Impact Analysis for Safety Prevention and Control of Special-Shaped Shield Construction Closely Crossing Multiple Operational Metro Tunnels in Shallow Overburden

Geotechnical and Geological Engineering - With the improvement of the urban rail transit network, crossing construction has become an inevitable situation in the construction of subway tunnels. The...     

中国东北地壳结构的地震层析成像

中国东北地区自晚古生代晚期以来,受古亚洲洋、蒙古—鄂霍茨克洋、太平洋构造域的叠加作用,壳幔结构极为复杂。本文收集中国东北地区国家地震台网接收的100 980个P波和91 030个S波到时数据,采用地震走时层析成像方法获得了该地区地壳P波和S波速度结构,进而获得了泊松比结构,用以探讨复杂的地壳结构。成像结果显示：中国东北地区地壳地震波速度结构呈明显的横向不均匀性,不同构造单元和构造单元内部都存在不同程度的不均匀性。松辽盆地整体上浅层地壳以低速异常为主,尤其是S波速度,但部分区域分辨率较低,中下地壳存在较大范围高速异常,推测与太平洋俯冲、后撤导致的岩石圈拆沉和热物质上涌等动力学过程有关;北部的大兴安岭重力梯级带和长白山一线主要表现为低速异常,表明具有大范围的岩浆作用,广泛岩浆作用为固体矿产资源的形成提供热源或物源;长白山、五大连池等近代活动的火山下方部分地壳区域均表现了较强低地震波速度和高泊松比异常结构特征,表明仍存在活动的可能。     

盐间页岩油韵律层地震响应模拟及页岩薄储层厚度预测

江汉盆地潜江凹陷潜江组页岩油储层的地质结构为韵律背景下的页岩薄层,由于地震分辨率的限制,常规地震勘探方法难以精确描述盐间页岩油薄储层厚度的空间展布。因此,应用现有地震资料,探索适用于韵律结构中页岩薄层的地震预测方法具有重要意义。本文通过地震传播矩阵方法计算并分析研究区目标韵律层的地震响应特征,系统模拟并分析非均匀薄互层结构中页岩薄层的厚度、纵波速度等变化时地震波的反射动力学特征,发现地震反射波形的振幅和相位随非均匀页岩薄层的纵波速度和厚度的变化产生明显的变化,这些变化是本文页岩薄层厚度预测的基础。结合测井分析构建韵律层地质地球物理模型,模型空间考虑了页岩薄层纵波速度和厚度共99种组合变化的情况。通过求取目标层实际地震反射波形与构建的模型空间中地震波形的最佳匹配,提出基于反射波形的页岩薄储层厚度的地震预测方法,预测研究区页岩薄层厚度变化范围为5~20 m,并且由西南向东北呈增加趋势。预测页岩薄层厚度与测井解释具有较高的一致性,验证了本文地震预测方法的有效性。     

Quantitative identification of cutoff wall construction defects using Bayesian approach based on excess pore water pressure

Acta Geotechnica - Cutoff wall has been widely used as a barrier to prevent the migration of contaminants in aquifers. Hydraulic impermeability and homogeneity should be ensured before operation....     

Carbon,nitrogen and phosphorus coupling relationships and their influencing factors in the critical zone of Dongting Lake wetlands,China

Wetland is a transition zone between terrestrial and aquatic ecosystems, and is the source and sink of various biogenic elements in the earth’s epipelagic zone. In order to investigate the driving force and coupling mechanism of carbon (C), nitrogen (N) and phosphorus (P) migration in the critical zone of lake wetland, this paper studies the natural wetland of Dongting Lake area, through measuring and analysing the C, N and P contents in the wetland soil and groundwater. Methods of Pearson correlation, non-linear regression and machine learning were employed to analyse the influencing factors, and to explore the coupling patterns of the C, N and P in both soils and groundwater, with data derived from soil and water samples collected from the wetland critical zone. The results show that the mean values of organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in groundwater are 1.59 mg/L, 4.19 mg/L and 0.5 mg/L, respectively, while the mean values of C, N and P in the soils are 18.05 g/kg, 0.86 g/kg and 0.52 g/kg. The results also show that the TOC, TN and TP in the groundwater are driven by a variety of environmental factors. However, the concentrations of C, N and P in the soils are mainly related to vegetation abundance and species which influence each other. In addition, the fitted curves of wetland soil C-N and C-P appear to follow the power function and S-shaped curve, respectively. In order to establish a multivariate regression model, the soil N and P contents were used as the input parameters and the soil C content used as the output one. By comparing the prediction effects of machine learning and nonlinear regression modelling, the results show that coupled relationship equation for the C, N and P contents is highly reliable. Future modelling of the coupled soil and groundwater elemental cycles needs to consider the complexity of hydrogeological conditions and to explore the quantitative relationships among the influencing factors and chemical constituents.     

Chronological and geochemical studies of the Middle Neoproterozoic mafic rock and turbidite in the Dahongshan orogenic belt on the northern margin of the Yangtze Block: Implications for the evolution of the back-arc basinSCIEI北大核心CSCD

扬子北缘~820Ma可能记录了从挤压环境向伸展环境的重要转换,是解决扬子新元古代演化争议的关键时间节点。本研究在扬子北缘大洪山造山带圆潭地区识别出一套基性岩和浊积岩组合。其中基性岩全岩Sm-Nd等时线年龄为845Ma±81Ma(MSWD=1.5),浊积岩碎屑锆石年龄谱包括四个主要峰值年龄(~835Ma、~1597Ma、~2002Ma、~2482Ma)和两个次要峰值年龄(~2680Ma、~2934Ma),综合前人研究成果将浊积岩的形成时代约束在835~820Ma。浊积岩与花山群的形成时代一致,应代表花山群的北向延伸。浊积岩的物源来自扬子北缘桐柏-大别地区,不同于前人对花山群的分析结果,指示花山群可能具有多个物源。以上地层碎屑锆石年龄谱和地层层序特征与弧后盆地相似。本研究基性岩样品具有低的SiO_(2)(45.41%~50.29%)、K 2O(0.03%~1.49%),高的TiO_(2)(1.42%~3.03%),和低的U/Th(0.15~0.29)、Th/Zr(0.003~0.011)和Nb/Y(0.059~0.147)以及正的εNd(t)(+1.18~+1.57),类似N-MORB地球化学特征。基性岩来自于软流圈,经历<3%部分熔融而生成,并在上升过程中受到了一定程度的地壳混染。综合以上分析,本文认为这些基性岩和浊积岩共同构成一套弧后背景环境岩石组合。