• Timber piles are made of tree trunks driven with small end as a point.
• Maximum length 35m optimum length 9m-20m
• Maximum load for usual conditions 450kn optimum load range 80kn-240kn
Disadvantages of using timber piles:
Difficult to splice, vulnerable to damage in hard driving, vulnerable to decay unless treated with preservations, if subjected to alternative wetting and drying, the useful life will be short, partly embedded piles or plies above the water table are susceptible to damage from wood bores and insects unless treated.
Advantages:
Comparatively low initial cost, permanently submerged are resistant to decay, east to handle, the best suited for friction piles in granular material.
Steel piles:-
• Maximum length partially unlimited, optimum length 12-50m
• Load for usual conditions = maximum allowable stress x cross sectional area.
• The members are usually roles ho shapes pipe piles. Wide flange beams and I beams proportioned to with stab the jar driving stress to which the pile may be subjected. In hp file the flange thickness = web thickness, piles either welded or seamless steel pipes, which may be driven open ended or closed end. Closed end piles are usually filled with concrete after driving.
• Open end piles may be filled but this is not often necessary ; dm.
Advantages:
Easy to splice, high capacity, small displacement, able to penetrate through light obstructions, best suited for end bearing in rock, reduce allowable capacity for corrosive locations or provide corrosion protection.
Disadvantages:
• vulnerable to corrosion
• Hp section may be damaged/deflected by major obstruction.
Concrete piles:-
• Concrete piles may be precast, prestressed cast in place, or of composite construction.
• Precast piles may be made using ordinary reinforcement or they may be prestressed.
• Precast piles using ordinary reinforcement are designed to resist bending stress during picking up and transport to site and banding moments from lateral loads and to provide sufficient resistance to vertical loads and any tension forces developed during driving.
• Prestressed piles are formed by tensioning high strength steel prestressed cables, and casting the concrete about the cable. When the concrete harden the prestressed cables are cut, with the tension force in the cables now producing comprehensive stress in the concrete pile. It is common to higher strength concrete (35-55mpa) in prestressed piles because of large initial comprehensive stress from prestressing. Prestressing the piles, tend to counteract any tension stresses during either handling or driving.
• Maximum length: 10-15m for precast, 20-30m for prestressed
• Optimum length 10-12m for precast 18-25 m prestressed.
• Loads for usual conditions 900 for precast 8500 kn for prestressed.
• Optimum load range : 350 - 3500 kn.
Advantages:
1. High load capacities, corrosion resistance can be attained, hard driving possible.
2. Cylinder piles in particular are suited for banding resistance.
3. Cast in place concerte piles are formed by drilling a hole in the ground and filling it with concrete. The hole may be drilled or formed by driving a shell or casting into the ground.
Disadvantages:
1. Concrete piles are considered parmenent, however certain soil contain materials that may form acids. That can damage the concrete.
2. Salt water may also adversely react with the concrete unless special precautions are take when the mix proportions are designed. Additionally, concrete plies used for marine structure may undergo abrasion from wave actions and floating bedris in the water.
3. Difficult to handle unless prestressed, high initial cost, considered displacement, prestressed piles are difficult to splice.
4. Alternate freezing thawing can cause concrete damage in any exposed situation.
Composite piles:
In general, a composite pile is made up of two or more sections of different piles type. The upper portion could be eased cast in place concrete combined with a lower portion of timber, steel H or concrete filled steel pipe pile. These piles have limeted application and arc employed under special conditions.
