INTRODUCTION

ASTM Standard: D-4318

When water is introduced to dry soil, it transforms from a hard to a soft condition. When water is added to a fine-grained soil, the consistency of the water changes from hard to semi-hard. If water is added continuously, the soil's consistency will shift from semi-hard to plastic, eventually reaching a liquid fluidity stage. When the soil reaches a liquid consistency, it loses its cohesive strength, making it impossible for it to maintain its shape under its own weight. It'll begin to lose its shape. As a result, the liquid limit of soil refers to the amount of water that is responsible for the soil's consistency.
            Technically speaking Liquid Limit is the water content wherein a pat of soil cutting it by standard dimension will flow in the same direction with a distance of 12 millimeters at 25 blows in the Casagrande apparatus.
            Identifying the liquid limit is very important for fine grained soils or cohesive soils, it also gives the information of what is the consistency of the soil to be used for construction, it also useful for identifying the consolidation properties of the soil and determines the allowable bearing capacity and settlement of the foundation (elastic, primary consolidated, pre consolidated, immediate).

Equipment’s to be used for this experiment:

 

Casagrande apparatus, Grooving tool, Porcelain evaporating dish, Spatula, Moisture Cans, Balance Scale, Oven, Plastic squeeze bottle, and Paper towels.

Procedure of the Liquid Limit Test – Percussion Cup Method:

1.) Obtain the weight of moisture can using the balance scale.

2.) Fill an evaporating dish halfway with air-dry soil that has been passed through a No.40 sieve. Mix the soil into a uniform paste with water from the plastic squeeze bottle.

3.) Fill the brass cup of the liquid limit device with a small amount of paste. Smooth the surface of the soil in the cup with the spatula until the soil reaches a maximum depth of about 8mm.

4.) Cut a groove along the midline of the dirt pat in the cup with the grooving tool.

5.) Turn the liquid limit device's crank at a pace of around 2 revolutions per second, and the liquid limit cup will rise and fall by 10mm vertically once for each revolution. The soil on the cup's two sides will start to flow toward the center. Count the number of blows N that the groove in the soil receives over a 1/2-inch distance.

            Collect a moisture sample from the soil in the cup of a moisture can if N is between 25 and 35. Close the can's lid and calculate the total mass of the can plus the moist dirt.

            N will be about 35 if the soil is too dry. In this scenario, use the spatula to transfer the soil to the evaporating dish. Using paper towels, thoroughly clean the liquid limit cup. Try again by adding more water to the soil in the evaporating dish.
            N will be less than 25 if the soil is excessively moist. Transfer the dirt in the cup to the evaporating dish in that case. Using paper towels, carefully clean the liquid limit cup. To dry the soil paste, stir it with the spatula for a while.

6.) More water should be added to the soil paste in the evaporating dish, and it should be completely mixed. At a blow count of 25, repeat Steps 3, 4, and 5 to produce a 1/2-inch groove closure in the liquid limit device. Take a sample of moisture from the cup. Fill the evaporating dish with the rest of the soil paste.

7.) To acquire a blow count of N between 15 and 20 for a groove closure of 1/2 in. in the liquid limit device, repeat steps 3, 4, and 5. Take a sample of moisture from the cup.

8.) Place the wet cans in the oven to dry to a uniform consistency. It should be mentioned that the tops of the moisture cans' covers should be removed and placed at the bottom of the cans in the oven.

 

Outcomes, Parameters, and Graphs to be obtained:      

            Moisture Content can be obtained by the ratio of the mass of can + moist soil deducted by mass of can + dry soil and the mass of can + dry soil deducted by the mass of can (ratio of mass of water and dry soil mass) and since for every trial the number of blow were obtained the liquid limit can be obtained using logarithmic scale wherein the x axis is the number of blows and the y axis is the moisture content. At 25 blows, the moisture content can be approximated as 35.2% (see graph and data)