Sand Replacement Test

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What is a sand replacement test?

The test conducted at the field to check the density of soil to ensure whether it has been compacted well as per the requirements is known as Sand Replacement Test.

They are otherwise known as Field Density Test or FDD Test of sand.

Density / Unit Weight – The unit weight of the material is defined as Mass per Volume (M/V)

Why do we use sand replacement tests?

The bearing capacity of a soil depends on the density of soil. The structural design was also calculated based on this. So to achieve the required soil density, we tend to compact and consolidate it well.

Once the compaction has been done, the sand replacement test (Cone test) will be used to determine the density of cohesionless soil.

Objective

The core test method is not possible to find the density of cohesionless soil. So the sand replacement test is used to determine the density of the soil as per the Indian Standard Code IS 2720 Part 28.

The sand replacement method is suitable for where the compacted soil layer does not exceed 150mm.

Apparatus Required

Oven
Trowel
Digging Tools
Weighing Machine
Sand Pouring Cylinder
Metal Tray with Central Hole
Metal container for collecting soil
Glass plate (450 Sqmm and 9mm thickness)
Cylindrical calibrating container (100mm internal diameter & 127.4mm long)

Precaution of Field Density Test

The sand is required as given below, to conduct the calibration for the apparatus.

The natural sand should be free from dust & other impurities.
The sand should retain in a 600-micron sieve passed through the 1mm sieve as per IS standard.
The sand must be dried in the oven after that; it must be allowed to the atmospheric humidity (takes 7 days).
Choose the levelled soil area to conduct the test.
Don’t forget to wear a hand glove when removing the dried sand from the oven.
Note accurate weight to avoid errors.

Calibration of Apparatus

First, we have to find the bulk weight of sand to determine the bulk unit weight of soil.

Measure the calibration container and find the volume.

V = (𝝿 hd²)/4 or (πr2h)

D = 10cm h = 12.74cm

V = 3.14 x 12.74 x 102/4) = 1000 cm³

Volume of Calibrating container V = 1000 cm³

Now take the sand pouring cylinder, which consists of the cone shape at the bottom (inside).
The cone has a slit hole at the top, which can open and close by the nob.
Fill the dried sand up to the top of the cylinder and note its weight as W₁.
Now place the sand pouring cylinder on the calibrating container and open the slit hole to drop the sand in the container.
Once the sand fall has over, close the slit & remove the cylinder. Now the sand has filled over the calibrating container in a cone shape.

Now take the weight of the cylinder, which contains the remaining sand as W₂.
Now we have to find the sand weight of the conical heap over the calibrating container. So to find the conical shape sand weight, place the sand pouring cylinder on the glass plate.
Now open the slit and allow sand to fall on the glass plate in a conical shape. Once the sand fall has over, close the slit & remove the cylinder. Now weight the sand in a conical heap as on the glass plate as W₃.
Now calculate the weight of sand, which fills the calibrating container (conical heap)as W_c.

W_c = W₁ – W₂ – W₃

Bulk density of Sand 𐊄s = Wc / Volume of Calibrating container

𐊄_s = W_c / V

DESCRIPTION	FORMULA/NOTATION	SAMPLE1	SAMPLE2	SAMPLE3
Wt of Sand pouring cylinder with sand	W₁
Wt of the pouring cylinder which consists of remaining sand after sand-filled over the calibrating container	W2
Wt of Conical shape sand	W3
Wt of sand to fill the calibrating container	Wc= W₁ – W2 – W3
Wt of empty calibrating container	V = (𝝿 x h x d2)/4
Bulk Density of Sand	𐊄_s = W_c / V

We just finished the calibration part.

Test Procedure

STEP 1 – The soil surface should be even & clean where the test is going to be conducted.
STEP 2 – Now place the metal tray over the soil surface & excavate the soil through the hole up to 12cm and collect the soil on the metal tray.
STEP 3 – Note the weight of excavated soil as W_e.
STEP 4 – Fill the dried sand up to the top of the sand pouring cylinder and note its weight as W1.
STEP 5 – Then place the sand pouring cylinder over the excavated soil area centre to the dug hole, release the sand to fall on the hole, and close the slit hole.
STEP 6 – Now weight the cylinder, which consists of remaining sand as W2.
STEP 7 – To find the conical heap of sand weight, place the sand pouring cylinder on the glass plate & open the slit hole to allow sand to fall on the glass plate in a conical heap. Once the sand fall has over, close the slit & remove the cylinder.
STEP 8 – Now weight the sand in conical shape as on the glass plate as W3.
STEP 9 – Then determine the weight of the Poured sand, which is filled on the excavated soil hole as Wp.

Wp = W1 – W2 – W3

The volume of the sand-filled to the hole V_h = W_p/𐊄_s

Now the bulk density of soil 𐊄_b = W_e / V_h

Take a small weight of the excavated soil & find the moisture content from the lab.

Now the dry bulk density of soil 𐊄_d = (𐊄_b/1 + m)

Do the test at least 3 different locations and average the value.

Sand Replacement Test Lab Report

DESCRIPTION	FORMULA / NOTATION	SAMPLE 1 (gram/cu. cm)	SAMPLE 2 (gram/cu. cm)	SAMPLE 3 (gram/cu. cm)
Wt of excavated soil	W_e
Wt of Sand pouring cylinder with sand	W1
Wt of the pouring cylinder which consists of remaining sand after sand-filled over the calibrating container	W2
Wt of Conical shape sand	W3
Wt of sand to fill the excavated hole	Wp = W1 – W2 – W3
The volume of the sand-filled to the hole	Vh = Wp/𐊄s
Bulk Density of Soil	𐊄_b = W_e/V_h
Moisture content	m
Bulk density of soil	𐊄_d = (𐊄_b/1 + m)