Code of practice for design and construction of pile foundations, Part 2: Timber piles

IS 2911 Part 2: Scope and Key Specifications

• Scope:
  IS 2911 Part 2 covers the design and construction of bored cast-in-situ piles used for foundation purposes.

• Key Aspects Included:

  • Design details: layout, cut-off levels, cap orientation (Clause 3.3)
  • Safe capacity of piles
  • Equipment and accessories for pile construction (Clause 4)

• Design Parameters:

  • Pile diameter typically ranges from 300 mm to 1200 mm
  • Safe load capacity depends on soil strata and pile dimensions
  • Cut-off level: pile length beyond which the pile is trimmed after concreting

• Typical Design Formula for Safe Load, Q_safe:
  [ Q_{safe} = \frac{Q_u}{FOS} ] Where:

  • (Q_u) = Ultimate load capacity (sum of skin friction + end bearing)
  • (FOS) = Factor of safety (usually 2.5 to 3)

• Ultimate Load Components:
  [ Q_u = Q_s + Q_b ]

  • (Q_s) = Skin friction along pile shaft
  • (Q_b) = End bearing at pile tip

• Typical Table Extract (Example):
  | Pile Diameter (mm) | Typical Safe Load (kN) | Application | |--------------------|------------------------|---------------------------------| | 300 | 150 - 300 | Light structures | | 600 | 600 - 1000 | Medium loads | | 900 | 1500 - 2500 | Heavy structures |

flowchart TD
    A[Soil Investigation] --> B[Determine Pile Type & Size]
    B --> C[Calculate Ultimate Load (Q_u)]
    C --> D[Apply Factor of Safety]
    D --> E[Safe Load Capacity (Q_safe)]
    E --> F[Design Pile Layout & Cap]

Summary: IS 2911 Part 2 guides design and construction of bored piles, emphasizing safe capacity, layout, and equipment. Use ultimate load formulas and safety factors to ensure reliability.

IS 2911 Part 2: Terminology & Definitions - Key Points

• Reference for Timber Terms: IS 707-1976 for timber-related terminology.

• Common Equipment Definitions:

  • Dolly: Hardwood cushion atop casing to absorb hammer blows.
  • Drop Hammer (on Monkey): Hammer raised by winch, falls by gravity.
  • Single/Double Acting Hammer: Powered by steam, air, or combustion; energy mainly from motive power, not gravity.
  • Kentledge: Deadweight for applying test loads on piles.
  • Pile Frame (Pile Rig): Steel structure guiding pile driving hammer for accurate positioning.

Summary Table of Equipment

This section primarily defines terms; detailed design formulas appear in later clauses. For timber terms, consult IS 707-1976.

flowchart LR
    A[Hammer Types] --> B(Drop Hammer)
    A --> C(Single/Double Acting Hammer)
    D[Equipment] --> E(Dolly)
    D --> F(Kentledge)
    D --> G(Pile Frame)

Necessary Information for Pile Foundation Design (IS 2911 Part 2)

Key Requirements (Clause 3.1)

• Site Investigation Data (per IS 1892-1979):
  • Trial borings extending ≥10 m below founding level or to firm strata.
  • Soil strength, compressibility tests, groundwater level, and chemical tests for sulphates, chlorides, etc.
• Local Experience: Driving records and boring reports near site for founding level assessment.
• Water-related Data: For marine/bridge piles, record flood levels, scour depth, tides, corrosive chemicals, and water flow.
• Structural Loads:
  • Vertical, lateral loads, moments, torques at pile cap top (excluding pile & cap weight).
  • Pile cap level and layout.
• Transient Loads: Seismic, wind, water forces separately indicated.
• Nearby Structures: Information on adjacent structures affecting foundation.

Additional Design Info (Clause 3.3)

• Pile layout within caps, cut-off and finished cap levels, orientation, and safe pile capacity must be specified.

Typical Safe Load Calculation (Conceptual)

[ Q_{safe} = \frac{Q_{ultimate}}{F.S.} ]

• (Q_{ultimate} = Q_{skin friction} + Q_{end bearing})
• Factor of Safety (F.S.) typically 2.5 to 3

Summary Table: Information Checklist

flowchart TD
    A[Site Investigation] --> B[Soil & Groundwater Data]
    A --> C[Chemical Tests]
    D[Local Experience] --> E[Founding Level]
    F[Water Conditions] --> G[Flood & Scour Data]
    F --> H[Corrosion

IS 2911 Part 2: Equipment and Accessories - Key Points

Equipment Definitions (Clause 4.2)

• Dolly: Cushion (hardwood or suitable material) on top of casing to absorb hammer blows.
• Drop Hammer (on Monkey): Hammer raised by winch, falling by gravity.
• Single/Double Acting Hammer: Powered by steam, compressed air, or combustion; energy mainly from motive power, not gravity.
• Kentledge: Deadweight for applying test load to piles.
• Pile Frame/Rig: Movable steel structure ensuring correct pile alignment during driving.

