The time-dependent stability of tunnels is an important and challenging topic, mainly when the tunnel is excavated in incompetent and weak rocks. The creep property of rock is one of the crucial mechanical properties of weak rock and the main factor affecting the long-term stability of rock masses. Also, water as an important environmental factor influences both the short-term and long-term behavior of rocks and is one of the causes of geotechnical engineering disasters, such as tunnel collapse, slope sliding, surface subsidence, etc. In this research, the effects of rock’s creep behavior and underground water on the long-term stability of the Shibli tunnels were analyzed. Geological maps and reports of Shibli tunnels show a highly jointed condition in the surrounding rocks which have been crushed by two orogenic stages. The Burger-creep visco-plastic model was used to simulate the tunnel host rock creep behavior. The model's parameters were adopted based on the displacement-based direct back analysis technique using a univariate optimization algorithm. In addition, the influence of underground water is assessed under the condition of the varying water table. Support capability diagrams were used to evaluate the loading created on the tunnel’s permanent lining due to the creep behavior of rock mass and underground water. This study suggests that the weak rock's creep behavior and underground water significantly affect the time-dependent stability of tunnels. Results show that the induced stresses due to the rock's creep behavior and underground water are more considerable in the tunnel spring-line. Also, the increasing 20 m in the water table approximately decreases ten years of tunnel lining stability time at the fault zone.
Article highlights
Rocks creep behavior and underground water significantly affect the time-dependent stability of tunnels in weak rocks.
Displacement-based direct back analysis using a univariate optimization algorithm was used to determine the CVISC model’s properties.
Increasing 20 m in the water table approximately decreases ten years of tunnel lining stability time at the fault zone.
The mechanical properties of frozen rocks vary significantly from the properties of the same lithology under ambient temperature. The goal of this paper is to investigate these changes in the physical and mechanical properties of rocks due to saturation and freezing. Besides, the attention was paid on discovering new correlations between the mechanical characteristics. To fulfill these objectives, 36 uniaxial compressive strength tests, 36 Brazilian splitting tests, and 48 point load tests were carried out. The samples were tested in air dry, water saturated, and frozen (− 20 °C) conditions. The measured physical and mechanical parameters were analyzed by using regression analyses. It was found that the average uniaxial compressive strength of frozen samples (21.93 MPa) is 86.4% more than saturated ones (11.76 MPa) but 25.9% less than dry specimens (29.62 MPa). Additionally, high correlations were established between uniaxial compressive strength and IS(50) under air-dry, saturated, and frozen conditions for the investigated marl samples. Furthermore, it is of particular interest to observe a high correlation with the determination coefficient (R2 = 0.95) between the constants of previously published linear regressions of UCS- Is(50) under dry status.
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