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Editor Work2009 Vol. 17, No. 1
Previous Issue
2009, 17(1): 3-18.
Abstract
1647KB
Longmen Shan is located the special joint between the Qinghai-Tibetan Plateau in the west and the Yangtze craton in the east. Consisting of a series of parallel imbricated thrusts, it develops, from the west to the east, the Maoxian-Wenchuan, Yingxiu-Beichuan and Pengxian-Guanxian faults.The Longmen Shan fault belt is a dangerous earthquake belt and the three main faults have occurred Ms. 7 earthquakes. The Yingxiu-Beichuan fault would be one of the most important causes of the earthquake hazard. According to the Qingshiping trench in the Pengxian-Guanxian fault, we believe that in this fault, the latest strong earthquake took place in 930 40 a. BP.Then we can preliminarily determine the recurrence interval of strong earthquakes should be at least about 1000 years. We think that the Longmen Shan fault zone and its inner faults belong not only to a low-frequency seismic activity region and also to a potential powerful earthquake region.
Wenchuan Earthquake is a thrust with strike-slip type. The surface ruptures are located in Yingxiu-Beichuan fault zone and Pengxian-Guanxian fault zone. The surface ruptures of the Yingxiu-Beichuan fault can be divided into two high-value and two low-value zones. The two high-value zones are located in the southern part of Hongkou, Yingxiu and the northern part of the Leigu, Beichuan- Dengjiaba area. The two low-value zones are located in mid-south part of the Baishuihe-Chaping area and Huangjiaba-Shikanzi, Pingwu areas. These four sections are divided by Xiaoyudong fault, Leigu fault and Dengjiaba fault. The two high-value areas were caused by the Xiaoyudong and Leigu faults. The scratches of the surface ruptures reveal the thrust movement occurred early and the strike-slip movement occurred lately during the earthquake. The earthquake is characterized by thrust and dextral strike-slip movement, which does not agree with both the crustal thickening model and the lateral extrusion model in the eastern margin of the Qinghai-Tibetan Plateau.
Based on the geological background, tectonic setting, stratigraphy and lithology, the active tectonics of Longmen Shan and surface ruptures of the Wenchuan Earthquake, a dynamical model to illustrate possible links between surface processes and upward extrusion of lower crustal flow channel at the eastern margin of the Tibetan plateau have been proposed. The result is the material in lower crust in the Longmen Shan moving as nearly-vertical extrusion and uplift, resulting in the surface rate of tectonic movement differing according to depth rate as well as the occurrence of large shallow Wenchuan Earthquake.
According to the hazards caused by Wenchuan Earthquake, this paper provides some suggestions on the reconstruction.
Longmen Shan is located the special joint between the Qinghai-Tibetan Plateau in the west and the Yangtze craton in the east. Consisting of a series of parallel imbricated thrusts, it develops, from the west to the east, the Maoxian-Wenchuan, Yingxiu-Beichuan and Pengxian-Guanxian faults.The Longmen Shan fault belt is a dangerous earthquake belt and the three main faults have occurred Ms. 7 earthquakes. The Yingxiu-Beichuan fault would be one of the most important causes of the earthquake hazard. According to the Qingshiping trench in the Pengxian-Guanxian fault, we believe that in this fault, the latest strong earthquake took place in 930 40 a. BP.Then we can preliminarily determine the recurrence interval of strong earthquakes should be at least about 1000 years. We think that the Longmen Shan fault zone and its inner faults belong not only to a low-frequency seismic activity region and also to a potential powerful earthquake region.
Wenchuan Earthquake is a thrust with strike-slip type. The surface ruptures are located in Yingxiu-Beichuan fault zone and Pengxian-Guanxian fault zone. The surface ruptures of the Yingxiu-Beichuan fault can be divided into two high-value and two low-value zones. The two high-value zones are located in the southern part of Hongkou, Yingxiu and the northern part of the Leigu, Beichuan- Dengjiaba area. The two low-value zones are located in mid-south part of the Baishuihe-Chaping area and Huangjiaba-Shikanzi, Pingwu areas. These four sections are divided by Xiaoyudong fault, Leigu fault and Dengjiaba fault. The two high-value areas were caused by the Xiaoyudong and Leigu faults. The scratches of the surface ruptures reveal the thrust movement occurred early and the strike-slip movement occurred lately during the earthquake. The earthquake is characterized by thrust and dextral strike-slip movement, which does not agree with both the crustal thickening model and the lateral extrusion model in the eastern margin of the Qinghai-Tibetan Plateau.
Based on the geological background, tectonic setting, stratigraphy and lithology, the active tectonics of Longmen Shan and surface ruptures of the Wenchuan Earthquake, a dynamical model to illustrate possible links between surface processes and upward extrusion of lower crustal flow channel at the eastern margin of the Tibetan plateau have been proposed. The result is the material in lower crust in the Longmen Shan moving as nearly-vertical extrusion and uplift, resulting in the surface rate of tectonic movement differing according to depth rate as well as the occurrence of large shallow Wenchuan Earthquake.
According to the hazards caused by Wenchuan Earthquake, this paper provides some suggestions on the reconstruction.
2009, 17(1): 19-28.
