关于地基承载力的探讨

以土质地基为研究对象 ,结合载荷试验 p s曲线 ,应用土体的极限平衡理论 ,对地基土的变形性状、地基土承载力以及承载力修正等问题进行了分析。分析结果显示 :地基土承载力不单是地基土抗剪强度指标的函数 ,同时还与作用其上的基础埋深及基础宽度等因素密切相关。进行地基基础设计时 ,应根据实际的基础埋深与宽度对勘察资料中的地基土承载力进行修正 ,并提出了有关承载力修正的建议     

A new method for testing pile by sin- gle-impact energy and P-S curve

Introduction Through many year's practices by vast numbers of scientific and technological workers andefforts from all aspects, the dynamic testing method of high-low strain has formally entered intothe technical code of foundation pile test of construction at last (The Industry Standards of thePeople's Republic of China, 2003). The striking mode of the dynamic testing method of high strainis stipulated as hammer in the code, the striking of rocket can also be used. The latter is widely…     

Bearing capacity of rock over mined cavities in Nottingham

A significant geohazard is created in Nottingham, UK, by hundreds of man-made caves cut in the weak sandstone beneath the city centre. Stability of the caves has been assessed by a single full-scale loading test, by numerical modelling with FLAC and by physical modelling in plaster. For typical caves 4 m wide, bearing capacity of the rock roof rises from 2 MPa where it is 1 m thick to 8 MPa where 3 m thick. Stability decreases over wider caves and where the loading pad edge is over the edge of the cave. Numerical modelling of a very wide cave revealed the failure mechanisms and also showed that an internal support wall increased roof bearing capacity by 50%. Local building regulations that require 3-5 m of rock cover over the sandstone caves appear to be conservative. In stronger rocks, including karstic limestone, a guideline that cover thickness exceeds 70% of the cave width appears to be appropriate.     

The structural role of Ti in aluminosilicate liquids in the glass transition range: insights from heat capacity and shear viscosity measurements

The shear viscosities and 1 bar heat capacities of glasses and melts along the 67mol% silica isopleth in the system SiO₂-Al₂O₃-Na₂O-TiO₂ have been determined in the temperature ranges 780-1140 K and 305-1090 K respectively. Anomalous behaviour of both these properties is observed for compositions rich in TiO₂ and/or Al₂O₃, an observation attributed to liquid-liquid phase separation followed by anatase crystallization. For samples which do not show anomalous behaviour, it is found that the partial molar heat capacity of the TiO₂ component previously determined in Al-free compositions reproduces our heat capacities to within 1.3%. Viscosity data show that addition of TiO₂ tends to increase viscosity and melt fragility at constant temperature. Furthermore, heat capacity and viscosity data may be combined within the framework of the Adam-Gibbs theory to extract values of the configurational entropy of the liquids and qualitative estimates of the variation of the average energy barrier to viscous flow. Configurational entropy at 900K is inferred to decrease upon addition of TiO₂, in contrast to previous results from Al-free systems. The compositional limit separating normal from anomalous behaviour, as well as the data for homogenous melts have been used to constrain the structural role of Ti in these samples. Our data are consistent with a majority of Ti in five-fold coordination associated with a titanyl bond, in agreement with previous spectroscopic studies. Furthermore, we find no evidence for a Ti-Al interaction in our samples, and we are led to the conclusion that Al and Ti are incompletely mixed, a hypothesis consistent with the observed reduction of configurational entropy upon addition of TiO₂, suggesting an important role of medium range order in controlling the variations in thermodynamic properties.     

Delayed geochemical hazard: Concept, digital model and case study

Delayed Geochemical Hazard (DGH briefly) presents the whole process of a kind of serious ecological and environmental hazard caused by sudden reactivation and sharp release of long-term accumulated pollutant from stable species to active ones in soil or sediment system due to the change of physical-chemical conditions (such as temperature, pH, Eh, moisture, the concentrations of organic matters, etc.) or the decrease of environment capacity. The characteristics of DGH are discussed. The process of a typical DGH can be expressed as a nonlinear polynomial. The points where the derivative functions of the first and second orders of the polynomial reach zero, minimum and maximum are keys for risk assessment and harzard pridication.The process and mechanism of the hazard is due to the transform of pollutant among different species principally. The concepts of "total releasable content of pollutant", TRCP, and "total concentration of active specie", TCAS, are necessarily defined to describe the mechanism of DGH. The possibility of the temporal and spatial propagation is discussed. Case study shows that there exists a transform mechanism of "gradual release" and "chain reaction" among the species of the exchangeable and the bounds to carbonate, iron and manganese oxides and organic matter, thus causing the delayed geochemical hazard.     

挤扩支盘桩极限承载力的预测

用双曲线方法对110根挤扩支盘桩的极限承载力进行预测,并与直杆桩预测结果进行对比。结果表明由于支盘桩受力性状复杂,加载前期和中期预测精度较高,后期较低,误差超过15%;支盘桩的沉降曲线出现台阶时预测值与实测值误差较大;支盘桩极限承载力的预测精度与工程地质条件和桩本身的参数密切相关,桩身参数和地质条件相同条件下各桩预测精度比较接近。总体上直杆桩的预测结果优于支盘桩。     

Analysis on Bearing Capacity of Tunnel-Type Anchorage of a Long-Span Suspension Bridge

INTRODUCTION Tunnel typeanchoragehasobviousadvantages inbearingcapacityversusinvestment(LiuandHu,1996).However,itisrarelyusedinapracticalpro jectbecauseofitsrequirementofgoodrockcondi tions.Siduhebridge(Fig.1),whichliesintheBa dongmountainsinthewestplatea…     

生态足迹模型在山区生态可持续评价中的初步应用--以1999年北京西部山区为例

在剖析生态足迹分析法的理论基础上，进一步考虑不同消费水平对生态足迹时空变异的影响，划分农村居民和城镇居民两类不同的消费群体，分别计算各自的生态足迹，其次进一步细化模型中人均水资源足迹，从而构建生态足迹与生态容量平衡模型。根据平衡模型计算出生态盈亏，得出区域生态持续性评价结果。并以1999年北京西部山区门头沟区为例，进行模型计算和生态可持续评价，结果表明1999年门头沟区处于生态赤字状态，说明该区生态系统处于不可持续状态。在对门头沟区的初步研究基础上，指出生态足迹作为山区生态可持续评价指标的优点及当前存在的缺点。     

载荷试验检测复合桩基承载力的影响因素

针对桩基检测中水泥土桩复合地基检测承载力实测值与设计值差别很大,从工程地质条件、地基处理情况、检测方法出发,通过实例分析了复合地基承载力取值的影响因素。分析表明:桩设计参数取值偏低、地基土的力学性能未充分利用、设计的安全储备偏大是影响承载力取值的主要因素,检测时桩间土含水量的变化也有一定程度的影响。     

含铁闪锌矿热容的实验测定与分析

利用美国ＤｕＰｏｎｔ公司的９９００型差示扫描量热仪对３个含铁闪锌矿样品的热容进行了实验测定,并讨论了定压摩尔热容实验值与实验温度的关系。实验结果表明,在实验条件下,含铁闪锌矿的定压摩尔热容与纯闪锌矿的定压摩尔热容存在显著差异,Ｆｅ置换Ｚｎ是造成这种差异的主要原因。