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Editor Work2008 Vol. 16, No. 6
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2008, 16(6): 721-729.
Abstract
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Wenchuan Earthquake occurred in the Longmen Mountain region, which geologic environment is very weak, and the earthquake with high magnitude, large energy, long duration and other characteristics. Wenchuan Earthquake directly induced thousands of rock fall and collapses. Some unique kinetics characteristics of these collapses have been found during the earthquake. Based on lots of collapse site investigations around Wenchuan area and combined with the characteristics of construction and slope broken patterns, the paper represents the kinetic characteristics of cracking, horizontal throwing and debris flows triggered by earthquake. It may provide some new clues to attribute the research on the causes of strong earthquake.
Wenchuan Earthquake occurred in the Longmen Mountain region, which geologic environment is very weak, and the earthquake with high magnitude, large energy, long duration and other characteristics. Wenchuan Earthquake directly induced thousands of rock fall and collapses. Some unique kinetics characteristics of these collapses have been found during the earthquake. Based on lots of collapse site investigations around Wenchuan area and combined with the characteristics of construction and slope broken patterns, the paper represents the kinetic characteristics of cracking, horizontal throwing and debris flows triggered by earthquake. It may provide some new clues to attribute the research on the causes of strong earthquake.
2008, 16(6): 730-741.
The landslide at Daguangbao and Hongdongzigou site is the largest among all landslides occurred during the Wenchuan Earthquake. Its volume is up to 742 Mm3, and its debris dam height reaches 690 m. So it is also the most largest scale landslide triggered by earthquake among all investigated landslides in China. Additionally, it has the highest debris dam originating from landslide in China. It is even one of a few super large-scale landslides known all over the world, whose individual volume is over 500 Mm3. The debris dam formed by this landslide can be the highest around the world. The landslide is located on the upper plate of the Causative Fault. It is nearly 7 km away from the triggering seismic fracture of Yingxiu-beichuan fault. The slope was an isolated ridge before the Earthquake. it's the ridge had its 3 sides cut. Its height difference reaches 1500 m. The strike of clinothen was almost vertical to the slope surface. the clinothen had perfect extension. They composed together the basic conditions of sliding surface formation. Our investigation and analysis show that the free surface conditions of the slope and the surface connectivity of limestone bedding plane were the base of landslide formation. And the ground movement resulted from the intensive quaking with large intensity and long duration was the radical triggering factor of the landslide. The mechanism and process of the landslide could be divided into 4 stages as follows: (a) the stage of slope body shatter, relaxation and disintegration, (b) the stage of high speed sliding, 9c) the stage of accumulation with shock, and (d) the stage of the second projectile and debris flow deposition. Because of destabilization and high speed sliding down, the slope mass composed a deposit body along main direction of sliding, 4.2 km long and 2.2 km wide. High-speed clastic flow crossed downstream Fengboyan, and formed a deposit zone of debris flow along Hongdongzigou, 1 km long.
The landslide at Daguangbao and Hongdongzigou site is the largest among all landslides occurred during the Wenchuan Earthquake. Its volume is up to 742 Mm3, and its debris dam height reaches 690 m. So it is also the most largest scale landslide triggered by earthquake among all investigated landslides in China. Additionally, it has the highest debris dam originating from landslide in China. It is even one of a few super large-scale landslides known all over the world, whose individual volume is over 500 Mm3. The debris dam formed by this landslide can be the highest around the world. The landslide is located on the upper plate of the Causative Fault. It is nearly 7 km away from the triggering seismic fracture of Yingxiu-beichuan fault. The slope was an isolated ridge before the Earthquake. it's the ridge had its 3 sides cut. Its height difference reaches 1500 m. The strike of clinothen was almost vertical to the slope surface. the clinothen had perfect extension. They composed together the basic conditions of sliding surface formation. Our investigation and analysis show that the free surface conditions of the slope and the surface connectivity of limestone bedding plane were the base of landslide formation. And the ground movement resulted from the intensive quaking with large intensity and long duration was the radical triggering factor of the landslide. The mechanism and process of the landslide could be divided into 4 stages as follows: (a) the stage of slope body shatter, relaxation and disintegration, (b) the stage of high speed sliding, 9c) the stage of accumulation with shock, and (d) the stage of the second projectile and debris flow deposition. Because of destabilization and high speed sliding down, the slope mass composed a deposit body along main direction of sliding, 4.2 km long and 2.2 km wide. High-speed clastic flow crossed downstream Fengboyan, and formed a deposit zone of debris flow along Hongdongzigou, 1 km long.
