Post on 24-Feb-2016
description
transcript
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!!