Observing artificially induced strain: implications for subglacial deformation

By analysing a series of four successive thin‐sections from a ceramic clay that was subjected to uniaxial compression, we were able to monitor the development of microstructures in a fine‐grained sediment. The artificially induced microstructures, such as unidirectional clay reorientations and linear and circular grain arrangements, are identical to features that have been observed in thin‐sections of subglacially deformed tills, and therefore may be used as representative analogues. We argue that the structures, reflecting slip, planar shear displacements as well as rotational movements, can be explained by assuming a Coulomb‐plastic response to imposed shear. We conclude that sediments subjected to subglacial deformation behave as Coulomb materials, at least during the final stages of the deformation. The present study bridges the gap between field studies, experimental studies and theoretical modelling. The microscopic observations assist in visualising inferred subglacial processes and facilitate up‐ and downscaling between diverse methodological approaches. Copyright © 2003 John Wiley & Sons, Ltd.     

Disjunctive Kriging with Hard and Imprecise Data

This paper presents a methodology for assessing local probability distributions by disjunctive kriging when the available data set contains some imprecise measurements, like noisy or soft information or interval constraints. The basic idea consists in replacing the set of imprecise data by a set of pseudohard data simulated from their posterior distribution; an iterative algorithm based on the Gibbs sampler is proposed to achieve such a simulation step. The whole procedure is repeated many times and the final result is the average of the disjunctive kriging estimates computed from each simulated data set. Being data-independent, the kriging weights need to be calculated only once, which enables fast computing. The simulation procedure requires encoding each datum as a pre-posterior distribution and assuming a Markov property to allow the updating of pre-posterior distributions into posterior ones. Although it suffers some imperfections, disjunctive kriging turns out to be a much more flexible approach than conditional expectation, because of the vast class of models that allows its computation, namely isofactorial models.     

废弃防空洞及软弱地基的加固处理

针对工程填土地层及废弃防空洞,拟采用锤击沉管挤密碎石桩法进行加固处理。但在处理部分防空洞后,因震动大、噪音高,对周边居民和民居影响严重而停工。通过多次试验,摸索出钻孔夯填法并结合灌浆法回填防空洞,喷浆桩法加固软弱地基等经验,并对废弃防空洞的回填加固机理进行了简要分析。经检测,加固处理效果显著。至今,住宅楼建成4年使用正常。     

软粘土层上的油罐差异沉降

根据某一大型油罐软基加固处理工程方案设计和优选需要,按照离心模型相似律,开展了三组模型试验,分别模拟了天然地基、土工合成材料袋装碎石垫层和既在填土层中设置袋装碎石垫层又在淤泥质粘土层设置土工合成材料排水板三种情况,以研究这一加固布置形式对减小高压缩性软土层地基上油罐罐底的差异沉降效果反应。模型油罐地基采用原型土重塑制备,现场土工合成材料袋装碎石采用柔性机织玻璃纤维细管塞装粗砂条模拟,并在不停机运转条件下模拟了多次充放水预压加载。试验结果表明,油罐软弱地基经土工合成材料袋装碎石加固后,罐底总沉降值和差异沉降值均明显小于天然地基情形下对应的沉降值,罐底畸变得到显著减小,就本文所述的土质条件、土层厚度和预压荷载强度,地基经加固处理后,油罐罐底畸变减小了近50 %。最后就土工合成材料在加固油罐地基布置形式的合理性进行了初步探讨。     

真空-堆载联合预压处理软基效果的室内试验研究

对甬-台-温高速公路采用真空-堆载联合预压处理软基前后的土样进行了室内试验分析,得出了合理的试验结论,即土的物理性质指标分别得到不同程度的降低,强度指标得到较大的提高。     

软土地基承载力原位测试及其相关性研究

选用平板荷载试验、轻便动力触探试验、十字板剪切试验等三种测试手段,对潭邵公路软土地基承载力进行了研究。通过对测试数据进行统计分析,建立了N10与Cu的回归方程,且其相关系数均在0.9以上,表明二者具有很强的相关性。以Cu-fk关系为桥梁,推导出N10-fk的关系表达式,该公式同时考虑了埋置深度对承载力的影响。该研究为湖南地区同类地基土承载力的确定提供了一种新方法。     

