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As carbon emission continue to rise and climate issues grow increasingly severe, countries worldwide have taken measures to reduce carbon emission. However, carbon dioxide is continuously flowing in the atmosphere and is easily influenced by neighboring cities' policies. Therefore, how to solve the problem of carbon emission spillover effect has become the key to improve policy efficiency. Cross-regional carbon governance provides a perspective on solving the carbon emission problem by regulating and guiding the cooperative behavior of cross-regional governance actors. Taking Chengdu-Chongqing area as an example, this study used the SDM to analyze the influencing factors and spatial spillover effects of emission. Then we used the system dynamics method to construct a dual-core carbon emission system, and simulated the spillover effect and emission reduction potential of Chengdu and Chongqing emission reduction policies under different policy schemes. The results reveal that the mobility of population and enterprises have a significant impact on carbon emission prediction. Carbon reduction policies exhibit the phenomena of "carbon transfer" and "free-riding." When Chengdu lowers its economic growth rate, it leads to the transfer of high energy-consuming enterprises to Chongqing, increasing carbon emission in Chongqing. The implementation of comprehensive carbon reduction policies in Chongqing has a positive effect on Chengdu. Emission reduction policies exhibit issues related to their temporal efficacy, as the effects of industrial structural policies in Chengdu yield opposite outcomes in the short and long term. Each city's unique circumstances necessitate tailored carbon reduction policies. In order to reduce carbon emissions, Chengdu and Chongqing require opposite population policies. • The mobility of population and enterprises have a significant impact on carbon emission prediction. • Cross-regional governance can solve the spatial spillover problem of carbon emissions. • Carbon reduction policies exhibit the phenomena of "carbon transfer" and "free-riding.". • The short-term effect of some carbon emission reduction policies is opposite to the long-term effect. [ABSTRACT FROM AUTHOR]

Granular materials are typically used as fills in earth structures, including foundation, embankment, and slope. The majority of these granular materials are built and maintained in unsaturated conditions. It is still an open question to develop simple and suitable models to capture the behaviors of unsaturated granular materials. This study aimed to formulate a model for describing the behaviors of granular materials under unsaturated conditions. An exponential function based on a phenomenological model was used to reproduce the asymptotic relationship between stress ratio and deviatoric strain during shearing, and a quantitative relationship considering variable void ratios was adopted to describe the changes of degree of saturation during shearing. In this new nonlinear model, nonlinear stiffness, nonlinear stress dilatancy, and critical state were introduced to enhance the model. Compared with the model for saturated soils, the new model for unsaturated soils could capture the suction effect on the behavior of stiffness and critical state. Finally, the new nonlinear model was used to simulate the behavior of saturated and unsaturated Chongqing granular fill and Beijing sand under triaxial stress conditions. The comparisons of experimental and simulated results showed that this model can consider the suction effect in reproducing the stress–strain and volumetric behavior of unsaturated granular materials. [ABSTRACT FROM AUTHOR]

The site formation for the construction of a new airport in a mountainous region is typically performed by cutting and filling a hill section. The fill materials are subjected to seasonal changes and large variations in water content. The water content change renders the fill material to be characterized as unsaturated or saturated. This study aims to investigate the influence of matric suction on the time-dependent compression behavior of one local soil as a fill material for the construction of a new runway of an airport in Chongqing city, a mountainous region in China. A series of unsaturated drained triaxial tests were conducted on this coarse-grained soil to obtain the relationship between the effective stress parameter, χ, and the matric suction. Subsequently, multistaged compression tests were performed on this soil using a newly designed suction-controlled oedometer apparatus. The influence of suction on the time-dependent compression behavior of the fill material is emphasized. The results indicate that the matric suction can increase the compression stiffness, and that the unloading–reloading index varies nonlinearly with suction. A linear relationship between the time-dependent compression coefficient and normalized effective vertical loading is established. The linear relationship is subsequently used to predict the time-dependent compression coefficient to describe the time-dependent behavior of the fill under unsaturated conditions. Further, a nonlinear function based on the work of Yin (Géotechnique 49(5):699–707, 1999) is adopted to describe the development of time-dependent compression. The results indicate that the prediction obtained from the two newly proposed methods are promising, and can predict the nonlinear time-dependent compression behavior of this coarse-grained soil. [ABSTRACT FROM AUTHOR]