2008, 16(6): 742-750.
The great Wenchuan Earthquake of Ms 8.0 grade took place in the Longmenshan fault zone of western Sichuan Province on May 12, 2008. Many tunnels on the highway from Dujiangyan to Wenchuan were damaged severely due to the site located near the epicenter. Through the on-site investigation and research, the data collection and analysis, this paper illustrates the failure types and characteristics of the mountain tunnels in the severe earthquake region. It further summarizes the basic types as the avalanche and sliding of tunnel opening, the rhegma of tunnel portal, the collapse of liner and surrounding rock, the crack and dislocation of liner, the uplift and crack of arch invert, the deformation and crack of preliminary bracing. Then, the influencing factors of the tunnel seismic damages are discussed by taking into account especially the controlling functions of the secondary faults of earthquake fractures, the contact zone between cover and bedrock, the unstable slope in the tunnel face, and the weak surrounding rock in high geostress environment on the strong seismic damages. Finally, some revelations of the tunnel earthquake-resistance are summarized based on the natural results of the mountain tunnel damages in Wenchuan Earthquake. It is suggested that in strong earthquake areas, a comprehensive aseismic design be conducted considering the slope of tunnel face, naked tunnel and tunnel portal structure as a system. For tunnel crossing the secondary faults of active fractures, the reinforced concrete structure should be used in the second lining along the faults and their bilateral some distances. For the contact zones between cover and bedrock, the change zones between weak and hard rockmasses, the jump zones of surrounding rock quality and so on, they should be treated by the methods of improving their mechanical property and making it gradual change in preliminary bracing.
The great Wenchuan Earthquake of Ms 8.0 grade took place in the Longmenshan fault zone of western Sichuan Province on May 12, 2008. Many tunnels on the highway from Dujiangyan to Wenchuan were damaged severely due to the site located near the epicenter. Through the on-site investigation and research, the data collection and analysis, this paper illustrates the failure types and characteristics of the mountain tunnels in the severe earthquake region. It further summarizes the basic types as the avalanche and sliding of tunnel opening, the rhegma of tunnel portal, the collapse of liner and surrounding rock, the crack and dislocation of liner, the uplift and crack of arch invert, the deformation and crack of preliminary bracing. Then, the influencing factors of the tunnel seismic damages are discussed by taking into account especially the controlling functions of the secondary faults of earthquake fractures, the contact zone between cover and bedrock, the unstable slope in the tunnel face, and the weak surrounding rock in high geostress environment on the strong seismic damages. Finally, some revelations of the tunnel earthquake-resistance are summarized based on the natural results of the mountain tunnel damages in Wenchuan Earthquake. It is suggested that in strong earthquake areas, a comprehensive aseismic design be conducted considering the slope of tunnel face, naked tunnel and tunnel portal structure as a system. For tunnel crossing the secondary faults of active fractures, the reinforced concrete structure should be used in the second lining along the faults and their bilateral some distances. For the contact zones between cover and bedrock, the change zones between weak and hard rockmasses, the jump zones of surrounding rock quality and so on, they should be treated by the methods of improving their mechanical property and making it gradual change in preliminary bracing.
2008, 16(6): 751-758.
