土工格室不同结点连接方式失效机制试验研究

结点连接方式对土工格室的性能至关重要。结点在加筋结构中往往会受到不同方向的作用力,然而对结点在不同受力状态下的失效机制缺乏系统的研究。通过对焊接、插接、铆接3种结点连接方式的土工格室进行单轴拉伸试验,研究了结点连接方式对土工格室条带性能的影响,比较了在不同受力状态下结点的失效模式及抗拉强度。此外,通过引入"条带强度保持率"、"条带变形保持率"、"结点强度发挥率"评价了不同结点连接方式的性能。结果表明:焊接结点对HDPE土工格室条带拉伸性能的协调发挥影响较低,为4.82%;而铆接结点对PET土工格室条带影响较高,为22.2%。焊接、铆接、插接结点主要受剥离强度的控制,但焊接结点的剥离结点强度发挥率可达28.3%,分别是插接、铆接结点强度发挥率的11.32倍、6.58倍,体现了焊接结点的性能优势。插接结点在3种受力状态下结点强度相差很大,需采取注塑等措施来改善结点在剪切、剥离作用下的强度,从而均衡发挥插接结点的性能。试验结果可为土工格室的合理选用以及加筋机理的研究提供参考。     

土工格室规格对加筋土剪切性能的影响

土工格室加筋结构由于抗震性好、施工简便、造价低廉,而广泛应用于公路、铁路等交通基础设施中。目前土工格室加筋结构中仅考虑了土工格室的抗拉强度,而未考虑土工格室规格的影响,使土工格室的选用主要依靠工程经验。通过对5种不同规格土工格室开展室内直剪试验,研究了条带高度、结点间距及法向应力对土工格室–砾砂剪切力学特性的影响,通过引入加筋强度系数评价了不同法向应力、土工格室规格的加筋效果,最后分析了土工格室规格对剪切强度参数的影响。试验结果表明：不同规格土工格室均可有效提高加筋结构的抗剪强度,其中抗剪强度随条带高度的增大、结点间距的减小而增大,同时条带高度对剪切强度的贡献约是结点间距的1.8倍。土工格室加筋砾砂的抗剪强度随法向应力增大而增大,但其加筋强度系数随法向应力的增大而减小。50kPa作用下,条带高度对加筋强度系数的增幅在12.57%以上,而结点间距对加筋强度系数的增幅却不足3.80%。土工格室加筋可显著提高填料的黏聚力,其中条带高度对黏聚力的提高尤为显著,增幅约为25%,而对内摩擦角提高相对较少,增量最大为5.11°。试验结果可为土工格室在实际工程中的应用和理论研究提供实验基础。     

基于响应面法的聚丙烯高强土工格室拉伸性能

为研究土工格室整体抗拉承载力与条带抗拉承载力、节点抗拉承载力之间的力学响应关系,采用双轴拉伸试验测定了不同高度、焊距的高强土工格室在不同加载速度下的破坏承载力;利用节点抗拉承载力与条带抗拉承载力之间的匹配关系,给出了土工格室抗拉承载力的设计参考值;采用响应面多因素试验分析法,研究了土工格室双轴拉伸承载力和变形对各影响因素的响应规律.结果表明:双轴拉伸试验中高强土工格室的破坏均发生在节点处,工程设计时应重点关注;对土工格室整体抗拉承载力的影响程度由大到小为土工格室高度>土工格室焊距>加载速度,研究结果可以为工程设计中土工格室的技术指标选择提供理论依据.     

