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 2014Settlement and Load Sharing Behavior of Piled Raft FoundationsBased on Long-Term Monitoring長期挙動観測に基づくパイルド・ラフト基礎の沈下と荷重分担挙動＊1＊2Kiyoshi Yamashita山下清Junji Hamada濱田純次＊3＊3Shuichi Wakai若井修一Tomohiro Tanikawa谷川友浩SummaryThis paper presents behavior of settlement and load sharing between piles and raft based on the long-term monitoring ofeleven structures. For the three out of the eleven structures, foundation behavior during the 2011 off the Pacific coast of TohokuEarthquake was successfully monitored. No significant changes in foundation settlement or load sharing were observed afterthe earthquake in these three buildings, and the foundation settlements were 18 to 27 mm and the ratio of the load carried bythe piles to the effective load generally decreased as the pile spacing was increased while the ratio of the load carried by thepilesvariedfrom0.4to0.9.Keywords: ?piled raft foundation, settlement, load sharing, monitoring, seismic loading梗概本文は，パイルド・ラフト基礎の沈下および杭とラフトの荷重分担性状について，11件の建物の長期挙動観測結果に基づき述べたものである。このうち3件の建物については，観測期間中に発生した2011年東北地方太平洋沖地震前後の基礎の挙動が観測されている。結論として，地震動による基礎の沈下量と荷重分担の変化は小さいこと，パイルド・ラフト基礎の沈下量は18～27mmであること，建物の有効荷重に対する杭の荷重分担率は0.4～0.9であるが杭間隔が増加すると減少する傾向を示すことが判明した。キーワード：パイルド・ラフト基礎，沈下，荷重分担，挙動観測，地震荷重1 INTRODUCTIONIn recent years, there has been an increasing recognition that the use of piles to reduce raft settlement can lead toconsiderable economic savings without compromising the safety and the performance of the foundations (Poulos, 2001). Piledraft foundations have been used in Japan for many buildings and the effectiveness of piled rafts in reducing average anddifferential settements has been confirmed not only on favorable ground conditions as shown by Katzenbach et al. (2000) andMandolini et al. (2005), but also on unfavorable ground conditions with ground improvement techniques (Yamashita et al.,2011a; Yamashita et al., 2011b; Yamashita, 2012). It has become necessary to develop more reliable seismic design methodsfor piled raft foundations, particularly in highly seismic areas such as Japan. However, only a few case histories on monitoringseismic soil-pile-structure interaction behavior exist (Mendoza et al., 2000).This paper presents behavior of settlement and load sharing between piles and raft based on the long-term monitoring ofeleven structures. For the three of the eleven structures, foundation behavior subjected to seismic motion during the 2011 offthe Pacific coast of Tohoku Earthquake was successfully monitored. First, performance of the piled rafts supporting the threestructures during the earthquake is presented, and the effects of the strong seismic motion on the foundation settlement and theload sharing between the piles and the raft are discussed. Next, based on the monitoring results, general aspects of thefoundation settlement and the load sharing between the piles and the raft are discussed.＊1 Executive Manager, Research & Development Institute, Dr. Eng.技術研究所専門役博士（工学）＊2 Chief Researcher, Research & Development Institute, Dr. Eng.技術研究所主任研究員博士（工学）＊3 Researcher, Research & Development Institute技術研究所研究員29