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
Cracks resulting from cyclic wetting and drying of expansive soils create discontinuities and anisotropy in the soil.The representative elementary volume(REV)defined by the continuous-media theory cannot be applied to...Cracks resulting from cyclic wetting and drying of expansive soils create discontinuities and anisotropy in the soil.The representative elementary volume(REV)defined by the continuous-media theory cannot be applied to cracked expansive soils that are considered discontinuous media.In this study,direct shear tests of three different scales(30 cm^(2),900 cm^(2),1963 cm^(2))and crack image analysis were carried out on undisturbed soil samples subjected to drying-wetting cycles in-situ.The REV size of expansive soil was investigated using the crack intensity factor(CIF)and soil cohesion.The results show that soil cohesion decreased with increasing sample area,and the development of secondary cracks further exacerbated the size effect of sample on cohesion of the soil.As shrinkage cracks developed,the REV size of the soil gradually increased and plateaued after 3−5 cycles.Under the same drying-wetting cycle conditions,the REV size determined using soil cohesion(REV-C)is 1.75 to 2.97 times the REV size determined using CIF(REV-CIF).Under the influence of shrinkage cracks,the average CIF is positively correlated with the REV size determined using different maximum permissible errors,with the coefficient of correlation greater than 0.9.A method for determining the REV-C based on crack image analysis is proposed,and the REV-C of expansive soil in the study area under different exposure times is given.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Project(41472240)supported by the National Natural Science Foundation of ChinaProjects(2015B25514,2015B17214)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Cracks resulting from cyclic wetting and drying of expansive soils create discontinuities and anisotropy in the soil.The representative elementary volume(REV)defined by the continuous-media theory cannot be applied to cracked expansive soils that are considered discontinuous media.In this study,direct shear tests of three different scales(30 cm^(2),900 cm^(2),1963 cm^(2))and crack image analysis were carried out on undisturbed soil samples subjected to drying-wetting cycles in-situ.The REV size of expansive soil was investigated using the crack intensity factor(CIF)and soil cohesion.The results show that soil cohesion decreased with increasing sample area,and the development of secondary cracks further exacerbated the size effect of sample on cohesion of the soil.As shrinkage cracks developed,the REV size of the soil gradually increased and plateaued after 3−5 cycles.Under the same drying-wetting cycle conditions,the REV size determined using soil cohesion(REV-C)is 1.75 to 2.97 times the REV size determined using CIF(REV-CIF).Under the influence of shrinkage cracks,the average CIF is positively correlated with the REV size determined using different maximum permissible errors,with the coefficient of correlation greater than 0.9.A method for determining the REV-C based on crack image analysis is proposed,and the REV-C of expansive soil in the study area under different exposure times is given.
