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 2014Fig. 24 Ratio of load carried by piles to effective load vs. timethe instrumented piles (αp’) and the elapsed time, for the six structuresshown in Figs. 1(d), 1(e), 1(f), 1(g), 1(j) and 1(k). The data for the13-story hospital were updated from those in the previous paper(Yamashita et al., 2011a). The values ofαp’were found to be quitestable after E.O.C.Figure 25 shows the values ofαp’at or after the end of theconstruction versus the pile spacing ratio (s/d) for the eleven structures.Here, s is the average center-to-center spacing between the instrumentedpile and the adjacent piles and d is the shaft diameter of the pile. Whiletheαp’versus s/d relationship for the ten structures was originallyshown in the previous paper (Yamashita et al., 2011a), the data for the12-story office building (k) were newly added and those for the 13-storyhospital (e), the hadron experimental hall (f) and the 12-story residentialbuilding (j) were updated. In addition, for the hadron experimental hallin Ibaraki and the 12-story residential building in Tokyo, the values ofαp’just before the 2011 off the Pacific coast of Tohoku Earthquake arealso shown in Fig. 25. There was a little decrease in the values ofαp’was observed for the former building, while little change was observedfor the latter building after the strong seismic motion as mentioned inChapter 3. While the value ofαp’varied from 0.43 to 0.93, it was foundthat the value ofαp’generally decreased as the pile spacing ratio wasincreased, as described in the previous paper (Yamashita et al., 2011a).Fig. 25 Ratio of load carried by piles to effective loadvs. pile spacing ratio5 CONCLUSIONSThrough the investigation of the settlement and the load sharing behavior of piled raft foundations by monitoring the elevenstructures, the following conclusions can be drawn:1) As for the effect of the seismic motion during the 2011 off the Pacific coast of Tohoku Earthquake on the three structures, (f),(j), (k), the foundation settlement increased by 4 mm to 25 mm in the hadron experimental hall located in Ibaraki, while littlechanges in foundation settlements were observed in the 12-story residential building and the 12-story office building locatedin Tokyo. During the earthquake, a small amount of load transfer from the piles to the soil occurred in the hadron experimentalhall and a very small amount of load transfer from the piles to both the soil and the D.M.W. occurred in the 12-storybuildings. Thereafter, the load sharing between the piles and the soil (i.e., raft) was irreversivle in the hadron experimentalhall, while the load transfer from the soil to the piles occurred in the 12-story buildings in relatively short period after theearthquake. As a result, no significant changes in foundation settlement or load sharing were observed after the earthquake.2) For the seven structures, the measured foundation settlements reached 18 to 27 mm 17 to 102 months after E.O.C. Themaximum settlement for the hadron experimental hall included the increment in settlement of 4 mm due to the strongseismic motion. It was found that the measured foundation settlements at the end of the observation were within a limited39