Engineering geological parameters affecting the response of Τhessaloniki's urban fill to a major seismic event

In urban areas where there has been continuous occupation of the land for centuries, there are likely to be large areas of filled ground. Fills may have arisen inadvertently from the rubble of demolished buildings and the slow accumulation of refuse. Old urban fills of this type may contain soil, rubble, refuse and even whole parts of past constructions. Despite the fact that areas covered with such deposits are generally prone to severe problems, especially under conditions of dynamic loading, still their influence, as a foundation material on the seismic behaviour of modern buildings is practically unpredictable.Thessaloniki is an old historical city of Macedonia, Greece with no less than 2300 years of continuous urban evolution. A thick and heterogeneous layer of artificial deposits covers the biggest part of the historical centre of the city, as is the case for many old historical cities. The presence of this extensive formation influences the urban development, as it constitutes the foundation of the majority of the buildings of the historical centre, and its investigation is essential for most of the major constructions proposed. The complexity and heterogeneity of Thessaloniki's fill makes the assessment of its engineering behaviour a rather complicated task. This is due to the big range of values of accumulated geotechnical data but also to the fact that these data have been produced by unrelated methods and applied tests.The aim of this paper is to assess the engineering performance of Thessaloniki's fill based on its behaviour as foundation material to a major seismic event. This is carried out by the evaluation of the influence of engineering geological parameters to the damage distribution of the 1978 earthquake, based on the official database which recorded the condition of all the buildings of the historical centre. The statistical elaboration of the damage distribution was carried out following a classification scheme for the fill, based on the fill's classes produced by this scheme, the fill's thickness and the combination of both.The results are given in terms of damage ratios i.e. the ratios of the number of buildings in each damage status per total number of buildings inspected. The correlation of the engineering response with the thickness of the fill showed that there is a significant increase of the percentage of damaged buildings with increasing thickness. However, further analysis of these results showed that the above increase does not apply to all classes equally, which actually suggests that different parts of the fill behave differently in respect to the fill thickness. These results clearly show that a classification scheme and the determination of the boundary conditions should be used as a combined tool from an engineering geological point of view, in order to form a basis for the better understanding of the engineering behaviour of such deposits, the interpretation of geotechnical data and the design of more sophisticated investigations.     

某机场高填筑体下伏地基土变形评价

某机场工程土石方总量超过4×107m3,填方边坡最大高度102m。填方地基为砂层、卵石层、粉质粘土、砾岩及泥岩等组成的第四系河流沉积,结构复杂,物理力学特性变化大,场地附近有3条大的活动断裂,地震烈度为 度。本文在研究了区域地质背景、填筑材料和施工方法的基础上,对九黄机场高填筑体下伏地基土的变形进行了分析评价。     

用变分方法估算淮河流域总体输送系数

利用2001年6～7月间在安徽肥西的边界层观测资料,利用变分方法计算地面动量通量和感热通量,进而分别估算该处动量总体输送系数和感热总体输送系数。用变分方法计算的地面粗糙度为0.03m。在中性条件下,10m高处平均动量总体输送系数和感热总体输送系数分别为4.83×10-3和3.81×10-3,比值是1.27。总体输送系数具有明显的日变化特征,中午时段最大,夜晚最小;总体输送系数与大气稳定度存在明显关联,文中给出它们之间的拟合关系式;随着高度的增加总体输送系数减少,但减少幅度逐渐变小。     

漏失量较大地层“戴帽”固井技术

对漏失量较大的岩溶地层进行“戴帽”固井时,由于打完水泥浆后注入替浆水的过程中及后期稳定液面变化很容易造成水泥浆被稀释,前者直接导致固井失败,后者又受很多因素的影响导致重叠管环空内没有水泥浆或者被稀释而形不成水泥塞。本文主要从钻杆下入位置以及注入替浆水的过程中和后期稳定液面变化这几个方面总结“戴帽”固井的关键,并结合工程实例提出了一些人为控制方法来提高固井的成功率。     

吹填软土低位真空预压室内试验及其数值模拟

以天津滨海新区临港工业区吹填软土为试验材料,以普通型竖向排水板、改进型竖向排水板及改进型横向排水板进行室内低位真空预压试验。结果表明,利用普通型竖向排水板进行低位真空预压试验,在真空-堆载联合作用下,28 d表层土体强度达到10 kPa,但中间土体强度偏低,整体呈两边硬中间软的夹心层;以改进型竖向排水板进行低位真空预压试验,前10 d土体强度增长与普通型竖向排水板试验接近,后期土体强度增长明显比前者快,28 d表层土体强度达到12 kPa,中间土体强度略有提高,但整体均匀性仍较差;以改进型横向排水板进行低位真空预压试验,28 d表层土体强度达到11 kPa,强度增长比改进型竖向排水板试验慢,但中部土体强度和整体均匀性均优于改进型竖向排水板试验。基于上述试验成果,运用有限元模拟低位真空预压试验过程,计算沉降量和孔隙水压力并与实测数据对比,发现两种竖向排水板试验计算结果与实测数据吻合较好,改进型横向排水板试验稍差,但基本上都能反映低位真空预压过程中土体沉降量和孔隙水压力变化趋势。     

