It is common knowledge that earthquakes produce structural cracking in buildings, especially in historic earthen buildings. Seismically induced cracks break a wall into independent blocks that pound each other during a tremor. The longer the seismic event, the greater wall or block displacement and damage to the structure. In cases of strong shaking, the damage can lead to partial or total collapse of the structure. More commonly the walls sustain a series of cracks that jeopardize the buildings structural stability without causing collapse.
Conservation professionals constantly confront the choice to either repair entire walls of earthen buildings that have been damaged during an earthquake or to demolish them. Philosophical and theoretical criteria for intervention advocate minimal interventions, allowing maximum retention of original fabric. Thus, any mechanical repair should restore continuity of the wall while ensuring physicochemical compatibility with original materials and construction techniques. Based on the heterogeneous nature of earthen materials, drilling and pinning for reattachment is often rejected as too unpredictable and structurally dangerous. Noninvasive structural grouting, defined as the injection of fluid mortars or adhesives to fill discontinuities and cracks and reintegrate detached wall sections, is seen as a more promising solution to the problem.
The Research Project
The study and testing of grouts in general has been a topic of interest for the conservation community since as early as 1970. The compatibility of lime- or earth-based grouting formulations with adjacent materials has been considered in work carried out at several sites (e.g., the GCI project in Cave 85 of China's Mogao Grottoes), but studies considering the efficiency of this method for seismic stabilization or the nature of the impact of a seismic event on the grout and/or its relationship with the original materials and structure are lacking. In an effort to address this issue, the EAI has undertaken a multidisciplinary program to analyze different methods of repairing seismically induced cracks.
In 2006 the Department of Engineering at the Pontificia Universidad Catolica del Peru (PUCP) started preliminary testing and bibliographical research in order to identify adequate structural grouting materials for adobe walls using locally available soil. Once this preliminary work was concluded, the GCI agreed to provide financial and technical support for a second research phase addressing both engineering and conservation issues. The objective of this phase was to compile information, conduct research, and to perform laboratory testing to identify and evaluate grouting materials that are compatible with original materials, structurally effective, and result in minimal impact on original fabric during a seismic event.
Structural Grouting Experts Meetings
In August 2007 the EAI hosted an experts meeting in collaboration with the Department of Engineering at the Pontificia Universidad Catolica del Peru in Lima. The meeting brought together an interdisciplinary group of fifteen professionals with expertise in earthen conservation, grouting materials and techniques, and seismic retrofitting of earthen sites. The primary objective of the meeting was—in a cross-disciplinary manner—to share knowledge and evaluate laboratory testing protocols and methodologies for the study of structural grouting in seismic areas. Meeting summary notes (5pp, PDF, 468KB), prepared by the EAI and reviewed by meeting participants, are available.
Participants in the 2007 Lima meeting have continued to exchange information, and a second experts meeting was held in July 2008 in Bath, England, as part of the VI International Conference on Structural Analysis for Historical Constructions.
Last updated: January 2011