Recommended Practice for Construction of Earth Embankments and Sub-Grade for Road Works (First Revision)

The scope of IRC 36 covers specifications for embankment construction and related earthwork for highways. Key parameters include soil classification (IS 1498), sieve sizes (2.00 mm, 425 micron, 75 micron), plasticity index, shrinkage limit, free swelling index, maximum dry density, and optimum moisture content. Compaction and density requirements are critical, as per Clause 8.3.9 and Clause 4.4.6, with Tables 3 and 4 specifying minimum relative compaction and dry unit weights for various embankment and subgrade materials.

Table 3: Compaction Requirements

Table 4: Density Requirements

These ensure suitable material quality and compaction for embankment stability and performance.

Sources: Clause 2.00, Clause 4.4.6, Clause 8.3.9, Table 3, Table 4

In IRC 36, key definitions related to soil compaction and embankment construction are supported by Tables 3 and 4, which specify compaction and density requirements. As per Clause 4.4.6, only materials meeting these criteria shall be used. Table 3 defines the relative compaction percentages of maximum laboratory dry density (IS 2720 Parts 7 or 8) for various works: for subgrade and earthen shoulders, not less than 97%; for embankments, not less than 95%; and for expansive clays in embankments (after treatment), not less than 95%. Table 4 specifies minimum dry unit weights for embankments and subgrade, varying by road type and embankment height, e.g., embankments up to 3 m height require at least 15.2 kN/m³ for NHs/SHs/MDRs and 14.4 kN/m³ for rural roads. These definitions and specifications ensure proper soil compaction and stability in embankment construction.

Sources: Clause 4.4.6, Table 3, Table 4

For selection of materials in IRC 36, key specifications include compaction, density, and soil classification as follows:

• Compaction Requirements (Table 3, Clause 4.4.6):

  • Subgrade and earthen shoulders: Relative compaction not less than 97% of max dry density (IS 2720 Part 7/8).
  • Embankment: Not less than 95%.
  • Expansive clays: Not allowed for subgrade; embankment allowed after treatment with min 95% compaction.

• Density Requirements (Table 4, Clause 4.4.6):

• Soil Classification (Clause 4.3.10, Table under Clause 2.16): Use IS 1498 classification based on plasticity, compressibility, and CBR values to assess suitability.

These criteria ensure material suitability for embankment and subgrade construction per IRC 36 requirements.

Sources: Clause 4.4.6, Table 3, Table 4, Clause 4.3.10, Clause 2.16

Key specifications for Soil Surveys and Investigations per IRC 36 include detailed soil classification and subgrade evaluation as per Clause 2.16. Soils are classified by grain size, plasticity, and organic content with typical group symbols (e.g., ML, CL, CH) and their corresponding unit dry weight and CBR values. For example, inorganic clays of low plasticity (CL) have unit dry weight 1.44-2.08 g/cm³ and CBR ≤ 15%. Highly organic soils like peat (Pt) are unsuitable as subgrade. Laboratory investigations should report sieve analysis, Atterberg limits (liquid limit, plastic limit, plasticity index), shrinkage limit, free swelling index, maximum dry density, optimum moisture content, soil classification per IS:1498, and CBR values (Clause 2.00 and 2.16). Material selection for subgrades and embankments must be based on these surveys and tests (Clause 3.2). The following table summarizes soil groups and properties:

Sources: Clause 2.16, Clause 2.00, Clause 3.2

Key structural features of embankments per IRC 36 include ensuring the embankment material has a minimum dry density of not less than 16.5 kN/m³ as per Clause 16.5. Lightweight fill materials such as cinder, pond ash, or fly ash are exceptions to Table 4 specifications. The embankment construction involves proper soil surveys, setting out construction limits, preliminary operations, and compaction control to achieve required density and stability. Drainage and allowance for settlement are also critical features to maintain embankment integrity. The embankment should be constructed in layers with adequate compaction and quality control as detailed in the relevant clauses (5, 8, 18, 19, 20, 21).

