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The initial stress state and stability of the surrounding rock mass will change during tunnel excavation. The rock mass even may collapse due to over-size displacement. A new method is presented in this paper for reliability analysis of tunnel excavation. The genetic algorithm is put forward to calculate the reliability index and failure probability for the complexity of the model. The proposed method is applied to reliability analyzing of a practical expressway tunnel. The result shows that the potential break areas appear at vault and spandrel of the tunnel. The reliability indexes and failure probabilities of the vault settlement and spandrel convergent reflect that the reliability of the unsupported construction can't meet the requirement of the specification. The tunnel must be supported in time. The initial stress state and stability of the surrounding rock mass will change during tunnel excavation. The rock mass even may collapse due to over-size displacement. A new method is presented in this paper for reliability analysis of tunnel excavation. The genetic algorithm is put forward to calculate the reliability index and failure probability for the complexity of the model. The proposed method is applied to reliability analyzing of a practical expressway tunnel. The result shows that the potential break areas appear at vault and spandrel of the tunnel. The reliability indexes and failure probabilities of the vault settlement and spandrel convergent reflect that the reliability of the unsupported construction can't meet the requirement of the specification. The tunnel must be supported in time.
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A quantitative analysis of microstructure of weathered granite under optical microscope by using Qwins image processing system is done in the paper and quantitative indexes, such as content, grain size, orientrf porosity, shape factor etc. are listed. According to the analysis result, the granite in Kwun Tong is moderately weathered fine-grained granite, and the granite in Shek Kip Mei is highly weathered coarse-medium-grained granite. A quantitative analysis of microstructure of weathered granite under optical microscope by using Qwins image processing system is done in the paper and quantitative indexes, such as content, grain size, orientrf porosity, shape factor etc. are listed. According to the analysis result, the granite in Kwun Tong is moderately weathered fine-grained granite, and the granite in Shek Kip Mei is highly weathered coarse-medium-grained granite.
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The devastation and casualties caused by the 1556 Huaxian great earthquake are the severest in the history of mankind. According to records, more than eight hundred and thirty thousands of peoples were killed by the great earthquake. Although the earthquake occurred more than 450 years ago, some geological relics caused by the earthquake are still very clear in some counties such as Weinan, Huaxian, Huayin and Tongguan, which are located in the eastern Guanzhong Basin, Shaanxi Province, China. In the study, four typical geo-heritages including seismogenic faults, seismic-cracks, earthquake rock avalanches and earthquake landslides are investigated by means of field work. The results show that these geo-heritages are the results of strong ground motion associated with tectonic stress field, types of rock and soil, geomorphology and hydrogeololgy. The geological relics caused by the Huaxian earthquake have great values in scientific research, scientific popularization and tourism. Therefore, the protection and use of the sites should be paid more attention. The devastation and casualties caused by the 1556 Huaxian great earthquake are the severest in the history of mankind. According to records, more than eight hundred and thirty thousands of peoples were killed by the great earthquake. Although the earthquake occurred more than 450 years ago, some geological relics caused by the earthquake are still very clear in some counties such as Weinan, Huaxian, Huayin and Tongguan, which are located in the eastern Guanzhong Basin, Shaanxi Province, China. In the study, four typical geo-heritages including seismogenic faults, seismic-cracks, earthquake rock avalanches and earthquake landslides are investigated by means of field work. The results show that these geo-heritages are the results of strong ground motion associated with tectonic stress field, types of rock and soil, geomorphology and hydrogeololgy. The geological relics caused by the Huaxian earthquake have great values in scientific research, scientific popularization and tourism. Therefore, the protection and use of the sites should be paid more attention.
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The reason of giant debris flow triggering was obtained by field investigation and analysis on the debris flow formation conditions: heavy rainfall happened in the upstream of Sanyanyu Gully and Luojiayu Gully.The recorded rainfall was 77.3mm in one hour from 23 to 24 oclock, August 7, 2010. The heavy rain caused powerful flash flood in the catchments,which destroyed several natural dams and prevention dams in the two gullies. Then the giant debris flows were formed. The debris flows were high density viscous debris flows. The total volume of debris flows and the volume of sediment in debris flows were estimated at 144.2104m3 and 97.7104m3, respectively. The large boulder involving in debris flows moved with powerful impact force and destroyed more than 5500 houses in depositional fans. The debris flows produced a dam with 550m in length, 70m in width, and 10m in height in Bailongjiang River. The dam blocked the river and formed a lake with 3km in length and half of Zhouqu city was inundated. As of August 18, 2010, the debris flows claimed 1287 death, with further 457 listed as missing. The tendency of debris flow development was obtained by a preliminary analysis of the initiation conditions of debris flows: (1) The debris flows will be triggered if there is a heavy rainfall in the upstream of debris flows gullies recently, but the scale of debris flows will be less than the scale of debris flows on August 7, 2010; (2) The debris flows will be triggered if there is a heavy rainfall in the upstream of debris flows gullies in a few years, the scale of debris flows will be a little bit less than the scale of debris flows on August 7, 2010; (3) The scale of debris flows 20 years later will be the same as the scale of debris flows before Wenchuan Earthquake if there is no more earthquake effect this area and a event of large scale debris flow has happened in these gullies. The reason of giant debris flow triggering was obtained by field investigation and analysis on the debris flow formation conditions: heavy rainfall happened in the upstream of Sanyanyu Gully and Luojiayu Gully.The recorded rainfall was 77.3mm in one hour from 23 to 24 oclock, August 7, 2010. The heavy rain caused powerful flash flood in the catchments,which destroyed several natural dams and prevention dams in the two gullies. Then the giant debris flows were formed. The debris flows were high density viscous debris flows. The total volume of debris flows and the volume of sediment in debris flows were estimated at 144.2104m3 and 97.7104m3, respectively. The large boulder involving in debris flows moved with powerful impact force and destroyed more than 5500 houses in depositional fans. The debris flows produced a dam with 550m in length, 70m in width, and 10m in height in Bailongjiang River. The dam blocked the river and formed a lake with 3km in length and half of Zhouqu city was inundated. As of August 18, 2010, the debris flows claimed 1287 death, with further 457 listed as missing. The tendency of debris flow development was obtained by a preliminary analysis of the initiation conditions of debris flows: (1) The debris flows will be triggered if there is a heavy rainfall in the upstream of debris flows gullies recently, but the scale of debris flows will be less than the scale of debris flows on August 7, 2010; (2) The debris flows will be triggered if there is a heavy rainfall in the upstream of debris flows gullies in a few years, the scale of debris flows will be a little bit less than the scale of debris flows on August 7, 2010; (3) The scale of debris flows 20 years later will be the same as the scale of debris flows before Wenchuan Earthquake if there is no more earthquake effect this area and a event of large scale debris flow has happened in these gullies.
