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Editor Work2008 Vol. 16, No. 2
Previous Issue
2008, 16(2): 145-154.
Abstract
The geological phenomenon of rock-mass unloading and its engineering geological problems during the hydroelectric project construction are discussion in this paper. The discussion is based on the engineering practices of many high dam construction projects in the mountainous area of south-west China over last 40 years. The process of cognitive on the rock-mass unloading geological phenomena and engineering practice experience in the engineering geology area of this country are introducing briefly. A systematic rock mass relaxed zone according to the mechanistic mechanism types of unloading fissures is suggested. The relaxed fissures and depth unloading zone can be discovered behind the normal unloading zone. This zone is named as a depth fissures and depth relaxed zone. It is also discussed on the basis of a series typical examples. A mechanistic mechanism model for the depth fissures and depth relaxed zone is suggested. Some practice problems of hydroelectric project construction in connection with rock-mass unloading are discussed too.
The geological phenomenon of rock-mass unloading and its engineering geological problems during the hydroelectric project construction are discussion in this paper. The discussion is based on the engineering practices of many high dam construction projects in the mountainous area of south-west China over last 40 years. The process of cognitive on the rock-mass unloading geological phenomena and engineering practice experience in the engineering geology area of this country are introducing briefly. A systematic rock mass relaxed zone according to the mechanistic mechanism types of unloading fissures is suggested. The relaxed fissures and depth unloading zone can be discovered behind the normal unloading zone. This zone is named as a depth fissures and depth relaxed zone. It is also discussed on the basis of a series typical examples. A mechanistic mechanism model for the depth fissures and depth relaxed zone is suggested. Some practice problems of hydroelectric project construction in connection with rock-mass unloading are discussed too.
2008, 16(2): 155-161.
The Daliushu Dam Site in the Heishanxia Gorge of the Yellow River is seated in the middle of Zhongwei-Tongxin active fault zone. It is apart 1.5 km from the seismogenic fault F201. The results of statistics indicated that the rupturing effects such as branch fractures and secondary fractures will be appeared around the adjacent 3~5 km area from seismogenic fault, if the Ms7.0 Earthquakes happen in the Qinghai-Xizang plateau and its margins. The Daliushu Dam Site is located in the zone of branch fracture occurrence when Ms7.0 Earthquakes happen., So, engineering rupturing effects will be in existence. Result of 3-D finite element analysis indicates that the dislocation ratio of the faults F93, F39, and F40 relative to the fault F201 arrives at 14.38%、12.0% and 9.84% respectively, when the rupturing effects of fault F201 happen.
The Daliushu Dam Site in the Heishanxia Gorge of the Yellow River is seated in the middle of Zhongwei-Tongxin active fault zone. It is apart 1.5 km from the seismogenic fault F201. The results of statistics indicated that the rupturing effects such as branch fractures and secondary fractures will be appeared around the adjacent 3~5 km area from seismogenic fault, if the Ms7.0 Earthquakes happen in the Qinghai-Xizang plateau and its margins. The Daliushu Dam Site is located in the zone of branch fracture occurrence when Ms7.0 Earthquakes happen., So, engineering rupturing effects will be in existence. Result of 3-D finite element analysis indicates that the dislocation ratio of the faults F93, F39, and F40 relative to the fault F201 arrives at 14.38%、12.0% and 9.84% respectively, when the rupturing effects of fault F201 happen.
2008, 16(2): 162-168.
This paper has systematicly managed and analysized the in-situ crustal stress measurements around the Ⅱ1~Ⅱ1 section at the dam site of Jinping first stage hydropower station. The results show that the geo-stress magnitudes at the right abutment slope foot are bigger than the ones at the left abutment slope foot at nearly same horizontal and vertical burying depths, which is controlled by rock mass constitution, and that the collapse engineering geology problem in the process of left abutment slope water diversion tunnelling at this crustal stress conditions is also related to the left abutment slope rock mass constitution, but not caused by rockbursts and so on. In addition, on the basis of all existed research achievements on deep fractures in the left abutment slope, a new model from geo-stress and strain energy enconcentrations is given to explain the deep fissures, and some suggestions on the possible engineering geology issues from rock mass constitution and geo-stress magnitudes are also given to pay much attention on the both abutment slopes in the hydropower station construction.
This paper has systematicly managed and analysized the in-situ crustal stress measurements around the Ⅱ1~Ⅱ1 section at the dam site of Jinping first stage hydropower station. The results show that the geo-stress magnitudes at the right abutment slope foot are bigger than the ones at the left abutment slope foot at nearly same horizontal and vertical burying depths, which is controlled by rock mass constitution, and that the collapse engineering geology problem in the process of left abutment slope water diversion tunnelling at this crustal stress conditions is also related to the left abutment slope rock mass constitution, but not caused by rockbursts and so on. In addition, on the basis of all existed research achievements on deep fractures in the left abutment slope, a new model from geo-stress and strain energy enconcentrations is given to explain the deep fissures, and some suggestions on the possible engineering geology issues from rock mass constitution and geo-stress magnitudes are also given to pay much attention on the both abutment slopes in the hydropower station construction.
