How acute stress turns hair white

"We were conducting a study on pain using black C57 mice, a dark-furred laboratory strain," the author said. "In this model, we administered a substance called resiniferatoxin to activate a receptor expressed by sensory nerve fibres and induce intense pain. Some four weeks after systemic injection of the toxin, a PhD student observed that the animals' fur had turned completely white."

The experiment was repeated several times until the researchers concluded that the phenomenon was indeed due to the application of resiniferatoxin, a naturally occurring chemical found in resin spurge (Euphorbia resinifera), a cactus-like plant native to Morocco.

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சின்ன எம்.ஜி.ஆர் ஜெய்சங்கரின் புகழ்

ஜெய்சங்கரை* வைத்து படம் எடுத்து ஒரு தயாரிப்பாளர் நஷ்டம் அடைந்தார், நடுவீதிக்கு வந்தார் என்று எவராலும் விரல் நீட்டி கூற முடியாது. காரணம் அவர் யாரிடமும் எனக்கு இவ்வளவு சம்பளம் கொடுங்கள் என்று கேட்டதில்லை.

முடிந்ததை கொடுங்கள் என்பார். அவர் வீட்டு பீரோ நிறைய திரும்பி வந்த காசோலைகள் பண்டல் பண்டலாக இருந்தது என்பார்கள்.

அதேபோல தோல்வி அடைந்த படங்களின் சம்பளத்தை திருப்பிக் கொடுப்பதை தொடங்கி வைத்தவரே ஜெய்சங்கர் தான். லைட் பாயிலிருந்து ரசிகன் வரை யார் அவரை உதவி என்று தேடிப்போனாலும் இருப்பதை கொடுக்கும் கொடை வள்ளலாக வாழ்ந்தார்.

எம்.ஜி.ஆரை சந்திப்பது கடினம். அப்படி சந்தித்து விட்டால் பெரியதாக அள்ளிக் கொடுப்பார். ஜெய்சங்கரை சந்திப்பது எளிது. அவர் சக்திக்கேற்ப கிடைக்கும். அதனால்தான் ஜெய்சங்கரை சின்ன எம்.ஜி.ஆர் என்பார்கள்.

வழக்கறிஞர்களும், நீதிபதிகளும் நிறைந்த பாரம்பரிய குடும்பத்தில் பிறந்தவர் ஜெய்சங்கர், சோ நடத்திய 'விவேகா பைன் ஆர்ட்ஸ்' நாடக குழுவில் நடித்துக் கொண்டிருந்தவர் 'இரவும் பகலும்' படத்தில் அறிமுகமானார்.

முதல் படமே வெற்றி பெற புகழ்பெற்றார் ஜெய்சங்கர். எம்.ஜி.ஆர், சிவாஜி என்ற பெரிய நடிகர்கள் ஒரு பக்கம், ஜெமினி கணேசன், ரவிசந்திரன் என இளம் பெண்களை கவர்ந்து கொண்டிருந்த ஹீரோக்கள் இன்னொரு பக்கம். இதற்கு இடையில்தான் ஜெய்சங்கர் புகுந்து தனக்கென ஒரு இடத்தை பிடித்தார். யார் நீ, பொம்மலாட்டம், குழந்தையும் தெய்வமும், மன்னிப்பு, பட்டணத்தில் பூதம் போன்ற படங்கள் அவரை அடுத்தடுத்த கட்டத்திற்கு நகர்த்திச் சென்றன.

மற்ற நடிகர்களிடமிருந்து தன்னை வேறுபடுத்திக் காட்ட ஹாலிவுட் ஹீரோக்களின் சாயலில் நடிக்க ஆரம்பித்தார். சிஐடி சங்கர், வல்லவன் ஒருவன், கருந்தேள் கண்ணாயிரம், கங்கா, ஜக்கம்மா, ஜம்பு, எங்க பாட்டன் சொத்து போன்ற படங்களில் ஜேம்ஸ் பாண்ட் பாணியில் நடித்தார். துணிவே துணை, கங்கா போன்ற படங்களில கவுபாய் கேரக்டர்களில் நடித்தார். இவர் காலத்தில்தான் ராஜ்கோகிலா, ஜெயமாலா, ராஜ்மல்லிகா, போன்ற கவர்ச்சி நடிகைகளும் சினிமாவுக்கு வந்தார்கள்.

