Code of practice for design and construction of diaphragm walls

IS 9556: Scope & Key Specifications for Bentonite Slurry in Diaphragm Walling

Scope (Clause 1.1)

• Covers design and construction of diaphragm walls.

Bentonite Slurry Specifications (Clause 6.1)

Additional Notes:

• Reinforcement steel must be clean and free from contaminants (Clause 4.6.1).
• Various cement and aggregate specifications referenced for concrete quality.
• Adjustments in construction methods and equipment terminology are noted in clauses 4.7 and 5.1.

This ensures bentonite slurry quality is controlled for effective diaphragm wall construction.

IS 9556: Terminology and Definitions - Key Points

• Scope (Clause 1.1): Covers design and construction of diaphragm walls, used as impervious cutoffs and retaining structures in hydraulic, civil, maritime, and industrial engineering.

• Design Considerations (Clause 1.5):

  • Diaphragm walls resist large horizontal earth pressures causing overturning.
  • Typical thickness: 1 m in soft clays (~1.5 t/m³ density), depths up to 65 m.

• Rounding Off (Clause 0.4):

  • Final test/calculated values must be rounded as per IS 2-1960.
  • Retain the same number of significant figures as the specified values.

Bentonite Slurry Specifications (Clause 6.1)

Summary Diagram: Diaphragm Wall Design Considerations

graph TD
    A[Diaphragm Wall] --> B[Earth Pressure]
    B --> C[Horizontal Forces]
    C --> D[Overturning Moments]
    A --> E[Impervious Cutoff]
    A --> F[Thickness ~ 1m]
    A --> G[Depth up to 65m]
    A --> H[Bentonite Slurry Properties]
    H --> I[Density 1.04-1.10 g/ml]
    H --> J[pH 9.5-12]
    H --> K[Viscosity 30-90 s]
    H --> L[Gel Strength 1.4-10 N/m²]

For detailed design, refer to IS 9556 clauses on structural design, construction techniques, and material specifications.

IS 9556 - Design Considerations for Diaphragm Walls

Key Design Inputs (Clause 3.1)

• Site Plans & Structural Drawings: Elevations, sections, foundation details, and nearby structures.
• Subsoil Investigations: Per IS 1892 & IS 4651; includes soil properties, rock formations.
• Groundwater Data: Table levels, fluctuations, flow, pH, acid radicals.
• Load Estimations: Construction and permanent loads.
• Hydraulic Conditions: Water levels, currents, scour, wave action (for river/sea structures).
• Machinery Details: Trenching, concreting, lifting equipment specs.
• Material Quality: Local materials for grout, RCC, plastic concrete.
• Auxiliary Machines: Cranes and other construction equipment.
• Exposed Faces: Specifications for walls exposed to environment.
• Underground Services: Existing utilities and obstacles.

Reinforcement Tolerances (Clause 11.5)

General Notes

• Follow IS 9556 for diaphragm wall design.
• Refer to IS 1892 and IS 4651 for soil and subsoil investigations.
• Use the Code of Practice for Ports and Harbours for hydraulic and environmental loading.
• Round numerical values as per relevant rules.

flowchart TD
    A[Site Investigation] --> B[Subsoil Properties]
    A --> C[Groundwater Data]
    B --> D[Load Estimation]
    C --> D
    D --> E[Design of Diaphragm Wall]
    E --> F[Reinforcement Placement]
    F --> G[Construction Machinery & Materials]

This structured approach ensures safe, durable diaphragm wall design under IS 9556.

IS 9556 - Materials Key Specifications & Formulas

1. Reinforcement Materials (Clause 4.6)

• Use mild steel bars per IS:432 (Part 1)-1966.
• Use deformed bars per IS:1139-1966.
• Use cold-worked high strength steel bars per IS:1786-1979.
• Structural steel sections per IS:226-1975.
• All steel must be clean, free from rust, oil, grease, paint to ensure proper bonding with concrete.

2. Cement Specifications

• Ordinary & Low Heat Portland Cement (3rd revision).
• Portland Slag Cement (3rd revision).
• Portland-Pozzolana Cement (2nd revision).

3. Aggregates

• Coarse & Fine Aggregates per IS:383 (2nd revision).
• Sand for masonry mortars per IS:2116.

4. Bentonite Slurry Tests (Clause 6.1)

5. Permissible Stresses in Reinforcement

• As per IS:456-1978 (refer for design stress limits).

Summary Diagram: Material Flow for Reinforced Concrete

flowchart LR
    Cement --> ConcreteMix
    Aggregates --> ConcreteMix
    Water --> ConcreteMix
    SteelBars --> Reinforcement
    Reinforcement --> ConcreteMix
    ConcreteMix --> HardenedConcrete

Note: Ensure all materials conform to respective IS standards for durability and safety.

