BN2001 Foundation Design Report: Preston Student Accommodation Project

This report provides a comprehensive analysis of pile foundation design for a proposed five-story steel-framed student accommodation building in Preston city centre. The report begins by emphasizing the importance of foundation design in civil engineering projects and the necessity of site investigation to determine the most suitable foundation type. Based on the site conditions, including the presence of man-made fill, a peat layer, and a fluctuating groundwater level, pile foundation is recommended. The report details the selection of pile foundations, considering factors such as proximity to existing buildings, the inclusion of a basement, and the heavy loads the building will impose. The design includes the pile, pile cap, and column, with a focus on the depth of the piles and the consideration of a basement. Different types of piles (concrete, steel, and composite) are discussed, along with their advantages and disadvantages. The geometric properties of the piles are also considered. The report also addresses basement design, recommending a tanked protection system and discussing construction materials such as poured concrete, precast panels, and masonry. The report references several sources to support its findings.

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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.

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Figure 1: Pile foundation section
The depth of foundation piles is very essential in this project considering the information
obtained from the geotechnical studies on the site. Approximately 8.4 meters below the ground
surface comprises of soil with low bearing capacity. This basically means that the depth of the
foundation should be at least 8.4 meters (1.4m deep manmade fill material layer and 7m deep
peat layer). Figure 2 below is a sketch showing the section of pile foundation for this project.
The sketch shows the column of the building resting on the pile cap of two piles. The pile cap
has reinforcement that to increase its strength. The pile foundation extends from the ground
surface through the soft soil to the hard rock where the load from the building is distributed.

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Figure 2: Pile foundation
It is important to note that the building in this project has a basement. This basement is
built on top of the pile foundation. This basically means that the basement columns and walls are
resting on the pile cap of the piles. The height of the basement is taken as 2.5m and the basement
is entirely below the ground surface. Considering this scenario where a depth of 2.5m below the
ground surface is taken up by the basement, it means that top of the pile cap will start at this
depth. The depth of the pile cap is 1m hence the remaining depth of the soft soil is 4.9m. The
depth of the pile in the hard rock or stable soil can be 2m. This means that the required length of
the piles to be used in this project is about 7m. The section of the pile foundation for this project
is shown in Figure 3 below.

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Figure 3: Pile foundation for the building with basement
Depending on cost, availability of materials, equipment and personnel, availability of site
space and accessibility to the site, the piles can either be concrete piles (cast in-situ or precast),
steel piles (hollow or H/I-section piles) or composite piles (steel and concrete). Each of these
categories of piles has its advantages and disadvantages hence the consultants will involve the
client in making the final decision on what type of piles to use for the project.
After identifying the most suitable type of pile foundation for this project, the next step is
to determine the appropriate geometric properties of the piles. This includes the shape of the pile
(square, rectangular, rectangular, box, tube, etc.), dimensions (width, breadth or diameter),
spacing, etc. (Salem, 2016). Each of these parameters has a significant effect on the effectiveness
and efficiency of the piles to perform their intended functions. The piles should also be protected
properly to prevent damage by factors such as water penetration (Kaneko, et al., 2018).
Basement

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Basements have become very crucial elements of modern buildings both for residential
and commercial use. These valuable spaces play a very key role in improving energy efficiency
by reducing space heating and cooling costs (About Home Design, (n.d.)). The basement also
provides structural stability and support of the building. The basement in this project will be used
as a storage space to accommodate larger utilities (mechanical plant room) and also as a
functional living space (student’s common room). The basement in this project will have
adequate waterproofing properties to protect the internal environment of the building.
Considering the site of the project and the findings from studies carried out on it, the suitable
type of basement construction for the building is tanked protection or type A basement
construction. This construction basically comprises of a water resistant membrane or layer that is
installed to the basement’s external face as shown in Figure 4 below The external water exerts
pressure on the membrane thus forcing it against the basement structure and creating strong
resistance against water penetration (First In Architecture, (n.d.)).
Figure 4: Section of basement wall
The basement will play a very essential role in protecting the building against water
penetration from below the ground. The basement can be constructed from poured concrete,
precast panels or masonry or concrete blocks. Poured concrete is the commonest and most

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preferred type of basement by many people. Construction of poured concrete basement starts by
pouring the basement foundation’s footing, installing formwork to hold the basement walls,
pouring the basement wall concrete and allowing them to dry. Concrete is considered the best
material for basement construction because it is the most durable, provides the minimum number
of joints thus reducing the likelihood of water penetration through cracks and joints, it is
permanently and totally repairable in case it fails, and it can be made watertight (Goldberg,
2017). Masonry or block wall is the most economical basement wall. The basement wall is
simply made of masonry or blocks that can be reinforced with steel rebars. Construction of
masonry or block basement wall also takes very minimal time. Precast panel basement wall is
becoming very common today as stakeholders in the construction industry focus on reducing
time, wastage and cost of construction and also improving efficiency. This method involves
molding walls in an offsite facility and transporting them to the site where they are installed on
ready foundation (My Foundation Repairs, 2018). Timber is also another material that can be
used in construction of pile foundation (Civiltoday.com, (n.d.)). The final choice of material will
be decided by the client in consideration of the project needs, client’s preference, availability of
materials, ease of construction, cost, etc.
References

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About Home Design, (n.d.). Building a Basement Do it Right the First Time. [Online]
Available at: http://www.about-home-design.com/building-a-basement.html
[Accessed 28 November 2018].
Civiltoday.com, (n.d.). What is Pile Foundation? Types of Pile Foundation. [Online]
Available at: https://civiltoday.com/geotechnical-engineering/foundation-engineering/deep-
foundation/176-pile-foundation-definition-types
[Accessed 28 November 2018].
First In Architecture, (n.d.). Basement Construction Details - Type A. [Online]
Available at: https://www.firstinarchitecture.co.uk/basement-construction-details/
[Accessed 28 November 2018].
Fleming, K., Weltman, A., Randolph, M. & Elson, K., 2009. Piling Engineering. 3rd ed. Londoon: Taylor
and Francis.
Goldberg, R., 2017. How to Create an Effective Basement. [Online]
Available at: https://www.houseplanninghelp.com/hph163-how-to-create-an-effective-basement-with-
andrew-mcinulty/
[Accessed 28 November 2018].
Kaneko, O; Kawamata, S; Nakai, S; Sekiguchi, T. & Mukai, T., 2018. Analytical study of the main causes of
damage to pile foundations during the 2011 off the Pacific coast of Tohoku earthquake. Japan
architectural Review, 1(2), pp. 235-244.
Letsios, C., Lagaros, N. & Papadrakakis, M., 2014. Optimum design methodologies for pile foundations in
London. Case Studies in Structural Engineering, 2(1), pp. 24-32.
My Foundation Repairs, 2018. Types of Basement Construction. [Online]
Available at: https://www.myfoundationrepairs.com/types-of-basement-construction/
[Accessed 28 November 2018].
Poulos, H., 2016. Tall building foundations: design methods and applications. Innovative Infrastructure
Solutions, 1(10), pp. 1-51.
Salem, L., 2016. Effect Of Pile Spacing On The Behavior Of Piled Raft Foundation Under Free Vibration
And Earthquake. Australian Journal of Basic and Applied Sciences, 10(12), pp. 240-247.