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From 12 to 14 of August 2010,heavy rain even rainstorms have been dropped in part of area in Sichuan province,and catastrophic debris flow have been induced in Qingping town of Mianzhu city,Yingxiu town of Wenchuan county and Longchi town of Dujiangyan city,which belonged to the worst-hit areas of the 5 12 Wenchuan earthquake.This disaster was referred by government as the 13 August 2010 catastrophic debris flow in Sichuan province.This debris flow disaster demonstrated that the debris flow in seismic zone or in none-seismic zone,pre-earthquake or post-earthquake had significant differences in distribution,forming condition,scale,moving style as well as other disaster mode and harmfulness.Firstly,a brief introduction to the 8 13 Qingping,Hongchungou of Yingxiu and Longchi debris flows have been made in this paper.The characteristic and formation reason of the 8 13 catastrophic debris flow,in Wenchuan earthquake region,have been analyzed and summarized and several revelations and suggestions to the prevention of the debris flow in disaster area have been put forward.The research result showed that the 8 13 debris flow not only had the characteristics of group properties,sudden features,destructiveness and hazard chain effect,but also had the significant characteristics of zonal distribution along the seismic fault,materials mainly coming from rock slide deposit which triggered by the Wenchuan earthquake and down-cutting being the mainly moving mode.Extraordinary abundant loose solid materials and local short-time heavy rainfall by the extreme climate in the earthquake region were the basic reason of the debris flow occurrence.In allusion to these new characteristics of the debris flow in Wenchuan earthquake region,the prevention measures to debris flow in earthquake region should be strengthened,especially those valleys of great debris flow hidden trouble.On the one hand,the standard of the garrison should be improved and the engineering management as well as specialty monitor should be intensified.On the other hand,risk management and control ideal should be brought in.The combination of prevention and administration,the combination of soft and hard,the combination of engineering measures and non-engineering measures,and the combination of administration and management was supposed to be focused on.What else,mobilizing the whole society to prevent geological disaster all together. From 12 to 14 of August 2010,heavy rain even rainstorms have been dropped in part of area in Sichuan province,and catastrophic debris flow have been induced in Qingping town of Mianzhu city,Yingxiu town of Wenchuan county and Longchi town of Dujiangyan city,which belonged to the worst-hit areas of the 5 12 Wenchuan earthquake.This disaster was referred by government as the 13 August 2010 catastrophic debris flow in Sichuan province.This debris flow disaster demonstrated that the debris flow in seismic zone or in none-seismic zone,pre-earthquake or post-earthquake had significant differences in distribution,forming condition,scale,moving style as well as other disaster mode and harmfulness.Firstly,a brief introduction to the 8 13 Qingping,Hongchungou of Yingxiu and Longchi debris flows have been made in this paper.The characteristic and formation reason of the 8 13 catastrophic debris flow,in Wenchuan earthquake region,have been analyzed and summarized and several revelations and suggestions to the prevention of the debris flow in disaster area have been put forward.The research result showed that the 8 13 debris flow not only had the characteristics of group properties,sudden features,destructiveness and hazard chain effect,but also had the significant characteristics of zonal distribution along the seismic fault,materials mainly coming from rock slide deposit which triggered by the Wenchuan earthquake and down-cutting being the mainly moving mode.Extraordinary abundant loose solid materials and local short-time heavy rainfall by the extreme climate in the earthquake region were the basic reason of the debris flow occurrence.In allusion to these new characteristics of the debris flow in Wenchuan earthquake region,the prevention measures to debris flow in earthquake region should be strengthened,especially those valleys of great debris flow hidden trouble.On the one hand,the standard of the garrison should be improved and the engineering management as well as specialty monitor should be intensified.On the other hand,risk management and control ideal should be brought in.The combination of prevention and administration,the combination of soft and hard,the combination of engineering measures and non-engineering measures,and the combination of administration and management was supposed to be focused on.What else,mobilizing the whole society to prevent geological disaster all together.
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The occurrence of rock avalanche always brings disastrous catastrophes because of its high speed and unexpected long runout. So,its kinematics or moving mechanism has been the focus of engineering geologists around the world since late 19th century. At present,there are four viewpoints abroad: air-lubrication model,grain flow model,momentum-transfer model and self-undrained loading model. Howver,they have not been widely accepted possibly because of complication. China is a country where frequent rock avalances occur. The research on this field is just at the beginning and most of the research results are qualitative. Based on a review of a plenty of literatures,this paper expounds the development status of study on the transport mechanism of rock avalanches in two aspects of theories and research techniques. It summarizes the existing numerous models,comments on the research difficulties at present. Finally,it puts forward the research directions in the future according to the present bottlenecks. This paper systematically sums up the relevant research status and can be helpful to the future research. The occurrence of rock avalanche always brings disastrous catastrophes because of its high speed and unexpected long runout. So,its kinematics or moving mechanism has been the focus of engineering geologists around the world since late 19th century. At present,there are four viewpoints abroad: air-lubrication model,grain flow model,momentum-transfer model and self-undrained loading model. Howver,they have not been widely accepted possibly because of complication. China is a country where frequent rock avalances occur. The research on this field is just at the beginning and most of the research results are qualitative. Based on a review of a plenty of literatures,this paper expounds the development status of study on the transport mechanism of rock avalanches in two aspects of theories and research techniques. It summarizes the existing numerous models,comments on the research difficulties at present. Finally,it puts forward the research directions in the future according to the present bottlenecks. This paper systematically sums up the relevant research status and can be helpful to the future research.
