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University of Cambridge
Embodied Energy of Underground Construction
1
INTRODUCTION
1.1
Background
Department of Engineering
Presently, there are concerns regarding the rate at which the human population is extracting
resources from the earth and emitting pollution and wastes to the environment. This has raised
issues of sustainability and efficiency in many areas of industry, including construction, which
presently uses about 50% of all resources used in the world [1]. To address this, one of the fields
of research has been the study of embodied energy.
Embodied energy is defined as the total energy that can be attributed to bringing an item to its
existing state and its units are in terms of joules, usually in the order of giga-joules (GJ) or terajoules (TJ). For the construction practice, embodied energy will include the energy used in the
extraction of the raw materials from the earth, the processing of the raw materials into finished
products, the transportation to the suppliers and then to the site, the construction process, the
demolition and recycling and the construction and maintenance of any associated temporary
works.
The topic of embodied energy has been chosen because it contributes to a significant part of the
energy consumed in the UK; 10% of the UK’s annual energy consumption is in the embodied
energy of new construction and renovation [2]. In addition, the average household uses about
1000GJ of embodied energy in materials during construction, this is equal to 15 years of
operational energy [3]. This implies that the choice of material and construction method can
significantly change the amount of embodied energy in a building and as the operational energy
efficiency increases, the embodied energy becomes more significant.
Research into embodied energy is important because embedded into the measurements are
associated environmental implications such as resource depletion and greenhouse gases. In fact,
research into the relationship between embodied energy and carbon dioxide, the main contributor
of the greenhouse gases, shows a high correlation; every GJ of embodied energy produces 0.098
tonnes of carbon dioxide [3]. Therefore, although there are no physical environmental impacts
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
associated with embodied energy, with the link to carbon dioxide, it now has a tangible meaning
and so sheds light on how embodied energy should be interpreted.
The research aims to provide information on the selection of construction materials and
procedures in future projects to maximise energy saving and the results will be used to make
comparisons with previous research and construction projects. This information will not only
contribute to the research completed already, but should also aid the construction industry. This is
due to the fact that a saving in energy equals a saving in total cost of the project through the use
of less materials and/or a more efficient method of construction. In addition, it may question
industry norms, where currently tried and tested methods are not re-designed due to time
constraints but are not the most environmentally friendly practices available. It is hoped that this
study will encourage companies, especially with the growing sustainability trend and the cost
saving incentive, to make the business more sustainable.
1.2
Literature Review
Research in embodied energy started in the mid 1970’s with concerns regarding material usage,
which then led to energy apprehension; this is shown in the paper by Chapman [4] which
incorporates these two topics. Further research commented on sustainable design to tackle these
issues [5] and in 1980, the topic became more mainstream when an economic value was attached
to embodied energy in a paper by Costanza [6]. It stated that there was a strong relation between
embodied energy and the dollar value since the primary factors of production such as land and
labour were not independent and also required energy in their production.
Research increased in the 1990’s with Australia and New Zealand leading the way and since
then, has included the amount of embodied energy in many areas of construction such as building
materials, fuels, operation and in the construction of housing and offices. More recently, the
study of embodied energy on the geotechnical side of the construction industry has also been
considered with a paper by Carley discussing the relative merits of concrete and steel piling [7]
and research into tunnelling using the Channel Tunnel Rail Link project by Workman [8].
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Embodied energy calculations have also been performed on various types of retaining walls as
part of the study to discover the contribution embodied energy has to offer for sustainable
construction. One was produced in 2004 by Giken, a steel piling manufacturing company in
Japan [9] and another by Kwong [10]. This research continues the study of retaining walls, both
as stand-alone structures and as part of a basement; this will aid the choice of retaining wall in
future projects.
1.3
Objectives
Two separate buildings will be considered which are for commercial purposes with a multi level
basement car park. The aim is to carry out an embodied energy analysis on the construction of a
building with emphasis on the design and analysis of different types of retaining walls, struts and
load bearing piles. This will allow comparisons to be made as to which retaining wall should be
proposed for environmental reasons and which strut arrangement to use in conjunction. There
will also be recommendations made on the layout of the load bearing piles and it would be of
interest how the embodied energy contribution of a basement compares to that of a building as a
whole. This will allow differences between two sites to be compared and conclusions drawn.
By completing this study, it should give an indication of a foundation system’s environmental
impact relative to other building projects and identify areas for energy saving.
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
2
EMBODIED ENERGY
2.1
Embodied Energy and Life Cycle Analysis
Department of Engineering
Embodied energy is defined as the total amount of energy that can be attributed to bringing that
item to its existing state and has an important role in part of the Life Cycle Analysis (LCA),
which is increasingly used as an environmental indicator.
The LCA assesses the total environmental impacts associated with the building during its
lifetime. This allows comparisons to be made between structures so that the ones with the least
liabilities are chosen to be constructed. It was introduced to investigate the performance of
industries as the study of individual components could be made more environmentally friendly
by displacing the negative effects of it elsewhere. For a building, LCA brings to attention the
complex impacts associated with construction, use and decommissioning. One of the analysis
tools for measuring LCA is embodied energy.
Figure 1: Life Cycle Analysis
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Due to the link between embodied energy and LCA, the stages of evaluation used in the
assessment of embodied energy take the LCA stages of resources excavation, manufacturing,
construction, operation, demolition and recycling as shown in Figure 1.
The embodied energy used in maintenance, demolition and recycling are difficult to predict,
therefore current LCA often ignores these stages and this will also be the case in this project.
Hence, the focus of this research will be on the first three stages. More specifically, this includes:
material energy that consists of the energy required to bring raw material to a state where it is
ready to be used as construction material, installation energy which is energy used to operate the
different machineries necessary to build the structure and transportation energy, the energy used
to transport materials and equipment from one place to another.
2.2
Types of Embodied Energy
There are two types of embodied energy, initial and recurring where initial embodied energy is
further discriminated into direct and indirect.
The initial embodied energy is defined as the non-renewable energy used in the mining,
processing and manufacturing of raw materials, and also includes transportation and installation
energy.
Direct energy, in this example, is the energy used in transporting building materials from factory
to site, and also the energy associated with assembling the actual structure.
Indirect energy would be seen as the material energy, which includes the acquiring, processing,
manufacturing and delivering of the structure’s building materials.
The recurring embodiment energy is the non-renewable energy used in the maintenance required
for the upkeep of the structure during its life time.
In this report, only the initial embodied energy values will be taken into account as the recurring
embodiment energy is difficult to calculate, as explained in Section 2.1. In regards to the initial
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
embodied energy, the direct energy will be represented by the transportation and installation
energy and for the indirect energy, the material energy.
2.3
Types of Analysis
There are three different ways of analysing embodied energy, although the most popular
technique is to use a hybrid of the methods. This is due to the fact that a hybrid analysis combines
