Landslide Control - Guidelines

IS 14680: Scope & Key Specifications

IS 14680 addresses landslide risk management, focusing on classification, investigation, and control measures.

Scope Highlights:

• Applies to landslide types and materials.
• Covers investigation methods (e.g., static/dynamic cone penetration tests).
• Provides control measures based on landslide classification.

Key Tables & Classifications:

Investigation:

• Conduct static/dynamic cone penetration tests to failure plane or hard rock.
• Use results to decide borehole locations and numbers.

References:

• IS 1498: Soil classification
• IS 1892: Subsurface investigation for foundation
• IS 14458 (Part 2): Retaining walls in hill areas

flowchart TD
    A[Landslide Types] --> B[Falls]
    A --> C[Topples]
    A --> D[Slides]
    A --> E[Lateral Spreads]
    A --> F[Flows]
    A --> G[Complex]

    B --> H[Control: Geotextile, Spot Bolting]
    C --> I[Control: Breast Walls, Soil Nailing]
    D --> J[Control: Slope Alteration, Reinforcement]
    E --> K[Control: Check Dams]
    F --> L[Control: Check Dams, Deep Piles]
    G --> M[Control: Combined Systems]

This summary aligns with IS 14680's scope for landslide classification, investigation, and control.

IS 14680 References Summary

This standard incorporates provisions from key Indian Standards, which are integral to its application:

Key Notes:

• These referenced standards provide essential guidelines on soil classification, foundation investigations, and retaining wall design.
• Users should consult the latest editions as standards are periodically revised.
• The technical committee composition (Annex A) includes experts from diverse fields ensuring comprehensive standard development.

Practical Tip:

For foundation design in hill areas, use IS 1892 for subsurface investigation methods and IS 1498 for soil classification to ensure accurate geotechnical assessment.

flowchart LR
    A[IS 14680 Standard] --> B[Soil Classification: IS 1498]
    A --> C[Subsurface Investigation: IS 1892]
    A --> D[Retaining Walls Design: IS 14458 Part 2]

This diagram shows the relationship between IS 14680 and its key referenced standards.

IS 14680 - Definitions (Clause 3.1) & Related References

Key Definitions:

• Clause 3.1 states that all definitions relevant to hill area development engineering are as per this standard.

• Engineering properties of subsoil include:

  • Index properties
  • Shear parameters
  • Compressibility characteristics

  These are detailed as per IS 1498:1970 (Soil classification and identification).

Important Referenced Standards (Table 2):

Summary:

• Use IS 1498 for soil property definitions.
• Use IS 1892 for subsurface investigation methods.
• Use IS 14458 (Part 2) for retaining wall design in hill areas.

Quick Reference: Soil Properties per IS 1498

flowchart LR
    A[IS 14680 Definitions] --> B[Soil Properties]
    B --> C[Index Properties (IS 1498)]
    B --> D[Shear Parameters (IS 1498)]
    B --> E[Compressibility (IS 1498)]
    A --> F[Subsurface Investigation (IS 1892)]
    A --> G[Retaining Wall Design (IS 14458 Part 2)]

For detailed design and soil characterization, refer to the above IS codes as per IS 14680 Clause 3.1.

IS 14680: Landslide Classification - Key Points

1. Types of Landslide Movements (Clause 4, Table 1)

2. Definitions

• Toe of Surface of Rupture (Clause 3.1.11):
  Intersection between the lower part of rupture surface and original ground, may be buried.

3. Investigation Guidelines (Clause 5.2)

• Conduct static/dynamic cone penetration tests (CPT) up to failure plane or hard rock strata.
• CPT results guide borehole location and number.

Summary Diagram of Landslide Types and Controls

graph TD
    A[Landslide Types] --> B[Falls]
    A --> C[Topples]
    A --> D[Slides]
    A --> E[Lateral Spreads]
    A --> F[Flows]
    A --> G[Complex]

    B --> B1[Earth/Debris/Rock Fall]
    C --> C1[Earth/Debris/Rock Topple]
    D --> D1[Rotational/Translational Slides]
    E --> E1[Earth/Debris/Rock Spread]
    F --> F1[Earth/Debris/Rock Flow]
    G -->

IS 14680: Investigations Required (Clause 5.1 & 5.2)

• Objective: Obtain subsoil profile and soil properties up to failure plane or hard rock strata.

• Investigation Methods:

  • Conduct Static/Dynamic Cone Penetration Tests (CPT) to determine soil stratification and strength.
  • Number and location of CPTs depend on site conditions and failure plane depth.
  • Use results to decide borehole locations.

• Reference Standards:

  • IS 1892: Code of practice for subsurface investigation for foundation.
  • IS 1498: Soil classification.
  • IS 14458 (Part 2): Design of retaining/breast walls in hill areas.

