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Editor Work2009 Vol. 17, No. 6
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2009, 17(6): 725-736.
Abstract
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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
2009, 17(6): 737-744.
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.
2009, 17(6): 745-751.
Shangjiang is one of the sites for constructing the leading dam to the middle reaches of Jinsha River Reservoir dam site. The maximum thickness of Quaternary soil is 206.2 m in the river at the possible dam site. The minimum height of the embankment dam is 249 m. The size of the dam. Construction of such dam is of a great difficulty. Through mapping, drilling, physical exploration, the work of physical and mechanical testing have revealed: (1) the bed deposits composed of the drift gravel, low liquid limit clay, gravel, fragments of stone, sand and gravel, etc; (2) the coarse-grained soil is relatively high intensity, clay of low liquid limit lower intensity, the relative weakness of the dam with the foundation for a complete; (3) the dam addresses in Longpan rift basin, where there is a major difference between the vertical structures of the neo-tectonics, and deposition area for the upper reaches of the Jinsha River. Preliminary study shows that the construction of a high earth-rock dam at the site is feasible. However, the need for the dam foundation treatment measures has to be taken by the project. The paper further discusses the effects of different programs caused by dam construction and engineering geological problems, the technology for the construction of the dam. The paper provides the geological basis for further research.
Shangjiang is one of the sites for constructing the leading dam to the middle reaches of Jinsha River Reservoir dam site. The maximum thickness of Quaternary soil is 206.2 m in the river at the possible dam site. The minimum height of the embankment dam is 249 m. The size of the dam. Construction of such dam is of a great difficulty. Through mapping, drilling, physical exploration, the work of physical and mechanical testing have revealed: (1) the bed deposits composed of the drift gravel, low liquid limit clay, gravel, fragments of stone, sand and gravel, etc; (2) the coarse-grained soil is relatively high intensity, clay of low liquid limit lower intensity, the relative weakness of the dam with the foundation for a complete; (3) the dam addresses in Longpan rift basin, where there is a major difference between the vertical structures of the neo-tectonics, and deposition area for the upper reaches of the Jinsha River. Preliminary study shows that the construction of a high earth-rock dam at the site is feasible. However, the need for the dam foundation treatment measures has to be taken by the project. The paper further discusses the effects of different programs caused by dam construction and engineering geological problems, the technology for the construction of the dam. The paper provides the geological basis for further research.
2009, 17(6): 752-761.
The paper attempts to address a worldwide difficult problem. This problem is how to predict the time of happening landslide. There is no solution yet because of the lack of clear recognition of mechanism about landside and no correct quantitative model to be set up. Accordingly, this paper is based on the geological condition, landslide examples, and external data at the Three Gorge project's bank slopes and southwest mountains, as well as experiences aboard. It demonstrates the necessary and full condition of landslide happening. So, this paper eliminates the terrain control theory and stratigraphic control theory for causing landslide. The paper elucidated that the necessary conditions of landslide is a slope that has easily slipping structure and the full conditions of landslide is the effect of inducing factors. So the dynamic variation of inducing factors is decisive for the time of happening landslide.
Whereas rock-landslides are the most widely distributed. They are induced by underground water. In order to set up a correct water-starting model, the paper sums up the recent theories of typical rock landslide characters as follows: (1) The sliding face is the through penetrative discontinuities with the most difference of water transmissibility; (2) The landslide body's length is bigger than its thickness. The ration of the length to the thickness is about 20; (3) The front of landslide is starting early; (4) There is the phenomena of water seepage or water sprinkling in the front of slope body before the occurrence of sliding; (5) The sum of effluent water width on the slope is much smaller than the total width of the front of landslide body. Further more, the paper applies the hydraulics and hydrogeology theory to pointing out the following problems associated with a rock stability model proposed by others in 1970. It is found that (1) The old model didn't point out conditions of the distribution of the weight of rock over through the penetrative discontinuities; (2) The distribution characters of crack water pressure in the old model is against the observed landslide phenomena and hydraulics theory: (3) The old model didn't considered the percentage of going through infiltration water. Finally, the paper sets up a new slope stability model and critical value calculation equation of water-start landslide. The model and the equation are formulated according to easily slip over dip slope and chair-shape slope characters. Then, it brings forward the method on how to acquire parameters of the combined internal friction angle and the percentage of going through infiltration water as follows: (1) The back-calculation parameters of landslide; (2) The method of observation and statistic about the dip angle of slip penetrative discontinuities without hydraulic pressure and the percentage of going through water; (3) The experiment of the shearing and simple hydrogeology; (4) The method of geophysical exploration.