the best of the techniques even though this means taking on all the disadvantages of them too.
However, since research in this field is still relatively new, it is not known which is the most
accurate type of analysis and hence a hybrid approach helps towards solving that. This project
will be making use of the hybrid analysis technique. The three separate types of analysis are
described below.
Statistical analysis uses published statistics to determine energy use by particular industries; it is
a speedy process and is useful in providing some related figures, such as the national usage of
material. The only problem with this method is that it is of no use if statistics are not kept
consistent, thorough, relevant and sufficiently detailed.
The Input – Output analysis uses economic tools to examine cash flows between different sectors
of the economy where money flows are examined to and from energy producing sectors and
comparing to known amounts of energy produced by each sector, therefore tracing energy flows
in the economy. Since every money transaction is recorded, every flow is captured but price
levels, technology and energy cost of capital are constantly changing hence this method may be
producing less accurate results.
Finally, the Process analysis which is the systematic examination of direct and indirect energy
starts with the final production and works backwards. This is the most common form of analysis
as the data can always usually be obtained. This method is seen as accurate and specific however
much time and effort is required in obtaining the results.
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
2.4
Department of Engineering
Calculation of Embodied Energy
The calculation of embodied energy involves the use of the Embodied Energy Intensity (EEI)
values. This indicates the amount of embodied energy required in producing 1kg of construction
material from the point of resource extraction to the end product; its units are MJ/kg or MJ/L for
liquids. There has been research into EEI values since 1979 and the School of the Environment at
the University of Brighton has produced a spreadsheet with all known EEI values, from which
this report’s calculations are based [11]. However, there are a range of values found for the EEI,
as shown in Table 1, and so the calculations take this into account with the minimum, average
and maximum values of embodied energy assessed; although the average value will be used
throughout.
Material
EEI Values
Minimum
Average
Maximum
Virgin Steel
20
55
60
Recycled Steel
9
10
18
Concrete
1.5
1.8
2.0
Table 1: Examples of the Range of EEI Values [11]
The difference in EEI values comes from the difference in calculation methods and the
assumptions used. These arise due to the use of different data sources as the specification and
quality of material will affect the constituents and the proportions required. In addition, there is
the complication of the way the EEI is estimated and there are unknown factors in the
calculations such as maintenance and demolition energy which need to be included. The average
EEI values shown in Table 1 are not the averages of the minimum and maximum values seen due
to the fact that there are more EEI values than is shown.
The method used in the embodied energy calculations has been the topic of previous research
where the values are in public domain to be accessed and are as shown in Figure 2.
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Figure 2: Embodied Energy Calculation Process
Figure 2 shows that the first step of the embodied energy calculation method is to calculate the
material energy. This is done by finding the total volume of each material used, hence its weight
and multiplying this by its EEI value. Next is the transportation energy which includes the
moving of the equipment and the material required. This is calculated using the litres of fuel
consumed by the vehicles multiplied by the respective EEI value for the fuel. The installation
energy is calculated by multiplying the amount of fuel and electricity used by the machinery with
its EEI value; this stage includes any temporary work required. All three values of the material,
transportation and installation energy are then summed to give the total embodied energy. Note
that excavation energy is not required in this project but would otherwise be included.
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
3
TYPES OF CONSTRUCTION
3.1
Retaining Walls
Department of Engineering
Retaining walls are structures which are built during excavation to contain the earth by
preventing downward motion of the soil and providing support for gradient changes. These are
usually of a temporary arrangement which can be stand alone structures or built as part of a larger
assembly. Figure 3 shows the types of retaining wall that are covered in this report.
Figure 3: Types of Retaining Wall
3.1.1
Steel Sheet Pile Walls
These are constructed by driving pre-manufactured steel sheets into the ground and are
considered to be the more economical where softer soils are concerned. Advantages of steel sheet
pile walls are that construction is relative quick in comparison to other retaining walls and
installation can be relatively quiet with certain driving methods such as vibration. However, they
are not very adaptable when conditions worsen where boulders or rocky surfaces occur, are not
completely watertight and may permit large ground movements.
3.1.2
Secant Pile Walls
Secant piles are a type of bored pile and are constructed in a way that each pile is intersected with
another. Usually, alternative (female) piles are cast along the required line of the wall such that
the remaining space is just short of the diameter of the intermediate (male) piles; the exact
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
spacing depends on the specifications of the project. The concrete for the female piles is added
and before it has fully set, the male piles are drilled such that holes are cut through the female
ones and the concrete poured in and a reinforcement cage lowered. This will form a watertight
wall even though this will depend on the amount of overlap and type of concrete cast. The
advantages of using secant pile walls is that only one pile needs to be bored at a time, which
means that when working close to other structures, their foundation would only be exposed to
risk for a short period. In addition, they can easily overcome more difficult ground and can be
constructed with minimum vibration. The disadvantage of using a secant pile wall is that they are
unsuitable for sites with high water table levels and may not necessarily be watertight in addition
to being a fairly expensive and lengthy process and has a limit of 20m deep; even though secant
pile walls can go deeper, there are difficulties attached.
3.1.3
Tubular Sheet Pile Walls
These are manufactured and driven into the ground in a similar way to the steel sheet pile walls.
The difference is that tubular sheet piles are circular in nature so that they are stiffer such that
they are less likely to deform. The benefits of the tubular sheet pile walls and the disadvantages
are the same as those for the steel sheet pile walls.
3.1.4
Diaphragm Walls
Diaphragm walls are the most expensive out of all the retaining walls considered. However,
formed from reinforced concrete and being completely watertight, they are also the only retaining
wall which may be used as part of the permanent structure. Although the cost is high for
diaphragm walls, for shallow depths they may be constructed without temporary supports as
cantilevers and they are able to be built beneath water tables. The common method of
construction uses bentonite slurry, which is pumped in to replace the soil as the excavation takes
place, as temporary support. A pre-fabricated reinforcement cage is then lowered in and the
bentonite slurry replaced with concrete and the wall left to set. Care must be taken to ensure that
no holes are present; otherwise this is the most stable of the retaining walls.
Sandra Wing Man Lee
- 10 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
3.1.5
Department of Engineering
Combi Walls
These are a combination of steel sheet piles and a king pile, where the latter is a tubular pile in
this project. This arrangement of traditional sheet piles being combined with circular piles gives
additional strength to the retaining wall, where the advantages and disadvantages of each have
been covered.
3.2
Anchors and Props
These are installed during excavation to aid the retaining walls in achieving their purpose. They
are not always necessary as demonstrated in the case of diaphragm walls but are common
practice.
3.2.1
Anchors
For the projects considered later, there is the option of installing either one or two sets of anchors;
the general installation method is described. After the retaining wall has been positioned, a small
excavation is made along the wall and the first set of anchors installed. This excavation-anchor
sequence is repeated until the base is reached. One round of the excavation-anchor sequence can
be seen in Figure 4. The only issue with anchors is that they may produce downward movement
of the wall due to the vertical components of the anchor forces.
Figure 4: Excavation-Anchor Sequence
There is a choice of using either one or two sets of anchors and to aid with the choice, in addition
to the calculations performed, the differences between using the one or two anchors should be
considered. Two rows would reduce the maximum bending moments in the wall and reduce the
