交通荷载作用下软基加筋道路加筋效果分析

为了研究交通荷载作用下考虑软土软化效应的软基加筋道路加筋效果的影响因素,首先以室内动三轴试验为基础,通过回归分析得到了软土在循环荷载作用下动模量衰减的经验公式;然后编制了用户子程序将该公式导入有限元分析软件ABAQUS中,采用有限元分析了荷载形式、荷载频率、筋材模量、加筋位置、加筋层数、软土层厚度等对加筋效果的影响。结果表明,随着荷载频率的增大,加筋效果呈减小趋势。加筋效果会随着筋材模量的增大和加筋层数的增多而增大。当筋材铺设在面层和基层之间时,加筋效果最好。在软土层厚度较小时,加筋效果随软土层深度增大有明显提高;但在软土层厚度较大时,加筋效果随软土深度增加提高较少。     

Effects of cross-anisotropy and stress-dependency of pavement layers on pavement responses under dynamic truck loading

Previous studies by the authors have determined pavement responses under dynamic loading considering cross-anisotropy in one layer only,either the cross-anisotropic viscoelastic asphalt concrete(AC)layer or the cross-anisotropic stress-dependent base layer,but not both.This study evaluates pavement stressestrain responses considering cross-anisotropy in all layers,i.e.AC,base and subbase,using finite element modeling(FEM) technique.An instrumented pavement section on Interstate I-40 near Albuquerque,New Mexico was used in ABAQUS framework as model geometry.Field asphalt cores were collected and tested in the laboratory to determine the cross-anisotropy(n-values) defined by horizontal to vertical modulus ratio,and other viscoelastic parameters as inputs of the model incorporated through user defined material interface(UMAT) functionality in ABAQUS.Field base and subbase materials were also collected and tested in the laboratory to determine stress-dependent nonlinear elastic model parameters,as inputs of the model,again incorporated through UMAT.The model validation task was carried out using field-measured deflections and strain values under falling weight deflectometer(FWD)loads at the instrumented section.The validated model was then subjected to an actual truck loading for studying cross-anisotropic effects.It was observed that horizontal tensile strain at the bottom of the AC layer and vertical strains in all layers decreased with an increase in n-value of the asphalt layer,from n1(anisotropy) to n=1(isotropy).This indicates that the increase in horizontal modulus caused the decrease in layer strains.It was also observed that if the base and subbase layers were considered stressdependent instead of linear elastic unbound layers,the horizontal tensile strain at the bottom of the asphalt layer increased and vertical strains on top of the base and subbase also increased.     

水泥混凝土加铺层的分缝机理研究

本文通过现场试验和冷冻试验,对不同结合类型双层道面的实际效果进行了观测,提出了部分结合式和隔离式双层道面的分缝要求.利用有限元理论编制了考虑结合面状况的双层道面有限元分析程序,并用室内试验和理论对比分析了程序的正确性.利用有限元程序分析了不对缝加铺层的荷载应力状态,提供了不对缝加铺层设计诺模图和计算方法.     

车载作用对下沉式道路结构的影响分析

运用有限元数值模拟方法讨论了汽车荷载作用下某下沉式道路结构的变形及受力情况,分析其结构内部可能产生破损的原因及位置,并进一步探讨在结构抗浮底基层厚度及其内部温度伸缩缝间距均保持一定的条件下,沥青混凝土面层模量及厚度、伸缩缝加强层模量及宽度和伸缩缝间距对道路结构应力的影响情况。研究结果表明,该道路极有可能在沥青混凝土面层的底部最先产生滑开型(II型)裂缝;低模量的沥青混凝土面层有利于降低其底部剪应力,且根据计算结果提供了该道路结构中沥青混凝土面层的理想厚度;伸缩缝加强层模量的适当提高有利于降低剪应力大小,并提出了该层的理想宽度;同时,还提供了车载作用下理想的伸缩缝宽度。     

