Shucai Li

Multilineage differentiation of dental follicle cells and the roles of Runx2 over-expression in enhancing osteoblast/cementoblast-related gene expression in dental follicle cells.

Objectives:  Dental follicle cells (DFCs) provide the origin of periodontal tissues, and Runx2 is essential for bone formation and tooth development. In this study, pluripotency of DFCs was evaluated and effects of Runx2 on them were investigated.

Risk assessment of water inrush in karst tunnels and software development

Water inrush makes time extended, instruments destructed, and casualty increased, which is the biggest threat for safe construction of tunnels in karst areas. A software system for risk assessment of water inrush was established with considering eight risk factors, including groundwater level, unfavorable geology, formation lithology, topography, strata inclination, excavation, advanced geological prediction, and monitoring. In the present software system, fuzzy mathematics and Analytical Hierarchy Process (AHP) were used to quantitatively describe the risk levels for each factor. The influence degree of each factor to water inrush was assigned an objective weight and a subjective weight, and the proportion of the two weights in the risk assessment was defined as weight distribution. The objective weights of the risk factors were obtained from more than 100 water inrush instances in karst tunnels, whereas the weight distribution was totally derived from expert field assessment and subjective weights were determined by using AHP in the risk assessment. Two case studies of karst tunnels were applied to check the reliability of the proposed software system, and the comparisons between the software assessment and practical excavation yield good consistency. Therefore, the software system can appropriately be used in practice to forecast water inrush in karst tunnels.

Time-Dependent Behavior of Diabase and a Nonlinear Creep Model

Triaxial creep tests were performed on diabase specimens from the dam foundation of the Dagangshan hydropower station, and the typical characteristics of creep curves were analyzed. Based on the test results under different stress levels, a new nonlinear visco-elasto-plastic creep model with creep threshold and long-term strength was proposed by connecting an instantaneous elastic Hooke body, a visco-elasto-plastic Schiffman body, and a nonlinear visco-plastic body in series mode. By introducing the nonlinear visco-plastic component, this creep model can describe the typical creep behavior, which includes the primary creep stage, the secondary creep stage, and the tertiary creep stage. Three-dimensional creep equations under constant stress conditions were deduced. The yield approach index (YAI) was used as the criterion for the piecewise creep function to resolve the difficulty in determining the creep threshold value and the long-term strength. The expression of the visco-plastic component was derived in detail and the three-dimensional central difference form was given. An example was used to verify the credibility of the model. The creep parameters were identified, and the calculated curves were in good agreement with the experimental curves, indicating that the model is capable of replicating the physical processes.

Fatigue Behavior of Granite Subjected to Cyclic Loading Under Triaxial Compression Condition

A series of laboratory tests were performed to examine the fatigue behavior of granite subjected to cyclic loading under triaxial compression condition. In these tests, the influences of volumetric change and residual strain on the deformation modulus of granite under triaxial cyclic compression were investigated. It is shown that the fatigue behavior of granite varies with the tendency for volumetric change in triaxial cyclic compression tests. In the stress–strain space, there are three domains for fatigue behavior of rock subjected to cyclic loading, namely the volumetric compaction, volumetric dilation with strain-hardening behavior, and volumetric dilation with strain-softening behavior domains. In the different domains, the microscopic mechanisms for rock deformation are different. It was also found that the stress level corresponding to the transition from volumetric compaction to volumetric dilation could be considered as the threshold for fatigue failure. The potential of fatigue deformation was compared with that of plastic deformation. The comparison shows that rocks exhibit higher resistances to volumetric deformation under cyclic loading than under plastic loading. The influence of residual strain on the fatigue behavior of rock was also investigated. It was found that the axial residual strain could be a better option to describe the fatigue behavior of rock than the loading cycle number. A constitutive model for the fatigue behavior of rock subjected to cyclic loading is proposed according to the test results and discussion. In the model, the axial residual strain is considered as an internal state variable. The influences of confining pressure and peak deviatoric stress on the deformation modulus are considered in a term named the equivalent stress. Comparison of test results with model predictions shows that the proposed model is capable of describing the prepeak fatigue behavior of rock subjected to cyclic loading.

Numerical Study on Crack Propagation in Brittle Jointed Rock Mass Influenced by Fracture Water Pressure

The initiation, propagation, coalescence and failure mode of brittle jointed rock mass influenced by fissure water pressure have always been studied as a hot issue in the society of rock mechanics and engineering. In order to analyze the damage evolution process of jointed rock mass under fracture water pressure, a novel numerical model on the basis of secondary development in fast Lagrangian analysis of continua (FLAC3D) is proposed to simulate the fracture development of jointed rock mass under fracture water pressure. To validate the feasibility of this numerical model, the failure process of a numerical specimen under uniaxial compression containing pre-existing fissures is simulated and compared with the results obtained from the lab experiments, and they are found to be in good agreement. Meanwhile, the propagation of cracks, variations of stress and strain, peak strength and crack initiation principles are further analyzed. It is concluded that the fissure water has a significant reducing effect on the strength and stability of the jointed rock mass.