Design Details (Clause 3.3)

• Layout of piles within cap
• Cut-off and finished cap levels
• Orientation of cap on foundation plan
• Safe capacity of each pile type

Reference for Storage (Clause 14.1)

• For equipment storage, refer IS 883-1970.

Typical Hammer Energy Formula (for design reference):

[ E = m \times g \times h ]

• (E) = Energy per blow (Joules)
• (m) = Mass of hammer (kg)
• (g) = Acceleration due to gravity (9.81 m/s²)
• (h) = Height of drop (m)

flowchart TD
    A[Pile Driving Equipment] --> B[Dolly]
    A --> C[Drop Hammer]
    A --> D[Single/Double Acting Hammer]
    A --> E[Kentledge]
    A --> F[Pile Frame]

For detailed specifications, consult IS 2911 Part 2 and related parts.

Design Considerations for Timber Piles as per IS 2911 Part 2

Key Specifications:

• Timber Species: Must conform to IS 3629-1966.
• Pile Length Tolerance:
  • For piles < 12 m: ±30 cm
  • For piles ≥ 12 m: ±60 cm
• Heartwood Diameter Ratio: For round piles,
  [ \frac{\text{Heartwood Diameter}}{\text{Pile Butt Diameter}} \geq 0.8 ]
• Ends of Piles: Both ends sawn at right angles and trimmed flush.

Preservative Treatment (Clause 6.1.2):

• Class B: For foundation and temporary work piles.
• Minimum diameter/side for compaction piles: 10 cm

Design Notes:

• Timber piles are used for load-bearing or ground compaction.
• Sawn timber piles for sheet piling are not covered.

Typical Design Checks Include:

• Load Capacity: Based on allowable bearing capacity of timber species.
• Buckling: Check slenderness ratio (Length/least lateral dimension).
• Durability: Adequate preservative treatment per class.

flowchart TD
    A[Timber Pile Design] --> B[Species per IS 3629]
    A --> C[Length Tolerance ±30 or 60 cm]
    A --> D[Heartwood Diameter ≥ 0.8 × Butt Diameter]
    A --> E[Ends sawn flush]
    A --> F[Preservative Treatment Class B]
    F --> G[Diameter ≥ 10 cm for compaction piles]

For detailed design, refer to IS 2911 Part 2 tables on allowable stresses and preservative treatment methods.

Classification of Timber Piles (IS 2911 Part 2)

• Class B Piles (Clause 6.1.2):
  • Used for foundation work other than those in Class A (6.1.1) and for temporary works.
  • For ground compaction, minimum cross-section:
    • Diameter or side ≥ 10 cm (square piles).

Timber Species & Specifications (Clause 7.1):

• Timber must conform to IS 3629-1966.
• Length tolerance:
  • For piles < 12 m: ±30 cm
  • For piles ≥ 12 m: ±60 cm
• For round piles:
  • Heartwood diameter / Butt diameter ≥ 0.8
• Ends of piles:
  • Sawn at right angles, trimmed flush removing knots and limbs.

Summary Table

flowchart TD
    A[Timber Piles] --> B[Class B Piles]
    B --> C[Foundation work other than Class A]
    B --> D[Temporary work]
    D --> E[Min diameter/side ≥ 10 cm]
    A --> F[Timber Species]
    F --> G[IS 3629-1966]
    F --> H[Length tolerance ±30/60 cm]
    F --> I[Heartwood diameter ratio ≥ 0.8]

This classification ensures durability and suitability of timber piles for different foundation applications.

Timber Species and Specifications – IS 2911 Part 2

• Timber Species: As per Clause 7.1, timber species must conform to IS 3629-1966 (Specification for structural timber in building).

• Pile Length Tolerance:

  • For piles < 12 m: ±30 cm
  • For piles ≥ 12 m: ±60 cm

• Round Piles:

  • Heartwood diameter / Butt diameter ≥ 0.8

• Ends of Piles:

  • Both ends sawn at right angles
  • Surface trimmed flush, knots and limbs removed

• Minimum Dimensions for Class B Piles (Clause 6.1.2):

  • Diameter or side (square piles) ≥ 10 cm

• Preservative Treatment:

  • As per IS 401-1967 (Code of practice for preservation of timber)
  • Mandatory where conditions are unfavorable (Clause 8.1)

Summary Table:

flowchart TD
    A[TIMBER SPECIES] --> B[Conform to IS 3629-1966]
    A --> C[Length Tolerance ±30 cm (<12m)]
    A --> D[Length Tolerance ±60 cm (≥12m)]
    A --> E[Heartwood Diameter Ratio ≥ 0.8]
    A --> F[Ends sawn square & trimmed]
    A --> G[Min Diameter/Side ≥ 10 cm]
    A --> H[Preservative Treatment per IS 401-1967]

This ensures durability, structural integrity, and compliance with IS 2911 Part 2 requirements for timber piles.

