Fibre-reinforced soil
by G. S. Dhillon
THE art of stabilisation of weak soils can be traced as far back as 5th century BC. We find that while building the Great Wall of China, the clay soil was admixtured with tamarisk branches and the historical building of Agar-Qut Ziggwarat of Baghdad, the dry clay (unburnt) bricks were reinforced with reed and straw.

Feb 28 : The day of Raman Effect
by Surjit Singh Bhatti
NATIONAL Science Day is celebrated every year in India to commemorate the announcement of the discovery of “Raman Effect” on February 28, 1928 by Sir C.V. Raman.

Fibre-reinforced soil
by G. S. Dhillon

THE art of stabilisation of weak soils can be traced as far back as 5th century BC. We find that while building the Great Wall of China, the clay soil was admixtured with tamarisk branches and the historical building of Agar-Qut Ziggwarat of Baghdad, the dry clay (unburnt) bricks were reinforced with reed and straw. The addition of straw of wheat or “turi” to the clay-mud plaster is also well tried and ancient.

This art came to be analysed through experimentation and the various parametes of soil strength characterised in early 1930s and the science of soil mechanics came into being, in which the “soil stablilisation” formed an important part. The admixtures used were those of lime, cement or well graded sand-gravel mixtures.

The concept of soil reinforced with fibres, came to be introduced around 1960s. The technique provided composite material formed by introduction of flat reinforcing strips horizontally in a frictional soil (sandy soils). Due to interaction between the soil and the reinforcement surface, greater frictional resistance is provided or increased in the angle of the internal friction of the soil i.e. the parameter governing the strength characteristics of the sandy soils.

The resultant interaction transmitted stress from the soil particles to the reinforcement and this resulted in stressing both soil and the reinforcement provided. The material behaved as a “composite material having improved properties”.

The above concept found large acceptance. For example, in Singapore it is essential to build all the embankments uitilising this technique as it saved valuable space and earthen embankments with very steep slopes could be built. Even at Ludhiana this technique has been adopted while building approaches to the overbridges where geo-fabric reinforcement has been used with great success.

Types

The soil reinforcements determined useful can be broadly classified into two categories: (i) inextensible inclusions e.g. metal strips and bars, (ii) extensible inclusions e.g. natural fibres or synthetic polymeric fibres. The soil composite obtained with polymeric fibres is usually called PLY soil.

The inclusions normally used have rupture strain greater than the maximum tensile strain the unreinforced soil can withstand. The function of the reinforcement amounts to imparting some strength but more important the ductility or greater extensibility before failure and smaller loss of post-peak strength compared to the original soil or unreinforced soil.

It is found that the “inextensible inclusions” get ruptured at strains less than the maximum tensile strain in the unreinforced soil and result in catastropic failures whereas the extensible inclusions can take up large strains and seldom rupture.

The influence of root on the shear strength and stability of the natural slopes is well known. The degree of increased strength imparted by the roots depend on the concentration and properties of the roots. The increase in strength of threefold can be obtained with the concentrations of roots varying between 0.2 and 1.0 per cent.

But this category of reinforcement has been found to have low resistance towards attack by alkalies and other chemicals. The other natural fibres like jute, bhabar, hump, munja, sisal, banana have tesed and found to be loose in strength when subjected to alternate “wetting & drying” in environment created by lime solution’s presence in the soil.

But the coir fibres have been found not to exhibit any loss of strength when subjected to the procedure listed above, i.e. alternate wetting and drying in lime saturations of the soil. The coir fibres have been found to have good strength characteristics and resistance to bio-degradation ove a long period of time.

Synthetic fibres comprise polypropylene, nylon and plastics and have greater resistance to attack by acids and alkalies or other chemicals. The polypropylene fibres have high tensile strength and melting point to 1650 C. Though this category has inherent defect of getting affected by the ultra-violet rays from sunshine but for buried material this negative point is not there.

Asbestos, glass, carbon fibres have been found to be resistant to alkalies and other chemical’s attack, but long exposure to such adverse environment in the case of asbestos fibres has been found to lead to corrosion damage.

Placement

The mode of placement of fibres in the soils is an important aspect. Any of the two modes is usually adopted. The fibres may be placed in a preferred direction or in random manner in the soil mass.

In oriented fibre-reinforced soils, the fibres are placed along a certain direction or at an angle with respect to expected shear failure plane. The optimum angle of placement with respect to the shear plane is found to be 600 and the minimum length of fibre to be 120 mm. But the task to do such placement is very tedious and so involved that except for the experimental research purposes, such mode is seldom adopted in practice.

In random method (RDFS), the fibres are mixed with the soil, in the same fashion as the the cement or lime or flyash, as done for stabilising a weak soil. This results in random distribution of fibres in the soil mass.

The inclusion of discrete fibres results in a significant increase in shear strength of soil. The main advantage of this mode is the ease of mixing, maintenance of strength isotropy and absence of the potential planes of weakness that develop parallel to the oriented reinforcement.

