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

IS 4968 (Part 1) - 1976: Scope Summary

This part of IS 4968 covers the methodology for subsurface sounding for soils, primarily focusing on soil investigation techniques to determine soil properties relevant for foundation design.

Key Points on Scope:

• Applies to subsurface soil exploration using sounding methods.
• Provides standard procedures for conducting soil sounding tests.
• Aims to determine soil stratification, bearing capacity, and soil consistency.
• Replaces references from IS 2131-1963 with IS 2131-1981 for related soil testing methods.

Typical Parameters and Formulas (General for Soil Sounding):

• Penetration Resistance (N): Number of blows per unit penetration (e.g., per 10 cm).
• Bearing Capacity Estimation: [ q_u = N \times C ] where ( q_u ) = ultimate bearing capacity, ( N ) = penetration resistance, ( C ) = empirical factor depending on soil type.

Common Tables (from IS 2131 and related):

flowchart LR
    A[Start Soil Sounding] --> B[Drive Penetration Rod]
    B --> C[Count Blows per 10 cm]
    C --> D{N-value obtained?}
    D -->|Yes| E[Estimate Soil Bearing Capacity]
    D -->|No| B
    E --> F[Classify Soil Type]
    F --> G[Report Soil Profile]

Note: For detailed formulas and tables, refer to IS 2131-1981 and IS 4968 (Part 1) full text.

IS 4968 Part 1 (1976) - Equipment for Dynamic Cone Penetration Test

Key Specifications from Clause 2.4 - Hoisting Equipment:

• Type: Suitable hoisting equipment like a tripod.
• Stability: Must be stable under impact forces from the hammer during testing.
• Operator Access: Provision for operator to climb and fix pulleys, ropes.
• Guides: Must have guides to keep the driving rod vertical during penetration.

Typical Setup:

• Tripod with pulley system.
• Hammer dropped vertically on the driving head.
• Rope and pulley for raising hammer.

Reference Update:

• Replace references to IS:2131-1963 with IS:2131-1981 for hammer specifications.

Additional Notes (Engineering Insight):

• Stability is crucial to avoid lateral movement affecting test accuracy.
• The height of tripod should allow free hammer drop (typically around 1 m).
• Guides ensure vertical alignment, minimizing bending stresses on the rod.

Simple Diagram of Tripod Setup:

graph TD
    Hammer -->|Drop| Driving_Head
    Driving_Head -->|Vertical Rod| Soil
    Tripod -->|Supports| Pulley
    Operator -->|Climbs| Tripod
    Pulley -->|Rope| Hammer

For detailed hammer weight and drop height, refer to IS 2131-1981.

IS 4968 Part 1 (1976) - Dynamic Cone Penetration Test Procedure

• Cone: 50 mm diameter, 60° apex angle.
• Assembly: Cone attached loosely or screwed to driving rod (A rod). Hammer head connected via rod coupling; guide rod 150 cm long fixed to hammer head.
• Hammer: 65 kg weight falling freely from 750 mm height.
• Test:
  • Keep assembly vertical with cone on soil surface.
  • Drive cone by repeated hammer blows.
  • Record number of blows per 100 mm penetration.
  • Continue until required depth or blows exceed 95 per 100 mm (stop to avoid equipment damage).

Key Specifications:

Notes:

• Substitute IS:2131-1981 for IS:2131-1963 for related references.
• Equipment must be kept vertical during test.

flowchart TD
    A[Start Test] --> B[Place cone on soil]
    B --> C[Drop 65 kg hammer from 750 mm]
    C --> D[Record blows per 100 mm penetration]
    D --> E{Blows > 95?}
    E -- Yes --> F[Stop test]
    E -- No --> G[Continue driving to required depth]
    G --> H[End Test]

This ensures consistent soil resistance measurement using the dynamic cone penetration method.

IS 4968 Part 1: Limitations and Stopping Criteria for 50 mm Cone Dynamic Penetration Test

• Cone size: 50 mm diameter, 60° cone.
• Hammer: 65 kg falling freely from 750 mm height.
• Penetration measurement: Number of blows per 100 mm penetration recorded.
• Stopping criteria:
  • Stop driving if blows exceed 95 blows/100 mm to prevent equipment damage (Clause 3.1 Note).
• Depth limitation:
  • For 62.5 mm cone (Part II), dry driving without bentonite slurry is limited to 9 m depth in medium to fine sands (Clause 62.5 Note).
• Correlation:
  • Number of blows (Ned) correlates qualitatively with soil bearing capacity and relative density but influenced by soil properties (Clause 0.2).

Summary Table: Stopping Criteria

Equipment Specification Reference:

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

flowchart TD
    A[Start Driving] --> B{Blows per 100 mm > 95?}
    B -- No --> C[Continue Driving]
    B -- Yes --> D[Stop Driving to avoid damage]
    C --> E{Depth reached?}
    E -- No --> B
    E -- Yes --> F[Record Data and Stop]

This ensures safe operation and reliable data per IS 4968 (Part I).

