Chapter No 01 GT2 Final

8/13/2019 Chapter No 01 GT2 Final

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Compiled by: Prof.B.S.Chawhan M.Tech(Geo-Tech Engg) !""#.Profe""orCE$Go%ernmen#.Engineering College&a%eri-'*(+,,+*-Till da#e)

GE-TEC&/0C!1 E/G0/EE20/G-00

C&!PTE2-*3(*)

S4S425!CE E6P12!T0/

$efini#ion:

The selection of the type and depth of the foundation, the bearing capacity and settlement analysis and the determinations of the

earth pressures, all depend upon soil properties. The field and laboratory investigations required to obtain the necessary soil data for

design are called soil exploration.Soil exploration is not only needed for the design and construction of new structures but is also needed, sometimes for remedial

measures if a structure starts cracking due to settlement.

E7plora#ion Programme:

The objectives of an exploration programmed are:

. !etermination of the extent in the hori"ontal direction and thickness in the vertical direction of the earth type of soil up to the

required depth.

#. !etermination of the ground water table below the ground surface.$. %btaining of samples of ground water , soil and rock of a si"e and condition adequate for positive identification of the material.

&. 'ield observation and testing for evaluating the in(situ soil properties to substantiate the laboratory determinations.

). *n case the survey is meant for exploring the sounding of material, it is essential to collect data regarding cubic content of each

deposit.

Me#hod" of e7plora#ion:

There are many methods of sub(surface exploration. These methods can be classified into three categories:

. Semi(direct methods.

#. !irect methods.$. *ndirect methods.

. Semi(direct methods+

The semi(direct methods include all operations that involve drilling of bore(holes into the ground for purpose of taking out the

samples.

uger borings, displacement borings, wash borings, percussion drilling and continuous sampling all fall under the category of

semi(direct method.

*t must be understand at the stage itself that the -advance of bore(holes and -taking of the samples are two separate, through

interconnected processes.#. !irect method:

The direct methods include the digging of trench and trial pits. ccessible borings are also included in this category.

$. *ndirect method:

/eo(physical methods and soundings or probabings fall into the indirect method. Pha"e" in S8b-"oil E7plora#ion:

The subsoil exploration involves four distinct phases

. 'act finding and geology survey.

#. 0econnaissance exploration.

$. !etailed exploration.

&. Special exploration.. 'act finding and geology survey:

1efore the actual explorations at site are started, it is always advisible and beneficial to know the geological history of the area

from the geological reports and maps. Soil survey maps of the area are also sometimes available and they can help in providing

information about the soils that the engineer may encounter in the field.

The geological survey means subsurface exploration and sampling which will provide information regarding:

. !epth to ground water

#. 2ressure of ground water $. Sequence thickness, extent and approximate identification of encountered strata.

*t include i3 collection of samples of ground water, soil and rock in different quantity and conditions, for positive identification

and laboratory tests and ii3 making observations and for field tests to determine condition of samples and to estimate physical

properties of the subsoil.

4aluable information about the general(geologic character of a site may be obtained from maps and publications of central and

institutional geological surveys and from the central and state agencies connected with the construction and planning of highways,

buildings, dams and other large projects.

The 5entral water and 2ower commission, central 0oad research *nstitute and 5entral 1uilding research *nstitute 6500* and

510*3 are among the many sources of such information.

Compiled by: Prof.B.S.Chawhan M.Tech(Geo-Tech Engg) lec#8rer in CE$ST90T2/2-(+**'-++,*+,+**)GEC2aich8r(+;,*+,+**-,*,+*)

1




2

'ooting 1 'ooting

/.B

Stress due to p dC#($m

d minCD 2 " E2 eoF<.

dC#1

c. 6 c3.8ighway embankment

2 " b. Sand

eo p /.B /.B 8

6a3 5lay 7

!C1earing hard strata orC7E#

!C.) to #m

6e3. 8igh embankment like lavees, earth dams, etc. 6f3. 5oncrete dam

1ack slope

!C#($m6d3. 5ut

5ut level

!C1

!C To firm strata or <.A)(mC#8 6h3. Tunnel

6g3 0etaining wall.

5ig.+. $ep#h of e7plora#ory boring".

$. !etailed explorations.

The purpose of the detailed explorations is to obtain comprehensive soil profiles and representative soil samples of the important

deposits. This helps in lowering deposits of good construction materials. Sometimes undisturbed samples of the soil strata are also

taken during this phase and sent to the laboratory for testing. Test pits and trenches are usually dug, for shallow foundation. nyone

of the semi(direct methods can be used for these exploratings.&. Special explorations.

Special explorations are carried out to obtain undisturbed soil samples from the critical soil layers. The samples are usually

<cms in diameter. ccessible borings for visual inspection are drilled during this programme. 'ield tests, if any, required to beconducted are carried out during this phase of investigation.

2ower driven augers, wash borings, percussion and rotary drilling methods are employed to advance the bore holes.

2ore(water pressure is determined in the materials of low permeability and pie"ometer or hydrostatic pressure cells are

employed for this purpose.

5onsolidation characteristics of a clayey layer, unconfined or triaxial compression strength of a soil and direct or torsion testing

of a soil is done on the samples obtain during this phase of investigation.

