Code of practice for the structural safety of buildings on shallow foundations on rocks

IS 13063: Scope - Key Specifications and Tables

1. Permissible Settlements and Distortions (Clause 5.2.4, Table 1)

• L₁ = length of deflected wall/raft or center-to-center column distance
• H = height of wall from foundation footing
• Values are guidelines; designer discretion is advised based on structure importance.

2. Foundations on Slopes of Tallus Deposits (Clause 8.12)

• For buildings up to 2 storeys on slopes >15°, flexible steel/wood framed structures with PVC cladding recommended.
• Minimum foundation depth in loose tallus deposits: 2 m.
• Refer to Fig. 17 (Still Foundation) for construction details (wood/steel pipe, PVC sheets).

References to Related IS Codes (Annex A)

• IS 456: Plain and Reinforced Concrete
• IS 875 (Part 2): Imposed Loads
• IS 1892: Subsurface Investigation
• IS 1904: Foundations in Soils
• IS 12070: Shallow Foundations on Rock
• IS 11315 series: Rock

IS 13063 - Definitions & Key Specifications Summary

1. Scope & Definitions:

   • IS 13063 excludes foundations under tensile loads.
   • Definitions refer to IS 2809:1972 (soil engineering terms) and IS 1904:1986 (foundation design & construction).

2. Permissible Settlements & Distortions (Clause 5.2.4, Table 1):

• Notes:
  • L₁ = length of deflected wall/raft or center-to-center column distance.
  • H = height of wall from footing.
  • Values are guidelines; designer discretion based on structure importance.

3. Foundations on Slopes (Clause 8.12):

   • For slopes >15°, flexible structures with shallow foundations (≥ 2 m depth) on talus deposits are recommended.
   • Example: Steel/wood framed structures with PVC cladding and wooden floors.

4. Referenced Standards (Annex A):

   • IS 1904:1986 - Foundations in soils.
   • IS 2809:1972 - Soil engineering glossary.
   • IS 456:1978 - Concrete design

IS 13063: General Requirements Summary

• Compliance: Clause 6.7.1 mandates adherence to IS 456:1978 for concrete design.

• Scope Limitation: Clause 1.2 excludes foundations under tensile loads.

• Definitions: Refer IS 2809:1972 and IS 1904:1986 for terminology.

Key Table: Maximum and Differential Settlements (Clause 5.2.4, Table 5.2.8)

• Notes:
  • L¹ = Length of deflected wall/raft or center-to-center column spacing (mm).
  • H = Height of wall from foundation footing (mm).
  • Values are guidelines; designer discretion based on structure importance is essential.
  • Higher settlements allowed for highly weathered/disintegrated rock.

Summary Formulae for Differential Settlement:

[ \text{Differential Settlement} = k \times L ]

Where k varies by structure type (refer table).

flowchart TD
    A[

IS 13063: Site Investigation Key Points

Objectives (Clause 4.1)

• Determine ground character & rock types, including discontinuities (see IS 11315 Parts 1-11).
• Assess groundwater conditions & piezometric pressures.
• Obtain engineering properties via lab/field tests.

Important Parameters (Clause 4.10.1)

• Rock type & origin.
• Discontinuity orientation, spacing, and condition (roughness, separation, weathering).
• Groundwater conditions.
• Major faults.
• Rock strength: uniaxial compressive strength, point load strength index.
• Drill Core Quality (RQD).

Permissible Settlements (Clause 5.2.4)

Higher settlements allowed for highly weathered/disintegrated rock.

Reference Standards

• IS 11315 (Parts 1-11) for rock mass evaluation.
• IS 2809:1972 and IS 1904:1986 for definitions and foundation guidelines.

