The Philippines is a country located in a region that is highly active for earthquakes, commonly referred to as the Pacific Ring of Fire. Along with the violent shaking during these seismic events, another serious threat often occurs: liquefaction. Understanding what liquefaction is, what causes it, and how to manage its risks is essential for protecting both properties and lives during an earthquake in the Philippines.
Understanding Liquefaction
Liquefaction happens when soil saturated with water loses its strength and stiffness due to the shaking caused by an earthquake. To picture this, think about squeezing a wet sponge. When you squeeze it, the water comes out, and the sponge can no longer hold its shape. In the same way, during liquefaction, the increase in water pressure in the soil means that the particles can’t support one another. Because of this, the ground can start to act like a liquid, similar to quicksand.
Why is Liquefaction Dangerous?
Liquefaction can cause several harmful and destructive effects:
- Building Settlement: When buildings are on soil that can liquefy, they might sink, tilt, or even collapse as the ground underneath them loses its ability to support weight. A notable example of this was during the 1990 Luzon earthquake, where serious damage occurred to buildings in Dagupan City due to liquefaction.
- Lateral Spreading: Liquefied soil can flow downhill or toward open areas like riverbanks, moving soil and structures along with it. This can be likened to a landslide, but instead of rain causing it, an earthquake changes the ground into a movable fluid.
- Sand Boils: Liquefied soil can push up through cracks in the surface, creating sand boils or small volcano-like structures. Although these may look minor, they indicate that the soil is unstable and can lead to further settlement and damage.
- Harm to Underground Infrastructure: Utilities buried underground, such as pipes and cables, can suffer damage as soil shifts due to liquefaction, which can interrupt essential services like water, electricity, and communications.
Regions in the Philippines at Risk for Liquefaction
Some places in the Philippines are more at risk for liquefaction compared to others. The reasons are varied:
- Close to Water: Areas near coastlines, rivers, and places with a high water table are particularly at risk. For instance, much of Metro Manila, especially waterfront areas like Manila Bay and parts along the Pasig River, have soils that may liquefy.
- Sandy and Silty Soils: Soils that are loose, sandy, or silty tend to liquefy more easily. The soil’s makeup influences how likely it is to react during an earthquake.
- Recently Deposited Sediments: Areas with new sediments like reclaimed land or river deltas are generally more vulnerable than older soils that have become compacted over time.
Some specific places that have shown a risk for liquefaction include:
- Metro Manila: Various districts, especially those with land that has been reclaimed or near Manila Bay.
- Dagupan City, Pangasinan: The city experienced significant liquefaction effects during the 1990 earthquake, highlighting its risks.
- Iloilo City, Iloilo: Certain locations near the Iloilo River have been identified as vulnerable as well.
- Ormoc City, Leyte: Areas close to rivers and the coast are at risk of liquefaction.
Follow us on LinkedIn!
The Philippine Institute of Volcanology and Seismology (PHIVOLCS) has created hazard maps to show areas at risk of liquefaction. Checking these maps for your specific area can help determine the potential dangers your property may face.
How to Identify Liquefaction Risks on Your Property
In addition to using PHIVOLCS hazard maps, it’s crucial to assess the specific vulnerabilities of your property. Pay attention to the following factors:
- Soil Type: Does your property have sandy or silty soil? A soil analysis by a professional geotechnical engineer will give you the most accurate determination of your soil’s composition.
- Groundwater Levels: Is the groundwater table near the surface? If possible, dig a small test pit or look at local well data.
- History of Earthquakes: Has your area experienced liquefaction in previous quakes? Local histories can reveal a lot about potential risks.
- Location Type: Is your property on reclaimed land or in a coastal area? Such places typically show a higher risk.
Consulting a Geotechnical Engineer: If you have concerns about your property, consulting a geotechnical engineer is key. They can perform detailed site assessments and tests to examine the liquefaction risks and suggest suitable strategies for mitigation.
How to Protect Your Property from Liquefaction
There are various methods to reduce the risks associated with liquefaction. The best techniques will depend on your property’s specific conditions and the type of building.
