STUDENT CODE OF ETHIC (SCE) DEPARTMENT OF INFRASTRUCTURE AND GEOMATIC ENGINEERING FACULTY OF CIVIL & ENVIRONMENTAL ENGINEERING
I, hereby confess that I have prepared this report on my own effort. I also admit not to receive or give any help during the preparation of this report and pledge that everything mentioned in the report is true.
_________________ Student Signature
Name
: …………………………………………
Matric No. : …………………………………………
Date
: …………………………………………
FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE AND GEOMATIC ENGINEERING
1.0 OBJECTIVE: To Determine the Lowest Moisture Content at Which the Soil Behaves Plastically. 2.0 LEARNING OUTCOME At the end of this experiment, students are able to: Conduct the plastic limit test. Identify the plastic limit value for a soil. Identify the importance and application of plastic limit test.
3.0 THEORY Plastic limit ( PL ) of soil is defined as the water content at which a soil will just begin to crumble when rolled into a thread of approximately 3 mm in diameter. It is water content at the boundary between the plastic and semi-solid states of consistency of the soil. Plasticity index (PI or I P) is the numerical difference of the liquid and plastic limit, and indicates the range of water content through which the soil remains plastic. PI = LL
– PL
For fine grained soils, determining the natural water content (the water content of a soil in an undisturbed condition in the ground) and relating it to the plastic and liquid limits can provide an indication of the soil’s consistency and/or sensitivity potential. One such relationship is the liquidity index. I L
w
PL
PI
Consistency index is defined as the ratio of the liquid limit minus the natural water content to the plasticity index of a soil. C r
LL
w
PI
Table 2.1 : Classification of soil according to plasticity. Plasticity Index (I P or PI) 0 <7 7-17 > 17
Degree of Plasticity Non-Plastic Low-Plastic Medium Plastic Highly
Type of Soil Sand Silt Silty clay or clayey silt Plastic Clay
Table 2.2 : Classification of soil according to liquidity indices. Liquidity Index (I L or LI) < 0.0 0.0-0.25 0.25-0.50 0.50-0.75 0.75-1.00 >1.00
Consistency Desiccated (dry) hard soil Stiff Medium to soft Soft Very soft Liquid
FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE AND GEOMATIC ENGINEERING TEST TITLE: PLASTIC LIMIT TEST
4.0 APPARATUS: 1. The most important piece of apparatus for this test is the hand of operator, which should be clean and free from grease. 2. Evaporating dish. 3. A separate glass plate reserved for rolling of threads. This should be smooth and free from scratches, and about 300 mm square and 10mm thick. The surface condition of the plate can affect the behaviour of rolled threads, and the use of unscratched glass reduces the likelihood of discrepancies. An alternative is to reserve one side of the mixing plate for thread rolling, and avoid mixing the soil on this area. 4. Two palette knives or spatulas. 5. A short length (say 100 mm) of 3mm diameter metal rod. 6. Standard moisture content apparatus (container, balance and oven)
Figure 2.1 : Apparatus for plastic limit test 5.0 PROCEDURES i)
Selection and preparation of sample (a) Take about 20 g of the prepared soil paste and spread it on the glass mixing plate. (b) Mix occasionally to avoid local drying out. (c) It is convenient to set aside this sample just before carrying out the liquid limit test.
Figure 2.2 : Prepared soil paste.
FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE AND GEOMATIC ENGINEERING TEST TITLE: PLASTIC LIMIT TEST
Rolling Into a Ball (a) When the soil is plastic enough, it is well kneaded and then shaped into a ball. (b) When slight cracks begin to appear on the surface, divide the ball into two portions each of about 10 g. (c) Further divide each into four equal parts, but keep each set of four parts together.
Figure 2.3 : Rolling into ball and four equal part of soil after divide.
iii)
Rolling Into a Threads (a) Using a steady pressure, roll this mass into a thread between the fingers of one hand and the surface of the glass plate. (b) The pressure should reduce the diameter of the thread from 6 mm to about 3 mm after between five and ten back-and-forth movements of the hand. (c) It is important to maintain a uniform rolling pressure throughout; do not reduce pressure as the thread approaches 3 mm diameter. (d) Dry the soil further by moulding between the fingers again, not by continued rolling which gives a dried crust. (e) Form it into a thread and roll out again as before. (f) Repeat this procedure until the thread crumbles when it has been rolled to 3 mm diameter. (g) The metal rod serves as a reference for gauging this diameter. (h) The first crumbling point is the plastic limit
Figure 2.4 : The soil specimen is rolled under the fingers into a thread 3 mm diameter.
FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE AND GEOMATIC ENGINEERING TEST TITLE: PLASTIC LIMIT TEST
iv) 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)
Figure 1.10: Process to take a moisture content.
FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE AND GEOMATIC ENGINEERING
Results Calculation (a) Calculate the moisture content of the soil in each of the two containers. Take the average of the two results. (b) If they differ by more than 0.5% moisture content, the test should be repeated.
Location : RECESS
Table 1: Example of Data Sheet. Loc. No. : 00123
Soil description: Silty CLAY
Sample No. :
Sample type : Undisturbed
Depth of Sample : 1.5 m
Operator: Mohd Fairus
Date Started :
Test Number Can Number
Units
Mass of can + moist soil (M cws)
gram
Mass of can + dry soil (M cs)
gram
Mass of can (Mc)
gram
Mass of dry soil (M s)
gram
Mass of water (Mw)
gram
Water content
%
Plastic limit
%
6
1
2
3
4
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
64
6.0 RESULT AND CALCULATIONS DATA SHEET Location : Soil description: Sample type : Operator:
Loc. No. : Sample No. : Depth of Sample : Date Started :
Test Number Can Number Mass of can + moist soil (M cws) Mass of can + dry soil (M cs) Mass of can (Mc) Mass of dry soil (M s) Mass of water (Mw) Water content Plastic limit
Units
1
2
3
gram gram gram gram gram % %
Plastic limit
=
%
Liquid limit
=
%
Plasticity index
= Liquid Limit – Plastic Limit =
%
4
FACULTY: CIVIL & ENVIRONMENTAL ENG. DEPARTMENT: INFRASTRUCTURE AND GEOMATIC ENGINEERING TEST TITLE: PLASTIC LIMIT TEST
11.0 QUESTIONS 1 (a) What is the definition of plastic limit? (b) A sample of wet clay and its container weigh 102 g.After oven drying the sample and the container weigh 60 g. What is the water content and plastic limit for the soil?
QUESTIONS 2 (a) What is the different between liquid limit and plastic limit? (b) A sample of wet clay weighs 176 g. After oven drying the sample weigh 60 g and its container is 7.32 g. What is the water content and plastic limit for the soil?
