My Experience Story

Story 4: Why We Need to Understand the Rock Structures?

Continued…… Story 3.

As we know on this site we always focus on the fundamentals of everything we discuss here. We always try to explain in a simple way and sometimes with a story, so that readers can understand it very easily and quickly. After reading the first 3 stories you got a little idea of rock and rock masses. Now we will discuss about rock structures. The Director of the Institute (ISM, Dhanbad) was a fantastic professor, researcher, and also an innovative personality. He always used to start his classes with an interesting story. In this chapter, I’ll just recall his speech and what he said in a class on rock mass classification.

History

Do you know – who is William Smith? No- no; I am not talking about Hollywood actor. William Smith from Great Britain, was a geologist in the 18th century. He was a renowned geologist who made significant contributions in the field of geology and even his research and published papers were an important foundation for the work of Charles Darwin. In 1815 he published a geological map of England and Wales. In early 18th century when people even didn’t know anything about rock at that time he prepared a details map based on different rock stratigraphy of a whole country. Can you believe, how much effort he made to prepare the map? The question is not on his effort the question is how? How he differentiated the strata of different areas?

See the below pictures of fossils collected by him in his lifetime (*taken from Wikipedia). At that time he recognized that strata contained distinct fossil assemblages which could be used to match rocks across regions.

He distinguished rocks based on different stratigraphy. Stratigraphy means simply the different origin, compositions, and arrangements of different rock layers (strata). In the early 90s, again discussion started on the classification of rock when there was a need for tunnel excavation for the development of roads and infrastructures. During the excavation of tunnels, engineers were facing issues of rockfall and even sometimes collapsing of the tunnel. The differentiation on the basis of stratigraphy which was done by William Smith was just a knowledge base. It couldn’t be applied in tunnel excavation. Then engineers applied a different technique to differentiate rocks from different-different sites. What was that?

Starting of modifications

One Italian-origin geotechnical engineer Mr. Karl von Terzaghi was a front-line designer and engineer of a hydroelectric power plant(Adolph von Pittel) in Croatia and Russia. During his tenure in that company, he was assigned to design and construct steel-reinforced structures and dams. He classified rockmasses on the basis of -“Upto how much load it can sustain and how much support is required to make the site safe”. At that time it was very popular for tunnel excavation. The classification system was named as ROCK LOAD CLASSIFICATION method. He develop this methodology in 1940s.

Then in 1950s, engineers had developed another classification system.

It was standup time classification system. In 1960s, Rock Quality Designation (RQD) was developed which is still being used by almost every geotechnical project. What is RQD?

People started drilling and extracting core before strating any excavation through rockmasses. After extracting teh cores, engineers simply measures how much intact cores they are getting. If the core is intact that mease the rock is strong and if the core is broken or fractured, then obviously the rock mass is weak. Examining the cores on the basis of intactness is very simple and was a perfect representation of the site specific rockmass. The simple formula of RQD is the ratio of intact core received divided by the total core drilled. It is represented in percent.

Now think about two different situation- One is the fractures of rock is horizontal direction and in second case the fractures of rock are in veritical orientation. Do you think if we excavate two tunnels in these two different conditions of rock structures, the stability of those two tunnels will be same?

In the case of horizontal discontinuties- those structures will act as a beam and can take sufficient load, but the case of vertical discontinuties those vertical blocks will have the tendency to fall with its own gravity load, hence stability condition will be little bit in lower side comparing to the first case. So we can understand, not only the intactness of the rock but also it depends on the orientation of the discontinuties and fractures.

Then in 1970s scientists developed another classification system that considered not only the strength of the rock but also the different conditions and orientations of discontinuties/fractures.

They named this classification system as Rock Mass Rating (RMR). Mr. Z. T. Bieniawski, a geotechnical engineer from Poland developed this classification system. It is simply the combination of rock strength, RQD and the parameters of discontinuties/ fractures (structures).

RMR= Intact Rock Strength + RQD + Discontinuity spacing + Discontinuity condition.

Scientists have prepared different chart for different parameters to convert the abovementioed parameters into different numbers. Later we’ll discuss about those charts and how to calculate RMR.

