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Editor Work2011 Vol. 19, No. 4
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2011, 19(4): 447-454.
Abstract
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The Zhanjiang clay has noticeable structures of effect to the soil's mechanical characteristics can not be neglected.This paper presents the relevance and correlation analysis on the physical and mechanical indexs of Zhanjiang clay.Furthermore,empirical formula of indexes' relations are established.The results show that the basic reasons for poor physical properties and good mechanical properties of Zhanjiang clay are high clay content,clay minerals,gelatinous organic matter,strong adhesive bonded connection and flocculated structure of flaky grains.The spatial variability of clay mechanical index in different regions is substantial.But,the spatial variability of cla physical index is small.The e-、L-、L-e、a1-2-e relationship are linear correlations that are significantly different with other clays in China.Accordingly it can not use the empirical formula developed from other local clays for engineering design.The results presented in this paper provide the basis of reliable design parameter selection for the Zhanjiang area clay foundation.
The Zhanjiang clay has noticeable structures of effect to the soil's mechanical characteristics can not be neglected.This paper presents the relevance and correlation analysis on the physical and mechanical indexs of Zhanjiang clay.Furthermore,empirical formula of indexes' relations are established.The results show that the basic reasons for poor physical properties and good mechanical properties of Zhanjiang clay are high clay content,clay minerals,gelatinous organic matter,strong adhesive bonded connection and flocculated structure of flaky grains.The spatial variability of clay mechanical index in different regions is substantial.But,the spatial variability of cla physical index is small.The e-、L-、L-e、a1-2-e relationship are linear correlations that are significantly different with other clays in China.Accordingly it can not use the empirical formula developed from other local clays for engineering design.The results presented in this paper provide the basis of reliable design parameter selection for the Zhanjiang area clay foundation.
2011, 19(4): 455-459.
The displacement-time relationship curves are got from laboratory tests for the deformation character analysis of the soft clay in unloading condition.The stress control triaxial compression apparatus is used and remade from the strain control compression apparatus.The following conclusions are gained from the analysis of the test results: (1)when the amount of the loading and the unloading are the same,the amount of the deformation produced in the unloading process is much smaller than the amount of the deformation produced in the loading process.The former is just about one tenth of the latter; (2)the resilience is very small,when the portion of the unloading is small; (3)the resilience will increase sharply,when the amount of the unloading is big enough; (4)the resilience deformation will trends to be stable,when the portion of the unloading exceeds another point.The finite element analysis software ABAQUS is used to simulate the laboratory test.The displacement-time relationship curves are got from the numerical simulation analysis.They revealed the following results: (1)the deformation-time curve in the unloading process is similar to the deformation-time curve in the loading process,when the amounts of the loading and unloading are the same; (2)the numerical calculated deformation increments are a little bigger than the deformation increments got from the indoor test in the initial and last periods of the whole unloading process,but fits well in the middle periods; (3)in every level of the unloading process,the relationships between the deformation and time got from the numerical simulation fit well with that got from the test.
The displacement-time relationship curves are got from laboratory tests for the deformation character analysis of the soft clay in unloading condition.The stress control triaxial compression apparatus is used and remade from the strain control compression apparatus.The following conclusions are gained from the analysis of the test results: (1)when the amount of the loading and the unloading are the same,the amount of the deformation produced in the unloading process is much smaller than the amount of the deformation produced in the loading process.The former is just about one tenth of the latter; (2)the resilience is very small,when the portion of the unloading is small; (3)the resilience will increase sharply,when the amount of the unloading is big enough; (4)the resilience deformation will trends to be stable,when the portion of the unloading exceeds another point.The finite element analysis software ABAQUS is used to simulate the laboratory test.The displacement-time relationship curves are got from the numerical simulation analysis.They revealed the following results: (1)the deformation-time curve in the unloading process is similar to the deformation-time curve in the loading process,when the amounts of the loading and unloading are the same; (2)the numerical calculated deformation increments are a little bigger than the deformation increments got from the indoor test in the initial and last periods of the whole unloading process,but fits well in the middle periods; (3)in every level of the unloading process,the relationships between the deformation and time got from the numerical simulation fit well with that got from the test.
2011, 19(4): 460-466.
During the cyclic triaxial test,the vibration loading produced by Shanghai underground subway running is simulated.The developmental law of acCumulated strain and pore water pressure of undisturbed muddy clay under this subway loading is studied.In addition,the effect of drained condition during cyclic loading on the properties of muddy clay is also analyzed.At the end of this paper,several important conclusions are presented,which are very useful to the predicting and controlling of tunnel settlement caused by subway running.
During the cyclic triaxial test,the vibration loading produced by Shanghai underground subway running is simulated.The developmental law of acCumulated strain and pore water pressure of undisturbed muddy clay under this subway loading is studied.In addition,the effect of drained condition during cyclic loading on the properties of muddy clay is also analyzed.At the end of this paper,several important conclusions are presented,which are very useful to the predicting and controlling of tunnel settlement caused by subway running.
2011, 19(4): 467-471.
Failures of Loess slopes have been a bottleneck of rural urbanization and ground transportation construction in loess area.They and their hazards have been a current research focus of in engineering geology.One of the bases to reveal loess slope failure mechanism is to examine loess stress and microstructure changed due to effects of shock(vibration)or dynamic loading.This paper is based on the GDS Lab System,uses the equivalent sine wave loading gradually under strain controlling.Dynamic triaxial tests on loess samples are carried out.It further uses the scanning electron microscope to observe the differences of microstructures before and after the test.It analyzes the reasons of decreasing in dynamic strength.The results show the following findings.There is an obvious phenomenon of stress relaxation during the cyclic loading test on Malan loess.The degree of stress relaxation decreases with the increasing of confining pressure and strain.The dynamic failure stress increases linearly with the increasing of confining pressure.The Mole-Coulomb failure criterion is used to get the dynamic strength.Comparing the static strength and the dynamic strength,the dynamic internal friction angle decreases significantly,while the dynamic cohesion decreases slightly.The internal reason of decreasing on strength is as follows.By the role of cycling dynamic loading,the macro-cementation structure damages.On the other hand,the relationship between particles contact way changes from the point to point contact to the surface to surface contact.Thereby,the strength of the Malan loess is reduced.The micro-structure type is also changed into a mosaic micropore macro-cementation structure.