2008, 16(2): 169-172.
Boring hole data showed that there was a deep overlay and an associated unloading and relaxation zone in the valley bottom of a hydroelectric station in southwestern China. The deep overlay could be vertically divided into three layers. The upper and lower parts were normal river faces, while the middle part was a sequence of aggradation of multi-genesis deposits. The rock mass in the valley bottom was relaxed on structure, bad integrality, splay cranny and fill with clay, weathering badly in the faces of cranny. Study on the relaxation zone in the base of river valley showed that when the river cut adown, it caused stress concentration and led to shearing failure. After far-flung unloading rebound and weathering, the rock mass in the valley bottom formed certain thickness of relaxation zone.
Boring hole data showed that there was a deep overlay and an associated unloading and relaxation zone in the valley bottom of a hydroelectric station in southwestern China. The deep overlay could be vertically divided into three layers. The upper and lower parts were normal river faces, while the middle part was a sequence of aggradation of multi-genesis deposits. The rock mass in the valley bottom was relaxed on structure, bad integrality, splay cranny and fill with clay, weathering badly in the faces of cranny. Study on the relaxation zone in the base of river valley showed that when the river cut adown, it caused stress concentration and led to shearing failure. After far-flung unloading rebound and weathering, the rock mass in the valley bottom formed certain thickness of relaxation zone.
2008, 16(2): 173-177.
The landslide, which is one of typical geological disasters, triggered by various factors. The Kangjiazui Landslide in the Three Gorges reservoir area formed in front of the alluvial fan in the old landslide debris flow and for the new sliding deformation. It has a Quaternary soil layer on the surface of the landslide mass. The sliding zone is celadon silty clay or clay. They had creep deformation after becoming saturation under the periodical soak of rainfall and the Three Gorges reservoir area sluice. The landslide was in the state of destabilization to limit stabilization and desiderated to prevent and cure. This paper gives a detailed description of the breakage process, appearances and the deduction process to take back into trace. The investigation clearly showed the landslide geological condition and the developing trend. It was analyzed the economy and advanced different deformation stages with targeted prevention programs. The preventive measures uses slide-resistant piles, drain ditch, and backfilling consolidation in partial of new landslide mass (strong deformation zone) and in the back of the landslide mass. The measures were slide-resistant piles and drain ditch. The calculation showed that it was in stable state. It also has some references to deal with some similar geological disasters.
The landslide, which is one of typical geological disasters, triggered by various factors. The Kangjiazui Landslide in the Three Gorges reservoir area formed in front of the alluvial fan in the old landslide debris flow and for the new sliding deformation. It has a Quaternary soil layer on the surface of the landslide mass. The sliding zone is celadon silty clay or clay. They had creep deformation after becoming saturation under the periodical soak of rainfall and the Three Gorges reservoir area sluice. The landslide was in the state of destabilization to limit stabilization and desiderated to prevent and cure. This paper gives a detailed description of the breakage process, appearances and the deduction process to take back into trace. The investigation clearly showed the landslide geological condition and the developing trend. It was analyzed the economy and advanced different deformation stages with targeted prevention programs. The preventive measures uses slide-resistant piles, drain ditch, and backfilling consolidation in partial of new landslide mass (strong deformation zone) and in the back of the landslide mass. The measures were slide-resistant piles and drain ditch. The calculation showed that it was in stable state. It also has some references to deal with some similar geological disasters.
2008, 16(2): 178-183.
Fracture of rock mass is quite important and exists broadly in geotechnical engineering such as slope ,underground and foundation construction. It is got more and more regarded by engineers. The stability of slope and rock mass bearing capacity of building foundation are influenced by seepage in the mass. A variety of methods for analyzing seepage flow in fractured rock mass are introduced and discussed in brief. These analyses provide references for the selection of proper mathematical models to solve specific seepage flow in fractured rock masses. Some problems are put forward which need to be further investigated. The equivalent continuum model at present is widely used. However, the fractured rock mass geometry parameter and efficiency hole degree and coefficient of permeability are still awaiting to be examined furthermore. Micromechanics coupled with seepage model would have great theorical value.
Fracture of rock mass is quite important and exists broadly in geotechnical engineering such as slope ,underground and foundation construction. It is got more and more regarded by engineers. The stability of slope and rock mass bearing capacity of building foundation are influenced by seepage in the mass. A variety of methods for analyzing seepage flow in fractured rock mass are introduced and discussed in brief. These analyses provide references for the selection of proper mathematical models to solve specific seepage flow in fractured rock masses. Some problems are put forward which need to be further investigated. The equivalent continuum model at present is widely used. However, the fractured rock mass geometry parameter and efficiency hole degree and coefficient of permeability are still awaiting to be examined furthermore. Micromechanics coupled with seepage model would have great theorical value.