IS 4968 Part 1 (Clause 5.1) — Reporting of Results

For subsurface sounding tests, the report must include:

• Number of blows (Ned): Recorded continuously for every 300 mm penetration. Present as:

  • A tubular statement or
  • A graph plotting Ned vs. depth.

• Additional essential data:

  • Date of probing
  • Elevation of ground surface
  • Depth and variation of water table (if known)
  • Total resistance at specified depths
  • Any interruptions in probing with reasons
  • Soil type or other relevant info
  • Diameter of cone used in test

Summary Table for Reporting

Graphical Representation

graph TD
  A[Depth (m)] --> B[Ned (blows/300mm)]
  B --> C[Graph: Ned vs Depth]
  C --> D[Interpretation of soil resistance]

This structured reporting ensures clarity and completeness for geotechnical evaluation per IS 4968 Part 1.

IS 4968 Part 1: Correlation with Other Methods

Key Points from Clauses:

• Clause 2.1:

  • Correlation between cone penetration values (Ned) and other penetration test values must be site-specific.
  • Tests should be conducted adjacent (3 to 5 m) to the cone test location for reliable correlation.

• Clause 62.5 (Note):

  • For 62.5 mm cone driven dry (without bentonite slurry) up to 9 m depth in medium to fine sands, CBRI Roorkee developed empirical correlations.
  • Use these correlations with caution due to soil variability.

Typical Correlation Formula (from CBRI, Roorkee):

(Ned = cone penetration value from IS 4968 Part 1)

Specifications:

• Use 50 mm cone without bentonite slurry for dynamic tests.
• Depth limit: up to 9 m for reliable correlations in sands.
• Adjacent testing is critical (3-5 m) for site-specific calibration.

flowchart LR
    A[Conduct Cone Penetration Test (Ned)] --> B[Conduct Adjacent Test (SPT, DCP)]
    B --> C[Develop Site-specific Correlation]
    C --> D[Apply Correlation for Soil Characterization]

Summary: IS 4968 Part 1 emphasizes site-specific correlation between cone penetration and other methods, using adjacent tests and empirical relationships primarily for sands up to 9 m depth. Use correlations cautiously and validate locally.

IS 4968 Part 1 (1976) covers safety and operational guidelines primarily for steel tubular scaffolding.

Key Safety & Operational Guidelines (Summary):

• Load Capacity: Ensure scaffolding components meet design loads as per IS 2131-1981 (updated standard for scaffolding loads).
• Material Specs: Use steel tubes conforming to IS 1161 for structural reliability.
• Assembly:
  • Tubes must be securely fastened with couplers.
  • Maintain verticality and plumb alignment.
• Inspection:
  • Regular checks for corrosion, deformation, and joint integrity.
  • Remove defective parts immediately.
• Working Platform:
  • Minimum plank width: 225 mm.
  • Guardrails at 1 m height to prevent falls.
• Safety Factors:
  • Use a safety factor of at least 4 on working loads.

Reference Table: Load Classes (from IS 2131-1981)

Formula for Load on Scaffolding:

[ P = w \times A ]

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

flowchart TD
    A[Start: Scaffold Design] --> B[Select Tube Size & Material (IS 1161)]
    B --> C[Determine Load Class (IS 2131-1981)]
    C --> D[Calculate Load P = w × A]
    D --> E[Assemble Scaffold with Couplers]
    E --> F[Check Verticality & Stability]
    F --> G[Install Guardrails & Platforms]
    G --> H[Regular Inspection & Maintenance]
    H --> I[Safe Operation]

For detailed specifications, refer to IS 4968 Part 1 and IS 2131-1981 for updated load tables and safety factors.

IS 4968 Part 1 (1976) - Key Annexures, Figures, and Specifications

The standard primarily covers the procedure and reporting for cone penetration tests (CPT). Key points and specifications include:

Key Reporting Requirements (Clause 5.1)

• Number of blows (Ned) recorded every 300 mm penetration.
• Data to be presented as a tubular statement or graph (Ned vs. depth).
• Include:
  • Date of probing
  • Ground surface elevation
  • Water table depth and variation
  • Total resistance at levels
  • Interruptions and reasons
  • Soil type, if available
  • Diameter of cone used

Important Figures and Dimensions (Clause 8.5)

• Cone and Cone Adopter dimensions are standardized (all in mm).
• Refer to Fig. 1 for exact cone and adopter dimensions.

Typical Cone Dimensions (from Fig. 1)

Summary Diagram (Cone and Adopter)

graph LR
A[Cone] -->|35 mm dia, 60 mm length| B[Cone Adopter]
B -->|100 mm length| C[Assembly]

Note: For detailed tables and exact figure dimensions, refer directly to IS 4968 Part 1, Fig. 1.

This standard ensures uniformity in CPT data collection and reporting, crucial for soil investigation and foundation design.