The instability of soil bank slopes induced by freeze-thaw cycles at the northern foot of Tianshan Mountain is very common.The failure not only caused a large amount of soil erosion,but also led to serious reservoir s...The instability of soil bank slopes induced by freeze-thaw cycles at the northern foot of Tianshan Mountain is very common.The failure not only caused a large amount of soil erosion,but also led to serious reservoir sedimentation and water quality degradation,which exerted a lot of adverse effects on agricultural production in the local irrigation areas.Based on field investigations on dozens of irrigation reservoirs there,laboratory tests were carried out to quantitatively analyze the freeze-thaw effect on the soil engineering characteristics to reveal the facilitation on the bank slope instability.The results show that the softening characteristics of the stressstrain curves gradually weaken,the effective cohesions decline exponentially,the seepage coefficients enlarge,and the thermal conductivities decrease after 7 freeze-thaw cycles.The freeze-thaw effect on the specimens with low confining pressures,low dry densities and high water contents is more significant.The water migration and the phase transition between water and ice result in the variations of the soil internal microstructures,which is the main factor affecting the soil engineering characteristics.Sufficient water supply and the alternation of positive and negative temperatures at the reservoir bank slopes in cold regions make the water migration and phase transition in the soil very intensely.It is easy to form a large number of pores and micro cracks in the soil freezing and thawing areas.The volume changes of the soil and the water migration are difficult to reach a dynamic balance in the open system.Long-term freeze-thaw cycles will bring out the fragmentation of the soil particles,resulting in that the micro cracks on the soil surfaces are developing continuously.The soil of the bank slopes will fall or collapse when these cracks penetrate,which often happens in winter there.展开更多
After water is impounded in a reservoir,rock mass in the hydro-fluctuation belt of the reservoir bank slope is subject to water saturationdehydration circulation(WSDC). To quantify the rate of change of rock mechanica...After water is impounded in a reservoir,rock mass in the hydro-fluctuation belt of the reservoir bank slope is subject to water saturationdehydration circulation(WSDC). To quantify the rate of change of rock mechanical properties, samples from the Longtan dam area were measured with uniaxial compression tests after different numbers(1,5, 10, 15, and 20) of simulated WSDC cycles. Based on the curves derived from these tests, a modified HoekBrown failure criterion was proposed, in which a new parameter was introduced to model the cumulative damage to rocks after WSDC. A case of an engineering application was analyzed, and the results showed that the modified Hoek-Brown failure criterion is useful.Under similar WSDC-influenced engineering and geological conditions, rock mass strength parameters required for analysis and evaluation of rock slope stability can be estimated according to this modified Hoek-Brown failure criterion.展开更多
In most cases, the slope stability of reservoir bank is analyzed on the premise that the location of phreatic surface is obtained. But many designers generalize a line as the phreatic surface through their experience ...In most cases, the slope stability of reservoir bank is analyzed on the premise that the location of phreatic surface is obtained. But many designers generalize a line as the phreatic surface through their experience to analyze the stability, which is unsafe in the project. To find a solution of the phreatic surface which is convenient to put into use and in accordance with the practice, the article, based on Boussinesq equation, infers analytic solutions suitable to the water level at different ratios and achieves an analytic solution equation through fitting curves. The correctness of the equation is also proved by the experiments of sand and sand-clay models and the inaccuracy of empirical generalization is analyzed quantitatively. The calculation results show that the inaccuracy through the method of experiential generalizing is so large that the designers should be awake to it.展开更多
为进一步加快构建新型电力系统,促进抽水蓄能电站数字化转型。笔者通过运用地理信息系统(geographic information system,GIS)技术和数字高程模型(digital elevation model,DEM)建立抽水蓄能电站库区淹没与库岸稳定分析系统,并从系统的...为进一步加快构建新型电力系统,促进抽水蓄能电站数字化转型。笔者通过运用地理信息系统(geographic information system,GIS)技术和数字高程模型(digital elevation model,DEM)建立抽水蓄能电站库区淹没与库岸稳定分析系统,并从系统的技术结构、三维可视化、库区淹没分析、库区浸没分析和库区塌岸分析等方面分析系统模块建设及其功能实现。结果表明,该系统可实现库区淹没范围、库区浸没范围和库区塌岸预测范围边界线的三维模拟分析及实时动态演示,相关的土地利用数据快速整合评估等。该系统可为合理确定抽水蓄能电站水库大坝位置,制定征地拆迁、土地赔偿、移民安置等方案提供科学的决策依据。展开更多