The intense rainfall on 24th September 2008 initiated widespread debris flows in Beichuan County, the epicenter of the Wenchuan Earthquake. These debris flows greatly impacted the community of the Beichuan County and caused 42 fatalities. The debris flows also damaged many roads and other infrastructures in the mountainous areas. Field reconnaisance and interpretations of aerial photographs were used to identify debris flow occurrences. Precipitation data were then utilized to analyze critical rainfall conditions leading to the debris flow initiation. This study examines the process of debris-flow initiation and transport in the study areas and presents field observations on the roles of rainfall, lithology, and faults. Particular emphasis is given to the roles of intense precipitation and source areas. The character and spatial distribution of lithology, faults and topography appear to control the initiation processes of debris flows in the mountainous area. The study results show that after the Wenchuan Earthquake, critical accumulated precipitation and hourly rainfall intensity necessary to initiate debris flow reduced to as low as 14.8%～22.1% and 25.4 %～31.6% respectively comparing with those before the earthquake. Through emergency field investigation, 72 debris-flows triggered by the rainfall were identified. Almost all debris flow gullies in the drainage basins have contained many seismic landslides, which supply debris flow source areas with huge loose material. Two types of failure mechanisms initiated the debris flows: the first initiation involved the mobilization of shallow landslides and the second process, which was explained with term of the fire-hose effect initiated debris flows. The overland flow of water resulting from intense rainfall was concentrated in steep channels and scoured debris from gully-bed loose deposits. The study also indicated that the region affected by the Wenchuan Earthquake become more vulnerable to debris flows in this period. Therefore it is important to assess debris flow risk and take hazard monitoring and early warning in the earthquake areas. The control work is also necessary for debris flow hazard mitigation.
The intense rainfall on 24th September 2008 initiated widespread debris flows in Beichuan County, the epicenter of the Wenchuan Earthquake. These debris flows greatly impacted the community of the Beichuan County and caused 42 fatalities. The debris flows also damaged many roads and other infrastructures in the mountainous areas. Field reconnaisance and interpretations of aerial photographs were used to identify debris flow occurrences. Precipitation data were then utilized to analyze critical rainfall conditions leading to the debris flow initiation. This study examines the process of debris-flow initiation and transport in the study areas and presents field observations on the roles of rainfall, lithology, and faults. Particular emphasis is given to the roles of intense precipitation and source areas. The character and spatial distribution of lithology, faults and topography appear to control the initiation processes of debris flows in the mountainous area. The study results show that after the Wenchuan Earthquake, critical accumulated precipitation and hourly rainfall intensity necessary to initiate debris flow reduced to as low as 14.8%～22.1% and 25.4 %～31.6% respectively comparing with those before the earthquake. Through emergency field investigation, 72 debris-flows triggered by the rainfall were identified. Almost all debris flow gullies in the drainage basins have contained many seismic landslides, which supply debris flow source areas with huge loose material. Two types of failure mechanisms initiated the debris flows: the first initiation involved the mobilization of shallow landslides and the second process, which was explained with term of the fire-hose effect initiated debris flows. The overland flow of water resulting from intense rainfall was concentrated in steep channels and scoured debris from gully-bed loose deposits. The study also indicated that the region affected by the Wenchuan Earthquake become more vulnerable to debris flows in this period. Therefore it is important to assess debris flow risk and take hazard monitoring and early warning in the earthquake areas. The control work is also necessary for debris flow hazard mitigation.
2008, 16(6): 759-763.
Our reconnaissance to the mountainous epicenter zones of the Wenchuan Earthquake shows that the geohazard distribution in the Longmen Shan is heterogeneous on both horizontal and vertical directions. The geohazards are concentrated along the seismic fractures and non-seismic fractures in horizontal and at the top, river shoulders and isolated topography in vertical. The movement process can be divided into three stages of zero-length accelerated launching, gliding and -landing. The development of the geo-hazards is controlled by the seismic fracture, high intensity, duration of the earthquake, topography effects, the composed lithology and textures of the mountainous slopes.
Our reconnaissance to the mountainous epicenter zones of the Wenchuan Earthquake shows that the geohazard distribution in the Longmen Shan is heterogeneous on both horizontal and vertical directions. The geohazards are concentrated along the seismic fractures and non-seismic fractures in horizontal and at the top, river shoulders and isolated topography in vertical. The movement process can be divided into three stages of zero-length accelerated launching, gliding and -landing. The development of the geo-hazards is controlled by the seismic fracture, high intensity, duration of the earthquake, topography effects, the composed lithology and textures of the mountainous slopes.
2008, 16(6): 764-773.
