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INFLUENCE OF CEMENTATION IN
THE CHARACTERIZATION OF GRANULAR SOILS USING SHEAR WAVE VELOCITY

1. Objective

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The
proposal is aimed at documenting and improving the state-of-the-art of
knowledge concerning the behavior cemented deposits using shear wave velocity.
The objective of the research work lies in evaluating the influence of degree
of cementation and variation of confining pressure in the shear wave velocity
of granular soils.

2. Introduction

Geotechnical
Engineers often encounter situations to deal with cemented deposits. Cemented
soils can be identified either as rocks or as soils, depending on the
experience and training of the observer. 
They occur in various geologic environments like deposits of loess,
volcanic ash, dune sands, and marine beach sands. These materials are typically
composed of sand or silt size particles and can have unconfined compressive
strengths from slightly greater than zero up to 690 kN/m. After failure in an
unconfined test, cemented soil exhibits brittle response and loses most or all
of its strength. Despite their relatively low strength, vertical to near
vertical slopes of are found in these materials. Cemented soils can exhibit
behavior which is different from those of uncemented soils. There are evidences
which shows the cementation can have considerable effects on small strain modulus,
shear strength, volume change and liquefaction behavior of granular soils. Most
of the research works on cemented deposits largely focuses on large strain
properties. Only limited database is available for small strain properties of
cemented deposits and need to be enhanced to highlight the critical role that
even small amount of cementation plays in the performance of soil. Seismic
damages have occurred on naturally cemented sands around the world. Further
with advent of deep mixing and chemical grouting technology, the need to
recognize cementation in design is becoming increasingly important.

2.1.
Natural cementation in Tamil Nadu

In
Tamil Nadu lying in the southern part of India cementation is found in Neyveli
formation, Small limestone deposits of kudankulam, Cudullore sandstones and
Ariyalur limestones. These are some of the areas of natural cementation.

2.2 Artificial
cementation in Tamilnadu  

2.2.1
Liquefaction potential of regions in Tamilnadu

The geological survey of India has included Tamil Nadu in
seismic zones II and III with Chennai and Coimbatore in zone III and
Pondicherry, Tanjavur and Madurai in Zone II. These places have seen sprawling
urban development in the past one or two decades. The geological division of
Anna University, Chennai is having statistical details of more than 150 seismic
events that have occurred in Tamil Nadu during the past few decades of which at
least three have Ritcher scale magnitudes more than 5. Most of the earthquakes
have a potential to cause liquefaction of soils especially when the landforms
are within 5km, 25km, 100km and 250km of epicentral distances of earthquake
magnitudes of 5,6,7 and 8 respectively (Boominathan 2015).  Bureau of Indian standards prescribes that
all submerged sand deposits with SP classification and N values less than 15 at
depths upto 5m and less than 25 at depths greater than 10m in seismic zone III
are likely to liquefy. Liquefaction occurs not only in sand deposits but also
soil with more than 35% fines. All this aforementioned criteria conform to the
potential susceptibility for liquefaction of soils in landforms bounded by Vedaranyam
in the south and Chennai in North.

            2.2.1.2 Artificial cementation

                        When a site under consideration
is susceptible to liquefaction hazard, one of the remedial measures is that the
cementing property of the soil mass can be improved by injecting clay/ cement
or sodium silicate/calcium chloride chemical grout. This induces artificial
cementation in the soil. Though these techniques have been used for long in
geotechnical Engineering, Yet until now surprisingly little research has been
directed at important engineering questions related to the past or future
performance of cemented deposits of Tamil Nadu during earthquakes.

Cementation caused by either natural or artificial soil
stabilization process will have influence on the small strain behavior of
soils. Hence cementation effect should be taken into account in the design of
foundation analysis, cyclic and dynamic response of soils and slope stability
problems.

