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First let us talk about the brief introduction about what is global warming, what is climate change; what is the relationship between these two. Now for very common meanings Global warming may be defined as;

    “A gradual increase in the overall temperature of the earth’s atmosphere generally attributed to the green house effect caused by increase levels of carbon dioxide, CFCs, and other pollutants”
global warming


Global Warming and Climate Change


Concept of greenhouse effect and green house gases


The sun, of course, is the ultimate source of heat energy reaching the Earth, fueling our weather systems, and establishing our major climate zones. There is, however, good evidence that larger variations in the sun's activity do occur. For example, during the last half of the 17th century, there was a period of greatly reduced solar activity.

Our atmosphere consists of many gases; some of these gases, such as carbon dioxide and water vapor, naturally absorb long-wave radiation that is emitted from the earth’s surface. Short-wave solar radiation enters the earth’s atmosphere and is absorbed by the earth’s surface. This radiation is then recycled and emitted as long wave terrestrial radiation. Gases such as water vapor and carbon dioxide absorb this radiation, hold it in the atmosphere, and keep the temperature of the earth warmer than it would otherwise be if there wasn’t an atmosphere. This is what meteorologists refer to as the “Natural Greenhouse effect”

How greenhouse gases causes global warming


This natural greenhouse effect has a balance and thus the earth is able to provide such an environment on which life can sustain; however human activities add additional trace gases into the atmosphere that causes problems; these additional trace gases absorb-out going long-wave radiation. These additional trace gases include methane, chlorofloro carbons, nitrous oxide, aerosols, zone,

The result is an increase in the amount of long-wave radiation that is being trapped by the atmosphere. It is believed that this could eventually increase the average overall global temperature.


Carbon dioxide "...is considered the trace gas of greatest importance because of the substantial increase in its atmospheric concentration as well as its probable continued rise due to global consumption of fossil fuels".

Due to these additional trace gases; earth’s mean surface temperature has increased by about 0.8 0 c, with about two-thirds of the increase occurring since 1980.

Introduction to climate change


Climate is defined as the analysis of accumulated weather data for long term patterns and trends. Climate change is therefore defined as "long-term weather patterns and trends becoming different over an extended period of time." For example, if the average temperature in Pakistan over the 20th century is significantly higher or lower than the average temperature in Pakistan, over the 19th century, this would be an example of climate change. Thus climate change can be defined as;

“a change in global climate patterns apparent from the mid to late 20th century onwards, attributed largely to the increased levels of atmospheric carbon dioxide produced by the use of fossil fuels.”

Global Warming Vs Climate Change


 'global warming' and 'climate change". In reality, the two terms mean different things, have both been used for decades.

Both of the terms in question are used frequently in the scientific literature, because they refer to two different physical phenomena.  As the name suggests, 'global warming' refers to the long-term trend of a rising average global temperature, which you can see here:

'Climate change', again as the name suggests, refers to the changes in the global climate which result from the increasing average global temperature.  For example, changes in precipitation patterns, increased prevalence of droughts, heat waves, and other extreme weather, etc.  These projections of future global precipitation changes from the 2007 IPCC report are an example of climate change.

How climate change and global warming is detected?


In general there are 10 indicators with the help of which we can detect climate change and global warming. There are 7 indicators that would be expected to increase in a warming world and 3 indicators would be expected to decrease;

Causes of Global Warming and Climate Change:


Changes in climate can result from both natural events and human activities. Examples of natural causes of climate change are volcanic eruptions, variations in the earth's orbit around the sun, and variations in solar output. Examples of human-induced causes of climate change include industrial pollutants and fossil fuels, warming of average annual temperatures due to urbanization, and changes in the earth's albedo due to deforestation of tropical rainforests. Climate change in the context of this paper refers to changes that result from human activities, especially as these changes relate to the issue of global warming. Of special importance is the "greenhouse gas" effect which is defined as, "The trapping of thermal emissions from the earth's surface by human-induced greenhouse gases”. If global warming is indeed happening, it is the greenhouse gas effect that is believed to be the most responsible.

