Method for subsurface sounding for soils, Part 2: Dynamic method using cone and bentonite slurry

IS 4968 (Part 2) - Introduction and Scope: Key Points

• Scope: Covers Dynamic Cone Penetration Test (DCPT) procedures for soil investigation.

• Reporting Requirements (Clause 4.1):
  Record the number of blows (Nebr) continuously for every 300 mm penetration in tabular or graphical form (Nebr vs. depth).
  Include:

  • Date of probing
  • Ground surface elevation
  • Depth and variation of water table
  • Total resistance at required levels
  • Interruptions and reasons
  • Soil type and other relevant info
  • Diameter of the cone used

• Cone Diameter: Typically 62.5 mm, with special considerations when slurry is used (Clause 62.5).

• Rounding Off: Follow IS 2-1960 guidelines for rounding test results.

Summary Table for Reporting DCPT (Clause 4.1)

flowchart TD
    A[Start DCPT] --> B[Record Nebr every 300 mm]
    B --> C{Report Format}
    C -->|Tabular| D[Create Table]
    C -->|Graph| E[Plot Nebr vs Depth]
    D --> F[Include Test Details]
    E --> F
    F --> G[Submit Report]

This ensures consistent, comprehensive documentation per IS 4968 (Part 2).

IS 4968 Part 2: Terminology and Definitions - Key Points

IS 4968 Part 2 (1976) primarily standardizes terms related to slurry abrasiveness testing.

Key Terminology:

• 62.5 mm Cone Penetration: A test parameter where a 62.5 mm cone is penetrated by circulating slurry to evaluate abrasive action.
• Nobr N: Represents the number of revolutions or cycles during the slurry abrasion test until a specified wear or penetration is observed.

Important Notes:

• The standard aligns with international practices while adapting to Indian field conditions.
• Results should be rounded off according to IS 2-1960 for consistency.

No explicit formulas or tables are provided in the clause, but typical abrasion tests involve:

Summary Diagram of Abrasion Test Setup:

flowchart LR
    A[Slurry Reservoir] --> B[Circulation Pump]
    B --> C[62.5 mm Cone Specimen]
    C --> D[Wear Measurement Device]
    D --> E[Data Recording]

Use IS 4968 Part 2 for consistent terminology in slurry abrasiveness testing and report results per IS 2-1960 rounding rules.

IS 4968 Part 2 (1976) — Apparatus and Equipment Key Points

Equipment Setup (Clause 3.1)

• Vane assembly: Vane connected to driving rods with vane borer/gravel trap in place.
• Driving head & guide rod: Fixed on driving rods; cone rests vertically on ground.
• Slurry circulation: Guide rod connected to water swivel via flexible tubes to bentonite slurry pump.
• Slurry tank: Filled with bentonite slurry; slurry prepared separately and stored in drums.
• Slurry consistency:
  • Medium to fine sand: 5% bentonite slurry.
  • Coarse sand: Thicker slurry as per circulation needs.
  • Hard water: Add 1% soap solution for better suspension.
• Hammer: Operated by rope, slides over guide rod to rest on driving head.
• Typical setup: Includes tripod, pulley for swivel, ropes for hammer and swivel (see Fig. 2 in IS).

Reporting (Clause 4.1)

• Number of blows (Nebr): Recorded continuously for every 300 mm penetration.
• Report includes:
  • Date of probing
  • Ground surface elevation
  • Water table depth & variation
  • Total resistance at levels
  • Interruptions & reasons
  • Soil type info
  • Cone diameter used

Summary Table: Bentonite Slurry Preparation

Equipment Assembly Diagram (Simplified)

graph TD
    A[Vane] --> B[Driving Rods]
    B --> C[Driving Head & Guide Rod]
    C --> D[Cone on Ground]
    C --> E[Water Swivel]
    E --> F[Flexible Tubes]
    F --> G[Pump for Bentonite Slurry]
    G --> H[Slurry Tank]
    C --> I[Hammer (Rope Operated)]
    E --> J[Pulley (Rope Holding Swivel)]

For detailed

IS 4968 Part 2 - Cone Specifications & Key Formulas

Cone Specifications (Clause 2.1)

• Material: Suitable steel with hardened tip.
• Shape & Dimensions: As per Fig. 1 (cone assembly), with threaded end to attach driving rods.
• Size: Typically 62.5 mm diameter cone.