100 படங்களுக்கு மேல் நடித்திருக்கும் ஜெய்சங்கர் கடைசி வரை தனக்கென தனி பாணி வைத்துக் கொண்டார். அவர் நடித்த வண்ணப் படங்கள் ஒரு சில தான். வண்ணப் படங்கள் வந்த பிறகும் நீண்ட நாள் கருப்பு வெள்ளை படங்களில் நடித்துக் கொண்டிருந்தவரும் ஜெய்சங்கர்தான். காரணம் அவர் கடைசி வரை சிறு தயாரிப்பாளர்களின் ஹீரோவாகவே இருந்தர்.

ரஜினி, கமலின் வருகைக்கு பிறகு அவரால் அவர்களுடன் போட்டிபோட முடியவில்லை. சினிமாவை விட்டு மெல்ல விலக ஆரம்பித்தார்.

சில ஆண்டுகள் இடைவெளிக்குப் பிறகு ஏவிஎம் தயாரித்த 'முரட்டுக்காளை' படத்தில் ரஜினிக்கு வில்லனாக நடித்தார். ஏற்கெனவே 'காயத்ரி' என்ற படத்தில் ஜெய்சங்கர் ஹீரோவாகவும், ரஜினி வில்லனாகவும் நடித்தது குறிப்பிடத்தக்து. முரட்டுக்காளை ஜெய் சங்கருக்கு ரீ எண்ட்ரியை கொடுத்தது. 61 வயதில் அவர் சாகும் வரையில் நடித்துக் கொண்டுதான் இருந்தார்.

இளைஞர்களுடன் இணைந்து 'ஊமை விழிகள்' போன்ற படங்களிலும் நடித்தார். 100 படங்களுக்கு மேல் ஹீரோ. எம்.ஜி.ஆர் போன்ற வள்ளல் குணம். அழகு குறையாத நடிகன், இத்தனை இருந்தும் ஜெய்சங்கரின் புகழ் இன்னும் குடத்திலிட்ட விளக்காத்தான் இருக்கிறது.

Carbon dioxide Removal from Biogas

A variety of processes are being used for removing CO2 from natural gas in petrochemical industries. Several basic mechanisms are involved to achieve selective separation of gas constituents. These may include physical or chemical absorption, adsorption on a solid surface, membrane separation, cryogenic separation and chemical conversion. 

Carbon dioxide is a noncombustible constituent of biogas lowers its heat value. Removal of carbon dioxide is not necessary when gas is to be used for cooking or lighting purposes only. A number of methods have been developed for CO2 removal (scrubbing) which depending upon the technique involved are called water-scrubbing, caustic-scrubbing, solid absorption, liquid absorption and pressure separation.

A brief description of these methods is as follows:

For biogas scrubbing physical/chemical absorption method is generally applied as they are effective even at low flow rates that the biogas plants are normally operating at. Also, the method is less complicated, requires fewer infrastructures and is cost-effective. 

Method # 1. Water Scrubbing:

One of the easiest and cheapest methods involves the use of pressurized water as an absorbent. The raw biogas is compressed and fed into a packed bed column from the bottom; pressurized water is sprayed from the top. The absorption process is, thus a counter-current one. This dissolves CO2 as well as H2S in water, which are collected at the bottom of the tower. 

In this method, gas is made to pass through water which absorbs part of CO2. The inherent limitation of this method is that it requires a large quantity of water. Based on studies carried out by H.M. Lapp, 7 ft3 (0.2 m3) of biogas at 68°F (20°C) and 1 atmospheric pressure (1.03 kg/cm2) requires 2.7 gallons (12.3 litres) of water for CO2 removal. CO2 is highly soluble in water. Spent water following absorption of CO2 becomes acidic and hence unsuitable for several applications as it corrodes metallic surface it comes in contact with.