size of the anchors; this would be cheaper since smaller diameters are economical to drill but
more may be required. Additionally, the height of the first excavation stage may be reduced and
Sandra Wing Man Lee
- 11 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
using two sets of anchors would prevent them getting too long, for example preference is given to
two 10m length anchors rather than one of 20m length.
3.2.2
Props
Unlike anchors, props do not pierce the earth. They either need space on the outer side of the wall
to support against, in this case with the berm method, or require a double wall where the prop sits
in the middle maintaining the excavation. An example of how a prop may be used can be seen in
Figure 5. This method is used where there may not be enough clear ground behind the excavation
for anchors to be placed or for the corners of the site.
Figure 5: An Example of the Use of a Prop
3.3
Load Bearing Piles
Load bearing piles form the foundation of a building and have the function of transferring load
from the superstructure through the ground into stronger strata. For any building, there may be
several load bearing pile layouts available where the depths, diameters, locations and numbers of
the load bearing piles will vary. Designs will depend on the function of the building and how it is
laid out with most decisions being based on experience, although this may not be the most energy
efficient option.
Sandra Wing Man Lee
- 12 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
4
RIVERSIDE SOUTH
4.1
Overview
Department of Engineering
The Riverside South site, Figure 6, is situated in the Docklands area of London and was
previously a dock which had plenty of activity throughout the time it was active, including a
variety of construction over the years. The main constructions have been the dock themselves,
which vary in material from wood to concrete, depending on the time they were erected. This
means that the site is contaminated with a lot of material, which will need to be determined
before further work continues. The proposed building to be built at this site will be 40 storeys,
about 150m in height, and have a three level basement at about -6m, where ground level is at
+5m, resulting in an expected 11m dig, with the toe of the retaining wall at close to -13m.
Figure 6: Site of Riverside South
Sandra Wing Man Lee
- 13 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
4.2
Department of Engineering
Construction
The options for Riverside South were provided by Arup and can be found in Table 2.
Type of Wall
Toe Level (MOD)
Steel Sheet Pile
-13
Secant Pile
-13
Tubular Sheet
Pile
Combi
-13
-13
Details
AZ48 Sheet Piles
1.2m diameter secant piles
@ 1.6 c/c
0.8m diameter tubular piles with
9mm thickness
0.965m diameter tubes @ 1.565m
c/c with PU Sheet Piles
Table 2: Retaining Walls Considered for Riverside South
Four retaining wall designs are being considered. The first is a steel sheet pile wall using the
heaviest AZ section available; this is due to the fact that the wall needs to be water-tight and so
this would prevent against corrosion, although over-designed structurally. Next is the secant pile
wall with concrete piles of 1.2m diameter with an overlap of 0.1m and the tubular sheet pile of a
standard size of 0.8m diameter with a tube thickness of 9mm. The last option is the combi wall
which incorporates both the steel sheet piles and the tubular sheet piles for added stiffness. Each
retaining wall will consider both the one and two anchor systems, which can be seen in Figure 7.
Figure 7: One and Two Anchor System
Construction will also consist of the load bearing piles which are in the preliminary stages of
design hence there is only one set of data available with a rough calculation of 614 load bearing
Sandra Wing Man Lee
- 14 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
piles at 0.9m diameter to a depth of -24MOD. Together with the basement design is the
approximation of 102 columns of sides 0.8m and length 10.4m with 4337m2 of slab per level.
4.3
Calculations
Although preliminary details had been provided by Arup for the retaining walls, further analysis
had to be made in order for the walls to be designed. This involved modelling programmes, such
as Frew which were provided by Arup. The details presented enabled a stiffness to be found for
each wall which was then entered into Frew along with the toe level of the wall, the soil profile,
the level at which the anchors would be inserted and the specification that deflection was not to
exceed 50mm at any point during installation. An example of Frew ouput can be seen in Figure 8.
Figure 8: An Example of Frew Graphical Output for the Secant Pile Wall with Two Anchors
Frew was run for every retaining wall option and this analysis produced the maximum bending
moments and from that information, the retaining walls could be designed, hence specifying the
amount of material required. This has been calculated for sections of 1m in length so that direct
comparisons can easily be made in the future.
Sandra Wing Man Lee
- 15 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
The steel and tubular sheet piles are produced as standard sizes and so no additional design was
necessary after a calculation check of the maximum bending moment before the volume of
material required for a 1m span was determined. This was also true for the combi wall since it is
a combination of the steel sheet and tubular piles. For the secant pile, another programme called
Adsec, also provided by Arup, was used to model a pair of piles to find their maximum bending
moment, which was adjusted by the amount of reinforcement present. Once the optimum design
was found, the volume of concrete and steel was calculated, hence producing the total amount of
material required and the embodied energy value for each retaining wall. The installation and
transportation embodied energy for these options were scaled from figures found in previous
research data where that project was also based in London [8][10].
The Frew analysis also produced the horizontal forces needed for the anchor; these had to be
resolved to find the actual anchor forces which can be found in Table 3, which shows the results
for the one anchor system, and Table 4, which shows the results for the two anchor system.
One Anchor System
Type of Wall
Anchor Force (kN)
Installation Depth (MOD)
Steel Sheet Pile
971.4
1
Secant Pile
912.0
1
Tubular Sheet Pile
856.1
1
Combi
868.3
1
Table 3: Retaining Walls and Anchor Combinations for One Anchor System
Two Anchor System
Type of Wall
Anchor One
Top Installation
Anchor Two
Bottom Installation
Force (kN)
Depth (MOD)
Force (kN)
Depth (MOD)
Steel Sheet Pile
384.0
3
320.0
-3
Secant Pile
470.4
1
320.0
-2.5
Tubular Sheet Pile
419.5
2.25
605.5
-3
Combi
348.8
2.25
640.2
-3
Table 4: Retaining Walls and Anchor Combinations for Two Anchor System
Sandra Wing Man Lee
- 16 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Several different options were investigated for the anchor design as there may have been a
difference in embodied energy between them and it was the most commonly used industry
standards that were picked. This is because, although not taken directly into account in this
project, if special sized anchors were recommended, extra machinery would have to be acquired,
hence using more embodied energy overall. The diameters that were considered were 0.12m,
0.15m and 0.20m which had their respective lengths and the number of steel bars required also
calculated. Again, the material, transportation and installation embodied energies was found.
The combinations of retaining wall and anchor systems were then compared so that a
recommendation could be made as to which arrangement would use the least embodied energy.
To calculate the embodied energy of the total basement, the dimensions and numbers of columns
and load bearing piles and the area of the slabs had to be found for the amount of energy
required. This detail was again supplied by Arup where the load bearing pile layout was
proposed. The retaining walls including the anchoring systems were then compared to the total
value of the basement.
Finally, the superstructure’s embodied energy was found through averaging the embodied energy
value for each floor, which included only the columns and slabs, and then the retaining walls and
the basement compared as a percentage of the total value.
4.4
Results and Discussions
4.4.1
Virgin Steel vs. Recycled Steel
For each of the retaining walls, the embodied energy calculation was produced assuming that
virgin steel would be used for one case and recycled steel for another. The results can be found in
Figure 9, which compares the overall embodied energy for the retaining wall options using either
the virgin steel or the recycled steel. It can be seen that the retaining walls using virgin steel has a
much greater embodied energy value than those using recycled steel. On average, the virgin steel
has an embodied energy of 151GJ more than that of recycled steel and in the most extreme case,
for the combi wall, the difference is 238GJ.
Sandra Wing Man Lee
- 17 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Figure 9: Comparison of Retaining Walls Using Virgin or Recycled Steel
The material energy in Figure 9 has been divided into concrete/mortar and steel so that the
different amounts consumed can be seen. From this, it can be noted that material energy makes
up most of the embodied energy value, accounting for a minimum of 92.3% of the total embodied