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Abstract Daguangbao landslide in Anxian county Gaochuan town is located on the upper plate of the Causative Fault of wenchuan earthquake. Its slide distance is 4.5 km, and its maximum width of accumulation is 2.2 km. The area is 7.8 km2, and estimated volume is 750 million m3. It is the largest landslide among individual landslides triggered by Wenchuan earthquake. Comparing with the other 178 large landslides in earthquake disaster area, Daguangbao landslide has the same characteristics as falls and slide disaster triggered by strong earthquake. They include shake debacle, unstability of debacle and slide mechanism, super-dynamic characteristics, large-scale and high-speed projectile, and long-distance movement.But it has itself standout trait, namely, a long-large sliding surface more than 1 km long and 100~250 m wide, which is in a class by itself. On the basis of the study last year, the author has further progressed the site investigation many times, and has finished mapping and sampling analysis. The preliminary view is that Daguangbao landslide occurring process is one-time completion. Composition of sliding zone is very complex. It is mainly composed of stronger weathering argillaceous limestone of Sinian, and its part stratum contains Devonian shawozi sub-group (Ds) and its associated phosphate ore. Its formation mechanism can be divided into the following 3 stages. (1) Stage of slope shattering cracking. Rear fracturing boundary and upstream fracturing boundary were shaped under strong earthquake, and they composed huge wedge Vwith downstream rock beddings. (2) Stage of friction decrease and slope shattering-sliding. Sliding bed at downstream boundary (the main controlling sliding surface) began shattering-cracking, relaxation, cutting expand-bulk enlarge. Strolling scrape effect made the friction decrease sharply, and made the huge wedge slide with high speed along bedding strike, like pulling drawer. (3) Stage of shattering-slidingshaking- accumulating. Landslide body rushed into Hongdongzi gully and was barred strongly by faced mountain,so it thrust up more than 500 m,and then its surficial loose accumulation with large inertia began fastly backing and shaking, accumulating, shaking level. Debris flows whose inertia force did not decrease imported landslide and enlarged ejection body. At last, it stopped at Dapianqiao bridge after flowing 1 km towards downstream of Hongdongzi gully. Key words Daguangbao landslide, character of landslide, model of geomechanics, formation mechanism, shattering expand and surper press Abstract Daguangbao landslide in Anxian county Gaochuan town is located on the upper plate of the Causative Fault of wenchuan earthquake. Its slide distance is 4.5 km, and its maximum width of accumulation is 2.2 km. The area is 7.8 km2, and estimated volume is 750 million m3. It is the largest landslide among individual landslides triggered by Wenchuan earthquake. Comparing with the other 178 large landslides in earthquake disaster area, Daguangbao landslide has the same characteristics as falls and slide disaster triggered by strong earthquake. They include shake debacle, unstability of debacle and slide mechanism, super-dynamic characteristics, large-scale and high-speed projectile, and long-distance movement.But it has itself standout trait, namely, a long-large sliding surface more than 1 km long and 100~250 m wide, which is in a class by itself. On the basis of the study last year, the author has further progressed the site investigation many times, and has finished mapping and sampling analysis. The preliminary view is that Daguangbao landslide occurring process is one-time completion. Composition of sliding zone is very complex. It is mainly composed of stronger weathering argillaceous limestone of Sinian, and its part stratum contains Devonian shawozi sub-group (Ds) and its associated phosphate ore. Its formation mechanism can be divided into the following 3 stages. (1) Stage of slope shattering cracking. Rear fracturing boundary and upstream fracturing boundary were shaped under strong earthquake, and they composed huge wedge Vwith downstream rock beddings. (2) Stage of friction decrease and slope shattering-sliding. Sliding bed at downstream boundary (the main controlling sliding surface) began shattering-cracking, relaxation, cutting expand-bulk enlarge. Strolling scrape effect made the friction decrease sharply, and made the huge wedge slide with high speed along bedding strike, like pulling drawer. (3) Stage of shattering-slidingshaking- accumulating. Landslide body rushed into Hongdongzi gully and was barred strongly by faced mountain,so it thrust up more than 500 m,and then its surficial loose accumulation with large inertia began fastly backing and shaking, accumulating, shaking level. Debris flows whose inertia force did not decrease imported landslide and enlarged ejection body. At last, it stopped at Dapianqiao bridge after flowing 1 km towards downstream of Hongdongzi gully. Key words Daguangbao landslide, character of landslide, model of geomechanics, formation mechanism, shattering expand and surper press
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The landslide at Daguangbao and Hongdongzigou site is the largest among all landslides occurred during the Wenchuan Earthquake. Its volume is up to 742 Mm3, and its debris dam height reaches 690 m. So it is also the most largest scale landslide triggered by earthquake among all investigated landslides in China. Additionally, it has the highest debris dam originating from landslide in China. It is even one of a few super large-scale landslides known all over the world, whose individual volume is over 500 Mm3. The debris dam formed by this landslide can be the highest around the world. The landslide is located on the upper plate of the Causative Fault. It is nearly 7 km away from the triggering seismic fracture of Yingxiu-beichuan fault. The slope was an isolated ridge before the Earthquake. it's the ridge had its 3 sides cut. Its height difference reaches 1500 m. The strike of clinothen was almost vertical to the slope surface. the clinothen had perfect extension. They composed together the basic conditions of sliding surface formation. Our investigation and analysis show that the free surface conditions of the slope and the surface connectivity of limestone bedding plane were the base of landslide formation. And the ground movement resulted from the intensive quaking with large intensity and long duration was the radical triggering factor of the landslide. The mechanism and process of the landslide could be divided into 4 stages as follows: (a) the stage of slope body shatter, relaxation and disintegration, (b) the stage of high speed sliding, 9c) the stage of accumulation with shock, and (d) the stage of the second projectile and debris flow deposition. Because of destabilization and high speed sliding down, the slope mass composed a deposit body along main direction of sliding, 4.2 km long and 2.2 km wide. High-speed clastic flow crossed downstream Fengboyan, and formed a deposit zone of debris flow along Hongdongzigou, 1 km long. The landslide at Daguangbao and Hongdongzigou site is the largest among all landslides occurred during the Wenchuan Earthquake. Its volume is up to 742 Mm3, and its debris dam height reaches 690 m. So it is also the most largest scale landslide triggered by earthquake among all investigated landslides in China. Additionally, it has the highest debris dam originating from landslide in China. It is even one of a few super large-scale landslides known all over the world, whose individual volume is over 500 Mm3. The debris dam formed by this landslide can be the highest around the world. The landslide is located on the upper plate of the Causative Fault. It is nearly 7 km away from the triggering seismic fracture of Yingxiu-beichuan fault. The slope was an isolated ridge before the Earthquake. it's the ridge had its 3 sides cut. Its height difference reaches 1500 m. The strike of clinothen was almost vertical to the slope surface. the clinothen had perfect extension. They composed together the basic conditions of sliding surface formation. Our investigation and analysis show that the free surface conditions of the slope and the surface connectivity of limestone bedding plane were the base of landslide formation. And the ground movement resulted from the intensive quaking with large intensity and long duration was the radical triggering factor of the landslide. The mechanism and process of the landslide could be divided into 4 stages as follows: (a) the stage of slope body shatter, relaxation and disintegration, (b) the stage of high speed sliding, 9c) the stage of accumulation with shock, and (d) the stage of the second projectile and debris flow deposition. Because of destabilization and high speed sliding down, the slope mass composed a deposit body along main direction of sliding, 4.2 km long and 2.2 km wide. High-speed clastic flow crossed downstream Fengboyan, and formed a deposit zone of debris flow along Hongdongzigou, 1 km long.
