东海气田群海底管道区浅层土性特点及地震液化判别
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摘要
管道工程的实施以海底土体为依托,预先查明土体的物理力学性质及其稳定性是管道设计、施工不可缺少的前期工作,影响着管道的安全。利用东海气田群海底管道路由区所获取的振动样品、钻孔样品和室内测试资料及原位海洋静力触探(CPT)资料,分析了浅层土体物理力学性质,定量估判了地震作用下土体液化可能性。研究结果表明:根据工程地质评价要求,研究区浅层土体(0～10m)可划分为粘性土、粉质土和砂性土3大类,根据分布位置,可将研究区划分为Ⅰ、Ⅱ、Ⅲ3个分区。在震级为6级的情况下,Ⅱ区和Ⅲ区的粉土和细砂不发生液化;震级为7级时,部分粉土和细砂发生液化,平均粒径为0.1～0.25mm的细砂液化可能性比平均粒径小于0.1mm的粉土液化可能性大;当震级提高到8级时,粉土和细砂基本发生液化。
With the exploitation of offshore oil and gas fields,the amount of submarine pipeline is increasing yearly.To ensure pipeline safety,the stability and mechanical features of the soil around the pipeline must be found out before hands.Under the action of earthquake and wave,the pore water pressure of the soil increases,and the effective stress decreases correspondingly.When the effective stress is zero,the soil liquefies.According to the requirements of engineering geology assessment,sub-bottom soils(0~10 m) in the research areas can be classified into three groups of clay soil,silt soil and sandy soil,of which the distributing pattern corresponds to the sedimentary environment,that is,fine-grained soil near shore and coarse-grained soil in central shelf.Clay is mainly distributed over the outlet of Xiangshan port and areas with water depth < 45 m,where the soil has high moisture content and medium to high plasticity.Silt soil is distributed over the mixed sedimentary area,which presents loose to medium dense state,mixed grain size and slightly larger wet density.Sandy soil is mainly distributed over the residual sand areas,and consists of fine sand and silt sand with clay content less than 15% and fine sand more than 70%.Based on CPT data and average particle size,using Timothy's liquefaction method,seismic liquefaction potential of the silt and fine sand in II and III band is analyzed,which shows that the silt and fine sand do not liquefy under an earthquake of magnitude 6,part of them will liquefy under an earthquake of magnitude 7,and all of the silt and fine sand will liquefy under an earthquake of magnitude 8.
With the exploitation of offshore oil and gas fields,the amount of submarine pipeline is increasing yearly.To ensure pipeline safety,the stability and mechanical features of the soil around the pipeline must be found out before hands.Under the action of earthquake and wave,the pore water pressure of the soil increases,and the effective stress decreases correspondingly.When the effective stress is zero,the soil liquefies.According to the requirements of engineering geology assessment,sub-bottom soils(0~10 m) in the research areas can be classified into three groups of clay soil,silt soil and sandy soil,of which the distributing pattern corresponds to the sedimentary environment,that is,fine-grained soil near shore and coarse-grained soil in central shelf.Clay is mainly distributed over the outlet of Xiangshan port and areas with water depth < 45 m,where the soil has high moisture content and medium to high plasticity.Silt soil is distributed over the mixed sedimentary area,which presents loose to medium dense state,mixed grain size and slightly larger wet density.Sandy soil is mainly distributed over the residual sand areas,and consists of fine sand and silt sand with clay content less than 15% and fine sand more than 70%.Based on CPT data and average particle size,using Timothy's liquefaction method,seismic liquefaction potential of the silt and fine sand in II and III band is analyzed,which shows that the silt and fine sand do not liquefy under an earthquake of magnitude 6,part of them will liquefy under an earthquake of magnitude 7,and all of the silt and fine sand will liquefy under an earthquake of magnitude 8.
引文
①虞志英,恽才兴,张国安,等.平湖油气田14”天然气管道芦洋海区段海床地形稳定性趋势分析[R].上海:华东师范大学河口海岸国家重点实验室,2002.