IS 9556: Equipment and Accessories — Key Points & Specifications

1. Equipment Selection (Clause 5.5)

• Choose rotary, percussion, grabbing equipment based on soil conditions.
• Select equipment for direct or reverse mud circulation as per site needs.
• Minimize vibrations and noise to avoid damage to nearby structures and people.
• Consider site constraints such as restricted space and headroom when selecting equipment.

2. Bentonite Slurry Specifications (Clause 6.1)

3. Additives (Clause 4.10)

• Retarding agents and expansive additives may be added to cement clay grout as required.

flowchart TD
    A[Soil Conditions] --> B[Select Equipment Type]
    B --> C{Rotary / Percussion / Grabbing}
    C --> D[Direct Mud Circulation]
    C --> E[Reverse Mud Circulation]
    B --> F[Consider Site Constraints]
    F --> G[Restricted Space / Headroom]
    B --> H[Minimize Noise & Vibrations]

This ensures proper equipment choice and slurry quality for diaphragm wall construction per IS 9556.

IS 9556 - Bentonite Slurry: Key Properties & Testing (Clause 6.1)

Additional Specifications:

• Bentonite Type: Sodium-based bentonite (Clause 4.8).
• Slurry Preparation: Use tanks and pumps of suitable capacity; maintain continuous circulation and mixing (Clause 5.2).
• Testing Frequency: Conduct tests repeatedly until stable slurry properties are achieved, considering blending and impurity removal (Clause 6.3).

Notes:

• For saline/contaminated groundwater, chemical processing of slurry may be required.
• Equipment like vibrating screens, hydrocyclones, centrifuges help clean slurry for reuse.

flowchart LR
    A[Bentonite Powder] --> B[Mix with Water]
    B --> C[Prepare Slurry]
    C --> D{Test Properties}
    D -->|Density| E[1.04-1.10 g/ml]
    D -->|pH| F[9.5 - 12]
    D -->|Viscosity| G[30 - 90 sec]
    D -->|Gel Strength| H[1.4 - 10 N/m²]
    D --> I{Stable?}
    I -->|No| B
    I -->|Yes| J[Use Slurry in Walling]

This ensures bentonite slurry meets IS 9556 standards for diaphragm wall construction.

IS 9556: Excavation and Trenching Methods - Key Formulas & Specifications

1. Trench Stability Using Bentonite Slurry (Clause 8.1)

• Hydrostatic Pressure from slurry stabilizes trench walls (65-80% of total stability).
• Slurry density (Ys) to ensure factor of safety (F=1) is:

[ Y_s = Y + \frac{C_u \cdot N_c}{H} ]

Where:

• (H) = trench depth
• (C_u) = undrained shear strength of clay
• (Y) = natural saturated soil density
• (N_c) = bearing capacity factor (varies 4 to 8, Fig. 3)

2. Bearing Capacity Factor (N_c) (Fig. 3)

• (N_c) depends on trench depth and geometry (D/B, L/B ratios).
• Typical range: 4 (surface) to 8 (deep trenches).

3. For Sandy Soils: Effective Unit Weight (Y_0)

[ Y_0 = Y_w + A \left( K_a Y' \right) \frac{1 - e^{-K_a \tan \delta'}}{K_a \tan \delta'} ]

Where:

• (Y_w) = unit weight of water
• (A) = reduction factor depending on trench length ratio (n) (Fig. 4)
• (K_a = \tan^2(45^\circ - \delta'/2)) (active earth pressure coefficient)
• (Y' = Y_{sat} - Y_w) (submerged unit weight)
• (\delta') = angle of internal friction

4. Trenching Equipment (Clause 5.1)

• Choose based on soil type, depth, length, and thickness of diaphragm wall.
• Equipment includes:
  • Rotary & percussion boring rigs
  • Trenching bucket shovels
  • Mechanical/hydraulic grabs
  • Mud circulation rigs (direct/reverse)
  • Special chiselling for gravel, boulders, rock

5. General Practice

• Keep trench filled with bentonite slurry of suitable viscosity during excavation

IS 9556 Guide Wall Construction - Key Points & Specifications

• Purpose: Guide walls are shallow walls on both sides of the diaphragm wall centerline to guide trench excavation and support bentonite slurry (Clause 2.6).

• Finished Face:

  • Must be vertical facing the trench (Clause 11.1).
  • No ridges or abrupt changes allowed.
  • Maximum deviation from straight line/profile = ±25 mm per 3 m length.

• Construction:

  • Should be built continuously and supported by adjoining panels (Clause 9.9).
  • After construction, guide walls must be propped to maintain tolerances (Clause 9.5).

