Liquefaction

Primary reference(s)

AGI, 2017. Liquefaction [soil]. American Geosciences Institute (AGI). Accessed 2 October 2024.

USGS, no date. Frequently asked questions: What is liquefaction? United States Geological Survey (USGS). Accessed 2 October 2024.

Annotations

Key relevant UN convention / multilateral treaty

Sendai Framework for Disaster Risk Reduction 2015-2030.

Drivers

Drivers of liquefaction are related to soil properties such as particle shape, grading, uniformity of grain size and relative density or voids ratio. Soil saturation can also influence liquefaction. Liquefaction can be triggered by rapid drawdown from erosion at the base of a slope. Liquefaction can also be triggered by intense rainfall (Najar et al., 2023) and earthquakes. Loading can also trigger liquefaction.

Impacts

The consequences to structures and infrastructure of liquefaction include: differential settlement of structures often resulting in cracking; loss of bearing support; flotation of buried structures such as sewer lines, tanks, and pipes; strong lateral forces against retaining structures such as seawalls; lateral spreading (limited lateral movement); and lateral flows (extensive lateral movement), particularly impacting on slopes or valley sides (e.g., Cubrinovski, 2013). 

 Earthquake-induced liquefaction can have varied effects on the surrounding built environment. Buildings, infrastructure, and utilities normally supported by the soil may sink, or undergo cracking or other structural damage; pile foundations may buckle or tilt; and lightweight, buried masses such as pipelines may become buoyant and float to the surface. Liquefaction can also cause rapid settling of sediments, flooding (including breaches of earthen embankments or other retaining structures), and lateral spreading of soils (Kramer, 1996).  

Liquefaction associated with the Christchurch earthquakes caused significant disruption to transport infrastructure, and to storm- and wastewater networks, and posed physical and mental health hazards for the exposed community and clean-up (Villemure et al., 2012; Cubrinovski, M., 2013.). From a human health perspective, the liquefaction material posed several hazards. Due to the extensive damage to the sewage disposal networks from lateral spreading and differential settlement, there was a risk that much of the liquefaction ejecta had been contaminated with raw sewage creating a long-term health risk to the population. During hot and windy conditions, the dry finer portions of silt were mobilised by the wind creating a possible respiratory health hazard. Many volunteers were involved in the clean-up operations. Indeed, the much-celebrated Student-Army was successfully used to coordinate the work around the city (Villemure et al., 2012). 

Multi-hazard context

The figure below summarises common interactions between liquefaction and other hazards. This information should be used with caution and not be solely relied upon in Disaster Risk Management, particularly as some interactions may not have been included. Note that hazardous events occurring together or locally in space or time may not necessarily cause, amplify or be otherwise related to each other. Specific examples of multi-hazard context can be found in the ‘Hazard drivers’ and ‘Impacts’ sections above. 

Multi-hazard diagram

Risk Management

The primary mitigation measure is to use planning to avoid development over liquefiable soils. These include in-situ testing of liquefaction resistance using standard penetration tests, cone penetration tests, shear wave velocity recordings, and dilatometer tests (Kramer, 1996); land microzonation via LPI or another assessment parameter that prohibits building on susceptible deposits (Lirer et al., 2019). Soil stabilization can be carried out via compaction methods or injection of grout, such as vibrostone columns and dynamic compaction (Shenthan et al., 2004). Other types of mitigation are incorporated in building design (NZGS and MB IE, 2017). During construction, controlling both the rate of excavation and the head, or increasing seepage flow paths to reduce seepage forces are the key methods used to minimise liquefaction (Pane et al., 2015). Nature-Based Solutions can be used to stabilise soil, such as vegetation for stabilising soils in coastal areas (e.g., Kumar et al., 2021).

Monitoring

The section and the table below offer an overview of monitoring liquefaction. This information can be used for forecasting within a national early warning system (EWS). Since EWS capacities and processes differ across countries, the most current and specific information regarding EWS should be obtained from the appropriate national or regional agency/authority responsible for disaster management.