A great number of collapse and slide geo-hazards had been triggered by 512 Wenchuan Earthquake, covering 0.1M km2 or so. Undoubtedly, their distribution was influenced by topography and morphology, stratigraphy, people's engineering operations, and so on. But their distribution mainly was controlled by the faults triggering seism, and they distributed along those faults like a ribbon. Based on the study in three geo-hazards concentration regions, namely, from Dujiangyan to Wenchuan, from Beichuan to Anxian and from Magong to Hongguang, the following fault effects of geo-hazards in Wenchuan Earthquake were found: (1) Because the triggering-earthquake faults were reverse fault, the distribution of geo-hazards showed clear Upper plate/lower plate effect. In detail, compared with lower plate, the upper plate had higher distribution density, wider scope and larger scale; (2) Intensely developed region of geo-hazard ranged from 0 to 7 km in upper plate. Moderately developed region ranged from 7 to 11km in upper plate, and from 0 to 5km in lower plate; Vast majority of lager-scale landslides were about 5km away from faults; (3) The transition and stagger parts of fractures are usually the concentration zone of geo-hazards, and large-scale geo-hazards also frequently happened here; (4) The advantage orientation of sliding was NW-SE, which was nearly orthogonal to the extension direction of the fault of Yingxiu-beichuan. This was closed correlation to the fact that the propagation of earthquake wave was perpendicular to the strike of fault; (5) Earthquake geo-hazards mainly developed in these regions where earthquake intensity was equal to or above IX. The density of development was nearly the same in XI intensity zone and X intensity zone. The geo-hazard density in IX intensity zone was only one-third of the two former zones. Whereas, the development density in VIII intensity zone was only one-tenth of XI intensity zone or X intensity zone.
A great number of collapse and slide geo-hazards had been triggered by 512 Wenchuan Earthquake, covering 0.1M km2 or so. Undoubtedly, their distribution was influenced by topography and morphology, stratigraphy, people's engineering operations, and so on. But their distribution mainly was controlled by the faults triggering seism, and they distributed along those faults like a ribbon. Based on the study in three geo-hazards concentration regions, namely, from Dujiangyan to Wenchuan, from Beichuan to Anxian and from Magong to Hongguang, the following fault effects of geo-hazards in Wenchuan Earthquake were found: (1) Because the triggering-earthquake faults were reverse fault, the distribution of geo-hazards showed clear Upper plate/lower plate effect. In detail, compared with lower plate, the upper plate had higher distribution density, wider scope and larger scale; (2) Intensely developed region of geo-hazard ranged from 0 to 7 km in upper plate. Moderately developed region ranged from 7 to 11km in upper plate, and from 0 to 5km in lower plate; Vast majority of lager-scale landslides were about 5km away from faults; (3) The transition and stagger parts of fractures are usually the concentration zone of geo-hazards, and large-scale geo-hazards also frequently happened here; (4) The advantage orientation of sliding was NW-SE, which was nearly orthogonal to the extension direction of the fault of Yingxiu-beichuan. This was closed correlation to the fact that the propagation of earthquake wave was perpendicular to the strike of fault; (5) Earthquake geo-hazards mainly developed in these regions where earthquake intensity was equal to or above IX. The density of development was nearly the same in XI intensity zone and X intensity zone. The geo-hazard density in IX intensity zone was only one-third of the two former zones. Whereas, the development density in VIII intensity zone was only one-tenth of XI intensity zone or X intensity zone.
2009, 17(1): 29-38.
Over 15,000 landslides were triggered by the Wenchuan Earthquake along the Main seismic fault and back fault of the Longmen Mt. tectonic belt. The area density of landslide coverage, i.e., the ratio of the landslide distribution and total area, is greater than 50 % in average and 70% in maximum along the Yingxiu-Gaochuan-Chenjiaba-Nanba of the main seismic fault. The enormous loosen rock masses easy for occurring landslides and debris flows will seriously threat the reconstruction and living, especially, during raining seasons.
The largest landslide triggered by the Wenchuan Earthquake is located at the Daguangbao, Anxian County, of the main seismic fault. The volume of the Daguangba landslide is 1.1 billion m3, and 4,500 m long from scarp to toe, 2,800 m long, 1,700 to 2,200 m wide and 200 m in average thickness, and 580 m in max thickness for accumulation. It is also the maximum volume of single landslide in China.
Much differences with other conventional landslides, the sliding surfaces are common incomplete and discontinued, and the exits were unclear in the epicenter area of the Wenchuan Earthquake, which illustrates the upper rock mass was strongly vibrated and separated, then thrown and crushed with the bedrock. The five patterns of the landslides are classified as staircase-shaped, convex-shaped, bowel-shaped, slump (vibrated-expansive)-shaped and huge rock-stone in a broad sense. The strong ground motion records and destroyed house cases present that the vertical seismic load is dominated within the epicenter area, i.e., the vertical is greater than the horizontal of seismic load. It provides an explanation why lots of landslides experienced the processes of broken-thrown-crushed-high speed debris flow.
Over 15,000 landslides were triggered by the Wenchuan Earthquake along the Main seismic fault and back fault of the Longmen Mt. tectonic belt. The area density of landslide coverage, i.e., the ratio of the landslide distribution and total area, is greater than 50 % in average and 70% in maximum along the Yingxiu-Gaochuan-Chenjiaba-Nanba of the main seismic fault. The enormous loosen rock masses easy for occurring landslides and debris flows will seriously threat the reconstruction and living, especially, during raining seasons.
The largest landslide triggered by the Wenchuan Earthquake is located at the Daguangbao, Anxian County, of the main seismic fault. The volume of the Daguangba landslide is 1.1 billion m3, and 4,500 m long from scarp to toe, 2,800 m long, 1,700 to 2,200 m wide and 200 m in average thickness, and 580 m in max thickness for accumulation. It is also the maximum volume of single landslide in China.
