环境地质学 Environmental Geology 主讲人：万新南教授 Prof. Wan xinnan 环境地质学 Environmental Geology

环境地质学Environmental Geology

主讲人：万新南教授　　　　 Prof. Wan xinnan

环境地质学 Environmental Geology

Part three 　　地球表层的塑造过程


6 、 Pre 降水、江河与洪水7 、 Mass Wasting Processes 　表层整体再塑

　　（滑坡、泥石流、溶蚀、塌陷）

8 、海岸线与海岸塑造过程9 、生态与植被



7 、 Mass Wasting Processes　　　　　　　　表层整体再塑

　（滑坡、泥石流、溶蚀、塌陷）



Mass　Wasting　Processes

There is nothing inorganic.... The earth is not a mere fragment of dead history, stratum upon stratum like the leaves of a book, to be studied by geologists and antiquaries 古玩家 chiefly, but living poetry like the leaves of a tree, which precedes flowers and fruit-not a fossil earth, but a living earth.... Henry David Thoreau




　A 、 Flowing sand, landslides, and rock falls are examples of mass wasting, the general term for gravitationally induced downslope movement of debris. B 、 Mass-wasting processes operate on sloping lands; eventually the debris reaches a stream or gully where fluvial processes continue the erosional process.　







Rockfall　　 Rockfall　occurs　where　a　cliff　of　bedrock　is　exposed　to　weathering　and　pieces　of　the　bedrock　are　pried　loose　and　fall,　bounce,　or　roll　to　rest　at　the　base　of　the　cliff.　The　resulting　deposit　is　called　talus 崩塌岩堆 (Behre,　1933;　Schumm　and　Chorley,　1966;　Rapp,　1976).　In　an　irregularly　eroded　cliff,　talus　cones　may　develop　in　the　gully 冲沟 head　areas　(Fig.6.2).　In　more　extensive　cliffs,　coalescing聚集 talus　cones　form　a　more　continuous　blanket　of　debris　referred　to　as　scree　山麓碎石 (Jeffreys,　1932;　Adrews,　1961).　




Rockfall　　 Talus　will　not　rest　at　an　angle　greater　than　the　angle　of　repose.　The　angle　of　repose　is　measured　similarly　to　dip　of　sedimentary　rocks,　i.e.,　from　the　horizontal,　and　is　typically　about　33-35°.　Bedrock　composition,　as　well　as　talus　particle　size,　angularity,　and　sorting,　has　some　effect　on　the　angle　of　repose;　large　angular　boulders　may　rest　at　up　to　40°.　The　angle　of　repose　of　open-pit　mine　　waste　rock　is　approximately　38°.　




Rockfall　　 One　of　the　world's　most　famous　talus　slopes　is　the　one　which　formed　an　impedment 障碍 to　prospectors 开拓者 during　the　Klondike　gold　rush　of　1898.　the　snow-covered　talus　slope,　called　the　Scales,　was　the　only　access　to　Chilkoot　Pass　and　the　Yukon　River.　The　pass　was　guarded　by　the　Canadian　Northeast　Police,　who　required　every　prospector　to　carry　1　ton　of　supplies　up　the　slope　and　into　the　interior.　




One　of　the　world's　most　famous　talus　slopes　is　the　one　which　formed　an　impedment 障碍 to　prospectors开拓者 during　the　Klondike　gold　rush　of　1898.　the　snow-covered　talus　slope,　called　the　Scales,　was　the　only　access　to　Chilkoot　Pass　and　the　Yukon　River.　The　pass　was　guarded　by　the　Canadian　Northeast　Police,　who　required　every　prospector　to　carry　1　ton　of　supplies　up　the　slope　and　into　the　interior.　




Creep　　 Creep　is　the　slow,　downslope　movement　of　soil,　weathered　rock,　or　other　surficial　debris.　Movement　is　by　quasiviscous　flow,　occurring　under　shear　stresses　sufficient　to　produce　permanent　deformation,　but　too　small　to　result　in　a　discrete　failure　surface　such　as　a　landslide.　




Creep　　 Creep　may　be　caused　by　numerous　phenomena.　For　example,　in　terrains　subject　to　frost,　rock　or　soil　may　get　heaved　up　perpendicular　to　the　slope　upon　freezing,　and　returned　vertically　downward　during　a　thaw.　Thus,　over　time,　material　on　a　slope　is　likely　to　move　downhill.　Micro-landslides　and　random　movements　such　as　overturned　trees,　etc.,　all　contribute　to　creep.　




Landslides　　 Landslide　is　the　process　whereby　a　

distinct　mass　of　rock　or　soil　moves　downslope　due　to　gravity.　Landslides,　unlike　creep,　have　one　or　more　distinct　failure　surfaces.　Landslide　velocities　are　typically　on　the　order　of　1　m/day　to　perhaps　300　km/hr　as　in　the　special　case　of　air-entrapped　landslides　generated　by　earthquakes.　Shreve　(1968)　believes　that　the　prehistoric　Blackhawk　Landslide　in　California　slid　at　immense　speeds　on　a　layer　of　compressed　air　that　was　trapped　beneath　the　debris.　The　landslide,　consisting　of　320　million　m3,　traveled　8　km　across　a　desert　floor　at　an　average　slope　of　2.5°.　[Hsu　(1975)　challenges　the　airlubrication 空气润滑 hypothesis 假说 in　favor　of　a　debris　flow　mobilized　by　collision　of　particles　within　a　dust-laden　cloud.].