The paper attempts to address a worldwide difficult problem. This problem is how to predict the time of happening landslide. There is no solution yet because of the lack of clear recognition of mechanism about landside and no correct quantitative model to be set up. Accordingly, this paper is based on the geological condition, landslide examples, and external data at the Three Gorge project's bank slopes and southwest mountains, as well as experiences aboard. It demonstrates the necessary and full condition of landslide happening. So, this paper eliminates the terrain control theory and stratigraphic control theory for causing landslide. The paper elucidated that the necessary conditions of landslide is a slope that has easily slipping structure and the full conditions of landslide is the effect of inducing factors. So the dynamic variation of inducing factors is decisive for the time of happening landslide.
Whereas rock-landslides are the most widely distributed. They are induced by underground water. In order to set up a correct water-starting model, the paper sums up the recent theories of typical rock landslide characters as follows: (1) The sliding face is the through penetrative discontinuities with the most difference of water transmissibility; (2) The landslide body's length is bigger than its thickness. The ration of the length to the thickness is about 20; (3) The front of landslide is starting early; (4) There is the phenomena of water seepage or water sprinkling in the front of slope body before the occurrence of sliding; (5) The sum of effluent water width on the slope is much smaller than the total width of the front of landslide body. Further more, the paper applies the hydraulics and hydrogeology theory to pointing out the following problems associated with a rock stability model proposed by others in 1970. It is found that (1) The old model didn't point out conditions of the distribution of the weight of rock over through the penetrative discontinuities; (2) The distribution characters of crack water pressure in the old model is against the observed landslide phenomena and hydraulics theory: (3) The old model didn't considered the percentage of going through infiltration water. Finally, the paper sets up a new slope stability model and critical value calculation equation of water-start landslide. The model and the equation are formulated according to easily slip over dip slope and chair-shape slope characters. Then, it brings forward the method on how to acquire parameters of the combined internal friction angle and the percentage of going through infiltration water as follows: (1) The back-calculation parameters of landslide; (2) The method of observation and statistic about the dip angle of slip penetrative discontinuities without hydraulic pressure and the percentage of going through water; (3) The experiment of the shearing and simple hydrogeology; (4) The method of geophysical exploration.
2009, 17(6): 762-768.
It examines a landslide group within the Ⅱ District at the East Open-pit Stope of Daye Iron Mine site. It is located in the slipping zone of the fault No. F25. It is a group of high and steep rocky slopes formed by manual mining excavation. The diorite and iron ores in the fault zone were fragmented into typical breccia and smithereens. The development of joints is relatively well. The landslide group is consisted of three main slide bodies, and some cataclastic rocks and soils. Its average length in plane is about 138 m. Its width is about 120m. Its height difference 85 m. Its overall slope angle is 36. Its total volume is about 1.1107 m3. The underlain bedrock is silty mudstone. The landslide body is consisted of silty clay including fragmentary rock blocks. Using analytical method of natural historical analysis and engineering geological analogy, this paper discusses the failure mechanism of the landslides. It is found that the formation and development of the landslide group is a result of the comprehensive effect due to many factors. The factors include the type and property of rock and soil, the structure of rock mass, the tectonics, the topography and the geomorphology, water, as well as other inducing factors. The stability of a typical landslide is analyzed and evaluated comprehensively using limit equilibrium method. For four working conditions are taken into account in the analysis. They are the present situation, the heavy rain, the seismicity and the combined effect of heavy rain and seismicity. It is found that the factors of safety are equal to e 1.256, 0.961, 1.198 and 0.954, respectively. The calculation results show that the rainfall is the main external cause that controls the stability of this landslide. A scheme for prevention and governance is proposed according to the actual situation of this landslide. It includes avoiding the use of the anti-slide pile strengthening and the blasting operation underground, provision of intercepting drains and drainage ditches in posterior wall and surface of landslide body, cement mortar caulking, load reducing and reverse pressing, as well sa slope surface greening.