Earth’s temperature depends on the balance between energy entering and leaving the planet’s system . When incoming energy from the sun is absorbed by the Earth system, Earth warms. When the sun’s energy is reflected back into space, Earth avoids warming. When energy is released back into space, Earth cools. Many factors, both natural and human, can cause changes in Earth’s energy balance, including:

·         Changes in the greenhouse effect, which affects the amount of heat retained by Earth’s atmosphere

·         Variations in the sun’s energy reaching Earth

·         Changes in the reflectivity of Earth’s atmosphere and surface

Since the Industrial Revolution began around 1750, human activities have contributed substantially to climate change by adding CO2 and other heat-trapping gases to the atmosphere. These greenhouse gas emissions have increased the greenhouse effect and caused Earth’s surface temperature to rise. The primary human activity affecting the amount and rate of climate change is greenhouse gas emissions from the burning of fossil fuels.

Green House Gases, sources, and participation in rising of global weather


The most important Green House Gases directly emitted by humans include CO2, CH4, nitrous oxide (N2O), and several others. The sources and recent trends of these gases are detailed below.

Carbon Di oxide CO2


Carbon dioxide is the primary greenhouse gas that is contributing to recent climate change. CO2 is absorbed and emitted naturally as part of the carbon cycle, through animal and plant respiration, volcanic eruptions, and ocean-atmosphere exchange. Human activities, such as the burning of fossil fuels and changes in land use, release large amounts of carbon to the atmosphere, causing CO2 concentrations in the atmosphere to rise.

Methane



Methane is produced through both natural and human activities. For example, natural wetlands, agricultural activities, and fossil fuel extraction and transport all emit CH4.

Methane is more abundant in Earth’s atmosphere now than at any time in at least the past 650,000 years. Due to human activities, CH4 concentrations increased sharply during most of the 20th century and are now more than two-and-a-half times pre-industrial levels. In recent decades, the rate of increase has slowed considerably.

Nitrous oxide



Nitrous oxide is produced through natural and human activities, mainly through agricultural activities and natural biological processes. Fuel burning and some other processes also create N2O. Concentrations of N2O have risen approximately 18% since the start of the Industrial Revolution, with a relatively rapid increase towards the end of the 20th century. In contrast, the atmospheric concentration of N2O varied only slightly for a period of 11,500 years before the onset of the industrial period, as shown by ice core samples. For more information on N2O emissions and sources, and actions that can reduce emissions,

Water Vapor


Water vapor is the most abundant greenhouse gas and also the most important in terms of its contribution to the natural greenhouse effect, despite having a short atmospheric lifetime. Some human activities can influence local water vapor levels. However, on a global scale, the concentration of water vapor is controlled by temperature, which influences overall rates of evaporation and precipitation.  Therefore, the global concentration of water vapor is not substantially affected by direct human emissions.

Ozone


Tropospheric ozone (O3), which also has a short atmospheric lifetime, is a potent greenhouse gas. Chemical reactions create ozone from emissions of nitrogen oxides and volatile organic compounds from automobiles, power plants, and other industrial and commercial sources in the presence of sunlight. In addition to trapping heat, ozone is a pollutant that can cause respiratory health problems and damage crops and ecosystems.

Chlorofluorocarbons (CFCs)


Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), together called F-gases, are often used in coolants, foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants. Unlike water vapor and ozone, these F-gases have a long atmospheric lifetime, and some of these emissions will affect the climate for many decades or centuries.

 Change in Reflectivity characteristic of atmosphere due to human activities


Human changes in land use and land cover have changed Earth’s reflectivity. Processes such as deforestation, reforestation, desertification, and urbanization often contribute to changes in climate in the places they occur. These effects may be significant regionally, but are smaller when averaged over the entire globe. In addition, human activities have generally increased the number of aerosol particles in the atmosphere. Overall, human-generated aerosols have a net cooling effect offsetting about one-third of the total warming effect associated with human greenhouse gas emissions. Reductions in overall aerosol emissions can therefore lead to more warming. However, targeted reductions in black carbon emissions can reduce warming.