energy for any one of the retaining walls, being much greater than the transport and installation
energies combined. In addition, it would suggest, comparing only the recycled steel values, that
the tubular sheet piles uses the least amount of embodied energy, followed by the steel sheet pile,
the combi wall and finally the secant pile.
4.4.2
Embodied Energy Errors
As mentioned previously, there is a large variation in the EEI values found; Figure 10 presents
the minimum, average and maximum values of embodied energy calculated for each retaining
wall. The maximum and minimum values found for EEI contribute to a great difference, where
the largest difference was 180GJ for the combi wall using virgin steel and the smallest difference
was 4GJ for the tubular pile wall using recycled steel. As presented in Figure 9, material energy
contributes most to the overall embodied energy value and this is also where the greatest
variation in EEI values is seen. The EEI values for virgin steel range from 20-60MJ/kg, recycled
Sandra Wing Man Lee
- 18 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
steel has a smaller range of 9MJ/kg and concrete has a range which is even smaller of 0.5MJ/kg.
It is because of this range of EEI values occurring in the material energy section, which makes
the largest contribution to the overall embodied energy value, that there are large embodied
energy errors.
Figure 10: Comparison of Retaining Walls with Associated Embodied Energy Errors
4.4.3
Anchor Systems
Figure 11 shows the embodied energy of the steel sheet pile wall with the anchor systems, where
both the one and two anchor systems have been analysed with differing diameters. There are two
main observations to be made from Figure 11. The first is that that all three anchors have similar
embodied energy values regardless of which anchor diameter is chosen. Since the differences
between them in embodied energy value is small, the recommendation is that the most commonly
used diameter should be chosen for installation purposes, which is the 0.15m. The second is the
embodied energy for the two anchor systems is less than that for the one anchor systems although
not by a significant amount. Hence, further evaluation should be made on whether to use the one
Sandra Wing Man Lee
- 19 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
or two anchor systems. Note that although the anchor systems have only been shown with the
steel sheet pile retaining wall case, the other retaining wall options also show similar results.
Figure 11: Comparison of One and Two Anchor Systems Using Different Diameters
Values found for the embodied energy of the anchors may seem small in comparison to those of
the retaining wall but are substantial as they equal and exceed those representing transportation
and installation. Although this may be a small fraction of the total embodied energy value, they
are significant enough; hence the design of the anchors was pursued.
To help decide whether the one or two anchor system should be recommended, more calculations
were made; these involved the spacing between the sets of anchors. The suggested spacing was
1.6m and so the calculations ranged from 1.0m to 2.0m at every 0.2m. The results are shown in
Figure 12, which was produced to show the embodied energy of the one anchor system at
different spacings, and in Figure 13, which shows the embodied energy of the two anchor system
at different spacings.
Sandra Wing Man Lee
- 20 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Figure 12: Comparison of One Anchor Systems Using 0.15m Diameter at Different Spacing
Figure 13: Comparison of Two Anchor Systems Using 0.15m Diameter at Different Spacing
Sandra Wing Man Lee
- 21 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
For the one anchor system, it would seem that in terms of embodied energy, the anchor spacing
should be either 1.0m or 1.4m as this produces the lowest value, although the differences in
embodied energy between the different spacings are small. For the two anchor system, the best
anchor spacing is much more difficult to distinguish and so it would seem that whichever anchor
spacing was chosen, it would not affect the embodied energy values. Hence the recommendation
would be for the two anchor system as this allows one less concern during design and it also uses
marginally less embodied energy than the one anchor system.
4.4.4
Contribution of the Retaining Walls as Part of the Basement
Figure 14 breaks down the overall embodied energy of the basement into that of the retaining
wall, load bearing piles, columns and slabs. It shows that the retaining wall contribution to the
whole basement is similar to the contribution from either the columns or the slabs and so this is
significant. However, it can be seen that the majority of the embodied energy is from the load
bearing piles. This implies that the choice of retaining wall is less relevant as part of a basement
as the embodied energy values of the basements are similar. It should be noted that retaining
walls can be stand-alone structures where the embodied energy of each design would become
more important.
Figure 14: The Contribution of the Retaining Walls as Part of the Entire Basement
Sandra Wing Man Lee
- 22 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
4.4.5
Department of Engineering
Contribution of the Basement as Part of the Total Building
It can be seen from Figure 15, which shows the embodied energy of the basement as a percentage
of the total building, that the contribution of the complete basement accounts for just over 40% of
the entire building. Therefore the basement can be seen to give quite a significant contribution to
the embodied energy of the entire building and so further investigations should be made to
minimise the contribution from it.
Figure 15: The Contribution of the Basement as Part of the Entire Structure Depending on Wall
Extending the investigation of the amount of contribution the basement makes in comparison to
the embodied energy of the total building, a rough calculation was made to investigate whether
the contribution of the embodied energy of the basement would change depending on the height
of the building. The results can be found in Figure 16, which shows the embodied energy of the
basement as a percentage of the total building depending on the number of storeys.
Sandra Wing Man Lee
- 23 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Figure 16: The Basement Contribution as Part of the Entire Structure Depending on Height
This shows that the embodied energy of the basement contributes much more to the total
embodied energy of the building as the number of storeys decrease. This is discussed in more
detail in Section 6.4.
It should be noted that Figure 16 shows a very rough calculation as the diameter, depth and
number of load bearing piles would change depending on the height of the building, which has
not been taken into account in this case.
4.5
Limitations and Accuracy of Results
4.5.1
Overall Embodied Energy Calculation
Focusing on the overall embodied energy values which consist of material, transportation and
installation energy, there are imperfections to the values found. In terms of the material energy,
the total amount of material used has not been taken into consideration, what has been accounted
Sandra Wing Man Lee
- 24 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
for is the amount of material required for the project; which is not the same. In truth, there will be
extra material through supply issues and waste and there may be unforeseen circumstances which
require the construction to be altered, resulting in more or less material usage.
Both the transportation and installation energies were taken from previous assignments [8][10].
This was possible as Riverside South was similar to the site on the previous project; however,
they are not identical. Hence more accurate results could have been found if the exact vehicles
and machinery were identified, although there would still be difficulties in calculating the exact
amount of fuel and electricity consumed. This is especially since the age of the vehicles and/or
machinery has not been taken into account and their efficient use of energy declines with age. In
addition, the transportation of the fuel before consumption has not been discussed where there are
extra costs and also losses associated with them. However, even with the real data available for
the site, the information will still be estimations of the quantities used, although it would provide
a better approximation, especially for the transportation energy values.
4.5.2
Inaccuracies Resulting From EEI Values
Another inaccuracy comes from the method of calculation using the EEI values. The calculations
have been performed using the average values found; however there is a large variation in the
overall embodied energy value as can be seen in Figure 10 and the discussions in Section 2.4 and
Section 4.4.2.
4.5.3
Unaccounted Embodied Energy
There are also other embodied energy values that have not been accounted for which would have
added to the total. One is the fact that human labour has not been included due to the assumption
that the energy contributed by manual labour is negligible in comparison to that used by the
vehicles and machinery. However, this also means that the transport required for the labour to
and from the site is not included and on a work site, there could be many members of staff, each
