ABSTRACT
Recent severe earthquakes like those of Bam (Iran 2001), Pisco (Peru 2007) and Maule (Chile 2010) showed the vulnerability of earthen structures that, in spite of their “green” appealing characteristics, reveal serious structural fragilities (Bui et al. 2011a). The seismic vulnerability combined
1 INTRODUCTION
In the current context of sustainable development, the renewed interest in raw earth as a building material derives from several qualities such as local availability and recyclability, suitability to satisfy the need of low cost housing, self-build practice and preservation of natural resources (PachecoTorgal, F. & Jalali, S. 2012). These features make earth material and the corresponding construction techniques extremely competitive if compared to the conventional ones. Since the physical-mechanical characteristics of earth material vary from one site to another the questions are: which construction technique is best to use? Which type of reinforcement is more suitable? In order to recover the existing buildings and to propose raw earth as a building material also for the new constructions, it is essential to develop a strengthening system able to attribute at earth material equal dignity as other building materials. As raw earth is a no tension material, it is necessary to combine it with a material able to compensate for its deficiencies. From these reflections came the idea to produce a composite consisting of raw earth and natural fiber fabric. Rammed earth material is ideally composed of sand, clay and gravel. These are mixed with their optimum moisture content and compacted inside temporary formworks. The earth composition varies greatly and always contains clay but should not include any organic components. Clay acts as the binder between the grains, a mixture of silt, sand and gravel up to a few centimeters diameter. Com-
with high expressive and environmental potential of this material justifies the research of efficient strengthening methods. Most of researches carried out in the field of the earthen constructions are related to architectural and historical aspects and to thermal and hygrothermal performances, while the structural and/or mechanical problems have been disregarded. Some researchers developed various techniques to characterize soil and to identify the clay minerals composition. Recently other studies focused on manufacturing process optimization, compaction energy, environmental comfort, durability and mechanical behaviour of earthen constructions (Morel & Pkla. 2002). Since 2005 the Civil Engineering Department of Aveiro, University, in Portugal, has been developing several scientific studies on the behaviour of adobe structures and their constituent materials. A research group from Catholic University of Peru (PUCP) is playing an important role on the acquisition of knowledge on earthen constructions behaviour and on the development of reinforcement solutions against earthquakes (Blondet et al. 2011). Several reinforcement solutions for seismic retrofit of existing adobe constructions have been studied with enveloping geosynthetic, plastic or metallic meshes. The use of vertical canes and horizontal ropes was compared and assessed (Figueiredo et al. 2013).
