青藏铁路沿线负温填土长期动力力学特性试验研究_董亮.pdf

复杂艰险山区重大工程与环境DOI:10.15961/j.jsuese.202200694青藏铁路沿线负温填土长期动力力学特性试验研究董亮1，姚昌瑞2,3*，田爽2,3，王柯2,3，苏永华1(1.中国铁道科学研究院集团有限公司铁道建筑研究所，北京 100081；2.哈尔滨工业大学 土木工程学院，黑龙江 哈尔滨 150090；3.黑龙江省寒区轨道交通工程技术研究中心，黑龙江 哈尔滨 150090)摘要：为了评价冻土区路基的稳定性，本文对土体长期振动荷载下的动力特性进行研究，通过室内试验和理论分析相结合的手段对青藏铁路沿线填土的动力力学特性（动剪切模量和阻尼比）进行了分析。首先开展了室内固结不排水长期循环三轴试验，分析了不同负温、循环应力比对路基粉质黏土和地基砂土的动剪切模量和阻尼比等动力特性的影响。结果表明，路基粉质黏土的动剪切模量与温度呈现明显的负相关性，且随着循环应力比增大而呈现出较明显的增长趋势，阻尼比随着动剪切模量的增长而减小；地基砂土的动剪切模量和阻尼比受温度的影响与粉质黏土的响应规律呈现相同趋势，在温度为10 与循环应力比为0.2的相同条件下动剪切模量增至1.22倍，而阻尼比则减少到0.66倍。值得注意的是，砂土动剪切模量在循环应力比约为1时响应达到峰值，即动应力幅值达到围压时循环应力比增大，阻尼比增大而动剪切模量则呈现减小的趋势。随后在Wichtmann提出的高周循环模型基础上，建立了动剪切模量预测模型，能良好地反映动剪切模量在温度和循环应力比影响下，随振动次数变化的响应规律，通过拟合参数w0反映动剪切模量随循环应力比先增后减的规律，拟合数学关系显示长期振动次数约在13 000次或振动时长8 min以上时，土体的动力响应规律发生了明显变化。最后，基于Hardin-Drnevich双曲线模型对动剪切模量和阻尼比的试验结果进行拟合，得到了动剪切模量与阻尼比的函数关系式，从而能大致预测阻尼比随动剪切模量变化的趋势及范围，随着归一化剪切模量的增大阻尼比呈现出减小的趋势。关键词：青藏铁路；负温动三轴试验；动力力学参数；循环应力比；高周循环预测经验模型中图分类号：TU435文献标志码：A文章编号：2096-3246（2023）02-0050-09Experimental Study on Long-term Dynamic and Mechanical Properties of NegativeTemperature Fill Along QinghaiTibet RailwayDONG Liang1，YAO Changrui2,3*，TIAN Shuang2,3，WANG Ke2,3，SU Yonghua1(1.State Key Lab.for Track Technol.of High-Speed Railway,China Academy of Railway Sciences Corp.Ltd.,Beijing 100081,China;2.School of Civil Eng.,Harbin Inst.of Technol.,Harbin 150090,China;3.Heilongjiang Research Center for Rail Transit Eng.in Cold Regions,Harbin 150090,China)Abstract:In order to evaluate the stability of roadbed in frozen soil area,the dynamic shear modulus and damping ratio of fill along QinghaiTibet railway are analyzed by means of laboratory test and theoretical analysis.Firstly,the long-term consolidation undrained cyclic triaxial testswere carried out to analyze the effects of different negative temperature and cyclic stress ratio on dynamic shear modulus and damping ratio ofsubgrade silty clay and foundation sand.The results show that for subgrade silty clay,the dynamic shear modulus is negatively correlated withtemperature,and increases with the increase of cyclic stress ratio,and the damping ratio decreases with the increase of dynamic shear modulus.For foundation sand,the dynamic shear modulus and damping ratio show the same trend under the influence of temperature as that of silty clay,but the value of dynamic shear modulus is about 110 MPa higher than that of damping ratio under the condition of 10 temperature and cyclic收稿日期:2022 07 06基金项目:中国铁道科学院集团有限公司基金项目（2020YJ037）作者简介:董亮（1979），女，研究员，博士.