Currently, a large number of underground metal structures are being built and operated in our country and worldwide. According to the current technical documentation, these facilities are subject to corrosion protection. The process of electrochemical corrosion of underground metal structures is suppressed by insulating coatings and cathodic polarization created by means of electrochemical corrosion protection. Long-term operation of underground structures leads to aging and destruction of protective coatings. As a result, the suppression of electrochemical corrosion requires an increase in the electric current of the cathodic protection. Previous studies have shown that there is a significant increase in the pH of the soil electrolyte and a decrease in the electrical resistivity of soils as a result of cathodic polarization of underground metal structures located in clay soils, which significantly increases their corrosive activity. In addition, cathodic polarization contributes to a change in the physicomechanical properties of dispersed soils composing the space around protected structures. The purpose of this research is assessment of cathodic polarization effect on the change in the properties of clay soils composing a space near underground cathodically protected engineering structures.