【作者】 赵莉；

【导师】 蔡袁强； 曹志刚；

【作者基本信息】 浙江大学 ， 岩土工程， 2017， 硕士

【摘要】 道路路基作为承载和传递车辆荷载的关键结构,在服役期内将承受数百万次交通荷载作用,掌握大次数交通循环荷载下路基的刚度变化及累积变形发展规律是保障道路长期服役性能的前提。粗粒碎石填料因其良好的力学性能及透水性能,且易于就地取材被广泛应用于路基层填筑工程。目前学者们针对交通循环荷载下路基粗粒填料的动力特性开展了一系列研究,获得了路基粗粒填料物理状态、交通荷载大小与循环次数等因素对道路路基回弹与累积变形的影响规律。在交通运输日益高速化、密集化趋势下,荷载频率作为反映交通荷载速度与密度的重要参数,其对路基粗粒填料长期动力特性的影响不容忽略。此外,地基翻浆等原因将使路基粗粒填料受到不同程度的污染,细粒污染将改变路基的内部结构与级配,降低路基的排水性能,对路基强度与变形特性造成显著影响进而影响到道路的长期服役性能。因此,有必要采用公路路基粗粒填料层所对应的典型频率荷载对其动力特性进行研究,并分析不同细粒污染程度下路基填料特性变化,以揭示荷载频率及细粒含量对路基粗粒填料的长期动力特性影响规律。本文利用GDS大型三轴试验系统进行了一系列不同频率与细粒含量下凝灰岩碎石填料的排水循环荷载试验,具体内容包括以下几个方面:1、针对不同车辆速度与行车密度等因素在道路路基中产生不同荷载频率这一实际工程问题,利用大型三轴循环试验系统在不同荷载频率下对公路路基粗粒填料开展饱和排水循环荷载试验。系统性地分析了荷载频率、循环应力比等对路基粗粒填料长期动力特性的影响规律,获得了循环荷载频率对路基填料体应变、回弹模量和轴向累积应变的影响规律。研究表明,在粗粒填料密实阶段,提高荷载频率使粗粒填料产生更大的体应变而更为密实,从而使粗粒填料回弹模量随荷载频率增加显著增大;在低循环应力比下,土体轴向累积变形随荷载频率变化相对较小,但在高循环应力比下,轴向累积变形随荷载频率增加明显增大。当粗粒土进入稳定变形阶段,荷载频率对路基粗粒填料体应变与轴向累积变形基本无影响。因此,控制路基中的循环应力比,可显著降低荷载频率对路基长期动力特性的影响。2、结合不同荷载频率下路基填料轴向累积应变试验数据,对路基填料大次数循环累积变形预测模型HCA模型(High-cycle Accumulation Model)进行改进。通过引入考虑荷载频率影响的因子ff,提出了可考虑荷载频率影响的路基填料轴向累积变形预测模型。研究表明,该模型可准确预测公路路基在典型频率荷载下的轴向累积变形,为更加全面地预测和控制道路工后沉降提供了有效工具。3、为研究交通循环荷载下受细粒污染的路基填料的动力特性,针对不同污染程度下的凝灰岩碎石填料开展了一系列大型三轴循环荷载试验研究。通过在粗粒填料中掺入不同含量高岭土来模拟污染路基填料。为考虑荷载频率与细粒含量对污染路基填料动力特性的耦合影响,开展了 5种不同污染程度下的路基填料在3种荷载频率下的大三轴循环荷载试验。着重分析了不同荷载频率及细粒含量下粗粒填料的孔压、体应变、回弹模量及轴向累积变形的变化规律,总结了细粒含量在不同荷载频率下对路基填料动力特性的影响规律。研究表明,细粒土对路基粗粒填料动力特性的影响分为三个阶段。首先,少量细粒土对粗颗粒土的润滑作用导致粗粒填料在循环荷载下的体应变和轴向累积应变增大;随着细粒含量进一步增大,粗粒填料孔隙被细粒填充而使其压缩性减小,体应变与轴向累积应变随之减小;当细粒含量增加到一定值后,粗粒填料渗透性显著降低,循环荷载下路基中孔压迅速累积,进而导致轴向累积应变急剧增大,回弹模量大幅减小。此外,细粒含量对粗粒填料长期动力特性的影响受荷载频率影响显著,高频荷载将加剧孔压累积,导致路基长期服役性能劣化。更多还原