2008, 16(2): 184-188.
The earthquake-induced soil liquefaction can result in serious damages to pile foundations. Therefore, it is an important task to study the failure mechanisms of pile foundations in liquefaction soils in earthquake geotechnical engineering. Until now, the seismic behaviors of pile-soil-structure systems have not been fully understood yet. Most of current researchers are focused on strength failure of pile material, in which it is difficult to consider complex influencing factors such as lateral spreading of liquefying soils, pile buckling, and dynamic interaction between soil and structures. In this paper, firstly, a series of damage cases of pile foundations in liquefied soils are summarized from historical reports in Chian and abroad. Then, the failure mechanisms of pile foundations as well as research advances are introduced and analyzed in detail. Finally, aimed at liquefaction soils, it is pointed out that further investigations on the failure mechanisms of pile foundations should be strengthened on the following issues (1) pile buckling instability in liquefying soils; (2) novel numerical simulation methods for pile failures in liquefaction soils, e.g. continuum elasoplasticity-fluid dynamics coupled method; and (3) dynamic interaction analyses of pile-soil-structure systems in liquefaction soils.
The earthquake-induced soil liquefaction can result in serious damages to pile foundations. Therefore, it is an important task to study the failure mechanisms of pile foundations in liquefaction soils in earthquake geotechnical engineering. Until now, the seismic behaviors of pile-soil-structure systems have not been fully understood yet. Most of current researchers are focused on strength failure of pile material, in which it is difficult to consider complex influencing factors such as lateral spreading of liquefying soils, pile buckling, and dynamic interaction between soil and structures. In this paper, firstly, a series of damage cases of pile foundations in liquefied soils are summarized from historical reports in Chian and abroad. Then, the failure mechanisms of pile foundations as well as research advances are introduced and analyzed in detail. Finally, aimed at liquefaction soils, it is pointed out that further investigations on the failure mechanisms of pile foundations should be strengthened on the following issues (1) pile buckling instability in liquefying soils; (2) novel numerical simulation methods for pile failures in liquefaction soils, e.g. continuum elasoplasticity-fluid dynamics coupled method; and (3) dynamic interaction analyses of pile-soil-structure systems in liquefaction soils.
2008, 16(2): 190-195.
It is noted that the loadings on slope retaining structures are calculated with the conventional earth pressure theory. The paper analyzes the limitations associated with the current method in the determination of loadings on slope retaining structures and puts forward a stability based method to determine the loadings on slope retaining structures . This proposed method can remedy the limitations of the conventional earth pressure theory.
It is noted that the loadings on slope retaining structures are calculated with the conventional earth pressure theory. The paper analyzes the limitations associated with the current method in the determination of loadings on slope retaining structures and puts forward a stability based method to determine the loadings on slope retaining structures . This proposed method can remedy the limitations of the conventional earth pressure theory.
2008, 16(2): 196-200.
Joint Roughness Coefficient (JRC ) is an equivalent index which describes mechanical effect of rock joint surface angle of ascent. This paper investigates the geometrical characters of Barton's straight edge method and derives a concise formula for JRC from the Barton's straight edge method. t The paper further tests the rationality and availability of JRC modified straight edge with practical example.
Joint Roughness Coefficient (JRC ) is an equivalent index which describes mechanical effect of rock joint surface angle of ascent. This paper investigates the geometrical characters of Barton's straight edge method and derives a concise formula for JRC from the Barton's straight edge method. t The paper further tests the rationality and availability of JRC modified straight edge with practical example.
2008, 16(2): 201-205.
It is analysed the mechanism of ground fissure in Heibei plain. From the Fig of Normalized Z index time series of rainy season in North China, one can get that the rain is corresponding earth fissure. It is founded that ground fissure is closely contacted with the change of groundwater. When the connection rigidity reduces, the structure loses its steadily. These changes occur and complete in instantaneous, and there is always following the appearance of earth fissure.
It is analysed the mechanism of ground fissure in Heibei plain. From the Fig of Normalized Z index time series of rainy season in North China, one can get that the rain is corresponding earth fissure. It is founded that ground fissure is closely contacted with the change of groundwater. When the connection rigidity reduces, the structure loses its steadily. These changes occur and complete in instantaneous, and there is always following the appearance of earth fissure.
2008, 16(2): 206-210.
