Swelling of soft rock, such as gypsum rock, is one of the major threats in tunnel engineering, causing structure damages such as floor heave and inward movement of sidewalls during construction and operation. It is of practical significance to study the swelling mechanical behavior of such rocks by tests. Swelling strain tests and swelling stress tests were performed by swelling test apparatus to study the variation of swelling strain with time and the swelling stress-strain relationship for gypsum rock samples, respectively. Three stages of the swelling strain on the time-strain curve of gypsum rock samples were noticed, which are defined as rapid swelling stage, slow swelling stage, and steady stage. And it was further found that the swelling strain caused in the slow swelling stage is of 76% of the total swelling strain. A constitutive model is proposed to describe the stress-strain relationship in swelling considering the swelling deformation and swelling pressure. The proposed model was verified using test data, which shows good agreements in describing the relationship between swelling strain and swelling stress, also in the conditions of maximum swelling strain and maximum swelling stress under lateral restraint situations.
The thaumasite sulfate attack (TSA) on tunnel concrete structure has been reported increasingly in the past decades. Previous investigations on the formation of thaumasite were focused on identifying the deterioration products and reaction mechanisms, while the occurrence time of TSA on tunnel concrete structures was not reported. A highway tunnel exposed to TSA was reported in the present study. The development of tunnel diseases and results of experimental tests conducted in the tunnel and in the laboratory were analyzed to investigate the occurrence time of TSA on concrete. Results revealed that the thaumasite was formed in a range of 18 to 36 months after the construction of Dugongling tunnel. The preconditions for the formation of thaumasite on tunnel concrete structures are available in Shanxi Province, China, due to the special conditions of stratum lithology and climate. The compositions of corrosion products of lining concrete under TSA varied for site studies and for laboratory tests. Site investigations on TSA on tunnel lining concrete should be paid more attention in further research.
For the purpose of exploring the influence of the location of the bionic micro grooves on the flow characteristics of the airfoil, three airfoil models with bionic grooves were established according to the different positions of the bionic grooves. Large eddy simulation is used to numerically simulate the flow of different airfoils. Compared with the smooth airfoil, the flow characteristics and aerodynamic performance parameters of the bionic micro-groove airfoil are analyzed at 6° angle of attack, 24 m/s and 30 m/s speed. The results show that the three types of bionic grooved airfoil suppress the thickness and flow length of the separation zone, making the reattachment position of the separation zone more forward than that of the smooth airfoil, thus having different degrees of separation of the airfoil surface boundary layer. Control effect. In addition, the existence of bionic micro-grooves reduces the vortex structure in the near-wall zone, reduces the center height of the separation zone, and reduces the normal velocity gradient, which weakens the energy dissipation in the flow. Airfoil-H1 airfoil has the best flow characteristics and aerodynamic performance at 24 m/s, the drag reduction rate is the largest, reaching 16.99%, and the lift-to-drag ratio increases by 16.34%. The Airfoil-H2 airfoil has the best effect at 30 m/s, the drag reduction rate is the largest, reaching 18.09%, and the lift-to-drag ratio increases by 18.86%. Airfoil-H3 airfoil has a lower effect, but the effect becomes more pronounced as the speed increases. As the mainstream speed increases from 24 m/s to 30 m/s, the optimal airfoil will gradually transition from Airfoil-H1 airfoil to Airfoil-H2 airfoil regardless of flow characteristics or aerodynamic performance parameters. It is found that there is the best matching value between the location of the bionic groove and the mainstream speed, so that the groove can play the best improvement effect.
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