Natural Hazards and Earth System Sciences, 5, 947–958, 2005 SRef-ID: 1684-9981/nhess/2005-5-947 European Geosciences Union © 2005 Author(s). This work is licensed under a Creative Commons License. Natural Hazards and Earth System Sciences Stepwise mitigation of the Macesnik landslide, N Slovenia M. Mikoˇ s 1 , R. Fazarinc 2 , B. Pulko 1 , A. Petkovˇ sek 1 , and B. Majes 1 1 Faculty of Civil and Geodetic Engineering, University of Ljubljana, Ljubljana, Slovenia 2 Water Engineering Ltd., Ljubljana, Slovenia Received: 1 August 2005 – Revised: 9 November 2005 – Accepted: 9 November 2005 – Published: 24 November 2005 Part of Special Issue “Documentation and monitoring of landslides and debris flows for mathematical modelling and design of mitigation measures” Abstract. The paper gives an overview of the history of evo- lution and mitigation of the Macesnik landslide in N Slove- nia. It was triggered in 1989 above the Solˇ cava village, but it enlarged with time. In 2005, the landslide has been threatening a few residential and farm houses, as well as the panoramic road, and it is only 1000 m away from the Savinja River and the village of Solˇ cava. It is 2500 m long and up to more than 100 m wide with an estimated volume in excess of 2 million m 3 . Its depth is not constant: on average it is 10 to 15 m deep, but in the area of the toe, which is retained by a rock outcrop, it reaches the depth of 30 m. The unstable mass consists of water-saturated highly-weathered carbonif- erous formations. The presently active landslide lies within the fossil landslide which is up to 350 m wide and 50 m deep with the total volume estimated at 8 to 10 million m 3 . Since 2000, the landslide has been investigated by 36 bore- holes, and 28 of them were equipped with inclinometer cas- ings, which also serve as piezometers. Surface movements have been monitored geodetically in 20 cross sections. This helped to understand the causes and mechanics of the land- slide. Therefore, landslide mitigation works were planned rather to reduce the landslide movement so that the resulting damages could be minimized. The construction of mitigation works was made difficult in the 1990s due to intensive land- slide movements that could reach up to 50 cm/day with an average of 25 cm/day. Since 2001, surface drainage works in the form of open surface drains have mainly been completed around the circumference of the landslide as the first phase of the mitigation works and they are regularly maintained. As a final mitigation solution, plans have been made to build a combination of subsurface drainage works in the form of deep drains with retaining works in the form of concrete ver- tical shafts functioning as deep water wells to drain the land- slide, and as dowels to stop the landslide movement starting from the slide plane towards its surface. Due to the length of the landslide and its longitudinal geometry it will be divided Correspondence to: M. Mikoˇ s (mmikos@fgg.uni-lj.si) into several sections, and the mitigation works will be exe- cuted consecutively in phases. Such an approach proved ef- fective in the 800 m long uppermost section of the landslide, where 3 parallel deep drain trenches (250 m long, 8 to 12 m deep) were executed in the autumn of 2003. The reduction of the movements in 2004 enabled the construction of two 5 m wide and 22 m deep reinforced concrete shafts, finished in early 2005. In Slovenia, this sort of support construction, known from road construction, was used for the first time for landslide mitigation. The monitoring results show that the landslide displacements have been drastically reduced to less than 1 cm/day. As a part of the stepwise mitigation of the Macesnik landslide, further reinforced concrete shafts are to be constructed in the middle section of the landslide to sup- port the road crossing the landslide. At the landslide toe, a support construction is planned to prevent further landslide advancement, and its type is still to be defined during the procedure of adopting a detailed plan of national importance for the Macesnik landslide. 1 Introduction The mitigation of large and deep landslides is a complex task. After their triggering, some important steps should be made before effective technical mitigation measures can be performed in the field. First, if necessary, any immedi- ate relief actions should be carried out in order to save lives and keep damage as low as possible. If the damage poten- tial (buildings, infrastructure, land) is present and if the first assumptions of the causes show a possible technical miti- gation, field observations and measurements should be car- ried out. The most common field investigations and mea- surements can be divided into surficial investigations (en- gineering geologic survey and mapping, geodetic measure- ments, geophysical measurements, measurements of surfi- cial deformations on the landslide surface, etc.), and subsur- face investigations and investigations in boreholes (ground water table measurements in piezometers, measurements for