Everything about sheet-pile walls: types, materials and construction methods

Sheet-pile walls are widely used for both large and small waterfront structures, ranging from small pleasure-boat launching facilities to large dock structures where ocean-going ships can take on or unload cargo. A pier jutting into the harbor, consisting of two rows of sheet piling to create a space between that is filled with earth and paved, is a common construction.

Sheet piling is also used for beach erosion protection; for stabilizing ground slopes, particularly for roads; for shoring walls of trenches and other excavations; and for cofferdams. When the wall is under about 3 m in height it is often cantilevered; however, for larger wall heights it is usually anchored using one or more anchors. The resulting wall is termed an anchored sheet-pile wall or anchored bulkhead.

Sheet pile wall types:

1. Wooden sheet piles

2. Steel sheet piles

3. Concrete

4. Light-gauge aluminium sheet piles

5. Vinyl sheet piles

6. Fiberglass sheet piles

Construction Methods

In the construction of sheet-pile walls, the sheet pile may be driven into the ground and then the backfill placed on the land side, or the sheet pile may first be driven into the ground and the soil in front of the sheet pile dredged. In either case, the soil used for backfill behind the sheet-pile wall is usually granular. The soil below the dredge line may be sandy or clayey. The surface of soil on the water side is referred to as the mud line or dredge line.

Advantages:

Steel sheet piling is the most common because of several advantages over other materials:

1. Provides high resistance to driving stresses.

2. Light weight

3. Can be reused on several projects.

4. Long service life above or below water with modest protection.

5. Easy to adapt the pile length by either welding or bolting

6. Joints are less apt to deform during driving.

This article comes from civilengineeringbible edit released

Steel sheet pile piling

Steel sheet pile construction to correctly select the “screen” piling method, piling machinery and water segment, so that after the board pile wall has enough rigidity and good waterproof role. And the sheet pile wall straight to meet the requirements of the foundation construction, the closure of the sheet pile wall also requires closure and closure.

This method is from the corner began by block plug, each piece of steel pile from the end of the fight to the end of the stop. Therefore, the pile driver walking route is short, the construction is simple, set up fast. However, due to single block into, easy to tilt to one side, the cumulative error is not easy to correct, the wall flatness difficult to control.

First set by the surveyor steel plate pile cofferdam axis, can be set at a certain distance from the guide pile, guide pile directly use steel sheet pile. And then lanyard as a wire, piling when using wire to control the axis of the steel sheet pile, in the case of high axial requirements, the use of guide frame.

Single pile by root continuous hit, pay attention to the pile top elevation should not be too much difference. In the process of plugging at any time to measure the slope of each pile is not more than 2%, when the skew is too large can not be used to adjust the way, pull up the re-hit.

Sheet Pile Design

Sheet pile wharf structure:

In front of the sheet pile wall: composed of vertical quay wall, neither through the air high-pile wharf, nor bulky gravity wharf, the disadvantage is that external force is not too large, used for medium and small pier.

Middle bar: power transmission structure in the middle, the main consideration is the need for preservation, is an important part of sheet pile wharf affect durability

Rear anchoring structure: This is a reduction from the sheet pile at a depth of role pile displacement and improve the force.

Top design guide beam or sheet pile cap beam, which is actually gravity quay parapet.

Tile dock calculation:

Buried depth (front and rear calculated soil pressure, the residual water pressure) in front of the sheet pile, internal forces (pileup load, mooring force, etc.), pull the lever (assuming drawbar pull rod arranged with the rear anchoring structure).

Design modulus first sheet pile is in pre-time need to be implemented, followed by external force according to the geological exploration is calculated, assuming sheet pile embedded depth (that is, applied to sheet piling focus).

Implementation of embedded depth (meet deformation requirements), determine the corresponding rod internal forces, in the best distance to determine the relevant anchoring structure and sheet pile (the force best), calculated value based on the implementation of the standard rod pull rod internal forces, after the turn, calculation rod sections, prefabricated rod.

Sheet pile design

Sheet pile design must account for earth, water, and adjacent structures. Sheet pile design can be straightforward in simple cases, and quite complex in some other conditions. Many unknowns and factors that influence the behavior of the sheet pile wall. Typically, there are two systems in sheet pile wall that must be designed: A) the sheet pile wall that retains the earth and water ( etc.), and b) the Support System (i.e. the internal or external bracing such as rakers, struts, or tiebacks) that supports the sheet pile wall.

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(This article comes from Deep Excavation editor released)

INSTALLATION OF RETAINING WALL – SHEET PILE WALL

The following pictorial guide illustrates the installation sequence of a typical sheet pile wall. This type of retaining wall was used for the construction of HarbourFront Station on the North East Line (NEL).

  1. Position of Sheet Pile
    A guide frame/guide beam is placed on the ground to set out the position of the sheet pile wall.
  2. Installation of First Sheet Pile
    The piling rig lifts up the first sheet pile and drives it into the ground, leaving about 1 metre length of the sheet pile above the ground level.
  3. Installation of Second Sheet Pile
    The piling rig drives the second sheet pile into the ground and the second sheet pile interlocks with the first sheet pile.
  4. Repetition of Process
    Process 2 and 3 repeats till the installation of sheet piles is completed within the length of the guide frame/ guide beam.
  5. Extension of Sheet Pile
    If the first set of sheet piles installed are not long enough to reach the required depth in the ground, extension of sheet piles is required. This is done by welding the ends of a second sheet pile length to the one driven in earlier and driving the combined length into the ground.