土工织物加固堤基的离心模型试验

<正> 一、前言具有一定抗拉强度的土工织物,在国内外已被广泛用作挡土结构物、堤坝边坡和堤基的加筋材料。工程实践表明,土工织物加固地基具有其独特的优点。在土体拉伸变形方向设置一定强度的土工织物形成的复合体(加筋土),其力学性能不仅与土体、土工织物的性能有关,同时还取决于土和土工织物的界面特性。由于土工织物侧限     

浅谈土工格室技术在特殊路基处治工程中的应用

土工格室是由高强度的HDPE宽带,经过强力焊接或铆接而形成的一片网状格室结构。其展开固定后与充填的填料共同构成具有强大侧向限制和较大刚度的结构体。它作为路基垫层,具备加筋、排水、调节应力及变形、提高土体抗渗能力的综合功效。本文结合江苏徐州某省道绕城公路穿越xxx煤矿采空区的路基填筑施工实例,全面阐述了该施工技术在煤炭采空区特殊路基处治中的施工工艺和特点,对稳定路基不均匀沉降取得了明显的施工效果,对类似工程具有借鉴作用。     

矩形钢管混凝土T型受压节点受力性能的有限元分析

在选择了合理的钢材和核心混凝土的本构关系模型的基础上,利用通用有限元软件ABAQUS对矩形钢管混凝土T型受压节点荷载-变形关系曲线进行了计算,计算曲线与实验曲线进行了比较,基本吻合,然后对矩形钢管混凝土T型受压节点荷载-变形关系进行了全过程分析。在本文研究结果的基础上,可采用ABAQUS对矩形钢管混凝土T型受压节点的工作机理进行更为深入的研究。本文的研究成果可为相关研究提供参考。     

改善冷轧带肋钢筋产品性能的若干问题

根据有限元模拟Ｙ型三辊孔型轧制中金属的变形特点,讨论了冷轧带肋钢筋产品的力学性能问题,指出了盘条的材质和冷轧变形条件是影响钢筋强度和伸长率的主要因素。文中把钢筋的伸长率分解为均匀伸长率和缩颈伸长率两部分,分别讨论了盘条材质上的缺陷和冷轧过程工艺因素对钢筋拉伸试样均匀伸长率和缩颈伸长率的影响,为提高冷轧钢筋产品性能开拓了思路。     

高心墙堆石坝坝坡加筋抗震稳定分析

目前强震区高土石坝抗震设计普遍采用加筋技术加固坝顶堆石,但加筋的效果如何评价是工程设计者关心的重要问题。传统的基于极限平衡的拟静力法无法反映坝体的动力特性及地震输入特性,得到的安全系数也不反映加筋坝体抗震的安全度。采用改进的Newmark滑块位移法对加筋堆石改善高坝坝坡的抗震稳定性,限制高土石坝地震变形等的工程效果进行了研究和探讨。计算中,首先依据堆石体和加筋堆石体的应力应变关系曲线得筋材与堆石的协调极限应变,进而确定筋材所能发挥的极限抗拉强度,利用瑞典-荷兰法结合蚁群复合形法搜索堆石加筋复合体潜在滑动体的位置,考虑竖向地震以及筋材与堆石的相互作用对滑动体屈服加速度的影响,改进了Newmark滑块位移法。结果表明,加筋减少地震变形最高可达80%,可有效地限制高土石坝坝顶的侧向滑动变形,提高坝体的抗震稳定性。     

土工直接拉伸试验装置的研制及应用

针对现有土工直接拉伸试验装置的不足,研制了一套卧式直接拉伸试验装置;装置由拉伸加载系统、数字液压伺服控制系统、数据采集分析系统3部分组成。试验装置可开展多种易成型材料的直接拉伸试验,能精确测试材料的抗拉强度并能给出拉应力-应变曲线;巧妙设计了加载夹具解决了试验材料与拉伸装置的连接难题;能精确连续控制试验拉力,并能获得材料抗拉强度峰后段的拉应力-应变曲线。使用新研制的试验装置开展了黏土、铁晶砂相似材料和水泥砂浆的直接拉伸试验,试验结果表明：在黏土直接拉伸试验所涉及的含水率范围内,当干密度保持不变时,黏土的抗拉强度随含水率的增加逐渐降低,而峰值拉应变则随含水率的增加逐渐增加;黏土达到峰值强度后,并不会突然断裂而是存在一个软化段,此时土体仍然具有一定的承载能力;铁晶砂相似材料的抗拉强度随着松香酒精溶液浓度的增加而提高;随灰砂比的提高,水泥砂浆的抗拉强度和拉伸弹性模量均相应提高。     

