ABSTRACT:

Ground support comprises a wide field of geotechnical engineering. Therefore some special topics are selected: Reinforcement and dowelling of soil and rock by nails, anchors, piles and jet-grouting. Thus, the ground becomes more or less a compound body which locally can be considered a quasi-monolith. In the case of retaining structures or underground excavations, prestressed anchors are used in addition to conventional reinforcement. The paper focuses on retaining structures, underpinning of buildings, and tunnelling. Residual shear strength of the ground is considered an essential value for parametric design analyses and risk assessment, and the observational method is favoured over the fully-engineered design.

INTRODUCTION

Building in unstable, heterogeneous, or soft ground includes a significantly higher calculated risk than is experienced by the other branches of civil engineering. In most cases, sophisticated theoretical models and calculations simply feign an accuracy which in practice does not exist. Statistical investigations do not really solve the problem either. This refers to the ground parameters as well as to the climatic data. But, parametric studies are essential for a reliable risk assessment and to follow the concept of most probable and most unfavourable conditions. This involves designs which can be improved in steps during construction or even in the long-term according to the observational method. Unstable terrain requires a "semi-empirical" design method based on comprehensive monitoring - and pre-planned safety measures which allow for future strengthening if the results of long-term measurements require such. The observational method has also proved suitable for deep excavations in urban areas and for tunnelling. Reinforcing or dowelling of soil or rock is a very appropriate method to achieve such goals, because this technique is adaptable to practically all local conditions with regard to morphology, spacing, forces etc.

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