The IS 2720 Part 29 (1975) outlines the procedure for measuring the in-situ dry density of fine-grained soils using the core-cutter technique, applicable when at least 90% of the soil passes a 4.75 mm sieve. This method is designed for natural or compacted soils devoid of coarse aggregates and provides a standardized approach for sampling, weighing, and computing the soil's dry density, ensuring reliable field compaction assessment.
Overview
The IS 2720 Part 29 (1975) outlines the procedure for measuring the in-situ dry density of fine-grained soils using the core-cutter technique, applicable when at least 90% of the soil passes a 4.75 mm sieve. This method is designed for natural or compacted soils devoid of coarse aggregates and provides a standardized approach for sampling, weighing, and computing the soil's dry density, ensuring reliable field compaction assessment.
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IS 2720 Part 29: Defining the Scope and Core Equipment for Dry Density Measurement Using Core-Cutter Method
| Parameter | Symbol | Unit | Remarks |
|---|---|---|---|
| Weight of core-cutter + wet soil | Ws | g | Measured during testing |
| Weight of empty core-cutter | Wc | g | Baseline core-cutter weight |
| Core-cutter volume | Vc | cm³ | Known and constant |
| Bulk Density | ρ_bulk | g/cm³ | Calculated as (Ws - Wc) / Vc |
| Soil Water Content | w | % | Calculated using soil weights |
| Dry Density | ρ_dry | g/cm³ | Derived from bulk density and moisture content |
[ \text{Bulk Density}, \quad \rho_{bulk} = \frac{W_s - W_c}{V_c} ]
[ \text{Water Content}, \quad w = \frac{W_2 - W_3}{W_3 - W_1} \times 100 ]
[ \text{Dry Density}, \quad \rho_{dry} = \frac{\rho_{bulk} \times 100}{100 + w} ]
IS 2720 Part 29: Required Equipment for Soil Moisture and Density Tests
Standard Reference: Equipment for moisture content determination must comply with IS 2720 Part 2 (1973).
Essential Instruments Include:
Additional Equipment for In-situ Density (Rubber Balloon Method):
| Parameter | Unit | Details/Remarks |
|---|---|---|
| Wet Sample Weight | g | |
| Oven-Dried Sample Weight | g | |
| Oven Temperature | °C | 105 ± 5 |
| Drying Duration | hours | Typically 24 |
| Calculated Water Content | % |
[ w = \frac{W_{wet} - W_{dry}}{W_{dry}} \times 100 ]
Where:
flowchart LR
A[Soil Sample] --> B[Weigh Wet Sample]
B --> C[Oven Dry at 105 ± 5°C]
C --> D[Cool in Desiccator]
D --> E[Weigh Dry Sample]
E --> F[Compute Water Content]
This section summarizes the apparatus and procedural steps for moisture content determination as per IS 2720 Part 29.
IS 2720 Part 29 (1975) – Sampling and Testing Procedures Overview
The standard outlines the approach for collecting soil samples for engineering analyses:
| Sample Type | Intended Use | Collection Tool | Approximate Size |
|---|---|---|---|
| Disturbed | Particle size, Atterberg limits | Auger, spade | 2-5 kg |
| Undisturbed | Strength, compressibility | Shelby tube | 50-100 mm diameter; length as required |
| Block Sample | Structural study | Excavation, trimming | Variable |
flowchart LR
A[Soil Layer] --> B[Sampling]
B --> C{Sample Type}
C --> D[Disturbed]
C --> E[Undisturbed]
C --> F[Block Sample]
D --> G[Auger or Spade]
E --> H[Shelby Tube]
F --> I[Excavation and Trimming]
For comprehensive procedures and specifications, refer to the full IS 2720 Part 29 (1975) documentation.