Me#hod" of E7plora#ion:

a. Boring:

The semi(direct methods are the auger borings , displacement borings , wash borings , percussion drilling and continuous

sampling.

a. !8ger Boring":

Soil uger is device that helps in advancing a borehole into the ground.

1ore hole is advanced by hand or power operation auger with periodic removal of material. *n some cases continuous auger may

be used requiring only one removal. 5asing is generally not used with auger boring. The following figure shows both hand(operated

and power operated.

5ig. ;(a). Po"#-hole a8ger


3




5ig.;(b). Power dri%en or helical a8ger.

!pplica#ion":

. 8and driven augers are used in soft to stiff cohesive soils, in sandy silty soils above water table.

#. 7ith hand auger, depth is usually limited to ?m.

$. 2ower driven augers can be used to great depths, even to $<m and used in almost all types of soils above water table.

&. This method provides almost continuous disturbed samples.). 9ndisturbed samples can be obtained at required depths by using proper samplers.

b. <a"h boring:

The following figure shows a wash boring explorations. =

A

?

@

5

) &

<

$

/ B

#

#

$

&

)

?

(2ump,#(Sump for wash water and collation of wash samples,$(T(section for return,&(!rill rod,)(2artial drill rod,?(T(section of

water swivel,A(swivel,=(Single hook for multiple blocks for pulling of casing,@(>anila hoisting rope,<(;otor,(>ipple,#(

casing,$(casing coupling,&(!rill rod coupling,)(!rive shoe,?(!rill bit,A(Three or four(legged derrick standard pipe or timber.

5ig. .<a"h boring e7plora#ion

1ore hole is advanced by chopping, twisting action of a light chopping bit and jetting action of a drilling fluid, usually water, under pressure, changes in soil strata are indicated by changes in the rate of progress of boring, examination of out coming slurry andcuttings in the slurry, casing are used whenever necessary to prevent cave(ins.

!pplica#ion":

. 7ash boring can be used in all types of soil except these containing boulders.

#. This can be used great depths, adopted easily at inaccessible locations.

$. 9ndisturbed samples whenever needed can be obtained by use of proper samplers.

&. Samples obtained are in highly disturbed and slurry form.

c. $i"placemen# Boring:

This is the simplest method of boring. 9se is made of the slit, cap or piston samplers.The operation involves+


4




. !riving of a closed sampler into the soil until the desired depth is reached.

#. 0otation of the sampler or release or withdrawal of the piston and

$. Taking the sample.

fter the withdrawal of the and removal of the sample, the sampler is again inserted into the bore hole and is forced down to the

depth where a new sample is desired.

!pplica#ion":

. This method is suitable for loose to medium cohesion less soils.

#. Soft to stiff cohesive soils.

$. *t is used for both reconnaissance as well as for detailed boring programme.d. Perc8""ion $rilling:

1ore hole is advanced by chopping action of heavy bit driven by power. 7ater is added at the bottom of bore hole during

chopping action, if the ground water is not already struck, Slurry formed at bottom of bore hole is removed by bailer or sand pump.

5asing is generally required.

5hanges in strata are predicted from the rate of progress of boring and examination of slurry bailed out.

!pplica#ion:

. *t can be used in all types including soils containing boulders.#. *t can be used for great depth.

$. 9se is limited because of difficulty in determining strata changes as chopping action can cause considerable disturbance and

because of high cost.

&. ;ay be used in combination with auger or wash borings when boulders are encountered.

). 9ndisturbed samples whenever needed can be obtained by use of proper samplers.

e. 2o#ary $rilling:

)

?

&

$

A

=

@#

<

#

$

&

(1ase plate,#(8oisting drum,$(Gelly,&(water swivel,)(cable,?(Bower most,A(Stand pipe,=(8ose,@(;ain mud pit,<(Setling pit,( 0eturn flow ditch,#(5asing,$(!rill cutter,&(!rilling bit.

5ig.'. Schema#ic "e#8p of a ro#ary drilling.

1ore hole is advanced by proper rotation of drilling bit and removal of cutting by circulating fluids which maybe water , bentonite

slurry or mud slurry.

7henever rock or boulders are encountered suitable bits vi", diamond studied bits with shots are to be use for drilling. 5asing

may or may not be needed during drilling. 5hanges in strata are indicated by change in rate of advancing of bore hole, action of

drilling tools, and examination of cuttings in drilling fluid.

!pplica#ion:


5




. *t can be used in all types of soils and rocks, can be used great depths.

#. 1eing increasingly used because of fast rate of progress in all soil types, but difficult to use at inaccessible locations because of

heavy machinery.

$. 9ndisturbed samples can be obtained at desired depths by using suitable samplers.

&. The bore(holes in this drilling range from <cms diameters.

). *t is uneconomical for holes of less than <cms diameter. f. Con#in8o8" Sampling:

*n this technique, the boring is accomplished entirely by sampling. *n exploration of rocks, core drilling is done for obtaining the

rock samples continuously. *n the soil too, when core barrels and piston samplers are used continuously to obtain the soil samples,the boring proceeds side by side.

!pplica#ion":

. *t is used extensively in detailed and special foundation explorations for important structures.

#. *t provides a more reliable and detailed information on soil conditions than any other method.

