The role of megatides and relative sea level in controlling the deglaciation of the British–Irish and Fennoscandian ice sheets

Key external forcing factors have been proposed to explain the collapse of ice sheets, including atmospheric and ocean temperatures, subglacial topography, relative sea level and tidal amplitudes. For past ice sheets it has not hitherto been possible to separate relative sea level and tidal amplitudes from the other controls to analyse their influence on deglaciation style and rate. Here we isolate the relative sea level and tidal amplitude controls on key ice stream sectors of the last British–Irish and Fennoscandian ice sheets using published glacial isostatic adjustment models, combined with a new and previously published palaeotidal models for the NE Atlantic since the Last Glacial Maximum (22 ka BP). Relative sea level and tidal amplitude data are combined into a sea surface elevation index for each ice stream sector demonstrating that these controls were potentially important drivers of deglaciation in the western British Irish Ice Sheet ice stream sectors. In contrast, the Norwegian Channel Ice Stream was characterized by falling relative sea level and small tidal amplitudes during most of the deglaciation. As these simulations provide a basis for observational field testing we propose a means of identifying the significance of sea level and tidal amplitudes in ice sheet collapse.     

寒区大坝心墙土料冬季冻融与防控监测

两河口水电站是雅砻江干流规划开发中的中游控制性龙头电站,大坝为300米级砾石土心墙堆石坝。由于地处川西高原气候区,冬季气候寒冷干燥,大坝心墙土料填筑过程中面临着冻融问题的困扰。基于一个完整冬季的现场监测,系统分析了这一寒区大坝心墙建筑过程中砾石土、接触黏土土料温度变化规律、冻融特征与影响因素以及现有保温措施防冻效果。结果表明,无保温措施条件下,砾石土、接触黏土均出现了负温冻结现象,其中砾石土最大冻结深度达20 cm,接触黏土达14 cm,土料冻结持续时间不超过1个昼夜,为短时冻土。土料降温冻结过程以与外界大气对流换热过程为主,受气温、风速条件影响显著,波动范围较大,而升温融化过程以太阳辐射增温过程为主,与有效辐射起始时间密切相关,因此波动范围较小。监测期内,采用三布两膜保温材料覆盖可有效防止心墙土料冻结的发生,有、无保温材料覆盖条件下浅层土料最低温度可相差约5℃。结合监测结果和现场实际,建议将现有心墙防渗土料半幅填筑方式转换为全幅填筑,并研发轻质、憎水保温材料及其快速收放机械设备,以提高填筑作业进度、强化防冻效果。系统完整的现场实测结果,可为未来寒区水电大坝建设提供基础数据和参考。     

羌塘盆地岩石物理力学特性分析及其孔壁稳定技术

羌塘盆地是青藏高原年平均地温最低、冻土层相对较厚的地区,所处的水文地质及工程地质环境极其复杂。由于勘探程度低,深孔钻探的实钻资料较少,缺乏对该区深部岩层的岩石物理力学特性研究。因此,结合地球物理测井技术、取心和实验测试结果对QK-7孔钻遇地层岩石物理力学参数进行分析,并对冻土带异常孔隙水压力极复杂地层孔壁稳定泥浆工艺技术进行总结和探索,以期为羌塘盆地油气资源战略开发深孔钻探的顺利实施提供基础理论支持。     

绝壁悬挑钻探施工平台研制

本文以长江巫峡黄岩窝和板壁岩特大型危岩带勘查水平孔施工为例,探索研究出在无地面支撑基础条件、近似直立的岩石绝壁上建设钻探施工平台的施工方案。采用斜撑和锚拉结构受力体系,通过力学分析和计算,形成了一套较完整的施工工艺,对解决类似的工程施工平台难题具有一定的指导和参考价值。     

金牛山矿山环境治理设计与施工实践

通过对烟台市牟平区金牛山矿山采矿历史遗留的老采坑硐（井）、塌陷带和采空区等综合恢复治理,详细介绍了采空区充填注浆的设计和施工工艺,消除了地质灾害隐患,改善了地质环境。该工程设计及成功实践对类似金矿塌陷带和采空区治理有很好的指导和借鉴作用。     

