Services: Liquefaction Mitigation

Conditions for Liquefaction: Saturated ground. Loose granular and other non-plastic soils. Strong ground motion. How Liquefaction Occurrs: Earthquake Shear strains transfer forces to pore water. Excess pore water pressure cannot dissipate fast enough. Effective stress is reduced to “zero” (lead to loss of bearing capacity) After shaking stops pore water pressures dissipate (leads to excessive settlement). Approach to Mitigation of Liquefaction Effects (Criteria) Counteract causes of liquefaction: Densify loose granular soil Dewater or control water pressure buildup (Drainage) Modify cohesive properties of soil Reinforce soil (reduce strain level during EQ) Remove and replace with nonliquefiable soil Control consequences of liquefaction: Reinforce and connect structural shallow foundation Install deep foundation designed for liquefiable soils Partial soil improvement (control deformations)

particle rearrangement due to seismic shaking Niigata, Japan, 1964 - Loss of Bearing Capacity due to Soil Liquefaction click to enlarge Typical sand Boils from Liquefaction click to enlarge

Applicable Improvement Criteria Based on Liquefiable Soil Type

	(A) Clean Sands <80% No 100 Sieve	(B) Silty Sands <15% Fines and <3% Clay	(C) Silty Sands / Sandy Silts <60% Fines and <8% Clay	(D) Non-Plastic Silts
Densification	XXX	XX	X (with pre-installed wicks)
Drainage	XX	X
Reinforcement		X	XX	XXX

Red = Soil type
Green = Criterion

Common Techniques and Type of Improvement

	Densification	Drainage	Reinforcement
Dynamic Compaction Vibro Tamper Vibro Compaction	XXX
Vibro-Stone Columns	XXX	X	X
Compaction Grouting	XX		X
Deep Mixing Permeation Grouting Jet Grouting			XXX

Green = Criterion
Red = Improvement Technique


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