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An- Najah National UniversityFaculty of Engineering
Civil Engineering Department
“LIQUEFACTION”
Prepared By: Husni M. Awwad Talal Z. Zammar
Supervisor: Dr. Isam Jardaneh
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Outline
BackgroundMechanism of LiquefactionCalculation of Liquefaction Remedial MeasuresSimulation
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History
Introduced by Arthur Casagrande (1935-8)
Serious attention because of Japan, Alaska and Nigata earthquake in 1964.
Evidence of liquefaction found in prior earthquakes
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Review
Liquefaction Definition: σ’=σt-uThe amplified movement of the ground,
occurring after earthquake when the ground becomes over saturated with water and transforms from solid to a liquid state due to increase in pore water pressure and reduction in effective stress.
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Look Closer
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Liquefaction phenomenon
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Mechanism of Liquefaction
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Types of FailureCyclic Mobility• Overturning
• Sand Boiling
•Subsidence and Settlement•Deferential Transient Motion
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Calculation of Liquefaction There are three major methods :
Grain size distributionThreshold strainCSR & CRR
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Grain Size Distribution
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Threshold Strain Equation:
Can be write in this formula :
ɣ= 1.2 a z/ v2s
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use of threshold strain
If ɣ thus computed for any depth in cohesionless deposit is less than the threshold strain (typically 0.0001 or 0.01 percent), then there is safety against liquefaction.
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Cyclic Stress Ratio (CSR) and Cyclic Resistance Ratio (CRR)
Calculation or estimation of two variables is required for evaluation of liquefaction resistance of soils (CSR), (CRR)
CSR = (τav/σ'vo) = 0.65 (amax/g)(σvo/σ'vo)rd
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Method for Evaluating CRR
1. Cone penetration test (CPT)2. Standard penetration test (SPT)3. Shear-wave velocity measurements (Vs )4. Becker penetration test (BPT)
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Standard Penetration Test (SPT)
(N1)60 = NmCNCECBCRCS
Correlations for Fines Content and Soil Plasticity
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Cone Penetration Test (CPT)
procedure are on average slightly smaller, and thus more conservative.
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Shear Wave VelocityThe advantages of using VS :VS can be accurately measured in situ using a
number of techniques .VS measurements are possible in soils that
are difficult to penetrate with CPT and SPT. measurements can be performed in small
laboratory specimens.VS is directly related to small-strain shear
modulus.
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Becker Penetration Tests (BPT)
CPT and SPT measurements, however, are not generally reliable in gravelly soils. Large gravel particles may interfere with the normal deformation of soil materials around the penetrometer increasing penetration resistance.
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Magnitude Scaling Factors
FS = (CRR7.5/CSR)MSF
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Remedial MethodsDeep Soil MixingCompaction GroutingDynamic CompactionVibrocompaction Vertical Drains “Wick Drain”Stone Columns
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Remedial Methods
Advantages :Reduce foundation settlement.Increase shear strength to improve slope
stability.Increase bearing capacityIncrease water permeability to accelerate
drainage and thereby accelerate foundation settlement.
Prevent soil liquefaction during earthquakes.
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Remedial MethodsDeep Soil Mixing1- Dry soil mixing2- Wet soil mixing
Compaction Grouting
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Remedial MethodsDynamic CompactionVibrocompaction
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Remedial MethodsPreloading ,Vertical Drainage , Wick Drain
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Remedial MethodsStone Column ,Vibro-Replacement1- Wet (top feed)2- Dry (bottom feed)
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Simulation
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Thank you very much for your
attention!!