Liquefaction Mitigation Techniques Updated 11-2 2007

I NTRODUCTION

Liquefaction is a phenomenon in which the strength and stiffness of a soil are reduced by

earthquake shaking or other rapid loading. Liquefaction and related phenomena have been

responsible for tremendous amounts of earthquake damage around the world.

In soil mechanics the term "liquefied" was first used by Hazen in reference to the 1918

failure of the Calaveras Dam in California. He described the mechanism of flow

liquefaction of the embankment dam as follows: If the pressure of the water in the pores is

great enough to carry all the load, it will have the effect of holding the particles apart and of

producing a condition that is practically equivalent to that of quicksand… the initial

movement of some part of the material might result in accumulating pressure, first on one

point, and then on another, successively, as the early points of concentration were liquefied.

Liquefaction occurs in soils at or near saturation, especially the finer textured soils. The

water must nearly fill the space between the particles. The water exerts pressure on the soil

particles that influences how tightly the particles are pressed together. Prior to an

earthquake, the water pressure is relatively low and the contact force between particles is

higher. Earthquake shaking can cause the water pressure to increase to the point where the

soil particles can readily move with respect to each other while the contact force between

particles are loosen. When liquefaction occurs, the strength of the soil decreases and the

ability of the soil to support building foundations and bridges are reduced.

1 | P a g eM. Tech, Dissertation Entitled

“Experimental Investigation on Compaction and Strength Behavior of Cement-Polypropylene Fiber Treated Expansive Soil”

Figure 1.1 (a): Large contact force available in between course soil particles with less pore water pressure before ground shaking.

Figure 1.1 (b): Contact force decreasing between soil particles while water pressure increasing after ground shaking.

LIQUEFACTION AND SEISMIC LANDSLIDES

LIQUEFACTION AND SEISMIC LANDSLIDES Over the years, some of the most spectacular, and costly damage to the earth slopes and the

foundation of structures has been due to liquefaction of sands during earthquake. When an

earthquake shakes loose saturated sand, the grain structure of soil tends to consolidate into

more compact packing. Since all these movements happen rapidly, there is no chance to

reduce the volume through the dissipation of pore water pressure from within the soil mass.

Therefore, the incompressible pore fluid takes up the entire applied stress and consequently,

the effective stress approaches zero and ultimately the deposit "liquefies." Since a liquid has

no shear strength, occurrences of disastrous consequences due to the failure of earth slopes

and foundations are inevitable.

The devastating effects of liquefaction drew considerable attention of geotechnical

earthquake engineers. In 1964, the Good Friday earthquake (M= 9.2) in Alaska and the

Neegata earthquake (M = 7.5) in Japan occurred. Both earthquakes produced splendid

examples of liquefaction leading to slope failures as well as foundation failures of bridges

and buildings. Even the recent earthquakes of India such as Bihar Earthquake of 1988, Uttar

Kashi Earthquake of 1991, Bhuj Earthquake of 2001, etc. have witnessed the liquefaction of

soil leading to slope and foundation failures.

Figure: 2

Figure: 3



Figure: 2 when liquefaction occurs, the

strength of the soil decreases and, the ability

of a soil deposit to support foundations for

buildings and bridges are reduced as seen in

the photo of the overturned apartment

complex buildings in Niigata in 1964.

Figure: 3 shows that sandy soil was

liquefied and behaved like fluid during the

Nisqually, Washington, and earthquake of

February 28, 2001. Many communities in

Kentucky are set on soft soils, especially

those along the Ohio and Mississippi River

Valleys. Those communities may also be

prone to liquefaction hazards.

Figure: 4

Figure: 5

Figure: 6

Figure: 7



Strong ground motion can also trigger

landslide known as earthquake-induced

landslides -- in areas with steep slopes,

such as eastern Kentucky. The slope

failure shown in Figure 4 was caused by

the Nisqually earthquake of February

28, 2001.

