Speech Title: Influence of Preexisting Discontinuities on Hydraulic Fracture Complexity in a Naturally Fractured Reservoir

Abstract: Preexisting discontinuities, such as joints and beddings, are widely distributed in unconventional reservoirs. During fluid injection, hydraulic fractures strongly interact with preexisting discontinuities, leading to great uncertainty in prediction of fracture geometry. To investigate how preexisting discontinuities affect fracture complexity, numerical simulations are carried out using the distinct element method. A discrete fracture network model for a shale reservoir in the southeastern Ordos basin, China is built. The results indicate that preexisting discontinuities strongly influence fracture complexity: they impose a barrier for fracture growth in most cases, and thus result in a smaller fracture area and a higher fluid pressure for fracture extension. However, the roles that joints and beddings play in fracture complexity differ. Compared with the bedding model, the joint model causes a less complex fracture geometry under the same injection condition, suggesting that the joints play a more significant role in reducing fracture complexity.

Speech Title: Structural Characteristics of Rock Mass and Driving Mechanism of Large Bedrock Landslides in Southeastern Tibet

Abstract: Recent technological developments including Unmanned Aerial Vehicles, terrestrial laser scanning, photogrammetry and point cloud analysis software tools greatly enhance our ability to investigate geometrical and mechanical characteristics of rock mass of high-relief slopes that are not accessible on site and spatial distribution of large bedrock landslides regionally. The presentation contains two parts, the first part focusing on the relationship between faulting and the spatial geometrical and mechanical characteristics of a rock mass controlled by faulting. Using the Yarlung Tsangpo Fault of southeastern Tibet as a case study, we propose the procedures, investigation approaches, evidence and criteria for quantitatively defining the threshold distance for damage zones combining the spatial variations of fracture density and rock mass strength. Influenced by tectonics, fracture density (the joint volumetric count, Jv) and cohesion of the rock mass show power curve relations with distance within the damage zone. The fault first affects the characteristics of rock mass structures, and then the characteristics of the rock structures influence the stability of slope leading to landslide. The second part focuses on the relationship between landslides and rock mass strength. Data show that, at the landscape scale, more landslides have occurred on the hillslopes with greater rock mass strength than on those with lower rock mass strength. It is concluded that the dominant drivers of large bedrock landslides in our study areas are rock uplift and river incision, rather than a reduction in rock strength as has been proposed in some tectonically passive regions.

Speech Title: A Constitutive Model of Compacted Clay under Coupled Chemo-Hydro-Mechanical Conditions

Abstract: Compacted clay is an ideal host material for the disposal of high-level radioactive waste, cut-off wall in contaminated site due to its low permeability, high adsorption capacity and good self-sealing characteristics. A coupled chemo-hydro-mechanical model for compacted bentonite based on the Barcelona expansive model (BExM) that distinguishes between the microstructure and macrostructure was developed. The effective stress principle was modified by introducing the osmotic stress pπ, which is considered to govern the elastic strain of the compacted clay. The yield functions were deduced, and the yield surface was depicted in the smatric-pπ-pnet space. Validation of the proposed model was conducted by simulating a series of wetting–drying tests on compacted clay under different net vertical stress and osmotic stress conditions and by salinization-desalinization tests on compacted bentonite at different vertical stresses.

Speech Title: Rock Mass Characterization and Assessment of Rock Slope Instabilities Using New Technologies

Abstract: The lecture will present how new technologies can be effectively used for the rock mass characterization and assessment of rock slope instabilities. The use of new technologies, such as UAV-enabled mapping and SfM photogrammetry, in combination with traditional field reconnaissance provides a very effective method for identifying the actual risk areas of slopes affecting infrastructure works and cultural heritage sites. The characterization and rock mass classification of rock masses in remote, inaccessible slopes has been facilitated. The applications related to slope stability assessment and risk mitigation for rock slopes will be demonstrated through specific case studies.