Method # 2.CHEMICAL ABSORPTION

Caustic Scrubbing:

Chemical absorption involves the formation of reversible chemical bonds between the solute and the solvent. Regeneration of the solvent, therefore, involves breaking of these bonds and correspondingly, a relatively high energy input. Chemical solvents generally employ either aqueous solutions of amines, i.e. mono-, di- or tri-ethanolamine or an aqueous solution of alkaline salts, i.e. sodium, potassium and calcium hydroxides. Biswas et al. reported that by bubbling biogas through 10% an aqueous solution of mono-ethanolamine (mea), the co2 content of the biogas was reduced from 40 to 0.5-1.0% by volume. A solution can be completely regenerated by boiling for 5 min and thus can be used again

This method works on the principle that when caustic solutions are made to react with CO2 bearing gas streams, an irreversible carbonate-forming reaction followed by reversible bicarbonate forming reac­tion take place as per the following equations. This process involves the use of hydroxides of sodium, potassium and calcium.

In most industrial applications, no attempt is made to regenerate spent bicarbonate solution due to high steam requirement for this process. Carbon dioxide absorption into alkaline solution is adversely affected by slow conver­sion of dissolved CO2 molecules into more reactive ionic species. Mixing of liquid during absorption helps to achieve diffusion of gas molecules in the liquid and prolongs their contact time which adds to the former’s absorptivity.

Normality of caustic solution also affects the rate of absorptivity. With sodium hydroxide solution (NaOH), for instance, it was found that the rate of reaction is more rapid if normality lies between 2.5 to 3. Potassium hydroxide (KOH) is more commonly used in industrial scrubbing but it suffers from the limitation that it is not readily available in rural areas where biogas plants are normally located.

Calcium hydroxide [Ca(OH)2] on the other hand is generally preferred for biogas scrubbing as this chemical is more readily available and cost of operating a lime-water scrubber is also relatively less. The main limitation of lime-water scrubbing are difficulties faced in controlling solution strength, and removal of large amounts of precipitate from mixing tank and scrubber.

In most cases, sediment and suspended particulate matter need be removed in order to avoid clogging in pumps, high-pressure spray nozzles, packing and bubbling ap­paratus. Sodium hydroxide has the major advantage of being available in easily handled pellet forms that enable rapid and simple recharging of the scrubber. However, with NaOH solutions problems of suspended particulate matter are not totally eliminated.

 The absorption of CO2 in alkaline solution is assisted by agitation. The turbulence in the liquid aids to the diffusion of the molecule in the body of liquid and extends the contact time between the liquid and gas. Another factor governing the rate of absorption is the concentration of the solution. The rate of absorption is most rapid with NaOH at normalities of 2.5-3.0. 
CARBON DIOXIDE REMOVAL USING AMMONIA IN BIOGAS 
Ammonia is used as an absorbent in chemical scrubbing to remove CO2 from biogas. A continuous system consisting of the 1L digester was used for biogas production which was bubbled through an absorbent in 500mL gas washing bottle at a constant temperature in a water bath. The obtained biomethane potential was found to be 0.387 m3 CH4/ kg VS which simply means that more methane gas can be obtained when using ammonia for absorption. An increase in the gas flow rate leads to an increase in the mass transfer coefficient resulting in an increase in the rate of absorption. The initial CO2 concentration affects the removal efficiency because more work needs to be done for biogas with a high initial concentration of CO2. NH3 has better absorption capacity because higher biogas purity was achieved at lower NH3 concentration. The removal efficiency for NH3 increased from 69%-79% on average with CH4 concentration reaching over 85% vol. This is equivalent to a calorific value ranging from 25- 33.5 MJ/Nm3 which is promising in terms of the gas ability to run in an automobile engine. 

Method # 3. Method Developed by the IARI, New Delhi:

T.D. Biswas, et al., developed another method for CO2 scrubbing. It was found that biogas can be removed by bubbling it through 10 per cent aqueous solution of mono-ethanolamine (MEA). By single bubbling through a plain column of 6 cm height, carbon dioxide content in biogas was reduced to 0.5-1 per cent by volume from the initial value of 40 per cent.

