Study of frozen rock mechanical properties is necessary for safe application of the artificial ground freezing method in excavation of Chinese western water-rich soft rock layers. Triaxial compression tests and NMR test for samples from the western Jurassic sandstone were performed to investigate rock mechanical properties affected by low temperature and confining pressure. The results show mechanical parameters such as peak strength, cohesion, internal friction angle, residual strength, and elasticity modulus increased with the decreasing temperature under stable pressure, and the above parameters increased with the increasing confining pressure at a certain temperature. In particular, the growth rate of the rock strength would decline when the temperature was below −10°C in this study. Strength attenuation coefficients increased with the decreasing temperature, which indicated higher brittleness, whereas plastic characters got more obvious with the increasing confining pressure at a stable temperature. Furthermore, during the first two freezing stages, porosity decreased sharply with obvious increase of pore (crack) ice content, while porosity varied little at the third stage, which was the reason for the growth rate of rock strength declining with continuous low temperature from microcosmic point of view.

Mudcake is an important factor affecting the bearing capacity of vertically loaded single piles. The model test and numerical calculation were used to analyse the stress and displacement characteristics of vertically loaded single piles under the conditions of different mudcake thickness and loading capacity. The effect of mudcake thickness on bearing capacity has been analyzed systematically, and its mechanism and changing laws were revealed. Eventually, the concept of the mudcake thickness effect was proposed, which must be considered fully during the construction of mud protection bored piles. The research results have important scientific value and guiding significance for understanding of the influence of pile side mudcake on the bearing capacity of vertically loaded single piles.

The study of freezing rock mechanical properties is getting more and more urgent because of coal mine construction in western China. Particle discrete element method (DEM) can describe discontinuous medium problem mathematically. In order to reveal the mechanical failure mechanism of frozen fine sandstone, the uniaxial compressive strength test of frozen fine sandstone was carried out, and then, DEM was used to simulate the uniaxial test of frozen fine sandstone. Furthermore, the nuclear magnetic resonance (NMR) technology was used to obtain pore distribution of the freezing sandstone. Finally, the results of NMR test and discrete element simulation were combined to reveal the microscopic mechanism of mechanical change in freezing fine sandstone. The DEM results show that the strength of frozen fine sandstone increases with the decrease of temperature. With the decrease of temperatures, strain softening occurs in frozen sandstone, which indicates that the discrete element simulation results are in good agreement with the uniaxial test results. Therefore, DEM can be used to simulate the mechanical behavior of frozen fine sandstone. At the same time, the DEM results also indicate that the formation and development of the shear band are the precursor of the failure of the sample. Furthermore, the NMR test confirms that temperature has a great impact on the pore distribution of sandstone. With the decrease of temperature, the pore ice content increases greatly, which induces a great decrease in NMR porosity and a vast decrease in the proportion of large and medium pores in all pores. Meanwhile, with the growth of the cohesion induced by increasing ice content, the uniaxial compressive strength increases macroscopically.

The problem of “difficult” freezing of the calcareous clay layer fractures in freezing pipes has been investigated. Based on the engineering background of the deep calcareous clay in the Yangcun Mine, model tests were carried out in order to conduct in-depth research on the development law of the freezing temperature field of this clay layer. The test results have shown that the calcareous clay has a freezing point of −1.3°C under the action of both the water and the soil’s chemistry and the supercooling temperature can be as low as −3.8°C because of its complex mineral composition causing poor thermal conductivity. This means that the calcareous clay will freeze slowly than the other layers of the soil. The time taking for the temperature fields to intersect is 2.5 h, which is equivalent to 127.6 days in the actual engineering. In the three sections, each temperature measurement point in the temperature field had an irregular saddle shape in the temperature space at the same time, and the ratio of the time between the formation and total melting of the frozen wall was 1 : 1.91. The development speed of the thickness of the frozen wall from 5 h to 16 h was 17.9 mm/h, and the development speed from 16 h to 70 h was 1.96 mm/h; corresponding to the actual development speed of the thickness of the frozen wall which were 0.0123 m/d and 0.0014 m/d, respectively. These speeds were significantly slower than the development speed of the thickness of the freezing wall of the general sandy clay layer, which were 0.0515 m/d in the early stage and 0.02 m/d in the later stage. The thin thickness and low strength of the frozen wall of the calcareous clay layer cause the fracture of the frozen pipes, which should be paid attention to in actual engineering construction.

Computer-assisted pulse nuclear magnetic resonance (NMR) can be used to get important parameters for pore structure characteristics of porous materials. In order to fully understand the effect of frozen soil thaw settlement, the mechanism of artificially frozen soil thaw settlement was examined from a microscopic perspective in conjunction with the frozen soil thaw settlement test. Additionally, to have a better understanding of how pore features change during the thaw settling process, the evolution of the pore size distribution in silty sand was studied. The findings demonstrate the porosity is obviously larger than the initial porosity after freeze-thaw, and the evolution of thaw settlement displacement is related to the change in porosity as thawing progresses, which grows exponentially with porosity. The fraction of medium and large pores (>0.1 μm) in the soil increases significantly during the thawing process. Accordingly, there is a slight increase in the proportion of pores (<0.1 μm) during the thawing progress. The variation in the pore size distribution of silty sand is compatible with that in settlement displacement during the thawing process. Additionally, the thaw settling rate’s development law is consistent with that of the proportion of pores. The number of medium and large pores is critical in determining the rate of thaw settlement. In other words, the development law of thaw settlement rate is consistent with the development law of medium and large pore size distribution.