SCIENCE TRIBUNE Thursday, June 20, 2002, Chandigarh, India
 


Take care of compaction
Jagvir Goyal
C
OMPACTION of soil, whenever and wherever laid, is of utmost importance to ensure good health of the structure built over it throughout the designed life of the structure. Good compaction of soil results in minimising of its settlement on application of load, increases its density thus increasing its shear strength and decreases its permeability leading to a fall in its water absorption and reduction in its swelling or shrinkage.

Biotech breast milk
G
ENETICALLY modified (GM) rice carrying a protein from human breast milk could be used to enhance infant formula, researchers hope. But at present, the protein would not gain approval for use in the United States, says Nature science update.

NEW PRODUCTS & DISCOVERIES
Convenience in a Stick

The latest craze in file swapping was triggered by MP3 files, then included digital images and has now reached data files that can easily reach megabyte dimensions. How do we transfer such files from one box to another?

  • Tool to peer into atomic nucleus

  • Superconducting transformer

  • Built-in brakes in skis

SCIENCE & TECHNOLOGY CROSSWORD
 

 
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Take care of compaction
Jagvir Goyal

COMPACTION of soil, whenever and wherever laid, is of utmost importance to ensure good health of the structure built over it throughout the designed life of the structure. Good compaction of soil results in minimising of its settlement on application of load, increases its density thus increasing its shear strength and decreases its permeability leading to a fall in its water absorption and reduction in its swelling or shrinkage. Whether it is the soil laid beneath a building or that under a floor or that in an embankment, its compaction has a direct effect on the future behaviour of the structure built over it.

Take the example of an earthen dam. Good compaction of soil laid in layers to raise it to its desired height will make the soil dense, thereby decreasing the seepage- loss of water stored behind the dam. The dam structure itself will have a longer life as water will not be able to make way into it. In case of an embankment, the chances of settlement of soil due to movement of heavy traffic over it will be minimised thus reducing the maintenance cost of the road built over it and making the embankment stand against the ravages of time.

Compaction of soil can be done either by expulsion of air entrapped in the soil or by expulsion of water present in its pores or by elastic compression of soil particles. Among these, the elastic compression of soil particles contributes negligibly whatever amount of compaction we may do. Compaction, therefore, will depend upon the expulsion of air and water from the soil. It has been noted that usually no water gets expelled from the voids during compaction. Only a gradual expulsion of water may take place from the pores of saturated cohesive soils under the action of continuously static loads. Thus during the compaction of soils, it is virtually the expulsion of air only that brings desired results and increases the density of soil.

How to achieve good results

Compaction of soil depends upon a number of factors. Among these the most prominent are a) The moisture content of soil b) Type of soil c) The method of compaction. Compaction of soil is measured in terms of dry density of soil. More is the dry density, more compact the soil is. The moisture content at which maximum dry density is achieved is called Optimum Moisture Content (OMC). Here it must be noted that this OMC is for a particular "compaction effort" applied to the soil. If we increase the compaction effort, the OMC will decrease for this new and increased effort and the density of soil will further increase. Thus there are two variable factors: OMC and compaction effort. More and more density can be achieved by increasing the compaction effort and decreasing the OMC for that effort. It should be borne in mind that the density of soil will increase only if the shear stress produced by the "compaction effort" is more than the shear strength of soil at its existing density and moisture content. The compaction effort should, therefore, be quite adequate.

Well-graded coarse soils can be compacted to a high density as compared to fine grained soils. OMC for fine grained soils is more than that for coarse grained soils because finer particles have larger surface area and need more water to wet themselves. Thus for same compaction effort, maximum dry density of fine grained soils shall be lesser than that for coarse grained soils. To achieve good results for a particular soil, a graph should first be prepared between the compaction effort and the OMC for that effort by applying different efforts and noting the OMC for each effort. The desirable as well as possible result should then be chosen as the target to be achieved. This is important because sometimes, the best compaction effort and the OMC may not be possible to achieve at a particular site.