The post-earthquake reconstruction of damaged cities and towns requires reasonable site selection and safety assessment. Site selection task involves complex factors such as earthquake fault, geologic hazard, site stability, national well-being and the people's livelihood, and economic development and sustainability. It is a task of complicated engineering system. Problem considerations can follow these basic principles: (a) to the towns which located at the earthquake fault zones and deterioration on geological environment and had severe hidden danger of geologic hazard, they must be removed to other places; (b) to the towns which was damaged, but is far away from the earthquake fault zones and does not exist geologic hazard, they should be in-situ reconstructed and the reconstruction should be carried out according to principles of science planning, avoidance norms, reasonable adjustment to the aseismicity standards. On the process of the post-earthquake reconstruction, attentions should be paid to the disguised geologic hazards, multiplicity of induced factors and long-term sustainability and to strengthen suitability evaluation on geological environment and risk assessment on geologic hazard. Based on the post-earthquake actual survey, this paper assesses the problems of site selections on the reconstruction of Beichuan town, Qingchuan town and Muyu town of Qingchuan County. Based on the evaluation of site engineering geology and geological environment, the paper gives some typical suggestions for the site selection on reconstruction of the towns.
The post-earthquake reconstruction of damaged cities and towns requires reasonable site selection and safety assessment. Site selection task involves complex factors such as earthquake fault, geologic hazard, site stability, national well-being and the people's livelihood, and economic development and sustainability. It is a task of complicated engineering system. Problem considerations can follow these basic principles: (a) to the towns which located at the earthquake fault zones and deterioration on geological environment and had severe hidden danger of geologic hazard, they must be removed to other places; (b) to the towns which was damaged, but is far away from the earthquake fault zones and does not exist geologic hazard, they should be in-situ reconstructed and the reconstruction should be carried out according to principles of science planning, avoidance norms, reasonable adjustment to the aseismicity standards. On the process of the post-earthquake reconstruction, attentions should be paid to the disguised geologic hazards, multiplicity of induced factors and long-term sustainability and to strengthen suitability evaluation on geological environment and risk assessment on geologic hazard. Based on the post-earthquake actual survey, this paper assesses the problems of site selections on the reconstruction of Beichuan town, Qingchuan town and Muyu town of Qingchuan County. Based on the evaluation of site engineering geology and geological environment, the paper gives some typical suggestions for the site selection on reconstruction of the towns.
2008, 16(6): 774-780.
The Du-Wen highway is a highway of high level standards in Western Sichuan mountainous areas to the Jiu Zaigou National Park. Also, it is the trunk road linking Dujingyan City and Wenchuan county town. The Du-Wen highway follows the Minjing river to the north and its length is 108 km. The road was totally destroyed by a great number of geohazards such as rock collapses and landslides during the Wenchuan Earthquake. The river valleys are very narrow and have high steep slopes with loose and cracked mountainous geomaterials. Considering the importance of the road to the rescue of disasters and reconstruction of the destroyed areas after the earthquake, it must be repaired in a very short period of time. This was a big challenge because there were so many landsides and the rain season was coming. Therefore, 3D-scanning technique was used to help the landform survey and slope stability evaluation. This paper analyzes the applicability and feasibility of the 3D laser scanning survey on this occasion and discusses the approach combined with traditional survey methods. The practices show that it had the characters of high precision, fast operation and high efficient. I It solved many difficult problems during the quickly repairing period 3 months. A general procedure is put forward to apply this technique to quick slope survey and investigation on urgent occasions.
The Du-Wen highway is a highway of high level standards in Western Sichuan mountainous areas to the Jiu Zaigou National Park. Also, it is the trunk road linking Dujingyan City and Wenchuan county town. The Du-Wen highway follows the Minjing river to the north and its length is 108 km. The road was totally destroyed by a great number of geohazards such as rock collapses and landslides during the Wenchuan Earthquake. The river valleys are very narrow and have high steep slopes with loose and cracked mountainous geomaterials. Considering the importance of the road to the rescue of disasters and reconstruction of the destroyed areas after the earthquake, it must be repaired in a very short period of time. This was a big challenge because there were so many landsides and the rain season was coming. Therefore, 3D-scanning technique was used to help the landform survey and slope stability evaluation. This paper analyzes the applicability and feasibility of the 3D laser scanning survey on this occasion and discusses the approach combined with traditional survey methods. The practices show that it had the characters of high precision, fast operation and high efficient. I It solved many difficult problems during the quickly repairing period 3 months. A general procedure is put forward to apply this technique to quick slope survey and investigation on urgent occasions.
