The temples, shrines, and memorials are historical and cultural landmarks and scientific and traditional knowledge have been playing a guiding role in building them over centuries. The organised urban construction in the Indian subcontinent is traced to the Indus Valley Civilization, which is probably more than 5000 years old. Such human settlements were the primordial flourishing cultural centres with diversity and distinct architectural foundations. The art and techniques of designing and constructing buildings have evolved over the period as a part of human history, depending on societal needs, cultural ideals, and technological progress. The monumental structures were constructed to symbolise the faith, power, wealth, and prosperity of contemporary society.
SCIENTIFIC BASIS OF RESILIENT STRUCTURES
The temples, constructed hundreds of years back, are the reflections and repositories of cultural heritage and technical advancements of the time. For example, the workmanship of the Brihadeshwara Temple (Thanjavur, Tamil Nadu) baffles modern-day architects as to how the monolithic ~ 80 tons granitic capstone was lifted and placed on top of the hollow vimana measuring 216 ft (66 meters), 1000 years back! Temples, being the abode of the divine almighty, are decorated with intricate carvings representing the rich culture of the society and are built with the best know-how to make it stable for the appreciation of future generations.
Image Courtesy: Dr VM Tiwari
Several grand structures, forts, shrines, and monuments like the Taj Mahal were built in the northern Indian region in the historical past. Traditionally, stone masonry and lime mortar have been used for long durability for old temples and other monuments in northern India, which are earthquake-resistant to certain extent. The earthquake resilience of these structures is time tested. For example, the 1905 Kangra earthquake (~ M 7.9) did not damage the Chamba temple. The grand Sri Ram Temple, Ayodhya, built in Nagara style, in sandstone and granite rock without any steel, is a living testimony of the science and technology-based physical structure of spirituality, culture, and architecture of modern India. It is planned to stand for over 1000 years for the worship of future generations.
Formal structural design for earthquake resilience structure in the northern Indian region started in the early 20th century, particularly for railways.
Being conscious of the Ganga plain’s vulnerability to the potential seismic hazards from the Himalayan earthquakes as observed during the Great Earthquake of 1934, which devastated north Bihar, the Construction Committee of Sri Ram Janmabhoomi Teerth Kshetra Trust approached the Council of Scientific and Industrial Research (CSIR) to investigate the site for seismic hazard and vulnerable geomorphology, and propose foundation design. It is worth mentioning that the CSIR is an umbrella organisation with a large number of institutes providing solutions on critical infrastructure projects, including Nuclear Power plant sites, roads, bridges, and some aspects of the new Parliament building, natural hazard assessment and rehabilitation plans to name a few relevant aspects (https://www.csir.res.in/).
The initial testing of the foundation design for Sri Ram Temple brought forth the limitations and challenges of alluvial soil on which the temple had to be built for millennium longevity. The geological and geotechnical investigations are critical for such construction in the Ganga Plain due to potential earthquake hazards such as ground displacement, soil liquefaction, etc. The geoscientific knowledge and computer simulations have facilitated for planning of geo-hazard resilience structural design, material selection, and foundation design for the large colossal structure of Sri Ram Temple at the Sri Ram Janmbhoomi Shthal Ayodhya. The geotechnical studies performed were similar to those undertaken for the large infrastructural projects. Further, advanced methodologies and models were employed for 3D structural analysis and design, optomechanical design for Surya Tilak of Shri Ram Lala on Shri Ram Navami, etc.
NEAR SUBSURFACE IMAGING
The multiparametric geological and geophysical studies for shallow sub-surface imaging and site-specific seismic hazard assessment were undertaken to understand the engineering properties of the topsoil and characterize engineering bedrock, which forms a stable base for the temple. Before the initiation of the investigations for shallow subsurface characterization of topsoil, a conscious discussion and brainstorming was done to aim at “locating and characterizing a stable lithological datum in the older alluvium (>10,000 years old), which will form the engineering base for the temple”. A team of CSIR-NGRI (National Geophysical Research Institute) & CSIR-CBRI (Central Building Research Institute) scientists, technical and project staff worked determinedly during the COVID-19 pandemic to carry out required geoscientific investigations at the construction site of Sri Ram Janmabhoomi Temple, Ayodhya, for sub-surface imaging and to simulate the site-specific earthquake hazard scenario, incorporating site-specific observations (NGRI-SEISM-2021-902). State-of-the-art non-invasive geophysical techniques, capable of exploring physical properties of the subsurface soil/rock layers from a few meters to >500m depth, were deployed at the site. These include Ground Penetration Radar (GPR), Multichannel Analysis of Surface Waves (MASW), Electrical Resistivity and IP tomography (ERT-IP), Deep Resistivity Sounding (DRS), seismometers and seismic accelerometers. These investigations were used for preparation of maps of soil types, structural layering of soil, moisture contents, stiffness, load-bearing capacity and liquefaction potential of the soil, presence of large archaeological discontinuity, etc.
