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Liquefaction in soils and its Remedial Measure
Abstract
Liquefaction occurs when vibrations i.e. earthquake within a mass of soil cause increased in pour
water pressure and decrease in effective stress. As a result, the soil behaves like a liquid, has an
inability to support weight and can flow down very gentle slopes. It is very dangerous for the
existing structure. Liquefaction most of the time occurs in loose saturated sandy soil. When
earthquake occurred in saturated soil the soil particles are apart from each other because voids are
filled with water and pour water pressure start increasing at one stage effective stress become equal
to zero.
Mechanism of Liquefaction
Soil is essentially a mixture of many soil particles remain in contact with many neighbor particles.
Contact forces produced by the weight of the particles. Liquefaction is the result of applying quick
loading and drop, on saturated sand and soil particles loosely packed trying to move into a denser
configuration. However, there is not enough water in the pores of the soil to be squeezed when
earthquakes occurred. There is an increased water pressure to reduce the contact forces between
the soil particles detached causing softening and weakening of the soil deposit. The soil particles
lose contact with one another due to pore water pressure. In such cases, the soil will have very
little strength, and will behave more like a liquid than a solid.
τf= (σ − u) tanϕ
The τf shear strength is dependent on the total stress & pore water pressure. Earthquake causes the
pore water pressure to increase and consequently reduce the shear strength. When pore pressure is
equal to total stress, soils full of fluid.
Causes of Liquefaction:
Liquefaction has been observed in earthquake for many years. Liquefaction occurs when the
structure of loose, saturated sand breaks down due to some rapidly applied loading. During an
earthquake there is not enough time for water in the pores to squeeze out. If the shear resistance of
soil becomes less than the static, driving shear forces so soil can undergo large deformation and is
said to liquefy.
Susceptibility of soils to Liquefaction in Earthquakes
The liquefaction is most commonly observed in shallow, loose soil saturated, non-cohesive soils
subjected to strong ground motions for earthquakes. In practice, the potential of liquefaction of the
soil deposit during an earthquake is often assessed by means of in situ penetration testing and
empirical procedures. Well graded soils, due to its stable configuration of inter locking, are less
prone to liquefaction. Koester (1994) stated that sandy soils with appreciable fines content can be
collapsible, perhaps because of the greater compressibility of fines between grains of sand.
Permeability also plays a significant role in liquefaction. When the pore water movement in the
soil is retarded by low permeability, pore-water pressures are likely to generate during cyclic
loading. Soils with high content of non-plastic fines are more likely to be liquefied because fines
inhibit drainage of excess pore-pressure. Gravelly soils are fewer tendencies to liquefaction due to
a relatively high permeability unless pore water drainage is impeded by less pervious, adjoining
deposits.
Case Study Niigata Earthquake 1964
Introduction:
The Niigata earthquake of June 16, 1964 had a magnitude of 7.5 and caused severe damage to
many structures in Niigata. The destruction was observed to be largely limited to buildings that
were founded on top of loose, saturated soil deposits. Even though about 2000 houses were
totally destroyed, only 28 lives were lost. The earthquake caused liquefaction over large parts of
the city.
Soil profile:
Topographically the city of Niigata may be divided into Aeolian sand dunes running parallel
with the coastline. The profile shows that soil is primarily sandy down to depths of 20 to 30
meters. Very loose sand for which value of N is less than 5 at some places extends to very great
depths. Within in the sandy strata there are isolated thin lenses of sandy silt, silty sand, or these
with the organic matter having high compressibility. Ground water table is quite shallow partly
due to ground subsidence in the area.
Liquefaction:
The Niigata earthquake 1964 brought liquefaction phenomena and their devastating effects to the
attention of engineers and seismologists. A remarkable ground failure occurred near the Shinano
river bank where the Kawagishi-cho apartment buildings suffered bearing capacity failures and
tilted severely (left). Despite the extreme tilting, the buildings themselves suffered remarkably
little structural damage.
Damage to building foundations:
To predict the nature of damage some of the buildings were excavated for direct inspection.
Damage to superstructure is examined on basis of type of foundation.
➢ Shallow foundations
Buildings on mat foundation suffered the least damage, buildings on strip footings
performed slightly performed better than the buildings on isolated footings. Buildings on
shallow foundations with N-values less than 15 suffered considerable damage in their
superstructure whereas few buildings founded on N-values greater than 15 were
damaged.
➢ Pile foundations
Degree of damage seemed to depend upon the depth of pile penetration and on soil at the
pile point. Short piles whose tips were located on soil with small N-value suffered severe
settlement and tilting. Probably because of the soil at pile tip completely lost its strength
due to liquefaction of soil during earthquake. Curve ABC gives critical N-values for
liquefaction. Damaged buildings are located below DBE and undamaged are located
above the curve. In zone ABD the soil above the pile tip was liquefied and soil at pile tip
was unaffected.
REMEDIAL MEASURE
Compaction grouting
Compaction grouting and grout is injection of low liquidity, still thick Homogeneous mass that did
enter the soil pores. Grout as a massive expansion, the soil around are displacement and dense
Shown in Figure pressure Grouting concept plan. According to Rubright and Welsh (1993), the
development of compaction Grouting technique in the early 50 in the United States. It has been
used successfully to correct structured settlement to prevent tunneling in soft soil foundation
settlement in urban areas, protection of the local area sinkholes structure and density of the
liquefiable soils.
