Geotechnical and environmental performance of retaining structures in unsaturated soils

Presently, environmental issues are considered as critical aspects concerning the market competitiveness in the building and construction sector. However, the construction sector is regarded as one of the main areas contributing to CO2 emissions and resource consumption worldwide. In recent years, industry and academia have been investing significantly in order to produce innovative low-carbon technologies. Other than the significant effort that has been invested in the energy and environmental efficiency of buildings, few research studies concerning geotechnical structure and infrastructure are available in the literature. These previously lacking research activities have been conducted in the framework of the European project TERRE (Training Engineers and Researchers to Rethink geotechnical Engineering for a low carbon future), which was devoted to expanding this innovation to the geo-infrastructure industry. Specifically, the performance of retaining structures in unsaturated soils is investigated in the attempt to optimize their design procedures. Moreover, the thesis deals with the quantification of the environmental impacts of geostructures by comparing conventional and low-carbon geotechnical design solutions. Geotechnical analyses and design procedures for retaining structures mainly consider the retained soils as dry or saturated. The partially saturated condition implies the presence of negative pore-water pressures (suction) that contribute to increasing both the strength and the stiffness of the retained geomaterial. Suction can be considered as a natural âlow-carbonâ soil reinforcement that can be deployed to reduce the overdesign of both temporary and permanent retaining structures. However, the advantages provided by the condition of partial saturation can evolve with time due to the influence of environmental actions. In this regard, analytical and experimental analyses have been performed to investigate the interaction between unsaturated soils and retaining structures. Simplified geomechanical analytical solutions are implemented in geotechnical design procedures and compared with experimental results. The latter have been conducted by adopting a 1g-physical model designed and built for this purpose. The apparatus is found to be capable of investigating several soil conditions. In particular, the horizontal component of the lateral earth thrust has been experimentally measured in both the at-rest and active states. The effects of the partial saturation have been observed by considering suction profile evolution. The analytical models have been found to be in generally good agreement with the performed tests. However, the water retention curve of the involved soils is found to play a key role in the computation of the lateral earth thrust. Moreover, in collaboration with the industrial partner Nobatek/Inef4, the life cycle assessment (LCA) methodology has been employed to demonstrate the potential benefits provided by the considered eco-friendly geotechnical solutions. Two types of geostructures are considered: a retaining wall designed according to the mechanics of unsaturated soils and a thermo-activated group of piles to satisfy the heating and cooling demand of an office building. By highlighting their potentials and critical issues, the performed analyses have shown a possible significant reduction of the environmental impacts associated with the adoption of these low-carbon solutions.

