Abstract

Work in excavations and trenches that have not been designed in keeping with accepted practices presents a serious risk of accidents. In this project, a practical guide to help construction professionals design safe excavations and trenches was developed in collaboration with a validation committee composed of specialists, workplace representatives, and prevention specialists.

The first part of the guide begins with an analysis of the statistics concerning trench-related accidents reported to the CSST between 1974 and 1994. This is followed by a discussion of the various methods available to analyse the stability of overburden and excavation slopes. Finally, the validity of current computational models was verified by comparing their predicted results with the behaviour of experimental excavations reported in the technical literature.

The second part of the guide is concerned with excavation slopes. A slope-stability program was used to generate tables of safe slopes for granular soils of various compactness in the presence or absence of a water table. Nomograms which take into account the effect of slope overloading and cracking are also presented.

The third part of the guide focusses on shored trenches. The observed effect of weather conditions on the behaviour of an experimental trench dug in clay soil is discussed, and nomograms for wood shoring of trenches of depths of no more than six metres are presented.