ブックタイトル竹中技術研究報告書No70

概要

竹中技術研究報告書No70

TAKENAKA TECHNICAL RESEARCH REPORT No.70 2014竹中技術研究報告No.70 2014reinforced concrete structure with a base isolation system oflaminated rubber bearings. The building is located inTokyo. The soil conditions, the foundation design and theinstrumentation, as well as the seismic response of the soilfoundation-structuresystem, were described in the previouspaper (Yamashita et al., 2011b; Yamashita et al., 2012). Inaddition, the monitoring results were updated from those inthe previous paper (Yamashita et al., 2013b).The total load was 198.8 MN. The average contactpressure over the raft was 199 kPa. To improve the bearingcapacity of the silty soil beneath the raft, as well as to copewith the liquefiable loose silty sand between depths of 3and 7 m below the ground surface, the grid-form deepmixing walls were constructed to a depth of 16 m with thebottom being embedded in the lower stiffer silty clay.Furthermore, to reduce the settlement to acceptable levels,sixteen 45-m-long PHC piles, 0.8 to 1.2 m in diameter,were used. The pile toes reached the very dense sand-andgravellayer sufficiently well enough to ensure the toeresistance as well as the frictional resistance. The piles wereconstructed by inserting a set of pile segments into a preaugeredborehole filled with mixed-in-place soil cement.Figure 1 1 shows the foundation plan with the locations ofthe monitoring devices.Figure 12 shows the measured vertical grounddisplacements near the center of the raft. The verticalground displacement at a depth of 5.8 m, which wasinitialised after the immediate settlement due to the castingof mat slab, was approximately equal to settlement of“piled raft foundation”. The foundation settlement reached14.3 mm at E.O.C. The foundation settlement reached 17.3mm on March 10, 2011, just before the 2011 off the Pacificcoast of Tohoku Earthquake. After the earthquake, thefoundation settlement increased by 0.3 mm from the pre-Fig. 12 Measured vertical ground displacements below raftFig. 13 Measured axial loads of piles 5B and 7BFig. 14Measured contact pressure with pore-water pressureFig. 15Load sharing among piles, deep mixing walls andsoil in tributary areaFig. 16Load sharing of effective load among piles, deep mixingwalls and soil in tributary area35