汶川地震砂砾土液化分布及土性特征初步研究
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摘要
通过汶川8.0级地震液化震害调查以及对工程地质条件和土层剖面的分析,给出此次地震砂砾土液化的分布和规模,并通过典型液化场地现场测试和室内试验,获取了地表喷出物与实际液化土类的关系以及液化砂砾土土性特征。分析结果表明,此次地震砂砾土液化真实存在且占主导地位,为此次地震全部液化点的80%～85%。成都地区和德阳地区的液化土层基本上均为砂砾土,分布在5个条形区域,约占此次地震液化总数的75%。绵阳地区地层不均匀性较强,液化土类为砂土、砂砾土混合型,其中砂砾土液化占到该地区液化点的1/3～2/3,约占此次地震液化总数的5%～10%。此次地震中粉砂、细砂占地表喷出物半数以上的现象只是一种表象,地表喷出物与地下实际液化土层的成分差异显著。典型液化场地勘察测试表明,液化场地地层总体较为简单,层序结构基本一致。液化土层中颗粒级配曲线总体平缓,光滑程度差,不均匀系数较大,曲率系数较小,粒径跨度大且存在粒组缺失现象,各场地级配形态差别显著。现有标准贯入试验在砂砾场地上不可行,建议采用超重型动力触探试验,同时现有基于砂土的剪切波速液化判别方法对砂砾土不适用,需另行考虑。
A distribution map is compiled of gravelly soils that liquefied during the 2008 Wenchuan,China Earthquake(Ms=8.0).The map is based on detailed field investigations and analysis of geological soil profiles.The geology is summarized on geological cross sections and borehole logs.Four typical liquefied sites were selected for drilling to collect soil samples,sounding to determine dynamic penetration(DPT)resistance,and measurement of shear wave velocities with SASW tests.From the field investigation,118 liquefied sites were identified and surface effects documented shortly after the earthquake.This investigation showed:①that sandboils indicative of liquefaction occurred extensively across hundreds of square kilometers of farmland,in 120 villages,and beneath 8 schools and 5 factories;②that ground fissures and ground displacements damaged some rural houses,school buildings,and manufacturing plants.In addition several wells malfunctioned primarily due to clogging with boiled up sand and gravel;③that the Chengdu plain is underlain by gravelly soils with thicknesses ranging from 0m to 541m and that looser layers within these gravel beds are the materials that liquefied;④that the observed liquefaction features developed in five long narrow zones across the plain which vary from 20km to 40km in length;⑤that these zones are underlain by fluvial and alluvial gravelly sediments deposited by ancient rivers;⑥that mean grain sizes of soil samples taken from the gravels that liquefied range from 1 mm to 30 mm;⑦that grain sizes of the sampled soils were generally larger than those from samples of overlying ejected in sand boil deposits;⑧thus subsurface layers of liquefied soil could not be directly correlated with the ejected soils.The compiled information enrichs the global database for gravelly soils that have liquefied and provides a database for development of improved methods for evaluating liquefaction resistance of gravelly soils.
A distribution map is compiled of gravelly soils that liquefied during the 2008 Wenchuan,China Earthquake(Ms=8.0).The map is based on detailed field investigations and analysis of geological soil profiles.The geology is summarized on geological cross sections and borehole logs.Four typical liquefied sites were selected for drilling to collect soil samples,sounding to determine dynamic penetration(DPT)resistance,and measurement of shear wave velocities with SASW tests.From the field investigation,118 liquefied sites were identified and surface effects documented shortly after the earthquake.This investigation showed:①that sandboils indicative of liquefaction occurred extensively across hundreds of square kilometers of farmland,in 120 villages,and beneath 8 schools and 5 factories;②that ground fissures and ground displacements damaged some rural houses,school buildings,and manufacturing plants.In addition several wells malfunctioned primarily due to clogging with boiled up sand and gravel;③that the Chengdu plain is underlain by gravelly soils with thicknesses ranging from 0m to 541m and that looser layers within these gravel beds are the materials that liquefied;④that the observed liquefaction features developed in five long narrow zones across the plain which vary from 20km to 40km in length;⑤that these zones are underlain by fluvial and alluvial gravelly sediments deposited by ancient rivers;⑥that mean grain sizes of soil samples taken from the gravels that liquefied range from 1 mm to 30 mm;⑦that grain sizes of the sampled soils were generally larger than those from samples of overlying ejected in sand boil deposits;⑧thus subsurface layers of liquefied soil could not be directly correlated with the ejected soils.The compiled information enrichs the global database for gravelly soils that have liquefied and provides a database for development of improved methods for evaluating liquefaction resistance of gravelly soils.
