IN-SITU THERMAL MEASURES

As seen in the previous section, heating of soil results in decreased compressibility and increased strength. Thermal improvement of soils has been utilized for over one hundred years. Thermal treatment has been used as a means for soil improvement of weak foundation material and stabilization of slopes. In-situ thermal treatment generally is achieved by the burning of liquid, gaseous, or solid fuels at the ground surface or in a borehole, and some times more advanced burning devises have been employed.

1 Ground Surface Heating

Ground surface treatment has typically involved the burning of coal or wood on the surface or in ventilated containers over an extended period. This proved to be difficult to control as the amount of heat being applied was not regulated. In the United States, in the late 1880s, clays were burned (wood) to create aggregate for highways and railroad ballast (Janiewicz, 1972).

2 Borehole Treatment

Borehole heat treatment has been used in the United States, Japan, Rumania, and Russia to stabilize plastic clay in-situ. Both super-heated air and fossil fuel sources have been used. Borehole treatments usually are categorized as closed or open-hole systems.

Closed-hole Systems

In Russia (USSR), methods for thermal treatment of soil by burning fuel in a closed system were investigated. The first applications involved introducing heated air under pressure into a boring, as seen in Figure 5 (Beles and Stanculescu, 1958).