2.3 Cementation and
cementing agents

                       Cementation in
sedimentary deposits binds individual grains together.  According to Krynine and Judd (1957) the most
common cements found in sedimentary rocks are: silica or sileceous cement;
calcium carbonate or calcareous cement; clay or argillaceous cement; and
iron-bearing minerals or ferruginous cement. The cementation may be present at
the time of deposition of soil, or precipitation from ground water percolation,
or may be formed by weathering of minerals present in the soil mass. The degree
of cementation depends on the amount and type of cementing agent, water
content, groundwater movement, and weathering. Silica cement is the strongest
and also the most resistant to weathering and water action. Clay cement is
strong and brittle in dry state but can change into a weak, ductile material in
moist condition. Carbonate cement is resistant to fluctuations in moisture
content but may be weakened by acidic action of groundwater.

 

3. Literature survey

            Tat-suoka et. al (1994), Yun and
Santamarina (2005) pointed out the importance of small strain shear modulus (Gmax)
in the analysis and design of geotechnical structures. Gmax is
calculated from the shear wave velocity using the relationship

                                                Gmax
=??s2

  
                     where ? is the
mass density and ?s is the shear wave velocity. Small strain modulus
and shear wave velocity are functions of parameters like effective confining
pressure, void ratio(Hardin and Richart,1963;Hardin and Drnevich,1972), cement
content(Acar and El-Tahir,1986) and stress anisotropy (Roesler,1979).

                        The
effect of shear stress in small strain modulus has been studied by many
researchers for various soils with contradictory findings. Yu and Richart
(1984) and Tatsuoka (1985) reported that the small strain shear modulus
decreases with increasing shear stress for effective principal stress ratio
greater than 3. Hoque and Tatsuoka (2004) showed that the small strain
stiffness, young’s modulus which is theoretically related to Gmax through
poisson’s ratio, is a function of the principal effective stress in that
direction, and is independent of stress path. The authors further reported that
the elastic stiffness of granular soil increases under applied shear stress
until the principal stress ratio reaches the value of 3 to 4; beyond this
ratio, stiffness decreases significantly due to plastic deformation. Yun and
Santamarina (2005) studied the effect of stress state on small strain shear
modulus of cemented sand during one dimensional consolidation. They reported
that at low strain levels the cemented sands in contractive state, underwent a
reduction in stiffness due to decementation.

                         Tatsuoka et.al (2007) termed the small strain
stiffness of cemented sands obtained from stress strain relationship using high
precision local strain instruments influenced by visco plastic strains as quasi
elastic stiffness.

                        Ravi
Sharma et.al (2011) established a relationship between shear wave velocity and
stress at failure for weakly cemented sands. Though there are many published
data on effect of small strain modulus on cemented sands they remain
inconclusive.

 

4.
Proposed work with methodology

Sampling

 

           

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5. Implementation

5.1. Sampling

            Two approaches are to
be undertaken towards experimenting with cemented sands.

The
properties of naturally occurring cemented sands in the Neyveli and
Kudankulam are to be determined by testing undisturbed block samples using
special sampling techniques.
 However, because of the difficulty in
obtaining these samples, and the likelihood that natural variability in
cementation would produce erroneous data trends, it is decided to also
fabricate artificially cemented samples in a controlled manner which would
model the naturally cemented soils.

By preparing artificially cemented samples in the
laboratory, a close control can be exercised over the density, level of
cementation, grain size and moisture content of the material. Effects of
variations in each of these parameters can also be studied by changing one at a
time, which is unlikely to be achieved by changing sites in the field.
Nevertheless, producing a material response like that of naturally cemented
sand by mix of sand and cementing agent is the major key to obtain meaningful
results. For this reason, considerable attention will be given to the mix
design.

5. 2.Materials and methods

 5.2.1 Cementing agents

For simulating artificial cementation in the laboratory Portland
cement II is to be used as cementing agents.

