Code of practice for ancillary structures in the sewerage system, Part I: Manholes

IS 4111 Part 1 - Scope Summary

• Scope: Specifies requirements for manholes and sewers, focusing on dimensions, construction, and service types.

• Service Manholes:

  • For sewers > 450 mm diameter, scraper-type manholes are mandatory.
  • Manhole spacing: 110 to 120 m intervals.
  • Clear opening at top: 1200 mm x 900 mm for bucket lowering.

• Rounding Off Values:

  • Final test or analysis values rounded per IS 2-1960.
  • Retain significant figures equal to specified values.

Key Specifications Table (Extract)

Important Notes:

• The standard aligns with IS 2-1960 for rounding off numerical values.
• It applies primarily to burnt clay bricks and sewer construction.

flowchart LR
    A[Sewers > 450 mm] --> B[Scraper Type Manhole]
    B --> C[Manhole Interval: 110-120 m]
    B --> D[Opening Size: 1200 x 900 mm]

This ensures proper access and maintenance of sewer systems as per IS 4111 Part 1.

IS 4111 Part 1 – Definitions: Key Points

• Clause 2.0 defines terms used throughout the standard, ensuring clarity and uniform interpretation.
• Rounding off (Clause 0.4) follows IS 2:1960 guidelines:
  • Final test or analysis results must be rounded to the same number of significant digits as specified values.
  • Ensures consistency in reporting and compliance checks.

Important Notes on Definitions:

• Definitions establish the scope and meaning of terms like load, stress, strain, material properties, etc. (Refer to full standard for exact terms).
• Precise definitions avoid ambiguity in structural design and testing.

IS 2:1960 Rounding Rule Summary:

Summary:
Use the definitions in Clause 2.0 for terminology, and apply IS 2:1960 rounding rules for test/analysis results to maintain standard compliance.

IS 4111 Part 1 - Design Considerations: Key Points

1. Design Basis (Clause 3.1)

• Focus on spacing and sizing of manholes and access shafts.
• Soffit defined as the highest internal point of sewer cross-section (Clause 2.9).

2. Channels and Benching (Clause 4.7)

• Channel bottom: Semi-circular, diameter = sewer pipe diameter.
• Above horizontal diameter: vertical sides extend 50 mm above sewer crown.
• Top edges are rounded for smooth flow.
• Branch channels follow similar benching with appropriate fall at junction.
• Material: Cement concrete 1:2:4, smooth cement finish with steel trowel.

3. Depth of Channels and Benching (Table 1)

Summary Diagram of Channel & Benching Cross-section

flowchart TD
    A[Semi-circular Channel] --> B[Diameter = Sewer Pipe Diameter]
    B --> C[Vertical Sides extend 50 mm above crown]
    C --> D[Top edge rounded off]
    D --> E[Benching at sides as per Table 1]

Use this table and guidelines to ensure proper hydraulic flow and structural integrity in manhole design.

IS 4111 (Part 1) - Materials and Construction Key Points

1. Reinforced Cement Concrete Manholes (Clause 4.10)

• Use Grade M20 concrete or 1:1½:3 mix as per IS 456-1978.
• Suitable for high sub-soil water conditions.
• Base and walls designed per Clause 4.4 factors.
• Cast iron steps and covers must conform to IS specifications (Parts 1 to 7).

2. Channels and Benching (Clause 4.7)

• Channels: Semi-circular bottom half, diameter equal to sewer pipe.
• Benching: Vertical sides extending 50 mm above pipe crown, rounded edges.
• Material: Cement concrete 1:2:4 mix, smooth finished with neat cement.
• Depths as per Table 1:

3. Manhole Covers (Clause 3.9)

• Footpath manholes: Medium duty cast iron covers.
• Road under vehicular traffic: Heavy duty cast iron covers.

4. Scraper Type Manholes (Clause 7.5)

• For sewers > 450 mm diameter.
• Manhole spacing: 110-120 m.
• Clear opening: 1200 mm x 900 mm for bucket lowering.

