条形荷载下土工格室加筋砂土路堤模型试验研究

为了探讨不同土工格室加筋方式对路堤应力变形特性和不均匀沉降的控制效果,分别对纯砂路堤边坡和土工格室加筋路堤进行多组模型试验,研究了土工格室焊距、埋深、加筋层数以及压实度对路堤承载力特性和变形特性的影响,同时结合土工格室材料应变的变化规律和加筋路堤的坡面变形状态分析了土工格室加筋路堤的破坏模式。试验结果表明:格室加筋效果随着焊距、加筋深度的减小而增加,随着压实度、加筋层数的增加而增加;土工格室加筋路堤承载力是纯砂的2.5倍左右,提高了路堤的极限承载力,减小了路堤沉降,并且土工格室加筋路堤坡面侧向位移比纯砂路堤减小了75%。     

高填方加筋新旧路堤现场试验与数值模拟分析

 结合山区高速公路拓宽工程,对土工格室处治高填方新旧路堤进行现场试验,分析加宽高填方路堤侧向位移、沉降及土压力变化规律,研究格室处治效果。在现场试验的基础上,采用三维薄膜单元模拟土工格室的立体加筋性能,建立三维弹塑性模型,分析土工格室受力特点,通过对相关参数的敏感性分析,揭示高填方加宽路堤的变形规律。结果表明,采用三维薄膜单元,能较好地反映土工格室处治现场高填方新旧路堤的规律。与现场试验相比,利用数值试验不仅能得到现场的加筋效果,而且还能通过分析筋材与填料参数的变化和筋材铺设间距来研究格室处治高填方路堤的规律,从而可进一步探讨格室加筋的机制。高填方路堤在加宽路基自重荷载作用下沉降主要集中在加宽路堤的中上部,侧向位移从路基顶面到底部依次逐渐减少。土工格室所在层位起到扩散荷载、减少侧向变形和不均匀沉降的作用。填料与筋材模量愈高,加筋间距愈小,加筋效果愈好,较为合理的铺设间距为2～3 m。该研究成果对高填方路堤加筋处理和新旧路基结合部处理均有借鉴意义。     

应用土工格室处治路基不均匀沉降

在分析路基不均匀沉降成因的基础上,通过对现有路基不均匀沉降处治措施的分析与评价,提出了土工格室处治路基不均匀沉降的方法,研究表明,土工格室复合体限制了周围土体的侧向变形,减小了路堤本身的压缩变形,是处治路基不均匀沉降的一种有效方法.     

不同拉压模量土工格室有限元模拟

将不同拉压模量理论应用于土工格室的有限元模拟中,考虑土体和土工格室的力学性能,选取一段软土路堤作为研究对象进行了有限元模拟与分析,将分析结论与以往方法所得结论进行对比,结果表明将不同拉压模量与数值模拟相结合适用于土工格室的有限元分析,与实际情况比较相符。     

拓宽路堤不均匀沉降敏感性因素仿真分析

采用FLAC3D三维有限差分分析软件,结合武汉市三环线武黄高速公路共线段拓宽工程,对拓宽路堤变形进行仿真分析。通过土工格栅加筋层数对不均匀沉降的敏感性分析,证明加筋层数对不均匀沉降有显著影响。对新路堤土体相关参数进行敏感性分析,得出土体剪切模量最为敏感的结论。     

土工格栅加筋拓宽路堤有限元分析

采用二维非线性有限元法对软土地基上的拓宽路堤土工格栅加筋作用和效果进行模拟分析。计算中采用一维抗拉单元来模拟土工格栅,采用接触面单元考虑筋土界面的状态非线性。研究土工格栅嵌入老路基长度、格栅设置层数对格栅拉力、拓宽路堤不均匀沉降和水平位移的影响。计算结果表明,格栅嵌入老路基长度越长,拓宽路堤侧向位移和新老路基差异沉降越小,增加格栅层数并不会显著减小拓宽路堤的差异沉降。     

土工格室加筋砂土地基沉降试验研究

土工合成材料可以有效提高地基的承载力与减小地基的表面沉降差异。在静荷载作用下,采用室内模型试验方法对纯砂地基和土工格室加筋地基的地基承载力和沉降情况进行了对比分析,研究了格室埋深、格室高度及筋材层数对距离基础不同远近处地基沉降的影响。研究结果表明,在荷载较小时,土工格室加筋地基作用效果相近;在荷载较大时,土工格室加筋效果提高显著;土工格室加筋地基不仅有效控制了基础沉降,而且减小了基础附近地基的沉降差异;筋材调节地基不均匀沉降的加筋效果随筋材埋深减小、筋材层数增加、格室高度增加而有不同程度的提高。     

