3.3 Liquefaction and lateral spreading
2 min read•july 25, 2024
turns solid ground into a liquid-like state during earthquakes, causing devastating effects. This phenomenon occurs when loses strength due to increased , leading to ground failures and structural damage.
Understanding liquefaction is crucial for earthquake engineering. We'll explore its triggering mechanisms, susceptibility factors, and consequences. We'll also delve into assessment methods and mitigation strategies to protect buildings and infrastructure in vulnerable areas.
Understanding Liquefaction and Lateral Spreading
Liquefaction and triggering mechanisms
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Top images from around the web for Liquefaction and triggering mechanisms
Soil liquefaction - Wikipedia View original
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- Liquefaction transforms saturated granular soil into liquid-like state temporarily loses strength due to increased pore water pressure
- from earthquake shaking rapidly increases pore water pressure decreases between soil particles
- Soil behavior during liquefaction loses reduces stiffness allows large deformations (, )
Factors of liquefaction susceptibility
- affect susceptibility most prone more vulnerable than dense
- influence risk and crucial
- impact susceptibility age of deposit and depositional environment (alluvial, coastal) matter
- determine likelihood and key factors
Consequences and Assessment of Liquefaction
Consequences of liquefaction
- Ground surface manifestations include sand boils and ground fissures
- causes of soil masses on or near free faces (riverbanks, waterfronts)
- Settlement leads to vertical deformation damages structures
- Built environment suffers damage to and
Assessment of liquefaction potential
- Simplified Procedure (Seed and Idriss) calculates
- Determines based on field tests (SPT, CPT, Vs)
- against liquefaction computed as
- Liquefaction-induced settlement estimated using or
- Lateral spreading displacement predicted with Youd et al. (2002) model or
Mitigation for liquefaction-prone sites
- include () () and ()
- Structural solutions involve () and
- Design considerations encompass
- Regulatory measures implement
Key Terms to Review (53)
Building Code Requirements: Building code requirements are sets of regulations and standards that govern the construction and design of buildings to ensure safety, health, and welfare for occupants. These codes include specific provisions related to structural integrity, fire safety, accessibility, and environmental sustainability, particularly in regions prone to natural hazards. Compliance with building codes is crucial to mitigate risks, especially in areas susceptible to events like liquefaction and lateral spreading during earthquakes.
Buoyancy of buried structures: Buoyancy of buried structures refers to the upward force that acts on submerged or partially submerged structures due to the displacement of soil or water. This phenomenon is significant in geotechnical engineering, especially during seismic events, where soil liquefaction and lateral spreading can dramatically alter the forces acting on underground facilities. Understanding this concept helps engineers design structures that can withstand the forces exerted by buoyancy in saturated conditions, especially when the surrounding soil loses strength.
Cyclic Loading: Cyclic loading refers to the repeated application of load or stress on a material or structure over time, which can lead to various responses and failures in geotechnical engineering. This phenomenon is crucial for understanding how soils behave under dynamic conditions, particularly during events like earthquakes, where the loading conditions can change rapidly and repeatedly. The impact of cyclic loading is evident in processes such as liquefaction and lateral spreading, where the soil's ability to support structures can significantly diminish due to repetitive stress.
Cyclic Resistance Ratio: The cyclic resistance ratio (CRR) is a measure of a soil's ability to withstand cyclic loading without undergoing significant deformation or failure, particularly during seismic events. It is essential in evaluating soil stability and performance during earthquakes, as it indicates how much cyclic stress the soil can endure before liquefaction or other types of failure occur. The CRR is derived from laboratory tests and is critical for assessing the potential for liquefaction and lateral spreading in saturated soils during seismic activity.
Cyclic Stress Ratio: The cyclic stress ratio (CSR) is a measure used to evaluate the potential for soil liquefaction during seismic events, defined as the ratio of the cyclic shear stress generated in the soil to the effective vertical stress. This term is crucial in understanding how soils respond to repeated loading conditions, such as those experienced during earthquakes, and is directly linked to soil behavior and stability under dynamic loading. A higher CSR indicates a greater likelihood of liquefaction, impacting both the stability of structures and the movement of soil.
