Method for subsurface sounding for soils, Part 1: Dynamic method using 50 mm cone without bentonite slurry
1976 Edition

Overview of IS 4968 (Part 1) - 1976: Scope

This section defines the methodology for subsurface soil sounding, focusing on soil investigation techniques essential for foundation design and related geotechnical assessments.

Main Highlights:

• Pertains to subsurface soil exploration via sounding techniques.
• Establishes uniform procedures for conducting soil sounding tests.
• Aims to determine soil layering, load-bearing capacity, and consistency.
• Updates references from IS 2131-1963 to IS 2131-1981 for related test methods.

Common Parameters and Calculations:

• Penetration Resistance (N): Number of hammer blows per unit penetration (e.g., per 10 cm).
• Estimating Bearing Capacity: [ q_u = N \times C ] where ( q_u ) is ultimate bearing capacity, ( N ) is penetration resistance, and ( C ) is an empirical coefficient varying with soil type.

Typical Soil Resistance Values (from IS 2131 and related standards):

flowchart LR
    Start[Initiate Soil Sounding] --> Drive[Drive Penetration Rod]
    Drive --> Count[Count Blows per 10 cm]
    Count --> Check{Is N-value obtained?}
    Check -- Yes --> Calculate[Estimate Bearing Capacity]
    Check -- No --> Drive
    Calculate --> Classify[Classify Soil Type]
    Classify --> Report[Generate Soil Profile Report]

Refer to IS 2131-1981 and full IS 4968 Part 1 documentation for detailed formulas and tables.

Equipment Specifications in IS 4968 Part 1 (1976) for Dynamic Cone Penetration

Hoisting and Support Equipment (Clause 2.4):

• Type: Utilize appropriate hoisting devices such as a tripod.
• Stability: Must withstand hammer impact forces without displacement.
• Operator Accessibility: Should allow safe access for pulley and rope adjustments.
• Guidance: Incorporate guides to maintain vertical alignment of the driving rod during testing.

Typical Test Assembly:

• Tripod fitted with pulley system.
• Hammer drop mechanism acting vertically onto the driving head.
• Rope and pulley for hammer lifting.

Reference Updates:

• Replace IS:2131-1963 references with IS:2131-1981 for hammer and related equipment criteria.

Engineering Considerations:

• Stability is critical to prevent lateral movement that could skew results.
• Tripod height should permit unobstructed hammer drop, commonly about 1 meter.
• Guides ensure the rod remains vertical, reducing bending moments.

Diagram of Tripod and Hammer Setup:

graph TD
    Hammer -->|Vertical Drop| Driving_Head
    Driving_Head -->|Vertical Rod| Soil_Surface
    Tripod -->|Supports| Pulley_System
    Operator -->|Accesses| Tripod
    Pulley_System -->|Controls| Hammer

For precise hammer weight and drop height, consult IS 2131-1981.

Dynamic Cone Penetration Testing as per IS 4968 Part 1 (1976)

• Cone Dimensions: 50 mm diameter with a 60° apex angle.
• Assembly Details: The cone may be loosely attached or screwed onto the driving rod (A rod). The hammer head is connected through a rod coupling, with a 150 cm guide rod fixed to the hammer head.
• Hammer Specifications: 65 kg weight dropped freely from a 750 mm height.
• Testing Steps:
  • Position the assembly vertically with the cone resting on the soil surface.
  • Drive the cone into soil by repeated hammer blows.
  • Record the number of blows per 100 mm penetration.
  • Continue until the target depth is achieved or the blow count exceeds 95 per 100 mm, at which point the test should be stopped to protect equipment.

Key Parameters:

Notes:

• Refer to IS 2131-1981 instead of IS 2131-1963 for related standards.
• Maintaining verticality during the test is essential.

flowchart TD
    Start[Test Initiation] --> Place[Place Cone on Soil]
    Place --> Hammer[Drop 65 kg Hammer from 750 mm]
    Hammer --> Record[Count Blows per 100 mm Penetration]
    Record --> Check{Blows > 95?}
    Check -- Yes --> Stop[Test Termination]
    Check -- No --> Continue[Proceed to Target Depth]
    Continue --> End[Test Completion]

This procedure ensures consistent measurement of soil resistance using the dynamic cone penetration technique.

Limitations and Stopping Guidelines for Dynamic Penetration with 50 mm Cone (IS 4968 Part 1)

• Cone Specs: 50 mm diameter, 60° apex.
• Hammer: 65 kg freely falling from 750 mm.
• Penetration Recording: Number of blows per 100 mm recorded.
• Stopping Rule: Cease penetration if blows exceed 95 per 100 mm to avoid equipment damage (Clause 3.1 Note).
• Depth Restrictions:
  • For 62.5 mm cones (Part II), dry penetration without bentonite slurry is limited to 9 m depth in medium to fine sands (Clause 62.5 Note).
• Correlation: Blow counts (Ned) relate qualitatively to soil bearing capacity and relative density but are affected by soil characteristics (Clause 0.2).

Stopping Criteria Summary:

Equipment Standards:

• Rods, hammer, and driving head comply with IS: 10589-1983 (Clause 2.1).

flowchart TD
    Start[Begin Driving] --> CheckBlows{Blows per 100 mm > 95?}
    CheckBlows -- No --> Continue[Continue Driving]
    CheckBlows -- Yes --> Stop[Stop to Protect Equipment]
    Continue --> CheckDepth{Target Depth Reached?}
    CheckDepth -- No --> CheckBlows
    CheckDepth -- Yes --> Record[Document Data and End]

Following these guidelines ensures safe operation and reliable test outcomes as per IS 4968 Part 1.

