Mingyang Wang

Study on the Characteristic Energy Factor of the Deep Rock Mass Under Weak Disturbance

This study aims to investigate the characteristic energy factor of the deep rock mass deformation subjected to the disturbance induced by excavation or explosion. Based on the well-known rock hierarchical structure, the equivalent average kinetic energy of the deep rock mass under weak disturbance is first introduced. The characteristic energy factor that reflects the instable deformation of the deep rock mass is derived using the principle of variation. The relationship between the characteristic energy factor and the energy hierarchical sequence of the deep rock mass deformation and failure has also been illustrated. We believe that the characteristic energy factor is closely related to the characteristic scientific phenomena of deep rock mass in essence, which can provide a new approach for the study of deep rock mass in the fields of nonlinear mechanics, statistic physical mechanics, and mechanics of explosion and geophysics.

A Variable-Parameter Creep Damage Model Incorporating the Effects of Loading Frequency for Rock Salt and Its Application in a Bedded Storage Cavern

Laboratory tests were conducted to assess the effects of the loading frequency on the time-dependent behavior and damage properties of rock salt under confining stress states. Axial two-stage irreversible deformation based on the loci of the minimum load of each cycle was observed, and this observation was similar to the result of conventional creep tests under static loads. The unloading modulus decreased exponentially with respect to time, and the damage variable was represented in terms of the decay of the material stiffness. To account for the effects of the loading frequency on the time-dependent degradation of rock salt, a unified damage evolution equation was formulated based on the experimental results. A creep damage model of rock salt was proposed by introducing non-stationary modular components into the Burgers viscoelastic model. Numerical simulation was performed using the newly developed model to evaluate the stability and serviceability of a storage cavern in a bedded salt formation under various loading scenarios. The simulated results indicate that a lower injection–withdrawal frequency results in a greater volume convergence rate and a wider dilatancy region of the storage cavern. Additionally, the stress concentration and dilatancy of the surrounding rock mass extend much deeper into the mudstone interbeds than into other regions of the cavern.

A Theoretical Explanation for Rock Core Disking in Triaxial Unloading Test by Considering Local Tensile Stress

Rock is a typical inhomogeneous material with a large number of flaws in different scales; the stress field of the rock in its elastic state consists of two parts: the elastic stress, which distributes uniformly in the entire region; and an additional stress, which only exists around the flaws. Theoretical expressions of the additional stress and local stress are derived based on the Maxwell model. Core disking which takes place under the condition that the axial stress is rapidly reduced while the confining pressure is kept unchanged is explained with a new method. Unloading duration’s effect on core disking is analyzed. A new criterion for core disking is presented based on attributing the core disking to the result of the exceedance of local tensile stress over the tensile strength. Based on our theoretical analysis and the conclusions from published resources, core disking is most likely to occur if the maximum principal stress is more than five to six times the tensile strength.

Weak disturbance-triggered seismic events: an experimental and numerical investigation

Geological masses can be regarded as rock blocks of different scale of structural planes with the ability to store various forms of energy. Propagation of stress waves generated by weak external disturbances in rock blocks may trigger the release of internal potential energies and slip movements along these structural planes, resulting in seismic events, such as residual deformations, fault-slip rock bursts, ground motions, etc. First, based on a simplified rock block system, a novel experimental system, and a numerical model, we investigated weak disturbance-triggered seismic events. We then conducted a theoretical analysis in which we quantitatively characterized the critical energy conditions of seismic events. The experimental and numerical results showed that the tensile stages of the stress waves generated by the disturbance loading reduced the normal stress on the interface of adjacent blocks, leading to an ultra-low friction phenomenon. This phenomenon resulted in the slip movements of the work block. The residual displacements and the critical energy conditions significantly depended on the initial stress states. As the initial shearing force ratio β increased, greater residual displacements were observed and lower disturbance energy was required to trigger a seismic event. When β was close to 1, even an extremely weak disturbance was able to trigger large residual displacements or sustainable slip failures. A dimensionless parameter k was introduced to characterize the critical energy conditions of the seismic events. The critical condition for initiating a slip was that k should exceed a critical value, while the critical conditions for a slip failure were that k should reach a larger critical value and the work block should be in a subcritical stress state. It can be concluded that disturbances, initial shear forces, and friction-weakening mechanisms are the most important factors, with the initial shear forces providing the potential energies, which are locked by the static friction force (the shear strength). The disturbances reduce the shear strength and weaken the restrictions. The friction-weakening mechanisms determine energy conversion coefficient efficiency.

