ABRASION ,ABRASION ,CAVITATIONCAVITATION, , CORROSIONCORROSION , AND , AND DECOMPOSITIONDECOMPOSITION

CAUSED CAUSED BY WATERBY WATER

Presented By: Presented By:

Ali Bux WassanAli Bux WassanDepartment of Mining Department of Mining

Engineering, MUET, JamshoroEngineering, MUET, Jamshoro

AbrasionAbrasion� wherever the running water carries the tools of

erosion such as sand, become the source of wearing away of the bedrock with the help of those tools.

� Abrasion involves loosening, disintegration, rubbing and grinding action on rocks

CavitationCavitation� It is particularly observed, where running water

suddenly falls with high velocity, such as at location from high level to low level

� It is known that when stream velocity exceeds 12 m/sec, the water pressure developed result in vertical sucking out of the material and thereby creating holes and depression that continue deepening with passage of time such holes are called “potholes”.

Corrosion:Corrosion:� The slow but steady chemical action of the

stream water on the rocks is expressed by the term “corrosion”

� This depends mostly on the composition of rock and also the composition of flowing water.

� The rocks which are not soluble in stream water may be corroded highly.

DecompositionDecomposition� Movements of water brings about the dissolution of

certain materials in rocks.

� This water may washout soft clays and other decomposed materials from joints and faults.

� It is the chemical action by which chemical weathering or chemical alteration takes place.

� Under varying humidity and alternate drying and wetting conditions, some rocks separate on their bedding planes, or in time, disintegrate completely.

� Alternate wetting and drying cause some rocks to expand (swelling) and contact (squeezing), thus affecting their properties.

� One to the dissolution of minerals, the hardness of water is enhanced, for example, chemical alteration due to water are;

1. If water consists of carbonic acid, it dissolves limestone and dolomite by removing calcium and magnese from the rock

� Chemical action of magnesium solution on rocks is more intensive than sodium chloride solution.

� Rock formations consisting of gypsum, rock salt, anhydrite are highly soluble minerals and subject to a rapid process of alteration

� Hydrochloride is an aqueous solution and is a strong corrosion liquid acid and very much soluble in water

++