青藏粉土-玻璃钢接触面力学特性直剪试验研究

Direct shear tests for mechanical characteristics of interface between Qinghai-Tibetan silt and fiberglass reinforced plastics

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.