Scrubbing column was made of an inexpensive plastic bubbler of 5 cm diameter and 15 cm height with only one orifice. The maximum removal of carbon dioxide was observed when bubbles moved out individually without colliding one another to form a continuous stream. Optimum gas flow rate to the regulator was estimated as 100 ml per minute which gave 60 ml of purified gas per minute in the reservoir.

The decrease in this rate of flow was not found to cause any further scrubbing. The initial pressure of the gas introduced into the bubbler was 10 cm of the water column and drop in pressure head was about 5 cm of the water column. Both caustic potash and monoethanolamine solution were effective in reducing the carbon dioxide content to 0.5 to 1 per cent.

Whereas spent caustic potash solution cannot be regenerated, MEA solution can be completely regenerated by boiling for five minutes and thus can be used again and again. Furthermore, MEA solution is far less caustic than other solutions used and therefore pose much fewer hazards for the skin. This method is thus very practical and economic for biogas scrubbing.

Method # 4. Pressure Separation:

This method works on the principle of compressing biogas beyond the limit of the critical partial pressure of impurities (CO2) with a temperature greater than the critical temperature of methane but below those of impurities. For instance, carbon dioxide liquefies when the gas temperature falls below 89.6 F (32 C) after compressing beyond 1106 psi (77.76 kg/cm).

Thanks, http://www.geographynotes.com/

Pressure Swing Adsorption (PSA) Systems for CO2 and Hydrogen Sulphide Scrubbing

Pressure swing adsorption (PSA) systems, can be thought of as being molecular-sieves for carbon. PSA has been described are the second most commonly used biogas upgrading technology in Europe, after water scrubbing which is most likely the most popular. A typical system is composed of four vessels in series that are filled with adsorbent media which is capable of removing not only the CO2 but also water vapour, N2, and O2 from the biogas flow.

Typically in order to eliminate CO2 from biogas, the PSA upgrading takes place over 4 phases: pressure build-up, adsorption, depressurization and regeneration. The pressure build-up occurs by equilibrating pressure with a vessel that is at depressurization stage. Final pressure build-up occurs by injecting raw biogas. During adsorption, CO2, N2, and O2 are adsorbed by the media and the purified gas discharges as pure methane to a quality which will be far less corrosive and has a higher calorific value.

Recently developed gas-liquid membranes have been introduced, which operate at atmospheric pressures thereby reducing the energy consumption of compression. The use of specific solvent solutions allows the separation and recovery of the H2S and CO2.

Another approach to improving the economics of gas upgrading has been to recover the CO2 by cooling and recovering dry ice. This can then be sold as an industrial gas whilst the biogas is either used in its more concentrated form (80-90% CH4) or further refined to vehicle quality standard (>96% CH4).

Pressure Swing Adsorption

Pressure swing adsorption (PSA) is a method for the separation of carbon dioxide from methane by adsorption/desorption of carbon dioxide on zeolites or activated carbon at alternating pressure levels. This technology is often applied in the gas treatment industry as it also effectively removes volatile organic compounds, nitrogen and oxygen from industrial gas streams.

"மனிதராக" வாழ்ந்து கொண்டிருக்கும் ஓர் ஆத்மீகத் துறவி ரதன தேரர்

மதம் கடந்து நல்லதொரு "மனிதராக" வாழ்ந்து கொண்டிருக்கும் ஓர் ஆத்மீகத் துறவி ரதன தேரர்.

இளம் வயதில் துறவறம் பூண்டு இலங்கையின் பல பாகங்களிலுமுள்ள தமிழ் மக்களுடன் இதய சுத்தியுன் உறவைப் பேணி தமிழ் மக்கள் சமகாலத்தில் படும்முகம் கொடுத்துக் கொண்டிருக்கும் அரசியல் மற்றும் பொருளாதார ரீதியாக சவால்களைக் கண்டு மனம் வருந்தி உண்மையை உணர்ந்துள்ள துறவி.