Impact or effects of global warming and climate change


Our lives are connected to the climate. Human societies have adapted to the relatively stable climate we have enjoyed since the last ice age which ended several thousand years ago. A warming climate will bring changes that can affect our water supplies, agriculture, power and transportation systems, the natural environment, and even our own health and safety. Carbon dioxide can stay in the atmosphere for nearly a century, so Earth will continue to warm in the coming decades. The warmer it gets, the greater the risk for more severe changes to the climate and Earth's system. Although it's difficult to predict the exact impacts of climate change, what's clear is that the climate we are accustomed to is no longer a reliable guide for what to expect in the future.

Effects of global warming and climate change can be observed in the following fields;

Agriculture


Agriculture and fisheries are highly dependent on specific climate conditions. Trying to understand the overall effect of climate change on our food supply can be difficult. Increases in temperature and carbon dioxide (CO2) can be beneficial for some crops in some places. But to realize these benefits, nutrient levels, soil moisture, water availability, and other conditions must also be met. Changes in the frequency and severity of droughts and floods could pose challenges for farmers and ranchers. Meanwhile, warmer water temperatures are likely to cause the habitat ranges of many fish and shellfish species to shift, which could disrupt ecosystems. Overall, climate change could make it more difficult to grow crops, raise animals, and catch fish in the same ways and same places as we have done in the past. The effects of climate change also need to be considered along with other evolving factors that affect agricultural production, such as changes in farming practices and technology.

Coasts


Climate change could affect coastal areas in a variety of ways. Coasts are sensitive to sea level rise, changes in the frequency and intensity of storms, increases in precipitation, and warmer ocean temperatures. In addition, rising atmospheric concentrations of carbon dioxide (CO2) are causing the oceans to absorb more of the gas and become more acidic. This rising acidity could have significant impacts on coastal and marine ecosystems.

The impacts of climate change are likely to worsen many problems that coastal areas already face. Shoreline erosion, coastal flooding, and water pollution affect man-made infrastructure and coastal ecosystems. Confronting existing challenges is already a concern. Addressing the additional stress of climate change may require new approaches to managing land, water, waste, and ecosystems.

Ecosystems


Climate is an important environmental influence on ecosystems. Climate changes and the impacts of climate change affect ecosystems in a variety of ways. For instance, warming could force species to migrate to higher latitudes or higher elevations where temperatures are more conducive to their survival. Similarly, as sea level rises, saltwater intrusion into a freshwater system may force some key species to relocate or die, thus removing predators or prey that were critical in the existing food chain.

Energy


Energy plays an important role in many aspects of our lives. For example, we use electricity for lighting and cooling. We use fuel for transportation, heating, and cooking. Our energy production and use is interconnected with many other aspects of modern life, such as water consumption, use of goods and services, transportation, economic growth, land use, and population growth. Our production and use of energy (most of which comes from fossil fuels) also contributes to climate change.

Forests


Climate changes directly and indirectly affect the growth and productivity of forests: directly due to changes in atmospheric carbon dioxide and climate and indirectly through complex interactions in forest ecosystems. Climate also affects the frequency and severity of many forest disturbances.

In conjunction with the projected impacts of climate change, forests face impacts from land development, suppression of natural periodic forest fires, and air pollution. Although it is difficult to separate the effects of these different factors, the combined impact is already leading to changes in our forests. As these changes are likely to continue in the decades ahead, some of the valuable goods and services provided by forests may be compromised.

Human Health


Weather and climate play a significant role in people's health. Changes in climate affect the average weather conditions that we are accustomed to. Warmer average temperatures will likely lead to hotter days and more frequent and longer heat waves. This could increase the number of heat-related illnesses and deaths. Increases in the frequency or severity of extreme weather events such as storms could increase the risk of dangerous flooding, high winds, and other direct threats to people and property. Warmer temperatures could increase the concentrations of unhealthy air and water pollutants. Changes in temperature, precipitation patterns, and extreme events could enhance the spread of some diseases.