Deep foundations: Deep foundations are specialized structures that transfer building loads deep into the ground, reaching a more stable layer of soil or rock. They are essential in areas where surface soils are weak or prone to movement, ensuring that buildings remain stable during events like earthquakes. These foundations include piles and drilled shafts, and their design considers factors like soil properties and potential ground movement.
Degree of Saturation: The degree of saturation refers to the ratio of the volume of water present in a soil to the volume of voids in that soil, often expressed as a percentage. It is a crucial parameter in understanding soil behavior, especially during events like liquefaction, where the amount of water in the soil affects its strength and stability under seismic loads. Higher degrees of saturation can lead to increased pore water pressure, which significantly influences how soils respond during earthquakes.
Dense Soils: Dense soils are characterized by a high level of compactness and low void ratios, which means they have minimal air spaces between particles. This compact nature increases the soil's ability to resist deformation and provides greater stability, making it important in contexts such as liquefaction and lateral spreading, where soil behavior under stress is critical. Understanding dense soils helps engineers evaluate ground conditions during seismic events and design structures that can withstand potential soil movement.
Densification: Densification refers to the process of increasing the density of soil, typically through the compaction of soil particles or the reduction of void spaces. This is crucial in understanding how soil behaves during seismic events, as denser soils generally have improved strength and stability, reducing the risk of liquefaction and lateral spreading.
Depth to water table: The depth to water table refers to the distance from the ground surface down to the top of the saturated zone where the soil or rock is fully saturated with water. This measurement is crucial for understanding groundwater levels, which play a significant role in geotechnical engineering, especially in the analysis of liquefaction and lateral spreading during seismic events. The proximity of the water table to the surface influences soil behavior under stress and can trigger destabilizing phenomena like liquefaction when saturated soils lose their strength during earthquakes.
Differential Settlement: Differential settlement refers to the uneven sinking or movement of different parts of a structure due to varying soil conditions, loading, or other factors. This uneven settling can lead to structural damage, such as cracking or tilting, which can be particularly problematic in areas affected by liquefaction and lateral spreading during seismic events. Understanding the implications of differential settlement is crucial for ensuring the stability and integrity of structures built on susceptible soils.
Drainage: Drainage refers to the process of removing excess water from soil or other surfaces to prevent saturation and maintain structural integrity. In the context of soil behavior during seismic events, effective drainage can help reduce pore water pressure, which is critical in minimizing liquefaction and lateral spreading risks. Proper drainage systems help facilitate the stability of structures built on or within potentially liquefiable soils by allowing water to flow away efficiently.
Duration: Duration refers to the length of time that ground shaking occurs during an earthquake. It plays a critical role in determining the impact of seismic waves on structures and soil, influencing phenomena such as liquefaction and soil-structure interaction. A longer duration can lead to increased damage, particularly in saturated soils, while also affecting the behavior of buildings under seismic loads.
Earthquake Characteristics: Earthquake characteristics refer to the specific features and behaviors of seismic events, including their magnitude, intensity, duration, depth, and frequency. These traits help in understanding the impact of earthquakes on structures, populations, and the environment. Recognizing these characteristics is essential for predicting earthquake behavior and mitigating potential damage during such events.
Effective Stress: Effective stress is the stress that contributes to the strength and stability of soil and is defined as the total stress minus the pore water pressure. This concept is crucial in understanding how soils behave under load, particularly in saturated conditions where pore pressures can significantly affect stability. It plays a vital role in assessing soil liquefaction potential and lateral spreading during seismic events.
Empirical Correlations: Empirical correlations refer to relationships established through observation and data analysis, often used to predict outcomes based on observed trends. These correlations are crucial in understanding phenomena like liquefaction and lateral spreading, where historical data helps engineers assess potential ground behavior during seismic events. By utilizing empirical correlations, engineers can make informed decisions about site assessments, risk evaluations, and mitigation strategies based on real-world observations.
Factor of Safety: The factor of safety is a ratio that measures the capacity of a structure or material to withstand loads beyond its expected maximum load. It is crucial in engineering to ensure that structures can handle unexpected stresses and are safe for use. A higher factor indicates greater safety, allowing for uncertainties in material properties, design assumptions, and loading conditions, especially relevant in evaluating potential hazards like liquefaction and the overall integrity in design philosophies.
Foundation failures: Foundation failures occur when the structural support of a building or other construction loses its ability to carry loads due to soil movement, erosion, or other factors. These failures can lead to severe damage or collapse of structures, often highlighted during seismic events or extreme weather conditions, emphasizing the importance of proper foundation design and site analysis.
