南海北部陆坡稳定性定量分析
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摘要
随着海洋工程的发展,海底滑坡作为一种潜在的地质灾害逐渐成为人们关注的热点.本文采用二维极限平衡法计算并分析了海底斜坡稳定性问题.通过对斜坡模型在各种条件下安全系数的计算,定量分析了斜坡内在因素(如斜坡角度、主要土力学参数)和主要触发机制(地震、快速堆积等)对安全系数的影响.理论计算表明,静态条件下,均质斜坡角度小于20°时,均处于稳定状态;对于含软弱层的斜坡,快速堆积等引起的不排水状态下斜坡安全系数明显降低,斜坡角度大于14°时就会发生失稳.拟静态条件下,当地震动峰值加速度(PGA)小于0.15g时,对于角度小于20°的均质斜坡处于稳定状态,但PGA大于0.25g时,角度大于13°的斜坡即处于失稳状态;对于含软弱层斜坡,PGA为0.1g时,角度大于10°的斜坡即处于不稳定状态;当PGA大于0.3g时,3°以上的海底斜坡即处于失稳状态,发生海底滑坡.结合南海北部陆坡海底地形、地貌特征,在静态条件下,均处于稳定状态;但在地震加载的拟静态下,根据南海北部地震动峰值加速度分布,台湾浅滩段则处于不稳定状态.这解释了该区域大陆坡折带处海底滑坡广泛发育的原因,也表明了地震是引发南海北部滑坡最主要的触发机制之一.
With the development of ocean engineering,submarine landslide becomes a focus topic for its potential harmfulness.In this paper,the stability of submarine slope in the northern South China Sea is analyzed using 2D limit equilibrium method.Based on calculation of safety factors under various conditions,the influence of slope internal factors(such as slope angle,the main parameters of soil mechanics) and main trigger mechanisms(earthquakes,rapid accumulation,etc.) on safety factor is analyzed quantitatively.Theoretical calculations show that,homogeneous submarine slopes with angle less than 20° are stable under static conditions.For submarine slopes with a weak layer,excess pore pressure generated by rapid accumulation can significantly reduce safety factor,which causes the slope instability with an angle greater than 14°.Under pseudostatic conditions,when the earthquake peak ground acceleration(PGA) is less than 0.15 g,the homogeneous slope with the angle less than 20° is stable.However,with the PGA greater than 0.25 g,the slopes with angle greater than 13° are in unstable state;For case of having a weak layer,when PGA=0.1 g,the slope with angle greater than 10° will be in an unstable state;when the PGA≥0.3 g,the submarine slopes with angle greater 3° will be instability.Combining with the topography,geomorphology characteristic,the northern slope of the South China Sea are stable under static conditions.However,in the case of earthquake loading,the Taiwan Bank section will be unstable,according to the distribution of PGA on the northern slope of the South China Sea.This is a reason for submarine landslides developed extensively in this area.In addition,results show that earthquake is one of the most important trigger mechanisms in the northern slope of the South China Sea.
With the development of ocean engineering,submarine landslide becomes a focus topic for its potential harmfulness.In this paper,the stability of submarine slope in the northern South China Sea is analyzed using 2D limit equilibrium method.Based on calculation of safety factors under various conditions,the influence of slope internal factors(such as slope angle,the main parameters of soil mechanics) and main trigger mechanisms(earthquakes,rapid accumulation,etc.) on safety factor is analyzed quantitatively.Theoretical calculations show that,homogeneous submarine slopes with angle less than 20° are stable under static conditions.For submarine slopes with a weak layer,excess pore pressure generated by rapid accumulation can significantly reduce safety factor,which causes the slope instability with an angle greater than 14°.Under pseudostatic conditions,when the earthquake peak ground acceleration(PGA) is less than 0.15 g,the homogeneous slope with the angle less than 20° is stable.However,with the PGA greater than 0.25 g,the slopes with angle greater than 13° are in unstable state;For case of having a weak layer,when PGA=0.1 g,the slope with angle greater than 10° will be in an unstable state;when the PGA≥0.3 g,the submarine slopes with angle greater 3° will be instability.Combining with the topography,geomorphology characteristic,the northern slope of the South China Sea are stable under static conditions.However,in the case of earthquake loading,the Taiwan Bank section will be unstable,according to the distribution of PGA on the northern slope of the South China Sea.This is a reason for submarine landslides developed extensively in this area.In addition,results show that earthquake is one of the most important trigger mechanisms in the northern slope of the South China Sea.
引文
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[2]McAdoo B G,Pratson L F,Orange D L.Submarine landslidegeomorphology,US continental slope.Marine Geology,2000,169(1-2):103-136.
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[8]Sultan N,Voisset M,Marsset B,et al.Potential role ofcompressional structures in generating submarine slope failuresin the Niger Delta.Marine Geology,2007,237(3-4):169-190.
