楚雄市地表水中有毒微藻的分布及藻类多样性抽样调查

为研究楚雄市区内地表水中有毒微藻的分布及藻类多样性,本文从楚雄市区内的龙江公园、桃源湖、花鸟市场、青龙河、铜鼓寨等水体采集水样,利用光学显微镜进行直接观察和水样富集后的观察,对水体中的微藻种类及多样性进行分析。结果显示,观察到的有毒微藻包括鱼腥藻、微囊藻;除此以外,其他藻类包括小球藻、盘星藻、栅藻等21种微藻;各个水体藻类Simpeson指数在0.944~0.995之间,差异较小,但Shannon-Wiener指数存在较大差异。楚雄市区内地表水中的微藻大多为无毒藻类,有毒微藻的仅有鱼腥藻和微囊藻,这一发现有利于有效利用楚雄市区内的藻类资源以及针对性地预防藻类引发的水环境安全问题。

Mechanical response of a tunnel subjected to strike-slip faulting processes,based on a multi-scale modeling method

The stick-slip action of strike-slip faults poses a significant threat to the safety and stability of underground structures.In this study,the north-east area of the Longmenshan fault,Sichuan,provides the geological background;the rheological characteristics of the crustal lithosphere and the nonlinear interactions between plates are described by Burger’s viscoelastic constitutive model and the friction constitutive model,respectively.A large-scale global numerical model for plate squeezing analysis is established,and the seemingly periodic stick-slip action of faults at different crust depths is simulated.For a second model at a smaller scale,a local finite element model(sub-model),the time history of displacement at a ground level location on the Longmenshan fault plane in a stick-slip action is considered as the displacement loading.The integration of these models,creating a multi-scale modeling method,is used to evaluate the crack propagation and mechanical response of a tunnel subjected to strike-slip faulting.The determinations of the recurrence interval of stick-slip action and the cracking characteristics of the tunnel are in substantial agreement with the previous field investigation and experimental results,validating the multi-scale modeling method.It can be concluded that,regardless of stratum stiffness,initial cracks first occur at the inverted arch of the tunnel in the footwall,on the squeezed side under strike-slip faulting.The smaller the stratum stiffness is,the smaller the included angle between the crack expansion and longitudinal direction of the tunnel,and the more extensive the crack expansion range.For the tunnel in a high stiffness stratum,both shear and bending failures occur on the lining under strike-slip faulting,while for that in the low stiffness stratum,only bending failure occurs on the lining.

Performance-based three-level fortification goal and its application in anti-dislocation countermeasures:A case study of Shantou Submarine tunnel

The dislocation momentum is the design basis for anti-dislocation to tunnel when a tunnel crosses an active fault.The influence of different dislocation levels on tunnel performances is not clear.Thus,based on seismic activity parameters at the site of interest and probability of fault dislocation,probability fault displacement hazard analysis(PFDHA)methodology was introduced in this paper to ascertain the fault dislocation level under different exceeding probabilities(63%,10%,and 2%–3%).Then,based on the definition of different ground motion strength and fortification goals of the tunnel,a three-level fortification goal with different performance requirements of the tunnel was proposed.The first attempt to use the proposed indexes including the maximum dislocation of the tunnel and maximum relative deformation of the tunnel was tried to evaluate deformation and failure states with an experimental approach.Subsequently,the feasibility of the three-level fortification goal was further investigated according to the self-defined qualitative description and quantitative indexes in the segmental design and sectional expansion tunnels comprehensively.The results show that the fault dislocations relying on PFDHA at the site of the Shantou Submarine Tunnel are firstly ascertained as 0.04,1.8,and 2.4 m respectively.Taking the fault dislocation as model input values into account,the dislocation mechanism of the tunnel under the three levels was revealed.More importantly,judging from the dislocation performance requirements of the three-level fortification goal,the tunnel deformation and failure states are mitigated by adopting the countermeasures.The sectional expansion design can well meet the requirements without the restriction of a strong earthquake,while the effectiveness of the segmental tunnel can be proved under frequently occurred and fortification earthquake.The final research results are expected to provide a new fortification goal for anti-dislocation hazard evaluation on expansion design in high-intensity seismic regions and segmental design in slight and moderate-intensity seismic regions.