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Abstract To study the enhancement effect of carbon nanotubes (CNTs) on the splitting tensile properties of foamed concrete backfill in which cement and fly ash were used as the cementitious materials and natural sand was used as the aggregate, specimens of CNT-modified foamed concrete backfill were prepared. Brazilian splitting tests were used to investigate the splitting tensile strength of the CNT-modified foamed concrete backfill, and the digital speckle correlation method was used to analyze the stress field characteristics and crack expansion law of the specimens during splitting tensile testing. The stress–strain characteristics and energy dissipation laws of the backfill were studied at various static loading rates, and a relationship between the splitting tensile strength, ultimate strain, and loading rate was established. The results showed that at the optimum CNT content of 0.05%, the peak strength and ultimate strain of the modified foamed concrete backfill increased by an average of 67.2% and 21.7%, respectively. Moreover, after modification with CNTs, the foamed concrete backfill was less likely to develop strain concentration areas before reaching peak strength. The triangular stable loadbearing structure formed by the modified foamed concrete backfill after splitting caused the end of the stress–strain curve to exhibit varying degrees of “backlash”. For the CNT-modified foamed concrete backfill, the peak strength correlated logarithmically with the loading rate, while the ultimate strain correlated as a power function of the loading rate. At a low loading rate, the CNT-modified foamed concrete backfill dissipated less energy, and the reverse was true for higher rates.

Abstract During gas injection in gas storage, the inner pressure increase, potentially leading to tensile failure of the cement sheath. At present, the fracture strength of cement stone is measured using the Brazilian splitting method (BSM), which is prone to errors due to stress concentration at the loading point. To overcome this drawback, a novel test device and measurement method were developed to assess the tensile. This device utilizes the tensile failure method (TFM) to evaluate the sealing integrity of the cement sheath. The tensile strength tested by the BSM was found to be 40% higher than that tested by the TFM. Furthermore, based on the optimization of the cement slurry for underground gas storage (UGS) in the Jidong oilfield using both the TFM and the BSM. We found that using the BSM cannot optimize the cement slurry that meets the requirements for gas storage well cementing. The latex cement slurry was selected by the TMF for UGS well.

The Q345qD bridge steels exposed to severe corrosion environments undergo mechanical property degradation, posing significant safety risks for sea-crossing bridges. Assessing the health of corroded bridge steel structures under load conditions in a manner that avoids causing damage can effectively prevent these intensifying safety hazards. To investigate the impact of corrosion on the mechanical performance of these steels, six sets of standard specimens underwent corrosion ranging from 0 to 896 h. Subsequently, during tensile testing, an image acquisition platform was established to utilize Digital Image Correlation (DIC) techniques for capturing and observing the tensile loading processes of various corroded specimens. Analysis of stress–strain curves and strain field evolution patterns provided insights into the deterioration of mechanical properties of Q345qD bridge steels after corrosion. For corroded bridge steel structures, defects caused by the corrosion pits can still result in localized strain concentration under low load levels. At higher load levels, mass loss due to corrosion or reduced cross-sectional dimensions of load-bearing elements are the primary causes of mechanical performance decline, precipitating overall structural failure. These findings provide some references for routine maintenance of steel structures of cross-sea bridges.

Splitting tensile failure is one of the main forms of instability failure of tunnel surrounding rock. At present, the mechanisms of rock crack propagation and energy evolution at the corresponding stages under dynamic splitting conditions have been rarely addressed. In this study, the splitting tests were carried out on Jinping marble samples using a split-Hopkinson pressure bar under different striking velocities. The dynamic damage processes of the samples were simulated with the ANSYS/LS-DYNA finite element software. From the perspectives of loboratory tests and numerical calculations, the mechanism of crack propagation and the characteristics of energy evolution during the splitting process of marble were comprehensively analyzed. The results show that the dynamic tensile strength of marble is linearly and positively related to the strain rate in the range of 5 s−1 to 35 s−1. The strain rate sensitivity of the Jinping marble is relatively low compared with the marbles of other regions. With the increase of the striking velocity, both the internal energy and kinetic energy of the system increase. At the moment of sample failure, the internal energy of the system drops to a minimum. Based on the calibrated parameters of Cowper-Symonds constitutive model, the final failure modes of the numerically simulated samples are basically consistent with the observed ones in the experiments. The research results of this study can provide guidance and reference for specific engineering applications.