1.4.11 Steel piles Steel piles:(figure 1.4)steel/Iron piles are suitable for handling and driving in long lengths.Their relatively small cross-sectional area combined with their high strength makes penetration easier in fimm soil.They can be easily cut off or joined by welding.If the pile is driven into a soil with low pH value,then there is a risk of corrosion,but risk of corrosion is not as great as one might think. ugh tar coating or cathodicprotection can be employed in permanent works It is common to allow for an amount of corrosion in design by simply over dimensioning the cross-sectional area of the steel pile.In this way the corrosion process can be prolonged up to 50 years.Normally the speed of in design,this value can be taken as X工 a)X- b)H- cross-section cross-section steelpipe Figure 1-6 Steel piles cross-sections 1.4.12 Composite piles Combination of different materials in the same of pile.As indicated earlier,part of a timber pile which is installed above ground water could be vulnerable to insect attack and decay.To avoid this,concrete or steel pile is used above the gaen8e"edlhiodplesnsledunderhegroundwaerad1.4.11 Steel piles Steel piles: (figure 1.4) steel/ Iron piles are suitable for handling and driving in long lengths. Their relatively small cross-sectional area combined with their high strength makes penetration easier in firm soil. They can be easily cut off or joined by welding. If the pile is driven into a soil with low pH value, then there is a risk of corrosion, but risk of corrosion is not as great as one might think. Although tar coating or cathodic protection can be employed in permanent works. It is common to allow for an amount of corrosion in design by simply over dimensioning the cross-sectional area of the steel pile. In this way the corrosion process can be prolonged up to 50 years. Normally the speed of corrosion is 0.2-0.5 mm/year and, in design, this value can be taken as 1mm/year a) X￾cross-section b) H - cross-section c) steel pipe Figure 1-6 Steel piles cross-sections 1.4.12 Composite piles Combination of different materials in the same of pile. As indicated earlier, part of a timber pile which is installed above ground water could be vulnerable to insect attack and decay. To avoid this, concrete or steel pile is used above the ground water level, whilst wood pile is installed under the ground water level (see figure 1.7)