青藏粉土-玻璃钢接触面力学特性直剪试验研究
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摘要
青藏直流±400 kV输变电工程中采用表面光滑的玻璃钢覆盖基础表面,以减少切向冻胀力对基础的冻拔作用。过去的研究鲜有涉及土体特别是冻土与玻璃钢基础接触面的力学特性,为指导冻土区基础设计和安全评价,采用应变直剪仪开展了多种含水率和温度条件下青藏粉土-玻璃钢接触面直剪试验研究。结果表明,青藏粉土-玻璃钢接触面屈服时相应剪切位移很小,应变硬化阶段短暂或不显著;冻结状态下接触面应力-位移性状呈脆性破坏型,存在明显峰值;融化状态时接触面的剪应力-位移性状呈塑性破坏型,其应力-位移关系曲线为弱软化型和屈服型,没有明显峰值;融化状态时接触面抗剪强度值随含水率的增加而缓慢减小,冻结状态时其强度随负温绝对值和含水率的增加而增大,且随着土体含水率的增大,温度降低导致接触面抗剪强度增强效果更加显著,土体含水率大于19%后抗剪强度趋于稳定;温度对抗剪强度的影响主要体现于黏聚力的改变,且随着含水率的增加,温度影响增强。接触面内摩擦角随负温绝对值增加而减小,随含水率的增加而减小。
To mitigate the effect of frost heave,a countermeasure of fiberglass reinforced plastics(FRP) covering was put forward and applied to the foundation engineering of Qinghai-Tibetan transmission line.There is limited information involved in the mechanical properties of the interface between soil and FRP.A series of laboratory direct shear tests of the interface between silt and FRP plate are performed.The results show that the yield shear displacement is very small;and the interface shows short or no significant strain hardening stage.For frozen samples,the strength of the interface is drastically lost when the load reaches its critical strength.For unfrozen samples,the shear stress-displacement behavior of the interface is ductile failure and there is no obvious peak.The shear strength of the interface slowly decreases with the increase in water content for unfrozen samples.The strength of frozen sample increases with the increasing of negative absolute temperature and water content.Moreover,the temperature effect on the shear strength of the interface is more significant if soil water content is higher.When the soil water content is greater than 19%,the shear strength stabilized.The impact of temperature on the shear strength is mainly reflected in the change of cohesion.With the increasing of water content,temperature effects enhanced.The internal friction angle of the interface decreases with the increase in the absolute value of negative temperature and decreases with the increase of water content.
To mitigate the effect of frost heave,a countermeasure of fiberglass reinforced plastics(FRP) covering was put forward and applied to the foundation engineering of Qinghai-Tibetan transmission line.There is limited information involved in the mechanical properties of the interface between soil and FRP.A series of laboratory direct shear tests of the interface between silt and FRP plate are performed.The results show that the yield shear displacement is very small;and the interface shows short or no significant strain hardening stage.For frozen samples,the strength of the interface is drastically lost when the load reaches its critical strength.For unfrozen samples,the shear stress-displacement behavior of the interface is ductile failure and there is no obvious peak.The shear strength of the interface slowly decreases with the increase in water content for unfrozen samples.The strength of frozen sample increases with the increasing of negative absolute temperature and water content.Moreover,the temperature effect on the shear strength of the interface is more significant if soil water content is higher.When the soil water content is greater than 19%,the shear strength stabilized.The impact of temperature on the shear strength is mainly reflected in the change of cohesion.With the increasing of water content,temperature effects enhanced.The internal friction angle of the interface decreases with the increase in the absolute value of negative temperature and decreases with the increase of water content.
引文
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[12]SADOVSIKIY A V.Adfreeze between ground and foundation materials[C]//Proceedings of 2th International Permafrost Conference.Yakutsk:[s.n.],1973:650-653.
[13]PERAMESWARAN V R.Creep of model piles in frozen soil[J].Canadian Geotechnical Journal,1979,16:69-77.
[14]陈肖柏,刘建坤,刘洪绪,等.土的冻结作用与地基[M].北京:科学出版社,2006.
[15]KO Sung-gyu,CHOI Chang-ho.Experimental study on adfreeze bond strength between frozen sand and aluminium with varying freezing temperature and vertical confining pressure[J].Journal of the Korean Geotechnical Society,2011,27(9):67-76.