Effects of geosynthetics on reduction of reflection cracking in asphalt overlays

An experimental program was conducted to determine the effects of geosynthetic reinforcement on mitigating reflection cracking in asphalt overlays. The objectives of this study were to assess the effects of geosynthetic inclusion and its position on the accumulation of permanent deformation. Geogrid position, type of existing pavement, temperature, and joint/crack opening were varied in 24 model specimens tested. Crack propagation under repeated loading was monitored. Results indicate a significant reduction in the rate of crack propagation in reinforced samples compared to unreinforced samples and type of old pavement (concrete or asphalt pavement), geogrid position and temperature affected the type of crack propagation in asphalt overlays. Placing the geogrid at a one-third depth of overlay thickness from the bottom provided the maximum service life.     

旧水泥路面碎石化加铺半柔性路面结构力学特性分析

本文采用ABAQUS有限元分析法建立了半柔性路面计算模型,模拟计算了水泥混凝土路面加铺半柔性路面应力,分析了不同因素对单层和双层加铺结构力学特性的影响。结果表明,对于旧板破碎化后加铺半柔性路面结构的应力,主要影响因素有半柔性层的模量和厚度以及碎石化旧板的模量,对于双层结构还包括了沥青混凝土层的厚度,增大沥青混凝土层厚度可以降低加铺层层底应力,其他因素则影响相对较小。此外,旧水泥路面碎石化加铺单层半柔性路面结构层厚度宜达到10cm以上,同时采用打裂压稳技术并保留旧板有足够的承载力,以降低半柔性层层底拉应力。     

基于扩展有限元法的加铺应力吸收层对反射裂缝影响浅析

基于福建某旧路改造工程,借助ABAQUS软件平台,模拟旧混凝土路面加铺沥青混凝土结构层,分析在荷载作用下沥青混凝土加铺层厚度、应力吸收层厚度和模量变化对应力值、弯沉值以及裂缝扩展的影响。研究表明,合理增加沥青混凝土加铺层厚度可有效防治面层反射裂缝,适当加铺应力吸收层可较好防治面层反射裂缝。研究结果可为类似工程提供借鉴。     

Static structural behavior of geogrid reinforced soil retaining walls with a deformation buffer zone

To understand the structural behavior of geogrid reinforced soil retaining walls (GRSW) with a deformation buffer zone (DBZ) under static loads, the model tests and the numerical simulations were conducted to obtain the wall face horizontal displacement, vertical and horizontal soil pressures, and geogrid strains. Results showed that compared with the common GRSW, the horizontal displacement of GRSW with DBZ decreased, and the horizontal soil pressure acting on the face panel of GRSW with DBZ increased. The vertical and horizontal soil pressures showed a nonlinear distribution along the reinforcement length, and the value was smaller near the face panel. The horizontal soil pressure acting on the face panel of GRSW with DBZ was greater than that of the common GRSW in the middle portion. The cumulative strain of the geogrid had a single-peak distribution along its length; the maximum strain of the geogrid was 0.45%, the maximum tension was approximately 29.12% of ultimate tensile strength.     

加固厚度对软土地层大直径盾构隧道抗浮的影响

为研究软土地层隧道工程中软土地基的加固厚度对隧道上浮量的影响,以珠海市横琴杧洲隧道为依托,采用小应变硬化模型(HSS模型)作为软土本构模型,在PLAXIS 3D软件中建立了软土地层大直径盾构隧道的有限元模型,计算并对比了不同环形加固厚度下的隧道上浮量、河底土体位移和隧道周围土体的受扰动范围。结果表明:未对软土进行加固时,数值模拟得到的土体位移与二维理论推导的结果吻合较好; 软基地层预加固处理能使加固土体与隧道整体抗浮,有效抑制隧道局部的上浮变形; 软土加固厚度为0.10D(D为隧道外径)时,河底上浮量和隧道上浮量分别比未加固时减小了32.8%和36.4%,隧道上浮量和地层受扰动区域随加固厚度增加逐渐减小; 该工程中隧道环形加固厚度大于0.20D时,计算得到的管片上浮量控制在30 mm以内,河底最大上浮量控制在20 mm以内; 根据管片接头错台量和隧道上浮量的关系得到可控制管片接头偏差在5 mm以内,满足规范中管片拼装和验收时接头允许偏差量的要求。     

