During the last 20 years in the Republic of Croatia, a large number of engineering projects have been undertaken in karst, allowing engineers to acquire experience in the behaviour of karst as a material in which structures are built. The paper presents the results of engineering geological research of the physical and mechanical properties of karst. The contribution provided by geotechnical measurements and numerical back analysis in developing theoretical knowledge on karst behaviour is pointed out. Using the example of three various construction pits, an interactive approach to design is presented which includes altering the design solution based on experience acquired during construction works. The paper presents experience gained in remedying a two-lane tunnel that had collapsed during construction works, the construction of a three-lane tunnel with very little overburden under residential buildings and the construction of a four-lane tunnel which leads to a six-lane width via a two-tunnel connection. Also pointed out is that future research into karst should be directed towards separating the influence of karstification of carbonate rock from the influence of construction works on the strength and stiffness of karst, and a more reliable estimate of long-term deformation of geotechnical structures carried out in karst.

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