How to compact the soils

To carry out the compaction of soil in the field, mechanical means are most suitable. A number of types of rollers are available for this purpose. However the type of rollers to be used depends upon the nature of soil to be compacted. For clayey soils, kneading type rollers are most suitable. Pneumatic or sheep foot rollers shall, therefore, prove better for such soils as these rollers penetrate into the soil. 95% of the modified proctor density can be achieved in these soils by using rubber tyred rollers with tyre load of 11 MT. For sandy or cohesionless soils, vibratory rollers are most suitable. Even 100% of modified proctor density can be achieved in these soils by using proper vibratory equipment. If rubber tyred vibratory rollers with 13.5 MT load are applied, even 103 to 104% of modified proctor density is achievable in these soils after making 30 passes of these rollers. Once the thickness of layers of soil to be laid and compacted is decided, the type and weight of rollers can also be decided as the thickness of layer also affects the choice of rollers. Lesser is the thickness of a layer, more is the compaction achieved for a given type of roller. After making right choice of rollers, the number of passes required to achieve the desired density should be observed in the field and followed for each layer to be laid.

The vibratory rollers consist of a smooth cylindrical steel drum with one rotating eccentric weight placed at the center of the drum. The rotating eccentric drum produces vibrations causing the roller to bounce against the soil. Vibrations do not allow the top layer of an embankment to achieve density. So the top layer should always be compacted by switching off the vibratory mode of the roller. Compaction performance of a vibratory roller depends upon its frequency, vibrating mass and amplitude. These parameters should therefore be examined while selecting a vibratory roller for the density to be achieved.

Checking the density

It is very important to check the actual density of soil rather than just passing the rollers over each layer a few times and believing that the soil has been compacted. To determine the maximum dry density of soil in the laboratory, a simple apparatus known as Standard Proctor Test Apparatus and Modified Proctor Test Apparatus may be used. Particulars of these apparatuses are given in Table 1.

Sometimes a mould of 15 cm diameter is used instead of 10 cm dia. In such case, the number of blows is increased from 25 to 56. Rest of the test procedure remains the same. As the number of layers is lesser and the energy input is also lesser in case of Standard Proctor Test, it gives lesser values of maximum dry density as compared to modified proctor test. Though the maximum values achieved by each type of test vary from soil to soil, it has been observed that 95% of standard proctor density is equivalent to 88 to 90% of modified proctor density. Standard Proctor Test is adopted for density checking of unimportant structures while the Modified Proctor Test is applied in harder conditions such as runways, sub-grades and embankments. In case of embankments and earthen dams, many builders make such an arrangement that the fleet of dumpers has to pass over the laid layers to reach their location. It is a good and practical method of imparting more density to the laid layers of the soil.

Field densities

Once the norms have been laid for a particular work with respect to the maximum dry density achieved by Standard Proctor Test or Modified Proctor Test, the field densities can be taken from time to time and compared with the norms. To check the field density, core cutters are used. Samples of compacted soil are drawn by use of core cutters, are weighed, dried to find the moisture content and the dry density achieved is arrived at.

It must be noted that an 80% of the Standard Proctor Test density is almost equivalent to soft soil. After all, compaction has to be achieved by expulsion of air only. Anybody can well imagine the little difference in air content of loose soil and compacted soil. A soil having a maximum dry density of 1.85 gram/cubic cm and a water content of 15% shall have an air content of about 10% only and percentage air voids of 4% only. Thus the compaction of soil should be fully taken care of to avoid any trouble at a later stage.

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Biotech breast milk

GENETICALLY modified (GM) rice carrying a protein from human breast milk could be used to enhance infant formula, researchers hope. But at present, the protein would not gain approval for use in the United States, says Nature science update.

Nutritionists agree that breast milk is best for a baby infant formula is not as nourishing as the real thing. So for mothers unable to breast-feed, the biotech industry is engineering crops or animals to make human breast milk proteins to ‘humanize’ formula.

Yuriko Adkins of the University of California, Davis and her colleagues, have modified rice plants to carry a human gene for a milk enzyme called lactoferrin. Babies need this to use iron efficiently and fight infection.

Rats fed the rice-raised ‘recombinant’ enzyme together with a second enzyme, Lysozyme, were better able to kill gastrointestinal bacteria, she told the Experimental Biology 2002 meeting this week in New Orleans. Sterilization inactivates the lactorferrin in current cow-based infant formula: the GM form is stable, the report said. PTI

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NEW PRODUCTS & DISCOVERIES

Convenience in a Stick

The latest craze in file swapping was triggered by MP3 files, then included digital images and has now reached data files that can easily reach megabyte dimensions. How do we transfer such files from one box to another?