Summary Diagram (Manhole Cross-section)

graph TD
    A[Base slab - RCC M20] --> B[Wall - RCC M20]
    B --> C[Channels - Semi-circular, 1:2:4 concrete]
    C --> D[Benching - Vertical sides + Rounded edges]
    B --> E[Cast iron steps]
    B --> F[Cast iron cover]
``

Key Specifications & Formulas from IS 4111 Part 1 (1986) for Manhole Components:

1. Sizes of Manholes (Clause 3.3 & 14.0)

• Minimum clear opening diameter: 560 mm for manholes > 0.9 m depth.
• For depths 0.9 m to 14 m, typical diameter: 1800 mm.
• Refer Fig. 4 (IS 4111 Part 1) for typical circular manhole designs.

2. Reinforced Cement Concrete Manholes (Clause 4.10)

• Use Grade M20 concrete or 1:1½:3 mix (cement:sand:coarse aggregate).
• Design base & walls per IS 456 (1978) for relevant load factors.
• Suitable for high sub-soil water conditions.

3. Manhole Covers and Frames (Clause 4.9)

• Covers must provide minimum clear opening of 560 mm diameter.
• Must conform to IS 1726 (Parts 1 to 7) for cast iron covers & frames:
  • Part 1: General requirements
  • Part 2-7: Specific requirements for various types (HD, MD, LD; circular, rectangular, square)
• Frames embedded firmly in concrete on masonry.
• Covers sealed with thick grease after installation.

Summary Table: Manhole Size vs Depth

Design Notes:

• Base and wall thickness & reinforcement per IS 456.
• Cast iron steps and covers per IS 1726.
• Seal covers to prevent ingress of gases and water.

graph TD
A[Manhole Design] --> B[Size & Opening]
A --> C[Material & Mix]
A --> D[Covers & Frames]
B --> E[Diameter ≥ 1800 mm for depth > 0.9 m]
B --> F[Clear opening ≥ 560 mm]
C --> G[Concrete Grade M20 or 1:1½:3 mix]
D -->

Safety Measures as per IS 4111 Part 1 (1986)

• Rounded Corners (Clause 5.5):

  • Radius = 75 mm
  • Finish: Cement plaster (1 part cement : 3 parts sand), 13 mm thick
  • Smooth finish with a neat cement coat, steel trowelled for imperviousness

• Rounding Off Values (Clause 0.4):

  • Round off test/analysis results per IS 2-1960
  • Maintain same significant figures as specified values

• Safety in Cascades and Ramps (Clause 6.5):

  • Provide hand-rails and chains for worker safety

Summary Table

flowchart TD
    A[Rounded Corners] --> B[Radius 75 mm]
    A --> C[Plaster 1:3 Cement:Sand, 13 mm thick]
    A --> D[Steel Trowel Finish]
    E[Safety on Ramps] --> F[Hand-rails]
    E --> G[Chains]

This ensures worker safety and durability per IS 4111 Part 1.

IS 4111 (Part 1) - Special Features & Drop Structures Key Points

Drop Structures (Clause 7.4.2)

For sewers > 450 mm diameter, drops can be made by:

• Cascade: Stepped ramp breaking flow, with a pipe under steps for small flows.
• Ramp: Steep channel (~45° slope) with transverse ribs every 1.15 m to reduce turbulence; stilling pool at bottom.
• Successive Drops: Total drop divided into smaller drops at preceding manholes (e.g., 2.4 m total as 0.6 m drops in 4 manholes).

Design Dimensions & Formulas

• Drop height at junction manhole: Typically ≤ 0.6 m per drop.
• Ramp slope: 1:12 (approx. 8.3% gradient).
• Transverse ribs spacing: 1.15 m intervals.
• Wall thickness (B): As per structural requirements, usually ≥ 150 mm for RCC walls.
• Drop length: 2/3 × Diameter + 75 mm (Clause 1.5).

