Transportation, Porosity, Permeability, Surface to volume ratio, Cohesion forces

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Kelly Lester
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1 3 rd lecture note of geotechnical engg. Paushali Effects of particle size can be felt in : Transportation, Porosity, Permeability, Surface to volume ratio, Cohesion forces How to physically separate soil particles based on their size distribution : By 1. sieving the most basic way of going about it 2. gravity separation method (actually weight dependant) 3. hydrometer analysis utilising terminal velocity principle that uses the formula for terminal velocity given by, where ~ density, D~ diameter of falling sphere, ~ fluid viscocity. Contrary to what was believed during classes during this period, there was no mention of velocity gradient anywhere at all while deriving the above working form. Actually, the mechanism is a as follows. When a body that s approx. spherical (in this case, the soil particle) falls through a fluid it drags the layer of the fluid(here, water) in contact with it. A relative motion between the different layers of the fluid is set and as a result the body experiences a retarding force, which we call the viscous drag. The factors that cause this force is encapsulated in the well mentioned Stokes Law, that tells us = rv where r ~ radius of the falling sphere, v ~ velocity at a given instant of the same Basically, the forces acting on the falling mass are given by this viscous drag(upwards), the force due to gravity (downwards) and the buoyant force (upwards, following Archimedes principle). As the drag continues to increase with increasing velocity(that s again due to acc. due to gravity), a time soon comes when the net downward force equals the upward counterpart, and the body is at equilibrium. As all the motion inducing forces are diminished at this point, there is no futher gain in the velocity of the sphere coming down; the constant velocity that emerges hence is called the terminal velocity. Mathematically, + = r + 4/3* = 4/3* r = 4/3*

2 =4 /18 = /18 Next, we deal with the volume-weight relationships in soil, where we assume 3 phases in a standard soil element such that a strata of soil can be considered to be built of separate layers of soil solids, water and air in all. The total volume of the soil sample can be expressed as As weight of air is near negligible, we can say Then, for our further use, we can define,, From these one can arrive at the relation Also there are,, from whence one can come at

and then,, Taking volume of soil solids as one(1), volume of voids automatically turns up as the void ratio(e),we can rewrite previous stuff as It is so as : Specific gravity of soil solids will be

3 and then,, Taking volume of soil solids as one(1), volume of voids automatically turns up as the void ratio(e),we can rewrite previous stuff as It is so as : Specific gravity of soil solids will be defined as the ratio of unit weight of soil solids to the unit weight of water. As the volume associated with the solid parts is 1, and density of same being given by the product of specific gravity and the unit weight of water, the weight linked with the soil solids is indeed the one we get above. Likewise (i)

4 (ii) - weight. And to make the maximum possible value, we need to nullify Now, compaction depends on other than obviously soil type : 1. Initially there is a positive correlation to weight of soil solids in a unit volume to increasing moisture; as when water is added into the soil during compaction, it acts as a softening/lubricating agent and helps soil particles slip over each other and move into a densely packed position. However there is a maximum value to this (i.e. the reverse effect of reduction in dry unit weight to increasing, as after an optimal amount of, the extra water takes up all those spaces that would otherwise have been occupied by soil particles. 2. As greater the degree of compaction or mechanical energy expended, greater is the compacted result with denser packing. It is generally measured by number of blows from (ii)

And recalling eqn (i) that tells us We obtain, The graph pertains to compaction events when the compactive effort is kept a same constant value throughout However while theory predicts maximal

5 And recalling eqn (i) that tells us We obtain, The graph pertains to compaction events when the compactive effort is kept a same constant value throughout However while theory predicts maximal density on total compression of soil so as to have no air left in the pores(any open spaces),it s impracticable to totally remove all air traces. Thus the dry unit weight curve falls short of meeting the hight point of zeroair-void curve, and literally falls off after the initial impression of ascending towards the

6 curve, straying down to the zone when addition of water is to its detriment rather than benefit. When compactive effect is added to the picture, the net effect is as the given figure Clay Minerals The latter is also known as gibbsite sheet..

7 . The negative charge to balance the potassium ions comes from the substitution of Aluminium for some silicon in the tetrahedral sheets...

8 Note have refrained from putting Debye Screening here that was covered during the same term as the requisite pdf has been made available to us all anyway.

Tikrit University. College of Engineering Civil engineering Department SOIL PROPERTES. Soil Mechanics. 3 rd Class Lecture notes Up Copyrights 2016

Tikrit University. College of Engineering Civil engineering Department SOIL PROPERTES. Soil Mechanics. 3 rd Class Lecture notes Up Copyrights 2016 Tikrit University SOIL PROPERTES College of Engineering Civil engineering Department Soil Mechanics 3 rd Class Lecture notes Up Copyrights 2016 1-Soil Composition -Solids -Water -Air 2-Soil Phases -Dry