冲击碾压改建旧水泥混凝土路面施工时的地基振动特性

为了解冲击碾压水泥混凝土路面施工时的地基振动与影响特性,基于动力三维有限元分析方法,考虑材料的弹塑性,对四楞冲击压路机冲击碾压水泥混凝土路面时地基的振动与传播特性进行了研究,并将数值计算结果与现场地基振动监测数据进行了对比分析;然后将冲击碾压地基实测振动信号作为输入,对离震源不同距离的砌体和框架建筑结构时程动力响应进行了计算,探讨了冲击碾压改建施工的安全防护标准。研究表明冲击碾压引起的地基振动具有冲击瞬态特性,地基振动中竖向振动加速度分量最大,横向振动和纵向振动加速度大小相当。振动加速度各分量沿道路横向距离10m范围内衰减变化显著,随着冲击破碎遍数递增,土基振动有增大现象。冲压振动与结构物的共振效应较小,对15m以外的完好建筑物影响很小。建议在普查无临界状态房屋条件下结构安全距离为15m,考虑对人的振动影响安全距离为20m。     

Effect of geosynthetic inclusion on the bearing ratio of two-layered soil

In this article, the load-settlement characteristics of unreinforced and reinforced two-layered soil during the loading process are investigated. A series of bearing ratio tests was performed on a granular soil as the base layer overlaying a cohesive soil as the subgrade layer. Three reinforcing conditions (unreinforced, reinforced with nonwoven geotextile, and reinforced with geogrid) at the interface of layers, with four compaction moisture contents (CMCs) of the subgrade layer and three thicknesses of the base layer for both soaked and non-soaked conditions are considered. The results show that the CMC of the subgrade layer has a significant effect on the behavior of two-layered soil, such as swelling amount and the efficiency of the reinforcements. Reinforcing with geogrid resulted in a considerable increase in strength of the soaked samples due to adhesion between geogrids and clayey subgrade layer. For nonwoven geotextiles, strength of the two-layered soil decreased at shallow penetration depths due to reinforcements; and as the penetration increased in depth, the strength also increased. Also, it was found that with decreases in base layer thickness, the test variable's value (i.e., CMC), and the type of geosynthetic reinforcement have significant effects on the behavior of two-layered soil.     

车辆荷载作用下双层路基层间动应力响应试验研究

针对层状路基土的动力响应与稳定性评价问题,以某双层路基为工程背景,利用现场实测数据,揭示出硬、软土层界面处存在动应力突变现象,并给出了动应力突变系数;根据室内模型试验数据,以动应力突变系数为试验指标,采用极差分析法对主要影响因素进行了排序;借助动三轴试验获得硬、软土体的临界动应力,推导得出两种土体的动应力水平关联性系数,并提出一种评价路基长期稳定性的"概率区域"方法。研究表明:路基运营后期,硬、软土层压缩模量之比将取代硬壳层厚度,成为影响层间响应的首要因素;埋置较深的下卧软土层是控制路基稳定性的关键层。     

Concrete slab analyses with field-assigned non-uniform support conditions

Intelligent compaction (IC) technologies have been used to locate and identify areas of soft, weak or non-uniform subgrade support, which can be linked to pavement performance to set realistic limits on allowable non-uniformity as identified by IC. Based on field data, finite element analyses were performed to investigate the impact of non-uniformities on concrete slab tensile stresses. Non-uniform support cases were modelled by deterministically and randomly assigning field-correlated moduli of subgrade reaction (k-values) to specific spatial areas in the foundation layer. Stresses depended on the size of the non-uniform area, the stiffness change between adjacent non-uniform areas, load location and configuration, and temperature differential. Cases with randomly assigned k-values showed as much as a 39% increase in peak slab tensile stresses relative to a uniform support condition, which could lead to premature slab failures. The ability of IC to locate foundation non-uniformities could increase the reliability of concrete pavements.     

Quality assurance and quality control of subgrade compaction using the dynamic cone penetrometer

The Dynamic Cone Penetrometer (DCP) is a device that is used in the construction industry for the assessment of in situ soil compaction quality. Over the past few decades, numerous correlations have been developed between the DCP test results and soil strength and stiffness parameters. This paper proposes a comprehensive set of criteria and recommendations for quality control (QC) of compacted subgrade that take into account the inherent statistical variability of DCP test results. For the development of the QC criteria, a new statistical methodology is used to extract representative test values from the raw field DCP test data. In order to use the proposed QC criteria, soils are first classified into two broad categories (fine-grained and coarse-grained) depending on their fabric and response to compaction efforts. Test results indicate that (i) for fine-grained soils, the DCP test values have good correlation with the plasticity index (PI), which is indicative of the type and amount of clay content of the soil and (ii) for coarse-grained soils, the DCP test values have good correlation with the optimum water content of the soil, which is directly related to its in situ density. DCP blow count correlation equations are presented for both soil categories. Recommendations for field DCP testing and data analysis are also provided to highlight the significance of the statistical distribution of the DCP test results in QC testing of compacted subgrade.     