Soil erosion and bank degradation is a major post-dam concern regarding the riparian zone of the Three Gorges Reservoir. The development and succession of vegetation is a main countermeasure,especially to enhance bank...Soil erosion and bank degradation is a major post-dam concern regarding the riparian zone of the Three Gorges Reservoir. The development and succession of vegetation is a main countermeasure,especially to enhance bank stability and mitigate soil erosion by the root system. In this study, the roots of four prevailing grass species, namely, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, in the riparian zone were investigated in relation to additional soil cohesion. Roots were sampled using a single root auger. Root length density(RLD) and root area ratio(RAR) were measured by using the Win RHIZO image analysis system. Root tensile strength(TR) was performed using a manualdynamometer, and the soil reinforcement caused by the roots was estimated using the simple Wu's perpendicular model. Results showed that RLD values of the studied species ranged from 0.24 cm/cm3 to20.89 cm/cm3 at different soil layers, and RLD were significantly greater at 0–10 cm depth in comparison to the deeper soil layers(>10 cm). RAR measurements revealed that on average 0.21% of the reference soil area was occupied by grass roots for all the investigated species. The measured root tensile strength was the highest for P. paspaloides(62.26MPa) followed by C. dactylon(51.49 MPa), H.compressa(50.66 MPa), and H. altissima(48.81MPa). Nevertheless, the estimated maximum root reinforcement in this investigation was 22.5 k Pa for H.altissima followed by H. compressa(21.1 k Pa), P.paspaloides(19.5 k Pa), and C. dactylon(15.4 k Pa) at0–5 cm depth soil layer. The root cohesion values estimated for all species were generally distributed at the 0–10 cm depth and decreased with the increment of soil depth. The higher root cohesion associated with H. altissima and H. compressa implies their suitability for revegetation purposes to strengthen the shallow soil in the riparian zone of the Three Gorges Reservoir. Although the soil reinforcement induced by roots is only assessed from indirect indicators, the present results still useful for species selection in the framework of implementing and future vegetation recovery actions in the riparian zone of the Three Gorges Reservoir and similar areas in the Yangtze River Basin.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2018YFC0809605,2018YFC0809600)the Key Research Program of Frontier Sciences of Chinese Academy of Sciences(Grant No.QYZDY-SSWDQC015)+2 种基金the National Natural Science Foundation of China(Grant No.41230630)the National Science Fund for Distinguished Young Scholars(Grant No.41825015)the Key Research Program of the Chinese Academy of Sciences(Grant No.ZDRW-ZS-2020-1)。
文摘The instability of soil bank slopes induced by freeze-thaw cycles at the northern foot of Tianshan Mountain is very common.The failure not only caused a large amount of soil erosion,but also led to serious reservoir sedimentation and water quality degradation,which exerted a lot of adverse effects on agricultural production in the local irrigation areas.Based on field investigations on dozens of irrigation reservoirs there,laboratory tests were carried out to quantitatively analyze the freeze-thaw effect on the soil engineering characteristics to reveal the facilitation on the bank slope instability.The results show that the softening characteristics of the stressstrain curves gradually weaken,the effective cohesions decline exponentially,the seepage coefficients enlarge,and the thermal conductivities decrease after 7 freeze-thaw cycles.The freeze-thaw effect on the specimens with low confining pressures,low dry densities and high water contents is more significant.The water migration and the phase transition between water and ice result in the variations of the soil internal microstructures,which is the main factor affecting the soil engineering characteristics.Sufficient water supply and the alternation of positive and negative temperatures at the reservoir bank slopes in cold regions make the water migration and phase transition in the soil very intensely.It is easy to form a large number of pores and micro cracks in the soil freezing and thawing areas.The volume changes of the soil and the water migration are difficult to reach a dynamic balance in the open system.Long-term freeze-thaw cycles will bring out the fragmentation of the soil particles,resulting in that the micro cracks on the soil surfaces are developing continuously.The soil of the bank slopes will fall or collapse when these cracks penetrate,which often happens in winter there.
