an- najah national university faculty of engineering civil engineering department

An- Najah National UniversityFaculty of Engineering

Civil Engineering Department

“LIQUEFACTION”

Prepared By: Husni M. Awwad Talal Z. Zammar

Supervisor: Dr. Isam Jardaneh

Outline

BackgroundMechanism of LiquefactionCalculation of Liquefaction Remedial MeasuresSimulation

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

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.

Look Closer

Liquefaction phenomenon

Mechanism of Liquefaction

Types of FailureCyclic Mobility• Overturning

• Sand Boiling

•Subsidence and Settlement•Deferential Transient Motion

Calculation of Liquefaction There are three major methods :

Grain size distributionThreshold strainCSR & CRR

Grain Size Distribution

Threshold Strain Equation:

Can be write in this formula :

ɣ= 1.2 a z/ v2s

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.

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

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)

Standard Penetration Test (SPT)

(N1)60 = NmCNCECBCRCS

Correlations for Fines Content and Soil Plasticity

Cone Penetration Test (CPT)

procedure are on average slightly smaller, and thus more conservative.

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.

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.

Magnitude Scaling Factors

FS = (CRR7.5/CSR)MSF

Remedial MethodsDeep Soil MixingCompaction GroutingDynamic CompactionVibrocompaction Vertical Drains “Wick Drain”Stone Columns

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.

Remedial MethodsDeep Soil Mixing1- Dry soil mixing2- Wet soil mixing

Compaction Grouting

Remedial MethodsDynamic CompactionVibrocompaction

Remedial MethodsPreloading ,Vertical Drainage , Wick Drain

Remedial MethodsStone Column ,Vibro-Replacement1- Wet (top feed)2- Dry (bottom feed)

Simulation

Thank you very much for your

attention!!