山崩
岩盤、風化層、或其混合
物因重力的吸引，往下坡
方向的運動即為山崩
1. 山崩與其衝擊
-當人口增加，都市與道路開始擴
張時，自然環境遭受破壞，山崩
對人類的威脅亦逐漸增加。
-增進對山崩與地質環境的瞭解，
有助於紓解其災害。
2. 山崩的形式
-山坡地的組成、含水量、邊坡的傾角
等因素影響山崩活動的形式與運動的
快慢。
兩種形式：
(1)涉及山坡地瞬間的破壞，導致黏滯
度高的塊體以崩移、掉落，或滑動
方式運動。
(2)沈積物混合著水份與空氣的流動。
2.1 山坡地的破壞
(1)崩移：質體沿著弧形上凹的滑動
面滑動。公路兩側的山坡地常因人為
的開挖調整，破壞了環境的自然平衡
狀態，導致崩移作用的發生。
崩移
(2)掉落：落石自懸崖上方垂直向下的
瞬時掉落，岩塊大小可能超過數百公
尺，當其撞擊地面時，可裂解成諸多
小塊體。
落石
岩屑掉落
(3)滑動：質體沿著平面狀滑動面的下
坡運動，一般以滑動方式進行。若有
斷層、葉理面，或層理面存在時，容
易產生滑動。
岩板滑動
岩屑滑動
流動
2.2 流動
(1)泥漿流：泛指飽和沈積物的流動。
岩屑流為比砂更為粗大的岩屑流動，
流速介於1m/year至100m/hour之間。
若岩屑流之含水量過高，導致整體岩
屑流呈現流體的特性時，則稱之為泥
流。
泥漿流
岩屑流
泥流
(2)粒狀流：未飽和的沈積物、空氣和
水份的流動，流動沈積物的重量由顆
粒彼此之間的接觸與碰撞來支撐。潛
移乃流速極慢，幾乎無法察覺的粒狀
流。土流比潛移流動迅速，且可延續
數天、數月，甚至於數年。
creep
潛移
顆粒流
土流
土流特徵
(3)顆粒流：相對的較為乾燥或半乾燥
的沈積物流動，空氣充滿沈積物顆粒
間的空隙。
岩屑崩進
The Blackhawk slide in southern California is a
good example of a long rock avalanche.
2.3 寒冷氣候的山崩
-高緯度或高山地區，解凍的冰水飽
和了風化層，造成地表舉升。年復一
年的冰凍、解凍作用造成地表反覆的
上升和下降，風化層如潛移般的往下
坡方向移動。
-寒冷地區淺層的冰在夏季溶解時，
冰水可飽和地表淺層的沈積物，若
坡度夠陡，可因重力吸引而形成解
凍土流。
石冰川
2.3 海底山崩
-海底山崩作用與陸域相似，海盤常
因海底崩移、滑動或流動而斷裂。
-大型之海底沖積扇常見山崩作用之
特徵。山崩區域顯示三個明顯的分
區：形成區-地層下陷與崩移活動區
；中央溝渠區-沈積物沿此區搬運；
堆積區-崩落物質重疊堆積於此區。
海底山崩
3 影響邊坡穩定的因子
重力→坡角
水份→邊坡之水文特性
地質材料之組成
觸發事件之發生與否
邊坡穩定的條件
剪力強度大於剪應力，
邊坡處於穩定狀態
Fs (安全係數) =剪力強度/剪應力
3.1重力與坡角
-剪應力與剪力強度為影響邊坡穩定
之兩大力量。重力為剪應力之主要
因子，其大小與坡角密切相關。剪
力強度則為抵抗物質滑動之內聚力
，與摩擦力、黏滯度與植生有關。
Fs (安全係數) =剪力強度/剪應力
-安全係數小於1時，則山崩明顯。
3.2 水份
-乾燥的砂傾倒於平坦的桌面時，堆
高成圓錐狀，其傾角稱為休止角。
若含水量逐漸升高，則可見砂堆轉
化成泥漿狀，容易流失。
-沈積物如粉砂和黏土，具有足夠的
黏滯力，但被水飽和之後，內部水
壓升高，細粒沈積物變得不穩定，
甚至開始流動。
3.3 困擾的地質材料
(1) 土壤液化：因含水量的升高，使
得土壤由固態轉化為液態的現象。
土壤液化時的含水量稱為液性限度
，其大小因土壤性質而異。黏土含
量高的土壤液性限度極大，不易液
化，呈現高度可塑狀態。
(2) 膨脹土壤：亦稱為收縮-膨脹土
壤，土體的體積可因飽和或乾燥而
膨脹或收縮。
(3) 敏感性土壤：此類土壤可因輕度
的擾動或再塑作用而喪失其剪力強
度。土壤結構受擾動呈現液化或壓
密現象之作用，即為再塑作用。
3.4觸發事件(trigger events)
(1) 地震和其他震動：突發的震動如
地震、爆炸、熱雷雨，或甚至於大
卡車路過，都可能升高剪應力，觸
發山崩。
(2) 火山噴發：大規模層狀火山坡角
大，內部包含不穩定的熔岩流與火
山碎屑物交替出現，潛在威脅大。
(3) 山坡地開發：河流在坡腳的底切
作用，人為不正常的開挖，以及坡
頂荷重的增加，都可能引起山坡地
的滑動。
(4) 水文特性的變化：不尋常或連續
性的降雨導致荷重增加，實為許多
流動的主因。
道路開挖前
道路開挖後
道路開挖前
道路開挖後
Landsliding study, why?
