Evolution characteristics and policy implications of new urbanization in provincial capital cities in Western China

Ultra-thick hard sandstone roofs present high thickness, poor delamination, and wide caving range. The strata pressure of the working face during actual mining increases, having a significant influence on the safe mining of the working face. Especially, in the mining areas of western China, the fully mechanized mining faces with high mining height and high-strength mining are more prominent. Understanding the fractures and stress evolution characteristics of the ultra-thick hard sandstone roof during actual mining is of high significance to control the dynamic pressure on the working face. In this paper, the typical ultra-thick hard sandstone roof of the Xiaojihan coal mine was taken as an example. The structural and chemical composition characteristics were analyzed. Besides, the fracture characteristics of ultra-thick hard roof during the working face mining were analyzed. Moreover, the fracture structure consistency was verified through physical simulation and a field measurement method. Finally, the stress evolution laws in the ultra-thick hard sandstone roof fracture were studied through numerical simulation. The findings demonstrated that (1) the ultra-thick hard sandstone roof was composed of inlaid coarse minerals, which had compact structure, while the Protodyakonov hardness reached up to 3.07; (2) under the high-strength mining condition of fully mechanized mining face with large mining height, the ultra-thick hard sandstone roof had the characteristics of brittle fracture, with a caving span of 12 m; (3) under the high-strength mining condition of fully mechanized mining face with large mining height, the ultra-thick hard sandstone roof followed the stress evolution laws that were more sensitive to the neighboring goaf. Therefore, it was necessary to reduce the fracture span or layering of ultra-thick hard sandstone roof through the manual intervention method adoption or increase either the strength of coal pillar or supporting body, to resist the impact generated during ultra-thick hard sandstone roof fracture.

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Loading Capacity of Sewage Sludge for Forestry Application in Chinese Provincial Capital Cities

Sustainability ◽

10.3390/su12187551 ◽

2020 ◽

Vol 12 (18) ◽

pp. 7551

Author(s):

Xiaoxia Zhang ◽

Tonggang Zha ◽

Jiangang Zhu ◽

Xiaoping Guo ◽

Yi Liu

Keyword(s):

Sewage Sludge ◽

Scientific Basis ◽

Mean Value ◽

Practical Significance ◽

Loading Capacity ◽

Capital Cities ◽

Control Threshold ◽

Provincial Capital ◽

Forestry Policies

The application of sewage sludge (SS) in forestry is considered a viable option. However, the long-term application of SS potentially leads to metal accumulation, posing an environmental risk. Understanding the loading capacity of SS for forestry application is therefore of great significance. We used data from published studies and statistical bulletins across 31 provincial capital cities (PCCs) in China to calculate the loading capacity (LC) of SS for forestry application for each PCC. The results are as follows: (1) the mean value of the priority control threshold was 33 t·ha−1·y−1 in 31 PCCs, while the variations ranged from 7 to 91 t·ha−1·y−1 among different PCCs. The priority control thresholds (Smins) of 1/2 PCCs were higher than 30 t·ha−1·y−1 (CJ-T 362-2011). The Smin values of Lanzhou, Tianjin, Hohhot, Shanghai, and Yinchuan were above 55 t·ha−1·y−1, but Smin values of Kunming and Changsha were below 10 t·ha−1·y−1. (2) Cd was the priority control metal in most of the PCCs (27/31), with the exception of Shanghai and Guangzhou (Cu), Beijing (Hg), and Tianjin (Zn). (3) The total loading capacity was 507 million t·y−1, which was 125 times higher than the total quantity of the dry SS (404 × 104 t) for the 31 PCCs. Our results have important practical significance for the use of urban sludge forest land in China and suggest that SS disposal policies need to be tailored to specific regions. We provide a scientific basis to guide the development of national and provincial forestry policies.

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Assessment of Potential Heavy Metal Contamination in the Peri-urban Agricultural Soils of 31 Provincial Capital Cities in China

Environmental Management ◽

10.1007/s00267-019-01196-1 ◽

2019 ◽

Vol 64 (3) ◽

pp. 366-380 ◽

Cited By ~ 8

Author(s):

Shaowen Xie ◽

Fen Yang ◽

Hanxiao Feng ◽

Chaoyang Wei ◽

Fengchang Wu

Keyword(s):

Heavy Metal ◽

Metal Contamination ◽

Heavy Metal Contamination ◽

Agricultural Soils ◽

Capital Cities ◽

Provincial Capital

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Research on the Pore Evolution of Sandstone in Cold Regions under Freeze-Thaw Weathering Cycles Based on NMR

Geofluids ◽

10.1155/2020/8849444 ◽

2020 ◽

Vol 2020 ◽

pp. 1-12

Author(s):

Zheng Pan ◽

Keping Zhou ◽

Rugao Gao ◽

Zhen Jiang ◽

Chun Yang ◽

...

Keyword(s):

Magnetic Resonance ◽

Pore Structure ◽

Western China ◽

Cold Regions ◽

Abrupt Decrease ◽

Evolution Law ◽

Red Sandstone ◽

Freeze Thaw ◽

Evolution Characteristics ◽

Pore Evolution

The evolution of the rock pore structure is an important factor influencing rock mechanical properties in cold regions. To study the mesoscopic evolution law of the rock pore structure under freeze-thaw weathering cycles, a freeze-thaw weathering cycle experiment was performed on red sandstone from the cold region of western China with temperatures ranging from -20°C to +20°C. The porosity, T2 spectral distribution, and magnetic resonance imaging (MRI) characteristics of the red sandstone after 0, 20, 40, 60, 80, 100, and 120 freeze-thaw weathering cycles were measured by the nondestructive detection technique nuclear magnetic resonance (NMR). The results show that the porosity of sandstone decreases first and then increases with the increase of the freeze-thaw weathering cycles and reaches the minimum at 60 of freeze-thaw weathering cycles. The evolution characteristics of porosity can be divided into three stages, namely, the abrupt decrease in porosity, the slow decrease in porosity, and the steady increase in porosity. The evolution characteristics of the T2 spectrum distribution, movable fluid porosity (MFP), and MRI images in response to the freeze-thaw weathering process are positively correlated with the porosity. Analysis of the experimental data reveals that the decrease in the porosity of the red sandstone is mainly governed by mesopores, which is related to the water swelling phenomenon of montmorillonite. Hence, the pore connectivity decreases. As the number of freeze-thaw cycles increases, the effect of the hydrophysical reaction on the porosity gradually disappears, and the frost heaving effect caused by the water-ice phase transition gradually dominates the pore evolution law of red sandstone.

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