静动载下筋材变化对加筋土挡墙性能影响分析

为了研究动静荷载下,加筋长度及筋材类型变化对加筋土挡墙工作性能的影响,进行了7种工况下的加筋土挡墙模型试验,对比分析了加筋土挡墙的水平土压力、水平土压力系数、墙面水平位移和加载板竖向沉降及筋材应变等参数的发展规律。试验结果表明:动载下加筋土挡墙筋材应变随着加载时间的增长、加筋长度的减小、位置高度的增加而增大,且顶层筋材应变远远大于其他层;加筋长度及筋材横肋的减少明显降低挡墙的承载性能,格栅横肋减少导致挡墙极限承载力降低18% ,加筋长度减少使面板水平位移最大增大了2.2倍;与静载作用下相比,动载下土工格栅的侧向约束作用及网兜效应能够得到更好地发挥。     

Centrifuge tests to investigate global performance of geosynthetic-reinforced pile-supported embankments with side slopes

Three centrifuge model tests were conducted to investigate the influence of the number of geosynthetic layers and the pile clear spacing on the global performance of Geosynthetic-Reinforced Pile-Supported (GRPS) embankments with side slopes constructed on soft soil foundations. This study found that the change of the geogrid number from one to two did not significantly affect the foundation settlement, the geogrid deflection, and the vertical stress at the embankment base. For the GRPS embankment with a single geogrid layer, the geogrid strain distribution at the embankment base showed an “M” shape along the transverse direction with the maximum strain near the embankment shoulder. When two geogrid layers with sand in between were used, the upper and lower layers showed different strain distributions with the maximum strains happening near the embankment shoulder and at the center of the embankment for the upper and lower layers respectively. The strains of the upper geogrid were smaller than those of the lower geogrid. Smaller pile clear spacing reduced the geogrid deflection and the foundation settlement. Despite the change of the pile clear spacing, the progressive development of soil arching with the normalized displacement at the embankment base followed a similar trend without an obvious stress recovery stage.     

双向土工格栅处理桥头跳车的有限元分析

用ABAQUS有限元法对利用双向土工格栅加筋桥头路堤,从而控制桥头跳车的问题进行研究。分析加筋层间距、加筋层数、加筋模量以及路堤填土的力学性质对桥头路堤的沉降、水平位移、竖向应力分布的影响规律。结果表明:以合理的方案对桥头路堤作加筋处理,可以有效控制桥头路堤的沉降,并使得桥台与路堤间的沉降能平顺过渡,为控制桥头跳车创造了有利条件。     

Effect of anisotropic characteristics on the mechanical behavior of asphalt concrete overlay

Asphalt concrete (AC) overlays placed over old asphalt pavement have become an alternative to repairing and reinforcing pavements. The strength contributed by the AC overlay is strongly influenced by the anisotropic properties of the pavement material. This study was conducted to analyze the influence of anisotropy, modulus gradient properties, and the condition of the AC overlay and old pavement contact plane on the mechanical behaviors of AC overlays, as well as to quantify the influence of the degree of anisotropy on the mechanical behaviors of AC overlay by a sensitivity analysis (SA). The mechanical behaviors of the AC overlay were numerically obtained using the three-dimensional finite element method with the aid of ABAQUS, a commercial program. Variations in the AC overlay’s modulus as a function of temperature as well as the contact state between the AC overlay and AC layer were considered. The SA is based on standardized regression coefficients method. Comparing the mechanical behavior in terms of surface deflection, stress, and strain of the anisotropy model against those corresponding to the isotropic model under static loads show that the anisotropic properties had greater effects on the mechanical behavior of the AC overlay. In addition, the maximum shear stress in the AC overlay was the most significant output parameter affected by the degree of anisotropy. Therefore, future research concerning the reinforcement and repair of pavements should consider the anisotropic properties of the pavement materials.     