(This article comes from www.lta.gov.sg editor released)

Types of Sheet Pile Walls

Sheet piles are pre-cast members comprising varieties ranging from simple wood planks and light gauge sheet metals to heavy sections made of reinforced concrete and structural steel members.

Timber sheet piles – These are generally used for temporary structures and braced sheeting in excavation works. If it is to be used in permanent structures above water table, some form of preservative treatment shall be given. Even given the preservative treatment the life of timber sheet pile is short, Timber sheet piles are joined by means of tongue and groove joint. Timber piles are not suitable in the strata consisting of gravel and boulders.

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Concrete sheet piles – These are pre-cast concrete members usually joined by tongue and groove joints as shown in Fig.2 below. They are relatively heavy and bulky and displace large volume of soil during driving. This large volume displacement increases the driving resistance. Handling and driving should not damage the piles and suitable reinforcement shall have to be provided for this purpose.

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Steel sheet piles – Steel sheet piles are the most common types. These piles have several advantages over the other types of piles. Some of the important advantages are:

  • It is resistant to high driving stresses developed while driving in hard and rocky material
  • It is lighter
  • It may be used several times
  • It can be used either below or above the water table
  • It has longer life
  • It has got high salvage value
  • Joints suitable for a particular job can be provided so that it does not deform during driving
  • The pile length can be increased either by bolting or welding

Steel sheet piles are available in market in several forms. In Fig.3 below, some common types are shown. The deep are webs and Z piles are used where large bending moments are to be resisted as in the case of anchored and cantilever walls. The shallow arc piles can be used where the bending moments to be resisted are less. Straight web sheet piles are used where the web will be subjected to tension as in the case of the cellular cofferdams. The ball socket types of joint offer less resistance to driving as compared to thumb and finger joint.

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(This article comes from Best Engineering Projects editor released)

The imperviousness of steel sheet pile walls

For practical design purposes it is advisable to assess the degress of the required seepage resistance in order that a cost effective solution may be selected. Depending on the requirements, there are basically three possible solutions:

  1. In applications such as temporary retaining walls a moderate rate of seepage is often tolerable. An SSP wall made of piles with the famous Larssen interlock provides sufficient seepage resistance.
  2. In applications where a medium to high seepage resistance is required – such as cut-off walls for contaminated sites, retaining structures for bridge abutments and tunnels – double piles with a workshop welded intermediate joint should be used. The workshop weld is as impervious as the steel itself. The free interlock of the double pile needs to be threaded on site with a filler material. The lower end of the resistance range is adequately served by the various bituminous fillers, but it is noted that their use is limited to water pressures less than 100 kPa.For high resistance requirements, as well as water pressures up to 200 kPa, a waterswelling product should be used as a filler material. A wall designed in this way is between 100 to 1000 times more impervious than the simple sheet pile wall with Larssen interlocks.
  3. A 100% watertightness may be obtained by welding every joint.
    Double piles with a workshop weld are used for the construction of the wall. The interlock that needs to be threaded on the job has to be welded on site after excavation.

If a comparison needs to be made between the rate of seepage of an SSP walls and a slurry wall, the table below may be used. For a given SSP walls, the hydraulic conductivity which a slurry wall of thickness D has to provide in order to obtain the same upper limit on the discharge – at the same water pressure – as the SSP wall, can be determined.

(This article comes from J Steel Australasia editor released)

Earth pressure due to compaction

If the soil behind a sheet pile wall is back filled in layers and subsequently compacted , the earth pressure on the wall at a certain depth below the surface of the back fill can exceed the active earth pressure due to self-weight in some circumstances.

DIN 4085:2007 provides design suggestions for applying the compaction pressure depending on the type of compaction (rolling or vibration) and the magnitude of the earth pressure (active earth pressure or steady-state earth pressure).

If the surface is subsequently loaded, e.g. by further layers of fill, the earth pressure due to compaction remains effective only to the extent that it exceeds the earth pressure due to addi-tional loads. From this it follows that in the majority of cases only the earth pressure due to compaction in the upper layers needs to be considered.

Calculating the excess hydrostatic pressure

In sheet pile walls with different water levels on either side, the excess hydrostatic pressure is included in the sheet piling calculation as a characteristic action. The excess hydrostatic pressure wu at depth z of the sheet pile wall is calculated from the difference in the hydrostatic pressures on the two sides.

wu (z )= wr (z ) − wl (z )= hr (z ) · γw − hl (z ) · γw

20151013 Excess hydrostatic pressure assumptions for a wall in stationary water

If we neglect the flow around the sheet pile wall, e.g. if the sheet pile wall is embedded in an impermeable stratum, the result is an excess hydrostatic pressure with a triangular distribution in the region of the one-sided hydrostatic load and a constant load in the lower region down to the base of the sheet piling.

Groundwater

The presence of groundwater in front of or behind the sheet pile wall has a direct effect on the earth pressure.

In stationary water, the buoyancy force of the groundwater acting on the granular structure reduces the effective unit weight of the soil such that only its submerged unit weight γ is effective. The active and passive earth pressures are therefore reduced.

If the groundwater flows around the sheet pile wall, then hydrodynamic pressures generate additional forces that act on the granular structure of the soil. The hydrodynamic pressure fs = i · γw increases the effective stresses on the side where the water flows downwards (normally the active earth pressure side) and reduces the effective stresses on the side where the water flows upwards (normally the passive earth pressure side). The exact calculation procedure is illustrated with an example in the follow picture. There, the intention was to illustrate the effect of the hydrodynamic pressure on the hydrostatic pressure, whereas here it is the effect on the active earth pressure.

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