Typical Tolerances Summary

Construction Recommendations

• Use continuous casting or concreting to avoid joints.
• Provide temporary props/bracing until diaphragm wall panels are cast.
• Ensure smooth vertical face to facilitate trench excavation and slurry containment.

flowchart LR
    A[Start Guide Wall Construction] --> B[Excavate to shallow depth]
    B --> C[Cast guide wall continuously]
    C --> D[Check verticality & surface smoothness]
    D --> E[Prop guide wall to maintain tolerance]
    E --> F[Proceed with diaphragm wall trench excavation]

This ensures trench stability and proper slurry containment per IS 9556.

IS 9556: Panel Construction and Jointing - Key Points

1. Panel Jointing Methods (Clause 10.2.6)

• Jointing between successive panels can be done by various methods shown in Fig. 6 (typically includes:
  • Tongue and groove joints
  • Steel connectors or dowels
  • Overlapping or keyed joints
• Purpose: Ensure adequate shear transfer and structural continuity.

2. Panel Design Considerations (Clause 12.1.3)

• Panels can be designed as independent units if:
  • Adjacent panels are not connected for shear transfer.
• If connected, design must ensure:
  • Continuity
  • Adequate shear transfer at joints

3. Secondary Panels (Clause 10.3.3 & 10.3.4)

• Secondary panel ends must be shaped for a good fit with primary panels.
• Construction techniques for secondary panels should be similar to successive panel methods.

Typical Joint Shear Transfer Calculation (General Engineering Practice)

[ V_j = \tau_j \times A_j ]

Where:

• ( V_j ) = Shear transferred at joint
• ( \tau_j ) = Allowable shear stress at joint (depends on material and joint type)
• ( A_j ) = Effective shear area of joint

Summary Table: Panel Jointing

flowchart LR
    A[Panel 1] -- Joint --> B[Panel 2]
    B -- Shear Transfer --> C[Continuity]
    C --> D{Design Approach}
    D -->|Connected| E[Design as continuous unit]
    D -->|Not Connected| F[Design as separate units]

Note: Refer to Fig. 6 in IS 9556 for detailed joint configurations and ensure joint design complies with shear transfer requirements

IS 9556: Concrete Placement and Reinforcement Key Points

Reinforcement Preparation (Clause 4.6.1)

• Reinforcement bars must be clean and free from mill scales, dust, rust, oils, grease, paint, or coatings to ensure proper bond with concrete.

Reinforcement Cage (Clause 4.6.3)

• Reinforcement should form a rigid cage matching panel joint types.
• Minimum clear spacing between bars: 100 mm for concrete flow.
• Cage ends must align with panel joints.

Positioning Tolerances (Clause 11.5)

• Longitudinal tolerance: ±75 mm along trench.
• Vertical tolerance: ±50 mm relative to guide wall top.

Concrete Mix (Clause 4.7)

• Water-cement ratio ≤ 0.6
• Slump: 150–200 mm for tremie concreting.
• Add 10% extra cement for underwater concreting.

Summary Table: Concrete & Reinforcement Parameters

flowchart TD
    A[Reinforcement Bars] --> B[Clean & Free from Contaminants]
    B --> C[Form Rigid Cage]
    C --> D[Maintain 100 mm Clear Spacing]
    D --> E[Position with Tolerances]
    E --> F[Concrete Placement]
    F --> G[Concrete Mix: W/C ≤ 0.6, Slump 150-200 mm]
    G --> H[Add 10% Extra Cement if Underwater]

This ensures durability, workability, and structural integrity during concrete placement.

IS 9556 - Wall Stability and Support Systems

Key Specifications (from Clause 12.1.4)

• Struts or anchors must be used to enhance wall stability and control deflections.
• Prestressed anchors/struts are preferred for better performance.
• Supports should be designed to resist lateral earth and water pressures acting on the wall.

Typical Design Considerations:

• Lateral Earth Pressure (P):
  [ P = K \times \gamma \times h^2 / 2 ] Where:

  • (K) = Earth pressure coefficient (active or passive)
  • (\gamma) = Unit weight of soil (kN/m³)
  • (h) = Height of wall (m)

• Anchor/Strut Force (T):
  Calculated based on lateral pressure and wall deflection limits.

Support System Design Table (Typical Values)

Summary Diagram

graph LR
A[Wall] --> B[Earth Pressure]
B --> C[Strut/Anchor]
C --> D[Foundation]

Note: For detailed design, refer to soil parameters, wall geometry, and IS 9556 clauses on diaphragm walls and support design.