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The deeply seated and 11.068 km long Yuanliangshan tunnel is a key project of the railway from Chongqing to Huaihua. The tunnel goes cross the Yuanliangshan syncline,a NESW trending tightly folded syncline,and cuts numerous NWNWW striking transverse faults. The core of the syncline composes of Permian and Lower Triassic carbonate rock strata,and the soluble rock terrain is enveloped on all sides by underlying Devonian and Silurian shale. The length of the tunnel drifted through the soluble carbonate rock mass is 2,2 km. On the ground surface,there are a lot of karstic depressions,dolines and sinkholes. Numerous karstic springs emerge out from the tips of the transverse faults on both wings of the syncline,where the carbonate rock strata contacts with the underlying shale. The elevations of the springs are usually higher than 850~900 m above the mean sea level. These elevations are regarded as the local discharge base level of the underground karstic water. The tunnel is situated at 400 to 450 m under this base level. During the drifting of the tunnel,three infilled huge karstic caves(Nos. 1#, 2#,and 3#)were exposed near by the axis,at the axis and at the east wing of the syncline,respectively. Water gushing and sand boiling hazards occurred many times while drifting through the sand infilled cave No. 2#. An unexpected and seldom observed blasting and shooting extrusion of clayey soil hazard occurred when the clayey soil infilled cave No.3# was just exposed. Through comprehensive analysis of the abundant data gathered during the construction of the tunnel,it is tentatively concluded: (1)an open primitive channel for the deep circulation of karstic water has been provided by the intersection of the two transverse faults(f7 and f9)with the longitudinal tension cracks nearby the axis,the bed separation void at the core of the syncline,and an interstratal shearing zone at the east wing of the syncline. A reversesiphonic circulation of karstic water was impelled by the potential difference between the underground water levels of the two transverse faults; (2)strong water conductive faults and cracks developed into caves through longtime differential dissolution and the water in these channels transformed into pipe flow; (3)by longtime strongly dissolution and erosion(and for the cave No.2 also roof collapse),the longitudinal tension crack,the bed separation void and the interstrated shearing zone were transformed into huge karstic caves; (4)caves were infilled due to the changing of hydrologic condition. The deeply seated and 11.068 km long Yuanliangshan tunnel is a key project of the railway from Chongqing to Huaihua. The tunnel goes cross the Yuanliangshan syncline,a NESW trending tightly folded syncline,and cuts numerous NWNWW striking transverse faults. The core of the syncline composes of Permian and Lower Triassic carbonate rock strata,and the soluble rock terrain is enveloped on all sides by underlying Devonian and Silurian shale. The length of the tunnel drifted through the soluble carbonate rock mass is 2,2 km. On the ground surface,there are a lot of karstic depressions,dolines and sinkholes. Numerous karstic springs emerge out from the tips of the transverse faults on both wings of the syncline,where the carbonate rock strata contacts with the underlying shale. The elevations of the springs are usually higher than 850~900 m above the mean sea level. These elevations are regarded as the local discharge base level of the underground karstic water. The tunnel is situated at 400 to 450 m under this base level. During the drifting of the tunnel,three infilled huge karstic caves(Nos. 1#, 2#,and 3#)were exposed near by the axis,at the axis and at the east wing of the syncline,respectively. Water gushing and sand boiling hazards occurred many times while drifting through the sand infilled cave No. 2#. An unexpected and seldom observed blasting and shooting extrusion of clayey soil hazard occurred when the clayey soil infilled cave No.3# was just exposed. Through comprehensive analysis of the abundant data gathered during the construction of the tunnel,it is tentatively concluded: (1)an open primitive channel for the deep circulation of karstic water has been provided by the intersection of the two transverse faults(f7 and f9)with the longitudinal tension cracks nearby the axis,the bed separation void at the core of the syncline,and an interstratal shearing zone at the east wing of the syncline. A reversesiphonic circulation of karstic water was impelled by the potential difference between the underground water levels of the two transverse faults; (2)strong water conductive faults and cracks developed into caves through longtime differential dissolution and the water in these channels transformed into pipe flow; (3)by longtime strongly dissolution and erosion(and for the cave No.2 also roof collapse),the longitudinal tension crack,the bed separation void and the interstrated shearing zone were transformed into huge karstic caves; (4)caves were infilled due to the changing of hydrologic condition.
