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When a penstock serves a water supply purpose for multiple hydrogenerators in a hydroelectric power plant (HPP), a bifurcation structure should be installed between the main pipe and the branch pipes. This study focuses on a rib-strengthened steel bifurcation structure (RSSBS) with an emphasis on its hydraulic load-bearing mechanism. The finite element method is used with the contact and material non-linearities considered. The numerical simulation results agree reasonably well with in-situ measured data. Our research has underlined the critical role of the crescent-shaped rib (CSR) in lessening the stress-concentration at the bifurcation. The CSR is found to separate from the surrounding concrete under the internal water pressure (IWP), thus causing less IWP to be transmitted to the concrete. Despite the fact that the CSR is not in tension-stress-only status, however, the tensile-stress level is well within an acceptable range. In this context, the CSR should not necessarily be in tension-stress-only status, which is recognized as an ideal stress state in the conventional design philosophy. The findings also suggest that the importance of the concrete should not be stressed too much in the structural design of RSSBSs considering its backfilling role. The role of the crescent-shaped rib in strengthening local stiffness is underlined. The rib is found to separate from the concrete under the internal water pressure. The simulation results agree reasonably well with in-situ measured data. [ABSTRACT FROM AUTHOR]

Existing design models of soil pressure at the top of buried steel pipes are limited to small-diameter pipes. This study aims to investigate the behavior and design model on the soil pressure for large-diameter pipes considering the pipe diameter, diameter-to-thickness ratio, and cover depth. The distribution and size of soil pressure are obtained from finite element models and compared with traditional design models. Sensitivity studies of soil parameters, trench parameters, and friction coefficients are discussed. Furthermore, an innovative design model of soil pressure for large-diameter pipes is proposed. The results indicate that the basic distribution pattern of soil pressure is the "inverted basin"/parabola for large/small-diameter pipes, respectively. Peak soil pressure typically appears in the pleura of pipes with great flexibility and deep cover depth. The modulus and Poisson's ratio of backfill and soil-soil friction coefficient have an influence range of within 10% for soil pressure, while trench parameters have a more significant influence. Prism load is too large at high cover depth, and Marston load is small at low cover depth. The proposed basin model for soil pressure adopts the form of "straight line + parabola" for distribution and "Marston + pleura" load for size, with high accuracy and strong adaptability. [ABSTRACT FROM AUTHOR]

Abstract Accurately predicting the propagation of hydraulic fracturing arising from the wellbore is essential in petroleum engineering, hydraulic engineering, etc. There are various factors influencing fracture propagation, such as the initial fracture orientation and in-situ stresses, while the limitation of appropriate methods and techniques hinders the further investigation on the propagating mechanism. In the study, a simulator based on High-order Generalized Finite Element Method (GFEM) is introduced to investigate the propagation behaviors of hydraulic fractures arising from the sidewall of wellbore. For better recognization of hydraulic fracturing, several numerical examples are performed based on the simulator. Different influencing factors are studied, including intersection angle between fracture and wellbore, in-situ stresses and fracture interactions. It is found that, regardless of in-situ stresses in the surrounding rock, pre-existing fractures approximately propagate straightforward along their initial directions and finally form planar fracture surfaces. Regarding in-situ stresses, with acute intersection angle between fracture and wellbore, fractures propagate toward the direction of the minimum principal stress. Besides, two parallel and opposite fractures individually arising from two parallel and non-coincidence wellbores always propagate towards each other after passing by each other. Moreover, the interactions between them become strengthened as the distance between them decreases. Finally, the propagating sequences of hydraulic fractures arising from a group of parallel wellbores are discussed. It is found that the sequence can influence the fracture geometry and previously propagated fractures can restrain the nearest fractures embedded in other wellbores propagating away from each other in subsequent stages. Highlights • 3D fractures arising from the sidewall of wellbore are studied via High-order GFEM. • Effect of intersect angle between fracture and wellbore on fracture path is studied. • Fractures with acute angles always propagate normal to the minimum in-situ stress. • Fractures are verified to propagate normal to each other after passing each other. • Fractures in previous stage restrain the deviation of fractures in subsequent stage. [ABSTRACT FROM AUTHOR]