Laboratory and field investigation of the effect of geogrid-reinforced ballast on railway track lateral resistance

Continuous welded rail (CWR) tracks have particular advantages over common tracks with jointed rails such as increased ride comfort, reduced noise and vibration and decreased maintenance costs due to the removal of joints in rail connections. Alternatively, some complications associated with CWR tracks, for instance increased lateral forces, are the main reason of track buckling and its subsequent lateral deformation. These problems are usually more severe in curved tracks. In order to overcome the large lateral forces caused by temperature deviations of CWR tracks which results in railway vehicle instability, the ballasted track lateral resistance should be improved. Among the various methods proposed in this area, no specific study has been carried out on the effect of geogrid reinforcement on ballasted track lateral resistance. Thus, the present research was allocated to investigating the effect of geogrid on the lateral resistances of both single tie and track panel via laboratory and field tests. In this regard, at the first stage, the ballast layer was reinforced with various number of geogrid layers, the effect of which was investigated by conducting the single tie push test (STPT) in the lab environment to assess the optimum number of geogrid layers and their installation levels along the ballast layer thickness. Afterwards, a test track was executed in the field including various sections which were reinforced in the same way as the lab tests. Consequently, many STPTs and track panel displacement tests (TPDTs) were accomplished. As a result, the STPTs in the lab and field confirmed more than 31% and 42% increase in single tie lateral resistance for ballast layers reinforced respectively with one and two geogrid layers, while these values were reached to 29% and 40% in the case of TPDT.     

复合道面结构抗冲击性能试验与数值模拟

采用大型落锤冲击机对一种新型复合道面板进行了冲击荷载作用下的动态响应试验,该新型复合道面板自上而下依次为:土工格栅加固的沥青混凝土(AC)层、高强度混凝土(HSC)层及复合水泥基(ECC)层。通过落锤冲击试验获得道面层结构的损伤形式及变形特征,随后采用混凝土损伤材料模型模拟复合道面体系中混凝土类材料的动力特性。对材料模型的主要参数进行验证和确定,包括界面特性和各层材料的动力增长因数。根据新型复合道面体系的实验室落锤冲击试验结果,通过比较其破坏形式、损坏直径及位移值对数值模型进行了校核和验证。结果表明:提出的考虑界面性能和动力增长因数的三维数值模型能够较准确地模拟该复合道面体系在冲击荷载作用下的真实特性,且验证后的模型可进一步应用于研究不同因素（材料强度、断裂能及层间界面）对新型复合道面体系在不同冲击荷载作用下抗冲击性能的影响。     

道路改造中白改黑施工技术的探讨

结合工程实例,就道路“白改黑”改造的关键技术进行了探讨,分别对水泥混凝土路面处理技术、防水卷材铺设及沥青混凝土罩面技术进行了论述,实践证明：“白改黑”技术的使用取得了良好的社会效益。     

Physical and numerical modelling of strip footing on geogrid reinforced transparent sand

This paper presents the results of laboratory scale plate load tests on transparent soils reinforced with biaxial polypropylene geogrids. The influence of reinforcement length and number of reinforcement layers on the load-settlement response of the reinforced soil foundation was assessed by varying the reinforcement length and the number of geogrid layers, each spaced at 25% of footing width. The deformations of the reinforcement layers and soil under strip loading were examined with the aid of laser transmitters (to illuminate the geogrid reinforcement) and digital camera. A two-dimensional finite difference program was used to study the fracture of geogrid under strip loading considering the geometry of the model tests. The bearing capacity and stiffness of the reinforced soil foundation has increased with the increase in the reinforcement length and number of reinforcement layers, but the increase is more prominent by increasing number of reinforcement layers. The results from the physical and numerical modelling on reinforced soil foundation reveal that fracture of geogrid could initiate in the bottom layer of reinforcement and progress to subsequent upper layers. The displacement and stress contours along with the mobilized tensile force distribution obtained from the numerical simulations have complimented the observations made from the experiments.     

