返包式土工格栅加筋土高挡墙现场试验研究

为了研究返包式土工格栅加筋土高挡墙结构的受力、变形状态,分析其作用机理,进行了包括加筋土墙体基底应力、墙背侧向土压力、拉筋拉力和墙面水平变形等内容的现场试验,研究了加筋土墙体基底垂直应力、不同层位的拉筋拉力沿筋长的分布规律,加筋土挡墙潜在的破裂面位置,墙背侧向土压力沿墙高的分布规律以及墙面水平变形规律。测试结果表明,加筋土挡墙基底垂直土压力沿土工格栅拉筋长度方向呈非线性分布,最大值发生在拉筋中部附近,向拉筋两端方向逐渐减少;实测墙背侧向土压力沿墙高呈非线性形式分布,其值小于主动土压力;上部墙体拉筋应变沿筋长呈单峰值分布,下部墙体拉筋应变沿筋长呈双峰值分布;上部墙体潜在破裂面形状与“0.3H法”接近,而下部墙体潜在的破裂面形状与朗肯主动土压力理论接近;施工期墙面最大水平变形位置在墙高的下部,竣工后墙面最大水平变形发生在墙顶处等结论。     

汇盛大厦水泥搅拌桩基坑支护设计

通过六盘水市汇盛大厦工程、水文及环境地质特征的介绍,确定该大厦基坑支护方案采用水泥搅拌桩挡土墙,并对该方案土压力、抗倾覆、抗滑动、抗渗透、墙体宽度等内容进行设计验算,满足规范要求。     

基坑降水中渗流破坏归类及抗突涌验算公式评价

基坑降水工程中的渗流引发一种体积力即渗流力,尤其当坑底下覆承压含水层时可能引发以下渗流破坏现象如流砂、管涌、坑底突涌安全等,需要进行安全验算。以力的性质将安全验算分为2种判别标准：一种为面积力安全验算,另一种为体积力安全验算。对于抗突涌安全验算公式,在目前规范公式的基础上考虑了被浮托土块侧面抗剪强度安全储备的发挥,并结合天津市区内典型地铁车站基坑几何性状和取值极为保守的土性参数进行验算,结果表明抗剪强度可发挥至少1/4以上抗突涌贡献,对于基坑下呈透镜体状分布局部承压砂层,发挥作用更大。如考虑抗剪强度发挥减少井孔数量,既可节约工程费用,又可减少钻孔处的安全隐患。     

双面直立互锚式挡土墙的受力和变形研究

一座总墙高为 9 6m的双面直立互锚式挡土墙首次应用于山区高等级公路工程中 ,为了研究墙体的水平位移、基底应力及墙背土压力的分布规律 ,对该挡土墙的变形和受力进行了现场原型观测 ,得到了拉筋拉力、墙面板所受土压力、基底应力及墙体的水平位移等变化和分布规律 ,研究结果可供今后设计和研究类似支挡结构时提供参考     

重力式挡土墙抗滑动稳定计算方法改进研究

针对目前重力式挡土墙抗滑稳定性计算方法中存在的缺陷,将挡土墙入土部分划分成小网格,遍历搜寻出抗倾覆稳定系数最小的点,此点就是挡土墙的实际倾覆转动点所在的位置,根据此转动点的位置,将挡墙两侧的土体划分成四个部分分别计算各部分土压力,再结合墙底与地基土摩擦力的分析,推导出改进的墙体抗滑动稳定系数的计算公式。还通过改变墙体的几何参数,分析了最小抗倾覆转动点的位置和墙体抗滑稳定性系数随墙体宽度、挡土墙入土深度等的变化规律。     

关于挡土墙的地基承载力验算及抗倾覆稳定性验算方法的探讨

通过对影响挡土墙抗倾覆稳定性问题的深入分析 ,提出了一种引入挡土墙主动土压力分项系数进行挡土墙抗倾覆稳定性验算的新方法。该方法将挡土墙的地基承载力验算与抗倾覆稳定性验算合并 ,概念清晰且计算结果可靠 ,并能与现行《建筑结构可靠度设计统一标准》(GB 5 0 0 68— 2 0 0 1 )及《建筑结构荷载规范》(GB5 0 0 0 9— 2 0 0 1 )协调一致     

