土工合成材料加筋土柔性桥台复合结构及应用

土工合成材料加筋土柔性桥台复合结构是美国“未来桥梁计划”中针对50多万座面临“更换问题”的中小型单跨桥梁而提出的一种新型技术，是土工合成材料加筋土柔性桥台技术的优化与提升。这种新型技术整体性好，可彻底避免传统桩承桥台与引道路基之间的差异沉降，近10年来已逐步在美国各州推广应用。在我国，尽管加筋土理论和技术应用取得了很大发展，但尚无真正的加筋土柔性桥台复合结构的工程实践方面的报道。文章收集了已有的加筋土柔性桥台复合结构工程案例和现场监测成果，整理归纳其结构特点和工作特性，结果表明：该结构通常具有统一的结构形式和技术特点，如加筋间距一般为0.2m、面层型式一般为模块式等；该结构具有施工简便快速、造价节省等优点，并表现出工后沉降小等良好的服役性能。     

Seismic performance of a whole Geosynthetic Reinforced Soil – Integrated Bridge System (GRS-IBS) in shaking table test

A scaled plane-strain shaking table test was conducted in this study to investigate the seismic performance of a Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) with a full-length bridge beam resting on two GRS abutments at opposite ends subjected to earthquake motions in the longitudinal direction. This study examined the effects of different combinations of reinforcement stiffness J and spacing S_v on the seismic performance of the GRS-IBS. Test results show that reducing the reinforcement spacing was more beneficial to minimize the seismic effect on the GRS abutment as compared to increasing the reinforcement stiffness. The seismic inertial forces acted on the top of two side GRS abutments interacted with each other through the bridge beam, which led to close peak acceleration amplitudes at the locations near the bridge beam. Overall, the GRS-IBS did not experience obvious structure failure and significant displacements during and after shaking. Shaking in the longitudinal direction of the bridge beam increased the vertical stress in the reinforced soil zone. The maximum tensile forces in the upper and lower geogrid layers due to shaking happened under the center of the beam seat and at the abutment facing respectively.     

Experimental study on the load bearing behavior of geosynthetic reinforced soil bridge abutments with different facing conditions

This paper presents an experimental study on reduced-scale model tests of geosynthetic reinforced soil (GRS) bridge abutments with modular block facing, full-height panel facing, and geosynthetic wrapped facing to investigate the influence of facing conditions on the load bearing behavior. The GRS abutment models were constructed using sand backfill and geogrid reinforcement. Test results indicate that footing settlements and facing displacements under the same applied vertical stress generally increase from full-height panel facing abutment, to modular block facing abutment, to geosynthetic wrapped facing abutment. Measured incremental vertical and lateral soil stresses for the two GRS abutments with flexible facing are generally similar, while the GRS abutment with rigid facing has larger stresses. For the GRS abutments with flexible facing, maximum reinforcement tensile strain in each layer typically occurs under the footing for the upper reinforcement layers and near the facing connections for the lower layers. For the full-height panel facing abutment, maximum reinforcement tensile strains generally occur near the facing connections.     

Applied bearing pressure beneath a reinforced soil foundation used in a geosynthetic reinforced soil integrated bridge system

Geosynthetic reinforced soil integrated bridge system (GRS-IBS) design guidelines recommend the use of a reinforced soil foundation (RSF) to support the dead loads that are applied by the reinforced soil abutment and bridge superstructure, as well as any live loads that are applied by traffic on the bridge or abutment. The RSF is composed of high-quality granular fill material that is compacted and encapsulated within a geotextile fabric. Current GRS-IBS interim implementation design guidelines recommend the use of design methodologies for bearing capacity that are based around rigid foundation behavior, which yield a trapezoidal applied pressure distribution that is converted to a uniform applied pressure that acts over a reduced footing width for purposes of analysis. Recommended methods for determining the applied pressure distribution beneath the RSF for settlement analyses follow conventional methodologies for assessing the settlement of spread footings, which typically assume uniformly applied pressures beneath the base of the foundation that are distributed to the underlying soil layers in a fashion that can reasonably be modeled with an elastic-theory approach. Field data collected from an instrumented GRS-IBS that was constructed over a fine-grained soil foundation indicates that the RSF actually behaves in a fairly flexible way under load, yielding an applied pressure distribution that is not uniform or trapezoidal, and which is significantly different than what conventional GRS-IBS design methodologies assume. This paper consequently presents an empirical approach to determining the applied pressure distribution beneath the RSF in GRS-IBS construction. This empirical approach is a useful first step for researchers, as it draws important attention to this issue, and provides a framework for collecting meaningful field data on future projects which accurately capture real GRS-IBS foundation behavior.     