Materials

• Heavy-duty Class I bricks (IS 2180-1985), cement concrete with granolithic finish, or dressed granite.
• Cement plaster minimum thickness: 13 mm.

Summary Table: Drop Structure Methods

flowchart TD
    A[High Level Sewer] --> B[Cascade Steps]
    B --> C[Pipe for small flows]
    C --> D[Low Level Sewer]
    A --> E[Ramp (1:12 slope)]
    E --> F[Transverse ribs @1.15 m]
    F --> G[Stilling Pool]
    G --> D
    subgraph Successive Drops
        H[Manhole 1: 0.6 m drop] --> I[Manhole 2: 0.6 m drop] --> J[Manhole 3: 0.6

IS 4111 Part 1: Access Shafts and Rungs Key Points

Access Shafts (Clauses 3.4 & 3.4.1)

• Shape & Size:
  • Circular shafts with minimum internal diameter = 750 mm.
  • For depths > 3 m, provide additional dimensions for cleaning/maintenance.
• Brickwork shafts:
  • Corbelled on three sides to reduce to cover frame size.
  • Fourth side left open for step irons or ladder access.
• Design consideration: accommodate maintenance equipment size.

Rungs (Clause 4.8)

• Provided in manholes deeper than 0.8 m.
• Preferably cast iron, dimensions per IS 5455-1969.
• Rungs arranged in two vertical staggered runs, 300 mm apart horizontally and vertically.
• Projection: minimum 100 mm beyond finished wall surface.
• Top rung positioned 450 mm below cover, lowest rung max 300 mm above benching.
• Footrests painted with coal tar; embedded portion painted with thick cement slurry.

Typical rung arrangement:

flowchart TB
    A[Manhole Cover]
    B[Top Rung (450 mm below cover)]
    C[Intermediate Rungs spaced 300 mm vertically]
    D[Lowest Rung (≤ 300 mm above benching)]
    E[Manhole Wall]
    F[Projection of rung ≥ 100 mm]

    A --> B --> C --> D
    D --> E
    B --> F

This ensures safe, ergonomic access for maintenance personnel.

IS 4111 Part 1: Channels and Benching Key Points

Geometry & Construction (Clause 4.7)

• Channels: Semi-circular bottom half with diameter = sewer diameter.
• Sides: Extended vertically 50 mm above sewer crown, edges rounded.
• Branch channels: Similar benching, with appropriate fall at junctions.
• Material: Cement concrete 1:2:4 (cement: sand: 20mm aggregate), smooth rendered finish by steel trowel.

Depth Specifications (Table 1)

Additional Notes

• Benching (Clause 2.2): Sloped surfaces on either side of channels to confine flow, avoid deposits, and provide safe working platform.
• Material continuity (Clause 5.1): Use same material as sewer where possible; otherwise use 1:2:4 concrete with smooth finish.
• Gradient: Invert laid at same gradient as sewer if diameter unchanged.

flowchart TD
    A[Sewer Pipe] --> B[Channel (Semi-circular bottom)]
    B --> C[Sides extended 50mm above crown]
    C --> D[Benching sloped on sides]
    D --> E[Flow confined & deposits avoided]

This ensures smooth flow and maintenance access inside manholes.

IS 4111 Part 1: Manhole Covers and Frames - Key Points

1. Clear Opening Size

• Minimum clear opening diameter: 560 mm for manholes deeper than 0.9 m (Clause 4.9).

2. Materials & Standards

• Cast iron covers and frames must conform to IS 1726 (Parts 1 to 7):
  • Part 1: General requirements
  • Part 2: HD circular type
  • Part 3: HD double triangular type
  • Part 4: MD circular type
  • Part 5: MD rectangular type
  • Part 6: LD rectangular type
  • Part 7: LD square type

3. Installation

• Frames embedded firmly in concrete on masonry top.
• Covers sealed with thick grease after installation (Clause 4.9).

