OPERATING INSTRUCTIONS
FOR
CBR APPARATUS
EQUIPMENT :
1.
Load Frame capacity 5000 kg electrically operated.
2.
Mould 150 mm dia x 175 mm high.
3.
Base plate for the mould.
4.
Collar 150mm dia x 50mm high.
5.
Penetration Piston face dia 50mm.
6.
Bracket for mounting the dial gauge.
7.
Displacer block 148 mm dia x 47.7 mm long.
8.
Surcharge weights 2.5 kg anuular and 2.5 kg slotted.
9.
Perforated Plate.
10. Tripod stand.
11. Cutting
collar.
12. Proving Ring
with calibration certificate.
INTRODUCTION : The CBR Test
Apparatus meets the requirements of IS 2720 (Part XVI). It is for the laboratory determination of CBR
ratio of undisturbed soil specimen obtained from the field and also remoulded
specimen of the soiled compacted in the
laboratory both in soaked and unsoaked state.
DESCRIPTION : The load
frame consist of four pillars hand operated is provided with strain dial gauge
bracket moves up and down on the one of the pillar and can be locked at any
desired position. A Proving Ring adopter
is provided in the center of loading screw.
The load application is achieved by the down ward movement of the load
screw in which the loading platen is mounted.
MOULD : The
mould (2) is a open ended cylinder. It is provided with two bosses for clamping.
BASE PLATE : It is
circular base plate with a recess for positioning either end of the mould. It has two studs both the mould and the
collar can be clamped each other.
COLLER : The collar
is an open cylinder and has two bosses. It is provided with a recess for
positioning on the mould.
PENETRATION PISTION : The piston
is a steel cylinder with face of 50 mm dia.
A reamed hole and locking screw are provided for a dial gauge bracket
standard threads are provided at one end for screwing into a Proving Ring.
DISPLACER BLOCK : The
displacer block 47.7 mm thick is made of steel and is completely machined from
all sides. This act as a false bottom in
the cylindrical mould during the compaction process to give a required height
of the compacted specimen. A handle is
provided to remove the displacer disc after compaction.
SURCHARGE WEIGHT : The
surcharge weight is an annular disc weighing 2.5 kg and is used in the
application of surcharged load on the soil surface during socking and
penetration.
PERFORATED PLATE : The
perforated brass plate has an adjustable stem and ock nut. It acts as a spacer between the soil surface
and dial gauge mounted on a tripod in the swell test.
TRIPOD : The tripod
is made of one piece to ensure proper alignment of stability at all times.
A clamp is provided to hold a dia gauge easy mounted. The tripod sits on the top of the mould in a
three point mounting.
CUTTING COLLER : The cutting collar is machined from seamless
steel tubing. Recess in the upper
section makes it possible to mount the
cutting collar at either end of the
mould to facilitate the taking of undisturbed soil samples.
PROVING RING : The Proving Ring is for measuring the applied
load and has capacity of 5000 kg. A
calibration chart is also provided showing the relation between deformation and
load.
DIAL GAUGE : The dial
gauge measure the penetration piston and swell of the specimen. It has a least count of 0.01mm and a range of
.01 x 25mm travel.
SPECIMEN PREPARATION : Fix the
steel cutting collar to the mould and push it as gently as possible in the
ground, digging out the soil as the mould is pushed in, remove the mould by
under digging. Trim the top and
undersides so that the correct length of specimen is obtained.
REMOULDED: The dry
density for remoulding shall be either the field density or the value of the
maximum dry density estimated by the compaction tests, or any other density
which the bearing ration is desired. The
moisture content used for compaction should be the optimum moisture content or
the field moisture as the case may be.
Take the material passing 20mm sieve.
Allowing for larger material shall be made by replacing it by an equal
amount of material which passes 20mm IS
sieve but retained at 4.75mm IS sieves.
STATE COMPACTION : Calculate
the weight of the wet soil at the required moisture contents to give the
desired density when occupying the standard specimen volume in the mould. Mix a batch of soil thoroughly with water to
give the required moisture contents.
Place the correct weight of the moisture soil in the mould clamped to
the base plate with a filter paper in between.
Place a filter paper ever the soil, position the displacer disc on the
top of the filter paper with threaded face up.
Keep the assembly in the Compression Machine. Press the displacer disc until it is flush with the rim of the
mould when required volume of specimen is obtained
although with some soil types it may be necessary to continue the loading
until, the displacer disc is just below the rim in order to allow for the
elastic recovery of the soil, when the load is removed.
DYANAMIC COMPACTION : Take a
representative sample of the soil weighing
approximate 4.5 kg or more for fine grained soils and 5.5 kg or more
granules soils and fix the roughly with water.
If the soil is to be compacted to the maximum dry density at the optimum
moisture contents determined in accordance with the Indian Standard
specifications using light compaction or heavy compaction taking the exact
weight of soils required and mix it thoroughly with the necessary quality of water
to give the determined optimum moisture contents.
