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1.
ABSTRACTThe main sources of uncertainty in the soil specification and mechanical behaviour consist of the lithological and heterogeneous randomness of soil deposits. It is quite obvious that the cone penetration testing (CPT) data and the variation of soil characteristics are not stationary. Hence, this paper investigates a new approach to realise a CPT data, taking both sources of uncertainty into consideration. In this regard, the first part of this study illustrates a simple approach to stratify the CPT data, using the Eslami–Fellenius chart of classification. In the second part, the non-stationary algorithm of generating random field is introduced to generate a multi-layer random field. This algorithm takes account of each layer’s statistical properties (i.e. standard deviation, mean, and the trend value), separately. To validate the proposed approach, 41 case histories from different worldwide sites, have been regenerated by considering both the stationary and non-stationary algorithms. The correlation coefficient between real and realised CPT data has been employed to show that the proposed non-stationary algorithm can simulate the CPT data more accurately in comparison with the stationary algorithm. 相似文献
2.
边坡可靠度分析中通常假定采用平稳或准平稳随机场表征土体参数的空间变异性,然而大量现场试验数据表明,土体参数如不排水抗剪强度沿土体埋深常呈现明显的非平稳分布特征,即其均值和标准差均随埋深发生变化,因此亟需发展土体参数非平稳随机场模型及其模拟方法。针对目前不能有效单独模拟土体参数趋势分量和随机波动分量的不确定性,提出了一种有效的不排水抗剪强度参数非平稳随机场模型,并给出了土体参数二维非平稳随机场模拟方法计算流程,同时将新提出的模型与现有非平稳随机场模型及平稳随机场模型进行了系统比较。最后通过不排水饱和黏土边坡算例验证了提出模型的有效性,并揭示了不排水抗剪强度非平稳分布特征对边坡可靠度的影响规律。结果表明：提出模型能够有效地单独模拟土体参数趋势分量和随机波动分量的不确定性,考虑土体参数均值和标准差随埋深增加而增大的特性,可为表征土体参数非平稳分布特征提供了一条有效的途径。此外,与采用非平稳随机场模拟土体参数空间变异性相比,采用常用的平稳随机场模型会低估边坡失效概率,从而造成偏危险的边坡工程设计方案。 相似文献
3.
相关距离是用随机场理论建模土层剖面的一个非常重要的参数,也是利用随机场理论进行岩土工程可靠性分析的关键所在。基于苏中地区某建筑工程原位静力触探测试数据中的锥尖阻力指标,针对粉质黏土层,利用不同取样间距对相关距离进行了统计计算,分析了取样间距对相关距离计算结果的影响及原因,提出了实际应用中基于尺度匹配原则的取样间距确定方法;随后,基于江苏中部某高速公路工程地质勘察所提供的大量原位静力触探测试数据,结合相关距离计算的平均零跨距法、递推空间法和相关函数法,对该区湖相沉积土层土性参数的竖直向和水平向相关距离进行了系统地统计分析。研究成果不仅提供了土性参数相关距离计算过程中取样间距的确定原则,而且获得了相关距离的区域性代表值,为区域性土性参数随机场模型的建立打下坚实的基础,能对苏中地区岩土工程可靠性分析提供参考。 相似文献
4.
Simulation of one-dimensional correlated fields using a matrix-factorization moving average approach
The simulation of one-dimensional stationary correlated fields is of increasing importance in the earth sciences. A new method for repeated generation of independent realizations, which are long and dense relative to the correlation scale of the underlying stochastic process, is examined here. This method is conceptually simple and easy to apply. It consists of a matrix-factorization technique for derivation of moving average coefficients which are used as weights in the construction of successive observations from linear combinations of random normal deviates. The matrix-factorization procedure is fast and need be performed only once for a given correlation function and density of observations. This technique can be used to generate evenly spaced observations in time or a single space dimension for any prescribed correlation function and marginal distribution which is Gaussian with arbitrary mean and variance. Tests of ensemble properties of generation procedures have been developed and results for this method compared with those for a popular generation technique. For correlation functions and generation conditions examined, the matrix-factorization moving average approach more accurately produces ensemble characteristics of the prescribed underlying process. For repeated generation of 2001 observations spaced evenly over realizations with length equal to 100 times the correlation scale, the moving average approach requires only about one fifth the CPU time used by the Shinozuka and Jan method to obtain similar accuracy. 相似文献
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6.
