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Cricket pitches and soil mechanics Trends Prof Yash
Pal THIS UNIVERSE |
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Cricket pitches and soil mechanics 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 tours. 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 at 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 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 in contact with the pitch. This
will slow the pace of the ball but will allow for greater turn,
whereas 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 to 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 puncture 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. 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 with 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 per cent of the maximum dry density
tested in laboratory as per IS 2720 Part 7. Laying the top soil: Top
soiled 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. * 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. |
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Trends Researchers at the University of Warwick are examining a way of using bacteria to manufacture a new suite of potential anti-cancer drugs that are difficult to create synthetically on a lab bench. The bacterium Streptomyces coelicolor naturally produce antibiotics called
prodiginines. This group of antibiotics has stimulated much recent interest as they can be used to target and kill cancer cells. A synthetic prodiginine analogue called GX15-070 is currently in phase 1 and 2 cancer treatment trials. However, analogues of other
prodiginines, such as streptorubin B, could be even more powerful anti- cancer tools, but they cannot currently be easily synthetically produced on a lab bench. Beware of cola drinks Middle age and older women may want to limit their consumption of cola-flavoured soft drinks. A new study links regular consumption of these beverages with reduced mineral density of hip bones in women past menopause. No similar hip vulnerability to cola showed up in men of the same age. The gender-specific finding was quite strong, notes Katherine L. Tucker of the Jean Mayer USDA Human Nutrition Research Center on Aging in Boston. Her team looked at study participants’ consumption of other soft drinks, other sources of caffeine, and calcium. Bats are not blind There really is nothing as “blind as a bat” ... because bats are not blind. They are, however, the world’s only flying mammal with more than 1000 species. Some are as tiny as a bumblebee, weighing about as much as a dime while the largest have wing spans approaching 1.8 metres (6 feet). These amazing critters have fascinated and repelled human mammals for thousands of years, but what we know about them is riddled with myths, misconceptions and misunderstanding. Toxin trouble A toxin that can make bacterial infections turn deadly is also found in higher plants, researchers at UC Davis, the Marine Biology Laboratory at Woods Hole, Mass. and the University of Nebraska have found. Lipid A, the core of
endotoxin, is located in the chloroplasts, structures that carry out photosynthesis within plant cells. |
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THIS UNIVERSE What is Dark Energy? We are passing through a unique period in the history of science. Based on observations and experiments in our laboratories, on internal consistency of the theories we had built we were convinced that our universe is structured and controlled only by four types of forces. These were gravitation, electromagnetism, the weak force and the strong force. These forces seemed to account for everything we saw or measured, here on earth or amongst stars and galaxies. There was no measurement or observation that was considered unexplainable. The basic principles incorporating these theories were not violated. The world of physics, chemistry, biology, geology and astronomy threw up nothing that required the existence of any other type of force or energy. We had also worked out theories that helped us to unify at least three of these four interactions. The only residual agenda in this connection was the unification of gravity with all the other forces. Some ingenious experiments looked for a possible fifth force if any. These could only put upper limits of the order of a millionth the strength of gravity but consistent with non-existence. Then came some surprising observations in astronomy and from cosmological theories. Some radical changes in the constitution and history of the universe have been indicated, even though we are far from understanding the science behind them. The proposal for existence of Dark Energy was one of the new hypotheses. This was entirely new. In addition we did have mounting evidence that a dominant fraction of the matter in the universe is not visible to us. It has gravity like all other matter but it is dark, in the sense that it does not emit any detectable radiation. The nature of this Dark Matter is still under discussion even though its existence is observationally is strongly indicated. I find the present situation rather uncomfortable. Till recently we did our physics through observation and theory connected with things and happenings on earth. We had tremendous success in understanding the external universe using the very same physics. Now the distant universe is beginning to suggest objects and laws that are difficult, if not impossible to test here on earth! I, for one, am beginning to have some doubts about the validity of the evolutionary or big bang model of the creation of the universe. In spite of the fact in many respects it seems so simple and compelling. In this regard let me give one of the evidences brought forth to suggest that the bulk of the energy in the universe resides in a repulsive field of Dark Energy. One of the methods used for determining the rate of expansion of the universe is to explore the relation between the red shift of astronomical objects and their distance. It is clear that we would have a handle on the distance of a distant object if it were assumed to be a standard candle and its brightness was measured. The rate at which it is receding from us would be known from the red shift of its spectral lines. A class of supernovae has been used to provide standard candles in this regard. It has been recently discovered that some of these supernovae at large red shifts appear to be too dim to be at the distance indicated by their red shifts if we use the standard value of the Hubble constant. This has been interpreted as indicating that universe has started to expand much faster than believed; this then is taken as an indicator of a large repulsive force embedded in the fabric of the universe. The energy associated with this force is the so-called Dark Energy! I cannot help being a little skeptical. Do we have enough confidence that the few supernovae we have used are truly standard light sources? Are we sure that the dimness of the sources is not due to absorption of their light by intervening dust clouds? Perhaps these doubts would be removed in time. However one is still left with a feeling that parameters are being chosen, somewhat arbitrarily, to make the universe completely consistent with the dominant model of big bang cosmology. We might end up getting a good parametric fit without true physical foundation. That would be, at best, some tentative progress, not a proper understanding. |
