高圧噴射攪拌工法における多扇形改良の適用性に関する研究

Jet grouting is a technique for ground improvement which employs high pressure cement slurry and high pressure air. This technique has been applied in various types of work, such as excavation support and the protection of departure and arrival shafts in tunnels. However, after the 2011 Great East Japan Earthquake, applications for liquefaction mitigation through a lattice- or wall-form arrangement of columns have increased. Until now, the lattice- and wall-form improvements were constructed with round columns generated by jet grouting. Because the columns were round, more soil was improved than what was actually required. Therefore, round column are not acceptable with respect to cost and environmental factors. Consequently, the MultiFan jet grouting method of ground improvement was developed in order to reduce the amount of redundantly improved soil. This method is comprised of partially formed, fan-shaped columns. In this paper, we geometrically examined the effectiveness of the MultiFan shape column for lattice- or wall-form ground improvements. The effectiveness of the MultiFan column was verified by comparing it with round and oval columns. Consequently, when the wall-form improvements were constructed, the MultiFan and oval columns demonstrated a smaller value of redundantly improved soil body than the round columns. On the other hand, when the same thickness of wall-form ground improvement was constructed, the spacing of each oval column was less than that of the MultiFan and round columns. In other words, more oval columns were required than the MultiFan or round columns. This revealed that improvement work could be carried out more effectively with MultiFan columns than with oval or round columns. Furthermore, we developed new equipment for this work, and carried out field tests to confirm its workability. Consequently, we were able to confirm our assumption that it is possible to construct the MultiFan shape columns for ground improvement work.