研究方向：高速、重载及既有线铁路工程的理论和技术.E-mail：*通信作者:姚昌瑞，E-mail：ycr_网络出版时间:2023 02 15 00:00:00 网络出版地址:https:/ http:/http:/ 第 55 卷 第 2 期工 程 科 学 与 技 术Vol.55 No.22023 年 3 月ADVANCED ENGINEERING SCIENCESMar.2023stress ratio of 0.2,which is 1.22 times,and the damping ratio is 0.66 times.It is worth noting that the dynamic shear modulus of sand responds tothe peak value when the cyclic stress ratio is about 1,which means that when the dynamic stress amplitude reaches the confining pressure,the dy-namic shear modulus tends to decrease while the damping ratio tends to increase with the increase of the cyclic stress ratio.Then,based on thehigh cycle model proposed by Wichtmann,the prediction model of dynamic shear modulus was established,which can well reflect the responselaw of dynamic shear modulus with vibration number under the influence of temperature and cyclic stress ratio.The fitting parameter w0 reflectsthe law of dynamic shear modulus increasing first and then decreasing with cyclic stress ratio.The fitted mathematical relationship shows that thedynamic response law of soil changes significantly when the number of long-term vibrations is about 13 000 or the vibration duration is more than8 minutes.Finally,based on Hardin-Drnevich hyperbolic model,the experimental results of dynamic shear modulus and damping ratio were fit-ted,and the functional relationship between dynamic shear modulus and damping ratio was obtained,so as to roughly predict the trend and rangeof damping ratio with the change of dynamic shear modulus.With the increase of normalized shear modulus,the damping ratio tended to de-crease.Key words:QinghaiTibet railway;dynamic triaxial test;dynamic mechanical parameters;cyclic stress ratio;multiple-cycle forecasting em-pirical model 青藏铁路多年冻土区路基工程占累计长度占区段线路总长度的96.5%，青藏铁路沿线路基面临着多年冻土温度场变化，路基动静承载力的变化两大工程问题，直接影响到寒区土工构筑物的安全和使用12。路基长期受到车辆、列车等振动荷载及低温条件的耦合作用影响，冻土路基填土在长期动力荷载作用下会改变原有的结构以及颗粒组成，力学性能也随之改变。后期维护涉及到温度场稳定性和力学场稳定性的评估，对土体长期振动荷载下动力特性的研究是评价冻土区的路基的稳定性的关键3。土的动剪切模量和阻尼比是两个重要的土动力学特性参数，在工程场地稳定性和安全性评价及验算中必不可少4。Hardin等5首先使用剪切模量和阻尼来描述土的动力力学特性，为国内外学者所广泛采用610。而寒区轨道路基在考虑列车荷载时的动力响应分析需对冻土在长期反复荷载下的动剪切模量和阻尼比进行研究。据此，国内外学者对冻土的长期动力力学特性开展了大量试验研究：Zhou等11通过室内试验重点研究了冻融循环次数和冻结温度对冻土动力响应的影响，采用冻融衰减系数对随着冻融循环次数而增加的材料性能劣化程度进行评价，建立了描述不同条件下动剪切模量和阻尼比的演化特征理论模型，结果发现：在3种低温冻结条件下，动剪切模量和阻尼比的临界循环数不同，不同条件下弹性模量随加载周期数呈现两阶段的演化特征。Tian等12通过开展一系列循环三轴试验研究了颗粒材料的特性，试验考虑了包括冻融循环效应在内的诸多因素，并根据试验结果给出了动剪切模量和阻尼比的预测经验模型；然后，基于HardinDrnevich模型，提出了确定最大动剪切模量的拟合方程，绘制了统一的归一化动剪切模量曲线，并与试验结果进行了验证。Lin等13针对冻融循环、循环应力幅值、围压、加载次数和加载频率影响因素，开展了3组不排水动三轴试验，对长期反复循环荷载下饱和粉质黏土的弹性