Ground improvement by jet grouting method in St. Kuzam tunnel: monitoring of performance.

The St. Kuzam tunnel on the D8 road in Croatia is a twin-tube road tunnel excavated through flysch and limestone. About 30m of the tunnel caved in whilst excavating from carbonate rock through to non-degraded and weakly-degraded siltstone. For subsequent excavation in this zone jet grouting was used. It has been established by means of boreholes and laboratory testing that jet grouting produced a new, relatively homogenous material with significantly improved properties. Numerical back analysis has also been carried out on the excavation and lining support system based on measurements of ground movement around the underground opening. The results, together with geotechnical measurements and monitoring, have contributed to a better understanding of rock mass behaviour and properties, and can be used in design of the primary support system, to predict progress and to estimate stand-up time of unsupported spans. Using the numerical analysis it was shown that the jet grouting improved the ground stiffness by factors of 4.31 to 5.03.
The St. Kuzam tunnel on the D8 road in Croatia is a twin-tube road tunnel excavated through flysch and limestone. About 30m of the tunnel caved in whilst excavating from carbonate rock through to non-degraded and weakly-degraded siltstone. For subsequent excavation in this zone jet grouting was used. It has been established by means of boreholes and laboratory testing that jet grouting produced a new, relatively homogenous material with significantly improved properties. Numerical back analysis has also been carried out on the excavation and lining support system based on measurements of ground movement around the underground opening. The results, together with geotechnical measurements and monitoring, have contributed to a better understanding of rock mass behaviour and properties, and can be used in design of the primary support system, to predict progress and to estimate stand-up time of unsupported spans. Using the numerical analysis it was shown that the jet grouting improved the ground stiffness by factors of 4.31 to 5.03.