[9]van Asch T W J,Malet J P,van Beek L P H,et al.Techniques,issues and advances in numerical modelling of landslide hazard.Bull.Soc.,2007,178(2):65-88.
[10]Mienert J.COSTA-continental slope stability:major aims andtopics.Mar.Geol.,2004,213(1-4):1-7.
[11]Nittrouer C A.STRATAFORM:overview of its design andsynthesis of its results.Mar.Geol.,1999,154(1-4):3-12.
[12]Bishop A W.The use of the slip circle in the stability analysisof slopes.Géotechnique,1955,5(1):7-17.
[13]Morgenstern N R,Price V E.The analysis of the stability ofgeneral slip surfaces.Géotechnique,1965,15(1):79-93.
[14]Spencer E.A method of analysis of the stability of embankmentsassuming parallel inter-slice forces.Géotechnique,1967,17(1):11-26.
[15]Biscontin G,Pestana J M,Nadim F.Seismic triggering ofsubmarine slides in soft cohesive soil deposits.Mar.Geol.,2004,203(3-4):341-354.
[16]Azizian A,Popescu R.Three-dimensional seismic analysis ofsubmarine slopes.Soil Dyn.Earthqu.Eng.,2006,26(9):870-887.
[17]Strasser M,Stegmann S,Bussmann F,et al.Quantifyingsubaqueous slope stability during seismic shaking:LakeLucerne as model for ocean margins.Marine Geology,2006,240(1-4):77-97.
[18]Lee H J,Edwards B D.Regional method to assess offshoreslope stability.J.Geotech.Engrg.,1986,112(5):489-509.
[19]王海荣,王英民,邱燕等.南海北部陆坡的地貌形态及其控制因素.海洋学报,2008,30(2):70-79.Wang H R,Wang Y M,Qiu Y,et al.Geomorphology and itscontrol of deep-water slope of the margin of the South ChinaSea.Atca Oceanologica Sinica(in Chinese),2008,30(2):70-79.
[20]Leynaud D,Sultan N,Mienert J.The role of sedimentationrate and permeability in the slope stability of the formerlyglaciated Norwegian continental margin:the Storegga slidemodel.Landslides,2007,4(4):297-309.
[21]Lykousis V,Roussakis G,Alexandri M,et al.Sliding andregional slope stability in active margins:North AegeanTrough(Mediterranean).Marine Geology,2002,186(3-4):281-298.
[22]章伟艳,张富元,陈荣华等.南海深水区晚更新世以来沉积速率、沉积通量与物质组成.沉积学报,2002,20(4):668-674.Zhang W Y,Zhang F Y,Chen R H,et al.Constituents ofmatter and sedimentation fluxes and sedimentation rates ofdeep-water sedimentation during the late pleistocene in theSouth China Sea.Acta Sedimentologica Sinica(in Chinese),2002,20(4):668-674.
[23]Huang W,Wang P X.A quantitative approach to deep-watersedimentation in the South China Sea:Changes since the lastglaciation.Science in China Series D:Earth Sciences,1998,41(2):195-201.
[24]邵磊,李献华,韦刚健等.南海陆坡高速堆积体的物质来源.中国科学(D辑),2001,31(10):828-833.Shao L,Li X H,Wei G J,et al.Provenance of a prominentsediment drift on the northern South China Sea.Science inChina(Series D)(in Chinese),2001,31(10):828-833.
[25]Bühring C,Sarnthein M,Erlenkeuser H.Toward a high-resolution stable isotope stratigraphy of the last 1.1my:Site1144,South China Sea.//Prell W L,Wang P,Blum P,et aleds.Proc.ODP,Sci.Results.2004,184:1-29.
[26]刘以宣.南海新构造与地壳稳定性.北京:科学出版社,1994:151-158.Liu Y X.Neotectonics and Crustal Stability of South ChinaSea(in Chinese).Beijing:Science Press,1994:151-158.
[27]陈仁法,康英,黄新辉等.南海北部地震危险性分析.华南地震,2009,29(4):36-45.Chen R F,Kang Y,Huang X H,et al.Seismic risk analysis inNorthern South China Sea.South China Journal ofSeismology(in Chinese),2009,29(4):36-45.
[28]Micallef A,Berndt C,Masson D G,et al.A technique for themorphological characterization of submarine landscapes asexemplified by debris flows of the Storegga Slide.Journal ofGeophysical Research,2007,112:F02001.
[29]李守军,初凤友,方银霞等.南海北部陆坡神狐海域浅地层与单道地震剖面联合解释—水合物区沉积地层特征.热带海洋学报,2010,29(4):56-62.Li S J,Chu F Y,Fang Y X,et al.Associated interpretation ofsub-bottom and single-channel seismic profiles from slope ofShenhu area in the northern South China Sea-characteristicsof gas hydrate sediment.Journal of Tropical Oceanography(inChinese),2010,29(4):56-62.
