I have heard reports that the cement grouting of impervious soils can be effectively replaced by the straight injection of heat. Is this true?
Yes, this is possible, although the practicality and economics are still somewhat uncertain. Reports show that the method has been used in Russia to increase the load-carrying capacity of foundations and to underpin buildings in danger of collapse. Heating to temperatures as high as 3,600 degrees F. may be necessary to cause the changes needed in the characteristics of a soil. This can be done either by the injection of hot compressed air into a borehole or by the injection of the incandescent products of combustion, so that the heat will penetrate the pores of the soil. Depths down to 50 feet can be satisfactorily stabilized in this way. The Russian method favors the use of gaseous fuels as being the most effective on the grounds of more uniform heating, easier control and reduced costs. In general, the higher the pressure, the cheaper and more effective the treatment. Only about 30 percent of the cost of a job is expended on gaseous fuel, while about 70 percent is expended on the boring and the maintenance of high air pressure.