地基动力特性参数分析中的点峰法与多峰法

长期以来我国规定用点峰法分析动力基础线位移幅频响应曲线,但得出的地基阻尼比偏低,因而在动力基础设计规范中的阻尼比也偏低。经测试分析比较,提出多峰法可以提高地基阻尼比。多峰法已用于液压振动台基础设计,较为经济,多年来使用良好。现对两个方法的区别包括刚度予以说明。     

长江口深水航道治理工程抗软化加固现场试验研究

在波浪作用下,导堤下近表层的②2-0土极易软化,曾使工程严重受阻。为此采用排水板和基床预压的抗软化加固方案,对方案进行现场试验验证。为在远离岸边且台风时监测,首次采用多个固定测斜仪的连续沉降板法监测沉降,精度达到0.001 mm。首次将自动监测仪器长期放入海底。从监测一年多的沉降和孔隙水压力曲线看,不仅规律性好,无异常点,而且在定量上准确、稳定。监测期间经几次台风袭击,未发生突降。试验验证了抗软化方案是非常成功的。     

Ultimate Bearing Capacity of Subsoils to Marine Pipelines

- Based on the theory of limit analysis, the Finite Difference Method (FDM) is established for evaluating the ultimate bearing capacity of subsoils to bear the unburied pipelines. The analytical results of bearing capacity of the ideal clay is given. The approach to bearing capacity evaluation of cohesionless subsoils without surcharge is suggested. The results from this method are consistent with those obtained from model tests.     

南京砂的结构特性与地铁地基液化判别

与圆颗粒的标准砂相比较,片状结构的砂的动力特性更为复杂,用规范法进行液化判别时会误判。为了将砂土片状结构特性考虑到判别过程中,建议了一个更为合理的Ncr 的经验公式,并利用该公式对南京地铁玄武门-南京站区间的砂土层进行液化判别,该区间会发生中等程度为主的液化,最后,将液化判别结果与规范法和室内动力实验结果相比较,分析发现,在南京地铁进行液化判别时,必须考虑片状结构特性对于液化影响;同时,给出了平均液化势随深度的变化情况,以及考虑砂土结构特性对判别结果的影响系数随土层深度的关系,提高了判别的精度。     

某石油化工场地土层挥发性有机物的污染特征

在调查华北平原一个污染年限超过35年的石油化工场地时,采用便携式仪器土层测气方法,快速、准确地测定了场地内40多个钻孔不同深度土层中挥发性有机物(VOCs)的浓度。基于对场地地质水文地质条件的认识,以及通过对大量数据的分析对比和应用空间变异分析方法,得出了对场地土层介质中VOCs污染特征的如下认识:(1)土层VOCs浓度的垂向变化可概括为污染源淋滤型、包气带扩散污染型、地下水波动带污染型和混合污染型四种污染类型;(2)在包气带砂土层和粉土层中,VOCs的扩散规律可近似用指数模型描述;(3)包气带土层中VOCs优先积聚在渗透性强的砂性土层中,砂土层中VOCs浓度是粉土层中VOCs浓度的1.5～12倍,平均3.76倍;(4)土层VOCs浓度的水平变异性表现为包气带土层的变异性要比地下水波动带土层大,且水平变异性能在25m尺度内得到充分显示;而土层VOCs浓度的垂向变异性随地而异,变化复杂,很难用统一的一个量化尺度来表征。本文对这一典型污染场地的剖析,有助于从事污染场地调查人员认识我国华北平原石油化工类场地的污染特征,并为调查与治理类似污染场地提供技术依据。     

Ground improvement and foundation practice for Persian Gulf Bridge (causeway); Bandar Abbas Harbor–Qeshm Island

National Persian Gulf Bridge is a communication route between Bandar Abbas port and Qeshm Island located on the southern border of Iran. This causeway has important role for facilitating the transportation system between Qeshm Island and mainland, i.e., Bandar Abbas. Based on geotechnical and geological site investigation records, the bridge is located on the deposits with high seismic possibility and subsequently significant dynamic loading. Therefore, adequate substructure design of this bridge as an offshore project is realized as a major requirement. The geophysical and geotechnical investigations have been done to obtain the subsoil characteristics of the project site. For this purpose, 18 boreholes have been performed to do in situ tests and extract samples for laboratory testings. Data synthesis indicates that in the zones close to Qeshm Island and in the deeper parts of the sea, the strata is made of clay with loose sands and some depths, with silty sands. Hence, instability issues, including the low bearing capacity and the high differential settlement, are significant aspects in analysis and design of substructure for this project. Also, in this paper, the subsoil conditions have been studied from in situ tests such as standard penetration test (SPT) and cone penetration test (CPT) results in order to achieve an appropriate foundation system. Moreover, the necessity of the ground improvement of the site has been investigated to propose an efficient technique for safe and secure construction. Based on the analysis and methods screened, the vibro-replacement method is considered as a suitable and efficient ground improvement method for this project.     

考虑非线性的建筑物地基地震液化简化分析方法

本文在建筑物地基地震液化总应力简化判别方法的基础上，考虑地基土壤的剪切非线性及饱和砂土Martin非线性孔压增长模型，提出了估计建筑物地基孔压增长的简化分析方法，这一方法可用来判别地基的初始液化问题。     

低丘红壤深层水分的CASCADE模型应用与管理

低丘红壤深层水分对建立合理的耕作制度和旱季作物水分调控有重要意义。花生地定位试验实测数据表明:旱地土壤水分垂直梯度变化趋势基本表现为增长型,土壤含水量受降雨影响在40cm土层旱季明显大于雨季。采用CASCADE模型模拟了不同年型低丘红壤地区花生地土壤含水量的动态过程,各层次模拟值与实测值的平均绝对偏差<4 7%,模型可用于分析红壤水分的季节性变化规律和采取抗旱措施。还针对水分利用存在的问题,从工程措施、生物措施和生产措施三方面进行红壤旱地水分资源的有效管理,提高红壤地区降水资源与深层水分的利用率。     

Fractional crystallization of salts from subsoil brines – I

Solar evaporation studies of subsoil brines from three different locations of Gujarat State in India were undertaken. Evaporation of brines from their initial densities to 29-30°Be’ density was studied and the data were compared with those of sea brine. From the experimental data, the change in the quality of salts crystallized at various density levels with changing ionic composition of brines is explained theoretically and the ionic composition of an ideal brine and proper density ranges for the recovery of high quality salt are identified. This revised version was published online in July 2006 with corrections to the Cover Date.     

天水市城区砂砾石地基的变形特征和承载力分析

本文通过对天水市秦州、麦积两区砂砾石地基进行大量颗粒分析、动力触探、灌砂法试验及人工回填打入预制桩、人工挖孔灌注桩静载荷试验,并对其各项试验结果进行统计,系统地总结了天水城区砂砾石的分布特征、颗粒组成、物理力学性质;并通过粒径直方图统计分析阐明了藉河流域颗粒级配明显好于渭河流域,承载力特征值亦高于渭河流域的几个关键问题,并通过对工程实例的试验检测,对涉及的砂砾石地基的承载力特征值及变形模量,桩的极限端阻力标准值、极限侧阻力标准值应用实际问题进行了对比、讨论和分析,因此对工程质量的检测和设计应用有着重要意义,可供类似工程参考。