Abstract
Although diaphragm walls are massive and responsible structures whose building history has many years' tradition, the discovery of a variety of material faults is still common throughout their exploitation. Some of the most common ones are associated with the occurrence of leaks along the wall surface. This paper reports on the results of a study conducted into concrete quality in an existing building structure. The issues identified in this case include the potential penetration of groundwater and particles suspended in non-cohesive soils into the bentonite suspension and into the concrete mixture. The scope of the analysis also involved the possible occurrence of a mixing zone of bentonite suspension with the concrete mixture. The solutions presented in this paper were practically tested using an existing structure and the results confirm that the adopted approach needs to be thoroughly researched. The laboratory specimens derived from an unreinforced diaphragm wall were subjected to the following tests: concrete bulk density in the air-dried state, water absorption by concrete, depth of water penetration under pressure, compressive strength and determination of the quantitative phase composition test using X-ray diffraction method. The results clearly demonstrate the decrease of the concrete quality applied in a monolithic diaphragm wall in comparison to the reference samples taken at the phase when it was built. Due to the fact that it was impossible to identify the impact of the particular variables on the investigated structure, this paper focuses on their descriptive assessment. This discussion is based on the analysis of the results defining the physical and mechanical properties of the examined concrete coupled with observations made by the author and insights derived from literature.
Highlights
Diaphragm walls have been built since 1960s and play the role of the retaining structures for deep trenches, parts of underground structures and often play the role of a foundation
The results gained from the analysis demonstrated that the particles of the suspension remained in the concrete structure
On the basis of the analysis of the results of research involving laboratory specimens derived from drilling performed in an existing diaphragm wall, we can clearly note that the physical and mechanical parameters of the examined concrete are considerably distinct from the properties of the material that was delivered to the building site in the past
Summary
Diaphragm walls have been built since 1960s and play the role of the retaining structures for deep trenches, parts of underground structures and often play the role of a foundation. The variety of the parameters that affect the parameters of concrete mixture throughout the phase when the structure is concreted are known to play a considerable role on the final quality of the structure. These parameters mainly include: contamination of the mixture by soil particles, influx of ground water and the risk of the potential mixing of bentonite suspension with the concrete mixture. The considerable porosity of the concrete in the investigated wall and the leaks visible on its surface seem to contradict these claims [3]
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