Assessment of Hydro-Mechanical Behavior of a Granite Rock Mass for a Pilot Underground Crude Oil Storage Facility in China

The hydro-mechanical behavior of a pilot underground crude oil storage facility in a granite host rock in China was analyzed using the finite element method (FEM). Characterization of hydro-mechanical behavior of the rock mass was performed using laboratory test, field monitoring, back analysis of field measurements and permeability tests. FEM numerical analyses were used to assess the hydro-mechanical behavior of the granite to study several design and construction issues. The containment properties of the storage facility were investigated without and with the water curtain system. Results showed that the stored oil would leak into rock mass if a water curtain system is not provided, whereas the containment property of the facility will be maintained when a water curtain system is in place. On the influence of cavern excavation sequence, it was indicated that the excavation of the caverns from left to right is a better choice than right to left for the containment property of the facility. On the influence of permeable condition, it was found that the extent of plastic zones, horizontal convergence and crown settlement under permeable condition are lower than those under impermeable condition due to the different stress paths in the rock mass experienced during excavation.

Numerical Study of Zonal Disintegration within a Rock Mass around a Deep Excavated Tunnel

AbstractZonal disintegration around a deep excavated tunnel is a characteristic of the rock mass intense fracturing phenomenon. In this paper, three-dimensional numerical tests on the failure processes of rock samples containing vertical wall semiarched tunnels are performed with the three-dimensional Realistic Failure Process Analysis (RFPA3D)–Parallel system model running on a Lenovo 1800 cluster, in order to study the configuration of zonal disintegration within the rock mass around the deep excavated tunnels. This study focuses on the zonal disintegration phenomenon in the tunnel longitudinal direction and the time-lag effect. Numerical results show that the microcracking in the disintegration zone within the model decreases gradually from the tunnel surface to the interior of the model along the tunnel longitudinal direction; the disintegration zone within the model also reduces, but the diameter of the disintegration zone becomes larger. Numerical results also indicate that an apparent time lag exis...

Experimental and numerical investigations on the shear behavior of a jointed rock mass

The original forming process of the earth crust is companied with internal in situ stress, which gradually complicates while the earth crust evolves with geological conformation movements, leading to the generation of large amounts of faults, joints and fissures. These structural planes, to some extent, remarkably reduce the strengths of rock mass, including the shear behavior. In this paper, the authors report a physical model test on jointed rock mass under direct shear stress state and also adopt a numerical method, Discontinuous Deformation Analysis for Rock Failure (DDARF), to simulate the shear failure process, the variation of stresses and displacements of some key monitoring points. The comparative analysis demonstrates that the numerical results are favorable with those obtained in the physical model test. Therefore, it is concluded that the method of DDARF could effectively simulate the shear behavior of jointed rock mass. Furthermore, other than the original physical model test, the numerical models with echelon joints under different axial loadings are also simulated. The crack initiation, extension, coalescence, and the ultimate shear failure are totally investigated, after which the shear behavior of numerical models in different cases are comparatively analyzed.

Predicting geological hazards during tunnel construction

Abstract The complicated geological conditions and geological hazards are challenging problems during tunnel construction, which will cause great losses of life and property. Therefore, reliable prediction of geological defective features, such as faults, karst caves and groundwater, has important practical significances and theoretical values. In this paper, we presented the criteria for detecting typical geological anomalies using the tunnel seismic prediction (TSP) method. The ground penetrating radar (GPR) signal response to water-bearing structures was used for theoretical derivations. And the 3D tomography of the transient electromagnetic method (TEM) was used to develop an equivalent conductance method. Based on the improvement of a single prediction technique, we developed a technical system for reliable prediction of geological defective features by analyzing the advantages and disadvantages of all prediction methods. The procedure of the application of this system was introduced in detail. For prediction, the selection of prediction methods is an important and challenging work. The analytic hierarchy process (AHP) was developed for prediction optimization. We applied the newly developed prediction system to several important projects in China, including Hurongxi highway, Jinping II hydropower station, and Kiaochow Bay subsea tunnel. The case studies show that the geological defective features can be successfully detected with good precision and efficiency, and the prediction system is proved to be an effective means to minimize the risks of geological hazards during tunnel construction.

Application of extenics theory for evaluating effect degree of damaged mountains based on analytic hierarchy process

Abstract An evaluating method is proposed to investigate effect degree of seven damaged mountains of Jinan city, based on matter element model deduced from the theories of extenics. Using the effect degree classification and influencing factors on damaged mountains, the elements in classical and sectorized field are defined, whereby an extension-evaluating model is developed to evaluate the classification of effect degree of damaged mountains by the correlation function of matter elements and extension sets. The analytic hierarchy process methodology for calculating weight aggregation of evaluating factors is proposed. The evaluating results are thus obtained through such an evaluation. An exemplification is shown that the present method is effective and applicable to forecast the classification of effect degree of damaged mountains more accurately and scientifically, which lends the support for control planning for damaged mountains and a more reliable basis for taking economic and reasonable supporting/reinforcing measures.