Water Resources and glaciers


Water resources are important to both society and ecosystems. We depend on a reliable, clean supply of drinking water to sustain our health. We also need water for agriculture, energy production, navigation, recreation, and manufacturing.

Many of these uses put pressure on water resources, stresses that are likely to be exacerbated by climate change. In many areas, climate change is likely to increase water demand while shrinking water supplies. This shifting balance would challenge water managers to simultaneously meet the needs of growing communities, sensitive ecosystems, farmers, ranchers, energy producers, and manufacturers.

In some areas, water shortages will be less of a problem than increases in runoff, flooding, or sea level rise. These effects can reduce the quality of water and can damage the infrastructure that we use to transport and deliver water.

Effect of Global Warming in Pakistan

Change of Raining Pattern


Global warming and climate change has a significant effect on raining pattern. Monsoon Rains in Pakistan is the major rainfall season in Pakistan which has been adversely effected by the climate change, the moon soon season has not only shifted but the intensity of rainfall and area or region has also changed, last year 1400 died in floods, 13,000,000 people displaced.

Melting of Glaciers in Northern Areas in Pakistan


Due to the climate change and global warming, there is an overall increase in the climate of northern areas of Pakistan, this causes an increase in the rate with which glaciers melt; this reduces the Ice Reserves for our home country.Melting of glaciers not only causes floods but also causes agricultural losses, water shortages, massive droughts and food shortages.
Increase of Temperature

In the major cities of Pakistan like Karachi,  Islamabad, Rawalpindi, significant increase of temperature and climate can be observed;  as shown by the following graph of mean temperature trend;

Effect on Ecosystem, Human Health and Marine Life;


There is a widespread adverse health effects due to extreme weather conditions. Several loss of marine life due to reduction in mangrove forests

One of very significant effect as observed in Pakistan is the formation of artificial Attabad Lake in Baltistan due to severe land sliding and snow storm.

According to IPCC(Intergovernmental Panel on Climate Change)study for  countries most at risk from climate related threats, Pakistan is  rated :

•        7th in flood,

•       12th in agriculture.

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California Bearing Ratio (CBR) test is a compressive nature penetration test. It was originally developed by Caltrans i.e. California Department of Transportation after World War II i.e. in the late 1930s. 
The test is specifically used to determine the mechanical strength as well as the potential strength of road subgrades and basecourses materials including the recycled material generally used for road and airfield pavements. CBR value is a percentage comparison with the standard crushed rock from California and thus this test is a comparison test.
The test is standardized by American Society Of Testing Materials (ASTM) as D1883-05 (this standard is used for laboratory prepared samples or re-molded samples) and D4429 (for on field soils); and by American Association of State Highway and Transportation officials (AASHTO) T193; and by British Standard as BS 1377; and by International Standard (IS) as 2720 (Part XVI).

Main components of Pavement design

The results obtained by CBR test are used with the empirical curves to determine the thickness of different layers of flexible pavement like subgrade, subbase, base courses. This is the most widely used method for the design of flexible pavement.
CBR value is used to quantify the response of the pavement foundation and subgrade to loading. CBR does not provide any data regarding the properties of the soil except as to compare its resistance to penetration to the base crushed rock’s resistance to penetration. Although CBR test is empirical and has some limitations but it is still used around the world due to its low equipment requirement, ease of performance prediction and history of use.
The two empirical methods for pavement design used now days are CBR method and Group Index Method. In CBR method beside many other steps one step is to determined the CBR value. This test allows the Engineer to design the Capping Layer and the sub-base layer by determining the strength of the underlying soil.
Flowchart for pavement design using CBR method
 

