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Unformatted text preview: in 4.3.1 and 4.3.2. of 4.3.1 Method Z  The loading system and bearing plate should be
seated by applying a load of 3.1 kN ( 310 kgf) ( 0.007 MPa for a standard
75 cm diameter plate ), when the design thickness of pavement is less than
40 cm which is normally used for lightly loaded pavements.
For heavy
duty pavements a seating loading of 6.2 kN ( 620 kgf) should be used.
The seating load will be allowed to remain
until practically
complete
deformation
has taken place, at this time a reading should be taken on
the dial gauges and adjusted to ‘zero ’ reading.
Cyclic loading under
may be
3.1 kN (310 kgf) or 6.2 kN ( 620 kgf) seating load, as required, 8 IS I 9214  1979 Then without releasing
used to assure good seating of the bearing plate.
the seating load an additional 31 kN ( 3 100 kgf) [that is, a total 34.1 kN
( 3 410 kgf.) or 37.2 kN (3 720 kgf) load depending on the type of the
pavement J should be applied to the plates and held until practically
complete settlement has taken place.
For recording
observations,
proforma
given at Appendix
A should
be used.
Prior to releasing the 31 kN ( 3 100 kgf) load, a value of KU
will be computed
for the average
deflection
at the plate rim by the
formula:
MPa/cm,
KU=7 0.70 or kgf /ems/cm where
d = deflection in cm. One of the procedures given in 4.3.1.1
and 4.3.1.2
should be then
followed depending
upon the type of subgrade and the value of uncorrected modulus of subgrade KU.
4.3.1.1
For cohesive
subgrades
with KU equal to 0.555 MPa/cm
( 5.55 kgf /cm*/cm ) or less, the load will be released. For some clayey soils
it may be necessary
to plot a timesettlement
curve to aid determiIn general,
the load will be
nation of practically
complete settlement.
held until the rate of deflection
of the bearing
plate is less than
O*OOO cm/min ( that is, O005 cm in 10 minutes ). This rate of settlement
5
indicates that the major portion of the settlement has occurred.
4.3.1.2 ,For granular subgrades, or cohesive subgrade with KU equal
to 0.555 lMPa/cm ( 5.55 kgf /ems/cm ) or more a loaddeflection
curve
should be obtained
by measuring
the successive deformations
caused by
increasing the load in increments
of 15.5 kN ( 1 550 kgf) to a maximum
of 93 kN ( 9 300 kgf).
The load should not be released between the
increments of loading.
Each increment of load shall be held for at least
15 minutes.
The final load of 93 kN ( 9 300 kgf) shall be held until
practically complete settlement is reached, but in not less than 15 minutes.
In general the 0,21 MPa ( 2.1 kgf /ems ) load should be held until the rate
of settlement of the plate is less than O*OOO cm/min ( that is, 0.002 cm in
2
10 minutes ). This rate indicates that the major portion of the settlement
has taken place.
4.3.2 Method II The
plate shall first be seated by applying a load
equivalent to a pressure. of 0.007 MPa ( 0.07 kgf /cm% ) and releasing it
after a few seconds.
A load sufficient to cause approximately
a 0*85mm
9 ISr9214 1979 settlement should be applied and when there is no perceptible increase in
settlement or in the case of clayey soils, when the rate of increase in settlement is less than 0.025 mm/min the average of the readings of the deflec,tion dial gauges should be noted. The load as measured by the pressure
gauge attached to the jack or by the proving ring should be noted, both
immediately before and after the deflection readings.
The load should
be increased until there is an additional settlement of approximately
0.25 mm and the load and d...
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 Spring '13
 PROF.DEEPANKARCHOUDHURY

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