of whom probably all drive into work individually. In addition to that would also be the
construction of temporary buildings and other amenities for their use which has not been taken
into account but would contribute towards the total embodied energy.
Sandra Wing Man Lee
- 25 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Another inaccuracy results from the transportation energy where the return journey of the
vehicles have not been accounted for and the routes taken have assumed to have been direct,
when in reality this is not necessarily the case. This could be due to the fact that there are route
restrictions due to the vehicles used, and there may have been accidents or maintenance which
would result in a longer diversion. In addition, there may be traffic issues, especially since the
site is in a city, where more fuel would be consumed and more pollution produced. In terms of
transportation energy, there is another inaccuracy. It has been assumed that due to the
environmental advantages, all materials have been sourced from local suppliers which may not be
the case due to quantities and costs. So although all the suppliers used do supply the materials
required, they may not have sufficient quantities at the prices required hence the actual mileage
and therefore the embodied energy values associated with transportation energy may be higher
than calculated.
In terms of the actual construction, not every process has been taken into account, such as soil
excavation, which would also contribute to the embodied energy value. This particular exclusion
may be significant at Riverside South due to the fact that this is a contaminated site as explained
in Section 4.1. There is also the fact that the retaining walls have been taken to be equal in all
properties when there would be differences in design life and whether further maintenance is
required, which have not been considered. When working on construction, there will also be
contingencies which allow for more time, material and costs which have not been discussed.
Sandra Wing Man Lee
- 26 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
5
WOOD WHARF
5.1
Overview
Department of Engineering
Wood Wharf, Figure 17, is the second site being considered and this is also in the Docklands
area. This is a similar site to the one at Riverside South, although there is no contamination of the
land at this site. The proposal is for the development of six commercial buildings between 6-50
storeys high and seven residential buildings varying between 30-50 storeys high. There will be
basements at about +0m, where ground level is at +5.4m, with the toe of the retaining wall at
close to -12m. For the cantilevered diaphragm walls, the toe level will be at approximately -18m.
Figure 17: Site of Wood Wharf
Sandra Wing Man Lee
- 27 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
5.2
Department of Engineering
Construction
The retaining wall options being considered for Wood Wharf were provided by Arup and can be
found in Table 5, which shows the seven retaining wall options being considered.
Type of Wall
Steel Sheet
Pile
Diaphragm
Option A
Diaphragm
Option B
Diaphragm
Option C
Diaphragm
Option D
Diaphragm
Option E
Diaphragm
Option F
Toe Level
(MOD)
Details
-12
AZ34 Sheet Piles, propped
-12
0.8m thick, propped
-12
0.8m thick, propped with concrete base
-12
1.0m thick, propped
-12
1.0m thick, propped with concrete base
-18
1.2m thick, no prop
-18
1.5m thick, no prop
Table 5: Retaining Walls Considered for Wood Wharf
The first retaining wall option is that of a steel sheet pile wall using the AZ34 section; this is the
only option which is not of the diaphragm type of wall. The next two are diaphragm walls of
0.8m thick where option B has an additional concrete base. This is repeated for options C and D
where option D has the concrete base, although both of these walls have a thickness of 1.0m. The
last two retaining wall options are the cantilevered diaphragm walls which vary in thickness,
either at 1.2m or 1.5m thick. The differences between the excavation methods: propped, propped
with concrete base and the no prop i.e. the cantilever option can be seen in Figure 18.
Sandra Wing Man Lee
- 28 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Figure 18: Differences between the Excavation Options
Construction will also consist of the load bearing piles which are in the preliminary stages of
design. Available for Wood Wharf are two load bearing pile layouts, option 1 of 50 piles at 1.5m
diameters to a depth of -32MOD and option 2 of 62 piles at a diameter of 1.2m to the same depth.
Together with the basement design is the approximation of 102 columns of sides 0.8m and length
10.4m with 2565m2 of slab per level.
5.3
Calculations
The initial design stages were similar to those made for the Riverside South site which can be
found in more detail in Section 4.3.
For the diaphragm walls, which have not been covered before, the use of Adsec was required to
find the maximum bending moment, which differed by the amount of reinforcement present.
Once designed, the embodied energy of the diaphragm walls were found as explained previously.
Anchor systems were not considered for this site and so there was no requirement for the analysis
of different temporary support systems. Instead, the prop system which is described in Section
3.2.2 is to be used during excavation and it was decided by Arup that the struts for each retaining
wall would be the same although the strut forces were different. The chosen strut was a circular
hollow tube of outer diameter 0.457m and thickness 12.5mm with an average length of 11m. This
made the contribution to the retaining walls to be an extra 26GJ/m.
Table 6 shows the retaining wall options with the forces required from the props during the
excavation stage and also the depths at which they are required to be installed. Option E and
option F are the cantilevered options and hence no prop data is available.
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Type of Wall
Prop Force (kN)
Installation Depth (MOD)
Steel Sheet Pile
267
+4.5
Diaphragm Option A
267
+4.5
Diaphragm Option B
267
+4.5
Diaphragm Option C
287
+4.5
Diaphragm Option D
287
+4.5
Diaphragm Option E
N/A
N/A
Diaphragm Option F
N/A
N/A
Table 6: Retaining Walls and Prop Combinations for Wood Wharf
Although the strutting system was the same for all retaining wall options, the embodied energy of
the retaining walls has still been evaluated separately so that the differences between the walls
can be examined. The embodied energy of the total basement and entire structure was also
calculated.
5.4
Results and Discussions
5.4.1
Virgin Steel vs. Recycled Steel
For each of the retaining wall options, the total embodied energy was found for both the virgin
steel case and the recycled steel case. Figure 19 shows the embodied energy of the retaining walls
when virgin steel is used and Figure 20 displays the case when recycled steel is used to calculate
the embodied energy of the retaining wall options. The graphs have been produced to the same
scale so that it can easily be seen that the retaining walls using virgin steel has a greater embodied
energy compared to those using recycled steel. For Wood Wharf, the average increase in
embodied energy by using virgin steel instead of recycled steel is 73GJ with the greatest
difference being 132GJ which is for the steel sheet pile wall. Again, the material energy
dominates the total embodied energy value, which is similar to Riverside South as discussed in
Section 4.4.1.
Sandra Wing Man Lee
- 30 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Figure 19: Comparison of Retaining Walls Using Virgin Steel
Figure 20: Comparison of Retaining Walls Using Recycled Steel
Sandra Wing Man Lee
- 31 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
It is of interest to note that if virgin steel was to be used that the steel sheet pile option no longer
becomes the best retaining wall due to large difference in embodied energy value between the
virgin and recycled steel.
Figure 19 and Figure 20 also shows that the cantilevered options, E and F, have a much greater
embodied energy value than the other retaining wall options which use a propping system. It is
due to the fact that if during excavation no strutting system is used, the deflection experienced in
the retaining wall will increase. To counter this, the section of the retaining wall needs to be
larger and the depth of the toe level needs to be deeper. All this will increase the total amount of
material used for the retaining wall and hence the cantilevered options have a higher embodied
energy value.
5.4.2
Embodied Energy Errors
Figure 21: Comparison of Retaining Walls with Associated Embodied Energy Errors
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Figure 21 shows the minimum, average and maximum values of embodied energy calculated for
each retaining wall option. Similar to the Riverside South site, there is a large variation in the EEI
values found. The largest difference was 144GJ for the diaphragm wall, option E, using virgin
steel and the smallest difference was 3GJ for the sheet pile wall using recycled steel. The reason
for the large variation is because of the range of EEI values which occur in the material energy
section which has the largest contribution to the overall embodied energy. A more complete
discussion can be found in Section 4.4.2.
5.4.3
Contribution of the Retaining Walls as Part of the Basement
Figure 22 shows the extent of the retaining walls’ contribution towards the embodied energy of
