IS 2720 Part 30 (1980) specifies the laboratory vane shear test method for determining the undrained shear strength of cohesive soils with low shear strength. This standard details the apparatus design, specimen preparation, test procedure, and calculation methods to ensure consistent and accurate measurement of soil shear strength under controlled laboratory conditions. It is essential for geotechnical engineers and soil testing laboratories involved in foundation design and soil characterization.
Overview
IS 2720 Part 30 (1980) specifies the laboratory vane shear test method for determining the undrained shear strength of cohesive soils with low shear strength. This standard details the apparatus design, specimen preparation, test procedure, and calculation methods to ensure consistent and accurate measurement of soil shear strength under controlled laboratory conditions. It is essential for geotechnical engineers and soil testing laboratories involved in foundation design and soil characterization.
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Contents
Structure
IS 2720 Part 30 - Scope & Key Formula Summary
Scope:
This part of IS 2720 covers the Vane Shear Test for determining the shear strength of cohesive soils in the field or laboratory.
Shear strength, ( S ), is calculated from the torque ( T ) applied to the vane:
[ \boxed{ S = \frac{T}{\pi \cdot d^2 \cdot h / 2 + \pi \cdot d \cdot h^2 / 2} } ]
Where:
Note: The formula assumes a cylindrical shear surface equal to the vane diameter, with uniform shear strength mobilized at the vane surface and center.
flowchart LR
A[Torque Applied (T)] --> B[Shear Surface (Cylindrical)]
B --> C[Shear Strength (S)]
C --> D[Soil Shear Resistance]
References:
IS 2720 Part 30: Apparatus Specifications for Vane Shear Test
[ S = \frac{T}{\pi \cdot d \cdot h \cdot r} ]
Where:
flowchart LR
A[Fix Vane & Shaft] --> B[Lower Vane Gradually]
B --> C[Fix Soil Specimen Tube]
C --> D[Rotate Vane at 0.1°/s]
D --> E[Measure Torque Accurately]
E --> F[Compute Shear Strength]
This ensures precise and reliable measurement of undrained shear strength using the vane shear test apparatus as per IS 2720 Part 30.
Specimen Dimensions:
Key Formula for Shear Strength (Clause 4.2):
[ S = \frac{T}{\pi D^2 H / 2} = \frac{2T}{\pi D^2 H} ]
Where:
Assumptions:
| Parameter | Dimension (mm) | Note |
|---|---|---|
| Vane Diameter | 30 | Essential dimension |
| Vane Height | 30 | Equal to diameter |
flowchart LR
A[Vane inserted in soil specimen]
B[Apply torque T]
C[Shear surface develops on cylinder of diameter D]
D[Measure torque at failure]
E[Calculate shear strength S = 2T / (π D² H)]
A --> B --> C --> D --> E
This concise guide covers specimen dimensions and key formulae per IS 2720 Part 30 for laboratory vane shear testing.
IS 2720 Part 30: Vane Shear Test - Key Test Procedure & Specifications
Dimensions: All in millimeters; essential dimensions are underlined (Clause 2.5, Fig. 1).
Test Procedure (Clause 3.2):
Apparatus (Fig. 2):
Computations (Clause 4.1):
[ \tau = \frac{T}{K \times L \times D^2} ]
Where:
flowchart TD
A[Insert Vane into Soil] --> B[Apply Torque Slowly]
B --> C[Record Maximum Torque]
C --> D[Rotate Vane 10 Revolutions Rapidly]
D --> E[Measure Remoulded Strength within 1 min]
E --> F[Calculate Shear Strength using Calibration Curve]
This summarizes the essential test steps and apparatus requirements per IS 2720 Part 30.
IS 2720 Part 30: Computation of Shear Strength by Vane Shear Test
Shear strength, ( S ) (kgf/cm²), is computed from the torque ( T ) (cm·kgf) using:
[ \boxed{ S = \frac{T}{\pi \cdot d^2 \left(\frac{h}{2} + \frac{d}{6}\right)} } ]
flowchart TD
A[Insert Vane in Soil] --> B[Rotate Slowly]
B --> C[Record Max Torque (T)]
C --> D[Calculate Shear Strength S]
D --> E{Remoulded Strength?}
E -- Yes --> F[Rotate 10 Revolutions Rapidly]
F --> G[Test within 1 min]
E -- No --> H[End]
This method gives undrained shear strength of cohesive soils per IS 2720 Part 30.
IS 2720 Part 30: Reporting of Results - Key Formulas & Specifications
The shear strength ( S ) of soil from vane shear test is computed as:
[ S = \frac{T}{K} ]
Where:
Assumptions:
| Parameter | Symbol | Unit | Notes |
|---|---|---|---|
| Torque | ( T ) | cm·kgf | Measured from apparatus |
| Shear strength | ( S ) | kgf/cm² | Calculated from torque and vane size |
| Vane diameter | ( d ) | mm | Essential for constant ( K ) |
| Remoulded strength | - | kgf/cm² | After rapid vane rotation |
flowchart LR
A[Apply Torque (T)] --> B[Measure Maximum Torque]
B --> C[Calculate Shear Strength S = T/K]
C --> D[Rotate Vane 10 revolutions]
D --> E[Measure Remoulded Strength]
E --> F[Report Results with Vane Dimensions]
Ensure adherence to IS 2720 Part 30 for accurate soil shear strength reporting.
