1.0 OBJECTIVE

To determine the liquid limits of soil using cone penetrometer methods

2.0 LEARNING OUTCOME

At the end of this experiments, students were able to:

Conduct the liquid limits experiment

Determine theliquid limit value soil

Identify the importanceand application of liquid limit test

3.0 TEORY

The properties of fine grains soils are largely dependent on their consistency, which is

itself related to the moister content of a dry sample of such a soil is increased is its state

gradually changes from that of a solid, through semi-solid, through plastic and finally

into a liquid form. The arbitrary boundaries between these phases are called the

"consistency limits" and the Atterberg limits provide a means of measuring and

describing the plasticity range in numerical terms. If sufficient water is mixed with

clay, it can be made into slurry, which behaves as a viscous liquid. This is known as the

liquid’ state. If the moisture content is gradually reduced by allowing it to dry out

slowly, the clay eventually begins to hold together and to offer some resistance to

deformation; this is the ‘plastic’ state. With further loss of water the clay shrinks and

the stiffness increases until there is little plasticity left, and the clay becomes brittle;

this is the ‘semi-solid’ state. As drying continues, the clay continues to shrink in

proportion to the amount of water lost, until it reaches the minimum volume attainable

by this process. Beyond that point further drying results in no further decrease in

volume, and this is called the ‘solid’ state.

These four states, or phases, are shown diagrammatically in Figure 1.1. The change

from one phase to the next is not observable as a precise boundary, but takes place as a

gradual transition. Nevertheless three arbitrary but specific boundaries have been

established empirically, as indicated in Figure 1.1, and are universally recognised. The

moisture contents at these boundaries are known as the:

Liquid limit (LL) (symbol wL)

Plastic limit (PL) (symbol wp) The Atterberg limits or consistency limits

Shrinkage limit (SL) (symbol w5)

The "liquid limit" (LL) is the minimum moisture content at which a soil is assumed to

flow under its own weight, which corresponds to 25 blows in the Casagrande test or 20

mm penetration in the Penetrometer test The "shrinkage limit" (SL) is the water content

at which further decrease in moisture does not cause a decrease in volume of the soil.

The "plasticity index" (P1) is the range of moisture content over which the soil is plastic

and is given by the expression,

PI = LL – PL

The moisture content range between the PL and LL is known as the plasticity index

(P1) (symbol Ip), and is a measure of the plasticity of the clay. Cohesionless soils have

no plasticity phase, so their PT is zero.

The tests to determine the Atterberg limits are carried out only on the fraction of soil

which passes a 425 pm sieve. For soils that contain particles coarser than that size, the

particles retained on the 425 pm sieve must be removed as part of the sample preparation

procedure. The relationship between the consistency limits and the volume of a soil

sample is shown in Figure 1.2.

4.0 APPARATUS TEST

1. Penetrometer apparatus complying with the requirements of BS 1377 : Part 2: 1990.

2. Cone for the penetrometer, the main features of which are as follows;

- stainless steel or duralumin,

- smooth and polished surface,

- length approximately 35 mm and cone angle 30

- sharp point and mass of cone and sliding shaft 80 g ± 0.1 g

3. Sharpness gauge for cone, consisting of a small steel plate 1.75 mm ±0.1 mm thick with

a 1.5 mm

± 0.02 mm diameter hole accurately drilled and reamed.

4. Flat glass plate, about 500mm square and 10mm thick, with bevelled edges and rounded

corners.

5. Metal cups, of brass or aluminium alloy, 55m diameter and 40mm deep. The rim must

be parallel

to the base, which must be flat.

6. Wash bottle containing distilled or de-ionised water.

7. Metal straight-edge, about 100 mm long

8. Palette knives or spatulas ( two 200 mm long x 30 mm, one 150 mm long x 25mm, one

100mm long x 20mm)

9. Moisture content apparatus .

Figure 1.3 :APPARATUS FOR CONER PENETROMETER LIQUID TEST

5.0 PROCEDURE

. Selection and preparation of sample

(a) Place a sample an about 300 gram soil passing 425 μm test sieve on the glass plate.

(b) Use the natural material if possible; if not use the wet preparation method.

(c) If the plastic limit test is also to be done, set aside a small portion in a sealed bag or

container before adding too much water, and while the soil is still firm.

(d)

Figure 1.4 : Selection and preparation of sample

2. Checking apparatus

(a) The cone designed specially for testing soils must be fitted.

(b) Mass of cone and stem 80±0.1 g. This is most important. The stem is hollow, so that

Lead - shot can be inserted to bring the cone and stem assembly to the specified

mass.

(c) Sharpness of the cone point can be checked by pushing the tip into the hole of the

sharpness gauge plate. If the point cannot be felt when brushed lightly with the tip

of the finger, the cone should be replaced.

