ABSTRACT

The use of chemicals in grouting evolved logically from cement grouting practice where direct injection of neat cement into fine fissures or small pores was only partially successful. At Thorne in Yorkshire, for example, two shafts started in 1909 came to a standstill at a depth of 150 metres due to heavy water ingress through porous sandstone which contained fine fissures. With a background of proven experience from Hatfield colliery in 1911, the Belgian engineer Franqois employed silicatization at Thorne in 1913, and this commercial success established the process in engineering practice. The technique involved the injection of sodium silicate and aluminium sulphate solution, after which neat cement grout was injected with comparable ease. Franqois concluded that the chemical gel acted simply as a lubricant, which perhaps explains why he did not develop the system for the treatment of alluvium, in spite of the fact that the use of sodium silicate as a grout had been known since 1886 through a patent by Jesiorsky.' In reality the chemical gel filled the fine fissures and pores, thereby sealing the walls of the major fractures. Without such a seal and under high injection pressures the water would have been driven from the cement grout into the porous structure of the rock, leaving the grout to stiffen prematurely. Following the early commercial successes in shaft sinking with silicatization, the method was employed in many other countries, particularly South Africa.'