 |
|
| SCIENCE & TECHNOLOGY |
|
|
|
Mitigating
quake misery Eco-friendly
pervious concrete Prof Yash
Pal This Universe |
|
|
Mitigating quake misery Sometimes a scientific finding or observation has tremendous impact on safety and security of society. In case the severity of the impact is properly recognised and understood by society and administration, then the adverse impact of scientific findings could be reduced or mitigated to a reasonable extent. But if is neglected then society has to undergo acute stress and a possible gory scenario. The authorised governmental agency for geological studies, the Geological Survey of India (GSI), after three years of field studies has come to a conclusion that the area in Uttarakhand is undergoing a high level of seismic probability. The geological and tectonic conditions are similar in Uttarakhand and Himachal Pradesh and the earthquake could occur in conglomerate of these two states. An earthquake of magnitude 8.0 in the above region could adversely affect the neighbouring states equally. The destruction during earthquake is measured on Modified Mercalli Intensity Scale (MM Scale). If the highest intensity near the epicentre were around IX to X (in Uttarakhand or Himachal) then the area of about 40 to 60 km radius from the epicentre would suffer heavy damage. The area in the 60 to 100 km radius would suffer non-repairable damage. Beyond this distance the damage would depend on various factors such as quality of structure, design, maintenance, geology etc. The area and the distribution of intensity in different neighbouring states will be in the range VI to VIII or so. The States and locations other than Uttarakhand and Himachal are: J & K (Udhampur and Kishtwar), Punjab (Pathankot, Hoshiarpur, Jalandhar, Ludhiana). Haryana (Yamunanagar, Panchkula, Jagadhari), Uttar Pradesh (Muzaffarnagar, Saharan-pur, Bijnore, Moradabad, Bareilly, Pilibhit). These are broad details and give the extent of likely damage. In addition, Delhi, which lies at a distance of about 270 to 350 km from the potential earthquake epicentre would suffer an entirely different type of damage. In National Capital Region (NCR) only tall structures (height more than 17 metres could suffer heavy damage. Houses with one to three floors may not suffer or the damage may be minimal. Similar damage was observed at Ahmedabad located at a distance of 320 km from the epicentre of the Bhuj earthquake of 26 January 2001. At present there is no mechanism to issue any seismic warning to common man. Most of the disaster management agencies come in picture during post-seismic period to clear the debris and corpses. The following is the list of short and very short-term earthquake precursors, which may help the common man to protect from the danger. Water precursors: About two to four weeks in advance, the water level in the wells suddenly rises or the dry wells are filled with water. The flow in river, tributaries or nullahs suddenly rises. Similar observations were found prior to the Gujarat (2001) and Kashmir (2005) earthquake. Thermal precursor: About three to four months before the earthquake the maximum and minimum temperatures go on rising. The readings are +1, +2.... etc (except on rainy days) and on the day of earthquake the temperatures are high by 7.0° to 12.0° C. Seismo-electro-magnetic precursor: As the geo-magnetic field reduces, it adversely affects the propagation, transmission and reception of radio waves. About five to seven days before the occurrence of earthquake, the reception on radio shifts. Suppose a radio station is transmitting at 1000 kHz then the same programme would be received in the potential epicentral area at 1100, 1200,.....1500, 1600 kHz. About three days before the earthquake the reception on landline would be of low quality. Telephones would suffer with repeated noise (Khar-Khar) and disturbances. The disturbances would rise till the time of the occurrence of earthquake. About 10 to 15 hours before the earthquake the reception on television suffers from audio, visual and spectral disturbances. The number of disturbances goes on increasing till earthquake time. About 100 to 150 minutes before the occurrence of the earthquake most of the mobile phones (cell phones) would start mal-functioning or non-functioning. This was observed prior to the Gujarat and Kashmir earthquakes. Abnormal animal behaviour: About 10 to 15 hours before the earthquake all birds, animals, reptiles become restless and make noise. They will not eat or drink but show their restlessness. Domestic animals such as cow, buffalow, bullock, donkey, dog, goat, cat etc become restless and make noise. Birds will not sit on trees or nests but would fly in groups at low height with shrilling noise. Reptiles get frightened and come out from their underground hideouts and move aimlessly in a directionless manner. This has been prior to all earthquakes for last several years. Prior to the earthquake and Tsunami of 26 December 2004, crabs, toads, snakes, turtles and some fishes were restless and came out of water. Ancient Indian scientist Varahamihir has mentioned about this precursor in his book. Abnormal human behaviour: Human beings are also affected. About 10 to 20 hours before the earthquake, there is about five to seven times rise in number of delivery and OPD cases. People get restless and disease symptoms appear without any provocation. Sudden rise in blood pressure, irritation, head-ache, migraine, respirtory troubles etc. are manifested on a large scale in hospital. The abnormal animal and human behaviour is due to rise in charged particles in the atmosphere. The seismo-electro-magnetic, animal and human precursors are seen about 10 to 15 hours before the quake. If such precursors are seen then verify that similar situation exists in all houses and the check by telephoning nearby locations up to 70 km. If such observations are reported from an extensive area, then the probability of occurrence of an earthquake within next few hours could be assumed to be high. At this time switch off electric, water and gas connections in the house and sit in open space away from the collapse range of houses and trees with some food and a portable radio or television. Remember that in the present conditions, it may be difficult to hear any precursory warning from the administration. It is for the common man to watch and draw his own conclusions and save himself. The writer is a research seismologist.