能否用齐次正态随机场模型来模拟土体性质的空间分布特性,其关键在于土性随机场模型是否具有平稳性和各态历经性。国内大多数研究都是在假定土性随机场模型是平稳随机场的条件下研究应用Vanmarcke 模型的。关于黄土的土性参数的空间特性研究亦是如此,未对其土性剖面随机场的平稳性及各态历经性进行检验。本文以西安市曲江某项目29个钻孔的双桥静力触探(CPT)数据为研究样本,首先讨论了关于原始数据的齐次化处理,即趋势分量的消除方法。然后对该场地黄土土性剖面随机场的平稳性及各态历经性进行了检验,检验结果表明:西安黄土梁洼地貌上的Q3黄土层、Q3古土壤层和Q2黄土层其土性随机场模型具平稳性和各态历经性。故Vanmarcke 随机场模型适用于模拟西安黄土土性剖面。 相似文献
7.
Spatial correlation structures are usually used while modelling inherent uncertainty associated with soil properties. To retrieve this information a sufficient number of measurements and equal intervals between measurements or samples are always required. However, in practice, it is not usual to conduct site investigation in that way subject to a limited budget. Therefore, it is of interest to understand the possible bias created by using samples with unequal intervals. This research focuses on estimating the vertical spatial correlation structures of cone penetration tests (CPT) data conducted at a liquefaction site in Taiwan. The appropriate fitting range used in calibrating the correlation model is also discussed. The results show that cone tip resistance has larger correlation distances than that of sleeve friction. The estimated correlation distances of the CPT profiles are similar while using an equal sampling interval within a certain fitting range (denoted as the critical interval of measurements in this research). The results indicate that the effect of using different curve-fitting ranges is relatively insignificant for correlation distances of sleeve friction, whereas the correlation distances of cone tip resistance are more sensitive to different curve-fitting ranges. Moreover, the mean values of correlation distances are more constant for the equal sampling interval cases than for the unequal interval cases. 相似文献
8.
群桩基础竖向承载力的可靠性分析 总被引：1，自引：0，他引：1
由CPT和静载试验结果综合确定钻孔灌注桩竖向极限承载力,以沿深度方向的一维平稳高斯随机场作为桩基土层土性参数的数学模型,利用相关函数法和变异函数法计算土层的相关范围,进而对相同场地各试桩的承载力进行折算后检验其概率分布,并估计有关统计参数;考虑群桩效应,由桩基沉降反算其作用效应,计算单桩及群桩的可靠度指标。并与未采用随机场模型的计算结果相比较,对竖向荷载下桩基可靠性进行了较系统的研究。 相似文献
9.
Cone Penetration Test (CPT) is widely utilized to gain regular geotechnical parameters such as compression modulus, cohesion coefficient and internal friction angle by transformation model in the site investigation. However, it is challenging to obtain simultaneously the unknown coefficients and error of a transformation model, given the intrinsic uncertainty (i.e., spatial variability) of geomaterial and the epistemic uncertainty of geotechnical investigation. A Bayesian approach is therefore proposed calibrating the transformation model based on spatial random field theory. The approach consists of three key elements: (1) three-dimensional anisotropic spatial random field theory; (2) classifications of measurement and error, and the uncertainty propagation diagram of geotechnical investigation; and (3) the unknown coefficients and error calibration of the transformation model given Bayesian inverse modeling method. The massive penetration resistance data from CPT, which is denoted as a spatial random field variable to account for the spatial variability of soil, are classified as type A data. Meanwhile, a few laboratory test data such as the compression modulus are defined as type B data. Based on the above two types of data, the unknown coefficients and error of the transformation model are inversely calibrated with consideration of intrinsic uncertainty of geomaterial, epistemic uncertainties such as measurement errors, prior knowledge uncertainty of transformation model itself, and computing uncertainties of statistical parameters as well as Bayesian method. Baseline studying indicates the proposed approach is applicable to calibrate the transformation model between CPT data and regular geotechnical parameter within spatial random field theory. Next, the calibrated transformation model was compared with classical linear regression in cross-validation, and then it was implemented at three-dimensional site characterization of the background project. 相似文献
10.
