Methods of test for soils, Part 36: Laboratory determination of permeability of granular soils (Constant head)

Scope & Key Specifications from IS 2720 Part 36:

• Scope: Determination of permeability of soil using constant head or falling head permeameter.

Key Parameters & Formulas (Clause 6.1 & Appendix A):

Equipment and Specimen Size (Clause 2.1 & Table 1):

• Porous discs/screens with permeability > soil specimen.
• Spring load: 2 to 4 kg to prevent volume change during test.

Summary Flowchart

IS 2720 Part 36 - Apparatus Key Points

Apparatus (Clause 2.8)

• Thermometers
• Clock with sweep second hand
• 250 ml graduated cylinder
• Mixing pan

Permeameter Specifications (Clause 2.1 & Table 1)

• Cylinder diameter (D):
  Minimum diameter depends on max particle size and soil grading:

• Porous discs/screens with permeability > soil permeability; openings ≤ 10% of finer soil size.
• Manometer outlets spaced ≥ cylinder diameter (L ≥ D).
• Spring-loaded top plate applying 2-4 kg load to prevent volume change during test.

Measurement & Calculations (Clause 4.2, 6.1 & Appendix A)

• Measure:
  • Diameter, D (cm)
  • Length between manometer outlets, L (cm)
  • Height of specimen, H = H1 - H2 (cm)
• Calculate:
  • Cross-sectional area, ( A = \frac{\pi D^2}{4} ) (cm²)
  • Volume, ( V = A \times H ) (cm³)
  • Dry unit weight, ( \gamma = \frac{W_s}{V} )
  • Void ratio, ( e = \frac{G_s \gamma_w}{\gamma} - 1 )
• Permeability calculation: [ k = \frac{Q L}{A h t} ] where:
  ( Q ) = volume of flow (cm³),
  ( L ) = length between manometer outlets (cm),
  ( A ) = cross-sectional area (cm²),
  ( h ) = head loss (cm),
  ( t ) = time (s).

flowchart TB
    A[Soil Specimen in Cylinder] --> B[Porous Disc (Bottom)]
    B --> C[Manometer Outlet h

IS 2720 Part 36 — Sampling & Sample Preparation: Key Points

Sampling (Clause 3.3)

• Remove oversize particles (see Clause 3.2).
• Use quartering method to select a representative sample.
• Sample size ≈ twice the volume needed to fill the permeameter chamber.

Miscellaneous Apparatus (Clause 2.8)

• Thermometer (for temperature measurement)
• Clock with sweep second hand (for timing flow)
• 250 ml graduated cylinder (for measuring flow volume)
• Mixing pan (for sample preparation)

Specimen Preparation (Clause 4 & 6.1 - Appendix A)

• Specimen dimensions:
  • Diameter, D (cm)
  • Length, L = H1 - H2 (cm)
• Calculate:
  • Cross-sectional area, ( A = \frac{\pi D^2}{4} ) (cm²)
  • Volume, ( V = A \times L ) (cm³)
  • Dry weight, ( W_s ) (g)
  • Dry unit weight, ( \gamma = \frac{W_s}{V} )
  • Water content, ( W = \frac{w}{0} )
  • Specific gravity, ( G_s )
  • Void ratio, ( e = \frac{G_s \gamma_w}{\gamma} - 1 )
• Temperature of water, T (°C) to be recorded.

Permeability Test Data Table (Clause 6.1)

Important Formulae Summary

[ A = \frac{\pi D^2}{4} \quad ; \quad V = A \times L ]

[ \gamma = \frac{W_s}{V} \quad ; \quad e = \frac{G_s \gamma_w}{\gamma} - 1 ]

IS 2720 (Part 36) - Preparation of Specimen for Permeability Test

Key Specifications & Steps:

• Sample Selection (Clause 3.3):

  • Remove oversize particles as per Clause 3.2.
  • Select a sample by quartering, approximately 2× the volume needed to fill the permeameter chamber.

• Permeameter Size (Clause 4.1):

  • Use sizes as prescribed in Table 1 (refer IS 2720 Part 36 Table 1 for dimensions).
  • Typical diameters (D) range from 50 mm to 100 mm depending on soil type.