Place the displacer block on the base
plate with its threaded face facing the base plate. Keep a coarse filter paper over it clamp the
mould with the extension collar, attached to the base plate. For light compaction method compact the way
soil into the mould three layer each layer being given 56 blows using the rammer weighing 2.6 kg dropping from a
height of 310mm and for heavy compaction method compact the wet soil in five
layers each layer being given 56 blows using the rammer weighing 4.8 kg
dropping from a height of 450mm.
Uniformly distribute the blows over the surface of each layer. Care shall be taken to keep the sleeve free
from the soil.
Remove the extension collar and
carefully trim the compacted soil even
with of the mould by means of a straight
edge. Patch up any holes that may
then develop on the surface of the
compacted soil by the removal of coarse material using the smaller size
material.
Dismantle the mould from the base plate
and record the weight of the mould
and the
compacted specimen. Remove the displacer disc from the plate and place a filter paper
over it. Invert the mould and clamp it
to the base plate.
TEST PROCEDURE OF SWELL TEST : Place a filter over the specimen if it is not
already there and position the perforated plate with adjustable stem on the
specimen. Adjust the stem height such
that it touches the plunger of the dial gauge fixed to the tripod when mounted
on the mould. Apply the weight to produce
a surcharge equal to the weight of the base material and pavement in actual
construction with 2.5 kg. The whole weight, however shall be less than 5 kg
immerse the whole mould and weight in a tank of water allowing free access of
water to the top and bottom of the specimen.
Fix the dial gauge to the tripod and mount it on the mould. Record the initial dial gauge reading. Keep
this set up as such undisturbed for 96 hours (presuming that the soil specimen
is fully saturated) note down the dial gauge reading everyday against the time
of reading. If the expansion cases within 96 hours the reading may be taken up
to the final expansion and report the total time of soaking. A shorter immersion period may be permissible
for soils that take up moisture readily, if test shows that the shorter period
does not effect the test results.
Maintain a constant water level in the tank throughout the period. At the end of the soaking period note the
final reading of the dial gauge, remove the tripod, take the mould out of the
water thank, remove the surcharge weight and the perforated plate.
Remove the free water and allow the
specimen to drain downwards for 15 minutes being careful to see that the
surface of the specimen is not disturbed during removal of the free water,
determine the weight of the mould with soaked soil sample.
PENETRATION TEST : Position the load frame on firm level base,
screw in the Proving Ring to the adapter, screw in the penetration piston (5) to the Proving Ring at its lower
end. Position the mould on the loading
plates of the load frame, place the surcharge weights, sufficient to produced
an intensity of loading equal to the weight of the base material and pavement
within 2.5 kg but not less than 5 kg. If the specimen has been soaked previously. The surcharge shall be equal to that used
during the soaking period.
Raise the loading platen and seat. The piston centrally on top of the specimen
and raise it clear of the specimen but not clear of a surcharge weight. Fix
dial gauge to the bracket.
Position the bracket in the reamed hole
of the penetration piston and adjust the length of its such that the
dial gauge plunger sets on the rim of the collar by the locking screw on the
penetration piston. Bring the piston in
contract with the specimen and apply the smallest possible load but in no case
in excess of 4 kg so that the full contact is established between the surface
of the specimen and the piston. Set the
Proving Ring dial gauge and penetration dial gauge to zero. Consider the initial load applied to the
piston as the zero load when determining the load/penetration relation.
Apply the load on the penetration piston
so that the penetration is approximate 1.25mm/min. Records the load reading at penetration of
0.5,2.0, 2.5, 3.0, 4.5, 7.5, 10.0 and 12.5 mm.
Record the maximum load and penetration if it occurs for a penetration
of less than 12.5mm at the end of the test dismantle the assembly and determine
the moisture contents taking about 20 to 50 gm. Of the soil from the top 3cm
layer of the specimen. If the average
moisture contents of the whole specimen
is desired, take the moisture contents of the whole specimen is desired, take
the moisture contents samples from the entire depth of the specimen.
CALCULATION
Df
-
ds
Expansion Ratio
x 100
H
Where df
= Final dial gauge reading in mm.
ds =
Initial height of the specimen in mm.
h = Initial height of the specimen in mm.
Plot the penetration/load curve. A correction is applied by drawing a tangent
to the curve at the point of greatest slope.
The corrected curve is this tangent plus the convex portion of the
original curve with the origin at the pt. Where the tangent cuts the horizontal
axis.
Corresponding to the penetration value
at which the California
Pt
Ps
Where Pt
= Corrected unit (or total) test load/corresponding to the chosen
penetration from the load/penetration curve.
Where Ps = Unit (or total) standard load for the same
depth of penetration as for Pt taken
from the following table.
Penetration
Depth (mm)
|
Unit
Standard Load (kg/cm2)
|
Total
Standard Load KG
|
2.5
|
70
|
1370
|
5.0
|
105
|
2055
|
7.5
|
134
|
2830
|
10.0
|
162
|
3180
|
183
|
183
|
3600
|
MAINTENANCE
1.
Keep all the parts clean and the dial gauge in their
boxes when not in use.
2.
Never oil the spindle of the dial gauge.
3.
Keep the exposed parts of the load frame greased and the penetration piston should be cleaned and greased when not in
use.
4.
Keep the cutting collar cleaned and greased.
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