This paper examines the effectiveness of technology using jet grouting. This technology is commonly used to strengthening the weak soil bases of buildings in dense urban areas. The paper presents the calculation research methodology and results of the effectiveness of this method on the example of shopping malls in St. Petersburg. Frame type buildings, having numerous cracks in the floor slabs, are considered. Bearing elements of these buildings are the columns, based on the individual pile foundations. Concrete floor slabs are supported by soil base. In the calculations, the soil base was modeled by volumetric finite elements and concrete floor slabs – by plate finite elements. Cement-soil elements (pillars) were modeled also by volumetric finite elements with different deformation modulus. It can be concluded from the calculation results that the above technique is effective in the presence of the weak soil layers and the increase in the modulus of cement-soil elements more than 400 MPa is impractical.