【作者】 仇敏玉；

【导师】 俞亚南； 张仪萍；

【作者基本信息】 浙江大学 ， 市政工程， 2011， 博士

【摘要】 道路沉降可以分为道路施工期沉降和道路工后沉降。道路施工期沉降一般通过填补加高等措施解决,道路工后沉降需对运营中的道路进行平整性修补,对道路的运营能力、维修成本影响较大。引起道路工后沉降的原因主要有：固结残余孔压消散、交通荷载等。精确预测道路在交通荷载作用下的工后沉降,对道路在设计、施工过程中采取有效措施来减少道路工后沉降具有重要的意义。论文针对这一问题开展了如下工作：首先,论文采用脉冲函数的有限差分近似表达式模拟交通荷载,反映交通荷载的作用点、轴重、行车速度。理论验证了该表达式模拟交通荷载特征与匀速移动荷载作用于弹性半空间表面的竖向动应力特征一致,试验验证了与实际行驶车辆在道路中引起的竖向动应力脉冲曲线特征结果一致。其次,基于原状杭州软粘土的三轴压缩试验结果中土体轴向应变和偏应力呈应力-应变硬化或者应力-应变软化形式、Es/E20re与q/q,呈非线性关系,论文提出了Hardening Soil (HS)修正模型。该修正模型能描述在三轴压缩试验中土的应变硬化及应变软化现象、非线性刚度软化现象,且该修正模型的应力-应变曲线与实测应力-应变曲线的相关系数大于0.97。第三,基于道路为半空间无限体,论文采用Plaxis有限元软件,建立了黏弹性人工边界有限元数值模型。其中黏弹性人工边界条件为在有限元模型的截断边界处：(])采用吸收边界模拟系统在振动过程中动应力波动向远场介质辐射的特点,消除了应力波在固定边界上的反射而导致振动波在有限域内的振荡反射,使得计算周期出现放大或缩小及卸载后出现动位移、动应力反复振荡的不正常现象；(2)采用锚锭杆单元模拟线性弹簧作用,解决吸收边界在低频作用下出现的漂移现象而导致动位移响应与理论值有较大差异的稳定问题。结果显示：黏弹性人工边界的有限元数值分析模型计算区域小,模拟交通荷载作用下道路的动响应准确性好。第四,基于循环三轴试验,采用εp-N与Up/σ.-N的幂函数关系拟合了累积塑性应变-加载次数及累积孔压比-加载次数的关系,考虑的影响因素涉及动偏应力幅值和振动频率等交通荷载因素,孔隙比、粒径、含水量、回弹模量等道路因素,初始静偏应力和围压等试验初始应力条件。第五,基于Plaxis有限元软件,采用脉冲函数的有限差分形式模拟交通荷载、以Hardening Soil非线性刚度软化修正模型模拟土的本构关系、以黏弹性人工边界模拟有限元模型边界上波的传播,建立模拟交通荷载作用下道路动响应的数值分析模型。利用上述数值分析模型,计算了交通荷载作用下道路的初始静偏应力、围压等试验初始应力条件和交通动偏应力幅值；计算了交通荷载的有效传递深度,并采用0.001%的最大竖向动应变为界定标准,得到交通荷载的传递深度在6～15m范围内；综合道路因素、交通荷载因素和试验初始条件多项因素的作用,计算了道路累积塑性应变和累积孔压。最后,利用分层总和法,以杭州市古翠路为例,预测道路在开放交通300天后的工后沉降值为0.046m,与现场原位监测结果一致。更多还原

【Abstract】 Road settlement can be divided into construction settlement and post-construction settlement. The construction settlement can be solved by filling soil. But it is difficult to mend the leak that caused by the post-construction settlement after the road is open. It will reduce the operational ability and increase maintenance cost of road. Both pore pressure dissipation and traffic load result in the post-construction settlement of road. Accurate prediction of post-construction settlement under traffic load is of great importance for controlling and reducing post-construction settlement by taking reasonable control measures in the design and construction. To solve this problem, the main studies of this thesis are as follows:First, a impulsive function of finite difference approximation expressions is used to describe the axle load, vehicle speed of traffic load in this paper. This function can simulate the vertical dynamic stress characteristics induced by uniform moving load moving on uniform elastic half-space surface or real traffic load moving on road, and it is verified by theory and field test.Secondly, by triaxial compressipon test, the relationship between axial strain and deviatoric stress is increasing or decreasing, and the relationship between Es/E50ref and q/qf are unlinear. Two equations were suggested to describe not only unlinear stiffness degradation but also strain softening and strain hardening in this paper. The correlation coefficient is 0.97 compared the new model with the measured stress-strain curve.Thirdly, The visco-elastic artificial boundary was built in Plaxis in this paper. It can simulate the dynamic stress fluctuations to the far-field in the vibration and eliminate the stress wave reflection in the fixed boundary by setting viscous absorbing boundary at the truncation boundary of finite element model. The spring unit setted on the viscous absorbing boundary simultaneously solves the drift of the finite element model in low frequency.The finite element model with the visco-elastic artificial boundary can accurately simulate the dynamic properties of road induced by traffic load, and it only needs a much smaller model size than that with fixed boundary.Fourthly, based on the cyclic triaxial experiments and the analysis of one factor, the relationships of accumulated plastic strain with load times and accumulated pore pressure with load times were fitted with power function. These factors included traffic load factors such as the amplitude of dynamic deciator stress and the rate of vibration, road factors such as void ratio, grain diameter, water content, resilience modulus and initial stress conditions such as initial static deviator stress, confining pressure.Finally, a numerical model to study the dynamic response in road induced by traffic load was built based on Plaxis FEM software in this paper. This model used an impulsive function to describe traffic load, the modified Hardening soil model to simulate the constitutive relation of soil and the visco-elastic artificial boundary to be combined with FEM. Using this numerical model, initial static deviator stress, confining pressure, the amplitude of dynamic deciator stress was calculated. The pass depth of traffic load was also calculated. The 6-15m of the pass depth was obtained acrroding to the standards defined by 0.001 percent the maxmen vertical dynamic strain. Then, accumulated plastic strain and accumulated pore pressure were calculated considering all of factors such as road factors, traffic load factors and initial experimental conditions. This numerical model was used to predict the post-construction settlement of Gu-cui road in Hangzhou. The 0.046m of the post-construction settlement after opening 300 days is according with the result of the field monitoring.更多还原