the whole basement, where the majority of the input to the embodied energy is again the load
bearing piles. Depending on the retaining wall, the embodied energy is similar to that of the
columns or slabs and hence significant in value as found in Section 4.4.4. However, the
cantilever wall options E and F have a considerably higher embodied energy value, making up
for the embodied energy of the columns and slabs combined. Therefore, the choice of retaining
wall is more important in Wood Wharf as the differences between the retaining wall options are
much greater and so could contribute considerably to the embodied energy of the basement.
Figure 22: The Contribution of the Retaining Walls as Part of the Entire Basement
Sandra Wing Man Lee
- 33 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
5.4.4
Department of Engineering
Contribution of the Basement as Part of the Total Building
Figure 23 shows the embodied energy of the basement as a percentage of the total building with
the use of load bearing pile option 1. It can be seen that generally, in agreement with Riverside
South, Section 4.4.5, that the type of retaining wall chosen is not that significant. Although in
Wood Wharf, it would seem that the steel sheet pile option is at least 1.7% less in embodied
energy than any of the other methods and the greatest difference is 5% which is between the steel
sheet pile and the diaphragm wall, option F. This is a much greater difference than previously,
where the greatest difference between the retaining walls was 1%, but still quite a small value. In
this sense, it would seem that the investigation specifically into retaining walls would seem
insignificant, however retaining walls are constructed as stand-alone structures and so the above
information would be required. In addition, the embodied energy of the basement contributed
more significantly on the Riverside South site and so the importance of them, and hence the
retaining walls can be seen to differ depending on the site.
Figure 23: Contribution of the Basement as Part of the Entire Structure Using Option 1
Sandra Wing Man Lee
- 34 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Looking into the differences due to the load bearing pile layouts, from the calculations, option 1
has an average basement contribution of 22% whereas option 2 has an average contribution of
20%. Although the difference is small, this suggests that a difference in load bearing pile layouts
may be significant to the overall embodied energy of the building.
5.4.5
Difference in Load Bearing Pile Layouts
Since the load bearing piles make the most significant contribution to the overall embodied
energy of the basement and may be important to the overall embodied energy of the building,
further study was made into this area. This was possible because there are two load bearing pile
layouts available for this site. For the evaluation of Figure 22 and Figure 23, the layout option 1
with 50 piles at 1.5m diameters to a depth of -32MOD was taken. The embodied energy
calculations were also performed for the alternative load bearing pile layout of 62 piles at a
diameter of 1.2m to the same depth and Figure 24 shows the difference between the two load
bearing pile layouts.
Figure 24: Comparison of the Two Load Bearing Pile Layouts
Sandra Wing Man Lee
- 35 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
It can be seen that there is a difference of about 14,000GJ in embodied energy between the two
pile layouts and with them contributing the main part of the overall embodied energy for the
basement, this needs to be looked into in more detail. However, it should be noted that previously
with Riverside South, once the retaining walls were compared with the embodied energy of the
entire building, the differences in the type of retaining wall became negligible. Hence this may
also be the case with the load bearing piles, although they produce a greater contribution to the
overall embodied energy.
5.5
Limitations and Accuracy of Results
For the Wood Wharf site, the Frew analysis for the retaining wall options were not available and
the designs of the retaining walls were given directly from Arup. This may affect the comparison
between the two sites as the retaining walls may not have been designed in the same manner.
However, the results are still valid and comparisons may still be made, even though they would
not be as ideal. The discussion of inaccuracies resulting from the variation of the EEI values for
Wood Wharf can be seen in Figure 21 in Section 5.4.2. Otherwise the inaccuracies are similar to
those for Riverside South which can be found in Section 4.5. From the analysis of the two sites, it
can be seen that the data produced is similar in terms of values found and conclusions drawn,
which reinforces the reliability of the results. With the embodied energy of the buildings being
comparable for both sites, data from this project could be used as assistance for future projects.
Sandra Wing Man Lee
- 36 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
6
COMPARISON OF CASE STUDIES
6.1
Embodied Energy per Meter of Retaining Wall
Department of Engineering
Only the steel sheet piling wall has been compared between the two sites as this is the only type
of retaining wall that is shared and hence could make a justified comparison.
Figure 25: Comparison between Sites of the Embodied Energy per Metre of Retaining Wall
Figure 25 shows the comparison of the overall embodied energy per metre for the steel sheet pile
wall between the two sites. It can be seen that the embodied energy for Riverside South is greater
than that for Wood Wharf, although the values are fairly similar. This helps support the
calculations of this project since separate data has been used to produce similar values. The main
difference between the two sites is that Riverside South uses AZ48 steel sheet piles which are
larger in size than the AZ34 used at Wood Wharf. Calculations have been made to suggest that
the AZ34 steel sheet piles could be used at both sites, which would make the difference in
embodied energy values between the two sites negligible but there are also other issues such as
soil profiles and lifetimes that have not been taken account of in the calculations. In general,
Figure 25 suggests that the embodied energy of the retaining walls are similar for both sites
Sandra Wing Man Lee
- 37 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
where although the soil profiles are similar they are not exact and hence data from this project
could be used as guidance for future projects in the Docklands.
6.2
Embodied Energy of Basement
As a reminder, Riverside South has a load bearing pile layout design for 614 load bearing piles of
diameter 0.9m to a depth of -24MOD. Option 1 for Wood Wharf consisted of 50 load bearing
piles of diameter 1.5m to a depth of -32MOD and option 2, of 62 load bearing piles of diameter
1.2m to the same depth. The embodied energy for the three level basements have been calculated
and then divided by the area of the building to enable a comparison to be made.
Figure 26: Comparison between Sites of Embodied Energy per Metre Square of the Basement
Figure 26 compares the difference in embodied energy of the basement per metre square between
the sites, which shows that Riverside South has the largest embodied energy value for the
basement per metre square as a whole, followed by option 1 at Wood Wharf and then by option
2. It suggests that a larger number of load bearing piles at a smaller diameter and less depth
utilises more embodied energy than a smaller number of load bearing piles which are larger in
diameter and greater in depth. However, there seems to be an optimum load bearing pile layout as
Sandra Wing Man Lee
- 38 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
can be seen from comparing options 1 and 2 from Wood Wharf. Although less load bearing piles
at greater diameters and depths exercise lower embodied energy values, option 2 with more load
bearing piles at smaller diameters has an embodied energy value lower than that of option 1
which has less load bearing piles with larger diameters. Without further investigation, an
optimum load bearing pile layout cannot be suggested but results shown in Figure 26 imply that
this could be found such that embodied energy is minimised.
6.3
Overall Embodied Energy of Complete Building
The values for the graph were calculated by summing the data for the 40 storeys and combining
that this with that for the three level basements before dividing by the area of the buildings.
Figure 27: Comparison between Sites of Embodied Energy per Metre Square of Building
Figure 27 compares the difference between the two sites of the overall embodied energy per
metre square of the whole building. It shows that Riverside South has the largest embodied
energy value overall for the building per metre square, although the embodied energy values are
similar. It would seem that by including the superstructure the large difference in embodied
energy values for the load bearing piles are no longer dominant. However, part of the difference
Sandra Wing Man Lee
- 39 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
between the two sites could be accounted for by the extra embodied energy for the load bearing
pile layout of the Riverside South site. In addition, the different steel sheet piles used as discussed
in Section 6.1 could also explain some of the difference in embodied energy and if this was the
case then the embodied energy values would be roughly the same.
