土工合成材料加筋的试验研究

以 6种不同种类的国产土工合成材料为加筋材料 ,即针刺无纺土工织物、涤纶纤维经编土工格栅、玻璃纤维土工格栅、单向塑料拉伸土工格栅、双向塑料拉伸土工格栅和土工网 ,进行三轴试验比较各种土工合成材料对砂的加筋效果 ;进行直剪试验和拉拔试验比较各种土工合成材料与填料 (砂和石灰粉煤灰 )的界面作用特性 ,得到一些有益的结论 ,可指导土工合成材料的优选和研究土工合成材料的加筋机理。     

浅谈土工格栅在公路工程中的应用

对塑料土工格栅、玻纤土工格栅和经编土工格栅的性能做了比较,对三种土工格栅的应用进行了总结,并对目前公路工程中的加筋选材问题提出了一些观点,以利于土工合成材料加筋技术在具体工程中的应用.     

塑料土工格栅在加筋土档土墙的应用

塑料土工格栅是一种新兴的土工合成材料 ,近年来在加筋土挡土墙中得到广泛的应用。文中详细叙述了塑料土工格栅加筋土挡土墙的特点 ,塑料土工格栅与土相互作用的两种加筋机理 :摩擦加筋理论和似粘聚力理论 ,总结了塑料土工格栅加筋土挡土墙的优越性     

土工合成材料与细粒尾矿界面作用特性的试验研究

以有色金属铜矿的细粒尾矿为加筋填料土，利用拉拔试验，研究土工合成材料(加筋带和土工格栅)在填料土不同密实度、含水量及垂直荷载作用下，土工合成材料与填料土的界面作用特性，以及细粒尾矿加筋的作用机理。     

土工合成材料施工损伤问题的探讨

土工合成材料加筋砂、石垫层是在基础下有效深度范围土体内铺设土工合成材料，通过土工格栅、土工织物等加筋材料与砂、石间的相互作用，可提高地基承载力和稳定性，这种地基处理方法因具有施工简便、无污染、造价低、工期短等优点而广泛应用。     

塑料土工格栅在加筋土挡土墙的应用

塑料土工格栅是一种新兴的土工合成材料，近年来在加筋土挡土墙中得到广泛的应用。文中详细叙述了塑料土工格栅加筋土挡土墙的特点，塑料土工格栅与土相互作用的两种加筋机理：摩擦加筋理论和似粘聚力理论，总结了塑料土工格栅加筋土挡土墙的优越性。     

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。     

不同土工格栅的筋土界面摩擦特性研究

土工格栅与土的界面作用特征直接影响加筋高填方路堤的安全与稳定性。以河北省邢汾高速公路加筋高填方路堤工程为背景．通过室内直剪试验．分析不同类型的土工格栅在砂土中的界面摩擦特性作用。试验表明随着上覆荷栽的增加,土工格栅与砂土的摩擦特性加强。双向土工格栅与砂土之间的界面凝聚力要高于单向土工格栅．而其界面摩擦系数相差不大。通过对格栅界面特性的研究．给土工合成材料的生产建设性的意见并为实际工程选用格栅材料提供参考。     

不同土工合成材料下新型加筋土界面特性

土工合成材料对加筋土结构的界面直剪特性具有重要的影响。通过一系列大型直剪试验对不同筋材下的Sandwich型加筋土筋土界面的直剪特性进行研究,研究不同竖向应力下不同种类加筋材料对Sandwich型加筋土界面直剪特性的影响。试验结果表明:土工格栅的加筋效果最佳,两种格栅的加筋界面抗剪强度明显高于土工织物;随着竖向应力的增加,筋土界面抗剪强度提高。结合理论分析,对不同的土工格栅进行直剪试验,得出土工格栅横、纵肋对界面剪切强度的提高值分别为15.3%和4.1%。     

基于渐近均匀化理论的格栅加筋路堤沉降计算

土工格栅作为特种土工合成材料的一种,由于将其加入路基土中后能有效降低路基整体沉降和不均匀沉降,已在交通工程中发挥着重要作用.将渐近均匀化理论运用到土工格栅加筋路堤沉降计算中,所得结果与已有实测值对比表明,该法计算土工格栅加筋路堤的沉降是可行的,从而提供了一种计算水平向增强体（土工格栅）复合地基沉降的新方法;该方法与现行沉降计算方法相比,步骤简单,方便实用.此外,分析沉降变形影响因素,可兼顾施工简便性和土工格栅生产工艺要求而得出路堤最佳加筋方案,为工程应用提供理论参考.     