• Initial Measurements (Clause 4.2):

  • Measure inside diameter, D of permeameter.
  • Measure length, L, between manometer outlets.
  • Measure depth, H1, from top plate surface to upper porous stone (average of 4 points).
  • Calculate cross-sectional area,
    [ A = \frac{\pi}{4} D^2 ]

• Volume of Soil Specimen:
  [ V = A \times H_1 ]

• Saturation & Evacuation:

  • Use device as per Fig. 2 for evacuating air and saturating specimen before testing.

Summary Table:

flowchart TD
    A[Sample Selection] --> B[Remove Oversize Particles]
    B --> C[Quartering to get 2x volume]
    C --> D[Fill Permeameter Chamber]
    D --> E[Measure D, L, H1]
    E --> F[Calculate A and V]
    F --> G[Evacuate & Saturate Specimen]
   

IS 2720 Part 36: Key Test Procedure Formulas & Specifications

1. Test Observations (Clause 6.2)

• Manometer readings: ( h_1 ), ( h_2 )
• Flow volume: ( Q ) (collected in time ( t ))
• Calculate:
  • Head loss:
    [ h = h_1 - h_2 ]
  • Hydraulic gradient:
    [ i = \frac{h}{L} ]
  • Permeability, ( k_r ), from flow data (see below)

2. Permeability Calculation (Darcy's Law)

[ k_r = \frac{Q \cdot L}{A \cdot h \cdot t} ] Where:

• ( Q ) = volume of water collected (m³)
• ( L ) = length between manometer outlets (m)
• ( A ) = cross-sectional area of specimen (m²)
• ( h ) = head loss (m)
• ( t ) = time (s)

3. Permeameter Specifications (Clause 2.1 & Table 1)

• Cylinder diameter ( D ): Minimum 8 to 12 times max particle size
• Table 1: Minimum Cylinder Diameter

• Porous discs/screens with permeability > soil, openings ≤ 10% of finer soil size
• Light spring load: 2 to 4 kg to prevent volume change during test

4. Initial Measurements (Clause 4.2)

• Diameter ( D ) of permeameter
• Length ( L ) between manometer outlets
• Depth ( H_1 ) (soil height excluding porous plates)
• Cross-sectional area:

IS 2720 Part 36 — Record of Observation: Key Formulas & Table Structure

Observation Data (Clause 6.2 & Appendix A)

• h1, h2: Manometer readings.
• Q: Volume of water collected.
• t: Time taken.
• h: Difference in manometer readings.
• i: Hydraulic gradient (h divided by length between manometer outlets L).
• kr: Coefficient of permeability, calculated from flow data.

Key Formulas

• Head difference:
  [ h = h_1 - h_2 ]

• Hydraulic gradient:
  [ i = \frac{h}{L} ]

• Coefficient of permeability (Darcy’s Law):
  [ k_r = \frac{Q \times L}{A \times t \times h} ]

Where:

• (Q) = volume of flow (cm³)
• (L) = length between manometer outlets (cm)
• (A = \frac{\pi D^2}{4}) = cross-sectional area of specimen (cm²)
• (t) = time (seconds)
• (h) = head loss (cm)

Specifications to Record

• Soil identification, specimen diameter (D), length (H1 - H2), area (A), volume (V), water content (W), dry weight (Ws), dry unit weight (γ), specific gravity (Gs), void ratio (e), and water temperature (T).

Summary Diagram

flowchart LR
    A[Measure h1, h2] --> B[Calculate h = h1 - h2]
    B --> C[Calculate hydraulic gradient i = h/L]
    D[Collect volume Q in time t]

IS 2720 Part 36 — Key Formulas & Specifications for Permeability Calculations

Initial Measurements (Clause 4.2)

• Diameter of specimen, D (cm)
• Length between manometer outlets, L (cm)
• Height of specimen, H = H1 - H2 (cm) (average from 4 points)
• Cross-sectional area,
  [ A = \frac{\pi}{4} D^2 \quad (cm^2) ]
• Volume of specimen,
  [ V = A \times H \quad (cm^3) ]

Observations & Calculations (Clause 6.2)

Permeability Calculation (Darcy’s Law)

