Presentation on theme: "“ LIQUEFACTION ” Prepared By: Husni M. Awwad Talal Z. Zammar Supervisor: Dr. Isam Jardaneh."— Presentation transcript:
“ LIQUEFACTION ” Prepared By: Husni M. Awwad Talal Z. Zammar Supervisor: Dr. Isam Jardaneh
Outline Background Mechanism of Liquefaction Calculation of Liquefaction Remedial Measures Simulation
History Introduced by Arthur Casagrande (1935-8) Serious attention because of Japan, Alaska and Nigata earthquake in Evidence of liquefaction found in prior earthquakes
Review Liquefaction Definition: σ’=σ t -u The 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.
Mechanism of Liquefaction
Types of Failure Cyclic Mobility Overturning Sand Boiling Subsidence and Settlement Deferential Transient Motion
Calculation of Liquefaction There are three major methods : Grain size distribution Threshold strain CSR & CRR
Grain Size Distribution
Threshold Strain Equation: Equation: Can be write in this formula : Can be write in this formula : ɣ = 1.2 a z/ v 2 s
use of threshold strain If ɣ thus computed for any depth in cohesionless deposit is less than the threshold strain (typically 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 = (τ av /σ' vo ) = 0.65 (a max /g)(σ vo /σ' vo )r d
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 = N m C N C E C B C R C S Correlations for Fines Content and Soil Plasticity
Cone Penetration Test (CPT) procedure are on average slightly smaller, and thus more conservative.
Shear Wave Velocity The advantages of using V S : V S can be accurately measured in situ using a number of techniques. V S measurements are possible in soils that are difficult to penetrate with CPT and SPT. measurements can be performed in small laboratory specimens. V S 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.
Remedial Methods Deep Soil Mixing Compaction Grouting Dynamic Compaction Vibrocompaction Vertical Drains “Wick Drain” Stone Columns
Remedial Methods Advantages : Reduce foundation settlement. Increase shear strength to improve slope stability. Increase bearing capacity Increase water permeability to accelerate drainage and thereby accelerate foundation settlement. Prevent soil liquefaction during earthquakes.