We formulate the problem of fully coupled transient fluid flow and quasi‐static poroelasticity in arbitrarily fractured, deformable porous media saturated with a single‐phase compressible fluid. The fractures we consider are hydraulically highly conductive, allowing discontinuous fluid flux across them; mechanically, they act as finite‐thickness shear deformation zones prior to failure (i.e., nonslipping and nonpropagating), leading to “apparent discontinuity” in strain and stress across them. Local nonlinearity arising from pressure‐dependent permeability of fractures is also included. Taking advantage of typically high aspect ratio of a fracture, we do not resolve transversal variations and instead assume uniform flow velocity and simple shear strain within each fracture, rendering the coupled problem numerically more tractable. Fractures are discretized as lower dimensional zero‐thickness elements tangentially conforming to unstructured matrix elements. A hybrid‐dimensional, equal‐low‐order, two‐field mixed finite element method is developed, which is free from stability issues for a drained coupled system. The fully implicit backward Euler scheme is employed for advancing the fully coupled solution in time, and the Newton‐Raphson scheme is implemented for linearization. We show that the fully discretized system retains a canonical form of a fracture‐free poromechanical problem; the effect of fractures is translated to the modification of some existing terms as well as the addition of several terms to the capacity, conductivity, and stiffness matrices therefore allowing the development of independent subroutines for treating fractures within a standard computational framework. Our computational model provides more realistic inputs for some fracture‐dominated poromechanical problems like fluid‐induced seismicity.

Behavior of typical rectangular bridge columns with substandard design details for seismic forces was investigated. The poor performance of this type of column attested to the need for effective and economical seismic upgrading techniques. A method utilizing fiber reinforced polymer (FRP) composites to retrofit existing bridge columns is investigated in this paper. High-strength FRP straps are wrapped around the column in the potential plastic hinge region to increase confinement and to improve the behavior under seismic forces. Five rectangular columns with different reinforcement details were constructed and tested under reversed cyclic loading. Two columns were not retrofitted and were used as control specimens so that their hysteresis response could be compared with those for retrofitted columns. The results of this study indicated that significant improvement in ductility and energy absorption capacity can be achieved as a result of this retrofitting technique.

Fluid perturbations play a pivotal role in triggering earthquakes. However, the role of fluid in the coseismic rupture process remains largely unknown. To this end, we develop a 2‐D fully dynamic spontaneous rupture model for fluid‐induced earthquakes. The effect of fluid in the preseismic quasi‐static regime is modeled as either pore pressure diffusion or fully coupled poroelasticity, using our Jin and Zoback (2017, https://doi.org/10.1002/2017JB014892) computational model. The two approaches lead to radically different predictions on the time of earthquake nucleation. Correspondingly, the evolved fluid pressure or poroelastic stress on the fault, together with the spatially altered density of the fluid‐saturated hosting rock, is passed to the dynamic regime. Under the assumption of an undrained coseismic fluid‐solid system, we discretize the fully dynamic Cauchy equation of motion subjected to an exact fault contact constraint using a split‐node finite element method in space and an implicit Newmark family finite difference method in time. Within each time step, a fully implicit Newton‐Raphson scheme is implemented iteratively for linearizing the fully discrete equations. Within each Newton iteration, a physics‐based and nonstationary preconditioner is designed to accelerate the convergence of the selected generalized minimal residual method iterative linear solver. The effect of fluid is highlighted throughout the discretization and computational procedures. Finally, by conducting a numerical experiment, we illustrate that a fully coupled poroelastic model can lead to significantly different predictions on coseismic rupture behaviors and wavefields compared to a decoupled model. Our computational model can also serve as one of the earliest full‐physics modeling tool for fluid‐induced earthquakes.

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To study the three-dimensional spatial and temporal distributions of dust in tunneling roadways, and to solve the problems of inadequate time and limited number of monitoring points, this paper designs a device for the real-time monitoring and storage of data on the concentrations of dust at multiple measuring points in the same section of a tunnel. The proposed device can measure the total concentration of dust and that of respirable dust in real time at different instances and locations, and using different working procedures. These measurements are used to study the temporal and spatial migration of dust. The results show that there was a sharp fluctuation zone 0-25 m from the heading face, about 25-40 m was high speed subsidence, beyond 40 m was gentle subsidence, The change of respiratory dust is much smoother. At different distances from the heading face, the total dust concentration exhibited a process of ''violent oscillation-rapid descent-stable descent,'' while the respirable dust exhibited a process of ''fluctuating ascent-gradual subsidence.'' Changes in the concentrations of total dust and respirable dust dust were consistent at different positions in the same section of the tunnel. The concentration of dust near the wall was low, and those along the sidewalk and air duct of the roadway were slightly higher than in the middle. The concentration of dust farther down the air duct decreased more slowly than that in the remaining lines of measurement. Small amounts of dust featuring large particles settled quickly. High concentrations of dust were observed to be intermittent, and the background value of dust concentration within 100 m of heading face was between 0.5 and 3 mg/m 3 .