Determination of water content of soil

 Determination of water content of soil — IS 2720 (Part 2) — step-by-step 

Below is a concise, lab-ready procedure following IS 2720 (Part 2) (oven-drying is the standard method). Key points are cited from the BIS standard PDF.  

 

1) Purpose 

Determine the water content ww of a soil sample (percent by dry mass) using the standard oven-drying method.  

 

2) Equipment & materials 

• Non-corrodible airtight containers with lids (moisture cans / small containers). 

• Accurate balance (sensitivity such that weighing error ≤ 0.04% of sample mass for oven method).  

• Thermostatically-controlled oven (interior non-corroding) capable of 110 ± 5 °C.  

• Desiccator (with desiccant), spatula/palette knife, scoop. 

• Optional: sand-bath, methylated spirit (for alcohol method), IR moisture meter or calcium-carbide rapid meter (see notes).  

 

3) Sample mass (recommended minimums) 

Choose a representative sample; recommended minimum masses (for ~90% passing the listed sieve) are: 

• 425 µm (0.425 mm) — 25 g 

• 2 mm — 50 g 

• 4.75 mm — 200 g 

• 10 mm — 300 g 

• 20 mm — 500 g 

• 40 mm — 1000 g 

(If the soil is coarser, take more material.)  

 

4) Procedure — oven-drying (standard method) 

1. Clean and dry the container and lid. Weigh container + lid; record this mass as W₁ (g).  

2. Take the required quantity of soil (representative, crumbled loosely). Place it in the container, replace the lid and weigh. Record this as W₂ (container + wet soil).  

3. Remove the lid; place the container (lid removed) in the oven maintained at 110 ± 5 °C. Dry for 24 hours.  

1. Note: for soils with gypsum, minerals with loosely bound water, or high organic content, oven-drying at 110 °C may be unsuitable — dry at about 60–80 °C for such soils.  

4. After drying, immediately replace the lid and cool the container in a desiccator to room temperature (avoid moisture pickup).  

5. Weigh container + dry soil and record mass as W₃ (g).  

 

5) Calculation (IS formula) 

The water content ww (percent) is: 

w=W2−W3W3−W1×100w = \frac{W_2 - W_3}{W_3 - W_1} \times 100  

where 

• W1W_1 = mass of empty container + lid (g) 

• W2W_2 = mass of container + wet soil (g) 

• W3W_3 = mass of container + dry soil (g).  

Worked numeric example (digit-by-digit): 

Let W1=35.00W_1 = 35.00 g, W2=58.23W_2 = 58.23 g, W3=52.10W_3 = 52.10 g. 

Numerator = W2−W3=58.23−52.10=6.13W_2 - W_3 = 58.23 - 52.10 = 6.13 g. 

Denominator = W3−W1=52.10−35.00=17.10W_3 - W_1 = 52.10 - 35.00 = 17.10 g. 

So w=(6.13/17.10)×100=35.8479%w = (6.13 / 17.10) \times 100 = 35.8479\%. 

Report to two significant figures as required by the code → 36%.  

 

6) Reporting & record 

• Report the water content to two significant figures and keep the test record (soil details, method used, W₁, W₂, W₃, calculations). A pro-forma is given in Appendix A of the standard.  

 

7) Quick alternatives & cautions 

• Sand-bath method (subsidiary): field alternative; dry to constant mass while avoiding overheating (watch paper turning brown).  

• Alcohol method: quick field method using methylated spirit — fire hazard; not suitable for soils rich in clay, gypsum, calcareous matter, or organic matter.  

• Rapid meters: infra-red lamp torsion balance and calcium-carbide gas-pressure meters are described in the standard (faster but have limitations).  

• Important: water-content specimens should be discarded after the test and must not be used for other tests.