It has often been said that the October,

1989 Loma Prieta earthquake in

California was the Geotechnical

Engineer's earthquake because of the

major impact the deep soft soils had on

the bridge and roadway damage. This

was the United States warning to pay

more attention to the importance of soil-

structure interaction and the disastrous

effects of not properly designing

structures constructed over these types

of foundation materials.

The earthquake picture illustrates the

permanent ground settlement due to

liquefaction along the perimeter of Port

Island (artificial fill) during the 1995

Kobe Earthquake, where the shore line

moved 6 to 9 ft outward into the sea and

settled as much as 3 ft.

Ground failure occurs due to

liquefaction, Loma Prieta earthquake.


Figure: 8

Earthquake ground shaking can do more than rattle your property at the surface. Under

certain conditions during moderate to great earthquakes, the earth supporting a home can

behave like a fluid (Liquefaction) or, in hillside terrain, can fail in blocks of earth and rock

that move downslope (Land sliding).

Figure: 9

Figure: 10



Ground shaking triggered liquefaction

in a subsurface layer of sand, producing

differential lateral and vertical

movement in a overlying carapace of

un-liquefied sand and silt, which

moved from right to left toward the

Pajaro River. This mode of ground

failure, termed "lateral spreading," is a

principal cause of liquefaction-related

earthquake damage.

Ground failure occurs due to

liquefaction as shown in the figure 10

Loma Prieta earthquakes.

TYPES OF GROUND FAILURE DUE TO EARTHQUAKE INDUCED LIQUEFACTION

Four primary types of ground failure are caused by liquefaction: lateral spread, ground

oscillation, flow failure, and loss of bearing strength. In addition, liquefaction may enhance

ground settlement and lead to eruption of sand boils (fountains of water and sediment

emanating from the pressurized, liquefied zone).

a) Lateral Spreads

Subsidence, or lowering of the ground surface, often occurs during earthquakes. This may

be due to downward vertical displacement on one side of a fault, and can sometimes affect a

huge area of land. Coastal areas can become permanently flooded as a result. Subsidence

can also occur as ground shaking causes loose sediments to “settle’ and to lose their load

bearing strength (see liquefaction, below) or to slump down sloping ground. Lateral

spreading occurs where sloping ground starts to move downhill, causing cracks to open up,

that are often seen along hill crests and river banks.

Damage caused by lateral spreads, though seldom catastrophic, is severely disruptive and

often pervasive. For example, during the 1964 Alaska earthquake, more than 200 bridges

were damaged or destroyed by spreading of floodplain deposits toward river channels. The

spreading compressed the superstructures, buckled decks, thrust stringers over abutments,

and shifted and tilled abutments and piers. Similar damage occurred during the 1991 Costa

Rica earthquake and during many previous large earthquakes.



Photo. Lateral spreading and ground failure at Raqui 2 Bridge.

The great M7.9 Denali Fault, Earthquake

of November 3, 2002. Alaska.

LIQUEFACTION AND SEISMIC LANDSLIDES b) Ground Oscillation

Where the ground is flat or the slope is too gentle to allow lateral displacement, liquefaction

at depth may decouple overlying soil layers from the underlying ground, allowing the upper

soil to oscillate back and forth and up and down in the form of ground waves. These

oscillations are usually accompanied by opening and closing fissures and fracture of rigid

structures such as pavements and pipelines.

c) Flow Failures

Flow failures are the most catastrophic ground failure caused by liquefaction. These failures

commonly displace large masses of soil tens of meters and in a few instances, large masses

of soil have traveled tens of kilometers down long slopes at velocities ranging up to tens of

kilometers per hour. Flows may be comprised of completely liquefied soil or blocks of

intact material riding on a layer of liquefied soil. Flows usually develop in loose saturated

sands or silt on slopes greater than 3 degrees.

d) Loss of Bearing Strength

When the soil supporting a building or other structure liquefies and loses strength, large

deformations can occur within the soil which may allow the structure to settle and tip.

