To analyse the different mechanism of polycarboxylate superplasticizer and polyester fibre and its effect on cement mortar during freeze-thaw cycles, by taking cement mortar as main research object and the proportion of additive as variables, the varying pattern of the mechanical properties, size and distribution of the pores of the cement mortar during freeze-thaw cycles were studied by the NMR technology for the first time. The influence of different proportion of additive on the changes of the surface scaling, mass, compressive strength, splitting tensile strength and elastic modulus of cement mortar after 0, 25, 50, 75 and 100 times freeze-thaw cycles was studied. Meanwhile, the T₂ spectra change law of the cement mortar under different freeze-thaw environment was analysed and the change rule between freeze-thaw cycle, additive proportion and the pore size within the cement mortar was obtained. Also, the relationship between the mechanical parameters and pore properties was studied. This study on the damage evolution mechanism of additive cement mortar during freeze-thaw process is of great theoretical and practical significance to the analysis and prevention of freeze-thaw disasters in cold area.

Predicting the strength evolution of fiber-reinforced cement mortar under freeze-thaw cycles plays an important role in engineering stability evaluation. In this study, the microscopic pore distribution characteristics of fiber-reinforced cement mortar were obtained by using nuclear magnetic resonance (NMR) technology. The change trend of T₂ spectrum curve and porosity cumulative distribution curve showed that the freeze-thaw resistance of cement mortar increased first and then decreased with the fiber content. The optimal fiber content was approximately 0.5%. By conducting mechanical experiments, it is found that the uniaxial compressive strength (UCS) of the samples exhibited the ‘upward convex’ evolution trends with freeze-thaw cycles due to cement hydration, and based on fractal theory, the negative correlation between UCS and D_min was established. Eventually, a freeze-thaw strength prediction model considering both porosity and pore distribution was proposed, which could accurately predict the strength deterioration law of cement-based materials under freeze-thaw conditions.

The reason for instability in a rock mass with a weak interlayer is not only the sliding failure of the rock interlayer structural plane but also the tip crack propagation caused by the stress concentration at the tip of the interlayer. In this study, a uniaxial compression test of an anchored rock mass with a weak interlayer was carried out to determine the influence of the anchorage on the failure pattern and the strength of samples with different interlayer dip angles. In addition, the coupled DEM–FEM numerical simulation method was used to study the internal stress evolution of the sample and the stress distribution of the anchor under the anchorage effect. The results showed that the anchorage effect on reinforcement and strength enhancement was greatest for the sample with an interlayer dip angle of 30°. Under the anchorage effect, crack initiation was limited and there was more shear failure in the samples. The reinforcement range of the anchorage effect for anchors with restrained ends was larger than for anchors with free ends. When the rock–anchor interface was unbonded, the effect of the free-ends anchor reflected the residual friction, but the restrained-ends anchor still worked by limiting the lateral expansion of the rocks. The stress values and deformation of the anchors decreased gradually with an increase in dip angle.

As a new type of retaining structure, lattice beams with tie-back anchor cables have been increasingly used in slope reinforcement and have achieved improved prevention effects. However, the simplified load distribution method (SLDM) at the node, which is the theoretical basis of internal force analysis for lattice beams, is not perfect at present. An alternative new load distribution method (NLDM) at the node based on the force method for the lattice beam was therefore introduced in this paper. Taking into account the loads acting on other nodes of the beams in both directions and according to the static equilibrium condition and deformation compatibility condition at the nodes, NLDM assigns the loads acting on the nodes to the cross beams and vertical beams, respectively, by constructing and solving a system of linear equations. In order to verify the superiority of NLDM, a case of slope reinforced by a lattice beam was introduced in this paper, and the load distribution of the nodes under the design condition was carried out based on both methods. Then, the deflections at the nodes of the lattice beam resting on the Winkler foundation, loaded with the known loads, were analyzed by the superposition method. The results of the deformation analysis showed that the deflections at the same nodes of the beams in both directions based on NLDM were almost equal, thus demonstrating the superiority of NLDM in terms of deformation compatibility. In addition, a comparative analysis of the theoretical bending moments of the lattice beam under the design and the actual working conditions based on both methods was also carried out. The results of the bending moment analysis showed that the bending moments of the cross beam differed significantly in the middle third of the beam length, while the bending moments of the vertical beams differed significantly at the beam sections where the maximum bending moments are located, and the theoretical bending moments under the actual working condition were in relatively good agreement with the measured values. Consequently, NLDM for the lattice beam was self-consistent in terms of the deformation compatibility at the node, and therefore the introduction of this new method provides an important theoretical basis for the accurate internal force analysis of lattice beams.