膨胀土路堑基床新型防水层振动荷载下服役性能试验研究

膨胀土路堑基床病害是铁路工程中亟需解决的关键技术问题。针对新建云桂线膨胀土地段高速铁路工程实际,开展膨胀土路堑基床模型室内激振试验,研究新型防水结构层在干燥、降雨、地下水位上升三种极端服役条件下的动力性能及防水效果,并结合现场实测数据进行了分析。分析结果表明：服役环境对新型基床结构的动力特性影响显著,降雨和地下水位上升均引起基床动应力、速度及加速度不同程度的增加;新型防水结构层可加快基床内部动应力的衰减,动应力沿横向距离近似呈“Z”形分布,在轨道正下方出现峰值,距线路中线5.0m以外受振动影响较小;新型防水结构层能满足的防水、隔水、抗振、减振的要求,对提高铁路线路的平顺性和稳定性具有积极意义。研究成果可为新建云桂膨胀土高速铁路工程建设及同类工程实践提供参考。     

压路机激励下重载铁路路桥过渡段动力特性研究

以蒙华重载铁路某路桥过渡区为试验对象,开展压路机激励下过渡区的动力特性试验,研究过渡区动力响应的分布规律;建立考虑振动轮-路基耦合的动力分析数值模型,研究过渡区等效刚度分布及振动轮-路基面接触力变化特性.结果表明:随着路基深度增大,动应力扩散角逐渐减小,埋深0.2～3.0 m处扩散角在78.20～55.00,倒梯形过渡...     

Pasternak 地基中土工格室加筋体的受力变形分析

为了研究路面荷载作用下土工格室加筋体的受力与变形机理,正确反映土工格室加筋体与地基之间的荷载传递模式,建立了考虑路基填料和地基土体剪切作用的土工格室加筋体简化分析模型。路基填料和地基土层采用双参数的Pasternak模型,克服了传统Winkler 地基模型无法考虑路基填料和地基中应力扩散的缺点。土工格室加筋体简化为埋置于地基中的有限长梁,以考虑其抗弯刚度的影响。基于特征值分解法求解土工格室加筋体变形微分控制方程,得到了准解析的解,并可直接得到路面荷载作用下土工格室加筋体的弯矩和剪力分布。该文模型在土层剪切刚度趋于足够小时,可退化到采用Winkler 地基时的土工加筋体分析模型。计算发现考虑土体的剪切特性对准确分析土工格室加筋体的受力和变形十分重要;同时发现当下卧地基较软弱时,土工格室加筋体的加固作用更加明显。     

Finite element modelling of field compaction of hot mix asphalt. Part I: Theory

This paper presents the theoretical background for the development of a constitutive model that is used in the simulation of the compaction of asphalt mixtures. The constitutive model is developed to comply with the principles of thermodynamics, and is derived to represent the macroscopic behaviour of an asphalt mixture as a highly compressible viscoelastic material. The paper presents the details of the mathematical formulation and the computational implementation of the model in the finite element package computer-aided pavement analysis 3D. The capabilities of the compaction model and its sensitivity to changes in model's parameters are illustrated using simple numerical applications. In a companion publication, (Masad et al., Finite element modelling of field compaction of hot mix asphalt. Part II: Application, International Journal of Pavement Engineering, Accepted, 2014), the model is verified against field compaction measurements which demonstrate the ability of the model to capture the general trends of the compaction observed in the field.     

A micromechanical compaction model for woven fabric preforms. Part I: Single layer

A micromechanical model was developed to investigate elastic compression behaviour during compaction of a single layer of woven fabric preform. The compaction model describes two important deformation mechanisms at different hierarchical levels, addressing micro-deformation of yarn cross-section compaction and macro-deformation of yarn bending accompanied by yarn waveform flattening. The stress carried by the fabric is decomposed into two parts in relation to two distinct mechanisms, coupled through the requirement of deformation compatibility. With this micromechanical model the effects of microstructures of single layer woven fabric on their compaction behaviour are evaluated. It is shown that both the macro-bending stiffness of fibre and the initial fibre packing ratio of yarn affect the compaction behaviour of single layer fabric preform. The prediction is correlated with experimental data available, and satisfactory agreement is observed.     

