Conducting research on the fatigue performance of concrete materials is of great significance for the anti fatigue design of concrete structures. Currently, indirect tensile or compressive strength tests are commonly used to study the fatigue performance of basalt fiber reinforced concrete, but there is little research on its fatigue performance under direct tensile conditions. Using a fatigue testing machine and a self-developed concrete axial tensile device, direct tensile fatigue tests of basalt fiber reinforced concrete were conducted under different fiber content and stress levels. Based on fatigue test data, the entire fatigue tensile process of basalt fiber reinforced concrete was analyzed, and the effects of fiber content and stress level on the fatigue life of concrete specimens were explored. Strain fatigue life curves of concrete with different fiber content were plotted. The experimental results indicate that the failure mode of basalt fiber reinforced concrete under cyclic loading is brittle failure; with the increase of basalt fiber content, the fatigue life of concrete first increases and then decreases. When the fiber content is 0.3%, the fatigue life of basalt fiber concrete is the highest compared to the benchmark concrete. When the fiber content is the same, the fatigue life of concrete decreases with the increase of stress level. The fatigue deformation process of basalt fiber reinforced concrete can be divided into three stages: the stage of fast strain growth, the stage of uniform strain growth, and the stage of rapid strain growth.

In order to study the axial tensile properties of polypropylene fiber reinforced concrete, an axial tensile test device for concrete is developed in this paper. The device is composed of three parts: rigid frame, spherical hinge and puller, and specimen fabrication part. The test device can accurately measure the tensile strength and peak tensile strain of concrete, and perfectly solves the eccentricity problem of concrete specimens under tension. It can measure the post peak segment tensile strain, such that the whole process tensile stress–strain curve can be obtained. The axial tensile test of polypropylene fiber concrete was carried out using the above test device, and the results show that the tensile strength of concrete can be clearly improved by adding polypropylene fiber, which makes the tensile failure of concrete show certain plastic characteristics. The test results show that with the increase in fiber content, the tensile strength of concrete increases first and then decreases. The effects of polypropylene fiber content and curing age on the tensile properties of concrete were studied and the optimum polypropylene fiber content was determined. When the fiber content is 0.9 kg/m³, the tensile strength of concrete reaches the maximum value. The splitting tensile test of concrete under the same condition was carried out simultaneously. The damage phenomenon and test results of the axial tensile test and splitting tensile test of concrete were compared and analyzed, and the applicability of the new developed device in the concrete axial tensile test was verified.

The low liquid limit silty soil in the North China plain area is generally unsuitable for direct use as roadbed and slope soil. In order to improve the performance of low liquid limit silty soil, xanthan gum was used as an improver. Through a series of tests, the improvement effect of xanthan gum on low liquid limit silty soil was studied. The test results showed that Xanthan gum as an improver could significantly improve the unconfined compressive strength of silty soil. With the increase in dosage and curing age, the unconfined compressive strength of improved silty soil continued to improve and eventually tended to stabilize. The optimal dosage and curing period were 2% and 7 days, respectively. In addition, Xanthan gum could greatly improve the permeability and disintegration of low liquid limit silty soil. The permeability coefficient of improved silty soil with a content of 0.75% Xanthan gum and a 7-day curing period was 4.73 × 10⁻⁴ m·s⁻¹, which was only 1.10% of that of plain silty soil at the same curing period. After immersion in water for 12 h, the soil only experienced slight disintegration. The scanning electron microscope image showed that the gel generated by the hydration reaction of Xanthan gum could improve the compactness and integrity of the soil by filling the voids, thus significantly improving the mechanical and hydraulic properties of the low liquid limit silty soil.

With the decreasing of shallow resources, underground roadways of resources exploitation have reached into deep rock mass with high geostress. A series of new failure phenomena such as zonal disintegration phenomenon were discovered in deep surrounding rock, which is completely different from shallow caverns. To reveal the formation mechanism of zonal disintegration, the geomechanical model test and energy mechanism analysis of zonal disintegration were carried out respectively. Taking the deep roadway of Dingji coal mine in China’s Huainan coal mine as engineering background, a 3D geomechanical model test was carried out relying on the high stress 3D loading test system. The zonal disintegration phenomenon was observed, and the oscillation law of displacement was measured. Based on the strain gradient theory and continuum damage mechanics, the elastoplastic damage model was established. An energy failure criterion was proposed by principle of energy dissipation and release. The ODE45 function in Matlab software was used to solve the displacements and stresses of excavated model roadway. The analytical solutions the and the geomechanical model test were basically consistent. The applicability of theoretical model and energy failure criterion were confirmed to explain the mechanism of zonal disintegration and it can be used to provide theoretical support for the failure and supporting design of surrounding rock in deep underground engineering.

To conduct a comparative analysis of the impacts of nanosilica (NS) and carbon nanotubes (CNTs) on the mechanical properties of polyethylene fiber-reinforced cementitious composites, seven groups of ECC specimens with different nanomaterial contents were prepared. The uniaxial compression and tensile tests were conducted, the mineral composition of the specimens was analyzed via X-ray diffraction, and the microstructure of the specimens was examined using a scanning electron microscope. The results show that both types of nanomaterials can effectively enhance the mechanical properties of ECC. Meanwhile, the mechanical characteristics of ECC exhibit a pattern of initial increase followed by a decrease as the nanomaterial content rises. NS exhibited superior performance in augmenting the compressive strength and early tensile crack strength of ECC; however, CNTs were more effective in enhancing the peak compressive strain and peak tensile strain of ECC. The difference between NS and CNTs in the enhancement of tensile strength was not significant. NS can consume more CH crystals to generate C-S-H gels to make the matrix material more dense, and can improve the properties of the transition zone at the fibre-gel interface to enhance the strength of ECC. While CNTs can bridge and inhibit crack extension on the micron scale, and can form a fibre mesh structure with PE fibres for more effective stress transfer, and can improve the deformation capacity of ECC on a macroscopic scale.