Sieve Analysis Data Entry
| Sieve Size (mm) | Wt. Retained (g) | % Retained | Cum. % Retained | % Passing |
|---|---|---|---|---|
| Total Sample Weight (g) | - | |||
Particle Size Distribution Curve
Key Parameters & Soil Classification
| Sieve (mm) | Wt. Ret. (g) | % Ret. | Cum. % Ret. | % Passing |
|---|
Theory, Formulas & Standards
Sieve Analysis (ASTM D6913 / IS 2720 Part 4 / BS 1377) determines the particle size distribution (PSD) of granular soils by passing them through a set of sieves with progressively smaller openings. The weight retained on each sieve is recorded and the percentage of material passing each size is calculated and plotted on a semi-log gradation curve.
Percentage Retained on each sieve:
Cumulative Percentage Retained:
Percentage Passing (Finer):
The gradation curve is used to read off key percentile diameters by interpolation:
| Parameter | Definition | Significance |
|---|---|---|
| D10 | Size at which 10% of sample is finer (Effective Size) | Controls permeability; used in filter design |
| D30 | Size at which 30% of sample is finer | Used to compute Cc |
| D60 | Size at which 60% of sample is finer | Used to compute Cu |
| D50 | Median particle size | Common descriptor of average grain size |
| D85 | Size at which 85% is finer | Used in filter and drainage design |
Cu measures the range of particle sizes present. A higher value means a wider distribution (more uniform gradation is paradoxically named).
Classification criteria: Cu ≥ 4 for gravel (GW), Cu ≥ 6 for sand (SW) to be considered well-graded.
Cc describes the shape of the gradation curve between D10 and D60.
For well-graded soils: 1 ≤ Cc ≤ 3. Values outside this range indicate gap-graded or poorly-graded soils.
| Gradation | Cu Criterion | Cc Criterion | Curve Shape | USCS Symbol |
|---|---|---|---|---|
| Well-Graded | ≥6 (Sand), ≥4 (Gravel) | 1 to 3 | Smooth S-curve | SW, GW |
| Poorly Graded | <6 (Sand), <4 (Gravel) | Any | Steep or flat | SP, GP |
| Gap-Graded | - | <1 or >3 | Stepped / irregular | SP, GP |
The Unified Soil Classification System classifies soils based on PSD and plasticity:
| Symbol | Name | % Fines | Cu | Cc |
|---|---|---|---|---|
| GW | Well-Graded Gravel | <5% | ≥4 | 1–3 |
| GP | Poorly Graded Gravel | <5% | <4 or Cu≥4 & Cc out of 1–3 | - |
| SW | Well-Graded Sand | <5% | ≥6 | 1–3 |
| SP | Poorly Graded Sand | <5% | <6 or fails Cc | - |
| GM/SM | Silty Gravel / Sand | 5–12% | Based on Atterberg limits | |
| GC/SC | Clayey Gravel / Sand | 5–12% | Based on Atterberg limits | |
AASHTO classifies soils into groups A-1 through A-7 based on sieve analysis and plasticity for highway subgrade applications. A-1 through A-3 are granular materials (good subgrades); A-4 through A-7 are silt-clay materials (poor subgrades).
For clean, uniform sands with D10 between 0.1 and 3 mm, hydraulic conductivity can be estimated:
where C ≈ 100 (cm/s/mm²) for clean sands and D10 is in mm. This formula is only valid for Cu < 5.
The x-axis (particle size) is plotted on a logarithmic scale because particle sizes in soil range across multiple orders of magnitude - from 0.001 mm (clay) to 100 mm (cobbles). A log scale compresses this range into a readable format and gives equal visual weight to each order of magnitude.
Frequently Asked Questions
1. What is sieve analysis and what does it measure?
Sieve analysis is a standard laboratory procedure (ASTM D6913, IS 2720 Part 4, BS 1377 Part 2) that determines the particle size distribution of granular soils or aggregates by passing the material through a nest of sieves with progressively smaller openings and measuring the weight retained on each sieve. It yields the percent passing versus particle size - the gradation curve.
2. What are D10, D30, and D60 and how are they read from the curve?
D10, D30, and D60 are the particle diameters at which 10%, 30%, and 60% of the soil (by weight) is finer, respectively. They are read by finding the corresponding percent-passing value on the y-axis of the gradation curve, then projecting horizontally to the curve and reading the x-axis (particle size). Interpolation is used between data points.
3. What is the Coefficient of Uniformity (Cu) and what does a high value mean?
Cu = D60/D10. It measures the spread of the particle size distribution. Cu = 1 means all particles are the same size (perfectly uniform). Cu > 6 for sand and Cu > 4 for gravel indicates a well-graded soil with a wide range of sizes. Very high Cu (e.g. > 20) can indicate a broad gradation, sometimes seen in alluvial deposits.
