This paper investigates the stability of unlined rectangular tunnels in rock masses subjected to surcharge loading using adaptive finite element limit analysis based on the generalized Hoek-Brown failure criterion. Both upper and lower bound solutions are employed to calculate the stability number of the problem, and the relative errors are found to be within ±7%. A sensitivity study relevant to the Hoek-Brown parameters (σ_ci, GSI, and m_i), the normalized cover depth of the tunnel (C/H), and the width to height ratio of tunnels (W/H) are conducted. At a given value of C/H, the stability number is found to be increasing continuously with decreasing W/H and with increasing GSI and m_i. The computational results are summarized in the form of design tables and charts for practitioners to use, and potential collapse mechanisms are provided and discussed in detail.

Using Esso AH-70 asphalt as the base asphalt, the modification mechanism for Qingchuan rock asphalt–modified asphalt was studied using asphalt component tests, differential scanning calorimetry, infrared spectrometry, and fluorescence microscopy. The performance of the Qingchuan rock asphalt–modified asphalt was analyzed based on modified asphalt index tests, the dynamic shear rheometer test and the bending beam rheometer test. Performance verification of the Qingchuan rock asphalt–modified asphalt was conducted using the rutting, mechanical property, small-beam bending, freeze-thaw split, indirect tensile fatigue, and small-sized acceleration loading tests. The results indicate that rock asphalt asphaltene has a high content of heteroatom groups as well as strong aromaticity and polarity. After the base asphalt is modified with rock asphalt, its microstructure is changed. The temperature sensitivity of rock asphalt–modified asphalt is decreased, and the temperature stability and water stability are strengthened. The rock asphalt modifier can obviously improve the antifatigue performance and high-temperature stability of its asphalt mixture. The dynamic stability of AC-20 with an 8 % rock asphalt content is 4,769 times/mm, which is 3.05-fold higher than the dynamic stability of the base asphalt. Under the same experimental conditions, the fatigue life of AC-16 with an 8 % rock asphalt content is 18-fold higher than that of its base asphalt mixture. Small-sized acceleration loading tests confirm that the antifatigue performance and antirutting performance of a 10 % rock asphalt–modified asphalt mixture increase by 120 % and 233 %, respectively, over those of its base asphalt. Additionally, the antifatigue and antirutting performances exceed those of the styrene-butadiene-styrene–modified asphalt mixture. Qingchuan rock asphalt can improve the comprehensive performance of an asphalt mixture, and it can be used in nonextreme low- temperature environments.

Vacuum–surcharge preloading is widely used in soft soil foundation reinforcement projects. To study the characteristics of the changes in pore water pressure and settlement of the soft soil foundation as a result of the effect of vacuum–surcharge preloading, in this paper, a consolidation model was established for large–sized sand–drain fluid–solid coupling along the depth direction while taking the sequence of the actual surcharge and vacuum into consideration by using FLAC^3D, and a soft foundation’s consolidation process was calculated and analyzed in detail. The results showed the following: (1) the sand drain could be used as a load boundary condition and a vacuum load could be realized by adjusting the pore pressure at the nodes. (2) For the effect of a single vacuum, the settlement and pore water pressure were evenly distributed on the horizontal plane, and the maximum calculated value of the surface settlement was 90.92 cm, but the phenomenon of a “pot–bottom shape” of the settlement and pore pressure gradually became obvious with the increase in the surcharge, and the maximum calculated value of the surface settlement was 153.01 cm. (3) In the numerical calculations, it was found that the pore pressure and settlement distinctly fluctuated once each level of surcharge was applied. The changes in the settlement were basically consistent with the measured values after the adjustment of positive and negative pressure, and the variation trend of the pore pressure was consistent with the measured value. (4) The depth affected by the vacuum could reach at least 16 m. All of these findings are expected to provide references for the calculation of consolidation in vacuum–surcharge preloading.