PSI - Issue 29

A. Boostani et al. / Procedia Structural Integrity 29 (2020) 79–86

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Boostani et al./ Structural Integrity Procedia 00 (2019) 000 – 000

1. History, construction and static consistency The Noh-Gunbad Mosque in Ba lkh is certa inly the most ancient mosque in Afghanistan, and one of the oldest monuments of a ll Islamic world; the few still standing parts are constantly exposed to weathering degradation and severe seismic risk. Such extraordinary building has an enormous importance due to the magnificent gypsum decoration and it is now the subject of a first intervention of reinforcement in order not to lose its va luable testimony. The Noh Gunbad mosque is currently in a state of extreme weakness, despite having a lready lost a ll its domes and large part of the arches system. “Noh Gunbad” in Dari language has the meaning of “nine domes”. In fact the old mosque, built a few kilometres from the city of Ba lkh in the North of Afghanistan, during the last decades of II century from Hegira (i.e. at the end of VIII a.C.) under the Governor Fazl, the Barmak ids (following the recent Chahryar Adle’s , (2011) hypothesis on dating) was origina lly composed by nine domes. The building has a perimeter of twenty meters, closed on three sides, inside which fifteen big arches supported the domes and relied on a system of columns partly isola ted, partly leaning on the outer wa lls. All the interna l surface of the monument was covered by a decoration made of carved gypsum and representingdifferent stylizedbeautiful drawings (once coloured too). Unfortunately, probably an earthquake, caused the partia l collapse of the mosque that is yet partia lly hidden, from the floor to the middle of the columns, by a thick layer of debris. The monument was, for the first time, made known to the internationa l community by the studies of preeminent scholars (Pougatchenkova, 968; Golombek, 1969; Sâ lek, 1983) and, finally, by the recent studies of ChahryarAdle (2011). Few years after 2001 the French Archaeologica l Delegation in Afghanistan (DAFA) took care of the monument, organizing, together with Associazione Giovanni Secco Suardo and WMF, a team of expert, involving University of Florence and French restores, with the a im to arrange a Plan of Conservation. In 2011 Aga Kan Trust for Culture (AKTC) started with the first phase of consolidation works rela ted to the standingarch system (nowcompleted). In the present phase, a imed to remove the debris in order to make visible the origina l architecture , the team faces with the need to consolidate the building, weakened aga inst earthquakes by the expected excavations. The topic of this paper is rela ted to a specific part of consolidation of the perimeterwa lls. The ancient mosque of Noh-Gonbad is a modest building in terms of its dimensions; its plan is a perfect square, which each side measuring 20 m. In its origina l configuration, it looked like a squared volume topped by nine domes, identica lly shaped, supported by fifteen arches. What characterizes this artefact is the audaciousness of the architectura l solutions, the origina lity of the materia ls used, and their combinations, Fig. 1. The portions of the perimeter wa lls represent the externa l, coarser shell of the mosque while the inner part is constituted by the massive, refined, and exquisitely decoratedarcadesystem, Fig.1b, c. The South and West perimeter wa lls are made up of three layers placed side by side and corresponding to different building materia ls: rammed earth constitutes the externa l and basement parts, the interna l layer is adobe and the inner part, constituted by the columns supporting the arches and domes, is made up of baked bricks, Fig. 1c. The North wa ll is, instead, a lmost entirely made byadobe. In the inner core of the mosque, the columns, which had to susta in the weight of the arcades and the domes, are exquisite examples of baked brickwork, carried out by an annular arrangement of rectangular bricks so as to form a simple but effective motif , Fig.1b; the rings of the a rcades are accommodated with square bricks. The masonry portions over abutments and springs of thearch rings, necessary for backfilling, are in adobe. Earthen mortar was used for arches, domes and adobe wa lls, while gypsum mortar was employed to bind the bricks of the columns. The decorative system consists of a shell coating the whole inner surfaces with magnificent motifs carved out of gypsumplaster and coloured in a lapis lazuli-basedpaint, Fig. 1d. Built in two layers of vertica l construction, the base structure of the South and West facing wa lls of the mosque, each measuring 20 meters in length, rests on a layer of well-made rammed earth blocks (Fig.1c). These blocks seem to have been cast in formwork, confirmed by the smooth surfaces at the edges of the blocks. This type of earthen masonry, about 90-100cm thick, reaches approx. 2.5 meters above ground level. The horizonta l widths vary between 70-90cm, with a consistent height of 90cm. Immedia tely above the rammed earth base layer of the southern and western wa lls, a second interna l envelope or skin of mud and baked brick was constructed to distribute the load of the large domes and as a ground layer for the application of the extensive stucco decorations. The externa l rammed earth wa ll (thickness of 45-50cm) and the interna lmud brick adobe wa ll are in place woven together but more often