Determination of In-situ Soil Dry Density by Sand Replacement Method

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The sand replacement test method is used to determine in situ dry density of soil. The procedures, materials, equipment, and specifications of this test is based on the Indian Standard (IS 2720 part 28). This test is of significant importance and it has been widely used in various construction project sites.

The field density of natural soil is required for the estimation of soil bearing capacity for the purpose of evaluation of pressures on underlying strata for computation of settlement, and stability analysis of natural slope.

The sand replacement test method is also used to determine the in-place density of compacted soil in order to compare it with the designated compaction degree, hence it specifies how much the compaction of the soil is close to the designated compaction degree.

Apparatus

1. Sand – pouring cylinder
2. Calibrating container, 100mm diameter and 150mm height
3. Soil cutting and excavating tools, such as scrapper tool, bent spoon
4. Plane surface: Glass or Perspex Plate or Other Plane Surface, 450mm square, 9mm thick or larger
5. Metal container to collect excavated soil
6. Metal tray, 300mm square and 40mm deep with a hole of 100mm in diameter at the center
7. Weighing balance accurate to 1 gram
8. Moisture content cans
9. Oven
10. Desiccator

Materials

Clean, uniform sand passing 1mm IS sieve and retained on 600micron IS sieve in sufficient quantity. It is required to be free from organic substances. The sand should have been dried in an oven and kept in suitable storage for a period of time to allow its water content to reach equilibrium with atmospheric humidity.

Calibrations

1. Measure the internal dimensions of the calibrating container and then calculate its volume.
2. Fill the sand-pouring cylinder with sand, within about 10mm of its top. Determine the weight of the filled cylinder (M₁).
3. Place the sand-pouring cylinder vertically on the calibrating container. Open the shutter to allow the sand run out from the cylinder. When there is no further movement of the sand in the cylinder, close the shutter.
4. Lift the pouring cylinder from the calibrating container and weigh it to the nearest gram (M₂).
5. Place the sand pouring cylinder on the glass plate. Open the shutter and allow the sand to run out of the cylinder until no further movement of the sand is noticed (sand fills the cone of the cylinder), and then close the shutter and remove the sand pouring cylinder carefully.
6. Take the sand on the glass plate and determine its weight (M3)
7. Repeat step 3 to step 6 two more times and record mean weight (mean M2 and M3)
8. Determine the dry density of sand, as shown in Table 1.

Table 1 Calibration for Dry Density of Sand

Sl. No.	Observations and Calculations	Determination No.
-	Observation	1	2	3
1	Volume of calibrating cone VC	-	-	-
2	Mass of pouring cylinder (M1), filled with sand	-	-	-
3	Mass of pouring cylinder after pouring sand into the calibrating container and cone (M2)	-	-	-
4	Mass of sand in the cone (M3)	-	-	-
Calculations
5	Mass of sand in the calibrating container, MC=(1) – (2) – (3)	-	-	-
6	Dry density of sand, ps=MC/VC	-	-	-

Procedure

1. Expose an area of about 450mm square on the surface of the soil mass. Trim the surface down to a level surface using a scrapper tool.
2. Place the metal tray on the leveled surface.
3. Excavate the soil though the central hole of the tray, using the hole in the tray as a pattern. The depth of the excavated hole should be about 150mm.
4. Collect all the excavated soil in a metal container, and determine the mass of the soil (M).
5. Remove the metal tray from the excavated hole.
6. Fill the sand pouring cylinder within 10mm of its top. Determine its mass (M₁).
7. Place the cylinder directly over the excavated hole. Allow the sand to run out the cylinder by opening the shutter. Close the shutter when the hole is completely filled and no further movement of sand is observed.
8. Remove the cylinder from the filled hole. Determine the mass of the cylinder (M₄).
9. Take a representative sample of the excavated soil. Determine its water content.
10. Determine the dry density of soil as shown in Table 2.

Table 2 Observations and Calculations for Dry Density Test of Soil

SI. No.	Observations and Calculations	Determination No.
-	Observation	1	2	3
1	Mass of excavated soil (M)	-	-	-
2	Mass of pouring cylinder (M1), filled with sand	-	-	-
3	Mass of pouring cylinder after pouring into the hole and cone (M4)	-	-	-
Calculations
4	Mass of sand in the hole, MS=M1 – M4- M3	-	-	-
5	Volume of sand in the hole V=Ms/Ps	-	-	-
6	Bulk density =M/V	-	-	-
7	Water content	-	-	-
8	Dry density using formula	-	-	-

Result

The dry density of the soil can be calculated using the following formula:

Dry density=Bulk density/(1+water content) Equation 1