Method for subsurface sounding for soils, Part 3: Static cone penetration test

Scope & Key Specifications from IS 4968 Part 3 (1976)

Scope:
This part covers the method for measuring friction resistance using a friction jacket attached to a static cone during cone penetration tests (CPT).

Key Formulas & Data

Correction Formula for Frictional Resistance

[ \text{Corrected Frictional Resistance} = z + 100 \times m \quad \text{(kN/m}^2) ]

Where:

• ( z = \frac{(x - y) \times b}{a} )
• ( x ) = Total resistance (kgf/cm²)
• ( y ) = Cone resistance (kgf/cm²)
• ( b ) = Cone base area (10 cm²)
• ( a ) = Friction jacket surface area (cm²)
• ( m ) = Mass of friction jacket (kg)

Cone Specifications (Clause 2.1)

• Apex angle: 60° ± 15'
• Base diameter: 35.7 ± 0.1 mm
• Cross-sectional area: 10 cm²
• Material: Hardened steel to prevent soil intrusion

Recommended Data Presentation (Clause 4.1)

• Tabulate results as per Appendix A format.
• Plot two graphs against depth (m):
  • Cone resistance (kN/m² or kgf/cm²)
  • Friction resistance (kN/m² or kgf/cm²)
• Include borehole log for correlation.

Summary Table Example (from Clause 9.806)

| Depth (m) | Total Resistance (kN/m²) | Cone Resistance (k

IS 4968 Part 3 - Equipment Requirements Summary

Key Specifications (Clauses 2.6, 2.6.1 & 2.7)

• Measuring Equipment (2.6):

  • Hydraulic measuring device with pressure gauges.
  • Plunger cross-sectional area: 10 cm² or 20 cm².
  • Two pressure gauges (high & low) connected to driving head.
  • For 2 to 3 t equipment with 20 cm² plunger area:
    • Gauge 1: 0–1000 kN/m² (0–10 kgf/cm²), markings every 25 kN/m² (0.25 kgf/cm²).
    • Gauge 2: 0–5000 kN/m² (0–50 kgf/cm²), markings every 50 kN/m² (0.50 kgf/cm²).

• Pressure Gauge Protection (2.6.1):

  • Smaller capacity gauge must be manually and automatically cut off when pressure exceeds capacity.

• Equipment Design (2.7):

  • Equipment must allow:
    • Pushing cone alone or friction jacket + cone alternatively.
    • Minimum penetration depth per push: 35 mm.
    • Continuous advancement of entire assembly when skin friction readings are not needed.

Pressure Gauge Connection Logic (Simplified)

flowchart LR
    A[Hydraulic Measuring Head] --> B[High Pressure Gauge]
    A --> C[Low Pressure Gauge]
    C --> D{Pressure > Capacity?}
    D -- Yes --> E[Cut off Low Pressure Gauge (Manual & Auto)]
    D -- No --> F[Gauge Operates Normally]

This ensures accurate pressure reading and equipment versatility during penetration tests.

IS 4968 Part 3 - Friction Jacket Key Points

1. Friction Jacket Material & Dimensions (Clause 2.2)

• Made of high carbon steel.
• Dimensions per Fig. 2 (not shown here).
• Outer diameter = d mm, length = h mm.

2. Key Parameters & Formulas (Clause 9.806)

• Mass of friction jacket = m (kg)
• Surface area of friction jacket:
  [ a = \pi d h \quad \text{(in cm}^2\text{)} ]
• Cone base area:
  [ b = 10 \text{ cm}^2 ]
• Correction factor for friction resistance:
  [ \text{Correction} = 100 \times m \quad \text{(kN/m}^2\text{)} ]

3. Frictional Resistance Calculation

• Convert kgf/cm² to kN/m² by multiplying by 98.0665.

4. Equipment Requirements (Clause 2.7)

• Allow pushing:
  • Cone alone
  • Cone + friction jacket together
• Minimum penetration depth: 35 mm per push.
• Option for continuous advancement if friction readings not needed.