Image Courtesy: Dr VM Tiwari
The GPR survey at Sri Ram Janmabhoomi temple complex identified buried well and other cultural discontinuities in the top soil, which were verified during the excavation
The DRS experiment was carried out to determine long term stratification and property including moisture bearing horizons in the soil, rock to a depth of >300 meters. The ERT-IP and MASW study at the temple complex provided high resolution data on the layered structure of the shallow subsurface soil for >50 m depth. Three distinct shallow subsurface stratigraphic layers were deciphered at the temple complex. The stiffness property and saturation levels of the soil layers were determined using MASW and ERT-IP experiments, which were performed in the multiple profile mode to get a dense coverage of the property. Several buried wells extending down to ~30m depth were identified with damaged well-lining and disturbed subsoil were identified in the GPR surveys. The identified buried structures were filled with cultural debris, inferred from lithologs of the soil cores taken through the boreholes, drilled for soil testing. The liquefaction potential analysis of the sediment layers at the temple complex was carried out with a Peak Ground Acceleration (PGA) of 0.25g and as per the procedure described in 1893 (Part 1):2016. Eleven temporary broadband seismometer stations were installed around the site for the seismic site amplification and micro-tremor observation between 28 December 2020 and 4 January 2021. It is a fast, cost-effective, and non-invasive method that provides an indication of the initial soil site frequency and amplification without earthquakes by performing horizontal-to-vertical spectral ratio (HVSR) analysis. The analysis provides assessment and is important if a large difference exists in the shear wave velocity of the shallow soil layers. The finding goes as input to the foundation design and site-specific earthquake hazard assessment.
Studies also clarified that paleochannel depression at the site is an old marginal abandoned channel along the meandering scar in the pre- Holocene Bhangar surface of the Older Gangetic Alluvium and is not related to the active flood plain of the river Saryu, which lies at >10m below the surface.
SIMULATIONS FOR SITE-SPECIFIC EARTHQUAKE HAZARDS
Several broadband seismometers and accelerometers were installed to record near surface geophysical micro-tremors to characterise the net effect of earthquake sources, seismic wave propagations and local site conditions. Following a standard procedure using deterministic ground motion prediction equations, Peak Ground Accelerations (PGA) at the site were estimated and for the simulations, an extreme Himalayan event of ~ M8.2 was considered. The required variables are considered from geophysical studies and logging for characterizing the subsurface soil. In addition to subsurface soil characterization, the response spectra of soil and proposed structures were modelled for various scenarios of Himalayan earthquakes. The modelled response spectra are compared with those observed during the 2015 Nepal earthquake of 7.8 and less magnitudes. The probabilistic and deterministic seismic hazard analyses were carried out and a design parameter has been proposed for a solid foundation that will be able to withstand an 8.2 magnitude earthquake on the Richter Scale. An estimate of horizontal shear force likely to be generated for such a massive sandstone masonry structure was made considering site-specific information. An existing CSIR-NGRI seismic station at Faizabad, ~10 km away from the temple site, was operational, recording continuous data on the ground rumblings including the 2015 Nepal earthquakes; it has proved advantageous as it provided observational control and verification tools for seismic hazard assessment simulations.
