指示元素垂向分带序列计算方法述评

计算和确定矿床原生晕指示元素垂向分带序列是地球化学找矿研究特别是矿床原生晕分析和研究的重要内容之一,国内、外地学者提出了多种计算方法。这里介绍几种常用的计算方法:分带指数法、广义衬值法、浓集重心法、浓集指数法、比重指数法、含量梯度法等,并指出这些方法的优点和不足,认为计算矿床原生晕指示元素垂向分带序列时,不宜采用传统的格里戈良分带指数法,而应采用广义衬值法、浓集重心法或比重指数法。     

滑坡支挡结构荷载取值问题研究

当前,在我国工程界,滑坡支挡结构上的荷载取值普遍以传递系数法的条间力(即剩余下滑力)为基础,本文对这种荷载取值方法存在的问题进行了分析,提出了以稳定性为基础确定滑坡支挡结构上荷载的方法,该方法能弥补现行荷载取值方法的不足。     

Dimensionless straight line fitting method for hydrogeological parameter determination

Aquifers may have alluvium deposits, weathered layers, fractured zones, and karstic formations separately or in mixture forms. Such geological configurations do not allow classical aquifer test applicability, due to a set of underlying assumptions that are not usually valid in nature. In practice, the Jacob straight line method is the most commonly used approach for aquifer parameter determinations. Constant transmissivity and storativity estimations depend on large time-drawdown plots on semilogarithmic paper as a straight line. A common mistake is that the appearance of a general trend as a straight line on semilogarithmic paper is taken as guaranteed for the application of Jacob method. Since Jacob straight line is the large time extension of Theis type curve, there is only one straight line on the semilogarithmic paper that can represent Jacob method, which is based on the assumption that the aquifer is porous and homogeneous. In such a case, the Jacob method slope should equal to 2.3, which shows its validity. Otherwise, a modification of Jacob method is suggested in this paper. The basis of the methodology is a dimensionless type straight line approach for the aquifer parameter assessment. Its application is presented for aquifer test data from Oude Korendjik porous medium aquifer data. The application results indicate that the classical Jacob straight line method might not be valid without a preliminary check. The dimensionless reevaluation of existing data helps to check the validity. The necessary formulations for the modification of the classical straight line method are derived, which reduce to classical Jacob method for a specific set of parameters.     

Pathline tracing on fully unstructured control-volume grids

The trend toward unstructured grids in subsurface flow modeling has prompted interest in the issue of streamline or pathline tracing on unstructured grids. Streamline tracing on unstructured grids is problematic because a continuous velocity field is required for the calculation, while numerical solutions to the groundwater flow equations provide velocity in discretized form only. A method for calculating flow streamlines or pathlines from a finite-volume flow solution is presented. The method uses an unconstrained least squares method on interior cells and a constrained least squares method on boundary cells to approximate cell-centered velocities, which can then be continuously interpolated to any point in the domain of interest. Two-dimensional tests demonstrate that the method correctly reproduces uniform and corner-to-corner flow on fully unstructured grids. In three dimensions using regular hexahedral grids, the method agrees well with established semianalytical methods. Tests also demonstrate that the method produces physically realistic results on fully unstructured three-dimensional grids.     

基于离散元法对边坡二维极限平衡法的探讨

边坡稳定性分析的极限平衡法是要做一定假设的。本文考虑了离散元与极限平衡法基于刚体理论的相似性,用离散元法计算出极限平衡法中的各个计算分量值,然后代入到常用极限平衡法中分析计算,根据离散元法的计算结果讨论了各极限平衡法中各种假设的合理性,为极限平衡法的计算提供了一个新思路。结果表明Bishop法与离散元法的计算结果比较接近,是本文经过离散元法计算后所推荐使用的方法。     

Time Series Reconstruction from Unequally Spaced Natural Archive Data

Some natural substrates record environmental information and, as such, provide a means to reconstruct the environmental conditions from the period these substrates were formed. Samples from environmental archives are not always equally spaced in distance. When a periodic time series model is estimated from these unequally spaced proxy records, the search for reasonable starting values is the main difficulty. In this work, a non-parametric method based on the regressive Fourier series is first presented, which reduces averaging errors starting from unequally spaced records. The method is applied to synthetic data and generally performs well in all circumstances. Secondly, a parametric method for the construction of a time base and the elimination of averaging errors from unequally spaced records is presented. This parametric method uses the non-parametric method to produce starting values for the parameters. The method is compared with the time series construction method with the averaging effect taken into account and it is observed that only the current method produces acceptable results. The statistical performance of the method is verified with a Monte Carlo simulation and the estimator is proven to be an efficient estimator. The applicability of the method is demonstrated on the vessel density measurement in a mangrove tree, Rizophora mucronata, which is a proxy for the rainfall in tropical coastal regions.     

