Foundation Design for Five Storey Steel Framed Student Accommodation Building

Foundation Design 1
PART 3: FOUNDATION DESIGN
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Foundation Design 2
Part 3: Foundation Design
Pile Foundation
Foundation design is very essential for any type of civil engineering structure such as
buildings, bridges, offshore platforms, power plant stations, etc. (Letsios, et al., 2014). The
foundation in this project is expected to provide adequate support for the proposed five storey
steel framed student accommodation building and transfer the total load of the building to the
ground. Considering the role and importance of foundation in this kind of building projects, it is
crucial to conduct relevant site investigation studies so as to gather information that will help in
designing the best type of foundation and construction method. The information helps engineers
and designers to identify the most suitable foundation type for the project in that particular site,
the materials to use, strategies of preventing possible defects, and methods of reducing the cost
of the foundation.
The most suitable foundation design recommended for the proposed five storey steel
framed student accommodation building in Preston city centre brownfield site is pile foundation.
Pile foundation has been selected in consideration of the ground or site conditions, nature of load
of the building, constructability, cost, closeness to other structures, sensitivity to vibration and
noise, presence of water, accessibility and durability of materials. Pile foundation are usually
used in areas where the soil strata near the ground level is not able to support heavy loads
whereas the hard rock strata is at a depth of between 5m and 50m below the ground surface. The
key factors that have been considered for the selection of pile foundation as the most suitable
type of foundation in this project are: the proposed building is within three meters of existing
buildings whose foundations are on silty clay soil and typically one meter deep below hence pile
foundation will minimize noise and vibration during construction; the building will have a

Foundation Design 3
basement where a mechanical plant room and student room will be situated thus pile foundation
will enable provision of these elements; it has been found from the borehole analysis conducted
on the site that there are manmade fill materials on the site comprising of organic waste, ash and
brick up to 1.4m deep below which lies a 7m deep peat layer (this means that a depth of about
8.4m below the ground surface is soft or weak strata that has weak bearing capacity thus not able
to support the building making pile foundation most suitable); and the groundwater level during
winter and summer is 1.4m and 2.5m below ground surface respectively (hence the water level in
the subsoil is high and also fluctuates significantly between seasons) . The building is also five-
storey hence the foundation will typically be supporting heavy loads.
Pile foundation is one of the types of deep foundation that is most suitable for storey or
high-rise buildings with heavy loads or located in areas with weak top soils (Poulos, 2016). The
foundation has the ability to transfer heavy loads exerted by the structure to a stable soil or hard
rock strata that is deeper into the ground (Fleming, et al., 2009). The foundation basically
comprises of a pile, pile cap and then a column built on top of it to carry the load as shown in the
sketch in Figure 1 below. The pile cap takes the load from the building’s superstructure and then
distributes it equally to the number of piles that transfers the load to the ground. Besides
transmitting the load to the ground, the piles also resist uplift, lateral and vertical load.