FOUNDATION DESIGN
The presence of a shallow moisture-rich soil layer extending towards the Saryu river bed, with the potential for moisture connectivity during the high flood, is moderately susceptible to liquefaction, when saturated, and numerous archaeological artefacts, wells extending beyond 15 meters from the surface (Fig. 1), led to the recommendation of the removal of the top 15 meters of soil and lay an engineered foundation over which the foundation for temple should be built. The foundation scheme of Shri Ram Temple is decided through a detailed deliberation of an independent expert committee. In the background of the above information, the excavation schemes, vetting of soil investigation schemes, foundation design parameters, design vetting of stone retaining structures at Mandir premises (plinth level) and concrete retaining wall at the periphery of the temple, estimation and vetting of liquefaction potential of the site were suggested to the construction agencies. The entire footprint of the foundation was excavated and filled with engineered fill (Roller compacted concrete) compacted in several layers. Over the foundation, the plinth has been constructed using granite stone, arranged in a staggering manner, and interlocked with each other using stone keys. Over the plinth, the superstructure is being constructed using Banshi Paharpur sandstones.
Image Courtesy: Ram Janmabhoomi Teerth Kshetra Trust
STRUCTURAL ANALYSIS AND DESIGN
Based on the information obtained from various inputs (geometrical characteristics, material properties, construction details, etc.), several computer simulations were made for assessing the structural behavior concerning gravity and lateral loadings. The Shri Ram Mandir structure at Ayodhya was modelled using both a) macro and b) micro modelling approaches and were analyzed for static and dynamic loading conditions. The dead load and live load were considered as static load input. The dynamic loadings, essentially the seismic and wind forces, were applied to the structure. The 3D structural analysis was carried out using commercially available Finite Element Method (FEM) based software packages. Seismic input was obtained based on the site-specific earthquake spectra provided by IIT Madras after a PSHA analysis on CSIR-CBRI and CSIR-NGRI data. The best-performed and architecturally suitable model was considered for construction after a detailed structural analysis of the 3D models, incorporating the design modifications and performance assessment of each model. The proposed design modifications are made considering the Nagara style of architecture intact. The proposed modifications have enhanced the architecture, ensuring the structural safety for the Maximum Considered Earthquake, i.e., for a 2500-year return period (Fig 2). The CSIR-CBRI officials have guided the construction agency, architect, and PMC regarding the adherence to the structural design performed by CSIR-CBRI and other construction SoPs. They have also given several expert opinions related to the construction issues and execution.
Based on astronomical calculations, an optical arrangement is being made in such a way that sunrays will fall on the forehead of Lord Shri Ram’s idol for about six minutes on Ram Navami day every year at 12 pm. Explicit building structural design for such optical arrangement and stability is made. The design also made provisions for the required opening and passages within the stone structure to enable solar light travel in a particular path for Surya Tilak of Shri Ram Lalla on Shri Ram Navami each year.
The design life of the structure is 1000 years, and it is a dry-jointed structure consisting of only interlocked stone with no steel reinforcement. The 161 ft high structure with three floors of 20ft has five mandaps: Garbh Griha, Gudh Mandapa, Ranga Mandapa, Prathana Mandapa, and Nritya Mandapa with double domes. The interior domes named Ghummat are supported by several columns placed in an octagonal manner whereas exterior domes named Samran are supported on columns arranged in a square fashion. Pillars/columns are constructed of 7 stone pieces interlocked with corbels present at different levels to support the beams and arches.
STRUCTURAL HEALTH MONITORING
Maintenance and preservation of such monuments are equally vital. Therefore, it is to have settlement monitoring of rafts and plinths, health monitoring of super structures and retaining walls including the scheme of installation. Different sensors are installed on the raft, plinth, and retaining structures, and information is collected and monitored in real-time.
*The writer is Director, CSIR-NEIST, Jorhat, & Outstanding Scientist, CSIR-NGRI, Hyderabad. The article is co-authored by Dr R Pradeep Kumar, Director, CSIR-CBRI, Roorkee; Dr AK Pandey, Chief Scientist, CSIR-NGRI, Hyderabad; Dr D Ghosh, Principal Scientist, CSIR-CBRI, Roorkee; and Dr M Samanta, Principal Scientist, CSIR-CBRI, Roorkee. The authors gratefully acknowledge the support of the Directors of CSIR Laboratories, Temple Trust, M/s CB Sompura, M/s L&T, and M/s TCE. Several colleagues who have contributed to the investigations and attended to the submitted technical reports are duly thanked.
