十三、風化作用(Weathering) [海枯石爛]

定義：

岩石在各種外營力作用下所發生的物理與化學變化的過程。

Weathering is the physical and chemical disintegration / or decomposition of geologic deposits.

Weathering may be defined as: that process of alteration of rocks occurring under the direct influence of air and water.

使岩石破碎疏鬆的作用:

物理性風化:使大塊岩石崩解或小粒的作用。

化學性風化:使岩石中礦物或化學成份改變。

生物性風化:生物的作用使原地發生破壞。

物理性：解壓、冰凍、溫差

化學性：溶解、氧化、水化、水解、碳酸化

(方解石、石灰岩、大理石最易被溶解，石英、砂岩最不易被溶解)

生物性：物理性、化學性

Karst topography:

An assemblage of landforms which result from the diversion of drainage system from the surface to underground , and with surface solution of rocks.

風化程度

風化係數:

新鮮岩石: K=1~0.9 (強度折減0~10%)

部分風化: 0.7<K<0.9 (強度折減10~80%)

完全風化: K<0.2 (強度折減 >80%)

DP (Decomposed Product)

Slake-Durability

聲波波速

壓力波波速(km/sec)	風化層名稱
1~2	劇風化
2~3	高度風化
2.5~5	弱風化
5~6	微風化

分級

分級依據:顏色、破碎程度、礦物或分變化、水文及力學性質。

Grade I: Fresh (下) :No fine fracturing can be detected using a hand lens.

II :Slightly Weathered (SW):The rock is so strong that more than a single blow with a geology pick is needed to break it

III: Moderately Weathered (MW):

A sample can be broken by one blow of a geology pick, but an NX core cannot be broken in the hand.

IV: Highly Weathered (HW):

A rock sample can be crushed by the blows of a geology harmmer. NX core samples can be broken with effort.

V: Combletely Weathered (CW):

A sample indents under the tip of a geology pick, and agitation of a sample in water disintegrates it.

VI: Residual soil (RS):

A sample can be indented with the thumb, excavated by hand easily, and disintegrated by agitation in water.

風化工程注意事項：

Deep exeavation to fresh rock

Grouting

Retaining Wall

Bolting open joint

岩石之抗風化能力

*熱帶以化學作用為主：

岩性	等級
石灰岩	1(最弱)
玄武岩	2
花崗岩	3
泥岩/頁岩	4
砂岩/石英岩	5(最強)

Slow weathering
	Quartz
	Pluscovite
	Orthoclase
	Biotite
	Hornblende, Sodium Plagioclasses Augite
	Olivine, Calcium Plagioclase
Rapid weathering

風化岩石之處理：

　

取決於「工程性質」、「風化層厚度」、「力學性質」

風化層數公尺內-------------à 挖除

風化層幾十工尺以上-------à 民用小工程：深基礎

重型水工：控除

雖風化層很厚，但有時地盤改良(如水泥灌漿)或可比挖除更佳。

岩石風化之預防：

原則：將岩石與水及大氣阻隔。

泥岩或含粘土性岩石在數分鐘就可開始風化

鋪蓋粘土、砂土、水泥、瀝青。

[Reference:]

潘國樑「應用環境地質學」(地景，1993)

洪如江「初等工程地質學大綱」地工技術叢書(1994)

陳惠芬「墾丁國家公園地質景觀簡介」墾丁國家公園解說手冊11 (1994)