13.2 Soil liquefaction (evaluation, mitigation, and design considerations)
4 min read•august 16, 2024
Soil can turn solid ground into a liquid-like state during earthquakes, causing massive damage. This section covers how to spot risky soils, predict liquefaction, and protect buildings and infrastructure.
We'll look at field tests, lab methods, and computer models to assess liquefaction risk. Then we'll explore ways to strengthen soil and design structures to withstand liquefaction, from to special foundations.
Soil Liquefaction: Phenomenon and Consequences
Liquefaction Process and Mechanisms
Top images from around the web for Liquefaction Process and Mechanisms
Frontiers | Injection-Induced Seismic Risk Management Using Machine Learning Methodology – A ... View original
Is this image relevant?
Induced seismicity - Wikipedia View original
Is this image relevant?
NHESS - A model for interpreting the deformation mechanism of reservoir landslides in the Three ... View original
Is this image relevant?
Frontiers | Injection-Induced Seismic Risk Management Using Machine Learning Methodology – A ... View original
Is this image relevant?
Induced seismicity - Wikipedia View original
Is this image relevant?
1 of 3
Top images from around the web for Liquefaction Process and Mechanisms
Frontiers | Injection-Induced Seismic Risk Management Using Machine Learning Methodology – A ... View original
Is this image relevant?
Induced seismicity - Wikipedia View original
Is this image relevant?
NHESS - A model for interpreting the deformation mechanism of reservoir landslides in the Three ... View original
Is this image relevant?
Frontiers | Injection-Induced Seismic Risk Management Using Machine Learning Methodology – A ... View original
Is this image relevant?
Induced seismicity - Wikipedia View original
Is this image relevant?
1 of 3
- Soil liquefaction occurs when saturated, loose, granular soils lose and behave like a liquid during rapid loading (earthquakes)
- Mechanism involves buildup of excess pore water pressure due to leads to reduction in and loss of soil structure
- Liquefaction susceptibility influenced by , relative density, grain size distribution, and groundwater conditions
- Spatial extent and duration of liquefaction effects vary based on site-specific conditions and earthquake characteristics
Impacts on Geotechnical Structures
- Foundation failures and settlement of buildings result from loss of soil bearing capacity
- Lateral spreading and ground deformation cause horizontal displacement of soil masses
- Instability of slopes and embankments increases risk of landslides and dam failures
- Uplift and flotation of buried structures (tanks, pipelines) due to buoyancy forces in liquefied soil
- Case histories illustrate severity of impacts
- 1964 in Japan caused widespread building tilting and bridge collapse
- 1989 Loma Prieta earthquake in California led to extensive damage in San Francisco's Marina District
Liquefaction Susceptibility Assessment
Field Testing Methods
- measures soil resistance to penetration of a split-spoon sampler
- provides continuous soil profile and measures tip resistance and sleeve friction
- Shear wave velocity measurements (Vs) determine small-strain soil stiffness using seismic methods
- Chinese Criteria and Modified Chinese Criteria assess liquefaction susceptibility based on soil characteristics and seismic parameters
- Seed and Idriss simplified procedure evaluates liquefaction potential incorporating corrections for fines content and overburden stress
Laboratory Testing Methods
- Cyclic triaxial tests subject soil samples to alternating compression and extension loads
- Cyclic simple shear tests simulate earthquake-induced stress conditions more accurately than triaxial tests
- Resonant column tests measure dynamic soil properties at small strains
- Factor of safety against liquefaction (FSL) compares cyclic resistance ratio (CRR) to cyclic stress ratio (CSR)
- Probabilistic liquefaction hazard analysis accounts for uncertainties in seismic loading and soil properties
Liquefaction-Induced Ground Failures
Lateral Spreading and Flow Slides
- Lateral spreading involves horizontal displacement of soil masses on gentle slopes or towards free faces (riverbanks, waterfront areas)
- Flow slides cause rapid, large-scale movements of liquefied soil masses on steeper slopes or areas with high static shear stresses
- Newmark sliding block method estimates permanent ground displacements due to lateral spreading
- Empirical correlations (Youd et al., 2002) predict lateral spreading displacements based on site geometry, soil properties, and earthquake characteristics
