船式支护在基坑中的应用     

何世达  徐忠  李燕枫 《岩土工程技术》2021,(1)

在深厚软土地区的基坑,对基坑底软土进行搅拌加固形成强度较高的底板而保证坑底稳定,侧壁采用支护桩支护保证侧壁的稳定使其不倾倒,支护桩与加固底板两者共同作用形成的船状结构支护体系类似轮船的船侧壁及船底板,以保证基坑的稳定。结合具体的工程实例,介绍了船式支护的侧壁及底板的设计方法。工程案例成功实施,监测结果表明,船式支护既可避免支护桩嵌固深度过长,又利于软土的土方施工及工程桩的保护,是安全可靠的,对类似工程有一定的参考意义。  相似文献   

Numerical analysis of the symmetric methods     

Ji-Hong Xu  A-Li Zhang 《Astrophysics and Space Science》1995,225(2):289-297

Aimed at the initial value problem of the particular second-order ordinary differential equations,y =f(x, y), the symmetric methods (Quinlan and Tremaine, 1990) and our methods (Xu and Zhang, 1994) have been compared in detail by integrating the artificial earth satellite orbits in this paper. In the end, we point out clearly that the integral accuracy of numerical integration of the satellite orbits by applying our methods is obviously higher than that by applying the same order formula of the symmetric methods when the integration time-interval is not greater than 12000 periods.  相似文献   

黑龙江省与呼伦贝尔盟土地类型的划分及其分布规律   总被引：1，自引：0，他引：1  

赵松乔  戴旭  申元村  杨柳林 《地理研究》1982,1(1):49-57

本文就土地研究的几个主要概念,即土地、土地分类、土地分级作了简要讨论,并结合黑龙江省及呼伦贝尔盟的具体条件,对为农、林、牧业服务的土地分类原则进行了初步探讨,还拟订了该区土地分级系统——土地类和土地型,及适合于大比例尺制图的土地组。在此基础上,将全区分为18个土地类、71个土地型。文章还从水平带性、垂直带性和土地结构三个方面,介绍了该区土地类型分布的一般规律。  相似文献   

短周期仪器记录在远震分析中的应用     

许康生 《地震地磁观测与研究》1992,13(2):15-19

地震泼由多种频率成份组成,在其传播过程中。由于地球介质的滤波作用,随着传播距离的增大。高频成份逐渐被衰减。周期越大的成份传播越远。因此,在地震观测上,不同频带的地震仪用于观测不同震中距范围的地震,使仪器较好地响应,就我国台网而言,短周期仪用于地方震、近震的监测,中长周期仪和长周期仪用于远震,极远震的监测,其中长周期仪偏重于记录极远震。但作者在实际分析工作中注意到,短周期仪的记录应用于远震,极远震的分析,显示出独特的作用,充分挖掘和利用短仪资料,将会更加丰富远震、极远震的震相资料。本文以高台地震台的资料为依据,从震中距和震级角度,与中长仪和长仪作比较,对短仪记录远震、极远震的震相及特征作了统计分析与初步探讨,并对新疆地区“影区”地震S波的记录、日本地区地震_PPcP等震相的出现提出了现象的存在,给出了相应的观测结果,以待步一步研究。  相似文献   

内蒙古正镶白旗碎斑熔岩岩石学特征及其岩相划分   总被引：4，自引：0，他引：4  

赖绍聪  徐海江 《岩石学报》1990,6(1):56-65

白旗碎斑熔岩为不规则穹状体,可分为边缘玻质碎斑熔岩、过渡霏细碎斑熔岩、中心粒状碎斑熔岩和根部花岗斑岩四个岩性带。从玻质碎斑熔岩到粒状碎斑熔岩,斑晶碎裂度逐渐减弱,珠边结构在粒状碎斑熔岩中最发育,根部花岗斑岩与正常次火山岩相近。碎斑熔岩中钾长石有序度低,指示了岩石高温成因特征。白旌碎斑熔岩属太平洋岩系钙碱质系列,原始岩浆由来源于上地幔和下地壳熔体的混熔作用形成。  相似文献   

云南大地热流及地热地质问题   总被引：46，自引：5，他引：41       下载免费PDF全文

汪缉安  徐青 《地震地质》1990,12(4):367-377

本文报道了云南20多个大地热流测试数据。据热流分布特点并参考前人有关资料,结合地球物理测深资料、岩石热物性与放射性生热率测试数据,对各区地壳深度范围的温度、热流配分组成作了粗略分析,划分出各有特征的若干地质-热流区。云南普遍地热偏高(滇东南小范围除外)的主要原因是新构造运动强烈;怒江以西近代岩浆活动亦强烈,具有典型的板块交汇带的基本地热特点  相似文献   

突发性地面增温与临震前兆——以1988年澜沧、耿马7.6,7.2级地震为例   总被引：6，自引：0，他引：6       下载免费PDF全文

徐秀登  强祖基  赁常恭 《地震地质》1990,12(3):243

本文通过较多的地面温度资料分析,认为1988年11月6日澜沧、耿马地震前几天,震区及其周围大范围的突发性地面增温异常是一种临震前兆,总结了增温异常的时空演变规律与地震活动的关系,并对其形成机制提出初步想法  相似文献   

