The recent debate about changes to the geological map in the Ħamrun area has important implications.
This geological map is regularly used by architects to assess the situation beneath their building projects. This is now required by regulations, namely SL623.06 ‘Avoidance of Damage to Third Party Properties’, which obliges anyone writing an excavation method statement to check and identify the geology as the first step of an investigative process.
Further scrutiny is then required on the ground characteristics, either via reports of previous investigations in the immediate vicinity or by excavating trial pits and drilling boreholes.
Understanding the geology of the islands has important ramifications, not only academically but also for practical applications such as construction. We live on an island that has been extensively studied from a geological standpoint, not least because it is ideal for field work. The overall geology is relatively uncomplicated, it is all rather accessible and it is also very interesting.
Many academics were drawn to the islands over the last 200 years, leaving behind a considerable body of literature, now appended by the work of local geologists who also made important contributions. Further research is to be encouraged and having a local chamber of geologists is, therefore, a step in the right direction.
The link between geology and construction goes beyond mere identification of rock typology. Buildings exert considerable pressure on the ground through their foundations and, conversely, excavation removes ground material that implies reduced confinement to the remaining rock. The ground is, therefore, a critical component of the load-transmission chain, essential for keeping a building safely in place.
The ground, therefore, also needs to be understood from an engineering point of view.
The behaviour of the ground as an engineering material has intrigued engineers for a very long time. This soon became critically important as buildings were built higher and basements were dug deeper. On a global level, the last 100 years have seen very rapid development of this relatively young subject, which is now embodied in the term ‘geotechnical engineering’.
Important concepts of this subject include soil mechanics and rock mechanics, which investigate behaviour of these two distinct types of ground materials under stress. At the local university, both subjects are compulsory for those who strive to join the structural and civil engineering professions.
Geology, as seen from an engineering perspective, has also created new professions: the engineering geologist and the geotechnical engineer. These professionals predict the behaviour of the ground as it is loaded, and work hand in hand with geologists to understand how its formation and origin influence its behaviour.
Together with laboratory technicians, they subject rocks and soils to mechanical tests and, through these, they derive mathematical descriptors of engineering behaviour.
Geotechnical engineers then use this information to design foundations, excavations, tunnels and retaining walls. They typically also work with structural engineers and with architects to ensure that the interface with the ground is addressed in a safe manner.
Unlike geology and geomorphology, geotechnical literature about the rocks and soils of our islands is practically inexistent or, perhaps, is still in its infancy. We still know very little about the mechanical characteristics of the various rock and soil layers. Incidentally, these are more complex and diverse than the geological classifications and delineations shown on the geological map, irrespective of its version.
Licensing needs to be complemented by regulations that encourage modern excavation design practices- Adrian Mifsud
This diversity is known from the work of local ground investigation companies, which have painstakingly assembled a voluminous database of information resulting from the thousands of boreholes that they have drilled all over the islands. This information is currently held within many ground investigation reports that are now being uploaded to the PA website as appendices to the excavation method statements required by SL623.06.
Indeed, middle globigerina is sometimes weaker than lower globigerina. The former layer is responsible for a series of failures in the Mrieħel area and for the cracks observed within St Mary’s church, in Birkirkara (Knisja l-Qadima). Yet, at the same time, and only 500 metres away, some of its facies are strong enough to support the towers of the Quad.
This demonstrates the futility of generalising the situation through a geological map. It accentuates the need for investigation on a case-by-case basis and exposes the potential danger that could be created by oversimplification of what is essentially a complex problem in a complex scenario.
Notwithstanding the criticism sometimes levelled at architects, several of them understand that geology is of consequence to their projects and excavations. Some architects think carefully about the problem, realise their limitations in this regard and actively and responsibly seek assistance to avert dangerous circumstances.
These are the silent ones who think ahead by commissioning real ground investigations, who approach the problem methodically and scientifically and who cause the least inconvenience to the neighbours. They actually exist but their work is obscured by many cut-and-paste method statements that are uploaded and that remain technically unchallenged, resulting in much inconvenience and damage, if not bad news.
Indeed, excavations can be designed and the disciplines and means to do so are readily available. These are backed by science and by collective experience, both of which are now extensive, worldwide. In the EU, excavation design is carefully delineated by standards that are also applicable in our country. Regulations are then required to ensure that such standards are upheld.
The recent licensing and classification of contractors is an important step in the history of our construction industry. Hopefully, it will soon identify those who can really excavate in a safe manner. Yet, excavation cannot remain at the sole discretion of chainsaw operators or of site operatives controlling excavation plant.
For maximum benefit, licensing needs to be complemented by regulations that encourage modern excavation design practices. Locally, these practices are not mandatory because SL623.06 defines only the format of an excavation method statement, rather than the soundness of its technical content.
In this sphere, the benefits of science have long been recognised in other countries. Locally, it is now time to apply these to problems that have plagued the local industry for a very, very long time.
Adrian Mifsud is an architect and geotechnical engineer and a lecturer at the Faculty for the Built Environment, University of Malta.