Directional rupture is one of the difficult problems in deep rock mechanics and engineering.A directional fracturing method with static expansive agent controlled by dense linear multi boreholes is proposed.A physical...Directional rupture is one of the difficult problems in deep rock mechanics and engineering.A directional fracturing method with static expansive agent controlled by dense linear multi boreholes is proposed.A physical experiment is designed and performed to investigate the basic laws of this method.The fracture initiation and propagation process,and the mechanism of directional fracturing are analyzed.The results indicate that a directional fracture is formed along the direction of boreholes layout through directionally fracturing with static expansive agents controlled by the dense linear multi boreholes.According to the variation of strain and the distribution of associated acoustic emission(AE)events and energy,the experiment can be divided into three stages.In the first stage,the static expansive agent expand slowly with no fracturing inside the rock.In the second stage,some initial micro-fracturing occurs inside the rock.In the third stage,a wide range of fracturing occurs inside the sample.The internal micro-fracturing planes are connected to form a macro-fracture.Finally,it propagates to the surface of the sample.The directional fracturing plane presents a relatively smooth plane with little bias but much local fluctuation.展开更多
In the face of the corona virus disease 2019(COVID-19)pandemic,it is essential to stabilize the security of urban“shopping baskets”.Through a survey and interviews with 46 agricultural cooperatives in Shanghai,this ...In the face of the corona virus disease 2019(COVID-19)pandemic,it is essential to stabilize the security of urban“shopping baskets”.Through a survey and interviews with 46 agricultural cooperatives in Shanghai,this paper analyzes the impact of the pandemic on vegetable production and offers suggestions on agricultural insurance.The research results show that:(1)the pandemic has impacted almost all stages of the vegetable supply chain but has had a greater impact on the sales stage;(2)the market risks of vegetable production have increased significantly,and the gap between the field price and the market price has widened.The sales price difference between traditional channels and e-commerce is notable;(3)farmers’incomes have generally declined due to the COVID-19 pandemic,and traditional small-scale farmers have suffered more losses;and(4)agricultural insurance plays an important role in stabilizing the supply of vegetables to the city.To minimize the impact of the pandemic on vegetable production and to stabilize both urban“shopping baskets”and farmers’incomes,it is necessary to further improve agricultural insurance,especially to provide insurance against market risks.展开更多
基金Project(2017YFC0603001)supported by the National Key Research and Development Program of ChinaProjects(51774272,52004269)supported by the National Natural Science Foundation of ChinaProject(2019M661995)supported by the China Postdoctoral Sciences Foundation。
文摘Directional rupture is one of the difficult problems in deep rock mechanics and engineering.A directional fracturing method with static expansive agent controlled by dense linear multi boreholes is proposed.A physical experiment is designed and performed to investigate the basic laws of this method.The fracture initiation and propagation process,and the mechanism of directional fracturing are analyzed.The results indicate that a directional fracture is formed along the direction of boreholes layout through directionally fracturing with static expansive agents controlled by the dense linear multi boreholes.According to the variation of strain and the distribution of associated acoustic emission(AE)events and energy,the experiment can be divided into three stages.In the first stage,the static expansive agent expand slowly with no fracturing inside the rock.In the second stage,some initial micro-fracturing occurs inside the rock.In the third stage,a wide range of fracturing occurs inside the sample.The internal micro-fracturing planes are connected to form a macro-fracture.Finally,it propagates to the surface of the sample.The directional fracturing plane presents a relatively smooth plane with little bias but much local fluctuation.
基金This study was supported by the Humanity and Social Science Youth Fund of the Ministry of Education of China(18YJC790157)the National Social Science Fund of China(16ZDA019).
文摘In the face of the corona virus disease 2019(COVID-19)pandemic,it is essential to stabilize the security of urban“shopping baskets”.Through a survey and interviews with 46 agricultural cooperatives in Shanghai,this paper analyzes the impact of the pandemic on vegetable production and offers suggestions on agricultural insurance.The research results show that:(1)the pandemic has impacted almost all stages of the vegetable supply chain but has had a greater impact on the sales stage;(2)the market risks of vegetable production have increased significantly,and the gap between the field price and the market price has widened.The sales price difference between traditional channels and e-commerce is notable;(3)farmers’incomes have generally declined due to the COVID-19 pandemic,and traditional small-scale farmers have suffered more losses;and(4)agricultural insurance plays an important role in stabilizing the supply of vegetables to the city.To minimize the impact of the pandemic on vegetable production and to stabilize both urban“shopping baskets”and farmers’incomes,it is necessary to further improve agricultural insurance,especially to provide insurance against market risks.
