Cases of simultaneous inrush of high-temperature water and harmful gases are infrequently reported in areas without geothermal anomalies,hydrocarbon source rock,or coal measures.For this,we investigated the origin,dev...Cases of simultaneous inrush of high-temperature water and harmful gases are infrequently reported in areas without geothermal anomalies,hydrocarbon source rock,or coal measures.For this,we investigated the origin,development,and formation of the high-temperature water and harmful gases that rushed into Bangfu tunnel,Southwest China.During excavation of the Bangfu tunnel through the F1-2 fault in sandstone,a significant incident occurred involving a sudden influx of high-temperature water(45.4℃)of NaeHCO_(3)type and harmful gases(CO_(2),H2S).An extensive geological examination uncovered a fault network extending from the crust to the mantle in the tunnel site area.The site features a substantial presence of both surface water and groundwater.Furthermore,within the middle crust at depths ranging from 19 km to 23 km,there are high-temperature ductile melts enriched with fluids and gases.Monitoring and experiments conducted on the harmful gases reveal that the primary source is identified in the crust,with the mantle source being secondary,followed by the atmospheric source being a minimal contribution.The hydrochemical and isotopic composition characteristics of the hightemperature rushed water indicate its evolution was formed through the infiltration of atmospheric precipitation from cold groundwater of the CaeHCO_(3)type.The mechanism underlying the formation of the inrush high-temperature water and harmful gases can be outlined as follows.The fault network,spanning from the crust to the mantle,serves as a migration pathway for the inflow substances.Mantlederived volatiles and high-temperature melts make heat energy facilitate the inrush activity,while groundwater contributes to heat transfer and acts as a medium for gas transport.As mantle-derived volatiles migrate towards the surface through the fault network,they mix with high-temperature melts and crust-derived gases,forming a crust-mantle mixed gas.Through processes such as deep hydrothermal circulation,shallow hydrothermal circulation,water/rock reaction,near-surface mixing,and dilution,CaeHCO_(3)type cold groundwater transforms into high-temperature water of NaeHCO_(3)type.The methodologies and findings of our research offer insights into the route selection,investigation,and construction of mountain tunneling projects under similar geological conditions.展开更多
The effects of cyclic heat treatments on the fracture shear behaviors are rarely reported.To enhance our understanding,granite fractures having almost the same roughness were first exposed to cyclic heating at 400C an...The effects of cyclic heat treatments on the fracture shear behaviors are rarely reported.To enhance our understanding,granite fractures having almost the same roughness were first exposed to cyclic heating at 400C and air-cooling treatments,and then direct shear tests were performed under four levels of normal loading.The influences of thermal cycles on roughness degradation and shear properties are analyzed.The roughness degradation in the joint roughness coefficient and the three-dimensional(3D)roughness metric exhibit linear increasing tendency with increasing thermal cycles.Typical fracture shear properties,including cohesion and friction angle,peak and residual shear strength,peak and residual shear displacement,and initial and secant shear stiffness,fluctuate generally within the first 10 thermal cycles,followed by gradual decreasing tendencies.The thermal effect on the shear properties become weaker as the number of heat treatments increases from 10 to 80.Nonuniform expansion and shrinkage of mineral grains after thermal treatments produce micro-cracks within the rock matrix and on the rock surface,suggesting that asperities are easier to be sheared-off.Thermal alteration in fracture peak-shear strength could be attributed to the deterioration in rock strengths and the mismatch in opposing fracture walls.The observations would provide better insights into rock friction after high temperatures in geothermal energy exploitation.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.42277173)National Key Research and Development projects of China(Grant No.2021YFB2600402)+1 种基金the Opening Fund of Key Laboratory of Geological Survey and Evaluation of Ministry of Education(Grant No.GLAB2022ZR03)the Fundamental Research Funds for the Central Universities.
文摘Cases of simultaneous inrush of high-temperature water and harmful gases are infrequently reported in areas without geothermal anomalies,hydrocarbon source rock,or coal measures.For this,we investigated the origin,development,and formation of the high-temperature water and harmful gases that rushed into Bangfu tunnel,Southwest China.During excavation of the Bangfu tunnel through the F1-2 fault in sandstone,a significant incident occurred involving a sudden influx of high-temperature water(45.4℃)of NaeHCO_(3)type and harmful gases(CO_(2),H2S).An extensive geological examination uncovered a fault network extending from the crust to the mantle in the tunnel site area.The site features a substantial presence of both surface water and groundwater.Furthermore,within the middle crust at depths ranging from 19 km to 23 km,there are high-temperature ductile melts enriched with fluids and gases.Monitoring and experiments conducted on the harmful gases reveal that the primary source is identified in the crust,with the mantle source being secondary,followed by the atmospheric source being a minimal contribution.The hydrochemical and isotopic composition characteristics of the hightemperature rushed water indicate its evolution was formed through the infiltration of atmospheric precipitation from cold groundwater of the CaeHCO_(3)type.The mechanism underlying the formation of the inrush high-temperature water and harmful gases can be outlined as follows.The fault network,spanning from the crust to the mantle,serves as a migration pathway for the inflow substances.Mantlederived volatiles and high-temperature melts make heat energy facilitate the inrush activity,while groundwater contributes to heat transfer and acts as a medium for gas transport.As mantle-derived volatiles migrate towards the surface through the fault network,they mix with high-temperature melts and crust-derived gases,forming a crust-mantle mixed gas.Through processes such as deep hydrothermal circulation,shallow hydrothermal circulation,water/rock reaction,near-surface mixing,and dilution,CaeHCO_(3)type cold groundwater transforms into high-temperature water of NaeHCO_(3)type.The methodologies and findings of our research offer insights into the route selection,investigation,and construction of mountain tunneling projects under similar geological conditions.
基金supports from the Natural Science Foundation of China(Nos.42177165 and 42277173)the National Key Research and Development Projects of China(No.2021YFB2600402)。
文摘The effects of cyclic heat treatments on the fracture shear behaviors are rarely reported.To enhance our understanding,granite fractures having almost the same roughness were first exposed to cyclic heating at 400C and air-cooling treatments,and then direct shear tests were performed under four levels of normal loading.The influences of thermal cycles on roughness degradation and shear properties are analyzed.The roughness degradation in the joint roughness coefficient and the three-dimensional(3D)roughness metric exhibit linear increasing tendency with increasing thermal cycles.Typical fracture shear properties,including cohesion and friction angle,peak and residual shear strength,peak and residual shear displacement,and initial and secant shear stiffness,fluctuate generally within the first 10 thermal cycles,followed by gradual decreasing tendencies.The thermal effect on the shear properties become weaker as the number of heat treatments increases from 10 to 80.Nonuniform expansion and shrinkage of mineral grains after thermal treatments produce micro-cracks within the rock matrix and on the rock surface,suggesting that asperities are easier to be sheared-off.Thermal alteration in fracture peak-shear strength could be attributed to the deterioration in rock strengths and the mismatch in opposing fracture walls.The observations would provide better insights into rock friction after high temperatures in geothermal energy exploitation.
