It is a good idea at this stage to give an example of a general pitch construction design for the sand-gravel slit installation that is being considered.
With an example of the design for this situation it will be much easier to determine the type of materials that are required as well as the overall quantities of materials that are required within the construction of the pitch.
An example of how the design arose may be as follows:
- The design has been based on an existing field with a soil of a heavy nature that puddles when it rains.
- It is also expected that 2 adult games will be played each week throughout the season (of 36 weeks) along with a number of cup and similar games. The total number of games is estimated as 90, which equates to 135 hours of use.
- The pitch is located in the North of England and minimal cancellation potential is required. However, the pitch is not to be designed so as games could still go ahead following exceptionally heavy downpours as this would be too prohibitive for the available budget.
- The design rate for the pitch is set at 2 mm/hr (or 48mm per day), which should theoretically accommodate the heaviest 24 hour rainfall expected in a 10-year period for the North of England.
- The pitch is expected to be maintained to an intermediate Performance Quality Standard, which is 'Standard' Quality (in contrast to 'High' or 'Basic') and is to reflect the good club level pitch that is required. Pitch usage is to be included as part of the overall management plan to ensure the quality of the pitch is maintained at the correct level.
The sand-gravel slits are to be at 1 m spacings, 250mm deep (100mm of sand overlaying 150mm of gravel) and 50mm in width.
As the pitch is being constructed on a field with a soil of a heavy nature, there will be a 12mm sand layer spread over the whole of the pitch (up to and including the perimeter drains) and worked into the existing sward. This will help to reduce or eliminate the potential for a corrugated surface to develop which can be a consideration on heavy soils.
Once a sand-gravel slit pitch has been constructed it is essential that regular sand top-dressing is applied as part of the ongoing maintenance programme. This is needed to ensure that the slits are kept open and remain functioning at the surface.
This will prevent the slits from sealing over with heavy soil which would otherwise result in a surface of poor playing quality.
Material Specifications
It is usually advisable for all materials which are to be used in the project to be approved by the Customer well before any material reaches the site.
Details of suppliers and samples should be provided within a stated time period (typically 14 days) after the contract has been awarded and before any work commences on site.
It will still be up to the Contractor to ensure that the materials are consistent and true to the original sample throughout the period of the contract and they comply with the relevant material specifications.
Delivery notes for materials may be requested as evidence of materials used.
Each individual material specification will need to be written to suit the particular situation, however, the details provided below could be used as a general starting point, although it is important to remember that they are illustrative examples only.
The minimum hydraulic conductivity rates should be determined by the requirements of the calculated design rate for the drainage system.
In addition, the particle size analysis should be appropriate for the design rate and availability of material.
There is little point specifying a material that may theoretically be ideal, but which cannot be sourced anywhere.
Depth, width or spacing of slit and spacing of laterals can be adjusted to accommodate materials that can be sourced more locally, although the material must obviously be suitable for the task. In addition the design rate may be adjusted to take into account the micro-climate of a site as this may be significantly different from data produced by a regional weather station.
Within the material specifications themselves, additional consideration may also be given to stating the desired shape of the gravel / sand particle, for example 80% of gravel to be sub-rounded to sub-angular.
Materials
(A) Drainage Trench Backfill Material
(1) Gravel: (typically 6 - 9mm, or 5 - 10mm diameter) or Lytag (typically 3 - 6mm diameter)
(2) Particle size analysis (by weight) for the 6 - 9mm gravel to be
- > 9mm: Maximum 10%
- 6 - 9mm: 10 - 60%
- 3 - 6mm: 10 - 60%
- < 3mm: Maximum 10%
Similar percentages would be used for the other trench backfill material.
(3) Hydraulic Conductivity: Minimum of 50,000 mm/hr
(4) The material must be resistant to crushing
(B) Sand Blinding Layer for Drainage Trench
(1) Particle size analysis (by weight) to be:
- 2.0 - 4.0mm: Maximum 15%
- 1.0 - 2.0mm: 20 - 80%
- 0.5 - 1.0mm: 20 - 50%
- 0.25 - 0.5mm: 10 - 30%
- < 0.25mm: Maximum 10%
(2) Hydraulic Conductivity: Minimum of 2,000 mm/hr
(C) Sandy-Soil Layer for Drainage Trench
(1) Particle size analysis (by weight) to be:
- 1.0 - 2.0mm: Maximum 5%
- 0.5 - 1.0mm: 10 - 30%
- 0.25 - 0.5mm: 10 - 50%
- 0.125 - 0.25: 10 - 30%
- 0.053 - 0.125mm: 5 - 15%
- less than 0.053mm: 5 - 15%
(2) Hydraulic Conductivity: Minimum of 50mm/hr
(3) Soil pH: 6.0 - 6.5
(D) Gravel for Sand-Gravel Slits
Fine Gravel: 3 - 6mm size (or Lytag)
(1) Particle size analysis (by weight) to be
- > 6mm: Maximum 10%
- 3 - 6mm: 80-100%
- < 3mm: Maximum 10%
(2) Hydraulic Conductivity: Minimum of 30,000 mm/hr
(3) The material must be resistant to crushing
(E) Sand for Sand-Gravel Slits
An accurate analysis would be provided once the precise analysis of the gravel is known, with a greater amount of coarse sand being stated if the gravel was mainly nearer 6mm than 3mm.
