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Targeting the balance between high strength and toughness of engineered cementitious composite (ECC), polyvinyl alcohol (PVA)-steel hybrid-fibre-reinforced engineered cementitious composites were developed in this study. Cylindrical specimens were tested under uniaxial compression to investigate the stress–strain behaviour of hybrid-fibre composites with particular focus on the impact of matrix strength and steel fibre content. The experimental results indicated that the mechanical properties of hybrid-fibre systems were improved with increasing content of steel fibre, and this enhancement became more and more pronounced with increasing matrix strength. The impact of additional steel fibre on compressive parameters, such as compressive strength, strain corresponding to peak stress, elastic modulus and toughness index, were also strongly influenced by the matrix strength. Positive responses due to steel fibre were reduced with decreasing matrix strength, and even transformed into a negative effect in a low-strength matrix. When considering both high strength and toughness, a moderate amount of steel fibres was favourable. Furthermore, a simple analytical model especially for hybrid-fibre-reinforced ECC was proposed to give satisfactory predictions of the complete stress–strain behaviour. It is expected that this model can be used as a first approximation for non-linear analysis of ECC structures.

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Understanding the change of permeability of rocks before and after heating is of great significance for exploitation of hydrocarbon resources and disposal of nuclear waste. The rock permeability under high temperature cannot be measured with most of the existing methods. In this paper, quality, wave velocity, and permeability of granite specimen from Maluanshan tunnel are measured after high temperature processing. Quality and wave velocity of granite decrease and permeability of granite increases with increasing temperature. Using porosity as the medium, a new wave velocity-permeability model is established with modified wave velocityporosity formula and Kozeny-Carman formula. Under some given wave velocities and corresponding permeabilities through experiment, the permeabilities at different temperatures and wave velocities can be obtained. By comparing the experimental and the theoretical results, the proposed formulas are verified. In addition, a sensitivity analysis is performed to examine the effect of particle size, wave velocities in rock matrix, and pore fluid on permeability: permeability increases with increasing particle size, wave velocities in rock matrix, and pore fluid; the higher the rock wave velocity, the lower the effect of wave velocities in rock matrix and pore fluid on permeability.

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When the upper parts of coal resources are exploited, the mining overburden separated strata may easily connect with the upper unconsolidated aquifers. This may cause the water-sand two-phase fluids in the aquifers to flow underground through the falling broken rock mass. It has been found that it is difficult to eliminate sand after it has entered a mine, which tends to severely restrict the restorations of mines and causes significant economic losses. This paper studied a seepage system dynamic model of watersand two-phase fluids in broken rock mass based on related two-phase flow theories. In addition, using FORTRAN language, it established a numerical calculation program to study the migration law of water-sand two-phase fluids flowing into broken rock mass and determined the main influencing factors on the seepage characteristic parameters of water-sand two-phase fluids in broken rock mass and the amounts of sand losses.

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