It examines a landslide group within the Ⅱ District at the East Open-pit Stope of Daye Iron Mine site. It is located in the slipping zone of the fault No. F25. It is a group of high and steep rocky slopes formed by manual mining excavation. The diorite and iron ores in the fault zone were fragmented into typical breccia and smithereens. The development of joints is relatively well. The landslide group is consisted of three main slide bodies, and some cataclastic rocks and soils. Its average length in plane is about 138 m. Its width is about 120m. Its height difference 85 m. Its overall slope angle is 36. Its total volume is about 1.1107 m3. The underlain bedrock is silty mudstone. The landslide body is consisted of silty clay including fragmentary rock blocks. Using analytical method of natural historical analysis and engineering geological analogy, this paper discusses the failure mechanism of the landslides. It is found that the formation and development of the landslide group is a result of the comprehensive effect due to many factors. The factors include the type and property of rock and soil, the structure of rock mass, the tectonics, the topography and the geomorphology, water, as well as other inducing factors. The stability of a typical landslide is analyzed and evaluated comprehensively using limit equilibrium method. For four working conditions are taken into account in the analysis. They are the present situation, the heavy rain, the seismicity and the combined effect of heavy rain and seismicity. It is found that the factors of safety are equal to e 1.256, 0.961, 1.198 and 0.954, respectively. The calculation results show that the rainfall is the main external cause that controls the stability of this landslide. A scheme for prevention and governance is proposed according to the actual situation of this landslide. It includes avoiding the use of the anti-slide pile strengthening and the blasting operation underground, provision of intercepting drains and drainage ditches in posterior wall and surface of landslide body, cement mortar caulking, load reducing and reverse pressing, as well sa slope surface greening.
2009, 17(6): 762-779.
As the access tunnel of underground mining, the mine shaft plays an important role in safety production. This paper examines the No.14 shaft that located on the support of ore body in Jinchang No.2 mine area. Its depth if 715.5 m. It intersected with the F207 fault. The surrounding rocks included ultramafic rock, granite, marble and dolerite. The shaft excavation was commenced in October 1999 and completed for using in 2002. It collapsed in March 2005. Based on the spot investigated data and numerical simulation method, this paper presents the deformation characteristics and damage mechanism of the No.14 shaft. The results show that there were such several damaged modes such as displacement and crack of shaft wall, fall, and breakage of shaft wall caused by impacting of falling substance. The convergence deformation of its surrounding rock was characterized by large deformation, rapid and long duration. Furthermore, the damage mechanism of the No.14 shaft was analyzed by numerical simulation. The result stated that the failures appeared possibly on the following positions of the shaft influenced by underground mining: (1)the upper part (0 to 200 m apart from the shaft head), where tension failure and shearing slide might happen. (2) the F207 fault zone (200 to 220 m apart from the shaft head), where the fault displacement might happen to induce shearing failure of the shaft. (3) the middle part (360 to 460 m apart from the shaft head), where the bulging damage might appear because of strong mining effect. (4) the influencing zone of the F16 fault (0 to 50 m apart from the shaft bottom), where the rock would loose due to the influence of the underground mining, which might induce the appearance of falling at the position of discontinuity plane traversing the shaft.