Numerical parametric study of geosynthetic reinforced soil integrated bridge system (GRS-IBS)

A 2-D finite flement model was developed in this study to conduct a FE parametric study on the effects of some variables in the performance of geosynthetic reinforced soil integrated bridge system (GRS-IBS). The variables investigated in this study include the effect of internal friction angle of backfill material, width of reinforced soil foundation (RSF), secondary reinforcement within bearing bed, setback distance, bearing width and length of reinforcement. Other important parameters such as reinforcement stiffness and spacing were previously investgated by the authors. The performance of GRS-IBS were investgated in terms of lateral facing displacement, strain distribution along reinforcement, and location of potential failure zone. The results showed that the internal friction angle of backfill material has a significant impact on the performance of GRS-IBS. The secondary reinforcement, setback distance, and bearing width have low impact on the performance of GRS-IBS. However, it was found that the width of RSF and length of reinforcement have negligible effect on the performance of GRS-IBS. Finally, the potential failure envelope of the GRS-IBS abutment was found to be a combination of punching shear failure envelope (top) that starts under the inner edge of strip footing and extends vertically downward to intersect with Rankine active failure envelope (bottom).     

循环荷载作用下格栅防护柔性埋地管道的性能分析

交通循环荷载下埋地管道性能与防护是当前研究的重点问题,首先针对格栅加筋柔性管道开展试验研究,分析管道埋深H为3D(D为管道外径)时循环荷载水平和频率、首层格栅埋深、长度、层间距和筋材层数对管道力学与变形性能的影响,试验结果表明:首层格栅最佳埋深u为0.4B(B为加载板宽度),最佳层间距ug为0.5B,最佳铺设长度L为5D;增加格栅层数能显著增强土体,从而有效减少管道变形和加载板沉降;提高荷载水平或降低荷载频率使管道变形、加载板沉降和格栅应变整体显著增加;格栅应变随其与加载板中心的距离增加而减小,格栅中心点应变随循环次数增加呈现先增加后减少的趋势。进而,基于有限元数值模拟分析管道埋深H、加载板宽度B和管径D对管道力学性能的影响,数值结果表明增加管道埋深或减小加载板宽度,管道径向变形减小;同等荷载作用下,减小管径时管道径向变形增大,筋材加筋效果减弱,适当增加管道直径,有利于筋材加筋作用的充分发挥,从而减小管道径向变形。     

Numerical evaluation of the performance of a Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) under different loading conditions

This paper presents the results of a finite element (FE) numerical analysis that was developed to simulate the fully-instrumented Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) at the Maree Michel Bridge in Louisiana. Four different loading conditions were considered in this paper to evaluate the performance of GRS-IBS abutment due to dead loading, tandem axle truck loading, service loading, and abnormal loading. The two-dimensional FE computer program PLAXIS 2D 2016 was selected to model the GRS-IBS abutment. The hardening soil model proposed by Schanz et al., (1999) that was initially introduced by Duncan and Chang (1970) was used to simulate the granular backfill materials; a linear-elastic model with Mohr-Coulomb frictional criterion was used to simulate the interface between the geosynthetic and backfill material. Both the geosynthetic and the facing block were modeled using linear elastic model. The Mohr-Coulomb constitutive model was used to simulate the foundation soil. The FE numerical results were compared with the field measurements of monitoring program, in which a good agreement was obtained between the FE numerical results and the field measurements. The range of maximum reinforcement strain was between 0.4% and 1.5%, depending on the location of the reinforcement layer and the loading condition. The maximum lateral deformation at the face was between 2 and 9 mm (0.08%–0.4% lateral strain), depending on the loading condition. The maximum settlement of the GRS-IBS under service loading was 10 mm (0.3% vertical strain), which is about two times the field measurements (～5 mm). This is most probably due to the behavior of over consolidated soil caused by the old bridge. The axial reinforcement force predicted by FHWA (Adams et al., 2011b) design methods were 1.5–2.5 times higher than those predicted by the FE analysis and the field measurements, depending on the loading condition and reinforcement location. However, the interface shear strength between the reinforcement and the backfill materials predicted by Mohr-Coulomb method was very close to those predicted by the FE.     

