宁夏清水河下游晚更新世冰卷泥的发现及意义

在宁夏清水河下游(北纬37.4°,海拔1230m左右)晚更新世湖相地层中,发现了晚更新世晚期的冰卷泥,表明当时多年冻土的南界在宁夏一带可扩展到北纬37.4°附近,与现今相比,年均气温降低了8～9℃。青藏高原东北缘的弧形山地中,晚更新世强烈的构造抬升以及末次冰期的干冷气候最终导致清水河堰塞成湖并在湖泊边缘的沉积物中形成了冰卷泥。     

冻土路基温度场室内足尺模型试验

取用多年冻土地区代表性土类进行冻土路基室内足尺模型试验,建立伴有相变的路基非稳态温度场的控制方程,在空间域内用采用混合单元的有限元网格划分,在时间域内用有限差分格式划分的混合解法进行有限元分析。通过对观测结果进行数值模拟,验证了数学模型的正确性。进一步分析路基温度场的变化规律与野外观测结果的变化规律,其一致性说明了室内模型试验可以模拟野外冻土路基的真实情况,为研究冻土路基温度场的变化规律提供了可靠依据。     

多年冻土区桥梁抗震研究进展

本项研究从冻土场地效应、冻土对桥梁地震响应的影响、冻土与桥梁结构相互作用3个方面总结了冻土区桥梁抗震的多年研究现状,旨在推动多年冻土区桥梁抗震理论的发展.结果表明:冻土场地地震效应显著,目前多年冻土区桥梁抗震设计中未充分考虑冻土场地效应的影响,且缺乏相应的抗震规范依据.大量数值分析结果显示,季节与多年冻土层均对桥梁地震响应产生显著影响,而目前多年冻土区桥梁结构-冻土体系的耗能机制及破坏特征的研究不充分,仍需大量震害调查和试验研究.对于多年冻土区桥梁工程广泛采用的桩基础形式,冻土层的存在使得地震作用下桩-冻土相互作用机理复杂化,桩-冻土相互作用理论计算模型有待完善.桥梁抗震分析中未充分考虑冻土水热效应的影响(冻土随温度和含水量等水热特性变化引起的力学性能的改变).上述问题都是今后多年冻土区桥梁抗震研究需重点关注的方向.     

109国道冻土路基动力融化固结研究

在冻土路基非稳态温度场控制方程和融化固结理论模型的基础上,以109国道橡皮山地区典型路基土体粉质黏土制做的圆柱体力学模型为研究对象,采用有限元软件ABAQUS建立计算模型,并与室内试验结果对比,提出了土体冻结和融化过程中的温度场和融化沉降的变化规律.研究结果表明:在动荷载作用下,土样变形量随时间而增大,最终达到了稳定形式,而在不同幅值动荷载作用下,土样变形量存在明显差异,在一定的范围内,动荷载幅值大小对冻结土体融化速率作用有限.     

New discoveries on the effects of desertification on the ground temperature of permafrost and its significance to the Qinghai-Tibet Plateau

The desert and permafrost conditions of the Qinghai-Tibet Plateau are unique.However,the effects of desertification on the ground temperature of permafrost are currently unclear.Recently,understanding this problem has become more urgent because of increasing desertification on the plateau.For this reason,an observational field experiment was undertaken by the authors at Honglianghe on the Qinghai-Tibet Plateau.Thermistor ground temperature probes were used,and synchronized contrasting observations were made in an open area.Observations of the ground temperature of permafrost below sand layers with a range of thicknesses were made from May 2010 to April 2011.The sand layers were found to play a key role in the protection of the underlying permafrost.The ground temperature below a permafrost table overlain by a thick sand layer was lower than that of the average annual temperature for the natural ground surface,and the temperature drop was roughly constant at 0.2°C.During the warmer part of the year (May to September),the maximum temperature drops over the five months were 3.40,3.72,4.85,3.16,and 1.88°C,respectively.The ground temperature near a permafrost table overlain by a thin sand layer was also lower than that of the average annual temperature for the natural ground surface.However,in this case the average of the annual maximum temperature drop was significantly less,0.71°C.The scientific significance of our preliminary conclusions is not only to present an exploration of the interaction between desertification and permafrost,but also to provide new engineering ideas for protecting the permafrost in regions where construction is required on the Qinghai-Tibet Plateau.     