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Identification of landslidingsurface is the crucial problem of landslide investigation and research. It is also important for landslide stability and construction design. The basic type of landslidingsurface is categorized to rock surface,sediment surface,and soil surface. The geological characters of landslidingsurface can be classified as smooth friction surface,striation,mudding zone and diamond shearing wedge with directional range. Based on this classification,it is generated that the main methods for landslidingsurface identification contains mechanical analysis,field geology judgment,site exploration,displacement monitoring and geophysical detection. Applicability of these methods is also discussed in the paper. Identification of landslidingsurface is the crucial problem of landslide investigation and research. It is also important for landslide stability and construction design. The basic type of landslidingsurface is categorized to rock surface,sediment surface,and soil surface. The geological characters of landslidingsurface can be classified as smooth friction surface,striation,mudding zone and diamond shearing wedge with directional range. Based on this classification,it is generated that the main methods for landslidingsurface identification contains mechanical analysis,field geology judgment,site exploration,displacement monitoring and geophysical detection. Applicability of these methods is also discussed in the paper.
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Abstract(3731)
484KB(2733)
A concept of Extreme Geo-Disaster and Risk is proposed in this paper.Extreme geo-disasters are considered to be geo-events of most low probability in the earth recent evolution.However,low probability of natural event does not mean that it will happen only in the far future,and it does not exclude that such geo-disasters may happen in relatively near future within our or next generations.Strong earthquake Ms 8.0 on 12th May, 2008 in Wenchuan,China,which caused large amount of fatalities and structure damage,showed the typical characteristics of an extreme natural disaster.It once again rang a tocsin to warning human society.It is a question,if human would forget it,when it passed and the terrible situation changed.Therefore,the author appeals that engineering geologists have to pay attention to and deal with such extreme disasters and risks.Scientific recognition of the level of natural dynamic forces responsible for extreme disaster provides an essential basis in the disaster prediction,and this should be one of the essential objectives of engineering geology.Regional study of geo-sphere dynamic processes may help in aiming at this purpose.To assess the potential risk an approach of impact area estimation is important and further analysis of relationship between the damaging effect and vulnerability damaged objects gives an assessed level of disaster risk.In the strategy of risk management a kind of precaution measure and warning should be focused instead of merely engineering protection.Social awareness and preparedness are equally important in the extreme risk mitigation.Accordingly a series of strategic measures may be worked out for the disaster reduction,which are different from that of normal safety design standard and mainly consist of non-engineering measures.In the progress of science and technology the human capability in reduction and management of extreme natural disaster should be much updated in the near future. A concept of Extreme Geo-Disaster and Risk is proposed in this paper.Extreme geo-disasters are considered to be geo-events of most low probability in the earth recent evolution.However,low probability of natural event does not mean that it will happen only in the far future,and it does not exclude that such geo-disasters may happen in relatively near future within our or next generations.Strong earthquake Ms 8.0 on 12th May, 2008 in Wenchuan,China,which caused large amount of fatalities and structure damage,showed the typical characteristics of an extreme natural disaster.It once again rang a tocsin to warning human society.It is a question,if human would forget it,when it passed and the terrible situation changed.Therefore,the author appeals that engineering geologists have to pay attention to and deal with such extreme disasters and risks.Scientific recognition of the level of natural dynamic forces responsible for extreme disaster provides an essential basis in the disaster prediction,and this should be one of the essential objectives of engineering geology.Regional study of geo-sphere dynamic processes may help in aiming at this purpose.To assess the potential risk an approach of impact area estimation is important and further analysis of relationship between the damaging effect and vulnerability damaged objects gives an assessed level of disaster risk.In the strategy of risk management a kind of precaution measure and warning should be focused instead of merely engineering protection.Social awareness and preparedness are equally important in the extreme risk mitigation.Accordingly a series of strategic measures may be worked out for the disaster reduction,which are different from that of normal safety design standard and mainly consist of non-engineering measures.In the progress of science and technology the human capability in reduction and management of extreme natural disaster should be much updated in the near future.
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The seismic geological context,morphology,formation mechanism and evolution of Wenjiagou high-speed and long-runout debris avalanche are introduced. The debris avalanche was located at Wenjiaogou syncline block between Yingxiu-Beichuan fault and Guanxian-Anxian fault of which severe activity provides precondition for the debris avalanche. It is 1360m high from the peak of debris avalanche source area to Wenjiagou valley mouth; seismic load shows remarkable amplification effect at the ridge due to the terrain of towering hill with deep valley at the foot,and directly results in the landslide. The peak values of ground motion acceleration in 3 directions in the ridge are aEW=2.4g,aNS=2.3g,aUP=1.2g(g: the acceleration of gravity). The Guanwushan formation(D2gn)limestone slope has layered structure with progressive strength. About 50m below the slope surface is loose structural Qel+dl~upper part of fresh rock,which is cut into initial landslide mass results from the tension-compression and shear coupling effect due to seismic P-wave and S-wave. The sliding mass shear out from edge of the 8th platform; the maximum traveling velocity of sliding mass is accelerated up to 93~122m s-1 in Wenjiagou valley upstream. Trapped air inside of the valley is compressed by upper part of landslide mass,the dry debris flow,at 2 turnings of Wenjiagou valley; distinct air cushion effect is generated. Besides,the bottom layer of debris flow is liquefied; effective dynamic friction coefficient is decreased with increasing of shearing velocity; all of these effects lead to the high-speed and long-runout traveling of debris flow. Simultaneously,the valley slope is scraped and crossed; the trees are cut as debris flow passes. After Wenchuan earthquake,up to Sept. 2009,rainfall has triggered several debris flows,which indicates the continuity and long-term nature of seismic geohazard. The seismic geological context,morphology,formation mechanism and evolution of Wenjiagou high-speed and long-runout debris avalanche are introduced. The debris avalanche was located at Wenjiaogou syncline block between Yingxiu-Beichuan fault and Guanxian-Anxian fault of which severe activity provides precondition for the debris avalanche. It is 1360m high from the peak of debris avalanche source area to Wenjiagou valley mouth; seismic load shows remarkable amplification effect at the ridge due to the terrain of towering hill with deep valley at the foot,and directly results in the landslide. The peak values of ground motion acceleration in 3 directions in the ridge are aEW=2.4g,aNS=2.3g,aUP=1.2g(g: the acceleration of gravity). The Guanwushan formation(D2gn)limestone slope has layered structure with progressive strength. About 50m below the slope surface is loose structural Qel+dl~upper part of fresh rock,which is cut into initial landslide mass results from the tension-compression and shear coupling effect due to seismic P-wave and S-wave. The sliding mass shear out from edge of the 8th platform; the maximum traveling velocity of sliding mass is accelerated up to 93~122m s-1 in Wenjiagou valley upstream. Trapped air inside of the valley is compressed by upper part of landslide mass,the dry debris flow,at 2 turnings of Wenjiagou valley; distinct air cushion effect is generated. Besides,the bottom layer of debris flow is liquefied; effective dynamic friction coefficient is decreased with increasing of shearing velocity; all of these effects lead to the high-speed and long-runout traveling of debris flow. Simultaneously,the valley slope is scraped and crossed; the trees are cut as debris flow passes. After Wenchuan earthquake,up to Sept. 2009,rainfall has triggered several debris flows,which indicates the continuity and long-term nature of seismic geohazard.
