Vibro-Compaction Methods - Ground Improvement - Lecture Slides, Slides of Geology

Download Vibro-Compaction Methods - Ground Improvement - Lecture Slides and more Slides Geology in PDF only on Docsity!

GROUND

IMPROVEMENT

Vibro-compaction

methods

Compaction at selected locations using vibrations and vibratory equipment results in compaction to largedepths.•

The zone of compaction around a single float is a

function of type of float•

The success of in situ densification depends on grain size distribution of the in situ soils, and that of backfillsoil

Soils in zones

A

and

B

can be compacted by the deep

vibratory compaction method

vibro Compaction

(also

called “

vibroflotation

”), while soils of zones

C

and

D

cannot be compacted by vibration alone.Soils in zone

C

are often found on sites where

liquefaction due to earthquakes is of concern. Thesesoils can be compacted during the installation of

Stone

Columns

Soils in zone

D

are not compactable by vibration, but

can be substantially reinforced, stiffened and drainedby installing

Stone Columns

•Vibro floatation refers to compaction of soil using avibrofloat

in

horizontal

motion

from

the

vibrator

inserted into the ground. Utilization of a top piledriving vibrator in a vertical mode is less efficient.•Utilization of the concept of frequency of vibrofloatmatching that of natural frequency of in-situ soil isalso done in vibro-compaction (Eg: Miller Resonatecompaction technique).•Vibro-replacement uses the same equipment as invibro-compaction and uses water/air as the jettingmedium, and graded stone aggregate as backfill.



Applicable soils



Coarse grained soils with silt/clay content less than 10-15%



Effects



Increased shear strength, Increased stiffness, Reducedliquefaction potential



Common applications



Buildings, Chemical plants, Storage tanks & silos,Pipelines, Wharf structures, embankments, Roads



Both land / offshore applications



Maximum depth

60 m



Principle of Vibro Replacement The stone columns and intervening soil form an integratedfoundation support system having low compressibility andimproved load bearing capacity. In cohesive soils, excesspore water pressure is readily dissipated by the stonecolumns and for this reason, reduced settlements occur ata faster rate than is normally the case with cohesive soils.

STONE COLUMNS

In soft clayey materials they are useful. 

Vibro - compozer (Japan)



Vibro-floatation (vibro-replacement) (European)

0.4 -1.0 m layers are compacted 

Casing driving



Boring (very similar to procedures in sands)



Sometimes injection

mortar columns



0.6 -1.0 m diameter depending on the material (up to 20m)



crushed rock 20 - 75 mm popular



Square or triangular pattern,

1.5 -3.5m

spacing



They provide strength reinforcement to the soil.



Settlement



Stability



They act like vertical drains.



0.3 m blanket: drainage and structural stressdistributing layer.



Columns should extend to a firmer soil below.



Because of the relatively high modulus of the columns,a large proportion of the vertical load applied to theground surface is transferred to the columns. They aresimilar to pile foundations (but, pile caps & structuralconnections are not required).



a conservative approach is treating stone columns likepiles where as in a rational approach, loads aredistributed between soil & stone columns as a ratio(stress concentration factor, n) of vertical stress (

s

) in

the stone column and the vertical stress

c

in the soft

ground.

s c

n

 











c

s

s

c

s

c

a

n n

a

n

and the settlement reduction ratio is





s

c

a

n

)

1

(

1

1









assum

ı

ng the clay and the

columns settle equal amount



settlement of a stone column foundation depends on;



column spacing



soil strength

.

.

25

F

S

c

u

v





For an equilateral triangular pattern of granularpilesEquivalent diameter= D

e

=1.05S

For square pattern = D

e

= 1.13S