二维微动剖面探测“孤石”:以深圳地铁7号线为例
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摘要
"孤石"是花岗岩不均匀风化所残留的风化核,在我国南方沿海地区普遍发育."孤石"埋藏分布随机,形状大小各异,给地铁盾构施工带来重大安全隐患,探测"孤石"一直是地铁工程勘察面临的难题.我们首次尝试利用二维微动剖面技术探测"孤石",在深圳地铁7号线车公庙—上沙段区间实测二条剖面,结合少量钻孔资料进行岩性层划分和"孤石"解释.实测结果显示,在二维微动视S波速度剖面上,素填土、粉质粘土、砾质粘性土等岩土层、全风化、强-中风化、微风化和未风化的花岗岩层,视S波速度值各不相同,剖面特征也存在较大差异,利用少量钻孔结果标定,易于划分;在强-中风化花岗岩层中,视S波速度(岩性)横向变化剧烈,局部发育"团块状"高速体,本文将其解释为未风化的花岗岩"孤石".本文结果表明,二维微动剖面技术探测"孤石"是有效的微动视S波速度剖面除能直观显示岩性的纵、横向变化,提供工程基岩面的埋深及起伏形态信息外,还可给出岩土层风化程度的判断信息,为高层建筑的桩基设计提供地球物理依据.作为一种全新的"孤石"探测手段,二维微动剖面技术尤其适用于交通繁忙、建筑物密集的、各种场源干扰严重的闹市区.
A "boulder stone" is referred to the remnant of a granite body which has been unevenly weathered.These "boulders" become a common geological feature in areas close to the shoreline in south of China.They are typically randomly distributed and buried in soil or weathered rocks with varying shapes and sizes.Their existence poses a serious operational risk to the subway tunnel construction.Boulder detection has been a difficult problem in geotechnical investigation and surveying for subway building.This paper documents the first application of a 2D microtremor profiling method to map spherically weathered "boulders".Principles of the method will be described followed by real application examples.Two microtremor profiles were obtained between Chegongmiao and Shangsha along subway line 7 in Shenzhen.The microtremor data,combined with limited drilling data,were used for lithostratigraphic classification and boulder interpretation.On the 2D profiles,we observed different apparent S-wave velocity values for different lithologic sediment layers,such as plain fill,silty clay,rudaceous sediments.In particular,there appeared a strong correlation between apparent S-wave velocity and the degree of weathering of the granitic layers(namely completely,strongly,moderately,slightly,and non-weathered).With the help of limited drilling data,it is possible to quantify,at least qualitatively,the degree of the granite weathering from the apparent S-wave velocity characteristics.Local high apparent S-wave velocity anomalies in otherwise moderately to strongly weathered granitic layers interpreted as unweathered "boulders".Our results demonstrate that the 2D microtremor profiling is a very effective technique for "boulder" detection and mapping.The lithological variation and weathering in both vertical and horizontal directions,the depth of the bedrock and its undulating configuration can be shown clearly in 2D microtremor apparent S-wave velocity profile.Therefore,the method can also provide geophysical basis for designing the pile foundations for the high-rise buildings.As a new method for "boulder" detection and mapping,the 2D microtremor profiling method is particularly useful in densely-populated urban areas with crowded high-rise buildings and heavy traffic.
A "boulder stone" is referred to the remnant of a granite body which has been unevenly weathered.These "boulders" become a common geological feature in areas close to the shoreline in south of China.They are typically randomly distributed and buried in soil or weathered rocks with varying shapes and sizes.Their existence poses a serious operational risk to the subway tunnel construction.Boulder detection has been a difficult problem in geotechnical investigation and surveying for subway building.This paper documents the first application of a 2D microtremor profiling method to map spherically weathered "boulders".Principles of the method will be described followed by real application examples.Two microtremor profiles were obtained between Chegongmiao and Shangsha along subway line 7 in Shenzhen.The microtremor data,combined with limited drilling data,were used for lithostratigraphic classification and boulder interpretation.On the 2D profiles,we observed different apparent S-wave velocity values for different lithologic sediment layers,such as plain fill,silty clay,rudaceous sediments.In particular,there appeared a strong correlation between apparent S-wave velocity and the degree of weathering of the granitic layers(namely completely,strongly,moderately,slightly,and non-weathered).With the help of limited drilling data,it is possible to quantify,at least qualitatively,the degree of the granite weathering from the apparent S-wave velocity characteristics.Local high apparent S-wave velocity anomalies in otherwise moderately to strongly weathered granitic layers interpreted as unweathered "boulders".Our results demonstrate that the 2D microtremor profiling is a very effective technique for "boulder" detection and mapping.The lithological variation and weathering in both vertical and horizontal directions,the depth of the bedrock and its undulating configuration can be shown clearly in 2D microtremor apparent S-wave velocity profile.Therefore,the method can also provide geophysical basis for designing the pile foundations for the high-rise buildings.As a new method for "boulder" detection and mapping,the 2D microtremor profiling method is particularly useful in densely-populated urban areas with crowded high-rise buildings and heavy traffic.
