Showing papers by "Kourosh Shahriar published in 2020"

Thermo-hydro-mechanical modeling of fault discontinuities using zero thickness interface element

Abstract: In this paper, a coupled thermo-hydro-mechanical (THM) simulation in a faulted deformable porous medium is presented. This model involves solving the mass conservation, linear momentum balance, and energy balance equations which are derived from the Biot's consolidation theory. Fluid pore pressure, solid displacement, and temperature are chosen as initial variables in these equations, and the finite element method in combination with the interface element is used for spatial discretization of continuous and discontinuities (fault) parts of the medium to solve the equations. The main purpose of this study is providing precise formulations, applicability, and ability of the triple-node zero-thickness interface element in THM modeling of faults. It should be noted that the system of equations is solved using a computer code written in Matlab program. In order to verify the developed method, simulations of index problems such as Mandel's problem, and coupled modeling of a faulted porous medium and a faulted aquifer are presented. The modeling results obtained from the developed method show a very good agreement with those by other modeling methods, which indicates its accuracy.

Effect of Segmental Joint on Internal Forces in Tunnel Lining under Seismic Loading by Numerical Method

Abstract: Although segmental tunnel linings are often used for seismic areas, the influence of segment joints on the segmental lining behavior under seismic loading has not been thoroughly considered in the literature. This paper presents the results of a numerical study investigating the effects of the rotational, axial, and radial joint stiffness of the longitudinal joints on the structural forces in segmental tunnel lining under seismic loading. A 3D finite element method is adapted to establish elaborate numerical models of the segments. The validity of the numerical model was tested by comparing the results obtained with the well-known analytical methods presented by Wang and Penzien. The results demonstrate that by increasing the rotational stiffness of the segmental joint, the bending moment increases. When the rotational stiffness ratio is less than 0.5, the positive and negative bending moment variations are more. The numerical modeling results show the variations in the bending moment and the difference between the positive and negative bending moment values increased by increasing the acceleration of seismic loading. Moreover, it is significant for the values. By increasing the rotational stiffness ratio of the segmental joint, the axial force ratio decreases. By increasing the axial and shear stiffness ratio of segmental joint, the variations in the bending moment and axial force in segmental lining is not significant and is ignorable in designing segmental lining.

Ground Control Methods in High-Stress Ground Conditions in Civil and Mining Tunnels- Case Studies, and Benchmarking

Abstract: Extreme ground behavior in high-stress rock masses such as rockburst prone and squeezing ground conditions are encountered in a range of underground projects both in civil and mining applications. Determining the most appropriate support system in such grounds is one of the major challenges for ground control engineers because there are many contributing factors to be considered, such as the rock mass parameters, the stress condition, the type and performance of the support systems, the condition of major geological structures and the size and geometry of the underground excavation. The main characteristics and support requirements of rockburst-prone and squeezing ground conditions are critically reviewed and characteristics of support functions are discussed. Different types of energy-absorbing rock bolts and other internal and external support elements applicable for ground support in rockburst-prone and squeezing grounds are introduced. Important differences in the choice and economics of ground support strategies in high-stress ground conditions between civil tunnels and mining excavations are discussed. Ground support benchmarking data and mitigation measures for mines and civil tunnels in burst-prone and squeezing grounds conditions are briefly presented by some examples in practice. The importance of the application of shotcrete shells with yielding elements in squeezing ground conditions has been presented in detail by a simplified Convergence Confinement Method (CCM) example.