Sijing Wang

A nonlinear dynamical model of landslide evolution

A nonlinear dynamical model for the evolution of landslide is proposed. The parameters of this model are obtained through an improved iterative algorithm of inversion developed in the paper. Based on the nonlinear dynamical model and nonlinear dynamical systems (NDS) theory, the approaches to determining the Lyapunov exponents, the predictable timescale and the stability criterion of the evolutional state of landslide are given. A case study of the Xintan slope is presented to illustrate the capability and merit of the nonlinear dynamical model.

A case history of Tunnel Boring Machine jamming in an inter-layer shear zone at the Yellow River Diversion Project in China

This is a case study of a Tunnel Boring Machine (TBM) jamming in a section of the Connection Works No. 7 tunnel of the Yellow River Diversion Project (YRDP) in China. Analysis of tunnel lithology, rock convergence by shearing, rock strength and ground stress, indicates that a high rate of convergence within an inter-layer shear zone in the lower part of an anticline was a dominant factor in the jamming. In addition, the shield encountered unfavorable tunnelling conditions in the form of wet clay, groundwater inflow, and cavities, coincident with tensile stresses in the lower part of an adjacent syncline. Based on these diagnoses, economical and quick measures were adopted, including additional excavation outside of the shield leaving free space to release the TBM. After 9 days of being jammed, the TBM was totally released and resumed normal excavation. This example highlights lessons learned from folding and inter-layer shear zone in TBM tunnelling.

A nonlinear catastrophe model of instability of planar-slip slope and chaotic dynamical mechanisms of its evolutionary process

This paper presents a nonlinear cusp catastrophe model of landslides and discusses the conditions leading to rapid-moving and slow-moving landslides. It is assumed that the sliding surface of the landslides is planar and is a combination of two media: one is elasto-brittle and the other is strain-softening. It is found that the instability of the slope relies mainly on the ratio of the stiffness of the elasto-brittle medium to the stiffness at the turning point of the constitutive curve of the strain-softening medium. A nonlinear dynamical model, which is derived by analyzing the catastrophe model and considering external environmental factors, is used to reveal the complicated mechanisms of the evolutionary process of the slope under environmental influence and to explore the condition of the occurrence of chaos and the route leading to chaos. The present analysis shows that, when the nonlinear role of the slope itself is equivalent to the environmental response capability, a chaotic phenomenon can occur and the route leading to chaos is realized by bifurcation of period-doublings.

Effects of the ratio of flaw size to specimen size on cracking behavior

To investigate the size effects on the cracking behavior of flaw-containing specimens under compressive loading, rectangular parallelepiped specimens containing a single centrally located flaw are numerically loaded using the bonded-particle model (BPM). Effects of the ratio of flaw size (length) to specimen size on cracking behavior are carefully studied. The numerical results show that increasing the ratio of flaw size to specimen size within a reasonable range (≤0.33) has no obvious effects on the first crack initiation stress, but decreases the uniaxial compressive strength. In specimens of a high flaw size to specimen size ratio, the newly generated cracks have longer extension length, which allows for easier crack identification as compared with that of the low ratio specimens. These phenomena are also observed in the physical test. Based on the present study, recommendations are given on choosing appropriate specimen widths in the BPM simulation. The failures of flaw-containing specimens as well as the outward bending effect of narrow specimens are also discussed.

The Cultural Relics Distribution Characteristics Along the Canal Line and Appraisal of its Influence by the Middle Route Project for Water Transferring from South to North China

Assessments of the impacts of environmental hazards on ecological systems and human health have become a subject of ever-increasing importance. In this work, we extend current ecological hazard evaluation to the problem of protecting cultural relics from hazards attributable to the presence of a large-scale canal system being planned in China. The development and utilization of water resources must be closely combined with the preservation of cultural relics. The Middle Route Project for Water Transfer from South to North China (MRWT) is a current example. In this paper, the engineering background of this project is briefly introduced. The distribution of cultural relics related to it is also summarized in terms of different geographical divisions. An influence index E = f(L, δh, k, I, v, s) is introduced to measure the comprehensive effect of the canal on cultural relics. Because this function is really established at the preconstruction stage, it is treated by use of fuzzy mathematics. Each cultural relic has its own E value. Cultural relics with E values greater than 0.75 should be paid high attention, while those with E less than 0.5 may generally be ignored. What must be preserved through use of engineering measures are cultural relics with E values greater than 0.9. As to those cultural relics with E ranging between 0.5 and 0.75, whether they should be preserved with engineering controls depends upon practical circumstances specific to each relic.