14
In recent years,the frequency of loess landslide occurrences has the trend of increasing.It is a basis of reducing the landslide hazard risk to investigate the triggering factors and forming mechanism of loess landslides.Field investigation for geological hazards on the Loess Plateau suggests that the induced factors of the loess landslides mainly include earthquakes,precipitations,frozen-thawing,river erosion and human engineering activities.Among them,precipitations and human activities are the most active agents to induce landslides.For the loess landslides triggered by earthquake,mass ejection,dust effect and loess liquefaction caused by seismic acceleration are the main reasons.For the landslides induced by river evolution,the triggering mechanism and failure mode are distinct in different river evolution stages,such as in the lateral and vertical river erosion stages.Whereas,the loess landslide mechanism types include water level raise due to frozen effect and loess strength decrease result from melting effect.The factors of precipitations can be classified as rainstorm and drizzle and of the ground water can be classified as locally concentrated groundwater with priory conducts,water level rising and density increasing.Those of human activities are slope cutting,irrigation,reservoir,and over-burdening.Based on the field investigation for various of loess landslides,the geological characters and triggering mechanism of the landslide triggering by different factors are discussed further in the paper. In recent years,the frequency of loess landslide occurrences has the trend of increasing.It is a basis of reducing the landslide hazard risk to investigate the triggering factors and forming mechanism of loess landslides.Field investigation for geological hazards on the Loess Plateau suggests that the induced factors of the loess landslides mainly include earthquakes,precipitations,frozen-thawing,river erosion and human engineering activities.Among them,precipitations and human activities are the most active agents to induce landslides.For the loess landslides triggered by earthquake,mass ejection,dust effect and loess liquefaction caused by seismic acceleration are the main reasons.For the landslides induced by river evolution,the triggering mechanism and failure mode are distinct in different river evolution stages,such as in the lateral and vertical river erosion stages.Whereas,the loess landslide mechanism types include water level raise due to frozen effect and loess strength decrease result from melting effect.The factors of precipitations can be classified as rainstorm and drizzle and of the ground water can be classified as locally concentrated groundwater with priory conducts,water level rising and density increasing.Those of human activities are slope cutting,irrigation,reservoir,and over-burdening.Based on the field investigation for various of loess landslides,the geological characters and triggering mechanism of the landslide triggering by different factors are discussed further in the paper.
15
Due to its unusually strong seismic shaking,the5 12Wenchuan Earthquake in 2008 induced hundreds of large-scale landslides.This paper is based on the interpreted data about 112 landslides,each of which has a plane area greater than 50000m2. It also uses the field investigation of representative large-scale landslides. It further conducts a systematic analysis on the distribution regularities of these large-scale landslides. It is suggested that the large-scale landslides not only show the distribution rules similar to those associated with the general landslides induced by Wenchuan Earthquake,but also present unique features in the distribution as well as sliding and moving ways. The occurrences of the large-scale landslides are usually attributed to the direct seismic forces resulting from the horizontal displacements of seismic faults. The distribution rules of large-scale landslides induced by Wenchuan Earthquake can be summarized as follows: (1)distance effect: about 80% large-scale landslides are distributed within the range of 5km from the Yinxiu-Beichuan fault(i.e. ,seismic fault ruptures). The farther the distance is,the lower the number of landslides is. (2) Locked segment effect: the large-scale landslides are mainly distributed in the five concentration zones closely related with the crossing,staggering and transforming section as well as the end of NE section of the seismic fault. The most concentrated zone is Hongbai-Chaping segment,where many large-scale landslides and the two largest landslides were induced by Wenchuan Earthquake. The second concentrated zone is Nanba-Donghekou segment at the NE end of the seismic fault,where the well-known Donghekou Landslide and Woqian Landslide are located. (3)Hanging wall effect: a vast majority of large-scale landslides (70%) are located in the hanging wall of the seismic fault,showing a clearHanging wall effect. (4)Direction effect: in the valley slopes almost perpendicular to the seismic fault,the number of large scale landslides at the slopes opposing the direction of seismic source are obviously higher than those facing the direction of seismic source,showingback slope effect.Meanwhile,the sliding and moving directions of large-scale landslides have some relations with the staggering direction of the seismic fault in each section.In Qingchuan area where the main fault activity was horizontal twisting and staggering,a considerable number of large scale landslides show the features of sliding and moving along the NE direction that was the staggering direction of the seismic fault. Due to its unusually strong seismic shaking,the5 12Wenchuan Earthquake in 2008 induced hundreds of large-scale landslides.This paper is based on the interpreted data about 112 landslides,each of which has a plane area greater than 50000m2. It also uses the field investigation of representative large-scale landslides. It further conducts a systematic analysis on the distribution regularities of these large-scale landslides. It is suggested that the large-scale landslides not only show the distribution rules similar to those associated with the general landslides induced by Wenchuan Earthquake,but also present unique features in the distribution as well as sliding and moving ways. The occurrences of the large-scale landslides are usually attributed to the direct seismic forces resulting from the horizontal displacements of seismic faults. The distribution rules of large-scale landslides induced by Wenchuan Earthquake can be summarized as follows: (1)distance effect: about 80% large-scale landslides are distributed within the range of 5km from the Yinxiu-Beichuan fault(i.e. ,seismic fault ruptures). The farther the distance is,the lower the number of landslides is. (2) Locked segment effect: the large-scale landslides are mainly distributed in the five concentration zones closely related with the crossing,staggering and transforming section as well as the end of NE section of the seismic fault. The most concentrated zone is Hongbai-Chaping segment,where many large-scale landslides and the two largest landslides were induced by Wenchuan Earthquake. The second concentrated zone is Nanba-Donghekou segment at the NE end of the seismic fault,where the well-known Donghekou Landslide and Woqian Landslide are located. (3)Hanging wall effect: a vast majority of large-scale landslides (70%) are located in the hanging wall of the seismic fault,showing a clearHanging wall effect. (4)Direction effect: in the valley slopes almost perpendicular to the seismic fault,the number of large scale landslides at the slopes opposing the direction of seismic source are obviously higher than those facing the direction of seismic source,showingback slope effect.Meanwhile,the sliding and moving directions of large-scale landslides have some relations with the staggering direction of the seismic fault in each section.In Qingchuan area where the main fault activity was horizontal twisting and staggering,a considerable number of large scale landslides show the features of sliding and moving along the NE direction that was the staggering direction of the seismic fault.
