Item 105 – SUBGRADE PREPARATION

105.1  Description

This Item shall consist of the preparation of the subgrade for the support of overlying structural  layers.     It shall extend  to full width of the roadway.     Unless  authorized  by the Engineer,  subgrade  preparation  shall  not  be  done  unless  the  Contractor  is  able  to  start immediately the construction of the pavement structure.

105.2  Material Requirements

Unless otherwise stated in the Contract and except when the subgrade is in rock cut, all materials below subgrade level to a depth 150 mm or to such greater depth as may be specified shall meet the requirements of Section 104.2, Selected Borrow for Topping.

105.3  Construction Requirements

105.3.1  Prior Works

Prior to commencing preparation of the subgrade, all culverts, cross drains, ducts and the like (including their fully compacted backfill), ditches, drains and drainage outlets shall be completed.     Any    work   on   the   preparation   of   thesubgrade shall not be started unless prior work herein described shall have been approved bythe Engineer.

105.3.2  Subgrade Level Tolerances

The  finished  compacted  surface  of  the  subgrade  shall  conform  to  the  allowable tolerances as specified here under:

Permitted variation from                                      +20mm

design LEVEL OF SURFACE                              -30mm

Permitted SURFACE IRREGULARITY

MEASURED BY 3-m STRAIGHT EDGE           30 mm

Permitted variation from

design CROSSFALL OR CAMBER                      +/-0.5%

Permitted variation from

design LONGITUDINAL GRADE                        +/-0.1%

over 25 m length

105.3.3  Subgrade in Common Excavation

Unless otherwise specified, all materials below subgrade level in earth cuts to a depth 150 mm or other depth shown on the Plans or as directed by the Engineer shall be excavated. The material, if suitable, shall be set side for future use or, if unsuitable, shall be disposed off in accordance with the requirements of Subsection 102.2.9.

Where material has been removed from below subgrade level, the resulting surface shall be compacted to a depth of 150 mm and in accordance with other requirements of Subsection 104.3.3. All materials immediately below subgrade level in earth cuts to a depth of 150 mm, or to such greater depth as may be specified, shall be compacted  in accordance with the requirements of Subsection 104.3.3.

105.3.4  Subgrade in Rock Excavation

Surface irregularities under the subgrade level remaining after trimming of the rock excavation shall be leveled by placing specified material and compacted to the requirements of Subsection 104.3.3.

105.3.5  Subgrade on Embankment

After  the  embankment  has  been  completed,  the  full  width  shall  be  conditioned  by removing any soft or other unstable material that will not compacted properly.    The resulting areas and all other low sections, holes, or depressions shall be brought to grade with suitable material.  The  entire  roadbed  shall  be  shaped  and  compacted   to  the  requirements   of Subsections 104.3.3.    Scarifying, blading, dragging, rolling, or other methods of work shall be performed or used as necessary to provide a thoroughly compacted  roadbed shaped to the cross-sections shown on the Plans.

105.3.6  Subgrade on Existing Pavement

Where the new pavement  is to be constructed  immediately  over an existing Portland Cement concrete pavement and if so specified in the Contract the slab be broken into pieces with  greatest  dimension  of  not  more  than  500  mm  and  the  existing  pavement  material compacted  as specified in Subsection  104.3.3, as directed by the Engineer.     The resulting subgrade  level shall, as part pavement  construction  be shaped to conform to the allowable tolerances of Subsection 105.3.2 by placing and compacting where necessary a leveling course comprising the material of the pavement course to be placed immediately above.

Where  the new pavement  is to be constructed  immediately  over an existing  asphalt concrete pavement or gravel surface pavement and if so specified in the Contract the pavement shall  be  scarified,  thoroughly  loosened,  reshaped  and  recompacted  in  accordance  with Subsection 104.3.3.   The resulting subgrade level shall conform to the allowable tolerances of Subsection 105.3.2.

105.3.7  Protection of Completed Work

The Contractor shall be required to protect and maintain at his own expense the entire work within the limits of his Contract in good condition satisfactory to the Engineer from the time he first started  work until all work shall have been completed.     Maintenance  shall include repairing and recompacting ruts, ridges, soft spots and deteriorated sections of the subgrade caused by the traffic of the Contractor’s vehicle/equipment or that of the public.

105.3.8  Templates and Straight-edges

The Contractor shall provide for use of the Engineer, approved templates and straight- edges in sufficient number to check the accuracy of the work, as provided in this Specification.

105.4  Method of Measurement

105.4.1    Measurement of Items for payment shall be provided only for:

1.  The compaction of existing ground below subgrade level in cuts of common material as specified in Subsection 105.3.3.

2.  The breaking  up or scarifying,  loosening,  reshaping  and recompacting  of existing pavement as specified in Subsection 105.3.6.    The quantity to be paid for shall be the area of the work specified to be carried out and accepted by the Engineer.

105.4.2    Payment for all work for the preparation of the subgrade, including shaping to the required levels and tolerances, other than as specified above shall be deemed to be included in the Pay Item for Embankment.

105.5  Basis of Payment

The accepted quantities, measured as prescribed in Section 105.4, shall be paid for at the  appropriate contract  unit  price  for  Pay  Item  listed  below  that  is  included  in  the  Bill  of Quantities which price and payment shall be full compensation for the placing or removal and disposal of  all materials including  all  labor,  equipment,  tools  and  incidentals  necessary  to complete the work prescribed in this Item.

Payment will be made under:

Pay  Item Number	Description	Unit of Measurement
105 (1)	Subgrade Preparation (Common Material)	Square Meter
105 (2)	Subgrade Preparation (Existing Pavement)	Square Meter
105 (3)	Subgrade Preparation (Unsuitable Material)	Square Meter