(d) The cone must fall freely when the release button is pushed, and the sliding shaft

must be clean and dry.

(e) The penetration dial indicator should be calibrated by inserting gauge blocks

between the stem of the indicator and the top of the cone sliding shaft. Alternatively

calibrated vernier calipers could be used.

(f) The apparatus must stand on a firm level bench.

(g) If the apparatus is fitted with an automatic timing device, this should automatically

lock the cone shaft assembly 5 seconds after pressing the button which releases it.

(h) This time interval should be verified against a reference timer.

3. Mixing and working

(a) Mix the soil paste on the glass plate with the spatulas for at least10 minutes.

(b) Some soils, especially heavy clays, may need a longer mixing time, up to 4 minutes.

(c) If necessary add more distilled or de-ionised water to give a cone penetration of about

15mm, and mix well in. It is essential to obtain a uniform distribution of water

throughout the sample.

(d) Keep the soil together near the middle of the glass plate, to minimise drying out due

to exposure to air.

Figure 1.5 : Process to mixing the soil

. 4. Placing in cup

(a) Press the soil paste against the side of the cup, to avoid trapping air.

(b) Press more paste well into the bottom of the cup, without creating an air-pocket,

(c) Fill the middle and press well down. The small spatula is convenient for these

operations,

(d) The top surface is finally smoothed off level with the rim using the straight-edge.

Figure 1.6 : Placing soil in a cup

5. Adjustment of cone

(a) Lock the cone and shaft unit near the upper end of its travel and lower the supporting

assembly carefully.

(b) Make sure that the tip of the cone is within a few millimeters from the surface of the

soil in the cup.

(c) Hold the cone, press the release button and adjust the height of the cone so that the tip

just touches the soil surface.

(d) A small sideways movement of the cup should just mark the surface.

Figure 1.7 : Adjustment of cone

(6) Adjustment of dial gauge

(a) Lower the stem of the dial gauge to make contact with the top of the cone shaft.

(b) Record the reading of the dial gauge to the nearest 0.1 mm (R1).

(c) Alternatively, if the pointer is mounted on a friction sleeve, adjust the pointer to read

zero (i.e. R1= 0).

(7) Measuring cone penetration

(a) Allow the cone to fall by pressing the button, which must be held in the pressed

position for 5 seconds, timed with a seconds timer or watch.

(b) If an auto-timer is used it is necessary only to press the button and release it

immediately.

(c) Automatic re-locking of the stem is indicated by a click. Record the dial reading to

the nearest 0.1 mm (R2).

(d) Record the difference between R1 and R2 as the cone penetration.

(e) If the pointer was initially set to read zero, the reading R2 gives the cone penetration

directly.

(f) A range of penetration values from about 15mm to 25mm should be covered, fairly

uniformly distributed.

Figure 1.9 : Press the button to fall the cone and take a reading

(8) Repeat penetration

(a) Lift out the cone and clean it carefully.

(b) Avoid touching the sliding stem.

(c) Add a little more wet soil to the cup, without entrapping air, smooth off, and repeat

stages (5), (6) and (7).

9) Moisture content measurement

This is placed in a numbered moisture content container, which is weighed, oven dried and

weighed as in the standard moisture content procedure according to BS 1377 : Part 2: 1990.

(a) Weight the empty moisture content container

(b) Take a moisture content sample of about 10 g from the area penetrated by the cone,

using the tip of a small spatula.

(c) Weight the wet sample

(d) Dry in the oven for about 24 hours (overnight)

(e) Weight the dry sample

(a) (b) (c)

(d) (e)

6.0 CALCULATION EXAMPLE

(1) Results Calculation and plotting

(a) The moisture content of the soil from each penetration reading is calculated from the

wet and dry weighings as in the moisture content test.

(b) Each cone penetration (mm) is plotted as ordinate, against the corresponding moisture

content (%) as abscissa, both to linear scales, on a graph as shown in Figure 1k. which

also shows typical data. The best straight line fitting these points is drawn.

(c) From the graph the moisture content corresponding to a cone penetration of 20mm is

read off to the nearest 0.1%, refer Figure 1.11.

(d) The result is reported to the nearest whole number as the liquid limit (cone test).

(e) The percentage of material passing the 425 um sieve is reported to the nearest 1%.

together with the method of sample preparation.

(f) The plastic limit and plasticity index are usually reported with the liquid limit.

Table 1 : Example of Data Sheet.