A media standard seems to emerge - USB enabled memory sticks - and there isn't a better word for it. It's Sony's name and they started it a few of years ago - when they introduced the Memory Stick at the PIMA 1999 in Las Vegas. They thought it would be a great idea to create their own standard of flash memory cards for their line of digital cameras.

Proprietary and expensive, until other companies adopted the form factor and then added a USB connector to the tiny memory card. Now everybody with a USB-capable computer can have one. Replacement for floppies? You bet it is! For everybody who has to copy files from one PC to another (even between PCs and Macintoshes) there is now a solution - quick and simple - have a "Stick".

Tool to peer into atomic nucleus

By using an ultra-powerful laser to set off energy bursts lasting a tiny fraction of a second, scientists may finally be able to see — and perhaps control — what happens in the heart of an atom, its nucleus.

This system, which its theorists call a "lasetron", could also briefly produce a massive magnetic field resembling that of a white dwarf star, opening the door to important new experiments in astro-physics.

A lasetron has not been built yet, but researchers, Alexander Kaplan and Peter Shkolnikov, in a recent paper published in Physical Review Letters, have proposed the idea and explained how and why the device should work.

This would be a completely new tool for nuclear science", a John Hopkins University press release quoted Kaplan as saying. "No one has ever seen the processes that occur within the nucleus of an atom. If we can produce very high intensity pulses, we could even control the nuclear reactions.

"It almost sounds like science fiction, but we might be able to slow down or accelerate nuclear fission. Using electromagnetic forces, we could try to control radioactivity, which no one has been able to do", the JHU release said. PTI

Superconducting transformer

Researchers have successfully developed a prototype coil for a superconducting transformer which is not only light and compact but also energy-efficient.

Scientists from the Technology Foundation STW and the University of Twente, The Netherlands, in cooperation with Smit Transformatoren and Smit Draad made the coil from superconducting wires, insulated using a newly patented method.

The superconducting wires are manufactured from a ceramic material BSCCO (pronounced bisko), a report in NWO Research Report said.

This so-called high-temperature superconductor only allows current to flow without resistance when the material is cooled to 196 degree centigrade.

The new insulation had to be able to withstand such low temperatures. Therefore the researchers chose a polyamide-film. PTI

Built-in brakes in skis

Scientists have developed a new generation of skis or snowboards that would be fitted with built-in electronic brakes which slow them down before things get too scary thereby lending a whole new dimension to snow sports.

The new braking system — developed by Victor Petrenko, an engineer at Dartmouth College’s Ice Research Lab in New Hampshire — involves running a pair of wires the length of the board or ski’s underside, one at each edge.

The wires are connected to opposite terminals of a 3-volt battery, making one wire positive and the other negative, a report in New Scientist said. PTI

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SCIENCE & TECHNOLOGY CROSSWORD

Clues :

Across

1. Australia leads the world in production of this mineral.

6. Symbol for Iridium.

7. Instrument used to measure the rate of evaporation of water.

9. Apparently human automation.

10. Water containing salts of Ca cium & Magnesium.

12. Centre established by Indian Council of Medical Research at Port Blair.

13. Nest of bird of prey.

16. Group of hard shelled snails that attack timber of ships.

19. An infectious disease.

20. Prescribed by doctors for acute constipation.

21. A gateway for diploma engineers to rise.

22. Resin in solid form is called so.

23. Small body of still water.

24. …km, a term used to tell how much material is carried to how much distance.

25. A transparent curved item for dispersion or concentration of light rays.

Down

1. An instrument used for stabilising voltage.

2. Smallest particle of an element.

3. The region of complete shadow.

4. Symbol for semi-metal Tellurium.

5. Another name for Acetylene.

6. Supplying water to land through channels.

8. Dry land or soil.

11. Unit of intensity of sound waves.

13. Effect caused by reflection of sound.

14. An inert gas used in electric tubes.

15. …..detached-house joined to another on one side only.

17. The remainder of a quantity or number.

18. Large breed of dog.

21. A computer language used in scientific modelling.

Solution to last week’s crossword:



 

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