【Abstract】 As the key structure that bears and transmits traffic loading to the soil,road base is subjected to massive cyclic loading during its service period.Therefore,a deep understanding of the development of stiffness and accumulated strain of road base under long-term traffic loading is the premise to assure the long-term road service performance.Unbound Granular Materials(UGMs)are widely used as road base fillings for its well mechanical and drainage properties.Nowadays,the scholars have made a series of researches on the dynamic behaviors of UGMs under traffic loading.The effects of different factors such as the physical states of UGMs and the loading amplitude on the resilient and accumulated strains of UGMs have been investigated.While under the tendency of fast development of intensive and high speed transportation,as a result,the influence of cyclic loading frequency on the long-term dynamic behaviors of UGMs can’t be ignored.Besides,the invasion of the fine particles from the subgrade caused by mud pumping will influence the strength and deformation properties of the road base fillings.The fines will change particle size distribution,permeability of UGMs and the interaction between grain networks,which will affect the long-term service performation.Therefore,in order toreveal the effects of the loading frequency and fines content on the long-term dynamic behaviors of UGMs,it’s necessary to carry out researches on the dynamic behaviors of UGMs with different fines contents under typical loading frequencies,and analyze the properties of UGMs under different degree of fines pollution.In this study,in order to investigate long-term dynamic properties of crushed tuff with different fines contents under cyclic loading with different frequencies,a series of cyclic large-scale triaxial tests have been conducted with GDS large-scale cyclic triaxial apparatus,the main research contents are listed as follows:1.In order to investigate the effects of loading frequency,a series of cyclic large-scale triaxial tests on the UGMs under saturated drained condition have been conducted with GDS large-scale cyclic triaxial apparatus.The influence of loading frequency and stress path on the long-term performance of UGMs are investigated systematically,and obtain the influence of loading frequency on the development of resilient modulus,volumetric strain and accumulated axial strain.The experimental results show that loadings with higher frequency results in a larger accumulated volume contraction during the stage of densification,and consequently the UGMs reach a higher resilient modulus value.The accumulated axial strains of UGMs are also different under loadings with different frequencies.At the stage of densification of UGMs,loadings with higher frequency leads to higher accumulated axial strain when cyclic stress ratios are high,while the loading frequency’s influence is minimized when the cyclic stress ratio is low.After the UGMs reach the stable deformation stage,loading frequency almost has no influence on the accumulated axial strain.Therefore,the effects of loading frequency on the long-term performance of road base can be significantly reduced by controlling the cyclic stress ratio in the UGMs to a low level.2.Combined with test data of accumulated axial strain under different loading frequency,the High-cycle Accumulation Model which predicts the accumulated strain of UGMs under large numbers of cyclic loading is modified.With the introduction of a new impact factor ff,a new model that considers the influence of the loading frequency is developed which can predict the settlement of road base based on HCA Model.The study shows that this model can predict the settlment of road base accurately under loading with different frequencies corresponding to typical loading frequencies.It provides an effecive tool to predict and control the post-construction settlement of road more comprehensively.3.In order to investigate the dynamic behaviors of road base with different degree of fines pollution under the traffic loading,a series of large-scale triaxial tests have been conducted on crushed tuff.Pollution road base filling materials are simulated by mixed with different magnitudes of fines contents.Large-scale triaxial cyclic loading tests are carried out on the road base with 5 magnitudes of fines contents subjected to 3 loading frequencies to consider the coupling effects of fines content and loading frequency,and focus on the development of excess pore pressure,volumetric strain,resilient modulus and accumulated axial strain.The studied results show that the effects of fines content of UGMs can be divided into three stages.Firstly,under low fines content condition,the fine particles can lubricate the contact of the UGMs which can increase the volumetric strain and accumulated axial strain;with the increase of fine particles,the voids of the UGMs are filled with the fine particles which makes the compressibility of the UGMs decrease,and consequently decreases the stains;when the fines content increases to a certain value,the permeability of the UGMs becomes low which makes the buidup of excess pore pressure.In this case,the axial strain increases significantly and the the resilient modulus decreases sharply.Moreover,the influence level of the fines contents on the UGMs’ long-term behaviors is highly influenced by loading frequency.In addition,high loading frequency will aggravate the excess pore pressure which makes the pavement’s long-term service ability degraded.更多还原