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Tissamaharama Temple PDF Print E-mail
Written by Administrator   
Thursday, 06 May 2010 05:30

CONSERVATION OF TISSAMAHARAMA

MAHA STUPA

 

The chief priest of the Tissamaharama temple had pointed out to the head of the State on one of his inspections in 1993 that the Tissa Maha stupa had developed series of vertical cracks right round the dome of the stupa. According to him, the phenomena had started  around 10 years before and was attributed the vibration caused by heavy lorries boulders to Kirinda down a road adjacent to the stupa. The author was requested to inspect the stupa immediately and submit a report. Accordingly an inspection was carried out by the SEC and a report  was submitted to the Department of Archaeology on 22nd June 1993. According to this report there were ten large structural cracks which were almost vertical and were  evenly distributed around the dome. Each crack had the widest separation at the middle of the dome, (where one could insert a clenched  fist ), and appeared to spread  towards the top square (Hatareskotuwa) and towards  the basal terraces (Pesawas). The structural integrity of the stupa was definitely impaired and was beyond restoration to its original condition except through removal of the separated section and re building. It was also evident that one could not predict when there would be a catastrophic collapse not unlink the one occurred at Mirisavetiya.

Ttssamaharama Maha Stupa (Mahanaga stupa?), had been restored fully 1900 with public donation. No records were available of the construction work, (except that the total cost of reconstruction was Rs. 19,000/=), nor how the ruins looked like before restoration works. In fact, little information  is available as to the period of original construction of four stupas found today at Tissa, the ancient Magama. (The stupas being Mahanaga, Yatala, Sandagiri and Menik Stupas ). The Mahanaga or the Tissamaharama stupa was probably built in early second half of the third century  BC by king Mahanaga (the first king of Mahanaga ), or by King Kavanthissa in first half of the second century BC. It appears that no restoration work was done on this stupa till the last half of the 19th century (1857-1900), after the last rifling of this stupa by King Magha(1215-1236 AD).

In early 1994, the Director General of Archaeology requested  the SEC  to submit proposal for the prevention of a catastrophic failure of the stupa, which was imminent. The proposal made by the SEC consisted of embedding horizontal reinforced concrete rings, nine in number,  placed just below the surface of the dome, suitably spaced between the Pesawa and the Hatareskotuwa. This proposal was submitted after computer assisted structural analysis by our engineers using available data (the quality of the surface bricks), and was carried out with the help of the civil engineering  department of  the university of Paradeniya. This proposal was accepted and the SEC started work on the first ring at the top most part of the stupa on 14th june 1995.

To construct  the RC ring beams in the dome, bricks on the surface of dome of dome had to be removed to a depth of about one foot and to a width of about a foot for each of the ring beams. Whist constructing the first beams , we  noticed that the original cracks had developed further since the first inspection and also the number of cracks had also gone up to 16 from the initial 10 The Hareskotuwa also showed cracks at certain places. It was evident that any tampering with the existing dome such as construction of trenches to embed the RC ring would further weaken the structure, especially the trenches which would have to be made on the vertical part of the dome. Two internationally reputed conservation engineering experts, (Mr.Alan Baxter and Professor Crochi ) were consulted by the Dept. of Archaeology and they too expressed concern about removal of any  brick work from the stupa  dome. Therefore, it was decided to stop embedding RC rings after the top most beams, and seek further proposal from the local engineering organizations for a suitable method that does not involve further weakening of the structure even temporarily during application of preventive measures.

The best proposal came from Professor Crochi who thought that the cracks which appeared almost 80 years after the restoration work would be due to the deformation of the inner body of the dome due to weathering of material and/or differential soil settlement, higher settlements being in the middle where the pressures are high. The latter  phenomena being more probable since the cracks appeared around the time the newirrigationscheme(Lanugamwehera), which would have raised the water table and lowered the friction angle and shear strength of the sandy clay soil. He recommended a series of tests and long term collection of data to ascertain the causes instability as well as the behavior of such large structures to the  Dept. of Archaeology. He recommended instead of an intrusive intervention an external “security network of circumferentisl cables “ around the anchored to a series of meridian strips. The cables were to be pre-tensioned and should be capable of post tensioning at a later date.

The SEC in April 1997, carried out an emergency intervention (the cracks were widening alarmingly), with a cost effective system based on the ideas proposed by Professor Crochi. It consisted of installation of two 1 inch diameter galvanized steel cables tied around the circumference of the dome around the middle. The cable ran along the circumference 6 feet apart over 16 nos. evenly spaced, 8’*4’ hot dipped galvanized steel bearing plates held in place over the surface of the dome by galvanized steel spikes at the four corners of each plate. Each cable was made in four segments with four separate hydraulic tensioning devices specially designed and manufactured for the purpose. After tensioning the cables, the hydraulic rams were removed and connectors were locked ir This experimental  procedure was carried out successfully and we were asked to install four more cables, two above and two below, these two cables. This time cables were and plates were of stainless steel. After placing these cables. The galvanized  steel cables were replaced with stainless steel ones. Frovisions have been made to install three more cables, if the requirement arises in the future. We also installed a RC beam circumferentially around the bottom of the dome. This beam was placed touching the dome on the top most Pesava and did not require any intrusion in to the dome itself. Presently, we have installed three RC beams and six stainless steel cables. This work was completed in Feb. 1998 (at a total cost Rs. 6 million), and appears the propagation of cracks (by then 19 in all), have ceased and structure is stable at present.

The Hatareskotuwa had developed some cracks by this time due to the settlement of the dome. The SEC was able to use a similar method to tie up the Hatareskotuwa externally at the top and the bottom, using mechanically tensioned steel ties with steel edge bearing pads.

Although Professor Crochi recommended a few years of observation on effects of this non intrusive intervention, the relevant authorities appear to be very confident of the ability of the “security net “ to hold the dome for some time, that they have now filled the cracks on the surface and re-plastered the whole stupa with the kind assistance public donors. It has been re painted recently and is awaiting the placement of the Top most part of pinnacle (Chuda Manikkyaya).

We at SEC are very happy that we were able prevent a catastrophic failure of one of most visited and venerated stupas in Sri Lanka. It is very likely that further interventions are required since the structural integrity of the stupa was already impaired when we stared this work to stop a catastrophic failure. Perhaps the next generation of engineers will able to offer a better solution in the future if and when another intervention is required. It would interest the reader to know that the Sandagiri Stupa which had been restored much later than Tissa Stupa had a catastrophic failure around an year ago.