Increasing demands for land use and population in mega cities is forcing more construction in the immediate vicinity of active fault lines. The construction industry is facing significant challenges and risks operating near/on Australia’s thousands of fault lines - distributed mainly in Western Australia, Central Australia and along the East Coast.
Research led by Associate Professor Behzad Fatahi and supported by PhD Candidate Habib Rasouli, contests the accepted industry wisdom that construction should not occur in regions where fault rupture is a major threat to buildings.
They have developed an innovative foundation system to allow for construction of even high-rise buildings on or near active fault lines, and an advanced three-dimensional computer model to evaluate the performance of this new foundation to protect the high-rise building against fault rupture.
To overcome the weakness of current foundation, the team propose a sand cushion between the building and its concrete piles; a gap is created between the base of the building and concrete piles and filled with sand. During the fault rupture, the piles could then easily separate from the base of the building, or slide without dragging the building down, reducing excessive building tilting and foundation failure.
The number of buildings that collapse or shear in half after earthquakes leads to the current industry belief that construction should not occur near fault lines. (Indeed, active faults could break through the ground surface, generating a widespread fault rupture event alongside the earthquake.) Historical field observations show how, for example, the 2004 Indian Ocean earthquake and tsunami killed more than 200,000 people in 14 countries when a 1600 km long fault ruptured for about 15m. The 2008 Sichuan earthquake (China, about 70,000 dead), the 1999 Chi-Chi earthquake (Taiwan, 2000+ dead ) and the Düzce-Bolu earthquake (Turkey, 500+ dead) all also show the vulnerability of surface structures - especially those resting on piles - to fault rupture incidents says Dr Fatahi.
Design codes are strict about not allowing building construction in the vicinity of fault lines, and usually impose a setback zone from the fault trace to avoid ruptures cross structures. Although a setback zone might be the best option, it is not always feasible as a safeguard for buildings, due to contemporary increases in population growth and land-use demand. Therefore the ‘business as usual’ view of avoiding construction in the vicinity of an active fault line needs reconsideration.
There is also the difficulty in finding the exact location of a fault outcrop. Dr Fatahi points out that engineering experience has proven that this cannot always safeguard buildings, as in the 1999 Kocaeli earthquake (Turkey) for instance, when a fault rupture incident with 4 km length caused significant destruction in the region.
Pile foundations are widely used in engineering practice to construct high-rise building sitting on soil deposits. While this type of foundation could successfully and safely transfer the massive loads of superstructure to the ground, its performance under a fault rupture incident would be unacceptable and catastrophic, as seen in the collapse of a basketball stadium in Denizevler during the Kocaeli earthquake.
When subjected to a fault rupture incident buildings sitting on the conventional pile foundations suffer significantly from tilting, while foundation failure is also observed.
Problems occur in a common pile foundation when the fault outcrops in the middle of the foundation, the moving tectonic plate or block drags the piles down, while the other piles remain within the static tectonic plate. This mechanism causes significant structural distress, building tilting, foundation failure and buildings to shear off.
Proving the possibility of safeguarding buildings sitting on their novel foundation, the new foundation system is detailed in an article in Computers and Geotechnics.
Image source: Computer modelling building tilt during fault event. Image: UTS