液化风险计算器

根据地震参数和地基条件估算土壤液化概率。

Assessment

了解地震中的土壤液化

液化是指饱和的松散颗粒状土壤在地震震动中失去其强度和刚度，表现得像液体而非固体。当地震波通过饱水的砂或粉土时，会增加土粒之间的水压（孔隙水压力）。如果该压力升高到等于上覆土壤的重量，土粒之间就会失去接触，土壤暂时像粘性流体一样流动。这种现象可导致建筑物下沉、倾斜或倒塌；管道和储罐等地下结构上浮到地面；以及斜坡发生侧向扩展破坏。

标准贯入试验（SPT）N值是评估液化敏感性的关键现场测量。它测量将取样管打入地下30厘米所需的锤击次数——N值越高表示土壤越密实、抗性越强。在饱和条件下SPT N值低于15的土壤通常被认为易于液化。地下水位深度同样重要：土壤必须饱和才能发生液化，因此地下水位浅（小于5米）的地区风险最高。填海造地和沿海填土特别脆弱，如1964年新潟地震和2011年克赖斯特彻奇地震所证实。

液化风险的关键因素

土壤类型：松散砂和粉砂最容易液化。粘土和砾石通常能抵抗液化，不过非塑性粉土在强烈震动下可能液化。
地下水位深度：较浅的地下水位（0-5米）大幅增加风险。地下水位深于15米的场地通常不会发生液化。
震动强度和持续时间：液化通常需要加速度超过0.1g的持续震动（数秒）。持续时间较长的地震会增加风险。
历史先例：过去地震中发生过液化的地区极有可能再次液化，因为导致液化的地质条件持续存在。

常见用途

在地震多发沿海地区进行房产评估时对液化可能性的初步评估。
了解哪些土壤条件和地震参数会导致液化。
评估填土地、填海造地或河流和海岸线附近场地的风险。
支持关于岩土地震工程的教育讨论。

How to Use

1
Enter Soil and Site Data
Input your site's soil type (sand, silt, clay, fill), water table depth, and layer thickness. Sandy soils saturated with water at depths less than 10 meters carry the highest liquefaction potential.
2
Specify the Earthquake Scenario
Enter the design earthquake magnitude (Mw) and peak ground acceleration (PGA) for your site. These can be obtained from the USGS seismic hazard map or from a site-specific hazard analysis at your return period of interest.
3
Interpret the Liquefaction Potential Index
Review your Liquefaction Potential Index (LPI) value and qualitative risk category. LPI < 5 is considered low risk; LPI 5–15 moderate; LPI > 15 high. The tool follows the Iwasaki (1982) framework widely used in Japanese and US engineering practice.

About

Soil liquefaction has been recognized as a major earthquake hazard since the 1964 Niigata and Alaska earthquakes, which produced dramatic documentary evidence of ground failure. The modern analytical framework for liquefaction assessment was developed largely by H. Bolton Seed and colleagues at UC Berkeley in the 1970s–80s, based on Standard Penetration Test (SPT) blow counts as a proxy for soil density and resistance. The Seed-Idriss Simplified Procedure, subsequently updated by Youd et al. (2001) and Idriss and Boulanger (2008), remains the standard for routine engineering practice and forms the basis of most liquefaction screening tools.

Liquefaction assessment methods fall into two categories. Deterministic methods compute a factor of safety for each soil layer using measured in-situ properties (SPT N-value, CPT qc, shear wave velocity Vs) and the earthquake loading expressed as the Cyclic Stress Ratio. Probabilistic methods (Cetin et al., 2004; Boulanger and Idriss, 2014) incorporate uncertainty in both the demand and capacity parameters to produce probability-of-liquefaction values rather than binary pass/fail outcomes. Probabilistic approaches are increasingly favored in performance-based earthquake engineering (PBEE) frameworks, where risk is expressed as expected losses over the lifetime of a facility.