6.4
Building Above Ground Instead of Below Ground
It has been seen in Section 4.4.5 and Section 5.4.4 that the basement contributes significantly to
the overall embodied energy of the building, especially if the building has fewer storeys, as seen
in Figure 16. Hence an argument would be that for low-rise buildings, instead of the three level
basements, perhaps the extra three levels could be constructed above ground. This is especially
since less material would have to be used with the walls not being as thick and generally
construction above ground is seen to take less time and effort and so this may minimise the
embodied energy value overall.
Wall Option
Description
Option 1 [15]
Contemporary
Option 2 [15]
Heavyweight Insulation
Option 3 [15]
Lightweight Insulation
Option 4 [16]
Option 5 [16]
Option 6 [16]
Details
115mm brick, 50mm air cavity,
110mm concrete block, 16mm plasterboard
115mm brick, 50mm cavity,
110mm concrete block, 16mm plasterboard
115mm brick, 66mm expanded polystyrene
16mm plasterboard
Wall from 3-Storey
19mm timber framework,
Office Building
75mm mineral wool, 6mm plasterboard
Wall from 12-Storey
114.3mm precast concrete, 63.5mm cavity,
Office Building
12.7mm plasterboard
Wall from 20-Storey
114.3mm precast concrete, 63.5mm cavity
Office Building
28.575mm steel, 12.7mm plasterboard
Table 7: External Wall Options
Table 7 shows the possible external wall options that an office building may use, so that this can
be compared with the embodied energy value of the basement. The calculations were completed
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
with the assumption that for a typical office building of 1m length that half of that would consist
of glass for the windows and the other half consisting of a sandwich of materials. The material
energy for insulation materials was found in Fordham [12], installation energy for an external
wall was found to be 1.74GJ/m2 [13] and the transportation energy was calculated by identifying
the local suppliers of those materials and calculating their distance from the site [14].
Figure 28 compares the embodied energy of the six external wall options as detailed in Table 7
with the average embodied energy of the retaining walls at both sites.
Figure 28: Comparison between the External Wall Options
For the external walls, there can be seen to be variations in embodied energy depending on which
external wall is chosen where the greatest difference is about 3,000GJ. In terms of insulation, the
lightweight insulation wall requires less embodied energy than that of the heavyweight
insulation; however this does not take into account the energy savings that may be made through
original investment in the heavyweight insulation. Hence given a choice, with the difference in
embodied energy values being only 842GJ, the heavyweight insulation should be chosen.
Comparing the office buildings, the walls from the 3-storey office building and the 12-storey
Sandra Wing Man Lee
- 41 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
office building have the lowest embodied energy values with the 20-storey office building having
the highest value. From this it can be seen that higher office buildings have a higher embodied
energy due to the extra steel frame required. However, by continuing to build upwards, it would
save in the overall embodied energy in comparison to constructing another building with its
initial works and time and effort for another site.
It is interesting to note that for the levels above ground, the installation energy makes the greatest
contribution to the overall embodied energy. This is unlike the previous embodied energy
breakdowns where material energy always dominated, suggesting that for above ground
construction, installation energy should be considered carefully. However, material energy still
makes a large contribution to the overall embodied energy value and transportation energy can be
seen to be minimal.
Comparing the external walls with the average retaining wall sees that the embodied energy for
the average retaining wall is more than double that for the external wall with the largest
embodied energy value and close to four times for the external wall with the smallest embodied
energy value. This suggests that for low-rise buildings, use of the retaining wall should be
avoided and so no basements should be constructed; although for higher buildings the difference
would be smaller and it may still be justifiable for basements to be formed.
Figure 29 compares the embodied energy values between the basements with a retaining wall,
which is an average of the Riverside South site and the two options at Wood Wharf, or external
wall, which is the average of the six external wall options. It can be seen that the retaining wall
option uses more embodied energy in comparison to the external wall option. For the external
wall, the materials with the highest embodied energy were glass and wall insulation and the
amount of glass is almost at its maximum value due to the definition of the external walls of the
building. Hence the value obtained is a higher end value, where the average embodied energy per
metre square when using the external walls is 11.9GJ/m2, of the 4-12GJ/m2 [17] range which is
generally used for calculating the embodied energy values for superstructures.
Sandra Wing Man Lee
- 42 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
Figure 29: Comparison between a Basement Using a Retaining Wall or External Wall
From this, the conclusion would be to construct the extra three levels above ground rather than as
a basement as the embodied energy is less although the transportation and installation energies
are similar in both cases. In addition, if the extra three levels above ground were still to be used
as a car park then the façade of them may not use as much glass and insulation, hence the
embodied energy value would be even lower. However, the choice in building above ground
instead of below ground also needs to take into account aesthetics of the façade, which are
ignored below ground, as the building may need to fit into its surroundings and conveniences
such as being able to enter the building to the reception area and not into a car park. Otherwise, if
only energy considerations were deliberated, then the extra storeys would be recommended to be
built above ground.
6.5
Comparison with Other Construction Projects
To understand the values produced for the buildings at Riverside South and at Wood Wharf, the
overall embodied energy values need to be compared to other construction projects. Table 8
shows the embodied energy values for other construction projects in comparison to the average
Sandra Wing Man Lee
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May 2007
University of Cambridge
Embodied Energy of Underground Construction
Department of Engineering
value of the three buildings presented in this report. The ratio column expresses the number of
other construction projects that could be completed using the same amount of embodied energy
as found in this report for a 40-storey office building.
Project
Embodied Energy (GJ)
Ratio
40-storey Office Building, UK [this report]
725,288
1
Typical UK Masonry house (100m2) [18]
414
1,752
Average House, Australia (125m2) [3]
625
1,160
Standard New US Home, USA (227m2) [19]
942
770
Single Storey Office Building, UK, (584m2) [13]
2,494
291
3 Storey Office Building, Australia (6500m2) [20]
69,875
10
52-storey Office Building, Australia, (130,000m2) [20]
2,589,400
0.3
Table 8: Comparison with Other Construction Projects
From Table 8 is can be seen that the overall embodied energy found for the 40-storey building
assessed in this report is equivalent to the energy required to build either 1,752 houses in the UK,
1,160 houses in Australia, 770 houses in the USA, 291 single storey office buildings, 10 3-storey
office buildings or approximately, a third of a 52-storey office building. It is interesting to note
the differences in embodied energy values for the different buildings examined in Table 8. These
can be explained by the choice of materials, the type of construction and the size of the buildings.
From this analysis through the comparison of difference construction projects, it can be seen that
embodied energy savings that were found earlier in the report which seemed insignificant overall
are actually important. For example, in Section 4.4.1 the maximum saving of embodied energy
per metre from using recycled steel instead of virgin steel was 238GJ and this would contribute to
57% of the total energy required for a house in the UK. Therefore, although the choice of
retaining wall was seen to be insignificant when compared to the basement and superstructure as
a whole, it can be seen to be important when compared with other construction projects. Pursuing
the same line of thought sees that the load bearing pile layouts should definitely be investigated
further as a change of layout gave a difference of 14,000GJ which is equivalent to the amount of
energy needed to build 34 houses in the UK.
Sandra Wing Man Lee
- 44 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
7
Department of Engineering
CONCLUSIONS
There are three groups of conclusions to be drawn from this report. From the analysis of the
retaining walls for the Riverside South and Wood Wharf sites, from the inclusion of the basement
and superstructure and from the comparison of the two sites and to other construction projects.
7.1
Drawn from Analysis of Retaining Walls