引文
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[12]何银武.论成都盆地的成生时代及其早期沉积物的一般特征[J].地质论评,1992,38(2):149-156(He Yinwu.The age of formation of the Chengdu Basin and features of its early deposits[J].Geological Review,1992,38(2):149-156(in Chinese))
[13]钱洪,唐荣昌.成都平原的形成与演化[J].四川地震,1997,3:1-7(Qian Hong,Tang Rongchang.On the formation and evolution of the Chengdu Plain[J].Earthquake Research in Sichuan,1997,3:1-7(in Chinese))
[14]李永昭,郭兵.成都平原的晚新生代构造[J].成都理工大学学报:自然科学版,2008,35(4):371-376(Li Yongzhao,Guo Bing.Cenozonic tectonics of Chengdu Plain,Sichuan,China[J].Journal of Chengdu University of Technology:Science&Technology Edition,2008,35(4):371-376(in Chinese))
[15]DB51/T5026—2001成都地区建筑地基基础设计规范[S](DB51/T5026—2001Design code for building foundation of Chengdu region[S](in Chinese))
[2]Seed R B,Cetin K O,Moss R E S,et al.Recent advances in soil liquefaction engineering,a unified and consistent framework[R].EERC,USA:Earthquake Engineering Research Center,2003
[3]任红梅,吕西林,李培振.饱和砂土液化研究进展[J].地震工程与工程振动,2007,27(6):166-174(Ren Hongmei,LüXilin,Li Peizhen.Advances in liquefaction research on saturated soils[J].Journal of Earthquake Engineering and Engineering Vibration,2007,27(6):166-174(in Chinese))
[4]刘恢先.唐山大地震震害[M].北京:地震出版社,1989
[5]石兆吉,郁寿松,丰万玲.土壤液化势的剪切波速判别法[J].岩土工程学报,1993,15(1):74-80
[6]Andrus R D,Stokoe K H II.Liquefaction resistance of soils from shear-wave velocity[J].Journal of Geotechnical and Geoenviromental Engineering,ASCE,2000,126(11):1015-1025
[7]GB50011—2001建筑抗震设计规范[S].北京:中国建筑工业出版社,2001(GB50011—2001Code for seismic design of buildings[S].Beijing:China Architecture&Building Press,2001(in Chinese))
[8]袁晓铭,曹振中,孙锐,等.汶川8.0级地震液化特征初步研究[J].岩土力学与工程学报,2009,28(6):1288-1296(Yuan Xiaoming,Cao Zhenzhong,Sun Rui,et al.Preliminary research on liquefaction characteristics of Wenchuan8.0earthquake[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(6):1288-1296(in Chinese))
[9]刘惠珊.砾石的液化判别探讨[C]//第五届全国地震工程学术会议论文集.北京,1998:183-188
[10]邓康龄.四川盆地形成演化与油气勘探领域[J].天然气工业,1992,12(5):7-12(Deng Kangling.Formation and evolution of Sichuan Basin and domains for oil and gas exploration[J].Atural Gas Industry,1992,12(5):7-12(in Chinese))
[11]刘兴诗.四川盆地的第四系[M].成都:四川科学技术出版社,1983
[12]何银武.论成都盆地的成生时代及其早期沉积物的一般特征[J].地质论评,1992,38(2):149-156(He Yinwu.The age of formation of the Chengdu Basin and features of its early deposits[J].Geological Review,1992,38(2):149-156(in Chinese))
[13]钱洪,唐荣昌.成都平原的形成与演化[J].四川地震,1997,3:1-7(Qian Hong,Tang Rongchang.On the formation and evolution of the Chengdu Plain[J].Earthquake Research in Sichuan,1997,3:1-7(in Chinese))
[14]李永昭,郭兵.成都平原的晚新生代构造[J].成都理工大学学报:自然科学版,2008,35(4):371-376(Li Yongzhao,Guo Bing.Cenozonic tectonics of Chengdu Plain,Sichuan,China[J].Journal of Chengdu University of Technology:Science&Technology Edition,2008,35(4):371-376(in Chinese))
[15]DB51/T5026—2001成都地区建筑地基基础设计规范[S](DB51/T5026—2001Design code for building foundation of Chengdu region[S](in Chinese))
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