ABSTRACT
In regions with a high groundwater table, underground structures such as tunnels, shafts and underground parking facilities are built in dry construction pits with sheet pile or diaphragm walls to retain the groundwater and the soil. Underwater pored concrete or grouted layers are used to ensure the vertical stability of the bottom of the pit or to reduce the amount of percolating groundwater. Until about 1985, such grouted layers consisted of permeation grouting. The injected fluid was a gel, usually a soft silica-gel. From around 1985, jetgrouting was also used. With this technique, the soil is cut by jetting and mixed and partly replaced by grout. The strength and stiffness of these grout layers is comparable with a poor concrete.