தற்காலத்தில் அவ்வாறு துறவறம் பூண்டு ஏனைய மக்களின் மனங்களைப் புண்படுத்திக் கொண்டிருக்கும் துறவிகள் மத்தியில் இவர் "சேற்றில் முளைத்த செந்தாமரைதான்"

இவர் உறவு வைத்துள்ள பெரும்பாலானோர் தமிழர்களே.

சரளமாக தமிழ் மொழி பேசும் இவர் ஹொரணைப் பகுதியொன்றிலுள்ள பாடசாலையில் தமிழ் ஆசிரியராகக் கடமை புரிந்து கொண்டிருக்கிறார்.

இவருடன் இன்று தொலைபேசியில் உரையாடும் சந்தர்ப்பம் கிடைத்தமைக்கு நான் பெரும் மகிழ்ச்சிஅடைகிறேன்.

இவருடைய தமிழ் மொழித் திறமையைக் கண்டு வியப்புற்றேன்.

இலங்கைத் தமிழ் மக்கள் படும் துன்பங்களை எண்ணி மனம் வருந்தினார்.

அவ்வாறு அவருக்கு தமிழ் மொழி தெரிந்த படியாலே அவரின் மன உட்கிடக்கை என்னவென்று புரிந்து கொள்ளக் கூடியதாக இருந்தது.

அவருடனான கருத்துப் பகிர்விலிருந்து அறியப்பட்டதொன்று என்னவென்றால்; தமிழர்களும் சிங்களவர்களும் மொழியால் மட்டுமே வேறுபாடு கொண்டவர்கள் என்றும் இலங்கை வரலாற்றில் இரு இனத்தவரும் அன்புடனும் ஒற்றுமையாகவும் வாழ்ந்து வந்தபோது குறுகிய மனப்பான்மை கொண்ட அரசியல் வாதிகளே தங்கள் சுயநலத்திற்காக பிரித்தாண்டு கொண்டிருக்கிறார்கள் என்ற உண்மையை கூறி கவலையடைந்தார்.

இப்படியான புத்த துறவிகளும் இருக்கத்தான் செய்கிறார்கள். ஓர் ஆன்மீகவாதி என்றால் இப்படித்தான் இருக்க வேண்டும்.

வாழ்த்துக்கள் தேரரே.

Shivapalan 

Ground Improvement Techniques

Purpose of ground improvement

Ground-improvement methods are those that are capable of improving certain characteristics (e.g. increase in bearing capacity, reduction in total as well as differential settlement, reduction in permeability, slope stability, prevention of soil erosion caused by piping and seepage, reduction of uplift pressure, decrease in liquefaction potential of soil, reduction of swelling and cracking of soils, identification of suitability of site to facilitate construction works, etc.) of poor ground for civil engineering constructions and various infrastructure developments. So a ground improvement method or technique is required to alter the state, nature, or mass behaviour of ground materials in a controlled manner in order to achieve an expected and satisfactory response to existing or projected environmental and engineering actions.

There are alternate options to ground improvement as well. These are

a.

to remove and replace the soil mass with another type of soils or other geomaterials of suitable quality for the construction work

b.

to bypass the poor soil with the help of a suitable technique like pile foundation

c.

to alter the design (height and configuration) of structures to overcome the ground limitations

d.

to change the construction site and look for a new one.

However, due to the scarcity of land in present conditions, heavy loading structures, competitive design, the need for speedy construction, and various political and economic issues, a ground-improvement technique may be the only feasible option for civil engineering constructions. 

The selection of ground-improvement techniques depends upon various factors like the cost and time available to complete the project, reasons for improving the ground, extent and depth of ground to be treated, geotechnical properties of the existing in situ soils/rocks, accessibility to the project site, availability of materials, equipments and manpower required to improve the ground, environmental factors, local experience, and preference of contractors and engineers.

The ground can be improved by adapting certain ground improvement techniques. Vibro-compaction increases the density of the soil by using powerful depth vibrators. Vacuum consolidation is used for improving soft soils by using a vacuum pump.

