In order to provide a new method for inhibiting the rise of capillary water, the influence of hydrophobic materials on the water-repellent performance of roadbed soils was investigated and the influence of hydrophobic substance dosage per unit area and action time on soil impermeability was analyzed. The results demonstrate that the permeability coefficient of the soil reduces dramatically as the amount of hydrophobic material per unit soil area increases, and start with an increment but later turned into a decrement with the action time. The permeability coefficient of the soil was 0.7892×10⁻⁷ cm/s as the minimum as with a drop of 98.86 percent under conditions of 125 g per unit area and an action time of 24 h. Furthermore, the organic silicone hydrophobic material will eventually form a dense hydrophobic film to block the infiltration of external water, thereby enhancing the hydrophobicity of the soil.

Subgrade soil is sometimes modified with lime to improve strength. In this study, lime modified soil (LMS) specimens are subjected to freezing–thawing cycles, the mechanical properties and microstructure of the specimens are investigated by resilient modulus test and scanning electron microscope test. The variation in pore microstructure is investigated by image analysis. The results indicate that the number and area of micropores are reduced due to phase change and expansion of water in the soil under freezing–thawing cycles, and the micropores are subsequently coalesced into macropores. The variations in porosity and resilient modulus are correlated. The largest effect to the microstructure and resilient modulus of LMS is observed after the first freezing–thawing cycle. The main reason for the attenuation in resilient modulus of LMS is attributed to the increase in porosity, decrease in bond strength among soil particles and increase in the number of narrow and long cracks in soil.

Soil treated with silicone hydrophobic material for a long time can effectively improve the saturated permeability of the ground, which has been confirmed. However, the long time will increase the cost in engineering construction. Secondly, the mechanism of alteration of soil–water properties by silicone hydrophobic materials is not understood. This lack of understanding is not conducive to the engineering application of silicone hydrophobic materials. Therefore, variable-head permeability and matrix suction tests under 15 different test conditions were conducted with different hydrophobic material dosage and action time as variables in this paper. The soil–water characteristic curve (SWCC) was plotted according to the test results, the unsaturated permeability coefficient was calculated, and curve fitting was performed. It can be seen from the test data that, with the increase in the dosage of hydrophobic materials and the action time, the permeability coefficient and the air-entry value showed a downward trend. Nevertheless, as the reaction proceeded, a mutation occurred at 4 h. When the minimum dosage and action time were used, the soil’s permeability coefficient and air-entry value decreased by 80.65% and 71.09%. The test results show that, even when the action time was 2 h, the hydrophobic material could maintain the permeability of the soil and reduce its air-entry value; thus, the hydrophobic material could effectively reduce the rise of capillary water in the soil and protect the roadbed.

To analyze the excavation stability and reasonable reinforcement measures of cutting slope with a goaf collapsed roadway and collapsed mining face, the finite element software Midas GTS NX was used to model and analyze the change in the slope stability coefficient under different excavation slope ratios. Combined with the scope of the project land, it is proposed that the slope ratio of grades 1–3 (close to the top of the cut) is 1:1.5, while the slope ratio of grades 4–6 (close to the bottom of the cut) is 1:1, to excavate the slope. During the excavation process, the change in the plastic zone after each level of slope excavation was further analyzed, and the control variable method was used to analyze the influence of the collapsed roadway and the collapsed mining face on the slope stability. We found that the collapsed mining face was one of the main factors affecting the stability of the slope. During the reinforcement of the slope, the reinforcement effects of different schemes were analyzed, and we found that the slope can be stabilized by reinforcement of the third- and fourth-level slopes adjacent to the collapsed mining face. In this study, the old goaf and cutting slope excavation are combined, and the stability of slope excavation with a goaf collapsed roadway and collapsed mining face is analyzed by coupling. This research provides a scientific basis for the stability analysis of cutting slope excavation in old goafs in the future and has great practical engineering significance.