高填方边坡失稳时间预测的实用模型

建立一种准确可靠的方法来预测高填方边坡因蠕变破坏而发生滑坡的时间是困难的,但对防止财产和生命损失又至关重要。在总结高填方土质边坡蠕变破坏过程中的位移、速度特征的基础上,通过改进Saito模型的应变率公式,提出了基于改进人工蜂群算法的滑坡中短期预测的实用模型。将进入加速变形阶段后的滑坡位移时间序列作为输入,通过人工蜂群算法反演实用模型参数后输出预测的滑坡时间。以3个高填方滑坡为实例,应用滑坡位移监测点的测量数据,验证了该方法在滑坡时间预测上的准确性和可靠性。同时,将该方法预测的滑坡时间结果与传统的Saito系列模型预测的滑坡时间结果进行了比较。结果表明,在通过滑坡位移的时间序列进行滑坡时间预测时,所提出的实用模型比两种Saito模型更准确可靠。     

Recent Advance and Prospects in the Structure and Thermal Elastic Properties of Lower Mantle Minerals

Lower mantle, ranging from 660 km to 2 890 km depth, occupies 49.2% of the Earth by mass and is at extremely high pressure and temperature conditions. Experimental studies on the physical properties of the lower mantle minerals, particular the structure, density, and sound velocity, etc., are important to understand the structure, composition, and dynamic behavior of the region. Here we summarize the recent experimental results on the structure and thermal equation of states of the lower mantle minerals, including bridgmanite, ferropericlase, CaSiO₃-perovskite, and silicate post-perovskite, and discuss the effect of pressure, temperature, composition, and Fe-spin transition on the density and bulk sound velocity of those minerals. This review aims to provide new insights into the lower-mantle structure and chemistry and help to understand the observed velocity anomalies in the lower mantle.     

高黏性新近吹填淤泥真空预压试验颗粒流宏微观分析

为了从宏观和微观角度探讨颗粒组成对淤堵层形成机理和加固效果的影响规律,依托天津某新近吹填造陆工程,先进行直排式真空预压法室内模型试验,然后基于颗粒流理论和PFC2D程序,在解决模拟过程中颗粒级配和孔隙比的二维转换、排水边界的等效模拟、真空渗流场的施加等问题后,对模型进行有效的模拟计算,进而将结果推广,开展了不同颗粒组成吹填土真空预压试验的颗粒流模拟,总结了排水速率变化及颗粒运移规律。结果表明:对吹填土真空预压过程进行二维颗粒流数值模拟是有效可行的;真空预压过程中细颗粒沿渗透路径迁移,在沿途滞留,导致渗透路径变短变窄,从而形成淤堵层;对于高黏性新近吹填淤泥,在相同真空荷载作用下,黏粒质量分数越大,初期排水速率增长越快,并且随着土体不均匀系数的提高,淤堵层变得易于形成且致密,排水速率衰减越快;粉粒质量分数越大,土体孔隙率变化越均匀,尤其当粉粒质量分数大于黏粒质量分数时,真空预压加固效果有明显改善。     

深厚淤泥地基中高路堤桥台基桩工作性状的现场实测与分析

针对位于深厚淤泥地基上的高路堤桥台的冲孔灌注桩,进行了1.5 a的现场实测,测试了修筑承台前、修筑桥台期间、邻近过渡段的路基填土期间、过渡段的路基填土期间及跨梁修筑后的桩身应变和桩侧土体孔隙水压力,也测试了基桩的挠曲变形和桥台的倾斜变形,基于实测结果对基桩的受力变形性状进行研究。结果表明,桥台基桩在承受上部结构荷载以前就产生了压缩变形;在上部桥台和台后填土的共同作用下,桩身前后侧的轴向应变虽都表现为压应变,但应变值相差较大;台后路基填土完成后,桩身最大负弯矩出现在淤泥层浅部,最大正弯矩出现在软硬土层交界处,桥台发生较小倾斜;跨梁的修筑使桥台台身又恢复到竖直状态。     

渗流作用下吹填土微观结构特征定量化研究

吹填土的工程性状受土体的物质组成和微观结构综合影响,而微观结构在以往的研究中涉及较少。以天津滨海地区吹填土为研究对象,进行室内渗流作用下吹填土的沉降试验。利用图像处理技术对土体的微观结构作定量分析,讨论天津滨海地区吹填土结构单元体、孔隙的大小、丰度和定向频率等评价指标在渗流作用下的变化情况及形成机理,可为评价吹填土的工程地质性质提供一定的理论依据。试验分析表明：随着渗流压力的增大,土中结构单元体从较为松散的状态转变为团聚状态,呈现出不同程度的扁圆形,但没有明显定向性;土体中的孔隙由于失去平衡,变为小而紧密的球形体,孔隙定向角集中分布在0°～10°。