Preloading method is used to remove pore water over time. Heating is used to form a crystalline or glass product by electric current. Ground freezing converts pore water to ice to increase their combined strength and make them impervious. Vibro-replacement stone columns improve the bearing capacity of soil whereas Vibro displacement method displaces the soil. Electro osmosis makes water flow through fine-grained soils.

Electrokinetic stabilization is the application of electro-osmosis. Reinforced soil steel is used for retaining structures, sloping walls, dams etc. seismic loading is suited for construction in seismically active regions. Mechanically stabilized earth structures create a reinforced soil mass.

The geo methods like Geosynthetics, Geogrid etc. are discussed. Soil nailing increases the shear strength of the in-situ soil and restrains its displacement. Micropile gives the structural support and used for repair/replacement of existing foundations.

Grouting is the injection of pumpable materials to increase its rigidity. The jet grouting is quite advanced in speed as well as techniques when compared with the general grouting.

Rapid urban and industrial growth demands more land for further development. In order to meet this demand land reclamation and utilization of unsuitable and environmentally affected lands have been taken up. These, hitherto useless lands for construction have been converted to be useful ones by adopting one or more ground improvement techniques. The field of ground improvement techniques has been recognized as an important and rapidly expanding one.

Latest Ground Improvement Techniques

Following are the recent methods of ground improvement Techniques used for stabilization of soil:

• Vibro Compaction
• Vacuum Consolidation
• Preloading of soil
• Soil stabilization by heating or vitrification
• Ground freezing
• Vibro-replacement stone columns
• Mechanically stabilized earth structures
• Soil nailing
• Micro-piles
• Grouting

Vibro-Compaction Method of Ground Improvement

Vibro-compaction sometimes referred to as Vibroflotation, is the rearrangement of soil particles into a denser configuration by the use of powerful depth vibration. Vibro Compaction is a ground improvement process for densifying loose sands to create stable foundation soils.

The principle behind Vibro compaction is simple. The combined action of vibration and water saturation by jetting rearranges loose sand grains into a more compact state.  Vibro Compaction is performed with specially-designed vibrating probes. Both horizontal and vertical modes of vibration have been used in the past.

The vibrators used by Terra Systems consist of torpedo-shaped probes 12 to 16 inches in diameter which vibrates at frequencies typically in the range of 30 to 50 Hz. The probe is first inserted into the ground by both jetting and vibration. After the probe reaches the required depth of compaction, granular material, usually sand, is added from the ground surface to fill the void space created by the vibrator. A compacted radial zone of granular material is created

Advantages of Vibro Compaction Method:

• Reduction of foundation settlements.
• Reduction of risk of liquefaction due to seismic activity.
• Permit construction on granular fills.

Vacuum Consolidation of Soil for Ground Improvement

Vacuum Consolidation is an effective means for improvement of saturated soft soils. The soil site is covered with an airtight membrane and vacuum is created underneath it by using dual venture and vacuum pump. The technology can provide an equivalent pre-loading of about 4.5m high conventional surcharge fill. Vacuum-assisted consolidation preloads the soil by reducing the pore pressure while maintaining constant total stress.

Applications of Vacuum Consolidation of Soil:

• Replace standard preloading techniques eliminating the risk of failure.
• Combine with a water preloading in the scare fill area. The method is used to build large developments on thick compressible soil.
• Combine with embankment pre-load using the increased stability

Preloading or Pre-Compression of Soil for Ground Improvement

Preloading has been used for many years without a change in the method or application to improve soil properties. Preloading or pre-compression is the process of placing additional vertical stress on a compressible soil to remove pore water over time. The pore water dissipation reduces the total volume causing settlement. Surcharging is an economical method for ground improvement. However, the consolidation of the soils is time-dependent, delaying construction projects making it a non-feasible alternative.

The soils treated are Organic silt, Varved silts and clays, soft clay, Dredged material The design considerations which should be made are bearing capacity, Slope stability, Degree of consolidation.