Gentle slopes: Gentle slopes refer to landforms that have a low angle of inclination, typically less than 10 degrees. These slopes can influence various geological processes, especially in the context of liquefaction and lateral spreading, as they tend to allow for easier movement of saturated soils during seismic events. The interaction of gentle slopes with ground motion can significantly affect the stability of structures and the distribution of stress in the soil.
Geologic Factors: Geologic factors refer to the physical and chemical properties of the Earth's materials that can influence the behavior of soil and rock during seismic events. These factors include soil type, density, composition, and the presence of groundwater, which can all play critical roles in phenomena such as liquefaction and lateral spreading. Understanding these factors is essential for predicting how different ground materials will react when subjected to shaking from earthquakes.
Ground Anchors: Ground anchors are devices used to secure structures to the ground, providing stability and resistance against forces such as soil movement or seismic activity. They are particularly important in situations where liquefaction occurs, as they help mitigate the lateral spreading of saturated soils during an earthquake. By transferring loads from structures into more stable soil layers or rock, ground anchors play a vital role in ensuring the safety and integrity of buildings in earthquake-prone areas.
Ground Fissures: Ground fissures are cracks or fractures that form in the ground due to various geological processes, often exacerbated by earthquakes or ground shaking. These fissures can occur suddenly and may indicate underlying soil instability, especially in areas prone to liquefaction and lateral spreading during seismic events.
Ground improvement techniques: Ground improvement techniques are methods used to enhance the physical properties of soil to improve its performance under various loads and conditions. These techniques are particularly important in areas prone to liquefaction and lateral spreading, where the ground can lose strength and behave like a liquid during seismic events. By implementing these techniques, engineers can reduce the risk of structural damage and increase the stability of foundations and infrastructure.
Groundwater conditions: Groundwater conditions refer to the state and behavior of water beneath the Earth's surface, including its availability, movement, and quality. These conditions play a crucial role in influencing soil properties and can significantly affect the stability of structures during seismic events, particularly in relation to phenomena like liquefaction and lateral spreading.
Grouting: Grouting is the process of injecting a fluid material into soil or rock to fill voids and improve stability. This technique is often employed to strengthen weak soils, reduce settlement, and mitigate the effects of liquefaction during seismic events. By enhancing soil properties, grouting plays a vital role in preventing lateral spreading and supporting structures in earthquake-prone areas.
Horizontal movement: Horizontal movement refers to the lateral displacement of soil and other materials during seismic events, primarily influenced by ground shaking and liquefaction. This phenomenon can lead to significant damage to structures and infrastructure as it causes the ground to shift unexpectedly, affecting the stability of buildings and roads. Understanding horizontal movement is crucial in assessing the risks associated with earthquakes, particularly in areas with loose or saturated soils.
Lateral Spreading: Lateral spreading is a phenomenon that occurs during seismic events, where loose, saturated soils lose strength and flow laterally, often causing ground movement that can damage structures. This movement can be triggered by liquefaction, where soil temporarily loses its solid properties due to increased pore pressure, leading to horizontal displacements. Lateral spreading can pose significant risks to infrastructure and natural features, contributing to ground failure in urban environments.
Liquefaction: Liquefaction is a phenomenon where saturated soil substantially loses its strength and stiffness in response to applied stress, typically during an earthquake. This process can lead to ground failure, causing structures to settle, tilt, or even collapse, as the soil behaves more like a liquid than a solid. Understanding liquefaction is crucial for assessing seismic risks and for designing structures that can withstand such ground behavior.
Loose Soils: Loose soils refer to sediments that have a low density and are not well-compacted, making them more susceptible to movement during seismic events. These soils often have high void ratios and can contain significant amounts of water, which contributes to their vulnerability to liquefaction and lateral spreading when subjected to strong shaking. Their behavior during earthquakes can lead to ground instability, significantly affecting structures built on or within them.
Magnitude: Magnitude is a numerical measurement that quantifies the size or energy release of an earthquake. It is a crucial metric in understanding seismic events and plays a vital role in assessing the potential impacts on structures and the environment. Magnitude is directly linked to seismic source characterization, as it helps in identifying the characteristics of the seismic source, as well as in ground motion prediction equations that model how the energy from an earthquake propagates through the Earth.