Driving Procedure (Clause 3.2)

• Hammer: 65 kg free-fall from 750 mm height.
• Driving:
  • Drive max 30 cm at a time, then pause 1-2 minutes.
  • Pump slurry continuously to avoid choking.
  • Rotate rods 4-5 turns intermittently to maintain hole.
• Blow Counts: Record blows per 100 mm penetration.

Stopping Criteria (Note in 3.2)

• Stop driving if:

  • 35 blows/100 mm (dry cone)

  • 20 blows/100 mm (with slurry)

Key Formula for Resistance (Clause 62.5 b)

• Resistance to penetration with slurry, Nobr:

  [ N_{obr} = \text{Number of blows per 30 cm penetration} ]

• This value correlates with Standard Penetration Test (SPT) value N (IS:2131).

Summary Table: Driving Parameters

flowchart TD
    A[Start Driving Cone] --> B[Drop 65 kg hammer from 750 mm]
    B --> C[Drive max 30 cm]
    C --> D{Blows > limit?}
    D -- Yes --> E[Stop Driving]
    D -- No --> F[Pause 1-2 min, rotate rods 4-5 turns]
    F --> G[Continue pumping slurry]
    G --> B

This ensures effective penetration and reliable soil resistance measurement per IS 4968 Part 2.

IS 4968 Part 2: Driving Rods and Vanes Key Specifications

• Driving Rod (A Rod) Dimensions (Clause 41.27):

  • Outer Diameter (OD): 41.27 mm
  • Internal Diameter (ID): 28.57 mm

• Driving Head (Clause 2.3):

  • Material: Mild steel
  • Diameter: 100 mm
  • Length: 100 to 150 mm
  • Threaded ends for coupling A rods

• Cone (Clause 2.1):

  • Material: Suitable steel with hardened tip
  • Threaded to attach to A rods
  • Dimensions & shape as per Fig. 1 (typical tapered steel cone)

• Vaned Assembly (Clause 2.2.1):

  • Four mild steel vanes welded immediately above the cone
  • Alternative: Gravel trap of wire gauze, 150 mm high, 5 mm mesh

Typical Assembly (Fig. 1 Conceptual)

graph TD
    Cone["Hardened Steel Cone"]
    Vanes["4 Mild Steel Vanes\n(welded above cone)"]
    GravelTrap["Alternative: Gravel Trap\nWire gauze 150 mm high,\n5 mm mesh"]
    DrivingRod["A Rod\nOD 41.27 mm\nID 28.57 mm"]
    DrivingHead["Driving Head\nDiameter 100 mm\nLength 100-150 mm"]

    Cone --> Vanes
    Cone --> GravelTrap
    Vanes --> DrivingRod
    GravelTrap --> DrivingRod
    DrivingRod --> DrivingHead

Summary

• Use 4 mild steel vanes welded above the cone or a 150 mm gravel trap (5 mm mesh).
• Driving rod OD/ID: 41.27 / 28.57 mm.
• Driving head: mild steel, 100 mm diameter, 100-150 mm length, threaded ends.
• Cone: hardened tip, threaded to rod.

This ensures proper driving and soil penetration per IS 4968 Part 2.

Hammer Specifications as per IS 4968 Part 2

• Material: Mild steel or cast iron body with a mild steel base.
• Dimensions:
  • Height: 250 mm
  • Diameter: Suitable to fit the rod and guide with clearance.
• Weight: Total 65 kg (hammer + chain).
• Central Hole:
  • Runs through entire length.
  • Diameter allows free passage of A rod and/or guide.
  • Clearance between hole and rod/guide: ~5 mm.
• Drop Height (Clause 3.2): Hammer is dropped freely from 750 mm height on the driving head.

Additional Notes:

• Automatic hammer drop control is preferred.
• Hoisting equipment (e.g., tripod) must be stable under hammer impact.
• Driving procedure includes stopping after every 30 cm penetration, turning rods 4-5 turns, and continuous slurry pumping.
• Stop driving if blows exceed 35/100 mm (dry) or 20/100 mm (wet).