Much differences with other conventional landslides, the sliding surfaces are common incomplete and discontinued, and the exits were unclear in the epicenter area of the Wenchuan Earthquake, which illustrates the upper rock mass was strongly vibrated and separated, then thrown and crushed with the bedrock. The five patterns of the landslides are classified as staircase-shaped, convex-shaped, bowel-shaped, slump (vibrated-expansive)-shaped and huge rock-stone in a broad sense. The strong ground motion records and destroyed house cases present that the vertical seismic load is dominated within the epicenter area, i.e., the vertical is greater than the horizontal of seismic load. It provides an explanation why lots of landslides experienced the processes of broken-thrown-crushed-high speed debris flow.
2009, 17(1): 39-49.
The 512 M8.0 Wenchuan Earthquake induced a lot of slope instabilities (including landslide reactions). Study areas of this paper are 11 severest disaster counties including Wenchuan, Beichuan, Qingchuan, Anxian, Pingwu, Maoxian, Jiangyou, Pengzhou, Shifang, Mianzhu, Lixian. The geological settings of the areas including it's the topography and geomorphology, geologic structure, and lithology are detailed in this paper.
The interpretation and study on aerial photographs, satellite images and radar images of the areas show that slope instabilities occurred in the forms of rock fall, landslide and debris flow. The main form of slopes instabilities was debris flow, which was resulted from high-speed movement of rock fall mass or sliding mass. Sometimes, debris flows turned into mud rock flows if there were water participation. Barrier lakes formed when slope instability plugged up rivers.
It is found that the distribution of slope instability has the obvious feature of cluster grouping. Slopes instabilities were all located along the Longmen Shan fault zone, and especially controlled by the Beichuan-Yingxiu Fault which is one of the three sub-faults of Longmen Shan fault.
According to the distributed area of slopes instabilities, Wenchuan ranks the first with area of 131.55 km2. Beichuan ranks the second with area of 45.57 km2. The other nine counties (or cities) with similar areas varied from 6 km2 to 17 km2, where Lixian had the least area of 6.25 km2. Each type of slope instability has different scales and frequencies in different counties. Landslide is the main form of slope instability in Qingchuan and Pingwu. Debris flow is the predominant form in Wenchuan , Maoxian, Anxian and Beichuan. Rock fall is the predominant form in Shifang, Pengzhou, Mianzhu and Jiangyou.
The differences mentioned above are principally controlled by stratigraphy and lithology, and also have close relationship with geological structure, topography, and geomorphology. It has been shown that the lithology has crucial influence on the distribution of different form of slope instability. After GIS based statistical analysis, it is concluded that: (1) The harder the lithology is, the higher the incidence ratio of rock falls and debris flows is; (2) The incidence ratio of landslides is higher in the areas with soft rock, secondary soft rock and secondary hard rock; (3) The incidence ratio of mud rock flows is highest in the areas with soft rock. Topography and geomorphology have an important influence on the distribution of different form of slope instability. It is indicated that the rock fall, debris flow and mudflow have the highest incidence ratio in slopes with an elevation from 1200 m to 2000 m. Landslides have the highest incidence ratio in slopes with an elevation from 800 m to 1200 m. Incidence ratio of rock fall and debris flow increases with slope gradient increasing except 11 to 20. However, incidence ratio of landslides and mudflow presents typical single peak characteristic, becomes highest in the areas with slope gradient from 11 to 20 . Statistics indicated that the influence of slope aspect is not obvious on the slope instability induced by the earthquake.
The 512 M8.0 Wenchuan Earthquake induced a lot of slope instabilities (including landslide reactions). Study areas of this paper are 11 severest disaster counties including Wenchuan, Beichuan, Qingchuan, Anxian, Pingwu, Maoxian, Jiangyou, Pengzhou, Shifang, Mianzhu, Lixian. The geological settings of the areas including it's the topography and geomorphology, geologic structure, and lithology are detailed in this paper.
The interpretation and study on aerial photographs, satellite images and radar images of the areas show that slope instabilities occurred in the forms of rock fall, landslide and debris flow. The main form of slopes instabilities was debris flow, which was resulted from high-speed movement of rock fall mass or sliding mass. Sometimes, debris flows turned into mud rock flows if there were water participation. Barrier lakes formed when slope instability plugged up rivers.
It is found that the distribution of slope instability has the obvious feature of cluster grouping. Slopes instabilities were all located along the Longmen Shan fault zone, and especially controlled by the Beichuan-Yingxiu Fault which is one of the three sub-faults of Longmen Shan fault.
According to the distributed area of slopes instabilities, Wenchuan ranks the first with area of 131.55 km2. Beichuan ranks the second with area of 45.57 km2. The other nine counties (or cities) with similar areas varied from 6 km2 to 17 km2, where Lixian had the least area of 6.25 km2. Each type of slope instability has different scales and frequencies in different counties. Landslide is the main form of slope instability in Qingchuan and Pingwu. Debris flow is the predominant form in Wenchuan , Maoxian, Anxian and Beichuan. Rock fall is the predominant form in Shifang, Pengzhou, Mianzhu and Jiangyou.
