Ground Improvement Technique-1

8/10/2019 Ground Improvement Technique-1

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A PAPER ON

GROUND IMPROVEMENT TECHNIQUE( GROUP 1 GEOTECHNICAL ENGINEERING)

Submitted by

Mr. Kshirsagar Aji!"a #$has Mr. Ra%&!ar #hrirag Pra'ha!ar

T.E.Civil T.E.Civil

[email protected] [email protected]

Under the guidance of

Pr. #. #. Ni*'a%!ar

!rof. Civil Engg. "eptt.# $.C.E.%arad&

D&+ar,*&, Ci-i% Egi&&rig G.C.E.Kara /101/
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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INDE2

Cha+,&r. Ti,%&

' (ntroduction

) $round (mprovement Techni*ue

+ ,ibroflotation Techni*ue

- !rocedure

/pplications

0 /dvantages

1 2imitations

3 Case Study

4 Conclusion

'5 6eference


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A3#TRACT

India has seen increasing growth in infrastructure development in the last decade. Since

all the structures directly rests on the soil, the study of the behavior of different types of soils is

very much necessary. The in-situ characteristics of a construction site are different from those

desired and almost always, far from ideal for a designated need. The presence of large deposits

of weak soils of varying types has necessitated the development and application of various

ground improvement techniques.

There are many methods of improving the characteristics of soil such as surface

compaction, drainage methods, Vibro compaction method, Vibro-displacement method,

compaction piles, Vibro-floatation, heavy tamping, pre-compaction and consolidation, dynamic

consolidation, grouting and inection, stabili!ation with chemicals, use of geo-te"tiles and geo-

membranes and other miscellaneous methods.

This paper will briefly discuss all the methods, giving special consideration to the

#Vibro-floatation$ method, due to its high efficiency in compacting the sandy soils, by

simultaneous vibration and saturation. The technique has also been used in a big way for

installation of stone columns for strengthening soft soils for foundation of steel cylindrical

storage tanks %more tan &''( all around the coasts of India for refineries and chemical plants.


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1) INTRODUCTION4

(n7situ sol characteristics of a construction site are different form those desired and8

almost al9ays8 far from ideal for a designated need. :ith increased urban development sites 9ith

favorable foundation conditions became depleted. /t times the civil engineer has been forced to

construct the structures at sites selected for reasons other than soil conditions. Thus it is

increasingly important for the engineer to kno9 the degree to 9hich soil properties may be

improved or other alternatives may be thought of for the construction of an intended structure at

the stipulated site.

(f unsuitable soil conditions are encountered at the site of proposed structure8 one of

the follo9ing four procedures may be adopted;

'& urther8 in case of e=isting structures e=hibiting foundation distress8 in place

foundation treatments may be used as corrective measures. ?o9 a days8 various processes

are available by 9hich the characteristics of the construction sites can be improved either to

facilitate the construction operations or to allo9 the increased bearing pressures or to reduce

the settlements. The techni*ues involved in the attainment of the re*uired improvement

facilities are referred to as geotechnical processA.


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) GROUND IMPROVEMENT TECHNIQUE#4

The various ground improvement techni*ues in practice are;/& Surface compaction.


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5) VI3RO67LOTATION TECHNIQUE4

The vibroflotation techni*ue for densifying loose sands originated in $ermany in

the thirties. Stone column installation using this techni*ue 9as developed in


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/) PROCEDURE4

,ibroflot vibroneedle& attached 9ith suitable follo9 on tubes about

-55mm diameter is sunk through the soft soil 9ith bottom 9ater jets and vibration. The vibration

is created by an eccentric 9eight rotated at vertical a=is at '355rpm giving a lateral oscillating

load of about '5 tons. The rotation of the eccentric 9eight is by hydraulic motor. ,ibration is

isolated at the castellation junction so that vibration does not propagate to the follo9 on tubes

figure no )& surging is done for a couple of times to push out the accumulate effluent.

/fter the final day is reached8 the ,ibro assembly is raised by 55mm to

055mm above the final depth and the top 9ater jets are opened and bottom 9ater jets reduced.

Use of compressed air is also in vogue. o9ever8 soil conditions need to be stiff and the position

of the 9ater table plays an important part in selecting compressed air as a jetting fluid. So far no

site is encountered in (ndia 9here compressed air can be utiliBed. '55mmF 1mm do9n stone

metal is poured around the ,ibroflot and allo9ed to sink against the up flo9ing 9ater. /fter

dumping about 5.-cum. of metal8 the vibroflot is lo9ered and allo9ed to penetrate inside the

stone metal. Compaction is indicated 9ith a sharp rising pressure gauge. "uring this operation

the above process is repeated to form a vibrostone column. (n case of loose sand compaction8

sand is poured through the annular space. /s the particles densify8 they assume their most

compact form.