For Existing Buildings
Improving the resistance of existing structures against liquefaction can sometimes be tougher and pricier than taking preventive measures in new builds, but various options are available:
- Ground Improvement Methods:
- Deep Soil Mixing (DSM): This method includes mixing the soil with cement or other stabilizing materials to create stronger columns within the soil.
- Compaction Grouting: This technique involves injecting grout into the soil under pressure to make it denser, which lowers the chances of liquefaction.
- Vibro-compaction: Using vibratory equipment, this method compacts the soil to increase its density and structure.
- Strengthening the Structure:
- Underpinning: This procedure strengthens the existing foundation by reaching down to more stable soil layers.
- Adding Shear Walls: These walls within the building can help resist lateral forces from liquefaction.
- Base Isolation: This advanced method separates the building from movements of the ground using special bearings. It’s generally used for important structures.
For New Construction
Including techniques to mitigate liquefaction during the design and building phase is the most efficient and cost-effective way to safeguard against it.
Follow us on LinkedIn!
- Site Selection: If possible, choose a location with stable soil and a low likelihood of liquefaction.
- Using Ground Improvement Techniques: The methods mentioned before, like DSM and compaction grouting, can also be applied during new construction.
- Foundation Design:
- Deep Foundations (Piles or Caissons): These extend down to layers of strong, less likely to liquefy soils.
- Reinforced Concrete Raft Foundation: This type of foundation spreads the load of the building over a larger area, reducing stress on soil.
- Soil Improvement Under Foundations: Enhancing the soil right beneath the foundation can greatly improve its ability to support the building.
- Drainage Systems: Installing drainage to lower the water table can help reduce liquefaction risks.
Building Regulations: Make sure your construction follows the Philippine National Structural Code (PNSC) and any local building regulations, as these often contain guidelines for construction in earthquake-prone areas, including strategies for addressing liquefaction. Sticking to these codes is vital for ensuring safety and durability in your structures.
Simple Steps You Can Take Today
You don’t need complex engineering to enhance safety in your home. Here are simple actions you can take now:
- Stabilize Heavy Items: Secure heavy furniture, appliances, and other objects to keep them from falling during an earthquake.
- Repair Weak Areas: Check your home for weak spots, like cracks in walls, and fix them quickly.
- Plan for Emergencies: Create a family emergency plan and have an emergency supply kit ready, including food, water, medical supplies, and a flashlight.
- Familiarize with Evacuation Routes: Know the safe ways out of your home and practice evacuating.
Frequently Asked Questions (FAQ)
- What should I do if I think my property might experience liquefaction?
- The best action is to talk to a geotechnical engineer, who can evaluate the site and provide guidance on mitigation methods specific to your property.
- How expensive is it to mitigate risks of liquefaction?
- The costs for mitigation can vary widely based on how serious the problem is, the kind of construction, and what methods would be used. Generally, improving the soil is pricier than modifying foundation designs. Consider getting quotes from different contractors profiled for this work.
- Are there government programs that help with liquefaction mitigation?
- At the moment, specific government programs for liquefaction mitigation at private residences aren’t very common. However, local government units (LGUs) and disaster preparedness agencies may offer resources related to earthquake safety. Checking with your LGU and the National Disaster Risk Reduction and Management Council (NDRRMC) can provide more information.
- Is it worth getting earthquake insurance in the Philippines?
- Having earthquake insurance can be valuable because it helps cover damages caused by earthquakes, including those from liquefaction. Consider your personal risk and potential repair costs when deciding if this insurance is right for you.
- How often do strong earthquakes that could cause liquefaction happen?
- Strong earthquakes can happen at any time, as they are not predictable. The Philippines is known for its frequent seismic activity, and recorded serious earthquakes that led to significant damage, including liquefaction, can occur every few decades. Continuous monitoring and being prepared are essential.
References
- Philippine Institute of Volcanology and Seismology (PHIVOLCS): Earthquake Information
- National Structural Code of the Philippines (NSCP)
- Various research papers and publications on liquefaction in the Philippines
- Geotechnical Engineering Textbooks
Being well-informed about liquefaction can not only protect your property but also safeguard your family during an earthquake. Seize the opportunity to learn and take steps toward preparedness and safety.