Maintenance and Calibration of Vane Shear Apparatus (IS 2720 Part 30)
Calibration Curve (Clause 4.1):
For vane testers not reading torque directly, provide a calibration curve to convert readings to torque (cm·kgf).
Check calibration curves periodically to ensure accuracy.
Dimension Checks (Clause 4.2 Note):
Periodically verify vane dimensions to avoid errors from distortion or wear.
Shear Strength Calculation (Clause 4.2):
[
S = \frac{T}{\pi \cdot d \cdot h}
]
Where:
Assumptions:
Post-Test Procedure (Clause 3.2):
After max torque, rotate vane rapidly for ≥10 revolutions. Determine remoulded strength within 1 minute.
| Parameter | Maintenance/Calibration Requirement |
|---|---|
| Calibration Curve | Must be provided and checked periodically |
| Vane Dimensions | Check regularly for wear/distortion |
| Shear Strength | Calculate using torque and vane dimensions |
| Post-Test Rotation | Rotate ≥10 revolutions rapidly after max torque |
graph LR
A[Torque Applicator Handle] --> B[Gear System]
B --> C[Torque Spring]
C --> D[Vane]
D --> E[Soil Sample]
F[Maximum Pointer] --> B
G[Strain Inducing Pointer] --> B
Ensure regular maintenance and calibration for reliable soil shear strength measurements.
IS 2720 Part 30 (1980) — Precautions and Safety Measures Summary
The code does not explicitly list safety measures but implies key precautions during soil shear strength testing (Vane Shear Test):
[ S = \frac{T}{\pi \cdot d^2 \cdot h / 2} ]
Where:
flowchart TD
A[Start Test] --> B[Check Vane Dimensions]
B --> C[Calibrate Equipment]
C --> D[Conduct Vane Shear Test]
D --> E[Calculate Shear Strength]
E --> F[Record & Analyze Results]
F --> G[Ensure Safety Throughout]
For detailed safety, refer to general lab safety standards and equipment manuals.
IS 2720 Part 30 (1980) — Key Formulas, Tables & Specifications for Vane Shear Test
[ S = \frac{T}{\pi D^2 H / 2 + \pi D H^2 / 2} ]
Where:
Note: The formula assumes:
flowchart TD
A[Apply Torque T] --> B[Shear Surface Cylindrical]
B --> C[Calculate Shear Strength S]
C --> D[Record Max Torque]
D --> E[Rotate Vane 10 Revolutions Rapidly]
E --> F[Measure Remoulded Strength]
For detailed dimensions, refer to Fig. 1 & 2 in IS 2720 Part 30.
Frequently Asked
According to IS 2720 Part 30 (1980), Clause 3.1, the required dimensions for soil specimens in the laboratory vane shear test are:
Additional key points:
This ensures minimal disturbance and accurate measurement of undrained shear strength in cohesive soils.
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Calculation of Undrained Shear Strength (Su) from Torque in IS 2720 Part 30
From the vane shear test:
The undrained shear strength ( S_u ) is calculated by relating the torque to the shear stress on the cylindrical surface and the two circular ends of the vane:
[ S_u = \frac{T}{\pi d^2 h/2 + \pi d h d/2} = \frac{T}{\pi d^2 h/2 + \pi d h \cdot d/2} ]
Simplified, the total shear area ( A ) resisting torque is:
[ A = 2 \times \text{area of circular ends} + \text{area of cylindrical surface} = 2 \times \frac{\pi d^2}{4} + \pi d h = \frac{\pi d^2}{2} + \pi d h ]
Thus,
[ S_u = \frac{T}{\frac{\pi d^2}{2} + \pi d h} ]
Where:
| Parameter | Description |
|---|---|
| ( T ) | Maximum torque at failure |
| ( d ) | Vane diameter |
| ( h ) | Vane height |
| ( S_u ) | Undrained shear strength |
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According to IS 2720 Part 30, the vane apparatus must have the following design features:
| Feature | Requirement |
|---|---|
| Number of blades | 4 blades at 90° intervals |
| Blade edge angle | 90° included angle (sharp) |
| Central rod diameter | ≤ 25 mm in soil-inserted portion |
| Rotation speed | ~1/60 rev/min (0.1°/s) |
| Torque measurement accuracy | 0.05 cm·kgf |
| Shear strength range | From 0.5 kgf/cm² |
| Corrosion protection | Required |
This ensures compliance with IS 2720 Part 30 for reliable vane shear testing.
To minimize disturbance when inserting the vane into the soil specimen per IS 2720 Part 30:
This careful vertical and slow insertion preserves soil structure and test reliability.
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According to IS 2720 Part 30, the recommended rotation speed during the vane shear test is:
This uniform slow rotation rate ensures accurate determination of maximum torque and shear strength.
| Test Stage | Rotation Speed |
|---|---|
| Initial shear test | ~0.1°/s (1/60 rpm) |
| Post max torque | Rapid rotation (≥10 revs) |
This slow, steady rotation minimizes disturbance and allows precise torque measurement for shear strength evaluation.
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