Moisture and salt content of soil are the two predominant factors influencing its shear strength. This study aims to investigate the effects of these two factors on shear strength behavior of loess in the Xining Basin...Moisture and salt content of soil are the two predominant factors influencing its shear strength. This study aims to investigate the effects of these two factors on shear strength behavior of loess in the Xining Basin of Northeast Qinghai-Tibet Plateau, where such geological hazards as soil erosion, landslides collapse and debris flows are widespread due to the highly erodible loess. Salinized loess soil collected from the test site was desalinized through salt-leaching in the laboratory. The desalinized and oven-dried loess samples were also artificially moisturized and salinized in order to examine how soil salinity affects its shear strength at different moisture levels. Soil samples prepared in different ways(moisturizing, salt-leaching, and salinized) were measured to determine soil cohesion and internal friction angle. The results show that salt-leaching up to 18 rounds almost completely removed the salt content and considerably changed the physical components of loess, but the soil type remained unchanged. As salt content increases from 0.00% to 12.00%, both the cohesion and internal friction angle exhibit an initial decrease and then increase with salt content. As moisture content is 12.00%, the salt content threshold value for both cohesion and internal friction angle is identified as 3.00%. As the moisture content rises to 16.0% and 20.00%, the salt content threshold value for cohesion is still 6.00%, but 3.00% for internal friction angle. At these thresholds soil shear strength is the lowest, below which it is inversely related to soil salinity. Beyond the thresholds, however, the relationship is positive. Dissimilar to salinity, soil moisture content exerts an adverse effect on shear strength of loess. The findings of this study can provide a valuable guidance on stabilizing the engineering properties of salinized loess to prevent slope failures during heavy rainfall events.展开更多
Firm joins were obtained between Ti（C,N）-based cermet and steel with Ag-Cu-Zn-Ni filler metal by vacuum brazing. The effects of technological parameters such as brazing temperature, holding time, and filler thicknes...Firm joins were obtained between Ti（C,N）-based cermet and steel with Ag-Cu-Zn-Ni filler metal by vacuum brazing. The effects of technological parameters such as brazing temperature, holding time, and filler thickness on the shear strength of the joints were investigated. The microstructure of welded area and the reaction products of the filler metal were examined by scanning electron microscopy （SEM）, metallographic microscope （OM）, energy-dispersive X-ray analysis （EDS）, and X-ray diffraction （XRD）. The brazing temperature of 870℃, holding time of 15 min, and filler thickness of 0.4 mm are a set of optimum technological parameters, under which the maximum shear strength of the joints, 176.5 MPa, is achieved. The results of microstructure show that the wettability of the filler metal on Ti（C,N）-based cermet and steel is well. A mutual solution layer and a diffusion layer exist between the welding base materials and the filler metal.展开更多
以锦屏I级水电站坝址微新大理岩岩体原位大剪试验结果为例,分析岩体质量指标与抗剪强度参数间的相关性。利用Copula理论可将边缘分布和相关结构分开研究的优点,建立小样本条件下各变量的边缘分布函数,并在分析岩体质量指标Q与抗剪强度参...以锦屏I级水电站坝址微新大理岩岩体原位大剪试验结果为例,分析岩体质量指标与抗剪强度参数间的相关性。利用Copula理论可将边缘分布和相关结构分开研究的优点,建立小样本条件下各变量的边缘分布函数,并在分析岩体质量指标Q与抗剪强度参数f,c间相关结构特点的基础上构造拟合Q-f,Q-c间关系的最优Copula函数。对于相同岩性的同类岩体,在已知Q条件下求条件概率便可得到抗剪强度参数估值的保证率,或可计算一定保证率下的抗剪参数估值。最后运用该函数分析常用的优定斜率法、最小二乘法的保证率,并与Hoek-Brown准则估值进行比较。研究结果表明,岩体质量指标与抗剪断内摩擦因素f呈较高的正相关关系,与抗剪断黏结力c则呈较高的负相关关系,而具有对称结构的Nelsen NO 1和Nelsen NO 2则分别是拟合Q-f、Q-c间关系的最优Copula函数。常用的最优斜率法与最小二乘法由于忽略岩体质量指标与抗剪强度参数的相关性,因此造成较大的偏差,而具有保证率为0.8的抗剪强度估值与Hoek-Brown经验准则相比更接近实际值。该方法注重充分地利用现场有限的数据信息,可以得到具有一定保证率的抗剪强度参数估值,为岩体抗剪强度参数估值提供一种新的途径。展开更多