The differences mentioned above are principally controlled by stratigraphy and lithology, and also have close relationship with geological structure, topography, and geomorphology. It has been shown that the lithology has crucial influence on the distribution of different form of slope instability. After GIS based statistical analysis, it is concluded that: (1) The harder the lithology is, the higher the incidence ratio of rock falls and debris flows is; (2) The incidence ratio of landslides is higher in the areas with soft rock, secondary soft rock and secondary hard rock; (3) The incidence ratio of mud rock flows is highest in the areas with soft rock. Topography and geomorphology have an important influence on the distribution of different form of slope instability. It is indicated that the rock fall, debris flow and mudflow have the highest incidence ratio in slopes with an elevation from 1200 m to 2000 m. Landslides have the highest incidence ratio in slopes with an elevation from 800 m to 1200 m. Incidence ratio of rock fall and debris flow increases with slope gradient increasing except 11 to 20. However, incidence ratio of landslides and mudflow presents typical single peak characteristic, becomes highest in the areas with slope gradient from 11 to 20 . Statistics indicated that the influence of slope aspect is not obvious on the slope instability induced by the earthquake.
2009, 17(1): 50-55.
The Hongshihe landslide dam, located at Qingchuan County, Sichuan Province, is one of the 34 large-scale landslide dams induced by the Great Wenchuan Earthquake on May 12, 2008. The Hongshi River was blocked by the Donghekou Landslide. The landslide debris formed the Hongshihe landslide dam approximately 50 m in height, 250 m in width, 500 m in length along the river. The dam reservoir capacity was estimated to be 6106m3. Field tests were conducted at the Hongshihe landslide dam after its breaching. The tests include soil erodibility tests and basic soil property tests. Based on in situ soil erosion resistance data, the breaching failure risk was studied. It is shown that the landslide soils can be eroded as long as there is overflow, which means the overtopping breaching failure risk of the Hongshihe landslide dam is quite high. Moreover, the breaching time is evaluated based on newly introduced empirical equations and is about 4.5 days. As the presence of boulders is not included in the analysis, the actual failure time could be longer than our estimation. The trend of soil erosion depth with time is also investigated. The methodology presented in the paper may provide some guidance in handling similar incidences in the future.
The Hongshihe landslide dam, located at Qingchuan County, Sichuan Province, is one of the 34 large-scale landslide dams induced by the Great Wenchuan Earthquake on May 12, 2008. The Hongshi River was blocked by the Donghekou Landslide. The landslide debris formed the Hongshihe landslide dam approximately 50 m in height, 250 m in width, 500 m in length along the river. The dam reservoir capacity was estimated to be 6106m3. Field tests were conducted at the Hongshihe landslide dam after its breaching. The tests include soil erodibility tests and basic soil property tests. Based on in situ soil erosion resistance data, the breaching failure risk was studied. It is shown that the landslide soils can be eroded as long as there is overflow, which means the overtopping breaching failure risk of the Hongshihe landslide dam is quite high. Moreover, the breaching time is evaluated based on newly introduced empirical equations and is about 4.5 days. As the presence of boulders is not included in the analysis, the actual failure time could be longer than our estimation. The trend of soil erosion depth with time is also investigated. The methodology presented in the paper may provide some guidance in handling similar incidences in the future.
2009, 17(1): 56-61.
Risk management of geohazards is a cognition and model of effective disaster mitigation in order to make recommendations for prevention, preparedness and response. The increased vulnerability and risk of many urban areas in strong seismic zone is a major reason for these areas suffering from more serious damage. This paper discusses some main aspects concerning risk management which involves risk analysis, action preparedness and disaster response for urban geohazard mitigation in strong seismic zone. Therefore, the research of risk management of geohazards becomes an important project for urban geohazard reduction. This paper describes the advances in risk management of geohazards and puts forward the future study contents and methodology. They involve in five aspects: (1) risk structure and risk quantizing analysis of urban geohazards in strong seismic zone; (2) establishment in risk criterion and risk principle of urban seismic geohazards; (3) study on methodology of risk management of urban geohazards in strong seismic zone; (4) effective monitoring and control mechanism for risk management of urban seismic geohazards; (5) study on patterns and systems for risk management of urban geohazards in strong seismic zone.
Risk management of geohazards is a cognition and model of effective disaster mitigation in order to make recommendations for prevention, preparedness and response. The increased vulnerability and risk of many urban areas in strong seismic zone is a major reason for these areas suffering from more serious damage. This paper discusses some main aspects concerning risk management which involves risk analysis, action preparedness and disaster response for urban geohazard mitigation in strong seismic zone. Therefore, the research of risk management of geohazards becomes an important project for urban geohazard reduction. This paper describes the advances in risk management of geohazards and puts forward the future study contents and methodology. They involve in five aspects: (1) risk structure and risk quantizing analysis of urban geohazards in strong seismic zone; (2) establishment in risk criterion and risk principle of urban seismic geohazards; (3) study on methodology of risk management of urban geohazards in strong seismic zone; (4) effective monitoring and control mechanism for risk management of urban seismic geohazards; (5) study on patterns and systems for risk management of urban geohazards in strong seismic zone.
2009, 17(1): 62-69.
The geological condition and excavation shape of a high rock slope at the water-intake of a hydropower station are very complex. The faults, joints and fissures develop well in the rock mass and cut each other, which makes the engineering geological property for the rock mass to degenerate. The average excavation inclination is 88 and the maximal height difference is 106 m including vertical height part of 81 m from the dam crest to the bottom of the water-intake. The maximal horizontal depth of excavation is about 170 m. During the slope excavation, a series of deformation and fracture phenomena appear along the concrete surface covering the slope. They mainly includes cracks and surface bulging. Combining the engineering geological conditions and the monitoring data of the scene, a systematic analysis is made on the mechanism of deformation and fracture. The results indicate that the unloading fracture zone of the high rock slope especially in a high-intensive geo-stress environment is very significant in rock slope engineering. So, the fracture system is the normal response of the unloading and relaxation. Base on the analysis, the assessment is made on the slope stability. The analytical results show that the slope is stable at present.