4. What is the Coefficient of Curvature (Cc) and why must it be between 1 and 3?
Cc = (D30)² / (D10 × D60). It describes whether the gradation curve has a smooth, continuous S-shape (well-graded) or an abrupt change (gap-graded). Values of 1–3 indicate a smooth curve without missing particle sizes. Values outside this range suggest that certain size fractions are absent, indicating gap-graded or poorly-graded behavior.
5. What is the difference between well-graded and poorly graded soil?
Well-graded soil (GW, SW) has a wide range of particle sizes with good representation of all sizes - its gradation curve is a smooth S-shape. It compacts well and has good load-bearing capacity. Poorly graded soil (GP, SP) has most particles in a narrow size range - the curve is steep. It has poor interlocking of particles and can be susceptible to liquefaction and piping.
6. What is gap-graded soil?
Gap-graded soil is missing certain intermediate particle sizes. Its gradation curve shows a relatively flat (horizontal) segment over the missing size range. Gap-graded materials are sometimes intentionally used in filters and drains to prevent particle migration, but they can be unstable for structural fill applications.
7. What USCS group does my soil belong to?
Using ASTM D2487: If more than 50% is retained on the No. 200 sieve (>0.075 mm), it's a coarse-grained soil. If more than 50% of the coarse fraction is retained on the No. 4 sieve (>4.75 mm), it's a gravel (G); otherwise, a sand (S). Then well-graded (W) vs poorly graded (P) is determined by Cu and Cc criteria. Use Atterberg limits for soils with 5–12% fines.
8. What are ASTM, IS, and BS sieve standards?
ASTM sieves (US): Follow ASTM E11, used in ASTM D6913 sieve analysis. Common sizes include 4.75, 2.0, 1.18, 0.6, 0.425, 0.3, 0.15, 0.075 mm. IS sieves (India): Follow IS 460, used in IS 2720 Part 4. BS sieves (UK): Follow BS 410, used in BS 1377 Part 2. The sieve sizes differ slightly between standards, particularly for finer sieves.
9. Why is a logarithmic scale used for the x-axis of the gradation curve?
Particle sizes in soils span several orders of magnitude (0.001 mm for clay to >100 mm for cobbles). A log scale compresses this enormous range into a readable plot and gives equal visual importance to each decade (e.g. 0.01–0.1 mm is visually equal to 0.1–1 mm). On a linear scale, fine particles would be compressed into an unreadable region.
10. How do I estimate permeability from sieve analysis?
Hazen's formula: k (cm/s) ≈ C × D10² (with D10 in cm), where C is a constant typically taken as 100 for clean uniform sand. This is valid only for Cu < 5. For other soils, the Kozeny-Carman equation or falling/constant head permeability tests should be used. Sieve analysis provides only an estimate of permeability, not a substitute for direct measurement.
11. What soil fraction cannot be analysed by sieve?
Particles smaller than 0.075 mm (No. 200 sieve) - silts and clays - cannot be distinguished by sieve analysis. Hydrometer analysis (ASTM D7928, IS 2720 Part 4) uses Stokes' law to measure settling velocities of fine particles in suspension, extending the PSD curve below 0.075 mm. A combined sieve and hydrometer analysis gives the complete PSD.
12. How much sample is needed for sieve analysis?
ASTM D6913 recommends minimum sample masses based on maximum particle size: ~500 g for sieve sets going to 4.75 mm, ~5 kg for sets including 19 mm, ~25 kg for sets including 75 mm. Larger samples reduce sampling error for coarser materials. The sample must be representative of the soil deposit, obtained using split-spoon or bulk sampling.
13. How does AASHTO classification differ from USCS?
AASHTO (M 145) focuses on suitability for highway subgrades. It uses the same sieve data but a different classification framework: A-1a, A-1b, A-2 are granular materials (good); A-3 is fine sand; A-4 through A-7 are silty/clayey soils (poor subgrades). AASHTO also uses the Group Index (GI) to rate suitability numerically. USCS is more widely used in geotechnical engineering globally.
14. What is the significance of % fines (passing No. 200 sieve)?
The percentage passing the 0.075 mm (No. 200) sieve is critical for soil classification. Less than 5% fines → clean gravel or sand (G, S). 5–12% fines → borderline, may need Atterberg limits. More than 12% fines → fine-grained component controls behavior (GM, GC, SM, SC). High fines content significantly reduces permeability and can cause frost heave and shrink-swell problems.
15. Can sieve analysis be done on wet or dry samples?
Dry sieve analysis is standard for most coarse-grained soils. Wet sieve analysis (washing the sample through sieves with water before drying and sieving) is required when fines are present, as clay and silt particles tend to clump and clog sieves when dry. ASTM D6913 specifies that samples with significant fines should be washed prior to sieving.