Summary Diagram (Friction Resistance Measurement)

flowchart TD
    A[Cone Alone] -->|Push 35 mm| B[Measure Cone Resistance (y)]
    C[Cone + Friction Jacket] -->|Push 35 mm| D[Measure Total Resistance (x)]
    B --> E[Calculate Frictional Resistance = (x - y) * (b/a)]
   

Mantle Tube Specifications & Key Points (IS 4968 Part 3)

• Material: Steel
• Length: 1 metre with flush coupling
• Diameter: May be uniform or non-uniform (non-uniform preferred for manual operation for ease)
• Purpose: Guides the sounding rod during cone penetration tests

Dimensions (from Fig. 5 & Clause 2.4)

Operational Procedure (Clauses 3.2 & 3.3)

• Mantle tube is connected to the cone-friction jacket and sounding rod assembly.
• Assembly is pushed vertically at 1 cm/s penetration rate.
• After every 1 m depth, add extension rods and mantle tubes.
• Resistance readings (cone + friction) are recorded continuously or at intervals.

Summary Diagram of Assembly Positions (simplified):

graph TD
    A[Top of Mantle Tube] --> B[Sounding Rod]
    B --> C[Cone & Friction Jacket Assembly]
    C --> D[Soil Penetration Point]

Note: The mantle tube ensures accurate guidance and measurement by preventing rod bending and providing stable penetration.

Penetration Rate (IS 4968 Part 3)

• Clause 2.5.2:
  For engine-driven equipment, maintain the penetration rate between 1 to 1.5 cm/s to ensure reliable test results.

Key Specifications (Clause 1.5 & Notes):

• m = mass of cone + rods

• n = number of rods |

• Gauge reading correction:
  If plunger area = 20 cm² and cone base = 10 cm², multiply gauge readings by 2 (ratio of areas).

Example Table of Cone Penetration Resistance (corrected):

Recommended Presentation (Clause 4.1 & Appendix A):

• Tabulate results with depth, gauge reading, and corrected resistance.
• Plot graphs of:
  • Cone resistance vs. Depth
  • Friction resistance vs. Depth
• Include borehole log for comprehensive soil profiling.

flowchart TD
    A[Start Test] --> B[Set Penetration Rate: 1-1.5 cm/s]
    B --> C[Record Gauge Reading]
    C --> D[Apply Correction: (m + n m₁) × 10 kN/m²]
    D --> E[Multiply by Area Ratio if needed]
    E --> F[Tabulate & Plot Results]
    F -->

IS 4968 Part 3 – Measuring Equipment Key Points

Measuring Head & Plunger Area

• Plunger cross-sectional area options:
  • 10 cm² (same as cone base area)
  • 20 cm²
• Cone base area = 10 cm²

Pressure Gauges for 20 cm² Plunger Area

Note: For 10 cm² plunger, gauge ranges and calculations must be adjusted proportionally.

Correction for Gauge Reading

[ \text{Corrected Resistance} = \text{Gauge Reading} + (m + n m_1) \times 10 \text{ kN/m}^2 ]

• (m) = mass of cone + accessories (kg)
• (n) = number of rods
• (m_1 = 1.5 \text{ kg}) (mass of each sounding rod)

Gauge Reading Adjustment for Plunger Area

[ \text{Adjusted Reading} = \text{Gauge Reading} \times \frac{\text{Plunger Area}}{\text{Cone Base Area}} ]

• For plunger area 20 cm² and cone base 10 cm², multiply gauge reading by 2

Additional Specifications

IS 4968 Part 3: Other Equipment Requirements - Key Points

• Cone and Friction Jacket Push Depths:

  • Cone alone: minimum 35 mm
  • Friction jacket above cone: minimum 35 mm
  • Cone + friction jacket together: minimum 35 mm
  • Allows separate or continuous pushing for skin friction measurement (Clause 2.7).

