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The Songnen Plain in China has a typical type of soda saline-alkali soil that frequently shrinks and cracks under natural conditions, especially during water evaporation. This study aims to study the effects of salt contents on the cracking process of soda saline-alkali soils and to make a quantitative analysis between crack length and some primary salt parameters of soda saline-alkali soils. To achieve the objectives, 57 soil samples with different salinity levels were selected and a laboratory-controlled desiccation cracking test was then conducted. Next, correlation analysis was carried out between extracted crack lengths and salt parameters of all the specimens. The results showed that there are clear linear dependencies between crack length and salinity, Na⁺, Cl⁻, and electrical conductivity (EC), and that CO₃²⁻ is also quite linear with crack length. The fitting results conducted from the verification experiment showed that Na⁺ content, Cl⁻ content, EC, and total salinity showed high prediction performance (R²>0.91 and RPD>2.5); that the CO₃²⁻ content had quite reasonable accuracy (R²= 0.78 and RPD = 1.82) but with less stability and poor reliability; that the prediction accuracy for pH, however, was very poor, with R² and RPD only 0.42 and 1.06, respectively.
Water inrush during the excavation of mines or mining is one of the great challenges in underground engineering work in China. To prevent and/or mitigate water inrush, natural sedimentary rocks with low-permeability, which include the mudstone and sandstone found in underground excavations, are exceptional materials for geological barriers. The aim of this work is to therefore investigate the hydraulic properties of sedimentary rocks in a deep tunnel, with the application of high-pressure packer tests (HPPTs). The experimental results indicate that both the mudstone and sandstone are low permeability. The measured injection pressure-flow rate (P-Q) can be divided into two phases: Phase I – a flow that is Darcian with a linear relationship, and Phase II – changes in the flow pattern with an exponential relationship. Water injection primarily triggers fracture dilation, and then results in an evident increase in hydraulic conductivity. The hydraulic conductivity versus water pressure distribution phase can be considered as three flow phases: the initial flow phase, initiation of flow communication phase, and non-steady state flow phase. The calculated original fracture apertures in mudstone and sandstone are, respectively, 0.37 and 0.33 mm. Furthermore, a conceptual model with two phases of fracture aperture versus water pressure is proposed.
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