Currently very often, the execution of the foundations of buildings requires to perform of deep excavations. Uncontrolled groundwater flow into the deep foundation, leaks and, caused by them, internal erosion processes are among the keys threats to the safety of deep excavations and nearby buildings. The presence of these processes can generate significant additional construction costs of building. The most effective method of detection of leaks of deep excavations is thermal monitoring method. This method has been verified and successfully used for over twenty years in western Europe. In recent years, it is introduced into implementation in Poland. The paper shows firstly a comprehensive analysis of the uncontrolled groundwater flow into the deep foundation. The scheme of works performed to construct the slurry walls as well as typical causes of leakage were discussed. Secondly, the authors, basing on their professional experience present the basic issues concerning the thermal monitoring method and the possibilities of its using to leakage detection of deep excavation construction before its performing. Finally, an example of thermal monitoring method application for the detection of leaks of deep excavation construction of one of subway station in Europe is presented.

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