• Measuring Equipment (Clause 2.6):

  • Hydraulic pressure gauges with plunger cross-section: 10 cm² or 20 cm².
  • Two pressure gauges per apparatus:
    • Low capacity gauge (manual/automatic cutoff beyond capacity).
    • High capacity gauge.
  • For 20 cm² plunger area, gauge ranges (2 to 3 t equipment):

    Gauge Type	Range (kN/m²)	Markings (kN/m²)
    Low Pressure	0 - 1000	25
    High Pressure	0 - 5000	50

• Design Note:

  • The standard provides testing procedure and essential equipment details but not full equipment design (Clause 1.1.1).

Summary Diagram of Equipment Push Options

flowchart LR
    A[Cone Alone] -->|Push 35 mm| B[Measure Penetration]
    C[Friction Jacket + Cone] -->|Push 35 mm| B
    D[Cone + Friction Jacket Together] -->|Continuous Push| B

This ensures flexibility in testing for separate or combined skin friction measurements.

IS 4968 Part 3 - Test Procedure: Key Formulas, Tables & Specifications

1. Test Data Presentation (Clause 4.1)

• Tabulate results using the pro forma in Appendix A.
• Plot two graphs vs depth (m):
  • Cone resistance (kN/m² or kgf/cm²)
  • Friction resistance (kN/m² or kgf/cm²)
• Include borehole log alongside.

2. Corrections for Friction Jacket (Clause 9.806)

• Corrected friction resistance:

[ \text{Corrected Friction} = \text{Measured Friction} + 100 m g ]

• Total resistance minus cone resistance gives frictional resistance:

[ \text{Frictional Resistance} = \frac{(x - y)}{a} \quad \text{where } x = \text{total resistance}, y = \text{cone resistance} ]

3. Correction for Gauge Reading (Clause 1.5)

• Mass of each sounding rod ( m_1 = 1.5 , \text{kg} )
• Cone base area ( b = 10 , \text{cm}^2 )
• Plunger area ( A_p ) (if 20 cm², multiply gauge reading by 2)
• Correction formula:

[ \text{Correction} = (m + n m_1) \times 10 , \text{kN/m}^2 ]

where:

• ( m ) = mass of equipment above cone,

• ( n ) = number of rods,

• ( m_1 ) = mass of each rod.

• Corrected cone penetration resistance:

[ R_c = \text{Gauge reading} + \text{Correction} \

Sequence of Sounding Operations (IS 4968 Part 3)

1. Setup (Clause 3.2.1):

   • Bring driving mechanism rack to top.
   • Connect cone-friction jacket assembly to first sounding rod and mantle tube.
   • Position vertically over test point via mantle tube guide.
   • Lower plunger to rest on sounding rod.

2. Pushing Procedure (Clause 3.2.3):

   • Push sounding rod at 1 cm/s until cone reaches required depth.
   • Record mean resistance from gauges, ignoring erratic fluctuations.
   • Push further to measure combined cone and friction resistance.

3. Equipment Specifications (Clause 2.6):

   • Plunger area: 10 cm² or 20 cm² (commonly 20 cm²).
   • Two pressure gauges: high and low pressure.
   • Example gauge range for 20 cm² plunger:
     • 0–1000 kN/m² (0–10 kgf/cm²) with 25 kN/m² markings.
     • 0–5000 kN/m² (0–50 kgf/cm²) with 50 kN/m² markings.

4. Corrections (Clause 1.5):

   • Correction factor = (m + n*m₁) × 10 kN/m², where:
     • m = number of rods,
     • m₁ = mass of each rod (1.5 kg),
     • Add correction to gauge reading.
   • If plunger area = 20 cm² and cone base area = 10 cm², multiply gauge reading by 2.

