基于Geddes公式计算新型带肋预应力管桩的沉降

在Geddes应力公式的基础上,对新型带肋预应力管桩的环状凸肋产生的影响做了假设:环状凸肋的受力可等效为对其下部土的挤密作用,即产生附加应力;为了方便计算,把该种附加应力简化沿环状凸肋两倍下部长度矩形分布的桩侧摩阻力,并推导出了适合新型带肋预应力管桩单桩沉降的计算公式;然后用Matlab软件进行编程计算。计算结果与现场试验结果相近,可做为工程估算。     

基于孔压静力触探(CPTU)测试的连云港海相粘土前期固结压力确定方法研究

首先回顾了基于孔压静力触探(CPTU)测试确定前期固结压力的方法,通过连云港海相粘土场地进行的CPTU试验资料,以室内固结试验得到的前期固结压力作为参考值评估了经验方法预测前期固结压力的有效性。最简单的方法是直接建立前期固结压力和净锥尖阻力的关系,同时也是最有效的方法。     

Reliability of shallow foundations designed against bearing failure using LRFD

Worldwide, there is growing interest in the development of a rational reliability-based geotechnical design code. The reasons for this interest are at least two-fold; first, geotechnical engineers face significantly more uncertainties than those faced in other fields of engineering, therefore there is a need to properly characterize and deal with these uncertainties. Second, for decades, structural engineers have used a reliability-based design code, and there is a need to develop the same for geotechnical engineers, in order that the two groups can ‘speak the same language’. This paper develops a theoretical model to predict the probability that a shallow foundation will exceed its supporting soil's bearing capacity. The footing is designed using characteristic soil properties (cohesion and friction angle) derived from a single sample, or ‘core’, taken in the vicinity of the footing, and used in a load and resistance factor design approach. The theory predicting failure probability is validated using a two-dimensional random finite element method analysis of a strip footing. Agreement between theory and simulation is found to be very good. Therefore, the theory can be used with confidence to perform risk assessments of foundation designs and develop resistance factors for use in code provisions.     

MCS-based probabilistic design of embedded sheet pile walls

A probabilistic approach to the design of embedded sheet pile walls is developed in this paper. The approach is based on Monte Carlo simulation (MCS), and it is used to investigate the performance of the partial factors and different design approaches in Eurocode 7 in achieving the target degrees of reliability. The approach is illustrated through an embedded sheet pile wall design example that has been used in literature for the evaluation of Eurocode 7. The approach deals rationally with the correlated load and resistance, and it bypasses a difficult but frequently asked question in Eurocode 7 (i.e. should the passive earth pressure be considered as a load (i.e. action) or a resistance?). The probabilistic design approach (DA) is also used to explore the effects of the soil unit weight variability and uncertainties in over-digging depth and wall friction. The effects of uncertainties in over-digging depth and wall friction are found to be significant. It is also found that, although the soil unit weight variability is generally minor, its effect on the design of embedded sheet pile walls is significant and should be properly accounted for in the design. The MCS-based probabilistic DA proposed in this study provides a straightforward way for proper consideration of such variability with relative ease.     

超长灌注桩桩身压缩综合系数反分析

基于超长桩现场试验和数值模拟资料,通过反分析得出了桩身压缩的综合系数,进而对综合系数与其他参数的关系曲线特点、综合系数的影响因素、综合系数的回归预测等进行了研究。结果表明：（1）极限状态下超长灌注桩的综合系数的变化范围为0.278 5～0.988,规范法中取定值0.5或1.0的做法是不合理的。（2）综合系数总体上随桩顶荷载、桩身压缩、桩身总位移、桩身刚体位移的增大而增大,但关系曲线型式存在多样化。（3）超长桩综合系数与长径比的相关关系不明显,但总体来说,综合系数随长径比的增加而降低。对超长嵌岩桩,不同场地桩的综合系数与长径比相关关系较好;对超长非嵌岩,不同场地桩的综合系数与长径比相关关系不明显,但对某场地5根桩,综合系数与长径比的指数相关关系达到0.990 1。（4）总的来说,持力层与上覆土层弹性模量比小的桩的综合系数-桩顶荷载曲线在弹性模量比大的上方。（5）建立的6个场地多根桩的综合系数与桩顶荷载关系的回归曲线的相关系数平均为0.977 6,可为该场地及类似场地桩的桩身压缩综合系数的预测和计算提供参考。     

