Umbrella Arch And Forepoling Support Methods: a Comparison

In tunneling, umbrella arch and forepoling are two pre-lining support techniques used in weak and medium strength rock tunnels for stabilizing roof and carrying boundary formation on roof itself. In the literature, confusion with respect to their usage may be seen. In order to overcome this misconception, a comparison is per-formed between two methods up to their operational parameters such as their dimensions and time periods due to application process. Case studies related to work time analysis for 2 umbrella arch and 2 forepoling tunnels (underground metro tunnel excavations and their crossing constructions) in difficult formation conditions are analyzed for classifying them. Projects using umbrella arch are named by Unkapanı - Yenikapı (#1) and 4.Levent-Ayazaga (#2) main metro lines in different locations in Istanbul. Besides, projects using forepoling technique are called as Unkapanı-Yenikapı (#3) and Kadıköy-Kartal (#4) metro line crossings of twin tunnels. The crossing of #4 includes work time periods of 13 days. When delays are included, average time coverage of forepoling of #4 is 6% of whole process consisting of other application sequences such as excavation, shotcrete, haulage of muck, injections etc. The crossing of #3 includes work time periods of 15 days. When delays are included, average time cover-age of forepoling of #3 is 6% of whole process, same with those of #4. Main tunnel of #2 covers 6 ring with 4m. When delays are included, average time coverage of um-brella arch of #2 is 12%, 66 of whole process. Main tunnel of #1 covers 4 ring with 4m. When delays are included, average time coverage of umbrella arch of #1 is 17,5% of whole process. Formation of area of work time analysis is also given in order to show interaction between work time periods and formations.