Rock Mechanics and Rock Engineering最新文献

A novel discrete element method (DEM) model is proposed to better reproduce the behaviour of porous soft rocks. With the final goal of simulating pile penetration problems efficiency and scalability are two underlining features. The contact model is based on the macro-element theory and employs damage laws to govern the plastic deformations developing at the microscale. To attain (i) high porosity states, (ii) represent irregular shaped grains and (iii) incorporate the physical presence of bond fragments, the model is cast within a far-field interaction framework allowing for non-overlapping particles to transmit forces. After presenting a calibration procedure, the model is used to replicate the behaviour of Maastricht calcarenite. In particular, the mechanical response of this calcarenite is explored within the critical state theory framework. Finally, the efficiency, performance and scalability of the model is tested by simulating physical model experiments of cone-ended penetration tests in Maastricht calcarenite from the literature. To boost efficiency of the 3D numerical simulations, a coupled DEM-FDM (Finite Differential Method) framework is used. The good fit between the experimental and numerical results suggest that the new model can be used to unveil microscopic mechanism controlling the macroscopic response of soft-rock/structure interaction problems.

The random rock failure process analysis (RRFPA) method was developed in this research to characterize the material spatial variability and uncertainty in rock failure modelling. The random field theory (RFT) was integrated with the traditional rock failure process analysis (RFPA) to model rock heterogeneity. In this approach, the variation of rock properties is represented as a function of relative distance, such that the influence of material intrinsic correlation on its fracturing behaviour can be appropriately captured. To validate the theory, 300 RRFPA simulations were conducted to investigate the failure characteristics of rock samples under compressive loading. The results showed that by incorporating a spectrum of material properties, the numerical outcomes exhibited distinct upper and lower bounds of stress across all testing scenarios, closely aligning with the experimental relationships. The histograms for uniaxial compressive strength and elastic modulus showed that both properties followed normal distributions, with the average values of 10.099 MPa and 1.818 GPa, respectively. The corresponding coefficients of variation were 0.450 and 0.038. The localized failure tended to result in a more rapid release of acoustic emission energy, but generated smaller cumulative energy compared to the overall failure pattern. In general, the maximum relative error of the RRFPA model was only 0.66% for uniaxial compressive strength, elastic modulus, and critical axial strain.

Stimulation operations enhance the performance of geothermal reservoirs by enhancing fluid flow and heat transfer. Predicting stimulation outcomes is challenging due to the complexity of reservoir properties and limited observations given by operational conditions. The stress state, natural geological structures, pressure distribution, and injection protocols play crucial roles in the engineering of a stimulation operation. This study provides in-depth observations from a hectometer-scale stimulation experiment conducted at the Bedretto Underground Laboratory for Geosciences and Geoenergies within a densely monitored crystalline rock volume with an overburden of more than 1 km. We found that hydraulic connectivity, pressure compartments, and the geomechanical characteristics of existing geological structures play important roles in the propagation patterns of seismic events. Notably, the initiation and distribution of seismicity are markedly influenced by the zonal pressure isolation and the propagation of nominal pressure diffusion fronts across the reservoir. Our findings highlight the necessity of adapting stimulation strategies according to the unique geomechanical and geological characteristics of the reservoir. This claim is supported by the distinct activation patterns observed between the first and second injection cycles in the current case study. The spatial extent of the stimulated volume can be partially controlled by the number of stimulation cycles and injection pressure level, as farther structures are more likely to be activated in the subsequent cycles. The results also indicate that the Kaiser effect can be attenuated due to changes in the flow pathway and stress caused during stimulation, consistent with a proposition from a recent study. Our findings underscore the critical importance of the interplay between hydraulic pressures and stress states to optimize the stimulation of fractured reservoirs.

Introduction: Relatively few studies rigorously examine the factors associated with health systems strengthening and scaling of interventions at subnational government levels. We aim to examine how The Challenge Initiative (TCI) coaches subnational (state government) actors to scale proven family planning and adolescent and youth sexual and reproductive health approaches rapidly and sustainably through public health systems to respond to unmet need among the urban poor.

Methods: This mixed-methods comparative case study draws on 32 semistructured interviews with subnational government leaders and managers, nongovernmental organization leaders, and TCI Nigeria staff, triangulated with project records and government health management information system (HMIS) data. Adapting the Consolidated Framework for Implementation Research (CFIR), we contrast experience across 2 higher-performing states and 1 lower-performing state (identified through HMIS data and selected health systems strengthening criteria from 13 states) to identify modifiable factors linked with successful adoption and implementation of interventions and note lessons for supporting scale-up.

Results: Informants reported that several TCI strategies overlapping with CFIR were critical to states' successful adoption and sustainment of interventions, most prominently external champions' contributions and strengthened state planning and coordination, especially in higher-performing states. Government stakeholders institutionalized new interventions through their annual operational plans. Higher-performing states incorporated mutually reinforcing interventions (including service delivery, demand generation, and advocacy). Although informants generally expressed confidence that newly introduced service delivery interventions would be sustained beyond donor support, they had concerns about government financing of demand-side social and behavior change work.

Conclusion: As political and managerial factors, even more than technical factors, were most linked with successful adoption and scale-up, these processes and systems should be assessed and prioritized from the start. Government leaders, TCI coaches, and other stakeholders can use these findings to shape similar initiatives to sustainably scale social service interventions.