IS 2720 Part 29 – Essential Computations for Soil Density Testing
[ \rho = \frac{W}{V} ]
[ w = \frac{W_w}{W_d} \times 100 ]
[ \rho_d = \frac{\rho}{1 + \frac{w}{100}} ]
flowchart LR
A[Soil Sample] --> B[Measure Core Cutter Volume (V)]
A --> C[Mass of Wet Soil (W_wet)]
C --> D[Dry Soil Mass (W_dry)]
B & D --> E[Calculate Bulk Density (ρ = W_dry/V)]
D & C --> F[Calculate Moisture Content (w = (W_wet - W_dry) / W_dry * 100)]
E & F --> G[Calculate Dry Density (ρ_d = ρ / (1 + w/100))]
This section consolidates the key formulas and apparatus requirements for determining soil density following IS 2720 Part 29.
IS 2720 Part 29: Guidelines for Reporting Results Using Core-Cutter Technique
Bulk Density (ρ): [ \rho = \frac{W_s - W_c}{V_c} \quad (g/cm^3) ] where:
Water Content (w) (%): [ w = \frac{W_2 - W_3}{W_3 - W_1} \times 100 ] where:
Dry Density (ρ_d): [ \rho_d = \frac{\rho \times 100}{100 + w} \quad (g/cm^3) ]
| Parameter | Test 1 | Test 2 | Test 3 |
|---|---|---|---|
| Weight of core cutter + wet soil (Ws) (g) | |||
| Weight of core cutter (Wc) (g) | |||
| Volume of core cutter (Vc) (cm³) | |||
| Bulk density (ρ) (g/cm³) | |||
| Weight of container + lid (W1) (g) | |||
| Weight of container + lid + wet soil (W2) (g) | |||
| Weight of container + lid + dry soil (W3) (g) | |||
| Water content (w) (%) | |||
| Dry density (ρ_d) (g/cm³) |
Ensure all data is carefully recorded following this format for consistency and traceability.
IS 2720 Part 29: Standard Template for Documenting Dry Density Test Results (Core Cutter Method)
Bulk Density (ρ): [ \rho = \frac{W_s - W_c}{V_c} \quad (g/cm^3) ] where:
Moisture Content (w %): [ w = \frac{W_2 - W_3}{W_3 - W_1} \times 100 ] where:
Dry Density (ρ_d): [ \rho_d = \frac{\rho}{1 + \frac{w}{100}} \quad (g/cm^3) ]
| Determination No. | 1 | 2 | 3 |
|---|---|---|---|
| Weight of core cutter + wet soil (Ws) (g) | |||
| Weight of empty core cutter (Wc) (g) | |||
| Weight of wet soil (Ws - Wc) (g) | |||
| Volume of core cutter (Vc) (cm³) | |||
| Bulk density (ρ) (g/cm³) | |||
| Container number for moisture test | |||
| Weight of container + lid (W1) (g) | |||
| Weight of container + lid + wet soil (W2) (g) | |||
| Weight of container + lid + dry soil (W3) (g) | |||
| Moisture content (w) (%) | |||
| Dry density (ρ_d) (g/cm³) |
Complete this proforma for each measurement to maintain consistency and accuracy.
Frequently Asked
Per IS 2720 Part 29 (1975), the core-cutter technique is intended for fine-grained soils where at least 90% passes through the 4.75 mm IS sieve, particularly soils without coarse aggregates. It is best suited for natural or well-compacted soils and is not recommended for coarse or aggregated soils. The method provides rapid results but with somewhat lower accuracy compared to other techniques.
The core-cutter apparatus per IS 2720 Part 29 includes:
Water content is measured by collecting a representative soil sample immediately after core extraction and sealing it in an airtight container to prevent moisture loss. Following IS 2720 Part 2 (1973), the sample is weighed wet (W_wet), oven-dried at 105 ± 5°C until constant weight, and then weighed dry (W_dry). The water content percentage (w) is calculated as:
[ w = \frac{W_{wet} - W_{dry}}{W_{dry}} \times 100 % ]
Multiple tests are recommended to ensure accuracy.
The procedure involves:
The core-cutter method offers moderate accuracy and is best suited for fine-grained, well-compacted soils. It is generally less precise than the sand replacement method, which is preferred for higher accuracy requirements. While faster and simpler, core-cutter sampling may cause some soil disturbance and is less suitable for coarse or loosely compacted soils. Nuclear density gauges and sand replacement methods typically provide better accuracy and are favored for critical engineering assessments.
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