IS 2720 Part 17 (1986) specifies standardized laboratory methods for determining the coefficient of permeability of soils using falling head and constant head tests. It applies to soils with permeability coefficients ranging from 10^-3 to 10^-7 cm/s and maximum particle size up to 9.5 mm. This standard guides engineers in accurately assessing soil permeability, critical for projects involving seepage analysis, foundation design, and earth dam construction.
Overview
IS 2720 Part 17 (1986) specifies standardized laboratory methods for determining the coefficient of permeability of soils using falling head and constant head tests. It applies to soils with permeability coefficients ranging from 10^-3 to 10^-7 cm/s and maximum particle size up to 9.5 mm. This standard guides engineers in accurately assessing soil permeability, critical for projects involving seepage analysis, foundation design, and earth dam construction.
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Contents
Structure
IS 2720 Part 17 - Scope & Key Specifications
This part covers the determination of permeability of soils by constant and falling head methods.
[ k_T = \frac{Q \times L}{A \times t \times h} ]
Where:
(k_T) = permeability at test temperature (cm/s)
(Q) = volume of water passed (cm³)
(L) = length of soil specimen (cm)
(A) = cross-sectional area (cm²)
(t) = time (s)
(h) = hydraulic head loss (cm)
Permeability correction to 27°C:
[ k_{27} = k_T \times \frac{\nu_T}{\nu_{27}} ]
Where (\nu_T), (\nu_{27}) are kinematic viscosities at test and 27°C respectively.
| Quantity | Unit | Symbol |
|---|---|---|
| Length | metre | m |
| Time | second | s |
| Permeability | cm/s | k |
[ W = \frac{W_t - W_s}{W_s} \times 100% ]
[ e = \frac{V_s - W_s/G_s}{W_s/\rho_w} ]
[ S = \frac{W \times G_s}{e} \times 100% ]
| Initial time (t_1) (s) | Final time (t_f) (s) | Initial head (h_1) (cm) | Final head (h_2) (cm) | ( \log_{10} \frac{h_1}{h_2} ) | ( k_T ) (cm/s) |
|---|
flowchart LR
A[Start Test] --> B[Measure Q, t, h, L, A]
B --> C[Calculate kT]
C --> D[Correct kT to k27]
D
IS 2720 Part 17 (1986) - Terminology & Key Formulas
| Parameter | Formula/Definition |
|---|---|
| Coefficient C | ( C = 2.303 \times a \times L ) |
| Permeability (K_T) | [ |
| K_T = \frac{\log_{10} \frac{h_1}{h_2} \times C}{t_f - t_1} \quad \text{(cm/s)} | |
| ] where: <br> (h_1, h_2) = initial & final head (cm), <br> (t_1, t_f) = initial & final time (s) | |
| Water Content (W%) | [ |
| W = \frac{W_t - W_s}{W_s} \times 100 | |
| ] where (W_t) = wet weight, (W_s) = dry weight | |
| Specific Gravity (G_s) | As per IS 2720 Part 3 |
| Degree of Saturation (S) | [ |
| S = \frac{W \times G_s}{e} | |
| ] where (e) = void ratio | |
| Void Ratio (e) | [ |
| e = \frac{V_v}{V_s} | |
| ] (volume of voids/volume of solids) |
| Quantity | Unit | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Pressure/Stress | pascal (N/m²) | Pa |
| Force | newton | N |
flowchart LR
A[Constant Head Tank] --> B[Permeameter]
B --> C[Soil Specimen]
C --> D[Water Flow]
D --> E[
IS 2720 Part 17: Apparatus, Materials & Key Formulas
| Parameter | Formula / Definition |
|---|---|
| Area of specimen, A | ( A = \pi \frac{D^2}{4} ) (D = diameter in cm) |
| Hydraulic gradient, i | ( i = \frac{h_1 - h_2}{L} ) (h = head in cm, L = length in cm) |
| Permeability (Constant Head), ( k_T ) | ( k_T = \frac{Q \times L}{A \times t \times h} ) (cm/s) |
| Water content, W (%) | ( W = \frac{W_t - W_s}{W_s} \times 100 ) |
| Void ratio, e | ( e = \frac{V_s}{V_w} - 1 ) or ( e = \frac{G_s \times W}{S} ) (from context) |
| Degree of saturation, S (%) | ( S = \frac{W \times G_s}{e} \times 100 ) |
| Permeability corrected to 27°C, ( k_{27} ) | ( k_{27} = k_T \times Y_{27} / Y_T ) (Y = viscosity correction factor) |
| Sl No. | Initial Time ( t_1 ) (s) | Final Time ( t_f ) (s) | Initial Head ( h_1 ) (cm) | Final Head ( h_2 ) (cm) | ( \frac{h_1}{h_2} ) | ( \log_{10} \frac{h_1}{h_2} ) | ( k_T = \frac{\log_{10} (h_1/h_2) \times C}{t_r - t_1} ) (cm/s) | Remarks | |--------|----------------
IS 2720 Part 17: Preparation of Test Specimen - Key Formulas & Specifications
[ k_T = \frac{Q \times L}{A \times t \times h} \quad \text{(cm/s)} ]
Where:
[ k_{27} = k_T \times \frac{\eta_T}{\eta_{27}} ]
flowchart LR
A[Measure Specimen
[ k_T = \frac{Q \times L}{A \times t \times h} \quad \text{(cm/s)} ]
Where:
[ k_T = \frac{2.303 \times a \times L}{A \times (t_r - t_1)} \times \log_{10} \frac{h_1}{h_2} \quad \text{(cm/s)} ]
Where:
| Parameter | Formula/Definition |
|---|---|
| Water content, (W) (%) | (\frac{W_t - W_s}{W_s} \times 100) |
| Void ratio, (e) | (\frac{V_s}{V_w} - 1) (from specimen volumes) |
| Degree of saturation, (S) (%) | ( \frac{W \times G_s}{e} \times 100 ) |
| Permeability at 27°C, (k_{27}) | Corrected using temperature factor (Y_{27}/Y_T) |
| Initial Time (t_1) (s) | Final Time (t_f
IS 2720 Part 17: Observations and Calculations Key Points
| Parameter | Observed Value | Calculated Value | Remarks |
|---|---|---|---|
| Load | |||
| Settlement | |||
| Time | |||
| Shear strength | |||
| Permeability |
flowchart TD
A[Observation] --> B[Record Data]
B --> C[Calculate Parameters]
C --> D[Present Data Sheet]
D --> E[Analyze Results]
Summary: Use standard formulas to calculate soil parameters from observations, record systematically in data sheets per Appendix B for clarity and consistency.