青藏高原腹地湖泊沉积对第四纪晚期古季风变化的响应   总被引：2，自引：0，他引：2  

胡东生  张华京  徐冰  李炳元  孔照辰  温景春 《干旱区地理》2006,29(4):483-489

通过对青藏高原腹地的综合科学考察和对中心钻孔岩芯剖面的最新研究,用层序地层学与年代地层学和气候地层学相结合的方法,分辨出可可西里地区湖泊沉积记录(孔深7.25 m)的第四纪晚期距今3万余年以来的古气候变化,沉积物磁化率等因子综合表征的高原古季风变化是波动发展的,发生在仙女木期地质环境事件中的季风活动具有强烈暴发的特点,是高原季风发展中的突变事件,而且地表热点效应对其起到了激发作用。综合分析的研究成果表明,它的变化频谱与激变因子及其运行机制是伴随着青藏高原地质效应的演变而发展的,为研究第四纪冰消期以来的气候变化提供了新的信息。  相似文献   

Na depletion in modern adakites via melt / rock reaction within the sub-arc mantle     

X.L. Xiong  B. Xia  J.F. Xu  H.C. Niu  W.S. Xiao 《Chemical Geology》2006,229(4):273-292

Interaction between slab-derived melt and mantle peridotite and the role of slab melt as a metasomatizing agent in the sub-arc mantle is being increasingly recognized. Adakite, the slab melt erupted on the surface, usually exhibits anomalously high MgO, CaO, Cr and Ni contents that indicate interaction with mantle peridotitite. Here we note that Cenozoic adakites have Na₂O contents below 5.8 wt.% with ∼95% samples lower than 5.0 wt.%, and are generally depleted in this component relative to experimental basalt partial melts (mostly beyond 5.0 wt.% and up to 9.0 wt.% Na₂O) produced under 1.5-3.0 GPa conditions that are most relevant to adakite production. We interpret the adakite Na depletion to be also a consequence of the melt / rock reaction that takes place within the hot mantle wedge. During ascent and reaction with mantle peridotite, primary adakite melts gain mantle components MgO, CaO, Cr and Ni but lose Na₂O, SiO₂ and perhaps K₂O to the mantle, leading to Na-rich mantle metasomatism. Selective assimilation of predominately mantle clinopyroxene, some spinel and minor olivine at high T/P has been considered to be an important process in producing high-Mg adakites from primary low-Mg slab melts [Killian, R., Stern, C. R., 2002. Constraints on the interaction between slab melts and the mantle wedge from adakitic glass in peridotite xenoliths. Eur. J. Mineral. 14, 25-36]. In such a process, Na depletion in the assimilated melt is the result of dilution due to the increase in melt mass. Phase relationships in the reaction system siliceous melt + peridotite and quantitative calculation suggest that assimilation of mantle clinopyroxene, olivine and spinel and fractional crystallization of sodic amphibole and orthopyroxene, under conditions of moderate T/P and increasing melt mass, is also an important process that modifies the composition of adakites and causes the Na depletion.  相似文献   

Cs and Cl NMR spectroscopy and molecular dynamics modeling of Cs and Cl complexation with natural organic matter     

Xiang Xu 《Geochimica et cosmochimica acta》2006,70(17):4319-4331

Interaction of dissolved aqueous species with natural organic matter (NOM) is thought to be important in sequestering some species and enhancing the transport of others, but little is known about these interactions on a molecular scale. This paper describes a combined experimental ¹³³Cs and ³⁵Cl nuclear magnetic resonance (NMR) and computational molecular dynamics (MD) modeling study of the interaction of Cs⁺ and Cl⁻ with Suwannee River NOM. The results provide a detailed picture of the molecular-scale structure and dynamics of these interactions. Individual NOM molecules are typically hundreds to thousands of Daltons in weight, and on the molecular scale their interaction with small dissolved species can be investigated in ways similar to those used to study the interaction of dissolved aqueous species with mineral surfaces. As for such surface interactions, understanding both the structural environments and the dynamics over a wide range of frequencies is essential. The NMR results show that Cs⁺ is associated with NOM at pH values from 3.4 ± 0.5 (unbuffered Suwannee River NOM solution) to 9.0 ± 0.5. The extent of interaction increases with decreasing CsCl concentration at constant pH. It also decreases with increasing pH at constant CsCl concentration due to pH-dependent negative structural charge development on the NOM caused by progressive deprotonation of carboxylic and phenolic groups. The presence of NOM has little effect on the ¹³³Cs chemical shifts, demonstrating that its local coordination environment does not change significantly due to interaction with the NOM. Narrow, solution-like line widths indicate rapid exchange of Cs⁺ between the NOM and bulk solution at frequencies of >10² Hz. The MD simulations support these results and show that Cs⁺ is associated with the NOM principally as outer sphere complexes and that this interaction does not reduce the Cs⁺ diffusion coefficient sufficiently to cause NMR line broadening. The ³⁵Cl NMR data and the MD results are consistent in demonstrating that there is no significant complexation between Cl⁻ and NOM in the pH range investigated, consistent with negative structural charge on the NOM.  相似文献