Because of the complex mechanism of active faults and their scrambling spread, it is difficult to evaluate the activity of fault system and get satisfied results by traditional methods. Using the theory of fractal can quantitatively analyze and evaluate the fault systems. The fractal dimension of a faults system shows the number of faults in a system, the size of the fault system, the combination mode of the fault system and the dynamics mechanism of the system. So, the fractal dimension can indicate the active and complex grade of a fault system. This paper uses fractal to analyze the faults in Hebei Plain. It gets the fractal dimension of the NNE faults is 1.358. The fractal dimension of the direction of latitude is 1.183. The high fractal dimension is consistent with many existing earthquakes and geological hazards occurred in the plain. At last, the paper analyzes and compares the earthquakes and fractal in the three zones: Hebei plain, Weihe basin and Chuandian zone. It is found that for the relationship between the earthquake spatial distribution and the fractal dimension, the fractal dimension in Hebei plain is the least one, and the earthquake zone is distributed along the NNE in Hebei plain.
Because of the complex mechanism of active faults and their scrambling spread, it is difficult to evaluate the activity of fault system and get satisfied results by traditional methods. Using the theory of fractal can quantitatively analyze and evaluate the fault systems. The fractal dimension of a faults system shows the number of faults in a system, the size of the fault system, the combination mode of the fault system and the dynamics mechanism of the system. So, the fractal dimension can indicate the active and complex grade of a fault system. This paper uses fractal to analyze the faults in Hebei Plain. It gets the fractal dimension of the NNE faults is 1.358. The fractal dimension of the direction of latitude is 1.183. The high fractal dimension is consistent with many existing earthquakes and geological hazards occurred in the plain. At last, the paper analyzes and compares the earthquakes and fractal in the three zones: Hebei plain, Weihe basin and Chuandian zone. It is found that for the relationship between the earthquake spatial distribution and the fractal dimension, the fractal dimension in Hebei plain is the least one, and the earthquake zone is distributed along the NNE in Hebei plain.
2008, 16(2): 211-215.
A characteristic of the surrounding rock deformation in tunneling is its tempo-spatial effect. According to the velocity, the deformation process can be generally divided into three phases, namely rapid deformation phase, steady deformation phase and rheologic phase. Based on the summary of the three phase classification about surrounding rock deformation, this paper focuses on both spatial and time effects of surrounding rock deformation, according to the field data which measured at the D-5H measuring section in Zhongliangshan tunnel. Spatial effect mainly acted in the first phase, resisted mainly by surrounding rock and primary lining. The time effect mainly acted in the third phase. Furthermore, the relationships among tempo-spatial effects and surrounding rock class and cave-in accidents are analyzed. The results show that more than 80% cave-ins happened in the first phase, 13% in the second, only about 7% in the third. Cave-in may happen in all the three phases in class Ⅳ and Ⅴ surrounding rock tunnel. For class Ⅲ, there were a few in rheologic phase. Nearly no cave-in happened in the classⅠandⅡsurrounding rock sections. It is significant for comprehending the law of surrounding rock deformation in detail, and is propitious to prevent and cure the tunnel hazards.
A characteristic of the surrounding rock deformation in tunneling is its tempo-spatial effect. According to the velocity, the deformation process can be generally divided into three phases, namely rapid deformation phase, steady deformation phase and rheologic phase. Based on the summary of the three phase classification about surrounding rock deformation, this paper focuses on both spatial and time effects of surrounding rock deformation, according to the field data which measured at the D-5H measuring section in Zhongliangshan tunnel. Spatial effect mainly acted in the first phase, resisted mainly by surrounding rock and primary lining. The time effect mainly acted in the third phase. Furthermore, the relationships among tempo-spatial effects and surrounding rock class and cave-in accidents are analyzed. The results show that more than 80% cave-ins happened in the first phase, 13% in the second, only about 7% in the third. Cave-in may happen in all the three phases in class Ⅳ and Ⅴ surrounding rock tunnel. For class Ⅲ, there were a few in rheologic phase. Nearly no cave-in happened in the classⅠandⅡsurrounding rock sections. It is significant for comprehending the law of surrounding rock deformation in detail, and is propitious to prevent and cure the tunnel hazards.
2008, 16(2): 216-221.
From August 7 to 9, 2005, a storm tide took place in Diaokou area of the Yellow River estuary as a result of the typhoon matsa. During the same period, field observation on the formation of sediment vertical transporting was carried out on tidal flat. Combining the observation result with the analysis of grain-sizes, a conclusion is drawn that some sediments of fine grain size had transported vertically to the tide flat surface under the loading of storm waves, and the exported sediments mainly consists of very fine silty grains. Furthermore, with the data of pore water pressure measured in-situ, an analysis of this phenomemen has been made on the foundation of the theory of sea bed dynamic response to wave loading.
From August 7 to 9, 2005, a storm tide took place in Diaokou area of the Yellow River estuary as a result of the typhoon matsa. During the same period, field observation on the formation of sediment vertical transporting was carried out on tidal flat. Combining the observation result with the analysis of grain-sizes, a conclusion is drawn that some sediments of fine grain size had transported vertically to the tide flat surface under the loading of storm waves, and the exported sediments mainly consists of very fine silty grains. Furthermore, with the data of pore water pressure measured in-situ, an analysis of this phenomemen has been made on the foundation of the theory of sea bed dynamic response to wave loading.
