A series of sheet piles driven into the ground side by side, form a continuous vertical wall which is referred to as a sheet pile wall. A sheet pile wall acts as a retaining wall but unlike the RCC or masonry rigid retaining walls, it is light in weight and flexible.
The sheet piles used are of timber, reinforced concrete or steel depending on the provision made for achieving stability. Sheet pile walls are of three types:
1) Cantilever sheet piling
2) Anchored sheet piling
3) Braced sheeting
Sheet pile walls are used in
- Light weight construction when the bearing stratum is poor for supporting the heavier RCC or masonry retaining wall.
- For temporarily retaining earthfills in some construction activities and
- Water front structures.
(This article comes from NPTEL editor released)
In order to have a more efficient usage of construction areas in congested urban areas a vertical development of buildings becomes necessary. Currently we more often face situations where urban buildings need as many parking spaces, so, due to lack of space, that requires the development of several underground floors.
The design and execution of deep excavations in congested urban areas is quite a challenge especially in terms of geotechnical engineering and it requires a good knowledge of the soil mechanics and soil interaction with the retaining walls of the excavation.
The analysis of excavation retaining walls can be performed using two calculation methods (sizing methods): Limit Equilibrium Method (LEM) and a numerical method – Stiffness Ratio Method (FEM/SRM).
(This article comes from GEOSTRU editor released)
What Is Sheet Piling? Sheet piling refers to the construction of a wall, temporary or permanent, that uses thin, interlocking steel sheets known as sheet piles. These sheet piles lock together and are then driven vertically into the ground, forming an effective retaining wall.
Sheet piles are thin sheets of material with interlocks built onto both of its ends. They can be made from wood or concrete, but the most commonly used sheet piles are made from steel. The interlocking design on their sides allow the sheet piles to connect to each other to form a continuous wall.
Sheet pile walls can be temporary or permanent. Temporary walls help prevent cave-ins at confined works sites and provide both easy access to the site and protection to the workers. Permanent walls support basement walls and prevent flooding along shorelines. Construction companies also use permanent sheet pile walls for home foundations and stabilizing a sloping terrain.
Sheet piles are cheap and recyclable. Builders are able to assemble sheet pile walls easily, and they are able to erect a wall of any length quickly. Sheet pile walls are also very durable and are capable of retaining both water and earth while resisting their pressures.
(This article comes from Geeks On Home editor released)
Sheet-pile walls are made from linked sheet piles that are long steel plates with a Z or U shape. These piles are connected together to make a sealed wall. Sheet piles are often connected together in pairs and installed using one of three methods:
- Vibration: this is the most common method. The first sheet pile of the wall is installed into the ground. A vibratory hammer with clamp is attached to the top of the second sheet pile, which is then interlocked with the first sheet pile, and the sheet pile is vibrated into the ground.
- Pressing: sheet piles can also be pressed into the ground when noise hindrance and vibration would otherwise cause problems. This, however, takes longer and is expensive. The sheet piles are pressed into the ground by a hydraulic machine.
- Excavation: sheet piles can also be excavated into the soil. A long trench is excavated which is then filled with cement bentonite (a thin concrete slurry) to prevent the walls from collapsing. The sheet piles are then installed in the trench and the cement bentonite is allowed to set.
(This article comes from Ballast Nedam editor released)
Quay structures are frequently built as combined sheet pile walls consisting of loadbearing piles and infill piles. In this arrangement, the in fill piles are often not driven as deep as the loadbearing piles. The passive earth pressure in the region below the infill piles can only be mobilised by the loadbearing piles. Every one of these generates a three-dimensional earth pressurefigure which, depending on the spacing of the loadbearing piles, can remain separate or can overlap. In the extreme case, the overlapping is so great that the loadbearing piles can be calculated as a continuous wall. DIN 4085:2007 section 6.5.2 contains further information on calculating the three-dimensional passive earth pressure.
The classic earth pressure distribution only occurs for the active earth pressure with a rotation of the wall about its base. In the case of unpropped cantilever retaining walls fixed in the ground, a classic pressure distribution is to be expected. In the case of stiffened or anchored walls, the stiffening elements and anchors act as supports that prevent free rotation. As a result of this, the earth pressure redistributes corresponding to the support points. On the passive earth pressure side, the classic distribution of the earth pressure occurs only in the case of a parallel displacement of the wall. When taking into account a redistribution of the active or passive earth pressure, the active or passive earth pressure determined in the classic way is redistributed according to the movement of the wall to be expected, whereby the total value of the resultant earth pressure normally remains the same.
DIN 4085:2007 provides guidance on the distribution of the active and passive earth pressure for various types of wall movement.
EAB 2006 provides information on the earth pressure redistribution for anchored and stiffened excavation enclosures. In this case, the number and position of the stiffening elements are particularly important. The follow picture shows the redistributionfigures for sheet pile walls with one support.
EAU 2004 contains earth pressure redistribution figures for anchored waterfront structures which also take into account whether the structure is built on land or in water. On land, the ground in front of the sheet pile wall is excavated so that the earth pressure redis- tributes towards the anchor position as the excavation proceeds. In water, the ground behind the wall is back filled in layers so that only a minimal redistribution of earth pressure takes place.