引文
[1]鲍晓东.深圳地区花岗岩残积土工程特性的研究.铁道勘察,2004,(2):72-74Bao X D.Engineering geological properties of the remaindersoil from weathering granite Shonzhen district.RailwayInvestigation and Surveying(in Chinese),2004,(2):72-74.
[2]古力.盾构机破碎孤石条件及预处理方法.隧道建设,2006,26(sup.2):12-13.Gu L.Qualifications for Boulder Breaking by Shield Machinesand Pretreatment of Boulders.Tunnel Construction(in Chinese),2006,26(sup.2):12-13.
[3]王典.地铁工程球状风化专题勘察方案研究.广州建筑,2011,39(2):43-46.Discussion about special investigation programes of sphericalweathering in subway project.Guangzhou Architecture(inChinese),2011,39(2):43-46.
[4]Okada H.“The Microtremor Survey Method”,Society ofExploration Geophysicists,Geophysical Monographs SeriesVol.12,translated by Koya Suto,Society of ExplorationGeophysicists,Tulsa,2003.
[5]Toksoz M N,Lacoss R T.Microtremors-mode structure andsources.Science,1968,159:872-873.
[6]Aki K.Space and time spectra of stationary stochastic waves,with special reference to microtremors.Bull.Earthq.Res.Inst.,1957,35:415-456.
[7]Horike M.Inversion of phase velocity of long-periodmicrotremors to the S-wave-velocity structure down to thebasement in urbanized areas.J.Phys.Earth,1985,33:59-96.
[8]Matsushima T,Okada H.Determination of deep geologicalstructures under urban areas using long-period microtremors.Butsuri-Tansa,1990,43:21-33
[9]Sato T,Kawase H,Matsui M,et al.Array measurement ofhigh frequency microtremors for underground structureestimation.Proceeding of the 4th International Conference onSeismic Zonation,Odawana,Japan,1991,Vol.2,409-416.
[10]Tokimatsu K,Miyadera Y.Characteristics of Rayleighwaves in microtremors and their relation to undergroundstructures.J.Struct.Constr.Eng.Trans.ArchitecturalInst.Japan(in Japanese with English abstract),1992,No.439,81-87.
[11]Chouet B,De Luca G.,Milana G.,et al.Shallow velocitystructure of Stromboli Volcano,Italy,derived from small-aperture array measurements of Strombolian tremor.Bull.Seismol.Soc.Amer.,1998,88(3):653-666.
[12]Kawase H,Satoh T,Iwata T,et al.S-wave velocitystructures in the San Fernando and Santa Monica areas.Proc.of the 2nd International Symposium on Effects ofSurface Geology on Seismic Motions,Tokyo,Japan,1998,2:733-740.
[13]徐佩芬,李传金,凌甦群等.利用微动勘察方法探测煤矿陷落柱.地球物理学报,2009,52(7):1923-1930Xu P F,Li C J,Ling S Q,et al.Mapping collapsed columnsin coal mines utilizing Microtremor Survey Methods.ChineseJ.Geophys.(in Chinese),2009,52(7):1923-1930
[14]凌甦群,三轮滋.瞬态面波法和微动勘探法在日本新瀉县中越地震灾区地质调查中的应用.见:刘云祯主编.工程物探新技术,北京:地质出版社,2006:80-85.Ling S Q,Miwa S.The evaluation of soil structures bySurface Wave Prospecting Method and Microtremor SurveyMethod—2004Mid Niigata Prefecture Earthquake.In:Liu YZ ed.A New Technique on Engineering Geophysical Method.Beijing:Geological Publishing House,2006:80-85.
[15]Xu P F,Ling S Q,Li C J,et al.Mapping deeply-buriedgeothermal faults using microtremor array analysis.Geophys.J.Int.,2012,188(1):115-122.
[16]Ling S Q.Research on the estimation of phase velocities ofsurface waves in microtremors[Ph.D.thesis](in Japanese).Hokkaido University,1994.
[17]Okada H.Theory of efficient array observations ofmicrotremors with special reference to the SPAC method.Exploration Geophysics,2006,37:73-85.
[18]Ohori M,Nobata A,Wakamatsu K.A comparison of ESACand FK methods of estimation phase velocity using arbitrarilyshaped microtremor array.Bull.Seism.Soc.Am.2002,92:2323-2332.
[19]张运标.深圳地区强风化花岗岩分带及地基评价.岩土工程界,2004,7(10):59-62.Zhang Y B.Strongly weathered granitic zonation andfoundation evaluation in Shenzhen.Geotechnical EngineeringWorld(in Chinese),2004,7(10):59-62.
