How to determine reasonable position and length of anchor cable is a frequently encountered but not well addressed problem in slope reinforcement projects. In this paper, the variable-modulus elastoplastic strength re...How to determine reasonable position and length of anchor cable is a frequently encountered but not well addressed problem in slope reinforcement projects. In this paper, the variable-modulus elastoplastic strength reduction method （SRM） is used to obtain the stress field, displacement field, and factor of safety of slope. Slope reinforcement using anchor cables is modeled by surface loading, i.e. different distributions of surface loading represent various reinforcement schemes. Optimal reinforcement scheme of anchor cables can be determined based on slope stress and displacement fields. By comparing the factor of safety and stress field before and after slope reinforcement, it is found that better rein-forcement results can be achieved if strong reinforcement is applied upon the regions with high stress and large displacement. This method can well optimize the arrangement of anchor cables. In addition, several cases are employed to verify the proposed method.展开更多
The composite pile consisting of core-pile and surrounding cement-enhanced soil is a promising pile foundation in recent years.However,how and to what extent the cement-enhanced soil influences the ultimate lateral re...The composite pile consisting of core-pile and surrounding cement-enhanced soil is a promising pile foundation in recent years.However,how and to what extent the cement-enhanced soil influences the ultimate lateral resistance has not been fully investigated.In this paper,the ultimate lateral resistance of the composite pile was studied by finite element limit analysis(FELA)and theoretical upper-bound analysis.The results of FELA and theoretical analysis revealed three failure modes of laterally loaded composite piles.The effects of the enhanced soil thickness,strength,and pile-enhanced soil interface characteristics on the ultimate lateral resistance were studied.The results show that increasing the enhanced soil thickness leads to a significant improvement on ultimate lateral resistance factor(N P),and there is a critical thickness beyond which the thickness no longer affects the N P.Increasing the enhanced soil strength induced 6.2%-232.6%increase of N P.However,no noticeable impact was detected when the enhanced soil strength was eight times higher than that of the natural soil.The maximum increment of N P is only 30.5%caused by the increase of interface adhesion factor(a).An empirical model was developed to calculate the N P of the composite pile,and the results show excellent agreement with the analytical results.展开更多
Fluctuating snow-covered elevation （FSCE） was conceptualized and proposed to characterize within-year variation of the border between snow-covered and snow-free area in mountainous regions. Two parameters, namely me...Fluctuating snow-covered elevation （FSCE） was conceptualized and proposed to characterize within-year variation of the border between snow-covered and snow-free area in mountainous regions. Two parameters, namely median of snow flee period （Tm） and snow free duration （AT）, were defined to quantify FSCE. A regression model of FSCE was developed for the Lhasa River Basin, Niyang River Basin, and Changdu region in eastern Tibet. Statistical analysis of the snow-products data with a spatial resolution of 25km×25km shows that： （1） Tm correlates weakly with geographical and topographic factors, having the yearly mean value of July 31; （2） △T correlates significantly with the average elevation of the snow-products cell, having the yearly mean value of nearly five months （i.e., 151 days）; （3） the region begins snow disappearance in late April and finishes snow coverage in mid November, being snow-free from late June to mid September and snow-covered from December to March in the next year. In addi- tion, snow-products with higher spatial resolution will be helpful to characterize FSCE in smaller spatial scales.展开更多
As one of the world's largest braided rivers,the Yarlung Zangbo River is subjected to the tectonic activities of the Tibetan Plateau,leading to the formation of alternating river patterns of wide-braided and incis...As one of the world's largest braided rivers,the Yarlung Zangbo River is subjected to the tectonic activities of the Tibetan Plateau,leading to the formation of alternating river patterns of wide-braided and incised gorges.Herein,a geometricbased method is proposed to estimate the sedimentation volume in the braided reaches of the middle Yarlung Zangbo River.This method utilizes the envelope of the geometric extension of the valley floor to approximate the sedimentation interface and is further calibrated against EH4 electromagnetic measurements.The calibrated method demonstrates high accuracy,exhibiting a mean absolute error of 10.4%compared with drilling measurements.The total sedimentation volume in the braided reaches of the middle Yarlung Zangbo River is 618.3 km^(3),with Rikaze and Shannan reaches being the major contributors.Overall,the new method provides an accessible yet reliable tool for estimating the sediment volume.This result enhances the understanding of sediment dynamics in braided channel systems and aids in the sustainable management of riverine environments on the Tibetan Plateau.展开更多
