INTRODUCTION:
With over fifteen
hundred rock-cut caves and temples in India, I have been interested in finding peer-reviewed
articles on the geotechnical aspects and structural engineering techniques used
to develop these massive and impressive structures. I was not successful in
locating peer-reviewed material that discusses in detail the engineering and
construction methods used to carve out these grand monuments; however, I found
information on the design of underground caverns. From a study of these
journals, I could understand the complexity of designing structures like the
Kailash temple at Ellora and the Ajanta caves. The design of these monuments
required the application of complex engineering principles.
STUDY OF ROCK
FORMATION
In the modern
era, the excavation of underground structures like caverns and tunnels begins
with the study of the type of rock formation. The formations are classified
into two main types.
1. WEAK
FORMATIONS. These are the formations of shale, clay, limestone, etc. Weak
formations are prone to crumbling. The Badami Caves are an example of weak
formation, as these are sandstone structures.
2. HEAVILY
JOINTED FORMATION OR HARD ROCK FORMATION. Granite, diorite, and basalt are
examples of heavily jointed formations. Natural hard rock cliffs and formations
have numerous cracks and discontinuities that break into many smaller blocks.
The types of failures experienced in hard rock formations are gravity-controlled
falling, sliding of blocks and collapse of rock columns. Mahabalipuram has
granite structures, while Ajanta and Ellora caves are carved out of basalt
rock.
TYPES OF
FAILURES IN ROCK EXCAVATION:
Any underground
excavation faces problems from failures in roofs and walls, from the collapse
or crumbling of either the roof or the wall. Modern underground cavern design
involves complex engineering calculations that primarily rely on geotechnical
data, rock mechanics principles, and numerical modelling to ensure stability
and safety. Key calculations include assessing in situ stresses,
determining rock mass strength, predicting failure modes, and designing support
systems.
The stability of
the excavation depends on the strength of the rock mass that surrounds the
excavation. Stress induced in the
structure being excavated is a function of the excavation shape and the in-situ
stress that existed before excavation. The strength of the rock formation is
often not uniform and varies.
ANCIENT SANSKRIT
TEXTS ON BUILDING PLANNING & CONSTRUCTION
In ancient
times, Sanskrit treatises like the Silpa Shastra, the Vastu shastra, the South
Indian Agama text and texts like the Samarangana Sutradhara provided the
calculations and methodology required to complete complex constructions,
including rock-cut monuments. The documents discuss in detail the construction
of towns, villages, public houses, residential areas and also deal with the
construction of the temples. These documents provide instructions on how a
building, such as a temple, must be developed from the blueprint phase to the final
consecration phase. The documents also provide complicated geometrical
calculations, units of ancient measurement and conversion from one unit of
measurement to another.
THE ANCIENT
ENGINEER
The master
architect/engineer who developed the plans and oversaw the construction was
called a Stapathi. The ancient treatises have dedicated chapters that discuss in
detail the qualification of a Stapathi. The documents also mention that the Stapathi,
who is engaged to oversee and plan the construction, must have sufficient practical
experience. The Stapathi must be proficient in engineering, designing machines,
carpentry, arithmetic, astronomy, geology, and astrology. The ancient texts
have details about building machines that were used to manipulate / harness
energy from the five elements. We normally assume that the massive stone
structures were carved with the help of a hammer and a chisel, but the ancient
documents specify the design of many machines that could be used to manipulate
the construction material.
The design and
construction of monuments like the Kailash Temple at Ellora were carried out by
a team of professionals who were quite proficient in engineering and
geotechnical sciences. The Samarangana Sutradhara, for example, discusses the study
of the site, soil verification and testing before commencing construction. The
site for the rock-cut temples and caves was carefully chosen and studied before
construction could begin. These complex structures were definitely not built by
primitive artisans who arbitrarily chose a location and started to chisel away
at the rock. There was careful planning and study of the rock layer at every
phase of the construction. The strength of jointed rock masses depends on the
interlocking blocks that exist between individual pieces. Damage to the
interlocking blocks during excavation results in instability. Hence, the
construction could not have proceeded without studying the exposed structure at
various phases.