上海规范重力式围护墙稳定性若干问题探讨

重力式围护墙是软土地区常用的基坑支护形式,目前关于重力式围护墙的可靠度分析还不够完善,各因素对稳定性的影响机制等也存在一些疑问。以收集到的上海地区重力式围护墙实际工程为例进行可靠度分析,对水泥土重力式围护墙稳定性分析中的相关问题进行了探讨。分析结果表明,上海地区实际工程的设计安全水准通常高于规范规定值,其中水平滑动多为重力式围护工程稳定性验算的控制失效模式;通过提高插入比和墙体宽度可改善水泥土重力式围护基坑的抗倾覆、抗水平滑动稳定性的安全状态;对于整体稳定性,提高插入比较有效,墙体宽度的变化对其影响不敏感。     

考虑连续墙接头效应的软土大型盾构工作井稳定性分析

基于地下连续墙分幅施工的工程实际状况,建立了连续墙不抗弯不抗剪柔性接头、抗剪不抗弯半刚性接头以及抗剪又抗弯刚性接头的力学模型。结合南京纬三路过江隧道盾构工作井地下连续墙的设计,通过数值模拟,研究了连续墙接头型式对于墙体水平位移以及支护体系受力的影响规律。研究成果表明,在做好连续墙接头防渗的前提下,采用柔性接头时墙体的水平位移较大,支护体系内力明显增高;采用半刚性接头时既可以有效地限制墙体的水平位移,又可以将墙体承担的土压力分担到临时支撑和环梁之上,降低连续墙墙体的内力;采用刚性接头时可以降低临时支撑、环梁以及内衬的内力,但连续墙墙体要能承担极大的竖向弯矩和数值相当的横向弯矩。综合考虑建议工作井采用抗剪不抗弯的半刚性接头。     

水泥土挡土墙稳定性分析

本文从水泥挡土墙的结构特征及破坏型式出发,分析了现地设计中的抗滑及抗倾覆稳定验算时的被动土压力的动用度,提出了基坑抗隆起稳定验算的新方法,并对某一典型工程实例进行分析,旨在提高水泥土搅拌桩作基坑围护结构的设计水准。     

逆作法施工中地下连续墙入土深度的探讨

基坑工程中围护结构入土深度,一般是由坑底抗隆起稳定性决定,现行规范规定推荐的圆弧滑动法的验算方法只是针对一般情况,特别是柔性围护结构。考虑逆作法施工的特点及其他一些有利因素的影响,提出修正的圆弧滑动法以适合刚性围护结构的抗隆起验算。并通过一个工程实例的设计验算,对逆作工况下地下连续墙入土深度进行一定的探讨和优化。     

Rock Kriging with the Microscope

An idea to consider rock textures from a geostatistical viewpoint is suggested. Mineral grains are coded by indicator functions. Four metrics are shown of interest for petrographic applications. The simplest one is used to calculate covariograms of indicators for platinum-bearing gabbronorite from the Pansky rock massif (Kola Peninsula, Russia) with maximal range of 2 units. This is generalized in the concept of a minimal cluster of mineral grains for the given rock. The theory allows us to combine grain-by-grain and cluster-by-cluster considerations of rock texture. It may be used to classify monotonous lithological series using nuances of rock textures.     

Living with the Anthropocene blues

In this short discussion, we consider societal responses to the (impending) ‘death of nature’ associated with the epoch now dubbed the Anthropocene. We forward the case for a geographical perspective that engages with psychological and psychoanalytic analyses to better understand responses and coping mechanisms, such as societal death anxiety.     

Some problems with the cumulus theory

There are a number of features in layered intrusions which do not appear to be consistent with the cumulus theory. The most important of these are: (1) Rhythmic layering in plagioclase-pyroxene cumulates from some intrusions (e.g. Jimberlana and Stillwater) may be inverted with the light plagioclase-rich cumulates at the base of the layer and heavy pyroxene-rich cumulates at the top. (2) Hydraulic sorting in rhythmically layered cumulates is often poor, suggesting that chemical and not mechanical processes control the distribution of minerals in this type of layered sequence. (3) The textures of cumulates from the steeply dipping marginal zone of Jimberlana, which cannot have formed by gravity settling, are indistinguishable from those found in the flatly dipping central layers of the intrusion. Similarly, it is difficult to explain the cumulate textures in the ‘overturned’ marginal layered series of Jimberlana. (4) Igneous layering, including cross-bedding, graded bedding and trough banding, has been described in layered sequences with near-vertical primary dips. (5) Calculations and experiments with a centrifuge furnace suggest that plagioclase cannot sink in Fe-rich tholeiitic liquids. (6) The settling of crystals as individual grains assumes that nucleation is homogeneous. This is unlikely.