2008, 16(2): 222-228.
There is a great area of loses along the Yili trunk ditch in Xinjiang province. The collapsibility of the losses with water has a great impact to construction in the region. On the basis of many tests, a detailed analysis about the grade, the initial pressure and the depth of loess collapaibilty, and the degree of loess collapaibilty along the ditch built by excavating is given in this paper. A deep analysis is also made to the collapaibilty along the ditch built by piling considering the unsaturation of loess. It reveals the grade of collapssility is Ⅰ～Ⅱ and belongs to the non-self-weight collapse loess in the field along the ditch and the loess would lose collapssility after being compacted. It is also found that the loess would lose its collapssility only by permutation and drainage. Other measures are not needed to remove the loess collapssility.
There is a great area of loses along the Yili trunk ditch in Xinjiang province. The collapsibility of the losses with water has a great impact to construction in the region. On the basis of many tests, a detailed analysis about the grade, the initial pressure and the depth of loess collapaibilty, and the degree of loess collapaibilty along the ditch built by excavating is given in this paper. A deep analysis is also made to the collapaibilty along the ditch built by piling considering the unsaturation of loess. It reveals the grade of collapssility is Ⅰ～Ⅱ and belongs to the non-self-weight collapse loess in the field along the ditch and the loess would lose collapssility after being compacted. It is also found that the loess would lose its collapssility only by permutation and drainage. Other measures are not needed to remove the loess collapssility.
2008, 16(2): 228-232.
The soft soil in Xuyi area has a very complicated origin and very special mineral compositions . The engineering geological property of this soft soil has been examined with the experimental tests including mineral compositions, chemical compositions, particle analysis, physical properties, expansive properties and compressibility in this paper. It's concluded that the soft soil with high clay content, better hydrophilicity, high liquid-plastic limit and high organic content. It cann't be filled for highway foundation directly. It's easy to be caky rolled in high water content and hard to be broken in little water content. So the result is not remarkable mingled with lime traditionally. It's a specific soft soil.
The soft soil in Xuyi area has a very complicated origin and very special mineral compositions . The engineering geological property of this soft soil has been examined with the experimental tests including mineral compositions, chemical compositions, particle analysis, physical properties, expansive properties and compressibility in this paper. It's concluded that the soft soil with high clay content, better hydrophilicity, high liquid-plastic limit and high organic content. It cann't be filled for highway foundation directly. It's easy to be caky rolled in high water content and hard to be broken in little water content. So the result is not remarkable mingled with lime traditionally. It's a specific soft soil.
2008, 16(2): 233-238.
Subgrade freeze-thawing injury is an important problem that has puzzled many engineers in the seasonal frost regions of northeast China such as the cit of Chang-chun. In winter. weather in Chang-chun is very frigidity. Water in subgrade is moving and assembling in some positions under gradient of ground temperature So, subgrade is frost heave. In spring, subgrade and ice lenses which assembled in some positions begin thawing. The subgrade soil is in saturation or over saturation states. The bearing capacity is very low. Under the action of traffic vehicles, bulges, elastic springs, fractures and soil boiling can appear on pavement, which give very bad injuries to communication, transportation, and economic construction. It is urgent and necessary to research every influencing factor that affects frost heave. Pores as one of important symbols of soil structure are main entryways of water movement in soil. They decide sensibility of frost heave of the soil. In the paper, the WD-5 SEM is used to collect microstructure photos of soils from three different locations nearby Chang-chun. The photos are further used to make quantitative analysis to microstructure of pores in soil. An image quantitative analysis system is used. The quantitative analysis results in the finding that microscopic pore diameters of three samples are mainly about 5 m. This pore size makes soils have property of frost heave. There aren't noticeable difference of microcosmic pores between vertical and horizontal sections from a same sample. There are radial or reticular structure of pores, and shapes of oblate or equiaxial. The analysis further leads to the finding that when pore shape fractal dimensions are higher, there are many big pores, and the pore distribution is simple. The research site is suitable for water movement in the subgrade, therefoe, the frost heave is strong.