Estimated daily flows along the Yarlung Zangbo River(YZR)for periods well before stream gauging began in the 1950s are needed to characterize long-term flow variabilities.To examine whether the recorded flow in recent...Estimated daily flows along the Yarlung Zangbo River(YZR)for periods well before stream gauging began in the 1950s are needed to characterize long-term flow variabilities.To examine whether the recorded flow in recent decades can sufficiently represent natural variability and change,daily flows were reconstructed using the autocalibrated variable infiltration capacity(VIC)model using preinstrumental proxy-based precipitation and temperature data for four mainstream stations in the YZR basin for the period 1473–2000.VIC performed well during calibration and validation for all stations,with the Nash–Sutcliffe coefficient of efficiency exceeding 0.55 and the correlation coefficient and the bias in the standard deviation being close to 1.This study showed that the annual or decadal flows have not significantly changed over the past 528 years.The longterm mean flow differed from that for the period 1951–2000 by only 6%–8%,although the reconstructed maximum annual flow was approximately 24%–35%higher and the minimum flow was 0%–9%lower than those for 1951−2000.Moreover,the flow in recent decades could not capture the persistently high or low flows and some extreme wet/dry years found in the preinstrumental period.The timing of the maximum daily flow was more concentrated,and its magnitude was slightly but not significantly higher.A comparison of flows at the four mainstream stations indicated that the annual and peak daily flows were not synchronous.The timing of floods was highly correlated among the three stations,apart from that at Lazi.Furthermore,flows at Nuxia demonstrated a pronounced response to the Indian Ocean Dipole approximately at 20-year periodicity,whereas those at Lazi were more strongly influenced by the North Atlantic Oscillation on an~50-year scale.This study improves our understanding of the long-term flow variability for the whole YZR basin and its potential climatic drivers for better water resource management and more effective flood hazard control.展开更多
基金funded by the National Natural Science Foundation of China (Grant Nos. 51378131 and 51378403)
文摘How to determine reasonable position and length of anchor cable is a frequently encountered but not well addressed problem in slope reinforcement projects. In this paper, the variable-modulus elastoplastic strength reduction method （SRM） is used to obtain the stress field, displacement field, and factor of safety of slope. Slope reinforcement using anchor cables is modeled by surface loading, i.e. different distributions of surface loading represent various reinforcement schemes. Optimal reinforcement scheme of anchor cables can be determined based on slope stress and displacement fields. By comparing the factor of safety and stress field before and after slope reinforcement, it is found that better rein-forcement results can be achieved if strong reinforcement is applied upon the regions with high stress and large displacement. This method can well optimize the arrangement of anchor cables. In addition, several cases are employed to verify the proposed method.
基金The work was supported by the National Natural Science Foundation of China(Grant No.51978540).
文摘The composite pile consisting of core-pile and surrounding cement-enhanced soil is a promising pile foundation in recent years.However,how and to what extent the cement-enhanced soil influences the ultimate lateral resistance has not been fully investigated.In this paper,the ultimate lateral resistance of the composite pile was studied by finite element limit analysis(FELA)and theoretical upper-bound analysis.The results of FELA and theoretical analysis revealed three failure modes of laterally loaded composite piles.The effects of the enhanced soil thickness,strength,and pile-enhanced soil interface characteristics on the ultimate lateral resistance were studied.The results show that increasing the enhanced soil thickness leads to a significant improvement on ultimate lateral resistance factor(N P),and there is a critical thickness beyond which the thickness no longer affects the N P.Increasing the enhanced soil strength induced 6.2%-232.6%increase of N P.However,no noticeable impact was detected when the enhanced soil strength was eight times higher than that of the natural soil.The maximum increment of N P is only 30.5%caused by the increase of interface adhesion factor(a).An empirical model was developed to calculate the N P of the composite pile,and the results show excellent agreement with the analytical results.