S#abili=a#ion of Bore &ole":

The problem of preventing caving of the sides and bottom of a hole and to avoid disturbance of the soil to be sampled is common

to all boring methods.9ncased, dry(bore holes are generally stable when they are shallow and above the ground water table, but danger of

caving increases rapidly with depth and the presence of free ground water. *n firm cohesive soils the hole may remain open for a

limited(length of time. 1ore(hole without any provisions for stabili"ation and extending below ground water level are often piston

samplers.

They are a number of methods for stabili"ation the bore(holes.

. Stabilisation with water.

#. Stabilisation with drilling fluid.

$. Stabilisation with 5asing.&. Stabilisation by free"ing.

). Stabilisation by /routing.

. S#abili"a#ion wi#h wa#er:

Suitable in rock and often in stiff cohesive soils. 7ater alone is not suitable or preventing caving of borings in soft or

cohesionless soils.

#. Stabilsation with drilling fluid:

n uncased bore(hole can be stabili"ed by filling it with a proportioned drilling fluid or mud, which when circulated also serves

to remove the churne(up soil from the bottom of the hole. !rilling fluid: satisfactory drilling fluid can be obtained by mixing locally available clays with water but it is often

advantageous and necessary to add commercially prepared products such as vol(clay or quaver. These commercial clay products

consists of highly colloidal, gel forming, thixotropic clays primarily bentonite with certain chemicals added to control dispersion

thixotropy, gel strength and viscosity.The stabili"ation effect of drilling fluid is caused part by its higher specific gravity compared to water and partly by the formation

of relatively impervious lining or mud coke on the sides of a bore hole.

$. Stabilisation with 5asing:

5asing or the lining of the bore hole with steel pipe provide the safest through relatively expensive method of stabili"ation of the

bore(hole. !ifferent types of casing are available.

&. Stabilisation by free"ing: bore(hole may be stabili"ed by free"ing the soil around it as the boring progress. This may be accomplished by replacing water

with kerosene or brine cooled by means of Hdry iceI. This method cannot be used when the ground is dry or nearly so and when there

is a strong water flow. So for it has been used for experimental purposes.

). Stabilisation by /routing:

bore(hole passing through "ones in rock cavities, faults and broken rock etc may be stabili"ed by filling the lower part of the

hole with cement grout and then re(boring the concrete plug.

Typical Boring 1og: boring log is a diagrammatic report on a bore hole. *t should be carefully written and should provide the following

information.

. *dentification of the job.

#. >umber of boring on the plan 6hori"ontal control3.

$. /round elevation of boring 6vertical control3.

&. !etailed information regarding the type of the soil available at various depths. This is written as per visual examination.

). /round water information.

?. Strength test values, if any tests are conducted in the field. These values must be shown on the boring log at the relevant

elevations at which the tests are conducted. 6The tests usually conducted in the field are the unconfined compression test, the vane shear test and the standard penetration test3.


6




The following figure shows a data field in a boring log.

/B > values wn B.B 2.* qu6tEm# 3

2roperty line 5lay fill grey coloured .<m

<m #m 7.T

1.8 .)m & ##J ))J #< &.@

1.1.0oad /rey sandy silt with little

&m clay

&m 1.8# $m ? #$.)J )=J #< ).<

&<m#m #m $.)m

1.8$ &.)m #)

1.8& ;ain 0oad ;edium dense fine sand

#m >

?.<m ?m $<

$<m

'oot path

5ig. >.(a). Si#e plan of boring for a ban? b8ilding. 5ig.> (b). Boring log of a bore hole wi#h / and labora#ory re"8l#".

The type foundation to be used for the various portions of the structure, the depth of foundation to be provided, the allowable

pressure to be used in designing the member and the expected settlement should be state unambiguously.

So8nding Te"#":

*n this method some sounding device like split spoon sampler, a cone or a rod is formed, statically or dynamically, into the soil.The energy consumed in penetration into soil is indication of consistency of soil.

Standard penetration test, dynamic cone penetration test and static cone penetration test are commonly adopted standard tests. !pplica#ion":

. This method can be in any type of soil and to any depth.#. !epth by static cone penetration is limited by the capacity of equipment.

$. 2resently $tonne and <tonne machine are in use.

&. Standard penetration test is done in a bore hole.

). Sounding methods are generally faster and cheaper than boring.

!. $ynamic So8nding.

7hen the probe is advanced with the help of dynamic load like a falling weight it is called dynamic sounding. B. S#a#ic So8nding.

*f the probe is subjected to a dead weight or hydraulic pressure and its penetration is measured, it is called static.

C. S#andard Pene#ra#ion Te"#(SPT):

This is most widely used sounding method. The S2T test is used extensively in soil exploration programmes.

The test consists of driving a standard split spoon sampler and S2T test equipments.

The test consists of driving a standard split spoon, )<.=mm outside diameter and $)mm inside diameter, into soil under the blows

of a drop weight 6hammer3 of ?)kg falling freely through A)cm.The number of blows required for $<cm of penetration of sampler in the soil is designated as > values and is termed as standard

penetration blow count.

ttempt has been made to correlate >(values to density of cohesionless soils and unconfined compressive strength of cohesive

soils. ttempt has also been made to correlate compressibility of soils to >(values. Such relations are utili"ed in arriving at allowable

bearing pressure of soil. Such approaches can be and are subjects of criticism. 1ut past experiences indicate that standard

penetration test can provide reliable and safe design criteria when used with caution keeping in mind the limitations of the test and its

application.

