GEM - Art

Stabilization and Conservation of Minaret Choli in Erbil

Choli minaret is dated to the Atabag period (12th century). The structure was built from low burnt bricks using gypsum based renders and mortars. Due to the long term effect of deterioration, the essential part of the architecture has disappeared and thus the leaning minaret is the last survival of the past mosque.
The current shape of the minaret covers the lower, seven-angle section of about 12 m high and upper broken cylindrical part of approximately 24 m high. The body shelters a double spiral staircase. A large extent of precious historic fragments of renderings and embossments were identified in the lower part of the object. Particularly large scale findings of Egyptian blue ceramic decoration in niches are considered as upmost important. All fragments of ceramic, brick and stucco decorations were seriously affected by weathering and mechanical damages.
Probably due to the sudden movement of the geological underground layers the whole structure lost its upper part. Subsequent long term effects of leaking rain water and the intensive weathering made the structure unstable and the surface of the minaret heavily deteriorated. There was also serious loss of joint material and decrease of binding media in the joint mortar.
The general assessment of the whole monument had carried out before the conservation and stabilization of the minaret started. The research covered photogrammetry documentation, 3D visualization, comprehensive geo-physical survey of the surroundings (incl. Micro-gravimetry, Shallow Refraction Seismology, Resistance methods and Seismic 3D/2D Tomography), comprehensive material research, geological survey and static measurements. General seismic study was carried out to identify the origin of inclination and reasons of the historic loss of the upper part of the minaret.
The policy of intervention was kept in terms of pure conservation of the historic landmark. The stabilization of the whole structure and conservation treatments of all surfaces were carried out without the tendency to reconstruct missing and unknown parts of the minaret.
The main task of the project was to make entire static masonry reinforcement of all walls. The total stabilization was done by inserting stainless steel spiral rods into the minaret walls to reconnect internal body wall with external shell. The re-connection of damaged parts was carried out using HELIFIX system.
The conservation of masonry covered repointing of all joints in the entire brick structure, consolidation of bricks and restoration of fragments of both ceramic and gypsum decorations including color and plastic retouching. The interior of both staircases has been rehabilitated. Only those bricks that have been deteriorated to the extent of losing their stability were replaced. Bricks for substitutions were handmade and produced according to the historic technology in the specialized brick workshop with the respect to the historic ratio of raw materials.
All refilling material followed the results of the research of ancient materials to be fully compatible with the original. Last remaining stucco architectural parts that were in acute danger of collapsing were re-attached back to the core of the minaret. As an adhesive media, the putty based on modified gypsum was used. Subsequently, all open spaces, crevices and cracks were thoroughly filled with the modified gypsum based filling material.
To prevent the loss of stability of surrounding area by soaking of soil by rain water, the circle around the minaret was fully drained. New pavement from burnt brick tiles called “farshi” was addopted.
 

Minaret Choli - Handing over ceremony

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