Sources: Clause 16.5, Clause 5, Clause 8, Clause 18, Clause 19, Clause 20, Clause 21

As per IRC 36 Clause 6.1, setting out construction limits begins with marking the road alignment on the ground using theodolite and total station equipment. The centre-line pegs are established at regular intervals along the road. At horizontal curves, pegs must be placed at the start and end of the curve and at the intersection points of tangents connected by the curve. Clause 6.4 references sketches (Fig. 1) that illustrate the setting out of control pegs for embankment construction, which are essential for defining construction limits precisely. Additionally, Clause 5.3 allows for steeper slopes than standard if mechanically stabilized, ensuring safety within construction limits. These procedures ensure accurate physical demarcation of the designed road alignment and construction boundaries.

Sources: Clause 5.3, Clause 6.1, Clause 6.4

Preliminary Operations in IRC 36 primarily involve setting out construction limits and preparing the site for embankment construction. As per Clause 6.4, sketches for setting out control pegs are provided (Fig. 1) to guide embankment layout. The key steps include soil surveys, investigations, and marking construction boundaries accurately before earthwork begins. These operations ensure proper alignment and dimensions of the embankment as per design. The Table of Contents indicates that detailed procedures and specifications for Preliminary Operations are covered in Section 7 (Page 12) of IRC 36. Unfortunately, specific formulas or detailed tables for Preliminary Operations are not provided in the retrieved context.

Sources: Clause 6.4, Section 7, Page 12

Key specifications for Borrow Pits and Material Handling per IRC 36 include:

• Test Pits (Clause 4.3.1): Test pits must be dug in borrow areas with depth not exceeding the likely borrow pit depth by more than 150 mm. Adequate samples should be taken from each borrow area.

• Location and Depth (Clause 8.1 & 8.1.4): Borrow pits must be located so they do not cut an imaginary line sloping 1 vertical to 4 horizontal from the edge of the final embankment section (see Fig. 2). This ensures stability and minimal adverse effects.

• Material Quality (Clause 8.1): Only approved materials are to be used, with the best materials reserved for the embankment top (subgrade).

• River Side Borrow Pits (Clause 10.3): Borrow pits near rivers should have their inner edge at least 15 m from the bank toe, considering flood magnitude and duration, and comply with Clause 8.1.3.

These rules ensure safe, efficient borrow pit design and material handling for embankment construction.

Sources: Clause 4.3.1, Clause 8.1, Clause 8.1.4, Clause 10.3

Key construction procedures for earth embankments and subgrade in IRC 36 include:

• Soil Layering and Compaction: Soil is spread in layers and compacted to specified densities (Clause 8.3.8).

• Selection of Compaction Equipment: Table 6 guides equipment choice based on soil type:

• Reference for Details: For comprehensive compaction procedures and equipment, refer to HAB Special Report No. 3 on earthwork compaction.

This ensures proper density and stability of embankments as per IRC 36 standards.

Sources: Clause 8.3.8, Table 6

For construction and maintenance of roads on a flood bank as per IRC 36, key specifications include:

• The toe of the flood bank on the rear side must have a cover of 0.75 m to 1.25 m over the saturation line, which is drawn at a slope of 1 vertical in 6 horizontal (1V:6H) from the high flood level on the river side (Clause 10, 1.25).
• Rear berms may be provided to ensure minimum cover over the saturation line as shown in Fig. 3.
• The slope of the saturation line may be adjusted based on soil nature.
• For repairing rain or water spillage damage, affected soil must be removed, refilled in layers, and compacted using mechanical means (vibratory roller, plate compactor, power rammer) to achieve required density per Tables 3 and 4 (Clause 9.4).
• If the cut is narrow, it must be widened to allow proper compaction equipment use.
• Testing for density is mandatory as directed by the Engineer-in-Charge.

These ensure stability and durability of flood bank roads against flooding and water damage.