[30]郑志昌,陈俊仁,朱照宇.南海海底土体物理力学特征及其地质环境初步研究.水文地质工程地质,2004,(4):50-65.Zheng Z C,Chen J R,Zhu Z Y.Physical and mechanicalcharacteristics of seabed soils and its geological environmentin South China Sea.Hydrogeology&Engineering Geology(inChinese),2004,(4):50-65.
[31]冯文科,石要红,陈玲辉.南海北部外陆架和上陆坡海底滑坡稳定性研究.海洋地质与第四纪地质,1994,14(2):81-94.Feng W K,Shi Y H,Chen L H.Research for seafloorlandslide stability on the outer continental shelf and the uppercontinental slope en the northern South China Sea.MarineGeology and Quaternary Geology(in Chinese),1994,14(2):81-94.
[32]Leynaud D,Mienert J,Nadim F.Slope stability assessment ofthe Helland Hansen area offshore the mid-Norwegianmargin.Marine Geology,2004,213(1-4):457-480.
[33]Hance J J.Development of a Database and Assessment ofSeafloor Slope Stability based on Published Literature.Austin:The University of Texas,245.
[34]Kvalstad T K,Nadim F,Kaynia A M,et al.Soil conditionsand slope stability in the Ormen Lange area.Marine andPetroleum Geology,2005,22(1-2):299-310.
[35]Seed H B,Tokimatsu K,Harder L F,et al.Influence of SPTProcedures in soil Liquefaction Resistance evaluations.Journalof Geotechnical Engineering,1985,111(12):1425-1445.
[2]McAdoo B G,Pratson L F,Orange D L.Submarine landslidegeomorphology,US continental slope.Marine Geology,2000,169(1-2):103-136.
[3]Chapron E,Beck C,Pourchet M,et al.1 8 2 2earthquake-triggered homogenite in Lake Le Bourget(NW Alps).TerraNova,1999,11(2-3):86-92.
[4]Hornbach M J,Mondziel S A,Grindlay N R,et al.Did asubmarine slide trigger the 1918Puerto Rico tsunami?Scienceof Tsunami Hazards,2008,27(2):22-31.
[5]Locat J,Lee H J.Submarine landslides:advances andchallenges.Canadian Geotechnical Journal,2002,39(1):193-212.
[6]Sultan N,Cochonat P,Canals M,et al.Triggering mechanismsof slope instability processes and sediment failures oncontinental margins:a geotechnical approach.Mar.Geol.,2004,213(1-4):291-321.
[7]Urgeles R,Leynaud D,Lastras G,eta l.Back-analysis and failuremechanisms of a large submarine slide on the Ebro slope,NWMediterranean.Marine Geology,2006,226(3-4):185-206.
[8]Sultan N,Voisset M,Marsset B,et al.Potential role ofcompressional structures in generating submarine slope failuresin the Niger Delta.Marine Geology,2007,237(3-4):169-190.
[9]van Asch T W J,Malet J P,van Beek L P H,et al.Techniques,issues and advances in numerical modelling of landslide hazard.Bull.Soc.,2007,178(2):65-88.
[10]Mienert J.COSTA-continental slope stability:major aims andtopics.Mar.Geol.,2004,213(1-4):1-7.
[11]Nittrouer C A.STRATAFORM:overview of its design andsynthesis of its results.Mar.Geol.,1999,154(1-4):3-12.
[12]Bishop A W.The use of the slip circle in the stability analysisof slopes.Géotechnique,1955,5(1):7-17.
[13]Morgenstern N R,Price V E.The analysis of the stability ofgeneral slip surfaces.Géotechnique,1965,15(1):79-93.
[14]Spencer E.A method of analysis of the stability of embankmentsassuming parallel inter-slice forces.Géotechnique,1967,17(1):11-26.
[15]Biscontin G,Pestana J M,Nadim F.Seismic triggering ofsubmarine slides in soft cohesive soil deposits.Mar.Geol.,2004,203(3-4):341-354.
[16]Azizian A,Popescu R.Three-dimensional seismic analysis ofsubmarine slopes.Soil Dyn.Earthqu.Eng.,2006,26(9):870-887.
[17]Strasser M,Stegmann S,Bussmann F,et al.Quantifyingsubaqueous slope stability during seismic shaking:LakeLucerne as model for ocean margins.Marine Geology,2006,240(1-4):77-97.
[18]Lee H J,Edwards B D.Regional method to assess offshoreslope stability.J.Geotech.Engrg.,1986,112(5):489-509.
