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Safety and verification concept

1.1 Principles of the safety and verification concept for waterfront structures

1.1.1 General

A structure can fail as a result of exceeding the ultimate limit state of bearing capacity ("ultimate limit state - ULS", failure of the soil or the structure, loss of static equilibrium) or the limit state of serviceability ("serviceability limit state - SLS", excessive deformations).

1.1.2 Normative regulations for waterfront structures

The "Eurocodes" (EC) - harmonised directives specifying fundamental safety requirements for buildings and structures - were drawn up as part of the realisation of the European Single Market. Those Eurocodes are as follows:

The Eurocodes "Basis of structural design" (DIN EN 1990) and "Actions on structures" (DIN EN 1991) with their various parts and annexes form the basis of European construction standards, the starting point for building designs throughout Europe. The other eight Eurocodes, along with their respective parts, relate to these two basic standards.

Verification of safety must always be carried out according to European standards. However, in some instances such verification is not possible with these standards alone; a number of parameters, e.g. numerical values for partial safety factors, have to be specified on a national level. Furthermore, the Eurocodes do not cover the entire range of German standards, meaning that a comprehensive set of national standards has been retained in Germany. However, this set of German standards along with its requirements may not contradict the regulations contained in the European standards, which in turn necessitated the revision of national standards.

For proof of stability according to the EAU, the standards DIN EN 1990, DIN EN 1991, DIN EN 1992, DIN EN 1993, DIN EN 1994, DIN EN 1995, DIN EN 1996, DIN EN 1997, DIN EN 1998, DIN EN 1999, and especially DIN EN 1997 (Geotechnical design), are of particular importance. DIN EN 1997-1 defines a number of terms and describes and stipulates limit state verification procedures. The various earth pressure design models for stability calculations are also included in the annexes for information purposes. A particular feature here is that three methods of verification using the partial safety factor concept are available for use throughout Europe.

The publication of DIN 1054:2010 ensured that any duplication of DIN EN 1997-1 was avoided, but specific German experience has been retained. This standard was combined with DIN EN 1997-1:2010 and the National Annex (DIN EN 1997-1/NA:2010) to create the EC 7-1 manual (2015).

The many years of experience with the specific boundary conditions of waterfront structures (e.g. greater tolerances for deformations compared with other engineering works) have led to the EAU containing a number of specific stipulations for the design of such structures that can deviate from those given in DIN EN 1997-1 and DIN 1054.

Those specific stipulations include, for example, the following:

• In some cases, lower partial safety factors for actions, action effects and resistances for the limit state of failure (Section 1.2.4, Tables 1.1 and 1.3).
• The determination of a characteristic resultant hydrostatic pressure by offsetting favourable and unfavourable hydrostatic pressures against each other where this is realistic (see Section 3.3.1).
• Simplified assumptions for hydrostatic pressure (see Section 3.3.2).
• Redistribution of active earth pressure independently of the method of construction for sheet pile walls (see Section 8.2.3.2).
• Increasing the theoretical anchor force by 15% for the robust construction of sheet pile wall components (see Section 9.2).

DIN EN 1997-2 covers the planning, execution and evaluation of soil investigations. As for part 1, this standard has been published together with DIN 4020:2010 and the National Application Document in the EC 7-2 manual (2011).

The execution of special civil engineering works is covered by European standards. In Germany, more specific information for such work is laid out in DIN SPEC publications.

Calculations for large-scale soil stabilisation measures (e.g. jet grouting, grout injection) in Germany are covered by DIN 4093.

Where standards are cited in the recommendations, the current version applies, unless stated otherwise. Standards quoted in the text are listed at the end of each chapter.

1.1.3 Geotechnical categories

The minimum requirements in terms of scope and quality of geotechnical investigations, calculations and monitoring measures are described by three geotechnical categories in accordance with EC 7: low (category 1), normal (category 2) and high (category 3) geotechnical difficulty. These are reproduced in DIN 1054, A 2.1.2. Waterfront structures should be allocated to category 2, or category 3 in the case of difficult subsoil conditions. A geotechnical expert should always be consulted.

1.1.4 Design situations

Load cases for verifying stability and allocating partial safety factors are defined in DIN 1054, Section 6.3.3. These result from the combinations of actions in conjunction with the safety categories for resistances. The following classifications apply to waterfront structures:

1.1.4.1 Design situation DS-P (persistent)

This design situation covers loads due to active earth pressures (separately for the initial and final states in the case of unconsolidated, cohesive soils) and excess water pressure in the case of the frequent occurrence of unfavourable inner and outer water levels (see Section 3.3.2), active earth pressure influences due to normal imposed loads and normal crane and pile loads, instantaneous surcharges due to self-weight and normal imposed loads.

1.1.4.2 Design situation DS-T (transient)

Transient situations, i.e. those related to a certain period of time, are allocated to design situation DS-T. They include, for example, situations during construction or repairs. For hydraulic engineering works, besides permanent actions and variable actions that occur regularly during the service life of the structure, which are all allocated to DS-P, transient actions include limited scour due to currents or ship propellers, excess water pressure in the case of rare occurrences of unfavourable inner and outer water levels (see Section 3.3.2) or wave loads according to Section 4.3.

1.1.4.3 Design situation DS-A (accidental)

This is as for design situation DS-T, but with extraordinary design situations such as unscheduled surcharges over a larger area, unusually extensive flattening of an underwater slope in front of the base of a sheet pile wall, unusual scour due to currents or ship propellers, excess water pressure following extreme water levels (see Section 3.3.2 or 6.2), excess water pressure following exceptional flooding of the waterfront structure, combinations of earth and hydrostatic pressures with wave loads resulting from waves that occur only rarely (see Section 4.3), combinations of earth and hydrostatic pressures with flotsam impact according to Section 6.2.5, all load combinations in conjunction with ice states or ice pressures.

1.1.4.4 Extreme case

When extremely improbable combinations of actions occur concurrently, then DIN 1054, Section A 2.4.7.6.1, A(4), A 2.4.7.6.3 and A(5), permit partial safety factors for actions and resistances to be taken as