基金supported by the National Natural Science Foundation of China under Grant No.50221903by the Ministry of Science and Technology of China under Grant No.2007BAC06B06
文摘Fluctuating snow-covered elevation （FSCE） was conceptualized and proposed to characterize within-year variation of the border between snow-covered and snow-free area in mountainous regions. Two parameters, namely median of snow flee period （Tm） and snow free duration （AT）, were defined to quantify FSCE. A regression model of FSCE was developed for the Lhasa River Basin, Niyang River Basin, and Changdu region in eastern Tibet. Statistical analysis of the snow-products data with a spatial resolution of 25km×25km shows that： （1） Tm correlates weakly with geographical and topographic factors, having the yearly mean value of July 31; （2） △T correlates significantly with the average elevation of the snow-products cell, having the yearly mean value of nearly five months （i.e., 151 days）; （3） the region begins snow disappearance in late April and finishes snow coverage in mid November, being snow-free from late June to mid September and snow-covered from December to March in the next year. In addi- tion, snow-products with higher spatial resolution will be helpful to characterize FSCE in smaller spatial scales.
基金supported by the National Natural Science Foundation of China(Grant Nos.52479073,52442908)。
文摘As one of the world's largest braided rivers,the Yarlung Zangbo River is subjected to the tectonic activities of the Tibetan Plateau,leading to the formation of alternating river patterns of wide-braided and incised gorges.Herein,a geometricbased method is proposed to estimate the sedimentation volume in the braided reaches of the middle Yarlung Zangbo River.This method utilizes the envelope of the geometric extension of the valley floor to approximate the sedimentation interface and is further calibrated against EH4 electromagnetic measurements.The calibrated method demonstrates high accuracy,exhibiting a mean absolute error of 10.4%compared with drilling measurements.The total sedimentation volume in the braided reaches of the middle Yarlung Zangbo River is 618.3 km^(3),with Rikaze and Shannan reaches being the major contributors.Overall,the new method provides an accessible yet reliable tool for estimating the sediment volume.This result enhances the understanding of sediment dynamics in braided channel systems and aids in the sustainable management of riverine environments on the Tibetan Plateau.
基金supported by the National Natural Science Foundation of China(Grant Nos.91747207,U2340223)the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2019QZKK0903).
文摘Estimated daily flows along the Yarlung Zangbo River(YZR)for periods well before stream gauging began in the 1950s are needed to characterize long-term flow variabilities.To examine whether the recorded flow in recent decades can sufficiently represent natural variability and change,daily flows were reconstructed using the autocalibrated variable infiltration capacity(VIC)model using preinstrumental proxy-based precipitation and temperature data for four mainstream stations in the YZR basin for the period 1473–2000.VIC performed well during calibration and validation for all stations,with the Nash–Sutcliffe coefficient of efficiency exceeding 0.55 and the correlation coefficient and the bias in the standard deviation being close to 1.This study showed that the annual or decadal flows have not significantly changed over the past 528 years.The longterm mean flow differed from that for the period 1951–2000 by only 6%–8%,although the reconstructed maximum annual flow was approximately 24%–35%higher and the minimum flow was 0%–9%lower than those for 1951−2000.Moreover,the flow in recent decades could not capture the persistently high or low flows and some extreme wet/dry years found in the preinstrumental period.The timing of the maximum daily flow was more concentrated,and its magnitude was slightly but not significantly higher.A comparison of flows at the four mainstream stations indicated that the annual and peak daily flows were not synchronous.The timing of floods was highly correlated among the three stations,apart from that at Lazi.Furthermore,flows at Nuxia demonstrated a pronounced response to the Indian Ocean Dipole approximately at 20-year periodicity,whereas those at Lazi were more strongly influenced by the North Atlantic Oscillation on an~50-year scale.This study improves our understanding of the long-term flow variability for the whole YZR basin and its potential climatic drivers for better water resource management and more effective flood hazard control.
