ATTERBERG LIMITSLiquid limit test:

A soil is place in the grooving tool which consists of a brass cup and a hard rubber base. A groove is cut at the center of the soil pat using a standard grooving tool. The cup is then repeatedly drooped from a height of 10 mm until a groove closure of 12.7 mm. The soil is then removed and its moisture content is determined. The soil is said to be at its liquid limit when exactly 25 drops are required to close the groove for a distance of 12.7 mm ( one half of an inch)

Plastic limit test:

A soil sample is rolled into threads until it becomes thinner and eventually breaks at 3 mm. it is defined as the moisture content in percent at which the soil crumbles when rolled into the threads of 3.0 mm. If it is wet, it breaks at a smaller diameter; if it is dry it breaks at a larger diameter.Shrinkage limit test:

It is performed in the laboratory with a porcelain dish approximately 45 mm in diameter and about 12.7 mm high.

The dish is completely filled with wet soil. The mass and volume of the wet soil is then recorded.

The dish is then oven dried, then the mass and volume of the oven dried soil is also recorded.

Significance of soil consistency

A knowledge of soil consistency or the relative ease with with the soil can be deformed is important in identifying the soil type.Soil consistency also describes us how the soil might perform when used as a construction material.

Consolidation Test

What is Consolidation?When a saturated clay is loaded externally, the water is squeezed out of the clay over a long time (due to low permeability of the clay).

When a compressive load is applied to soil mass, a decrease in its volume takes place, the decease in volume of soil mass under stress is known as compression.

The property of soil mass pertaining to its tendency to decrease in volume under pressure is known as compressibility.

In a saturated soil mass having its void filled with incompressible water, decrease in volume or compression can take place when water is expelled out of the voids.

Such a compression resulting from a long time static load and the consequent escape of pore water is termed as consolidation.

1D LAB CONSOLIDATION TESTWe want to find the following parameters to estimate the amount and rate of consolidation settlementCompression indices:Coefficient of consolidation:

Equipment

The ring containing the soil sample can be fixed to the container by a collar (fixed ring cell, Figure b) or is unrestrained (floating ring cell, Figure c).

*Cc, Cr , and

1D LAB CONSOLIDATION TESTA disk of soil is enclosed in a stiff metal ring and placed between two porous stones in a cylindrical container filled with water.A metal load platen mounted on top of the upper porous stone transmits the applied vertical stress (vertical total stress) to the soil sample. Both the metal platen and the upper porous stone can move vertically inside the ring as the soil settles under the applied vertical stress.

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1D LAB CONSOLIDATION TESTIncremental loads, including unloading sequences, are applied to the platen, and the settlement of the soil at various fixed times under each load increment is measured by a displacement gage. Each load increment is allowed to remain on the soil until the change in settlement is negligible and the excess porewater pressure developed under the current load increment has dissipated. For many soils, this usually occurs within 24 hours, but longer monitoring times may be required for exceptional soil types, for example, montmorillonite.

Each load increment is doubled. The ratio of the load increment to the previous load is called the load increment ratio (LIR); conventionally, To determine Cr, the soil sample is unloaded using a load decrement ratioload decrement divided by current loadof 2.

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1D LAB CONSOLIDATION TESTWhat data are collected?Initial height of the soil, Ho, which is fixed by the height of the ring.Current height of the soil at various time intervals under each load (timesettlement data).Water content at the beginning and at the end of the test, and the dry weight of the soil at the end of the test.

What plots are prepared?Time (log scale) versus height (to find Cv using Casagrande and Fadum (1940) method, and C)Square root of time versus height (to find Cv using Taylors method)Vertical effective stress (log scale) versus void ratio at the end of each increment ( to find Cc, Cr and zc

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e log v plotloadingv increases &e decreasesunloadingv decreases &e increases (swelling)- from the above data

Compression and recompression indicesCc ~ compression indexCr ~ recompression index (or swelling index)