Subgrade freeze-thawing injury is an important problem that has puzzled many engineers in the seasonal frost regions of northeast China such as the cit of Chang-chun. In winter. weather in Chang-chun is very frigidity. Water in subgrade is moving and assembling in some positions under gradient of ground temperature So, subgrade is frost heave. In spring, subgrade and ice lenses which assembled in some positions begin thawing. The subgrade soil is in saturation or over saturation states. The bearing capacity is very low. Under the action of traffic vehicles, bulges, elastic springs, fractures and soil boiling can appear on pavement, which give very bad injuries to communication, transportation, and economic construction. It is urgent and necessary to research every influencing factor that affects frost heave. Pores as one of important symbols of soil structure are main entryways of water movement in soil. They decide sensibility of frost heave of the soil. In the paper, the WD-5 SEM is used to collect microstructure photos of soils from three different locations nearby Chang-chun. The photos are further used to make quantitative analysis to microstructure of pores in soil. An image quantitative analysis system is used. The quantitative analysis results in the finding that microscopic pore diameters of three samples are mainly about 5 m. This pore size makes soils have property of frost heave. There aren't noticeable difference of microcosmic pores between vertical and horizontal sections from a same sample. There are radial or reticular structure of pores, and shapes of oblate or equiaxial. The analysis further leads to the finding that when pore shape fractal dimensions are higher, there are many big pores, and the pore distribution is simple. The research site is suitable for water movement in the subgrade, therefoe, the frost heave is strong.
2008, 16(2): 239-244.
Stability of slope roadbed in the permafrost regions of Qinghai-Tibet railway is a potential threat to the railway long-term operation. Assessment of stability of the current and future slope roadbed can guide the roadbed project to correctly design and construction, thus ensuring to operate the railway safely. Changes of ground temperature of permafrost make the analysis of the slope roadbed stability different from others. The location of the freezing-thawing interface is an all-important constraint of the stability of the slope roadbed. Through monitoring the ground temperature at the Anduo section for three years, the changes of the roadbed ground temperature are analyzed and the change trend of the ground temperature in the next 50 years is predicted. The stability model of the present and future slope roadbed is established and the stability of the slope roadbed is calculated and analyzed. Through these investigations, conclusions can be made as follows: (1)filling the railway embankment makes the permafrost temperature field redistribute; the asymmetry of the slope direction and the geometric asymmetry make the ground temperature field asymmetric; (2)based on the location of the freezing-thawing interface and the ground temperature characteristics of the active layer, the frozen roadbed can be divided into four different times, namely, the severe winter period (January-February), the spring and summer melting active period (March-August), the largest thawing depth period (September-October) and the refreezing active period (November-December); (3)the numerical analysis results show that 20 years later, the permafrost of the Anduo test section roadbed will completely degrade, and the stability coefficient in the largest thawing depth period is the minimum in the forecast 10th year.
Stability of slope roadbed in the permafrost regions of Qinghai-Tibet railway is a potential threat to the railway long-term operation. Assessment of stability of the current and future slope roadbed can guide the roadbed project to correctly design and construction, thus ensuring to operate the railway safely. Changes of ground temperature of permafrost make the analysis of the slope roadbed stability different from others. The location of the freezing-thawing interface is an all-important constraint of the stability of the slope roadbed. Through monitoring the ground temperature at the Anduo section for three years, the changes of the roadbed ground temperature are analyzed and the change trend of the ground temperature in the next 50 years is predicted. The stability model of the present and future slope roadbed is established and the stability of the slope roadbed is calculated and analyzed. Through these investigations, conclusions can be made as follows: (1)filling the railway embankment makes the permafrost temperature field redistribute; the asymmetry of the slope direction and the geometric asymmetry make the ground temperature field asymmetric; (2)based on the location of the freezing-thawing interface and the ground temperature characteristics of the active layer, the frozen roadbed can be divided into four different times, namely, the severe winter period (January-February), the spring and summer melting active period (March-August), the largest thawing depth period (September-October) and the refreezing active period (November-December); (3)the numerical analysis results show that 20 years later, the permafrost of the Anduo test section roadbed will completely degrade, and the stability coefficient in the largest thawing depth period is the minimum in the forecast 10th year.
2008, 16(2): 245-249.
Qinghai-Tibet permafrost is one of the productions of high altitude and iciness weather in the geological period, and also is one of the three puzzles in the Qinghai-Tibet Railway construction. Moreover, the work of engineering geological characteristic and evaluations for the permafrost ground is a foundation for a reasonable and dependable engineering design. Based on these reasons and the 15 types of geomorphic distributions along the Qinghai-Tibet Railway, 70 typical profiles in the study area are chosen to carry out geological investigation. We use the methods combining geological drilling in the field and laboratory experiments and analyses. We examine the geological characteristics of each section and evaluate engineering geological types of each section. the investigation shows: it has many types of permafrost in Qinghai-Tibet permafrost areas, extensive distribution of permafrost of high ice content and thick ground ice, different ground temperatures in different sections, and the complex geologic structures of the project, interlaced distributions of engineering geological sections of different types. The results can provide the foundation for control disasters along Qinghai-Tibet Railway in use period. They can also be used as a reference for railway construction of the similar regions.
