Since the beginning of civilization people have always wanted to live near bodies of water. As building construction has advanced so has the need for stable structures that can resist the forces of nature. Earthquake-prone regions are particularly difficult to build in. Soil near rivers, as well as areas that are close to the ocean, can lose strength during an earthquake and turn into a soup-like consistency. Among other problems, structures built on top of the unstable soil can settle and tilt.
We have a project in Long Beach, California where unstable soil has become an issue for the property owner; the potential for liquefaction is standing in the way of a development project. Long Beach has a well-known history of severe earthquakes. Our role is to identify how bad the problem is and then develop a solution for improving the soil condition.
The problem can be mitigated by one, or all, of the following techniques: dewatering, drainage, densification, solidification, and reinforcement. One of the more reliable techniques is soil densification. Densification can be improved with methods such as vibro-replacement, vibro-compaction, sand compaction piles, and dynamic compaction. It helps to eliminate the volumetric change by reducing void space, which helps eliminate the chances of liquefaction.
Another reliable method is solidification. Solidification attempts to limit soil particle movement to allow for cohesive strength. Soil reinforcement can help to limit horizontal movement of the ground.
An alternative option is to separate the structure from the soil that may liquefy and place it on stilts. Stilts, or pile foundations, must be installed in to a stronger soil layer than the soil that is liquefying. This must be done with pliable materials that allow movement, but have enough structural integrity so as not to break.
Have experience with building in liquefaction zones? Let us know in the comments. You can also contact us if you need help with liquefaction mitigation issues.