Sheet Piles.doc

Sheet Piles Sheet piling consists of a series of panels with interlocking connections, driven into the ground with impact or vibratory hammers to form an impermeable barrier. This method is one of the easiest and quickest ways in which to form a watertight retaining wall in soft or loose saturated soil profiles. Sheets can be made from a variety of materials such as steel or precast concrete. Sheet piling has been a proved technology within the construction industry for years.

Steel Sheet Piles These are steel sections which have the facility to interlock one with another and which can be driven into the ground to form a watertight wall. Metal sheet piling shall be interlocked joint strength in tension. The interlocks of sheet piling shall be free-sliding, provide a swing angle suitable for the intended installation but not less than 5 degrees when interlocked, and maintain continuous interlocking when installed. Sheet piling shall be full-length sections. The sheet pile sections can be extracted once they have performed the function for which they were installed and this can reduce the cost considerably. The steel sheet piles can either be used as a cantilever walls or as braced/tied back walls. POSITIVE FEATURES   

Fast method for forming a wall or cofferdam in soft or loose saturated soil profiles. Sheet piles can be extracted and used many times thus reducing costs. The extraction of temporary works is often a requirement satisfied by steel sheet piles.

NEGATIVE FEATURES    

Sheet piles are imported and are expensive. Delays in procurement can delay the start of a contract. Installation needs to be carried out by persons skilled in the operation. High noise levels associated with installation.

TYPICAL USES FOR WHICH SHEET PILES ARE INSTALLED ARE:      

Temporary river. Temporary level. Temporary Permanent Permanent Temporary

cofferdam for the construction of the pile cap for a pier in the cofferdam for the construction of a pump house below ground cofferdam for the construction of a basement to a building. wall as part of the construction of a harbor quay. cut-off wall to restrict the flow of ground water. or permanent retaining walls.

The cost of steel sheet piles is high so their use is generally only justified economically for temporary support of excavations below the water table in soft saturated soil profiles. Despite the high costs, sheet piles are often used for certain

permanent works or in situations where the speed of installation is a distinct advantage.

Precast Concrete Sheet Piles Precast concrete sheet piles are mainly used in marine and river structures. The main advantages of using concrete sheet piles as opposed to steel are availability, cost and better resistance to corrosion. Concrete sheet piles are often cast on site or in a nearby precast factory so availability and cost where large quantities are concerned are distinct advantages over steel. Their better resistance to corrosion is an added plus in marine and river works. They are suited to long straight earth retaining walls where water tightness on the joints is not of prime importance. Conversely they should not be used on small cofferdams where leakage on the joints is not acceptable. Because of the crosssectional area of the pile they can also be used a load bearing units as well as soil retaining. They are normally used on permanent works or on major temporary works and are generally not suited to the smaller temporary retaining structure. The piles are cast on site or in a precast factory. They can be ordinary reinforced or pre stressed. A typical section would be 600 x 250 with and overall length of 9 or 12 meters. During casting careful attention should be given to the high strength concrete required and good vibration and subsequent curing are essential to a sound pile. Handling of the piles off the casting bed and the stacking should also be carefully monitored so that the piles are not cracked. Driving is normally carried out using percussion hammers acting on the usual helmet with hard and soft timber packing. The driving of concrete sheet piles is a tricky operation and experienced personnel should be employed. Attention should be given to all the points raised under the steel sheet pile section with regard to driving.