Guidelines for retaining wall for hill area, Part 3: Construction of dry stone walls

IS 14458 (Part 3): 1998 - Retaining Walls for Hill Areas (Guidelines)

Scope Summary:

• Applies to design and construction of retaining walls in hill areas.
• Covers technical guidelines for stability, drainage, and materials.
• Focus on walls retaining soil on slopes, considering seismic and rainfall conditions typical to hilly terrain.

Key Specifications (General):

• Wall Types: Gravity, cantilever, counterfort, and anchored walls.
• Design Considerations:
  • Earth pressure (active, passive, and at-rest)
  • Seismic forces (as per IS 1893)
  • Drainage to prevent hydrostatic pressure
• Materials: Concrete, masonry, and reinforced concrete.

Important Formulas (from general retaining wall design principles):

• Active Earth Pressure (Rankine):
  [ P_a = \frac{1}{2} \gamma H^2 K_a ] where
  (\gamma) = unit weight of soil,
  (H) = height of wall,
  (K_a = \tan^2(45^\circ - \frac{\phi}{2})), (\phi) = angle of internal friction.

• Factor of Safety (FoS):
  [ FoS = \frac{\text{Resisting Forces}}{\text{Driving Forces}} \geq 1.5 ]

Typical Table (Earth Pressure Coefficients):

If you need detailed design tables or drainage specifications, refer to IS 14458 (Part 3) full text or IS 456 for concrete design.

IS 14458 covers retaining walls but Parts 3, 9, and 10 focus on different types. For Design Considerations in retaining walls (especially RCC cantilever, buttressed, L-type, and reinforced earth walls), key points include:

General Design Considerations (from IS 14458 + related IS codes like IS 456 & IS 3370)

• Earth pressure: Use Rankine or Coulomb theory for active, passive, and at-rest pressures.
• Water pressure: Consider hydrostatic forces if water table is present.
• Factor of Safety (FoS): Typically 1.5 for sliding and overturning.
• Structural stability: Check for sliding, overturning, bearing capacity, and structural strength.
• Reinforcement: Design per IS 456 for RCC elements.

Key Formulas:

• Active Earth Pressure (Rankine):
  [ P_a = \frac{1}{2} \gamma H^2 K_a ]
  where
  ( \gamma ) = unit weight of soil,
  ( H ) = height of wall,
  ( K_a = \tan^2(45^\circ - \frac{\phi}{2}) ) (active earth pressure coefficient),
  ( \phi ) = angle of internal friction.

• Overturning Moment:
  [ M_o = P_a \times \frac{H}{3} ]

• Sliding Force:
  [ F_s = P_a ]

Typical Tables (from IS 14458 & IS 456):

Design Steps Summary:

1. Calculate earth and water pressures.
2. Check stability (sliding, overturning, bearing).
3. Design reinforcement for bending and shear.
4. Consider drainage and backfill compaction.

flowchart TD
    A[Calculate Earth & Water Pressure] --> B[Check Stability]
   

IS 14458 Part 3: Materials and Stone Selection for Dry Stone Masonry Retaining Walls

Key Specifications:

• Stone Identification: As per IS 1123:1975 for natural building stones.
• Stone Size:
  • Minimum: 225 mm × 100 mm × 75 mm (~5 kg)
  • Maximum: 600 mm × 200 mm × 300 mm (~45 kg)
• Stone Shape: Rough, flat stones preferred for better friction and interlocking.
• Stone Placement: Largest dimension placed across wall length for stability.
• Inward Slope of Wall Face:
  • Minimum: 1 Vertical : 6 Horizontal
  • Maximum: 1 Vertical : 3 Horizontal
  • Base preferably at right angles to wall face for seismic stability.

Filling Material:

• Use coarse angular particles (broken stone dust, stone chips, sandy/gravelly soil).
• Avoid fine-grained soils or smooth river shingle (reduce friction).
• Fill voids after each stone layer; moistening and ramming recommended.

Backfill:

• Hand-packed, non-cohesive, free-draining material.
• Minimum width: 500 mm
• Top layer (300-500 mm) impervious to reduce water ingress.

Summary Table:

flowchart TD
    A[Stone Selection] --> B[Size: 225x100x75 mm to 600x200x300 mm]
    A --> C[Shape: Rough, flat stones]
    A --> D[Placement: Largest dimension across wall length]
    E[Wall Face] --> F[Inward slope 1V:6H to 1V:3H]
    E --> G[Base at right angle to wall face

IS 14458 Part 3: Construction of Dry Stone Walls – Key Points

• Design Reference: Dry stone masonry retaining walls are designed per Part 2 of IS 14458; computer programs may be used.

• Stone Selection: Use stones identified as per IS 1123; strength depends on mineral composition.

• Wall Geometry:

  • Base slope: Preferably at right angles to wall face.
  • Inward slope (batter): Minimum 1 vertical : 6 horizontal (1:6), maximum 1 vertical : 3 horizontal (1:3).
  • This slope improves keying, reduces toe pressure, and enhances sliding resistance and seismic stability.

