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The micro–composition of the soil is closely related to its engineering properties. In Northeast China, seasonal freezing and thawing can induce deterioration of the physicomechanical characteristics of saline soil, which can ultimately lead to engineering failures and geological disasters. To investigate the micro composition evolution including the microstructure and grain size distribution of saline soil under the influence of freeze–thaw cycles, mercury intrusion porosimetry (MIP) and laser particle size analysis (LPSA) were used to test undisturbed saline soil specimens undergoing different freeze–thaw cycles. The pore size distribution curves showed a double–peak shape and the grain size distribution curves showed a bidirectional change. Overall, the pores >0.4 μm increased while the pores smaller than 0.4 μm decreased with increasing freeze–thaw cycles. Moreover, the grain size distribution showed a different changing trend at a pore diameter of approximately 10 μm. During the whole freeze–thaw cycle process, the fragmentation of coarse particles (> 10 μm) and the aggregation of fine particles (< 10 μm) were evident, causing the transformation of different pore sizes, and the bidirectional change existed synchronously in the whole process. The freeze–thaw cycles for saline soil caused the lyotropic salt precipitation and dissolution and the ice volumetric expansion and ice segregation to change the grain size distribution leading to the evolution of pore distribution, ultimately changing the soil micro–composition and resulting in the change of macro engineering characteristics. The study is useful for understanding the change in the engineering properties of saline soil under freeze–thaw cycles from a microscale perspective. • The PSD evolution of undisturbed saline soil shows a bimodal trend. • The fragmentation and aggregation of particles occur synchronously. • FT cycles change the grain size distribution resulting in the PSD evolution. [ABSTRACT FROM AUTHOR]

A stepwise algorithm for determining the intersections between fractures is presented. The stepwise approach is based on the bounding volume technology and separating axis theorem. The length and orientation distribution of the fracture intersections can be obtained by the stepwise approach. The stepwise approach is used to study the connectivity of the rock mass at Songta hydropower station. According to the traces data acquired from a tunnel namely PD231, a DFN model was generated for intersection analysis and connectivity analysis. The results of intersection analysis show that the stepwise approach is effective. Connectivity parameters such as the average number of fracture intersections per fracture, and the length of intersection lines per unit volume, can be calculated. The mean length of intersections is 1.184 m and the variance is 0.622 m. The self-intersection behavior and direction vector of the intersections are studied. The simulations show that the sub-vertical joint set 3 and the shallow joint set 1 constitute the main flow pathways in the fractured rock at dam site. Besides, the results suggest that the sub-vertical joint sets (joint set 2 and 3) are more connected than the shallow joint set (joint set 1). [ABSTRACT FROM AUTHOR]