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 This test enables the direct measurement of the undrained shear resistance ofsaturated cohesive soils.

It can be carried out either in the eld, on the wall or at the bottom of an excavation, oreven in a laboratory on a conned specimen.

 The test consists of forcing into the soil a vane equipped with four orthogonal bladesand then rotating until the soil failure. Maximum torque value must be measured andrecorded.

Afterwards the remoulding shear resistance of the soil can be measured rotating thevane for several turns.

 The vanes have a rectangular shape and a height double their diameter, according tothe recommendation included in the !"#$#% & '()&&* and A+TM +tandard $ode '%-&*/ in the latter one also vanes having a tapered end are allowed.

 The above mentioned codes prescribe that the rotation must be carried out at a rate of0.(10. degrees2sec. '31( degrees2min*.

#ver the blades of the vane, a thin enlarging ring can be applied so that the main partof the resistance due to the soil friction along the tract of the rod inserted into the soildoes not a4ect the measures.

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 Tests can be also carried out at the bottom of a borehole/ in this case the vane must

penetrate at least ve times the hole diameter into the soil below the bottom of thehole to be sure that undisturbed soil will be tested 'A+TM % -&*.

 Test is carried out as follows5

 

• push the rod supporting the vane to the estimated test depth/

• rotate the vane from the surface at the prescribed rate, using the relevant torque

wrench/

• measure the maximum torque required to reach the soil failure and 6o on

rotating regularly the vane for at least complete turns measuring and recordingthe residual torque.

 To carry out deep vane tests with the 7agani 6eotechnical quipment static or dynamic

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penetrometers the following procedure is suggested.

 

• %rive the pie8ocone and its casing tubes till the depth next to that of the test.

• 7erform a static test '$7T1$7T!* up to the depth close to where the vane test has

to be carried out/ the related steel casing shall be inserted after the penetrationof each rod.

• 9ithdraw only rods and tip, leaving the casing in place.

• :ower the vane ;oined to the relevant rods and force it below the hole bottom to

reach the undisturbed soil.

•

+et the thrust bearing among rod and casing. +et the centered sleeve to supportthe extension rods.

• :oc< the screw to fasten extension rods to supporting sleeve.

• Apply the torque wrench.

• $arry out the test.

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Vanes which can be used together with the different types of casing tubes are the following:

 

Penetrometers Inner / Outer diameter of the casing tubes Vane size%7M 010 T6 010

0 2 mm =x()

 T6 31(00 T6 31(-0 T6 &100

2 >= mm30x0-0x-=x()

 

Calculation of the undrained shear resistance

!ndrained shear resistance at failure '+u'?@** is calculated by the maximum torquerequired to cut the soil included into the cylinder obtained rotating the vane blades.

 The general formula, referred to rectangular vanes having height '* and diameter '%*,is5

+u'?@* B T 2''p %2* '2% C a2** '(*

where5

 T B maximum applied torque 'deducted any friction*.a B factor depending by the assumed shear stress distribution at the ends of the

cylinder obtained rotating the vane blades and amounting to 2 for uniform shearstress.

?or rectangular vanes having 2% B , equation '(* is reduced to5

+u'?@* B 3T 2 &p % B 0.&T 2 % '*

 The remoulded shear strength value is calculated using the above mentioned formula'* introducing the value of the torque, free from any friction, measured after somevane rotation turns, that is when the soil o4ers a fast constant resistance.