Failures of Loess slopes have been a bottleneck of rural urbanization and ground transportation construction in loess area.They and their hazards have been a current research focus of in engineering geology.One of the bases to reveal loess slope failure mechanism is to examine loess stress and microstructure changed due to effects of shock(vibration)or dynamic loading.This paper is based on the GDS Lab System,uses the equivalent sine wave loading gradually under strain controlling.Dynamic triaxial tests on loess samples are carried out.It further uses the scanning electron microscope to observe the differences of microstructures before and after the test.It analyzes the reasons of decreasing in dynamic strength.The results show the following findings.There is an obvious phenomenon of stress relaxation during the cyclic loading test on Malan loess.The degree of stress relaxation decreases with the increasing of confining pressure and strain.The dynamic failure stress increases linearly with the increasing of confining pressure.The Mole-Coulomb failure criterion is used to get the dynamic strength.Comparing the static strength and the dynamic strength,the dynamic internal friction angle decreases significantly,while the dynamic cohesion decreases slightly.The internal reason of decreasing on strength is as follows.By the role of cycling dynamic loading,the macro-cementation structure damages.On the other hand,the relationship between particles contact way changes from the point to point contact to the surface to surface contact.Thereby,the strength of the Malan loess is reduced.The micro-structure type is also changed into a mosaic micropore macro-cementation structure.
2011, 19(4): 472-477.
This paper examines a typical gneiss forming the foundation Xiaowan Hydropower Station.Grinding test is ued to analyze the formation environment and mineral composition of the biotite granite gneiss.The results confirm the relationship of the rock strength with its mineral content and mineral strength.Furthermore,acoustic emission is carried out during the uniaxial compression tests of the biotite granite gneiss samples.The acoustic emission process is examined during the biotite granite gneiss instability and rupture.the AE results are used to analyze the crack propagation with time,stress and strain.The results are meaningful for the analysis of rock fracture instability mechanism.They reveal that the gneiss is hard-very hard rock.Acoustic emission activities substantially follow the same patterns.There is a clear point of AE enhancement.Acoustic emission ring count rate of rock rock failure process is suitable for predicting for all stages of the breakdown of rocks.The relations of gneiss stress-strain are in the form of polynomials of second orders.The relations of strain-the cumulative number of AE are in the forms of polynomials of third orders.It will help us to better understand the failure mechanism and the precursor of rock failure criterion.
This paper examines a typical gneiss forming the foundation Xiaowan Hydropower Station.Grinding test is ued to analyze the formation environment and mineral composition of the biotite granite gneiss.The results confirm the relationship of the rock strength with its mineral content and mineral strength.Furthermore,acoustic emission is carried out during the uniaxial compression tests of the biotite granite gneiss samples.The acoustic emission process is examined during the biotite granite gneiss instability and rupture.the AE results are used to analyze the crack propagation with time,stress and strain.The results are meaningful for the analysis of rock fracture instability mechanism.They reveal that the gneiss is hard-very hard rock.Acoustic emission activities substantially follow the same patterns.There is a clear point of AE enhancement.Acoustic emission ring count rate of rock rock failure process is suitable for predicting for all stages of the breakdown of rocks.The relations of gneiss stress-strain are in the form of polynomials of second orders.The relations of strain-the cumulative number of AE are in the forms of polynomials of third orders.It will help us to better understand the failure mechanism and the precursor of rock failure criterion.
2011, 19(4): 478-482.
By means of the wetting-drying cycle tests of triaxial and direct-shear on the expansive soil.The test finds that with first wetting-drying cycle triaxial test,the crack ratio in expansive soil sample surface is the largest increase,with second to fourth wetting-drying cycle,the crack ratio in expansive soil sample surface is the bigger increase.And the crack ratio in expansive soil sample surface is the little increase,with the wetting-drying cycle is more than five.And the same result is finds in the direct-shear test.All in all,With the number of times wetting-drying cycle increasingly,the crack ratio in expansive soil sample surface is constantly increasing.
By means of the wetting-drying cycle tests of triaxial and direct-shear on the expansive soil.The test finds that with first wetting-drying cycle triaxial test,the crack ratio in expansive soil sample surface is the largest increase,with second to fourth wetting-drying cycle,the crack ratio in expansive soil sample surface is the bigger increase.And the crack ratio in expansive soil sample surface is the little increase,with the wetting-drying cycle is more than five.And the same result is finds in the direct-shear test.All in all,With the number of times wetting-drying cycle increasingly,the crack ratio in expansive soil sample surface is constantly increasing.
2011, 19(4): 483-486.
The adjusted levee around Eastern Tai Lake is formed of cohesive hydraulic fills,which include lots of pebble-shaped clods.The paper conducts a preliminary research on the formation mechanism,internal structure characteristics and mechanical characteristics through field investigation,laboratory tests,etc.The results show that: the hydraulic fills are of uneven characteristics.The pebble-shaped clods are of good properties while the remoulded silt clay is of bad properties.The hydraulic fills are of small permeability and long consolidation time.The soil test parameters do not conform with sites,the reason of which is that the prevailing soil test equipments are not suitable for the uneven fills.The parameters from in-situ tests can reflect the properties of the fills.The suitable ground treatment measures are water draining associated with heaped load or cement-soil mixing pile.
The adjusted levee around Eastern Tai Lake is formed of cohesive hydraulic fills,which include lots of pebble-shaped clods.The paper conducts a preliminary research on the formation mechanism,internal structure characteristics and mechanical characteristics through field investigation,laboratory tests,etc.The results show that: the hydraulic fills are of uneven characteristics.The pebble-shaped clods are of good properties while the remoulded silt clay is of bad properties.The hydraulic fills are of small permeability and long consolidation time.The soil test parameters do not conform with sites,the reason of which is that the prevailing soil test equipments are not suitable for the uneven fills.The parameters from in-situ tests can reflect the properties of the fills.The suitable ground treatment measures are water draining associated with heaped load or cement-soil mixing pile.
2011, 19(4): 487-491.
Through the comparison tests of embedding vibrating string stress meter in concrete,which is wrapped with and without plasticine at the measuring area,the confine conditions' influence on the outcomes of the stress meter was studied when it's measuring the stress of concrete.The results showed that: based on the assumption that on any cross section the strain of concrete and stress meter are the same,vibrating string stress meter can relatively accurately measure the stress of concrete,but the measured value is a little smaller than the real one; wrapped with plasticine at the measuring area,the stress meter's confine condition is laterally flexible which is more similar to the free boundary condition on which it's calibrated,thus it can measure the stress of concrete more accurately,but its accuracy decreases with the increase of load; when the stress meter is directly embedded in concrete,its nominal axial stiffness will be increased because of the lateral constraint of concrete,thus its measured value will be correspondingly smaller.
