Modern Concrete Technology and Placement Methods and Their Influence on Water Proofing Performance of Diaphragm Walls

Embedded retaining walls are a well-established method to construct retention systems fordeep excavations and to create a barrier against the inflow of groundwater. Several factorsneed to be considered when selecting the most suitable wall type to achieve compliance with the project requirements and specifications. The selection of there taining wall type provides a direct link to the expected grade of water proofing performance which is the focus of this paper. It should be noted that embedded retaining walls in general should not be assumed to beabsolutely water tight as complete water tightness is neither practical nor economical. Even cast in-place concrete diaphragm walls with very low permeability can’t be considered completely water tight despite having the least number of vertical construction joints of all embedded retaining wall systems. British Standard BS 8102:1990 clearly highlights therequirement of additional water proofing elements and methods to meet the relevant waterproofing levels for such walls and basements in general. However, unless the diaphragm wall (or other wall type) itself provides adequate and realistic water retention performance, the performance of the additional tanking can be put at risk, too. The required performance criteria for fresh tremie concrete to be used for the construction of diaphragm walls, must be selected to achieve optimal concrete density to fully comply with the expected structural, durability and water proofing performance criteria of the entire basement.