The geological condition and excavation shape of a high rock slope at the water-intake of a hydropower station are very complex. The faults, joints and fissures develop well in the rock mass and cut each other, which makes the engineering geological property for the rock mass to degenerate. The average excavation inclination is 88 and the maximal height difference is 106 m including vertical height part of 81 m from the dam crest to the bottom of the water-intake. The maximal horizontal depth of excavation is about 170 m. During the slope excavation, a series of deformation and fracture phenomena appear along the concrete surface covering the slope. They mainly includes cracks and surface bulging. Combining the engineering geological conditions and the monitoring data of the scene, a systematic analysis is made on the mechanism of deformation and fracture. The results indicate that the unloading fracture zone of the high rock slope especially in a high-intensive geo-stress environment is very significant in rock slope engineering. So, the fracture system is the normal response of the unloading and relaxation. Base on the analysis, the assessment is made on the slope stability. The analytical results show that the slope is stable at present.
STABILITY CHECKING AND ANCHORING FORCE RESEARCH OF WATER-INTAKE SLOPE AT XIAOWAN HYDROPOWER STATION
2009, 17(1): 70-75.
During the construction of Xiaowan hydropower, based on field investigation, project researchers analysed and checked orientation and property of every controlling structural planes in the water-intake slope, and determined seven movable blocks. Based on the block theory, this paper calculated stability coefficient and anchoring force of every movable block. The result shows that the main block controlling the stability of the water-intake slope is located on south side of the f89-1 fault. Its lower limit anchoring force is 351029 kN. Based on this anchoring force and the result of 2D limiting equilibrium analysis, the total anchoring force of the water-intake slope is determined as 516121.5 kN. It is evidently less than the former result.
During the construction of Xiaowan hydropower, based on field investigation, project researchers analysed and checked orientation and property of every controlling structural planes in the water-intake slope, and determined seven movable blocks. Based on the block theory, this paper calculated stability coefficient and anchoring force of every movable block. The result shows that the main block controlling the stability of the water-intake slope is located on south side of the f89-1 fault. Its lower limit anchoring force is 351029 kN. Based on this anchoring force and the result of 2D limiting equilibrium analysis, the total anchoring force of the water-intake slope is determined as 516121.5 kN. It is evidently less than the former result.
2009, 17(1): 76-80.
The rock mass quality surrounding the underground plant of a pumped storage station is classified with BQ and Q classification systems. The distribution of rock masses with poor quality is pointed out. The results indicate that the rock mass quality is commonly at the gradeⅡor Ⅲ. On the other hand, the result of wave velocity testing shows that the wave velocity of the rock mass of gradeⅡor Ⅲ is between 4200~5300 ms-1, and these rock mass has good stability. However, the wave velocity of the grade Ⅳand Ⅴ is less than 4000 ms-1. Especially, the rock mass wave of the grade Ⅴ is less than 2200 ms-1. The rock mass quality indices from the two classification systems have similarities. The two indices have the relationship of exponential function. The relation between wave velocity and \[BQ\] is linear. For the same project, the classification results from the two classification systems are different, but the classification bases are similar, which are dominated by the geological elements. So, there are the methods for conversion and comparison between the two classification systems.
The rock mass quality surrounding the underground plant of a pumped storage station is classified with BQ and Q classification systems. The distribution of rock masses with poor quality is pointed out. The results indicate that the rock mass quality is commonly at the gradeⅡor Ⅲ. On the other hand, the result of wave velocity testing shows that the wave velocity of the rock mass of gradeⅡor Ⅲ is between 4200~5300 ms-1, and these rock mass has good stability. However, the wave velocity of the grade Ⅳand Ⅴ is less than 4000 ms-1. Especially, the rock mass wave of the grade Ⅴ is less than 2200 ms-1. The rock mass quality indices from the two classification systems have similarities. The two indices have the relationship of exponential function. The relation between wave velocity and \[BQ\] is linear. For the same project, the classification results from the two classification systems are different, but the classification bases are similar, which are dominated by the geological elements. So, there are the methods for conversion and comparison between the two classification systems.
2009, 17(1): 81-87.
The instability of a cut slope at Yuanjiawan section of Lan-Lin expressway is typically controlled and influenced by human activities, under the influence of obvious neotectonic movement, strong fold and fault structures, formed in dip bedded sandy conglomerate intercalated with shale of broken loose structure and serious surface weathering. The paper employs the analysis methods of engineering geology combined with Flac3D numerical simulation and analyses the sliding characteristics of repetition, succession, similarity and gradual increase, as well as the damaged form of independency and variety, because of a variety of the transformation forms of the human activities. The results show that the instability is characterised by evolutional process of continuously increasing damaged scale at the cut slope by human beings and gradually developed to the present natural state.
The instability of a cut slope at Yuanjiawan section of Lan-Lin expressway is typically controlled and influenced by human activities, under the influence of obvious neotectonic movement, strong fold and fault structures, formed in dip bedded sandy conglomerate intercalated with shale of broken loose structure and serious surface weathering. The paper employs the analysis methods of engineering geology combined with Flac3D numerical simulation and analyses the sliding characteristics of repetition, succession, similarity and gradual increase, as well as the damaged form of independency and variety, because of a variety of the transformation forms of the human activities. The results show that the instability is characterised by evolutional process of continuously increasing damaged scale at the cut slope by human beings and gradually developed to the present natural state.