Table: Sample Gauge Reading & Corrected Cone Resistance

IS 4968 Part 3: Anchoring and Setup for Static Cone Penetration Test

Key Specifications:

• Anchoring:
  Equipment must be securely anchored at the test point to provide the necessary reaction force (Clause 3.2). Soil screw anchors of suitable capacity are recommended.

• Setup:
  The cone, friction jacket, and assembly must be capable of being pushed separately or together through minimum increments of 35 mm (Clause 2.7).

• Penetration Rate:
  The cone should be advanced at a steady rate of approximately 1 cm/s (Clause 3.2.2) to standardize results.

Important Notes on Penetration Rate Effects:

Procedure Summary:

• Push only the cone for cone resistance measurement.
• Use slow gear clutch and steady handle operation.
• Record mean resistance from Bourdon gauge, ignoring erratic fluctuations.
• After reaching the deepest point, extract the entire assembly carefully (Clause 3.4).

flowchart TD
    A[Start Test Setup] --> B[Anchor Equipment Securely]
    B --> C[Push Cone Alone (min 35 mm increments)]
    C --> D[Record Cone Resistance @ 1 cm/s]
    D --> E{Need Skin Friction?}
    E -- Yes --> F[Push Friction Jacket + Cone Separately]
    E -- No --> G[Push Entire Assembly Together]
    F & G --> H[Reach Deepest Point]
    H --> I[Extract Assembly Carefully]
    I --> J[End Test]

This ensures reliable, standardized static cone penetration testing per IS 4968 Part 3.

IS 4968 Part 3 – Initial Positioning Key Formulas & Tables

Key Parameters:

• Mass of each sounding rod, m₁ = 1.5 kg

• Cone base area, b = 10 cm²

• Plunger area (variable, see Note)

• Correction factor:
  [ \text{Correction} = (m + n m_1) \times 10 \text{ kN/m}^2 ] where:

  • ( m ) = mass of cone + friction jacket (kg)
  • ( n ) = number of rods used

• Note: If plunger area = 20 cm² and cone base area = 10 cm², multiply gauge readings by 2 (plunger area / cone base area).

Correction for Cone Penetration Resistance:

[ \text{Corrected Resistance} = \text{Gauge Reading} + \text{Correction} ]

Sample Table for Depth vs. Resistance (kN/m²):

Friction Jacket Correction:

• Mass of friction jacket, m (kg)
• Friction jacket surface area, ( a = \pi d h ) (cm²)
  where:
  • ( d ) = outer diameter
  • ( h ) = length of jacket
• Correction added to frictional resistance:
  [ 100 m g \quad \text{kN/m}^2 ] (where ( g ) is acceleration due to gravity)

Summary:

• Apply mass correction for rods + cone + friction jacket.
• Adjust gauge reading by area ratio if plunger area differs.
• Use corrected values for accurate soil resistance.
• Refer to Appendix A for pro forma record keeping.

flowchart TD
   

Combined Cone and Friction Resistance Measurement (IS 4968 Part 3)

Key Specifications:

• Cone apex angle: 60° ± 15'
• Cone base diameter: 35.7 ± 0.1 mm
• Cone base area, b: 10 cm²
• Friction jacket dimensions:
  • Outer diameter, d (mm)
  • Length, h (mm)
• Correction factor: 100 m × g kN/m² (where m = mass of friction jacket in kg, g = acceleration due to gravity)

Important Formulas:

1. Friction jacket surface area, a: [ a = \pi \times d \times h ]

2. Correction to frictional resistance: [ \text{Corrected friction resistance} = z + 100mg ] where ( z = ) measured frictional resistance (kN/m²), ( m = ) mass of friction jacket (kg), ( g = 9.81 , m/s^2 ).

3. Frictional resistance, z: [ z = \frac{(x - y)}{a} ] where

   • ( x = ) total resistance (cone + friction jacket) in kN/m²,
   • ( y = ) cone resistance alone in kN/m²,
   • ( a = ) friction jacket surface area (m²).