IS 2720 Part 17: Presentation of Results (Clause 6.4)
| Parameter | Observation Data | Calculation Formula | Result | Units |
|---|---|---|---|---|
| Initial reading | e.g., 10 mm | |||
| Final reading | e.g., 5 mm | |||
| Change in parameter | Final - Initial | 5 mm | mm | |
| Calculated property | Formula (e.g., moisture %) | Computed value | % |
If you want, I can provide a sample data sheet template or calculation example.
IS 2720 Part 17: Constant Head Method - Key Formulas & Data Sheet
| Parameter | Symbol | Unit | Notes |
|---|---|---|---|
| Diameter of specimen | D | cm | Measured directly |
| Length of specimen | L | cm | Measured directly |
| Cross-sectional area | A = πD²/4 | cm² | Calculate from diameter |
| Volume of specimen | V = A × L | cm³ | |
| Head loss | h = H₁ - H₂ | cm | Difference in water heads |
| Hydraulic gradient | i = h / L | - | Dimensionless |
| Quantity of flow | Q | cm³ | Volume collected during time t |
| Time | t | seconds | Duration of flow measurement |
| Permeability | k_T = Q × L / (A × t × h) | cm/s | Formula for permeability |
| Temperature of water | T | °C | For correction to 27°C |
[ \boxed{ k_T = \frac{Q \times L}{A \times t \times h} } ]
IS 2720 Part 17: Falling Head Permeability Test - Key Data & Calculation
[ k = \frac{aL}{At} \ln \frac{h_1}{h_2} \quad \text{(cm/s)} ]
Where:
| Parameter | Value | Unit |
|---|---|---|
| Diameter, D | 7.0 | cm |
| Length, L | 10.0 | cm |
| Area, A | 38.5 | cm² |
| Standpipe area, a | 1.0 | cm² |
| Initial head, h₁ | 50 | cm |
Frequently Asked
IS 2720 Part 17 (1986) covers laboratory determination of soil permeability.
| Soil Type | Particle Size Range | Test Method |
|---|---|---|
| Clay, silt | < 0.075 mm | Falling head test |
| Sand, gravel | > 0.075 mm (up to gravel) | Constant head test |
This ensures accurate permeability measurement relevant to foundation and geotechnical design.
Preparation of Soil Samples for Permeability Testing as per IS 2720 Part 17
This ensures no leakage and representative permeability results.
Differences between Falling Head and Constant Head Permeability Tests (IS 2720 Part 17):
| Aspect | Falling Head Test | Constant Head Test |
|---|---|---|
| Test Setup | Specimen connected to a stand-pipe with water level falling over time. | Specimen connected to a constant head reservoir maintaining steady water level. |
| Measurement | Time taken for water level to fall from initial head (h₁) to final head (h₂). Multiple readings ensure consistency. | Volume of water collected over a fixed time once steady flow is established, repeated thrice. |
| Applicability | Suitable for soils with low to medium permeability. | Suitable for soils with medium to high permeability. |
| Flow Condition | Unsteady flow (head decreases with time). | Steady-state flow (constant head maintained). |
| Calculation | Uses time and change in head to compute permeability coefficient. | Uses flow rate, head difference, and specimen dimensions to compute permeability. |
[ k = \frac{aL}{At} \ln \frac{h_1}{h_2} ]
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This diagram shows the two setups: constant head with reservoir and falling head with standpipe.
According to IS 2720 Part 17, temperature effects on permeability are accounted by adjusting the permeability value at the test temperature ( T ) to a standard reference temperature of 27°C using viscosity coefficients.
[ k_{27} = k_T \times \frac{Y_{T}}{Y_{27}} ]
Where:
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This ensures permeability values are comparable regardless of test temperature variations.
According to IS 2720 Part 17 (1986), the key equipment and apparatus for permeability tests include:
The test setup ensures precise measurement of head loss and flow rate to calculate permeability coefficients for soils with permeability in the range 10⁻³ to 10⁻⁷ cm/s and particle size up to 9.5 mm.
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This setup applies for both falling head and constant head permeability tests.
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