Behaviour of geogrid reinforced soil retaining wall with concrete-rigid facing

Monitoring was carried out during construction of a cast-in-situ concrete-rigid facing geogrid reinforced soil retaining wall in the Gan (Zhou)-Long (Yan) railway main line of China. The monitoring included the vertical foundation pressure and lateral earth pressure of the reinforced soil wall facing, the tensile strain in the reinforcement and the horizontal deformation of the facing. The vertical foundation pressure of reinforced soil retaining wall is non-linear along the reinforcement length, and the maximum value is at the middle of the reinforcement length, moreover the value reduces gradually at top and bottom. The measured lateral earth pressure within the reinforced soil wall is non-linear along the height and the value is less than the active lateral earth pressure. The distribution of tensile strain in the geogrid reinforcements within the upper portion of the wall is single-peak value, but the distribution of tensile strain in the reinforcements within the lower portion of the wall has double-peak values. The potential failure plane within the upper portion of the wall is similar to “0.3H method”, whereas the potential failure plane within portion of the lower wall is closer to the active Rankine earth pressure theory. The position of the maximum lateral displacement of the wall face during construction is within portion of the lower wall, moreover the position of the maximum lateral displacement of the wall face post-construction is within the portion of the top wall. These monitoring results of the behaviour of the wall can be used as a reference for future study and design of geogrid reinforced soil retaining wall systems.     

A theoretical strain transfer model between optical fiber sensors and monitored substrates

This study proposed an analytical model to investigate strain transfer mechanism between FBG sensor and measured geogrid. Both geometric and mechanical parameters (bonding length, bonding thickness, bonding width, and Young's modulus) of interaction interface can be taken into account in this model. Both laboratory tensile tests of geogrid and experimental data in published literatures were used to verify the developed model. Validation study shows that the maximum relative error between experimental values and theoretical values is 8.2%, indicating that this theoretical model can be used to reflect geogrid deformation. Parametric study indicates that bonding length, bonding thickness, bonding width, Young's modulus of adhesive layer, and substrate layer have significant influence on strain transfer coefficient. Grey Relational Analysis (GRA) method was used to analyze influencing sensitivity of different parameters. GRA parameter values of bonding width and length are higher than 0.72, indicating that bonding width and bonding length are relatively dominant factors affecting average strain transfer coefficient in comparison with bonding thickness, Young's moduli of substrate and adhesive layers (their related GRA values are all lower than 0.692).     

深基坑开挖对坑底桩受力变形特性的影响研究

随着基坑开挖深度不断加大,基坑开挖过程对已施工坑底工程桩的受力和变形影响不容忽视,针对该问题,对深开挖条件下桩基进行了桩身内力及位移的工程现场实测。对比分析不同位置及不同长度的坑底桩基在开挖过程中的受力和变形规律。结合工程建立三维数值分析模型,基桩采用钢筋混凝土损伤模型,探究了基坑开挖深度、桩的相对位置等因素对桩身轴力、桩土侧摩阻力和桩身刚度的影响规律。结果表明：基坑开挖过程中,桩身受拉力作用;桩身混凝土在产生塑性应变前,桩身拉力随开挖深度增加逐渐增大;桩身混凝土应变超过极限拉应变后,拉力开始逐渐降低,桩身塑性区侧摩阻力变化显著。此外,坑底桩位置和桩长是影响其受力变形特性的重要因素。相同位置处,长桩的桩顶竖向位移更小;靠近基坑中心部位的桩顶竖向位移大,桩身塑性拉应变区较大。