Reporting Requirements under IS 4968 Part 1 (Clause 5.1)

Reports for subsurface sounding tests must include:

• Number of blows (Ned): Recorded continuously for every 300 mm penetration. Presented as a tabulated statement or graph (Ned vs. depth).

• Additional Data to Include:

  • Date when probing was conducted
  • Ground surface elevation
  • Water table depth and fluctuations, if known
  • Total soil resistance at various depths
  • Any interruptions during probing with explanations
  • Soil type or relevant descriptions
  • Diameter of cone used during the test

Summary of Reporting Parameters:

Graphical Data Representation:

graph TD
  Depth[Depth (m)] --> Ned[Blows per 300 mm]
  Ned --> Graph[Plot Ned vs Depth]
  Graph --> Analysis[Interpret Soil Resistance]

This structured reporting format ensures clarity and completeness for geotechnical analysis as per IS 4968 Part 1.

Correlation of IS 4968 Part 1 with Other Penetration Tests

Essential Points (Clauses 2.1 and 62.5 Note):

• Correlations between cone penetration values (Ned) and other test results are site-specific.
• Adjacent testing (within 3 to 5 meters) is recommended for accurate correlation.
• For 62.5 mm cones driven dry up to 9 m in medium to fine sands, empirical correlations developed by CBRI Roorkee apply but should be used cautiously due to soil variability.

Typical Empirical Correlations:

(where (N_{ed}) is the dynamic cone penetration value from IS 4968 Part 1)

Specifications:

• Use 50 mm cone without bentonite slurry for dynamic tests.
• Reliable correlations are limited to depths of about 9 m in sandy soils.
• Adjacent testing is critical for calibration.

flowchart LR
    ConductCPT[Perform Cone Penetration Test (Ned)] --> AdjacentTest[Conduct Adjacent Tests (SPT, DCP)]
    AdjacentTest --> Correlation[Develop Site-Specific Correlation]
    Correlation --> Application[Apply Correlation for Soil Analysis]

In summary, IS 4968 Part 1 emphasizes the importance of localized empirical correlation between cone penetration and other soil strength tests, especially for sandy soils up to 9 meters depth.

IS 4968 Part 1 (1976) also outlines safety and operational recommendations primarily concerning steel tubular scaffolding used during testing.

Key Safety and Operational Points:

• Load Carrying Capacity: Scaffolding must comply with design load requirements as per IS 2131-1981.
• Material Standards: Steel tubes should conform to IS 1161 for structural integrity.
• Assembly Guidelines:
  • Tubes must be fastened securely using couplers.
  • Maintain vertical and plumb alignment.
• Inspection Protocols:
  • Regularly check for corrosion, deformation, and joint strength.
  • Replace or remove damaged components immediately.
• Working Platforms:
  • Minimum plank width of 225 mm.
  • Guardrails installed at a height of 1 meter for fall prevention.
• Safety Factors: A minimum safety factor of 4 on working loads is recommended.

Load Classifications (from IS 2131-1981):

Load Calculation Formula:

[ P = w \times A ]

Where:

• (P) = total applied load (kN)
• (w) = load intensity from the table (kN/m²)
• (A) = platform area (m²)

flowchart TD
    DesignStart[Start Scaffold Design] --> Material[Select Tubular Steel (IS 1161)]
    Material --> LoadClass[Determine Load Class (IS 2131-1981)]
    LoadClass --> Calculate[Compute Load: P = w × A]
    Calculate --> Assembly[Assemble Scaffold with Couplers]
    Assembly --> Check[Verify Verticality and Stability]
    Check --> Install[Install Guardrails and Platforms]
    Install --> Inspect[Regular Inspections and Maintenance]
    Inspect --> SafeUse[Ensure Safe Operation]

For comprehensive specifications, refer to IS 4968 Part 1 and IS 2131-1981.

IS 4968 Part 1 (1976) - Supplementary Annexures and Figures

This standard focuses on procedural and reporting aspects of the cone penetration test (CPT). Key elements include:

Reporting Requirements (Clause 5.1):

• Blow counts (Ned) recorded every 300 mm penetration.
• Data presented as tabulated statements or graphical plots (Ned versus depth).
• Include:
  • Date of test
  • Ground surface elevation
  • Water table depth and fluctuations
  • Resistance values at various depths
  • Interruptions with explanations
  • Soil type, if determined
  • Cone diameter used in testing

Important Figures and Dimensions (Clause 8.5):

• Standardized dimensions for cone and cone adapter are provided.
• Refer to Figure 1 for exact measurements in millimeters.

Typical Cone Dimensions (from Figure 1):

Illustrative Diagram (Cone and Adapter):

graph LR
    Cone[35 mm Diameter, 60 mm Length Cone] --> Adapter[100 mm Length Adapter]
    Adapter --> Assembly[Complete Assembly]

Note: Consult IS 4968 Part 1 Figure 1 for detailed dimensional tables.

These annexures provide consistency in CPT data collection and reporting, essential for soil investigation and foundation engineering.