Fig. Conceptual Drawing of Soil Densification by Compaction Grouting.
Permeation grouting
Permeating Grouting is a low viscosity liquid for injecting particles small changes in the pore
spaces of the soil on the physical structure of the soil. The main objectives or cementing soil
particles or enhanced permeation Grouting on the ground is by entering the soil pores reduces
water flow. Concept mapping is permeating Grouting as shown in Figure 9. Permeating Grouting
dates back to the 19th century (Glossop, 1961). Penetration Grouting technique has been
successfully used to control of groundwater flow, stability of soft ground Foundation excavation,
consolidation of existing Foundation and to avoid regulation and induced earthquake Liquefaction.
Fig. Conceptual Diagram of Soil Solidification by Permeation Grouting.
Jet grouting
Jet grouting and high pressure fluid are used to replace with the weak soils. The General
installation process begins with the storm a small hole, usually 90the final depth of 150 mm
diameter, as shown in the figure. Deep in the mix in the soil through a small nozzle as a rotating
drill pipe has been deleted. Cuttings a steady stream of from the ground up to the pressure of the
Jet to the point you need to prevent buildings foundation spray pressure causes deformation of the
Earth's surface. According to Bell (1993), a lot of the early generation Jet Grouting took place in
Japan and Europe in the late 70 ' s technology has been the world's. The technique has been used
worldwide to underpin existing foundations, support excavations, control ground water flow, and
strengthen liquefiable soils.
Fig. Procedure for Jet Grouting (Ichihashi et al.1992).
In situ soil mixing
In situ soil mixing is the mechanical mixing of soil and the stabilizer with a rotating propel lerand
mixing bar. Plot of soil by mixing process is in place shown in Figure. How to exercise to penetrate
the ground, stabilizer is pumped through the rotating shaft. Uniform mixing of the shaft mix to
inject stabilizer soil. After reaching the designed depth second mixing occurs both exercises will
be removed. Broomhead and Jasperse (1992), plenty of space for mixing soil development
occurred in Japan in the past 20 years. It has been successfully used to control the flow of
underground water support to stabilize embankments and slopes, excavations to increase stability
and the liquefaction-induced ground movements.
Fig. Conceptual Drawing of the In Situ Soil Mixing Technique.
Low vibration drain pile
Ono et al. (1991) described a low vibration system for constructing gravel drain pile susing a large
casing auger. The construction sequence of this system is illustrated in Fig The casing is screwed
downward into the ground, while simultaneously pouring water into the casing to sediment flow
into the casing. Gravel is discharged into the casing upon reaching the final depth. As the casing
is unscrewed, gravel is pushed out the end of the casing and compacted by a rod. One study showed
that standard penetration resistances measured at the midpoint between piles after installation were
about 5 blow counts higher than before installation. The most important factors affecting
densification are the shape of the impact surface of compaction rod, the number of compactive
strokes, and the stroke length. When drains are installed without the compaction rod, little
densification occurs. The low vibration drain pile technique has been used in Japan for liquefaction
remediation near existing structures.
Fig. A Low Vibration Procedure for Installing Gravel Drain Piles
REFFRENCE
•
Andrews, D.C.A. and Martin G.R. (2000) “Criteria forLiquefaction of Silty Soils”, Proc.
12th WCEE, Auckland, NewZealand.
•
Chen and Juang (2000). Liquefaction likelihood classification
•
Seed H.B., Tokimatsu, K., , L.F., and Chung, R. (1985),“Influence of SPT Procedures in
Soil Liquefaction ResistanceEvaluations” J. Geotechnical Engg.
•
Olson, S. M. and Stark, T. D. 2002. Liquefied strength ratio from liquefaction flow
failurecase histories. Canadian Geotechnical Journal
•
Kramer, L., Steven (1996). "Geotechnical earthquake engineering." Prentice Hall Series.
•
Ichihashi, Y., Shibazaki, M., Hiroaki, K., Iji, M., and Mori, A. (1992). “Jet Grouting in
AirportConstruction,” Proceedings, Grouting, Soil Improvement and Geosynthetics.
GeotechnicalSpecial Publication No. 30, held in New Orleans,
•
One, Y., Ito, K., Nakajima, Y., and Oishi, H. (1991). “Efficient Installation of Gravel
Drains,”Proceeding. Second International Conference on Recent Advances in
Geotechnical EarthquakeEngineering and Soil Dynamics, held in St, Louis, Missouri, on
11-15 March, S. Parkash, Ed.,University of Missouri-Rolls,
U PICIUN (IU.
1. Individual Proposal is required to include the following items.
(linimum # of page: 5. Maximum of page; 10) (Due: Thur, Sept 6, 2018)
Title
--- Introduction
Problems
...Methodologies and Scientific Discussion
Expected Results & Outcomes
Cited References
2. Preliminary (Progress) Report: Including the following items
nber 18, 2018)
Title
Abstract
Introduction
Materials and Methods
Observation
- Analysis of the Results & Discussion
Conclusion
--References
- Appendix
3. Final Report: (Due Ther 29, 2018 for Dec Graduates,
Thur. December 6, 2018 for Regular Students)
Format: same as the Progress Report