[20]常士骠,《工程地质手册》编写委员会.工程地质手册(第三版).北京:中国建筑工业出版社,1992.978.Chang S B,et al.Engineering Geology Field Manual(ThirdEdition).Beijing:China Architecture&Building Press,1992.978.
[2]古力.盾构机破碎孤石条件及预处理方法.隧道建设,2006,26(sup.2):12-13.Gu L.Qualifications for Boulder Breaking by Shield Machinesand Pretreatment of Boulders.Tunnel Construction(in Chinese),2006,26(sup.2):12-13.
[3]王典.地铁工程球状风化专题勘察方案研究.广州建筑,2011,39(2):43-46.Discussion about special investigation programes of sphericalweathering in subway project.Guangzhou Architecture(inChinese),2011,39(2):43-46.
[4]Okada H.“The Microtremor Survey Method”,Society ofExploration Geophysicists,Geophysical Monographs SeriesVol.12,translated by Koya Suto,Society of ExplorationGeophysicists,Tulsa,2003.
[5]Toksoz M N,Lacoss R T.Microtremors-mode structure andsources.Science,1968,159:872-873.
[6]Aki K.Space and time spectra of stationary stochastic waves,with special reference to microtremors.Bull.Earthq.Res.Inst.,1957,35:415-456.
[7]Horike M.Inversion of phase velocity of long-periodmicrotremors to the S-wave-velocity structure down to thebasement in urbanized areas.J.Phys.Earth,1985,33:59-96.
[8]Matsushima T,Okada H.Determination of deep geologicalstructures under urban areas using long-period microtremors.Butsuri-Tansa,1990,43:21-33
[9]Sato T,Kawase H,Matsui M,et al.Array measurement ofhigh frequency microtremors for underground structureestimation.Proceeding of the 4th International Conference onSeismic Zonation,Odawana,Japan,1991,Vol.2,409-416.
[10]Tokimatsu K,Miyadera Y.Characteristics of Rayleighwaves in microtremors and their relation to undergroundstructures.J.Struct.Constr.Eng.Trans.ArchitecturalInst.Japan(in Japanese with English abstract),1992,No.439,81-87.
[11]Chouet B,De Luca G.,Milana G.,et al.Shallow velocitystructure of Stromboli Volcano,Italy,derived from small-aperture array measurements of Strombolian tremor.Bull.Seismol.Soc.Amer.,1998,88(3):653-666.
[12]Kawase H,Satoh T,Iwata T,et al.S-wave velocitystructures in the San Fernando and Santa Monica areas.Proc.of the 2nd International Symposium on Effects ofSurface Geology on Seismic Motions,Tokyo,Japan,1998,2:733-740.
[13]徐佩芬,李传金,凌甦群等.利用微动勘察方法探测煤矿陷落柱.地球物理学报,2009,52(7):1923-1930Xu P F,Li C J,Ling S Q,et al.Mapping collapsed columnsin coal mines utilizing Microtremor Survey Methods.ChineseJ.Geophys.(in Chinese),2009,52(7):1923-1930
[14]凌甦群,三轮滋.瞬态面波法和微动勘探法在日本新瀉县中越地震灾区地质调查中的应用.见:刘云祯主编.工程物探新技术,北京:地质出版社,2006:80-85.Ling S Q,Miwa S.The evaluation of soil structures bySurface Wave Prospecting Method and Microtremor SurveyMethod—2004Mid Niigata Prefecture Earthquake.In:Liu YZ ed.A New Technique on Engineering Geophysical Method.Beijing:Geological Publishing House,2006:80-85.
[15]Xu P F,Ling S Q,Li C J,et al.Mapping deeply-buriedgeothermal faults using microtremor array analysis.Geophys.J.Int.,2012,188(1):115-122.
[16]Ling S Q.Research on the estimation of phase velocities ofsurface waves in microtremors[Ph.D.thesis](in Japanese).Hokkaido University,1994.
[17]Okada H.Theory of efficient array observations ofmicrotremors with special reference to the SPAC method.Exploration Geophysics,2006,37:73-85.
[18]Ohori M,Nobata A,Wakamatsu K.A comparison of ESACand FK methods of estimation phase velocity using arbitrarilyshaped microtremor array.Bull.Seism.Soc.Am.2002,92:2323-2332.
[19]张运标.深圳地区强风化花岗岩分带及地基评价.岩土工程界,2004,7(10):59-62.Zhang Y B.Strongly weathered granitic zonation andfoundation evaluation in Shenzhen.Geotechnical EngineeringWorld(in Chinese),2004,7(10):59-62.
[20]常士骠,《工程地质手册》编写委员会.工程地质手册(第三版).北京:中国建筑工业出版社,1992.978.Chang S B,et al.Engineering Geology Field Manual(ThirdEdition).Beijing:China Architecture&Building Press,1992.978.
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