(1) Particle size analysis (by weight) to be:
- 1.0 - 2.0mm: Maximum 5%
- 0.5 - 1.0mm: 10 - 30%
- 0.25 - 0.5mm: 50 - 80%
- 0.125 - 0.25: 10 - 20%
- less than 0.125mm: Maximum 10%
(2) Hydraulic Conductivity: Minimum of 500 mm/hr
(F) Sand for 12mm Top-dressing Layer
(1) Particle size analysis (by weight) to be:
- 1.0 - 2.0mm: Maximum 3%
- 0.5 - 1.0mm: 5 - 20%
- 0.25 - 0.5mm: 40 - 60%
- 0.125 - 0.25: 20 - 40%
- less than 0.125mm: Maximum 10%
(2) Hydraulic Conductivity: Minimum of 200 mm/hr
(G) Pre-seeding Fertiliser
- Mini-granular type
- 6% nitrogen / 9% phosphate / 6% potash
- or to be of a similar type with a unit ratio of 1:1½:1; ±10% of either nutrient.
(H) Spring / Summer Fertiliser
- Mini-granular type
- 10-20 % nitrogen / 5-10% phosphate / 5-10% potash
- or to be of a similar type with a unit ratio of 2:1:1; ±10% of either nutrient.
(I) Autumn Fertiliser
- Mini-granular type
- 4 - 11 % nitrogen / 2 - 6% phosphate / 4 - 10% potash
- the nitrogen content will depend at what stage of the autumn the fertiliser is applied.
(J) Grass Seed for Football Pitch
- 100% Perennial Ryegrass, consisting of three different turf-type cultivars, each being one-third of the total.
The cultivars may also be named, or alternatively those within the STRI's annual Turfgrass Seed publication that meet a certain level of criteria may be deemed as acceptable. For example, Perennial Ryegrass Cultivars should appear in both the top 25% of cultivars for football type use within the wear tolerance criterion, plus the top 33% from the visual merit criterion.
In addition it may be considered appropriate to state that one, two, or all cultivars used have also been in the lists for at least three years and state some criteria that they should have achieved over the period of time.
(K) Grass Seed for Reinstatement of Surrounds
- 10 - 40% Chewings Fescue;
- 10 - 40% Strong Creeping Red Fescue
- 5 - 20% Browntop Bent
- 0 - 30% Smooth Stalked Meadow Grass
- 10 - 25% Perennial Ryegrass
The cultivars may also be named and qualified by various criteria as stated in the seed for the football pitch. For example, Strong Creeping Fescue Cultivars must appear in the top 50% of cultivars for the mean figure for shoot density and visual merit.
(L) Drainage Pipes
These should be in accordance with BS 4962 and should be UPVC flexible, perforated and corrugated.
The diameter of the pipes should be:
- Perimeter pipes: 100mm internal diameter (110mm external diameter)
- Lateral pipes: 53mm internal diameter (60mm external diameter)
(M) Drainage Pipe Connections
All of the pipe connections should be purpose made in accordance with BS 4962.
(N) Material for Manholes/Inspection Pits/Silt Traps/Outlets etc.
Wherever possible quote the current British Standard for material that is to be used within this section.
The outlet pipe should be a rigid drainage pipe (state diameter, e.g. 150mm) in accordance with BS 4660.
Silt traps (state size, for example 900 x 600mm) may be constructed with bricks that should be in accordance with the relevant British Standard., with Class B engineering bricks being used.
Mortar and concrete should comply with codes of practice / specifications for Highways Works to ensure the material is laid and compacted in the correct conditions. For example, concrete should not be mixed when the air temperature is at or below 38° F and the concrete itself has a temperature of between 41° F and 90° F when deposited.
Manhole covers should comply with BS 497 and state size, for example 600mm x 450mm.
Where steps are to be used within inspection pits then these should comply with BS 147.
Manholes may be constructed from precast concrete sections that comply with BS 5911: Part 1.