Conversely, buried tanks and piles may rise buoyantly through the liquefied soil. For

example, many buildings settled and tipped during the 1964 Niigata, Japan earthquake. The

most spectacular bearing failures during that event were in the Kwangishicho apartment

complex where several four-story buildings tipped as much as 60 degrees. Apparently,

liquefaction first developed in a sand layer several meters below ground surface and then

propagated upward through overlying sand layers. The rising wave of liquefaction



weakened the soil supporting the buildings and allowed the structures to slowly settle and

tip.

FACTORS AFFECTING THE SUSCEPTIBILITY OF A SOIL TO

LIQUEFACTION:

There are several factors that can affect the susceptibility of a soil to liquefaction:

1) The particles size distribution of the soil: poorly-graded soils are most susceptible to

liquefaction.

2) Whether the soil is loose or dense: loose soils are much more susceptible to

liquefaction.

3) Whether the soil is saturated or not: only saturated soils can undergo liquefaction.

POSIBLE WAY OF LIQUEFACTION MITIGATION

There are basically three possibilities to reduce liquefaction hazards when designing and

constructing new buildings or other structures as bridges, tunnels, and roads.

a) Avoid Liquefaction Susceptible Soils: The first possibility is to avoid construction

on liquefaction susceptible soils. There are various criteria to determine the liquefaction

susceptibility of a soil. By characterizing the soil at a particular building site according

to these criteria one can decide if the site is susceptible to liquefaction and therefore

unsuitable for the desired structure.

b) Build Liquefaction Resistant Structures: If it is necessary to construct on

liquefaction susceptible soil because of space restrictions, favorable location, or other

reasons, it may be possible to make the structure liquefaction resistant by designing the

foundation elements to resist the effects of liquefaction.

c) Improve the Soil: The third option involves mitigation of the liquefaction hazards by

improving the strength, density, and/or drainage characteristics of the soil. This can be

done using a variety of soil improvement techniques.



LIQUEFACTION AND SEISMIC LANDSLIDES BASIC OF COMPACTION GROUTING

Soil liquefaction is considered as one of the most significant geotechnical hazards and

recent large scale earthquakes, such as the 1995 Kobe Earthquake, 1999 Kocaeli Earthquake

and 2007 Niigataken Chuetsu oki Earthquake, have highlighted the need to mitigate the

damage. Currently, several remedial measures are available for treating or improving sites

susceptible to soil liquefaction. These measures include; densification, solidification,

replacement, lowering of water table, and dissipation of excess pore water pressure. In

selecting the appropriate remedial measures, various factors, such as effectiveness of

improvement, required areas and depth of improvement, effects on surrounding

environment, cost and ease of execution, and level of desired improvement, should be

considered.

Because of its versatility and economy in improving ground beneath and around existing

facilities, compaction grouting is gaining interest among engineers. Originally from the

United States, compaction grouting technology has been implemented in Japan only in the

early 1990s. Although initially developed for settlement control and re-leveling, the

technology has been used to solve a number of geotechnical problems, among them the

treatment of liquefiable soils. This paper discusses two case histories of compaction

grouting application as a remedial measure against liquefaction, with emphasis on the

lessons learned from the grouting process and the merits of compaction grouting as a

practical method of ground improvement.

Compaction grouting involves the injection of a very stiff grout (soil-cement-water mixture

with sufficient silt sizes to provide plasticity, together with sand and gravel sizes to develop

internal friction) that does not permeate the native soil, but results in controlled growth of

the grout bulb mass that displaces the surrounding soil. The primary purpose of compaction

grouting is to increase the density of soft, loose or disturbed soil, typically for settlement

control, structural re-leveling, increasing the soil’s bearing capacity, and mitigation of

liquefaction potential.

As shown in Figure, compaction grouting involves the installation of casing to the required

depth into a pre-drilled hole (70~100mm diameter). The stiff grout is then pumped through



the casing at high pressure until typically one of three criteria is reached, i.e., (1) target

volume; (2) maximum pressure; or surface (sub-surface) heave. The grouting is performed

in typically 0.3~0.9m intervals or stages, thus forming a column of interconnected grout

bulbs. At each stage, the soil particles are displaced radially from a growing bulb of grout

through cavity expansion effects into a closer spacing, thus increasing the density of the

adjacent soil around the bulb. Note that the strength of the grout is unimportant because the

purpose of the technique is to densify the surrounding soil by displacement. Compaction

grouting can either be performed “top-down,” i.e., from the upper to the lower limit of the

treatment zone or, more commonly, in a “bottom-up” process from the lower limit upwards.

Figure shows a typical process of injecting the grout.



LIQUEFACTION AND SEISMIC LANDSLIDES There are many numbers of techniques for liquefaction mitigation is available now days.

Selection of the best ground improvement technique for any project requires a wide range of

knowledge, experience and skill in an array of ground improvement approaches. Subsurface

conditions can vary greatly within a single job site and the characteristics of the in situ soil

play a crucial role in determining which ground improvement method is best.

Table no: 1 Summary of Anti-Liquefaction Measures and their Effects

Sr. No

LiquefactionCountermeasure

Main ActionAgainstLiquefaction

Densification

LateralCompaction

Drainageand PorePressureRelief

Remarks

1Chemical Grouting

cementation No No No Shallow Depths

2Conventional Piling

Bypassliquefiable layer

Yes for driven pile

No NoDriven piles can induce localized Densification

3 Stone ColumnsTransfer load tocompetent soil

YesYes(Medium)

YesProven performance in liquefaction Zones

4 Geopier

Transfer load to SurroundingImprovedGround

Yes Yes YesProven performance in liquefaction Zones

5Compaction Piling

Densification Yes No No

Effective for shallow depths but laboriousInstallation

6Resonant Column

Densification Yes No NoDensification is achieved for Shallow depths

7Dynamic Compaction Densification

Densification Yes slight NoShallow dept effectiveness < 8.0 meters

8 Vertical Drains Pore water relief no No YesEffective for Rapid Pore Pressure relief

9Compaction Grouting

Densification Yes Yes No Shallow soils

10 Jet Grouting Transfer load to competent soil

Yes(slight

Yes(slight)

No Essentially used to bypass liquefiable



soils

DEPTH OF ANALYSIS FOR LIQUEFACTION EVALUATION

Traditionally, a depth of 15 m has been used as the depth of analysis for the evaluation of

liquefaction. The Seed and Idriss EERI Monograph on “Ground Motions and Soil

Liquefaction During Earthquakes” (1982) does not recommend a minimum depth for

evaluation, but notes 12 m as a depth to which some of the numerical quantities in the

“simplified procedure” can be estimated reasonably. Liquefaction has been known to occur

during earthquakes at deeper depths than 15 m given the proper conditions such as low-

density granular soils, presence of ground water, and sufficient cycles of earthquake ground

motion. Experience has shown that the 15 m depth may be adequate for the evaluation of

liquefaction potential in most cases; however, there may be situations where this depth may

not be sufficiently deep.

It is recommended that a minimum depth of 15 m below the existing ground surface or

lowest proposed finished grade (whichever is lower) be investigated for liquefaction

potential. Where a structure may have subterranean construction or deep foundations (e.g.,

caissons or piles), the depth of investigation should extend to a depth that is a minimum of 6

m below the lowest expected foundation level (e.g., caisson bottom or pile tip) or 15 m

below the existing ground surface or lowest proposed finished grade, whichever is deeper.

If, during the investigation, the indices to evaluate liquefaction indicate that the liquefaction

potential may extend below that depth, the exploration should be continued until a

significant thickness 3 m, to the extent possible) of no liquefiable soils are encountered.



Liquefaction Mitigation Techniques Updated 11-2 2007

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Transcript of Liquefaction Mitigation Techniques Updated 11-2 2007