IS 9556: Quality Control & Permissible Stresses Summary

1. Permissible Stresses

• In Concrete (Clause 12.2.2):
  Follow IS 456-1978 for permissible concrete stresses.
  Typical permissible compressive stress, ( f_{c} ), depends on concrete grade:

  Concrete Grade	Permissible Stress ( f_{c} ) (MPa)
  M20	7.5
  M25	8.3
  M30	9.0

• In Reinforcement (Clause 12.2.3):
  Permissible tensile stresses in steel bars per IS 456-1978:

  • Mild steel: 140 MPa
  • HYSD bars: 230 MPa

2. Quality Control of Reinforcement (Clause 4.6 & 4.6.1)

• Use reinforcement conforming to:

  • IS 432 (Part I) - Mild steel bars
  • IS 1786 - Cold worked high strength deformed bars
  • IS 1139 - Deformed bars
  • IS 226 - Structural steel sections

• Reinforcement must be clean, free from rust, oil, grease, paint, or loose mill scales to ensure proper bonding.

Quick Reference Table: Permissible Stresses in Reinforcement (IS 456-1978)

flowchart TD
    A[Reinforcement Quality Control] --> B[Conformance to IS Standards]
    B --> C{Steel Types}
    C --> D[IS 432 (Mild Steel)]
    C --> E[IS 1786 (Cold Worked Bars)]
    C --> F[IS 1139 (Deformed Bars)]
    C --> G[IS 226 (Structural Steel)]
    A --> H[Clean, Free from Contaminants]
    H --> I[Ensures Proper Bonding with Concrete]
``

IS 9556 - Special Construction Techniques for Diaphragm Walls

Key Techniques (Clauses 10.3.4, 10.4.1, 10.4.7)

• Successive Panel Method: Panels are constructed one after another, ensuring structural continuity.
• Direct Circulation Method: Uses rotary/percussion rigs with bentonite slurry pumped through rods for excavation and support.
  • Suitable for shallow depths and lighter cuttings.
  • Involves special cutters for jointing and elliptical tremie pipes for backfilling.
• Panel Types:
  • Primary panels (I) and Secondary panels (II) differ in size and shape due to stop end tubes.
• Joint Types (Fig. 6):
  • Plain butt joint
  • Joints with asbestos or shaped forms
  • Plastic concrete joints for reinforced concrete

Construction Stages (Fig. 8)

1. Excavation by overlapping boreholes.
2. Reinforcement cage insertion.
3. Concreting through special tremie pipes.

Specifications

• Guide walls must be constructed continuously for stability (Clause 9.9).
• Use of bentonite slurry as drilling fluid to support trench walls.
• Special equipment: rotary rigs, cutters, tremie pipes.

Summary Table: Panel Construction

flowchart TD
    A[Start Excavation] --> B[Overlapping Boreholes]
    B --> C[Insert Reinforcement Cage]
    C --> D[Concreting via Tremie Pipe]
    D --> E[Panel Completion]
    E --> F[Construct Next Panel]

This concise overview aligns with IS 9556 clauses for special construction techniques in diaphragm walls.

IS 9556: Dimensional Tolerances and Finishing for Diaphragm Walls

Key Specifications:

• Recess Positioning (Clause 11.4):
  Inserts forming recesses in diaphragm walls must be positioned within ±150 mm vertically and horizontally.

• Panel Clearance (Clause 9.3):
  Minimum clearance between finished diaphragm wall and guide: 50 mm for straight panels. Increase clearance for curved panels accordingly.

• Surface Preparation (Clause 4.6.1):
  Reinforcement bars and steel must be clean—free from millscale, dust, rust, oils, grease, paint, or coatings to ensure proper concrete bonding.

Typical Dimensional Tolerances (based on IS and good practice):

Notes:

• Tolerances ensure structural integrity and fitment of panels.
• Surface cleanliness is critical for bond strength.
• Always verify with project-specific documents for stricter tolerances.

flowchart LR
    A[Design] --> B[Reinforcement Cleaning]
    B --> C[Panel Fabrication]
    C --> D[Dimensional Checks]
    D --> E[Wall Construction]
    E --> F[Insert Recess Positioning ±150 mm]
    E --> G[Panel Clearance ≥ 50 mm]

This summary aligns with IS 9556 clauses and common engineering practice for diaphragm walls.

IS 9556 - Safety and Environmental Guidelines: Key Specifications

Bentonite Slurry (Clause 6.1)

General Safety Guidelines (Clause 5.5)

• Select equipment (rotary, percussion, grabbing) based on soil conditions.
• Ensure vibrations/noise do not damage people or existing structures.
• Consider site constraints like restricted space or headroom when choosing equipment.
• Use direct or reverse mud circulation methods suitable for the site.

Summary: Maintain bentonite slurry properties within specified limits to ensure stability and environmental safety during diaphragm wall construction. Equipment choice must prioritize safety and minimal disturbance.

flowchart TD
    A[Soil Conditions] --> B[Select Equipment]
    B --> C{Site Constraints?}
    C -->|Yes| D[Adjust Equipment Choice]
    C -->|No| E[Proceed]
    E --> F[Control Vibrations & Noise]
    F --> G[Safe Construction Environment]