不同压实条件下富水粉土道基变形规律的数值研究

传统基于有限元的数值方法很难对长期飞机荷载作用下粉土道基的变形演化进行计算。建立一种考虑土体干密度影响的重塑饱和粉土边界面模型,利用带误差控制的显式积分算法,将其写成可供有限元软件调用的用户自定义材料子程序,以此建立单元土体固结不排水动三轴试验进行模拟,验证模型具备描述饱和粉土的动力特性。随后建立分层压实和不同压实度的跑道数值模型,对飞机循环荷载作用下的道基变形进行了数值分析。结果表明,随着循环次数的增加,道基变形虽持续增加,但发展速率逐渐减小,循环加载50次后粉土道基变形基本稳定;94%压实度道基模型经历相同的循环加载次数后累积塑性位移小于分层压实模型,表明虽然在实际工程中往往通过分层压实的方法降低造价,但在一定荷载影响范围内,仍然需要将压实度严格控制。

飞机荷载作用下湿化对粉土道基应力响应的影响

中国西北、华北地区因地制宜,选取粉土作为道基填料,在机场的服役过程中,“锅盖效应”或降雨入渗等易引发局部积水而使粉土道基湿化。在飞机荷载作用下,粉土湿化对不同跑道结构参数的道基应力响应影响显著。本文通过自研的湿化粉土道基加载模型试验系统,研究了粉土不同湿化程度的土体应力响应特征,并且建立数值仿真模型,分析了道面板相互作用机制,面层和基层厚度、刚度等不同跑道结构参数下湿化对道基敏感区域应力响应特征的影响规律。结果表明:道面板间接缝传荷能力对道基应力响应的影响较小。粉土湿化促进了道基中的应力叠加效应,也增加了道基应力响应对跑道结构参数变化的敏感性,但降低了应力响应深度对跑道结构参数变化的敏感性。在受荷较大的道面板中心点下,粉土湿化下水泥道面板刚度对道基应力响应的影响较小,基层弹性模量是道基应力响应的主要影响因素;面层厚度和基层厚度是受荷道面板外侧角点下道基应力响应的主要影响因素,合理的基层参数能有效地降低湿化对道基受力状态的影响。研究成果能为机场工程跑道结构设计、优化及道基病害处理等提供技术依据。

飞机荷载作用下湿化粉土道基变形特性研究

为探明飞机荷载作用下湿化道基的变形特性,研制模型试验系统,并结合相应数值模型,开展飞机荷载作用下不同湿化程度的道基变形演化规律研究。研究结果表明:北京大兴区粉土渗透性强,持水能力较差,粉土饱和度75%时达到最大持水能力。道基变形主要发生在粉土达到最大持水能力前,山皮石垫层与粉土道基分界面处出现了较大不均匀变形,而垫层的设置能有效降低加载区下卸荷不均匀变形。加载区下,随深度增加沉降横向分布呈现深“U”形—浅“U”形—深“V”形—浅“V”形的演化特征,不均匀变形横向分布主要集中于加载区及其5 m范围内;沉降竖向分布呈现指数降低和线性降低趋势,加载区下受荷敏感区域位于垫层表面以下6 m深度范围内。飞机荷载主要影响深度与受荷敏感深度相同,湿化作用降低了受荷敏感深度内应力集中效应,增加了飞机荷载影响范围以及不均匀变形,对不均匀变形横向分布范围无显著影响。

Influence of the boundary effect on the mechanical response test of pavement cushion under the wetting effect of silt

Through a self-developed model test system,the mechanical properties of silt and the deformation characteristics of airport runways were investigated during the period of subgrade wetting.Based on the test results,the reliability of the numerical simulation results was verified.Numerical models with different sizes were established.Under the same cushion parameter and loading width ranges,the effects of the cushion parameters and loading conditions on the mechanical responses of the cushion before and after subgrade wetting were analyzed.The results show that the internal friction angles of silt with different wetting degrees are approximately 34°.The cohesion is from 8 to 44 kPa,and the elastic modulus is from 15 to 34 MPa.Before and after subgrade wetting,the variation rates of the cushion horizontal tensile stresses with the same cushion parameters and loading width ranges are different under the influence of boundary effects.After subgrade wetting,the difference in the variation rates of the cushion horizontal tensile stresses under the same cushion parameter range decreases compared with that before subgrade wetting;however,this difference increases under the same loading width range.Before and after subgrade wetting,the influence of the boundary effect on the mechanical response evaluation of the cushion is not beneficial for optimizing the pavement design parameters.When the cushion thickness is more than 0.25 m,the influence of the boundary effect can be disregarded.