The final paper "Weak rock mass" looks at the characteristics of weak rock mass, which due to its increased exposure to weathering is a challenge in design and construction. Based on rock mass classification, which is classifying the rock mass on the basis of the mutual relations of characteristics, the strength and deformability of the rock mass can be determined. In addition to other physical and chemical factors that affect the degradation of the strength parameters of weak rock mass, it is very important how water affects the behavior of the rock and what impact it has on engineering works. Exposure to factors which contribute weathering potentially leads to degradation of strength parameters, which can lead to long-term overload on the rock mass. In order to prevent increased load and high stresses, it is necessary to stabilize the rock mass by substructure adapted to the excavation conditions in low rock mass. In addition to classical and modern design and construction methods, it is necessary to rely on the observation method in difficult geotechnical conditions of low rock mass, which can predict potential problems of instability during construction and prevent unwanted displacements or rock mass collapse.