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Soil improvement with mini jetgrout columns and geogrid reinforced mechanical fill system under a machine foundation

A shallow (mat) foundation of 21 m x 21 m plan dimensions was constructed using fiber reinforced concrete in an automotive spare part factory in Kocaeli, Turkey. After placing two similar ma-chines of 785 tons and 605 tons weight on the same foundation, differential settlements were observed. The machines are 5,2 m wide and 15,7 m long each, and the clear distance between them is 6,0 m. Both of the machines were leveled with adjustment screws on their frames a couple of times, but the settlements of 0,5 – 2,0 millimeters continued after each adjustment without coming to an end. As it was reported by the owner that the machines cannot be put into service unless the settlements finish, a soil improvement system has been designed, which aimed at finishing the settlements in a very short time. According to the borings, the subsoil profile consists of soft to very stiff gravelly clay layer under a 1,5 m thick uncon-trolled manmade fill layer. Geogrid reinforced mechanical fill laid over mini jetgrout columns is thought to be the most suitable solution. As compaction problems occurred on the clay layer, lime stabilization has also been applied at the excavation base. After finishing the soil improvement the RC foundation has been reconstructed and the machines have been reassembled by the end of year 2011. Geotechnical engineering works were performed by GEOCON on a “design and construct” basis. Both the structural and geotech-nical design engineers have signed and stamped a “zero settlement commitment” after finishing the works, stating that “no settlement will occur” under the machine working loads. Until March 2018, no further settlement has been reported by the owner of the factory. Both of the machines are still in opera-tion as of the preparation date of this paper. Summary information about the soil conditions, soil im-provement system design and construction processes and the foundation system have been presented in this study.