5.2.2
Sample preparation

The cemented sands are to prepared by under compaction
method as done by Saxena et al in 1988 in their reserach.The cemented sands
will be cured under water at a temperature of 25°C in PVC perforated moulds for
14 days to 6 weeks depending upon the cementing agent used. The effectiveness
of the cementing agents will be evaluated in terms of shear strength, moisture
content and microstructural changes of the treated sands.

5.2.3
Laboratory testing program

A
comprehensive laboratory testing program is planned to evaluate the small
strain behavior of both naturally and artificially cemented sands and briefed
below.

5.2.3.1
SEM analysis

Scanning electron microscope analysis (SEM) will be used
to study the micro structural changes in artificially cemented sands and to
identify the cementing agents and their distribution in naturally cemented
sands.

5.3 Index properties          

5.3.1
Determination of Index properties

Standard
geotechnical tests to determine the index properties conforming to IS 2720 part
3 (1980) will be performed on the cemented sands.

5.3.2Evaluation
of small strain behavior of the cemented samples

 To define the
strength and the small strain behavior of the artificially cemented sands using
shear wave velocity by bender element test.

6.
Work plan

Week

Progress of work

1st
&2nd week

Sampling
and evaluation of index properties

3rd
& 4th week

Curing
of samples

5th
to 22nd week

 Curing of samples and Bender element tests
on cured samples

23rd
& 24th week

Interpretation
of results and report preparation

 

7.
Expected outcomes and deliverables

By the end of this research
program the following will be achieved

(1)The behavior of cemented
sands in south India will be well documented

(2)The influence of degree of
cementation and variation of confining pressure in the shear wave velocity in
granular soils will be understood.

 (3) On a broader perspective, the research
program will be a first step towards developing a method in consideration of
cementation seismic design.

8.
Applications

            The emphasis on small strain parameters
of cemented sands will reflect the mere surface characterization with seismic
waves, and potential identification of lightly cemented sites with seismic
methods.

9.
Conclusion

            The behavior of natural and artificially cemented sands
is affected by cement content, confining pressure and low cementation history.
Cemented sands exhibit dilative behavior at low confining pressures and high
confining pressure can cause breakdown of cementation. Hence overloading
cemented soils will cause decrease in shear modulus. The small strain modulus
(Gmax) is an important elastic modulus and is being used
increasingly in the analysis. Having discussed the variability in the published
data on the small strain behavior of cemented sands, it is important to study
the influence of cementation in the characterization of granular soils.

10. References

1.
A.L Fernandez and J.C Santamarina (2001): Effect of cementation on the small
strain parameters of sands. Can. Geotechnical Journal 38: 191-199

2.
Ravi Sharma, Christopher Baxter and Michael Jander (2011): Relationship between
shear wave velocity and stresses at failure for weakly cemented sands during
drained triaxial compression. Japanese Geotechnical society 51, 761-771

3.
Rinaldi V.A and Santamarina J.C (2006): Cemented soils: small strain stiffness.

4.
T.Matthew Evans and Zhangwei Ning (2013): Wave propagation in assemblies of
cemented spheres.

5.
Surendra K. Saxena, Krishna R. Reddy, Anestis S.Avramdis (1988): Proceeding of
9th world conference on earthquake engineering Vol 3.

6.
Yalcin B. Acar, M. ASCE and El-Tahira. El-tahir(1986): Low strain dynamic
properties of artificially cemented sands. Journal of Geotechnical engineering
112 (11): 1001-1015

7.
Luling Yang, Lynn Salvati(2010): Small strain properties of sands with
different cement types. Fifth international conference on recent advances in
geotechnical earthquake engineering and soil dynamics.

 

11.
Financial assistances

S.No.

Particulars

Cost(Rs)

1

Consumables(Hydraulic oil, rubber membrane,
cement, sand, O-rings, stationery)

20,000/-

2

Travel

2,000/-

3

Miscellaneous

3,000/-

                                               
       Grand total

25000/-

 

 

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