engleski

Experiences Obtained by Execution of High Pre-Cuttings and Tunnels in Rock of the HSSR Type in Croatia

The paper presents investigation works, design solutions, building and monitoring on relatively high precuttings and tunnels in weak rock. On the section under construction Kupjak-Vrbovsko, near the locality of Ravna Gora, two tunnels were excavated "Javorova Kosa" ; and "Pod Vugles", with the total length of about 2 km. The tunnels are built in the categories of Hard Soils-Soft Rocks type. That category comprises rocks which are mostly unstable against the influence of weather. Investigation works for this type of rocks are specific in relation to other geotechnical investigations and must be aimed on testing of the watering of soft rocks and the corresponding Geodurability classification. For the need of the project documentation, there were extensive geological, engineering-geological, hydrogeological and geophysical investigations carried out along the "Javorova Kosa" and "Pod Vugles" section, with investigation drilling and geotechnical laboratory testing of representative samples. For excavation of tunnels, the pipe roof technology was applied. With the purpose of reducing the hazard and the risk during excavations and primary securing, "RMR", "Q" and "Geodurability" classifications were carried out, which was not the case in the practice of tunnel construction in the Republic of Croatia until then. The "JAK" (Jasarevic & Kovacevic, 1996) classification procedure was also carried out, which was verified in carbonate rock masses through existing investigations, but not in classic Paleozoical deposits too. According to the guidelines of the International Tunneling Association (ITA), the procedure of the construction of tunnels which is constantly adjusted to progressing can be realized by combining of the calculation methods, the empirical way of designing and the direct interpretation of in situ measurements. During that, in situ measurements of deformations of the massif, and deformations and strains in the support are constantly used for the confirmation of the design or its replacement. The starting sections with intensive instrumentation give input data for that procedure. The interpretation of the measured values provides an insight into the conduct of the massif as the reaction on the progressing of tunnel. The in situ measurements do not verify only the stability and the applied project calculation model, but they also verify the basic concept of the reaction of the massif on the excavation of the tunnel opening and the effectiveness of safety constriction elements. For the most critical and representative sections in tunnel set aside in advance by classification and categorization procedures in an exceptionally heterogeneous and anisotropy rock mass, a complete program of measurements was carried out consisting of measuring of the convergence in the tunnel, measuring of vertical and horizontal displacement of the terrain, measuring of displacement of the ground around the underground opening, and measuring of the strain in substructure elements. Thereby the hazard and risk during the excavation and primary securing works is reduced. Monitoring enabled corrections of design solutions for securing the works (drainage, long prestressed anchors, and reinforced jet concrete) during the construction in accordance with the results of measurements.

investigation works; design solutions; building; monitoring

nije evidentirano