Qinghai-Tibet permafrost is one of the productions of high altitude and iciness weather in the geological period, and also is one of the three puzzles in the Qinghai-Tibet Railway construction. Moreover, the work of engineering geological characteristic and evaluations for the permafrost ground is a foundation for a reasonable and dependable engineering design. Based on these reasons and the 15 types of geomorphic distributions along the Qinghai-Tibet Railway, 70 typical profiles in the study area are chosen to carry out geological investigation. We use the methods combining geological drilling in the field and laboratory experiments and analyses. We examine the geological characteristics of each section and evaluate engineering geological types of each section. the investigation shows: it has many types of permafrost in Qinghai-Tibet permafrost areas, extensive distribution of permafrost of high ice content and thick ground ice, different ground temperatures in different sections, and the complex geologic structures of the project, interlaced distributions of engineering geological sections of different types. The results can provide the foundation for control disasters along Qinghai-Tibet Railway in use period. They can also be used as a reference for railway construction of the similar regions.
2008, 16(2): 250-254.
There is a potential threat to long-period operation in the sector of embankment upon the slope. Process of infiltration can not only disturbe field of temperature, but creates infiltrating force. The force can reduce the stability of embankment on the slope in the southern limit region of the permafrost zone. Stability of embankment of the Qinghai-Tibet railway on slope is analyzed in the event of rainstorm where the result of infiltrated calculation is used. Consequently, the stability continuously decreases. The minimal value appears after about two days of rainfall.
There is a potential threat to long-period operation in the sector of embankment upon the slope. Process of infiltration can not only disturbe field of temperature, but creates infiltrating force. The force can reduce the stability of embankment on the slope in the southern limit region of the permafrost zone. Stability of embankment of the Qinghai-Tibet railway on slope is analyzed in the event of rainstorm where the result of infiltrated calculation is used. Consequently, the stability continuously decreases. The minimal value appears after about two days of rainfall.
2008, 16(2): 255-257.
The paper introduces the method of fuzzy comprehensive evaluation as well as its application procedures. Based on the analysis of factors on the very length's tunnel of Shitai special railway line for passenger transport, this paper establishes a fuzzy decision matrix of predicting the gushing water into the tunnel. The factors include geological formation, wall rock sorts, rainfall, and environmental characteristic in the ground surface. The results show that the method is quite capable of predicting the amount of water inflow.
The paper introduces the method of fuzzy comprehensive evaluation as well as its application procedures. Based on the analysis of factors on the very length's tunnel of Shitai special railway line for passenger transport, this paper establishes a fuzzy decision matrix of predicting the gushing water into the tunnel. The factors include geological formation, wall rock sorts, rainfall, and environmental characteristic in the ground surface. The results show that the method is quite capable of predicting the amount of water inflow.
2008, 16(2): 258-262.
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.
2008, 16(2): 263-267.
The coordinating function between the primary supporting and the broken rock has the prominent character of uncertainty. The main effecting factors are as follows: the non-uniformity of primary supporting coming from the construction, the effect coming from the uncertainty of actual surrounding rock, the uncertainty of internal force distribution in primary supporting coming from the non-uniformity of releasing stress on surrounding rock. The retaining of primary supporting and the self-stabilization capability of rock are regarded as a dual-media (i.e., the bearing complex model). The displacement objective function is constructed by the least square formulas. Combining with the optimization method of simplex, the model with the bearing complex is applied to back-analysis of road tunnel. The results reveal the coordinating function between the primary supporting and the broken rock zone. In contrasts to the inversion result without considering the uncertainty of the primary supporting, the accuracy of inversion is improved 39% and the accuracy of prediction is improved 13%. Thus, The proposed method and the results can be used as reference to the construction and design of road tunnel with similar conditions.
The coordinating function between the primary supporting and the broken rock has the prominent character of uncertainty. The main effecting factors are as follows: the non-uniformity of primary supporting coming from the construction, the effect coming from the uncertainty of actual surrounding rock, the uncertainty of internal force distribution in primary supporting coming from the non-uniformity of releasing stress on surrounding rock. The retaining of primary supporting and the self-stabilization capability of rock are regarded as a dual-media (i.e., the bearing complex model). The displacement objective function is constructed by the least square formulas. Combining with the optimization method of simplex, the model with the bearing complex is applied to back-analysis of road tunnel. The results reveal the coordinating function between the primary supporting and the broken rock zone. In contrasts to the inversion result without considering the uncertainty of the primary supporting, the accuracy of inversion is improved 39% and the accuracy of prediction is improved 13%. Thus, The proposed method and the results can be used as reference to the construction and design of road tunnel with similar conditions.
2008, 16(2): 268-272.
