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

Abstract

Neelagiri stupa, constructed in 2nd Century BC, is a colossal ruined stupa, situated in the woods of the Lahugala Wildlife sanctuary in Ampara district of the Eastern province Sri Lanka. Current status of the stupa has a circumference of 182m (600ʹ) and a height of 22.6m (74ʹ). Presently, one side of the stupa has collapsed and some vertical cracks are visible on the east 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 any major restoration work in order to reach its full height. With this objective, a series of experimental testing and numerical modeling was performed. The foundation of the stupa was assessed by using Ground Penetration Radar (GPR) method. According to the GPR measurements, the stupa spreads 2.87m away from the basal rings to a depth of 3m 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 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 Neelagiri stupa have higher capacity than those of 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 generate within the existing stupa due to its self-weight is well below than the compressive strength and the tensile strength of ancient bricks. Further, the study suggests two alternative shapes (bubble and paddy heap shapes) to complete stupa restoration. Suitable shape is proposed for restoration and the different restoration options have been analysed with respect to structural performance along with the existing conditions.