The article deals with improving the construction properties of soils due to their reinforcement by geosynthetics, namely the geogrid. Geosynthetics have been widely used in the construction of extended objects: the mound of roads and railways, dams, retaining walls. The article includes a description of the possible destruction of reinforced soil base under load. It is established that the soil reinforcement by geogrids prevents adhesive failure (slip). The definition of carrying capacity of geogrid reinforced foundation is considered in terms of spatial task for the case when the ratio of base length to its width is not more than 5. The solution presented in the form of the equilibrium conditions of active and passive earth pressure. The coefficient of geogrid space work for water-saturated silt and fine sands is derivered. The optimal size and depth of geogrid inception are determined.