13 風化與土weathering and soil(中文3900字,英文1900字)
地表狀況
地層剖面最上面數米深處一般包括：土、坡積土和風化巖石。其工程性質不同于最底層的基巖。
土 ：是礦物碎屑和植物風化后的混合體，通常小于1米厚，通常被分為上層腐殖質和富含粘土的下層土。
風 化：巖石、坡積土與空氣和水接觸后，被自然侵蝕和分解的過程。風化深度一般小于10米。
坡積土：泥沙經過運輸、沉積在基巖表面上；大多數非固結粘土、沙和粗碎屑碎片;一般屬于第四紀，因時間太短不能固結；厚度在0到大于50米之間。
崩積層：邊坡碎片，移動的滑坡體主要由重力引起；因此輸送泥沙的程度：滑移體>崩積層>土，包括由蠕變和片狀沖積層產生的碎片，巖屑堆。喪失植被和地表水增加產生的片狀沖積層。
基覆面：被埋坡積土與巖石的界面；普遍存在于軟土、坡積土和堅硬巖石之間的顯著邊界；不容易在風化巖石深剖面作界定；若在坡積土沉積之前形成的侵蝕面，形成的地形可能跟現在的表面完全無關。
工程土：不用劈裂或爆破即可開挖的軟弱材料，因此包括：土、坡積土、軟巖和弱風化巖石。
13 weathering and soil
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GROUND CONDITIONS
Top few metres of the ground profile generally consist of soil ,drift and weathered rock,withengineering properties very different from those of the underlying bedrock.
Soil: mixture of weathered mineral debris and plant material,
usually<1 m thick;many divide into plant-rich topsoil and clay-rich subsoil.
Weathering：the natural decay and break down of rock or drift in contact with air and water;generally < 10m deep.
Drift transported,superficial sediment deposited on top of the bedrock; mostly unconsolidated clay,sand and coarser clastic debris; generally Quaternary age ,
hence too yang to be consolidated;varies in thickness from 0 to >50m.
Colluvium:slope debris,
moved downslope largely by gravity alone;extent of sediment transport therefore drift>colluvium>soil;
includes debris from creep and sheetwash,also head and
scree.Sheetwash by surface water increases greatly with loss of vegetation. 【www.3462644.buzz】
Rockhead:the buried drift/rock interface;commonly a conspicuous boundary between weak soils and drift and strong rock;may be less well defined in deep profile of weathered rock;formed as erosion surface before drift deposition so its topography may be totally unrelated to modern surface.
Engineering soil:weak material which can be excavated without ripping or blasting,therefore including soil,drift,weak rocks and weathered rock. 【本文來自56doc.com】
