In this study consecutive consolidated isotropically drained triaxial tests for the coefficient of earth pressure at rest(K_0) were carried out to investigate its rules of evolution as well as its strength characteris...In this study consecutive consolidated isotropically drained triaxial tests for the coefficient of earth pressure at rest(K_0) were carried out to investigate its rules of evolution as well as its strength characteristics for normal,consolidated saturated silt under high pressure.The tests results indicate that:1) for normal,consolidated saturated silt,K_0 values increase as the consolidation stress increases at high pressure levels,while the nonlinear characteristics of K_0 are inconspicuous compared to cohesive soils;2) the Jaky and Roscoe equations,used to calculate K_0,are only suitable for certain soils,but cannot represent these values for normal, consolidated saturated silt due to the variation in bilinear strength at high pressure;and 3) there are close relations between the nonlinear characteristics of K_0 and the void ratio,measured in the tests.Both share the same functional form while under pressure. Based on our experimental results,we developed an empirical linear model to interpret the rules of nonlinear variation for the coefficient of earth pressure at rest.展开更多
The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest,K0,was investigated under high pressures.The results indicate that the rigid pressure chamber and flex...The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest,K0,was investigated under high pressures.The results indicate that the rigid pressure chamber and flexible lateral confining pressure medium method gives a stress ratio at the initial stage that is not the real K0.Moreover,K0 increases during the loading process becoming greater at high pressures.In the unloading process,however,K0 increases only at the initial stage but decreases thereafter.In addition,the incremental magnitude definition,K0=dσ3/dσ1,gives higher values than the total magnitude definition,K0=σ3/σ1,under loading.This is also true during initial stages of unloading.The experiment results also indicate that earth pressure at rest in deep and thick soils can be estimated by a power function of axial and confining pressures.It is necessary to choose the appropriate K0 to avoid some accidents.展开更多
In order to obtain the earth pressure coefficient at rest (K0) at higher consolidation pressures during secondary compression, a series of K0 tests for saturated reconstituted clay were conducted. The results indicate...In order to obtain the earth pressure coefficient at rest (K0) at higher consolidation pressures during secondary compression, a series of K0 tests for saturated reconstituted clay were conducted. The results indicate that the measured K0 in secondary compression can be described by equations related to internal friction angle, secondary compression coefficient, compression index, recompression index, and sediment time. Effects of consolidation pressures and sediment time on K0 during secondary compression can be attributed to cementation (part of cohesion) increase and internal friction angle decrease. Cementation increase leads to nonlinear variation for K0 and internal friction angle decrease results in increase of K0. K0 computed by equations associated with internal friction angle is overestimated at apparent lower consolidation pressures with different sediment time, which agrees with the measured values well at apparent higher consolidation pressures.展开更多
Background and Objectives:The aims of this study were(1)to examine the diagnostic accuracy of resting timeaveraged distal coronary pressure(Pd)to mean aortic pressure(Pa)ratio to predict hyperemic fractional flow rese...Background and Objectives:The aims of this study were(1)to examine the diagnostic accuracy of resting timeaveraged distal coronary pressure(Pd)to mean aortic pressure(Pa)ratio to predict hyperemic fractional flow reserve(FFR)and(2)to identify a resting Pd/Pa value that can preclude the need for hyperemic FFR assessed with use of a monorail pressure catheter.Methods:A total of 191 stenoses were assessed.After exclusions,157 FFR data sets from 103 patients were analyzed.Results:Resting Pd/Pa showed poor agreement with hyperemic FFR(r=0.619,P<0.001).The receiver operating characteristic curve for resting Pd/Pa with reference to hyperemic FFR of 0.80 or less showed an area under the curve of 0.800(95%confi dence interval 0.732– 0.868,P<0.001),with the greatest diagnostic accuracy of 74.5%for resting Pd/Pa of less than 0.85.Resting Pd/Pa of 0.96 or greater had a sensitivity of 100%and a negative predictive value of 100%,and resting Pd/Pa of 0.82 or less had a specifi city of 98.9%and a positive predictive value of 94.1%to predict abnormal FFR of 0.80 or less.These results were consistent regardless of the vessels studied,the location of lesions,and the severity of stenosis.Conclusions:Resting Pd/Pa showed poor agreement with hyperemic FFR assessed with use of a monorail pressure microcatheter.However,resting Pd/Pa of 0.96 or greater had excellent sensitivity and negative predictive value to predict normal hyperemic FFR,and resting Pd/Pa of 0.82 or less had excellent specifi city and positive predictive value to predict abnormal hyperemic FFR.展开更多
According the Coulomb earth pressure theory,it is obtained that,for normally consolidated soils,the lateral pressure coefficient of a soil at rest is equal to 1,and it is independent of the soil type,either granular o...According the Coulomb earth pressure theory,it is obtained that,for normally consolidated soils,the lateral pressure coefficient of a soil at rest is equal to 1,and it is independent of the soil type,either granular or cohesive;or that the material is in a loose or compact state;hard or a soft cohesive soil.Also,a methodology to calculate the earth pressure for intermediate states between at rest condition and the active pressure is presented.In addition,a methodology to calculate the earth pressure for intermediate states between at rest condition and the passive pressure is presented.Two practical examples are presented:one for a frictionless wall;and another for a coarse wall.Practical recommendations are given for the use of the lateral earth pressure coefficient for different applications.展开更多
基金Financial support for this work,provided by the National Natural Science Foundation of China (No.50534040)the Project of the Science and Technology Ministry of China(No.2006BAB16B01)the Post Graduate Research Project of Jiangsu Province (No.CX08B_103Z),
文摘In this study consecutive consolidated isotropically drained triaxial tests for the coefficient of earth pressure at rest(K_0) were carried out to investigate its rules of evolution as well as its strength characteristics for normal,consolidated saturated silt under high pressure.The tests results indicate that:1) for normal,consolidated saturated silt,K_0 values increase as the consolidation stress increases at high pressure levels,while the nonlinear characteristics of K_0 are inconspicuous compared to cohesive soils;2) the Jaky and Roscoe equations,used to calculate K_0,are only suitable for certain soils,but cannot represent these values for normal, consolidated saturated silt due to the variation in bilinear strength at high pressure;and 3) there are close relations between the nonlinear characteristics of K_0 and the void ratio,measured in the tests.Both share the same functional form while under pressure. Based on our experimental results,we developed an empirical linear model to interpret the rules of nonlinear variation for the coefficient of earth pressure at rest.
