考虑蠕变、地震效应的土工格栅砂性土加筋挡墙弹塑性有限元分析

土工合成材料加筋土挡土墙具有优良的抗震性能,但是由于加筋用的土工合成材料具有显著的蠕变及应力松弛特性,需要深入研究加筋土挡墙在经历蠕变后的地震动力行为及震后的进一步蠕变以理解其全面的静动力学性能。在已有研究的基础上,应用笔者提出的土工合成材料循环受载、蠕变和应力松弛统一本构模型模拟土工格栅的力学行为,考虑到土工格栅加筋土挡土墙的填土一般为砂性土,而砂性土一般蠕变变形较小,本文应用可以模拟砂土述砂性土非线性静动力性能的广义塑性模型模拟填土,未考虑其蠕变变形。结果表明,在正常加筋长度和密度情况下,加筋土挡墙在经受地震前的蠕变变形会趋于稳定,但筋材内力重分布明显;地震作用使得加筋土挡墙产生较大变形,加筋内力出现较大增长,但结构并未破坏;地震后加筋土挡墙蠕变变形继续发展,而土工格栅加筋会出现内力松弛现象。     

土工合成材料对路堤长期稳定性及工后沉降的负面影响分析

从土工合成材料作用机理着手,分析了在高速公路软基处理中使用土工合成材料会对路堤长期稳定性及工后沉降产生负面影响。土工合成材料的长期强度损失及模量的降低会降低路堤的长期稳定性。土工合成材料的长期变形和松弛对工后沉降也会产生一定的不利影响。某高速公路试验段实测资料表明,一层土工布对工后沉降的影响可忽略不计,两层土工布约增加工后沉降40～50mm。     

基于特种筋材蠕变试验预应变加筋法应用研究及计算模型

通过对目前广泛应用于加筋土工程的特种筋材——CE131土工网、SDL25土工格栅进行了不同应力水平作用下的长期荷载蠕变试验。为比较不同强度土工合成材料的蠕变特性,研究制作6个CE131土工网试样和4个SDL25土工格栅试样。通过大量的试验结果分析,得出特种筋材CE131土工网、SDL25土工格栅的长期强度为抗拉强度的30%～40%,并提出在长期强度条件下特种筋材的预应变值大小及其计算公式。这对施工中的预应变加筋法技术有重要的参考价值。     

基于特种筋材蠕变试验预应变加筋法 应用研究及计算模型

 通过对目前广泛应用于加筋土工程的特种筋材——CE131土工网、SDL25土工格栅进行了不同应力水平作用下的长期荷载蠕变试验。为比较不同强度土工合成材料的蠕变特性，研究制作6个CE131土工网试样和4个SDL25土工格栅试样。通过大量的试验结果分析，得出特种筋材CE131土工网、SDL25土工格栅的长期强度为抗拉强度的30%～40%，并提出在长期强度条件下特种筋材的预应变值大小及其计算公式。这对施工中的预应变加筋法技术有重要的参考价值。     

软土地基加筋土挡墙数值模拟及稳定性探讨

 对一软土地基加筋土挡墙建立二维数值模型,模拟其在分级堆载情况下挡墙和地基内的沉降、水平位移、土压力,以及土工格栅轴向应变的变化规律,模拟结果与现场实测结果基本吻合。采用有限元强度折减法计算的挡墙稳定性和滑裂面位置与实测情况一致,表现为深层滑动失稳。模拟和实测的各层筋材最大应变出现在距墙面4～6 m的位置,与目前土工合成材料加筋挡墙设计理论的朗肯破坏面位置不同,其原因是目前的挡墙设计理论基于刚性地基假定,未考虑地基变形对筋材应变分布及稳定性的影响。采用该数值模型探讨加长挡墙底部筋材对其稳定性的影响,得出挡墙稳定性与底部筋材加长长度和层数关系密切。得到的挡墙稳定性与筋材加长长度和层数的关系曲线,对于软土地基加筋土挡墙设计有指导意义。     

地震作用下模块式面板土工合成材料加筋土挡墙的内部稳定分析

由于造价低廉,性能优良且外表美观,模块式面板土工合成材料加筋土挡墙在我国交通及城建等领域有着广泛的应用前景。大量的工程实践证明,土工合成材料加筋土挡墙的抗震性能良好,但仍有必要进行合理的抗震设计,而内部稳定校核是加筋土挡墙抗震设计的一个重要环节,它一定程度上决定了高烈度地震区加筋土挡墙的配筋方式及配筋密度。应用非线性动力有限元法分析不同加筋长度、加筋间距及不同地震作用下模块式土工合成材料加筋土挡墙在地震作用下的内部稳定,研究了筋材蠕变对加筋土挡墙动力内部稳定的影响,并将有限元分析的结果与国外规范建议的内部稳定校核结果进行比较。研究结果表明,在正常配筋密度条件下,各层筋材最大内力的位置与规范建议的位置有一定的区别,墙体下部更加远离面板;且筋材的最大内力沿高度的分布与该规范计算结果差别较大;而筋材蠕变使筋材的内力出现重分布。     