2009, 17(1): 88-93.
This paper is based on lots of dynamic consolidation data in collapsible loess area. It uses the method of frequency statistics to determine factor weights according to the concept of variable weight. It sets up a case-based reasoning model in association with fuzzy analogy preferred ratio for predicting the effective depth of collapsible loess treated with dynamic consolidation. Examples of dynamic consolidation are taken as base cases, while examples that will be analyzed are taken as target cases in this model. Corresponding evaluation index is selected as the fuzzy factor. The similarity of fuzzy factors between base cases and target cases is calculated. The similar series are determined. The most similar base case to target case is found out in terms of the effective reinforced depth. Finally, the effective reinforced depth of dynamic consolidation can be predicted. It is shown from examples that the differences between the predicted and measured values are within 10%. Therefore, this is an effective method with high prediction precision and worth to be used.
This paper is based on lots of dynamic consolidation data in collapsible loess area. It uses the method of frequency statistics to determine factor weights according to the concept of variable weight. It sets up a case-based reasoning model in association with fuzzy analogy preferred ratio for predicting the effective depth of collapsible loess treated with dynamic consolidation. Examples of dynamic consolidation are taken as base cases, while examples that will be analyzed are taken as target cases in this model. Corresponding evaluation index is selected as the fuzzy factor. The similarity of fuzzy factors between base cases and target cases is calculated. The similar series are determined. The most similar base case to target case is found out in terms of the effective reinforced depth. Finally, the effective reinforced depth of dynamic consolidation can be predicted. It is shown from examples that the differences between the predicted and measured values are within 10%. Therefore, this is an effective method with high prediction precision and worth to be used.
2009, 17(1): 94-99.
After the railroad has been constructed in permafrost regions, the balance of heat income and expense will be changed to a new one. At the same time, the change acts on the feature of permafrost. Based on the monitored data along the Qinghai-Tibet railway, the changes of permafrost under the railway are analyzed. The results indicate that the permafrost table was raised and the ground temperature increased. The permafrost thermal thawing sensitivity and permafrost thermal stability of permafrost under the roadbed have respectively increased and decreased comparing with those of permafrost under the nature surface after construction of ordinary embankments. All the changes of permafrost may influence the stability of the railway embankment.
After the railroad has been constructed in permafrost regions, the balance of heat income and expense will be changed to a new one. At the same time, the change acts on the feature of permafrost. Based on the monitored data along the Qinghai-Tibet railway, the changes of permafrost under the railway are analyzed. The results indicate that the permafrost table was raised and the ground temperature increased. The permafrost thermal thawing sensitivity and permafrost thermal stability of permafrost under the roadbed have respectively increased and decreased comparing with those of permafrost under the nature surface after construction of ordinary embankments. All the changes of permafrost may influence the stability of the railway embankment.
2009, 17(1): 100-104.
The huge deep saline aquifer buried in Songliao sedimentary basin is a one of good geological media for CO2 geological storage. Reliable and reasonable estimation of CO2 storage capacity is an important factor for site selection and development. The universal pyramid method is introduced to assess the CO2 storage capacity for the sedimentary basin. The deep saline aquifer of Songliao basin is mainly made up of Cretaceous Nenjiang Group sandstone and Qingshankou Group sandstone. The saline aquifer has well developed porosity and the continuous sealing trap is overlying it. All of these determine that it can be used to CO2 storage. The pyramid method is applied to the deep saline aquifer of Songliao basin and the effective storage capacity of CO2 is about 6916Gt.
The huge deep saline aquifer buried in Songliao sedimentary basin is a one of good geological media for CO2 geological storage. Reliable and reasonable estimation of CO2 storage capacity is an important factor for site selection and development. The universal pyramid method is introduced to assess the CO2 storage capacity for the sedimentary basin. The deep saline aquifer of Songliao basin is mainly made up of Cretaceous Nenjiang Group sandstone and Qingshankou Group sandstone. The saline aquifer has well developed porosity and the continuous sealing trap is overlying it. All of these determine that it can be used to CO2 storage. The pyramid method is applied to the deep saline aquifer of Songliao basin and the effective storage capacity of CO2 is about 6916Gt.
2009, 17(1): 105-110.
The expression of the potential energy of the total piles in row with top brace retaining system in long strip foundation pit is established. According to the minimum potential theory, a solution to the maximum displacement of the top beam and the pile is derived. Then the expression of the piles in row with the top brace is given. The effects of the retaining structural parameters on the maximum displacement are discussed. At last, a practical example is presented. The calculated result is compared with the measured result. The comparison shows the method is feasible．
The expression of the potential energy of the total piles in row with top brace retaining system in long strip foundation pit is established. According to the minimum potential theory, a solution to the maximum displacement of the top beam and the pile is derived. Then the expression of the piles in row with the top brace is given. The effects of the retaining structural parameters on the maximum displacement are discussed. At last, a practical example is presented. The calculated result is compared with the measured result. The comparison shows the method is feasible．
2009, 17(1): 111-114.