Through the comparison tests of embedding vibrating string stress meter in concrete,which is wrapped with and without plasticine at the measuring area,the confine conditions' influence on the outcomes of the stress meter was studied when it's measuring the stress of concrete.The results showed that: based on the assumption that on any cross section the strain of concrete and stress meter are the same,vibrating string stress meter can relatively accurately measure the stress of concrete,but the measured value is a little smaller than the real one; wrapped with plasticine at the measuring area,the stress meter's confine condition is laterally flexible which is more similar to the free boundary condition on which it's calibrated,thus it can measure the stress of concrete more accurately,but its accuracy decreases with the increase of load; when the stress meter is directly embedded in concrete,its nominal axial stiffness will be increased because of the lateral constraint of concrete,thus its measured value will be correspondingly smaller.
2011, 19(4): 492-497.
Take Loess-like silt in areas of Sanmenxia for the study, using unconsolidated undrained shear test method on the unsaturated soils triaxial test instrument, the test were carried by controlling the different dry density and moisture content of the remoded soil preparing to different state of the samples. The results are as follows, Density and moisture content of the test specimen has an important impact on the stress-strain curve of loess-like silt and there will be two kinds of curves such as stress softening curve and stress hardening curve under the different density and moisture content; Partial destruction stress of the test specimen is increasing while the density is increasing and is increasing while the moisture content is decreasing, partial destruction stress of specimen with 7% moisture content is about twice that of specimen with 13% moisture content. Under unsaturated condition, the simple and double-shear planes are main types of the shear failure planes of the test specimen, and under certain moisture content,the destruction shape of the test specimen can appear two kind of phenomena of the dilating and the shrinking with the different dry density.
Take Loess-like silt in areas of Sanmenxia for the study, using unconsolidated undrained shear test method on the unsaturated soils triaxial test instrument, the test were carried by controlling the different dry density and moisture content of the remoded soil preparing to different state of the samples. The results are as follows, Density and moisture content of the test specimen has an important impact on the stress-strain curve of loess-like silt and there will be two kinds of curves such as stress softening curve and stress hardening curve under the different density and moisture content; Partial destruction stress of the test specimen is increasing while the density is increasing and is increasing while the moisture content is decreasing, partial destruction stress of specimen with 7% moisture content is about twice that of specimen with 13% moisture content. Under unsaturated condition, the simple and double-shear planes are main types of the shear failure planes of the test specimen, and under certain moisture content,the destruction shape of the test specimen can appear two kind of phenomena of the dilating and the shrinking with the different dry density.
2011, 19(4): 498-504.
Wenchuan Earthquake,with high intensity and long period,caused masses of rolling rocks which derived from block stones of rock slopes divided by structure faces and big size corestones of soil slope.The block stones are projected with initial speeds.Their movements on slope surfaces are the combination of sliding,rolling and jumping.Based on the field investigation,this paper chooses two typical unsteady slopes caused by the earthquake to study movement characters of rolling rocks.Three findings are as follows.(1)The more the rolling rocks have equal three dimensions in length,width,and height,the farther the rock movement distance.But for platy rolling rocks,if their narrow side touchdown firstly,and collide elasticcally,they will jump at a high speed and move long-distance; (2)At the 1/2 height of slope surface or higher,rolling rock movement is sliding,rolling mainly.At the lower positions,it is jumping-rolling,jumping-sliding; (3)Big size(mass)rolling rocks mostly stay at the first touchdown or the wide gently areas at the slope toe areas.The way to consume energy is friction or collision disintegration,in which the ratio of platform block is 54% and trees(shrub) is 12%. By inversion,renew coefficient Rn and Tangentially renew coefficient Rt are obtained.For the bare bedrocks,Rn=0.3 and Rt=0.6. For the overlay,Rn=0.2and Rt=0.8.For moving rolling rocks,their bounce heights are between 0.49~3.10m.The ratio of the maximum rolling height and the farthest movement distance is 1/2.
Wenchuan Earthquake,with high intensity and long period,caused masses of rolling rocks which derived from block stones of rock slopes divided by structure faces and big size corestones of soil slope.The block stones are projected with initial speeds.Their movements on slope surfaces are the combination of sliding,rolling and jumping.Based on the field investigation,this paper chooses two typical unsteady slopes caused by the earthquake to study movement characters of rolling rocks.Three findings are as follows.(1)The more the rolling rocks have equal three dimensions in length,width,and height,the farther the rock movement distance.But for platy rolling rocks,if their narrow side touchdown firstly,and collide elasticcally,they will jump at a high speed and move long-distance; (2)At the 1/2 height of slope surface or higher,rolling rock movement is sliding,rolling mainly.At the lower positions,it is jumping-rolling,jumping-sliding; (3)Big size(mass)rolling rocks mostly stay at the first touchdown or the wide gently areas at the slope toe areas.The way to consume energy is friction or collision disintegration,in which the ratio of platform block is 54% and trees(shrub) is 12%. By inversion,renew coefficient Rn and Tangentially renew coefficient Rt are obtained.For the bare bedrocks,Rn=0.3 and Rt=0.6. For the overlay,Rn=0.2and Rt=0.8.For moving rolling rocks,their bounce heights are between 0.49~3.10m.The ratio of the maximum rolling height and the farthest movement distance is 1/2.
2011, 19(4): 505-510.
On April 14, 2010at 07: 49(Beijing time),a catastrophic earthquake with Ms 7.1 occurred beneath the central of the Tibetan Plateau in Qinghai,China.With visual interpretation of remote sensing imageriesand verifications of field check,about 2036 landslides are found in a total area of 1.194 square kilometers.They are triggered by the ground motion of the earthquake.They are extensively mapped over a rectangle landslide limit area of about 1455.3 square kilometers.Using both landslide area(LA)and landslide number(LN)to carry out statistical analysis on 3 categories of controlling parameters for landslides triggered by earthquake: 1)earthquake parameters(distance from earthquake epicenter,distance from macroscopical epicenter,distance from the main surface rupture,and PGA), 2)topographic parameters(elevation,slope angle,slope aspect,topographic position,distance from drainages),and 3)road parameters(distance from roads).The results are as follows: ① both LA and LN have strong positive correlations with distance from main surface rupture,landslides often occurred at a distance of 1.5km from the main surface rupture.Macroscopical epicenter also has some influence on the landslide distribution.The region about at a distance of 22km from the macroscopical epicenter is landslide intensive region.Both distance from earthquake epicenter and PGA have no obvious effect on the earthquake triggered landslides; ② most of the Yushu earthquake triggered landslide occurred in the areas about the following topographic controlling parameters,elevation as 3800~4000m and 4200~4600m,slope angle as 20~35,slope aspect as NE and E,topographic position as middle slope and lower slope are landslide.Landslides have strong positive correlations with distance from drainages; ③ the closer to the roads,landslide more occurring.Most of the landslides occurred within 300m from the roads.
