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CONSTRUCTION OF CRICKET PITCHES - A SCIENTIFIC APPROACH:

(By: Daljeet S. Sidhu)

The game of cricket is more dependent on the quality of the playing surface than any other sport. Good cricket can only be played if a pitch provides consistent ball bounce of an acceptable height, with the ball coming off the pitch onto the bat at a fast enough pace to make a lively and entertaining game. It is a widely held belief that the quality of pitches in India is a major factor for poor performance on overseas tour. Our batsmen are habitual of slow and low bounce. They hardly have any practice on fast and bouncy pitch. This article is an effort to start a debate to explore the use of principals of Soil Mechanics and Engineering Techniques in construction of fast and bouncy pitches.

Let us have a look on the structural component of a typical cricket pitch:

It consists of

1.         Compacted Bed                      2.        Base (compacted Gravel and Sand)

3.         Layer of clayey loam and     4.        Top Soil

Compacted bed is the  natural earth base over which the base material consisting of natural crushed gravel and Sand is laid and compacted to the maximum density with heavy rollers of 6-8 ton capacity. Its function is to provide the support to the top layers and drain out the excessive water from the upper layers. Intermediate coarse sand layer is provided where top layer is of shallow thickness and base is of coarse gravel, it acts as a filter for fine clay particles. The top layer is the very vital part of the cricket pitch it  consist of combination of Clay + Silt + Sand. The ratio of the these soil ingredients governs the pace, bounce and spin characteristics of the cricket pitch. Higher sand content in the top soil will help to provide grip to the ball when it comes into contact with the pitch. This will slow the pace of the ball but will allow for greater turn. Where as clayey soils have a high binding strength which is responsible for pace and bounce. The greater the binding strength of soil the greater the pace and the higher the bounce. The inorganic materials present in top soil causes the damping effect and slow down the pace and lower the bounce.

Construction Steps:

Layout of the pitch: The pitch is laid  running from north to south, it is 74 feet long (including return crease)  and 12 feet  wide at appropriate place keeping boundary in view so that centre of Pitch and Filed should coincide.

Excavation of trench: the trench is excavated to the required thickness varying from 12 -18 inches depending upon the individual requirements. The excavated surface is checked for its percolation properties, if it does not allow water to percolate in case of clayey soils 6 to 8 inches dia bore holes should be dug at spacing 3 feet in all directions sufficient deep to puncher the impervious layer and fill it with clean sand filled in layers and compacted so that it work  as a drainage system. The bed is then compacted with heavy road roller upto the 95% of maximum dry density as per IS:2720 Part-7. Line the vertical sides of the excavation with polythene/plastic sheet to prevent encroachment of invader grass species of out field.

Lining of vertical sides of Pitch trench with polythene sheet

 Laying of the Base Course:

The base course is laid with well graded crushed  gravel passing through 1/2” sieve and compacting it at predetermined  water content and dry density with a heavy road roller to the maximum dry density in 3 inches layers.

Laying of intermediate Coarse Sand layer:

This layer of Coarse Sand is provided to serve as filter layer. It stop the washing away of top soil into the gravel of base layer. It is compacted heavy road roller flooding is also helpful in compaction of sand. Compaction should be checked with cutting core while layer is wet enough, sample should be dried in oven at 105 degree centigrade for 6 hours. Dry density is = dry weight / volume of core. It should be at least 95% of the maximum dry density tested in laboratory as per IS 2720 Part 7.  

Laying the top soil:

Top soil is most important delicate part of the pitch structure. Generally it is   4-6 inches deep but For good pace and bounce it should have 6-9 inches thickness. If the thickness of top layer is more than 6 inches the top 4 inch should be pure pitch soil rest can be loamy soil.  Thickness of top layer is generally governed by local environmental conditions. Deep pitches don’t dry easily in humid areas.

Properties of Top Soil:

a) Composition:-The top soil should have of 30-50 % of clay, 30-50% Silt, 10-15% coarse Sand,  Organic matter 3-8 % Linear shrinkage:    8 -15%, Free Swell Index 15-35% Calcium carbonate &  Sodium should not be more than 5% and PH value above 5.5.

b) Binding Strength:-Roll the soil into a worm approximately 0.5 inch in diameter on a plate and cut into cylinders 1 inch long. Carefully mould each cylinder into a Motties (Balls) and then roll between the palms of the hands. Place the two sets of Motties onto clean plates and allow to air dry in a cupboard for 5 days (sun or oven dried samples crack due to shrinkage thus does not give representative results).  Place each dried Motty in turn on a metal plate placed on a zeroed bathroom scale and break by slowly increasing foot pressure on a small flat metal plate placed on top of the Motty. Note the reading on the scale when the Motty breaks.  Discount the lowest value in each set and obtain the mean value of the rest. Soil with Readings between 70 and 125 kg are considered good top soil for fast pitches.