Fluid-driven fractures in granular materials

The initiation and propagation process of a fluid-driven fracture in granular materials is inherently a hydro-mechanical coupling problem. The bonded-particle method (BPM) was utilised to simulate the hydraulic fracturing process in granular materials, and different failure mechanisms were evaluated by analysing the formation of microcracks. Hydraulic conductivity is determined by pore size and connectivity in the direction of flow. A strain-dependent formulation was presented to highlight the inherent link between hydraulic conductivity and pore size. The results show that the BPM is capable of realistically predicting fluid-driven fractures in granular material. Using the BPM, the numbers of fluid-driven fractures induced by different failure modes can be determined. It is concluded that for consolidated formations, the initiation and propagation of fluid-driven fractures are dominated by tensile failure, which has been recognised in the field of geology and geomechanics. However, for unconsolidated formations, shear failure seems to be more important during the hydraulic fracturing process. As described in this article, the number of shear failure cracks is twice that of tension failure cracks, which has not been widely recognised. Overall, the simulation results of the fluid-driven fracture are in accordance with the experimental data observed by other researchers.

Information Entropy in Predicting Location of Observation Points for Long Tunnel

Based on the Markov model and the basic theory of information entropy, this paper puts forward a new method for optimizing the location of observation points in order to obtain more information from limited geological investigation. According to the existing data from observation points data, classification of tunnel geological lithology was performed, and various lithology distribution were determined along the tunnel using the Markov model and theory. On the basis of the information entropy theory, the distribution of information entropy was obtained along the axis of the tunnel. Therefore, different information entropy could be acquired by calculating different classification of rocks. Furthermore, uncertainty increases when information entropy increased. The maximum entropy indicates maximum uncertainty and thus, this value determines the position of the new drilling hole. A new geology situation will be decided by the maximum entropy for the lowest accuracy. Optimal distribution will be obtained after recalculating, using the new location of the geology situation. Taking the engineering for the Bashiyi Daban water diversion tunneling in Xinjiang as a case, the maximum information entropy of the geological conditions was analyzed by the method proposed in the present study, with 25 newly added geology observation points along the axis of the 30-km tunnel. The results proved the validity of the present method. The method and results in this paper may be used not only to predict the geological conditions of underground engineering based on the investigated geological information, but also to optimize the distribution of the geology observation points.

The Quantified Characterization Method of the Micro-Macro Contacts of Three-Dimensional Granular Materials on the Basis of Graph Theory

We have attempted a multiscale and quantified characterization method of the contact in three-dimensional granular material made of spherical particles, particularly in cemented granular material. Particle contact is defined as a type of surface contact with voids in its surroundings, rather than a point contact. Macro contact is a particle contact set satisfying the restrictive condition of a two-dimensional manifold with a boundary. On the basis of graph theory, two dual geometrical systems are abstracted from the granular pack. The face and the face set, which satisfies the two-dimensional manifold with a boundary in the solid cell system, are extracted to characterize the particle contact and the macro contact, respectively. This characterization method is utilized to improve the post-processing in DEM (Discrete Element Method) from a micro perspective to describe the macro effect of the cemented granular material made of spherical particles. Since the crack has the same shape as its corresponding contact, this method is adopted to characterize the crack and realize its visualization. The integral failure route of the sample can be determined by a graph theory algorithm. The contact force is assigned to the weight value of the face characterizing the particle contact. Since the force vectors can be added, the macro contact force can be solved by adding the weight of its corresponding faces.

The Stability Analysis Method of the Cohesive Granular Slope on the Basis of Graph Theory

This paper attempted to provide a method to calculate progressive failure of the cohesive-frictional granular geomaterial and the spatial distribution of the stability of the cohesive granular slope. The methodology can be divided into two parts: the characterization method of macro-contact and the analysis of the slope stability. Based on the graph theory, the vertexes, the edges and the edge sequences are abstracted out to characterize the voids, the particle contact and the macro-contact, respectively, bridging the gap between the mesoscopic and macro scales of granular materials. This paper adopts this characterization method to extract a graph from a granular slope and characterize the macro sliding surface, then the weighted graph is analyzed to calculate the slope safety factor. Each edge has three weights representing the sliding moment, the anti-sliding moment and the braking index of contact-bond, respectively, E1E2E3E1E2E3. The safety factor of the slope is calculated by presupposing a certain number of sliding routes and reducing Weight E3 repeatedly and counting the mesoscopic failure of the edge. It is a kind of slope analysis method from mesoscopic perspective so it can present more detail of the mesoscopic property of the granular slope. In the respect of macro scale, the spatial distribution of the stability of the granular slope is in agreement with the theoretical solution.

Study on the Fractal Characteristics of Fracture Network Evolution Induced by Mining

The evolution and distribution of fracture network induced by mining is essential to determine the mechanical properties and permeability of disturbed rock mass. In this paper, the similar material model tests are employed to simulate the stress variation, cyclic breaking, and fracture formation and distribution status of the overlying strata with different loading conditions, rock properties, and mining process. The fractal dimension of mining-induced fracture network varied with mining advancing, and the evolvement laws of fracture network with mining advancing and different mining advancing footage are concerned and obtained. By establishing the relationship between the fractal dimension and the mining length in different horizontal and vertical zones, it demonstrates that the fractal dimensions in horizontal and vertical zones have a self-similar characteristic, and the distribution of the fractal dimension of the mining-induced fractures shows generally the “W”-type trend.