Etude de la pathologie des fissurations de bâtiment suite au phénomène de dissolution du gypse cas des bâtiments de Ouled Djellal.

Abstract

This thesis investigates the pathology of building cracks caused by ground movement resulting from gypsum dissolution in Ouled Djellal. The research begins with a comprehensive literature review addressing gypsum soils, the dissolution process, associated geohazards, structural risks, assessment methodologies, and engineering solutions within a broader risk management framework. A pre-diagnosis phase was conducted on 55 buildings, revealing significant damage affecting structural and non-structural elements. Issues included tilting, cracking, swelling, detachment of exterior cladding, and functional impairments such as door and window sticking. Environmental analysis led to the hypothesis that these issues stem from ground movement triggered by the dissolution of gypsum, primarily initiated by water infiltration due to leakage.A detailed diagnostic phase followed, focusing on 11 buildings to confirm the failure mechanisms hypothesized earlier. The findings revealed the presence of gypsiferous soils, which considerably degrade mechanical behavior when exposed to moisture. This hydro-collapse phenomenon is driven by the dissolution and transport of soil particles within the Pliocene layer (3 to 7 meters deep), where the building foundations are anchored. The affected soil comprises sandy clay, sandstone, and a conglomerate matrix, characterized by pores, cavities, and cracks that contribute to instability. Additionally, inadequate foundation designs—featuring isolated and combined footings—have exacerbated the damage. Differential settlement, caused by the heterogeneity of the soil’s depth and composition, was identified as the primary failure mechanism, resulting in stress concentrations and material degradation. Based on these findings, a comprehensive risk management strategy is proposed. Preventive measures include improved water management, piezometric monitoring, and ongoing observation of subsurface warning signs. Remedial techniques discussed include grouting using the GIN method and the enlargement of isolated footings to form cross-strip footings. The recommendations also integrate urban planning strategies for both local (Ouled Djellal) and national implementation.