Structural Assessment and Restoration of Neelagiri Maha Seya in Ampara, Sri Lanka

NeelagiriMaha Seya, constructed in the 2nd Century BC, is a colossal ruined stupa, situated in the woods of the Lahugala wildlife sanctuary in the Ampara district of the Eastern province, Sri Lanka. The stupa has a circumference of 182 m (600’) and a height of 22.6 m (74’). Presently, one side of the stupa has collapsed and some vertical cracks are visible on the eastern side of lower dome section of the stupa. Therefore, it is essential to carry out proper investigation on the current condition of the stupa before undertaking any major restoration work to restore the stupa to its original height. With this objective, a series of experimental testing and numerical modeling were performed. The foundation of the stupa was assessed using the Ground Penetration Radar (GPR) method. According to the GPR measurements, the stupa spreads 2.87 m away from the basal rings to a depth of 3 m from the existing ground level. It is apparent from GPR data, there exists gravel type rock below 3 m level from the existing ground and the stupa rests on matt gravel layer. Material properties of the ancient bricks of the stupa were evaluated with adequate laboratory testing. Test results showed that ancient bricks of the Neelagiri stupa have higher capacity than the modern bricks. Numerical analysis of the stupa was carried out using the general finite element software package SAP2000 to assess the stresses developed in the stupa due to its self-weight. The results showed that the stresses developed within the existing stupa due to its self-weight were well below the compressive strength and the tensile strength of the ancient bricks. Further, the study suggests two alternative shapes (bubble and paddy heap shapes) for completing the stupa restoration. A suitable shape is proposed for the restoration and the different restoration options have been analyzed with respect to structural performance along with the existing conditions.