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0) APPLICATION#4

'& ost ,ibroflotation applications have been to depths less than )5m although depth of

+5m has been attained successfully. The ma=imum depth appears limited mainly by the

ability of the crane to pull the vibroflot out of the ground.

)& The t9o most important factors contributing to successful densification are the grain siBe

distribution of the soil and the nature of the backfill material used.

+& The grain siBe distribution of in7situ soil suitable for ,ibroflotation is sho9n in the figure.

This techni*ue is best suited for densifying very loose sand belo9 the 9ater table that have

grain siBe distribution falling 9ithin entirely Bone


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'& ?o material cost e=cept backfill material.

)& Complete uniformity in density and hence better control on settlement H $ives high

bearing capacity.

+& uch *uicker in operation than the conventional impact type hammer.

-& Computer controlled up and do9n movement of the ,ibroprobe using force pull7do9n

speeds up the column installation by maintaining a ma=imum level of *uality thanks to

the patented "ouble 2ock.

& >aster than pile driving.

9) LIMITATION#4

'& The method is not suitable for gravel8 dense sand and cemented sand as the rate of probe

penetration is reduced.

)& The effect becomes still less 9hen the 9ater table is located at a greater depth8 under

these conditions ,ibroflotation might prove to be uneconomical.

+& The specialiBed rig re*uires a high initial investment. 6e*uires 9ell trained operator for

the computer controlled pneumatic transport system.

-& The site boundary if need to be properly densified to perform8 may re*uire several meters

of vibroflotation beyond the site boundary depending on the depth of ground treatment

and properties.

:) CA#E #TUD;4


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1) Viigure sho9s the

layout of the stone column used at this site. Stone columns resting on the bottom stiff

silty clays 9ere adopted. Columns 9ere installed by vibroflotation techni*ue. igh

design intensities of '1tonFs*.m. necessitated triangular spacing of '.m centre to

centre. /t least t9o ro9s of stone columns 9ere provided beyond the ring beam on

9hich the shells of the storage tanks are supported. Under 9ater at a height ').m

during hydrotest8 the total settlement 9as about )45mm 9here as computed

settlement of untreated soil 9as about 355mm.


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) 3a'ra%a 7&r,i%i


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densify soil to counteract likely li*uefaction 9as felt by the o9ner and their consultants.

The structure included '50m tall prilling to9er8 compressor8 tank for ammonia and

naphtha8 a pipe rack8 process column of height up to 15m8 a t9o span 9orkshop8 bagging

plant etc.

(n vie9 of kno9n e=cellent performance of vibroflot compaction ,ibro7

compaction& in densifying sands including fine sand8 the consultants selected vibroflot

compaction. Stone backfill 9as proposed because of its very high permeability and

thereby faster release of pore pressure in case of an earth*uake. / trail 9as initially made

on a '5m I '5m area at the centre of prilling to9er foundation 9ith a '.m triangular

spacing. The proposed foundation 9as an annular raft.

!re and post compaction S!TJs and field lo9 tests on single as 9ell as on +

column group 9ere conducted. The load tests 9ere performed up to an intensity of +1.

tonFs*.m. and the resultant settlements at the test load 9ere 9ell 9ithin '5mm. block

vibration test carried out on stone columns gave significant improvement in the dynamic

properties of the subsoil.

=) CONCLU#ION4


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'& The above case studies and the e=perience gained in strengthening the foundation soil by

vibroflotation for more then '55 tanks and its application to other structures justify its use

both from technical as 9ell as economic considerations.

)& This type of techni*ue of improving is most suitable for cohesionless soils.

+& This method should be adopted because of its ease in operation than conventional impact

type hammer.

-& Tests such as Cone !enetration Test and Standard !enetration Test must be carried out

before and after the application of this techni*ue to check the standards.

1>) RE7ERENCE4

1) Ti*&s j$ra% ?s,r$?,i a &sig.

) G&,&?hi?a% &gi&&rig '" P$r$sh,ha*a Raj.

5) Traa%gar H$s& Cs,r$?,i Iia Li*i,&. (r*&r%" C&*iia

C*+a" Li*i,&).

/) I6si,$ &&+ si% i*+r-&*&, '" K"%& D R%%is

0) D&&+ ?*+a?,i gra$%ar si%s '" Dr@ K@ Rai&r Massars?h.

8) $ra% Iia #?i&," #i% M&?hai?s a 7$a,i

Egi&&rig.

9) BBB.g&r$*.?*
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Ground Improvement Technique-1

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