Mitchell's solution is commonly used to determine the required strength of vertically exposed cemented backfill in mines. Developed for drained backfill, Mitchell model assumed a zero friction angle for the backfi...Mitchell's solution is commonly used to determine the required strength of vertically exposed cemented backfill in mines. Developed for drained backfill, Mitchell model assumed a zero friction angle for the backfill. Physical model tests were performed. Good agreements were obtained between the required strengths predicted by the analytical solution and experimental results. However, it is well-known that zero friction angle can only be possible in terms of total stresses when geomaterials are submitted to unconsolidated and undrained conditions. A revisit to Mitchell's physical model tests reveals that both the laboratory tests performed for obtaining the shear strength parameters of the cemented backfill and the box stability tests were conducted under a condition close to undrained condition. This explains well the good agreement between Mitchell's solution and experimental results. Good agreements are equally obtained between Mitchell's experimental results and FLAC3 D numerical modeling of shortterm stability analyses of exposed cemented backfill.展开更多
Since the wear problems play a crucial role in the relatively moving systems, in this paper, the effect of counter-face roughness on the wear of extruded PTFE （polytetrafluoroethylene） which is a very common materia...Since the wear problems play a crucial role in the relatively moving systems, in this paper, the effect of counter-face roughness on the wear of extruded PTFE （polytetrafluoroethylene） which is a very common material for sliding bearing applications has been investigated to contribute related literature. PTFE is well-known for its exceptional tribological properties, and good toughness, and high thermal stability. It can also be used in dry sliding applications. PTFE is commonly used to reduce friction between relatively moving surfaces, lts wear rate can be reduced by adding micro or nano-sized fillers such as Al2O3, TiO2, SiO2, MoS2, Al, Pb, ZnO, Cu, ZrO2, Ni, CNF （carbon nano fiber）, carbon fiber, glass fiber, bronze, and graphite powder into the PTFE. In this study, an experimental research was carried out for filled and unfilled PTFE to compare their behaviors under different speeds and loads. Test materials were unfilled PTFE, PTFE ＋ wt. 5% Al2O3, PTFE ＋ wt. 15% Al2O3. Formation of transfer film was examined in dry sliding condition against stainless steel counter faces. All tribological tests were carried out in a commercially available tribo-tester sliding against AISI-416 C stainless steel. As a result of a series of systematic experiments, remarkable results have been obtained to make a distinctive comparison between unfilled and filled PTFE. The variation of friction coefficient with sliding distance during the tests has also been recorded. At the end of the tests, wear rate of related PTFE specimen was calculated based on measured data. Wear rate is found very high for unfilled PTFE, however, the lowest wear rate is recorded for PTFE ＋ wt. 15% Al2O3 as expected. The coefficient of friction remained approximately stable during the wear tests. Transfer films were inspected by observing the discs＇ surface with optical microscope.展开更多
Non-cohesive soils have been widely used in construction of high-speed railway for their excellent physical and mechanical properties,and the determination of maximum and minimum dry density of such soils containing o...Non-cohesive soils have been widely used in construction of high-speed railway for their excellent physical and mechanical properties,and the determination of maximum and minimum dry density of such soils containing oversize particles is an important topic.In this study,the influence of oversize particles on dry density of non-cohesive soils is investigated by packing tests.Test results show that oversize particles will make"extra"voids around their surfaces,which increase significantly if the size ratio of oversize material to matrix material is not very big.The dry density of the total material will be overestimated by Elimination Method due to the omission of the"extra"voids.Thus,a geometric model is proposed by which the"extra"voids can be taken into account,and a new oversize correction method for non-cohesive soils is developed.Test results confirm the applicability of this method on the condition of oversize fraction being less than 40%by mass.展开更多
基金financial support from China Scholarship Council(CSC)under the Grant CSC No.201406460041financial support from the Natural Sciences and Engineering Research Council of Canada(NSERC 402318)+4 种基金the Institut de Recherche Robert-Sauvéen Santéet en Sécuritédu Travail(IRSST 2013-0029)Fonds de Recherche du Québec-Nature et Technologies(FRQNT 2015-MI-191676)the industrial partners of Research Institute on Mines and Environment(RIME UQAT-Polytechnique)The financial support from the National Science and Technology Support Program of China(No.2013BAB02B02)the Scientific Research Fund of Beijing General Research Institute of Mining and Metallurgy of China(No.YJ201507)
文摘Mitchell's solution is commonly used to determine the required strength of vertically exposed cemented backfill in mines. Developed for drained backfill, Mitchell model assumed a zero friction angle for the backfill. Physical model tests were performed. Good agreements were obtained between the required strengths predicted by the analytical solution and experimental results. However, it is well-known that zero friction angle can only be possible in terms of total stresses when geomaterials are submitted to unconsolidated and undrained conditions. A revisit to Mitchell's physical model tests reveals that both the laboratory tests performed for obtaining the shear strength parameters of the cemented backfill and the box stability tests were conducted under a condition close to undrained condition. This explains well the good agreement between Mitchell's solution and experimental results. Good agreements are equally obtained between Mitchell's experimental results and FLAC3 D numerical modeling of shortterm stability analyses of exposed cemented backfill.
文摘Since the wear problems play a crucial role in the relatively moving systems, in this paper, the effect of counter-face roughness on the wear of extruded PTFE （polytetrafluoroethylene） which is a very common material for sliding bearing applications has been investigated to contribute related literature. PTFE is well-known for its exceptional tribological properties, and good toughness, and high thermal stability. It can also be used in dry sliding applications. PTFE is commonly used to reduce friction between relatively moving surfaces, lts wear rate can be reduced by adding micro or nano-sized fillers such as Al2O3, TiO2, SiO2, MoS2, Al, Pb, ZnO, Cu, ZrO2, Ni, CNF （carbon nano fiber）, carbon fiber, glass fiber, bronze, and graphite powder into the PTFE. In this study, an experimental research was carried out for filled and unfilled PTFE to compare their behaviors under different speeds and loads. Test materials were unfilled PTFE, PTFE ＋ wt. 5% Al2O3, PTFE ＋ wt. 15% Al2O3. Formation of transfer film was examined in dry sliding condition against stainless steel counter faces. All tribological tests were carried out in a commercially available tribo-tester sliding against AISI-416 C stainless steel. As a result of a series of systematic experiments, remarkable results have been obtained to make a distinctive comparison between unfilled and filled PTFE. The variation of friction coefficient with sliding distance during the tests has also been recorded. At the end of the tests, wear rate of related PTFE specimen was calculated based on measured data. Wear rate is found very high for unfilled PTFE, however, the lowest wear rate is recorded for PTFE ＋ wt. 15% Al2O3 as expected. The coefficient of friction remained approximately stable during the wear tests. Transfer films were inspected by observing the discs＇ surface with optical microscope.
基金supported by the National Basic Research Program of China("973"Project)(Grant No.2013CB036204)
文摘Non-cohesive soils have been widely used in construction of high-speed railway for their excellent physical and mechanical properties,and the determination of maximum and minimum dry density of such soils containing oversize particles is an important topic.In this study,the influence of oversize particles on dry density of non-cohesive soils is investigated by packing tests.Test results show that oversize particles will make"extra"voids around their surfaces,which increase significantly if the size ratio of oversize material to matrix material is not very big.The dry density of the total material will be overestimated by Elimination Method due to the omission of the"extra"voids.Thus,a geometric model is proposed by which the"extra"voids can be taken into account,and a new oversize correction method for non-cohesive soils is developed.Test results confirm the applicability of this method on the condition of oversize fraction being less than 40%by mass.
