2.2 Design situations
(1)P Both short-term and long-term design situations shall be considered.
(2) In geotechnical design, the detailed specifications of design situations should include, as appropriate:
- the actions, their combinations and load cases;
- the general suitability of the ground on which the structure is located with respect to overall stability and ground movements;
- the disposition and classification of the various zones of soil, rock and elements of construction, which are involved in any calculation model;
- dipping bedding planes;
- mine workings, caves or other underground structures;
- in the case of structures resting on or near rock:
- interbedded hard and soft strata;
- faults, joints and fissures;
- possible instability of rock blocks;
- solution cavities, such as swallow holes or fissures filled with soft material, and continuing solution processes;
- the environment within which the design is set, including the following:
- effects of scour, erosion and excavation, leading to changes in the geometry of the ground surface;
- effects of chemical corrosion;
- effects of weathering;
- effects of freezing;
- effects of long duration droughts;
- variations in ground-water levels, including, e.g. the effects of dewatering, possible flooding, failure of drainage systems, water exploitation;
- the presence of gases emerging from the ground;
- other effects of time and environment on the strength and other properties of materials; e.g. the effect of holes created by animal activities;
- ground movements caused by subsidence due to mining or other activities;
- the sensitivity of the structure to deformations;
- the effect of the new structure on existing structures, services and the local environment.
(1)P At the geotechnical design stage, the significance of environmental conditions shall be assessed in relation to durability and to enable provisions to be made for the protection or adequate resistance of the materials.
(2) In designing for durability of materials used in the ground, the following should be considered:
a) for concrete:
- aggressive agents in the ground-water or in the ground or fill material, such as acids or sulfate salts;
b) for steel:
- chemical attack where foundation elements are buried in ground that is sufficiently permeable to allow the percolation of ground-water and oxygen;
- corrosion on the faces of sheet pile walls exposed to free water, particularly in the mean water level zone;
- the pitting type of corrosive attack on steel embedded in fissured or porous concrete, particularly for rolled steel where the mill scale, acting as a cathode, promotes electrolytic action with the scale-free surface acting as an anode;
c) for timber:
- fungi and aerobic bacteria in the presence of oxygen;
d) for synthetic fabrics:
- the ageing effects of UV exposure or ozone degradation or the combined effects of temperature and stress, and secondary effects due to chemical degradation.
(3) Reference should be made to durability provisions in construction materials standards.