- Finite element and finite difference numerical modeling simulates complex liquefaction-induced ground deformations and their effects on structures
Settlement and Stability Analysis
- Liquefaction-induced settlement assessment involves estimating reconsolidation settlement and deviatoric strain-induced settlement
- Post-liquefaction strength analysis evaluates stability of slopes and embankments after liquefaction occurs
- Numerical modeling techniques (FLAC, PLAXIS) simulate coupled soil-water-structure interaction during liquefaction
- Probabilistic approaches incorporate uncertainties in soil properties and seismic loading for comprehensive risk assessment
Mitigation Measures for Liquefaction Risk
Ground Improvement Techniques
- Densification methods increase soil density and reduce liquefaction susceptibility
- Vibro-compaction uses vibratory probes to densify granular soils
- Dynamic compaction involves dropping heavy weights from significant heights
- Grouting and chemical stabilization strengthen soil matrix
- Cement grouting creates a solidified soil mass
- Colloidal silica improves liquefaction resistance while maintaining permeability
- Stone columns or gravel drains provide both reinforcement and drainage
- Deep soil mixing creates soil-cement columns to increase strength and stiffness
Structural and Drainage Solutions
- Deep foundations (piles, caissons) transfer loads to non-liquefiable layers
- Ground anchors and tie-backs resist lateral spreading forces on retaining structures
- Seismic isolation systems reduce inertial forces on structures during earthquakes
- Drainage systems dissipate excess pore water pressure and prevent liquefaction
- Gravel drains provide vertical drainage paths
- Prefabricated vertical drains (PVDs) accelerate and pore pressure dissipation
- Performance-based design approaches optimize mitigation strategies using probabilistic seismic hazard analysis and fragility curves
- Post-treatment verification testing (SPT, CPT) confirms effectiveness of ground improvement measures
- Monitoring systems (piezometers, inclinometers) assess performance of mitigation measures during and after seismic events
Key Terms to Review (18)
ASCE 7: ASCE 7 is a standard published by the American Society of Civil Engineers that provides minimum design loads for buildings and other structures. It serves as a crucial reference for engineers in assessing and designing structures to withstand various forces, including seismic, wind, and snow loads, ensuring safety and reliability in construction.
Cone penetration test (CPT): The cone penetration test (CPT) is a field test used to determine the geotechnical properties of soil by pushing a cone-shaped probe into the ground at a constant rate. This test provides continuous data on soil resistance, allowing for an understanding of various soil characteristics, which is essential for assessing shear strength and evaluating soil liquefaction potential in different drainage conditions, soil types, and stress histories.
Consolidation: Consolidation refers to the process by which soil decreases in volume over time due to the expulsion of water from its pores under sustained load. This process is critical in understanding how soils behave under load and is closely linked to factors such as soil-water interaction, effective stress, and drainage conditions.
Cyclic loading: Cyclic loading refers to the repeated application of loads on a material or structure over time, which can cause fatigue and potential failure. This type of loading is critical in understanding how soils behave under varying stress conditions, especially when assessing their shear strength and susceptibility to phenomena like liquefaction. The effects of cyclic loading can vary based on factors such as drainage conditions, soil type, and the soil's stress history, making it essential to consider when designing structures in geotechnical engineering.
Depth of water table: The depth of the water table refers to the level below the ground where soil or rock is saturated with water. This depth can significantly influence various geological and engineering factors, especially in relation to soil liquefaction, where the presence of water can reduce soil strength during seismic events or other disturbances.
Effective Stress: Effective stress is the stress that contributes to the strength and stability of soil, representing the difference between total stress and pore water pressure within the soil. This concept is crucial in understanding how soil behaves under various conditions, particularly in the context of fluid movement, consolidation, and strength properties of soils.