Scope and Objective of the CBR Test

The Objective of the California Bearing Ratio test is to determine the CBR value for a soil under consideration as a pavement foundation.
CBR is generally used for cohesive soils where effect of water content on CBR is more and generally CBR is determined for a range of water content but it can also be performed for cohesionless soils or coarse grained materials where the effect of water content on CBR is small and thus CBR is performed at Optimum Moisture Content (OMC).
According to ASTM; CBR is primarily intended for evaluating the strength of materials having maximum particle sizes less than ¾ inches or 19 mm, but this restriction is not strict one; if the sample has a material larger than 19 mm; equal amount of such material be replaced by material of size smaller than 19 mm but from the same representative sample.
If the sample to be tested contains much fraction of particles of sizes 3 in (Sieve No. 4), the CBR results will fluctuate and thus more trials are required to establish a reliable CBR; thus generally the sample to be tested consists of particles smaller than 19 mm but larger than 3 in.
CBR test can be performed for both in soaked conditions or un-soaked conditions; but mostly soaked conditions is preferred so as to evaluate the material strength in worst conditions. 

Description of Apparatus

Apparatus required to perform the CBR test is as follows;
  • Molds:  Cylindrical mold with an internal diameter of 6 in. and a height of 7 in. with an extension collar of 2 in. height and a perforated base plate.
  • Spacer Disk: A circular disk of metal 5 – 15/16 in. diameter and 2.416 in. height.
  • Rammer: A rammer of mass 4.54 kg (10 lbs)
  • Apparatus for measuring expansions. This consists of a swell plate with adjustable stem and a tripod support for a dial indicator.
  • Surcharge weights: Several slotted or split metal plates of 149.2 mm; diameter and 5 lb weight.
  • Penetration Piston: A metal Piston of circular cross – section having diameter of 1.954 in. Area = 3in2 and not less than 4 inches in length.
  • Loading Device: A compression type apparatus capable of applying a uniformly increasing load up to 10,000 lb at a rate of 1.3 mm/min.Soaking Tank: A tank suitable for maintaining the water level of 1 in, above the top of specimen.
  • Drying Oven: Oven Capable of maintaining a temperature of 110 + 5 0C for drying samples.
  • Moisture content Containers
  • Miscellaneous: Tools such as mixing pans, spoons, straightedge, filter paper, balances etc.

Test procedure

  1. Approximately 18 kg soil pass of 19mm sieve and retain of sieve no. 4 is taken.
  2. Moisture and dry density curve is obtained using the standard AASHTO T 99 or T 180.
  3. Optimum Moisture Content (OPC) is obtained from the graph between moisture content and dry density
  4. Prepare the sample by adding optimum moisture content and then compact the soil in five layers by applying 10,30 and 65 blows respectively in three CBR molds using 10 lb rammer having 18 in. height of fall. The compacted densities of the three specimens range from 95 percent to 100 % of the maximum dry density  already determined by the T 180 compaction test.
  5. Soaking: Place the swell plate with adjustable stem on the soil sample in the mold and apply sufficient annular weights to produce an intensity of loading equal to the mass of sub-base and base courses and surfacing above the tested material, but not less than 4.54 kg (10 lbs) . Place the tripod with dial indicator on top of the mold and make an initial dial reading.
  6. Immerse the mold in water to allow free access of water. Place the sample in water for 96 hours (4 days)
  7. Make a dial reading on soaked specimen and calculate swell as a percentage of initial sample height.
  8. Remove the sample from tank and allow to drain for 15 minutes.
  9. Penetration Test: Place the mold on the loading frame and adjust its potion until the piston is centered on the specimen.
  10. Seat the penetration piston with a 44 N (10 lb) load, and set both the load dial and the strain dial to zero. This initial load is considered as the zero load when determining the stress-penetration relationship.
  11. Place the surcharge weights on the specimens equal to that used during soaking. Apply load at a rate of 1.3 mm / min and record the load for penetration of 0.025 in, 0.05 in, 0.075 in, 0.10 in and so on up to 0.5 inches.
  12. Stress strain curve: Plot curves between load and penetration for each specimen. Apply the corrections to the curves if required. Take the readings of load for 0.1 in and 0.2 in. penetration and find CBR for both penetrations. The greater values is the required CBR for that specimen. Also find the dry density for each specimen.
  13. CBR = Test load value, divided by, the standard load, multiplied by 100.
  14. Design CBR: it is calculated by plotting a graph between CBR values and dry densities of all the three specimens and then calculating the design CBR against value of 85 % maximum dry density.

