This paper presents an overview of the different earth building techniques, the latest innovations and the normative aspects. The oldest man made earth constructions known to exist date back to 10 000 BC. Since then, earth has remained a popular building material throughout history. With time, different techniques evolved, starting from sundried adobe blocks to cob constructions, rammed earth walls and compressed earth bricks. Today these techniques are still being optimized and alternative binders, specifically adapted admixtures and surface treatments are being developed. Even though nearly one third of the world’s population lives in an earth construction, few specific building standards and testing methods exist. Many of the tests used today are based on tests for concrete and thus do not take into account the complex nature of earth constructions, such as their sensitivity to water. RILEM, the union of Laboratories and Experts in Construction Materials, Systems and Structures, set up a new Technical Committee in 2016: TC TCE (Testing and Characterisation of Earth-based building materials and elements). This committee, consisting of an international group of experts on the topic, aim to define testing procedures for earth as a building construction material. To end with, this paper also gives a short introduction to “Deep soil mixing”, an “earth” building technique dedicated to geotechnical engineering.
International audienceThe fundamental understanding of the behaviour of dry sand as it is being vibrated is necessary to properly address a number of engineering issues, such as the vibrocompaction process. The present paper first summarizes experimental works focusing on the effects of vibrations on the volume change of dry cohesionless soils. Original experiments characterizing the behaviour of dry sand subjected to vertical vibration are then presented. The volume change and the motion pattern displayed by vertically vibrated sand particles are discussed. When cohesionless soil, placed in a cylindrical container, is vertically vibrated under the gravitational field (g), experiments performed on dry Fontainebleau sand allow the distinction between three types of dynamic behaviours depending on the acceleration amplitude (a): the densification behaviour (a/g < 1), the instability surface behaviour (a/g ≈ 1), and the vibrofluid behaviour (a/g > 1). In the densification range, the sand simply settles. When the acceleration amplitude is increased beyond 1g, granular convection is observed and there is an instability in the sand mass leading to the emergence of an inclined free surface. If the acceleration amplitude is further increased, the free surface progressively flattens. There is an impressive dilatation of the whole sample and grain saltation is observed. The sand becomes fully vibrofluidized. The efficiency of the vibrocompaction process is finally discussed especially with regard to these dynamic behaviours
In the deep mixing method, the ground is mechanically mixed in place while a binder, often based on cement, is injected. After hardening of the soilcement mixture, called soil mix material, soil mix elements are formed in the ground. Originally known as a ground improvement technique, the deep mixing is more and more applied for the construction of earth-water retaining structures within the framework of excavation works. After a short introduction to the execution aspects of the method, the authors discuss the hydro-mechanical properties of the soil mix material mainly based on the results of the BBRI Soil Mix project (2009)(2010)(2011)(2012)(2013). A design approach dedicated to the soil mix retaining walls and developed in collaboration with the SBRCURnet is then presented. In this methodology, which is in line with the structural Eurocodes, design rules are adapted to the functions of the soil mix wall (earth-water retaining, bearing and cut-off functions) including the temporary or permanent character of the application. Based on the result of large-scale bending tests, the interaction between the soil mix material and the steel reinforcement is considered in the calculations allowing a reduction of the steel section between 10 and 40 %.
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