16
The rock mass forming the dam foundation of Xiao Wan hydroelectric station during excavation revealed a series of deformation and fracture phenomena. It mainly behaved as a split plate and surface rock bursts, and cracks along the existing structure, expansion and dislocation, and so on. On the basis of the analyses of the above-mentioned phenomena, this paper studies the geological mechanic response of the rock mass due to the dam foundation excavation in the high in-situ stress environment. It is found that the rock mass deformation during excavation is mainly concentrated on the shallow surface of the dam foundation, which has time effect characteristics. According to analyses of deformation-destruction phenomenon and the study of deformation responses, the mechanism of deformation-destruction is understood. The mechanism applies to the excavation of the hard rock river bed of the dam foundation in the high in-situ stress environment. Shallow and superficial transformation result from the stress redistributed during down-cutting of river and unloading of excavation. Ultimately, it can be summarized that the deformation and fracture of river bed are a pressure rupture-unloading rebound model, and the pressure-rupture is the main type. The rock mass forming the dam foundation of Xiao Wan hydroelectric station during excavation revealed a series of deformation and fracture phenomena. It mainly behaved as a split plate and surface rock bursts, and cracks along the existing structure, expansion and dislocation, and so on. On the basis of the analyses of the above-mentioned phenomena, this paper studies the geological mechanic response of the rock mass due to the dam foundation excavation in the high in-situ stress environment. It is found that the rock mass deformation during excavation is mainly concentrated on the shallow surface of the dam foundation, which has time effect characteristics. According to analyses of deformation-destruction phenomenon and the study of deformation responses, the mechanism of deformation-destruction is understood. The mechanism applies to the excavation of the hard rock river bed of the dam foundation in the high in-situ stress environment. Shallow and superficial transformation result from the stress redistributed during down-cutting of river and unloading of excavation. Ultimately, it can be summarized that the deformation and fracture of river bed are a pressure rupture-unloading rebound model, and the pressure-rupture is the main type.
17
Digitalmodeling of comp lex three - dimensional geological body is always a difficulty in p re - p rocessing of FLAC3D. Therefore, a new modelingmethod is put forward in this paper. The three - dimensional geological information of ground surface and strata interfaces are extracted and transformed in the Surfer software. Using Surfer as a transitional p latform, the information can be exported from Surfer and then is retransformed by p rogram made by Fish language embedded in FLAC3D. According to above p rocess, the model data for FLAC3D is generated and comp lex three - dimensional geologicalmodel can be created quickly and accurately in p re - p rocessing of FLAC3D. The feasibility and simulating effect of the method is verified by combining p ractical p roject. The result shows that the modeling method is simp le, p ractical and with bettermaneuverability. Thereby the method is a new, good approach in pre - processing of FLAC3D. Digitalmodeling of comp lex three - dimensional geological body is always a difficulty in p re - p rocessing of FLAC3D. Therefore, a new modelingmethod is put forward in this paper. The three - dimensional geological information of ground surface and strata interfaces are extracted and transformed in the Surfer software. Using Surfer as a transitional p latform, the information can be exported from Surfer and then is retransformed by p rogram made by Fish language embedded in FLAC3D. According to above p rocess, the model data for FLAC3D is generated and comp lex three - dimensional geologicalmodel can be created quickly and accurately in p re - p rocessing of FLAC3D. The feasibility and simulating effect of the method is verified by combining p ractical p roject. The result shows that the modeling method is simp le, p ractical and with bettermaneuverability. Thereby the method is a new, good approach in pre - processing of FLAC3D.
