Liquid LImit.pptx

A liquid limit test of soil is done to get the information on fine-grain soil (cohesive soil) about the consolidation properties of soil while calculating allowable bearing capacity & settlement of the foundation.

this ppt covers the test procedure and its calculation single point method also.

1. 1 Testing of Soil, Atterberg's Limits

2. 2 The physical properties of fine-grained soils, especially of clay differ much at different water contents. Clay may be almost in liquid state, or it may show plastic behavior or may be very stiff depending on the moisture content. Plasticity is a property of outstanding importance for clayey soils, which may be explained as the ability to undergo changes in shape without rupture.   Atterberg in 1911 proposed a series of tests, mostly empirical, for the determination of the consistency and plastic properties of fine soils. These are known as Atterberg limits and indices. Liquid limit : defined as the minimum water content at which the soil will flow under the application of a very small shearing force Plastic limit : defined as the minimum moisture content at which the soil remains in a plastic state. Plasticity Index (PI) : is defined as the numerical difference between the liquid limit and plastic limits. PI thus indicates the range of moisture content over which the soil is in a plastic condition. Shrinkage limit : is the maximum moisture content at which further reduction in water content does not cause reduction in volume. It is the minimum water content that can occur in a clayey soil sample, which is completely saturated. Consistency limits and the plasticity index vary for different soil types. Hence these properties are generally used in the identification and classification of soils.

3. 3 Liquid limit test: (Mechanical liquid limit device)   Apparatus :   Mechanical liquid limit device consists of a cup and arrangement for raising and dropping through a specified height and standard grooving tools.   Balance of 200 g capacity and sensitive to 0.01 g.   Oven to maintain 105 to 110 C. Spatula Palette Knives Beaker Container air-tight IS Sieve 425-micron sieve as per IS-460. Procedure :  About 120 g of dry pulverized soil sample passing 425 micron IS sieve is weighed and mixed thoroughly with distilled water in the evaporating dish to form a uniform thick paste. The liquid limit device is adjusted to have a free fall of cup through 10 mm. A portion of the paste is placed in the cup above the lowest spot and squeezed down with the spatula to have a horizontal surface. The specimen is trimmed by firm strokes of spatula in such a way that the maximum depth of soil sample in the cup is 10 mm. The soil in the cup is divided along the diameter through the center line of the cam followed by firm strokes of the grooving ……..

4. 4 Procedure : ….. tool so as to get a clean sharp groove. Grooving tool (b) may be used for all soils, where as grooving tool (a) may be used only in clayey soils free from sand particles or fibrous materials.   The crank is rotated at the rate of two revolutions per second (either by hand or electrically operation) so that the cup is lifted and dropped. This is continued till the two halves of the soil cake come into contact at the bottom of the groove along a distance of about 10 mm, and the number of blows given is recorded. A representative soil is taken, placed in the moisture container, lid placed over it and weighed. The container is dried in oven and the dry weight determined the next day for finding the moisture content of the soil. The operations are repeated for at least three more trials with slightly increased moisture contents each time, noting the number of blows so that there are at least four uniformly distributed readings of number of blows between 15 and 35 blows. Calculations :   Taking the number of blows in the log scale on the X-axis, and the water content in arithmetic scale on the Y-axis plots the flow curve. The flow curve is straight line drawn on this semi-logarithmic plot, as nearly as possible through three or more plotted points. The moisture content corresponding to 25 blows is read from this curve, rounding off to the nearest whole number and is reported as the liquid limit (LL or wl ) of the soil. The slope of the straight-line flow curve is the flow index. It may be calculated from the Following formula

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6. 6 Calculations :   Liquid Limit - Flow curve shall be plotted on semilogarithmic graph, moisture content read from 25 drops as read from the curve. Flow Index – W1-W2, Log10 = N2/N1 shall be recorded as 10 drops Plasticity Index – IP = WL-WP Toughness Index – I T = IP/I F Liquidity Index – I L = Wo-WP/IP Consistency Index Ic = WL-Wo/Ip Wo – Natural moisture content in soil. Single Point Method, Liquid Limit Wn (Moisture Content) 1.3215 – 0.23 log N , Plastic Limit Wn Wn 0.77 Log D 9 (0.65+0.0175)

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