Water Inrush Analysis of the Longmen Mountain Tunnel Based on a 3D Simulation of the Discrete Fracture Network

Abstract The construction of tunnels and underground engineering in China has developed rapidly in recent years in both the number and the length of tunnels. However, with the development of tunnel construction technology, risk assessment of the tunnels has become increasingly important. Water inrush is one of the most important causes of engineering accidents worldwide, resulting in considerable economic and environmental losses. Accordingly, water inrush prediction is important for ensuring the safety of tunnel construction. Therefore, in this study, we constructed a three-dimensional discrete network fracture model using the Monte Carlo method first with the basic data from the engineering geological map of the Longmen Mountain area, the location of the Longmen Mountain tunnel. Subsequently, we transformed the discrete fracture networks into a pipe network model. Next, the DEM of the study area was analysed and a submerged analysis was conducted to determine the water storage area. Finally, we attempted to predict the water inrush along the Longmen Mountain tunnel based on the Darcy flow equation. Based on the contrast of water inrush between the proposed approach, groundwater dynamics and precipitation infiltration method, we conclude the following: the water inflow determined using the groundwater dynamics simulation results are basically consistent with those in the D2K91+020 to D2K110+150 mileage. Specifically, in the D2K91+020 to D2K94+060, D2K96+440 to D2K98+100 and other sections of the tunnel, the simulated and measured results are in close agreement and show that this method is effective. In general, we can predict the water inflow in the area of the Longmen Mountain tunnel based on the existing fracture joint parameters and the hydrogeological data of the Longmen Mountain area, providing a water inrush simulation and guiding the tunnel excavation and construction stages.

A theoretical derivation of the dilatancy equation for brittle rocks based on Maxwell model

In this paper, the micro-cracks in the brittle rocks are assumed to be penny shaped and evenly distributed; the damage and dilatancy of the brittle rocks is attributed to the growth and expansion of numerous micro-cracks under the local tensile stress. A single crack’s behaviour under the local tensile stress is generalized to all cracks based on the distributed damage mechanics. The relationship between the local tensile stress and the external loading is derived based on the Maxwell model. The damage factor corresponding to the external loading is represented using the p–alpha (p–α) model. A dilatancy equation that can build up a link between the external loading and the rock dilatancy is established. A test of dilatancy of a brittle rock under triaxial compression is conducted; the comparison between experimental results and our theoretical results shows good consistency.

Study on the Application of the Kent Index Method on the Risk Assessment of Disastrous Accidents in Subway Engineering

With the development of subway engineering, according to uncertain factors and serious accidents involved in the construction of subways, implementing risk assessment is necessary and may bring a number of benefits for construction safety. The Kent index method extensively used in pipeline construction is improved to make risk assessment much more practical for the risk assessment of disastrous accidents in subway engineering. In the improved method, the indexes are divided into four categories, namely, basic, design, construction, and consequence indexes. In this study, a risk assessment model containing four kinds of indexes is provided. Three kinds of risk occurrence modes are listed. The probability index model which considers the relativity of the indexes is established according to the risk occurrence modes. The model provides the risk assessment process through the fault tree method and has been applied in the risk assessment of Nanjing subways river-crossing tunnel construction. Based on the assessment results, the builders were informed of what risks should be noticed and what they should do to avoid the risks. The need for further research is discussed. Overall, this method may provide a tool for the builders, and improve the safety of the construction.