01 sc-liquid limit test PDF

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LIQUID LIMIT TEST

LEARNING OUTCOMES At the end of this experiment, students should be able to:

1.1



Conduct the liquid limit experiment.



Determine the liquid limit value for soil.



Identify the importance and application of liquid limit test.

INTRODUCTION

Liquid limit can define as minimum water content at which the soil is still in the liquid state, but has a small shearing strength against flow. The liquid limit (LL) is conceptually defined as the water content at which the behavior of a clayey soil changes from plastic to liquid. However, the transition from plastic to liquid behavior is gradual over a range of water contents, and the shear strength of the soil is not actually zero at the liquid limit. The precise definition of the liquid limit is based on standard test procedures described below.

1.2

OBJECTIVES

The objectives of this experiment are to determine the Liquid Limits of Soil Using Cone Penetrometer Methods.

1.3

THEORY 1

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 recognized. 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 2

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" (PI) 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 (PI) (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.

Figure 1.1: Phases of soil and the Atterberg limit

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Figure 1.2: Consistency limits/volume relationship of a cohesive soil 1.4

1.

APPARATUS

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

2.

3.

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

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

4

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 cone penetrometer liquid test

1.5 1.

PROCEDURES 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.

Figure 1.4: Selection and preparation of sample 5

2.

Checking apparatus (a) The cone designed especially 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-ionized 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 minimize drying out due to exposure to air.

Figure 1.5: Process to mixing the soil

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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

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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).

Figure 1.8: Adjustment of dial gauge 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 second’s 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 (R 2). (d) Record the difference between R1 and R2 as the cone penetration. (e) If the pointer was initially set to read zero, the reading R 2 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

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)

(e)

(d)

Figure 1.10: Process to take a moisture content.

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1.6

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 weighing 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.

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Table 1: Example of Data Sheet Location : RECESS

Loc. No. : 00123

Soil description: Silty CLAY

Sample No. :

Sample type : Undisturbed

Depth of Sample : 1.5 m

Operator: A . Z. S

Date Started :

Test Number Dial Gauge Reading (Start) Dial Gauge Reading (End) Cone penetration Average penetration Can Number Mass of can + moist soil (Mcws) Mass of can + dry soil (Mcs) Mass of can (Mc) Mass of dry soil (Ms) Mass of water (Mw) Water content

6

Unit s mm mm mm mm

1

2

3

0 15.5 15.1 15.5 15.1 15.30

2 21.1 21.3 19.1 19.3 19.20

1 24.1 23.9 23.1 22.9 23.00

5 30.4 30.2 25.4 25.2 25.30

gram gram gram gram gram %

11 46.76 32.51 8.31 24.20 14.25 58.88

21 57.20 38.31 8.35 29.96 18.89 63.05

32 63.60 41.64 8.26 33.38 21.96 65.79

41 71.72 45.78 8.29 37.49 25.94 69.19

63.54

Figure 1.12: Graph for Liquid limit

Calculation of moisture content;

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1.7 1.

REFERENCES Das, Braja M., 2014. “Principles of geotechnical engineering”: Cengage Learning. (TA710 .D37 2014)

2.

Morris, A., 2012. “Geotechnical engineering of soil”: Auris Reference. (TA705 .G49 2012)

3.

Braja, M.D., 2010. “Principle of Geotechnical Engineering”: McGrawHill. (TA710.D37 2010)

4.

Cheng Liu & Jack B. Evett, 2008. “Soils and Foundations”: Prentice Hall. (TA710.L58 2008)

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1.8

ADDITIONAL THEORY

............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ (10 marks) 13

1.9

DATA Data Sheet

Location : Soil description: Sample type : Operator: Test Number Dial Gauge Reading (Start) Dial Gauge Reading (End) Cone penetration Average penetration Can Number Mass of can + moist soil (Mcws) Mass of can + dry soil (Mcs) Mass of can (Mc) Mass of dry soil (Ms) Mass of water (Mw) Water content

Loc. No. : Sample No. : Depth of Sample : Date Started : Unit s mm mm mm mm

1

2

3

m

4

Unit s gra m gra m gra m gra m gra m %

Plot result semi-log graph and determine the liquid limit. Liquid Limit (LL) =

% (25 marks) APPROVED BY

=

14

1.10

ANALYSIS & RESULT

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