Civil Engineering August 2021 | Vol 29 No 7

Civil Engineering August 2021 19 including those that arise from extracting, transporting, manufacturing, and installing building materials on site, as well as the operational and end-of-life emissions associated with those materials. Embodied emissions account for approxi- mately 10% of global emissions. The building sector is the single largest sector generating CO 2 emissions which can be traced throughout the life of the building, from extraction of raw materials to the demolition and disposal of waste material at the end of the structure’s service life. It is therefore important to evaluate emissions from buildings as part of the design and evalua- tion process to make meaningful progress towards reducing or negating emissions from buildings. CARBON EMISSIONS IN GEOTECHNICAL CONSTRUCTION Emission sources are grouped into seven categories: materials, energy, freight, mobilisation, transportation, asset and waste. A brief description of each category is given below: Q Q Materials – related to manufacturing of materials used in construction e.g. cement, steel, additives Q Q Energy – related to energy used on site e.g. diesel for equipment, electricity for running offices Q Q Freight – related to transportation of construction materials Q Q Mobilisation – related to transporta- tion of major equipment Q Q Transportation – related to transpor- tation of people Q Q Asset – related to manufacturing of equipment Q Q Waste – related to transport and disposal of waste produced. Emissions have been evaluated for various geotechnical projects involving piling, lateral support or ground improvement works, as summarised in Figure 3. Although these projects are of various sizes, it does provide an understanding of the main emission sources for various types of geotechnical products. The average CO 2 emissions from the three product categories is given in Table 1. Emissions for piling projects are mainly derived from the materials used in construction, accounting for, on average, 80% to 90% of emissions on piling projects. Emissions from the materials category can be further broken down into cement (83%), aggregates (2%) and steel (15%). Emissions from lateral support type projects are also dominated by materials, but to a lesser extent than piling type projects, with a range of 30% to 60% of total project emissions. Lateral support systems which make use of piles (such as contiguous or secant pile walls) generate emissions closer to the upper value of this range, whereas systems which don’t include piles (such as soil nails or micropile walls) generate emissions closer to the lower value of this range. The balance of emis- sions is generated, approximately equally, from energy and transportation sources. In contrast to piling and lateral sup- port, emissions on ground improvement projects are dominated by energy usage, accounting for 50% to 80% of total project emissions. Figure 3 CO 2 emissions on geotechnical projects Emission (tCO 2 e) 2 250 2 000 1 750 1 500 1 250 1 000 750 500 250 0 Geotechnical projects Materials Energy Freight Mobilisation Transportation Asset Waste P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 L1 L2 L3 L4 L5 G1 G2 G3 G4 G5 G6 G7 G8 Lateral support Ground improvement Piling Table 1 Average CO 2 emissions on geotechnical projects Emission source Piling Lateral support Ground improvement Materials 75 48 9 Energy 15 26 70 Freight 2 1 5 Mobilisation – – 1 Transportation 7 25 7 Asset 1 – 9 Waste – – –