Applications of Preloading of Soil

• Reduce post-construction
• Settlement
• Reduce secondary compression.
• Densification
• Improve bearing capacity

Thermal Stabilization of Soil for Ground Improvement

Heating or vitrification breaks the soil particle down to form a crystalline or glass product. It uses electrical current to heat the soil and modify the physical characteristics of the soil. Heating soils permanently alters the properties of the soil. Depending on the soil, temperatures can range between 300 and 1000 degree Celsius. The impact on adjacent structures and utilities should be considered when heating is used. .

Applications of Vitrification of Soil:

• Immobilization of radioactive or contaminated soil
• Densification and stabilization

Ground Freezing Technique for Ground Improvement

Ground freezing is the use of refrigeration to convert in-situ pore water to ice. The ice then acts as cement or glue, bonding together adjacent particles of soil or blocks of rock to increase their combined strength and make them impervious. The ground freezing considerations are Thermal analysis, Refrigeration system geometry, Thermal properties of soil and rock, freezing rates, Energy requirements, Coolant/ refrigerant distribution system analysis.

Applications of Ground Freezing Technique

• Temporary underpinning
• Temporary support for an excavation
• Prevention of groundwater flow into the excavated area
• Temporary slope stabilization
• Temporary containment of toxic/hazardous waste contamination

Vibro-Replacement Stone Columns for Ground Improvement

Vibro-Replacement extends the range of soils that can be improved by vibratory techniques to include cohesive soils. Reinforcement of the soil with compacted granular columns or “stone columns” is accomplished by the top-feed method. The important Vibro-replacement stone columns are Ground conditions, Relative density, Degree of saturation, Permeation.

Principles of Vibro-Replacement Technique

The stone columns and intervening soil form an integrated foundation support system having low compressibility and improved load-bearing capacity. In cohesive soils, excess pore water pressure is readily dissipated by the stone columns and for this reason, reduced settlements occur at a faster rate than is normally the case with cohesive soils.

There are different types of installation methods which can be broadly classified in the following manner:

• Wet top feed method
• Dry bottom feed method
• Offshore bottom feed method

Summary of Vibro Replacement Method

Principle	Reinforcement Drainage
Applicable soil(s)	Mixed deposits of clay, silt and sand Soft and ultra-soft silts (slimes) Soft and ultra-soft clays Garbage fills
Effect(s)	Increased shear strength Increased stiffness Reduced liquefaction potential
Common applications	Airport taxiways and runways Chemical plants Storage tanks & silos Pipelines Bridge abutments and approaches Offshore bridge abutments Road and railway embankments
Maximum depth	20-40 m
Land / offshore application	Both

Applications of Vibro-Replacement for Ground Improvement:

• Reduction of foundation settlement
• Improve bearing capacity/reduce footing size requirements
• Reduction of the risk of liquefaction due to seismic activity
• Slope stabilization
• Permit construction on fills
• Permit shallow footing construction

Ground Type	Relative Effectiveness
Sands	Excellent
Silty sands	Excellent
Silts	Good
Clays	Marginal to good
Minespoils	Excellent (depending on gradation)
Dumped fill	Good
Garbage	Not applicable

Mechanically Stabilized Earth Structures

A segmental, precast facing mechanically stabilized earth wall employs metallic (strip or bar mat) or geosynthetic (geogrid or geotextile) reinforcement that is connected to precast concrete or prefabricated metal facing panel to create a reinforced soil mass.

Principles of Mechanically Stabilized Earth Structures:

• The reinforcement is placed in horizontal layers between successive layers of granular soil backfill. Each layer of backfill consists of one or more compacted lifts.
• Free-Draining, non-plastic backfill soil is required to ensure the adequate performance of the wall system.
• For walls reinforced with metallic strips, the load is transferred from the backfill soil to the strip reinforcement by shear along with the interface.
• For walls with ribbed strips, bar mats, or grid reinforcement, the load is similarly transferred but an additional component of strength is obtained through the passive resistance on the transverse members of the reinforcement.
• Facing panels are typically square, rectangular, hexagonal or cruciform in shape and are up to 4.5m ^2 in area.
• MSEW- Mechanically Stabilized Earth Walls, when the face batter is generally steeper than 70 degrees.
• RSS- Reinforced Soil Slopes, when the face batter is shallower.