Key Specifications Summary

Conceptual Diagram (Wall Batter)

graph LR
A[Hill Face] --> B[Dry Stone Wall]
B --> C[Base at right angle]
B --> D[Inward slope 1:6 to 1:3]

This ensures a stable, durable dry stone retaining wall with good seismic resistance and minimal sliding risk.

IS 14458 Part 3: Placement of Backfill - Key Points

From Clause 6.2 (Dry Stone Masonry Backfill):

• Use broken stone dust, stone chips, gravelly/sandy soils, or soil mixtures to fill voids after each stone layer.
• Avoid fine-grained soils and smooth river shingle (reduce friction, lubricate joints).
• Use coarse angular particles for better friction and stability.
• Moistening filler material with water and ramming improves load distribution and wall strength.

From Clause 7 (Backfill Placement):

• No dumping of stones; use hand packing to maximize internal friction angle.
• Backfill width: minimum 500 mm.
• Backfill material: non-cohesive, free draining except top layer.
• Top layer thickness: 300 to 500 mm, made impervious to minimize water ingress.

Summary Table:

Diagram: Backfill Layers

graph TD
    A[Retaining Wall] --> B[Backfill (≥ 500mm, non-cohesive)]
    B --> C[Top Layer (300-500mm, impervious)]
    B --> D[Lower Layers (free draining)]

Note: Proper backfill placement ensures drainage and stability, preventing water pressure buildup and structural failure.

IS 14458 Part 3 (1998) provides guidelines for dry stone retaining walls in hill areas, focusing on drainage to ensure stability.

Key Drainage Requirements:

• Drainage is critical to prevent water pressure buildup behind the wall.
• Provide weep holes or drainage pipes at regular intervals (typically 1.5 to 3 m apart).
• Use filter material (e.g., gravel or coarse sand) behind the wall to facilitate water flow.
• Ensure a drainage layer of at least 300 mm thickness behind the wall.
• Slope the backfill to direct water to drainage outlets.
• Avoid clayey soils directly behind the wall to reduce water retention.

Typical Specifications:

Formula for Hydrostatic Pressure (to design drainage):

[ P_w = \gamma_w \times h_w ]

• (P_w) = water pressure at depth (h_w)
• (\gamma_w) = unit weight of water (9.81 kN/m³)
• (h_w) = height of water column behind wall

flowchart LR
    Backfill -->|Water flow| DrainageLayer
    DrainageLayer -->|Water flows| WeepHoles
    WeepHoles -->|Water exits| Outside

Summary: Proper drainage with filter material, drainage layers, and weep holes spaced 1.5-3 m apart is essential to avoid hydrostatic pressure and ensure dry stone wall stability in hill areas per IS 14458 Part 3.

IS 14458 (Part 3): Toe Protection for Hill Road Masonry Retaining Walls

The code emphasizes safety against overturning, shearing, and bearing pressure at the toe of the retaining wall.

Key Specifications:

• Top width of wall: 600 mm
• Assumption: Adequate frictional bond and interlocking stones for unit action.

Toe Protection Criteria:

1. Overturning Stability: [ \text{Sum of resisting moments} \geq \text{Sum of overturning moments} ]

2. Shear Stress Check: [ \tau = \frac{V}{A} \leq \tau_{\text{allowable}} ] where (V) = shear force, (A) = shear area.

3. Bearing Pressure at Toe: [ q = \frac{P}{A_{\text{toe}}} \leq q_{\text{safe}} ] where (P) = resultant vertical load, (A_{\text{toe}}) = area at toe, (q_{\text{safe}}) = safe bearing capacity of foundation soil.

Practical Notes:

• Use rectangular stones with sufficient overlap for interlocking.
• Ensure toe width and foundation depth to distribute pressure within safe limits.
• Check sliding resistance via friction between wall base and foundation.

flowchart LR
    A[Retaining Wall Loads] --> B{Check Stability}
    B --> C[Overturning Moment]
    B --> D[Shear Stress]
    B --> E[Bearing Pressure at Toe]
    C --> F[Resisting Moments ≥ Overturning Moments]
    D --> G[Shear Stress ≤ Shear Strength]
    E --> H[Pressure ≤ Safe Bearing Capacity]

This ensures toe protection by maintaining stability and soil safety under hill road retaining wall loads.

IS 14458 Part 3 does not explicitly provide detailed clauses for Bonding Elements for Stability in reinforced earth retaining walls. However, based on standard practice and related IS codes (like IS 456 and IS 1893), key points are:

Key Specifications for Bonding Elements:

• Material: High tensile steel strips or geosynthetics with adequate tensile strength.
• Spacing: As per design load and soil parameters, typically 0.6m to 1.2m vertically and horizontally.
• Length: Must extend into the reinforced soil mass beyond the failure plane, usually 0.7 to 1.0 times the wall height.
• Anchorage: Proper embedment in compacted backfill for effective load transfer.

Typical Formula for Bond Length ( L_b ):

[ L_b = \frac{T}{q \times p} ] Where:

• ( T ) = Tensile force in the strip
• ( q ) = Allowable soil pressure on the strip
• ( p ) = Perimeter of the strip cross-section in contact with soil

Stability Checks:

• Ensure bonding elements resist pullout and tensile failure.
• Factor of safety against pullout typically ≥ 1.5.