Story 3: Difference between Geotech and Rock Mechanics

Continued….. Go to Story 2

In story-02 we understood- what is rock mechanics; and now we will understand how it is connected with geotech. Generally, it seems that geotech and rock mechanics, both the terms are similar or the same; but it’s not. In this chapter, we will also understand why rock strength is not the only parameter that affects stability. What are the other parameters, that affect the stability of rock structure?

After a few days of classroom training, we got a full list of classes for the next 3 months. The coordinator made this list of classes. He included lots of other subjects, i.e. geophysics, environmental engineering, soil mechanics, engineering geology, etc. At that time we were confused, about why these subjects have been included in the list. We are here to gain knowledge about rock mechanics but why has the coordinator included these unnecessary subjects? We thought that 6 months are not required to complete the training which was allocated. They don’t have sufficient content, hence added some additional subjects. But slowly we understood – rock mechanics and geotechnical engineering are not the exactly same thing. Geotech has a bigger scope of areas which includes many earth science-related studies and rock mechanics is specifically the study of the behavior of rock and rock masses.

Let’s understand it with a simple story written through Artificial Intelligence (AI)-

Once upon a time in the land of Engineeringville, there were two neighboring kingdoms: Geotechnicalia and Rocktonia. Each kingdom had its unique expertise and focus, and they coexisted peacefully but didn’t always understand each other’s work.

In Geotechnicalia, the engineers were known for their deep knowledge of the Earth’s materials and their behavior under various conditions. The Geotechnicalians were responsible for designing stable foundations for buildings, bridges, and other structures. They were often consulted when constructing tunnels, dams, and retaining walls, as well as assessing slopes for potential landslides. Their expertise was vital in ensuring the safety and stability of structures and infrastructure.

In contrast, the neighboring kingdom of Rocktonia was home to experts in Rock Mechanics. The Rocktonians specialized in studying the behavior of rocks and rock masses in isolation. They worked with miners, tunneling projects, and the petroleum industry, analyzing how rocks fractured, deformed, and interacted with underground stresses. Their knowledge was essential in ensuring the efficiency and safety of mining operations and underground excavations.

One sunny day, an ambitious engineer from Geotechnicalia named Georgina embarked on a journey to explore the nearby kingdom of Rocktonia. She was curious about their specialized field and hoped to learn from their expertise.

As she crossed the border, she met a friendly Rocktonian named Rocky, who was intrigued by Georgina’s knowledge of soil mechanics and geotechnical engineering. Georgina, in turn, was fascinated by Rocky’s profound understanding of rock properties and mechanics.

Over cups of tea, Georgina and Rocky exchanged stories about their respective kingdoms’ projects. Georgina shared how she had worked on building skyscrapers with strong foundations, while Rocky spoke of his experiences studying rock formations for mining operations.

One evening, as they sat by a campfire, Georgina asked Rocky, “What exactly sets Rock Mechanics apart from Geotechnical Engineering?”

Rocky smiled and began his tale:

“In our kingdom of Rocktonia, Rock Mechanics is like exploring the secrets locked within the Earth’s crust. We study the strength, deformation, and fracture properties of rocks, both in the laboratory and in the field. By understanding these characteristics, we can predict how rocks will behave under different stress conditions and how they might respond to mining activities.”

Georgina nodded thoughtfully and responded, “In Geotechnicalia, we focus on a broader range of materials, including soils, sands, and clays. Our work involves understanding the interactions between these materials and structures, as well as their response to changes in environmental conditions like rainfall and earthquakes. We aim to ensure the stability and safety of various civil engineering projects.”

Rocky chimed in, “Ah, that’s fascinating! It seems we share some common ground in studying material behavior but have different applications.”

As they continued their discussions, Georgina and Rocky realized that their kingdoms’ expertise complemented each other perfectly. They decided to collaborate on a project where they could combine their knowledge to design an underground tunnel passing through both soil and rock formations.

The collaboration was a tremendous success, and the tunnel they built became a symbol of harmony between Geotechnicalia and Rocktonia. The project exemplified how bridging the gap between different engineering disciplines could lead to innovative solutions and safer infrastructure.

