Determining Soil Density with the Sand Replacement Method

Soil density plays a crucial role in construction projects, influencing factors like bearing capacity, settlement, and slope stability. The Sand Replacement Method, based on Indian Standard (IS 2720 part 28), is widely employed for determining the in-situ dry density of soil. This method aids in evaluating how well the compacted soil aligns with the designated compaction degree.

Importance in Construction

Accurate field density measurements are essential for assessing soil bearing capacity, which, in turn, informs calculations for underlying strata pressures, settlement estimates, and natural slope stability analyses.

Apparatus and Materials

The Sand Replacement Test involves specific apparatus and materials:

Apparatus:

• Sand-pouring cylinder
• Calibrating container
• Soil cutting tools (scrapper tool, bent spoon)
• Glass or Perspex Plate
• Metal containers and trays
• Weighing balance
• Moisture content cans
• Oven
• Desiccator

Materials:

• Clean, uniform sand (passing 1mm IS sieve)
• Calibrating container
• Metal tray

Calibration Process

Before conducting the test, calibration is crucial:

1. Measure the calibrating container’s internal dimensions and calculate its volume.
2. Fill the sand-pouring cylinder, determine its weight, and calibrate the sand-pouring process.

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

Testing Procedure

1. Expose a 450mm square area on the soil surface using a scrapper tool.
2. Place the metal tray on the leveled surface.
3. Excavate the soil through the central hole of the tray, with a depth of about 150mm.
4. Collect excavated soil in a metal container and determine its mass (M).
5. Fill the sand pouring cylinder, determine its mass (M1).
6. Place the cylinder over the excavated hole, allow sand to fill it, and close the shutter.
7. Remove the cylinder, determine its mass (M4), and sample the excavated soil for water content.
8. Calculate the dry density of soil.

SI. No.	Observations and Calculations	Determination No.
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 (M4)	–
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	–

Results

The dry density of the soil is determined using the formula:

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

This comprehensive method ensures accurate in-situ soil density measurements, vital for successful construction outcomes.