On April 14, 2010at 07: 49(Beijing time),a catastrophic earthquake with Ms 7.1 occurred beneath the central of the Tibetan Plateau in Qinghai,China.With visual interpretation of remote sensing imageriesand verifications of field check,about 2036 landslides are found in a total area of 1.194 square kilometers.They are triggered by the ground motion of the earthquake.They are extensively mapped over a rectangle landslide limit area of about 1455.3 square kilometers.Using both landslide area(LA)and landslide number(LN)to carry out statistical analysis on 3 categories of controlling parameters for landslides triggered by earthquake: 1)earthquake parameters(distance from earthquake epicenter,distance from macroscopical epicenter,distance from the main surface rupture,and PGA), 2)topographic parameters(elevation,slope angle,slope aspect,topographic position,distance from drainages),and 3)road parameters(distance from roads).The results are as follows: ① both LA and LN have strong positive correlations with distance from main surface rupture,landslides often occurred at a distance of 1.5km from the main surface rupture.Macroscopical epicenter also has some influence on the landslide distribution.The region about at a distance of 22km from the macroscopical epicenter is landslide intensive region.Both distance from earthquake epicenter and PGA have no obvious effect on the earthquake triggered landslides; ② most of the Yushu earthquake triggered landslide occurred in the areas about the following topographic controlling parameters,elevation as 3800~4000m and 4200~4600m,slope angle as 20~35,slope aspect as NE and E,topographic position as middle slope and lower slope are landslide.Landslides have strong positive correlations with distance from drainages; ③ the closer to the roads,landslide more occurring.Most of the landslides occurred within 300m from the roads.
2011, 19(4): 511-515.
Danbobei gully is the main tributary of Ya-lung River and is at the right bank of the river middle reaches.The gully occurred many debris flowsin the past.This paper analyzes the dynamic characteristics of debris flows in Danbobei gully.It summarizes the formation conditions of the debris flows.It confirms that the debris flows in Danbobei gully are gully rainfall type with low-frequency and high viscous debris flows.It analyzes the debris flow characteristics of the movement such as the flow velocity,the discharge,punching power and the transporting quantity.The debris flows may cause the Ya-lung River mainstream to the left shift.The construction of hydropower station and safety operation influence have realistic meanings.According to the characteristics of development activity of the debris flows and theirformation reasons,it is also suggested that building barricade wall at the left bank of the early construction site and the upper reaches materials site.The wall should occupy fewer flood channel cross sections for preventing blocking the river.
Danbobei gully is the main tributary of Ya-lung River and is at the right bank of the river middle reaches.The gully occurred many debris flowsin the past.This paper analyzes the dynamic characteristics of debris flows in Danbobei gully.It summarizes the formation conditions of the debris flows.It confirms that the debris flows in Danbobei gully are gully rainfall type with low-frequency and high viscous debris flows.It analyzes the debris flow characteristics of the movement such as the flow velocity,the discharge,punching power and the transporting quantity.The debris flows may cause the Ya-lung River mainstream to the left shift.The construction of hydropower station and safety operation influence have realistic meanings.According to the characteristics of development activity of the debris flows and theirformation reasons,it is also suggested that building barricade wall at the left bank of the early construction site and the upper reaches materials site.The wall should occupy fewer flood channel cross sections for preventing blocking the river.
2011, 19(4): 516-529.
This paper is based on the types of giant landslides and their relevant distribution from Longyangxia valley and Liujiaxia valley along the upper Yellow River.It investigates the relationship between the giant landslides and the evolution of Yellow river.The Gonghe,Guide and Xunhua basins experienced erosion and deplanation due to water during the B section of Kunhuang tectonic movement(~0.8Ma B.P).On the other hand,the field from Lijiaxia valley to Gongboxia valley and eastern Duolonggou near Longyangxia valley experienced denudation.The Gonghe tectonic movement of ~125kaB.P.caused that Yellow River cut through this study area,and shaped several high and steep slopes along the Upper Yellow River,which included the early rapid downward erosion with the maximum eroseion of ~30~50kaB.P.at Jianzha Basin and the later intermittent erosion.The early rapid downward erosion triggered the early high-speed giant landslides and the later intermittent erosion triggered the later climate-driven giant landslides.Therefore,the staged ed erosion of Upper Yellow River caused by tectonic uplift is the principle reason for occurrence of giant landslides.Earthquake and clogging river are triggers for occurrence of giant landslides in the study area.Above all,the mechanism of giant landslides from Longyangxia valley to Liujiaxia valley along the upper Yellow River includes three types: earthquake-triggered giant landslides; banks rebuilding-triggered giant landslides; and climate-triggered giant landslides.
This paper is based on the types of giant landslides and their relevant distribution from Longyangxia valley and Liujiaxia valley along the upper Yellow River.It investigates the relationship between the giant landslides and the evolution of Yellow river.The Gonghe,Guide and Xunhua basins experienced erosion and deplanation due to water during the B section of Kunhuang tectonic movement(~0.8Ma B.P).On the other hand,the field from Lijiaxia valley to Gongboxia valley and eastern Duolonggou near Longyangxia valley experienced denudation.The Gonghe tectonic movement of ~125kaB.P.caused that Yellow River cut through this study area,and shaped several high and steep slopes along the Upper Yellow River,which included the early rapid downward erosion with the maximum eroseion of ~30~50kaB.P.at Jianzha Basin and the later intermittent erosion.The early rapid downward erosion triggered the early high-speed giant landslides and the later intermittent erosion triggered the later climate-driven giant landslides.Therefore,the staged ed erosion of Upper Yellow River caused by tectonic uplift is the principle reason for occurrence of giant landslides.Earthquake and clogging river are triggers for occurrence of giant landslides in the study area.Above all,the mechanism of giant landslides from Longyangxia valley to Liujiaxia valley along the upper Yellow River includes three types: earthquake-triggered giant landslides; banks rebuilding-triggered giant landslides; and climate-triggered giant landslides.
2011, 19(4): 530-540.
In recent years,the frequency of loess landslide occurrences has the trend of increasing.It is a basis of reducing the landslide hazard risk to investigate the triggering factors and forming mechanism of loess landslides.Field investigation for geological hazards on the Loess Plateau suggests that the induced factors of the loess landslides mainly include earthquakes,precipitations,frozen-thawing,river erosion and human engineering activities.Among them,precipitations and human activities are the most active agents to induce landslides.For the loess landslides triggered by earthquake,mass ejection,dust effect and loess liquefaction caused by seismic acceleration are the main reasons.For the landslides induced by river evolution,the triggering mechanism and failure mode are distinct in different river evolution stages,such as in the lateral and vertical river erosion stages.Whereas,the loess landslide mechanism types include water level raise due to frozen effect and loess strength decrease result from melting effect.The factors of precipitations can be classified as rainstorm and drizzle and of the ground water can be classified as locally concentrated groundwater with priory conducts,water level rising and density increasing.Those of human activities are slope cutting,irrigation,reservoir,and over-burdening.Based on the field investigation for various of loess landslides,the geological characters and triggering mechanism of the landslide triggering by different factors are discussed further in the paper.