-for engineer to distinguish and
recognize the different phenomena
for purposes of design and also to
take the remedial or safety
measures.
-for geologist to interpret the past
and predict the present trends of
topography.
A. Processes of Landsliding
It is a continuous series from cause to
effect. Landslides take place when
geologic, topographic and climatic
influences are common.
The process leading to the development
of slide has its beginning with the rock
formation, when its physical properties
are determined, and includes all crustal
movement, erosion, weathering, until
some action sets a mass of it in motion
downhill. All true slides involve the
failure of earth material under shear
stress.
B. Stability Treatment
-modification of factors contribute to
slope shape : unloading the active
part and loading its toe.
-drainage of the sloped area :
subsurface and surface drainage
system.
-supporting an anchorage of a sliding
slope: retaining walls, grouting, castin piles, anchorage (rock bolt,
monostrand, tendon), etc.
“All methods should prevent the
water in near-surface layer from
freezing.”
C. Solution of Problem
-avoidance of potential slides.
-excavation : economic consideration.
-drainage.
-restraining structures.
邊坡穩定處理
擋土牆
排水
開挖
植生
擋土牆 + 岩錨
植生
擋土牆 + 柵欄
明隧道
Factors That Contribute to
High Shear Stress
a. Removal of lateral support
a) erosion by :
(1) streams and rivers in the
production of most natural slopes.
(2)
glacial ice, many valleys in
mountains regions were deeply cut by
glaciers,
when
ice
retreated,
landslides occurred on a large scale.
(3) waves, and longshore current or
tidal currents.
(4) Subaerial weathering, wetting
and drying, and frost action.
b) creation of new slope by previous
rockfall, slide, subsidence or largescale faulting.
c) human agencies
(1) cuts, quarries, pits, and canals.
(2) removal of retaining walls, sheet
piling, etc.
(3) draining of lakes or drawdown of
reservoirs.
b. Surcharge
a) natural agencies
(1)
weight of rain, hail, snow, and
water from springs.
(2) accumulation of talus overriding
landslide material.
b) human agencies
(1) construction of fill.
(2) stockpiles o fore or rock.
(3) wastepiles from strip mining.
(4) weight of buildings and other
structures and trains.
(5) weight of water from leakage
pipelines, sewers, canals, reservoirs,
etc.
d. Transitory earth stresses
Earthquakes have triggered a great
many landslides, both small and very
large and disastrous. Their action is
complex, involving both increase in
shear stress, and, in some examples,
decrease in shear strength.
They produce horizontal accelerations
that may greatly mod blasting,
machinery, and traffic also produce
transitory earth stresses.ify the state of
stress within slope-forming material.
In the case of potential circular-arc
failure, horizontal acceleration causes
a moment about the center of the arc,
which when directed toward the free
slope adds to its instability.
d. Regional tilting
Progressive increase in slope angle
through regional tilting has been
suspected as a contributing cause to
some landslides. The slope must
obviously be on the point of failure for
such a small and slow-acting change to
be effective.
e. Removal of underlying support
a) undercutting of banks by rivers
and waves
b) subaerial weathering, wetting and
drying, and frost action .
c) subterranean erosion
(1) removal of soluble material such as
carbonates, salt, or gypsum, collapse of
caverns
(2) washing out of granular material
beneath firmer material
d) human agencies, such as mining
e) loss of strength in underlying material
(1) large masses limestone over shale
(2) compact till over clay
failure by lateral spreading
f) lateral pressure due to
(1) water in cracks and caverns
(2) freezing of water in cracks
(3) swelling – hydration of clay, hydration
of anhydrite
Factors That Contribute to
Low Shear Strength
Factors can be divided into two
groups. The first group includes
factor deriving from the initial state
or inherent characteristics of the
material.
The second group includes the
changing or variable factors that
tend to lower shear strength of the
material.
a. Initial state
a) composition
b) texture
(1) loose arrangement of individual
particles in sensitive clays, marl, loess,
sands of low density, and porous organic
matter.
(2) roundness of grains.
b) gross structure
(1) discontinuities such as faults, bedding
planes, foliation in schist, cleavage, joints,
and brecciated zones.
(2) massive beds over weak or plastic
materials.
(3) strata inclined toward free face.
(4) alternation of permeable beds and
weak impermeable beds.
b. Changes due to weathering and other
physico-chemical reactions
a) physical disintegration of granular
rocks under frost action, thermal
expansion.
b) hydration of clay materials.
c) base exchange in clays (influence on
physical properties of clays).
d) drying of clays (results in cracks and
loss of cohesion and allows water to seep
in).
e) drying of shale may create cracks on
bedding and shear planes.
f) removal of cement by solution.
c. Changes in intergranular forces
due to pore water
a) buoyancy in saturated state
decreases effective intergranular
pressure and friction.
b) intergranular pressure due to
capillary tension in moist soil is
destroyed upon saturation.
c) seepage pressures of percolating
ground water result from viscous
drag between liquid and solid grains.
d. Changes in structure
a) fissuring of pre-consolidated clays
due to release of lateral restraint in a
cut.
b) effect of disturbance or remolding
on sensitive materials such as loess
and dry or saturated loose sand.