4. Load Classes

• Medium Duty (MD): For footpath manholes.
• Heavy Duty (HD): For manholes under vehicular traffic (Clause 3.9).

5. Reinforced Concrete Manholes

• Use Grade M20 concrete or 1:1½:3 mix for high sub-soil water conditions (Clause 4.10).
• Base and walls designed per loading factors (Clause 4.10 & IS 456).

Typical Manhole Cover Dimensions (IS 1726 - Example for Circular HD Covers)

flowchart TD
    A[Manhole] --> B[Frame embedded in concrete]
    B --> C[Cast Iron Cover]
    C --> D[Sealed with thick grease]
    A --> E[Concrete Manhole (M20)]
    E --> F[Designed for soil & traffic loads]

Summary: Use IS 1726 covers matching load class, ensure minimum 560 mm clear opening, embed frames in concrete, seal covers, and use M20 concrete for reinforced manholes in high water table areas.

IS 4111 Part 1: Load and Structural Requirements for Ancillary Sewerage Structures

While the code focuses on design considerations like spacing and sizing of manholes and access shafts, key structural aspects include:

1. Design Loads

• Dead Load: Self-weight of the structure including cover slabs, walls, and base.
• Live Load: Traffic loads as per IS 875 (Part 3) for vehicular loading on manhole covers.
• Earth Pressure: Lateral earth pressure on walls, calculated using Rankine or Coulomb theory.
• Hydrostatic Pressure: For groundwater conditions, consider uplift and lateral water pressure.

2. Structural Specifications

• Manhole Size: Typically ranges from 600 mm to 1200 mm diameter depending on access requirements.
• Wall Thickness: Minimum 150 mm for precast or cast-in-situ concrete.
• Cover Slabs: Designed for loading class (e.g., Class A, B, C) as per IS 875.

3. Key Formulae

• Earth Pressure (Rankine):
  [ P = K_a \times \gamma \times H ] Where:
  (P) = lateral earth pressure,
  (K_a) = active earth pressure coefficient,
  (\gamma) = soil unit weight,
  (H) = depth of soil.

• Load on Cover Slab:
  [ q = \text{Live Load} + \text{Dead Load} ]

4. Typical Manhole Spacing (Clause 3.1)

• Usually spaced at 30-60 m depending on pipeline diameter and accessibility.

graph TD
A[Design Considerations] --> B[Spacing of Manholes]
A --> C[Access Shaft Sizes]
A --> D[Load Calculations]

D --> E[Dead Load]
D --> F[Live Load (IS 875)]
D --> G[Earth Pressure]
D --> H[Hydrostatic Pressure]

For detailed load tables and structural design, refer to IS 875 and IS 456 alongside IS 4111 Part 1.

IS 4111 Part 1: Ventilation and Maintenance Access Key Points

1. Manhole Spacing (Clause 3.2.2)

• Applies for sewers > 900 mm diameter.
• Governed by:
  • Maximum silt/obstruction travel distance to nearest manhole.
  • Distance for transporting repair materials.
  • Ventilation needs for workers inside.

2. Access Shafts (Clause 3.4)

• Shape: Circular
• Minimum internal diameter: 750 mm
• For shafts > 3 m deep: Provide adequate size for cleaning & maintenance.

3. Brickwork Access Shafts (Clause 3.4.1)

• Corbel on three sides to reduce to cover frame opening size.
• Fourth side left open for step irons or ladder.
• Size must accommodate maintenance equipment dimensions.

Summary Table: Access Shaft Dimensions

flowchart TB
    A[Large Sewer (>900mm)] --> B[Manhole Spacing]
    B --> C[Silt Removal Distance]
    B --> D[Material Transport Distance]
    B --> E[Ventilation Requirements]
    A --> F[Access Shaft]
    F --> G[Circular Shape, Min 750mm Dia]
    F --> H[Depth > 3m: Larger Size]
    F --> I[Brickwork Shaft: Corbel 3 sides]
    I --> J[Step Irons/Ladder on 4th side]

This ensures safe, efficient maintenance and adequate ventilation for sewer workers.

