Pyritic heave in Ireland: A case study in selection

Fred Shrimer, Anett Briggs

Dans les comptes rendus d’articles de la conférence: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Engineering Geology and Rock Mechanics

ABSTRACT: Cases of structural distress in residential and commercial construction were identified in Dublin, Ireland, beginning in 2005-6. Initially incorrectly diagnosed, in-depth investigations indicated that hundreds, and then thousands, of cases of heave had resulted from the use of structural fill that had been produced from quarrying of low-quality mudstone rock that contained pyrite. It was determined, on the basis of petrographic studies supplemented by additional analyses, that the mudstone contained fine-grained and framboidal pyrite that rapidly decomposed to form gypsum which, in turn, produced upward and lateral displacement of building elements. Slab heave, cracking and distortion of walls, jammed doors and broken pipes were typical manifestations of the heave. This confirmed the field observations that had been made in hundreds of structures over a number of years. Geotechnical laboratory testing confirmed that the heave mechanism could be replicated, adding credence to the concept.

RÉSUMÉ: Les casses de détresse structurelle dans la construction résidentielle et commerciale ont été identifiés à Dublin, en Irlande, à partir de 2005-6. Initialement mal diagnostiqué, des enquêtes approfondies ont indiqué que des centaines, puis des milliers de cas de soulèvement avaient résulté de l'utilisation de remblais de structure qui avait été produite à partir de l'extraction de mudstone faible qualité roche contenant de la pyrite. Il a été déterminé, sur la base des études pétrographiques complétées par des analyses supplémentaires, que le mudstone contient de la pyrite fine et framboïdale qui décompose rapidement pour former du gypse qui , à son tour, produit vers le haut et un déplacement latéral des éléments de construction. Dalle soulèvement, la fissuration et la déformation des murs, des portes coincées et tuyaux brisés étaient des manifestations typiques de la houle. Cela confirme les observations de terrain qui ont été faites dans des centaines de structures sur un certain nombre d'années. Modélisation de laboratoire géotechnique a confirmé que le mécanisme de soulèvement pourrait être reproduit, en ajoutant foi à la notion. 1. INTRODUCTION In the 1990s, the Republic of Ireland was undergoing a significant economic boom, with rapid population growth that drove a wave of construction across the country. This was particularly strong in and around Dublin (population: approximately 1.25 million), where rapid population growth fuelled the demand for more housing, roads, infrastructure and other construction. Given this period of sustained and dramatic growth, the demand for aggregates to supply structural fill, road base materials, asphalt aggregate and concrete aggregate to service the variety of projects increased dramatically as well. This demand resulted, to varying degrees, in depletion of some existing aggregate sources; the aggregate industry responded by opening new sources of aggregate or making plans to assess and open new supplies soon. The regulatory framework surrounding the opening of new aggregate pits and quarries in Ireland, at the time, was not onerous with respect to material quality- environmental and social obligations were of primary importance. As might be anticipated, sites considered for aggregate production should ideally be located as near the point of use as practicable, since aggregate tends to be a low-cost bulk product. The cost of transporting the material to its market is desired to be kept low, in order for the supplier to remain competitive. Therefore, in the case of the city of Dublin™s aggregate market, new aggregate sources tended to be located only a little farther away from the city than previous or existing sources, to minimize transportation costs. This paper examines issues related to the use of aggregates from a source that was opened in response to the building boom in Dublin in the 1990s and early 2000s. 2. BUILDING PROJECTS In order to meet the demand to provide low- to medium-cost housing for the population growth, numerous developments of residential housing were constructed. These ranged appreciably in terms of design and cost; however, in general, much of the construction was focused on ‚entry-level™, medium-density, attached condominium-style residences. These developments were typically located on larger plots of land and could be built en masse to provide construction efficiencies. Commonly, the developments (see Photograph 1) were on the order of hundreds of housing units per site. The typical layout included common roadways and surface parking areas. Many of the structures were two storey, although some were three- and four-storey constructions. Typical construction design consisted of

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