In recent years,the frequency of loess landslide occurrences has the trend of increasing.It is a basis of reducing the landslide hazard risk to investigate the triggering factors and forming mechanism of loess landslides.Field investigation for geological hazards on the Loess Plateau suggests that the induced factors of the loess landslides mainly include earthquakes,precipitations,frozen-thawing,river erosion and human engineering activities.Among them,precipitations and human activities are the most active agents to induce landslides.For the loess landslides triggered by earthquake,mass ejection,dust effect and loess liquefaction caused by seismic acceleration are the main reasons.For the landslides induced by river evolution,the triggering mechanism and failure mode are distinct in different river evolution stages,such as in the lateral and vertical river erosion stages.Whereas,the loess landslide mechanism types include water level raise due to frozen effect and loess strength decrease result from melting effect.The factors of precipitations can be classified as rainstorm and drizzle and of the ground water can be classified as locally concentrated groundwater with priory conducts,water level rising and density increasing.Those of human activities are slope cutting,irrigation,reservoir,and over-burdening.Based on the field investigation for various of loess landslides,the geological characters and triggering mechanism of the landslide triggering by different factors are discussed further in the paper.
2011, 19(4): 541-549.
Loess collapse is a type of very common geological disasters in the loess plateau area of Northwest China.At first,this paper studies loess topography,loess type and structure,loess vertical joints,slope erosion,rainfall and human activities.The results show that both the vertical joints in loess and erosion at the toe of slope are the main causes of loess collapse.Secondly,based on field investigation and analysis on the geological phenomena,four typical failure modesare put forward to describe different types of loess collapses.They are tensile crack-falling,tensile crack-toppling,tensile crack-subsiding and tensile crack-sliding.By means of discrete element method,a typical loess slope of Heilonggou is simulated.The failure process of loess collapse includes erosion flaking,local recessing,vertical joints opening,drop breakup,accumulation at the toe of the slope.Research findings in the paper are significant to prevention and treatment for loess collapse in the loess plateau area of Northwest China.
Loess collapse is a type of very common geological disasters in the loess plateau area of Northwest China.At first,this paper studies loess topography,loess type and structure,loess vertical joints,slope erosion,rainfall and human activities.The results show that both the vertical joints in loess and erosion at the toe of slope are the main causes of loess collapse.Secondly,based on field investigation and analysis on the geological phenomena,four typical failure modesare put forward to describe different types of loess collapses.They are tensile crack-falling,tensile crack-toppling,tensile crack-subsiding and tensile crack-sliding.By means of discrete element method,a typical loess slope of Heilonggou is simulated.The failure process of loess collapse includes erosion flaking,local recessing,vertical joints opening,drop breakup,accumulation at the toe of the slope.Research findings in the paper are significant to prevention and treatment for loess collapse in the loess plateau area of Northwest China.
2011, 19(4): 550-554.
A geological model is established for loess slopes in Heifangtai in Gansu Province It is based on the direct shear tests and the repeated direct shear tests of Heifangtai loess soils.It also collects the physical character and shear strength of soil,and the height and angle of 21 slopes at Heifangtai.The failure probability of the slopes were calculated by the Monte-Carlo method.The results show that cohesion of loess in Heifangtai is nearly zero,and the probability of the slopes is correlated with the angle of slope.If 5%is acceptable probability,the stable angle of slope is 27.2.The slope with angle more than 27.2needs to be protected as soon as possible.
A geological model is established for loess slopes in Heifangtai in Gansu Province It is based on the direct shear tests and the repeated direct shear tests of Heifangtai loess soils.It also collects the physical character and shear strength of soil,and the height and angle of 21 slopes at Heifangtai.The failure probability of the slopes were calculated by the Monte-Carlo method.The results show that cohesion of loess in Heifangtai is nearly zero,and the probability of the slopes is correlated with the angle of slope.If 5%is acceptable probability,the stable angle of slope is 27.2.The slope with angle more than 27.2needs to be protected as soon as possible.
2011, 19(4): 555-563.
Baota landslide,a typical ancient rock slide,is used as an example to show why there are still mistakes in its boundary even after three times geological investigation in large scale have been carried out.It involves many problems like the evidence for the determination of ancient landslide,methods of analysis and identification,direction and method of exploration.The determination of landslide mainly depends on the geological phenomena and topography.In addition to the evidence of slide plane,there are multiple solutions for the phenomena of geology,topography and morphology.Thus a synthetic comparison and analysis of multiple factors should be conducted.The fallacy is pointed out for the slope body of Wang-Jialiang which is determined as the western slide body of Baota landslide.Evidences on the geological phenomena and topography are provided.Methods of identification of ancient landslide based on landslide geomorphology and topography are presented in this paper.Lessons,which are learned from the survey and exploration of the landslide,are discussed at last.
Baota landslide,a typical ancient rock slide,is used as an example to show why there are still mistakes in its boundary even after three times geological investigation in large scale have been carried out.It involves many problems like the evidence for the determination of ancient landslide,methods of analysis and identification,direction and method of exploration.The determination of landslide mainly depends on the geological phenomena and topography.In addition to the evidence of slide plane,there are multiple solutions for the phenomena of geology,topography and morphology.Thus a synthetic comparison and analysis of multiple factors should be conducted.The fallacy is pointed out for the slope body of Wang-Jialiang which is determined as the western slide body of Baota landslide.Evidences on the geological phenomena and topography are provided.Methods of identification of ancient landslide based on landslide geomorphology and topography are presented in this paper.Lessons,which are learned from the survey and exploration of the landslide,are discussed at last.
2011, 19(4): 564-569.
Granite is widely distributed in the southeast area of Fujian Province.Granite spherical weathering and the relative engineering geological problems are very prominent because of differences of mineral compositions,regional geologic structure and warm-wet climate in this area.Spherically weathered rock blocks of various sizes fall from the top of slope or roll along slope surface.Collapse and landslide occur because of rainfall or excavation near slopes mixed with weathered spherical rock blocks and residual soil.When tunneling in stratum of spherical weathering,concentration of stresses can occur in the primary support of working face.Then,instability of rock and ground subsidence can appear.Latent spherical weathering rock may be identified as bedrock.It is very difficult to drill for pile foundation.Bare spherical weathered rock can threaten the bridge pile and abutment on the steep slope.
