Determination of Compaction of Soil : Part I

OBJECTIVE The objective of this test is determination of water content-dry density relation using light compaction. THEORY Compaction, in general, is the densification of soil by removal of air, which requires mechanical energy. The degree of compaction of a soil is measured in terms of its dry density. The degree of compaction depends upon the moisture content, the amount of compactive effort or energy expended and the nature of the soil. A change in moisture content or compactive effort brings about a change in density. Thus, for compaction of soil, a certain amount of water and a certain predetermined amount of rolling are necessary. The following are the important effects of compaction: (i) Compaction increases the dry density of the soil, thus increasing its shear strength and bearing capacity through an increase in frictional characteristics; (ii) Compaction decreases the tendency for settlement of soil; and, (iii) Compaction brings about a low permeability of the soil. The dry density is maximum at the optimum water content. A curve is drawn between the water content and dry density to obtain the maximum dry density and optimum water content. Compaction method cannot remove all the air voids and therefore, the soil never becomes fully saturated. Thus the theoretical maximum dry density is only hypothetical. For given water content, theoretical maximum density is obtained corresponding to the condition when there are no air voids (i.e. degree of saturation is equal to 100%). The theoretical maximum dry density is also known as saturated dry density. In this condition, the soil becomes saturated by reduction in air voids to zero but with no change in water content. The soil could also become saturated by increasing the water content such that all air voids are filled. The line indicating theoretical maximum dry density can be plotted along with the compaction curve. APPARATUS REQUIRED 1) Moulds: dimension of mould (height 127mm and inner diameter 100 mm) 2) Sample extruder 3) Weighing balances 4) Oven 5) Container: to determine water content. 6) Steel straightedge: 30 cm in a length and having one beveled edge. 7) Sieve: 4.74mm and 19 mm IS-Sieve 8) Mixing tools: tray or pan, spoon, trowel and spatula 9) Metal rammer: having mass of moving part 2.6 kg ± 25 gm and the length of guide pipe shall be such that as to give a fall of 310 ± 0.5 mm. PROCEDURE a) Take a representative portion of air dried soil material and of sufficient quantity such that 6 kg of material passing through 20 mm IS sieve for soils not susceptible to crushing during compaction, or 15 kg of material passing through 19-mm IS sieve for soils susceptible to crushing during compaction. b) Sieve the 15 kg sample through 19-mm IS sieve and broken down sample so that, it will sieved through 4.75-mm sieve. c) Take five samples each of 2.5 kg and mixed each sample thoroughly with a suitable amount of water i.e. for sandy and gravelly soil, moisture content 4 to 6 % and for cohesive soil, moisture content less than 8 to 10 % below plastic limit are required. d) Keep the soil samples in desiccators for 16 hrs such that water is soaked uniformly. e) Weight the empty mould with base plate which is m1 and measure the volume of the mould (V). f) Place the mould in solid place and use oil or grease in mould, collar and rammer so that soil will not attached in mould. Fill the mould with soil sample prepared in three layers and each layer is given 25 blows from 2.6 kg rammer and from height 310mm above soil. After each layer compaction, scrub surface of soil with spatula so that another layer bond together then keep another layer and give 25 blows. g) Remove the collar and remove the extended soil and leveled the compacted soil by using straightedge. h) Weight the mould with base plate and soil sample (m2). i) Then remove the soil specimen from mould and take the soil of different three layers for determination water content (w). j) Repeat the test for at least five times such that maximum dry density will occur at range of water content. Instructor: Dr. Radhakanta Koner, Department of Mining Engineering, IIT(ISM) Dhanbad Students: MTech students of Mining Engineering, IIT(ISM) Dhanbad Course Name: Geomechanics Practical (MNC505) Session: 2020-21, Monsoon Acknowledgment Prabhat Kumar Mandal Krishna Murari Birju Gope Vijay Karanga