Foundation design: Foundation design is the process of determining the appropriate type and size of a foundation to support a structure, ensuring its stability and safety under various loads and conditions. This process involves analyzing soil properties, loads from the structure, and environmental factors to create a foundation that effectively transfers these loads to the ground.
Ground improvement: Ground improvement refers to a set of techniques used to enhance the physical properties of soil to increase its load-bearing capacity, reduce settlement, or improve stability. This process is particularly relevant in situations where natural soil conditions may not be suitable for construction, helping to ensure safety and longevity of structures. Effective ground improvement methods can also mitigate issues like soil liquefaction during seismic events.
Kobe Earthquake: The Kobe Earthquake, also known as the Great Hanshin Earthquake, was a devastating seismic event that struck the city of Kobe, Japan, on January 17, 1995. It caused widespread destruction and loss of life, revealing critical vulnerabilities in urban infrastructure and prompting significant advancements in the understanding of soil liquefaction and its impacts on engineering and design.
Liquefaction: Liquefaction is the process by which saturated or partially saturated soil substantially loses strength and stiffness in response to applied stress, often due to seismic shaking, transforming it temporarily into a fluid-like state. This phenomenon significantly impacts the stability of structures and ground during earthquakes and is crucial to understanding various geotechnical challenges.
NEHRP: The National Earthquake Hazards Reduction Program (NEHRP) is a U.S. government initiative aimed at reducing the risks and impacts associated with earthquakes. It focuses on improving the understanding of seismic hazards, enhancing building codes, and fostering research to develop effective mitigation strategies, particularly in regions prone to seismic activity.
Niigata Earthquake: The Niigata Earthquake was a devastating seismic event that struck the Niigata Prefecture in Japan on June 16, 1964, registering a magnitude of 7.5. This earthquake is particularly significant in the study of geotechnical engineering as it led to major advances in understanding soil liquefaction, a phenomenon that caused extensive damage during the event and reshaped approaches to earthquake-resistant design.
Pore pressure generation: Pore pressure generation refers to the increase in pore water pressure within soil or sediment during loading or stress conditions, which can significantly affect the soil's mechanical behavior. This phenomenon is crucial in understanding soil liquefaction, as elevated pore pressures can reduce effective stress, leading to a temporary loss of strength in saturated soils. Understanding how pore pressure develops helps in evaluating potential liquefaction risks and implementing design considerations for structures in seismic-prone areas.
Seismic design: Seismic design refers to the process of creating structures that can withstand the forces generated by earthquakes. This involves understanding how seismic waves propagate through the ground and how they affect different types of soil and structures, which is crucial for ensuring safety and stability during seismic events. Effective seismic design integrates knowledge of soil behavior under dynamic loads, especially when evaluating phenomena like soil liquefaction, to mitigate potential risks and enhance structural resilience.
Shear Strength: Shear strength is the maximum resistance of a soil or rock to shear stress, which is critical in understanding how materials behave under loading conditions. This concept is essential in various aspects of geotechnical engineering, as it influences stability, load-bearing capacity, and the overall performance of structures in contact with soil.
Soil Type: Soil type refers to the classification of soil based on its physical and chemical properties, including grain size, texture, structure, and mineral content. Understanding soil types is crucial because it directly influences construction practices, the behavior of soil under load, and how soils respond to environmental changes such as drainage and compaction.
Standard penetration test (spt): The standard penetration test (SPT) is a widely used in-situ testing method for assessing the geotechnical properties of soil by measuring the resistance of soil to penetration from a drop-weight hammer. This test helps engineers and geologists gather valuable information about soil strength, stratification, and other physical characteristics, making it crucial in the field of geotechnical engineering and in evaluating soil liquefaction potential during seismic events.
Vibration compaction: Vibration compaction is a soil improvement technique that uses mechanical vibrations to increase the density of soil by rearranging the soil particles. This method is particularly effective in granular soils and helps to reduce void spaces, thereby increasing the soil's strength and stability. Understanding vibration compaction is crucial for evaluating the potential for soil liquefaction, as properly compacted soils are less susceptible to liquefaction during seismic events.