加筋挡土墙长期工作性能的黏弹塑性有限元分析

随着工程上的广泛应用，作为设计中的关键技术问题之一，土工合成材料加筋挡土墙长期工作性能的合理评价日益得到重视，对此必须考虑加筋材料的非线性蠕变效应。对于加筋挡土墙，采用黏弹塑性流变模型和黏弹性本构模型分别考虑填土与土工合成材料的非线性蠕变性，合理考虑筋材与填土、填土与面板及面板之间的相互作用效应，同时在计算中反映逐层填筑过程，采用增量一初应变迭代法，对土工合成材料加筋挡土墙结构的工作性能评价发展了二维有限元数值分析方法。基于Denver黏性土试验挡土墙的试验结果确定计算参数，利用所建议的分析方法对Denver黏性土试验挡土墙进行了数值计算与分析，通过与实测结果及与常规方法的对比分析，论证了所建议的有限元数值分析方法的合理性及其可靠性。     

不同筋材界面剪切试验研究

为了研究废旧轮胎、土工格室和土工格栅3种不同土工合成材料的筋-土界面抗剪特性,对试样开展了一系列大型直剪试验。对比了3种筋材的加筋效果,并研究了竖向荷载对筋-土界面抗剪强度和剪应力-剪切位移曲线特征的影响。试验结果表明:筋-土界面的剪切应力与剪切位移关系为非线性;几种不同筋材加筋效果较为显著,其中废旧轮胎的加筋效果最为明显;筋-土界面的黏聚力提高较大,内摩擦角变化相对较小,表明筋-土界面主要依靠提高黏聚力增大其抗剪强度。确定了各筋材加筋界面抗剪强度指标,并分析了3种筋材的加筋机理。     

关于土工合成材料加筋设计的若干问题

目前土工合成材料加筋技术被广泛应用,但人们对于加筋土中筋材与土间的相互作用的机理的认识还不够深入,因而在设计中总体上趋于保守。结合岩土工程的设计理论,指出土工合成材料在设计方法方面的不合理性;对于加筋挡土墙、加筋土坡、加筋软土地基上的土堤和桩网结构的设计分别进行了讨论;结合一些案例中的实测和预计的筋材应变和应力,进一步指出目前设计的保守性。最后指出,目前基于极限平衡法的设计不尽合理,而通过变形协调的筋土共同作用的研究,采用更能反映其相互作用机理的设计方法是非常必要的。     

单向土工格栅加筋土的流变模型

在研究HDPE单向土工格栅的蠕变和应力松弛特性的基础上，建立了单向土工格栅的流变模型。将加筋土视为由筋、土组成的宏观均匀材料，建立单向土工格栅加筋土体的流变模型。分析表明，在承受长期荷载作用的加筋土的本构关系中，必须考虑由聚合物为原料制作的筋材所具有的明显时间相关的力学行为。     

A new apparatus for the study of pullout behaviour of soil-geosynthetic interfaces under sustained load over time

At present, the design of geosynthetic-reinforced soil structures is executed with reference to the tensile strength of the reinforcement obtained from in-air short-term tensile tests, decreasing this value by means of several factors. Among these, the creep effect resulting from in-air tensile creep tests reduces tensile strength the most. Consequently, this procedure does not take into account the effects of soil confinement and interaction on the tensile response of the reinforcements. This paper illustrates a new large-scale pullout prototype apparatus, with the capacity to investigate the behaviour of a geosynthetic reinforcement embedded in a compacted soil and subject to a tensile load kept constant over time. The apparatus allows the verification of how the soil can modify the prediction of the long-term behaviour of geosynthetics. Results in terms of confined tensile strains were analysed, and the comparison of those values with the strains obtained by in-air tensile creep tests has led to the conclusion that the creep reduction factor might be conservative. Moreover, the confined tensile strains were related to the apparent coefficients of friction to propose a new procedure capable of determining the design interaction parameter under long-term pullout load as a function of the allowable reinforcement strains.     