Landslides　　 Landslide　activity　typically　increases　

after　prolonged　rains,　or　after　the　frost　leaves　the　ground　in　the　spring.　The　novelist　Firtsch　(1980)　describes　the　ominous　hazard　of　landslides　which　weighs　heavily　on　the　minds　of　people　who　live　in　the　steep　slopes　of　the　Swiss　Alps:　




Landslides　　 Classification　of　landslides.　For　si

mplicity,　landslides　can　be　classified　into　two　groups:　1)　translational,　and　2)　rotational.




Landslides　　 Translational　landslides　(Fig.6.8)　slid

e　along　a　bedding　plane　or　other　plane　of　weakness　in　the　rock.　The　entire　mass　moves　parallel　to　this　plane,　as　illustrated　in　the　rock　slide　in　Fig.6.1.　




Landslides　　 Probably　the　largest　translational　lan

dslide　to　occur　in　historic　times　happened　in　1925　in　the　Gros　Ventre　River　Valley　in　Wyoming　(Fig.6.8A).　About　40　million　m3　of　Pennsylvania　Tensleep　Sandstone　slid　on　a　bedding　plane　inclined　about　20°.　Heavy　rain　and　stream　undercutting　at　the　base　of　the　mountain　slope　contributed　to　the　failure　(Voight,　1978).　A　45　km2　lake　formed　behind　the　debris;　two　years　later　the　dam　was　overtopped　by　heavy　spring　runoff,　and　six　people　drowned 淹死 in　the　ensuing 跟着发生 flood.　The　1903　landslide　disaster　at　the　mining　town　of　Frank,　Alberta,　was　a　translational　slide　which　developed　along　a　prominent　set　of　joints　which　dip　into　the　valley.




Landslides　　 Rotational　landslides　(“slumps”　or　“s

lips”)　develop　in　surficial　deposits　or　weathered　rock　(fig6.1).　They　may　be　natural　in　origin　or　induced　by　man.　The　failure　surface　is　roughly　arcuate 弧形 in　cross　section　(spoon-shaped　in　three　dimensions).　At　some　places　the　occurrence　of　a　landslide　at　the　base　of　a　hill　may　leave　the　hillslope　above　unsupported,　and　so　another　landslide　occurs　(Crandell,　1951).　The　chain-reaction　type　of　stair-stepping　slope　failure　up　a　hill　is　called　progressive　failure.　




Landslides　　 22　　Mathematical　analysis.　　Mathe

matical　models　of　landslide　stability　are　presented　in　Terzaghi　(1950;　1962),　Scheidegger　(1961).　Stout　(1969),　Jaeger　(1972),　Schuster　and　Krizek　(1978),　and　Huang　(1983).　Most　problems　involving　the　stability　of　slopes　are　associated　with　the　design　and　construction　of　unbraced 无支挡 cuts　for　highways.　A　very　generalized　rule-of-thumb　is　given　by　Terzaghi　and　Peck　(1948):




Landslides　　 The　role　of　rock　anisotropies　is　very　

important　in　the　design　of　stable　slopes.　Fig4.24　shows　an　example　of　a　stereographic　solution　of　a　possible　wedge　failure　due　to　two　prominent　planar　anisotropies　on　a　deep　cut.　The　use　of　stereoplots　in　analysis　of　slope　stability　is　explained　in　other　Chapter.




Landslides　　 Consider　the　landslide　cross　section　

shown　in　Fig.6.16　having　a　unit　thickness　of　1　m.　Assume　the　debris　consists　of　three　layers　of　known　density　and　shearing　strength　as　shown.　First　assume　a　trial　failure　plane　#1　(ABCD).　The　slide　can　be　arbitrarily　divided　into　a　convenient　number　of　slices,　and　the　moment　of　each　computed　.　Accurate　drafting　and　measurement　of　moment　arms　is　necessary.　The　sum　of　the　eight　driving　moments　is　29,507　kN-m.　The　resisting　moment　is　then　determined,　and　is　equal　to　the　shearing　strength　(in　this　case　the　so-called　undrained　shear　strength　Su　is　used)　times　the　length　of　arc　in　each　slice　times　the　moment　arm.　The　sum　of　the　resisting　moments　is　calculated　to　be　34,500　kN-m.　The　factor　of　safety,　F.S.,　is　equal　to　the　ratio　of　resisting　moment　to　driving　moment:

　　　　　　　　　　　　　　　　　　　　F.S.　　　　　　　　　　　　　　(2.2.9)In　this　case:FS=34,156/29,507=1.16




Landslides　　 Consider　the　landslide　cross　section　

shown　in　Fig.6.16　having　a　unit　thickness　of　1　m.　Assume　the　debris　consists　of　three　layers　of　known　density　and　shearing　strength　as　shown.　First　assume　a　trial　failure　plane　#1　(ABCD).　The　slide　can　be　arbitrarily　divided　into　a　convenient　number　of　slices,　and　the　moment　of　each　computed　.　Accurate　drafting　and　measurement　of　moment　arms　is　necessary.　The　sum　of　the　eight　driving　moments　is　29,507　kN-m.　The　resisting　moment　is　then　determined,　and　is　equal　to　the　shearing　strength　(in　this　case　the　so-called　undrained　shear　strength　Su　is　used)　times　the　length　of　arc　in　each　slice　times　the　moment　arm.　The　sum　of　the　resisting　moments　is　calculated　to　be　34,500　kN-m.　The　factor　of　safety,　F.S.,　is　equal　to　the　ratio　of　resisting　moment　to　driving　moment:

　　　　　　　　　　　　　　　　　　　　F.S.　　　　　　　　　　　　　　(2.2.9)In　this　case:FS=34,156/29,507=1.16

第二部分　地球的

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环境地质学 Environmental Geology 主讲人：万新南教授 Prof. Wan xinnan 环境地质学 Environmental Geology