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Physical properties of rock masses

Most of the engineering structures like dams, tunnels, underground power house, roads etc. involves large volume of rock mass. The rock mass is generally more heterogeneous than intact rock. The rock mass contains discontinuity planes in the form of joints and fault planes, bedding plane and foliations. These discontinuity planes are responsible to give different physical properties to rock mass compared with intact rock sample from the same rock mass. These discontinuity planes are responsible to control the  strength and the deformability of the rock mass.

 Three sets of overstressed discontinuities. (Picture by  Prof. Kurt Klima, Graz, Austria)

Discontinuities Characteristics

The important factors of discontinuity planes which influence the properties of the rock mass are; i) Orientation, ii)  Spacing, iii) Continuity, iv) Surface Characteristics, v) Separation of disco-ntinuity Surface and vi) Thickness and nature of filling material.

Orientation:

Orientation of the disco-ntinuity  planes  play  an important role in the strength of the rock mass. The rock mass fail along one or more discontinuity planes.

The role of orientation of discontinuities becomes most important for rock slope stability if:

(a) discontinuity plane or plunge of line of intersection of two wedge forming planes day light the slope at less than the slope angle.

(b) whether the dip of the joint plane or plunge of the line of intersection exceed the angle of internal friction.

If these conditions are prevailing the slope is kinematically  unstable. The  orientation  of  discontinuities  also  influence  the strength of rock
mass.

 Characteristics of Discontinuities (Hudson 1989)

Spacing:

The spacing of discontinuity affect the overall strength of the rock mass. If the spacing is less the strength will be less and if it is more strength will be more.

Continuity:

The continuity of discontinuity planes influence the stability of the rock mass provided the orientation of discontinuity is kinematically critical. If the continuity of the discontinuity planes is more the strength of the rock mass will be less in comparison to case when continuity is less and there are bridges in between.

Surface Characteristics:

Three factors are involved when the surface characteristics of discontinuities are considered.

a)    The waviness or undulation of the surface, which results in variations in orientation or attitude along a given discontinuity.

For joint roughness assessment though there are many methods but very widely used method is to compare the roughness profiles provided by Barton and Choubey (1977).

 Discontinuities due to Cooling of volcanic rocks (Picture by  Prof. Kurt Klima, Graz, Austria)

b)    The smaller scale roughness of the surface, which provides friction between two adjacent blocks.

c)    The physical properties of the infilled material between the two surfaces of discontinuity plane.

Waviness and roughness are first and second order irregularities based on their relative magnitudes. The projections in a rough discontinuity surface are called asperites. Waviness has a greatest influence on the rock mass strength than roughness. For two adjacent block to move along a wavy surface, there must be displacement normal to the surface. The amount of displacement is controlled by roughness angle  and the wavelength of the wave. The waviness angle reduces the dip angle  and thus tendency for sliding is also reduced.

Separation and Filling of Joints:

The separation of joint surface and the presence of filling material in between has a great influence on the strength of jointed rock mass. The separation width affects the shear strength of the joint. If the joint is tight the asperites in the joint surface will interlock and will improve the shear strength.

Whereas if the separation is wide the influence of the infilling material will reduce the shear strength.

References

Goodman, R.E., 1989, “Introduction to Rock Mechanics”, John Wiley and Sons, New York.

Hoek, E and Bray, J.W., 1997, “Rock Slope Engineering”, E&FN Spon and Imprint of Chapman and Hall, 2-6 Boundary Row, London SEI 811 N, UK.

Johnson, R.B and Degraff, J.V, 1991 “Principles of Engineering Geology”, John Wiley and Sons, New York..

Diwali or Deepavali
In Hindi, Deepavali literally means a ‘row of lamps’ and Diwali as it is popularly known, means the ‘festival of light’! We celebrate Diwali in the month of Kartik (October- November) on the darkest moonless night or Amavasya! It is the main festival of many Hindus and celebrated with lights, crackers, sweets and feasts throughout India. Prayers are offered to invoke the blessings of Goddess Lakshmi, the Hindu Goddess of wealth. It marks the coming of winter and the beginning of a new year for the people of Gujrat, the Marwaris and businessmen.