As the access tunnel of underground mining, the mine shaft plays an important role in safety production. This paper examines the No.14 shaft that located on the support of ore body in Jinchang No.2 mine area. Its depth if 715.5 m. It intersected with the F207 fault. The surrounding rocks included ultramafic rock, granite, marble and dolerite. The shaft excavation was commenced in October 1999 and completed for using in 2002. It collapsed in March 2005. Based on the spot investigated data and numerical simulation method, this paper presents the deformation characteristics and damage mechanism of the No.14 shaft. The results show that there were such several damaged modes such as displacement and crack of shaft wall, fall, and breakage of shaft wall caused by impacting of falling substance. The convergence deformation of its surrounding rock was characterized by large deformation, rapid and long duration. Furthermore, the damage mechanism of the No.14 shaft was analyzed by numerical simulation. The result stated that the failures appeared possibly on the following positions of the shaft influenced by underground mining: (1)the upper part (0 to 200 m apart from the shaft head), where tension failure and shearing slide might happen. (2) the F207 fault zone (200 to 220 m apart from the shaft head), where the fault displacement might happen to induce shearing failure of the shaft. (3) the middle part (360 to 460 m apart from the shaft head), where the bulging damage might appear because of strong mining effect. (4) the influencing zone of the F16 fault (0 to 50 m apart from the shaft bottom), where the rock would loose due to the influence of the underground mining, which might induce the appearance of falling at the position of discontinuity plane traversing the shaft.
2009, 17(6): 780-787.
The activity law of the active fault F2 nearby Kizil Reservoir area in Xinjiang has a major impact on the safety of Kizil Reservoir. The analysis of short leveling long observation sequence striding the active fault F2 shows that the lower wall of the fault F2 continuously performed a ground tilting movement from south to north in the past 40 years. The ground tilting movement not only affected the calculation result of short leveling elevation difference, but also affected the calculation result of two parameters including horizontal twisting amount and sliding angle of the dislocation model. As a result, the evaluation of the activity of the active fault F2 cannot be objectively assessed. In this paper, the year-variable-rate of the ground inclining at the point of 12 m along the measurement line direction on the footwall of the active fault F2 is obtained to be about 0.224 mm/a (from 1979 to 2006). The the year-variable-rate is obtained using the trend analysis of artificial short leveling foresight reading long sequence from the first deformation monitoring station (FDMS). This rate of the ground inclining activity at the FDMS along the direction of measuring line between hanging wall and footwall is identified and verified with the surface Subsidence Rate isoline map on both sides of the reservoir area nearby the active fault F2. I They are respectively 0.03 mm/a and 0.07 mma-1(from 1991 to 2002). The results of the calculation and analysis from the horizontal twist amount and the sliding angle indicate that although the activities of the active fault F2 over the past 10 years have some close relationships with the reservoir sluice, the reservoir water infiltration down along the active fault, the river path change and the crustal movement, we still cannot conclude that the activities are being or have intensified.
The activity law of the active fault F2 nearby Kizil Reservoir area in Xinjiang has a major impact on the safety of Kizil Reservoir. The analysis of short leveling long observation sequence striding the active fault F2 shows that the lower wall of the fault F2 continuously performed a ground tilting movement from south to north in the past 40 years. The ground tilting movement not only affected the calculation result of short leveling elevation difference, but also affected the calculation result of two parameters including horizontal twisting amount and sliding angle of the dislocation model. As a result, the evaluation of the activity of the active fault F2 cannot be objectively assessed. In this paper, the year-variable-rate of the ground inclining at the point of 12 m along the measurement line direction on the footwall of the active fault F2 is obtained to be about 0.224 mm/a (from 1979 to 2006). The the year-variable-rate is obtained using the trend analysis of artificial short leveling foresight reading long sequence from the first deformation monitoring station (FDMS). This rate of the ground inclining activity at the FDMS along the direction of measuring line between hanging wall and footwall is identified and verified with the surface Subsidence Rate isoline map on both sides of the reservoir area nearby the active fault F2. I They are respectively 0.03 mm/a and 0.07 mma-1(from 1991 to 2002). The results of the calculation and analysis from the horizontal twist amount and the sliding angle indicate that although the activities of the active fault F2 over the past 10 years have some close relationships with the reservoir sluice, the reservoir water infiltration down along the active fault, the river path change and the crustal movement, we still cannot conclude that the activities are being or have intensified.
