MECHANICAL METHODS (SIEVE ANALYSES).
This
method is used in the analysis of particles greater than 0.002mm in
diameter. The selection of sieve for this test depends on the soil to be
tested and the coarser the clay the larger the top of the sieve.
A
known quantity of soil is sieved through a stack of sieves with
progressively smaller mesh openings, from top to bottom of the stack.
This
grain size analysis cannot provide information on the shape of soil
grains, (weather angular, rounded, sub-angular, sub-rounded), it cannot
also determines the individual grain sizes, but it bracket the various
ranges of sizes possible within the different sieves, that is the
percentage of the sizes present.
The various ranges are obtained by relating the quantity of clay retained in a sieve with the total sample (Lambe; 1951).
Grains
sizes and aggregate development are important factors for the
prediction of mechanical performance of clay rock (Bowel; 1978).
Information
obtained from the grin size analysis is present in the form of a curve.
Grain sizes are plotted by using the percentage passing against grain
diameter (also sieve size).
The shape of the grain sizes curve
indicates the distribution of the grains. A smooth curve covering a wide
range of size represents as well graded or non-uniform clay whose curve
contains a vertical or nearly vertical portion is deficient in certain
grain sizes in the region of the vertical slope. A consisting of few
grain size is a poorly graded or uniform clay (Lambe; 1951).
PROCEDURE FOR MECHANICAL METHOD
Clay particles were gently separated from each other.
The sieves set (stack of sieves) are then arranged in descending order from the top with a retainer beneath it 500g of sample was weight and poured into the sieve stack.
Sieve stack is the placed on the mechanical sieve shaker for about 5min.
Sieve stack is known separated one by one retrieving the clay fraction retained by then mesh of each sieve.
Clay fraction retained on each sieve is then weighted.
Statistical data of the result of the analysis will then be prepared.
APPARATUS
Stack of sieves, weighting balance, oven, collating pan, mechanical soil pulverize.
3.3.6 ATTERBERG CONSTITENCY LIMIT
Atterberg, a Swedish scientist in 1911 propose atterberg constituency limits. Clay constituency is defined as the physical forces of cohesion and adhesion action within the clay at various moisture content.
Water content in the clay is essentially a solid (e.g. mud, brick), a plastic (e.g. clay ready for molding), a liquid (e.g. shiny).
Atterberg defined the boundaries of three state of in terms of limit as follow:
Liquid limit (wl): the boundaries between the liquid and plastic state.
Plastic limit (wp): the boundaries between the plastic and semi solid state.
Shrinkage limits (ws): The boundaries after which the clay begins to shrink.
Atterberg limits tests are accurate methods which reflect the influence of water content, grain size and mineral composition upon the mineral behaviors of clays; they also involve measuring quantitatively the degree of plasticity of clays. The atterberg limit test carried out in this project include liquid limit test, plastic limit test and shrinkage limit tests.
3.3.6.1 LIQUID LIMIT TEST
Liquid limit test can be defined (Atterberg.1911) as the moisture content below which clay behaves as a plastic material and above which the remolded material behave as viscous fluid. The limit is arbitrarily defined as water content at which the clay placed in a brass cup, cit which a standard grove will undergo a groove closure of 12.7mm when dropped 25 time (Bowels,1978).
PROCEDUERE
Pulverize dry sample was passed through a sieve of diameter 0.4mm. About 500g of the soil sample was poured on glass plate and mixed with water carefully to form a uniform paste with use of spatula. Some of the paste was put in cup of liquid limit device.
The surface was smoothing and excess paste was returns the glass paste. The grooving tool was used in holding device tightly to draw the groove. The crank was turned and required number of blow was obtained as the groove close by the flow of the soil. Number of blow was recorded the blows count were obtained by turn the crank of the liquid limit device at the rate of two revolutions as second on till the groove closes due to fluid flow. A representation portion of the sample was taken at this point and tested for water content determination. The paste in the liquid limit device was removed into plate and two drops of water was added to it and the procedure was repeated for four different numbers of blows the water content was determined. The minimum of blows is 10 and the maximum number of blows is 50. If the number of blows that closes the grooves less than 10, that means the clay as passed the liquid limit test. The excess of liquid limit test is to determine the maximum amount of water that the clay can take before it starts behaving like liquid.
