Highway Construction
Highway Construction
Embankment Construction
Materials and General Requirements
The materials used in embankments, subgrades, earthen, shoulders, and miscellaneous backfills shall be soil, moorum, gravel, a mixture of these.
Clay having liquid limit exceeding 70 and plasticity index exceeding 45; shall be considered unsuitable for embankment.
Sub-grade and top 500mm portion of the embankment just below sub grade shall be non-expansive in nature.
Density requirements of embankment and subgrade materials
| S.No. | Type of Work | Maximum laboratory dry unit wt. |
| 1 | Embankments up to 3m height, not subjected to extensive flooding. | Not less than 15.2kN/m3 |
| 2 | Embankments exceeding 3m height or embankments of any height subject to long periods of inundation | Not less than 16.0kN/m3 |
| 3 | Subgrade and earthen shoulders/verges/backfill | Not less than 17.5kN/m3 |
Construction Operations
When necessary, the original ground shall be levelled to facilitate placement of first layer of embankment, Scarified, mixed with water and then compacted by rolling so as to achieve minimum dry density.
The embankment and subgrade material shall be spread in layers of uniform thickness not exceeding 200mm by mechanical means, finished by a motor grader and compacted.
Clods or hard lumps of earth shall be broken to have a maximum size of 75mm when being placed in the embankment and a maximum size of 50mm when being placed in the subgrade.
Construction of Granular Sub-Bases
This work shall consist of laying and compacting well graded material o prepared subgrade.
The material shall be laid in one or more layers as sub-base or lower sub-base and upper sub-base.
The water absorption value of the coarse aggregate if is greater than 2%, the soundness test shall be carried out.
Water-bound Macadam Sub-Base/Base
This work shall consist of clean, crushed aggregates mechanically interlocked by rolling and bounding together with screening, binding material where necessary and water laid on a properly prepared sub-base/subgrade/base or existing pavement, as the case may be and finished.
Wet-Mix Macadam Sub-Base
This work shall consist of laying and compacting clean, crushed, graded aggregate and granular material, premixed with water, to a dense mass on a prepared subgrade/sub-base/base or existing pavement.
The material shall be laid in one layer or more as necessary to lines, grades and cross-sections.
The thickness of a single compacted Wet-Mix Macadam layer shall not be less than 75mm.
When vibrating or other approved types of compacting equipment are used, the compacted depth of a single layer of the sub-base course may be increased to 200mm.
Preparation of Base and Surface Courses (Bituminous)
This work shall consist of preparing an existing granular or black-topped surface to specified lines, grades and cross-section in advance of laying a bituminous course.
The work shall consist of scarifying and re-laying the granular base course or scarifying the existing surface, filling of potholes, sealing of cracks and application of a profile corrective course as necessary.
Prime Coat over Granular Base
This work shall consist of application of single cost of low viscosity liquid bituminous material to an absorbent granular surface preparatory to any superimposed bituminous treatment or construction. Objective is to ping in the capillary voids of the porous surface and to bend the loose material particles on existing surface using a binder of low viscosity which can penetrate into voids.
Tack Coat
This work shall consist of application of a single coat of low viscosity liquid bituminous material to an existing road surface which is relatively impervious preparatory to another bituminous construction over it.
Bituminous Macadam
The work shall consist of construction, in a single course, of compacted crushed aggregates premixed with a bituminous binder, to serve as base/binder course, laid immediately after mixing, on a base prepared previously.
Surface Dressing
This work shall consist of the application of one coat or two coats of surface dressing, each coat consisting of a layer of bituminous binder sprayed on the base prepared previously, followed by a cover of stone shipping properly rolled to form a wearing course.
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