7 Design considerations
The basis standards for the design of all elements of sheet pile wall structures are :
- ENV 1991-1:1994 Eurocode 1 – Basis of design and actions on structures – Part 1 : Basis of design;
- ENV 1992-1-1:1994 Eurocode 2 – Design of concrete structures – Part 1-1 : General rules and rules for buildings;
- ENV 1993-1-1:1994 Eurocode 3 – Design of steel structures – Part 1 : General rules and rules for buildings;
- ENV 1993-5:1998 Eurocode 3 – Design of steel structures – Part 5 : Piling;
- ENV 1997-1:1994 Eurocode 7 – Geotechnical design – Part 1 : General rules.
7.2 Selection of sheet pile
7.2.1 The selection of sheet pile types, profile and quality, as well as the dimensions of the primary elements of combined walls shall, as a minimum, comply with the general design considerations.
For steel sheet piles account shall be taken of the cross-section classification in accordance with ENV 1993-5:1998.
The selection shall ensure adequate driveability as established in 5.2.
7.2.2 When shear forces cannot fully be transmitted by the interlocks, this shall be taken into account in accordance with ENV 1993-5:1998 when selecting the sheet pile profiles.
7.2.3 In the case of combined walls the sheet pile profile for the secondary elements shall be selected not only on the basis of strength considerations but also on flexibility and driveability. Account shall be taken of the tolerances which can occur after driving the primary elements, as indicated in figure 6 (see 8.6.2).
NOTE The danger of de-clutching depends mainly on the following conditions :
- accuracy of positioning and verticality of the primary elements;
- soil conditions;
- the deformation behaviour of the sheet piles.
- - - - - - - - - - - - design
- ____________ as built
|a primary element
c transversal tolerance
|b secondary element
d longitudinal tolerance
7.3 Other structural elements
7.3.1 In addition to the sheet pile wall itself, the selection of the elements which are necessary for the sheet pile wall structure, such as anchorages, struts and walings, shall take account of adverse loading and site conditions.
7.3.2 Ground anchorages shall comply with prEN 1537.
7.4 Sequence of execution
7.4.1 The various stages of the works shall be established in accordance with the design.
7.4.2 The criteria for progressing from one stage to the next shall be defined. As a minimum for each stage of the execution works, this involves the following :
- the levels and tolerances for filling and excavation;
- the levels and tolerances of the groundwater and the free water;
- the characteristics of the materials and the quality of the fill along both sides of the sheet pile wall and in front of the anchor plates;
- the displacements of the sheet pile wall, as anticipated at the end of the various stages;
- restrictions regarding surcharges.
7.5 Specific design considerations
The following matters should be specified in the design if appropriate :
- method of fixing the interlocks;
- method of attaching the connectors to the primary elements of a combined wall, taking into consideration table 15 of EN 10248-2:1995;
- quality of the weldings;
- method of cutting steel elements;
- method to assist driving and the depth to which it may be applied;
- shape of rock shoe and other measures necessary to secure the toe of the sheet piles in the bedrock;
- in soft clays, overlying bedrock, the method of preventing the clay from squeezing through the gap between the pile toe and the bed-rock;
- quality of the backfill or the method of placement thereof;
- prestressing of the struts or anchorages in order to reduce displacements in the ground behind the sheet pile wall;
- time restraints during critical execution sequences;
- methods and levels of de-watering;
- type, kind and method of coating steel elements and preserving wooden parts;
- cathodic protection methods;
- compatibility of the interlock sealant and the coating material;
- special requirements regarding the permeability of the sheet pile wall, including performance criteria for materials, procedures and testing;
- the method to secure the position of the toe of sheet piles when close excavation in rock is carried out;
- consequences of extracting the sheet piles on adjacent buildings, installations and services, on settlements of the soil surface and on the creation of a link between soil layers with different groundwater regimes;
- measurements needed to check settlements, displacements and vibrations.