岸滩侧蚀崩塌速率的试验量测方法

岸滩侧蚀崩塌现象普遍存在于冲积河流演变过程中,是河道治理需重点关注的问题之一,岸滩侧蚀崩塌速率的准确量测则是崩岸机理及其治理措施研究的关键基础。基于图像处理技术,建立了河岸侧蚀崩塌速率试验量测系统,通过图像追踪河岸模型上边缘示踪网格位置变迁,提出了一种河岸侧蚀崩塌速率测量方法。以试验水槽为例,对河岸侧蚀崩塌速率进行了量测,并与经验公式计算值进行了比对,两者基本吻合,可较好地反映流速、土体级配等岸滩侧蚀崩塌速率的影响因素及其变化规律。研究成果可为江河崩岸机理的深入研究提供技术支撑。     

An improved search strategy for the critical slip surface using finite element stress fields

The finite element method can be used to advantage in slope stability problems. This paper proposes a technique to search for the critical slip surface as well as to define and calculate the factor of safety for the slope, when the finite element method is used to model its formation. First, stresses are estimated at each Gaussian point from the finite element analysis. Then, the global stress smoothing method is applied to get a continuous stress field. Based on this stress field, the factor of safety is calculated for a specified slip surface by a stress integration scheme. An improved search strategy is proposed for a noncircular critical surface which starts with a search method for a circular critical surface. During the search process, points defining a trial slip surface can freely move in the finite element mesh subject to some kinematical constraints. This method can be applied to both the limit equilibrium method and the finite element method. Effects of the slope stress history and soil parameters on the resulting critical surface are investigated.     

锚杆(索)加固边坡的最小势能稳定分析方法研究

最小势能边坡稳定性分析方法是一种正处于发展完善中的新型边坡稳定分析方法。建立了采用锚杆(索)加固边坡后的最小势能稳定分析新方法,并进一步提出了一个考虑滑床剪切势能影响的近似计算模型,算例表明：（1）最小势能边坡稳定分析方法的结果,不论有无锚固均与现在工程常用的极限平衡方法的结果较为一致,表明了这一新方法的适用性;（2）滑床剪切势能计算模型引进与否对单一地层边坡的安全系数影响微小,可忽略不计,而对多地层边坡有较明显影响。总之,最小势能方法求取安全系数的过程简洁、概念明确合理、结果可显式表示,与极限平衡方法或有限元方法等方法相比,更具有实用价值。     

Application of the representer method for parameter estimation in numerical reservoir models

A data assimilation method was applied to estimate poorly known parameters (permeabilities) in a numerical reservoir model. Most variational methods for data assimilation are based on the assumption that the model is perfect except for the poorly known parameters. The representer method allows also for model errors, i.e. for uncertainties in the state variables (pressures and saturations). The method is based on minimizing a cost functional, assuming all the errors and parameters to be multivariate Gaussian random variables with given mean and covariances. The uncertain parameters and variables are expanded into a finite sum of basis functions called representers, and the gradients of the cost functional are obtained with an adjoint method. This approach gives an optimal parametrization in the sense that the final result is equal to the solution of the full inverse problem. The method was tested on a simple one-dimensional model to simulate two-phase (oil-water) flow through a heterogeneous reservoir. The results show that the method is able to provide an acceptable estimate of the permeability field. We used pressure measurements from a small number of observation wells in between the injection and production wells, but the representer method could be used equally well to assimilate data from other sources. The method appears to be a promising data assimilation tool for applications in reservoir engineering.     

变水头入渗试验推求垂向渗透系数的计算方法

在Philip与Nestingen土壤水运动计算方法基础上,推导出描述单环变水头入渗试验中水深变化过程的计算公式,提出了确定土壤垂向渗透系数的MP方法.利用土壤非饱和数值模拟及室内土槽入渗试验得到的单环水位变化过程,验证了MP方法推求土壤垂向渗透系数的可靠性.结果表明:MP方法推求的土壤垂向渗透系数比目前采用的Philip方法、Nestingen方法及Green-Ampt方法精度更高,具有广泛的应用前景.     

基于离散元的重力坝多滑面深层抗滑稳定分析

重力坝的深层抗滑稳定分析多采用刚体极限平衡法和非线性有限元法,但刚体极限平衡法不能反映坝基岩体渐进失稳过程和破坏的力学机制,非线性有限元法模拟岩体不连续效率低,且还未有统一的失稳判据。基于离散块体边界应力计算结果,提出重力坝坝基多滑面抗滑稳定安全系数计算公式,并探讨了以坝体-坝基系统能量突变作为坝基失稳判据的物理意义。通过与非线性有限单元法、刚体极限平衡法计算结果的比较,验证了所提方法及判据的可靠性及合理性。结合向家坝水电站重力坝泄12#坝段进行计算分析,结果表明：基于离散元强度储备系数法搜索的坝基失稳通道由坝基岩体屈服区和结构面滑移带组成,所提计算方法与判据适用于实际工程的坝基深层抗滑稳定计算分析,且计算结果偏安全。     

用相关函数优化法计算离散线性水文模型参数

借助于日降雨和出流资料系列,采用相关函数优化方法确定离散线性水文模型参数是一种新的方法.文中选用4个流域8年日降雨和径流资料系列来检验相关函数优化法(6年作为率定期,2年作为验证期),所得结果与常规最小二乘法计算的结果进行比较表明:新方法计算精度比常规最小二乘法计算的精度有所提高,常规最小二乘法仅是相关函数优化法的一种特例.     