Recycled steel should always be chosen above virgin steel due to the large differences in
embodied energy.

Material energy is the greatest contributor to the overall embodied energy value; hence
focus should be on minimising material usage.

Choice of material for construction will be important.

Supplies of material should be locally sourced to reduce transportation energy.

Installation methods should be kept simple and efficient to minimise installation energy.

Steel sheet or tubular piles should be considered first when designing a retaining wall.

Cantilever retaining walls will always produce higher embodied energy values and so
should be avoided.

Two anchor systems should be chosen, where there is a choice of a one or two anchor
system for embodied energy and convenience reasons and for its advantages.
7.2
Drawn from Further Analysis Including the Basement and Superstructure
The above conclusions are valid and in addition:

The load bearing piles make up the majority of the embodied energy of the basement and
so should be the main focus to minimise embodied energy.

The layout of the load bearing piles, the number, diameter and depth, affects the total
embodied energy value of the basement.

For each load bearing pile layout, there should be an optimum layout to be found such
that the embodied energy can be minimised; as the largest contributor, this should make a
difference.

The choice of retaining wall is not the most important factor when considering the
basement and superstructure.
Sandra Wing Man Lee
- 45 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
7.3
Department of Engineering
Drawn from Comparisons of Riverside South and Wood Wharf
The previous conclusions also apply and in addition:

For buildings of 10-20 storeys the basement contributes a significant proportion of the
overall embodied energy value.

For low-rise buildings, basement construction should be avoided although it can be
justified for high-rise buildings.

Generally, construction above ground will minimise embodied energy.

For above ground construction, installation energy carries a significant contribution to the
overall embodied energy value and so needs to be considered more carefully.

Heavyweight insulation should be chosen above lightweight insulation due to the savings
experienced during its lifetime.

Where possible, embodied energy should always be minimised as for large construction
projects, the wasted embodied energy could complete a small building assignment.

Comparing the two sites sees that the embodied energy of the retaining walls and the
overall superstructure are similar.

Future studies should be able to apply embodied energy values from similar projects for
comparison with their calculations.
Sandra Wing Man Lee
- 46 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
8
Department of Engineering
AREAS FOR FURTHER STUDY
Additional calculations should be made on other types of retaining walls such as contiguous and
double wall options so that more comparisons can be made to ensure that the best retaining wall
in terms of minimising embodied energy can be found. It may be worthwhile considering the
anchors and props in more detail as there are several types of anchors available and different
propping systems. Extensions to the calculations already made for the cantilever walls should
also be considered as these seem to have higher embodied energy values but may involve less
manual work, which has not been considered in this project. This also suggests that the LCA
calculations could be extended to include areas which have been missed off in this report such as
the maintenance, demolition and reuse/recycle stages.
With the knowledge that the load bearing pile layouts contribute the majority to the embodied
energy values of the basement, it would be valuable to investigate this further. This could be done
by keeping the depths the same and varying the diameters and locations and therefore the number
of load bearing piles required. From this, more detail could be found as to how exactly load
bearing piles affect the total amount of embodied energy. Following on from this idea, the
contribution of the basement levels to the embodied energy of the superstructure could also be
looked at into more carefully. Especially as this may form the argument as whether basement
levels should be built above ground instead if the levels were to contribute a greater value of
embodied energy below ground. Perhaps there are case studies to be examined concerning this
and if embodied energy values were always lower above ground, then why this is not considered
more often should also be addressed.
If future projects are available in the same area of the Docklands, the calculations made for
Riverside South and Wood Wharf could be repeated so that the results found in this project could
be compared and hopefully confirmed to be of similar values. This would enable the data found
in this report and others to be combined for future use.
Sandra Wing Man Lee
- 47 -
May 2007
University of Cambridge
Embodied Energy of Underground Construction
9
Department of Engineering
REFERENCES
The data provided by Arup from which the embodied energy values were calculated, are based on
confidential documents and therefore, the data used is not referenced.
[1]
[2]
[3]
[4]
[5]
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“Embodied Energy and Energy Conscious Design: An Evaluation of Compatibility”,
Doctors, S., Cornell University, 1978.
[6]
“Embodied Energy and Economic Valuation”, Costanza, R., Science, Volume 210,
Number 4475, pp. 1219-1224, 12 Dec 1980.
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www.maps.google.co.uk
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Thomas, R., Cambridge University Press, 1996.
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
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Vol 31, Issue 4, pp. 307-317, 1996.
National College for School Leadership, www.apps.kent.gov.uk
LCA of home in Michigan, www.umich.edu/~nppcpub/research/lcahome/homelca0.html
Hybrid Embodied Energy Case Studies, http://buildlca.rmit.edu.au
Sandra Wing Man Lee
- 48 -
May 2007