Building a new station closely above an existing tunnel is a relatively difficult problem in underground construction. This paper uses numerical simulation methods and analyzes the distribution of plastic zones in the tunnel of the No. 1 Subway Line during the above construction of the Dongdan station for the No. 5 Subway Line in Beijing. It found that the symmetrical andrectangular distribution of plastic zones for the large-span station floor s influenced by existing line. Changing extent of different parts were also found on the plastic zones of the existing tunnel under backfill, sandy soil, clay interbedding,. The plastic zone valuesabout the side face of the existing line are the largest. Simulation on the reinforcement scheme was also conducted to guarantee the stabilization of the surrounding ground.
Building a new station closely above an existing tunnel is a relatively difficult problem in underground construction. This paper uses numerical simulation methods and analyzes the distribution of plastic zones in the tunnel of the No. 1 Subway Line during the above construction of the Dongdan station for the No. 5 Subway Line in Beijing. It found that the symmetrical andrectangular distribution of plastic zones for the large-span station floor s influenced by existing line. Changing extent of different parts were also found on the plastic zones of the existing tunnel under backfill, sandy soil, clay interbedding,. The plastic zone valuesabout the side face of the existing line are the largest. Simulation on the reinforcement scheme was also conducted to guarantee the stabilization of the surrounding ground.
2008, 16(2): 273-277.
The monitored displacement of the slope is usually oscillated and fluctuated, i.e. the direction of the lateral displacement changes with time. This paper analyzes the similarities and the dissimilarities in the oscillation and fluctuation of the time~displacement curve with some examples. It is found that fluctuation was caused by the slope condition, water, human activity and temperature. The finding can provide useful information on the analysis of the oscillation and fluctuation of the monitored displacement curve for slopes.
The monitored displacement of the slope is usually oscillated and fluctuated, i.e. the direction of the lateral displacement changes with time. This paper analyzes the similarities and the dissimilarities in the oscillation and fluctuation of the time~displacement curve with some examples. It is found that fluctuation was caused by the slope condition, water, human activity and temperature. The finding can provide useful information on the analysis of the oscillation and fluctuation of the monitored displacement curve for slopes.
2008, 16(2): 278-282.
Slope critical sliding field algorithm is a new method in slope stability analysis. It can quickly and accurately determine the arbitrary shape of critical sliding surface of multi-layer and multi-step slopes, and give an overall evaluation of the global and local stability of slope. This paper firstly uses the critical sliding field algorithm to probe the sliding surface of Longqiao waste-dump slope with the original design of 15 slope angle. The global safety factor of slope is found to be 1.42. The results show that the original design of 15 slope angle is too conservative. Then the expending method of the critical sliding field algorithm is used to carry out the reverse analysis. Given safety factor of 1.30, the optimum slope angle is found to be 17. The results can be used to supervise the future dumping work of mines.
Slope critical sliding field algorithm is a new method in slope stability analysis. It can quickly and accurately determine the arbitrary shape of critical sliding surface of multi-layer and multi-step slopes, and give an overall evaluation of the global and local stability of slope. This paper firstly uses the critical sliding field algorithm to probe the sliding surface of Longqiao waste-dump slope with the original design of 15 slope angle. The global safety factor of slope is found to be 1.42. The results show that the original design of 15 slope angle is too conservative. Then the expending method of the critical sliding field algorithm is used to carry out the reverse analysis. Given safety factor of 1.30, the optimum slope angle is found to be 17. The results can be used to supervise the future dumping work of mines.
2008, 16(2): 283-288.
Under the influence of geomorphology, climate and hydrology, rock and soil characteristics, local geology and so on, the rock masses forming the northern Mogao Grottoes in Dunhuang have formed several types of variations and deformations. The variations include surface weathering and load discharging. The deformations contain rock fall, crag and collapse, split and crannies (structural cranny, discharged cranny, horizontal cranny and vertical cranny) due to artificial digging, gravity, wind erosion, rain erosion and flood erosion. These variations and deformations have generated great dangers to grotto safety and stability of the rock mass. Using potassium silicate material and coal ashes, the crannies are grouted and the surface weathering layers are sprayed. The variations and deformations of the rock masses and surface weathering have been decreased. The rock masses are reinforced and the grottoes are well protected. The method is an effective reinforcement countermeasure for cultural relic protection in the loess and arid region.
Under the influence of geomorphology, climate and hydrology, rock and soil characteristics, local geology and so on, the rock masses forming the northern Mogao Grottoes in Dunhuang have formed several types of variations and deformations. The variations include surface weathering and load discharging. The deformations contain rock fall, crag and collapse, split and crannies (structural cranny, discharged cranny, horizontal cranny and vertical cranny) due to artificial digging, gravity, wind erosion, rain erosion and flood erosion. These variations and deformations have generated great dangers to grotto safety and stability of the rock mass. Using potassium silicate material and coal ashes, the crannies are grouted and the surface weathering layers are sprayed. The variations and deformations of the rock masses and surface weathering have been decreased. The rock masses are reinforced and the grottoes are well protected. The method is an effective reinforcement countermeasure for cultural relic protection in the loess and arid region.
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