This paper presents and analzes the monitored results of the surface settlement, subsection-settlements at a soft soil ground treated with vacuum drainage preloading in the coastal region of Tianjin. The total surface settlements reached about 80 to 160 mm. They were composed of the construction settlement and the pre-construction settlement. By subsection-settlement monitoring, the main settlement happened in the dredged fill and marine soft soil. The disturbed soil which produced by construction induced the avoidable errors of the subsection-settlement. With drainage strips, the characters of soils were changed. Through theoretic deduction and practical calculation on the soil consolidation degree, the results suggest that the correlative way in the foundation treatment manu should be adopted and the immediate settlement should not be ignored. At the site of the vacuum drainage preloading, the special character of the soft soil and its influence on the construction of excavation, pile foundtion etc should be investigated further more.
This paper presents and analzes the monitored results of the surface settlement, subsection-settlements at a soft soil ground treated with vacuum drainage preloading in the coastal region of Tianjin. The total surface settlements reached about 80 to 160 mm. They were composed of the construction settlement and the pre-construction settlement. By subsection-settlement monitoring, the main settlement happened in the dredged fill and marine soft soil. The disturbed soil which produced by construction induced the avoidable errors of the subsection-settlement. With drainage strips, the characters of soils were changed. Through theoretic deduction and practical calculation on the soil consolidation degree, the results suggest that the correlative way in the foundation treatment manu should be adopted and the immediate settlement should not be ignored. At the site of the vacuum drainage preloading, the special character of the soft soil and its influence on the construction of excavation, pile foundtion etc should be investigated further more.
2009, 17(1): 115-118.
A key problem in the reinforcement design of soil slope is how to determine the most dangerous sliding circle surface and calculate the minimum safety factor. The traditional optimization algorithm is very easy to fall into the local minimum and not find the real most dangerous sliding circle surface. And some optimize effect of the intelligent optimization algorithm is not very satisfactory because of their immature. For this reason, a new intelligent optimization algorithm is developed for searching the optimal solution. It is the chaos optimization algorithm combinating the Bishop method. Chaostic movement has its inherent characteristics, ergodicity, randomness and regularity. The optimization algorithm adopts these inherent characteristics to loop through all the state and get out of the local optimal solutions. It has a strong global search capability. The engineering application case indicates that the chaos optimization algorithm can get the optimization result, and the genetic algorithm and improved simulated annealing algorithm can not successfully solve the problem. Comparison to the enumeration method indicates that the chaos optimization algorithm is a reliability method. The chaos optimization algorithm can successfully solve the problem that how to search the best solution of soil slope. It is expected that the chaos optimization algorithm would be widely used in slope engineering.
A key problem in the reinforcement design of soil slope is how to determine the most dangerous sliding circle surface and calculate the minimum safety factor. The traditional optimization algorithm is very easy to fall into the local minimum and not find the real most dangerous sliding circle surface. And some optimize effect of the intelligent optimization algorithm is not very satisfactory because of their immature. For this reason, a new intelligent optimization algorithm is developed for searching the optimal solution. It is the chaos optimization algorithm combinating the Bishop method. Chaostic movement has its inherent characteristics, ergodicity, randomness and regularity. The optimization algorithm adopts these inherent characteristics to loop through all the state and get out of the local optimal solutions. It has a strong global search capability. The engineering application case indicates that the chaos optimization algorithm can get the optimization result, and the genetic algorithm and improved simulated annealing algorithm can not successfully solve the problem. Comparison to the enumeration method indicates that the chaos optimization algorithm is a reliability method. The chaos optimization algorithm can successfully solve the problem that how to search the best solution of soil slope. It is expected that the chaos optimization algorithm would be widely used in slope engineering.
2009, 17(1): 119-125.
An elasto-plastic model of intact rock is established and added to the existing numerical manifold method (NMM) for deformation and strength analysis. The corresponding VC++ program is then developed. For verification, several load simulations of rock specimens are carried out. The computed results show a favorable agreement with either analytical or physical test results. Since the NMM has the inherent advantage in dealing with rock discontinuities, the new NMM program equipped with the capacity of elasto-plastic analysis can be an effective tool for more geotechnical projects. . The stability of a rock slope is analyzed with the program. In addition, rock bolts are taken into account in the simulation process. Different rock bolting design schemes are compared through the numerical simulation. The computed results offer the displacement field, the stress distribution and the evolution of plasticity, which show that rock bolts can prevent the joints in the slope from cracking and the prestressed bolts can efficiently restrict the evolution of plasticity. In addition, it is observed that rock bolts combine the rock blocks on both sides of the joint to deform consistently, enhancing the entirety of the rock slope.
An elasto-plastic model of intact rock is established and added to the existing numerical manifold method (NMM) for deformation and strength analysis. The corresponding VC++ program is then developed. For verification, several load simulations of rock specimens are carried out. The computed results show a favorable agreement with either analytical or physical test results. Since the NMM has the inherent advantage in dealing with rock discontinuities, the new NMM program equipped with the capacity of elasto-plastic analysis can be an effective tool for more geotechnical projects. . The stability of a rock slope is analyzed with the program. In addition, rock bolts are taken into account in the simulation process. Different rock bolting design schemes are compared through the numerical simulation. The computed results offer the displacement field, the stress distribution and the evolution of plasticity, which show that rock bolts can prevent the joints in the slope from cracking and the prestressed bolts can efficiently restrict the evolution of plasticity. In addition, it is observed that rock bolts combine the rock blocks on both sides of the joint to deform consistently, enhancing the entirety of the rock slope.
2009, 17(1): 126-132.
