Building on hazardous ground without pre-disaster design measures creates catastrophic risk for the families and workers who will one day occupy the space. Heavy rainfall heightens sinkhole risk, earthquakes liquefy loose soil, storm surge carves away coastlines and rising temperatures thaw permafrost. Proactive, hazard-specific construction is the only way to protect the people inside.
Heavy Rainfall Primes Sinkhole-Prone Ground for Structural Hazards
When rainwater soaks into the ground, it dissolves soluble rock, such as limestone, and may break down similar formations, including gypsum and salt beds. The process leaves empty cavities below the surface. Water keeps moving through those voids, drawing surrounding sediment downward and slowly enlarging the opening until the ground above loses its support.
The surface may settle gradually into a depression or give way all at once as a sinkhole, and because all of this happens underground, nothing at the surface may signal that support is thinning until failure is already underway. Heavier rainfall can further speed this sequence.
Before building begins, ground stabilization techniques, such as grouting and soil compaction, can be used to address underground voids. Investigating the site first may also show engineers where voids sit and how far they have grown. Treating a located void may then keep it from enlarging beneath a finished structure.
Soil Liquefaction Turns Seismic Activity Into Foundation Failure
Liquefaction is when water-saturated soil, typically sand or silt, temporarily loses its strength during strong earthquake shaking. The ground can then flow like a liquid.
Shaking increases the pressure in the water trapped between particles, pushing those particles out of contact with one another. Once contact is lost, the soil can no longer support the weight above it, so structures built on top may tilt, sink or shift unevenly.
Riverbanks, shorelines and parcels on reclaimed land often have granular soil that tends to behave this way under seismic stress. Historical site records and borings taken before construction can reveal these conditions, which gives project teams time to flag a susceptible area ahead of a quake.
Any ground movement under mats or equipment may be an early sign that the soil is losing strength, and trained team members who spot it can alert a supervisor before the shift spreads. A timely stop to review the site may keep a small settlement from becoming a structural failure.
Storm Surge Can Accelerate Coastal Erosion
Storm surge pushes abnormally high water onto the coast, and the waves riding on top of it can batter the sand and soil that support coastal structures. As waves strike the shoreline again and again during a storm, they may strip away the sediment a foundation depends on.
A Nature Climate Change study of tide-gauge records since 1950 found that many U.S. coastal regions experience stronger or more frequent surges than earlier estimates suggested. Where surges meet rising seas, floodwater and breaking waves are more likely to reach foundations.
The same study questioned the figures many project teams rely on. Traditional methods had set storm-surge hazard levels too low at 85% of tide-gauge sites nationwide. Since protection plans draw on these likelihoods, a foundation sized to an understated figure may face a storm it was never built to withstand.
Before construction begins, project teams can assess a coastal site for long-term exposure to erosion. Once the risk is identified, resilient foundation designs can be selected to withstand the gradual loss of supporting soil in that zone.
Warming Temperatures Can Collapse Permafrost’s Load-Bearing Capacity
Permafrost is soil, sediment or rock that stays at or below 32° Fahrenheit for at least two years. It occupies roughly 23 million square kilometers, about 25% of the exposed land in the Northern Hemisphere.
Permafrost contains ice in lenses and layers, and its thickness can range from under 1 meter to over 1,500 meters. When temperatures climb, the ice that once gave the ground its rigidity is lost, leading to sinking, shifting or uneven settling of anything built above.
A foundation that was stable while the ground was frozen solid cannot be assumed to remain stable once the ground thaws. Hazard-specific structural designs intended to limit heat transfer into the soil may help keep the ground frozen, keeping the support beneath a structure intact.
For example, a new school in Kaktovik, Alaska, rests on pilings set alongside thermosiphons charged with gas that keep the ground beneath the foundation frozen and stable. Pile work was timed for winter, when freezing temperatures make drilling holes and setting piles easier. Since the thermosiphons were part of the design from the start, heat management is built in.
Turning Pre-Disaster Design Principles Into Action
While the four natural disaster hazards differ in mechanism, the proactive response to each follows a consistent pattern built on three measures:
- Ground stabilization: Treating unstable or void-prone subsurface conditions before construction begins can be especially useful on sites prone to sinkholes or liquefaction.
- Resilient foundations: Foundations designed to remain stable under conditions that could compromise a standard foundation may better withstand gradual soil loss from erosion or shifting due to seismic activity.
- Hazard-specific structural design: Tailoring a structure to the risk profile of its site may involve limiting heat transfer into permafrost or accommodating lateral ground movement in seismic zones.
These approaches tend to work best as a combination, and choosing the right one depends on understanding a site’s hazard profile before the first foundation is poured.
Protecting Occupants Requires Building Before Disaster Strikes
When a natural disaster strikes, the soil beneath a building either holds or fails, so proactive, pre-disaster construction is the only safe option. Heavy downpours, earthquakes, storm surge and warming are all foreseeable triggers.
Industry professionals planning projects on sinkhole-prone, liquefiable, coastal or frozen ground can begin with a risk assessment before breaking ground. Identifying the hazard first gives every later design decision a firm footing.