Sheet pile walls can be threaded into precut trenches, or pressed, impact-driven or vibrated into position. Threading and pressing do not involve any knocks or shocks, which is a complete contrast to impact driving and vibration methods. In difficult soils, the driving can be eased by pre-drilling, water-jetting, pre-blasting or even by replacing the soil.
When driving sheet pile walls, it is possible for the sheet piles to start leaning forwards or backwards with respect to the direction of driving (as the follow picture shows). Forward lean is caused by friction in the interlocks and by compaction of the soil while driving the previous sheet pile. The driving force is transferred to the pile concentrically, but the reaction forces are distributed unevenly across the sheet pile. Backward lean can occur in dense soils if the previous sheet pile has loosened the soil. To prevent leaning of sheet piles, they should be held in a guide frame or trestle. Vertical alignment during driving can be impaired by obstacles in the soil or hard strata at unfavourable angles.
Retaining wall structures are generally simulated with 2D equivalent models for FEM purposes (which is, of course, not possible with distinctly 3D problems such as the corners of excavations). Resolved structures such as struts, anchors, staggered sheet pile walls or bearing pile walls can be taken into account approximately in the 2D equivalent model but assuming equivalent stiffnesses related to a 1 m length of wall. Every individual case must be checked to ensure that the equivalent structure does not exhibit any unrealistic properties. Examples of this are: 2D equivalent anchors may not relieve the earth pressure acting on the retaining wall, 2D equivalent walls for staggered sheet pile walls may not be impermeable at the level of the staggered pile ends, 2D equivalent walls for bearing pile walls may not mobilise any unrealistically large passive earth pressures. It is not always clear whether all the deformations and stresses calculated with the 2D equivalent model are on the safe side; see (HÜGEL , 2004), for example. Examples of complex 3D analyses of sheet piling structures can be found in (BOLEY ET AL., 2004) and (M ARDFELDT, 2006).
Generalisation of the subsoil
Soil strata and groundwater conditions should be generalised in the finite element model depending on the database. However, when doing so, it must be ensured that the mechanical and hydraulic behaviour of the finite element model is comparable with the initial problem.
Subsoil segment and boundary conditions
The size of the subsoil segment should be specified such that the boundaries do not have any signi ficant effect on the deformations at the point of load transfer or such that the boundary conditions are known. Estimates of the dimensions necessary can be found in (MEISSNER, 2002) for the case of excavations.
Retaining wall structures are generally designed to be so stiff that finite element analyses may be based on geometric linearity. In the case of a yielding earth resistance and/or yielding anchorage, comparative analyses can be used to check whether geometric non-linearity needs to be taken into consideration.
Sheet pile walls are usually discretised with structural elements (beam or shell elements). This type of discretisation can lead to problems if under vertical loading a signi ficant part of the load is carried via the base of the wall. In the case of individual sections, an extension of interface elements can be taken into consideration at the base of the wall so that the sheet piling section can penetrate into the ground and no unrealistic stress peaks can occur in the body of soil below the base of the wall – see recommendation E4-15 in (S CHANZ, 2006). In the case of combined sheet pile walls under vertical loading where significant bearing pressures are mobilised, a bearing pressure can be modelled with the help of a stiff transverse beam at the base of the wall (MEISSNER, 2002).
In the case of a staggered sheet pile wall, the 2D equivalent model must take into account the fact that the base of the equivalent wall is permeable.
Where possible, the force transfer between sheet pile wall and soil should be modelled with interface elements or by way of kinematic contact formulation. This guarantees that no tensile stresses are transferred along the sheet pile /soil boundary surfaces and that, with corresponding action effects, irreversible sliding between sheet pile wall and soil can take place. Bilinear contact and friction principles are used for this in the simplest case.
Verification of the loadbearing capacity of the steel sheet pile section can be carried out via an elastic analysis of the permissible stress. This corresponds to the EAB method for excavations and the EAU method for waterfront structures. However, current research into the determination of the ultimate load capacity Rd,i of steel sheet piles at the ultimate limit state enables the advantages of plastic design to be exploited for sheet pile walls as well. Information on the plastic method of analysis can be found in K ALLE, (2005) and DIN V ENV 1993-5 (1998).The follow example shows the design for the elastic-elastic case to DIN 18800 (1990).
Example: Simpli fied analysis of material failure of sheet pile wall to DIN 18800-1 (1990)
The analysis of material failure of the sheet pile wall is carried out for the system shown in example 6.10 and 6.11.
From the structural calculations we get the following actions:
||due to permanent loads
||due to variable loads
|Resultant anchor forceA [kN /m]
|Horizontal equivalent force C [kN /m]
|Bending moment Mmax [kNm /m]
|Normal forceNmax [kN /m]
Requirements for the material resistances can be found in the respective standards.
Select: HOESCH 1605 section
steel grade S 240 GP, min. yield strength fy,k = 240 N/mm2
Partial safety factor to DIN 18800: γM=1.10
For simplicity, the comparative stress analysis for the maximum design loads M maxand Nmaxis carried out, the shear stress analysis will be neglected.
The limit condition to DIN 1054:2005-01 is rewritten for the limit condition regulated in the standard. In the case of verifying the sheet pile wall section
Ed ≤ R M,d becomes σd ≤ fy,d
The following applies
The analysis is satisfied; the degree of utilisation of the section amounting to μ = 75% may be optimised if