基金supported by the National Natural Science Foundation of China under No. 41630639the National Basic Research Program of China (2014CB744703)+1 种基金Natural Science Basic Research Plan in Shaanxi Province of China (No. 2016JQ4014)China Postdoctoral Science Foundation (2016M602743)
文摘After water is impounded in a reservoir,rock mass in the hydro-fluctuation belt of the reservoir bank slope is subject to water saturationdehydration circulation(WSDC). To quantify the rate of change of rock mechanical properties, samples from the Longtan dam area were measured with uniaxial compression tests after different numbers(1,5, 10, 15, and 20) of simulated WSDC cycles. Based on the curves derived from these tests, a modified HoekBrown failure criterion was proposed, in which a new parameter was introduced to model the cumulative damage to rocks after WSDC. A case of an engineering application was analyzed, and the results showed that the modified Hoek-Brown failure criterion is useful.Under similar WSDC-influenced engineering and geological conditions, rock mass strength parameters required for analysis and evaluation of rock slope stability can be estimated according to this modified Hoek-Brown failure criterion.
文摘In most cases, the slope stability of reservoir bank is analyzed on the premise that the location of phreatic surface is obtained. But many designers generalize a line as the phreatic surface through their experience to analyze the stability, which is unsafe in the project. To find a solution of the phreatic surface which is convenient to put into use and in accordance with the practice, the article, based on Boussinesq equation, infers analytic solutions suitable to the water level at different ratios and achieves an analytic solution equation through fitting curves. The correctness of the equation is also proved by the experiments of sand and sand-clay models and the inaccuracy of empirical generalization is analyzed quantitatively. The calculation results show that the inaccuracy through the method of experiential generalizing is so large that the designers should be awake to it.
文摘为进一步加快构建新型电力系统,促进抽水蓄能电站数字化转型。笔者通过运用地理信息系统(geographic information system,GIS)技术和数字高程模型(digital elevation model,DEM)建立抽水蓄能电站库区淹没与库岸稳定分析系统,并从系统的技术结构、三维可视化、库区淹没分析、库区浸没分析和库区塌岸分析等方面分析系统模块建设及其功能实现。结果表明,该系统可实现库区淹没范围、库区浸没范围和库区塌岸预测范围边界线的三维模拟分析及实时动态演示,相关的土地利用数据快速整合评估等。该系统可为合理确定抽水蓄能电站水库大坝位置,制定征地拆迁、土地赔偿、移民安置等方案提供科学的决策依据。
基金Financial support for this study was jointly provided by the National Natural Science Foundation of China (Grant No. 41201272)the Chinese Academy of Sciences Action-plan for West Development (Grant No. KZCX2-XB3-09)the Chinese Academy of Science (Light of West China Program)
文摘Soil erosion and bank degradation is a major post-dam concern regarding the riparian zone of the Three Gorges Reservoir. The development and succession of vegetation is a main countermeasure,especially to enhance bank stability and mitigate soil erosion by the root system. In this study, the roots of four prevailing grass species, namely, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, in the riparian zone were investigated in relation to additional soil cohesion. Roots were sampled using a single root auger. Root length density(RLD) and root area ratio(RAR) were measured by using the Win RHIZO image analysis system. Root tensile strength(TR) was performed using a manualdynamometer, and the soil reinforcement caused by the roots was estimated using the simple Wu's perpendicular model. Results showed that RLD values of the studied species ranged from 0.24 cm/cm3 to20.89 cm/cm3 at different soil layers, and RLD were significantly greater at 0–10 cm depth in comparison to the deeper soil layers(>10 cm). RAR measurements revealed that on average 0.21% of the reference soil area was occupied by grass roots for all the investigated species. The measured root tensile strength was the highest for P. paspaloides(62.26MPa) followed by C. dactylon(51.49 MPa), H.compressa(50.66 MPa), and H. altissima(48.81MPa). Nevertheless, the estimated maximum root reinforcement in this investigation was 22.5 k Pa for H.altissima followed by H. compressa(21.1 k Pa), P.paspaloides(19.5 k Pa), and C. dactylon(15.4 k Pa) at0–5 cm depth soil layer. The root cohesion values estimated for all species were generally distributed at the 0–10 cm depth and decreased with the increment of soil depth. The higher root cohesion associated with H. altissima and H. compressa implies their suitability for revegetation purposes to strengthen the shallow soil in the riparian zone of the Three Gorges Reservoir. Although the soil reinforcement induced by roots is only assessed from indirect indicators, the present results still useful for species selection in the framework of implementing and future vegetation recovery actions in the riparian zone of the Three Gorges Reservoir and similar areas in the Yangtze River Basin.