Reconsidering traditional timber joinery for sustainable structures

Jan Friedrich Georg Brütting, Corentin Jean Dominique Fivet

Timber construction plays an important role in architectural history, in modern construction methods and in sustainable design, for which wood-only joinery techniques have been used for centuries. Traditional joinery typologies are the product of successive, empirical improvements over generations of artisans [1]. However, over the industrialization era, many traditional wood-only construction techniques were abandoned in favor of more profitable connections with mechanical fasteners [2]. This shift of practice lead to the development of connections with quantifiable capacity but neglecting the intrinsic anisotropic properties of natural timber. Specialized knowledge of carpenters and typical building traditions were lost. Yet, examples of historic timber buildings with a life span of multiple centuries have demonstrated many advantages of interlocking timber joints, e.g. in severe loading cases as in the case of earthquakes [2]. New technologies and recent developments in digital fabrication allow the custom and automated manufacturing of traditional wood-only connections for new buildings [3]. A big potential of such contact-only connections is their fast assembly and non-destructive disassembly. Remarkable examples include the Japanese Ise-Shrines, which are rebuilt in a 20-year frequency for the past 1300 years. Traditional joinery techniques allow for sustainable solutions through the replacement, long-term maintenance and repair of structural elements [4]. They also ease recycling and energy-recovery. In times of global environmental problems where the building sector is highly responsible for resource depletion, greenhouse-gas emissions and waste pollution, these advantages will become even more important for regenerative architecture or transformable building design. Buildings need to become more adaptable to frequent changes in ownership or use to avoid superfluous demolition. For example in Japan in the past, entire cities made from timber were constructed for disassembly and transport in order to accommodate for recurrently changing administrative centers [3]. Some joint typologies were designed to allow the later vertical or horizontal extension of buildings [2]. In Japan also, contemporary buildings are not understood as permanent edifices but as structures made to be replaced or removed. This could only be achieved through highly developed timber joinery techniques. A combination of traditional joinery with contemporary post and beam construction and CNC prefabrication is already well established in Japan in the construction of residential buildings [3]. However, a straightforward application of traditional joinery techniques in today’s construction is not always possible. In the past, the structural integrity of traditional joinery techniques was proven mainly through in-situ, de-facto testing. Today, building codes include little-to-no information about the application of wood-only carpentry connections in comparison to those with mechanical fasteners [2]. Research on interlocking joints concentrates on a very precise analysis of few different joint typologies. There are limitations in literature in terms of analyzing a variety, or a library of ancient interlocking wood joints to develop an extensive relative comparison between them. As a first step, the present research initiates a FEM campaign to catalog a library of Asian joints. To align traditional techniques with modern construction and typically used North American timber, solid Douglas fir was considered as the material. The goal of the analysis is to extract the relative capacity and stiffness of different joints to understand their mechanical behavior. This comparative record, which should be extended to additional Asian and European joint types, will allow academics and designers to push the capabilities of these ancient techniques while benefitting from modern materials, construction techniques and fabrication tools. Other research will also address the optimization of joint geometries to customize demanded capacity or stiffening. In addition, Life Cycle Assessment of constructions with conventional and advanced traditional joinery technology will be carried out to quantify potential environmental savings.

2018

Geotechnical analysis of energy piles

Lyesse Laloui, Alessandro Francesco Rotta Loria

This study proposes an analysis of the multiphysical phenomena and mechanisms governing the thermo-mechanical behaviour of energy piles. The analysis is based on the results of a series of full-scale in-situ tests, laboratory experiments and numerical analyses. First, the thermo-mechanical behaviour of energy piles is considered. Attention is given to both single and groups of energy piles. Next, the response of soils and concrete-soil interfaces subjected to temperature changes is reviewed. The behaviours of clayey soils in different overconsolidation states as well as of both concrete-sand and concrete-clay interfaces are analysed. Finally, aspects considered of paramount importance for the analysis and design (e.g., geotechnical and structural) of energy piles are presented. Both floating and end-bearing energy piles are investigated. The goal of this paper is to increase the confidence of civil engineers on the performance of energy piles.

2016

Re:Crete - A Footbridge made of Reused Concrete Blocks

Maléna Bastien Masse, Jan Friedrich Georg Brütting, Julie Rachel Devènes, Corentin Jean Dominique Fivet, Célia Marine Küpfer

Today, concrete is the most widely used construction material worldwide. Strong, versatile, durable, and vector of economic development, this exceptional material is also the principal cause of greenhouse-gas emissions, material depletion and waste generation by the construction industry. Hence, reusing concrete elements extracted from obsolete building structures has large potential to significantly reduce the environmental impact of construction. To demonstrate the potential of such an unusual strategy for bridge construction, this paper shows the construction of the Re:Crete arch prototype. It is made of 25 reclaimed concrete blocks connected through post-tensioning to create a 10-m span arch. The complete design-and-build workflow of the prototype is presented, including the structural design of the arch, the sourcing of the reusable concrete elements and the assembly. The Re:Crete arch prototype mechanical properties and environmental impact are assessed through non-destructive investigation, load testing and Life-Cycle Assessment. The results show that the reuse of concrete blocks leads to a comparable structural behaviour as a similar arch made of new or recycled concrete, with an environmental footprint reduced by more than 70%.

Asociación Española de Ingeniería Estructura2022

Reconsidering traditional timber joinery for sustainable structures

Jan Friedrich Georg Brütting, Corentin Jean Dominique Fivet

2018