What is Pipe Piling?

Pipe piling is a structural building material used to support and stabilize a building’s foundation. When the soil below a building is loosely packed, it may not offer enough strength to keep the building stable over time. A pipe piling can be used to distribute the weight of the building deeper into the earth, where the soil is often more tightly packed. Pipe piles are also used to support exceptionally large or heavy buildings, where even standard soil cannot offer adequate support. Finally, a pipe piling may be required when the land area is too small to accommodate spread footers or foundations, forcing buildings to dig deeper to achieve sufficient ground stability.

Most forms of pipe piling consist of heavy-duty steel pipes, which are often galvanized with zinc to increase moisture and corrosion-resistance. When only a standard level of support is required, an open-ended pipe is often used. If additional support is required, these pipes may be capped with steel plates to form close-ended pilings. Installers can then fill the pipe with concrete and rebar to add extra strength and stability.

Piles are driven into the ground using large machines known as pile drivers. These machines contain hydraulic systems which exert extremely high levels of force to drive the piles into the ground. By driving the piles directly into the soil without drilling holes first, the soil itself helps to support and stabilize the piles. As the pile is driven underground, the soil is displaced, which increases friction and pressure around the pile to hold it in place.

Engineers and installers determine the placement for each pipe pile based on the building loads at various locations. A very heavy load, such as a piece of industrial equipment, may need to sit directly over a pile to ensure adequate support. When building loads are evenly distributed, installers may use a concrete pile cap to support the building. This allows the pipe pilings to be equally spaced below the building, then connected together with the pile cap to act as a large foundation system.

Each pipe piling must be carefully chosen based on building forces, soil conditions and local building codes. A geotechnical engineer can test the soil to determine whether piles are needed. The structural engineer then determines the size and material needed for each pipe piling, as well as the required depth. When a single pipe is not long enough to reach this depth, piles may be joined together using butt welds or splicing sleeves.

(This article comes from wiseGEEK editor released)

DRIVEN SHEET PILES

Driven sheet piles are thin interlocking steel sheets used to construct a continuous barrier in the ground. Interlock is typically achieved by clutching the edge of one pile into the previous pile.

A wide range of sheet pile sections and profiles are available from many steel manufacturers. c sections have a weaker interlock than hot-rolled sections. In hard driving conditions this interlock might “unzip” or cause alignment problems which would require replacement of the sheet piles. Cold-rolled sections also are usually thinner than hot rolled and thus may be more prone to overstressing during driving.

Sheet piled retaining walls are often restrained by use of internal propping, bracing, anchors or deadmen. It is often possible to extract and reuse sheet piles making this an economically attractive retaining wall system.

One of the main applications for sheet piles is for temporary retaining walls or cofferdams used to allow permanent in ground construction to be undertaken. The durability of sheet piles can be extended with protective coatings.

Driven sheet piles are often installed by vibrating hammers operated off leaders mounted on tracked base machines or suspended from crawler cranes. Diesel impact hammers and hydraulic press in machines can also be used to drive or push the piles into place. Sometimes water jetting or preboring is used to assist penetration through stiff or hard layers.

(This article comes from PILING CONTRACTORS editor released)

Structural Factors of Safety for Steel Sheet Piling

Most steel sheet piling is still designed using allowable stress design methods; thus, a factor of safety is usually specified that reduces the allowable stress in the pile from the yield stress. The allowable stress is thus

Equation 2-1: σallow = Freduction σy

where

  • σallow = Allowable Stress of the Material
  • Freduction = Reduction factor of safety
  • σy = Yield Stress of the Material, psi or kPa

With steel piling in pure bending (see below), there are two reduction factors used:

For static loads, for permanent works the reduction factor is generally 0.65, or the allowable stress is 65% of the yield stress. For the grades listed above:

ASTM A328: σallow = (0.65)(39) ≈ 25 ksi

ASTM A572, ASTM A690: σallow = (0.65)(50) ≈ 32.5 ksi

For earthquake loads, the reduction factor is generally (1.33)(0.65) ≈ 0.87, or the allowable stress is 87% of the yield stress. Using this increased value for earthquake loads presupposes a static analysis to insure that the static case is not in fact the governing case for a particular situation. For the grades listed above:

ASTM A328: σallow = (0.87)(39) ≈ 34 ksi

ASTM A572, ASTM A690: σallow = (0.87)(50) ≈ 43.5 ksi

(This article comes from Pile Buck International editor released)

Definition of Sheet Piling

Sheet piling is a type of deep foundation used in construction work. As opposed to shallow foundation, deep foundations like sheet piling provide a more structurally sound design for large buildings and heavy loads.