Evaluating long-term benefits of geosynthetics in flexible pavements built over weak subgrades by finite element and Mechanistic-Empirical analyses

Finite element (FE) models were developed to evaluate the benefits of geosynthetic reinforcement in flexible pavements built over weak subgrades. The parametric study was conducted to evaluate the effect of different variables such as base thickness, geosynthetic type, geosynthetic stiffness, and double-geogrid layers. FE analyses were performed for 100 load cycles, and the permanent deformation (PD) was used to calibrate the empirical parameters in MEPDG equations for each layer, which were used to extrapolate PD data for the service life of pavements. The PD curves for unreinforced and similar reinforced sections were used to evaluate the Traffic Benefit Ratios (TBR) at different rut depths. The results showed that the inclusion of one geogrid/geotextile layer at the base-subgrade interface could significantly reduce pavement rutting. The use of geogrid is more effective than geotextile in reducing pavement rutting. The derived TBR values range from 1.91 to 8.9 for one geogrid layer and from 1.71 to 5.92 for one geotextile layer. The TBR values increase with increasing the rutting depth and geosynthetic stiffness. The TBR value demonstrates an optimum at a base thickness of 10 in. The results demonstrated the superior benefits of using double geogrid layers compared to single-layer cases.     

Bearing capacity of square footings on geosynthetic reinforced sand

The results from laboratory model tests and numerical simulations on square footings resting on sand are presented. Bearing capacity of footings on geosynthetic reinforced sand is evaluated and the effect of various reinforcement parameters like the type and tensile strength of geosynthetic material, amount of reinforcement, layout and configuration of geosynthetic layers below the footing on the bearing capacity improvement of the footings is studied through systematic model studies. A steel tank of size 900 × 900 × 600 mm is used for conducting model tests. Four types of grids, namely strong biaxial geogrid, weak biaxial geogrid, uniaxial geogrid and a geonet, each with different tensile strength, are used in the tests. Geosynthetic reinforcement is provided in the form of planar layers, varying the depth of reinforced zone below the footing, number of geosynthetic layers within the reinforced zone and the width of geosynthetic layers in different tests. Influence of all these parameters on the bearing capacity improvement of square footing and its settlement is studied by comparing with the test on unreinforced sand. Results show that the effective depth of reinforcement is twice the width of the footing and optimum spacing of geosynthetic layers is half the width of the footing. It is observed that the layout and configuration of reinforcement play a vital role in bearing capacity improvement rather than the tensile strength of the geosynthetic material. Experimental observations are supported by the findings from numerical analyses.     

Large scale direct shear tests of soil/PET-yarn geogrid interfaces

The interface shear strength of soil against geosynthetic is of great interest among the researchers in geosynthetic properties. This study conducts a series of large scale direct shear tests to investigate the interface shear strength of different soils (sand, gravel, and laterite) against PET-yarn geogrids of various tensile strengths, percent open area, and aperture patterns. First, the appropriateness of different set-ups of a lower shearing box is examined in this study. It reveals that a lower box which is filled with the test soil and is of the same size as the upper box is more suitable for testing the soil/geogrid interface. The test results show that the soil/PET-yarn geotextile interface has significantly lower shear strength than soil strength. The ratio of shear strength soil/PET-yarn geotextile interface to internal shear strength of soil is about 0.7–0.8 for Ottawa sand and for laterite, and it is about 0.85–0.95 for gravel. On the other hand, the soil/geogrid interface has higher shear strength. The ratio of shear strength soil/PET-yarn geogrid interface to internal shear strength of soil is about 0.9–1.05. It is found that the shear strength ratio of soil/PET-yarn geogrid interface is positively correlated to the transverse tensile strength of the PET-yarn geogrid. However, it is negatively correlated with the aperture length and percent open area of the PET-yarn geogrid. The interface shear test results of PET-yarn geogrid against different soils are compared with the test results predicted by a classical model for analyzing the applicability of the classical model. Further, a simple model is proposed herein to estimate the bearing resistance provided by the transverse ribs of geogrid. It shows this component to be about 0–15% when PET-yarn geogrid is against Ottawa sand or laterite, while it is smaller when the PET-yarn geogrid is against gravel.     

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.     

