TABLE OF CONTENTS A selection of construction methods and stages that take into account the underground conditions is of great importance for a successfully execution of a deformation free excavation and will be described briefly in the following.
The installation of the bottom support on the bottom of an excavation that lies in the soft soil immediately after full excavation or partial excavation is also of great importance for the stability of the excavation and settlement behaviour of nearby buildings founded on shallow foundation. Thereby, a distinction has to be made between the following cases:
If the soft soil layer is relatively homogeneous, possesses high plasticity, contains no fine sand seems and no groundwater is available, the excavation bottom can be sealed of in sections with base concrete slab immediately after the final excavation.
In all other cases, however, a geotextile filter mat, a layer of non-compacted filter material (about 10 cm thick) e.g. split gravel and then a watertight geomem-brane are laid in respective order on bottom of the excavation before the placement of a sub-base or bottom support concrete slab. Drainage pipes can also be inserted in this layer to provide temporal drainage during the construction period. Refer to Fig. 4.25 and 4.26 for illustrations. Therewith, the excavation can also be protected against possible piping failure.