4. Cone resistance correction: Correct for dead weight of cone and rods; also adjust for ram area to cone base area ratio (see Appendix A of IS 4968 Part 3).

Table Extract (Sample Data):

IS 4968 Part 3: Correction of Cone Resistance

Key Formulas:

1. Correction for Dead Weight:

[ q_c = q_{measured} + \frac{(m + n m_1) \times g}{b} ]

• (q_c) = corrected cone resistance (kN/m²)
• (q_{measured}) = gauge reading (kN/m²)
• (m) = mass of cone + friction jacket (kg)
• (m_1) = mass of each sounding rod (1.5 kg)
• (n) = number of rods in use
• (g) = acceleration due to gravity (≈ 9.81 m/s²)
• (b) = base area of cone (10 cm² = 0.001 m²)

2. Correction for Ram Area to Cone Base Area Ratio:

[ q_c = q_c \times \frac{A_p}{b} ]

• (A_p) = plunger area (cm²)
• (b) = base area of cone (cm²)

Important Specifications:

Correction for Friction Jacket:

[ \text{Correction} = 100 \times m_g \times \frac{a}{b} \quad \text{kN/m}^2 ]

• (m_g) = mass of friction jacket (kg)
• (a = \pi d h) = surface area of friction jacket (cm²)
• (b) = base area of cone (cm²)

Example Table Extract (Gauge Reading vs Corrected Resistance):

IS 4968 Part 3: Limitations of the Test - Key Formulas & Tables

1. Corrections for Cone Resistance (Clause 4.2)

• Corrected Cone Resistance = Measured resistance + Correction for dead weight of cone, friction jacket, and sounding rods.
• Correction factor accounts for:
  • Mass of sounding rods, ( m_1 = 1.5 , kg )
  • Cone base area, ( b = 10 , cm^2 )
  • Plunger area (e.g., if plunger area = 20 cm², multiply gauge reading by 2)

Correction formula:

[ \text{Correction} = (m + n m_1) \times 10 , kN/m^2 ]

• ( m ) = mass of cone and friction jacket (kg)
• ( n ) = number of rods in use

2. Friction Resistance Correction (Clause 9.806)

• Friction jacket mass = ( m_f , kg )
• Friction jacket surface area:

[ a = \pi \times d \times h ]

where ( d ) = diameter, ( h ) = length of friction jacket.

• Correction added to friction resistance:

[ \text{Correction} = 100 \times m_f / a \quad (kN/m^2) ]

3. Example Table of Corrected Cone Penetration Resistance (kN/m²)

4. Summary of Limitations

• Corrections must be applied for dead weights and area ratios.
• Gauge readings depend on plunger and cone base areas.
• Friction jacket resistance requires correction for jacket mass and surface area.
• Results should be tabulated and graphed with depth for clarity (see Appendix A).

flowchart TD
    A[Measured Cone Resistance]

IS 4968 Part 3: Correction Calculations for Static Cone Penetration Test (SCPT)

Key Parameters & Constants

• Mass of each sounding rod, m₁ = 1.5 kg

• Cone base area, b = 10 cm²

• Plunger area (example) = 20 cm²

• Correction factor for gauge reading:
  [ \text{Corrected Resistance} = \text{Gauge Reading} + (m + n m_1) \times 10 \text{ kN/m}^2 ] where:

  • ( m ) = mass of cone and friction jacket (kg)
  • ( n ) = number of rods in use

• If plunger area ≠ cone base area, multiply gauge reading by:
  [ \frac{\text{Plunger area}}{\text{Cone base area}} = \frac{20}{10} = 2 ]

Correction Example Table (Depth vs Resistance)

Friction Jacket Correction (Clause 9.806)

• Friction resistance correction:
  [ \text{Corrected Friction} = z + 100 m g / a ] where:
  • ( m ) = mass of friction jacket (kg)
  • ( g ) = acceleration due to gravity
  • ( a ) = surface area of friction jacket (cm²)
  • ( z ) = measured friction