Key Table: Landslide Classification & Control Measures (Clause 4)

Investigation Depth & Procedure Summary

flowchart TD
    A[Start Investigation] --> B{Determine Depth}
    B -->|Failure Plane| C[Conduct CPT Tests]
    B -->|Hard Rock| C
    C --> D[Decide Borehole Locations]
    D --> E[Collect Soil Samples]
    E --> F[Analyze Soil Properties]
    F --> G[Design Control Measures]

Summary: IS 14680 mandates detailed soil investigation (CPT + boreholes

IS 14680: Landslide Preventive Techniques - Key Points

1. Classification (Clause 6.1)

• Direct Methods:
  • Restraining structures (retaining walls, anchored walls, piles)
  • Easing pressure by excavation
  • Reconstruction using reinforced earth
  • Rock reinforcement
• Indirect Methods:
  • Erosion control
  • Surface and sub-surface drainage improvement

2. Sub-surface Drainage (Clause 6.1.7.1)

Effective for deep-seated landslides by reducing pore water pressure at failure plane.

3. Construction Details (Fig. 7 Summary)

• Horizontal drain pipe: Slotted PVC, encased in geotextile.
• Installation: Pre-drilled borehole, negative gradient.
• Check valve: Prevents pipe sliding out.

4. Equipment

• Must access difficult terrain, steep slopes, and heights.
• Drilling rigs capable of angled boreholes (±30°).

Summary Diagram (Horizontal Drain Installation)

flowchart LR
    A[Pre-drilled Borehole] --> B[Insert 50mm Slotted PVC Pipe]
    B --> C[Check Valve at Entry]
    B --> D[Geotextile Shroud]
    D --> E[Prevents Soil Entry]
    C --> F[Water Drainage Out]

This concise summary aids design and implementation of landslide preventive measures per IS 14680.

IS 14680: Direct Methods for Landslide Prevention

Direct methods focus on physically stabilizing the slope. Key categories include:

1. Restraining Structures

   • Retaining walls
   • Anchored walls
   • Restraining piles

2. Easing Pressure by Excavation

   • Remove soil from the upper slope to reduce driving forces.

3. Reconstruction of Slope Using Reinforced Earth

   • Use of geosynthetics or metallic strips to reinforce soil layers.

4. Rock Reinforcement

   • Rock bolts, anchors, and mesh to stabilize rock slopes.

Key Specifications & Considerations:

• Subsurface Investigation: As per IS 1892:1979, assess soil type, strength, and groundwater conditions.
• Soil Classification: Follow IS 1498:1970 for soil identification.
• Design of Retaining Walls: Refer IS 14458 (Part 2):1997 for hill area retaining walls.

Typical Design Parameters for Retaining Walls (Example):

flowchart TD
    A[Landslide Prevention] --> B[Direct Methods]
    B --> B1[Restraining Structures]
    B --> B2[Excavation]
    B --> B3[Reinforced Earth]
    B --> B4[Rock Reinforcement]
    A --> C[Indirect Methods]
    C --> C1[Erosion Control]
    C --> C2[Drainage Improvement]

For detailed design, consult the referenced IS codes and site-specific geotechnical data.

IS 14680 - Restraining Structures: Key Points & Formulas

1. Purpose & Use

• Restraining structures control slope stability for heights ≤ 4 m.
• Suitable for restricted spaces; often rigid retaining walls.
• Used to stabilize dangerous slopes or landslides.

2. Types & Construction

• Rigid Retaining Walls: Require skilled labor and expensive planking.
• Temporary Structures:
  • Use empty bitumen drums (height ≤ 3 m).
  • Drums arranged in two rows, interconnected by MS flats/rods.
  • Example: 50 × 6 mm MS flat @ 2 m c/c spacing for connections.

3. Design References

4. Basic Stability Considerations (General)

• Check sliding, overturning, bearing capacity.
• Use soil parameters from IS 1498.
• Typical design formula for factor of safety against sliding:

[ F_s = \frac{c' A + W \tan \phi'}{H} ]

Where:

• (c') = effective cohesion,
• (A) = base area resisting sliding,
• (W) = weight of wall and soil,
• (\phi') = effective angle of internal friction,
• (H) = horizontal sliding force.

5. Example: Bitumen Drum Restraining Structure

graph LR
A[Empty Bitumen Drum] --> B[Remove top & bottom covers]
B --> C[Arrange in two rows]
C --> D[Connect vertically & horizontally]
D --> E[Use 50x6 mm MS flats @ 2m c/c]

For detailed design, refer IS 14458 (Part 2):1997 for retaining/breast walls.