外包内翻U形钢-混凝土组合梁与矩形钢管混凝土柱连接节点抗震性能试验研究

为研究外包内翻U形钢-混凝土组合梁与矩形钢管混凝土柱连接节点的抗震性能,进行了内隔板式、贯通隔板式、穿心式共3个节点试件的拟静力试验,考察了不同形式节点试件的破坏形态、承载力、变形能力、耗能能力、刚度退化等.试验结果表明:正弯矩作用下由于U形钢冷弯区发生撕裂破坏,导致各试件的正向承载力为全塑性理论计算值的60％-84％...     

Development and mechanical properties of HDPE/PA6 blends: Polymer-blend geocells

Geocells are three-dimensional expandable panels composed of polymers such as polyolefin polymers. Currently, geocells are being extensively used in various geotechnical engineering applications; however, its applications are limited because of the sizeable long-term deformation under constant loading and poor tensile strength. Owing to the rapid growth rate of geocells, it has become necessary to develop a polymer material with excellent creep resistance and tensile strength. To this end, a polymer-blend geocell (PBG) is developed in this study using a twin-screw extruder with high-density polyethylene (HDPE), polyamide 6, and compatibilizer. The polymer formula is determined by the tear fracture surface and scanning electron microscopy. The tensile properties of the blends with different formulas are studied in terms of yield strength, tensile strength, and elongation at break. Finally, three types of PBG and HDPE geocells are selected to study the long-term creep behavior using accelerated creep tests. The analysis results of raw creep data, master creep curve, and isochronous creep curves indicated that the PBG had a better creep resistance than the HDPE geocells.     

Investigation of factors influencing behavior of single geocell-reinforced bases under static loading

Geocell, one type of geosynthetics manufactured in the form of three-dimensional interconnected cells, can be used as a reinforcement to improve the behavior of base courses by providing lateral confinement to increase their stiffness and strength and reduce surface permanent-deformation. However, the use of geocells for base reinforcement is hindered by the existing gap between applications and theories. This study experimentally investigated the factors influencing the behavior (stiffness and bearing capacity) of single geocell-reinforced bases including shape, type, embedment, height of geocells, and quality of infill materials. Three of the four types of geocells investigated in this study were made of novel polymeric alloys using a new manufacturing technology. Repeatability and potential scale effects on test results were examined. The test results showed that the geocell placed in a circular shape had a higher stiffness and bearing capacity than that placed in an elliptical shape. The performance of the geocell-reinforced base depended on the elastic modulus of the geocell sheet. The unconfined geocell had a lower stiffness but a higher ultimate load capacity than the confined geocell. The benefit of the geocell was minimized when the infill material, quarry waste with apparent cohesion, was used as compared with the Kansas River sand without apparent cohesion. The single geocell-reinforced base had a lower stiffness and bearing capacity than the multiple geocell-reinforced base.     

Failure mechanisms of geocell walls and junctions

Geocell panels are honeycomb-like systems used to provide earth reinforcement. Strips of perforated high-density polyethylene sheets, also known as cell-walls, are welded together at locations known as junctions. The cell-wall and junctions are designed to support and transfer tensile and shear loads and the integrity of these is essential for the appropriate performance of geocells in practice. Nevertheless, there is no standardized test procedure to assess the strength of the cell-wall or junction, and limited research has been undertaken regarding the failure mechanisms of geocell panels when subjected to various loading scenarios. This paper aims to examine the responses of geocell junctions and cell-walls under various loading conditions. An extensive testing program was undertaken to assess the geocell junctions, which included uniaxial tensile, shear, peeling and splitting strength tests. The uniaxial tensile strength, trapezoidal tearing strength, and creep tests were carried out on the geocell walls. A ductility ratio was developed to measure the rapidness of failure under different short-term loading scenarios for both the cell-wall and junction. This paper presents the observed failure patterns and an evaluation of the implications of the practical uses of geocells.     