2008, 16(6): 780-787.
The seepage control system in municipal solid waste (MSW) landfill is to prevent the spread of pollutants. This paper presents a literature review of the studies on clayey seepage control systems in MSW landfills. It further presents the mechanism of clayer seepage control system. The developments of the studies of the clayey seepage control systems in MSW landfills include the retardation characteristics, the contaminant transport, the modification and substitute, and the design on the seepage control system. It is pointed out that the unsaturated permeability, adsorption effect and optimize design based on adverse-adsorption are the key topics in the future study of clayey seepage control systems for MSW landfills.
The seepage control system in municipal solid waste (MSW) landfill is to prevent the spread of pollutants. This paper presents a literature review of the studies on clayey seepage control systems in MSW landfills. It further presents the mechanism of clayer seepage control system. The developments of the studies of the clayey seepage control systems in MSW landfills include the retardation characteristics, the contaminant transport, the modification and substitute, and the design on the seepage control system. It is pointed out that the unsaturated permeability, adsorption effect and optimize design based on adverse-adsorption are the key topics in the future study of clayey seepage control systems for MSW landfills.
2008, 16(6): 788-792.
The site condition was complex, where the Second Tailrace Surge Chamber for the Jinping First Stage Hydropower Station was built . During the excavation of JPTSC2 between the chainage Nos. 0＋320 to 0＋360 degrees and from 0＋0 to 0＋120 degrees, falling of rock blocks often occurred. They were induced by the complex geological conditions, which was a big issue. So it was very important to judge and forecast where the big block would fall. After comprehensive analyzed, three conditions causing the big block falling were put forward. The first condition was that the rock block had to be cut by joint Nos. ①, ④ and the fault f18. The second was that the scale of rock block would be decided by the extended length of joint Nos ① and ④. The third one was that the block should be found at the lower side of the fault f18. Then searching work was carried on the three conditions. Finally a big block was found, its volume would be about 50 m3, its weight would be about 133.5 tons. Block Theory was used to calculate,the safety factor of the block of 1.05. It would be dangerous. So, some relevant countermeasures are suggested.
The site condition was complex, where the Second Tailrace Surge Chamber for the Jinping First Stage Hydropower Station was built . During the excavation of JPTSC2 between the chainage Nos. 0＋320 to 0＋360 degrees and from 0＋0 to 0＋120 degrees, falling of rock blocks often occurred. They were induced by the complex geological conditions, which was a big issue. So it was very important to judge and forecast where the big block would fall. After comprehensive analyzed, three conditions causing the big block falling were put forward. The first condition was that the rock block had to be cut by joint Nos. ①, ④ and the fault f18. The second was that the scale of rock block would be decided by the extended length of joint Nos ① and ④. The third one was that the block should be found at the lower side of the fault f18. Then searching work was carried on the three conditions. Finally a big block was found, its volume would be about 50 m3, its weight would be about 133.5 tons. Block Theory was used to calculate,the safety factor of the block of 1.05. It would be dangerous. So, some relevant countermeasures are suggested.
2008, 16(6): 793-797.
Weak structure face is the key point of rock slope stability. In particular, the anti-dip weak structure face at back edge of the slope can control the stability of that slope. Such problem is complex because the stress applied to the face at the back edge sometimes is not clear. This paper presents a numerical analysis of such a rock slope problem. It is to assess the stability of a rock slope inside the approach channel of Jingping Hydroelectric Power Station. The factor of safety of the rock slope is found to be 1.191. The rearward rock mass is found to have no stress to the front slide block. Both the numerical method and the limit equilibrium method were used to discuss the parametric sensitivity of the weak structure face. The results of the two methods show that the numerical method with strength reduction is suitable to assess the stability of this rock slope.