Mandatory Geotechnical Investigations: Mandatory geotechnical investigations refer to required assessments that evaluate the physical and engineering properties of soil and rock layers at a construction site. These investigations are crucial for understanding the subsurface conditions to ensure that the design and construction of structures are safe and effective, particularly in areas susceptible to liquefaction and lateral spreading during seismic events.
Mud Spouts: Mud spouts are geological features that occur when liquefied soil and sediment, often resulting from seismic activity, are expelled from the ground in a fluid or semi-fluid state. They are commonly associated with processes like liquefaction, where saturated soil loses its strength and behaves like a liquid during an earthquake, leading to the eruption of mud and water at the surface.
Newmark Sliding Block Analysis: Newmark Sliding Block Analysis is a method used to evaluate the stability of slopes during seismic events by analyzing the potential for block sliding. This approach simplifies complex soil behavior under earthquake loading into a rigid block sliding over a frictional surface, allowing for the estimation of the critical acceleration required to initiate sliding. It connects well with issues of liquefaction and lateral spreading, as these phenomena often influence how soil behaves under seismic forces.
Peak Ground Acceleration: Peak Ground Acceleration (PGA) is a critical measure in earthquake engineering that represents the maximum acceleration experienced by the ground during an earthquake, typically expressed in units of g (gravity). It serves as a key parameter in assessing seismic hazards and designing structures to withstand ground motions, influencing various engineering practices and safety measures.
Performance-Based Approach: The performance-based approach is a methodology in engineering that focuses on assessing and ensuring the desired performance of structures under various conditions, particularly during seismic events. This approach shifts the focus from traditional code compliance to evaluating how well a structure meets specific performance objectives, including safety, functionality, and damage control in the aftermath of an earthquake, thus addressing issues like liquefaction and lateral spreading more effectively.
Piles: Piles are long, slender columns made of wood, concrete, or steel that are driven into the ground to support structures above by transferring their load to deeper, more stable soil or rock. They are particularly important in areas susceptible to liquefaction, where the ground loses strength and stability during seismic events, as they provide essential resistance to lateral spreading and help stabilize buildings and infrastructure.
Pipelines: Pipelines are large tubes or conduits used for transporting fluids, such as oil, gas, water, or other materials, from one location to another. In the context of liquefaction and lateral spreading, pipelines are critical infrastructure that can be severely affected by ground movements during an earthquake, potentially leading to leaks, ruptures, and hazardous situations. Understanding how pipelines respond to soil liquefaction and lateral spreading is vital for assessing risks and planning effective mitigation strategies.
Pore water pressure: Pore water pressure refers to the pressure exerted by water within the soil's pores or voids, which plays a crucial role in the behavior of saturated soils. This pressure influences soil strength, effective stress, and can significantly impact geotechnical stability, especially during seismic events. Changes in pore water pressure during earthquakes can lead to phenomena such as liquefaction, where saturated soils lose strength and behave more like a liquid, contributing to lateral spreading and ground failure.
Proper drainage: Proper drainage refers to the effective management of water runoff to prevent accumulation and ensure that excess water is directed away from structures and vulnerable ground. This is particularly important in preventing liquefaction, where saturated soil loses strength and stiffness, leading to instability during seismic events. Effective drainage systems help maintain soil integrity, reducing the risk of lateral spreading and associated damage.
Reinforced Earth Structures: Reinforced earth structures are composite materials that combine soil with reinforcement elements, such as geogrids or steel strips, to improve their stability and load-bearing capacity. This technique is particularly effective in managing the risks associated with ground movement, like liquefaction and lateral spreading, by providing additional support and enhancing the overall resilience of earth structures during seismic events.
Sand boils: Sand boils are small, localized eruptions of water and sand that occur during seismic events, particularly in conditions where soil is saturated with water. They form as a result of liquefaction, where the ground temporarily loses its strength and behaves like a liquid due to intense shaking. Sand boils can be indicators of soil instability and are often associated with lateral spreading, as they can compromise the integrity of structures built on or near such soils.