KAILASH TEMPLE -
ELLORA
For this
article, I am focusing on the Kailash temple, a monolithic structure at Ellora.
The basalt cliff is part of the Deccan plateau, which was formed by layers of
volcanic lava. The cooling of lava created a network of interconnected
fractures, cracks and columns in the basalt. Modern excavation uses rigorous
structural monitoring and reinforcement. The ancient engineers from this time
period also followed such procedures, as evidenced by the partially built
vihara in cave 24 at Ajanta.
ANCIENT
BLUEPRINT
The building of the
Kailash temple started with a proper plan (blueprint). The Vastu Shastra texts
define blueprint types that follow a grid system for planning the structure and
the space within the temple. The method of making the blueprint is called
padavinyasa system. Depending on the scale and complexity of the planned
temple, the plan for the temple is drawn on an 8X8, 9X9 or 10X10 intricate grid.
A detailed plan of the temple with ventilation holes, drains and arches on
doorways was mapped on a grid-based plan, which allowed for designing a
symmetrical layout.
STRUCTURAL DESIGN
& SEISMIC RESILIENCE
The texts on
constructing temple like the Vastu Shastra or the Samarangana Sutradhara, also
classify the temples based on the type of spires; curvilinear shikara style,
gopuram style, etc. The temple tower on the vertical axis was modelled after
mountains like Mount Meru, Mount Mandhara, Mount Kailasha, etc. The number of
storeys on the temple tower was based on the mountain model selected for the
temple tower. The tapered pyramidal structure of the temple tower facilitates
downward load transfer and minimises lateral thrust. The lateral thrust is the
horizontal force generated by building elements like arches, walls, etc., that push
outwards against their support or adjacent soil. For example, arches convert
vertical loading into diagonal forces that exert horizontal thrust at their base.
The stepped tiered structure of the tower minimised vertical loading. The temple
has a low centre of gravity because of its tapered pyramidal structure with a wide
base. This design, along with load-bearing components like beams that were
carved out of the same monolithic rock, makes the temple exhibit inherent
seismic resilience.
TOP-DOWN
CONSTRUCTION METHOD
The construction
team used a top-down approach. At first,
a narrow tunnel was drilled closer to the roof. From there, the team excavated
downward and outward. The advantage of this method was that scaffolding was not
needed.
At each layer,
the team had to stop, study the strength of the rock and then either continue
with their work or make in-situ modifications.
The Kailash temple has a network of staircases and interconnecting
corridors. The load-bearing pillars and beams have been carved out of the rock.
Taking into consideration the staircases and corridors, the top-down
construction method with in-situ alterations to avoid faults in the rock was a
very complicated process. When even a 2D drawing of this temple is difficult to
create, imagine an intricately carved structure that was excavated one hundred
feet into the hill. The design also incorporated ventilation systems, a drainage
system for drainage of rainwater, and temperature control through passive
cooling. There was no room for error. Even with in-situ modifications, the
overall design with passageways, doors, staircases, vents and drains had to
comply with the original plan. With free-standing structures, it is relatively
easy to make corrections and alterations, whereas with carving a monolithic structure
like the Kailash Temple, there is no room for error because the design is
literally set in stone!
REFERENCES:
Methodological
Elements of Indian Temples – Laxmi Singh
Practical Rock
Engineering – Evert Hoek
Building Materials
of the Hindu Temples Part II GRANITES and other ROCKS - Dr Uday Dokras, PhD, Sweden,
Srishti Dokras, Architect
Temple
engineering and seismic design in ancient Indian architecture: An inquiry into
structural intelligence and earthquake resilience - Sikhasree Ray and
Santigopal Jana