   Test results, table ,graphs and calculations

Step 1: Getting the relationship and graph between moisture content and dry density
Moisture Density Relationship

Dry Density (lb/cft)
Sample No.
Moisture Content (%)
Dry Density (lb/cft)
1


2


3


4


5



Step 2: Finding the density of the three samples each of 10 blows, 30 blows and 60 blows

Step 3: Load v/s Penetration Graph
Load Penetration Curve

For sample made with 10 blows
Sr.No
Load (lbs)
Penetration (mm)
1
0.5 mm

2
1.0 mm

3
1.5 mm

4
2.0 mm

5
2.5 mm

6
3.0 mm

7
3.5 mm

8
4.0 mm

9
4.5 mm

10
5.0 mm

11
5.5 mm

12
6.0 mm

13
6.5 mm

14
7.0 mm

15
7.5 mm

16
8.0 mm

17
8.5 mm

18
9.0 mm

19
9.5 mm

20
10 mm


For sample made with 30 blows
Sr.No
Load (lbs)
Penetration (mm)
1
0.5 mm

2
1.0 mm

3
1.5 mm

4
2.0 mm

5
2.5 mm

6
3.0 mm

7
3.5 mm

8
4.0 mm

9
4.5 mm

10
5.0 mm

11
5.5 mm

12
6.0 mm

13
6.5 mm

14
7.0 mm

15
7.5 mm

16
8.0 mm

17
8.5 mm

18
9.0 mm

19
9.5 mm

20
10 mm


For sample made with 60 blows
Sr.No
Load (lbs)
Penetration (mm)
1
0.5 mm

2
1.0 mm

3
1.5 mm

4
2.0 mm

5
2.5 mm

6
3.0 mm

7
3.5 mm

8
4.0 mm

9
4.5 mm

10
5.0 mm

11
5.5 mm

12
6.0 mm

13
6.5 mm

14
7.0 mm

15
7.5 mm

16
8.0 mm

17
8.5 mm

18
9.0 mm

19
9.5 mm

20
10 mm

Summary of CBR Test and conclusion

Sample No.
Compaction Effort
Dry Density (lb/cft)
CBR value (%)
1.
10
113
14.5
2.
30
121
28
3.
65
125
34.5

Maximum Dry density _____________________ (lb./cft)
95% of maximum dry density________________(lb/cft)
Resultant CBR or Designed CBR __________________ (lb/cft)
CBR - Density Relation

Limitations

The laboratory and field compaction methods are not identical, however, comparative tests indicate that reasonable correlation of results can be obtained from field compact materials and samples compacted under similar conditions in the laboratory.
Because added strength to highly stabilized surfaces such as asphaltic concrete is neglected, the assumption of a completely saturated subgrade condition sometimes results in a too conservative factor of safety.

Because many of the procedures are of an arbitrary nature, you must run the test to exact standards in order for the design tables to be valid.

Conclusion:

California bearing ratio is a widely used method to design the flexible pavements, beside all the limitations it is easy to perform and still does not need any big instruments etc. The value of the CBR test is then compared with the following table to get the quality of material from which the required thicknesses and other parameters are decided.
CBR VALUE
SUBGRADE STRENGTH
COMMENTS
3% and less
Poor
" Capping is required 
3% - 5%
Normal
Widely encountered CBR range capping considered according to road category
5% - 15%
Good
"Capping" normally unnecessary except on very heavily trafficked roads.

MKRdezign

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