· Restoration of Alberite Dolmen
Villamartín, Cádiz, Spain
The Alberite Dolmen is located 5 km south of Villamartín, close to the Alberite Stream. It is made up of a 20-metre gallery (a passage grave or passage tomb) with ochre paintings and engravings, with a funeral chamber at the end. The remains of a man and a woman were found there with grave goods and signs of ritual fires. Carbon 14 radiometric dating techniques placed the dolmen at around 4000 BC.
With 35 vertical orthostats laid out in two relatively parallel lines with internal jambstones segmenting the corridor which also served as a support for the roof slabs. The entrance of the dolmen is east facing and has an antechamber and funeral chamber at the western end. Almost all the vertical orthostats have a reddish pigmentation, some bearing decorative suns, snakes or other anthropomorphic elements.
The Alberite Dolmen dominates an open landscape at the foot of the Sierra de Cadiz mountains. It is located in the bowl of the River Guadalete, which runs a little to the north, made of fertile agricultural soil with clayey deposits and plentiful sandy silt which facilitates farming. Different streams drain the flatland into the river, and a marked anthropisation of the landscape can be observed, moderated by the ploughing of the land.
The dolmen sits on a marly-limestone outcrop upon which a significant stratum has been formed, mainly of a dark brown or blackish silty clay, with abundant roots and organic remains. This level, corresponding to the agricultural land, has outcrops of greyish breccioid limestone on marly clay, with the top of the level lying at an average depth of around two metres.
This gentle, undulating landscape of arable land contrasts with the rocky formations of the mountains, where there are several quarries used in the construction of the funeral monument and which, together with the river deposits, provided copious raw materials and resources for the communities which populated the area.
The important archaeological work undertaken in Alberite have led to the questioning of the Mediterranean origins of megalithism in the peninsula, and it has been related to the Atlantic context with a new chronology now going back to the fifth millennium BC, according to the results of dating tests.
∧ 2001. Starting point
< 2005. After restoration works
The project has three main lines of intervention:
1 Restoration of the dolmen
This provides a solution to the technical problems of stability, lateral earth pressure and drainage. The dolmen is comprehensively restored, repairing the orthostats and elevating the surrounding land to protect the gallery with a rammed earth wall in the voussoir of the orthostats.
2 The construction of a new roof
This is a very complex construction, using tubular steel girders. It measures 28.15 m x 17.50 m, with a surface area of 500 m² and only four points of support at the corners. It has a spherical surface and is covered with curved, earth-coloured, prefabricated concrete panels. This is a reference to the now-disappeared tumulus and is designed to protect the dolmen and the paintings on the orthostats from the weather.
3 Open-air museum
Under the large covering roof, the tomb and the perimeter area with explanatory panels are integrated with other remains at the site, allowing the megalithic tomb to be visited without entering into the gallery.
The support structure of the roof was a great challenge. It was first optimised by means of an iterative analysis-dimensioning process undertaken by the Structural Optimisation Group of the Polytechnic University of Cartagena.
The tubes had to be taken to the workshop pre-curved as it was impossible to do this in situ due to their diameter. The geometrical complexity of each node required meticulous spatial planning of the cutting for each tube and meticulous welding, especially at the critical points. The singular geometry of the roof panels was made by using different curved moulds for groups of identical panels. Each one was reinforced with a steel frame around the perimeter and steel diagonals, and they were assembled using threaded bars and bolts set into the panel.
“The final project to be executed closely followed the opinion of the experts and the conceptual approach proposed was backed by a battery of prior studies.[…]
[…] The reconstruction of the original tumulus was ruled out and it was decided to use a protective cover made with materials that would not create ambiguity or confusion in the interpretation of the archaeological remains…”
> Illustration numbers
1 Roof of insulating, reinforced concrete sandwich panels with glass fibre, mounted on screwed supports
2 Tubular steel structure in the form of a spherical shell, on four external reinforced concrete corner supports
A Gallery dolmen with burial chamber. Dated 4000 BC
B Pavement in white aggregate for drainage of the dolmen gallery
C Perimeter exhibition area around the tomb and original covering slabs
D Filled with natural earth to form a new tumulus
“… The new aerial cover above and around the dolmen can house an open exhibition space where additional information will explain the meaning and importance of Alberite I without the need necessarily to enter the gallery. The intention was to combine the protection of the megalithic monument with a perimeter museum space, all of which would come under a large covering roof whose geometry is an abstract reference to the tumulus which once covered it. The construction, which is technically very complex, has resulted in a very daring architectural structure. […] The new infrastructure has quickly become reasonably well integrated into the landscape, one of the objectives of the author of the restoration project.” 1
1GUTIÉRREZ LÓPEZ, J.M., PH Boletín del Instituto Andaluz del Patrimonio Histórico, nº 67 Especial, August 2008, pp. 170-175
A BIOMIMETIC APPROACH
“It will be a surprise to many biologists that snails are found in large numbers on the dry, barren surfaces of certain hot deserts. The surface temperature of these deserts may reach 70°C and more than a year may pass between rains. The temperature of snails located on various natural substrates and fully exposed to the sun was recorded on a total of 40 days in July and early August 1969. The records showed a rather uniform pattern, although there were some characteristic differences. In the total range of the solar spectrum, therefore, we can say that the snails reflect well over 90% of the incident radiant energy. The highest temperature, 65°C, was that of the soil surface in the sun. Heat therefore flows into the shaded area under the snail where the temperature is lower (60°C). Since the snail is cooler again, heat flows from the substrate into the snail. This heat flow, however, is impeded by two important circumstances. Firstly, the snail shell is in direct contact with the rough soil surface only in a few spots, and a layer of still air separates much of its bottom surface from the ground, forming an insulating air cushion”.2
2 SCHMIDT-NIELSEN K; TAYLOR CR; SHKOLNIK A. (1971). Desert snails: problem of heat, water and food. J. Exp. Biol., vol 5 (1971) p 385-398
Insulated sandwich concrete panel system maximises thermal efficiency by combining insulation with the high thermal mass properties of concrete. Covering design favours ventilation having also a high solar reflection factor
Restoration of the megalithic monument and construction of a new protective covering
Villamartín, Cádiz. Spain
- latitude 36.8159º N
longitude 5.6367º W
elevation a.s.l. 139 m
Restoration of dolmen.
Chronology 4000 BC
Climate protection of orthostats and paintings by a new covering design.
In heritage terms, conceptual simulation of a tumulus with a minimal distortion of ecosystems
Ventilation and reduction of direct insolation.
Improve of thermal conditions
Regional Government of Andalusia. Spain
José Carlos Sánchez-Romero
Studio of Architecture
Pedro Lobato Vida
Pascual Martí Montrull, Concepción Díaz Gómez. Structural Optimization Group. Technical University of Cartagena
Mariano Delgado Cordero
Miguel Portilla Castillo
José María Gutiérrez López
Welded tubular structure
Manuel Conde Argudo
5b: Courtesy of JM Gutierrez
9a: © JCSR Studio of Architecture
12: © JCSR