Location : RECESS Loc. No. : 00123

Soil description: Silty CLAY Sample No. : 6

Sample type : Undisturbed Depth of Sample : 1.5 m

Operator: A . Z. S Date Started :

Test Number Units 1 2 3 4

Dial Gauge Reading (Start) mm 0 2 1 5Dial Gauge Reading (End) mm 15.5 15.1 21.1 21.3 24.1 23.9 30.4 30.2

Cone penetration mm 15.5 15.1 19.1 19.3 23.1 22.9 25.4 25.2

Average penetration mm 15.30 19.20 23.00 25.30

Can Number 11 21 32 41

GRAPH FOR LIQUID LIMIT TEST

0

5

10

15

20

25

30

58 60 62 64 66 68 70

Moisture content (%)

Pen

etra

tion

of c

on

e (m

m)

63.54

Mass of can + moist soil (Mcws) gram 46.76 57.20 63.60 71.72

Mass of can + dry soil (Mcs) gram 32.51 38.31 41.64 45.78Mass of can (Mc) gram 8.31 8.35 8.26 8.29Mass of dry soil (Ms) gram 24.20 29.96 33.38 37.49Mass of water (Mw) gram 14.25 18.89 21.96 25.94Water content % 58.88 63.05 65.79 69.19

Figure 1.12 : Graph for Liquid limit

Calculation of moisture content;

w=

mw

m s

=14 .2524 .20

=0 .5888 or 58.88 %

7.0 RESULT AND CALCULATIONS

DATA SHEET

Location : Loc. No. :

Soil description: Sample No. :

Sample type : Depth of Sample : m

Operator: Date Started :

Test Number Units 1 2 3 4

Dial Gauge Reading (Start) mm 0 0 0 0Dial Gauge Reading (End) mm 15.0 14.9 21.1 21.4 24.9 25.5 28.0 27.9Cone penetration mm 15.0 14.9 21.1 21.4 24.9 25.5 28.0 27.9Average penetration mm 14.9 21.3 25.2 27.9

Can Number Units L1 L2 L3 L4

Mass of can + moist soil (Mcws) gram 14 16 18 21

Mass of can + dry soil (Mcs) gram 12 13 13 13Mass of can (Mc) gram 9 10 10 9Mass of dry soil (Ms) gram 3 3 3 4Mass of water (Mw) gram 2 3 5 8Water content % 66.67 100.00 166.67 200.00

Plot result semi-log graph and determine the liquid limit.

Liquid Limit (LL) = 116.25 %

8.0 CALCULATIONS

Cone penetration = Dial gauge reading end – dial gauge reading start

= 15.0 – 0

= 15.0mm

Mass of dry soil (Ms) = [mass of can + dry soil (Mcs)] – [mass of can (Mc)]

= 12 – 9

= 3 gram (L1)

Mass of water (Mw) = [mass of can + moist soil (Mcws)] – [mass of can (Mc)]

– [ mass of dry soil (Ms)]

=14 – 9 – 3

= 2 gram (L1)

Moisture content , w = [ Mw / Ms ] x 100

= 66.67 %

9.0 DISCUSSION

This testing method is used as an integral part of several engineering

classifications systems to characterize the fine-grained fractions of soils and to specify

the fine-grained fraction of construction materials. The liquid limit, plastic limit and

plasticity index of soils are also used extensively, either individually or together, with

other soil properties to correlate with engineering behavior such as compressibility,

permeability, compactibility, shrink-swell and shear strength.

The importance of the liquid limit test is to classify soils. Different soils have

varying liquid limits. The liquid limit from this experiment that we get are 116.25 %

this liquid limit we get after plot the graph.

10.0 CONCLUSION

The subject of the study is the liquid limit that is an empirically determined state at

which a transition from a softly plastic to liquid state occurs, therefore after its achieving soil

starts to behave as a liquid substance.

The liquid limit measurement is principal especially for finding consistency states

playing a decisive role for determining the key standard characteristics of soils representing

important geotechnical parameters of fine-grained soils for investigations of the so-called

first geotechnical category.

In conclusion before realization of the tests the sample set up for 24 hours for the

purpose of even distribution of moisture.

11.0 QUESTION

QUESTION 1

a) What are the definitions of liquid and plastic limit?

- Liquid Limit is the water content, in percent, of a soil at the arbitrarily defined boundary between the semi - liquid and plastic states.

- Plastic Limit is the water content, in percent, of a soil at the boundary between the plastic and semi - solid states.

b) A sample of wet clay and its container weight 102g. After oven drying

the sample and the container weight 60g. What is the water content ?

42g

QUESTION 2

a) What are alternatives methods to define liquid limit and give brief

explanation

The liquid limit is determined through the use of Casagrande device

Through the first method we determine the liquid limit when a sample

of soil with a horizontal and smooth surface placed in the bowl of the

device and divided by a grooving tool into two parts which need 25

hits of the bowl to the base to close the gap between them in a length

of 12.5+-0.5 mm namely at a rate of 2 hits per second.

b) Briefly explain why the reading is taken after 5 second.

To allow the cone fall until get the max liquid limit.