Correla#ion" #o mea"8red %al8e" of SPT:

The >(values of S2T as measured in field may to be correlated. There are two types of corrections generally applied to measured >(4alue.


7




. Type of correction is applied when S2T is conducted in fine or silty, saturated sand and when the recorded blow count is grater

than )6>K)3.

This correction as recommended by Ter"aghiIs and 2eck6@?A3 is as follows+

>C)LE#6> * ()3(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((63

7here, > and > * are corrected and actual blow counts respectively.

Tripod

A)cm drop

).)kg pin guided drive weight or hammer.

!rive head

0ods

/ B

5asing

5oupling

!rive shoe

0ods

).cm split barrel sample spoon being driven ahead

of casing into undisturbed soil 'or standard penetration resistance measurement sample spoon is driven $<cm

5ig.3(a). S#andard Pene#ra#ion Te"# e@8ipmen#.

Tool steel drive shoe

Thread for wash pipe 'lat for wranch #cm

'lat for wranch

=cm )).)cm A.)cm=cm

5ig.3 (b). S#andard Spli#-Spoon Sampler

#. The other type of correction is known as correction for overburden pressure. This correction is applied only to cohesionless soils

6dry, moist or wet3. The correction is suggested by /ibbs and 8olt" 6@)A3 and as widely is as follows+

7

35

+

′=

σ

> > , for

2

0 /28 mt ≤σ (((((68ere 0

σ is in tEm# 3 (((((((((((((((((((((((((6#3

69

345

+

′=

σ

> > , for

2

0 /276 mk> ≤σ (((((68ere 0

σ is in k>Em# 3 (((((((((((((((6$3

7here, > and > * are corrected and measured blow counts respectively and 0σ is the effective overburden pressure at the depth of

S2T.

*t is considered advisible to place an upper limit of # for overburden correction with this limit, equation 6#3 and 6$3 becomes,

> >

> ′≤+

′= 2

7

35

σ

, for2

0 /28 mt ≤σ (((((68ere 0

σ is in tEm# 3(((((((((((((((((6&3


8




> >

> 2

69

345≤

+

′=σ

, for2

0 /276 mk> ≤σ (((((68ere 0

σ is in k>Em# 3 ((((((6)3

The overburden correction is gradually presented in eqn63 M6#3M6$3 for the following respective two cases,. 7ater table at great depth greater than ?.)m below ground level with assumed density of soil as .AtEm$ 6?.Ak>Em$ 3.

#. 7ater table at ground level and assumed submerged density of soil as .<tEm$ 6@.=k>Em$ 3.

/ of SPT and Con"i"#ency of "oil:

5onsistency of a soil granular soil is indicated by its relative density and that of a cohesive soil by its unconfined compression

strength.Table( represents empirical relationships currently in use in obtaining relative density of cohesionless soils from > values of

S2T. 'rom > values angle of internal friction, N of soil can be obtained from table(.

Table(. mpirical values of N, !r and unit weight of granular soils based on the S2T with correction for saturation effect and for overburden, if any

!escription 4ery Boose Boose ;edium !ense 4ery dense

0elative density,!r 6J3 <

)

$

)

?

)

=) <<

S2 blow count, >

<&

<

$

<

)<

pproximate angle of internal friction, N #)<($<< #A <($#< $<<($)< $)<(&<< $=<(&$<

pproximate range of moist unit weight, tEm$ .(.? .&)(.=) .A)(#.< .A)(

#.#)

#.(#.&<

O!r Cemax(e emax(emin

Geophy"ical E7plora#ion:

!. Elec#rical 2e"i"#i%i#y Me#hod:

The following figure shows the electrical resistivity method setup.

;illimeter

2otential electrode

2otential electrode

5urrent electrode 5urrent electrode

5 ! 1

r r # r $ r &

5ig. . Elec#rical 2e"i"#i%i#y mea"8remen# "e#8p.

0esistivity is a fundamental property of a material and is defined as the resistance in ohms , between opposite faces of a unit cube

of that material.

*f 0 is the resistance of a block of length B and of cross(section area , then the resistivity

B

, 0= ρ ((((((((((((((((((((((((((((((((((((((63

The conductance of a material is the reciprocal of its resistance. 'ro the above figure, the potential at 5 and ! resulting from the

current flow will be:

−=

21

11

2 r r

* 4

c

π

ρ ((((((((((((((((((((((((6#3

−=

43

11

2 r r

* 4

d

π

ρ (((((((((((((((((((((((6$3

The potential difference measured by a voltmeter connected across 5 and ! will be:


9




−−

−==−

4321

1111

2 r r r r

* 4 4 4 cd d c

π

ρ

8ence,

−−

−

=

4321

1111

12

r r r r

*

4 cd π ρ (((((((((((((6&3

This is the fundamental equation of resistivity method and gives the resistivity in terms of measurable quantities. *f the electrodes are placed at equal distances,

i.e.,22

32

41

r r r r === , then equation 6&3 reduces to

1.2 r 0π ρ =

7here, *

4 0

cd = (((((((((((((((((((((((((((((((((((((((((((((((((6)3

7here, 0 is measured in P and r in cm+ therefore the units of resistivity Q is Pcm. The value of 0 equals the voltage measured

between the central electrodes divided by current * measured by an ammeter.