IS 2911 Part 2 – Preservative Treatment of Timber Piles

Key Specifications:

• Timber species: As per IS 3629-1966, with heartwood diameter ≥ 0.8 × butt diameter for round piles.
• Pile length tolerance:
  • ±30 cm for piles < 12 m
  • ±60 cm for piles ≥ 12 m
• Both ends sawn square and trimmed flush.

Preservative Treatment (Clause 8.1 & 11.1):

• Treatment must comply with IS 401-1967 (Code of Practice for Preservation of Timber).
• Treatment is mandatory especially under adverse environmental conditions.
• After driving:
  • Cut pile tops to a true plane.
  • Apply preservative on cut ends immediately.
  • Metal top covers (if specified) to be placed immediately after treatment.
  • All holes/cuts for framing must be treated.

Definitions:

• Treated pile: Timber impregnated with preservative to prevent biological deterioration.

Typical Treatment Process (per IS 401-1967):

flowchart TD
    A[Timber Selection] --> B[Check Species & Dimensions per IS 3629]
    B --> C[Preservative Treatment per IS 401]
    C --> D[Driving Pile]
    D --> E[Cut Pile Top to True Plane]
    E --> F[Treat Cut Ends with Preservative]
    F --> G{Metal Top Cover Specified?}
    G -- Yes --> H[Place Metal Top Cover]
    G -- No --> I[Complete Installation]

Summary: Use durable heartwood species, treat all piles per IS 401-1967, especially cut ends after driving, and protect pile tops with preservative and metal covers if specified.

IS 2911 Part 2: Working Stresses and Load Factors Summary

• Working Load (Clause 2.22): Load assigned to a pile in design; basis for allowable stresses.

• Working Stress (Clause 9.1):

  • Use working stresses as per IS 883-1970 (Timber Code).
  • During pile driving, stresses can be exceeded up to 100% temporarily.

• Allowable Stresses (Clause 10.1):

  • Follow IS 456-1978 for stresses in concrete and reinforcement in pile caps.

Key References:

Typical Working Stress Concept:

[ \sigma_{working} \leq \sigma_{allowable} ]

• Where (\sigma_{allowable}) is from IS 883 for timber piles.
• Temporary driving stresses can be up to (2 \times \sigma_{allowable}).

Load Factor Considerations:

• No explicit load factors in IS 2911 Part 2; design factors follow IS 456 for concrete.
• Pile working load is ultimate load divided by a factor of safety (typically 2 to 3).

flowchart TD
    A[Ultimate Load on Pile] --> B[Divide by Factor of Safety]
    B --> C[Working Load]
    C --> D[Check Working Stress ≤ Allowable Stress]
    D -->|Pass| E[Safe Design]
    D -->|Fail| F[Redesign Required]

For detailed values, consult IS 883 for timber allowable stresses and IS 456 for concrete stresses.

Design of Pile Cap (RCC) as per IS 2911 Part 2

Key Specifications:

• Depth of Pile Cap (Clause 10.2):
  Must be sufficient for anchorage of both column and pile reinforcements.

• Levelling Course (Clause 10.5):
  A 75 mm thick concrete levelling course is provided under the pile cap.

• Clear Cover (Clause 10.5):
  Minimum clear cover for main reinforcement in the cap slab = 75 mm.

• Working Stresses (Clause 9.1):
  Use working stresses as per IS 883-1970, which can be exceeded by up to 100% during pile driving.

Design Considerations:

• Layout and setting out of piles within the cap must be clearly indicated (Clause 3.3).
• Cut-off levels and finished cap levels must be defined.
• Orientation of cap in foundation plan and safe pile capacity must be specified.

Typical Design Formulae for Pile Cap:

• Ultimate Load on Pile Cap, (P_u):
  [ P_u = \sum P_i + \text{Load from superstructure} ]

• Bending Moment in Cap:
  [ M = \frac{P \times e}{n} ]
  where (P) = load, (e) = eccentricity, (n) = number of piles.

• Shear Design:
  Check for one-way and two-way shear as per IS 456.

Reinforcement Detailing:

• Main reinforcement anchored properly into pile heads.
• Distribution steel to prevent cracking.

flowchart TD
    A[Load from Superstructure] --> B[Pile Cap]
    B --> C[Piles]
    B --> D[Levelling Course (75mm)]
    B --> E[Reinforcement with 75mm Clear Cover]

For detailed reinforcement and sectional design, refer to IS 456 and IS 2911 Part 2 clauses on reinforcement anchorage and shear.