Describing how soil properties vary spatially is of particular importance in stochastic analyses of geotechnical problems, because spatial variability has a significant influence on local material and global geotechnical response. In particular, the scale of fluctuation θ is a key parameter in the correlation model used to represent the spatial variability of a site through a random field. It is, therefore, of fundamental importance to accurately estimate θ in order to best model the actual soil heterogeneity. In this paper, two methodologies are investigated to assess their abilities to estimate the vertical and horizontal scales of fluctuation of a particular site using in situ cone penetration test (CPT) data. The first method belongs to the family of more traditional approaches, which are based on best fitting a theoretical correlation model to available CPT data. The second method involves a new strategy which combines information from conditional random fields with the traditional approach. Both methods are applied to a case study involving the estimation of θ at three two-dimensional sections across a site and the results obtained show general agreement between the two methods, suggesting a similar level of accuracy between the new and traditional approaches. However, in order to further assess the relative accuracy of estimates provided by each method, a second numerical analysis is proposed. The results confirm the general consistency observed in the case study calculations, particularly in the vertical direction where a large amount of data are available. Interestingly, for the horizontal direction, where data are typically scarce, some additional improvement in terms of relative error is obtained with the new approach. 相似文献
11.
在场地岩土工程勘察中,为使所取土样之间满足数据独立性的要求,本文提出应使钻孔取样间距等于土的相关距离,这样能真实、准确地反映地基土的特性。根据Vanmarcke提出的随机场模型,结合数理统计和随机过程理论,采用递推平均法计算得到土的相关距离,其计算数据来自现场静力触探试验。 相似文献
12.
An accurate representation of permeability anisotropy is needed to model the rate and direction of groundwater flow correctly.
We develop a wavelet analysis technique that can be used to characterize principal directions of anisotropy in both stationary
and non-stationary permeability fields. Wavelet analysis involves the integral transform of a field using a wavelet as a kernel.
The wavelet is shifted, scaled, and rotated to analyze different locations, sizes, and orientations of the field. The wavelet
variance is used to identify scales and orientations that dominate the field. If the field is non-stationary, such that different
zones of the field are characterized by different dominant scales or orientations, the wavelet variance can identify all dominant
scales and orientations if they are distinct. If the dominant scales and orientations of different zones are similar, the
wavelet variance identifies only the dominant scale and orientation of the primary zone. In this paper, we present a combined
wavelet analysis and filtering approach to identify all dominant scales and orientations in a non-stationary permeability
field. We apply the method to permeability data obtained in the laboratory from the Massillon sandstone. 相似文献
13.
Numerous methods have been proposed to assess the axial capacity of pile foundations. Most of the methods have limitations
and therefore cannot provide consistent and accurate evaluation of pile capacity. However, in many situations, the methods
that correlate cone penetration test (CPT) data and pile capacity have shown to provide better results, because the CPT results
provide more reliable soil properties. In an attempt to obtain more accurate correlation of CPT data with axial pile capacity,
gene expression programming (GEP) technique is used in this study. The GEP is a relatively new artificial intelligent computational
technique that has been recently used with success in the field of engineering. Three GEP models have been developed, one
for bored piles and two other models for driven piles (a model for each of concrete and steel piles). The data used for developing
the GEP models are collected from the literature and comprise a total of 50 bored pile load tests and 58 driven pile load
tests (28 concrete pile load tests and 30 steel pile load tests) as well as CPT data. For each GEP model, the data are divided
into a training set for model calibration and an independent validation set for model verification. The performances of the
GEP models are evaluated by comparing their results with experimental data and the robustness of each model is investigated
via sensitivity analyses. The performances of the GEP models are evaluated further by comparing their results with the results
of number of currently used CPT-based methods. Statistical analyses are used for the comparison. The results indicate that
the GEP models are robust and perform well. 相似文献
14.