Recent advances in geosynthetic-reinforced retaining walls for highway applications

Geosynthetic-reinforced retaining (GRR) walls have been increasingly used to support roadways and bridge abutments in highway projects. In recent years, advances have been made in construction and design of GRR walls for highway applications. For example, piles have been installed inside GRR walls to support bridge abutments and sound barrier walls. Geosynthetic layers at closer spacing are used in GRR walls to form a composite mass to support an integrated bridge system. This system is referred to as a geosynthetic-reinforced soil (GRS)-integrated bridge systems (IBS) or GRS-IBS. In addition, short geosynthetic layers have been used as secondary reinforcement in a GRR wall to form a hybrid GRR wall (HGRR wall) and reduce tension in primary reinforcement and facing deflections. These new technologies have improved performance of GRR walls and created more economic solutions; however, they have also created more complicated problems for analysis and design. This paper reviews recent studies on these new GRR wall systems, summarizes key results and findings including but not limited to vertical and lateral earth pressures, wall facing deflections, and strains in geosynthetic layers, discusses design aspects, and presents field applications for these new GRR wall systems.     

U型桥台常见病害机理与加固技术研究

U型桥台作为经典的桥台结构形式,在桥梁设计中运用十分广泛。在桥梁运营过程中,U型桥台由于受力形式复杂,容易出现各种病害。根据大量的现场调查,U型桥台的常见病害具有共性。本文在归纳U型桥台主要病害类型的基础上,深入分析U型桥台病害机理,提出U型桥台加固方法。运用ANSYS有限元软件的非线性分析功能,建立加固前后桥台的三维空间实体模型,通过不同高度和宽度的桥台受力分析,对比研究加固前后U型桥台的应力和位移情况,从而对各种加固方法的加固效应加以评估。研究表明:土压力等荷载作用下导致的台身主拉应力偏大,尤其是前墙与侧墙交汇处,是桥台台身开裂的主要内因,因地制宜采用合适的加固方式可有效防止桥台开裂。     

Measured and simulated results of a Kenaf Limited Life Geosynthetics (LLGs) reinforced test embankment on soft clay

For the first time, woven Kenaf Limited Life Geosynthetics (LLGs) were used for short term reinforcement of full scale embankment constructed on soft clay and their behavior is presented. The observed data in terms of settlements, excess pore water pressures and deformations or stresses in the reinforcements were compared with the simulated data. Two types of Kenaf LLGs were utilized, namely: coated and not coated with polyurethane. The coating can reduce water absorption and increase their life time. Subsequently, numerical simulations were performed on the behavior of Kenaf LLGs reinforced embankment using 2D and 3D finite element software. The rates of settlement from FEM 2D method overestimated the observed settlements data while the FEM 3D predictions agreed with observed settlements due to the three-dimensional geometrical loading of the embankment with length to width ratio (L/B) of 1.0. Regarding the maximum excess pore-water pressures at the locations of 3 m and 6 m depth, the FEM 2D analyses overestimated while the FEM 3D simulation yielded satisfactory agreement with the observed data. The reinforcement deformations and stresses in both coated and non-coated Kenaf LLGs reinforcement have higher values at the middle portions of the embankment and the predicted results from FEM 3D simulation yielded closer deformations of Kenaf LLGs reinforced than the FEM 2D simulation. Consequently, FEM 3D simulation captured the overall behavior of the Kenaf LLGs reinforced embankment with more reasonable agreement between the field observations and the predicted values compared to the FEM 2D simulation. The behavior of the sections on coated and non-coated LLGs were similar. The Kenaf LLGs can be applied for short term embankment reinforcement in order to improve the stability of embankment on soft clay.     