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[4]SEED H B,IDRISS I M.Simplified procedures for evaluating soil liquefaction potential[J].Journal of Soil Mechanics and Founda-tion Division,1971,97(9):1 249-1 273.
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[6]ROBERTSOM P K,WRIDE C E.Evaluating cyclic liquefactionpotential using the cone penetration test[J].Canadian Geotechni-cal Journal,1998,35(3):442-459.
[7]GB 50011—2001Code for seismic design of buildings[S].2008.GB50011—2001建筑抗震设计规范[S].2008.
[8]YOUD T L,IDRISS I M.Liquefaction resistance of soils:Summary report from the 1996NCEER and 1998NCEER/NSF work-shops on evaluation of liquefaction resistance of soils[J].Journalof Geotechnical and Geoenvironmental Engineering,ASCE,2001,127(10):817-833.
[9]CARRARO J A H,BANDINI P,SALGADO R.Liquefaction re-sistance of clean and nonplastic silty sand based on cone penetra-tion resistance[J].Journal of Geotechnical and GeoenvironmentalEngineering,ASCE,2003,129(11):965-976.
[10]TIMOTHY D,STARK M,SCOTT M,et al.Liquefaction re-sistance using CPT and field case histories[J].Journal ofGeotechnical Engineering,ASCE,1995,121(12):856-869.
[1]LI Jia-biao.Regional geology of East China Sea[M].Beijing:China Ocean Press,2008:154-360.李家彪.东海区域地质[M].北京:海洋出版社,2008:154-360.
[2]LIU Zhen-xia,BERNE S,LATALANTE Scientific Party.Pa-leochannels and Paleodeltas in the continental shelf of the EastChin Sea[J].Marine Geology&Quaternary Geology,2000,20(1):9-14.刘振夏,BERNE S,LATALANTE科学考察组.东海陆架的古河道与古三角洲[J].海洋地质与第四纪地质,2000,20(1):9-14.
[3]LI Ping,LI Pei-ying,LIU Le-jun,et al.The engineering geolog-ical feature of seabed sediment in oil and gas recources area of EastChina Sea[J].Advances in Marine Science,2002,20(4):27-33.李萍,李培英,刘乐军,等.东海油气资源区海底沉积物的工程地质特征[J].海洋科学进展,2002,20(4):27-33.
[4]SEED H B,IDRISS I M.Simplified procedures for evaluating soil liquefaction potential[J].Journal of Soil Mechanics and Founda-tion Division,1971,97(9):1 249-1 273.
[5]LIAO S C,VENEZIANO D,WHITMAN R V.Regression modelsfor evaluation liquefaction probability[J].Journal of Geotechnical andGeoenvironmental Engineering,ASCE,1988,114(4):389-411.
[6]ROBERTSOM P K,WRIDE C E.Evaluating cyclic liquefactionpotential using the cone penetration test[J].Canadian Geotechni-cal Journal,1998,35(3):442-459.
[7]GB 50011—2001Code for seismic design of buildings[S].2008.GB50011—2001建筑抗震设计规范[S].2008.
[8]YOUD T L,IDRISS I M.Liquefaction resistance of soils:Summary report from the 1996NCEER and 1998NCEER/NSF work-shops on evaluation of liquefaction resistance of soils[J].Journalof Geotechnical and Geoenvironmental Engineering,ASCE,2001,127(10):817-833.
[9]CARRARO J A H,BANDINI P,SALGADO R.Liquefaction re-sistance of clean and nonplastic silty sand based on cone penetra-tion resistance[J].Journal of Geotechnical and GeoenvironmentalEngineering,ASCE,2003,129(11):965-976.
[10]TIMOTHY D,STARK M,SCOTT M,et al.Liquefaction re-sistance using CPT and field case histories[J].Journal ofGeotechnical Engineering,ASCE,1995,121(12):856-869.
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