« Previous | Contents | Next »
Listen
SPECIFICATION FOR THE REINSTATEMENT OF OPENINGS IN ROADS
S5 Backfill
S5.1 Backfill Material Classification
S5.1.1 General
Backfill materials, whether imported to site or derived on-site from excavated materials, shall be classified as follows:
S5.1.2 Class A - Graded Granular Materials
1) Materials with a maximum of 10% by weight passing a 63 micron (m) BS sieve, and with all material passing a 425 micron (m) BS sieve showing a plasticity index of 6 or less, determined in accordance with BS1377: Part 2: Method 5.4, are classified as Class A Graded Granular Materials.
2) Class A graded granular materials shall include Granular Sub-base Material Type 2 (excluding natural sands and gravels) and Granular Sub-base Material Type 1.
S5.1.3 Class B - Granular Materials
Materials with a maximum of 10% by weight passing a 63 micron (m) BS sieve are classified as Class B Granular Materials.
S5.1.4 Class C - Cohesive/Granular Materials
Mixtures of granular, silt and clay materials with between 10% and 80% by weight passing a 63 micron (m) BS sieve are classified as Class C Cohesive/Granular Materials.
S5.1.5 Class D - Cohesive Materials
Clay, silt or mixtures of clay and silt with at least 80% by weight passing a 63 micron (m) BS sieve are classified as Class D Cohesive Materials.
S5.1.6 Class E - Unacceptable Materials
Materials listed as unacceptable in paragraphs 2 ii) and 3 of SHW Clause 601 shall not be used, at any level, within the permanent structure of any reinstatement. Materials classified as unacceptable are listed in Appendix A1.
S5.1.7 All backfill materials shall be used in accordance with Appendix A1.
S5.1.8 All backfill materials shall be compacted in accordance with Appendix A8.
S5.2 Alternative Reinstatement Materials
S5.2.1 Alternative Reinstatement Materials (ARMs) may be used for the entire backfill layer, or any part thereof, in accordance with Appendix A9.
S5.3 Additional Requirements
S5.3.1 Frost Heave Susceptibility
1) Frost susceptible material is deemed to be material with a mean heave greater than 15 mm when tested in accordance with BS 812: Part 124: (as amended by SHW Clause 705).
2) Where frost susceptible materials already exist within 450 mm of the surface, such materials may be reinstated to the same levels but, generally, frost susceptible material shall not be used within 450 mm of a road surface. However, 300 mm of wholly bituminous material is considered to provide adequate insulation and may be used as an alternative.
3) In the event of prior notification by the Authority, where the existing depth of non-frost susceptible materials is greater than 450 mm below the road surface and the Authority requires such a thickness of non-frost susceptible material to be maintained, then only non-frost susceptible materials shall be used for the relevant depth.
4) All frost heave susceptibility testing shall be carried out by a laboratory holding current UKAS accreditation for specified method of testing, unless otherwise agreed.
S5.3.2 Maximum Particle Size
The maximum particle size for all granular backfill materials used as backfill shall comply with the following requirements:
1) All granular backfill materials shall pass through a 75 mm BS sieve.
2) All granular backfill materials used in the reinstatement of trenches less than 150 mm wide shall pass through a 37.5 mm BS sieve.
S5.3.3 Surround to Apparatus as Backfill
Where the excavation depth does not allow the use of a separate backfill layer, the sub-base layer shall be laid directly onto the surround to apparatus. In such cases, the surround material shall represent backfill material and shall be classified in accordance with Section S5.1, for the purposes of determining the requirements for sub-base reinstatement in accordance with Section S6.2.
S5.3.4 Protective Measures
Preformed modules or other protective measures may be placed within the backfill, according to the Undertaker's requirements.
S5.3.5 Chalk
1) Imported chalk materials used as backfill shall comply with the following requirements:
a) The saturation moisture content of the chalk shall be determined prior to its use.
b) The chalk shall be laid and compacted to an approved compaction procedure developed in accordance with Section NG1.6 3). The compaction procedure shall be proven with chalk materials of similar saturation moisture content.
2) Excavated chalk to be re-used as backfill shall comply with the following requirements:
a) Excavated chalk shall be stockpiled for re-use and shall not be subjected to multiple handling.
b) During wet weather, excavated chalk shall be protected against water ingress at all times.
3) Chalk materials shall be assessed by breaking up excavated fragments by hand, or by driving a steel pin into unexcavated deposits, and classified in accordance with Table S5.1. If the classification falls between two densities, then the chalk shall be assumed to be at the lower of the two densities.
Chalk Density | Physical Assessment | Backfill Suitability |
High | Very difficult/impossible to break up by hand
Difficult to hammer in steel pin | Carriageways, footways & verges |
Medium | Some difficulty in breaking up by hand
Some effort needed to hammer in steel pin | Footways & verges only |
Low | Easy to break up or crush by hand
Steel pin can be pushed in by hand | Unsuitable for use in any reinstatement |
Notes to Table S5.1:
1) Chalk often contains flint inclusions and care should be taken to ensure that:
a) the steel pin does not strike a flint
b) the hand crushing sample does not contain any flints. |
Table S5.1 - Suitability of Chalk Materials for Use as Backfill
4) Chalk materials shall be compacted in accordance with Appendix A8.2.
« Previous | Contents | Next »