This mode can advantageously employed as a ground improvement mode, with respect to embankments and other similar problems.

Review of the published material relating to RDFS indicate the following:

• Kaolinite clay when impregnated with paper pulp fibres, show the increased strength, the effective angle of internal friction increases from 200 to 310 and composties acquire greater stiffness.
• Fine grained sand reinforced with discrete mild steel fibres has been found to acquire increased strenth as shown by the increase of angle of internal friction to 430 to 360 for the parent soil.
• Angular crushed sandy gravel (0.6 to 5.0 mm) mixed with polypropylene fibres was found to impart increased shear strength and the extent of increased was found to increase with increase of percentage of fibres up to 3 per cent.
• In the case of flyash, reinforcement with randomly distributed synthetic fibres has been found to improve the strength of the flyash reinforced sample.
• The inclusion of fibres result in significant increase in shear strength of sandy soils and the sand fibre composite could sustain large axial strains exhibiting greater ductility in the composite. In the case of silty sand and clayey soils the inclusion of fibres shows increased cohesion (though the angle of internal fricition may remain unaffected, yet there is an overall gain in strength). The increase in strength in the form of bearing capacity of soil for the sandy soils is found to increase with the increase in the concentration of fibres upto 2 per cent. However the campaction tests reveal that the presence of synthetic fibres offered resistance to compaction, resulting in lower “dry density”.
  
  
  

Feb 28 : The day of Raman Effect
by Surjit Singh Bhatti

NATIONAL Science Day is celebrated every year in India to commemorate the announcement of the discovery of “Raman Effect” on February 28, 1928 by Sir C.V. Raman. Earlier, Raman had sent a communication, jointly with K.S. Krishnan, on this discovery, to the British journal Nature. The Paper was published on March 31, 1928 and stunned the entire scientific world on account of its simplicity on the one hand and profound significance, on the other.

Raman’s discovery stands out much above the works of many of his contemporaries as the experimental equipment was of the simplest type, mostly hand-assembled. It consisted of just a pocket type spectroscope and a mercury lamp. Yet this discovery is in the same class as X-rays. Overnight, Raman joined the grand band of the German spectroscopists represented by Fraunhofer, Bunsen and Kirchoff. At the time of Raman’s death in 1970, the number of applications of Raman Effect had become so large that more that 10,000 research papers had been devoted to describe these. Today, Raman is as well-known throughout the scientific world as Newton, Young, Helmholtz or Rayleigh.

The starting point of his investigations, which ultimately led to the discovery of Raman Effect, was his observation of the deep blue colour of the Mediterranean during his first voyage of Europe in 1921. The blue colour of the sea or of the sky, he found, is due to elastic scattering of light by molecules of water or air. While all light rays of other colours are, largely, absorbed and converted into heat, the blue colour rays are diffused back. Blue of the sea is not simply the reflection of blue of the sky, as Lord Rayleigh had said. Also, the wavelength of a part of the incident beam is changed by the scattering medium. The observed changes yield information regarding the medium, including its molecular structure.

The Raman spectra of molecules of the scatterer gives the basic elements of their symmetry, thermodynamic quantities and functional groups. Using the powerful, monochromatic lasers as the source it is possible now to analyse most inorganic, organic, gaseous and crystalline systems, specially those used in industries. It is not surprising therefore, that in December, 1930, C.V. Raman was awarded the Nobel Prize for Physics which is the highest international honour. This was the second such honour conferred on an Indian after the Nobel Prize for literature given to Rabindra Nath Tagore in 1913.

Raman’s contributions to science, however, were not limited to the discovery of the optical effect bearing his name. He studied gemstones, diamonds, violin, piano and veena, drums, physiology of vision and magneto-optics. The colour of foliage, flowers and crystals had a special charm for him. He also gave a theory, along with N.S. Nagendra Nath, regarding the diffraction of ultrasonic waves which are used in various high-speed information processing systems today. Besides, he set up a unique institute called Raman Research Institute at Bangalore after his retirement as Director of the Indian Institute of Science. Above all, Raman lit the torch of scientific research for a large number of his students and others who have done much distinguished work.

It is natural and appropriate that the day of announcement of this important discovery of “Raman Effect”, considered to be among the best three or four of the century, be celebrated as National Science Day of India. For, it not only reminds us of Raman’s works, it also inspires us to work for science despite our infrastructural handicaps. The future belongs to those who can excel in science and technology. India can enter the 21st century with confidence if the youth of India today in colleges and universities, specially those who are studying science, draw inspiration from the works of Indian scientists like Sir C.V. Raman and work hard.

The writer is from the department of applied physics, Guru Nanak Dev University.

1. A space observatory (an orbiting telescope) to be launched abroad the US space shuttle Columbia in April, 1999, has been named after an India-born astrophysicist who shared the the 1983 Nobel Prize in Physics. Name this astrophysicist. In which aspect of astrophysics did he make his main theoretical contribution?

2.Which medium is generally used for preserving embryos, tissues ets. for a long period for later use? At what temperature are these preserved? What is this techinque of preservation called?

