cementation: When fluids deposit ions to create a cement that hardens loose sediments. compaction: When sediments are squeezed together by the weight of sediments and rocks on top of them.

Cementation is the process of precipitation of mineral matter (cements) in pores within sediments or rocks. Cements even form crusts on surfaces at sediment-water or sediment-air interfaces. Precipitation of cements can occur at any stage from deposition, through burial, to uplift and re-exposure.

happens when sediments are deeply buried, placing them under pressure because of the weight of overlying layers. This squashes the grains together more tightly.

Compaction and Cementation They are compacted, reducing the available pore space and expelling much of the pore-water. Dissolved minerals in the ground water precipitate (crystallize) from water in the pore spaces forming mineral crusts on the sedimentary grains, gradually cementing the sediments, thus forming a rock.

As the layers of sediment build up, the pressure on the lower layers increases. The layers are squeezed together and any water mixed in with the sediments is forced out. This process is called compaction.

In sedimentology, compaction is the process by which a sediment progressively loses its porosity due to the effects of pressure from loading. When a layer of sediment is originally deposited, it contains an open framework of particles with the pore space being usually filled with water.

noun. the act of compacting or the state of being compacted. Geology. the consolidation of sediments resulting from the weight of overlying deposits.

Methods of compaction of soil used in field

1. Smooth wheeled roller.
2. Sheep foot roller.
3. Pneumatic roller.
4. Vibratory roller.
5. Impact rammers.

Compaction is the application of mechanical energy to a soil to rearrange the particles and reduce the void ratio. The principal reason for compacting soil is to reduce subsequent settlement under working loads. Compaction can prevent the build up of large water pressures that cause soil to liquefy during earthquakes.

MDD – Maximum Dry Density. MWD – Maximum Wet Density. OMC – Optimum moisture Content. Zero Air Voids – is the relationship between dry density and corresponding moisture contents, for a specific particle density, assuming that all of the voids are completely filled with water.

95% compaction means that the soil on the construction site has been compacted to 95% of the maximum density achieved in the lab. Remember the test in the lab uses a specific compaction effort so it is possible to achieve compaction above 100% in the field.

The curve showing the relationship between the density (dry unit weight) and the water content of a soil for a given compactive effort.

The determination of maximum dry density and optimum moisture content of the soil is a measure of compaction level of soils. Both the tests help to determine the optimum moisture content that is required for soil to attain maximum compaction i.e maximum dry density for performing construction.

For compacting soil containing coarse material upto 37.5mm size, the 2250cc mould should be used. A sample weighing about 30kg and passing through the 37.5mm IS Sieve is used for the test. Soil is compacted in five layers, each layer being given 55 blows of the 4.9kg rammer. The rest of the procedure is same as above.

The california bearing ratio test is penetration test meant for the evaluation of subgrade strength of roads and pavements. The results obtained by these tests are used with the empirical curves to determine the thickness of pavement and its component layers.

Water contain can’t be greater than 100% cause it’s impossible to get obtain marks greater than the total marks.

The amount of water is determined by subtracting the dry weight from the initial weight, and the moisture content is then calculated as the amount of water divided by the dry weight or total weight, depending on the reporting method.

Usually water content refers to wet basis while moisture content refers to a dry basis. So basically water content = (total weight – dry weight)/total weight and moisture content = (total weight – dry weight)/dry weight.

The void ratio is thus a ratio which can be greater than 1. It can also be expressed as a fraction. Void ratio and porosity differ only in the denominator.

The void ratio of a dense sandy gravel soil is about 0.3, that of a loose sand is about 0.6, while the void ratio of clays (in natural conditions) varies between 0.5 and 1.0 and decreases with depth of the soil layers.

noun. Definition of void (Entry 2 of 3) 1a : opening, gap. b : empty space : emptiness, vacuum. 2 : the quality or state of being without something : lack, absence.

To calculate the void ratio we must first calculate the volume of solids. Then we can find the volume of voids by subtracting the volume of solids from the total volume.

Tetrahedral void is the vacant space between four touching spheres. Since, one sphere touches three spheres present in the layer below and three spheres present in the above layer, there are two tetrahedral sites associated with one sphere.

The atom in the tetrahedral void is in contact with four atoms placed at four corners of a tetrahedron. This void is formed when a triangular void made coplanar atoms (first layer) is in contact with the fourth atom above or below it (second layer).

Now let us discuss the octahedral voids in HCP lattice. We know that the void surrounded by four spheres sitting at the corners of a regular tetrahedron is called a tetrahedral.

We can see from the figure that the octahedral holes are present at edge centres and body centre in a fcc unit cell.

A.In a one-unit cell there are 12 octahedral voids and all are completely inside the unit cell.

In ccp and hcp lattices, there are two tetrahedral holes per packing atom.