Saturation and Preloading Effects on the Cyclic Behavior of Sand

In order to study pore water pressure response and liquefaction characteristics of sand, which has previously experienced liquefaction, two series of cyclic triaxial tests were run on medium dense sand specimens. In the first test series the influence of the soil saturation under undrained cyclic loading has been studied. It summarizes results of cyclic triaxial tests performed on Hostun-RF sand at various values of the Skempton’s pore-pressure coefficient. Analysis of experimental results gives valuable insights on the effect of soil saturation on sand response to undrained cyclic paths. In the second series of tests, the preloading influence on the resistance to the sands liquefaction has been realized on samples at various histories of loading. It was found that a large preloading induces a reduction of the resistance of sands to liquefaction.     

Scale Effects of Shallow Foundation Bearing Capacity on Granular Material

Scale effects of shallow foundation bearing capacity on granular materials were investigated to further evaluate the trend of decreasing bearing capacity factor, Nγ, with increasing footing width, B, observed by other researchers. Model-scale square and circular footing tests ranging in width from 0.025 to 0.914?m were performed on two compacted sands at three relative densities. Results of the model-scale footing tests show that the bearing capacity factor, Nγ, is dependent on the absolute width of the footing for both square and circular footings. Although this phenomenon is well known, the current study used a large range of footing sizes tested on well-graded sands to show that the previously reported modifications to the bearing capacity factor, Nγ, using grain-size and reference footing width do not sufficiently account for the scale effect seen in the test results from this study. It also shows that behavior of most model-scale footing tests cannot be directly correlated to the behavior of full-scale tests because of differences in mean stresses experienced beneath footings of varying sizes. The relationship of the initial testing conditions (i.e., void ratio) of the sand beds and mean stress experienced beneath the footing (correlated to footing size) to the critical state line controls footing behavior and, therefore, model-scale tests must be performed at a lower density than a corresponding prototype footing in order to correctly predict behavior. Small footings were shown to have low mean stresses but high Nγ values, which indicates high operative friction angles and may be related to the curvature of the Mohr–Coulomb failure envelope.     

Tensile Strength Characteristics of Unsaturated Sands

Tensile strength characteristics of unsaturated sands are examined through a combined theoretical and experimental study. The characteristics of tensile strength in all three water retention regimes of pendular, funicular, and capillary are examined. A simple direct tensile strength apparatus is employed to determine tensile strength for sands with a broad range of particle sizes from silty sand to fine sand and medium sand over a full range of degree of saturation. Tensile strength characteristic curves (TSCC) are established experimentally for these sands and are used to validate the existing theories for tensile strength in the pendular regime. The TSCC for sand characteristically exhibits two zeros at 0 and near 100% saturation, and two peak values occurring in the pendular and capillary regimes, respectively. A minimum tensile strength is observed in the dense fine sand, indicating that either water bridges or pore pressure contributes exclusively to the tensile strength in the funicular regime of this sand. The maximum tensile strength for the silty sand is 1,448?Pa, the fine sand is 1,416?Pa, and the medium sand is 890?Pa. Comparison between the soil–water characteristic curves obtained for these sands indicates that the peak tensile strength in the capillary regime is highly correlated to the air-entry pressure. Photographs of the failure surfaces clearly delineate distinct geometric characteristics for different water retention regimes. Analysis of the patterns of failure surfaces in different water retention regimes indicates that the effective stress principle is valid for tensile stress failure in unsaturated sands.     

Subelement Form-Drag Parameterization in Rough-Bed Flows

Spatial averaging of the Reynolds-averaged Navier–Stokes equations gives the double-averaged Navier–Stokes equations, for which boundary drag appears naturally and explicitly in momentum conservation equations. Increasing use of the double-averaged equations, e.g., for relating flows to three-dimensional bed roughness, for evaluation of profiles of flow stresses and velocities in ecologically significant regions below roughness tops, and for modeling purposes, requires parameterization of boundary drag at subelement scales. Based on seven flows over repeated square-rib roughness and ten flows over repeated fixed simulated sand waves, with measured velocities and bed pressures, expressions for form-drag coefficient CD = f (elevation below roughness top, relative roughness submergence, roughness steepness) are obtained for each of the two-dimensional roughness types. Using these equations, form drag variation with elevation below roughness tops can be calculated using either the double average of the square of local velocity (preferred based on conceptual considerations, trends in coefficient prediction, and also overall drag prediction) or the squared local double-averaged velocity, the roughness area being normal to the flow in each case. Integration of subelement drag given by these expressions is shown to give form-drag coefficient magnitudes and trends for complete individual elements comparable to those obtained by other authors based on measurements or numerical simulations. The ranges of roughness steepness and relative roughness submergence upon which the present equations have been derived need to be noted in consideration of application of the equations. In addition, effective application of the expressions is limited in regions of strongly negative double-averaged velocity. Further work remains to determine drag parameterization for alternative roughness geometries.     