Sheet Piling Design

  • Sheet piles are long interlocking structural sections. With a vertical interlocking system, sheet piles create continuous walls for construction projects.

Sheet Piling Uses

  • Sheet piles create an extended barrier from soil or water for either permanent or temporary use. The steel sheets resist the lateral bending forces, strengthening the overall foundational structure.

Temporary vs. Permanent

  • Sheet piles can temporarily create access and a safe working environment for construction sites. Sheet piles are helpful in the permanent design of a building to create a basis for other foundational components.

(This article comes from eHow editor released)

Installing sheet piles in confined space in Finland

City of Espoo in Finland is investing significantly in infrastructure in various locations. Areas around Leppävaara neighborhood have seen a lot of new development in the recent history. Besides of all new development one of the ongoing project is to upgrade the pedestrian street and market square of older commercial area. Civil engineering company E.M. Pekkinen is completing the scheme that includes sheet piling, other piling works, ground improvement, relocating utilities and finally paving and landscaping.

Most of the work is carried out in limited space with minimum disturbance to shops and other businesses along the pedestrian street. Excavations for utility works require temporary retaining walls. Installations of the sheet piles in these conditions and very close to building walls take both carefully chosen equipment and experienced personnel. E.M. Pekkinen is experienced piling and civil engineering provider.

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(This article comes from MOVAX 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.

Suitability for welding

Weldinginvolves fusing together two identical or very similar steels to form one homogenous component, and this is done by melting them together at their interface through liquefaction or plastic deformation. This can be carried out with or without the addition of another material. Arc welding is a very common method (manual metal-arc welding, shielded metal-arc welding). In this method an electric arc is generated between an electrode, which supplies the welding material, and the component. The suitability for welding depends not only on the material, but also on its shape, the dimensions and the fabrication conditions. Killed steels should generally be preferred.

According to EAU 2004 section 8.1.6.4 (R 67), and taking into account general welding speci- fications, arc welding can be used for all the grades of steel used for sheet piles. The building authority approvals must be adhered to for high-strength steel grades S 390 GP and S 430 GP. In addition, the carbon equivalent CEV should not exceed the value for steel grade S 355 to DIN EN 10025 table 4 if welding is to be employed.

Furthermore, EAU 2004 section 8.1.6.4 (R 67) recommends using fully killed steels of the J2 G3 or K2 G3 groups to DIN EN 10025 in special cases, e.g. where plastic deformation due to heavy driving is expected, at low temperatures, in three-dimensional stress conditions and when the loads are principally dynamic, because of the better resistance to embrittlement and ageing required. Welding electrodes conforming to DIN EN 499, DIN EN 756 and DIN EN 440 or the speci fication of the supplier should be selected. According to EAU 2004 section 8.1.18.2 (R 99), basic electrodes or filler materials with a high basicity should generally be used. The follow table provides general information about the selection of suitable electrodes according to DIN EN 499.

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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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The effect of groundwaterflows on hydrostatic and earth pressures

If the base of the sheet pile wall is not embedded in an impermeable stratum, groundwater can flow under the sheet piling structure. Proper planning and design of sheet pile walls located in groundwaterflows calls for a knowledge of the effects of the flowing groundwater.

As the groundwaterflows from regions of high hydraulic head to regions with a lower head, the hydrodynamic pressure is directed downwards on the excess hydrostatic pressure side and upwards on the opposite side. This means that the hydrostatic pressure on the excess hydrostatic pressure side is lower and that on the opposite side higher than the hydrostatic pressure.

The hydrodynamic pressure also acts on the granular structure of the soil: it increases the effective particle-to-particle stresses on the excess hydrostatic pressure side and decreases them on the opposite side. This means that the active earth pressure on the excess hydrostatic pressure side is increased, and the passive earth pressure on the opposite side is decreased.

Taking into account the groundwater flows has a beneficial effect on the excess hydrostatic pressure and a detrimental effect on the passive earth pressure. Whether on the whole a more favourable or less favourable in fluence prevails, must be investigated in each individual case. Generally, there are three ways of considering the hydrostatic pressure on a wall in flowing groundwater:

  1. Ignore the flow and assume the excess hydrostatic pressure according to section 4.2.
  2. Perform calculations with the help of a flow net.
  3. Perform calculations with the help of an approximation method assuming modified unit
    weights.

In the majority of cases it is sufficient to ignore the groundwater flow and assume the excess hydrostatic pressure according to section 4.2. If high excess hydrostatic pressures are present, then more accurate flow net calculations are advisable in the case of strati fied soils with different permeabilities. In addition, an accurate investigation of the flow conditions is necessary for verifying resistance to hydraulic ground failure, especially in the case of large water level differences and strata with low permeability near the surface on the passive earth pressure side.