A continuous/discontinuous Galerkin framework for modeling coupled subsurface and surface water flow

We consider conjunctive surface-subsurface flow modeling, where surface water flow is described by the shallow water equations and ground water flow by Richards’ equation for the vadose zone. Coupling between the models is based on the continuity of flux and water pressure. Numerical approximation of the coupled model using the framework of discontinuous Galerkin (DG) methods is formulated. In the subsurface, the local discontinuous Galerkin (LDG) method is used to approximate ground water velocity and hydraulic head; a DG method is also used to approximate surface water velocity and elevation. This approach allows for a weak coupling of the models and the use of different approximating spaces and/or meshes within each regime. A simplified LDG method based on continuous approximations to water head is also described. Numerical results that investigate physical and numerical aspects of surface–subsurface flow modeling are presented. This work was supported by National Science Foundation grant DMS-0411413.     

Models of natural and human dynamics in forest landscapes: Cross-site and cross-cultural synthesis

We synthesize the study of coupled natural and human systems across sites and cultures through a process of simplification and abstraction based on multiple dimensions of human-nature connectedness: satisfaction of basic needs, psycho-cultural connectedness and regulation of use of natural resources. We thus provide both a place-based and general understanding of value-driven anthropogenic environmental change and response. Two questions guide this research: what are the crucial stakeholder values that drive land use decisions and thus land cover change? And how can knowledge of these values be used to make decisions and policies that sustain both the human and natural systems in a place? To explore these questions we build simulation models of four study sites, two in the State of Texas, United States, and two in Venezuela. All include protected areas, though they differ in the specifics of vegetation and land use. In the Texas sites, relatively affluent individuals are legally converting forests to residential, commercial, and industrial uses, while in Venezuela landless settlers are extra-legally converting forests for purposes of subsistence agriculture. Contemporary modeling techniques now facilitate simulations of stakeholder and ecosystem dynamics revealing emergent patterns. Such coupled human and natural systems are currently recognized as a form of biocomplexity. Our modeling framework is flexible enough to allow adaptation to each of the study sites, capturing the essential features of the respective natural and anthropogenic land use changes and stakeholder reactions. The interactions between human stakeholders are simulated using multi-agent models that act on forest landscape models, and receive feedback of the effects of these actions on ecological habitats and hydrological response. The multi-agent models employ a formal logic-based method for the Venezuelan sites and a decision analysis approach using multi-attribute utility functions for the Texas sites, differing more in style and emphasis than in substance. Our natural-systems models are generic and can be tailored according to site-specific conditions. Similar models of tree growth and patch transitions are used for all the study sites and the differing responses to environmental variables are specified for each local species and terrain conditions.     

考虑泥浆套不同形态的顶管管壁摩阻力计算公式

大直径、长距离顶管施工常通过注浆形成泥浆套来减小阻力,泥浆套的形态及其完整性对管壁摩阻力大小有决定性作用,现有摩阻力计算公式一般未考虑不同泥浆套形态对摩阻力的影响,计算结果与实际情况相差较大。根据不同施工状况对顶管外壁泥浆套的可能形态进行了分类及成因分析,提出了判断3种常见泥浆套形态的方法。利用半无限弹性体中柱形圆孔扩张理论探讨了注浆压力对泥浆套厚度的影响,结合非线性流体力学计算泥浆与管壁接触产生的摩阻力,最终采用挖掘面稳定假设,针对3种泥浆套形态提出了摩阻力计算公式。采用该方法对工程案例进行计算,计算结果与实测数据对比表明：现有摩阻力计算公式的计算结果过于保守,所提出的计算公式是合理和有效的。     

煤矿井简检查孔施工技术探讨

介绍了煤矿井筒检查孔的特点和技术、质量要求,总结了以往工程中的经验教训,针对工程中的技术难点,如取心、孔斜控制、抽水作业和冲洗液选择与维护等影响质量、工期的关键环节提出了技术措施,为优质、高效施工此类工程提供借鉴.     

土层锚杆抗拔力的影响因素及其计算公式的修正

通过对土层锚杆抗拔力影响因素的探讨,得出土层锚杆抗拔力设计值的较为准确的计算公式,进而可以节省锚杆材料或使锚杆工程更安全。