The phenomenon concerning the temporary strength loss of saturated soil is called liquefaction. The stiffness behaves more like a liquid due to increased pore water pressure. Liquefaction occurs by shaking or other disturbances.

This is mostly identified with earthquakes. High ground shaking can cause liquefaction of loose and saturated soil. It can cause great destruction to construction and infrastructure. 

It is one of the most dangerous and misunderstood soil hazards. It can occur during strong earthquakes. Weak saturated soils may lose strength. The ground will be seemingly solid, but while shaking, it will behave like a liquid. This may result in tilting, settlement of structures or collapsing.

This isn’t just theory. It occurred in 1964 in the Nigata, Japan earthquake. It was also the case with the 1989 Loma Prieta and 1994 Northridge earthquakes. In those cases, buildings sank. Highways buckled. Buried tanks and pipes floated to the surface. The losses were huge and critical.

Even minor earthquakes might be able to lead to liquefaction if case soils are in good condition. This is the reason why California needs site-specific studies.

One of the issues that is of concern in California is liquefaction. It occurs when porous and wet soil becomes weakened in the event of an earthquake. The Earth acts as a liquid. This causes buildings and roads to sink or shift. It is capable of ruining the base, saying, and infrastructure.

Southern California is under a huge threat. Here, earthquakes are frequent. Many areas have sandy soils and shallow groundwater. These are ideal conditions for liquefaction. That’s why California has strict rules to address it.

California Building Code (CBC)  claim certain liquefaction guidelines. The set of guidelines enables engineers to construct safer buildings. They also help cities reduce disaster damage. Understanding the CBC is key for developers, engineers, and contractors.

Liquefaction can happen without warning. During strong shaking, the soil may suddenly soften. Foundations lose support. Buildings tilt or collapse. Underground utilities rise or crack.

The 1989 Loma Prieta and the 1994 Northridge earthquakes were observed to have liquefaction. Entire neighborhoods had been harmed. Roads cracked. Homes were destroyed. These events proved the danger.

To avoid future losses, California requires site investigations. This is especially true in mapped hazard areas. These investigations protect lives and property. They also help avoid project delays and lawsuits.

In short, a Liquefaction Analysis is required in Southern California and isn’t just a safety net. It is your first layer of protection against construction failure, delays, and liability.

Liquefaction is not a hazard at every site. But in certain areas, it’s very likely. The California Geological Survey (CGS)  maps these areas. The maps are called Seismic Hazard Zones Maps. If your property falls inside one, you must evaluate the soil.

You can view these maps online. Visit the CGS Seismic Hazard Portal. Just enter your address or use the GIS layers to check. If your site is inside a mapped zone, then CBC compliance is required.

There can also be rules of local jurisdictions. The Los Angeles Department of Building and Safety (LADBS) frequently demands liquefaction studies. It doesn’t require only in the hazard areas, but in any suspicious one too.

They can examine past landslides, groundwater levels, and previous data of the site. Other Counties, i.e., San Bernardino, Orange and Ventura, are under a similar system. Liquefaction review is virtually always required for projects involving map or grading permit.

The rules are provided in the  California Building Code (CBC) and in particular Chapters 16 and 18. These chapters define seismic loading conditions and soil classifications.

Chapter 16 requires you to consider all seismic risks, including liquefaction. It sets the base seismic design criteria. Chapter 18 requires geotechnical investigations. If liquefaction is a possibility, the investigation must be detailed.

This has to be analysed in line with CGS Special Publication 117A (SP 117A). This report shows the engineers the method of carrying out liquefaction hazard evaluations. It covers field operations, test procedures and mitigation strategies. Engineers must follow these protocols to be compliant.

SP 117A  also requires professionals to assess the likelihood and consequences of liquefaction. This means calculating ground displacement, settlement depth, and risk to structures.

Field investigations start with drilling. Geotechnical engineers take soil samples at various depths. They can apply rotary drilling machines or cone penetration apparatus. Standard Penetration Test (SPT) and Cone Penetration Test (CPT) are two of the common tests.

