NUMERICAL STATISTICAL ANALYSIS OF UMBRELLA DRAIN PERFORMANCE IN DEEP CIRCULAR LINED TUNNELS UNDER STEADY-STATE SEEPAGE

One of the major issues in design and construction of tunnels is seepage and it's been highlighted by an extra force which is generated by pore water pressure and directed towards the tunnel walls. Since this extra seepage force may lead to instability in soils and weak rocks with low permeability, the necessity of drainage in such tunnels is visibly clear. Drainage systems in tunnels have dierent types and materials and the most common ones are peripheral lter drainage and pin-hole drainage systems. Despite the drainage system importance, very limited studies have been conducted on the drainage systems and the eective factors aecting their performance. The need for such systems is clearly felt during construction of many tunnels during the writers eld studies.
In this article, Umbrella drainage system is presented as a new alternative drainage system for the tunnels under steady state seepage condition. The arrangement of this system is an smart combination of Pin-Hole drainage system and it is inspired by forepoling method of support installation. In this study, the performance of the aforementioned drainage system is investigated through numerical statical three dimensional analysis of the lining for deep circular tunnels subjected to steady-state seepage by using ABAQUS nite element software. Furthermore an optimum arrangement for pipes in the drainage system is presented by taking into account the maximum eective principle strain for the lining of a tunnel as a monitored parameter. Also the eective factors affecting the drainage tube of the draining system is to investigated. Moreover, all of the factors with an in- uence on the drainage tube of this draining system is explored through investigating the pore water pressure distribution on the surface of the lining of a tunnel and considering it as a type of eective loading in designing the lining of the tunnel and also estimating the drained volumetric discharge of the drainage tubes.