3. FOIP is a new name in Internet technology. What does FOIP stand for?

4. Organic compounds like bezene, which have ring like structures made of six carbon atoms, constitute a particular group with a common name. What is this name?

5. What is the name given to a biological rhythm having a duration of about a day that involves a cyclic variation in the intensity of a metabolic or physiological process in an organism?

6. The colours of the strips of a carbon registor from its end are respectively violet, black and golden. Neglecting tolerance, what is the value of its resistance?

7. A duck can comfortably move this way or that on the surface of water in a pond by ejecting oil from its feathers. Which property of water explains this?

8. Which disease is caused when too many white blood cells are formed in blood and they interfere with many body functions, lowering body’s defences?

9. What is common about “tiger oscar”, kissing garami”, “pearl cichlid” and “silver dollar”? 10. CSIR is an apex body in India whose main function is to conduct, promote, guide and coordinate scientific and industrial research in India through a huge network of laboratories and institutions. What is the full name of this body and where are its headquarters?

Answers:

1. Subramanyam Chandershekhar; structure and evolution of stars. 2. Liquid nitrogen; minus 196 degree celsius; cryopreservation 3. Fax over internet protocol 4. Aromatic compounds 5. Circadian rhythm or clock 9. Seven ohms 7. Surface tension 8. Leukemia 9. These are varieties of fish 10. Council of Scientific and Industrial Research, New Delhi.

Nearly invisible galaxies

Dark galaxies, which give off little light despite massive amounts of matter, may fill most of the universe, AFP reports, quoting US astronomers.

“There might be in our universe a large population of dark galaxies that contain too few stars to be discovered,” said astronomer John Kormendy of the University of Hawali.

“They very well may outnumber all the luminous galaxies combined,” he said.

Unlike the spiral luminous galaxies that we can see, like Milky Way, these dark galaxies contain fewer stars and a large amount of dark matter, undetectable to the human eye.

The astronomers reached these conclusions after studying infrared images of several spiral-shaped galaxies taken by the Hubble telescope.

Although the outline of these galaxies is invisible to most telescopes, because of their intense gravity, astronomers believe, they contain massive quantities of matter.

Trying to get a better look at the galaxies’ mysterious halos, a team from the University of Berkely aimed Hubble’s powerful eye on the brightest part of galaxy NGC-5907, some 40 million light-years away.

“If the halo had a normal, stellar population, we should have seen over 100 bright stars in our images. Much to our surprise, we only saw a handful of them,” said Michael Liu of Berkeley.

“This halo is composed of mostly faint low-mass dwarf stars with very few giant stars, which is very strange,” he continued.

Although practically invisible, these are real galaxies, not fragments, Kormendy insisted.

“Their density in dark matter is about 100 times larger than in a giant galaxy and their high density suggests that they were formed very early in the history of the universe,” he said.

The astronomers, who have long known that stars, planets, comets and visible galaxies constitute only about ten per cent of the universe now believe these dark galaxies may form a significant part of the remaining dark matter.

But the astronomers realise they are far from deciphering the universe.

“We are still groping, as if we are in a black room trying to make a black puzzle,” said Vera Rubin of Washington’s Carnegie Institute.

“These studies are certainly two pieces of that puzzle,” she added.

Unjamming info superhighway

Scientists at the University of Southampton’s optoelectronics research centre in England have found a method of compensating for the way a light signal broadens out, or ‘chirps’, as it passes along a glass fibre in a fibre optic cable.

Uncontrolled chirping limits the amount of data that can be transmitted as individual signals broaden and blur into one another.

The British scientists have developed a one-metre-long optical fibre grating with its own controlled ‘chirp’ built in.

The chirped gratings can be inserted along the cable to recompress broadened signals, thus improving the real fibre and avoiding the costly and complicated necessity of digging up the fibre-optic cable that has already been laid in the ground and replacing it, reports British Commercial News.

The chirped gratings are compact, low-cost and can be inserted easily into existing optical fibres.

The development of the new system has virtually opened up the potential for limitless transmission distances by enabling signals to be boosted within the fibre-optic cables, thereby overcoming transmission loss.

A field trial of the new optical fibre grating, which will help transmit huge amount of data, is currently under way.

Solid-state vertical gyroscope

US researchers have come up with a new high-speed gyrocope to measure angular momentum more accurately.

The new instrument, developed by Crossbow Technology Inc. in California, can be used to measure roll and pitch in camera and antenna, automotive testing, marine motion monitoring and sensing and stabilisation of unmanned vehicles.

The new gyro combines silicon micromachined (microelectromechanical systems) technology and high-speed digital signal processing to produce a device that is more cost-effective than its mechanical predecessors, while delivering performance similar to vertical gyros costing three to four times as much.

The system has an in-built software to calculate the angle correctly which gives it an advantage over the conventional mechanical machine, reports Mechanical Engineering.

It is packaged in a rectangular aluminium housing that is a little more than three inches on a side.