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Cover stress re-establishment has a significant influence on the deformation and development of permeability in the fractured rock mass, which control the surface subsidence and water inflow after longwall caving mining. This paper reviews previous studies on cover stress reestablishment in the goaf after coal mining, and proposes a new analytical model based on the stress-strain characteristics of the caved rock mass and the voussoir beam theory. A scale model test is also conducted to study the cover stress re-establishment based on a coal mining case. A function was derived for cover stress re-establishment in the goaf, which can be approximately described as a logarithmic function and which agreed well with two completely re-established monitoring sites from the scale model test. The scale model test also indicated that cover stress reestablishment presents a hysteresis phenomenon. A 'stress balance' model was built for calculating the distance of cover stress re-establishment in the goaf, and the result from the model was lower than the results from the previous two methods. The cover stress re-establishment function and the 'stress balance' model will be of great significance for better understanding the stress distribution in the goaf. longwall mining, goaf, caving, fracturing, cover stress re-establishment, calculation model.

There is a close relationship between tensile strength of soil and crack development, but the tensile stress-strain in full failure process is rarely studied because challenges exist in accurately measuring shear strain using traditional methods. In this paper, we employed a newly developed diametric splitting testing apparatus and particle image velocimetry (PIV) system to study the tensile strength of compacted unsaturated expansive soil with different water contents and initial dry densities. Soil water characteristic curves of compacted expansive soil with different initial dry densities were determined using the filter paper method. Test results show that the tensile strength increases first and then decreases with increasing water content, and there is a critical water content for the peak load vs. water content curve. The diametric splitting test process can be divided into four stages on the basis of the plotted load-displacement curves: a stress contact adjustment stage (I); stress approximately linear increasing stage (II); tensile failure stage (III); and residual stage (IV). Under the same water content, the angle between the major directions of the displacement vector and the major crack decreases with increasing the dry density, especially when the fissure appears. Using the particle image velocimetry technique, the displacement and strain during the test process recorded is helpful for better understanding the soil failure mechanism.

Globally 2 degree target by 2100 was confirmed in the international negotiation process in recent years. The remained question is whether this target is feasible or not by thinking slow progress in last decades even though Kyoto Protocol set up targets by 2010. The IPCC called research teams on modeling to analyze the possible pathway, policies options, and cost benefit analysis for GHG mitigation. China’s CO2emission from energy and cement process already accounts for nearly 24% of global emission, and the trend is expected to keep increasing. The role of China in the global GHG mitigation is crucial. This paper presents the scenario analysis for China’s Energy System in the background of global 2 degree target, and discussed the feasibility for the lower CO2emission scenario in China. The finding says it is possible for China to limit CO2emission, reach emission peak before 2025, which make the global 2 degree target feasible, in Which energy system development is a kry . And recent progress of key technologies, availability for further investment on low carbon, policy implementation make it much big possibility for China to go to low carbon emission development pathway.

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