Spectral and Multiscale Signal-to-Noise Thresholding of Spherical Vector Fields

The basic concepts of spectral and multiscale selective reconstruction of (geophysically relevant) vector fields on the sphere from error-affected data is outlined in detail. The reconstruction mechanism is formulated under the assumption that spectral as well as multiscale approximation is well-representable in terms of only a certain number of expansion coefficients at the various resolution levels. It is shown that spectral denoising by means of orthogonal expansions in terms of vector spherical harmonics reflects global a priori information of the noise (e.g., in form of a covariance tensor field), whereas multiscale signal-to-noise thresholding can be performed under locally dependent noise information within a multiresolution analysis in terms of spherical vector wavelets. An application of the multiscale formalism to Earth's magnetic field determination is presented.     

华北北部场源前兆观测资料分析(一)──场源前兆特征与机制

1976年唐山地震前，在距震源很远的地区内都观测到一些前兆趋势变化，如重力、重力位二次徽商W△、水氧、地电阻率、水位和油井出油量等变化。作者认为这些变化不是由震源体直接引起的，而是在区域应力场的作用下，在某些活动断层附近，浅层岩，尤其是含水砂岩层和含油层受挤压出现的一些与地震有关的异常现象。其特征是：（1）异常范围大，可能在距震源很远的地方发生，但就同一种方法的多个观测点来说却又是局部的，即只有其中部分测点才能观测到异常，不少测点观测不到异常。（2）异常发生的时间大致相同。有些异常有同步变化的特征，如同时上升或同时下降。（3）临震前多数异常有恢复的趋势。这些特征与引起异常的机理有关。作者还从理论上计算了这种趋势异常量级，重力变化100×10-6cm／s2左右，重力位二次微商变化（1～2）×10－9／s2，地电阻率变化2％～3％，Rn变化7．4～11．1Bq／L，这样的变化量在活动断层附近的一些台站可能观测到。作者还研究了干旱降雨对某些前兆的影响，其影响量级可以被一些方法观测到，因此在确定是否是地震异常时，必须注意利用综合分析的方法排除干旱降雨的影响，减少异常的多解性。     

砂岩岩脉(岩墙、岩床)的一种可能成因——冲蚀沟槽的充填

黄河三角洲的边滩、心滩上发育了大量冲蚀沟槽（冲槽）．这些冲蚀沟槽深数厘米至1m～2m，宽数厘米至数米，长数十厘米至十几、二十余米，但以深数十厘米，宽数厘米至十余厘米，长数米者多见。形态多样，有直立板片状、直立楔状、“⊥”状、梯形状、“U”形状及树枝状等，其内有时被风成砂充填。经成岩作用后，它们便会转变成砂岩岩脉（岩墙、岩床）。因此，冲蚀沟槽的（砂）充填可能是一种砂岩岩脉（岩墙、岩床）的形成方式．     

临兴上古生界致密储层裂缝发育特征及对致密气富集影响

临兴区块上古生界储集层为致密砂岩，裂缝发育特征及对致密气富集影响尚不清楚，一定程度上制约了甜点区预测。 根据岩心、露头、薄片及测井资料，分析了研究区裂缝发育特征，探讨了裂缝对致密砂岩气富集的影响。临兴区块上古生界主 要发育高角度缝，其次为中低角度缝及水平缝，微观上根据裂缝与矿物颗粒的相对位置关系，可识别出粒内缝、粒缘缝和穿粒 缝，其中粒缘缝最为发育。受塑性泥岩阻挡，裂缝垂向延伸较差，一般延伸1~2 m后消失于泥岩层中，受燕山期北西—南东向 地应力影响，裂缝走向多为北东—南西向，裂缝密度一般2~5条/ｍ。裂缝可改善储集空间、提高油气充注效率，储层裂缝发育 区渗透率可增大1~2个数量级，含气饱和度高，此外，研究区裂缝是油气垂向运移的有效通道，影响着石盒子组及石千峰组致 密气的富集，在后期的勘探开发过程中应充分寻找裂缝发育区，并通过进一步压裂获得高产。