Summary diagram of Site Investigation process:

flowchart TD
    A[Start Site Investigation] --> B[Identify Rock Type & Discontinuities]
    B --> C[Measure Groundwater & Piezometric Pressure]
    C --> D[Conduct Lab & Field Tests for Rock Properties]
    D --> E[Evaluate Rock Strength & RQD]
    E --> F[Assess Settlement & Stability per IS 13063]
    F --> G[Foundation Design Recommendations]

This framework ensures a thorough geotechnical evaluation for safe foundation design on rock masses.

IS 13063: Loads on Foundation & Allowable Bearing Pressures

1. Loads on Foundation (Clause 5.1)

• Consider dead loads, live loads, wind loads, and seismic loads.
• Loads should be combined as per relevant IS codes (e.g., IS 875 for loads).

2. Allowable Bearing Pressure (Clause 5.2)

• Safe bearing pressure (q_safe) must satisfy Clauses 5.2.1 & 5.2.2.
• Estimated per IS 12070:1987 guidelines.

3. Increase in Safe Bearing Pressure (Clause 5.2.6)

• Increase by 25% if wind loads are considered.
• Increase by 33% if seismic loads are considered.
• Maximum q_safe ≤ allowable pressure of foundation concrete/masonry or concrete over rock, whichever is lower.

4. Weak Seams in Rock (Clause 8.1.1)

• If weak seams cover < 20% of base area, moments and shear forces multiplied by 1.5.
• If weak seams cover > 20%, design assumes no bearing on weak strata (refer to FIG. 6 & FIG. 7 in IS 13063).

Key Formula Summary

Bearing Pressure Concept Diagram (Simplified)

flowchart TD
    A[Foundation Base] --> B{Weak Seams Area?}
    B -->|< 20%| C[Increase M & V by 1.5x]
    B -->|≥ 20%| D[No Bearing on Weak Strata]
    C --> E[Design Foundation]
    D --> E

This ensures safe design considering rock quality under foundations per IS 13063.

IS 13063: General Design Requirements - Key Points

1. Foundation Clearance from Trees (Clause 4.11.7):

   • No large trees within 8 m of building foundations to avoid root damage and soil disturbance.

2. Compliance with IS 456:1978 (Clause 6.7.1):

   • Structural design must follow IS 456 for concrete structures ensuring safety and durability.

3. Settlement Limits (Clause 5.2.4, Table 5.2.8):
   Maximum and differential settlements allowed for various structures on rock mass:

• L₁ = length of deflected wall/raft or column spacing
• H = height of wall from foundation

4. Notes:
   • Settlements are indicative; final permissible values depend on structure importance and design judgment.
   • This code does not cover foundations under tensile loads (Clause 1.2).

flowchart LR
    A[Site Investigation] --> B[Design per IS 456]
    B --> C[Check Tree Clearance (≥8m)]
    C --> D[Settlement Analysis]
    D --> E{Structure Type}
    E -->|Steel| F[Max 12mm, Diff. 0.0033L₁]
    E -->|RCC| G[Max

IS 13063: Treatment of Joints and Solution Cavities

1. Treatment of Joints (Clause 7.1.1)

• Vertical joints (1- several cm wide):
  • Clean to 4-5 times the joint width depth.
  • Fill with cement grout: 1 part cement + 1 part sand + water (pourable consistency).
  • Large, wider spaces filled with dental concrete (1:1 cement-sand slurry).

2. Solution Cavities (Clause 7.3)

• Cavities common in certain limestone horizons.
• Exploration to locate unfavorable horizons.
• If cavity area < 20% of foundation base:
  • Reduce safe bearing pressure as per IS 12070:1987.

3. Special Treatments (Clause 8.1.2 & 8.2.1)

• If weak seams > 20% of base area:
  • Apply treatment per Clause 8.2 (e.g., excavation, filling).
• Foundation design:
  • Bearing pressure inversely proportional to strata compressibility.
  • Design foundation section accordingly.

