GROUND STABILITY AND SAFE TRENCHING

The control of ground water by pumping (sump pumping and well pointing) are discussed, and side support systems (continuous and non- continuous support) are described. The safety of trenching for underground service may be secured by one of the many techniques (1) groundwater may be drawn down such that trenching is carried out in dry ground. This cound be achieved by a single or double sided "rolling" wellpoint installation. However, in clean gravels and coarse sands sump pumping may be addeptable. (2) The sides of the trench may be supported by a form of continuous or non-continuous planking and strutting. Where the former system is required, the moveable cofferdam meets safety requirements. Where non- continuous support is required, support systems are utilized which can be installed by the operator working from the ground surface until the sides of the trench are securely supported. (3) The achievement of stabilization by use of methods (1) and (2) in varying proportions. (4) Shallow depth excavations are based more on empirical assessments. Hence it is more important that safety aspects are given major consideration.