Experimental Study of Fine Sand Particle Settling in Turbulent Open Channel Flows over Rough Porous Beds

Results are presented from laboratory studies investigating the behavior of fine sand particles within turbulent open channel flow conditions flowing over rough, porous beds. A particle tracking technique was employed to record and analyze sand particle motion within the flow, while mean and fluctuating flow velocities were measured by an acoustic Doppler velocimeter probe. Measured particle settling rates show a strong influence from flow turbulence, being generally enhanced in the near-bed and intermediate flow regions and retarded in the outer flow region, compared to their fall velocity in still water conditions. Experiments also reveal the relative degree of settling enhancement to increase with decreasing particle size. Correlation between particle and small-scale fluid motions is demonstrated through a quadrant analysis technique, with higher-order events for the two phases found to be dominated by ejections and sweeps associated with the bursting process. Particle interactions with large-scale turbulent flow structures, revealed through flow visualization with a moving frame of reference, are found to result in particle accumulation in peripheral trajectories on the downflow side of local eddy structures. Analytical and theoretical considerations suggest that both these turbulence scales provide preferential transportation mechanisms that will account for the enhanced sand particle settling rates observed.     

Effect of Surface Coating Strengthening on Humidity Resistance of Sodium Silicate Bonded Sand Cured by Microwave Heating

The microwave heating sodium silicate bonded sand (SSBS) process is regarded as the most likely molding sand to realize green casting, owing to its low sodium silicate addition, rapid hardening speed, high strength, and excellent collapsibility. However, SSBS can absorb water easily in the air at room temperature. A surface coating strengthening method was used to improve the humidity resistance of SSBS. The properties of SSBS treated by the surface coating strengthening method were compared with that without any treatment. The experimental results indicated that humidity resistance had been improved greatly using the surface coating strengthening method, and comparing to SSBS without any treatment, the compressive strength (σ_6h) of the treated SSBS increased 2.32 times and the moisture absorption rate (w_6h) can be decreased by 45%. The morphology results revealed that there was a surface coating around the treated SSBS. The linear scanning indicated that the nonhygroscopic coat components presented on the boundary of the treated SSBS, and the surface phase analysis manifested that the boundary of the treated SSBS emerged new three phases, including Al₂TiO₅, PbTiO₃, and NaAlO₂, which reduced the free sodium ion content and improved the humidity resistance of SSBS.     

新型耐磨耐蚀砂磨锅的研究

对化工研磨行业广泛应用的砂磨锅进行了失效分析、锅壁结构改进及选用新型耐磨耐蚀材料等方面的研究。提出了新型波纹形护板结构砂磨锅和采用ＭＳ５铸钢制造砂磨锅，并取得良好的效果。     

Field and Laboratory Testing of St. Peter Sandstone

The purpose of this project was to evaluate mechanical properties of St. Peter sandstone by in situ testing, and to compare the field data with laboratory results. Direct shear tests were conducted to evaluate the strength-dilatancy behavior, and thin-section microscopy was used to help explain the significant friction angles associated with the material. St. Peter sandstone is nearly cohesionless, but it possesses a friction angle of 57–63° at low confinement. The large angle of internal friction at failure may be due to locking of sand particles or to postdepositional quartz overgrowths. Tests on pulverized densely packed sand and loosely packed sand were conducted in the same manner as the intact specimens and yielded friction angles of about 42 and 34°. Pressuremeter tests were performed in situ and the results were interpreted using an elasto-plastic analysis in terms of total stresses. By appropriate consideration of system stiffness, Young’s modulus was found to be about 0.5 GPa, slightly lower than the laboratory value, although unload-reload cycles were not attempted. Assuming associative behavior, the friction angle was estimated to be at least 56°.     

重温历史经验，进一步改建三门峡水利枢纽，解决潼关以上库区继续淤积和洪涝灾害问题

本文回顾了三门峡水库兴建和运用中的经验教训，回顾了周总理的翔和决策，研究和分析了三门峡水库泥沙淤积给潼关以上库区带来的严重影响，文中指出：三门峡水利枢纽虽经两次改建，潼关以上黄渭洛河汇流区的淤积局面并未得到根本改变。潼关河床高程1996年达328．6m，比建库前抬高5．2m，潼关河床的过水断面现在只有建库前的1／3左右。由于潼关的“卡口”和侵蚀基面的抬升，使渭河、北洛河、小北干流发生严重淤积，并且淤积还在向上游延伸，渭河下游建库以来至1995年共淤积泥沙12．7亿m^3，渭河下游已由地下河变成了地上悬河。本文建议进一步改建三门峡水枢纽，增大泄洪能力，降低潼关高程，解决潼关以上库区继续淤积和洪涝灾害问题，为西部大开发作贡献。     

人工砂石粉含量超标对常态混凝土性能的影响试验研究

人工砂石粉含量增大，可以改善碾压混凝土性能，对常态混凝土性能同样具有益化作用。通过正交试验，利用石粉含量不超过２０％的人工砂，可配得Ｃ２０－Ｃ３０、抗渗等级Ｓ８、抗冻等级Ｓ８、抗冻等级Ｄ１５０以上的常态混凝土，并能大为改善混凝土拦和物和易性，减少混凝土胶凝材料用量，降低混凝土生产成本约１５元／ｍ＾３。