SOIL LIQUEFACTION-Presentation-

SPECIAL FOUNDATIONS

Student:LAZAR GheorgheGroup 3409

Liquefaction is a process in which the seismic shear waves cause an increase

in the pore water pressure in a cohesionless soil stratum. This increase in pore pressure reduces the effective stress confining the soil. This reduction causes a reduction of shear modulus of

the soil, which in turn, results in increased soil deformation.

Key Elements of Soil Liquefaction Engineering

Ground failures associated to liquefaction

1. Loss of bearing strength – the ground can liquefy and lose its ability to support structures.

Fig. 1. Niigata - JapanThese tilted buildings and liquefaction in this area are probably the most well known examples of liquefaction and loss of bearing strength

2. Lateral spreading - the ground can slide down very gentle slopes or toward stream

banks riding on a buried liquefied layer.

Fig.2. Lateral-spreading induced failure of a dike in Nantou

Fig.3. Lateral spreading and settlement of a concrete dike

3. Sand boils - sand-laden water can be ejected from a buried liquefied layer

and erupt at the surface to form sand volcanoes; the surrounding ground often fractures and settles.

Fig.5. Widespread sand boiling in Zhangbin Industrial Park

Fig.4. Large scale sand boiling in Zhangbin Industrial Park, Zhanghua

4. Flow failures — earth moves down steep slope with large displacement and much internal disruption of material.

5. Ground oscillation — the surface layer, riding on a buried liquefied layer, is thrown back and forth by the shaking and can be severely deformed.

6. Flotation — light structures that are buried in the ground (like pipelines, sewers and nearly empty fuel tanks) can float to the surface when they are surrounded by liquefied soil.

7. Settlement-when liquefied ground re-consolidates following an earthquake, the ground surface may settle or subside as shaking decreases

and the underlying liquefied soil becomes more dense.

Tilting of a resident building in Wufeng

Settlement on a street of Nantou City

Ground improvement and structural solutions that are available to reduce hazard from liquefaction.General Category Mitigation Methods Notes

I. Excavation and/or compaction

a. Excavation and disposal of liquefiable soils

b. Excavation and recompaction

c. Compaction (for new fill)

 

II. In-situ ground densification

a. Compaction with vibratory probes (e.g.: Vibroflotation, Terraprobe, etc.)

b. Dynamic consolidation (Heavy tamping)

c. Compaction piles

d. Deep densification by blasting

e. Compaction grouting

Can be coupled with installation of gravel columns

Can also provide reinforcement

III. Selected other types of ground treatment

a. Permeation grouting

b. Jet grouting

c. Deep mixing

d. Drains

o Gravel drains

o Sand drains

o Pre-fabricated strip drains

e. Surcharge pre-loading

f. Structural fills

Many drain installation processes also provide in-situ densification.

IV. Berms, dikes, sea walls, and other edge containment structure/systems

a. Structures and/or earth structures built to provide edge containment and thus to prevent large lateral spreading.  

V. Deep foundationsa. Piles (installed by driving or vibration)

b. Piers (installed by drilling or excavation) Can also provide ground

densification

VI. Reinforced shallow foundations

a. Grade beams

b. Reinforced mat

c. Well-reinforced and/or post-tensioned mat

d. "Rigid" raft

 

REFERENCES:i. Liquefaction, Flow, and Associated Ground Failure -

T. Leslie Youd , United States Department of the Interior

ii. Recent advances in soil liquefaction engineering: A unified and consistent framework – R.B. Seed, K.O. Cetin, R.E.S. Moss, A.M. Kammerer, J. Wu, J. M. Pestana, M. F. Riemer, R.B. Sancio, J.D. Bray, R. E. Kayen, and A. Faris, 26th Annual ASCE Los Angeles Geotechnical Spring Semina, April 30, 2003

iii. http://geomaps.wr.usgs.gov/sfgeo/liquefaction/iv. Seismic Design Criteria for soil liquefaction – J.M.

Ferritto, NAVAL FACILITIES ENGINEERING SERVICE CENTER June 1997

v. Characteristics of liquefied sands during Mino-Owari, Tohnankai and Fukui Earthquakes – Hideaki Kishida

vi. http://www.ces.clemson.edu/chichi/TW-LIQ/Album.htm