Summary Table:

flowchart TD
    Hammer[Hammer (65 kg, 250 mm height)]
    Rod[A Rod]
    Guide[Guide]
    Hole[Central Hole (~5 mm clearance)]
    Drop[Drop Height: 750 mm]
    Hammer --> Hole
    Hole --> Rod
    Hole --> Guide
    Hammer --> Drop

This ensures the hammer drives the cone efficiently and safely as per IS 4968 Part 2.

Pumping Unit for Bentonite Slurry (IS 4968 Part 2, Clauses 2.6 & 3.1)

• Pump Capacity: 35 to 45 l/min
• Operating Pressure: 700 to 850 kN/m² (7 to 8.5 kgf/cm²)
• Components:
  • Slurry pump
  • Suction hose assembly
  • Swivel assembly (connected via flexible tubes)
  • Vane borer with 4 vanes and drill holes for slurry escape (for deeper circulation)
• Assembly:
  • Vane connected to driving rods with gravel trap
  • Driving head with guide rod fixed on rods
  • Cone rests vertically on ground
  • Swivel held by rope over pulley
  • Hammer slides over guide rod, resting on driving head
• Slurry Preparation:
  • Bentonite slurry of suitable consistency (5% for medium/fine sand; thicker for coarse sand)
  • Add 1% soap solution in hard water for better suspension
  • Slurry stored in drums, tank inlet protected from debris and kept immersed

Typical Flow Setup (Simplified)

flowchart LR
    SlurryTank -->|Flexible tube| SwivelAssembly -->|Flexible tube| PumpingUnit
    PumpingUnit -->|Suction hose| SlurryTank
    DrivingRods --> VaneBorer --> Cone
    Hammer --> DrivingHead --> DrivingRods

This setup ensures continuous slurry circulation to facilitate soil penetration testing at various depths.

IS 4968 Part 2 — Test Procedure Key Points

Setup (Clause 3.1)

• Vane connected to driving rods with vane borer/gravel trap.
• Driving head fixed; cone rests vertically on test point.
• Guide rod connected via swivel & flexible tubes to bentonite slurry pump.
• Slurry tank filled with bentonite slurry:
  • 5% bentonite for medium/fine sand.
  • Thicker slurry for coarse sand.
  • Add 1% soap solution in hard water for better suspension.
• Hammer operated via rope slides over guide rod onto driving head.
• Typical assembly shown in Fig. 2 (tripod setup).

Test Execution (Clause 62.5 b)

• When 62.5 mm cone penetrated by circulating slurry, number of blows ( N_{obr} ) recorded.

Reporting (Clause 4.1)

• Record blows ( N_{ebr} ) continuously for every 300 mm penetration.
• Report in tabular or graph form (blows vs depth).
• Include:
  • Date, ground elevation, water table depth/variation.
  • Total resistance at levels.
  • Interruptions and reasons.
  • Soil type, cone diameter.

Important Formula

[ N_{obr} = \text{Number of blows for 62.5 mm penetration} ]

Notes

• Follow IS:2-1960 for rounding off results.
• Protect slurry inlet from debris.
• Maintain vertical alignment and steady slurry circulation.

flowchart TD
    A[Vane + Driving Rods] --> B[Driving Head + Guide Rod]
    B --> C[Cone on Ground]
    C --> D[Slurry Circulation via Swivel & Tubes]
    D --> E[Bentonite Slurry Tank]
    F[Hammer on Guide Rod] --> B
    E -->|Slurry pumped| D

This ensures proper dynamic cone penetration testing per IS 4968 Part 2.

IS 4968 Part 2: Equipment Assembly and Setup for Dynamic Cone Penetration Test

Key Specifications & Setup (Clauses 2.1, 2.4, 3.1):

• Cone:

  • Steel cone with hardened tip.
  • Dimensions as per Fig. 1 (standard shape & size).
  • Threaded for attachment to driving rods.

• Hoisting Equipment:

  • Tripod or equivalent stable hoisting device.
  • Must withstand hammer impact during cone driving.
  • Equipped with ladder/quilt for operator access.
  • Pulley for ropes and swivel assembly.
  • Guides to keep driving rods vertical.

• Assembly:

  • Vane connected to driving rods with vane borer/gravel trap.
  • Driving head fixed with guide rod on rods.
  • Cone rests vertically on test point.
  • Guide rod connected via swivel and flexible tubes to slurry pump.
  • Slurry tank filled with bentonite slurry (5% for medium/fine sand; thicker for coarse sand).
  • Hammer with rope slides over guide rod, resting on driving head.