Ishika and Phalguni

Celebrations with lights, crackers and sweets

Prayers for Goddess Lakshmi- the Hindu Goddess of wealth
This festival actually starts from the thirteenth day of the waning moon in Kartik and goes on till the dooj or the second day of waxing moon. There are five days of Diwali. Each day has a special significance.

The first day is called Dhanteras. This day is very important for the business community of India. ‘Dhan’ means wealth and ‘teras’, the thirteenth day of the Hindu month. According to ancient Indian medicine science, or Ayurveda, it is the birthday of lord Dhanwantari! He is the god who grants immortality. On this day, people pray for lots of money and success in the year. Lord Dhanwantari was the divine physician, so people worship him as a symbol of good health on this day! People generally buy new utensils or metal objects as auspicious items, which they believe will ward off evil and ill health for the rest of the year and bring peace and prosperity.

However, there is another noteworthy reason for this day! God Yam, the god of Death, is worshipped on this day to provide prosperity and well being to people. There is a story behind this.

Years ago, King Hima was a worried man. As per horoscope predications, his 16 year old son was doomed to die on the fourth day of his marriage by snakebite!

“The poor prince,” cried everyone, “he is fated to die!” But the prince’s wife would have none of that! On the fourth day of their marriage, she lit countless oil diyas all over the place. She also heaped ornaments and gold and silver coins at the entrance of the prince’s chambers! Then in a lovely lilting sing song way, the princess went on telling stories to her prince.Meanwhile, Yam, the God of Death, disguised himself as a snake and slithered to the prince’s room! But he could not enter the prince’s room! Why? The snake was blinded by the bright lights of the diyas and the ornaments! The snake halted in his tracks. Faintly melodious songs floated to him.

“What are those sounds coming from the chambers?” thought the snake. That was actually the princess singing to her prince. Yam was curious. He went closer. Drawn to the wonderful musician notes, he slithered atop the stack of ornaments. Soon, Yam was lost to the mesmerizing tunes! He sat there through out the night and quietly left in the morning; without harming the prince! Since then, Dhan-teras came to be known as the day of ‘Yamadeepan’! Lamps are kept lit throughout the night in respect to Yam, the God of Death, to prevent untimely deaths!

The second day of Diwali is called Naraka Chaturdashi or chhoti Diwali! The legend goes that on this day lord Krishna destroyed the demon Narakasur and made the world free from his terror! Narakasur was the son of Goddess Earth and had a demonic bent of mind.

He liked to live in filth and was destructive by nature. He harassed the gods living in the heaven as well as the saints praying on earth! One day, he overthrew the king of Suraloka called Aditi. More over, he carried away 16,000 women and imprisoned them in his palace! Aditi was the relative of satyabhama, lord Krishna’s wife!
Satyabhama Killing Narakasura
“This is outrageous!” cried the Gods! “Shame on Narakasura!” “Yes sir, this is terrible indeed!” agreed lord Krishna’s wife Satyabhama. Satyabhama pleaded to her husband Krishna, “please, dear husband, give me a chance to vanquish this evil demon!” Krishna thought deeply and then replied, “All right, dear wife. You may vanquish Narakasura. But, on the battle ground, I shall be your charioteer!”

With Krishna as the charioteer, Satyabhama entered the battle-field. During the war, Krishna pretended to faint thus giving his wife a chance to behead the monster! Narakasura was killed and once again, good prevailed over evil. This event is celebrated with much rejoicing especially in southern India and Assam. Lamps are lit as a mark of celebration. On this day, houses are washed, painted and decorated; all filth is discarded. Children light crackers, eat sweets and generally have fun on this day.

The third day is considered actual Diwali! It is on this day that Lord Ram, Lord vishnu’s seventh incarnation, returned to his city Ayodhya with his wife Sita, after killing the lankan ruler Ravan. Lord Ram has been exiled for fourteen years and the people of Ayodhya welcomed him with lights and flowers. It is also an important day because this is the only day of the year, when Goddess Lakshmi comes down to earth. People perform Lakshmi puja (worship of Goddess Lakshmi) on Diwali, seeking wealth and prosperity for the whole year. People are even expected to take a traditional oil bath and be very, very clean!

 Lord Rama Returns to Ayodhya

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