Analysis of the Stability and Mechanical Characteristics of the Jointed Surrounding Rock and Lining Structure of a Deeply Buried Hydraulic Tunnel

On-site monitoring and numerical simulation have been combined to analyze the stability of the jointed surrounding rock and the stress inside the lining structure of a sample deeply buried hydraulic tunnel.We show that the deformation around the tunnel was mainly concentrated in the range 51.37 mm∼66.73 mm,the tunnel circumference was dominated by shear failure,and the maximum plastic zone was about 3.90 m.When the shotcrete treatment was performed immediately after the excavation,the deformation of the surrounding rock was reduced by 58.94%∼76.31%,and the extension of the plastic zone was relatively limited,thereby leading to improvements in terms of the stability of surrounding rock.When the support was provided at different time points,the stress of the surrounding rock in the shallow part of the tunnel was improved everywhere.In the tunnel section with high ground stress and joint development,when 10 cm steel fiber concrete spray layer and 40 cm C25 concrete secondary lining were used,the maximum tensile stress on the lining structure was 0.89 MPa,i.e.,it was less than the tensile strength of concrete,which indicates that the internal force of the lining can meet the overall requirements.

Carboxylated carbon nanotubes with high electrocatalytic activity for oxygen evolution in acidic conditions

Since most electrocatalysts for oxygen evolution reaction(OER),except for precious metal oxides RuO_(2) and IrO_(2),are unstable in harsh acidic solutions,it is highly desirable to develop high-performance OER electrocatalysts for acidic media,though it is still a big challenge.Herein,we report a simple strategy to produce carboxyl-enriched multiwalled carbon nanotubes(COOH-MWNTs)that exhibit stable and high electrocatalytic activities for OER in acidic solutions,showing an overpotential at a current density of 10 mA cm^(–2) and a Tafel slope as low as of 265 mV and 82 mV dec^(–1),respectively.As far as we are aware,these results represent the best OER performance for metal-free electrocatalysts,even comparable to those of RuO_(2) and IrO_(2).We have further revealed the catalytic mechanism,which involves one electron lose from the COOH-MWNTs catalyst at the beginning of the OER process to trigger H_(2)O molecule oxidation by forming peralcohol,followed by the recapture of one electron from water molecule to oxidize water and to recover the initial state for the COOH-MWNTs catalyst.The unravel of this new OER mechanism is important as it provides new insights into the crucial role of organic functional groups in electrocatalytic processes.Also,the mechanistic understanding can be used to guide the design and development of novel metalfree catalysts for acidic OER electrocatalysis and beyond.