Thermally unstable maghaemite and its palaeoclimatic significance in Chinese loess

Magnetite and maghaemite are the two main contributors to magnetic susceptibility in the Chinese loess/palaeosol sequence. Due to the close similarity in physical properties, early investigators treated them together as "magnetite". Utilising the property of thermally instability of maghaemite, we have been able to separate it from magnetite in loess and palaeosol samples from the upper parts of the Xifeng and Luochuan sections on the central Chinese Loess Plateau and compare its variation with depth and horizon. Our results indicate that thermally unstable maghaemite is relatively enriched in both 1) weakly weathered loess units and 2) towards the west, the direction of dust supply, suggesting that maghaemite is at least partially (coarse grains) of detrital aeolian origin while some pedogenic maghaemite (extra fine grains) occurs in the palaeosols. The physical meaning of magnetic susceptibility, therefore, needs to be reconsidered as a synthetic indicator reflecting the palaeoenvironment for both source area and deposition area. Thermally unstable goethite is a minor magnetic component of palaeosol samples, but it may play a significant role in determining characteristic magnetic remanence of weakly weathered loess samples, especially when one applies alternating-field cleaning.     

黄土震陷试验与评价

通过对兰州中川民用机场扩建工程场地黄土的震陷试验,研究探讨了该场地黄土的震陷特性,并对震陷进行了评价和分区预测。     

运营公路路基压实黄土的湿陷性研究

通过对临潼～渭南高速公路和312国道甘肃段不同交通量的路基黄土做比较研究,总结出黄土湿陷系数的变化规律。     

高填方路基工后沉降控制后处理技术

介绍一种高填方路基工后沉降控制后处理技术，针对高填方路基工程中代表性的高填方软土路基，采用无砂混凝土小桩复合地基后处理技术，实现工后变形控制的技术机理，并通过工程试验分析提出工程设计与施工的建议。     

铁路膨胀土路基工程病害与防治措施初探

我国膨胀土分布非常广泛,极易造成路基工程病害,若防治措施不当,对工程危害极大。结合西安南京铁路工程实践,从膨胀土路基出现的各类病害入手,根据膨胀土的工程特性及其病害产生的原因,提出了病害防治的措施及处理方法。     

黄土公路隧道衬砌开裂分析

衬砌开裂是黄土公路隧道普遍存在的病害。为了预防和处治衬砌开裂,保证黄土隧道结构的长期稳定性,针对甘肃省榆中县新庄岭黄土公路隧道衬砌开裂的病害特征,运用数值仿真、实测等手段分析了病害产生的机理和原因。结果表明,黄土浸水导致土体强度降低、变形增大,从而增大了围岩塑性区范围和变形压力,恶化了衬砌结构受力状况,使衬砌结构拱顶内侧及拱脚外侧被拉裂,进而使拱脚内侧被压裂。根据隧道病害状况,提出了采用环氧树脂嵌补及凿槽嵌入钢拱架法处治衬砌开裂的建议,为分析和处治黄土公路隧道衬砌开裂提供了依据。     

Test of magnetic susceptibility and grain-size age models of loess

Ages of the stratigraphic boundary MIS1/2 and MIS3/4 of the Yuanbu loess section in Linxia are used as the basis of the nodal control age. The age of MIS1/2 and MIS3/4 are obtained from the latest international research result—the climatic events recorded in the stalagmite in the Hulu Cave in Nanjing, that MIS1/2 is 11.5 kaB.P. and MIS3/4 is 59.8 kaB.P.. The ages of the two climatic events contain three nodal age control models (Model 1: 0 kaB.P.—59.8 kaB.P.; Model 2: 0 kaB.P.—11.5 kaB.P. and 11.5 kaB.P.—59.8 kaB.P.; Model 3: 11.5 kaB.P.—59.8 kaB.P.), which are used as the nodal control age separately. The deposition times of various stratigraphic horizons are calculated by using the magnetic susceptibility age model and grain-size age model, and then compared with each other. In addition, the AMS14C age, OSL age and the ages of YD and H events are compared with the ages of the corresponding horizons calculated by the three models of nodal control ages. From the analyses of lithologic characters and climatic stages it has been found that both the magnetic susceptibility age model and the grain-size age model have some defects. Because the accurate control ages are selected as the nodal points of the glacial period or interglacial period, the stratigraphic deposition times determined by the high resolution of magnetic susceptibility age model and grain-size age model approximate to the actual ages. As for the relative accuracy of the two age models, the magnetic susceptibility age model is more accurate than the grain-size age model.     

Test of magnetic susceptibility and grain-size age models of loess

Ages of the stratigraphic boundary MIS1/2 and MIS3/4 of the Yuanbu loess section in Linxia are used as the basis of the nodal control age. The age of MIS1/2 and MIS3/4 are obtained from the latest international research result—the climatic events recorded in the stalagmite in the Hulu Cave in Nanjing, that MIS1/2 is 11.5 kaB.P. and MIS3/4 is 59.8 kaB.P.. The ages of the two climatic events contain three nodal age control models (Model 1: 0 kaB.P.—59.8 kaB.P.; Model 2: 0 kaB.P.—11.5 kaB.P. and 11.5 kaB.P.—59.8 kaB.P.; Model 3: 11.5 kaB.P.—59.8 kaB.P.), which are used as the nodal control age separately. The deposition times of various stratigraphic horizons are calculated by using the magnetic susceptibility age model and grain-size age model, and then compared with each other. In addition, the AMS14C age, OSL age and the ages of YD and H events are compared with the ages of the corresponding horizons calculated by the three models of nodal control ages. From the analyses of lithologic characters and climatic stages it has been found that both the magnetic susceptibility age model and the grain-size age model have some defects. Because the accurate control ages are selected as the nodal points of the glacial period or interglacial period, the stratigraphic deposition times determined by the high resolution of magnetic susceptibility age model and grain-size age model approximate to the actual ages. As for the relative accuracy of the two age models, the magnetic susceptibility age model is more accurate than the grain-size age model.     

论陕西黄土高原地貌的景观美学属性

文章以陕西黄土高原地貌景观作为审美对象，提出了陕西黄土高原地貌景观的空间组合结构概念，在此基础上进行了黄土高原地貌景观的美学特征分析，认为应充分挖掘其旅游潜力，强化宣传，将自然和人文旅游景观组合推出，打造黄土高原地貌旅游品牌，丰富和深化陕北旅游的内容和内涵．     

一次性浇筑地铁长轨枕双侧沟式整体道床技术应用

地铁轨道道床浇筑混凝土时,水沟里的水容易通过水沟和道床两次浇筑混凝土的接触缝进入道床,对道床产生破坏,以致使道床混凝土松动,直接影响地铁线路的稳定。详细探讨了一次性浇筑地铁长轨枕双侧沟式整体道床技术的应用。