[19]王海荣,王英民,邱燕等.南海北部陆坡的地貌形态及其控制因素.海洋学报,2008,30(2):70-79.Wang H R,Wang Y M,Qiu Y,et al.Geomorphology and itscontrol of deep-water slope of the margin of the South ChinaSea.Atca Oceanologica Sinica(in Chinese),2008,30(2):70-79.
[20]Leynaud D,Sultan N,Mienert J.The role of sedimentationrate and permeability in the slope stability of the formerlyglaciated Norwegian continental margin:the Storegga slidemodel.Landslides,2007,4(4):297-309.
[21]Lykousis V,Roussakis G,Alexandri M,et al.Sliding andregional slope stability in active margins:North AegeanTrough(Mediterranean).Marine Geology,2002,186(3-4):281-298.
[22]章伟艳,张富元,陈荣华等.南海深水区晚更新世以来沉积速率、沉积通量与物质组成.沉积学报,2002,20(4):668-674.Zhang W Y,Zhang F Y,Chen R H,et al.Constituents ofmatter and sedimentation fluxes and sedimentation rates ofdeep-water sedimentation during the late pleistocene in theSouth China Sea.Acta Sedimentologica Sinica(in Chinese),2002,20(4):668-674.
[23]Huang W,Wang P X.A quantitative approach to deep-watersedimentation in the South China Sea:Changes since the lastglaciation.Science in China Series D:Earth Sciences,1998,41(2):195-201.
[24]邵磊,李献华,韦刚健等.南海陆坡高速堆积体的物质来源.中国科学(D辑),2001,31(10):828-833.Shao L,Li X H,Wei G J,et al.Provenance of a prominentsediment drift on the northern South China Sea.Science inChina(Series D)(in Chinese),2001,31(10):828-833.
[25]Bühring C,Sarnthein M,Erlenkeuser H.Toward a high-resolution stable isotope stratigraphy of the last 1.1my:Site1144,South China Sea.//Prell W L,Wang P,Blum P,et aleds.Proc.ODP,Sci.Results.2004,184:1-29.
[26]刘以宣.南海新构造与地壳稳定性.北京:科学出版社,1994:151-158.Liu Y X.Neotectonics and Crustal Stability of South ChinaSea(in Chinese).Beijing:Science Press,1994:151-158.
[27]陈仁法,康英,黄新辉等.南海北部地震危险性分析.华南地震,2009,29(4):36-45.Chen R F,Kang Y,Huang X H,et al.Seismic risk analysis inNorthern South China Sea.South China Journal ofSeismology(in Chinese),2009,29(4):36-45.
[28]Micallef A,Berndt C,Masson D G,et al.A technique for themorphological characterization of submarine landscapes asexemplified by debris flows of the Storegga Slide.Journal ofGeophysical Research,2007,112:F02001.
[29]李守军,初凤友,方银霞等.南海北部陆坡神狐海域浅地层与单道地震剖面联合解释—水合物区沉积地层特征.热带海洋学报,2010,29(4):56-62.Li S J,Chu F Y,Fang Y X,et al.Associated interpretation ofsub-bottom and single-channel seismic profiles from slope ofShenhu area in the northern South China Sea-characteristicsof gas hydrate sediment.Journal of Tropical Oceanography(inChinese),2010,29(4):56-62.
[30]郑志昌,陈俊仁,朱照宇.南海海底土体物理力学特征及其地质环境初步研究.水文地质工程地质,2004,(4):50-65.Zheng Z C,Chen J R,Zhu Z Y.Physical and mechanicalcharacteristics of seabed soils and its geological environmentin South China Sea.Hydrogeology&Engineering Geology(inChinese),2004,(4):50-65.
[31]冯文科,石要红,陈玲辉.南海北部外陆架和上陆坡海底滑坡稳定性研究.海洋地质与第四纪地质,1994,14(2):81-94.Feng W K,Shi Y H,Chen L H.Research for seafloorlandslide stability on the outer continental shelf and the uppercontinental slope en the northern South China Sea.MarineGeology and Quaternary Geology(in Chinese),1994,14(2):81-94.
[32]Leynaud D,Mienert J,Nadim F.Slope stability assessment ofthe Helland Hansen area offshore the mid-Norwegianmargin.Marine Geology,2004,213(1-4):457-480.
[33]Hance J J.Development of a Database and Assessment ofSeafloor Slope Stability based on Published Literature.Austin:The University of Texas,245.
[34]Kvalstad T K,Nadim F,Kaynia A M,et al.Soil conditionsand slope stability in the Ormen Lange area.Marine andPetroleum Geology,2005,22(1-2):299-310.
[35]Seed H B,Tokimatsu K,Harder L F,et al.Influence of SPTProcedures in soil Liquefaction Resistance evaluations.Journalof Geotechnical Engineering,1985,111(12):1425-1445.
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