Liquefaction Potential Calculator

Evaluate soil liquefaction risk during earthquakes based on SPT data and seismic parameters

Input Parameters

Earthquake Parameters
Soil Layer Parameters
SPT Parameters
Correction Factors
LPI Options

Results

Factor of Safety (FS)

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Enter parameters and click calculate

Liquefaction Potential

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LPI will be calculated when enabled

Detailed Results
Parameter Value Description
Corrected N60 - Energy-corrected SPT N-value
(N1)60 - Overburden and energy corrected N-value
CSR7.5 - Cyclic Stress Ratio (M=7.5)
CRR7.5 - Cyclic Resistance Ratio (M=7.5)
MSF - Magnitude Scaling Factor
Kσ - Overburden Correction Factor
rd - Stress Reduction Factor
Interpretation Guide
Factor of Safety (FS) Against Liquefaction
  • FS ≥ 1.2: Liquefaction unlikely
  • 1.0 ≤ FS < 1.2: Marginal case, further analysis recommended
  • FS < 1.0: Liquefaction likely, mitigation measures required
Liquefaction Potential Index (LPI)
  • LPI = 0: No liquefaction hazard
  • 0 < LPI ≤ 5: Low liquefaction hazard
  • 5 < LPI ≤ 15: High liquefaction hazard
  • LPI > 15: Very high liquefaction hazard

Site Planning & Practical Guidance

When to Use This Analysis

Project Stage: Use during preliminary design phase for:

  • Site Selection: Compare multiple building sites for seismic risk. This calculation is often used alongside a soil bearing capacity analysis to get a complete picture of ground conditions.
  • Foundation Planning: Determine if deep foundations or soil improvement needed. If high risk is indicated, you may want to run a parallel pile capacity estimate to assess deep foundation alternatives.
  • Permit Documentation: Support building code compliance for seismic zones
  • Insurance Assessment: Evaluate site risk for project insurability
  • Bid Preparation: Account for potential ground improvement costs
Field Data Preparation Checklist

Before running calculations, verify your field data:

  • ✅ SPT Log Review: Check for refusal points and unusual blow counts
  • ✅ Water Table Verification: Confirm monitoring well readings represent current conditions
  • ✅ Seasonal Adjustment: Account for wet vs dry season groundwater variations. You can use the active earth pressure calculator to understand how these changes affect lateral loads on substructures.
  • ✅ Layer Identification: Clearly define soil layer boundaries from bore logs
  • ✅ Hammer Type Confirmation: Verify energy ratio matches your SPT equipment
  • ✅ Fines Content: Use sieve analysis results, not visual estimates
Interpreting Results for Construction Planning

Factor of Safety (FS) Translation:

  • FS > 1.4: Proceed with standard foundation design
  • FS 1.2-1.4: Consider minor precautions in sensitive structures
  • FS 1.0-1.2: Consult geotechnical engineer - may need ground improvement
  • FS < 1.0: Mitigation required (stone columns, deep foundations, or site avoidance)

LPI Planning Response:

  • LPI 0-5: Monitor during construction, but no special measures
  • LPI 5-15: Design for liquefaction - consider raft foundations. A shallow foundation settlement estimate can help quantify potential differential movement.
  • LPI >15: Redesign approach or implement soil stabilization
Common Field Estimation Mistakes
  • Ignoring Seasonal Variation: Water table can vary 1-3 meters between seasons
  • SPT Hammer Inconsistency: Different crews get different energy ratios
  • Layer Thickness Oversimplification: Real soils vary more than bore logs show
  • Missing Correction Factors: Rod length and borehole diameter matter
  • PGA Source Confusion: Using wrong seismic zone maps or outdated codes
Material & Logistics Considerations

When FS indicates liquefaction risk:

  • Ground Improvement Materials: Plan for aggregate delivery for stone columns
  • Deep Foundation Equipment: Schedule pile drivers or caisson rigs early
  • Dewatering Needs: Account for extended dewatering if improving saturated soils
  • Testing Requirements: Additional CPT or pressuremeter tests may be needed
  • Schedule Impact: Ground improvement adds 2-8 weeks to project timeline
Contractor Q&A: Liquefaction Analysis

Q: How much should I trust a single layer analysis?

A: Never base decisions on one layer. Run multiple depths and create a soil profile. The weakest layer controls overall performance.

Q: What's the biggest margin of error in these calculations?

A: SPT blow count variability is ±30%. Always use multiple boreholes and consider statistical analysis for critical projects.

Q: When should I call a geotechnical engineer?

A: Immediately if FS < 1.2, LPI > 5, or if you're designing hospitals, schools, or emergency facilities.

Q: Can weather affect my results?

A: Yes. Heavy rain can temporarily raise water tables. Take measurements during representative conditions, not right after storms.

Cross-Check & Validation Steps

Before finalizing your assessment:

  • Run calculations with minimum and maximum realistic parameter values
  • Compare with CPT data if available (cone penetration test)
  • Check against local building department liquefaction maps
  • Review historical performance of nearby structures in past earthquakes
  • Consider non-liquefiable crust layer effects on foundation performance
  • Verify design earthquake parameters match current building codes
Important Limitations & Professional Judgment

This tool provides preliminary screening only. Always consult a licensed geotechnical engineer for final design decisions. Field conditions vary, local building codes differ, and critical structures require more sophisticated analysis including laboratory testing and dynamic site response analysis.

Practical Next Steps Based on Results
  • Low Risk (FS > 1.4): Document analysis, proceed with foundation design
  • Medium Risk (FS 1.0-1.4): Additional borings, consider conservative design
  • High Risk (FS < 1.0): Geotechnical consultation, ground improvement planning
  • Very High Risk (LPI > 15): Reevaluate site suitability or budget for extensive mitigation