Summary Table for Joint Treatment

flowchart TD
    A[Identify Joints/Cavities] --> B{Joint Width}
    B -->|Small| C[Clean 4-5x width]
    C --> D[Fill with cement grout]
    B -->|Large| E[Fill with dental concrete]
    A --> F{Cavity Area < 20%?}
    F -->|Yes| G[Reduce bearing pressure (IS 12070)]
    F -->|No| H[Apply special treatment (Clause 8.2)]

This ensures structural integrity by proper joint filling and foundation design adjustments based on cavity extent.

IS 13063: Special Treatments & Foundations on Different Rock Masses

Key Specifications & Formulas

1. Foundation on Different Rock Masses (Clause 8.9)

• When part of the foundation rests on hard rock and part on soft rock:
  • Provide a settlement joint at the interface.
  • The minimum depth of soft rock under footing = ≥ (1/3) × footing width.
  • The other footing must rest solely on hard rock.

2. Foundation Rocks of Different Compressibilities (Clause 8.2)

• Ensure compatibility of compressibility to avoid differential settlement.
• Design must consider the compressibility difference and provide joints or cushioning.

3. Important Rock Mass Characteristics (Clause 4.10.1)

Evaluate:

• Rock type, discontinuity orientation, spacing, and condition.
• Groundwater, faults, rock strength (uniaxial compressive strength, point load index).
• Drill Core Quality (RQD).
• Refer IS 11315 (Parts 1-11) for detailed evaluation.

4. Solution Cavities (Clause 7.3)

• If cavities cover <20% of foundation base, reduce safe bearing pressure per IS 12070:1987.

Summary Table: Foundation Treatment on Mixed Rock Masses

flowchart TD
    A[Foundation on Mixed Rock] --> B[Hard Rock Footing]
    A --> C[Soft Rock Footing]
    B --> D[Stable Base]
    C --> E{Soft Rock Depth ≥ 1/3 Width?}
    E -- Yes --> F[Provide Settlement Joint]
    E -- No --> G[Increase Soft Rock Depth or Cushion]

Note: Always refer to IS 11315 for rock mass characterization and IS 12070 for cavity treatment guidelines.

IS 13063 - Safety Factors Against Sliding and Overturning

1. Factor of Safety Against Overturning (Clause 5.3.2)

• When considering dead load (D), live load (L), earth pressure (E), uplift (U), wind or seismic forces (W/S):
  [ FOS_{overturning} \geq 1.5 ]
• When considering only D, L, E, U (no wind/seismic):
  [ FOS_{overturning} \geq 2.0 ]

2. Factor of Safety Against Sliding (Clause 5.3.1.1)

• When considering D, L, earth pressure, water pressure, uplift, and wind/seismic forces:
  [ FOS_{sliding} \geq 1.5 ]
• When considering only D, L, earth pressure, water pressure, uplift (no wind/seismic):
  [ FOS_{sliding} \geq 1.75 ]

Summary Table

Conceptual Diagram

graph LR
    A[Loads on Structure] --> B{Load Types}
    B --> C[Dead Load (D)]
    B --> D[Live Load (L)]
    B --> E[Earth Pressure (E)]
    B --> F[Water/Uplift Pressure (U)]
    B --> G[Wind/Seismic Forces (W/S)]

    A --> H[Check Stability]
    H --> I[Overturning]
    H --> J[Sliding]

    I --> K[Apply FOS: 1.5 or 2.0]
    J --> L[Apply FOS: 1.5 or 1.75]

Note: Always use the more conservative factor of safety when wind or seismic effects are present.

IS 13063: In Situ Testing Methods – Key Points

Recommended In Situ Tests (Clause 4.8, 4.9.7.3 & 4.9.7.4)

• Very weak/weathered rock:
  • Plate Load Test
  • Pressure Meter Test
  • In Situ Shear Test
• Moderately jointed rock:
  • Point Load Strength Index
  • Uniaxial Compression Strength
  • In Situ Shear Test

Adhesion & Friction Parameters (Clause 5.3.1.3 & Table 2)

• Adhesion and friction values are determined by in situ block shear tests.
• These values are critical for foundation-rock interaction and sliding resistance.

Practical Use Formula for Sliding Resistance:

[ F = c \times A + N \times \mu ] Where:

• (F) = sliding resistance force
• (c) = adhesion (kg/cm²)
• (A) = contact area (cm²)
• (N) = normal force (kg)
• (\mu) = coefficient of friction

flowchart TD
    A[Rock Mass] --> B{Condition}
    B -->|Very weak/weathered| C[Plate Load Test]
    B -->|Very weak/weathered| D[Pressure Meter Test]
    B -->|Very weak/weathered| E[In Situ Shear Test]
    B -->|Moderately jointed| F[Point Load Strength Index]
    B -->|Moderately jointed| G[Uniaxial Compression]
    B -->|Moderately jointed| E
    E --> H[Shear Strength Parameters]
    F --> I[Strength Index]
    G --> J[Compressive Strength]

This summary helps select appropriate tests and design parameters for rock foundation assessment as per IS 13063.

Foundation Design Adjacent to Sloping Ground (IS 13063)

Key Specifications & Conditions

• Clause 6.5.3:

  • If bedding/weak planes dip towards slope, foundation must avoid exposing weak planes on slope surface.
  • Achieved by:
    • Shifting foundation away from slope, or
    • Increasing foundation depth.
  • (Refer Fig. 3B in IS 13063)

• Clause 8.4 (Moderate Slopes < 15°):

  • Embed footing ≥ 30 cm inside rock to ensure safety against sliding.
  • Check factor of safety (FOS) against sliding ≥ 1.10 even without down-slope bearing.
  • (Refer Fig. 9)

• Clause 8.3 (Steep Slopes > 15°):

  • Avoid foundation on steep slopes if possible. If necessary:
    • Embed foundation depth d ≥ 60 cm inside rock.
    • Calculate FOS including down-slope bearing.
    • Check stability without down-slope bearing; use anchors if needed.
    • Provide level benches if feasible; still check sliding as if no bench.
    • Anchors must be embedded in fresh rock beyond slump mass.
  • (Refer Fig. 8)

Sliding Stability Formula (Generalized)

[ FOS = \frac{\text{Resisting Forces}}{\text{Driving Forces}} \geq 1.10 ]

Where:

• Resisting forces include frictional resistance and bearing on down-slope face.
• Driving forces include lateral earth pressure and structural loads.

Summary Table

flowchart LR
    A[Foundation Adjacent to Sloping Ground]
    A --> B{Slope Angle

IS 13063: Stability of Area and Slope Considerations

1. General Stability of Area (Clause 4.11)

• For hilly terrain, detailed slope stability analysis is mandatory before construction.
• Determine maximum allowable load on slopes considering soil and rock strength.
• Implement regulations to control construction in sensitive or unstable areas.

2. Stability Against Overturning and Sliding (Clause 5.3 & 5.3.1)

• Factors of Safety (FoS) must be checked for:

  • Overturning: FoS ≥ 1.5 (typical)
  • Sliding: FoS ≥ 1.5 (typical)

• Basic formulas:

  • Overturning Stability: [ \text{FoS}_{\text{overturning}} = \frac{\text{Resisting Moments}}{\text{Overturning Moments}} \geq 1.5 ]

  • Sliding Stability: [ \text{FoS}_{\text{sliding}} = \frac{\text{Resisting Forces}}{\text{Driving Forces}} \geq 1.5 ]

3. Slope Stability Analysis (Clause 4.11.3)

• Use methods like Limit Equilibrium, Slip Circle, or Finite Element Analysis.