|
|
Eco-friendly pervious concrete Pervious concrete is one of the new and innovative materials which assists in reduction of storm-water run-off in pervious concrete pavements. Pervious concrete in its earliest form has been in use in US for more than 150 years, although it was not until a little over 20 years ago that it was successfully employed in several locations as discussed below. This innovative material comprises of cement, gravel and water (sometimes called as No Fines Concrete also). Absence of sand or fine aggregate permit the properly placed pervious concrete to have about 15 to 20% of void space, which permit water to pass through without causing any damage to the matrix of the porous concrete. In pavements made of porous concrete, percolation allows for a “recharge” of groundwater tables and also the system provides a ‘key-tool’ in effort to reduce storm water run-off. Pervious concrete pavements have also been permitted within ‘drip-lines’ of trees, as the pavements allow a passage of air to the roots. Because the roots receive sufficient air, they tend to grow out and not up, thus preventing the surface of the pavements from “popping-up”. The other known uses for this type of concrete are:- i) Tree protection, ii) Storm water runoff iii) Increase of pervious area on site provided with concrete pavements and iv) Porous under-drain or filter layer under concrete structures.
Design considerations For proper design, one of the steps is to make the system function properly and for that key element is the thickness of the porous or pervious slab. Typical thickness used is around 15 cm. On account of higher stress level around the free edges of the slab, greater thickness needs be provided, in the form of thickened edge or curbing. Value of permeability obtained is around 2000 inches per day. But percolation rate gets controlled by the nature of sub-grade existing below the pavement. If the previous concrete is to be placed in situ, then steps have to be taken for its “rolling” or compaction and for that “steel Pipe Roller” may provide some degree of compaction needed. It is important that concrete placed is not “over compacted” as void space will get reduced, thus losing its important characteristic property. In certain locations, it is essential that below the canal lining, a layer of filter material is provided along with pressure release valves for controlling hydraulic pressure exerted on the canal lining. This is needed to control the stability of the canal lining. Pervious concrete’s pre-cast blocks or slabs can be used. It would also quicken the construction pace. For tackling the problem of waterlogging of Muktsar area of Punjab, it is proposed to “re-line” the canal system. comprising the Sirhind Feeder and the Rajasthan Feeder, to reduce the extent of seepage taking place, which is leading to waterlogging. The type of lining for re-lining proposed is double-tile lining with filter material placed below the lining along with pressure release valve. Instead of providing conventional gravel layer below the canal lining as filter, pre-cast blocks of pervious concrete will result in faster and economical construction work. Pervious concrete provides a new and innovative “green” i.e. eco-friendly mode for providing pavements in many locations without posing a threat to the trees as in the case of the current tile or concrete pavements which tend to choke off the water and air supply to the roots resulting in their slow death. For canal projects also (both for new as well as repair of existing ones) this material will save time and money.
|
|
This Universe How can we measure very long distances in Light Years? For example a star is 8000 LY from earth. How can we be definite about this distance? It is practically not possible. Your question is very natural. Let us start with the basics. You know that we become aware of distance because we have two eyes. It would not be possible if we had only one eye. The direction of an object in front of the two eyes would be slightly different, because the eyes are separated
from each other. Our brain does the calculation of this triangulation problem and gives us a perception of depth, or distance. The first method of measuring distances of stars used a variation of this method. We know that the largest distance between two telescopes on earth could be the diameter of the earth orbit around the sun. This is about 300 million km. The direction of a star far away from us would be slightly different when viewed from opposite ends of the earth orbit. It turns out that for a star a little more than 3 light years away, the difference in angle would be only about one second of arc. This is 1/60x60 of a degree. This is close to the angular resolution of rather large telescopes. Incidentally this angle is called the parallax. With the largest telescopes we might do better but it is not good enough for most of the stars in our galaxy, forget about so many galaxies much further away from our own. The distance of the star nearest to us (called Proxima Centuri) is 4.3 light years. Therefore the method of triangulation does not seem to be very useful for taking the measure of this vast universe. But scientists and astronomers do not give up easily. Where exact measurements are not possible they devise more approximate techniques that suffice to give a general picture. If all the stars were of equal intrinsic brightness then we would be able to estimate their distance by using the simple reasoning that the stars will dim inversely as the square of their distance. But all stars do not have the same intrinsic brightness (absolute magnitude). They are not like standard light bulbs. This problem was partly addressed through the discovery that there were some stars whose luminosity, or apparent magnitude, varied with time and the period of this variation depended on the intrinsic luminosity (absolute magnitude) of that star. These stars are called Cephied variables. Thus knowing both the absolute magnitude and the apparent magnitude one can calculate the distance using the inverse square law. Such stars have also been found in distant galaxies. The method most used for estimating the distances of extremely distant objects is of cosmological origin. In an expanding universe recession velocity of a star is proportional to its distance if we assume a constant rate of expansion. Further the object, faster is the rate at which it moves away from us. The rate of expansion of the universe has been estimated with some definiteness though its exact value keeps changing a little. Fortunately we have a good physical way of measuring recession velocities. This is through Doppler effect that leads to reddening of spectral lines. This parameter is known as the red shift. The red shift then becomes a measure of
the distance. Readers wanting to ask Prof Yash Pal a question can
e-mail him at palyash.pal@gmail.
com
|