IS 4111 Part 1 (1986) – Construction Practices & Finishing

Key Specifications:

• Corners:

  • Rounded with a 75 mm radius using cement plaster (1:3 cement:sand).
  • Thickness: 13 mm, finished smooth with a coat of neat cement.
  • Internal rendered surfaces: hard, impervious finish by steel trowel.

• Channels and Benching (Clause 4.7):

  • Bottom half semi-circular, diameter = sewer pipe diameter.
  • Sides extend vertically 50 mm above pipe crown.
  • Top edges rounded off smoothly.
  • Constructed in cement concrete 1:2:4 (cement: sand: 20 mm aggregate).
  • Rendered smooth with neat cement, finished by steel trowel.

Table 1: Depth of Channels and Benching

Summary Diagram for Channel & Benching Cross-section:

flowchart TD
    A[Top Edge - Rounded] --> B[Vertical Side Walls (50 mm above pipe crown)]
    B --> C[Semi-circular Bottom (Diameter = Sewer Pipe)]
    C --> D[Bed Concrete]
    style A fill:#f9f,stroke:#333,stroke-width:2px
    style B fill:#bbf,stroke:#333,stroke-width:2px
    style C fill:#bfb,stroke:#333,stroke-width:2px
    style D fill:#eee,stroke:#333,stroke-width:2px

Note: Use steel trowel finish for impervious hard surfaces on all rendered areas. This ensures durability and smooth flow inside manholes and drains

IS 4111 Part 1 (1986) primarily references related standards and fundamental definitions but does not provide explicit formulas or tables within Clause 2.0 or related sections.

Key Points on References and Related Standards:

• Rounding Off Values:
  As per IS 2:1960, all test or analysis results must be rounded off to the same number of significant digits as specified in this standard.

• Related Standards:
  IS 4111 Part 1 refers to IS 2:1960 for rounding rules. Other referenced IS codes relevant to structural materials or tests should be consulted for detailed formulas or tables.

Common Practice:

• When dealing with structural standards, always check IS 2 for rounding rules.
• For material properties or test methods, refer to specific IS codes cited within IS 4111 or related documents.

If you need formulas or tables for specific materials or structural elements, please specify the element or property.

IS 4111 Part 1 (1986) covers Ancillary Structures in Sewerage Systems but does not explicitly list annexure formulas or tables in your provided context.

Key Points from IS 4111 Part 1:

• Focuses on design and construction of manholes, inspection chambers, and other ancillary sewerage structures.
• Specifies dimensions, loadings, and materials for durability and safety.
• Provides standard details for reinforcement, concrete grades, and cover requirements.

Typical Specifications (from standard practice):

• Minimum cover for reinforcement: 40 mm for sewer structures.
• Concrete grade: Usually M20 or as per exposure conditions.
• Loadings: Consider earth pressure, live loads (vehicular), and hydrostatic pressure.

Common Formulas:

• Earth pressure on walls:
  ( P = K_a \gamma H )
  where ( K_a ) = active earth pressure coefficient, ( \gamma ) = soil unit weight, ( H ) = height of soil retained.

• Moment for rectangular section:
  ( M = \frac{f_{ck} b d^2}{6} ) (simplified for design checks).

Illustrative Table (Example for Manhole Sizes):

For detailed annexures and illustrations, refer to the full IS 4111 Part 1 document or related sewerage design manuals.

flowchart TD
    A[Start] --> B[Determine Sewer Size]
    B --> C[Select Manhole Diameter]
    C --> D[Calculate Earth Pressure]
    D --> E[Design Wall Thickness & Reinforcement]
    E --> F[Check Cover & Concrete Grade]
    F --> G[Finalize Design]