Search

Tailings impoundments are often prone to failure due to various causes related to complex loading conditions. For instance, tailings impoundments can fail during or after a seismic event, mainly because of the liquefaction of loose, cohesionless tailings. To improve the seismic stability of impoundments, the density of the tailings can be increased or waste rock inclusions (WRI) can be added in the impoundment. This paper presents the results of numerical analyses of the impoundments loaded with a variety of ground motions with different frequencies, scaled at two different levels of intensity representative of two mining regions of Eastern Canada. The results show that the conventional impoundments are subjected to medium to high displacements at the end of shaking; these show a high probability of rupture during the earthquake or in the post-seismic phase. Tailings densification can decrease the volume of liquefied tailings and displacements during the seismic phase but does not significantly reduce the probability of post-seismic failure. WRI can slightly reduce the volume of liquefied tailings, depending on the intensity of the motions, but the reinforcement reduces significantly the lateral displacements; impoundments with WRI show even better performances during the post-seismic phase. The use of WRI is deemed a good approach to ensure the seismic stability of tailings impoundments and reduce the risk of seismically induced failure. [ABSTRACT FROM AUTHOR]

Unconventional oil and gas formations are abundant, have become an increasingly important part of the global energy supply, and are attracting increasing attention from the industry. Predicting key reservoir properties plays a significant role in both geological science and subsurface engineering workflows. With the advent of horizontal well drilling and multiple-stage hydraulic fracturing, the Montney Shale formation is one of the most promising and productive shale plays in Canada. However, very few academic papers discuss its in situ stress, reservoir pressure, and permeability, which are essential for the development of the Montney Shale. The objective of this study is to analyze the geo-stress, the pore pressure, and several key reservoir properties by using diagnostic fracture injection test (DFIT) data from the Montney Shale. One horizontal well from the Wapiti field has been analyzed with a set of DFIT data, and its results show that the general pressure and Gdp/dG responses from Well-A indicate a signature of height recession/transverse storage. In the study, the Tangent Line method, the Compliance method, and the Variable Compliance method have been applied to estimate the key reservoir properties. As a result, the Well-A DFIT analysis estimates that the closure pressure is ranging from 34.367 to 39.344 MPa, contributing to the stress gradient from 14.09 to 16.13 KPa/m for the formation. The pore pressure is ranging from 20.82 to 24.58 MPa, contributing to the pore pressure gradient from 8.54 to 10.07 KPa/m for the formation. The porosity is ranging from 3% to 6%. These reservoir properties are contoured cross the Montney Shale formation. Using the DFIT's numerical simulation and history matching, the reservoir permeability is 0.024 md, fracture length is 13.44 m, and fracture geometries are analyzed by different models. Moreover, the physics behind the DFIT are analyzed and discussed in detail. For the first time, three different analysis methods have been applied to estimate a series of key reservoir properties for the case wells in the Montney Shale formation. This approach can not only reduce the potential prediction error caused by a single method application but also increase the persuasiveness of the assessment and save time, ensuring the efficient implementation of engineering operations. Given the significance of quantifying in situ stress and reservoir pore pressure in unconventional hydrocarbon exploration and development, this study could help the operator to quickly understand the stress regimes, the fracture geometry, and the formation properties of the Montney Shale formation in the Wapiti field. Furthermore, the interpreted results demonstrated in this paper are adding substantial business value to the asset, especially in terms of improving the hydraulic fracturing design and, thus, accelerating the cashflow from production. [ABSTRACT FROM AUTHOR]

• Seismic design parameters are proposed for the Moment-resisting Knee-braced Frame. • The study is carried out within the framework of Canadian standards. • All potential hazard sources expected on the Canadian west coast are considered. • The MKF shall be designed as a moderately ductile system. • Overstrength and ductility factors of 1.6 and 3.0 are proposed for the MKF system. • The proposed seismic design parameters are verified by comprehensive nonlinear analyses. This paper proposes and verifies the seismic design parameters, including overstrength-related force modification factor, ductility-related force modification factor, deflection amplification factor, and design period, for the steel Moment-resisting Knee-braced Frame (MKF) system. The building selected in this study is an office located in Vancouver, British Columbia, Canada, in which MKFs act as the lateral load-resisting system. 14 prototype frames spanning a wide range of geometrical configurations are designed following the requirements of the 2015 National Building Code (2015 NBC) of Canada. Nonlinear static analyses are carried out on the prototype frames to determine the preliminary ductility and overstrength factors. Six new MKFs (assessment frames) are designed using the proposed overstrength and ductility factors, and their seismic and collapse performances are examined by comprehensive numerical analyses, considering the effects of the potential sources of ground motion expected on the Canadian west coast, namely subduction intraslab, subduction interface and shallow crustal events. The results of this study suggest that the MKF system shall be designed as a moderately ductile system using overstrength and ductility factors of 1.60 and 3.0, respectively, with a height not exceeding 40 m in regions of high seismicity. [ABSTRACT FROM AUTHOR]

This paper advances a framework for evaluating mesh sensitivity in numerical models of systems involving strain-weakening materials, and demonstrates its application in the case study of the failure at the Mount Polley TSF in Canada. Numerical studies are combined with analytical arguments and physical evidence to establish that this failure was caused in part by the localisation of strain in a shear band with a thickness 0 < h sb ≤ 12.5 cm, and to rule out the possibility of slippage along a pre-sheared plane in the foundation. The range of model responses is bound by an upper limit representing the least conservative case of "no weakening," and a lower limit representing the most conservative case of strain localisation within an infinitely thin shear band, predicting the highest and the lowest stability levels, respectively. The limit states are discoverable using a new method presented here. The model's convergence is shown to vary at mesh discretisation levels above the minimum established by the upper limit state analysis; higher mesh resolutions yield lower stability levels, approaching asymptotically the floor value established by the lower limit state analysis. A conceptual relationship between a model's discretisation, the shape of the strain-weakening curve and convergence is formulated. [ABSTRACT FROM AUTHOR]