Numerical study of geosynthetic reinforced soil bridge abutment performance under static and seismic loading considering effects of bridge deck

Although the use of Geosynthetic Reinforced Soil (GRS) bridge abutments has been increasing, the seismic performance of such structures has remained a significant concern due to their unknown behavior in load-bearing and stress distribution under bridge load and seismic conditions simultaneously. This paper investigates the static and dynamic response of GRS bridge abutment. A series of numerical models representing the realistic field conditions of these structures, including two reinforced soil walls and a single span deck that restrains the top of walls, rather than equivalent surcharge load, was developed. The calibrated numerical model in FLAC program was used to evaluate the effects of horizontal restraint from the deck on the GRS wall displacements and reinforcement loads at the end of construction and under harmonic base acceleration up to 0.5 g. Results indicated that the restraint mobilized from the bridge deck presence, considerably affected the results at both the end of construction and after the dynamic load was applied. Moreover, a series of the parametric studies were performed to investigate the influences of backfill soil relative compaction, reinforcement stiffness, reinforcement length, and reinforcement vertical spacing on the response of GRS abutments at the end of construction and post dynamic state.     

交通荷载作用下桥头跳车的加筋效应分析

采用土工格栅与土动力相互作用模型并计入格栅纵肋、横肋效应,对某桥台试验进行了加筋和不加筋对比分析,结果表明:土工格栅被拉伸后形成的兜起效应提高了路基的承载能力、减小了填土内的破坏区域,有效地消减由于交通荷载作用产生的桥台与填土之间的沉降差。     

大曲率桥梁的安装过程和梁格模型的准确性分析

分析了施工方法对大曲率桥梁应力和变形方面的影响,对利用梁格模型预测施工方法的准确性进行了分析。研究包括施工过程中的应力和变形分析,并将其与梁格模型预测的结果对比。研究结果表明:1)在梁安装过程中会产生翘曲应力;2)在梁安装过程中改进梁格模型的预测数值会比经典梁格模型的预测更为准确;3)当梁由外向内安装时,梁格模型预测的变形要小于梁从内向外安装时的数值。     

Welding stresses and distortions in multi-cellular box girders

The formation of residual stresses and deformations in weldments is reviewed and an experimental study of eight multi-cellular model steel girders is described. These models represent, to approximately quarter-scale, the construction of double-bottom ships' hulls. Details of the fabrication and welding procedure are given and measured values of residual strains, stresses and deformations are presented. Clear patterns of behaviour are identified and a comparison of experimental and predicted values shows reasonable agreement.     

桥涵台背回填钻孔注浆处理施工工法

从桥头跳车产生的原因方面进行了论述,介绍了桥梁台背的加固思想和加固机理,并阐述了台背加固的技术要求及施工方法,加固处理后压实度和承载力得到了较大提高,加固效果良好。     

Experimental study on the load bearing behavior of geosynthetic reinforced soil bridge abutments on yielding foundation

This paper presents an experimental study of the load bearing behavior of geosynthetic reinforced soil (GRS) bridge abutments constructed on yielding clay foundation. The effects of two different ground improvement methods for the yielding clay foundation, including reinforced soil foundation and stone column foundation, were evaluated. The clay foundation was prepared using kaolin and consolidated to reach desired shear strength. The 1/5-scale GRS abutment models with a height of 0.8 m were constructed using sand backfill, geogrid reinforcement, and modular block facing. For the GRS abutments on three different yielding foundations, the reinforced soil zone had relatively uniform settlement and behaved like a composite due to the higher stiffness than the foundation layers. The wall facing moved outward with significant movements near the bottom of facing, and the foundation soil in front of facing showed obvious uplifting movements. The vertical stresses transferred from the footing load within the GRS abutment and on the foundation soil are higher for stiffer foundation. The improvement of foundation soil using geosynthetic reinforced soil and stone columns could reduce the deformations of GRS abutments on yielding foundation. Results from this study provide insights on the practical applications of GRS abutments on yielding foundation.     

