What Is Soil Liquefaction?
Soil liquefaction occurs when layers of soil situated below the groundwater table temporarily lose their load-bearing strength and begin to behave as a viscous liquid rather than a solid mass.
In geotechnical survey work, the project designer either commissions the survey directly or asks the contractor to engage a geotechnical specialist. A ground investigation comprises two stages: the first involves collecting data from the site, and the second involves preparing a report based on that data.
Ground investigations are carried out in accordance with the earthquake regulation that came into force in 2019. For buildings with a foundation area of less than 300 square metres consisting of a single block, a minimum of three boreholes must be drilled. One additional borehole is required for every further 300 square metres of foundation area. The structural design is then drawn up on the basis of these ground investigation reports.
So far, this may appear perfectly straightforward. The difficulty, however, is this: a ground investigation should not be limited to simply identifying the soil classification of the site. Critically, and perhaps most importantly of all, it should include an analysis of the risk of soil liquefaction and, where necessary, an assessment of potential ground improvement measures. Any geotechnical specialist, project designer, or supervising authority that overlooks this may be taking on a level of responsibility they are wholly unprepared to bear. The reason is simple: if a soil liquefaction risk is present but no improvement work is carried out, a building, however solidly constructed, may sustain serious damage in an earthquake as a direct result of that liquefaction.
It is to be hoped that the relevant authorities will take note and introduce new regulation in this area. In the meantime, under the current system, every contractor must require their geotechnical specialist to carry out a specific assessment of soil liquefaction risk. If ground improvement is found to be necessary, the contractor must then engage with their structural engineer accordingly and take whatever protective measures are required. The recent earthquake made painfully clear that every building has a responsible party, and that responsibility does not end the moment the flats are sold.
Until the Ministry introduces the necessary studies and regulations to address this properly, the responsibility for protecting yourselves rests with you.
In Conclusion
What is ultimately at stake here is human life. Just as a single mistake by a doctor can cost a patient their life, a comparable error by the contractor, engineer, geotechnical specialist, and supervising authority involved in constructing a hospital on that site can cost dozens of lives. The weight of that responsibility must never be underestimated.