土工格栅加固斜坡路堤的数值模拟

土工格栅具有强度高、延伸率低等特点,在路基适当位置铺设土工格栅可有效改善路堤应力环境,减小沉降和侧向变形。通过数值模拟方法研究了铺设土工格栅前后路堤水平位移、垂直位移的变化。计算结果表明,土工格栅对路堤的水平位移和垂直位移起到了较好的抑制作用,对水平位移的抑制作用更为明显;加筋层数对路堤变形的影响较小,多层加筋的效果和一层加筋相比并不明显。研究成果对路基工程设计具有一定的参考价值。     

软土地基加筋土路堤变形及稳定性分析

软土地基加筋土路堤进行了数值模拟,分析了筋材类型和加筋方式对路堤变形及稳定性的影响。研究结果表明:在软土地基和路堤之间铺设土工格栅可以有效提高路堤稳定性;增加路堤加筋层数不如增加底层筋材力学指标对路堤稳定性的影响效果明显;在固结过程中,加筋土路堤对地基侧向位移影响深度约为2H(H为路堤高度),研究成果对软土地基加筋土路堤的设计和施工具有指导意义。     

土工格栅处理软土路基的有限元分析及应用研究

采用有限元软件PLAXIS,对土工格栅处理软土路基的变形特性及其影响因素进行了研究,分析表明,土工格栅对减小软基侧向位移、降低土体应力水平以及提高路基路堤安全系数有明显效果.通过在江苏某高速公路软土路段中的应用,并对路基侧向位移及沉降的实测研究,掌握了经土工格栅处理后,软土路基的基本变形规律.     

考虑填料–土工格室相互作用的加筋路堤力学响应研究

针对有砟轨道加筋路堤计算分析中难以考虑土工格室对碎石填料嵌锁及摩擦作用的现状,在大比尺直剪试验基础上建立考虑填料–格室相互作用的三维计算模型。通过室内模型试验验证该计算的可靠度和优越性,进而系统地分析有/无加筋情况下,填料强度、土工格室刚度及地基压缩性等参数对路堤力学响应的影响。结果表明:土工格室的嵌锁作用使得加筋对路堤响应的影响在其布设层发挥程度更大,该影响通过填料与格室及填料内的摩擦作用向周围传递且不断衰减;填料强度较低或地基较软时能加强土工格室对路堤响应的影响,对于填料内摩擦角为20°和地基变形模量为5 MPa的工况而言,加筋后基床侧向位移峰值分别降低60%和72%,应力峰值亦显著降低且分布区域明显扩大;土工格室弹性模量为0.2~2.5 GPa时,路堤力学响应受其影响较大。     

Vibration response of machine foundations protected by use of adjacent multi-layer geocells

The response of soil beds reinforced with multi-layer geocell systems that support machine foundations is investigated by laboratory testing that incorporates vertical machine vibrations of a square concrete foundation (400 × 400 mm) resting on soil that is unreinforced or reinforced with single-, double- or triple geocell layers. The tests are performed under three different vibration moment levels and three static force levels using a mechanical oscillator and concrete blocks, respectively. The vibration responses are studied in terms of resonant amplitude, resonant frequency, shear modules and damping coefficient. The results reveal that the resonant amplitude significantly reduced in the presence of geocell reinforcement whereas the resonant frequency, shear modulus and damping coefficient increased. In the range of applied vibration load and frequency, and hence the induced amplitude, maximum improvement (i.e., the greatest reduction in vibration amplitude) was observed in the presence of the triple-layer geocell reinforcement. Since the rate of improvement decreases steadily with an increase in the number of geocell layers, thus, further geocell layers would deliver little further benefit. The optimum placement depth of the first geocell layer and vertical spacing of the geocell layers were found to be 0.1 and 0.05 of the foundation's width respectively.     

土工格室加筋地基承载力研究

土工格室被应用于道路、地基、边坡与渠道的保护以及重力式支挡结构,其中,加筋地基可以通过格室侧壁的限制和摩擦力改善砂、石等填料的工程性质,将土工格室层视为基础的旁侧荷载可提高地基承载力。根据土工格室加筋土体的力学机理,采用极限平衡分析法,利用三角形条块法求作用在三角形刚性楔形体两滑动剪切面上的被动土压力,并考虑了土体与土工格室侧壁相互作用对地基承载力的贡献,提出土工格室加筋软基承载力公式,并采用已有模型试验结果,验证了公式的合理性和正确性。     

Performance of a road embankment on soft clay supported on a Geocell mattress foundation

A five kilometre-long road was constructed in the New Territories of Hong Kong between 1989 and 1992. Part of the road crossed an alluvial plain on an embankment, and at two locations on the alluvial plain this embankment was underlain by soft clay deposits. A geocell mattress was used as the means of supporting the embankment on these soft clay deposits. Wick drains were installed beneath the embankment to speed up consolidation of the soft clays, and using staged construction the embankment was built up to a maximum height of 10 m.