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 41572306, 41162010)Natural Science Foundation of Qinghai Province (Grant No.2014ZJ-906)+3 种基金Hundred Talents Program in Chinese Academy of Sciences (Grant No. Y110091025)Scientific and Technologic Support Plan of Qinghai Province (2015-SF-117)Changjiang Scholar Program and Innovative Research Team Building, MOE Grant Number (IRT_17R62)the 111 Project (Grant No. D18013)
文摘Moisture and salt content of soil are the two predominant factors influencing its shear strength. This study aims to investigate the effects of these two factors on shear strength behavior of loess in the Xining Basin of Northeast Qinghai-Tibet Plateau, where such geological hazards as soil erosion, landslides collapse and debris flows are widespread due to the highly erodible loess. Salinized loess soil collected from the test site was desalinized through salt-leaching in the laboratory. The desalinized and oven-dried loess samples were also artificially moisturized and salinized in order to examine how soil salinity affects its shear strength at different moisture levels. Soil samples prepared in different ways(moisturizing, salt-leaching, and salinized) were measured to determine soil cohesion and internal friction angle. The results show that salt-leaching up to 18 rounds almost completely removed the salt content and considerably changed the physical components of loess, but the soil type remained unchanged. As salt content increases from 0.00% to 12.00%, both the cohesion and internal friction angle exhibit an initial decrease and then increase with salt content. As moisture content is 12.00%, the salt content threshold value for both cohesion and internal friction angle is identified as 3.00%. As the moisture content rises to 16.0% and 20.00%, the salt content threshold value for cohesion is still 6.00%, but 3.00% for internal friction angle. At these thresholds soil shear strength is the lowest, below which it is inversely related to soil salinity. Beyond the thresholds, however, the relationship is positive. Dissimilar to salinity, soil moisture content exerts an adverse effect on shear strength of loess. The findings of this study can provide a valuable guidance on stabilizing the engineering properties of salinized loess to prevent slope failures during heavy rainfall events.
基金supported by the National Natural Science Foundation of China (No. 50074014)
文摘Firm joins were obtained between Ti（C,N）-based cermet and steel with Ag-Cu-Zn-Ni filler metal by vacuum brazing. The effects of technological parameters such as brazing temperature, holding time, and filler thickness on the shear strength of the joints were investigated. The microstructure of welded area and the reaction products of the filler metal were examined by scanning electron microscopy （SEM）, metallographic microscope （OM）, energy-dispersive X-ray analysis （EDS）, and X-ray diffraction （XRD）. The brazing temperature of 870℃, holding time of 15 min, and filler thickness of 0.4 mm are a set of optimum technological parameters, under which the maximum shear strength of the joints, 176.5 MPa, is achieved. The results of microstructure show that the wettability of the filler metal on Ti（C,N）-based cermet and steel is well. A mutual solution layer and a diffusion layer exist between the welding base materials and the filler metal.
文摘以锦屏I级水电站坝址微新大理岩岩体原位大剪试验结果为例,分析岩体质量指标与抗剪强度参数间的相关性。利用Copula理论可将边缘分布和相关结构分开研究的优点,建立小样本条件下各变量的边缘分布函数,并在分析岩体质量指标Q与抗剪强度参数f,c间相关结构特点的基础上构造拟合Q-f,Q-c间关系的最优Copula函数。对于相同岩性的同类岩体,在已知Q条件下求条件概率便可得到抗剪强度参数估值的保证率,或可计算一定保证率下的抗剪参数估值。最后运用该函数分析常用的优定斜率法、最小二乘法的保证率,并与Hoek-Brown准则估值进行比较。研究结果表明,岩体质量指标与抗剪断内摩擦因素f呈较高的正相关关系,与抗剪断黏结力c则呈较高的负相关关系,而具有对称结构的Nelsen NO 1和Nelsen NO 2则分别是拟合Q-f、Q-c间关系的最优Copula函数。常用的最优斜率法与最小二乘法由于忽略岩体质量指标与抗剪强度参数的相关性,因此造成较大的偏差,而具有保证率为0.8的抗剪强度估值与Hoek-Brown经验准则相比更接近实际值。该方法注重充分地利用现场有限的数据信息,可以得到具有一定保证率的抗剪强度参数估值,为岩体抗剪强度参数估值提供一种新的途径。
