soil investigation methods

8/18/2019 Soil Investigation Methods

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Soil investigation methods

Semi direct methods


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TECHNIQUES FOR LABORATORY INVESTIATIONS OF SOIL

AN! ROC" SA#$LES


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A%ge& Bo&ingSuitable soil strata

• Soft soil- Up to depth of 3 to 6 m

• Clays (Soils which can stay open without casing or

drilling mud)

• Silts• Partially saturated sands

• Sandy soils with the help of casing


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A. Screw/Worm Auger-gravelly or stony soils

B. Barrel Auger

C. Sampling Tube

. utch mud Auger!. "eat Auger


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Sam'ling () a Hand A%ge&


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Procedure

• Hand Auger Up to 3 ! 6 m

• "echanical Auger Up to #$ m%

• &lade of length '%3 - '% m is chosen

• otated until it is full of soil

• *ithdrawn to remo+e the soil to note the soil types at

+arious depths• epeat the process till , ! #' m as it gets difficult to

go after it


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Advantages Limitations

• Useful or Su.surface /n+estigations

of Highway0 ailways And Air ields

• 12plorations one apidly And

1conomically

• Simple0 4ight0 le2i.le0 /ne2pensi+e

/nstruments

• ifficult for hard soil and soil containing

5ra+els

• Used up to 6 m ("anually) #$m

("echanically)

• or sandy soil this method is slow and

expensive

• ot suita.le for - large cobbles,

boulders or other o.struction which

pre+ents drilling of the hole%


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A%ge& *ith Shell (o&ing

• Casing is provided in case o# wea$ strata

• %irst the casing is driven and then the auger

• Boring rig is used #or power driving &hand rig#or depth up to '( m)

• So#t roc$s are bro$en using chisel bits

• Sand pumps are used in the case o# sandy soils.


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Advantages Limitations

• "a7ing deep .ore

• Useful when depth of e2ploration

is small

• /n+estigations are done 8uite

rapidly and economically .y

auger .oring

• Used up to $ m ("anually) 'm

("echanically)

• Auger .oring is that the soil

sample are highly distur.ed

• /ts .ecome difficult to locate the

e2act changes in the soil strata


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+ash Bo&ing• *ere #irst an open hole is #ormed on the ground so

that the soil sampling or roc$ drilling operation

can be done below the hole.• The hole is advanced by chopping and twistingaction o# the light bit.

• Cutting is done by #orced water and water +et

under pressure through the rods operated insidethe hole.

• a pipe o# (cm diameter is held vertically and #illed with water using hori,ontal lever arrangement and


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• by the process o# suction and application o#pressure soil slurry comes out o# the tube andpipe goes down.

• This can be done up to a depth o# m 01m

&e2cluding the depth o# hole already #ormed be#orehand)

• 3ust by noting the change o# colour o# soilcoming out with the change o# soil character can

be identi#ied by any e2perienced person.


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Advantage Limitations

• the use o# ine2pensive andeasily portable handling anddrilling e4uipment

• 9he soil immediately .elow thehole remains relati+ely un-

distur.ed

• &oring can .e used in most typeof soil

• 9he accurate identification of soilstrata is difficult due to mi2ing ofthe material as they are carried tothe surface%

•9he method is unaccepta.le foro.taining soil samples%

• not suitable #or very so#t soil#ine to medium grainedcohesionless soil and incemented soil


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Rota&) !&illing

• use#ul in case o# highly resistant strata• #inding out the roc$ strata and also to assess the

4uality o# roc$s #rom crac$s #issures and +oints. andcan be used in sands and silts

• There are two #orms o# rotary drilling open-holedrilling and core drilling.

• Open-hole drilling uses a cutting bit to brea$ downall the material within the diameter o# the hole.

• 5n core drilling a diamond or tungsten bit cuts ahole in the roc$ and an intact core enters the barrel

which is then removed as a sample.


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• the bore holes are advanced in depth by rotarypercussion method

• A heavy string o# the drill rod is used #or cho$ingaction.

• The bro$en roc$ or soil #ragments are removed bycirculating water or drilling mud pumped throughthe drill rods and bit up through the bore hole #rom which it is collected in a settling tan$ #orrecirculation.


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• %or deep holes and unstable soils drilling #luids are

use#ul as they serve to stabili,e the bore hole

• rilling mud is slurry o# bentonite in water

• The drilling #luid causes stabili,ing e##ect to the bore

hole partly due to higher speci#ic gravity as compared with water and partly due to #ormation o# mud ca$eon the sides o# the hole.

• As the stabili,ing e##ect is imparted by these drilling

#luids no casing is re4uired i# drilling #luid is used.

Need further reading- Bentonite slurry


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$e&,%ssion !&illing

• 5n case o# hard soils or so#t roc$ auger boring or wash boring cannot be employed. %or such

strata percussion drilling is usually adopted.

• 5s used to construct large diameter bore holes inloose so#t hard roc$y and boulder-gravel-sand

clay&mi2ed ) #ormations.• 5s most suited to drill in stratum where large boulders in abundance are encountered atdi##erent depths.


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• advancement o# hole is done by alternatively li#ting anddropping a heavy drilling bit which is attached to the lower end

o# the drilling bit which is attached to the cable. Addition o# sandincreases the cutting action o# the drilling bit in clays. Whereas when coarse cohesionless soil is encountered clay might have to be added to increase the carrying capacity o# slurry.

• A#ter the carrying capacity o# the soil is reached churn bit isremoved and the slurry is removed using bailers and sandpumps.

• Change in soil character is identi#ied by the composition o# the

outgoing slurry.

• The stro$e o# bit varies according to the ground condition.6enerally it is 7(-011cm in depth with rate o# 8(-91 drops/min.


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Advantage Limitations

•5t can be used in most o# thesoils and roc$s and can drillany material

• 5t is not economical #or hole o#diameter less than 01cm

•the material at the bottom o#the hole is disturbed by heavy blows o# the chisel and hence itis not possible to get good4uality undisturbed samples

•

5t cannot detect thin strata as well.

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