The goal is to understand the soil layers. Engineers want to know the grain size, density, and water content. They also look at the depth of the water table. Liquefaction is most likely within the top 50 feet of soil.

Lab tests are also done. These measure moisture content, strength, and other key properties. Engineers use the data to run calculations. They estimate the amount of stress the soil can withstand during shaking.

They use models and more advanced numerical tools. These include the Seed and Idriss simplified method. The final result will indicate if liquefaction is likely. It also warns about the potential damage it may cause.

If the risk is high, they estimate how much the ground might sink. This helps design the right mitigation.

If engineers find that liquefaction may occur, then action is required. The CBC does not allow construction on unstable soil without mitigation. You must reduce the risk to an acceptable level.

There are several ways to do this. One method is soil improvement. You can densify the ground using vibro-compaction or stone columns. Another method is dewatering, which lowers the groundwater table.

You can also change your foundation. Use deep foundations like drilled piers or piles that reach stable layers. You may design a mat foundation to spread the load more evenly.

For utilities and roads, flexible joints and reinforced subgrades can help. Drainage improvements may also reduce liquefaction potential.

All mitigation methods must be described in the geotechnical report. The report must include calculations, construction specs, and long-term performance plans.

Once the geotechnical report is complete, it goes to local agencies. In Los Angeles, this is handled by LADBS. Their geology section reviews the report. They check whether SP 117A  was followed. They may request additional data or clarification.

For public projects, reviews may also involve Metro, Caltrans, or the County of Los Angeles Department of Public Works. These agencies often require peer reviews. This ensures independent verification of results.

Reports must be signed and stamped by a California-licensed geotechnical engineer. The data must be clear, and the mitigation methods must be feasible.

If the report is accepted, it becomes part of your building permit file. If not, it must be revised. Revisions can delay your project. That’s why it’s critical to use experienced professionals.

The review process can take time. Start early. Use qualified engineers. Make sure your report follows all rules.

Many project delays occur due to late geotechnical discovery. It is most recurring in Los Angeles and its surroundings.

At this moment, mitigation for liquefaction becomes costly. Moreover, it takes more time as compared to if identified earlier.

Similarly, the design variations, even for individual work towards the end, influence badly. This pressure highly disturbs the budget, schedule and structural system.

However, if liquefaction is entirely ignored, it is worse than anything. In this case, the risk is passed on to the occupants and property owners.

Evaluating liquefaction during the due diligence or schematic design phase saves time later. Developers should always check the CGS Seismic Hazard Zone maps before purchasing or designing a site. A quick GIS search can reveal whether a full liquefaction analysis is needed.

The California Building Code (CBC) doesn’t just exist to make construction harder. Its purpose is to reduce damage during earthquakes and keep buildings safe for occupants. Liquefaction is a hidden hazard that can have massive impacts.

But it is predictable. With modern tools and data, engineers can assess liquefaction risk accurately. With proper use of the results, foundations can be designed to withstand the seismic forces and ground deformation.

Mitigation techniques are proven. When implemented correctly, they reduce the risk to acceptable levels. Following the CBC means following best practices. It also means complying with the law and avoiding costly litigation after an event.

Local Resources and Agencies

In California, many agencies help oversee liquefaction safety. Here are some of the key ones:

·         Caltrans Geotechnical Manual: https://dot.ca.gov

·         Metro Design Criteria: https://www.metro.net/projects/

·         California Building Code Reference: https://www.dgs.ca.gov/BSC

These sites give maps, manuals, and technical forms. Use them as part of your due diligence.

Liquefaction is a silent killer. But it can cause big damage. In Southern California, it is a part of nearly every project.

If your site is in a hazard zone, take it seriously. Follow SP 117A. Test the soils. Submit a full report. Use real mitigation.

Doing this keeps people safe. It also keeps your project moving. CBC rules are strict, but they save lives.

Need help understanding CBC liquefaction requirements?  📞 Contact Our Geotechnical Support Team Today!