北京东坝中路红松园基坑支护施工组织方案

北京东坝中路红松园工程由多种建筑形式组成,根据其周边环境及岩土工程条件、地下水情况,基坑支护设计方案分5个区域采用4种不同的支护形式,2个区域采用土钉墙+预应力锚杆护坡桩方案,另外3个区域分别采用预应力锚杆护坡桩方案、挡土墙+预应力锚杆护坡桩方案、锚杆复合土钉墙方案。本文还介绍了基坑降水及抗浮设计情况以及基坑支护施工技术方案。     

河南信息南广场基坑支护技术

河南信息南广场基坑支护工程,分别采用了桩锚支护、微型桩+预应力锚杆复合土钉墙支护和微型桩复合土钉墙支护体系,具体介绍了护坡桩、预应力锚索、微型桩、预应力锚杆、土钉墙、花管桩设计施工方案以及基坑监测变形异常后采用的应急处理方案,技术成果为类似工程的设计施工提供参考。     

Processes and mechanisms of multi-collapse of loess roads in seasonally frozen ground regions: A review

Usually, the collapsible loess widely distributed across the world can serve as a type of foundation soil that meets its strength requirement after dense compaction and elimination of collapsibility. However, many problems such as cracks and differential settlement still occur in loess roads in the seasonally frozen ground regions after several years of operation. Many studies have demonstrated that these secondary or multiple collapses primarily result from the repeatedfreezing-thawing, wetting-drying, and salinization-desalinization cycles. Therefore, we conducted a research program to (1) monitor the in-situ ground temperatures and water content in certain loess roads to understand their changes, (2) study the effects of freezing-thawing, wetting-drying, and salinization-desalinization cycles on geotechnical properties and micro-fabrics of compacted loess in the laboratory, and (3) develop mitigative measures and examine their engineered effectiveness, i.e., their thermal insulating and water-proofing effects in field and laboratory tests. Our results and advances are reviewed and some further research needs are proposed. These findings more clearly explain the processes and mechanisms of secondary and multiple collapse of loess roads. We also offer references for furtherstudy of the weakening mechanisms of similar structural soils.     

资源02C卫星P／MS相机内方位几何标定方法研究

为解决国产资源02C卫星影像相机内方位几何标定问题,提出了一种利用公众地理信息数据进行高精度相机内方位在轨几何标定的方法。该方法利用资源02C卫星影像与公众地理信息数据自动配准获取的海量地面控制点并进行附加自检校参数的最小二乘平差,实现了资源一号02C卫星P／Ms相机的内方位标定,精度可以达到子像素级。     

Long‐term seismic performance of reinforced concrete bridges under steel reinforcement corrosion due to chloride attack

This work presents a new seismic evaluation methodology for corroded reinforced concrete bridges on the basis of nonlinear static pushover analysis. Corrosion of steel reinforcement by chloride attack is considered. At the material level, the effects of corrosion are considered by modeling the degradation of the mechanical properties of steel reinforcement, softening of cover concrete under compression, degradation of core concrete due to confinement steel corrosion, and reduction of bond strength between concrete and steel reinforcement. At the structural level, the effects of corrosion on both flexural behavior and shear behavior, and their interaction are considered. Eleven bridges of various structural types in Taiwan that are located within 6.5 km of their nearest coastline are analyzed to identify their long‐term seismic performance. Relationships between the yield and collapse peak ground accelerations (PGAs), and service time and corrosion level are established for each bridge. Analysis results show that chloride corrosion starts in 2–32 years. The transverse steel reinforcement typically starts corroding before the longitudinal steel reinforcement, as the former has a thicker cover. Research results show that collapse PGA reduces by 0.94% or 1.23% per 10 years when the mean value plus 1 or 2 standard deviation of the collapse PGA values are considered, respectively. Therefore, we suggest increasing the design PGA from 4.70% to 6.15% for a bridge adjacent to a coastline to ensure adequate long‐term seismic performance for 50 years, the typical design life span of a regular bridge. Copyright © 2013 John Wiley & Sons, Ltd.