Granite is widely distributed in the southeast area of Fujian Province.Granite spherical weathering and the relative engineering geological problems are very prominent because of differences of mineral compositions,regional geologic structure and warm-wet climate in this area.Spherically weathered rock blocks of various sizes fall from the top of slope or roll along slope surface.Collapse and landslide occur because of rainfall or excavation near slopes mixed with weathered spherical rock blocks and residual soil.When tunneling in stratum of spherical weathering,concentration of stresses can occur in the primary support of working face.Then,instability of rock and ground subsidence can appear.Latent spherical weathering rock may be identified as bedrock.It is very difficult to drill for pile foundation.Bare spherical weathered rock can threaten the bridge pile and abutment on the steep slope.
2011, 19(4): 570-576.
This paper develops a model about stress waves propagation in rock slope body according to the theory of stress waves propagation.Based on the theories of elasticity,it derives the elastic-dynamics equations and potential functions.Taking SH wave propagation as an example,the stress waves superposition at different parts of the slope is discussed.The sloping surface and slope crest are departed into two independent free surfaces.They do not affect each other in the process of reflecting stress waves.The stress waves superposition beside the two free surfaces are analyzed respectively.The amplitude of the superposed wave is discussed.It reveals the rules of both vertical and horizontal dynamic response amplifications of the slope.The rule for the vertical dynamic response amplification is that getting closer to slope surface,the particles' oscillation amplitude increase.The rule for the horizontal dynamic response amplification is that near slope crest,the particles' oscillation response increases,and reaches to the largest at slope crest.The condition for the two rules being cyclic variation is that the slope height is larger than 1/4 wavelength of SH wave.
This paper develops a model about stress waves propagation in rock slope body according to the theory of stress waves propagation.Based on the theories of elasticity,it derives the elastic-dynamics equations and potential functions.Taking SH wave propagation as an example,the stress waves superposition at different parts of the slope is discussed.The sloping surface and slope crest are departed into two independent free surfaces.They do not affect each other in the process of reflecting stress waves.The stress waves superposition beside the two free surfaces are analyzed respectively.The amplitude of the superposed wave is discussed.It reveals the rules of both vertical and horizontal dynamic response amplifications of the slope.The rule for the vertical dynamic response amplification is that getting closer to slope surface,the particles' oscillation amplitude increase.The rule for the horizontal dynamic response amplification is that near slope crest,the particles' oscillation response increases,and reaches to the largest at slope crest.The condition for the two rules being cyclic variation is that the slope height is larger than 1/4 wavelength of SH wave.
2011, 19(4): 577-581.
As a superficial failure mode of slope especially high and steep slope,rock falls is one of the severe geological disasters.It is always the emphasis in slope engineering investigation for its characteristics of sudden occurrence,fast speed and violent power.Due to the dangerous rock masses triggering rock falls disasters mostly scatter at top of high and steep slopes and it will cost huge manpower and material resources with the attempt to manage the disasters totally there,it mostly adopts rockfalls prevention solutions before rockfalls causing disaster now.After some proper simplification in theory based on practical situation,this paper applies kinematics into some typical Rock falls disaster in Slope Engineering Investigation along a road to calculate and analyze the motion trail of rock falls,likes rock falls velocity,bounce height,displacement and kinetic energy.As a result,rock falls could cover the road with a serious impact on the normal operation of road and pedestrians safety.It is suggested that SNS flexible active protection net should be adopted to prevent rock falls and provides specific fixed locations and relevant parameters.
As a superficial failure mode of slope especially high and steep slope,rock falls is one of the severe geological disasters.It is always the emphasis in slope engineering investigation for its characteristics of sudden occurrence,fast speed and violent power.Due to the dangerous rock masses triggering rock falls disasters mostly scatter at top of high and steep slopes and it will cost huge manpower and material resources with the attempt to manage the disasters totally there,it mostly adopts rockfalls prevention solutions before rockfalls causing disaster now.After some proper simplification in theory based on practical situation,this paper applies kinematics into some typical Rock falls disaster in Slope Engineering Investigation along a road to calculate and analyze the motion trail of rock falls,likes rock falls velocity,bounce height,displacement and kinetic energy.As a result,rock falls could cover the road with a serious impact on the normal operation of road and pedestrians safety.It is suggested that SNS flexible active protection net should be adopted to prevent rock falls and provides specific fixed locations and relevant parameters.
2011, 19(4): 582-587.
Ganxigou belongs to tributaries of Qian River,in the front margin of the central Longmeng Mountain folded zone,and it belongs to erosion structural and river landforms.The valley is developing and deeply dissected,whose rainfall and river waters are rich.Geologic hazards are also developing due to widespread mining.Typical geologic hazards are mainly Dabaiyan collapse bodies,Datuanbao collapse bodies and Ganxigou potential Debris flow.Dabaiyan overthrust collapse bodies formed after Wenchuan Earthquake.After Yingxiu-Beichuan faults thrusted,hanging limestone slipped out of hillside and formed scarp.Under the gravity or the surface water flow,hanging broken material slipped from the thrust.Datuanbao deposit changed in the overall deformation modes from tipping to tip-break-accumulating at the basis of previous tipping deformation and slipped under earthquake-induced effects.Ganxigou drainage basin develops geologic hazards and formed provenance which may cause debris flow.
Ganxigou belongs to tributaries of Qian River,in the front margin of the central Longmeng Mountain folded zone,and it belongs to erosion structural and river landforms.The valley is developing and deeply dissected,whose rainfall and river waters are rich.Geologic hazards are also developing due to widespread mining.Typical geologic hazards are mainly Dabaiyan collapse bodies,Datuanbao collapse bodies and Ganxigou potential Debris flow.Dabaiyan overthrust collapse bodies formed after Wenchuan Earthquake.After Yingxiu-Beichuan faults thrusted,hanging limestone slipped out of hillside and formed scarp.Under the gravity or the surface water flow,hanging broken material slipped from the thrust.Datuanbao deposit changed in the overall deformation modes from tipping to tip-break-accumulating at the basis of previous tipping deformation and slipped under earthquake-induced effects.Ganxigou drainage basin develops geologic hazards and formed provenance which may cause debris flow.
2011, 19(4): 588-593.
