Cave Temples - Engineering Marvels!

 

The Ajanta and Ellora Caves in Maharashtra India are an architectural wonder! It ’s mind-boggling to look at beautiful structures carved out of rock mass. Many people, unfortunately, are unable to appreciate the engineering skill of the monument creators. Sadly, people think that a group of ancient people with primitive tools just carved their way through the rock. To my dismay, I even heard an orator mention in a discourse that the ancient monolithic structures were built because the people of that period didn’t know the science of laying foundation! I challenge anyone who thinks like this to carve even a simple structure out of a piece of stone!

 

Excavating and sculpting grand structures like temples is not an easy feat. It is not simply the case of removing pieces of unwanted rock and tunnelling ones way through the surrounding rock. Rock is a very treacherous medium through which to travel. (Ref: http://umich.edu/~gs265/tunnel.htm) Even rocks which look sturdy contain numerous faults and cracks. Tunnelling through such rock without studying each rock in detail could trigger a collapse of the structure. 

 

Rock monuments may collapse due to many types of failure; coulomb slip failure which causes the rock to slip along the fault plane, brittle failure caused by the brittle fracture of the surrounding rock mass, weathering of the newly exposed rock mass. The deeper the tunnel is bored, the failure is dominated by new stress-induced fractures which grow rapidly and envelope the whole boundary of the excavation. Constructing monuments in rock masses is not an easy feat and a very good understanding and application of Engineering Mechanics principle is required to prevent failures. Tunnelling through rocks and mountains is very hazardous. The developers are faced with great uncertainty because, while they can examine the exterior of the rock masses visible to them, they have no idea about the structure of the rock which is beneath the outer layer. They must also take into account the geology of the area. Ajanta and Ellora caves were carved out of rocks found in areas of high seismic activities. The engineering properties of rock vary significantly and are dependant on many conditions like the direction of loading. The presence of groundwater also poses significant hurdles in completing the construction. 

 

The engineers must first evaluate the site. They must take into account the topography and climate of the area. They must study the structural stability of the rock mass which is influenced by seismicity, faults and fractures in the rock. They must take into account the permeability of water and the flow rate of groundwater. They must study the effects of weathering on the rock. They must evaluate the rock for discontinuities and defects. In-situ testing of the rock under dynamic load is essential to ensure that the structure will not collapse. Testing of the rocks in the area being considered for excavation is not always straightforward. There are a number of method for testing the rocks, both to determine the in-situ stress on the rock, as well as the rock's ability to withstand this stress. This second part often involves uniaxial and triaxial compression tests to determine the "strength" of the rock. (Ref: http://umich.edu/~gs265/tunnel.htm) 

 

They must also design the structure very carefully and select the geometry which will give stability to the structure. Most tunnels don’t have flat roofs because flat roofs are more susceptible to collapse. It is also not simply the case of removing excavated rock within to create a space. Let us take the example of a circular tunnel. The area of a circle is pir2. Doubling the diameter of the tunnel results in increasing the area by 4 times. The rock which is removed was in equilibrium with the surrounding structure and now that equilibrium is disturbed. The surface area of the excavation is doubled and the forces which are acting on the roof to bring down the tunnel are working on twice as large an area. Hence, excavations cannot be completed without providing some additional supports like using beams and cantilevers. 

 

Hence, we can see that carving out stone monuments is not an easy feat as it involves an advanced knowledge of mathematics and the study of mechanics. To such skilled technicians with advanced engineering skills, building a foundation would have been a piece of cake!

 

Apart from the study of mechanics, they also had to apply their knowledge of analytical geometry and advanced mathematics. If a tunnel was off by even one degree, a few miles from the structure the error would be so great that corridors and staircases will never connect! The design life of these structures is over two thousand years! The engineers who designed these structures had to extrapolate the strength of the rock masses over a period of more than a thousand years because the strength of the rocks will gradually weaken due to weathering and seismicity. The structures had to be designed accordingly and this is why they are still standing.

 

Next time someone undermines the engineering skills required to construct rock monuments, don’t be afraid to challenge them as excavating even a simple tunnel through hills and mountains requires complicated use of engineering mechanics. To the modern Civil and Structural Engineers, the grand structures in Ajanta and Ellora covered from roof to floor is a true engineering marvel which cannot even be replicated in our time with the help of modern tools, lasers and 3D modelling software.