Sheet piles

SHEET PILES

Sheet Piling is used in cases when- Enclosing a site or part thereof to prevent the escape of loose sub-soil to safeguard against settlement of structure which is to be erected on it.

Retaining the side of trenches and generally excavations. Forming cofferdams (watertight enclosures necessary in construction of foundations in water). Their most common use is within temporary deep excavations. They are considered to be most economical where retention of higher earth pressures of soft soils is required. They have an important advantage in that they can be driven to depths below the excavation bottom and so provide a control to heaving in soft clays or piping in saturated sands.However sheet piles are more costly and less adaptable to hard driving conditions particularly where boulders or irregular rock surfaces occur. There are 3 main types of sheet pile walls.

Cantilever

Anchor

Propped

Sheet pile are either of- Steel

Reinforced concrete

Timber

STEEL SHEET PILES

Trough shaped when driven,the piles are interlockedwith alternate one reversed.

Lenghts- 5.5m for smaller sections 18m for larger sections

The maximum lengths of piles depend upon,

The depth of penetration

Nature of soil

Made of three grades of steel, e.g. mild steel, copper steel and high tensile rust-resisting steel.

When used for permanent work the piles should be coated with acid free tar or similar preservatives. Steel sheet piles

Sheet piling driving

DRIVING SHEET PILES

The frame equipment is similar to that of other types of piles, but of lighter construction.

The hammers employed are to be of single-acting type for clay soil.

Double-acting for sand and gravel soil.

Alternatively, in the absence of a frame, hammer suspended from the jib of a crane can be used.

A driving cap or anvil block is used as a protection against damage.

In order to maintain a straight line of vertical piles, it is necessary to provide one or two pairs of horizontal timbers, called waling, which are bolted to temporary wood square sectioned piles.

The wood piles are driven in at 3m to 4.5m apart.

If a frame is employed, only one pair of waling is necessary at groung level otherwise, a second pair of waling is required.

There is a tendency of the piles to wander or lean forward in the direction of driving, which can be avoided or minimized if the work is carried out in the following manner.

a. A series or panel of, say, pair of piles (no. 1) is carefully driven to part penetration.b. The pair at the opposite end (no. 2) is then partially driven, followed in turn by pairs 3,4,5,6.

BOX PILES

The interlocking steel sheet piles are formed into box piles for permanent works and where large carrying capacity is required.

Box Piles consist of two ordinary sheet piles of any of the layer sections which are welded together at intervals along the interlocks.

Steel sheet piles are often used for temporary work and after the piles have served their purpose they are withdrawn.

The method of withdrawal is to apply a metal grips or tongs at the top end of the piles which is then lifted by a rope from winch on crane.

A double-acting pile hammer is inverted and fitted with extractor grips.

The main application of steel sheet piles is in retaining walls and cofferdams erected to enable permanent works to proceed.

REINFORCED CONCRETE SHEET PILE Used for permanent work

In section, it is rectangular or tongued or grooved or V-jointed.

The feet are shaped obliquely or beveled and feather edged.

If driving through resistant strata, the feet are protected by metal shoes and the heads are shaped to receive the driving helmet.

If the soil is water logged and the piling system is to be water tight, cement grout is poured down the joints to affect a seal.

TIMBER SHEET PILES

Used for temporary work.

225-280mm wide and at least 50mm thick.

Butt or V-jointed and feet are beveled and shoed with shoe iron.

Temporary wood piles and waling are as described for sheet piles are provided to ensure accurate driving.