Long-term mechanical analysis of tunnel structures in rheological rock considering the degradation of primary lining

Rock load on lining structures increases over time for tunnels buried in rheological rock,and in addition deterioration of primary lining is common due to its structural characteristics and service environment attack,where these delayed features affect the mechanical response of tunnels.However,accounting for these delayed features in long-term stability assessment of tunnel structures is complex and has not attracted enough attention.In this paper,an analytical approach is proposed for investigating long-term mechanical response of tunnel structures in rheological rock influenced by degradation of primary lining.For this purpose,degradation of primary lining,char-acterized by decreasing concrete stiffness over time,is quantitatively described by an exponential model.The rheological characteristic of surrounding rock is simulated by the Burgers model.The time-varying solutions for rock deformation and support pressure are obtained by considering the coordinated interaction between surrounding rock and linings,and their correctness is verified by comparing them with numerical results.The results revealed that the pressure imposed on linings due to the rheological behavior of surrounding rock increases over time.As the primary lining degrades,the rheological load is transferred from primary lining to secondary lining,leading to increasing pressure on secondary lining;and a faster degradation rate of primary lining leads to greater pressure on secondary lining.Therefore,the primary lining should not be overlooked in long-term safety assessment of operation tunnels because of its role in bearing and transmitting load.Finally,the tunnel’s design and operational maintenance strategy are discussed when the delay effects of surround-ing rock and lining are taken into account.

Biological characteristics of cell lines of human dental alveolus

Objective To investigate the biological characteristics of cell lines of healthy and diseased human dental alveoli. Methods Primary cell lines from either healthy or diseased human dental alveoli were obtained. Two cell lines, H-258 and H-171 derived from healthy and diseased human tissues respectively, were selected for morphological study and research on their growth and aging, using cell counting, and histochemical and immunohistochemical staining. Results Primary cell lines were successfully established from innormal dental alveoli. After freezing and thawing for three times, cell growth was continued and no morphological alterations were observed. The doubling time was 53.4 hours and mean division index (MDI) was 4‰. Cells were kept normal after twenty generations with no obvious reduction of doubling time and MDI. Of twenty-six primary cell lines derived from healthy human dental alveoli, only three cell lines achieved generation. After freezing and thawing for twice, cultured cells were still alive at a decreased growth speed, with doubling time of 85.9 hours and MDI of 3‰. Both cell lines, H-171 and H-258, shared the characteristics of osteoblast. Conclusions Primary cell lines of diseased human dental alveoli show greater growth potential. All cell lines of dental alveoli share characteristics of osteoblast. The technique we developed may be put into practice for the treatment of abnormal dental alveoli.