2009, 17(6): 788-795.
he shape of the groundwater table is a sign of the characters of the flow field. Its cause of formation is very important to the seepage and feasibility of project. The rock permeability is not uniform in space even in the small district of one project. It has the characters of strong anisotropy and notable zoned phenomenon in those mountain-canyon regions, especially in southwest China. This leads to the result that the profile shapes of groundwater table may be of gentle U shape, gradient W shape or W shape. Such result means a possible occurrence of a special phenomenon that there are strips of lower water table in the bank areas near the river. Moreover, the actual conditions in the district of Jiudianxia hydro-project give an example that the characters of strong anisotropy and notable zone of rock permeability may fully arouse strips of lower water table in the bank though without strong vadose zones, which dispels the worry about the seepage and provides good reference to other hydro-projects.
he shape of the groundwater table is a sign of the characters of the flow field. Its cause of formation is very important to the seepage and feasibility of project. The rock permeability is not uniform in space even in the small district of one project. It has the characters of strong anisotropy and notable zoned phenomenon in those mountain-canyon regions, especially in southwest China. This leads to the result that the profile shapes of groundwater table may be of gentle U shape, gradient W shape or W shape. Such result means a possible occurrence of a special phenomenon that there are strips of lower water table in the bank areas near the river. Moreover, the actual conditions in the district of Jiudianxia hydro-project give an example that the characters of strong anisotropy and notable zone of rock permeability may fully arouse strips of lower water table in the bank though without strong vadose zones, which dispels the worry about the seepage and provides good reference to other hydro-projects.
2009, 17(6): 796-801.
Rock slope has weak structural planes. They are propitious to stability. The primary stability problem of rock slope i the surface rock block stability. Blasting vibration with excavation is an important factor in stability evaluation of surface rock blocks. This paper examines the case of a granite slope on middle Dadu River. It summarizes the rule of the failure rock blocks on surface characteristics. Secondly, it measures the blasting vibration acceleration curve of a potential failure block. Finally, it completes the slope stability evaluation. As a result, the volume of failure blocks is always less than 10 m3. 80% failure blocks are formed by weak structural planes, and 70% of these are along the slope benches. Comparing with rock mass near the block, the block vibration time is longer but with lower climax and lower frequency. Equivalent-statical method is more appropriate in practice.
Rock slope has weak structural planes. They are propitious to stability. The primary stability problem of rock slope i the surface rock block stability. Blasting vibration with excavation is an important factor in stability evaluation of surface rock blocks. This paper examines the case of a granite slope on middle Dadu River. It summarizes the rule of the failure rock blocks on surface characteristics. Secondly, it measures the blasting vibration acceleration curve of a potential failure block. Finally, it completes the slope stability evaluation. As a result, the volume of failure blocks is always less than 10 m3. 80% failure blocks are formed by weak structural planes, and 70% of these are along the slope benches. Comparing with rock mass near the block, the block vibration time is longer but with lower climax and lower frequency. Equivalent-statical method is more appropriate in practice.
2009, 17(6): 802-808.
The geo-characteristics of the lower elevation bank slope of Xiaowan Hydrostation were systematically and widely observed at the foundation of dam, the slope of water-cushion pond and lower elevation drainage galleries. Based on field investigation and 2D finite element analysis of elasticity and plasticity, the exogenetic reconstruction characteristics of lower elevation bank slope were more understood. (1) Its development was based on the reconstruction of rock association and structure, including the stretch and slippage of old gentle joints, the stretch and slippage of deep joints and their changing of occurrence, the new generation of a great number of middle-gentle cracks, the weaker and weaker exogenetic reconstruction inwards. (2) The generation mechanism and model of gentle cracks triggering from exogenetic reconstruction in lower elevation was established, and the formation process was analysed. (3) During the 2D finite element analysis of elasticity and plasticity, the slack boundary due to unloading in lower elevation was studied on the basis of the indexes of tensilely destroyed zone distribution, shearing strain and point safety degree. As a result, the obvious depth affected by exogenetic reconstruction on the bottom of valley would reach 6 to 9 m.