Groundwater protection in fractured media: a vulnerability-based approach for delineating protection zones in Switzerland

A vulnerability-based approach for delineating groundwater protection zones around springs in fractured media has been developed to implement Swiss water-protection regulations. It takes into consideration the diversity of hydrogeological conditions observed in fractured aquifers and provides individual solutions for each type of setting. A decision process allows for selecting one of three methods, depending on the spring vulnerability and the heterogeneity of the aquifer. At the first stage, an evaluation of spring vulnerability is required, which is essentially based on spring hydrographs and groundwater quality monitoring. In case of a low vulnerability of the spring, a simplified method using a fixed radius approach (“distance method”) is applied. For vulnerable springs, additional investigations must be completed during a second stage to better characterize the aquifer properties, especially in terms of heterogeneity. This second stage includes a detailed hydrogeological survey and tracer testing. If the aquifer is assessed as slightly heterogeneous, the delineation of protection zones is performed using a calculated radius approach based on tracer test results (“isochrone method”). If the heterogeneity is high, a groundwater vulnerability mapping method is applied (“DISCO method”), based on evaluating discontinuities, protective cover and runoff parameters. Each method is illustrated by a case study.     

简单土坡稳定可靠度计算方法的研究

根据土条间的几何关系提出了土坡稳定分析的辐向条分法，并利用高斯积分法计算出安全系数和极限状态方程的系数，再用改进的JC法求出土坡最小安全系数和最小可靠度指标，辐向条分法是一种高效、准确的土坡稳定性计算方法。     

Restoration of seismic data using the two-dimensional DMO equation

This paper presents a method for restoring missing seismic traces by using the two-dimensional dip moveout (DMO) equation. A fundamentally new formulation of the initial-boundary-value problem based on the Goursat problem is proposed. A modified finite element method is used for numerical solution. The method is tested on model examples and actual seismic data.     

岩锚吊车梁设计计算方法研究

通过对现有岩锚梁设计计算方法的分析,指出了设计的基本假设中存在的缺陷,在原有研究的基础上,建立了综合考虑岩壁变形、锚杆变形和岩锚吊车梁变位的岩锚吊车梁设计计算方法。同时,建议了岩壁弹性抗力系数的取值方法,并采用数值方法模拟锚杆拉拔试验,建立了岩石锚杆水平弹性刚度系数的求算公式。最后,按一般方法和改进方法针对3个不同实例分别进行了计算,并与数值计算的结果进行了对比分析。     

Design method for local load on a geosynthetic reinforced soil structure

This paper presents a method for the design of geosynthetic reinforced soil structures, adapted for the case of a local surcharge load. The load has an important influence on the mechanical behaviour of the reinforcement. The basic calculation method is described and a design calculation method is proposed for the case of a locally loaded structure. This new approach is validated on the basis of experimental results obtained on several full-scale embankments, locally loaded to failure. These experimental results are compared to the results of calculation with partial safety factors from Eurocode 7.     

P-III分布参数的概率权重矩法S函数计算

概率权重矩法是一种估计统计分布参数的方法.本文根据不完全Γ函数在无限区间积分,推导了P-Ⅲ分布参数的S函数的计算公式.通过现有计算公式比较,其计算结果具有较高的计算精度,避免了的大量的数值积分计算.文中公式只要借助于计算编程进行求解,给定超几何函数项一定的截断误差,其运算具有较高的运行速度.文中计算公式是一种P-Ⅲ分布参数S函数的计算途径.     

Reliability analysis of soil liquefaction based on standard penetration test

A review of probabilistic and deterministic liquefaction evaluation procedures reveals that there is a need for a comprehensive approach that accounts for different sources of uncertainty in liquefaction evaluations. For the same set of input parameters, different models provide different factors of safety and/or probabilities of liquefaction. To account for the different uncertainties, including both the model and measurement uncertainties, reliability analysis is necessary. This paper presents a review and comparative study of such reliability approaches that can be used to obtain the probability of liquefaction and the corresponding factor of safety. Using a simplified deterministic Seed method, this reliability analysis has been performed. The probability of liquefaction along with the corresponding factor of safety have been determined based on a first order second moment (FOSM) method, an advanced FOSM (Hasofer–Lind) reliability method, a point estimation method (PEM) and a Monte Carlo simulation (MCS) method. A combined method that uses both FOSM and PEM is presented and found to be simple and reliable for liquefaction analysis. Based on the FOSM reliability approach, the minimum safety factor value to be adopted for soil liquefaction analysis (depending on the variability of soil resistance, shear stress parameters and acceptable risk) has been studied and a new design safety factor based on a reliability approach is proposed.