Foundation Types

This chapter is organized into sections on loadings, pile structures, gravity platforms, anchor uplift capacity, jack-up platforms, and hydraulic filled islands. 

---

Standard geotechnical test reports address typical static properties of soil such as shear strength and bearing capacity but may not provide dynamic properties unless they are specifically requested. In these situations, it is necessary to use the static properties. Dynamic soil properties which are reported may be based on low strain amplitude tests which may or may not be applicable to the situation of interest. Soils reports will generally provide vertical and lateral stiffness values for the foundation type recommended. These can be used along with ultimate bearing capacities to perform a dynamic response calculation of the foundation for the applied blast load. 

Examples of marine foundation types—(a) t) cal piled steel jacket structure, (b) typical gravity structures (i) Co eep and (ii) Howard-Doris, (c) hybrid sted gravity structure (i) RDL hybrid and (ii) sandpooL (Continued)... 

Examples of marine foundation types—(d) typical tension leg structure and (e) guyed tower structure. (From Gibson, R.E. and Dowse, B.E.W., Canadian Geotech. /, 18 171-178,1981. Reprinted with permission of Canadian Geotechnical Journal.)... 

For a more detailed review of substructure and foundation types, see TRB 2011, AWS Traewind 2009, and Tveiten et al. 2011. 

The oil and gas industry has operated offshore for decades and has developed many best practices and standards that can be used as a foundation for offshore wind development. Oil and gas developers started with practices and equipment for land-based applications and adapted them to the marine environment, as offshore wind developers have started to do. The oil and gas industry s understanding of seabed geology and meteorological conditions and their effects on design and operations is proving beneficial to the offshore wind industry. The wind industry is using innovations such as jack-up vessels and different foundation types, which were first developed by the oil and gas industry (Melnyk and Andersen 2009). 

The damage is illustrated by the magnitude of the base shear force transmitted to RC building superstructures by the soil foundation. The stability of the superstructure is defined by the absolute peak values of vertical subsidence, lateral drift motion and tilting angle. The relative performance of each foundation type is presented in the subsequent subsections. 

For example, the interaction between geotechnical and structural design of spread footings is too often reduced to little more than communicating an allowable bearing pressure, as if this single parameter was sufficient. Foundation types are sometimes selected without sufficient attention to the various soil-structure interaction considerations, which sometimes results in a foundation system that is unnecessarily expensive. 

A foundation problem, to explore the effect of changing foundation type and stiffness on total and differential settlements and bending moments in the substructure of a 6-story reinforced concrete office building supported by ds, strips or a raft. 

Selection of foundation type must be based on an assessment of the magnitude and direction of loading, depth of suitable bearing materials, seismic activity, evidence of previous flooding, potential for liquid action, undermining or scour, swelling potential, frost depth, and ease and cost of construction. 

Site and subsurface characteristics directly affect the choice of foundation type, capacity of the foundation, foundation construction methods, and bridge cost. Subsurface and foundation conditions also frequently directly or indirectly affect the route alignment, bridge type selection, and/or foundation span lengths. Therefore, an appropriately scoped and executed foundation investigation and site characterization should include the following ... 

The site characterization report should provide solutions to the geotechnical issues and contain geotechnical recommendations that are complete, concise, and definitive. The recommended foundation and geotechnical systems should be cost-effective, performance-proven, and constructible. Where appropriate, alternative foundation types should be discussed and evaluated. When construction problems are anticipated, solutions to these problems should be described. 

If the estimated differential settlement between two adjacent supports founded on shallow foundation is excessive, the foundation type should be changed to deep foundation unless ground improvement to reduce foundation settlement is a viable option. 

It is important to recognize that both the permissible total and the differential settlement for structures should not depend on the footing size, rather on some factors such as the span length, esthetics, and so on, discussed earlier that are related to the type and other characteristics, and use of the supported structure. Thus, for a given structure, the maximum amount of both total and differential settlement need to be defined in terms of some limiting values that should not depend on the size of the footing or even the foundation type. 

Bridge foundations are often constructed in difficult ground conditions such as landslide areas, hq-uefiable soil, collapsible soil, soft and highly compressible soil, swelling soil, coral deposits, and underground caves. Special foundation types and designs maybe needed under these circumstances. 

Number of floors Construction material Date of built Preservations conditions Hydrodynamics of r/c Existence of underground floors Foundations type Occupation form Number of utilization units... 

Differential settlements give rise to problems for all foundation types. Shallow foundations experience similar kind of problems as discussed above with respect to the infrastructure. Vertical and horizontal soil displacements near piles result in negative skin friction and bending moments. Damage to foundations is difficult and costly to repair, so measures are based on prevention rather than on mitigation. Some examples of possible measures are ... 

Kappos AJ, Sextos AG (2001) Effect of foundation type and compliance on the lateral load response of R/C bridges. J Bridg Eng ASCE 6(2) 120-130 Kappos AJ, Sextos AG (2009) Seismic assessment of bridges accounting for nonlinear material and soil response, and varying boundary conditions. In Coupled site and soil-structure interaction effects with application to seismic risk mitigation, NATO science for peace and security, series-C. Springer, Dordrecht, pp 195-208... 

RDN road network RDNOl bridge (material, type of deck, deck stmctural system, pier to deck connection, type of pier to deck connection type of section of the pier, spans, type of connection to the abutments, skew, bridge configuration, foundation type, seismic design level)... 

---