The geo-characteristics of the lower elevation bank slope of Xiaowan Hydrostation were systematically and widely observed at the foundation of dam, the slope of water-cushion pond and lower elevation drainage galleries. Based on field investigation and 2D finite element analysis of elasticity and plasticity, the exogenetic reconstruction characteristics of lower elevation bank slope were more understood. (1) Its development was based on the reconstruction of rock association and structure, including the stretch and slippage of old gentle joints, the stretch and slippage of deep joints and their changing of occurrence, the new generation of a great number of middle-gentle cracks, the weaker and weaker exogenetic reconstruction inwards. (2) The generation mechanism and model of gentle cracks triggering from exogenetic reconstruction in lower elevation was established, and the formation process was analysed. (3) During the 2D finite element analysis of elasticity and plasticity, the slack boundary due to unloading in lower elevation was studied on the basis of the indexes of tensilely destroyed zone distribution, shearing strain and point safety degree. As a result, the obvious depth affected by exogenetic reconstruction on the bottom of valley would reach 6 to 9 m.
2009, 17(6): 809-817.
There exists a plenty of ancient landslides in the new Badong county. Examples are Huangtupo landslide and Zhaoshuling landslide. It is of very importance for landslide prevention to study rock mass structure. Firstly, based on geological prospecting data of monitoring profile (300 m deep) at New Badong City, the third member of the Badong Formation of Middle Trassic (T2b3) strata are divided into 24 sections according to the rock core color, lithology and structure. Secondly, according to the tine section identification, x-ray diffraction mineral analysis and detailed measurement of rock core, it is found that the T2b3 strata were deposited in coastal environment that underwent repetitious marine transgression and regression. Lastly, the action mechanism of the interlayer weakness zones with ancient landslides is investigated. It indicates that the 13 strips transfixion weak-soft zone which develops in the T2b3 strata can be divided into a weak intercalation of rich in clayish fine, a cataclasite weak-soft zone, a corrosion transformation weak-soft zone and a soft rock weak-soft zone. Weakness zones are mainly distributed in the open platform (shelf lagoon) and the restricted platform (inter-tidal belt). The interface between T2b3 and T2b3 is continues transition without sliding conditions. The weakness zones give important effect to ancient landslides and will aggravate deep deformation of bank slope under long-term soak when the water level is uplifted to 175 m in the Three Gorges Reservoir.
There exists a plenty of ancient landslides in the new Badong county. Examples are Huangtupo landslide and Zhaoshuling landslide. It is of very importance for landslide prevention to study rock mass structure. Firstly, based on geological prospecting data of monitoring profile (300 m deep) at New Badong City, the third member of the Badong Formation of Middle Trassic (T2b3) strata are divided into 24 sections according to the rock core color, lithology and structure. Secondly, according to the tine section identification, x-ray diffraction mineral analysis and detailed measurement of rock core, it is found that the T2b3 strata were deposited in coastal environment that underwent repetitious marine transgression and regression. Lastly, the action mechanism of the interlayer weakness zones with ancient landslides is investigated. It indicates that the 13 strips transfixion weak-soft zone which develops in the T2b3 strata can be divided into a weak intercalation of rich in clayish fine, a cataclasite weak-soft zone, a corrosion transformation weak-soft zone and a soft rock weak-soft zone. Weakness zones are mainly distributed in the open platform (shelf lagoon) and the restricted platform (inter-tidal belt). The interface between T2b3 and T2b3 is continues transition without sliding conditions. The weakness zones give important effect to ancient landslides and will aggravate deep deformation of bank slope under long-term soak when the water level is uplifted to 175 m in the Three Gorges Reservoir.
2009, 17(6): 817-822.
The carbonate rock area in the Chenqi village of Puding County, Guizhou Province is an area of karst rocky desertification. This paper examines the stability of brown clayey soil in the karst rocky desertification. The paper uses the wet sieving method. The results show that cracking of the brown clayey soil aggregates due to encountering water occurs in the early soaked stage. The less the initial water content of the brown clayey soil aggregates is, after soaked with rainwater, the quicker the cracking of soil aggregates is. Stability of the brown clayed soil aggregates is good for the soil with high water content. So, for prevention of rocky desertification of the carbonate rock area, it is important to take into consideration of the effect of desiccation climate and evaporation quantity on the soil loss.