Bentonite Slurry Preparation:

• 5% bentonite for medium/fine sand.
• Thicker slurry for coarse sand.
• Add 1% soap solution for hard water to improve suspension.

Reporting (Clause 4.1):

• Record blows per 300 mm penetration.
• Include date, ground elevation, water table depth, total resistance, interruptions, soil type, cone diameter.

Typical Setup Diagram (Fig. 2):

graph TD
  A[Tripod Hoist] --> B[Pulley for Swivel]
  B --> C[Rope for Holding Swivel]
  A --> D[Ladder for Operator]
  E[Driving Rods] --> F[Cone Assembly]
  G[Hammer with Rope] --> F
  H[Slurry Tank] --> I[Pump] --> J[Flexible Tubes] --> K[Swivel] --> E
  F -->|Vertical Guides| E

This setup ensures accurate, stable, and repeatable dynamic cone penetration tests as per IS 4968 (Part 2).

IS 4968 Part 2: Driving and Slurry Circulation Method - Key Points

Pumping Unit for Bentonite Slurry (Clause 2.6)

• Pump capacity: 35 to 45 l/min
• Pressure: 700 to 850 kN/m² (7 to 8.5 kgf/cm²)
• Includes suction hose and swivel assembly for slurry circulation.

Assembly & Operation (Clause 3.1 & 3.2)

• Vane borer with 4 vanes and drill holes fitted between driving rod and cone to aid slurry escape.
• Cone driven by a 65 kg hammer dropped freely from 750 mm height.
• Slurry circulation starts simultaneously with driving.
• Driving limited to 30 cm increments, then paused for 1-2 minutes while slurry pumping continues.
• Driving rods rotated 4-5 turns intermittently to maintain hole and slurry flow.
• Record number of blows per 100 mm penetration.
• Stop driving if blows exceed:
  • 35 blows/100 mm (dry cone)
  • 20 blows/100 mm (circulating slurry)

Slurry Preparation Notes

• Medium/fine sand: 5% bentonite slurry.
• Coarse sand: thicker slurry as required.
• Hard water: add 1% soap solution for better suspension.

Summary Table

Process Flow (Mermaid Diagram)

flowchart TD
    A[Prepare Bentonite Slurry] --> B[Fill Slurry Tank]
    B --> C[Assemble Driving Rod, Vane Borer, Cone]
   

IS 4968 Part 2 — Recording and Interpretation of Results (Clause 4.1)

Key Requirements for Reporting:

• Blows (Nebr): Record continuously for every 300 mm penetration.
• Present data in tabular form or as a graph (Nebr vs. depth).
• Include the following details in the report:

Additional Notes:

• Use bentonite slurry circulation for the 62.5 mm cone as per Clause 3.1.
• Follow IS:2-1960 for rounding off final values.
• Data interpretation often includes plotting Nebr vs. depth for soil stratification.

Typical Data Table Format (Example):

graph TD
A[Start Test] --> B[Record Nebr every 300 mm]
B --> C[Log Date, Elevation, Water Table]
C --> D[Record Total Resistance]
D --> E[Note Interruptions & Soil Type]
E --> F[Plot Nebr vs Depth Graph]
F --> G[Interpret Soil Layers]

This structured recording ensures reliable interpretation of soil resistance and stratigraphy from dynamic cone penetration tests.

Correlation of Penetration Tests (IS 4968 Part 2 - 1976)

• N = Standard Penetration Test (SPT) resistance (blows/30 cm) as per IS:2131-1963
• Ned = Resistance to 50 mm cone penetration (IS:4968 Part 1)
• Nobr = Resistance to 62.5 mm cone penetration using bentonite slurry (IS:4968 Part 2)

Key Correlations (Central Building Research Institute, Roorkee)

Important Notes:

• For medium to fine sands, Nobr and N values are approximately equal when using bentonite slurry.
• Site-specific correlations should be developed by conducting tests within 3-5 m proximity.
• Use correlations cautiously; regional variations exist.
• Diameter of cone standardized to 62.5 mm; other sizes withdrawn.
• Bentonite slurry improves test reliability and continuity.