Shanghai center project excavation induced ground surface movements and deformations

Empirical data on deep urban excavations can provide designers a significant reference basis for assessing potential deformations of the deep excavations and their impact on adjacent structures. The construction of the Shanghai Center involved excavations in excess of 33-m-deep using the top-down method at a site underlain by thick deposits of marine soft clay. A retaining system was achieved by 50-m-deep diaphragm walls with six levels of struts. During construction, a comprehensive instrumentation program lasting 14 months was conducted to monitor the behaviors of this deep circular excavation. The following main items related to ground surface movements and deformations were collected: (1) walls and circumferential soils lateral movements; (2) peripheral soil deflection in layers and ground settlements; and (3) pit basal heave. The results from the field instrumentation showed that deflections of the site were strictly controlled and had no large movements that might lead to damage to the stability of the foundation pit. The field performance of another 21cylindrical excavations in top-down method were collected to compare with this case through statistical analysis. In addition, numerical analyses were conducted to compare with the observed data. The extensively monitored data are characterized and analyzed in this paper.     

Erection behavior and grillage model accuracy for a large radius curved bridge

The effects of construction procedures on the stresses and deformations in a large radius, horizontally curved, plate girder, bridge were examined along with the accuracy with which grillage models predicted the construction behavior. The examination included a study of the stresses and deformations during construction and a comparison of those quantities to the grillage model predictions. Results from the study indicated that, for the structure that was examined: (1) appreciable warping stresses were generated during girder erection; (2) the classical grillage model predictions were less accurate during girder erection while the “modified” model predictions were more accurate during deck placement; and (3) the predicted grillage model deflections were smaller for an exterior-to-interior girder erection procedure than an interior-to-exterior procedure.     

Performance of geosynthetic-reinforced flexible pavements in full-scale field trials

The paper presents the results of a series of full-scale trials carried out in Thailand examining the performance of geosynthetics as reinforcement for flexible pavements. The geosynthetics were embedded at different pavement depths and the structural response was monitored across four test sections by means of strain gauges, pressure sensors, deflection points and deflection plates. The results show that all reinforcement configurations helped reduce the vertical static stresses developed at the base of the pavement by up to 66% and by up to 72% for dynamic stresses. The performance enhancement expected to prolong the lifespan of the base layers. The reinforcement layers closer to the base experienced the highest lateral strains of up to 0.13%, providing evidence that geosynthetics can also effectively reduce lateral spreading. All reinforcement configurations helped enhance rut resistance with maximum traffic benefit ratio (TBR) of 13.70, effectiveness ratio (EF) of 12.70 and minimum rutting reduction ratio (RRR) of 0.74. The best configuration included a geotextile within the asphalt concrete layer and a geogrid under the base layer. Non-linear finite element analyses of the test sections predicted very well the strains and stresses in the pavement. The study provides a benchmark for future studies in this field and concludes that geosynthetics can help increase maintenance periods and extend the lifetime of flexible pavements.     

Repeated loading of soil containing granulated rubber and multiple geocell layers

Sandy soil/aggregate, such as might be required in a pavement foundation over a soft area, was treated by the addition of one or more geocell layers and granulated rubber. It was then subjected to cyclic loading by a 300 mm diameter plate simulative of vehicle passes. After an initial study (that established both the optimum depth of the uppermost geocell layer and of the geocell inter-layer spacing should be 0.2 times plate diameter), repeated loading was applied to installations in which the number of geocell layers and the presence or absence of shredded rubber layers in the backfill was changed. The results of the testing reveal the ability of the composite geocell-rubber-soil systems to ‘shakedown’ to a fully resilient behavior after a period of plastic deformation except when there is little or no reinforcement and the applied repeated stresses are large. When shakedown response is observed, then both the accumulated plastic deformation prior to a steady-state response being obtained and the resilient deformations thereafter are reduced. Efficiency of reinforcement is shown to decrease with number of reinforcement layers for all applied stress levels and number of cycles of applied loading. The use of granulated rubber layers are shown to reduce the plastic deformations and to increase the resilient displacements compared to the comparable non-rubber construction. By optimal use of geocells and granulated rubber, deformations can be reduced by 60–70% compared with the unreinforced case while stresses in the foundation soil are spread much more effectively. On the basis of the study, the concept of combining several geocell layers with shredded rubber reinforcement is recommended for larger scale trials and for economic study.