This paper mainly researches the structural characteristic and the stability analysis of Mahe collapse body.First of all,the range of slope and changing shape in landscape orientation restraint the application of drilling exploration.It is difficult to figure out the loose coverage thickness,fluctuating bedrock beneath and situation of developing weathered layer exactly.Hence,this paper adopts SSP(Seismic Scatter Profile)method to explore the structural characteristic of Mahe collapse body.Furthermore,this paper evaluates the stability of Mahe collapse body under three conditions(natural condition、earthquake condition and rainfall condition)by using various LEM(Bishop、Janbu、Morgenstern-Price)and then calculating and comparing the safety factors of discontinuity between bedrock and coverage.Finally,this paper concludes that the geological structure of Mahe collapse body is approximately sorted into three layers.The upper layer close to surface is loose coverage with a thickness about 30~40mm,not cementitious; The medium layer is a medium to strong weathered layer with a thickness about 10~15mm,weathered strongly,fractured intensively; The bottom layer is a relatively intact rock mass under 40~50m depth with a wave velocity above 2500m s-1; As to stability evaluation,there are two unstable conditions:the collapse body may occur failure along the bottom boundary of coverage or weathered layer under earthquake condition,while the collapse body may also occur failure along the bottom boundary of weathered layer under rainfall condition.
This paper mainly researches the structural characteristic and the stability analysis of Mahe collapse body.First of all,the range of slope and changing shape in landscape orientation restraint the application of drilling exploration.It is difficult to figure out the loose coverage thickness,fluctuating bedrock beneath and situation of developing weathered layer exactly.Hence,this paper adopts SSP(Seismic Scatter Profile)method to explore the structural characteristic of Mahe collapse body.Furthermore,this paper evaluates the stability of Mahe collapse body under three conditions(natural condition、earthquake condition and rainfall condition)by using various LEM(Bishop、Janbu、Morgenstern-Price)and then calculating and comparing the safety factors of discontinuity between bedrock and coverage.Finally,this paper concludes that the geological structure of Mahe collapse body is approximately sorted into three layers.The upper layer close to surface is loose coverage with a thickness about 30~40mm,not cementitious; The medium layer is a medium to strong weathered layer with a thickness about 10~15mm,weathered strongly,fractured intensively; The bottom layer is a relatively intact rock mass under 40~50m depth with a wave velocity above 2500m s-1; As to stability evaluation,there are two unstable conditions:the collapse body may occur failure along the bottom boundary of coverage or weathered layer under earthquake condition,while the collapse body may also occur failure along the bottom boundary of weathered layer under rainfall condition.
2011, 19(4): 594-600.
Underground mining under slope can not only cause that the construction of rock mass is destructed and the mechanical properties are reduced,but also lead to that the state of stress is redistributed and affect the deformation and stability of slope greatly.This paper takes the underground mining of B900 under the east slope of the Antaibao open mine as example.Based on the deformation monitoring data,the deformation law and mechanism are summarized.The stability of slope is estimated by the method of stereographic projection analysis,FLAC numerical simulation and limit equilibrium method.Stability evaluation shows that: under the influence of the underground mining,the stability will be reduced,but the overall landslide does not be occurred,the disrupted type of the slope is the sliding collapse.The conclusion is the same to the field practical situation,and can supply reference to similar mining area.
Underground mining under slope can not only cause that the construction of rock mass is destructed and the mechanical properties are reduced,but also lead to that the state of stress is redistributed and affect the deformation and stability of slope greatly.This paper takes the underground mining of B900 under the east slope of the Antaibao open mine as example.Based on the deformation monitoring data,the deformation law and mechanism are summarized.The stability of slope is estimated by the method of stereographic projection analysis,FLAC numerical simulation and limit equilibrium method.Stability evaluation shows that: under the influence of the underground mining,the stability will be reduced,but the overall landslide does not be occurred,the disrupted type of the slope is the sliding collapse.The conclusion is the same to the field practical situation,and can supply reference to similar mining area.
2011, 19(4): 601-605.
This paper presents the field static loading tests on Vibrating Gravel Pile Foundation in Mu Us Desert.The effective length of the gravel pile and the bearing capacity of the Vibrating Gravel Pile Foundation are studied.The test results show that the critical loads of the natural base,gravel pile,soil between piles and the compound foundation are 128 kPa, 1019.2 kPa, 318 kPa,and 535 kPa,and the limit loads of the natural base and the soil between piles are 320 kPa and 318 kPa respectively.The limit loads of the gravel pile and the compound foundation are more than 3312.4 kPa and 2072 kPa respectively.The results also show that although the effective length of the gravel pile reaches 8m,the loads are supported mainly by the upper 4m of the gravel pile.The work of this paper makes great significance to practice of the gravel Pile Foundation in the Mu Us Desert.
This paper presents the field static loading tests on Vibrating Gravel Pile Foundation in Mu Us Desert.The effective length of the gravel pile and the bearing capacity of the Vibrating Gravel Pile Foundation are studied.The test results show that the critical loads of the natural base,gravel pile,soil between piles and the compound foundation are 128 kPa, 1019.2 kPa, 318 kPa,and 535 kPa,and the limit loads of the natural base and the soil between piles are 320 kPa and 318 kPa respectively.The limit loads of the gravel pile and the compound foundation are more than 3312.4 kPa and 2072 kPa respectively.The results also show that although the effective length of the gravel pile reaches 8m,the loads are supported mainly by the upper 4m of the gravel pile.The work of this paper makes great significance to practice of the gravel Pile Foundation in the Mu Us Desert.
2011, 19(4): 606-609.
Based on the field SPT,the Rational Spacing between Vibroflotation sand Piles in Aeolian Sand of the Mu Us Desert is studied in this paper.The results show that the spacing of 1.4m was the most effective pile spacing.It is suggests that the compaction effects mainly depend on the pile spacing under the same conditions of sand layers,vibration force,vibration frequency as well as the construction technology.In the case of the tests in this paper,where the diameter of the tested sand piles is 1m,the pile spacing should be controlled within 1.6m.Considering the inexpensive of the sand pile construction,the small pile spacing is recommended based on the analysis of the tests.
Based on the field SPT,the Rational Spacing between Vibroflotation sand Piles in Aeolian Sand of the Mu Us Desert is studied in this paper.The results show that the spacing of 1.4m was the most effective pile spacing.It is suggests that the compaction effects mainly depend on the pile spacing under the same conditions of sand layers,vibration force,vibration frequency as well as the construction technology.In the case of the tests in this paper,where the diameter of the tested sand piles is 1m,the pile spacing should be controlled within 1.6m.Considering the inexpensive of the sand pile construction,the small pile spacing is recommended based on the analysis of the tests.
2011, 19(4): 610-614.
