NUMERICAL SIMULATION AND ANALYSIS OF HORSESHOE-SHAPED VORTEX IN NEAR-WALL REGION OF TURBULENT BOUNDARY LAYER

The low-Reynolds-number full developed turbulent flow in channels is simulated using large eddy simulation（LES）method with the preconditioned algorithm and the dynamic subgrid-scale model,with a given disturbance in inlet boundary,after a short development section.The inlet Reynolds number based on momentum thickness is 670.The computed results show good agreement with direct numerical simulation（DNS）,which include root mean square fluctuated velocity distribution and average velocity distribution.It is also found that the staggered phenomenon of the coherent structures is caused by sub-harmonic.The results clearly show the formation and evolution of horseshoe vortex in the turbulent boundary layer,including horseshoe vortex structure with a pair of streamwise vortexes and one-side leg of horseshoe vortex.Based on the results,the development of the horseshoe-shaped coherent structures is analyzed in turbulent boundary layer.

Effect of surcharge loading on horseshoe-shaped tunnels excavated in saturated soft rocks

Underground facilities are usually constructed under existing buildings,or buildings are constructed over existing underground structures.It is then imperative to account for the current overburden loads and future surface loadings in the design of tunnels.In addition,tunnels are often constructed beneath the groundwater level,such as cross-river tunnels.Therefore,it is also important to consider the water pressure impact on the tunnel lining behaviour.Tunnels excavated by a conventional tunnelling method are considered in this paper.The hyperstatic reaction method(HRM)is adopted in this study to investigate the effect of surcharge loading on a horseshoe-shaped tunnel behaviour excavated in saturated soft rocks.The results obtained from the HRM and numerical modelling are in good agreement.Parametric studies were then performed to show the effects of the water pressure,surcharge loading value and its width,and groundwater level on the behaviour of the horseshoe-shaped tunnel lining,in terms of internal forces and displacements.It displays that the bending moment,normal forces and radial displacements are more sensitive to the water pressure,surcharge loading and groundwater level.

Failure behavior of horseshoe-shaped tunnel in hard rock under high stress:Phenomenon and mechanisms

A particle flow code(PFC) was first applied to examining the mechanical response of a horseshoe-shaped opening in prismatic rock models under biaxial compression. Next, an improved complex variable method was proposed to derive the stress distribution around the opening. Lastly, a case study of tunnel failure caused by rock burst in Jinping Ⅱ Hydropower Station was further analyzed and discussed. The results manifest that a total of four types of cracks occur around the opening under low lateral confining stress, namely, the primary-tensile cracks on the roof-floor, sidewall cracks on the sidewalls, secondary-tensile cracks on the corners and shear cracks along the diagonals. As the confining stress increases, the tensile cracks gradually disappear whilst the spalling failure becomes severe. Overall, the failure phenomenon of the modelled tunnel agrees well with that of the practical headrace tunnel, and the crack initiation mechanisms can be clearly clarified by the analytical stress distribution.

Key Technologies and Applications of the Design and Manufacturing of Non-Circular TBMs

With the rapid development of the exploitation of underground space, more and more large- or super- large-diameter tunnel-boring machines （TBMs） are being employed to construct underground space projects. At present, because conventional circular TBMs cannot completely meet the requirements of underground space exploitation regarding the cross-section and space-utilization ratio, non-circular TBMs. which are the tunneling equipment for an ideal cross-section, have become the new market growth point. This paper first presents the technical features and development status of non-circular TBMs. Next, in reference to typical projects and technological innovation, this paper investigates key techniques including shield design optimization, multi-cutterhead excavation, special-shaped segment erection, and soil conditioning in loess strata for a rectangular pipe-jacking machine and a horseshoe-shaped TBM, in order to provide a set of feasible solutions for the design, manufacture, and construction of non-circular TBMs. Relevant engineering practice shows that non-circular TBMs with customized design and manufacture have great advantages in terms of construction schedule, settlement control, and space utilization.

A Mixed Metal Phosphate Containing Two Types of Phosphoric Anionic Groups: Cs2Ga4(P2O7)2(P4O(13))

A new mixed metal phosphate of Cs2Ga4P8O(27), which also can be written as Cs2Ga4(P2O7)2(P4O(13)), was synthesized by high temperature solid state syntheses and structurally characterized by X-ray single-crystal diffraction for the first time. The title compound crystallizes in monoclinic system with space group P21/c(No.14), and features a 3D framework which can be considered as alternating layers of {Ga2(P4O(13))}n and {Ga2(P2O7)2}n^(2n-) parallel to the bc plane further connected by Ga-O-P linkages, where Cs^+ cations are located in the free space between two adjacent layers to charge the valence. The Ga^(3+) cations in the compound contain two kinds of coordination models(4 and 6). Furthermore, the title compound coexists of two phospho-ric anionic groups which are non-condensed horseshoe-shaped(P4O(13)) and two(P2O7) with different symmetries. The density functional theory calculations indicate that Cs2Ga4P8O(27) is a direct band gap insulator with flat valence and dispersive conduction bands and a band gap of 4.13 eV.