Types of Soil Testing for Construction

TYPES OF SOIL TESTING FOR CONSTRUCTION  

Soil tests are carried out to ensure optimum conditions for the soil hence making sure the working conditions are as per requirements for a smooth construction. Technically it is the first step in any construction activity as the entire load of a structure is transferred to the soil and if the soil conditions are not optimum, chances of structure failure are quite high. 

Different types of soil tests are carried out accordingly.

1. Core cutter method:

This method is used to find the in-situ dry density of soil. 

( condition: it is only used in case of fine grained soil )

This method involves,

• a cylindrical core cutter ( 130mm in length and 100mm in diameter )
• a steel dolly ( 25mm high and 100mm in diameter )
• steel rammer ( 9kg mass and 900mm length )
• weighing balance

PROCEDURE:

• Determine the volume of core cutter by measuring the internal dimensions.
• Calculate the weight of core cutter without dolly.
• Drive the cutter into the soil by placing dolly over the cutter.
• Remove the cutter containing soil.
• Remove the dolly and trim off the excess soil.
• Calculate the weight of cutter filled with soil.
• Take the representative sample and repeat the test three/four times and calculate the average density.

2. Sand Replacement Method:

This method is also used for dry density testing of soil.

This method involves,

• sand pouring cylinder
• calibrating container
• tray with circular hole
• chisel

PROCEDURE:

• Fill the cylinder with uniformly graded sand up to a height of 10mm below the top.
• sand is made to pass through 600 micron sieve and retained on 300mm sieve.
• This weight is recorded as M1.
• Place the sand pouring cylinder over a plane surface and open the shutter to allow the sand to fill the cone.
• This weight is recorded as M2.
• Collect the sand on the plane surface and transfer it back to the pouring cylinder.
• Place the sand pouring cylinder over the cylindrical can and allow the sand to fall into the cylindrical can till it is full. 
• Once the sand is filled, close the shutter.
• Measure the weight of pouring cylinder again and this is noted as M3.
• Calculate the unit weight of sand.

3. Calculation of Liquid Limit using Casagrande's apparatus:

Liquid limit refers to the moisture content at which the soil sample can flow and close a groove of standard width.

This method involves,

• Casagrande's apparatus
• Grooving tool
• Wash bottle 
• Palette knives

PROCEDURE:

• Pass approximately 120g of soil sample through a 425 micron IS sieve and mix it with distilled water.
• Take into consideration that the paste should be consistent.
• Place the sample in the cup and with the help of a spatula, spread it across the entire cup to be uniform.
• With the help of a grooving tool, make a sharp groove along the diameter from the center.
• Drop the cup from a height of 10mm by cranking it at a rate of 2 revolutions/sec until the two halves of the soil cake come in contact with the bottom of the groove at a distance of 12mm.
• Make a note of the number of drops required to close the gap of 12mm.
• Repeat the procedure about 4 times and record the observations.
• Plot a graph of the recordings and the moisture content corresponding to 25 drops is taken as the liquid limit of the soil.

4. Shrinkage limit test on soil:

When the water content is sufficient enough to fill all the pores of the soil and the soil is saturated, that is known as shrinkage limit. It is defined as the lowest water content at which the soil is completely saturated.

This method involves,

• Shrinkage dish
• Evaporating dish
• Glass cup
• Spatula
• 425 micron IS sieve
• Balance
• Mercury

PROCEDURE:

• Pass 100g of soil sample through 425 micron IS sieve.
• Mix 30g of soil sample with distilled water in an evaporating dish till the voids are completely filled.
• Weigh an empty shrinkage dish. This weight is taken as W1.
• Grease the inside of the dish to prevent adhesion and fill the shrinkage dish in 3 equal layers.
• Weigh the shrinkage dish with wet soil. This weight is taken as W2.
• First the sample is dried at room temperature for approx. 24 hours and then shifted to oven at 105 - 110 degree celsius. 
• Note the weight of oven dried shrinkage dish. This weight is taken as W3.
• Remove the soil cake from the shrinkage dish. 
• Remove the excess mercury from the paste by placing sponge on top of the soil cake. Gently transfer this over a dry container and make a note of the weight as Ws.
• Carry out the necessary calculations.

5. Proctor's Compaction Test:

Compaction refers to the mechanical effort applied over a soil in order to rid it of the void space between particles. 

This method involves,

• Rammer of mass 2.6kg
• Compaction mould of capacity 1000ml
• IS sieve ( 4.75mm )
• Oven 
• Weighing balance 
• Mixing pan
• Spatula
• Mixing tools

PROCEDURE:

• Pass 20kg soil through 4.75mm IS sieve.
• Calculate the percentage retaining on sieve and the percentage passing the sieve.
• 100mm of mould is used for this procedure. Mix both the soil percentages.
• Grease the mould and base plate and weigh them to the nearest accuracy.
• Add water to the soil and keep it in an air tight container for about 18 - 20 hours for maturing and mix it thoroughly.
• Divide the sample into 6 parts.
• Take 3kg of soil and place it in the mould in 3 equal layers.
• Take one third of the sample and compact it by giving 25 blows of the rammer. Distribute the blows uniformly over the soil layer. Repeat it for the second and third layer.
• Trim the excess soil and remove the mould. Weigh the sample.
• Determine the water content for the top, middle and bottom layer and carry out the necessary calculations.