Experimental studies of the geosynthetic anchorage – Effect of geometric parameters and efficiency of anchorages

The soil reinforcement by geosynthetic is widely used in civil engineering structures: embankments on compressible soil, slope on stable foundations, embankments on cavities and retaining structures. The stability of these structures specially depends on the efficiency of the anchors holding the geosynthetic sheets. Simple run-out and wrap around anchorages are two most commonly used approaches. In order to improve the available knowledge of the anchorage system behaviour, experimental studies were carried out. This paper focuses on a three-dimensional physical modelling of the geosynthetics behaviour for two types of anchors (simple run-out and wrap around). The pull-out tests were performed with an anchorage bench under laboratory controlled conditions with three types of geosynthetic (two geotextiles and one geogrid) and in the presence of two types of soil (gravel and sand).The results show that there is an optimum length for the upper part of the geosynthetic for the wrap around anchorage.     

Characterization of geogrid mechanical and chemical properties from a thirty-six year old mechanically-stabilized earth wall

The mechanical properties of geosynthetic reinforcements are known to be time-, environment- and stress-dependent. Characterization of these reinforcement properties is often assessed under controlled laboratory settings and extrapolated to the design life of geosynthetic-reinforced soil structures. However, despite the wide application of geosynthetic reinforcement in earth retaining structures, there is limited evaluation of how mechanical properties of geosynthetic materials change in situ on constructed works; and primarily limited to case studies within the first decade following construction. This study describes the change in mechanical properties of geogrids retrieved from the facing of the wrapped-face of one of the oldest geosynthetic-reinforced mechanically-stabilized earth (MSE) walls in the United States, constructed in 1983 in a relatively harsh, coastal environment. Laboratory characterization of mechanical and chemical properties of the geogrid are presented, and compared to properties of archived samples, as well as samples from another structure exhumed 8 and 11 years after its respective construction. The laboratory test results demonstrate that the geogrid mechanical and chemical properties have not significantly changed in the 35+ years of service. While the data from this study represents a limited set of conditions, these results demonstrate that geogrids may perform well long after construction.     

Experimental studies on inclined pullout behaviour of geosynthetic sheet Vis-À-Vis geogrid - Effect of type of anchor and sand

This paper presents the details of an experimental investigation using large-scale inclined pullout apparatus on sheet geosynthetic and geogrid embedded in run-out, I-type, and L-type anchors. The influence of the type of sand on the behaviour of the sheet and the geogrid is also investigated. The results show that in both the sheet and the geogrid, I-type anchor provides approximately 50% and L-type anchor provides 90% higher pullout force than the run-out anchor. The maximum pullout force increases by more than 20% as the inclination of pullout force increases from 0° to 30° for both the sheet and the geogrid.     

A preliminary study of the application of the strain-self-sensing smart geogrid rib in expansive soils

Flexible conductive materials are widely used in structural health monitoring; it is also known in geotechnical engineering. In this preliminary study, a strain-self-sensing smart geogrid rib was proposed to monitor the induced strain by wetting-drying cycles of the expansive soil. After the calibration, a physical modeling test was conducted with the smart geogrid rib reinforced in expansive soils under three wetting-drying cycles. Results demonstrated: that the smart geogrid rib was capable of self-sensing its strain; the strain self-sensed by the smart geogrid rib was in good agreement with that measured by FBG strain sensors before cracks were generated; it could capture the crack propagation of expansive soils during wetting-drying cycles by the discrepancy compared to FBG sensors. Further study will be continued for the mechanism of the geogrid instead of the geogrid rib and the application to real-time monitoring of the performance of the geosynthetic expansive soil slopes.     

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.     

桩承式加筋路堤土拱及格栅受力模型试验研究

介绍了桩承式加筋路堤足尺模型实验装置,该实验装置利用PVC材料水袋模拟桩间软土,从而在一定程度上能够控制桩土差异沉降。路堤填筑过程中测试了路堤内部土压力以及格栅拉力,并且重点分析了桩帽和桩间不同位置处土压力以及格栅拉力随填筑高度的变化规律。实验结果表明,路堤在填筑过程中发生了明显的土拱效应,路堤填筑完成后桩土应力比约为8.46,土拱高度约为1.125倍桩间净距;单向土工格栅能够进一步将桩间上方土压力传递到桩顶上方;随着路堤填筑高度的增加,格栅拉力增长并不大,路堤横向滑移引起的格栅拉力可以忽略不计。