The treatment characteristics, quality control measures and outcomes of two different jet-grout based soil treatments are described in detail. In the first one, a jet-grouted slab was built to limit retaining wall movements in a cut-and-cover tunnel. Quality control relied on borehole core quality assessment and laboratory testing. Core quality was very sensitive to coring practices. The strength and stiffness of the jet-grouted slab were deemed adequate and the structure successfully contributed to minimal wall movements. In the second case, a jet-grouted treatment was designed to provide strengthening and impermeabilization around a tunnel excavated on silty sands below the water table and underneath another tunnel. Control was based on extensive coring, cross-hole seismic surveys and permeability tests. The results were generally favourable and where defects were detected, reparation was undertaken. However, in spite of all those actions, a number of deficiencies escaped detection and only became apparent during the excavation of the tunnel resulting in significant construction problems.