Applications of Mechanically Stabilized Earth Structures:

• RSS structures are cost-effective alternatives for new construction where the cost of embankment fill, right-of-way, and other consideration may make a steeper slope desirable.
• Another use of reinforcement in engineered slopes is to improve compaction at the edges of a slope to decrease the tendency for surface sloughing.

Design:

Current practice consists of determining the geometric reinforcement to prevent internal and external failure using limit equilibrium of analysis.

Soil Nailing Technique for Ground Improvement

The fundamental concept of soil nailing consists of reinforcing the ground by passive inclusions, closely spaced, to create in-situ soil and restrain its displacements. The basic design consists of transferring the resisting tensile forces generated in the inclusions into the ground through the friction mobilized at the interfaces.

Applications of Soil Nailing Technique:

• Stabilization of railroad and highway cut slopes
• Excavation retaining structures in urban areas for high-rise building and underground facilities
• Tunnel portals in steep and unstable stratified slopes
• Construction and retrofitting of bridge abutments with complex boundaries involving wall support under piled foundations

Micropiles for Ground Improvement

Micropiles are small diameter piles (up to 300 mm), with the capability of sustaining high loads (compressive loads of over 5000 KN). The drilling equipment and methods allow micropiles to be drilled through virtually every ground conditions, natural and artificial, with minimal vibration, disturbances and noise, at any angle below horizontal. The equipment can be further adapted to operate in locations with low headroom and severely restricted access.

Applications of Micropiles for Ground Improvement

• For Structural Support and stability
• Foundation for new structures
• Repair / Replacement of existing foundations
• Arresting / Prevention of movement
• Embankment, slope and landslide stabilization
• Soil strengthening and protection

Example of Micro Piles for Ground Improvement:

In India, in some circumstances steel pipes, coated wooden piles are used as cost-effective Options in improving the bearing capacity of foundation or restrict Displacements to tolerable levels and similar uses in the stabilization of slopes, strengthening of foundations are common.

Sridharan and Murthy (1993) described a Case study in which a ten-storeyed building, originally in a precarious condition due To differential settlement, was restored to safety using micropiles. Galvanized steel Pipes of 100 mm diameter and 10 m long with bottom end closed with shoe, driven at An angle of 60o with the horizontal were used and the friction between the pile and the soil was used as the design basis in evolving the remedial measures.

General Grouting for Ground Improvement

Grouting is the injection of pumpable materials into a soil or rock formation to change the physical characteristics of the formation. Grouting selection considerations are Site-specific requirement, Soil type, Soil profitability, Porosity. Grouting can be prevented by Collapse of granular soils, Settlement under adjacent foundations, Utility damage, Daylighting. Grouting can provide Increased soil strength and rigidity, reduced ground movement, Predictable degree of improvement.

Steps for General Grouting Technique for Soil Stabilization

• Identify underground construction problem.
• Establish objectives of grouting program.
• Perform special geotechnical study.
• Develop initial grouting program.
• Develop performance prediction.
• Compare with other solutions.
• Refine design and prepare specifications.

Grouting Techniques

The various injection grouting techniques used by grouting contractors for ground improvement/ground modification can be summarized as follows:

• Permeation
• Compaction Grouting
• Claquage
• Jet Grouting

Jet Grouting Technique for Ground Improvement

Jet grouting is a general term used by grouting contractors to describe various construction techniques used for ground modification or ground improvement. Grouting contractors use ultra high-pressure fluids or binders that are injected into the soils at high velocities. These binders break up the soil structure completely and mix the soil particles in-situ to create a homogeneous mass, which in turn solidifies.

This ground modification / ground improvement of the soil plays an important role in the fields of foundation stability, particularly in the treatment of load bearing soils under new and existing buildings; in the in-depth impermeabilization of water-bearing soils; in tunnel construction; and to mitigate the movement of impacted soils and groundwater.
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