Summary Table: Bonding Element Parameters

flowchart LR
    A[Reinforced Earth Wall] --> B[Facing]
    A --> C[Backfill]
    C --> D[Bonding Elements]
    D --> E[Embedment Length]
    D --> F[Tensile Strength]
    D --> G[Spacing]
    E --> H[Stability Against Pullout]

For detailed design, refer to IS 14458 Part 10 and IS 456 for reinforced concrete elements.

Supervision and Quality Control – IS 14458 (Part 3)

Though the code lacks a dedicated clause on supervision and quality control, key practices can be inferred:

Key Specifications:

• Drainage: Excavated material must not obstruct drainage at the toe (Clause 8.2). Proper sloping below the toe level is essential.
• Toe Protection: Mandatory for walls >3 m height to prevent erosion from water velocity.
• Bonding Elements: For walls >3 m, provide RCC bonding elements spaced at 1 m intervals both lengthwise and vertically. Typical size:
  • Cross-section: 75 mm × 75 mm or 100 mm × 100 mm
  • Length = Wall thickness + 150 mm (75 mm projection on each face)
• Stone Filling: Must be well-packed, especially in stepped faces to avoid sliding and back pressure.

Quality Control Checklist:

• Ensure no raised tops obstruct drainage.
• Verify proper placement of face stones and filling.
• Check bonding elements for correct size, spacing, and projection.
• Inspect toe protection for erosion resistance.

Summary Table: RCC Bonding Element Dimensions

flowchart TD
    A[Excavation & Drainage] --> B[Check drainage slope below toe]
    B --> C[Place Toe Protection if wall height > 3m]
    C --> D[Construct Wall with RCC Bonding Elements]
    D --> E[Spacing: 1m both ways; Size: 75x75 or 100x100 mm]
    E --> F[Hand pack stone filling properly]
    F --> G[Final Inspection: Drainage, Bonding, Toe Protection]

Note: Maintain strict supervision on drainage, bonding element placement, and stone filling to ensure wall stability and durability in hill areas.

IS 14458 Part 3 (1998) provides guidelines for maintenance and repair of retaining walls in hill areas, though it lacks detailed clauses or tables.

Key Maintenance & Repair Guidelines (General Practice):

• Inspection Frequency: Regular visual checks for cracks, bulging, seepage, and settlement.
• Crack Repair:
  • Use epoxy injection or cement grout for minor cracks.
  • For wide cracks, remove and replace damaged sections.
• Drainage Maintenance:
  • Ensure weep holes and drainage pipes are clear.
  • Prevent water accumulation behind the wall to reduce hydrostatic pressure.
• Reinforcement Exposure:
  • Clean exposed steel and apply anti-corrosion coatings.
• Backfill Compaction:
  • Recompact loose backfill to prevent settlement.
• Structural Strengthening:
  • Use buttresses or anchors if wall stability is compromised.

Typical Formulas for Stability Checks (for repair assessment):

• Factor of Safety (FoS) against sliding:
  [ FoS = \frac{\text{Resisting Forces}}{\text{Driving Forces}} \geq 1.5 ]

• Factor of Safety against overturning:
  [ FoS = \frac{\text{Moments resisting overturning}}{\text{Moments causing overturning}} \geq 2.0 ]

Summary Table: Common Repair Actions

For detailed structural design and repair, refer to IS 456 and IS 3370 for concrete repair and IS 2911 for soil-structure interaction.

IS 14458 Part 3: Committee Composition Summary

The technical committee for IS 14458 Part 3 consists of experts from diverse institutions related to hill area development, engineering, and construction. The detailed composition is provided in Annex A of the standard.

Key Highlights of Committee Composition:

• Chairman: Dr. Gopal Ranjan (University of Roorkee)
• Members: Representatives from:
  • Public Works Departments (J&K, Simla)
  • Indian Institutes (Roorkee, IIT Delhi, IIRS Dehra Dun)
  • Central Government bodies (CWC, IRC, Ministry of Surface Transport, Ministry of Railways)
  • Research organizations (CBRI Roorkee, Structural Engineering Research Centre Chennai)
  • Development Boards (Sikkim Hill Area Development Board, U.P. Hill Area Development Board)
  • Geological, Meteorological, and Environmental institutes
  • Construction and material promotion councils

Purpose:

• To ensure multidisciplinary inputs for hill area retaining wall guidelines.
• To cover structural, geotechnical, environmental, and material aspects.

Diagram: Committee Structure Overview

graph TD
    A[Chairman: Dr. Gopal Ranjan] --> B[Public Works Departments]
    A --> C[Academic Institutions]
    A --> D[Central Government Bodies]
    A --> E[Research Organizations]
    A --> F[Development Boards]
    A --> G[Environmental & Geological Institutes]
    A --> H[Construction & Material Councils]

For detailed member names and affiliations, refer to Annex A of IS 14458 (Part 3): 1998.