18
Wenjia gully is located at the epicenter area of the 2008 Wenchuan Earthquake.A huge landslide was ever triggered by the earthquake.During the passed three flood seasons,at least five typical debris flows occurred at Wenjia gully.In particular,a severest debris flow occurred on Aug.13, 2010. It had a volume up to 3.1107m3.Five residents lost their lives unfortunately and hundreds of new-built houses were buried during the catastrophic event.However,it was fortunate that almost all the residents evacuated successfully before the debris flow occurred.In this paper,on the basis of tracking investigation,the mechanism and characteristics of the Wenjia-gully debris flows were discussed and some suggestions were put forward.The acknowledges obtained after investigation and analysis are as follows: (1)The debris flows were caused by both Wenchuan earthquake and strong rainfall.As the debris flow formation is concerned,a circle was presented as runoff-erosion-collapse-engulfment-erosion-collapse-enlargement-,and so on; (2)The critical rainfall initiated debris flow was significantly decreased and a power-law relation is existed between debris flow magnitude and daily rainfall,which can be used to predict the volume of debris flow on the basis of weather forecasting; (3)As the occurrence process is concerned,the debris flow lasted for a long duration and moved a far distance; (4)In terms of destroying process,a clear chain characteristic was taken on with several damage ways; (5)Debris flow magnitude was enlarged and the frequency was higher obviously. Wenjia gully is located at the epicenter area of the 2008 Wenchuan Earthquake.A huge landslide was ever triggered by the earthquake.During the passed three flood seasons,at least five typical debris flows occurred at Wenjia gully.In particular,a severest debris flow occurred on Aug.13, 2010. It had a volume up to 3.1107m3.Five residents lost their lives unfortunately and hundreds of new-built houses were buried during the catastrophic event.However,it was fortunate that almost all the residents evacuated successfully before the debris flow occurred.In this paper,on the basis of tracking investigation,the mechanism and characteristics of the Wenjia-gully debris flows were discussed and some suggestions were put forward.The acknowledges obtained after investigation and analysis are as follows: (1)The debris flows were caused by both Wenchuan earthquake and strong rainfall.As the debris flow formation is concerned,a circle was presented as runoff-erosion-collapse-engulfment-erosion-collapse-enlargement-,and so on; (2)The critical rainfall initiated debris flow was significantly decreased and a power-law relation is existed between debris flow magnitude and daily rainfall,which can be used to predict the volume of debris flow on the basis of weather forecasting; (3)As the occurrence process is concerned,the debris flow lasted for a long duration and moved a far distance; (4)In terms of destroying process,a clear chain characteristic was taken on with several damage ways; (5)Debris flow magnitude was enlarged and the frequency was higher obviously.
19
At 14:28(Beijing time)of May 12, 2008,a catastrophic earthquake with surface wave magnitude of 80 struck Sichuan province of China. Tens of thousands of landslides were triggered by this earthquake over a broad area. A total of 48007 landslides were interpreted from aerial photographs and multisource remote sensing imageries,verified by field check. A spatial database,including landslides and associated controlling parameters which may have influence on the occurrence of landslides,was developed and analyzed using geographical information system(GIS)technology. The eight factors that influence landslide occurrence,including seismic intensity,lithology,slope angle,faults,elevation,slope aspect,drainages and roads were created in raster data format base on GIS platform. The landslide susceptibility index of all ranks in each impact factor was calculated,using the certainty factor analysis method. Earthquakeinduced landslide susceptibility areas of 16 impact factor combination categories were analyzed and mapped one after another,using the GIS raster analysis methods. The susceptibility result of the highest AUC(Area Under Curve)was used to create susceptibility map by using Natural Breaks law. The resulting susceptibility map showed five classes of landslide susceptibility,ie.〖KG-*5〗,extremely high,high,moderate,low,and extremely low. The validation results showed satisfactory agreement between the susceptibility map and the existing data on landslide distributions. The area with extremely high and high susceptibility accounts for about 1169046 km2, 2402% of the study area,includes landslide areas of 52484 km2, 7373% of all landslide areas. The susceptibility success accuracy was up to 82107% in the form of AUC. At 14:28(Beijing time)of May 12, 2008,a catastrophic earthquake with surface wave magnitude of 80 struck Sichuan province of China. Tens of thousands of landslides were triggered by this earthquake over a broad area. A total of 48007 landslides were interpreted from aerial photographs and multisource remote sensing imageries,verified by field check. A spatial database,including landslides and associated controlling parameters which may have influence on the occurrence of landslides,was developed and analyzed using geographical information system(GIS)technology. The eight factors that influence landslide occurrence,including seismic intensity,lithology,slope angle,faults,elevation,slope aspect,drainages and roads were created in raster data format base on GIS platform. The landslide susceptibility index of all ranks in each impact factor was calculated,using the certainty factor analysis method. Earthquakeinduced landslide susceptibility areas of 16 impact factor combination categories were analyzed and mapped one after another,using the GIS raster analysis methods. The susceptibility result of the highest AUC(Area Under Curve)was used to create susceptibility map by using Natural Breaks law. The resulting susceptibility map showed five classes of landslide susceptibility,ie.〖KG-*5〗,extremely high,high,moderate,low,and extremely low. The validation results showed satisfactory agreement between the susceptibility map and the existing data on landslide distributions. The area with extremely high and high susceptibility accounts for about 1169046 km2, 2402% of the study area,includes landslide areas of 52484 km2, 7373% of all landslide areas. The susceptibility success accuracy was up to 82107% in the form of AUC.
20
Abstract The Donghekou landslide-debris flow is a typical rapid long run-out landslide triggered by the great Wenchuan earthquake. It started from the elevation of 1300m and caused 780 deaths, with a total long run-out of 2400m. Field investigations show that, during the sliding process from start-up to stop, this landslide-debris flow experienced the following five dynamical stages, such as the starting-up stage, the gravity speed-up stage, the enclosure air cushion effect stage, the impact reentry stage and the long run-out sliding accumulation stage. Finally, it reached the Honghuadi village, which is located at the left bank of the Xiasihe River, and the dammed lakes occurred. By analyzing the geological setting and feature of this landslide-debris flow, we can draw a conclusion that the initiation of Donghekou landslide-debris flow is mainly affected by the fault crush belt, the local convex landform and the phyllite and carbon slate with weak mechanical property; for the rapid and long run-out sliding of this landslide-debris flow, the water containing condition of the slope debris on sliding route is an important factor besides the advantage landform. Abstract The Donghekou landslide-debris flow is a typical rapid long run-out landslide triggered by the great Wenchuan earthquake. It started from the elevation of 1300m and caused 780 deaths, with a total long run-out of 2400m. Field investigations show that, during the sliding process from start-up to stop, this landslide-debris flow experienced the following five dynamical stages, such as the starting-up stage, the gravity speed-up stage, the enclosure air cushion effect stage, the impact reentry stage and the long run-out sliding accumulation stage. Finally, it reached the Honghuadi village, which is located at the left bank of the Xiasihe River, and the dammed lakes occurred. By analyzing the geological setting and feature of this landslide-debris flow, we can draw a conclusion that the initiation of Donghekou landslide-debris flow is mainly affected by the fault crush belt, the local convex landform and the phyllite and carbon slate with weak mechanical property; for the rapid and long run-out sliding of this landslide-debris flow, the water containing condition of the slope debris on sliding route is an important factor besides the advantage landform.
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