Unless instructed otherwise the Contractor shall use topsoil stockpiled as part of the site clearance works. Should there be a shortage of stockpiled topsoil then the Contractor shall obtain the approval of the Engineer for the importation of topsoil from sources external to the Site.
All topsoil shall be spread to a uniform layer thickness, as shown on the approved drawings or as instructed by the Engineer, over all exposed earthworks surfaces to be grassed. The topsoil shall be clean friable soil, free from excessive amounts of gravel, have less than 20% sand and have no other debris or fragments which, in the opinion of the Engineer, could affect later plant growth or maintenance.
The topsoil shall not be spread when the ground or the topsoil is excessively wet or plastic or otherwise in a condition detrimental to successful construction of the work. If the Engineer approves placement of the topsoil when it is wet or plastic then it shall be loosely spread and traffic kept off and the topsoil allowed to dry before being worked.
For larger scale spreading, the topsoil shall be smoothed with a chain-harrow or similar towed by a light tractor to produce a smooth, evenly graded, open textured surface, free draining and which will not pond water. All minor depressions, wheel marks and other irregularities shall be eliminated.
For smaller scale spreading, the topsoil shall be lightly compacted or consolidated and shall be laid proud of adjoining features (such as kerb and channel, path, crossings, etc) by not more than 25mm to allow for settlement provided that it does not cause water to pond on any footpath or vehicle crossing area.
All finished levels shall be those specified on the approved design plans or to a 2 to 2.5% slope. New areas shall be neatly contoured into adjoining grassed areas. The top 25mm of topsoil shall have a loose tilth. No soil shall be cultivated or handled when the moisture content is at a level where soil structure damage will result.
Definitions in this section