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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 -1- 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 -2- 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 -3- 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 -4- 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 -5- 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 -6- 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 -7- 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 -8- 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 -9- 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 - 29 - 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 - 32 - 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 - 40 - 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 - 43 - 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] “Rough Guide to Sustainability”, Edwards, B. & Hyett, P., RIBA Publications, 2002. Crane Environmental Ltd., www.crane-environmental.co.uk CSIRO, www.cmmt.csiro.au “The Energy Costs of Materials”, Chapman, P.F., Energy Policy, 1975. “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. “Environmental Impact on Piling”, Carley, S., Thesis, Cambridge University, 2002. “Embodied energy on Tunnel Construction”, Workman, R., Thesis, Cambridge University, 2004. “Method Comparison for Construction of Retaining Wall on Slope Embankment”, Giken, technical report, Japan, 2004. “Embodied Energy of Underground Tunnels”, Kwong, K.H.W., Thesis, Cambridge University, 2006. “Chart for Embodied Energy Coefficients”, School of the Environment, Brighton University, 2006. “Environmental Design: an Introduction for Architects and Engineers”, Fordham, M., Taylor & Francis, 2006. “Life-Cycle Operational and Embodied Energy for a Generic Single-Storey Office Building in the UK”, Yohanis, Y.G. & Norton, B., University of Ulster, 1999. www.maps.google.co.uk “Design with Energy: the Conservation and Use of Energy in Buildings”, Littler, J. & Thomas, R., Cambridge University Press, 1996. [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] “The Way we Build Now: Form, Scale and Technique”, Orton, A., Van Nostrand Reinhold (UK), 1988. “Life Cycle Energy Use in Office Building”, Cole & Kenman, Building and Environment, 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