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Fig. 1. Restitution des premiers resultats des fouilles archeologiques sous la cathedrale St Pierre a Gen£ve.

A. Croce, Co-Chairtnan

INTRODUCTION TO THE TOPIĆ MONUMENTS AND OLD CITIES

1.- The present Conference is'considering geo-technical engineering from two different points of view. The first one is the. traditional, let me say cJLcu>64.CjoI gzottchnicb, a powerful tool to un cferstand and control the mechanical behaviour of soils and rocks.

Recently, however, geotechnical engineering has taken a new aspect; it is called to use its sci entific and technological knowledge in a wider horizon.

In fact the present Session is concerned about the heritage of the past; another Session n, 6, was concerned about the present environment :both Sessions, however, have to look ahead in the di stant futurę.

The specific aspects of our problems are the pte-ej^ca-Cejice of 6-OiucAlwa and the large tim When the construction already exists, the engi-neer needs, first of all, to look to the old eon struction with a large-minded approach.

Apart from unforeseen difficulties which his stu dies bring to light, he sets himself an ambitio us goal: the reconstruction of the history of the mechanical behaviour of both the subsoil and the overlying structures.

The engineer has firstly to go back in time with the help of every source of information,secondly to consider architectural criteria and construc

St Pierre de Gen£ve, avec ses croisśes d’ogives porteuses, qui sont des ares en plein cintre, comme dans le grand nombre des śglises gothiąues de France, tśmoigne du sens aigu des bćitisseurs du XIIIe S pour allśger les constructions et assurer la descente des charges des structures conęues pour travailler uniquement en compression.

C'est lorsque une dćfaillance des mat£riaux ou des fondations entraine des tassements ou des d£formations que la stabilitś est compromise.

En donnant le moyen aux fondations de St Pierre de suivre d'śventuels tassements profonds, sans se dćformer et en rśduisant les tassements dif-fśrentiels, on a cherchć A amśliorer la stabi-litś gśnśrale de la structure sans avoir A inter-venir dans celle-ci et sans altśrer la puretś de sa conception comme ouvrage en pierres de taille.

On a cherchś non seulement a conserver 1*aspect du monument mais aussi son caractdre.

Les archśologues ont beaucoup apprćciś un sys-tdme de confortation qui leur assurait toute sścuritś dans leurs travaux, sans interfśrer dans ceux-ci.

tion methods wich differ morę from present ones, the further back in time he goes.

He also has to analyse the loads, deformations and displacements. In addition, he finds the si gns left by various agents which have operated slowly and slowly throughout the centuries.

At the end, when he succeedes,he makes his judg ment on the actual State of the construction.

The next step to be done is to design and carry out the plan; it is the most difficult and dan-gerous step, like therapy following diagnosis. Two fundamental requirements are to be met.

The first is a cultural requirement, that is,to hand on the futurę generations the possibility of AeacUng the quintessential message of the old constructions.

The second requirement is a technical one, that is, an acceptable level of static safety.

These two basie requirements are in contrast. This is the main reason why very often therapy to save old buildings and monuments is morę difficult than diagnosis.

2.- The discussion, which is now to begin, will be developed following the course set by the Cha irman.

The rangę of problems is quite wide. Is it possi ble to discover some methodological aspects of

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