Seive analysis & Hydrometer analysis to find % age of clay

Binding Strength Test

 The naturally available top soil may need addition of one or other type of soil to make it good top soil. Fortunately in India vast variety of soils are available. The one sample of top soil Taken form Village Pamal Near Ludhiana has the following properties.

Coarse Sand 5%, Silt 50% and clay 45% (Tested as per IS 2720 Part-4) Liquid Limit 44% Plastic Limit 28% and PI 16 (IS 2720 Part-5), Linear shrinkage 11% (IS 2720 Part-20), Free Swell Index 25% (IS 2720 Part-40)

and strength (½” x 1” cylinder of soil converted into motty) 95 Kg. simply adding some 5 % of fine sand will make it good top soil. The most of pitches constructed with this soil has become slow with passage of time due to poor laying, irrigation, compaction and maintenance techniques.

 Laying and Compaction of Top Soil:

The adopted proportion of mix is tested in laboratory for its optimum moisture content and corresponding maximum dry density as per IS 2720 part 7 and tested chemically for its fertilizer requirement for growth of grass. The mixture is laid in 2 inch thick layers and compacted to the maximum density with heavy roller weighing more than 1500 Kg. Before laying further layer previous layer should be scarify to make good bond between the layers. If layers are formed in the top soil the grass roots don’t go deep in the deeper layers during shrinkage pitch disintegrates and pieces comes out easily. Consolidation (Removal of water from soil mass with applied force) is a slow process it takes long time. Whereas compaction (Removal of air from soil mass with applied load) is easy but does not serve the purposes incase of cricket pitches. The top soil should be consolidated to achieve at least 85% of the maximum dry density determined as per IS 2720 Part 7. Rolling is based on a compromise to keep grass alive and get the firmest wicket possible.  After compacting the top surface is made level with straight edge the permitted unevenness in 3 feet long straight edge is 1/16 inch (3 mm).

Planting The Grass:

Plant sprigs 40 mm apart or spread sprigs over the area after watering, cover with a thin (5 mm) layer of finely crushed bulli and roll with a light roller. Once established, top dress to level three or four times. Fertilise monthly, irrigating the fertiliser in. Roll in all directions - across, diagonally and in line with the pitch. Repeat this often after flooding (with fine mist sprinkling set) Cut regularly to a height of 20 mm.

Testing of Pitch:

The pitch is tested for its bounce by free dropping a hockey ball having same weight as cricket i.e 156 g from a height of 3 M and the bounce is noted. The bounce should be uniform. The quality of pitch is classified from the bounce as given below

Some Important Points:

*           The pitch should not be played on during the first season to allow for good root development

*           A heavy roller should not be over-used when the pitch is too dry. It will promote surface crumbling and horizontal shearing.

*           Core should regularly be cut out to know the amount of compaction achieved.

*           The final roll is designed to give a glazed surface. A light roller is used after water has been sprinkled onto the surface so that it becomes slightly pugged. (means workable and kneaded clay with water).

*           Slow rolling as opposed to fast rolling. Slow when damp, and faster when drier. Slow in the morning and fast in the afternoon

*           The slope of the pitch should not exceed 1% and it should follow the slope pattern of the oval

*           The pitch square should be about 75mm above the level of the outfield to allow for surface drainage off the pitch.

*           Irrigation is best done by using sprinklers which give a fine mist spray. Large droplets or free flooding are likely to wash away the binding clay particles and cause potholes on the pitch. Avoid pools of water lying on the pitch surface. Water penetrates very slowly in top soil. Loose water drags fine clay particles in deeper layers and spoil the top soil quality.

*           There should be no mat of grass and the surface soil should be visible between the blades of grass.

*           Before laying the top-soil, it should be air-dried and rolled on a hard surface (e.g. a car park) to ensure a degree of uniformity in particle size. This also allows an opportunity to remove stones, roots and other unwanted debris

 Bill of Quantities and Cost

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Disclaimer: (The information provided herein are for general guidance and is intended to provide general information only before actual construction of a pitch follow the rules framed by governing body of your area. www.beforeconstruction.com   does not take any responsibility on any account)