IS 14680: Excavation Methods for Landslide Control

Key Excavation Methods (Clause 6.1.2)

• Removal of Unstable Material: Eliminates weak soil to increase stability.
• Slope Flattening: Reduces slope angle to decrease driving forces.
• Benching of Slopes (6.1.2.3):
  • Slopes divided by near-horizontal benches.
  • Bench width ≥ 8 m for independent slope action.
  • Benches have V-shaped/gutter sections with drainage and catch basins.
  • Drainage ditches lined/paved to prevent erosion/percolation.
• Change of Line or Grade (6.1.2.4):
  • Adjust slope alignment or elevation to reduce driving forces.
  • Includes partial or complete removal of unstable soil at head or toe.

Stability Enhancement Principles

• Benching segments slope, reducing effective height and driving force.
• Drainage on benches prevents water infiltration, a key destabilizing factor.
• Flattening and line changes reduce slope angles and loads.

Reference Standards

Simplified Illustration of Benching

graph TD
    A[Slope Top] --> B[Bench 1 (≥ 8m wide)]
    B --> C[Slope Segment 1]
    C --> D[Bench 2 (≥ 8m wide)]
    D --> E[Slope Segment 2]
    E --> F[Bench Drainage with Catch Basins]

Summary: Use benching with ≥8 m wide benches and proper drainage, flatten slopes, and adjust line/grade to improve slope stability per IS 14680 Clause 6.1.2.

IS 14680: Reconstruction of Slope Using Reinforced Earth

Key Components (Clause 6.1.3)

• Backfill: Selected granular material.
• Reinforcement: Metallic strips (6.1.3.1) or geofabric (6.1.3.2).
• Facing: Precast concrete skin panels.

Design Principles

• Acts as a gravity retaining structure on a stable foundation.
• Must resist:
  • Overturning
  • Internal shear
  • Sliding at/below base

Important Specifications

• Economical for heights > 5.0 m (Clause 5.0).
• Use caution in seismic zones due to reduced soil-reinforcement friction.

Basic Stability Checks

Reinforcement Length (Lr)

• Typically, (L_r = (0.7 \text{ to } 1.0) \times H) (H = height of wall)
• Ensure sufficient embedment length beyond failure plane.

flowchart TD
    A[Granular Backfill] --> B[Reinforcement Layer]
    B --> C[Precast Concrete Facing]
    C --> D[Stable Foundation]
    D --> E[Resists Overturning, Sliding, Shear]

For detailed design, refer to IS 14680 clauses and use soil parameters for friction, cohesion, and reinforcement properties.

IS 14680 - Rock Reinforcement Key Points

Rock Reinforcement (Clause 6.1.4)

• Used to stabilize rockslides and rockfalls by anchoring unstable rock masses.
• Methods include rock bolts, anchors, shotcrete, and mesh.

Important Specifications:

• Rock bolts/anchors: Typically tensioned steel bars grouted into drilled holes.
• Length and spacing depend on rock mass quality and slope geometry.
• Grouting ensures load transfer and corrosion protection.

Design Considerations:

• Assess rock mass strength and discontinuities.

• Determine anchor load capacity using:

  [ P = A_s \times f_y ]

  where:

  • (P) = design load,
  • (A_s) = cross-sectional area of bolt,
  • (f_y) = yield strength of steel.

• Factor of Safety (FoS) usually between 1.5 to 2.5.

Related IS Codes for Reference:

Summary Table: Typical Rock Bolt Parameters

flowchart TD
    A[Unstable Rock Mass] --> B[Drill Holes]
    B --> C[Insert Rock Bolts/Anchors]
    C --> D[Grouting]
    D --> E[Tensioning]
    E --> F[Stabilized Rock Slope]

For detailed design, refer to IS 14680 clauses and related IS standards for soil and foundation investigation.

IS 14680: Erosion Control Measures — Key Points & Formulas

1. Slope Preparation & Vegetation

• Seed bed preparation: Sound off tops, regrade, rake topsoil ~20 mm thick.
• Seeding: Seeds/root slips dibbled 150-200 mm apart (row to row and plant to plant).
• Asphalt emulsion mulch: Applied at 0.9 litre/m² (~1.0 mm thick film) to protect soil and promote vegetation.

2. Jute/Coir Netting for Slope Protection

• Slope grading and leveling.
• Seeding at 5 kg/acre or root slips at 150 mm spacing.
• Coir/jute netting anchored with 150 mm iron nails.
• Netting acts as a check dam, reducing soil erosion and nutrient loss.

3. Bally Benching

• Terracing method to reduce slope steepness and control erosion (details in Clause 6.1.5).

4. Surface Water Control (Clause 6.1.6.1)

• Catch water drains: Gradient 1:50 to 1:33; lined and maintained to avoid washout.
• Road side drains: Bed slope 1:20 to 1:25; types include dry rubble masonry, angle drain, kerb and channel drain.
• Cross drains: Spaced 4-6 per km; culverts, scuppers, causeways to prevent flooding.