The embankment was fully instrumented with pneumatic piezometers, inclinometers, hydrostatic profile gauges, settlement plates, surface settlement markers, and lateral movement blocks. This paper presents the results of the instrumentation monitoring and the performance of the geocell mattress foundation during the construction of the embankment. At one section, unusually high excess pore water pressures and a slight heave of the toes of the embankment were recorded. The accompanying small lateral extension and the deflected shape of the geocell mattress indicated that it had behaved as a raft foundation to the embankment.     

某地铁车站软土深基坑加固效果研究

采用水泥土搅拌加固软土深基坑土体是工程中常用的有效方法。本文采用有限差分软件FLAC3D建立某地铁车站深基坑的数值计算模型,并对未加固和加固两种设计方案进行了施工全过程数值模拟,对两种方案的土压力、地下连续墙水平位移以及邻近铁路路堤沉降的模拟计算结果进行了对比分析。结果表明:三轴水泥土搅拌桩对于软土深基坑加固效果显著,能够有效的减少围护结构的侧向位移和地表沉降;当周边环境对基坑变形有严格要求时,对土体进行加固,提高土体强度是十分有效的措施。     

轮胎与格室加筋路堤性能及承载力研究

为研究废旧轮胎与土工格室加筋路堤边坡的性能,分别对废旧轮胎、土工格室加筋路堤边坡开展了室内模型试验,并考虑了填料两种不同相对密度的影响。试验结果表明:相对素土路堤而言,废旧轮胎和土工格室加筋路堤均能有效地提高承载力,增强其稳定性,减小不均匀沉降。加筋后均有效地增大了附加应力的扩散角,使得附加应力分布更为均匀,并且素土路堤与加筋路堤中轴线上附加应力差值随路堤深度增大而减小。中轴线以外的质点侧向位移随路堤深度的增加,呈现出先增大后减小的趋势,几种路堤中,废旧轮胎加筋路堤侧向位移最小。加筋效果随相对密度增大而减小,在低相对密度条件下,加筋后承载力能达到素土路堤2倍以上,而在高相对密度下却不足2倍。最后根据土工格室加筋地基承载力计算方法及对废旧轮胎加筋机理分析,提出了关于废旧轮胎加筋地基承载力计算方法。     

Uplift capacity of horizontal anchor plate in geocell reinforced sand

The paper investigates the uplift performance of horizontal anchor plate in geocell reinforced sand through a series of model tests. It is noted that the unreinforced anchor plate undergoes a clear failure at a displacement of about 3% of its width, whereas with the provision of geocell and a layer of geotextile right below the geocell mattress significantly increases the uplift capacity by about 4.5 times higher than that of unreinforced sand and could sustain anchor displacement of more than 60%. Results indicates that the geocell mattress by virtue of its rigidity distributes the uplift load in the lateral directions to a larger area, thereby reducing the stress in the overlying soil mass and hence increases the performance of anchor plate system. The provision of the additional geotextile layer right below the geocell mattress is found to be very effective in increasing the stiffness as well as load carrying capacity of anchor plate system. The optimum size (i.e., width and length) of geocell mattress giving adequate load carrying capacity of anchor plate is found to be 5.4 times of anchor width (5.4B). The comparison of model tests results with 3D numerical analysis shows good agreement, indicating that the proposed model is able to capture the uplift load-displacement behaviour of geocell reinforced anchor plate system.     

Centrifuge modeling of a geogrid-reinforced embankment with lime-stabilized soil as backfill on soft soil

A centrifugal model test was performed to investigate the behavior of a geogrid-reinforced embankment on a 20 m thick soft silty clay subsoil. The lime-stabilized soil embankment was 4 m high, 26 m wide with slopes of 1:1.5 and included sand wick drains. Displacements, earth pressures and pore water pressures were measured during the test. Test results showed settlement on the front face of the foundation was approximately 90% of that measured by displacement sensors; the elastic displacement was approximately 11% of the total displacement; and the reinforced embankment remained serviceable despite a 300 mm wide crack on the embankment surface and up to 1.73 m settlement at the centerline of the embankment.