From that day forward, the two kingdoms maintained a strong bond of friendship, sharing knowledge and wisdom, and working together to solve complex engineering challenges. And so, the tale of Geotechnicalia and Rocktonia reminds us that collaboration and understanding can lead to remarkable achievements in the realm of engineering and beyond.

So we have understood today- geotech is the combination of Soil mechanics and Rock Mechanics. Obviously there are many more areas of Geotech, but at this stage let’s understand it this way.

Now let’s understand why rock strength is not the ultimate parameter to judge stability.

Let’s consider that you are a bodybuilder and you can lift 100 kg weight very easily, you have strong muscles, biceps, triceps, etc. Now consider a situation, that- one of your body parts is broken or you have a fracture in your bone. Will you be still able to lift 100 kg weight easily?

The answer is – “No”.

Well, now consider one of your body parts is broken but that part is your ‘pinky toe’ (5th small figure of your leg) of your leg. Then obviously it will not have that much effect on your body strength and you can still lift 100kg.

Well, now consider another situation, your ‘pinky-toe’ is broken but your doctor has not fixed it perfectly and you have tremendous pain in that figure, and due to the pain you have a high fiver, then will you be able to lift 100kg? Maybe NO.

As you can see here the same person with the same strength has different power in different conditions. Exactly the same is applicable to rock also. No rock on this earth is completely solid. Every rock has at least some fractures or discontinuities and that is why we call it rock mass. Solid rock is an imaginary and theoretical term. All rock/rock masses have discontinuities. From the above example, you can understand that- based on the different conditions of fractures the same entity (here it is a rock) can have different stability conditions.

The most critical and major parameter which affects the stability of rock structure is discontinuity. The condition of discontinuity. We have to understand- how many sets of discontinuities are there inside a rock mass (now you have understood the difference between rock and rock mass). We have to understand the condition of discontinuity, and there are many other parameters of discontinuity that we’ll understand in the next chapter.

You can watch this video on discontinuity survey in geotech How to Perform Discontinuity (Joint) Survey of Rock Mass | Scanline Method

Story 2: Understanding the Basics of Geotechnical Engineering

Continued…. (Go to Story 1)

At the initial stage, we were completely blank about the theories and the real problems of mining industries on the geotechnical part. Obviously, we studied a lot of theories during our college days but after 3-4 years of practical experience- we were utterly blank at that time. Interestingly after 3 months of classroom training, slowly we understood the basic fundamentals, i.e. what is geotechnical engineering? what is rock mechanics? Why it is important? What is the difference between Geotechnical engineering and rock mechanics? How to manage the stability of an open pit slope etc.?

On the first day, one of the professors from ISM- Dhanbad came to the classroom at around 10 O’clock in the morning. His first question to us was-“Do you know why you are here? How much your organization (HZL) has paid for this?”. We really didn’t know the answer to the second question, but obviously, the answer to the first question was- “we are here for the training on rock mechanics.” When the professor told that almost 1 Cr rupees have been paid by our company to complete this training, instantly a special respect from the heart went beyond mere admiration and appreciation.

Now the prof said- “What’s your responsibility?”. He continued. “Your responsibility is to behave like a good student, not an engineer.” He repeated the sentence- “Your responsibility is to behave like a good student, not an engineer.”

His next sentence was- “if you understood the above sentence, then you have understood the definition of rock mechanics”. How?

In a particular situation, how you are behaving defines your character and the same is applicable for rockmass also. Here we came to the institute to learn something. Hence it’s right to behave like a student to maximize our learning curve. If we behave like a competent engineer then we’ll not be able to learn in full swing. Exactly the same is applicable to Rockmass also. How a rockmass is behaving in a particular situation, in a stressed field how does a rock or rock mass mechanically behave, the study of this is called “rock mechanics”. It was so simple.

In the institute, your learning will not depend on how much you are physically strong. Rather it will depend on your IQ level, your mental level, your mental stability, your concentration, and many other parameters. But obviously, physical strength is also a parameter that gives you confidence and keeps diseases away to focus on your study. Exactly the same is applicable to rockmass also. The hardness and strength of rock is one of the important parameters to decide the stability of a structure or any slope, but it is not the only parameter to decide the stability of any slope or rock structure. You can get tons of examples where 30MPa compressive strength’s rock is not failing but 100MPa’s rockmass is sliding/failing. In the next story, we will understand what are those parameters which affect the stability of a rock structure.