We present a general framework that enables decision-making when a threshold in a process is about to be exceeded (an event).
Measurements are combined with prior information to update the probability of such an event. This prior information is derived
from the results of an ensemble of model realisations that span the uncertainty present in the model before any measurements
are collected; only probability updates need to be calculated, which makes the procedure very fast once the basic ensemble
of realisations has been set up. The procedure is demonstrated with an example where gas field production is restricted to
a maximum amount of subsidence. Starting with 100 realisations spanning the prior uncertainty of the process, the measurements
collected during monitoring bolster some of the realisations and expose others as irrelevant. In this procedure, more data
will mean a sharper determination of the posterior probability. We show the use of two different types of limits, a maximum
allowed value of subsidence and a maximum allowed value of subsidence rate for all measurement points at all times. These
limits have been applied in real world cases. The framework is general and is able to deal with other types of limits in just
the same way. It can also be used to optimise monitoring strategies by assessing the effect of the number, position and timing
of the measurement points. Furthermore, in such a synthetic study, the prior realisations do not need to be updated; spanning
the range of uncertainty with appropriate prior models is sufficient. 相似文献
15.
Mohamed Metwaly Mohamed Ahmed Khalil El-Said Al-Sayed Abeer El-Kenawy 《Arabian Journal of Geosciences》2013,6(9):3527-3533
This study provides an evaluation of the subsurface oil contaminant flow in an oil production field at the Wadi Feiran fan, along the Gulf of Suez, Egypt. The 2D electrical resistivity tomography technique has been applied along four profiles surrounding the spill location of oil dump site. Theoretical soil resistivity response versus fluid resistivity for different cation exchange capacity values has been studied. Then, a physical model for the current situation of flowing the oil over the groundwater (sea invaded water) of saturated fluvial sediments has been introduced. It was supposed that the crude oil has higher resistivity values and turned to be conductive far away from the oil spill source under the effect of microbial biodegradation. Such conditions of contaminated distribution and its resistivity values have been considered during the inversion and interpretation of the acquired data sets. The processed 2D resistivity profiles reveal that oil plumes are accumulated in the seawater invasion direction, whereas it has low signatures along the profiles parallel to the shore line. 相似文献
16.
《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2013,7(3-4):207-217
The present study comprises Monte-Carlo simulation assisted analysis of foundations resting on reinforced earth beds using the concept of beams on an elastic foundation, treating the modulus of subgrade reaction (MSR) as a stationary stochastic field characterised by mean, variance, autocorrelation function (ACF) and the autocorrelation distance (ACD). Realisations of the MSR, generated by solving a stochastic differential equation, are fed to a deterministic distributed parameter model to generate realisations of two dependent stochastic fields, namely deflection and bending moment in the foundation beam, and two random variables, namely the location of occurrence of maximum deflection and the bending moment. Subsequently these realisations are analysed to evolve probability distribution functions, variance and ACF of the dependent stochastic fields and the random variables. It is revealed that the ACF of these fields is independent of the ACF of the MSR. Further, variance of deflection is found to increase as the ACD of the MSR increases, implying requirement of a larger factor of safety when random soils display low frequency (macro level) variations. On the other hand, variance of the bending moment is larger at smaller ACDs of the MSR, indicating that for bending moments a larger factor of safety is required when the random soils display high frequency (micro level) variations. 相似文献
17.
高精度测定渗透系数（K）的重要性不言自明,但是现阶段野外试验手段能够提供的关于K的信息不能满足高度非均质地层中污染物迁移预测模拟的需求。直接推进注入记录器(Direct Push Injection Logger, DPIL)和直接推进渗透仪(Direct Push Permeameter, DPP)是新发展的水文地质参数测量仪器,能够使K值的测定达到前所未有的分辨率和成本效益水平。工具向地下推进过程中,通过对注水量、注水压力和其它的水文地球物理参数的同步监测,直接推进技术(Direct Push, DP)能快捷准确地获得地层渗透系数的垂向分布。DP技术几乎适用于所有野外松散地层,并且对场地的干扰很小。因此,它克服了许多基于既有井的传统含水层测试方法的局限性。最近在美国MADE试验场的一个案例研究表明,使用DPIL/DPP可以获得空间分辨率达15cm的K值垂向分布。未来,高精度直接推进技术还可以与新一代的地球物理技术,例如高精度探地雷达相结合,以实现不同位置DP测定K值的互联以及整个试验场K值三维分布的确定。 相似文献
18.
