The migration of groundwater often results in subgrade damage such as fracturing, pavement pumping, and cracking in seasonally frozen soil areas. Indoor tests were performed to simulate moisture migration in different soil types usually found in seasonally frozen soil areas. The results indicate that the moisture migration rate of the wetting front in clay is the fastest, followed by that in fine sand and silt. In addition, the migration height of fine sand is much lower than that of both clay and silt, whereas the water flux is larger than that of clay and silt. Moreover, under a freeze-thaw cycle, the trends of water content change and temperature distribution of the three samples at the initial state and final state were similar. Based on the gravity, matric, and temperature potentials, the moisture migrated continuously throughout the freezing process, and the temperature gradient could cause moisture to migrate faster than usual. According to the mechanism of moisture migration in the indoor tests, a case study and field test of the Jixi–Nehe Highway were undertaken in Heilongjiang Province, China. The field test results show that the moisture migration in the seasonally frozen region is consistent with the results of the indoor tests. Highway construction could significantly increase the water content of soil at the original position in the subgrade. Some measures were put forward to protect the subgrade from damage caused by moisture migration.

The mechanical strength of the landslide deposits directly affects the safety and operation of the roads in the western mountainous area of China. Therefore, the research is aimed at studying the mechanisms of a landslide deposit sample with different rock particle contents by analyzing its characteristics of the stress‐strain behavior, the “jumping” phenomenon, the volumetric strain, and the shear strength parameters via a large‐scale direct shear test. Stress‐strain results show that stress‐strain curves can be divided into 3 different stages: liner elastic stage, yielding stage, and strain‐hardening stage. The shear strength of SRM behaves more like “soil” at a lower rock particle content and behaves more like “rock joints” at a higher rock particle content. Characteristics of the “jumping” phenomenon results show that the “intense jumping” stage becomes obvious with the increasing rock particle content and the normal stress. However, the lower the rock particle content is, the more obvious the “jumping” phenomenon under the same normal stress is. Volumetric strain results show that the sample with a lower rock particle content showed a dilatancy behavior under the low normal stress and shrinkage behavior under the high normal stress. The dilatancy value becomes smaller with the increasing normal stress. The maximum shear stress value of the rock particle content corresponds to the maximum value of dilatancy or shrinkage. We also conclude that the intercept of the Mohr failure envelope of the soil‐rock mixture should be called the “equivalent cohesion,” not simply called the “cohesion.” The higher the normal stress and rock particle content are, the bigger the equivalent cohesion and the internal friction angle is.

The contents of both water and rock particles are important factors affecting the mechanical strength of a soil–rock mixture (SRM) filled subgrade in the western mountainous area of China. Therefore, the purpose of this paper is to study the mechanisms of reconstituted landslide deposit samples with different water and rock particle contents by analysing the characteristics of shear strength, volumetric strain and ‘jumping’ phenomenon via large-scale direct shear tests. The results show that the influence of water content on shear strength is greater than the influence of rock particle content under a lower normal stress, and the results are reversed in the case of a higher normal stress. The effect of water content on the equivalent cohesion is bigger, especially for the sample with a high rock particle content. The friction angle of the specimen with same water content increases with the increasing rock particle content, but when the number of rock particles increases to a certain extent, there is a little effect on the friction angle. However, the friction angle decreases with increasing water content at the same rock particle content. Specimens with the same rock particle content change from dilation to compression with increasing water content. Finally, the continuous stage of the ‘intense jumping’ at different water content has been analysed. The ‘jumping’ phenomenon of samples with low water and rock particle content will first strengthen and then weaken the samples with increasing normal stress.

In a cost-saving move, the soft rocks composed of highly-weathered phyllites available on-site were used to fill the subgrade in the eastern Ankang section of the expressway of Shiyan to Tianshui, China. Cement admixture was used to improve the performance of the weathered phyllites. In order to determine the best mix ratio, values corresponding to compaction performance, unconfined compressive strength, and the California bearing ratio (CBR) were analyzed for variable cement content weight percentages (3%, 4%, 5%, and 6%) using test subgrade plots in the field. Field measurements of resilience modulus and deflection confirmed that the strength of the subgrade increased as the cement ratio increased. In order to further evaluate the cement/phyllite mixture, the performance of the 3% cement ratio sample was evaluated under saturated conditions (with various levels of moisture addition and soaking time) using both the wetting deformation and resilient modulus values. Results suggest that moisture added and soaking time are key factors that affect the seepage depth, water content, and resilient modulus. The recommend values for the cement addition and for the water content are given out. This study can aid in prevention of highway damage by improving the foundation capacity and lengthening the lifecycle of the highway in phyllite distributed region at home and abroad

To investigate the deformation property of weathered phyllite filling subgrade under the comprehensive effect of water and load, three weathered phyllite soil column models were filled and their deformations were tested through a laboratory test and numerical simulation in this article. The results show that the deformation of the weathered phyllite soil column models were greatly influenced by the water replenishment conditions and load conditions, and the deformation of models increased with the increase of the moisture content and load. Moreover, the larger the load, the longer the time required for the weathered phyllite soil column model to reach stability. In addition, the numerical simulation results were compared with the test results, and it was found that they were similar. Consequently, the numerical simulation can be used to reflect the deformation of weathered phyllite filling subgrade under the effect of water and load and provide some guidance for the design of the weathered phyllite filling subgrade.