Pullout tests on diagonally enhanced geocells embedded in sand to improve load-deformation response subjected to significant planar tensile loads

This paper presents pullout test results on conventional (ordinary) and diagonally enhanced geocells under surcharge pressures of 3, 13, 23 and 33 kPa. Extensive pullout tests on scaled geocells embedded in silica sand are performed to investigate the effects of improvements on load-deformation response, strength and stiffness. Conventional web-shaped geocells are having a small stiffness when subjected to planar tension attributed to deformability of webs. Therefore, conventional geocells may not function properly when subjected to tensile forces along the main plane in service. A special geocell is fabricated in this study, similar to tendoned geocells, through adding diagonal members along the induced tensile load to overcome the shortcomings of conventional geocells. The test results have shown that both the stiffness and ultimate resistance of the diagonally enhanced geocells have significantly improved with respect to the conventional ones. Afterwards, three experiments were carried out on a small-scale shallow footing resting on sand reinforced with geocells, indicating improvement in bearing capacity as well as load-settlement response of footings supported by the diagonally enhanced geocells as compared to conventional geocells.     

Internal stability analysis of geocell-reinforced slopes subjected to seismic loading based on pseudo-static approach

Seismic stability analysis of geocell-reinforced slopes (GRSs), considering shear and moment strength in addition to tensile resistance for geocells, is a novel topic for which scarce studies are found in the literature. Despite few available studies, an analytical approach is presented in this study to investigate the seismic internal stability of GRSs, employing the pseudo-static method based on a limit state approach. Results are given in terms of conventional design charts representing the required total strength and critical length of geocells. The results show that with increasing the horizontal seismic acceleration (k_h), the internal stability degenerates since the required strength and critical length of geocells increase. For GRSs subjected to greater k_h, the effect of increasing the vertical seismic component (k_v) on increasing the required strength and length of geocells is more considerable than those subjected to lower k_h values. Parametric analyses are conducted, under various seismic conditions, to investigate the effect of increasing the geocell height and raising the number of geocell layers, leading to the reduction in the required strength and length of geocells. Such effects are found to be dependent on the parameters such as the intensity of seismic excitation, material properties and geometry of slope.     

Static stability analysis of geocell-reinforced slopes

This paper presents an analytical approach to investigate the stability of geocell-reinforced slopes using the limit equilibrium method (LEM). The so-called Horizontal Slice Method (HSM) is employed to simulate horizontal geocell layers. Each geocell layer acts as a beam providing bending and shear resistance in addition to axial strength. A formula is devised by picking relevant governing equilibrium equations, fitted to the new concept employed exclusively for analysis of geocell-reinforced slopes. Parametric studies are conducted to evaluate the effects of increasing the geocell height and replacing geogrids by geocells with various heights for slopes with different characteristics. The results showed that such actions would reasonably reduce the required tension and length of the reinforcement layers, meaning that the stability condition is improved and the less lengthy reinforcement system is formed. Output values also showed dependency on the slope angle and its material properties.     

Response of pavement foundations incorporating both geocells and expanded polystyrene (EPS) geofoam

The suitability of geocell reinforcement in reducing rut depth, surface settlements and/or pavement cracks during service life of the pavements supported on expanded polystyrene (EPS) geofoam blocks is studied using a series of large-scale cyclic plate load tests plus a number of simplified numerical simulations. It was found that the improvement due to provision of geocell constantly increases as the load cycles increase. The rut depths at the pavement surface significantly decrease due to the increased lateral resistance provided by the geocell in the overlying soil layer, and this compensates the lower competency of the underlying EPS geofoam blocks. The efficiency of geocell reinforcement depends on the amplitude of applied pressure: increasing the amplitude of cyclic pressure increasingly exploits the benefits of the geocell reinforcement. During cyclic loading application, geocells can reduce settlement of the pavement surface by up to 41% compared to an unreinforced case – with even greater reduction as the load cycles increase. Employment of geocell reinforcement substantially decreases the rate of increase in the surface settlement during load repetitions. When very low density EPS geofoam (EPS 10) is used, even though accompanied with overlying reinforced soil of 600 mm thickness, the pavement is incapable of tolerating large cyclic pressures (e.g. 550 kPa). In comparison with the unreinforced case, the resilient modulus is increased by geocell reinforcement by 25%, 34% and 53% for overlying soil thicknesses of 600, 500 and 400 mm, respectively. The improvement due to geocell reinforcement was most pronounced when thinner soil layer was used. The verified three-dimensional numerical modelings assisted in further insight regarding the mechanisms involved. The improvement factors obtained in this study allow a designer to choose appropriate values for a geocell reinforced pavement foundation on EPS geofoam.     