The carbonate rock area in the Chenqi village of Puding County, Guizhou Province is an area of karst rocky desertification. This paper examines the stability of brown clayey soil in the karst rocky desertification. The paper uses the wet sieving method. The results show that cracking of the brown clayey soil aggregates due to encountering water occurs in the early soaked stage. The less the initial water content of the brown clayey soil aggregates is, after soaked with rainwater, the quicker the cracking of soil aggregates is. Stability of the brown clayed soil aggregates is good for the soil with high water content. So, for prevention of rocky desertification of the carbonate rock area, it is important to take into consideration of the effect of desiccation climate and evaporation quantity on the soil loss.
2009, 17(6): 823-829.
The caverns No. 1 to No. 5 of Longyou cavern group had been fully filled with water for many hundreds years. In 1992, the water was pumped out d for tourism. Because of the dramtic changes of the condition and the alternation bettween drying and wetting, the rock mass weathering and the damages have been substantial. Such as, the rock pillar No. 3-2 of the cavern No. 3 has developed many cracks. This pillar has to be reinforced immediately. To provide the basis for the pillar reinforcement, it is needed to fully understand the situation of the deformation development in the pillar. This paper presents the monitoring results of the widths and the lengths of the cracks with the jointmeters of JSYCB-73 series and steel ruler. On the basic of the data obtained from the monitoring and the geology conditions, this paper further analyzes the causes of the cracking. The following findings are obtained: (1) part of the weights of concrete materials that are used to reinforce the other part of the cavern increased the load on the pillar；(2) the leakage of the cavern, the alternation bettween drying and wetting and the changes of the temperature enlarged the weathering, which reduced the pillar strength；(3) the two above factors made the growth of cracks in the pillar. Based on the findings, taking into account the cultural relics and the tourism, this paper suggests the protection measures. They include the water-control, unloading the load, installing rock bolts and hoops. The monitored data after the pillar reinforcments show that the cracks has stopped developping，and the pillar has been stable.
The caverns No. 1 to No. 5 of Longyou cavern group had been fully filled with water for many hundreds years. In 1992, the water was pumped out d for tourism. Because of the dramtic changes of the condition and the alternation bettween drying and wetting, the rock mass weathering and the damages have been substantial. Such as, the rock pillar No. 3-2 of the cavern No. 3 has developed many cracks. This pillar has to be reinforced immediately. To provide the basis for the pillar reinforcement, it is needed to fully understand the situation of the deformation development in the pillar. This paper presents the monitoring results of the widths and the lengths of the cracks with the jointmeters of JSYCB-73 series and steel ruler. On the basic of the data obtained from the monitoring and the geology conditions, this paper further analyzes the causes of the cracking. The following findings are obtained: (1) part of the weights of concrete materials that are used to reinforce the other part of the cavern increased the load on the pillar；(2) the leakage of the cavern, the alternation bettween drying and wetting and the changes of the temperature enlarged the weathering, which reduced the pillar strength；(3) the two above factors made the growth of cracks in the pillar. Based on the findings, taking into account the cultural relics and the tourism, this paper suggests the protection measures. They include the water-control, unloading the load, installing rock bolts and hoops. The monitored data after the pillar reinforcments show that the cracks has stopped developping，and the pillar has been stable.
2009, 17(6): 829-835.
This paper presents the results of the field water flushing tests into sinkhole, exploration, investigation and laboratory sediment percentage tests in loess. It aims to examine the three dimensional distribution, hydrographic characteristics and erosion characteristics of the large-scale natural pipe-cave network in loess. The findings are summarized as follows. At first, the erosion process of the natural pipe-cave system in loess was periodical. Secondly, each of the water flow curves in the pipe-cave system includes three different characteristic stages: (a) the amount of water flow kept increasing, (b) the amount of water flow became constant, and (c) the amount of water flow became reducing. During (a), the retardance effect of water flow always happened. During (b), the amount of water flow had a limited fluctuation And the seepage quantity increased as the injected water increased. Thirdly, the changes of sediment percentage during the three stages were analyzed from the sediment percentage-time curves. The erosion velocity shows a positive correlation with the flow quantity from the accumulative comparison of erosion quantity in the designed cases. Finally, the causes of all the processes, phenomena and results mentioned above are explained. The data obtained from this work provide a valuable base for the research on both the mechanism and the velocity of sub-erosion in loess.