• Key parameters:

  • Soil cohesion (c)
  • Angle of internal friction (\phi)
  • Unit weight (\gamma)
  • Slope angle (\beta)

• Factor of Safety for slope: [ \text{FoS} = \frac{\text{Shear Strength}}{\text{Shear Stress on failure plane}} \geq 1.5 ]

Summary Table: Typical Factors of Safety (IS 13063)

flowchart LR
    A

IS 13063: Foundation on Soluble Rocks – Key Points

1. Grouting of Joints in Soluble Rocks (Clause 6.3)

• For dolomite on limestone with water-charged joints:
  • Grout joints with 1:1 cement-sand mortar.
  • Depth of grouting = effective width of foundation.
  • Refer IS 6066:1984 for grouting procedure.

2. Drill Holes for Solution Cavities (Clause 4.9.5)

• For limestone/dolomite with groundwater flow and risk of cavities:
  • Drill holes to a depth of 1.5 × effective foundation width below foundation level.
  • Purpose: Detect and treat solution cavities.

3. Effective Width of Foundation

• Effective width (b_eff) depends on foundation type and loading.
• Used as a reference depth for grouting and drilling.

Summary Table

Conceptual Diagram: Grouting and Drilling Depth

graph TD
  A[Foundation Base]
  B[Effective Width (b_eff)]
  C[Grouting Depth = b_eff]
  D[Drill Hole Depth = 1.5 × b_eff]
  A --> B
  B --> C
  B --> D

Note: Always verify local site conditions and consult IS 6066 for detailed grouting methods.

Raft Foundations Adjacent to Hill Slopes — IS 13063 Key Points

1. Planning (Clause 8.11)

• Place heavier parts of the building uphill on the raft for better stability.

2. Foundations on Moderate Slopes (<15°) (Clause 8.4)

• Embed footing at least 30 cm inside rock.

• Check sliding safety factor (FS) against sliding along rock surface:

  [ \text{FS} \geq 1.10 ]

• Consider bearing resistance on down slope face.

• Even without down slope bearing, FS ≥ 1.10 must be ensured.

3. Foundations on Steep Slopes (>15°) (Clause 8.3)

• Embed foundation depth ( d \geq 60 \text{ cm} ) inside rock.
• Calculate ( d ) to satisfy FS against sliding including down slope support.
• Check stability without down slope bearing; if inadequate, provide rock/cable anchors.
• Anchors must be embedded in massive, fresh rock beyond slump mass.
• Provide level benches if possible, but check sliding as if no benches exist.

Typical Formula for Sliding Safety Factor:

[ FS = \frac{\text{Resisting Forces (Friction + Bearing)}}{\text{Driving Forces (Shear + Weight Component)}} ]

Summary Table:

flowchart LR
    A[Building on Hill Slope] --> B{Slope Angle}
    B -->|<15°| C[Embed footing ≥30cm]
    B -->|>15°| D[Embed footing ≥60cm + Anchors]
    C --> E[Check FS ≥1.10 including down slope bearing]
    D --> F[Check FS ≥1.10 including down slope bearing]
    F --> G{FS < 1.10 without down slope bearing?}
   

IS 13063: References and Annexures - Key Points

1. Annex A: List of Referred Indian Standards

• Essential adjuncts for foundation design and testing.
• Includes codes for concrete (IS 456:1978), design loads (IS 875:1964), soil investigation (IS 1892:1979), foundation design (IS 1904:1986), rock testing (IS 9143:1979), and more.
• Rock mass characterization extensively covered by IS 11315 series (Parts 1 to 11).
• Example:

2. Foundations on Slopes of Tallus Deposits (Clause 8.12)

• For slopes > 15°, buildings up to two storeys require flexible structures.
• Foundation depth in loose tallus deposits: ≥ 2 m.
• Use of steel or wooden framed structures with light cladding (PVC sheets) and roofing.
• Refer to Fig. 17 for Still Foundation design (wooden floor beams + PVC walls).

3. Settlement Guidelines (Table 5.2.8)

• Maximum settlement and differential settlement limits for various structures on rock mass: