Shrinkage Limit Test as per IS-2720-Part-6-1972

 Shrinkage Limit Test as per IS-2720-Part-6-1972 

The Shrinkage Limit Test is a crucial procedure in soil mechanics, as outlined in IS-2720-Part-6-1972 (reaffirmed in 2001). This test evaluates the water content at which soil transitions from a saturated state to a semi-solid state, marking a pivotal boundary in the behavior of soil as it undergoes moisture variations. 

Shrinkage Limit Test as per IS-2720-Part-6-1972 

Theory of the Shrinkage Limit 

At the shrinkage limit, the reduction in water content no longer decreases the soil's volume. Conversely, adding more water results in an increase in volume. This phenomenon is essential for understanding how different soils, particularly expansive ones like black cotton soil, behave through wet and dry cycles due to seasonal changes. Recognizing this limit helps engineers design structures that account for potential soil movement, ensuring stability and longevity. 

Need and Scope 

The shrinkage limit test is vital in geotechnical engineering, especially in regions where soils experience significant volume changes with moisture fluctuations. Knowing the shrinkage limit aids in predicting soil behavior during construction projects, thus minimizing risks associated with ground movement. 

Apparatus Required 

To conduct the Shrinkage Limit Test, the following apparatus is necessary: 

1. Evaporating Dish (Porcelain) 
2. Spatula and Straight Edge 
3. Balance (Sensitive to 0.01 g) 
4. Shrinkage Dish (Circular, made of porcelain or non-corroding metal) 
5. Glass Cup (50-55 mm in diameter, 25 mm in height) 
6. Two Glass Plates (75x75 mm; one plain, one with prongs) 
7. Thermostatically Controlled Oven 
8. Wash Bottle (Distilled Water) 
9. Graduated Glass (25 ml capacity) 
10. Mercury 
11. Grease 

Procedure 

Preparation of Soil Paste 

1. Sample Preparation: Take approximately 100 g of soil passing through a 425 μm sieve. Mix 30 g of this soil with distilled water to create a creamy paste, ensuring the water content is slightly above the liquid limit. 

Filling the Shrinkage Dish 

• Grease Application: Apply a thin layer of grease inside the shrinkage dish to prevent soil adhesion. 
• Layering Soil: Fill the dish in three layers, tapping gently after each layer to eliminate air bubbles and ensure compaction. Strike off excess soil for a smooth finish. 
• Weight Measurement: Immediately weigh the dish with wet soil and record the weight. 
• Drying Process: Air-dry the soil cake for 24 hours until it lightens, then oven-dry at 105-110°C for another 24 hours. 

Volume Determination 

• Cooling: Remove the dried soil disk from the oven and cool it in a desiccator before weighing. 
• Volume of Wet Soil: Submerge the shrinkage dish in mercury, allowing it to overflow, then measure the displaced mercury volume to determine the wet soil volume. 
• Volume of Dry Soil: Similarly, immerse the dried soil pat in mercury using the glass cup method to find its volume. 

Tabulation and Results 

Here's the requested table formatted for clarity: 

Sr. No	Determination	No. 1	No. 2	No. 3
1	Wt. of container in gm (W1)
2	Wt. of container + wet soil pat in gm (W2)
3	Wt. of container + dry soil pat in gm (W3)
4	Wt. of oven-dry soil pat in gm (W0 = W3 - W1)
5	Wt. of water in gm (W2 - W3)
6	Moisture content (%) (W = (W2 - W3) / (W3 - W1) * 100)
7	Volume of wet soil pat (V), in cm³
8	Volume of dry soil pat (Vd) in cm³
	a. Weight of displaced mercury in gm (Wm)
	b. Specific gravity of the mercury (Gm)
9	Shrinkage limit (WS = [W - {(V - Vd) * (γw / Wo)}] x 100)
10	Shrinkage ratio (R = {(V - Vd) / Vd} * 100 / (W - Ws))

 

Interpretation 

The shrinkage limit correlates with the degree of expansion in soils, categorized as follows: 

• > 15%: Low expansion 
• 10-16%: Medium expansion 
• 7-12%: High expansion 
• < 11%: Very high expansion 

Understanding these correlations helps engineers assess the risk of soil movement and design appropriate foundations or structures. 

Conclusion 

The Shrinkage Limit Test is an essential tool in geotechnical engineering. It provides valuable insights into the behavior of soils under varying moisture conditions, enabling better predictions of soil performance in engineering applications. By conducting this test, engineers can effectively mitigate risks associated with soil shrinkage and swelling, ultimately contributing to the safety and durability of civil engineering projects.