This paper presents the results of the field water flushing tests into sinkhole, exploration, investigation and laboratory sediment percentage tests in loess. It aims to examine the three dimensional distribution, hydrographic characteristics and erosion characteristics of the large-scale natural pipe-cave network in loess. The findings are summarized as follows. At first, the erosion process of the natural pipe-cave system in loess was periodical. Secondly, each of the water flow curves in the pipe-cave system includes three different characteristic stages: (a) the amount of water flow kept increasing, (b) the amount of water flow became constant, and (c) the amount of water flow became reducing. During (a), the retardance effect of water flow always happened. During (b), the amount of water flow had a limited fluctuation And the seepage quantity increased as the injected water increased. Thirdly, the changes of sediment percentage during the three stages were analyzed from the sediment percentage-time curves. The erosion velocity shows a positive correlation with the flow quantity from the accumulative comparison of erosion quantity in the designed cases. Finally, the causes of all the processes, phenomena and results mentioned above are explained. The data obtained from this work provide a valuable base for the research on both the mechanism and the velocity of sub-erosion in loess.
2009, 17(6): 842-846.
It is found in engineering practice that soft soil solidified with cement is influenced by humid acid. It has been an important issue of geotechnical engineering research to identify the effect due to components of soil humic acid to soil-cement curing. This paper uses actual soft soil samples for comparative tests. Qualitative and quantitative analyses are conducted on the composition of cement stabilized soil with humic acid. The test results show the different effects of cement with humic acid for different cement contents from various places. The results shows that by Infrared spectroscopy test with the increasing of humic acid, the Cation exchange capacity of cement-soil cation increased with the increasing of cement content. For soils with cement-soil of 5%, 10%, or 20%, it is revealed form the gray relational analysist that fulvic acid makes great effort on the cement-soil unconfined compressive strength. The components of cement-soil humic acid could react with Ca2+ and Al3+ in cement-soil environment, which would produce calcium, aluminum and other key complex. They may affect the hydration reaction of cement, reduce the curing effect of cement.
It is found in engineering practice that soft soil solidified with cement is influenced by humid acid. It has been an important issue of geotechnical engineering research to identify the effect due to components of soil humic acid to soil-cement curing. This paper uses actual soft soil samples for comparative tests. Qualitative and quantitative analyses are conducted on the composition of cement stabilized soil with humic acid. The test results show the different effects of cement with humic acid for different cement contents from various places. The results shows that by Infrared spectroscopy test with the increasing of humic acid, the Cation exchange capacity of cement-soil cation increased with the increasing of cement content. For soils with cement-soil of 5%, 10%, or 20%, it is revealed form the gray relational analysist that fulvic acid makes great effort on the cement-soil unconfined compressive strength. The components of cement-soil humic acid could react with Ca2+ and Al3+ in cement-soil environment, which would produce calcium, aluminum and other key complex. They may affect the hydration reaction of cement, reduce the curing effect of cement.
2009, 17(6): 852-856.
Abstract: Over the last seventeen years, the Journal of Engineering Geology has gained a great growth. At present, the Journal has received good scores in various evaluation indices. The aim of this paper is to develop a clear strategy for the development of the Journal. Therefore, we have made a statistic assessment on the data and evaluation indices of the Journal in recent years. The results are reported in this paper. They can be used as a solid basis to further improve the quality of the Journal.
Abstract: Over the last seventeen years, the Journal of Engineering Geology has gained a great growth. At present, the Journal has received good scores in various evaluation indices. The aim of this paper is to develop a clear strategy for the development of the Journal. Therefore, we have made a statistic assessment on the data and evaluation indices of the Journal in recent years. The results are reported in this paper. They can be used as a solid basis to further improve the quality of the Journal.
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