Weak structure face is the key point of rock slope stability. In particular, the anti-dip weak structure face at back edge of the slope can control the stability of that slope. Such problem is complex because the stress applied to the face at the back edge sometimes is not clear. This paper presents a numerical analysis of such a rock slope problem. It is to assess the stability of a rock slope inside the approach channel of Jingping Hydroelectric Power Station. The factor of safety of the rock slope is found to be 1.191. The rearward rock mass is found to have no stress to the front slide block. Both the numerical method and the limit equilibrium method were used to discuss the parametric sensitivity of the weak structure face. The results of the two methods show that the numerical method with strength reduction is suitable to assess the stability of this rock slope.
2008, 16(6): 798-805.
This paper is based on types and characteristics of clay minerals forming the argillanceous cement of the sandstone at Longyou Grottoes in Zhejiang Province. The water samples were further collected separately from (1) water seepage in accumulation on the ground level within the caves, (2) water seepage infiltrated through cracks on the ceiling of caves, (3) surface water outside the caves, as well as (4) the water from Qujiang River near Longyou Grottoes. They were investigated and analysed using chemical analysis methods. The results show that the mineral components and structure of the sandstone depended on the water quality. The interaction between water and sandstone was the main cause of different quality of the water seepage. Sandstone samples from the caves were prepared and then immersed separately in the above water samples and distilled water. Each of the immersion water was sampled and analysed at regular intervals. The mechanism of the chemical interaction between water and sandstone could be found. The chemical interaction results indicate that the main impact of the water seepage infiltrated after atmospheric precipitation on Longyou Grottoes is a series of reactions such as hydration, dissolution and oxidation which take place during the infiltration process. Hence, the mineral components and the structure of the sandstone are changed. The quality of the water seepage is implicated directly in these reactions. Therefore, the clay minerals and the water seepage can interact on each other. Such characteristics of the clay minerals in sandstone with water are the main reason causing weathering of the sandstone.
This paper is based on types and characteristics of clay minerals forming the argillanceous cement of the sandstone at Longyou Grottoes in Zhejiang Province. The water samples were further collected separately from (1) water seepage in accumulation on the ground level within the caves, (2) water seepage infiltrated through cracks on the ceiling of caves, (3) surface water outside the caves, as well as (4) the water from Qujiang River near Longyou Grottoes. They were investigated and analysed using chemical analysis methods. The results show that the mineral components and structure of the sandstone depended on the water quality. The interaction between water and sandstone was the main cause of different quality of the water seepage. Sandstone samples from the caves were prepared and then immersed separately in the above water samples and distilled water. Each of the immersion water was sampled and analysed at regular intervals. The mechanism of the chemical interaction between water and sandstone could be found. The chemical interaction results indicate that the main impact of the water seepage infiltrated after atmospheric precipitation on Longyou Grottoes is a series of reactions such as hydration, dissolution and oxidation which take place during the infiltration process. Hence, the mineral components and the structure of the sandstone are changed. The quality of the water seepage is implicated directly in these reactions. Therefore, the clay minerals and the water seepage can interact on each other. Such characteristics of the clay minerals in sandstone with water are the main reason causing weathering of the sandstone.
2008, 16(6): 806-812.
During construction, a huge collapse occurred between the down lines from K225 to K283 of the Fengyakou tunnel of Yuanmo highway in Yunnan Province. This paper analyses the reasons for the cause of the huge collapse. It is found that the collapse was due to the section located at a fault zone with rich groundwater and slurry often gushing. The paper provides the treatment measures including surface treating, underground treating and drainage in the collapsed tunnel. Monitored results showed that e the stress and deformation of the preliminary bracing and second lining of the tunnel cross section had no change, which indicate that the force and deformation were becoming stable, and the change was with in the limits. The monitored results also showed that the treatments were not only reliable in theory, but also sound in practice, and can be a good guide and reference for the treatment of similar highway tunnel collapses.
During construction, a huge collapse occurred between the down lines from K225 to K283 of the Fengyakou tunnel of Yuanmo highway in Yunnan Province. This paper analyses the reasons for the cause of the huge collapse. It is found that the collapse was due to the section located at a fault zone with rich groundwater and slurry often gushing. The paper provides the treatment measures including surface treating, underground treating and drainage in the collapsed tunnel. Monitored results showed that e the stress and deformation of the preliminary bracing and second lining of the tunnel cross section had no change, which indicate that the force and deformation were becoming stable, and the change was with in the limits. The monitored results also showed that the treatments were not only reliable in theory, but also sound in practice, and can be a good guide and reference for the treatment of similar highway tunnel collapses.
