The specifications in this section apply to compaction of the following:
• All waterworks and sewer service cuts, repairs, replacements, main breaks, extensions etc.
• All shallow cuts by utility companies.
• All cuts for the installation of streetlight ducts and bases.
• On all existing or proposed streets, lanes or easements for the full width of the right-of- way where the city is responsible for maintenance.
A trench or cut shall be defined as that portion of any excavation extending from within 300mm below the pipe to the finished subgrade surface.
A trench or cut is further divided into the pipe zone and the street zone defined as follows:.
1) Pipe Zone
The pipe zone is defined as that area of a trench or cut from 300 mm below the conduit to 300 mm above the conduit.
The method of bedding, backfill and compaction and type of equipment used in water and sewer installations shall comply with:
• Standard Specifications Waterworks Construction
504.03.00
• Standard Specifications Sewer Construction
403.04.00
403.07.01
403.08.02
2) Street zone
The street zone is defined as that area of a trench or cut from: • The top of the pipe zone to the finished sub-grade surface, and/or
304.00.00 UTILITY TRENCH BACKFILL REGULATIONS
36 2012 ISC: PROTECTED
The street zone shall be backfilled in uniform lifts with native material, and each lift shall be mechanically compacted. Thicknesses of lifts are determined by testing procedures during the construction process.
When soils removed from any trench appear unsuitable for replacement in the trench due to moisture content or for other reasons, and suitable material is not available in the construction area, the street zone shall be backfilled with compacted crushed gravel. At the discretion of the Engineer and if trench width permits, base gravel or bank gravel (pitrun) may be used for backfill. Under no circumstances shall frozen material be used for backfill. Positive drainage to the storm sewer system shall be provided from all granular backfill material.
The use of Granulite, drainage gravel and/or other gap graded material as backfill material in the street zone is prohibited unless the material is enveloped in a drainage membrane and positive drainage to the storm sewer system is provided. Please refer to section 320.00.00 – Agricultural Crossings.
304.02.00 – Moisture Requirements
Soil used for trench backfill shall be within optimum to +2% of its optimum moisture content. Subject to approval by the Engineer, the moisture content for the last metre of backfill may be lowered if warranted by soil conditions.
Granular material shall be within -3 percent to optimum moisture content.
304.03.00 – Density Requirements
304.03.01 – Summer Compaction
Table 7: Compaction Requirements for Utility Trench Backfilling Compaction
Percent of Soils Maximum Density Pipe Zone
(Unless otherwise specified) Minimum 95.0
304.00.00 UTILITY TRENCH BACKFILL REGULATIONS
ISC: PROTECTED 2012 37
Requirements apply to the full width of the right-of-way with the exception of the boundary area from the property line up to one (1) meter from the constructed or designed surface installation. In the boundary area the soil shall be compacted to a minimum of 90 percent of the soil's maximum density.
304.03.02 – Winter Compaction
All settlements related to winter backfill operations shall be reworked and re-compacted by the utility to a minimum standard density of 97% of the maximum obtainable density by no later than the following May 31.
304.04.00 – Non-Shrink Fill
Specifications
• Compressive strength two (2) to five (5) MPa. • Aggregate Grading:
Table 8: Aggregate Grading Specifications for Non-Shrink Fill Material
Sieve Size Percent Passing by Weight
5.0 mm 55 - 100
2.0 mm 37 - 67
0.08 mm 0 - 30
PI 10 maximum
• Binder
Portland cement type 10 or Lime/Fly Ash.
304.04.01 – Placing
Non-shrink Fill (N-S Fill) shall be cast on the compacted backfill from one meter below sub- grade to base of asphalt. N-S Fill shall be rodded or vibrated to eliminate voids, rough areas, honeycombing, and to ensure contact with the sides of the trench.
304.05.00 – Control Density Fill
304.05.01 – General
A flowable fill with self levelling properties for trench backfill consisting of fine aggregate, sand and cementacious content, the control density fill shall be resistant to settlement after hydration.
304.00.00 UTILITY TRENCH BACKFILL REGULATIONS
38 2012 ISC: PROTECTED
304.05.02 – Materials
Portland cement shall conform to the requirements of CSA Standard CAN3-A5-M, Type 10 or Type 30.
Supplementary cementing materials, when permitted, shall conform to the requirements of CSA Standard CAN3-A23.5-M.
Both fine and coarse aggregate shall conform to the requirements of CSA Standard CAN3-A23.1-M. The gradation shall conform to Table 1 of the CSA Standard. Mixing water used shall meet the requirement of CAN3-A23.1-M.
Air-entraining admixtures shall conform to the requirements of CSA Standard CAN 3-A266.1-M.
304.05.03 – Mix Design
The supplier shall immediately after award of Tender and prior to any delivery of control density fill, submit to the Engineer for approval, the proposed mix design including source of proposed aggregates.
• Slump of the control density fill shall be between 150 to 250 mm.
• Minimum performance values at one (1) day shall be a CBR of 15 and compressive strength of 0.10 MPa.
• Maximum performance values at twenty eight days shall be a CBR of 60 and compressive strength of 0.60 MPa.
304.05.04 – Trench Restoration
The utility shall be bedded and protected prior to placing the control density fill. It shall be struck off at a level corresponding to 100 mm below the pavement surface or to the bottom of the existing asphalt whichever is the greater.
304.00.00 UTILITY TRENCH BACKFILL REGULATIONS
ISC: PROTECTED 2012 39