Sources: Clause 10, 1.25, Clause 9.4

Key special construction considerations in IRC 36 include mechanical stabilization of slopes steeper than standard (Clause 5.3), and strict compaction and density requirements for embankment and subgrade materials (Clause 4.4.6). The compaction must meet relative compaction percentages per IS 2720, as shown in Table 3, and density requirements per Table 4. For example, embankments up to 3 m height require a minimum dry unit weight of 15.2 kN/m³ for National Highways (NHs), State Highways (SHs), and Major District Roads (MDRs), and 14.4 kN/m³ for rural roads. Embankments over 3 m or subject to inundation require higher densities (16.0 kN/m³ for NHs/SHs/MDRs). Subgrade and earthen shoulders require even higher densities (17.5 kN/m³ for NHs/SHs/MDRs). These ensure stability and durability under special conditions.

Sources: Clause 5.3, Clause 4.4.6, Table 3, Table 4

For the construction of earthen shoulders as per IRC 36, Clause 15 specifies that earthen shoulders shall be constructed using the same material as the subgrade, specifically the top 500 mm portion of the embankment. This material must be compacted to the same density requirements detailed in Tables 3 and 4 of the code. Additionally, the construction of shoulders should be coordinated to progress simultaneously with the construction of the pavement layers (Clause 15.1). For embankments in waterlogged or marshy areas, a coarse sand blanket layer must be provided as per IRC 34 (Clause 14.2). The minimum dry density for subgrade and earthen shoulders is specified as not less than 15.2 kN/m³ (Clause 15.2).

Sources: Clause 14.2, Clause 15.1, Clause 15.2

For flyash embankment construction as per IRC 36, the term 'flyash' includes pond ash, bottom ash, or mound ash, but not fine flyash alone (Clause 16.1). Key requirements include:

• Use flyash from nearby thermal power plants with an appropriate soil cover.
• Particle size analysis (wet sieve) and Maximum Dry Density & Optimum Moisture Content per IS 2720 (Part 8) must be provided for compaction control (Clause 16.1).
• Soil cover must meet requirements specified in Tables 3 and 4 (Clause 16.1).
• Earth shoulders (top 500 mm) should be of subgrade material and compacted as per Tables 3 and 4 (Clause 15.1).
• Minimum dry density for embankment fill should be not less than 16.5 kN/m³ (Clause 16.5).

Refer to IRC:SP:58 for detailed guidelines on flyash use in road embankments.

Sources: Clause 16.1, Clause 15.1, Clause 16.5

Key specifications for compaction control and testing as per IRC 36 include:

• Density of Compaction: Must comply with values given in Tables 3 and 4 (Clause 8.3.9).
• Field Density Measurement: Use sand-replacement method and/or Nuclear Densometer as per IS 2720 (Part 8 and Part 7) (Clause 20.6).
• Recompaction Requirement: If specified density is not achieved, loosen the entire layer depth, adjust moisture to optimum, and re-compact (Clause 20.6).
• Quality Control Tests (Clause 21 and 2.00):
  • Particle size analysis using 2.00 mm, 425 micron, and 75 micron IS sieves
  • Plasticity Index
  • Shrinkage Limit
  • Free Swelling Index
  • Maximum Dry Density and Optimum Moisture Content from Standard/Modified Proctor tests
  • Soil Classification as per IS 1498
  • CBR for subgrades

These ensure embankment material suitability and proper compaction for pavement stability.

Sources: Clause 8.3.9, Clause 20.6, Clause 21, Clause 2.00

Quality control and acceptance criteria for embankment and subgrade materials per IRC 36 are governed mainly by compaction and density requirements. As per Clause 4.4.6, only materials meeting these criteria shall be used.

Table 3: Compaction Requirements specify:

• Subgrade and earthen shoulders: minimum 97% relative compaction of max dry density (IS 2720 Part 7/8)
• Embankment: minimum 95% relative compaction
• Expansive clays: Not allowed for subgrade; embankment allowed after treatment with minimum 95% compaction

Table 4: Density Requirements specify minimum dry unit weights:

These ensure adequate strength and stability of road embankments and subgrades.

Sources: Clause 4.4.6, Table 3, Table 4