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Adsorbed gas, the presence of which is a significant difference between the shale gas and conventional gases, has attracted considerable attention, particularly in China. A series of shale gas adsorption isotherms were measured at 30 °C and at pressures up to 10.94 MPa for the lower Silurian marine shale of the Longmaxi Formation collected in southeastern Chongqing, China. The maximum adsorbed gas content was 0.72–3.89 m 3 /t. Using measurements of the total organic carbon (TOC), thermal maturity, X-ray diffraction and low-pressure nitrogen adsorption, the basic characteristics of the shale reservoir were analyzed. The Ono–Kondo model was used to fit the measured methane adsorption isotherms with correlation coefficients as high as 0.9896–0.9976. The model characterized the filling adsorption features of nanopores under supercritical conditions. Monolayer saturated adsorption is generally less than the maximum adsorption, suggesting that as pressure increases, methane adsorption tends to become a multilayer adsorption. Among the geological parameters, TOC displayed a strong positive correlation with shale gas adsorption capacity. No obvious relation between the shale gas adsorption capacity and the clay was observed, indicating that organic matter has more significant contribution to shale gas adsorption than clay. The adsorption capacity significantly increased linearly with increasing total surface area, suggesting significant effects of pore structure on the shale gas storage. On the basis of the pressure sensitivity of adsorption rate, the adsorption process was divided into three stages: (1) an initial low-pressure stage, (2) an intermediate-pressure stage, and (3) a high-pressure stage. The third stage displayed methane desorption at high pressure. The similarities and differences of the Langmuir model and the Ono–Kondo model were assessed. An evaluation of which model is more accurate is difficult because both models can show good fits to experimental data. However, considering the methane adsorption mechanism, the Ono–Kondo model appears to be more reliable in describing the process of methane adsorption in shale because it predicts a more reasonable supercritical adsorption and can reflect the adsorption transformation from monolayer to multiple layers. [ABSTRACT FROM AUTHOR]

• A new method of simulating soil spatial variability based on the UHPM is proposed. • Ignoring soil spatial variability leads to small monitoring result. • The influence of horizontal and vertical SOF on the crown settlement is studied. High-speed railways (HSRs) are extensively constructed in China, with the help of tunnels to cross through complex geological conditions. The sequential excavation method (SEM) is vastly adopted in the construction of loess tunnel. This study performs a probabilistic analysis of crown settlement, taking into account the spatial variability of the surrounding soil through Monte Carlo (MC) simulations. To illustrate the influence of horizontal and vertical scale fluctuations (SOFs) on crown settlement, an anisotropic random field of loess elastic modulus is simulated using the spectral representation method (SRM) and unified Hermite polynomial model (UHPM) for the random finite difference method (RFDM). The mean crown settlements obtained through stochastic analysis are consistently larger than the deterministic results in the 1st, 6th, and 9th construction steps. The maximum probabilities of stochastic crown settlement exceeding the deterministic results are 77.3% and 78.2% with varying horizontal and vertical SOFs, respectively. Amplification factors of 1.417 and 1.306 are necessary to ensure that the stochastic crown settlement of the HSR tunnel, constructed in spatially variable loess, satisfies a 5% and 10% exceeding probability. This study provides valuable guidance for the construction of HSR tunnels. [ABSTRACT FROM AUTHOR]