IntermediateTopic 41 of 112Civil & Structural
Liquefaction
Saturated loose sand loses strength during earthquakes.
In depth
Loose saturated sands under earthquake shaking build up pore pressure, ru→1, and lose strength, flowing like liquid, causing building tilting, lateral spreading and sand boils. Assessment compares cyclic stress ratio with resistance from SPT or CPT. Mitigation: densify, drain, replace.
Key points
- 1964 Niigata and 1989 Loma Prieta
- Susceptible: loose, clean sands
- Flow slides
ExampleBuildings in Christchurch 2011 settled and tilted due to liquefaction.
What is Liquefaction?
Saturated loose sand loses strength during earthquakes.
Why is it important to understand liquefaction?
Liquefaction can cause sudden loss of support under buildings during earthquakes, so it must be assessed in susceptible sites.
What causes liquefaction?
Cyclic loading increases pore pressure in loose, saturated sand until the effective stress falls near zero and the soil behaves like a liquid.
How is liquefaction prevented?
Densifying the sand, draining the pore pressure, or using stone columns can reduce the risk.
How is Liquefaction used in practice?
Typical applications include assessing a waterfront site with loose sand for liquefaction risk, designing ground improvement to prevent liquefaction under a school and checking the foundation of a bridge crossing a river delta.
What should I learn before Liquefaction?
Study "Ground improvement" first (topic 40 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
What are the key points of Liquefaction?
1964 Niigata and 1989 Loma Prieta. Susceptible: loose, clean sands. Flow slides.
Can you give an example of Liquefaction?
Buildings in Christchurch 2011 settled and tilted due to liquefaction.
What comes after Liquefaction?
The next topic is "Tunnelling and excavation", which builds directly on this one.
How difficult is Liquefaction?
It is classed as Intermediate in Civil & Structural (topic 41 of 112). It is an intermediate topic. Work through the beginner topics in Civil & Structural first.