Optimising the environmental impact of deep foundations

A recent UN report has shown that the construction industry is one of the seven major sectors that contribute significantly to environmental pollution and was responsible for around 20% of energy-related CO2 emissions in 2020, and this is expected to increase during the upcoming years unless preventive actions are taken (UN Environment program, 2021). Many studies have addressed the carbon footprint of superstructures including life cycle assessments, trials to reduce the quantity of material used in construction and discovering new production techniques with lower environmental impact (Hawkins et al., 2020). However, the carbon footprint of substructures has only been investigated to a limited extent, this is believed to be due to a lack of certainty in the mechanical behaviour of soil and its interaction with structures as well as the construction complexity for deep foundations (Sandanayake et al., 2016)

Form-Finding approach for flexibly formed concrete elements

There is no reason why concrete elements should be prismatic. Concrete is mouldable and can be cast in efficient forms which follow the stresses varying along the length of a concrete element. One option to achieve this is to use fabric as flexible formwork. Fabric deforms under the hydrostatic pressure exerted by wet concrete during construction, creating the shape of hardened concrete. The final shape needs to be known in advance to be able to perform the analysis and design of structural elements. This paper presents a form-finding approach capable of predicting the shape in cross-section of flexibly formed concrete elements. The approach is shown to predict geometry appropriately, based on the results of an experimental investigation, particularly when applied to complex shapes. The influence of construction tolerances, practical aspects and limitations of the approach are also discussed.</p

A design methodology to reduce the embodied carbon of concrete buildings using thin-shell floors

This paper explores the potential of thin concrete shells as low-carbon alternatives to floor slabs and beams, which typically make up the majority of structural material in multi-storey buildings. A simple and practical system is proposed, featuring pre-cast textile reinforced concrete shells with a network of prestressed steel tension ties. A non-structural fill is included to provide a level top surface. Building on previous experimental and theoretical work, a complete design methodology is presented. This is then used to explore the structural behaviour of the proposed system, refine its design, and evaluate potential carbon savings. Compared to flat slabs of equivalent structural performance, significant embodied carbon reductions (53–58%) are demonstrated across spans of 6–18 m. Self-weight reductions of 43–53% are also achieved, which would save additional material in columns and foundations. The simplicity of the proposed structure, and conservatism of the design methodology, indicate that further savings could be made with future refinements. These results show that considerable embodied carbon reductions are possible through innovative structural design, and that thin-shell floors are a practical means of achieving this.</p

Optimizing the embodied carbon of concrete piles - case study

A recent UN report has shown that the construction industry is one of the seven major sectors that contribute significantly to environmental pollution and was responsible for around 20% of energy-related CO2 emissions in 2020, and this is expected to increase during the upcoming years unless preventive actions are taken. Many studies have addressed the carbon footprint of superstructures and proposed innovative conceptual designs with a lower carbon footprint. However, the carbon footprint of substructures has only been investigated to a limited extent, this is believed to be due to a lack of certainty in the mechanical behaviour of soil and its interaction with structures as well as the construction complexity for deep foundations. This project aims to establish a robust algorithm for optimising the environmental impact of concrete piles bored or driven in different soil types. This will be achieved through varying different design parameters (concrete grade, steel-to-concrete ratio and pile slenderness ratio) across a multi-level optimisation algorithm tested for different pile-design cases. The change of these parameters will in turn lead to innovative conceptual designs for deep foundations corresponding to a better environmental impact while achieving the required load-bearing capacity. The analysis results show that piles with low capacities favor concrete with low compressive strength and high slenderness ratios. However, for piles with larger capacities, there exist critical threshold values for concrete compressive strength, steel reinforcement ratio and slenderness ratio corresponding to designs with the lowest environmental impact, these values are case-dependent and vary with the properties of soil and concrete used. The algorithm is tested on an existing case study of deep foundations for a mono-rail train bridge and a potential carbon saving of 72.4% is achieved. The findings also highlight the potential for future carbon reduction through a novel conceptual pile design utilising the lowest possible amount of concrete while achieving higher load-bearing capacity