ABSTRACT: Extended disorder in the Temple of Apollo Epicurius, Bassae, is thought to be due to joint deformability of the rock foundation, triggered by transient ground water flow. This view is supported by in-situ measurements. Control of rock displacements is proposed to be done by an appropriate underground drainage system.
RESUME: Le desordre enregistre au Temple d'Apollo Epicurius Bassae, a ete attribue à la deformabilite des joints de la masse rocheuse excitee par le moųvement de l'eau souterrainne. Cette these a ete confirmee par des mesures in-situ. L' auteur a propose un système de drainage souterrain pour contrôler les mouvements du Temple.
ZUSAMENFASSUNG: Die ausgedehnte Verdrangung des Tempels von Apollo Epicurius, Bassae, ist auf eine Fuge-Verlegung zuruckzufuhren, die aus einem unstaten Grundwasser-Lauf veranlasst wird. Die controlle dieser Verlegung wird, nach Vorschlag, mittels einer geeigneten unterirdischen Kanalisation ausgefuhrt.
1 INTRODUCTION The need for restoration of the Temple of Apollo Epicurius, a chef-d'ouevre of Ictinos built in the midwest of Peloponnese, Greece, during the latter fifth century BC, has long been recognized as a task of primary national importance. When the Temple was discovered by Bocher in 1765 AD, 36 of the 38 columns of the peristyle were still standing; however, the rest of its structural elements (ceiling, entablature, walls of cella, coffers of pronaos and opistodomos etc) have all collapsed. Fifty years later, Coquerelle faced a nearly similar situation. Nowadays, things appear to be worse, as horizontal displacements at the top of most columns are recorded as large as 250 mm and floor differential settlements approximate 100 mm; hense, the stability of the Temple seeks to question (fig 1). This disorder was thought to be due to inadequate foundation on the underlying limestone (fig 3). Certain restoration works have been performed within the first decade of the 20th century; however, on account of the Ministry of Culture, systematic investigations were only put forward after 1975. They included archaeological trenches, levelling measurements, seismic risk evaluation of the major area, several verifications of the structural integrity and stability of the monument, as well as an investigation programme of geological - geotechnical nature. This programme involved geological mapping, geoelectrical sounding, five exploratory boreholes, laboratory tests, Lugeon permeability tests, the installation of three piezometers and two in-situ direct shear tests (fig 2). Critical evaluation of the above data was of considerable significance in identifying confidently the role of ground waters as triggering mechanism in the evolution of differential ground and foundation movements, as well as in composing an appropriate geotechnical proposal for their control. This paper presents and discusses the basic points of this proposal followed by the first set of geodetic levelling results that support, the proposal, made by the author (Costopoulos 1984).
2 GROUND CONDITIONS 2.1 Geologic setting The Temple has been founded on the top of an anticline with a N.NE-S.SW direction. The wider area is composed of thin bedded (100 mm), platy, white to gray-white limestones of the Upper Cretaceous, laminated with thin (10 mm) bands of red clay-shales-and marls. The rock material appears semi-crystalline with local calcite or Pyrite vanes and signs of incomplete fissility. Bedding appears fairly normal with dips 25 to 40 degrees East. The rock mass is intensively folded and strongly fractured or brecciated, often exhibiting karstic cavities and minor displacements. The bedrock is normally covered by up to 4 m of topsoil consisting of soft clayey material mixed with limestone fragments. Over the narrow area of the Temple, the relief of the calcareous bedrock has been investigated by 88 geoelectrical soundings using the Sclumberger electrode array. The method revealed a strongly uneven and saddled weathering mantle of thickness fluctuating between 5 and 20 m (fig 2). A series of seismographic and microtremor measurements over the site indicated the occurence of shallow earthquakes and a very short predominant period of the ground (0.13 sec).
2.2 Geotechnical data The clayey material filling the joints - and used normally as earthfill - was classified as a highly plastic silty clay, with low sand content (13. 5%)and occasional organic material (2.5%). Atterberg limits varied between 55% and 66%(wL), 22% and 24%(wp), water content was almost 33%,while the specific gravity of solids was 27 MN/m3. Consolidation tests indicated a range of 3x10–4 to 34x10–4 cm2/sec for the coefficient of consolidation and a range of 0.26 to 0.36 for the compression index.