The No.1 cave and other four caves of Longyou Grottoes have been used for tourism and research over sixteen years. Within these years, plentiful and substantial socioeconomic performance and academic achievement have been obtained. But, these caves have been damaged to some extent by action of natural powers. Pillars, walls and roofs of the grotto have been cracked, because argillaceous sandstone forming the caves are prone to weathering and flowing deformation, and destruction by reasons of alternation of wetting and drying and temperature fluctuation. Roofs, pillars and walls of the caves were failed in the mode of punching shear, shearing and bending under action of weight because of insufficient strength, and external force in the process of exploitation aggravated the destruction. Layout of reinforcement should adopt integrated design and be carried into execution step by step for these failure modes. Pillars and walls should be reinforced firstly, and then roof of caves. Pillars and walls should be reinforced by pillars mostly and the roofs should be reinforced by beams. Both reinforcement instruments should be connected and form an artistic reinforcement system.
The No.1 cave and other four caves of Longyou Grottoes have been used for tourism and research over sixteen years. Within these years, plentiful and substantial socioeconomic performance and academic achievement have been obtained. But, these caves have been damaged to some extent by action of natural powers. Pillars, walls and roofs of the grotto have been cracked, because argillaceous sandstone forming the caves are prone to weathering and flowing deformation, and destruction by reasons of alternation of wetting and drying and temperature fluctuation. Roofs, pillars and walls of the caves were failed in the mode of punching shear, shearing and bending under action of weight because of insufficient strength, and external force in the process of exploitation aggravated the destruction. Layout of reinforcement should adopt integrated design and be carried into execution step by step for these failure modes. Pillars and walls should be reinforced firstly, and then roof of caves. Pillars and walls should be reinforced by pillars mostly and the roofs should be reinforced by beams. Both reinforcement instruments should be connected and form an artistic reinforcement system.
2009, 17(1): 132-137.
There is medium Karst nature dolomite limestone at a mud storage site in Pingnan. Due to geological actions, the limestone has numerous crannies. The Karst in the dolomite limestone developed along the geology structure asymmetrically when the dolomite limestone influenced by the climate condition of high annual precipitation, high annual evaporation and high air temperature. And there are fourteen Karst areas at site. Karst is severer at shallow depth than at deep depth. The shallow Karst forms are sinkholes and Karst pits (Karst grooves). The main deep Karst form is Karst cranny. The Karst forms small underground river net and the underground water link with the underground water outside the site. The seepage at the site is pipe-seepage and cranny scatter seepage. There are strong, medium, and weak Karst seepage areas according to the seepage intensity. The method to deal with the seepage in the strong Karst seepage area is to silting the small Karst forms, step over the big Karst forms with boards, then carpet use clay and anti-seepage cloth. The method to deal with the seepage in the other Karst seepage areas are to silt the small Karst forms, chisel off the extrusive, then carpet use clay and anti-seepage cloth.
There is medium Karst nature dolomite limestone at a mud storage site in Pingnan. Due to geological actions, the limestone has numerous crannies. The Karst in the dolomite limestone developed along the geology structure asymmetrically when the dolomite limestone influenced by the climate condition of high annual precipitation, high annual evaporation and high air temperature. And there are fourteen Karst areas at site. Karst is severer at shallow depth than at deep depth. The shallow Karst forms are sinkholes and Karst pits (Karst grooves). The main deep Karst form is Karst cranny. The Karst forms small underground river net and the underground water link with the underground water outside the site. The seepage at the site is pipe-seepage and cranny scatter seepage. There are strong, medium, and weak Karst seepage areas according to the seepage intensity. The method to deal with the seepage in the strong Karst seepage area is to silting the small Karst forms, step over the big Karst forms with boards, then carpet use clay and anti-seepage cloth. The method to deal with the seepage in the other Karst seepage areas are to silt the small Karst forms, chisel off the extrusive, then carpet use clay and anti-seepage cloth.
2009, 17(1): 138-144.
After having been operated for several years, a highway tunnel produces the diseases of lining cracks and tunnel settlement in loess area. Analysis of the development process of the diseases indicates that the main causes are loess characteristics, surface water and the depth of loess tunnel. In response to the diseases, a finite element analysis is conducted for four different conditions of the reinforcement measures. The numerical results show that the local structural reinforcement, surface water treatment, and the soil-structure interaction can reduce stress concentration and improve the tunnel stress distribution. The reinforcement at the bottom corners of tunnel arch structures can strengthen the overall stress distribution more reasonable and enhance the tunnel ability to undertake external loading. Hence, the tunnel lining cracks should be repaired and strengthened. At the same time, the arch foot foundation should be reinforced with root pile and rammed-pedestal pile. These measures would improve the safety of the tunnel capacity.
After having been operated for several years, a highway tunnel produces the diseases of lining cracks and tunnel settlement in loess area. Analysis of the development process of the diseases indicates that the main causes are loess characteristics, surface water and the depth of loess tunnel. In response to the diseases, a finite element analysis is conducted for four different conditions of the reinforcement measures. The numerical results show that the local structural reinforcement, surface water treatment, and the soil-structure interaction can reduce stress concentration and improve the tunnel stress distribution. The reinforcement at the bottom corners of tunnel arch structures can strengthen the overall stress distribution more reasonable and enhance the tunnel ability to undertake external loading. Hence, the tunnel lining cracks should be repaired and strengthened. At the same time, the arch foot foundation should be reinforced with root pile and rammed-pedestal pile. These measures would improve the safety of the tunnel capacity.
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