地面沉降对路基上双块式无砟轨道平顺性的影响

高速铁路无砟轨道对于基础沉降变形特别敏感,地面沉降会显著影响路基上无砟轨道的受力变形及使用寿命,影响高速列车安全平稳运行。该文针对路基上双块式无砟轨道,基于有限元方法建立了梁-板-实体空间耦合模型,对地面不均匀沉降的幅值、范围及型式与双块式无砟轨道系统平顺性的关系开展了研究。结果表明:无砟轨道及路基各层沉降量随着地面沉降量增加基本成线性增加,支承层和路基表层间沉降差较大易出现离缝问题;地面沉降量20mm、沉降范围小于15m时,路基及轨道结构离缝现象明显,沉降范围大于15m时结构变形趋于平缓、轨面曲率半径增大;地面错台和折角型不均匀沉降均易导致无砟轨道及路基在折角点出现沉降差、结构离缝甚至开裂,折角值大小直接影响轨面平顺性。     

Systematic back-calculation protocol and prediction of resilient modulus for MEPDG

A research focusing on the characterisation of representative local material properties was conducted to facilitate the full implementation of the Mechanistic-Empirical Pavement Design Guide for roadway designs in Wyoming. As part of the test program, falling weight deflectometer deflection data were collected from 25 test sites in Wyoming for back-calculation of subgrade resilient modulus. Also, subgrade materials from these test sites were sampled for laboratory resilient modulus measurement in accordance with the AASHTO T 307. The back-calculation is a user-dependent procedure and produces a non-unique resilient modulus estimation. To alleviate this limitation, this paper focuses on the recent development of a systematic back-calculation protocol for subgrade resilient modulus using MODCOMP6 software. The protocol is intended for use on a flexible pavement with a crushed base. The proposed procedure discusses pre-analysis checks, seed modulus adjustment, pavement structure adjustment and program termination criteria. A correlation study was conducted to correct back-calculated resilient modulus to laboratory-equivalent values. The results conclude that a non-zero intercept linear regression model provides a better correlation than the widely used zero intercept linear regression model. Furthermore, better correlations are achieved when the back-calculated resilient modulus of a lower subgrade layer and resilient modulus measured at higher laboratory test sequences Nos. 11 to 15 are considered. The non-zero model based on M_r test sequence No. 14 and lower subgrade layer yields the best correlation. For the zero model, a C-factor of 0.645 based on M_r test sequence No. 15 and lower subgrade layer yields the best correlation.     

Field evaluation and analysis of road subgrade dynamic responses under heavy duty vehicle

The study of dynamic responses of a layered road system under heavy duty vehicle is one of the most important areas in the field of transportation. This paper introduced a field testing programme of traffic-induced road vibration in Guangxi, China and investigated the subgrade vibration induced by a heavy duty truck with various axle weights and speeds through a series of field tests. The vertical stress and acceleration of the road subgrade at different depths from the tests were presented and analysed. According to the test road, a semi-analytical model of the layered road was established via the stiffness matrix method and the heavy duty vehicle was simulated by ten moving rectangular load pressures. Numerical results in the space domain were derived by performing Fast Fourier Transform and were used to compare its results with the field measurements. The agreement between the numerical and the field results was good, which indicates that the proposed method is useful in predicting the dynamic stress and acceleration of a multi-layered road structure.     

A numerical model of fibrous filters containing deposit

This work is aimed at developing numerical methods to model the effects that particle deposit collected by fibrous filters has upon the flow field within the filter and hence upon further deposition. A numerical model of the flow field has been developed using the Boundary Element Method. The model contains a two-dimensional single fibre with the boundary conditions applied on the computational domain accounting for the neighbouring fibres. A layer of porous material is assumed to cover the fibre modelling deposited particulate. The width of the porous layer, which varies along the fibre surface, is defined by particle behaviour determined in earlier work, [Dunnett SJ, Clement CF, A numerical study of the effects of loading from diffusive deposition on the efficiency of fibrous filters. J Aerosol Sci 2006; 37: 1116–1139]. Once the flow field is known the motion of the particles in the flow is modelled. Small particles are considered where diffusion is the main mechanism by which they are captured by the fibres. Various situations are considered and the flow and particle behaviour investigated. In particular the effect of existing porous deposit on the fibres upon further deposition is studied.     

Finite element modelling of field compaction of hot mix asphalt. Part II: Applications

A constitutive model is developed and implemented in the finite element system three-dimensional computer-aided pavement analysis for the simulation of hot mix asphalt field compaction. The details of this model are presented in a companion paper (Masad et al., Finite element modelling of field compaction of hot mix asphalt. Part I: Theory, International Journal of Pavement Engineering, Accepted, 2014). This model is based on nonlinear viscoelasticity theory and can accommodate large deformations that occur during the compaction process. The model was used to study the influence of frequency and amplitude of vibratory compaction rollers on the level of compaction. In addition, it was used to analyse the influence of various methods for compacting longitudinal joints on the percent air voids near these joints. The model was used to simulate the compaction of asphalt pavements with different structures and compacted using various equipment and patterns. The finite element results of the level of compaction and percent air voids were in reasonable agreement with the measurements. The model offers the opportunity to simulate and predict the compaction of asphalt mixtures under various rolling patterns and for different pavement structures.     