IS 2911 Part 2: Installation and Driving of Piles – Key Points

1. Site Investigation (Clause 3.1)

• Minimum depth: Trial borings should extend at least 10 m below pile founding level or to firm strata.
• Tests required: Strength, compressibility, groundwater level, chemical tests (sulphates, chlorides).
• Additional data: Local driving experience, water levels, scour depth, tidal info (for marine/bridge works).
• Load data: Vertical, lateral, moments, torques at pile cap top (excluding pile/pile cap weight).
• Transient loads: Seismic, wind, water forces must be separately indicated.
• Nearby structures: Provide sufficient info for interaction assessment.

2. Pile Tip Specifications (Clause 12.2)

• Shape: Pointed tip as truncated cone or pyramid.
• Tip area: 25 cm² to 40 cm².
• Tip length: 1.5 to 2 times pile diameter or square side.

3. Capping (Clause 11.2)

• Capping is done only after piles are correctly positioned.

Summary Table: Pile Tip Dimensions

flowchart TD
    A[Site Investigation] --> B[Trial Borings ≥ 10m below founding]
    B --> C[Soil & Chemical Tests]
    C --> D[Load Data: Vertical, Lateral, Moments]
    D --> E[Driving Experience & Water Data]
    E --> F[Pile Driving]
    F --> G[Pile Tip: Truncated Cone/Pyramid]
    G --> H[Capping after correct positioning]

This ensures safe, efficient pile installation per IS 2911 Part 2.

Control of Alignment and Handling — IS 2911 Part 2

Key Specifications (Clause 12.5)

• Vertical piles deviation: ≤ 1.5% of length
• Raker piles deviation: ≤ 4% of length (up to 1 in 6 rake no capacity reduction)
• Positional tolerance at working level:
  • Single pile: ≤ 50 mm
  • General piles: ≤ 75 mm
• For deep cut-off piles, design must consider worst-case combined tolerances of position and inclination.
• Piles exceeding tolerances must be replaced or supplemented.

Handling (Clause 14.2.1)

• Support piles at multiple points during storage to prevent bending damage.

Control of Driving (Clause 13.1)

• Maintain competent inspector on-site to record:
  • Installation sequence
  • Pile dimensions & reinforcement
  • Depth driven
  • Driving & concreting times
  • Cut-off/working level
  • Other observations

Summary Table: Alignment Tolerances

flowchart LR
    A[Pile Installation] --> B[Check Alignment]
    B -->|Within tolerance| C[Proceed with Capping]
    B -->|Exceeds tolerance| D[Redesign or Replace Pile]
    C --> E[Record Driving Data]
    E --> F[Store & Handle Carefully]

This ensures structural integrity and correct load transfer per IS 2911 Part 2.

IS 2911 Part 2: Recording of Data (Clause 13)

A competent inspector must record the following during pile installation:

• Sequence of Installation: Order of pile driving within a group.
• Pile Dimensions: Length, diameter, reinforcement details, and pile mark.
• Depth Driven: Total penetration depth at each stage.
• Time Taken: Duration for driving and concreting.
• Cut-off/Working Level: Final level after driving.
• Observations: Any anomalies like sudden changes in penetration rate (Clause 12.9).

Important Notes:

• Sudden changes in penetration rate not due to soil must be investigated to avoid pile damage.
• Data recording ensures quality control and helps assess pile performance.

Reference Table: Typical Data Sheet Fields

This systematic recording is critical for pile integrity and compliance with IS 2911 Part 2.

Handling and Protection of Piles as per IS 2911 Part 2

Key Specifications:

• Timber species & specs: Conform to IS 3629-1966.
• Pile length tolerance:
  • ±30 cm for piles < 12 m
  • ±60 cm for piles ≥ 12 m
• Round piles: Heartwood diameter ≥ 0.8 × pile butt diameter.
• Ends: Sawn square, flush trimmed (knots/limbs removed).

Handling & Storage:

• Piles must be supported at multiple points to avoid excessive bending (Clause 14.2.1).
• Ends should be protected to prevent damage during transport and storage.
• Store piles on level ground, elevated from soil to prevent moisture damage.

Inspection & Recording (Clause 13.1):

• Record pile installation sequence, dimensions, reinforcement details.
• Record driving depth, time for driving/concreting.
• Note cut-off/working level and any anomalies.

Summary Table: Pile Length Tolerance

flowchart TD
    A[Timber Pile] --> B[Check Species & Specs (IS 3629)]
    B --> C{Length < 12 m?}
    C -->|Yes| D[Length ± 30 cm]
    C -->|No| E[Length ± 60 cm]
    D & E --> F[Check Heartwood Diameter ≥ 0.8 × Butt Diameter]
    F --> G[Ends sawn square & trimmed]
    G --> H[Support at multiple points during storage]
    H --> I[Inspect & Record Installation Data]

This ensures pile integrity and durability during handling and installation.