[16]LADANYI B,THERIAULT A.A study of some factors affecting the adfreeze bond if piles in permafrost[C]//Proceedings of Geotechnical Engineering Congress.Canada:[s.n.],1990:213-224.
[17]CHOI Chang-ho,KO Sung-gyu.A study for predicting adfreeze bond strength from shear strength of frozen soil[J].Journal of the Korean Geotechnical Society,2011,27(10):13-23.
[18]赵联桢,杨平,王海波.大型多功能冻土-结构物接触面循环直剪系统研制及应用[J].岩土工程学报,2013,35(4):707-713.ZHAO Lian-zhen,YANG Ping,WANG Hai-bo.Development and application of large-scale multifunctional frozen soil-structure interface cycle-shearing system[J].Chinese Journal of Getechnical Engineering,2013,35(4):707-713.
[2]孙玉良,王亮.钢筋混凝土桥桩切向冻胀力及抗冻拔计算[C]//第三届全国冻土学术会议论文选集.北京:科学出版社,1989:150-156.
[3]吕睿,李卫平,陶连银.北-宝220 kV线路129#塔塔基破坏原因分析与鉴定[J].水利水电工程设计,2000,19(3):23-24.LV Rui,LI Wei-ping,TAO Lian-ying.Analysis and evaluation on damage for tower foundation of Bei-Bao220 kV transmission line[J].Design of Water Resources&Hydroelectric Engineering,2000,19(3):23-24.
[4]LYAZGIN A L,LYASHENKO V S,OSTROBORODOV S V,et al.Experience in the prevention of frost heave of pipe foundations of transmission towers under northern conditions[J].Power Technology and Engineering,2004,38(2):124-126.
[5]姜和平,刘兆瑞.冻土地区±500 kV直流输电线路地基与基础设计[J].内蒙古电力技术,2006,24(4):1-4.JIANG He-ping,LIU Zhao-rui.±500 kV direct current transmission line ground and foundation design in frozen ground area[J].Inner Mongolia Electric Power,2006,24(4):1-4.
[6]WYMAN G E.Building transmission in subarctic alaska[J].Line Design,2010,3:104-110.
[7]PERAMESWARAN V R.Adfreeze strength of frozen sand to model piles[J].Canadian Geotechnical Journal,1978,15(4):494-500.
[8]WEAVER J S,MORGENSTERN N R.Simple shear creep tests on frozen soils[J].Canadian Geotechnical Journal,1981,18:217-229.
[9]童长江,管枫年.土的冻胀与建筑物冻害防治[M].北京:水利电力出版社,1985.
[10]LADANYI B,FORIERO A.Evolution of frost heaving stresses actinzg on a pile[C]//Proceedings of 7th International Permafrost Conference.Yellownife:[s.n.],1998:623-633.
[11]PENNER E,GOLD L W.Transfer of heaving forces by adfreezing to columns and foundation walls in frostsusceptible soils[J].Canadian Geotechnical Journal,1971,8:514-526.
[12]SADOVSIKIY A V.Adfreeze between ground and foundation materials[C]//Proceedings of 2th International Permafrost Conference.Yakutsk:[s.n.],1973:650-653.
[13]PERAMESWARAN V R.Creep of model piles in frozen soil[J].Canadian Geotechnical Journal,1979,16:69-77.
[14]陈肖柏,刘建坤,刘洪绪,等.土的冻结作用与地基[M].北京:科学出版社,2006.
[15]KO Sung-gyu,CHOI Chang-ho.Experimental study on adfreeze bond strength between frozen sand and aluminium with varying freezing temperature and vertical confining pressure[J].Journal of the Korean Geotechnical Society,2011,27(9):67-76.
[16]LADANYI B,THERIAULT A.A study of some factors affecting the adfreeze bond if piles in permafrost[C]//Proceedings of Geotechnical Engineering Congress.Canada:[s.n.],1990:213-224.
[17]CHOI Chang-ho,KO Sung-gyu.A study for predicting adfreeze bond strength from shear strength of frozen soil[J].Journal of the Korean Geotechnical Society,2011,27(10):13-23.
[18]赵联桢,杨平,王海波.大型多功能冻土-结构物接触面循环直剪系统研制及应用[J].岩土工程学报,2013,35(4):707-713.ZHAO Lian-zhen,YANG Ping,WANG Hai-bo.Development and application of large-scale multifunctional frozen soil-structure interface cycle-shearing system[J].Chinese Journal of Getechnical Engineering,2013,35(4):707-713.
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