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In excavation works, there are limitations in the ability to model earth retaining structures and select soil parameters for design. This is because of the variable and complicated retaining wall structure conditions. The soil and structure behaviour are often monitored to confirm the safety of excavation works during construction. The data are rarely used to improve predictions and modify the design of subsequent stages of construction. The back-analysis of excavations made after construction is very useful in the evaluation of the assumptions and parameters which influence the behaviour (Lambe, 1973). However, it may be advantageous to use the measured data to rationalize the design at the later stages of construction. This is an extension of the observational method described by Peck (1969). In this Paper, the observational construction method is proposed whereby the excavation sequence is modified and optimized during construction. An example of its application is given. The method can be used to revise and confirm the design assumptions, for example by back-analysing the initial excavation stages. The new design assumptions can then be used to predict the precise behaviour of the subsequent stages. The measured data are also used to rationalize the excavation work during the subsequent stages. La modélisation des structures de soutènement et la sélection des paramètres des sols sont difficiles à utiliser pour le projet des travaux d'excavation. Ceci est dû à la variabilité et à la complexité du terrain et des structures de soutènement. Le comportement du sol et des structures de soutènement associées est souvent enregistré pour assurer la sécurité des travaux lors de l'excavation. Si les données sont généralement utilisées pour assurer la sûreté de la construction, elles sont par contre rarement employées pour tester les prévisions et modifier le projet aux différentes étapes de la construction. Une rétro-analyse des excavations, après construction, se révèle très utile pour mettre en évidence les hypothèses et les paramètres du comportement (Lambe, 1973). Il est toutefois plus intéressant d'utiliser les données mesurées pour optimiser les étapes ultérieures de la construction, ce qui correspond à une extension de la méthode d'observation décrite par Peck (1969). L'article propose une méthode de construction par observation où la séquence d'excavation est progressivement modifiée et optimisée. Un exemple est présenté. La méthode peut être utilisée pour modifier ou confirmer les hypothèses de design, par exemple par rétro-analyse des étapes initiales d'excavation. De nouvelles hypothèses de design peuvent alors être mises en oeuvre pour prédire exactement le comportement aux étapes suivantes. Les données mesurées sont également utilisées pour optimiser les travaux d'excavation aux différentes étapes.

The surveyed building consists of a 234m high skyscraper ， which is connected to two 30m ・ high low − rise structures ． The total area of the building is 200rn × 84m． The high − rise part is suppo 「Ied by a spread f() undation on the Tokyo Gravel Stratum at GL − 29m and 匸 he low − rise parts are supported by pile fc 〕 undations with the lower end of the piles on the same s1ratum ． This paper describes the results of the field measurements of the ground heave and settlement on the bearing stratum during construction period ， and compares the results with the predicted ground heave and settlement ，

The ultimate bearing capacity formulas of foundation and penetration foundation have been specified in the guideline published by Architectural Institute of Japan for design of building foundation. The rigid plastic finite element method was developed by Tamura and Ohtsuka and has been applied to estimate the ultimate bearing capacity of footing. The characteristic of this method is to employ limited soil constants in comparison with deformation analysis. It only uses the strength parameters as cohesion, c and friction angle, φ since it deals with the limit state directly by disregarding the deformation of building and ground. Through a series of rigid plastic finite element analyses, the comparison of ultimate bearing capacities of penetration foundation between the simulation results and the formula of Architectural Institute of Japan was conducted for two layered soil system of clay. The change in failure mode of ground was discussed with the geometrical ratio between the width of footing and the height of surface layer. The strength ratio of the surface and the second layers of ground was clearly shown to affect the formation of failure mode. The applicability of rigid plastic FEM was demonstrated to the assessment of ultimate bearing capacity of two layered clayey soil system.

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