2008, 16(6): 813-819.
In this paper, the pile and soil stress and displacement of CFG pile composite foundation of high-speed railway are numerically simulated under rigid and flexible loading conditions. The numerical results indicate the settlement and the ratio of pile loading distribution in the flexible loading test are less than those in the rigid loading test. So there is a difference settlement between pile and soil. Field loading tests were carried out to study and validate results of the rigid and flexible loading tests of the CFG pile composite foundation. It was found that the composite foundation bearing capacity under railway flexible load was controlled by the soil between piles. The soil between piles was the first to damage, then the whole composite foundation failed. The test results show that the flexible loading test with cushion is available and can simulate the bearing capacity of CFG pile composite foundation more reasonable. The tests also provide a basis for the design of CFG pile composite foundation under flexible conditions.
In this paper, the pile and soil stress and displacement of CFG pile composite foundation of high-speed railway are numerically simulated under rigid and flexible loading conditions. The numerical results indicate the settlement and the ratio of pile loading distribution in the flexible loading test are less than those in the rigid loading test. So there is a difference settlement between pile and soil. Field loading tests were carried out to study and validate results of the rigid and flexible loading tests of the CFG pile composite foundation. It was found that the composite foundation bearing capacity under railway flexible load was controlled by the soil between piles. The soil between piles was the first to damage, then the whole composite foundation failed. The test results show that the flexible loading test with cushion is available and can simulate the bearing capacity of CFG pile composite foundation more reasonable. The tests also provide a basis for the design of CFG pile composite foundation under flexible conditions.
2008, 16(6): 820-825.
This paper presents an experimental study on the swelling and shrinking property of clay treated with STW type stabilizers. The experimental results indicate that STW type stabilizer can reduce the swelling and shrinking property of clay effectively. The sizes of soil particle and the content of STW type stabilizer have different effects on the swelling and shrinking property of the treated clay. The expansion of the treated clay with an average particle size of 0.75 mm reaches the lowest value. The swelling and shrinking property of the treated clay decreases as the content of STW type stabilizer increases. Finally, the paper discusses the mechanism of the STW polymer soil stabilizers in modification of the clay swelling and shrinking property.
This paper presents an experimental study on the swelling and shrinking property of clay treated with STW type stabilizers. The experimental results indicate that STW type stabilizer can reduce the swelling and shrinking property of clay effectively. The sizes of soil particle and the content of STW type stabilizer have different effects on the swelling and shrinking property of the treated clay. The expansion of the treated clay with an average particle size of 0.75 mm reaches the lowest value. The swelling and shrinking property of the treated clay decreases as the content of STW type stabilizer increases. Finally, the paper discusses the mechanism of the STW polymer soil stabilizers in modification of the clay swelling and shrinking property.
2008, 16(6): 826-832.
This paper presents the principals of bored pile test using Brillouin optical time domain reflectometer (BOTDR). The formulas used to calculate the displacement, flexibility, axial force, skin friction and end-bearing resistance of piles were presented. This technique was applied to pile static load tests under complex geological conditions to detect the strains and internal forces in different types of bored piles. The test results indicate that the abnormities of the strain distribution along the piles were found at the positions of hole collapse, weak intercalation, and/or formation interface. On account of the differences of the field conditions and construction techniques, the end-bearing resistances didn't exert fully; the skin friction served as the main resistance to the loads. The piles bearing characteristics were different each other.
This paper presents the principals of bored pile test using Brillouin optical time domain reflectometer (BOTDR). The formulas used to calculate the displacement, flexibility, axial force, skin friction and end-bearing resistance of piles were presented. This technique was applied to pile static load tests under complex geological conditions to detect the strains and internal forces in different types of bored piles. The test results indicate that the abnormities of the strain distribution along the piles were found at the positions of hole collapse, weak intercalation, and/or formation interface. On account of the differences of the field conditions and construction techniques, the end-bearing resistances didn't exert fully; the skin friction served as the main resistance to the loads. The piles bearing characteristics were different each other.
