S5 Backfill

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 mass passing a 63 micron (µm) BS sieve, and with all material passing a 425 micron (µm) 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 may include Granular Sub-base Material Type 2 to SHW Clause 804 (excluding natural sands and gravels) and Granular Sub-base Material Type 1 to SHW Clause 803.

S5.1.3 Class B - Granular Materials

Materials with a maximum of 10% by mass passing a 63 micron (µm) 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 mass passing a 63 micron (µm) 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 mass passing a 63 micron (µm) 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 The requirements of Appendix A1 shall apply to unbound backfill materials.

S5.1.8 All backfill materials Classes A to D 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 - 124 (as amended by SHW Clause 801.8).

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 the 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 to Apparatus

Preformed modules or other protective measures may be placed within the backfill, according to the Undertaker's requirements.

S5.3.5 Chalk

1) Not used: