Due to the effects of seismic wave field interference, the reflection events generated from interbedded and superposed sand and shale strata no longer have an explicit corresponding relationship with the geological in...Due to the effects of seismic wave field interference, the reflection events generated from interbedded and superposed sand and shale strata no longer have an explicit corresponding relationship with the geological interface. The absorption of the near-surface layer decreases the resolution of the seismic wavelet, intensifies the interference of seismic reflections from different sand bodies, and makes seismic data interpretation of thin interbedded strata more complex and difficult. In order to concretely investigate and analyze the effects of the near-surface absorption on seismic reflection characteristics of interbedded strata, and to make clear the ability of current technologies to compensate the near-surface absorption, a geological model of continental interbedded strata with near-surface absorption was designed, and the prestack seismic wave field was numerically simulated with wave equations. Then, the simulated wave field was processed by the prestack time migration, the effects of near-surface absorption on prestack and poststack reflection characteristics were analyzed, and the near-surface absorption was compensated for by inverse Q-filtering. The model test shows that： （1） the reliability of prediction and delineation of a continental reservoir with AVO inversion is degraded due to the lateral variation of the near-surface structure; （2） the corresponding relationships between seismic reflection events and geological interfaces are further weakened as a result of near-surface absorption; and （3） the current technology of absorption compensation probably results in false geological structure and anomaly. Based on the model experiment, the real seismic data of the Dagang Oil Field were analyzed and processed. The seismic reflection characteristics of continental interbedded strata were improved, and the reliability of geological interpretation from seismic data was enhanced.展开更多
Slopes consisting of interbedded strata of soft and hard rock mass, such as purplish red mudstone and grey brown arkosic sandstone of Jurassic age, are very common in Sichuan basin of China. The mudstone is soft whil...Slopes consisting of interbedded strata of soft and hard rock mass, such as purplish red mudstone and grey brown arkosic sandstone of Jurassic age, are very common in Sichuan basin of China. The mudstone is soft while the sandstone is hard and contains many opening or closing joints with a high dip angle. Some are nearly parallel and the others are nearly decussated with the trend of the slopes. Many natural slopes are in deformation or sliding because of those reasons. The stability of cutting slopes and supporting method to be taken for their stability in civil engineering are important. In this paper, the stability and deformation of the slopes are studied. The methods of analysis and support design principle are analyzed also. Finally, the method put forward is applied to study Fengdian high cutting slope in Sichuan section of the express way from Chengdu to Shanghai. The results indicate that the method is effective.展开更多
Water-and-mud inrush disasters have become a major challenge in underground engineering for the construction of tunnels in sandstone and slate interbedded Presinian strata.Disaster prediction and prevention rely in pa...Water-and-mud inrush disasters have become a major challenge in underground engineering for the construction of tunnels in sandstone and slate interbedded Presinian strata.Disaster prediction and prevention rely in part on realistic modeling and observation of the disaster process,as well as the identification and examination of the underlying mechanisms.Based on the geological conditions and the historical records of the Xinping Tunnel on the China–Laos Railway,an engineering geological model of the water-and-mud inrush was established.A physical model test that accurately reproduced water-and-mud inrush during tunnel excavation in sandstone and slate interbedded strata was also carried out.Then,testing was conducted that examined the stress and strain,seepage pressure,and high-leakage flow of the surrounding rock.The results indicated that the water-and-mud inrush proceeded through three stages:seepage stage,high-leakage flow stage,and attenuation stage.In essence,the disaster was a catastrophic process,during which the water-resistant stratum was reduced to a critical safety thickness,a water-inrush channel formed,and the water-resistant stratum gradually failed under the influence of excavation unloading and in situ stress–seepage coupling.Parameters such as the stress and strain,seepage pressure,and flow of the surrounding rock had evident stage-related features during water-and-mud inrush,and their variation indicated the formation,development,and evolution of the disaster.As the tunnel face advanced,the trend of the stress–strain curve of the surrounding rock shifted from sluggish to rapid in its speed of increase.The characteristics of strain energy density revealed the erosion and weakening effect of groundwater on the surrounding rock.The seepage pressure and the thickness of the water-resistant stratum had a positive linear relationship,and the flow and thickness a negative linear relationship.There was a pivotal point at which the seepage pressure changed from high to low and the flow shifted from low to high.The thickness of the water-resistant stratum corresponding to the pivotal point was deemed the critical safety thickness.展开更多
针对土砂互层隧道易出现大变形问题,以浩吉铁路阳城隧道为例,通过分析大变形原因、围岩预加固和逐榀换拱等方面,对大变形控制技术进行研究,最后以现场监测结果对大变形段的施工效果进行评价。研究结果表明:1)土砂互层地层围岩性质差,围...针对土砂互层隧道易出现大变形问题,以浩吉铁路阳城隧道为例,通过分析大变形原因、围岩预加固和逐榀换拱等方面,对大变形控制技术进行研究,最后以现场监测结果对大变形段的施工效果进行评价。研究结果表明:1)土砂互层地层围岩性质差,围岩强度不均导致应力集中、偏压以及施工针对性不足等是隧道大变形发生的主要原因。2)围岩压力和格栅钢架应力总体表现为前期波动变化、后期逐步趋于稳定的变化趋势,而喷射混凝土则表现为明显的迅速增长、增长放缓和逐渐稳定3个阶段。围岩压力和支护结构受力变化范围均处于安全状态。3)大变形段支护结构的材料性能未被充分利用。喷射混凝土的最大压应力为1523k Pa,为混凝土极限强度的6.3%;格栅钢架最大压应力值为24553 k Pa,是其极限强度的6.1%。4)对大变形段进行整治后的围岩压力为0~85 k Pa,喷射混凝土应力为-2400~420 k Pa,钢架应力为-33000~1600 k Pa,表明隧道结构处于稳定状态且具有较大的安全储备。隧道现场试验结果表明,本文提出的大变形控制技术对整治土砂互层隧道的大变形问题具有较大的可行性。展开更多
基金supported by the National 973 Key Basic Research Development Program(No. 2007CB209608)National 863 High Technology Research Development Program(No.2007AA06Z218)
文摘Due to the effects of seismic wave field interference, the reflection events generated from interbedded and superposed sand and shale strata no longer have an explicit corresponding relationship with the geological interface. The absorption of the near-surface layer decreases the resolution of the seismic wavelet, intensifies the interference of seismic reflections from different sand bodies, and makes seismic data interpretation of thin interbedded strata more complex and difficult. In order to concretely investigate and analyze the effects of the near-surface absorption on seismic reflection characteristics of interbedded strata, and to make clear the ability of current technologies to compensate the near-surface absorption, a geological model of continental interbedded strata with near-surface absorption was designed, and the prestack seismic wave field was numerically simulated with wave equations. Then, the simulated wave field was processed by the prestack time migration, the effects of near-surface absorption on prestack and poststack reflection characteristics were analyzed, and the near-surface absorption was compensated for by inverse Q-filtering. The model test shows that： （1） the reliability of prediction and delineation of a continental reservoir with AVO inversion is degraded due to the lateral variation of the near-surface structure; （2） the corresponding relationships between seismic reflection events and geological interfaces are further weakened as a result of near-surface absorption; and （3） the current technology of absorption compensation probably results in false geological structure and anomaly. Based on the model experiment, the real seismic data of the Dagang Oil Field were analyzed and processed. The seismic reflection characteristics of continental interbedded strata were improved, and the reliability of geological interpretation from seismic data was enhanced.
文摘Slopes consisting of interbedded strata of soft and hard rock mass, such as purplish red mudstone and grey brown arkosic sandstone of Jurassic age, are very common in Sichuan basin of China. The mudstone is soft while the sandstone is hard and contains many opening or closing joints with a high dip angle. Some are nearly parallel and the others are nearly decussated with the trend of the slopes. Many natural slopes are in deformation or sliding because of those reasons. The stability of cutting slopes and supporting method to be taken for their stability in civil engineering are important. In this paper, the stability and deformation of the slopes are studied. The methods of analysis and support design principle are analyzed also. Finally, the method put forward is applied to study Fengdian high cutting slope in Sichuan section of the express way from Chengdu to Shanghai. The results indicate that the method is effective.
基金the National High-Speed Rail United Foundation of China(No.U1934213)。
文摘Water-and-mud inrush disasters have become a major challenge in underground engineering for the construction of tunnels in sandstone and slate interbedded Presinian strata.Disaster prediction and prevention rely in part on realistic modeling and observation of the disaster process,as well as the identification and examination of the underlying mechanisms.Based on the geological conditions and the historical records of the Xinping Tunnel on the China–Laos Railway,an engineering geological model of the water-and-mud inrush was established.A physical model test that accurately reproduced water-and-mud inrush during tunnel excavation in sandstone and slate interbedded strata was also carried out.Then,testing was conducted that examined the stress and strain,seepage pressure,and high-leakage flow of the surrounding rock.The results indicated that the water-and-mud inrush proceeded through three stages:seepage stage,high-leakage flow stage,and attenuation stage.In essence,the disaster was a catastrophic process,during which the water-resistant stratum was reduced to a critical safety thickness,a water-inrush channel formed,and the water-resistant stratum gradually failed under the influence of excavation unloading and in situ stress–seepage coupling.Parameters such as the stress and strain,seepage pressure,and flow of the surrounding rock had evident stage-related features during water-and-mud inrush,and their variation indicated the formation,development,and evolution of the disaster.As the tunnel face advanced,the trend of the stress–strain curve of the surrounding rock shifted from sluggish to rapid in its speed of increase.The characteristics of strain energy density revealed the erosion and weakening effect of groundwater on the surrounding rock.The seepage pressure and the thickness of the water-resistant stratum had a positive linear relationship,and the flow and thickness a negative linear relationship.There was a pivotal point at which the seepage pressure changed from high to low and the flow shifted from low to high.The thickness of the water-resistant stratum corresponding to the pivotal point was deemed the critical safety thickness.
文摘针对土砂互层隧道易出现大变形问题,以浩吉铁路阳城隧道为例,通过分析大变形原因、围岩预加固和逐榀换拱等方面,对大变形控制技术进行研究,最后以现场监测结果对大变形段的施工效果进行评价。研究结果表明:1)土砂互层地层围岩性质差,围岩强度不均导致应力集中、偏压以及施工针对性不足等是隧道大变形发生的主要原因。2)围岩压力和格栅钢架应力总体表现为前期波动变化、后期逐步趋于稳定的变化趋势,而喷射混凝土则表现为明显的迅速增长、增长放缓和逐渐稳定3个阶段。围岩压力和支护结构受力变化范围均处于安全状态。3)大变形段支护结构的材料性能未被充分利用。喷射混凝土的最大压应力为1523k Pa,为混凝土极限强度的6.3%;格栅钢架最大压应力值为24553 k Pa,是其极限强度的6.1%。4)对大变形段进行整治后的围岩压力为0~85 k Pa,喷射混凝土应力为-2400~420 k Pa,钢架应力为-33000~1600 k Pa,表明隧道结构处于稳定状态且具有较大的安全储备。隧道现场试验结果表明,本文提出的大变形控制技术对整治土砂互层隧道的大变形问题具有较大的可行性。