[ k_r = \frac{Q \times L}{A \times t \times h} \quad (cm/s) ]

Where:

• (Q) = volume of flow (cm³)
• (L) = length between manometer outlets (cm)
• (A) = cross-sectional area (cm²)
• (t) = time (s)
• (h) = head difference (cm)

Soil Parameters

• Water content, (W = \frac{W_w}{W_s} \times 100%)
• Dry unit weight,
  [ \gamma_d = \frac{W_s}{V} ]
• Specific gravity, (G_s) (from lab tests)
• Void ratio,
  [ e = \frac{G_s \gamma_w}{\gamma_d} -

IS 2720 Part 36: Presentation of Results - Key Points

Data Sheet Parameters (Appendix A)

• Soil Identification
• Specimen Dimensions:
  • Diameter, D (cm)
  • Length, L = H1 - H2 (cm)
  • Area, A = πD²/4 (cm²)
  • Volume, V = A × L (cm³)
• Soil Properties:
  • Water content, W (%)
  • Dry weight, Ws (g)
  • Dry unit weight, γ = Ws / V (g/cm³)
  • Specific gravity, Gs
  • Void ratio, e = (Gs × γw / γ) - 1
  • Temperature of water, T (°C)

Tabulated Results Format (Clause 6.1)

Calculations (Clause 6.2)

• Head difference:
  [ h = h_1 - h_2 ]
• Hydraulic gradient:
  [ i = \frac{h}{L} ]
• Permeability:
  [ k_r = \frac{Q \times L}{A \times t \times h} ]

Notes:

• Round off final values as per IS 2-1960.
• Record remarks for anomalies or observations.

flowchart TD
    A[Start: Measure h1, h2, Q, t] --> B[Calculate h = h1 - h2]
    B --> C[Calculate i = h / L]
    C --> D[Calculate kr = (Q × L) / (A × t × h)]
    D --> E[Record all values in data sheet]
    E --> F[Round off results as per IS 2-1960]
   

IS 2720 Part 36: Inspection and Quality Control Key Points

Key Parameters & Formulas

Permeability Calculation

[ k_r = \frac{Q \times L}{A \times h \times t} ]

• ( Q ) = Quantity of flow (cm³)
• ( t ) = Time (seconds)
• ( A ) = Cross-sectional area (cm²)
• ( h ) = Head difference (cm)
• ( L ) = Length of specimen (cm)

Quality Control Procedure Summary

• Record manometer readings ( h_1 ), ( h_2 ).
• Measure flow volume ( Q ) over time ( t ).
• Calculate head ( h ), gradient ( i ).
• Compute permeability ( k_r ).
• Document remarks and anomalies.

IS 2720 Part 36 - Data Sheet for Observations and Calculations

Key Parameters to Record (Appendix A):

• Soil Identification
• Diameter of specimen, D (cm)
• Spacing between manometer outlets, L (cm)
• Length of specimen (H1 - H2) (cm)
• Cross-sectional Area, A = πD²/4 (cm²)
• Volume of specimen, V = A × (H1 - H2) (cm³)
• Water content, W (%)
• Dry weight of soil specimen, Ws (g)
• Dry unit weight, γ = Ws / V (g/cm³)
• Specific gravity, Gs
• Void ratio, e = (Gs × γw / γ) - 1
• Temperature of water, T (°C)

Observations & Calculations Table Columns:

Important Formulas:

• Hydraulic head difference:
  [ h = h_1 - h_2 ]

• Hydraulic gradient:
  [ i = \frac{h}{L} ]

• Coefficient of permeability (Darcy’s law):
  [ k_r = \frac{Q \times L}{A \times t \times h} ]

Notes:

• Measure D, L, H1 carefully (average of 4 points for H1).
• Use duplicate top plate with openings for accurate H1.
• Record manometer readings (h1, h2), flow quantity Q, and time t.
• Calculate head difference, gradient, and permeability.
• Remarks for anomalies or observations.

flowchart TD
    A[Start Test] --> B[Measure D, L, H1, H2]
    B --> C[Calculate A, V]
    C --> D[Record h1, h2, Q, t]
    D --> E[Calculate h