Evaluation of creep behavior of high density polyethylene and polyethylene-terephthalate geogrids

The tensile creep behavior of polyethylene-terephthalate (PET) and high density polyethylene (HDPE) geogrids was evaluated using five test methods: the short- and long-term stepped isothermal method (SIM), the short- and long-term time-temperature superposition (TTS), and the conventional method. SIM and TTS are acceleration tests using elevated temperatures. SIM uses a single specimen throughout all temperature steps in contrast to TTS in which a new specimen is employed for each temperature step. The test results indicate that at the same percentage of ultimate tensile strength, PET geogrid exhibited less creep deformation than the HDPE geogrid. The HDPE geogrid exhibited primary, secondary, and tertiary creep stages before rupture, whereas only primary creep and tertiary creep were detected in the PET geogrid. Furthermore, the strain rate of the primary creep stage was found to be independent of the applied loads for the PET geogrid, while it increased exponentially for the HDPE geogrid. The activation energies deduced from different accelerated creep tests were very similar for the PET geogrid. In contrast, the activation energies were higher from the short-term acceleration tests than from the long-term tests for the HDPE geogrid. The four-parameter Weibull model was able to predict the linear and non-linear creep behavior up to 100 years based on 10-h creep testing data. The creep reduction factor of 100 years design life was evaluated and higher values were resulted from the HDPE geogrid than from the PET geogrid.     

Uniaxial compressive behavior of scrapped tire and sand-filled wire netted geocell with a geotextile envelope

Cellular structures are widely used in civil engineering. Their design is based on the understanding of the mechanical behavior of geocells. This paper investigates the response of a single geocell to a uniaxial compression test. The geocells were cubic, either 500 mm or 300 mm on a side. The fill materials were sand and scrapped tire and sand mixtures in different mass ratios. The envelope of the geocell was made up of a hexagonal wire netting cage and a containment geotextile. The response of the geocell is discussed based on the axial load and displacement measurements as well as the change in geocell volume.The axial load was found to be globally governed by the interaction between the fill material and the envelope, which depends on the shape of the wire mesh and the volumetric behavior of the fill material.     

Combining EPS geofoam with geocell to reduce buried pipe loads and trench surface rutting

This paper reports full scale experiments, under simulated heavy traffic, of geocell and EPS (expanded polystyrene) geofoam block inclusions to mitigate the pressure on, and deformation of, shallow buried, high density polyethylene (HDPE) flexible pipes while limiting surface settlement of the backfilled trench. Geocell of two pocket sizes and EPS of different widths and thickness are used. Soil surface settlement, pipe deformation and transferred pressure onto the pipe are evaluated under repeated loading. The results show that using EPS may sometimes lead to larger surface settlements but can alleviate pressure onto the pipe and, consequentially, result in lower pipe deformations. This benefit is enhanced by the use of geocell reinforcement, which not only significantly opposes any EPS-induced increase in soil surface settlement, but further reduces the pressure on the pipe and its deformation to within allowable limits. For example, by using EPS geofoam with width 0.3 times, and thickness 1.5 times, pipe diameter simultaneously with geocell reinforcement with a pocket size 110 × 110 mm² soil surface settlement, pipe deformation and transferred pressure around a shallow pipe were respectively, 0.60, 0.52 and 0.46 times those obtained in the fully unreinforced buried pipe system. This would represent a desirable and allowable arrangement.