Xavier Emery 《Mathematical Geology》2007,39(6):607-623
Conditioning realizations of stationary Gaussian random fields to a set of data is traditionally based on simple kriging.
In practice, this approach may be demanding as it does not account for the uncertainty in the spatial average of the random
field. In this paper, an alternative model is presented, in which the Gaussian field is decomposed into a random mean, constant
over space but variable over the realizations, and an independent residual. It is shown that, when the prior variance of the
random mean is infinitely large (reflecting prior ignorance on the actual spatial average), the realizations of the Gaussian
random field are made conditional by substituting ordinary kriging for simple kriging. The proposed approach can be extended
to models with random drifts that are polynomials in the spatial coordinates, by using universal or intrinsic kriging for
conditioning the realizations, and also to multivariate situations by using cokriging instead of kriging. 相似文献
19.
《Boreas: An International Journal of Quaternary Research》2018,47(1):80-105
Using extensive data sets from three separate areas in the German North Sea sector, consisting of seismic grids, cores and in‐situ cone penetration tests (CPT), we have established a revised stratigraphical framework for the mid to late Quaternary deposits of the German North Sea sector. This framework consists of four regional unconformities and 15 other local unconformities derived from seismic profiles. Using these unconformities, along with lithological and geotechnical data, it was possible to define and correlate 14 major units and 21 subunits within the framework. The Quaternary cover in the area is characterized by a variety of environmental settings ranging from glacial terrestrial and fluvial to lacustrine as well as brackish and marine environments with associated erosion, reworking and deposition. The complexity of Quaternary deposits within the area is explained by its history of repeated ice advances interrupted by marine transgressions and exposed periglacial landscapes. Within the framework, eight buried tunnel valleys and two shallow buried river valleys are identified from seismic profiles with four phases of tunnel valley generation inferred. These phases of tunnel valley generation are associated with the Elsterian (three) and Saalian (one) glacial stages. Infill of these tunnel valleys consists of glaciofluvial sands, thick sequences of marine and lacustrine fine‐grained sediments and some reworked till remnants. Elsewhere, extensive tabular units have formed consisting of marine and fluvial sediments. We compare this new stratigraphy with previous stratigraphies for the German North Sea sector, attribute informal stratigraphical names and offer preliminary correlations with established stratigraphies from other sectors of the North Sea. 相似文献
20.
The reproduction of the non-stationary distribution and detailed characteristics of geological bodies is the main difficulty of reservoir modeling. Recently developed multiple-point geostatistics can represent a stationary geological body more effectively than traditional methods. When restricted to a stationary hypothesis, multiple-point geostatistical methods cannot simulate a non-stationary geological body effectively, especially when using non-stationary training images (TIs). According to geologic principles, the non-stationary distribution of geological bodies is controlled by a sedimentary model. Therefore, in this paper, we propose auxiliary variables based on the sedimentary model, namely geological vector information (GVI). GVI can characterize the non-stationary distribution of TIs and simulation domains before sequential simulation, and the precision of data event statistics will be enhanced by the sequential simulation’s data event search area limitations under the guidance of GVI. Consequently, the reproduction of non-stationary geological bodies will be improved. The key features of this method are as follows: (1) obtain TIs and geological vector information for simulated areas restricted by sedimentary models; (2) truncate TIs into a number of sub-TIs using a set of cut-off values such that each sub-TI is stationary and the adjacent sub-TIs have a certain similarity; (3) truncate the simulation domain into a number of sub-regions with the same cut-off values used in TI truncation, so that each sub-region corresponds to a number of sub-TIs; (4) use an improved method to scan the TI or TIs and construct a single search tree to restore replicates of data events located in different sub-TIs; and (5) use an improved conditional probability distribution function to perform sequential simulation. A FORTRAN program is implemented based on the SNESIM. 相似文献