Interfacial interactions between fiber reinforcement and soil play an important role in reinforce benefit.Understanding the interfacial mechanical behavior is helpful to apply effectively the fiber reinforcement in geotechnical engineering practice.The objective of the present work is to study the interfacial micro-mechanical behavior of discrete polypropylene fiber reinforced soil.Three soil types(fiber reinforced raw soil, cement soil and lime soil)commonly used in the field were taken into account.The evolution of the interfacial microstructure and fiber surface morphology in these soil types were characterized by using scanning electron microscopy(SEM).It was found that the bond strength between fibers and soil matrix and the associated interfacial friction are the dominant mechanism of fiber reinforced soil.They seem to be controlled by the soil properties and interface condition(microstructure, soil composition, fiber surface roughness etc.).In fiber reinforced raw soil, the fiber surface is attached by many clay minerals.In fiber reinforced cement soil, the interfacial bond strength plays a main role in the interfacial mechanical behavior.In fiber reinforced lime soil, evident plastic deformation is observed on fiber surface, which greatly improved the interfacial friction.
Interfacial interactions between fiber reinforcement and soil play an important role in reinforce benefit.Understanding the interfacial mechanical behavior is helpful to apply effectively the fiber reinforcement in geotechnical engineering practice.The objective of the present work is to study the interfacial micro-mechanical behavior of discrete polypropylene fiber reinforced soil.Three soil types(fiber reinforced raw soil, cement soil and lime soil)commonly used in the field were taken into account.The evolution of the interfacial microstructure and fiber surface morphology in these soil types were characterized by using scanning electron microscopy(SEM).It was found that the bond strength between fibers and soil matrix and the associated interfacial friction are the dominant mechanism of fiber reinforced soil.They seem to be controlled by the soil properties and interface condition(microstructure, soil composition, fiber surface roughness etc.).In fiber reinforced raw soil, the fiber surface is attached by many clay minerals.In fiber reinforced cement soil, the interfacial bond strength plays a main role in the interfacial mechanical behavior.In fiber reinforced lime soil, evident plastic deformation is observed on fiber surface, which greatly improved the interfacial friction.
2011, 19(4): 615-619.
Based on the point estimate method and finite element strength reduction method,this paper calculates the reliability indexes of 4 typical cutting slopes in different loess regions.The results show that: the stability coefficient of case 2 is 1.46,but its failure probability is 19.2%; although case 1and 4are similar in slope type,the lithology and layer thickness,etc,the difference between their failure probabilities can reach 29.8%,parameter variation is the main reason of causing the difference.Using point estimation method to calculate slope reliability can be an appropriate way to solve the problem that soil parameters discreteness influences slope stability assessment.
Based on the point estimate method and finite element strength reduction method,this paper calculates the reliability indexes of 4 typical cutting slopes in different loess regions.The results show that: the stability coefficient of case 2 is 1.46,but its failure probability is 19.2%; although case 1and 4are similar in slope type,the lithology and layer thickness,etc,the difference between their failure probabilities can reach 29.8%,parameter variation is the main reason of causing the difference.Using point estimation method to calculate slope reliability can be an appropriate way to solve the problem that soil parameters discreteness influences slope stability assessment.
2011, 19(4): 620-625.
Upon drying,desiccation cracks would occur in expansive soils due to evaporation and volume shrinkage.The presence of cracks may significantly weaken soil engineering properties.Better understanding the characteristics of tensile strength during drying is very helpful to study the essential mechanisms of desiccation crack initiation and propagation.In this investigation,Romainville expansive soil was used and several groups of initially saturated slurry specimens were prepared.The specimens were then dried in room condition to different water content.Direct tensile test was performed on these specimens by employing the modified super mini-penetrometer(SMP-1).The evolution of tensile strength with water content was quantitatively characterized.In addition,vapor equilibrium technique was applied to control the soil suction during drying,and the effect of suction on tensile strength was also studied.The results indicate that,during drying,the specimen tensile strength generally increases exponentially with decreasing water content.Before the water content is lower than plastic limit(40%),the tensile strength and the increase rate is very low; after the water content reaches the plastic limit,a slight decrease of water content can lead to significant increase of the tensile strength.With increasing suction,the specimen water content decreases exponentially as expected,and the tensile strength increases linearly.It is found that the evolution behaviour of soil tensile strength during drying is mainly connected with pore water properties,water-soil interactions,contact behviour between soil particles and soil structure.
Upon drying,desiccation cracks would occur in expansive soils due to evaporation and volume shrinkage.The presence of cracks may significantly weaken soil engineering properties.Better understanding the characteristics of tensile strength during drying is very helpful to study the essential mechanisms of desiccation crack initiation and propagation.In this investigation,Romainville expansive soil was used and several groups of initially saturated slurry specimens were prepared.The specimens were then dried in room condition to different water content.Direct tensile test was performed on these specimens by employing the modified super mini-penetrometer(SMP-1).The evolution of tensile strength with water content was quantitatively characterized.In addition,vapor equilibrium technique was applied to control the soil suction during drying,and the effect of suction on tensile strength was also studied.The results indicate that,during drying,the specimen tensile strength generally increases exponentially with decreasing water content.Before the water content is lower than plastic limit(40%),the tensile strength and the increase rate is very low; after the water content reaches the plastic limit,a slight decrease of water content can lead to significant increase of the tensile strength.With increasing suction,the specimen water content decreases exponentially as expected,and the tensile strength increases linearly.It is found that the evolution behaviour of soil tensile strength during drying is mainly connected with pore water properties,water-soil interactions,contact behviour between soil particles and soil structure.
2011, 19(4): 626-632.
Long-term stability of dam abutment resistance body is very important for a hydropower station.The abutment resistance body stability of complex rock mass dam under the action of water thrust is particularly important.There are widely altered rocks in the dam abutment of a hydropower station in Southwest China.On the basis of altered rock rheological property and its viscous-elastic-plastic constitutive model,the stress and deformation fields characteristics in the resistance body slope have been simulated with 3D numerical method during the reservoir operation period.The study results show that te third stress field is formed after 6months of water storage.The dam abutment resistance body is in the most dangerous situation.Local destruction between altered rock and fault may appear.According to the simulated deformation value and plastic zones after 5 years of water storage,the abutment resistance body of the whole dam is in a long-term stable state.
Long-term stability of dam abutment resistance body is very important for a hydropower station.The abutment resistance body stability of complex rock mass dam under the action of water thrust is particularly important.There are widely altered rocks in the dam abutment of a hydropower station in Southwest China.On the basis of altered rock rheological property and its viscous-elastic-plastic constitutive model,the stress and deformation fields characteristics in the resistance body slope have been simulated with 3D numerical method during the reservoir operation period.The study results show that te third stress field is formed after 6months of water storage.The dam abutment resistance body is in the most dangerous situation.Local destruction between altered rock and fault may appear.According to the simulated deformation value and plastic zones after 5 years of water storage,the abutment resistance body of the whole dam is in a long-term stable state.
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