisfactory accuracy of the theoretical approach to the determination of cone index of weakly bearing soil.