Summary Diagram

flowchart LR
    SPT["Standard Penetration Test (N)"]
    Cone50["50 mm Cone Penetration (Ned)"]
    Cone62["62.5 mm Cone Penetration (Nobr)"]

    SPT -->|Correlation| Cone50
    SPT -->|Correlation| Cone62
    Cone62 -->|With Bentonite| SPT

Reference: IS 4968 Part 2 (1976), Clause 62.5 and related notes.

IS 4968 Part 2 (1976) covers Safety and Maintenance of Steel Structures but lacks explicit clauses in your context.

Key Points (General Engineering Practice):

• Safety Factors:

  • Use partial safety factors for loads and materials as per IS 456 or IS 800.
  • Typical safety factor for steel = 1.5 (for yield strength).

• Inspection & Maintenance:

  • Regular visual inspections for corrosion, cracks, deformation.
  • Maintenance includes cleaning, painting, and repair of damaged members.

• Load Checks:

  • Check for accidental loads, wind, seismic effects per IS 875 & IS 1893.

• Corrosion Protection:

  • Use protective coatings; reapply every 3-5 years depending on environment.

Typical Safety Formula:

[ \text{Design Strength} = \frac{f_y}{\gamma_m} ] where

• ( f_y ) = yield strength of steel
• ( \gamma_m ) = partial safety factor (usually 1.5)

Maintenance Schedule Example:

If you need specific tables or formulas, IS 800 and IS 875 are recommended references for safety factors and load considerations.

IS 4968 Part 2: Typical Equipment Assembly for Cone Penetration Test

Key Components & Specifications:

• Cone (Clause 2.1):

  • Made of suitable steel with a hardened tip.
  • Threaded to attach to A rods (outer dia. 41.27 mm, inner dia. 28.57 mm).
  • Dimensions per Fig. 1 (cone shape & size).

• Driving Rods & Vanes (Clause 3.1):

  • Vanes or gravel trap connected to rods.
  • Driving head fixed with guide rod; cone rests vertically on ground.
  • Slurry circulation via flexible tube connected to swivel and pumping unit.
  • Bentonite slurry:
    • 5% for medium/fine sand
    • Thicker for coarse sand
    • Add 1% soap in hard water for suspension.

• Hoisting Equipment (Clause 2.4):

  • Tripod or equivalent, stable under hammer impact.
  • Operator access for pulley and rope fixing.
  • Guides to keep rods vertical.

Assembly Flow:

graph TD
  A[Cone] --> B[Driving Rods with Vanes/Gravel Trap]
  B --> C[Driving Head with Guide Rod]
  C --> D[Hoisting Equipment (Tripod)]
  D --> E[Hammer with Rope]
  C --> F[Flexible Tube to Swivel]
  F --> G[Pumping Unit with Bentonite Slurry]

Summary Table:

This setup ensures proper penetration testing with slurry circulation and stable equipment handling.

IS 4968 Part 2: Slurry Preparation Guidelines Summary

Key Specifications:

• Slurry Type: Bentonite slurry.
• Consistency:
  • Medium to fine sand → 5% bentonite slurry.
  • Coarse sand → Thicker slurry, adjusted for circulation.
• Additives: For hard water, add 1% soap solution to improve bentonite suspension.

Pumping Unit (Clause 2.6):

• Capacity: 35 to 45 l/min
• Pressure: 700 to 850 kN/m² (7 to 8.5 kgf/cm²)
• Components: Suction hose, swivel assembly, vane borer (4 vanes + drill holes for slurry escape).

Slurry Circulation Setup (Clause 3.1):

• Slurry tank filled with prepared bentonite slurry.
• Pump inlet tube protected against debris, immersed in slurry.
• Slurry circulated through flexible tubes and swivel to the cone assembly.

Practical Notes:

Slurry Penetration Check (Clause 62.5 b):

• Use 62.5 mm cone penetration by circulating slurry as a consistency check.

flowchart TD
    A[Slurry Tank filled with Bentonite Slurry] --> B[Pump (35-45 l/min, 7-8.5 kgf/cm²)]
    B --> C[Flexible Tube + Swivel Assembly]
    C --> D[Cone Assembly with Vane Borer]
    D --> E[Slurry Circulates into Soil]
    E --> F[Soil Penetration Test]

Summary: Prepare slurry with 5% bentonite for medium/fine sands, thicker for coarse sands; add 1% soap in hard water. Use specified pump and circulation setup for effective soil penetration testing.