Effect of soil-reinforcement interaction coefficient on reinforcement tension distribution of reinforced slopes

This paper examines the effect of the mobilized reinforcement tension within reinforced soil slope at a different level of soil-geosynthetic interaction. The mobilized reinforcement tension is assumed, in most design methods for the internal stability of reinforced slopes, to be equal to mobilized soil forces computed using a limit equilibrium method. However, comparison with the reinforcement tension force measured in the field has shown that this approach is conservative. This paper examines the effects of the soil-reinforcement interaction coefficient on the tensile redistribution of geosynthetics. The modified process of Bishop Method of slope stability analysis is used to locate the critical slip surface and to calculate the mobilized reinforcement tensile force. The reinforcement forces obtained from field data and on centrifuge model test results for a reinforced slope problem are used to examine the relationship between mobilized reinforcement tensile force and mobilized soil shear strength.     

Experimental evaluation of geosynthetics as reinforcement for shotcrete

One of the commonly used stabilization systems for rock tunnels is shotcrete. This fine aggregate mortar is usually reinforced for improving its tensile and shear strength. In deep tunnels, its capacity to absorb energy has been recently considered for design purposes, as large displacements of the wall are expected. Two of the most used materials of reinforcement are steel welded-wire mesh and fibers (steel or polypropylene) in the shotcrete mix. This study presents the results and discussion of an experimental test program conducted to obtain the load-deformation curves of reinforced shotcrete, according to ASTM C 1550, using geosynthetics grids and geotextiles as alternative reinforcement materials. In addition, plain shotcrete and steel welded-wire mesh reinforced shotcrete specimens are also considered in the experimental program as benchmark cases. The experimental results are analyzed in terms of maximum strength and toughness. Results show that the use of geosynthetics as a reinforcement material is a promising alternative to obtain shotcrete with energy absorption capacity comparable with the most common reinforcement materials used.     

加筋土护岸挡墙的黏弹塑性有限元分析

结合重庆渝中区长江滨江路加筋土护岸工程的安全性评估和加固方案研究,发展了二维有限元数值分析方法。分析中考虑加筋材料的非线性蠕变效应,土体采用黏弹塑性流变模型和加筋材料采用黏弹性模型,并考虑加筋材料与填土、填土与面板及面板之间的相互作用;计算模拟了加筋土工程逐层填筑的施工过程,采用增量–初应变迭代法对各种工况进行了分析计算。计算结果与传统方法计算结果、现场实测数据进行了对比,初步证明本文方法的有效性,并得到了高大加筋土挡墙的破坏发展模式、加筋材料拉力分布规律以及加筋土护岸挡墙的安全性指标。     

GFRP筋的高温蠕变性能试验分析

通过对21组,共72根不同应力状态、不同温度下GFRP筋的蠕变性能进行的试验和分析,表明:随时间的延长GFRP筋的应变逐渐增大,而同一应力水平的GFRP筋试件随温度的升高,应变有增大的趋势。根据试验结果,可以确定预应力GFRP筋增强混凝土构件在火灾高温条件下GFRP筋的预应力损失值。     

Long-term behavior of GRS retaining walls with marginal backfill soils

The creep of geosynthetics leads to the increase of Geosynthetic-Reinforced Soil (GRS) wall's deformation. More importantly, the influences of creep of geosynthetics are also affected by the creep properties of soils. In this paper, a Finite Element procedure was validated against a model test on the creep response of a clay–geotextile composite. An extensive parametric study was then carried out to investigate the long-term response of 8-meter-high model GRS walls with marginal backfill soils. The influences of backfill creep, reinforcement creep, reinforcement stiffness, reinforcement length and reinforcement spacing were analyzed. A long-term analysis was conducted for 5 years and the results at the end of construction (EOC) and 5 years afterwards were compared. It is found from the analysis that the relative creep rate between geosynthetic reinforcement and backfill soil influenced not only wall deformation but also reinforcement loads and stress states in the soils. The load distribution in backfill soil and reinforcement is the result of battling between their time-dependent properties. Large reinforcement creep can lead to large post-construction deformation and increase in soil stress; on the other hand, large soil creep can induce a significant increase in reinforcement load. It is hence necessary to take into account the relative creep rate of reinforcement and backfill soil in the design of GRS walls. It may not be adequate to consider only the long-term strength of reinforcement, which is the state-of-the-practice at present.     