The 2010–2011 Canterbury earthquake sequence in New Zealand produced an unprecedented dataset for liquefaction research. The earthquakes affected Christchurch—a city founded on Holocene fluvial sediments—causing liquefaction across 80% of the residential Red Zone, the area ultimately purchased by the government for permanent managed retreat. GNS Science and the University of Canterbury deployed a multi-technique investigation including aerial photography, LiDAR surveys, and thousands of CPT soundings to map spatial variability in liquefaction manifestation at block-by-block resolution. The resulting Christchurch Liquefaction Vulnerability dataset is now one of the most comprehensive post-earthquake geotechnical records ever assembled and has driven significant advances in simplified liquefaction assessment procedures.

FAQ

What is soil liquefaction?

Soil liquefaction is a phenomenon in which saturated, loosely packed granular sediment (typically sand or silt) temporarily loses its shear strength and behaves as a fluid when subjected to rapid cyclic loading such as earthquake shaking. The mechanism involves the buildup of excess pore water pressure: when the soil grains are rapidly jostled, the water between them cannot escape fast enough, and the pore pressure increases until it equals the confining stress, at which point the soil loses all effective stress and grain-to-grain contact. The soil-water mixture flows laterally under gravity, causing ground failure. Structures founded on liquefied soil can sink, tilt, or experience foundation failure even if they themselves are seismically well designed.

哪些类型的土壤最容易发生液化？

Liquefaction susceptibility is highest in saturated, loose to medium-dense clean sands and non-plastic silts with low plasticity (PI < 12), at depths less than 20 meters, with water table within 3 meters of the surface. The Chinese Criteria (Seed and Idriss, 1982) identified fine sands with fines content less than 15% as most vulnerable. Recent research has extended liquefaction risk to low-plasticity silts and some sensitive clays (the 'cyclic softening' mechanism). Poorly compacted fills—including hydraulic fills used to reclaim land—are particularly susceptible and are responsible for much liquefaction damage in New Zealand (2010–2011 Canterbury earthquakes), Japan (Tokyo Bay waterfront, 2011), and San Francisco (Marina District, 1989 Loma Prieta).

How does liquefaction damage buildings?

Liquefaction causes damage through several mechanisms. Sand boils (or sand volcanoes) form when pressurized pore water and sand erupt to the surface through cracks or utility penetrations. Differential settlement occurs when liquefied zones compact unevenly after pore pressure dissipates, tilting or cracking structures. Lateral spreading is perhaps the most destructive mechanism: when liquefied ground near a slope or riverbank flows laterally by meters to tens of meters, it ruptures pipelines, buckles roads, and moves building foundations. The 1964 Niigata earthquake caused entire apartment blocks to tilt 15–40 degrees through liquefaction-induced settlement; the 2011 Christchurch earthquake sequence caused NZ$1.5 billion in liquefaction-related building losses in residential areas.

Can liquefaction risk be reduced?

Liquefaction risk can be significantly reduced through ground improvement and structural mitigation techniques. Vibro-compaction and vibro-replacement (stone columns) densify loose granular soils in place or replace susceptible soils with dense aggregate columns. Dynamic compaction uses heavy tamper drops to densify surface layers. Deep soil mixing and jet grouting inject binders (cement or lime) to create strengthened columns or grids within susceptible zones. For new construction, mat foundations that 'float' on the soil, deep pile foundations extending through susceptible layers to bearing strata, and perimeter sheet pile walls to contain lateral spreading all reduce liquefaction vulnerability. For existing structures, perimeter soil treatment and underpinning with micropiles can retrofit foundation performance.

What is the Liquefaction Potential Index?

The Liquefaction Potential Index (LPI), proposed by Iwasaki et al. (1982) and widely adopted in Japanese seismic design practice, is a single-value parameter that integrates the factor of safety against liquefaction over the full soil profile to a depth of 20 meters. The factor of safety at each depth (FS = CRR/CSR) is computed from the Cyclic Resistance Ratio (CRR—the soil's capacity to resist liquefaction) and Cyclic Stress Ratio (CSR—the seismic demand). FS values less than 1.0 indicate liquefaction; these layers contribute most to the LPI with depth-weighting that emphasizes shallow soils. LPI ≤ 2 is considered very low risk; 2–5 low; 5–15 high; > 15 very high. The index correlates reasonably well with observed surface manifestations of liquefaction from earthquakes in Japan, New Zealand, and Taiwan.