2008, 16(6): 833-838.
his paper classifies the acoustic emissions of sandstone into five stages according to the different deformation stages. They are the preliminary stage of loading, the density stage, the crack stable growth stage, the crack unsteady growth stage and the damage stage. According to distinct acoustic emission of each stage, it is found that the Kaiser point is relevant with the starting point of crack stable growth stage. The paper further presents that the upper limit of Kaiser points is the end-point of crack stable growth stage, or is the initial point of crack unsteady growth stage. The Kaiser point is affected by many factors such as parallelism between two planes of rock sample and loading rate of press machine. If the planes of rock sample are not flat, strong acoustic emission may occur at preliminary stage of loading. If loading rate is bigger, there may not be acoustic emission or the acoustic emission is covered up by latter signals. The paper calculates the values and directions of the three principal stresses of ground stress at 670 m depth below. Compared with field stress-relief method and hydraulic fracturing technique, the three principal values were basically consistent, but their directions were not wholly equal.
his paper classifies the acoustic emissions of sandstone into five stages according to the different deformation stages. They are the preliminary stage of loading, the density stage, the crack stable growth stage, the crack unsteady growth stage and the damage stage. According to distinct acoustic emission of each stage, it is found that the Kaiser point is relevant with the starting point of crack stable growth stage. The paper further presents that the upper limit of Kaiser points is the end-point of crack stable growth stage, or is the initial point of crack unsteady growth stage. The Kaiser point is affected by many factors such as parallelism between two planes of rock sample and loading rate of press machine. If the planes of rock sample are not flat, strong acoustic emission may occur at preliminary stage of loading. If loading rate is bigger, there may not be acoustic emission or the acoustic emission is covered up by latter signals. The paper calculates the values and directions of the three principal stresses of ground stress at 670 m depth below. Compared with field stress-relief method and hydraulic fracturing technique, the three principal values were basically consistent, but their directions were not wholly equal.
2008, 16(6): 839-843.
This paper examines the cracks appeared in the retaining wall beside the FeiYuze tunnel uplink secondary lining vault. The seismic CT technology was used to investigate the engineering geology structure of the covering rock mass above the tunnel. The results indicate that the rock mass had three fracture zones along tunnel axial and the rock mass quality in the small mileage entrance section was poor. The rock section was treated accordingly. The fiber Bragg grating (FBG) sensor method was further used to monitor the tunnel structure. The results indicate that the loose and fractured rock mass were upgrated well by the applied reinforcements. Therefore, the seismic CT and FBG methods can confirm their examination results.
This paper examines the cracks appeared in the retaining wall beside the FeiYuze tunnel uplink secondary lining vault. The seismic CT technology was used to investigate the engineering geology structure of the covering rock mass above the tunnel. The results indicate that the rock mass had three fracture zones along tunnel axial and the rock mass quality in the small mileage entrance section was poor. The rock section was treated accordingly. The fiber Bragg grating (FBG) sensor method was further used to monitor the tunnel structure. The results indicate that the loose and fractured rock mass were upgrated well by the applied reinforcements. Therefore, the seismic CT and FBG methods can confirm their examination results.
2008, 16(6): 844-852.
This paper presents an overview and analysis of the NSFC proposals in engineering geology from 2003 to 2007 with respect to submitted proposals, funded projects, applicant institutions and research teams. The engineering geology is one of the fastest developing disciplines in geology in China. The distribution of investigators in basic research is not balanced among the different institutions. The amount of proposals and grants is matched with the proportion of engineering geologists in geology. The proposed budgets are met basically. The quality of the proposals has yet to be improved. Attention needs to be paid on the development of the national scientific talents in engineering geology, especially young scientific talents.
This paper presents an overview and analysis of the NSFC proposals in engineering geology from 2003 to 2007 with respect to submitted proposals, funded projects, applicant institutions and research teams. The engineering geology is one of the fastest developing disciplines in geology in China. The distribution of investigators in basic research is not balanced among the different institutions. The amount of proposals and grants is matched with the proportion of engineering geologists in geology. The proposed budgets are met basically. The quality of the proposals has yet to be improved. Attention needs to be paid on the development of the national scientific talents in engineering geology, especially young scientific talents.
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