It is probable that heterogeneous and self-nucleation are the dominant nucleation mechanisms during the formation of cumulates. This gives rise to two possibilities. Firstly, that most grains nucleate against pre-existing settling crystals to form composite grains which gravitate to the floor of the chamber. Secondly, that the cumulus grains nucleate in situ at the temporary floor of the magma chamber.     

Optimization with the Gradual Deformation Method

Building reservoir models consistent with production data and prior geological knowledge is usually carried out through the minimization of an objective function. Such optimization problems are nonlinear and may be difficult to solve because they tend to be ill-posed and to involve many parameters. The gradual deformation technique was introduced recently to simplify these problems. Its main feature is the preservation of the spatial structure: perturbed realizations exhibit the same spatial variability as the starting ones. It is shown that optimizations based on gradual deformation converge exponentially to the global minimum, at least for linear problems. In addition, it appears that combining the gradual deformation parameterization with optimizations may remove step by step the structure preservation capability of the gradual deformation method. This bias is negligible when deformation is restricted to a few realization chains, but grows increasingly when the chain number tends to infinity. As in practice, optimization of reservoir models is limited to a small number of iterations with respect to the number of gridblocks, the spatial variability is preserved. Last, the optimization processes are implemented on the basis of the Levenberg–Marquardt method. Although the objective functions, written in terms of Gaussian white noises, are reduced to the data mismatch term, the conditional realization space can be properly sampled.     

Volatile interactions with the lunar surface

The Moon is generally depleted in volatile elements and this depletion extends to the surface where the most abundant mineral, anorthite, features <6 ppm H₂O. Presumably the other nominally anhydrous minerals that dominate the mineral composition of the global surface—olivine and pyroxene—are similarly depleted in water and other volatiles. Thus the Moon is tabula rasa for the study of volatiles introduced in the wake of its origin. Since the formation of the last major basin (Orientale), volatiles from the solar wind, from impactors of all sizes, and from volatiles expelled from the interior during volcanic eruptions have all interacted with the lunar surface, leaving a volatile record that can be used to understand the processes that enable processing, transport, sequestration, and loss of volatiles from the lunar system. Recent discoveries have shown the lunar system to be complex, featuring emerging recognition of chemistry unanticipated from the Apollo era, confounding issues regarding transport of volatiles to the lunar poles, the role of the lunar regolith as a sink for volatiles, and the potential for active volatile dynamics in the polar cold traps. While much has been learned since the overturn of the “Moon is dry” paradigm by innovative sample and spacecraft measurements, the data point to a more complex lunar volatile environment than is currently perceived.     

Spinning with the dinosaurs: the fossil record of spiders

When most people hear the word 'fossil' they tend to conjure up images of giant dinosaurs such as Tyrannosaurus rex or shelled marine invertebrates. Prior to the Hollywood blockbuster movie Jurassic Park , which was based on recreating dinosaurs through extracting their DNA from fossil mosquitoes preserved in amber, few non-palaeontologists would entertain the notion that small, soft-bodied organisms such as insects occur in the fossil record. However, insects and spiders are common as fossils in amber, where they are often preserved with life-like fidelity, and they also occur to a lesser degree in carbonate rocks.     

借助于钻探现场数据库进行最优化钻进

本文提出了利用钻探现场数据库实现优化钻进的方法。该数据库通过钻进监测系统实时采集钻进参数,手工输入地层情况、钻进成本等在钻探过程中发生的其它数据,使钻进参数与地层情况及钻进成本联系起来,从而较容易地实现最优化钻进,特别是最小成本钻进。      

关于加强与ICDP合作的建议

1996年 2月 ,我国和德国、美国一道成为ＩＣＤＰ(国际大陆科学钻探计划 )的第一批成员国 ,宣告了ＩＣＤＰ的正式启动。通过和ＩＣＤＰ的合作 ,大大促进了我国大陆科学钻探计划的实施。大别 -苏鲁科学钻探项目得到ＩＣＤＰ财政、技术、人才培养和科学管理上的重要支持 ,是这一项目得以作为国家重大科学项目和ＩＣＤＰ项目及早顺利实施的重要原因之一。这是我们及时参加ＩＣＤＰ成功之点。回忆我们参加ＩＣＤＰ的初衷 ,除了促进大别 -苏鲁科学钻探项目尽早上马之外 ,最根本的目的还在于 ,通过参加ＩＣＤＰ(包括实施大别-苏