基金Projects 50534040 supported by the National Natural Science Foundation of ChinaBK2007040 by the Natural Science Foundation of Jiangsu ProvinceCX08B_103Z by the Post Graduate Research Projects of Jiangsu Province
文摘The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest,K0,was investigated under high pressures.The results indicate that the rigid pressure chamber and flexible lateral confining pressure medium method gives a stress ratio at the initial stage that is not the real K0.Moreover,K0 increases during the loading process becoming greater at high pressures.In the unloading process,however,K0 increases only at the initial stage but decreases thereafter.In addition,the incremental magnitude definition,K0=dσ3/dσ1,gives higher values than the total magnitude definition,K0=σ3/σ1,under loading.This is also true during initial stages of unloading.The experiment results also indicate that earth pressure at rest in deep and thick soils can be estimated by a power function of axial and confining pressures.It is necessary to choose the appropriate K0 to avoid some accidents.
基金Projects(50534040, 50974117) supported by the National Natural Science Foundation of ChinaProject(20110491489) supported by China Postdoctoral Science FoundationProject(2011QNA03) supported by Fundamental Research Funds for Central Universities, China
文摘In order to obtain the earth pressure coefficient at rest (K0) at higher consolidation pressures during secondary compression, a series of K0 tests for saturated reconstituted clay were conducted. The results indicate that the measured K0 in secondary compression can be described by equations related to internal friction angle, secondary compression coefficient, compression index, recompression index, and sediment time. Effects of consolidation pressures and sediment time on K0 during secondary compression can be attributed to cementation (part of cohesion) increase and internal friction angle decrease. Cementation increase leads to nonlinear variation for K0 and internal friction angle decrease results in increase of K0. K0 computed by equations associated with internal friction angle is overestimated at apparent lower consolidation pressures with different sediment time, which agrees with the measured values well at apparent higher consolidation pressures.
文摘Background and Objectives:The aims of this study were(1)to examine the diagnostic accuracy of resting timeaveraged distal coronary pressure(Pd)to mean aortic pressure(Pa)ratio to predict hyperemic fractional flow reserve(FFR)and(2)to identify a resting Pd/Pa value that can preclude the need for hyperemic FFR assessed with use of a monorail pressure catheter.Methods:A total of 191 stenoses were assessed.After exclusions,157 FFR data sets from 103 patients were analyzed.Results:Resting Pd/Pa showed poor agreement with hyperemic FFR(r=0.619,P<0.001).The receiver operating characteristic curve for resting Pd/Pa with reference to hyperemic FFR of 0.80 or less showed an area under the curve of 0.800(95%confi dence interval 0.732– 0.868,P<0.001),with the greatest diagnostic accuracy of 74.5%for resting Pd/Pa of less than 0.85.Resting Pd/Pa of 0.96 or greater had a sensitivity of 100%and a negative predictive value of 100%,and resting Pd/Pa of 0.82 or less had a specifi city of 98.9%and a positive predictive value of 94.1%to predict abnormal FFR of 0.80 or less.These results were consistent regardless of the vessels studied,the location of lesions,and the severity of stenosis.Conclusions:Resting Pd/Pa showed poor agreement with hyperemic FFR assessed with use of a monorail pressure microcatheter.However,resting Pd/Pa of 0.96 or greater had excellent sensitivity and negative predictive value to predict normal hyperemic FFR,and resting Pd/Pa of 0.82 or less had excellent specifi city and positive predictive value to predict abnormal hyperemic FFR.
文摘According the Coulomb earth pressure theory,it is obtained that,for normally consolidated soils,the lateral pressure coefficient of a soil at rest is equal to 1,and it is independent of the soil type,either granular or cohesive;or that the material is in a loose or compact state;hard or a soft cohesive soil.Also,a methodology to calculate the earth pressure for intermediate states between at rest condition and the active pressure is presented.In addition,a methodology to calculate the earth pressure for intermediate states between at rest condition and the passive pressure is presented.Two practical examples are presented:one for a frictionless wall;and another for a coarse wall.Practical recommendations are given for the use of the lateral earth pressure coefficient for different applications.