Some resistivity values of various soils are shown in below table+

Type of ;aterial ρ 6P(cm3

7et to moist clayey soils )<($<<

7et to moist silty clay and silty soils $<<(&)<

;oist to dry silty and sandy soils )<<()<<<

7ell fractured to slightly fractured bed rock with moist soil(filled cracks. )<<<($<<<<

Sand and gravel with silt $<<<<

Slightly fractured bedrock with dry soil filled cracks, sand and gravel with layer of silt. $<<<<(#&<<<<

;assive bed rock and hard rock+ 5oarse dry sand gravel deposit. K#&<<<<

!d%an#age" $i"ad%an#age"

. The method is very rapid and economical for large projects

where only average conditions are required.

. This method is that it is capable of only detecting strata

having quite different properties, i.e., rock and water table.

#. *t is good for depths upto $<m and instrumentation is

simple.

$. *t provides no simple for definite identification and therefore

should always be supplemented by borings.

&. *t needs a specialist for proper interpretation of results as

the results are known to be influenced by surface irregularities.

B. Sei"mic 2efrac#ion Me#hod:

The following figure shows the seismic refraction waves+

/eophones 5onnected to automatic time recorder with multiple channel

Shot point B B# B$ B&

/.B !

Boose, dry top soil

8 4

8 # 1 5 5lay, compacted soil weathered rock

4 #

;assive sound rock 5ig. A(a). ne "ho# poin# wi#h m8l#iple geophone me#hod.


10




/eophone

2egs or shot point

8ammer

B B# B$ B& B)

/.B

Boose, dry top soil

8

8 # 5lay, compacted soil weathered rock

;assive sound rock

5ig.b. ne geophone wi#h m8l#iple "ho# poin# me#hod.

5ig.A. Sei"mic refrac#ion me#hod of "#ra#igraphic e7plora#ion a# a loca#ion.

T

T $T R

T #

T T

B

B BLB# BLB#LB$

5ig.A(c). Plo# of "ei"mic refrac#ion me#hod of e7plora#ion da#a.

*t was mentioned earlier that in the seismic method the difference in elastic properties of various soil soil types and rocks are used

for their identification. The velocity of propagation of a wave or impulse in an elastic body is known to be a function of /, the shear

modulus, and , the unit weight of the material.

n impulse will produce three types of waves, in soil media.

. Surface or 0ayleigh wave

#. Shear or transverse wave

$. Bongitudinal or compression wave.The velocities of these waves are related to properties of transmitting medium by the following equation+

5.0

=

ρ

/4 s (((((((((((((((((((((((((((((((((((((((((63

+=

5.0

3

41 / G 4 p

ρ (((((((((((((((((((((((((6#3

7here,

4 sCvelocity of shear wave.

4 pCvelocity of compression wave


11




/Cshear modulus of material

GCbulk modulus of material

QCbulk mass density of materialCEg

Cbulk density of material

gCacceleration due to gravity

from eqn 63 and 6#3 it is clear that 4 p is greater than 4 s. 'igure #6a3 M 6b3 shows a typical soil formation with the direction of waves. The exploration by seismic refraction method is

generally conducted in one of the two ways+

. ;ultiple geophone with multiple shot point fig.#6b3, and#. %ne geophone with multiple shot point fig.#6b3.

*n one shot point, as soon as the charge goes off the recorder starts recording the time 6tC<3 and records the time taken for the

first arrival of the wave at various geophone. time(distance record 6B in T , BLB# in T # , etc3 is made from recording of time starts

when the hammer strikes the first peg at B and the recorder reads, the time taken for the first arrival of the wave at the geophone.

>ext, time is recorded from when the hammer strikes the peg at6BL B# 3 distance from the geophone till the first arrival of the wave

at the geophone and the process is repeated for all the pegs. This also produces a time(distance record like the previous method.

'rom fig#6a3 and 6b3, it is easy to visuali"e that the waves will travel either through the top layer along ! or partly through thetop layer and partly through the second layer 615!3.

*n the latter, the path length is more than that in the former but the velocity of travel in 15 is higher. Therefore, the thickness of

the top layer and the velocities in the layers will influence the arrival time by the two routes. The time distance plot gives the velocity

of wave prorogation through the strata and also the thickness of strata.

*n both the methods, B is usually kept quite small 6about $m3, so that B and T will give the velocity in the top layer. 7ith the

velocity of top layer known, it can be seen whether the BLB# and T # data shows the first arrival is through second layer. This also

becomes evident when time(distance data is plotted fig@$3. The velocity 4 # and thickness 8 can be obtained from the time distance

data.

1

1

T

B4 = (((((((((((((((((((((((((((((((((((((((63

*f( )

1

21

24

B BT

+= then the wave travelled through top soil and reached as first arrival, otherwise it travelled partly through top

layer and partly through the second. >ext, from fig6$3, the third point 6BLB#LB$ ,T $ 3 does not lie on the same straight line indicating that the velocity of propogation is

different from 4 .