Read the first story- Story 1: Starting my Career as a Geotech Engineer

Watch this video on rock mechanics- Lec01:Rock mechanics||Rock engineering||What is a Rock, What is Rock mechanics, What is Rock mass

Story 1: Starting my Career as a Geotech Engineer

In 2011, when I joined a Mining MNC company in India, I had the opportunity to work as an operation engineer. My responsibility was mainly on HEMM’s fleet management, haul road management, dewatering, dumping, drilling activity management etc. At that time, I didn’t have any idea about geotech engineer and geotechnical engineering. From 2011 to 2014, I continuously worked there with the same responsibility in 3-shift operations. Initially, it was very difficult for me to digest all the activities which were running in mining operations because of many reasons.

Challenges faced-

The first one is the language barrier. In the maximum mining industry, shopfloor workers generally communicate with each other through their mother tongue, and in my case it was Rajasthani. Although the Rajasthani language is slightly similar to Hindi, the accent was completely different. The second thing was the completely different climate and food. I am from the eastern part of India (west Bengal). You can easily understand how much different the climate is from east to west, around 2000km from my home town. But somehow I managed and showed my dedication in day-to-day activity which was noticed by my manager and after 3 years my manager gave me an opportunity for a geotechnical training.

Initially, I thought- it was normal training for a short period, maybe for 3-4 days or one week, but when my manager told me that it is a complete one-year’s intensive course, I was a little bit nervous about the proposal. The reason was the bond for the next 3 years. I got an official mail to sign a bond paper against the training of 1 year at an institute- Indian School of Mines, Dhanbad; a reputed scientific institute for mining engineering.

Finalization of the training-

Ultimately after a lot of discussions- management reduced the bond period to 2 years. A total of 15 mining engineers and geologists were selected for the intensive course. The name of the course was- “An intensive course on rock mechanics in hard rock mining”.

I booked my train ticket in Purba Express and started my journey from Rajasthan to Delhi and Delhi to Dhanbad for the training and on 1st January 2014, I reached Dhanbad. On the first day, when I entered my room at the Executive development center- I had no idea about the happiest part of my life.

Training course-

This training was the key to my career as a Geotech Engineer. The total course was divided into 4 parts- 1st 3 months was classroom training and then the next 3 months was practical training. Again next 3 months were classroom training as well as field training in various mining industries and the last 3 months were on projects. Our classroom training was from 9 O’clock in the morning till 5 O’clock in the evening. The first 3 months I really enjoyed the flow of life, there in the Executive Development Centre. We used to start our day from morning 9:00AM. Generally, our duty hours was from 7:45AM in our company till 6 PM in the evening, but here it was from 9:00 AM. If you are an engineer you can understand the happiness of getting an extra hour to sleep in the morning time and we were not different.

Happy Moments-

We were getting hour monthly salary as usual. Not only the salary but also the incentives and extra pocket money. Can you imagine? An engineer is doing classroom training like a college student and getting paid fully with extra pocket money. At least I didn’t have any idea about this situation and really enjoyed every moment in the first 3 months period.

After 3 months we returned back to our workplace in Rajasthan and took small-small projects on the topics which we learned at Indian School of Mines. I took a project on “blast damage criteria. After 3 months again we reached the institute and started classroom and practical training. Our practical training were both in laboratory as well as on field training. We visited various coal and metal mines in the eastern part of India. We visited Narwapahad mines of UCIL, Jaduguda, Khurda mines of HCL etc. and we also visited various coal mines.

But till then we were just enjoying the moments without a deep understanding of the fundamentals of geotechnical engineering. The real understanding came when we started working on real problems. After visiting so many mines and after understanding their practical problems, we started thinking about the solution, but at that time we didn’t have any solution, we just understood the problems. A clear understanding of problems was the pillar of our carrier as a geotech engineer.

You can see this post also– https://waartsy.com/how-a-geotechnical-engineer-confirms-the-stability-of-a-slope-through-numerical-simulation/

In the next part (story 2)- I’ll share my experience, how I took a project on the combination of Geotech and blasting, and how I came to a solution to a practical problem.

Cont…