花石峡气候变化与多年冻土退化的关系预测

根据２１４国道沿线花石峡地区的气候变化特征和自然地理及地质水文条件，以该区长石头山连续多年冻土区４０ｍ深实测地温为基础，并以年平均气温升速率０．４℃／１０ａ为前提，对该区气候变化与多年并土退化的关系等进行了模拟预测。     

多年冻土地区不同入模温度下桩基温度场数值分析

考虑基桩传热、地基冻土、大气温度变化、混凝土中水泥水化热、混凝土入模温度变化及其相互作用,建立温度场数值分析模型.通过数值分析,研究了青藏铁路多年冻土区在寒季桩基的回冻过程,混凝土入模温度的提高及其对施工的影响.研究发现,混凝土水化热对地温的扰动随着回冻时间的增加而减少,回冻两个月后单桩桩身表面处地温平均值在入模温度5℃及12℃条件下分别达到了天然孔地温平均值的57.3%及53%,因此要等混凝土水化热对地温的热扰动完全消除再施工是不现实的.在实际工程中,只要基桩承载力满足施工要求即可.     

多年冻土地区湿度对水泥稳定砂砾强度的影响

多年冻土地区路面水泥稳定砂砾基层应用中，普遍存在基层上下松散、中部板结的“夹层”现象。在定性分析的基础上，通过模拟多年冻土地区基层下垫层的可能湿度状况养生的强度试验，定量分析了湿度对水泥稳定砂砾强度形成的影响，探讨了“夹层”现象产生的原因。研究得出，垫层含水量小于基层混合料最佳含水量时，对基层混合料强度形成有明显影响，抗压强度随垫层含水量的减小而降低；模拟湿度养生混合料的强度形成过程与标准养生基本相近，但14d后强度增长显著减缓；混合料形成骨架结构时，可以减轻水分损失对混合料后期强度形成的影响。结果表明：多年冻土地区特殊的湿度条件是水泥稳定砂砾基层出现“夹层”现象的主要原因，在基层施工中针对特殊湿度条件采取有效工程技术措施，可以避免“夹层”现象的出现。     

Analysis on Ground Temperature Changes and Thermal Effects of Duct-Ventilated Embankment of the Qinghai-Tibet Railway

1Preface TheStatekeyproject Ge’ermu LhasaSection ofQinghai TibetRailwayhasadistanceof550km runningoncontinuouspermafrostregions.Within thispart,permafrosthasthemostsignificant impactonthestabilityoftheroadbed.Thedouble effectsofglobalwarmingandtheconstructionof therailwaywillmakethepermafrostdegrade,causingthedesigningandconstructionofthe roadbedextremelydifficult[1].Thenaturalthermal regimesofpermafrostandgroundiceareimportant factorsthatwillaffectthestabilityofroadbed.Theselectionofroad…     

Discussion on Theoretical Analysis and Calculation of Settlement and Cracking in Subgrade in Permafrost of the Qinghai-Tibet Plateau

Thedeformingprocessofroadbedsbuilton altitudepermafrostisverycomplicated,whichis relatedtothemechanicsofnon saturatedsoil underlowatmosphericpressure.Thedeformation ofroadbedisalsocloselylinkedtowatermigration andthermalsieveeffect.NowbothinChinaand abroad,there’ssomeunderstandingofwater migrationandthermalsieveeffect.Butsofar,no researchwaseverdoneontheirimpactson roadbeddeformation,northere’sanyresearchon themechanicsofnon saturatedsoilunderlow atmosphericpressure.Thestabilityofroadbedis …