A sub-atmospheric chemical vapor deposition process for deposition of oxide liner in high aspect ratio through silicon vias

The formation of a Through Silicon Via (TSV) includes a deep Si trench etching and the formation of an insulating layer along the high-aspect-ratio trench and the filling of a conductive material into the via hole. The isolation of the filling conductor from the silicon substrate becomes more important for higher frequencies due to the high coupling of the signal to the silicon. The importance of the oxide thickness on the via wall isolation can be verified using electromagnetic field simulators. To satisfy the needs on the Silicon dioxide deposition, a sub-atmospheric chemical vapor deposition (SA-CVD) process has been developed to deposit an isolation oxide to the walls of deep silicon trenches. The technique provides excellent step coverage of the 100 microm depth silicon trenches with the high aspect ratio of 20 and more. The developed technique allows covering the deep silicon trenches by oxide and makes the high isolation of TSVs from silicon substrate feasible which is the key factor for the performance of TSVs for mm-wave 3D packaging.     

任意荷载作用下层状横观各向同性弹性地基的直角坐标解

首次建立了在直角坐标系下层状地基力学问题的通用解法,改变了过去仅能在柱坐标系下进行求解此类的状况。首先将坐标系的原点选在荷载影响范围以外足够远处,从直角坐标系下的横观各向同性弹性问题的基本方程出发,利用Laplace变换及其微分性质,建立了单层横观各向同性弹性地基的状态控制方程,并利用状态空间理论给出了单层地基的解答。然后再利用传递矩阵技术,给出了任意荷载作用下的层状横观各向同性弹性地基的解析解。用提供的方法求解层状横观各向同性地基的非轴对称问题比在极坐标下求解简单、快捷。     

Mesoscopic scale analyses of textile composite reinforcement compaction

Transverse compaction of textile composite reinforcements is an important deformation mode arising during composite forming and manufacture. The mesoscopic simulations of the transverse compression of textile preforms presented in this paper are based on 3D FE models of each yarn in contact with friction with its neighbours. A hypoelastic model based on the fibre rotation depicts the mechanical behaviour of the yarn. The compression responses of several layer stacks with parallel or different orientations are computed. The numerical simulations show good agreement when compared to compaction experiments. The mesoscopic simulations can be used as virtual compression tests. In addition they determine the internal geometry of the reinforcement after compaction. The internal geometry can be used to compute the permeability of the deformed reinforcement and to calculate the homogenised mechanical properties of the final composite part.     

Influence of compaction direction on performance characteristics of roller-compacted HMA specimens

Hot mix asphalt (HMA) slabs produced by roller compaction can be used to core and cut specimens for further testing. The relation between the direction of compaction and testing in the laboratory is not always the same relation as it is between the direction of compaction and actual loading in the field. This paper presents outcomes of a study analysing the influence of the compaction direction on performance characteristics of roller-compacted HMA specimens. Performance parameters of a base layer mix are obtained from performance-based test methods, including high-temperature, stiffness, fatigue and low-temperature tests. The relation between direction of compaction and specimen testing is varied in all three dimensions to find relevant influences. From the results, it can be concluded that all obtained performance parameters are sensitive to the anisotropy of the material due to compaction, especially for stiffness and fatigue performance. For the high-temperature performance, specimens from path- and force-controlled compaction were compared. The applied compaction work rather than the compaction method is linked to the difference in the corresponding results. The uniformity of the compaction in terms of the variation of bulk density of the specimens reflects on the scattering of test results.     

嵌套效应对单向织物压缩行为的影响

通过分析纤维束受压横截面的变化,并基于经典的纤维束本构关系,建立了任意嵌套状态下两层单向织物压缩厚度与外部载荷、层间偏移量之间关系的理论模型。在此基础上进一步建立了多层织物的压缩响应模型。通过对上述模型数值求解,预测了不同层数织物压缩响应。结果表明:同等受力条件下,织物的平均每层厚度随着偏移率的增加而减小;在一定压力下多层织物的平均每层厚度分布近似符合正态分布,且随着层数的增多,分布将会越来越集中;对于大于10层的织物可直接采用压力与内部层间距的期望的变化曲线表征多层织物的压缩性能。经验证,该模型与实验数据吻合较好,从而验证了模型的正确性。