GFRP筋活性粉末混凝土梁受力性能试验研究

为了研究GFRP筋活性粉末混凝土梁的受力性能,对8根梁进行三分点加载试验,获得了试验梁的开裂弯矩、极限弯矩以及各级荷载作用下的变形及裂缝分布与开展。试验结果表明：活性粉末混凝土试验梁纯弯区段开裂应变 (750×10-6) 约为普通混凝土梁的7倍,开裂弯矩及截面塑性系数计算应考虑纵向受拉GFRP筋的有利影响。GFRP筋活性粉末混凝土梁正截面受弯破坏形式可分为纵向受拉GFRP筋被拉断而受压边缘活性粉末混凝土未被压碎的受拉破坏,受压边缘活性粉末混凝土被压碎(5500×10-6)而纵向受拉GFRP筋未被拉断的受压破坏,以及纵向受拉GFRP筋被拉断的同时受压边缘活性粉末混凝土被压碎的界限破坏等三种。对于受压破坏可按拉区应力为0.25倍活性粉末混凝土抗拉强度来考虑拉应力对正截面受弯承载力的贡献。对于受拉破坏则基于材料应力-应变关系通过数值积分迭代计算正截面受弯承载力。刚度及裂缝宽度计算的关键是合理计算使用阶段GFRP筋的拉应力,在计算GFRP筋拉应力时所用弯矩应为外荷载弯矩减去拉区活性粉末混凝土拉应力合力对压区合力点的弯矩。图9表12参10     

土工合成材料双向拉伸多功能试验机的研制及初步应用

为揭示土工合成材料双向拉伸状态下的力学特性,自主研制了一台双向拉伸多功能试验机,能够进行瞬时和长期蠕变双向拉伸试验。瞬时拉伸采用电机控制,可以实现两个方向任意比例下应力和应变加载;蠕变拉伸采用法码加载,可同时进行3组大变形蠕变拉伸试验。经初步应用表明,该试验机能够进行复杂应力、应变路径下土工合成材料双向拉伸试验,为土工合成材料双向拉伸力学特性的研究提供了一种科学有效手段。     

Residual Deformation of Geosynthetic-Reinforced Sand in Plane Strain Compression Affected by Viscous Properties of Geosynthetic Reinforcement

A series of plane strain compression (PSC) tests were performed on large sand specimens unreinforced or reinforced with prototype geosynthetic reinforcements, either of two geogrid types and one geocomposite type. Local tensile strains in the reinforcement were measured by using two types of strain gauges. Sustained loading (SL) under fixed boundary stress conditions and cyclic loading (CL) tests were performed during otherwise monotonic loading at a constant strain rate to evaluate the development of creep deformation by SL and residual deformation by CL of geosynthetic-reinforced sand and also residual strains in the reinforcement by these loading histories. It is shown that the creep deformation of geosynthetic-reinforced sand develops due to the viscous properties of both sand and geosynthetic reinforcement, while the residual deformation of geosynthetic-reinforced sand during CL (defined at the peak stress state during CL) consists of two components: i) the one by the viscous properties of sand and reinforcement; and ii) the other by rate-independent cyclic loading effects with sand. The development of residual deformation of geosynthetic-reinforced sand by SL and CL histories had no negative effects on the subsequent stress-strain behaviour and the compressive strength was maintained as the original value or even became larger by such SL and CL histories. The local tensile strains in the geosynthetic reinforcement arranged in the sand specimen subjected to SL decreased noticeably with time, due mainly to lateral compressive creep strains in sand during SL of geosynthetic-reinforced sand. This result indicates that, with geosynthetic-reinforced soil structures designed to have a sufficiently high safety factor under static loading conditions because of seismic design, it is overly conservative to assume that the tensile load in the geosynthetic reinforcement is maintained constant for long life time. Moreover, during CL of geosynthetic-reinforced sand, the residual tensile strains in the geosynthetic reinforcement did not increase like global strains in the geosynthetic-reinforced sand that increased significantly during CL. These different trends of behaviour were also due to the creep compressive strains in the lateral direction of sand that developed during CL of geosynthetic-reinforced sand.     

配筋再生混凝土棱柱体徐变试验研究

再生混凝土的徐变是工程中亟待解决的基础问题,而目前对于配筋再生混凝土棱柱体徐变的试验研究鲜见报道。为此,对11个配筋再生混凝土棱柱体试件进行长期轴压荷载下的徐变试验,变化参数包括再生粗骨料取代率、再生细骨料取代率和应力比。对比分析了不同设计参数配筋再生混凝土棱柱体的初始应变、徐变应变及变化参数对其长期轴压荷载下徐变的影响。结果表明：再生粗、细骨料的掺入会增大配筋再生混凝土棱柱体的徐变,其中再生细骨料对徐变的影响相对明显;应力比对其初始应变影响较大,较高应力比下配筋再生混凝土棱柱体的徐变应变明显增大;配筋再生混凝土棱柱体徐变过程中截面纵筋与混凝土的应力重分布,钢筋所承担应力的比例增加,其徐变有所减小。基于试验结果,给出了配筋再生混凝土棱柱体在长期轴压荷载下变形计算的实用公式,计算结果与实测变形符合较好。