Typical Drain Slope & Spacing

Asphalt Emulsion Application Formula

[ \text{Volume of Emulsion} = 0.9 , \text{litres/m}^2 ]

• Forms ~1 mm thick protective film on soil surface.

Diagram:

IS 14680 – Control of Surface Water (Clause 6.1.6)

Key Specifications & Formulas:

1. Catch Water (Interceptor) Drains

• Purpose: Intercept and divert uphill run-off to protect unstable slopes.
• Location: Carefully placed based on detailed topography.
• Gradient:
  [ \text{Slope} = \frac{1}{50} \text{ to } \frac{1}{33} \quad (2% \text{ to } 3%) ]
• Construction: Lined drains to avoid washout; interconnected if slide area is large.
• Discharge: Divert water into chutes, natural drains, or culverts leading to natural watercourses.

2. Road Side Drains

• Purpose: Drain water from road surface and hill slope below catch water drains.
• Types: Dry rubble masonry, semi-circular saucer, rectangular, trapezoidal, angle, or kerb & channel drains.
• Bed Slope:
  [ \text{Slope} = \frac{1}{20} \text{ to } \frac{1}{25} \quad (4% \text{ to } 5%) ]
• Velocity Control: Use stepped drains or check walls to reduce scour.
• Shoulder Width: 0.3 m between drain edge and hill slope.
• Lining: Generally lined; unlined allowed on hard/stiff strata.

3. Cross Drains

• Spacing: 4 to 6 per km depending on terrain.
• Purpose: Prevent overloading of side drains and road flooding.
• Structures: Culverts, scuppers, causeways, bridges at natural water crossings.

Drain Types Illustration (Fig. 3)

flowchart LR
    Runoff --> CatchWaterDrain[Catch Water Drain]
    CatchWaterDrain --> Chute[Natural Hill-side Chute]
    Chute --> Cul

IS 14680 - Sub-Surface Drainage (Clause 6.1.7)

Key Specifications & Methods

1. Horizontal Drains (Clause 6.1.7.1 a)

   • Pipe: 50 mm diameter perforated/slotted rigid PVC.
   • Perforation: Upper 2/3rd of pipe length.
   • Installation: Boreholes drilled at 5° to 15° negative gradient.
   • Equipment: Drilling rig capable of ±30° from horizontal.
   • Anti-slip: Check valve on first pipe length.
   • Protection: Geotextile shroud to prevent clogging.

2. Deep Trench Drains (Clause 6.1.7.1 b)

   • Depth: Effective for <5 to 8 m.
   • Core: Permeable gravel (16-32 mm or 35-70 mm).
   • Filter: Surround gravel with filter fabric/geotextile.
   • Backfill: Clean gravel up to water-bearing layer, overlapped geotextile, then local soil.

Surface Drainage (Clause 6.1.6)

• Catch Water Drains: Gradient 1:50 to 1:33, lined, to intercept and divert surface runoff.
• Road Side Drains: Slope 1:20 to 1:25, lined/unlined, with options: angle drain, kerb & channel drain.
• Cross Drains: Spaced 4-6 per km, includes culverts, causeways.

Summary Table: Horizontal Drain Design Parameters

Conceptual Diagram of Horizontal Drain Installation

graph LR
A[Surface] --> B[Pre-drilled Borehole at 5-15°]

IS 14680 - Equipment and Accessories: Key Points

The code provides guidelines for equipment and accessories primarily related to hill area development, including trench drains and geotextile overlapping.

Key Specifications:

• Overlapping of Geotextile: Must ensure continuous filtration and separation; overlaps typically range from 0.3 m to 0.5 m depending on site conditions.

• Gravel and Boulder Layers: Used in trench drains for filtration and drainage; sizes and gradation should comply with drainage requirements to avoid clogging.

• Cross Sections of Trench Drains:

  • Collector Drain: Designed to collect and convey water efficiently.
  • Feeder Drain: Feeds water into the collector drain.

• Typical Dimensions (from Fig. 8):

  • Trench width: 0.3 m to 0.6 m
  • Depth: As per design infiltration and flow requirements.

Recommended Practice:

References for Design:

• IS 1498: Soil classification
• IS 1892: Subsurface investigation
• IS 14458 (Part 2): Retaining wall design in hill areas

flowchart TD
    A[Surface Water] --> B[Feeder Drain]
    B --> C[Collector Drain]
    C --> D[Outlet]
    subgraph Trench Drain Cross Section
        E[Geotextile Layer]
        F[Gravel Layer]
        G[Boulder Layer]
    end
    B --> E --> F --> G --> C

Summary: Use proper geotextile overlapping, graded gravel and boulder layers, and trench drain dimensions as per IS 14680 Fig. 8 for effective hill area drainage systems.