Therefore,

2

321

1

1

3

2

4

B B B

4

8

T

++

+= ((((((((((((((((6#3

ly **

2

4321

1

1

4

2

4

B B B B

4

8 T

++++= ((((((((6$3

%r2

4

344

BT T =−

%r34

4

2T T

B4

−= ((((((((((((((((((((((((((((((((((6&3

Substituting the values of 4 # in equation 6#3,

2

* 1

2

321

31

4

4

B B BT 8

++−= (((((((6)3

'rom figure6&3, the first intersection is at U and it means that a wave travelling by ! route and 15! route would be take the same

time to reach a point at a distance of U from the shot point. *n another wards,

21

1

1

1 2

4

U

4

8

4

U +=

2*

2

12

1

U

4

4 4 8

−=∴ ((((((((((((((((((((((((6?3


12




Meri#" $emeri#"

. *t can be used for exploring up to a depth of $<<m . *t is more sophisticated instruments and an expert for accurate

interpretation and programming the exploration work.

#. The seismic velocity of successively deeper subsurfacelayers increases with depth below ground surface.

#. *t cannot detect an area having a layer with high velocity ofwave prorogation over a layer with low velocity of wave

prorogation.

The following are the range of velocities of seismic waves in materials at shallow depths.Type of "oil eloci#y of wa%e propoga#ion(m,")

. Top soil and sand #<<($?<

#. Boose and dry soil )<(<<<

$. Sandy clay &<<(?<<

&. /ravel &=<(A=<

). /lacial till )&<(#<<

?. 7ater saturated loose soil $=<(=<<

A. 5lay and wet soils A)<(@)<

=. 5oarse and compacted soil @<<(#))<

@. Sandstone and cemented soils @<<(&#<<

<. Shale(marl =<<()<<

. Bime stone(chalk =<<(?$<<

#. ;etamorphic and 4olcanic rocks $<<<(??<<$. Sound plutonic rocks $<<<(A)<<

&. Vointed granite #&<<(&)<<

). 7eathered rocks ?<<($<<<

Type" of Sample":

Soil samples are of two types+

. !isturbed samples

#. 9n(disturbed samples

. a. 0epresentative samples

b. >on(representative samples.

. $i"#8rbed "ample":

The properties of the soil depend to a large extent on the structural configuration of the soil particles in the natural state. This is

specially true in the case of cohesive soils. *f a sample during the process of sampling gets disturbed, the sample is designated as a

disturbed sample.a. 0epresentative sample:

*n case soil sample brought to the surface from some depth retains all the constituents present in the soil in its natural state at

that particular depth from which it is taken, the sample is designated as a representative sample.

b. >on(representative sample:

*n case some constituents of the soil are lost during the process of sampling or if some constituents of the soil other layers get

mixed up with the sample from a particular depth, the sample may be designated as non(representative.

The representative samples of a soil are suitable for classification and chemical tests , but the non(representative samples only

give an indication of the major stratifications of the soil.

+. $i"#8rbed "ample:

sample of soil which retains the natural soil structure after sampling is called an undisturbed sample. This type of

sampling is used for more precise tests like the shear strength or the consolidation test.

Sampler": (Type" of Sampler"):

!. Spli# "poon Sampler B. Thin-<alled Sampler"

5. Pi"#on "ampler" 5utting edge

a. &ydra8lically pera#ed Pi"#on "ampler Split tube Thin tube opens along this line

b. Bi"hop "ampler. $II #&II . Spli# Spoon "ampler: 8ead 6top3

#< .)II


13




5ig.*. Spli# Spoon Sampler.

split spoon sampler consists of a thick walled steel tube split lengthwise. *t carries a cutting edge called a cutting shoe at the

low end and a head at the upper end. The maker of the sampler currently available in the market have an outer diameter ranging from

#inches to &.)inches and the internal diameter ranging from .)inches to &inches. The overall length in all cases is #&inches. The

*ndian Standard recommends a si"e, outer diameter )<.=mm, and inner diameter $)mm. The sampler is lowered into the bottom of the

borehole with the help of drilling rods and is driven into the soil with hammer blows. fter penetration to full depth, it is pulled out.The cutting shoe and the head are removed and the soil is examined visually. Then it can be bottled and sealed for shipment to the

laboratory for further examination.

split spoon sampler is used in the standard penetration test is conducted. 2roperties of cohesive soils are obtained from theundisturbed samples and for sampling thin(walled tubes popularly known as Shelby tubes are used.

1. Thin-<alled T8be "ampler": Bength as specified method

;ounting hole <mm min dia

#mm ;in Thickness as specified

5ig.. Thin-<alled T8be Sampler.

thin(walled tube sampler is a seamless tube with very thin walls. The *ndian Standard *nstitution recommends that the tubes

shell be &<mm to #)mm in outside diameter and should be made of steel, brass or aluminum. The si"es and wall thickness asrecommended by *S* of these tubes are given below,

Table(. Sampling tube dimensions.

%utside diameter in mm &< )< )) ?

)

A) #)

7all thickness in mm #.) #.

)

#.

)

A

A $.

)

The length of tubes shall be <times the diameter for sampling in sandy soils and it shall be <()times the diameter for sampling

in clays, subject to a maximum of ?<cms.The lower end of the tube is sharpened to form a cutting edge. %ne typical tube is shown in above figure.

The tube can be fitted to a head attached to a drilling rod. Static force is applied to push the tube in the bottom of the bore hole

dug to the required depth.

C. Pi"#on Sampler":Sometimes it happens that the soil tends to drop out from the sampler while being withdrawn. *n such cases piston samplers are

available in the market. !r.%sterbarg developed a piston sampler whose principle is explained in below figure, and this is the most

advantageous amongst all the piston samplers.

!rill rod

Sampler head

2ressure cylinder

8ollow rod

'ixed piston

5ig. +."#erberg" Pi"#on Sampler.

*f a pit has been dug to the level where a sample is needed, a cake of the soil can be cut with a spatula and sealed on all sides.This probably is the best method of sampling but expensive.


14




Sample $i"#8rbance:

Some sample disturbance by any one of the sampling techniques 6!isturbed sample, undisturbed sample, representative samples

or non(representative samples3 however sophisticated they may be, usually occurs. s for as the sampling by the use of the tube

samplers is connected the area ratio is an index to the sample disturbance.

rea ratio is defined as+

100*2

22

i

ie

r

!

! ! ,

−

= ((((((((((((((((((((((((((((((((63

7here, !eCexternal diameter of the sampling tube.

!iCinternal diameter of the sampling tube and it represents approximately the ratio between the volume of displaced soil and the

volume of the sample. *f this ratio is W<J, the disturbance is considered negligible. The area ratio of the split spoon sampler is

approximately $<J and hence a sample obtained is a disturbed sample. The ratios for the sampling tubes mentioned in above table(

are less than <J and hence a sample obtained with these tubes is an undisturbed sample. !rea ra#io (!r ) 2eco%ery 2a#io (2r ) Clearance 2a#io (C r ):

!rea 2a#io(!r ):

!c !i !<

5utting edge or !rive shoe

!< !c D#<< !i

7here,

!oC%utside diameter of sampling tube, !iCinside diameter of sampling tube, !cCinside diameter of cutting edge.

!cW!iW!o.

rea ratio, 100*2

22

i

ie

r

!

! ! ,

−

= ((((((((((((((((((((((((((6#3

*nside 5learance ratio, 100*c

cicr

!

! ! * −= (((((((((((((((((((((((((((((6$3

%utside clearance ratio, 100*

c

co

r

!

! !%

−= (((((((((((((((((((((((((((6&3

. rea ratio for undisturbed samples obtaining is maximum permissible area ratio is #J for )<mm diameter samplers, )J for

A)mm diameter samplers and #<J for <<mm diameter samplers.

#. *nside clearance ratio for undisturbed samples obtaining should be between <.) to $J for different types of samplers. Bow value

of clearance ratio is recommended for sampling in sands while clearance ratio upto $J may be needed in obtaining good sample

recovery in certain clays.Table(#. *nside 5learance ratio for Samples for undisturbed sampling.

Sl.>

o

*nside 5learance ratio of sampler Soil Type

bout <.)J Sands, silts and soft clays# bout .)J Stiff and hard clays below ground water level

$ bout $J Stiff expensive clays below ground water level

2eco%ery ra#io(2r ):

The practical requirement to be satisfied by a sample for accepting it is an undisturbed sample is given by recovery ratio. The

overall condition of a soil sample taken in a tube is represented by the total recovery ratio is defined as+

Total recovery ratioCBength of the sample before withdrawalE2enetration of sampler below the bottom of the bore hole.CBE8O<<

/ross recovery ratioC!istance from the top of the sample to the cutting edgeE2enetration of sampler below the bottom of the bore

holeCB s E8

The gross recovery ratio should be used in computing the recovery ratio for soil sample.

The net recover ratioC>et length of the sampleE2enetration of sampler below the bottom of the bore holeCBn E8 Compiled by: Prof.B.S.Chawhan M.Tech(Geo-Tech Engg) lec#8rer in CE$ST90T2/2-(+**'-++,*+,+**)GEC2aich8r(+;,*+,+**-,*,+*)

15




*t is generally used as a measure of the condition of the recover section in core boring operation * rock.

0ocks are described according to 0.X.! 60ock Xuality !esignation3 as follows+

0.X.! <(#) #)()< )<(A) A)(@< @<(<<

!escription

4ery poor 2oor 'air /ood xcellent

. The following "i=e" of "ampling #8be" are a%ailable in #he mar?e#:

.$ in mm 3' * '*

0.$ in mm 3+ *3 ;'

1eng#h in mm >** >** >**8# of #he"e which one" wo8ld yo8 "elec# for ob#aining 8ndi"#8rbed "oil "ample" from a bore hole.

Solution+ /iven data:

a.

%.! in mm A) < )<

*.! in mm A# <A $)

Bength in mm ?<< ?<< ?<<

To find: a. 7hich one would you selectY.

2rocedure:

. rea ratio, %5.8100*

72

7275100*

2

22

2

22

=

−

=

−

=

i

ie

r

!

! ! ,

#. rea ratio, %69.5100*107

107110100*

2

22

2

22

=

−

=

−

=

i

ie

r

!

! ! ,

$. rea ratio, %10.104100*35

3550100*

2

22

2

22

=

−

=

−

=

i

ie

r

!

! ! ,

Commen#: Samplers with si"es %.!C<mm. *.!C<Amm, and %.!CA)mm,*.!CA#mm have area ratio less than <J. Therefore, any

one of them may be used.

>ormally boreholes are of diameter <<mm and hence a sampler with %.!.<mm will require holes of larger diameter. 8ence

from the point of view of economy, sampler with %.!CA)mm is preferred.

98ne-98ly,+*A;,98ly,+**;

+. $e#ermine #he area ra#io" of #he "ampler of #he following da#a and commen# on #he %al8e".

i Spli# "poon "ampler $oF'*mm $i F;'mm

ii. $ri%e #8be $*F**mm $i FA*mm

iii. Shelby #8be $oF'*mm $i F3mm.

where

$oF8#"ide diame#er of "ampling #8be $i F0n#ernal diame#er of "ampling #8be.

Solution: /iven !ata:

a. Split spoon sampler, !oC)<mm, !iC$)mm

b. ii. !rive tube !<C<<mm, !iC@<mm

c. iii. Shelby tube !oC)<mm, !iC&Amm.

To find: a. r CY. 2rocedure:

. rea ratio for Split spoon sampler, %10.104100*35

3550100*2

22

2

22

=

−

=

−

=

i

ie

r

!

! ! ,

#. rea ratio for !rive tube, %46.23100*90

90100100*

2

22

2

22

=

−

=

−

=

i

ie

r

!

! ! ,

$. rea ratio for Shelby tube, %17.13100*47

4750100*

2

22

2

22

=

−

=

−

=

i

ie

r

!

! ! ,


16




Commen#: rea ratio as per as possible it should be W<J. 1ut here K<J and nearly it should be consider $.AJ is used for

undisturbed samples M !oC)<mm and !iC&Amm is used as Shelby tube.

May,98ne-+**

;. ! "ampling #8be ha" inner diame#er 3*mm and #ha# of a c8##ing edge i" e@8al #o >mm. Their o8#er diame#er" are 3+ and

3mm re"pec#i%ely. $e#ermine #he in"ide clearance o8#"ide clearance and area ra#io of #he "ampler. Thi" #8be i" p8"hed a# #he

bo##om of a borehole #o a di"#ance of ''*mm and leng#h of "ample co%ered i" ';*mm. 5ind #he reco%ery ra#io.

Solution: /iven data:

a. !csC!icCA<mm, b.!cC!icC!iC?=mm, c. !eCA#mm, d. !eC!oCA&mm, e. distanceC))<mm, f. BC)$<mm.

To find: a. r CY, b.* cCY, %cCY. 2rocedure:

. rea ratio, %425.18100*68

6874100*

2

22

2

22

=

−

=

−

=

i

ie

r

!

! ! ,

#. *nside 5learance ratio, %94117.2100*68

6870100* =

−=

−=

c

ci

cr

!

! ! *

$. %utside clearance ratio, %77.2100*72

7274100* =

−=

−=

c

co

r

!

! !%

&. The recovery ratioCBength of the sample before withdrawalE2enetration of sampler below the bottom of the bore hole.CBE8O<< 0r C)$<E))<O<<C@?.$?$?J

98ly,+**3 '. Gi%en #he following da#a from "ei"mic refrac#ion #e"# plo# #ime %er"8" di"#ance and comp8#e wa%e %eloci#ie" + ; and

#hic?ne""e" of 0 and 00 layer".

$F;*m T F*.*"ec

$+FA*m T +F*.'"ec

$;F+*m T ;F*.+*"ec

Solution: /iven data:a. !C$<m T C<.<sec

b. !#C@<m T #C<.)sec

c. !$C#<m T $C<.#<sec

To find: a. 4 ,4 # ,4 $ and thicknesses of * and ** layers.

2rocedure:

. 2lot time versus distance graph i.e., !istance6meters3 along U(axis and Time6sec3 along Z(axis+

T $

T #Time 6sec3 t # T t

< ! !# !$

!istance in mts

#. 'rom plot, t C<.<A)sec, t #C<.)sec.

$. 4elocity of wave in * layer, 4 +

sm

T

!4 /300

1.0

30

1

1

1 ===

&. 4elocity of wave in ** layer,4 #+

smT T

! !4 /1200

1.015.0

3090

12

12

2 =

−−

=−−

=

). 4elocity of wave in ** layer,4 $+

smT T

! !4 /2400

15.020.0

90210

23

23

3 =

−−

=−−

=


17




?.

0

2

1

47.14

25.01200

300sin

=∴

===

α

α 4

4

A.0

3

2

30

50.02400

1200sin

=∴

===

β

β 4

4

=. Thickness of * layer is given by the following equation+

mt 4

D 62.1147.14cos*2

075.0*300

cos2

11

1 ===

α

@. Thickness of ** layer is given by the following equation+

<.( ) ( )

mt t 4

D 72.2730cos*2

075.0115.0*1200

cos2

122

2 =

−=

−=

β

98ne,98ly-+*

>. $e#ermine #he area ra#io for #he following de#ail" and "#a#e #he #ype of "ampler. 8#er dia of c8##ing edge i" 3'mm wall

#hic?ne"" i" .3mm.


18




G $-14C


19

Chapter No 01 GT2 Final

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Transcript of Chapter No 01 GT2 Final