Saturated Soil: Saturated soil refers to a condition in which all the voids or pores within the soil are filled with water. This state can significantly influence the behavior of the soil during seismic events, particularly in relation to liquefaction and lateral spreading, as it affects the soil's strength and stability. When saturated soil is subjected to rapid loading, such as during an earthquake, the pore water pressure increases, reducing the effective stress and potentially leading to failure.
Shear Strength: Shear strength is the ability of a material to resist sliding or shearing forces when subjected to stress. It plays a critical role in understanding how soils behave under loading conditions, particularly during seismic events, where sudden ground movements can lead to instability and failure. The shear strength of soil is influenced by factors such as cohesion, friction, and the effective stress within the material, which are essential for evaluating risks related to liquefaction and lateral spreading during earthquakes.
Site-specific seismic hazard analysis: Site-specific seismic hazard analysis is a detailed evaluation that assesses the potential seismic hazards for a particular location, considering local geological, geotechnical, and seismic data. This analysis helps determine how ground motion, fault activity, and site conditions could affect structures in the event of an earthquake. It plays a crucial role in designing buildings and infrastructure that can withstand seismic forces, particularly in areas prone to liquefaction and lateral spreading.
Soil Characteristics: Soil characteristics refer to the physical and chemical properties of soil that influence its behavior during seismic events. These properties include texture, density, moisture content, and shear strength, all of which play a crucial role in understanding how soil responds to shaking and can lead to phenomena like liquefaction and lateral spreading.
Stabilization: Stabilization refers to the process of enhancing the strength and stability of soil or structures to prevent failure or excessive deformation, especially during seismic events. This term is crucial when discussing liquefaction and lateral spreading, as it involves measures that can mitigate the negative effects these phenomena have on buildings and infrastructure during earthquakes. By employing techniques to stabilize the ground, engineers can improve the resilience of structures against seismic forces and ensure safety for occupants.
Stone Columns: Stone columns are deep foundation elements made of aggregate materials that improve the load-bearing capacity and stability of soil, particularly in areas susceptible to liquefaction and lateral spreading during seismic events. These columns are constructed by inserting stone or aggregate into the ground, which densifies the surrounding soil and provides additional support. They play a critical role in mitigating the effects of ground movement by reducing pore water pressure and enhancing overall soil strength.
Uniformly graded sands: Uniformly graded sands are a type of soil that consist of particles that are similar in size, resulting in a narrow range of particle diameters. This characteristic makes them less effective at interlocking compared to well-graded sands, leading to a greater susceptibility to liquefaction under seismic loading. In the context of ground shaking during an earthquake, these sands can lose strength and behave like a liquid, resulting in lateral spreading and potential structural damage.
Utilities: Utilities refer to essential services and infrastructure necessary for the functioning of a community or society, including water, electricity, gas, and sewage systems. These services are vital for public health, safety, and overall quality of life, making their stability particularly important in areas susceptible to natural hazards such as earthquakes. The disruption of utilities during seismic events can significantly hinder recovery efforts and exacerbate the effects of damage.
Vibro-compaction: Vibro-compaction is a ground improvement technique used to densify loose, cohesionless soils by utilizing vibration to rearrange soil particles and reduce voids. This method enhances the load-bearing capacity of the ground and minimizes the risk of liquefaction during seismic events. The process involves inserting a vibrating probe into the soil, which generates vibrations that cause soil particles to settle more closely together, increasing the overall stability of the ground.
Volumetric Strain Approach: The volumetric strain approach is a method used to analyze soil behavior under loading conditions, specifically during events such as earthquakes. This approach focuses on the changes in volume of a soil sample when subjected to stress, which is crucial for understanding phenomena like liquefaction and lateral spreading. By quantifying how much a soil volume decreases or increases, engineers can better predict how soils will react during seismic activities.
Youd et al. model: The youd et al. model is a widely recognized framework for understanding liquefaction and lateral spreading during earthquakes, particularly in saturated, loose, sandy soils. This model provides critical insights into the conditions that lead to soil liquefaction, which can result in significant ground deformation and structural damage. It combines empirical data and theoretical analysis to evaluate the triggering factors and effects of liquefaction, guiding engineers in assessing risks and designing resilient structures.
Zoning restrictions: Zoning restrictions are regulatory measures established by local governments to control land use and development within specific areas. These restrictions help ensure safety and minimize risks associated with natural hazards, such as earthquakes, by dictating how land can be utilized and what types of structures can be built in various zones.