Finite Element Model of Grout Injection in Stone Masonry Walls with a Rubble Core

Multi-wythe masonry walls are a common structural component of heritage buildings. Typically construction is composed of two dressed outer wythes and a rubble core. These structures are susceptible to environmental... [ view full abstract ]

Multi-wythe masonry walls are a common structural component of heritage buildings. Typically construction is composed of two dressed outer wythes and a rubble core. These structures are susceptible to environmental degradation, as infiltration of water (coupled with freeze-thaw action in colder climates) can break down the existing mortar which in turn, can be flushed out of the wall in subsequent wetting cycles. The resulting increasingly un-bonded core material applies increasing pressure on the outer wythe, leading to lateral displacements and possible failure of the wall. With the core being composed of irregular stones and containing little of the original mortar, failure is dominated by rotation and sliding of the stones, rather than failure of the stone units. Finite element modelling of the walls of the Prince of Wales Fort in northern Canada has enhanced understanding of this mode of failure of multi-wythe stone masonry walls. Micro-modelling techniques were employed to model the stones and grout individually, allowing for a parametric study on the impact of varying contact and material properties. Results indicate that a significant reduction in either the strength or bonding capacity of the mortar will lead to instability in the wall sections. The research identifies a new general mechanism of failure for multi-wythe masonry walls and their susceptibility to environmental conditions, of which practicing engineers should be aware when assessing heritage masonry structures. For a multi-wythe wall, it is not just the integrity of the joint mortar in the external wythes that needs to be considered for maintenance.