基于极限平衡法的特殊土高填方路基稳定性分析

通过极限平衡法研究路基填料、高度、坡率等不同因素对特殊土高填方路基稳定性的影响,研究结果表明:路基高度对稳定性影响显著,路基坡率越缓,膨胀土路基的稳定性越好,1∶1.5～1∶1.75的边坡坡率是较为合适的;地形坡度对路基自身稳定性较小;提高地基的内摩擦角来可相应提高路基的稳定性安全系数,但当地基强度超过路基填料强度时,...     

高速路工程中的路基石灰改良土试验检测与填筑施工研究

随着我国经济的不断发展,我国目前对高速公路建设项目的开展越来越多,而对与高速公路路基的石灰改良土施工技术,一般需要对石灰改良土进行试验测试,并对石灰改良土进行填筑施工,确保高速公里路基的施工质量。通过对高速公路工程中的路基改良石灰土的概念进行阐述,并研究路基石灰改良土试验检测方式,探究高速路工程中的路基石灰改良填筑施工的具体方法。此研究的主要目的是为了明确石灰改良土在路路工程施工中的优势,确保高路公路路基工程质量。     

基于Geo-Slope软件分析的石灰改良土路基边坡稳定性研究

以某高速公路A场区工程边坡设计为例,以石灰改良土壤为基础,将素土和石灰改良土进行对比,以安全系数K为指标,运用边坡稳定性分析中常用的摩根斯坦-普赖斯内插法(Morgenstern-Price)、简布法(Janbu)、毕肖普法(Bishop)和常规条分法(Ordinary)4种分析方法,基于Geo-slope软件分析讨论以石灰改良土边坡的不同坡率和对边坡稳定性的影响。     

既有线开行重载列车路基边坡稳定性分析

既有线开行大轴重列车是发展重载铁路的重要途径,但提高轴重会引起路基边坡稳定性的降低。通过采用传统极限平衡法(M-P法)、二维强度折减法、三维强度折减法探讨了重载铁路路基边坡的稳定性及破坏模式。结果表明:三种方法计算的安全系数比较接近,三维强度折减法计算的值略大;列车轴重、路基高度、路基坡度、抗剪强度指标是影响重载铁路路基边坡稳定性及破坏模式的重要因素,路基填料抗剪强度和路基高度的影响程度大于边坡坡率和轴重。     

黏性土低边坡坡率取值公式法的探讨

黏性土低边坡是公路建设中的挡墙、涵洞、排水沟、挖方边坡及桥台基础等开挖中常常遇到的一种边坡。针对黏性土低边坡以下未进行分亚类且各高度下开挖坡率值的大小直接影响到工程安全和经济造价的问题,本文提出根据不同高度对低边坡进行亚类分级,并在绵西高速公路B2标段黏性土处于不同塑性状态试验资料分析的基础上,创新性尝试提出可采用坡率公式取值法的新方法。该坡率公式法较好地利用了土体内部抗剪强度,公式计算得出的坡率通过边坡稳定性计算及现场试验,效果较好。可在保证边坡安全的基础上有效地减少工程量,节约造价。为今后类似黏性土低边坡坡率取值提供一种新的探讨思路,同时也为边坡精细化提供参考。     

广河高速连接线路堑边坡设计

简要介绍了广河高速连接线路堑边坡防护设计思路,并对边坡设计方案进行了具体阐述,内容包括边坡坡形、坡率的选择、边坡稳定性评价、边坡加固和防护等,为类似工程积累了经验。     

石灰改良土路基填筑试验段施工技术

为满足列车高速运行时路基强度、变形以及路基工后沉降的要求,在缺乏优质填料的情况下,采用改良土来改善土的结构,提高承载力,以满足工程需要,并降低成本,缩短工期,取得较好的经济效益.本试验段施工通过科学试验,找出最佳和最经济的改良方法、最佳的配合比参数和施工工艺以指导全线施工.以工程实例形式详细介绍了石灰改良土路基填筑试验段施工技术,包括路基施工和路基表层以下石灰改良土施工.     

建筑垃圾填筑路基边坡稳定性分析

为了明确建筑垃圾再生材料填筑路基的边坡稳定性,采用规范简化Bishop法和强度折减有限元法,对天津地区常用的路基断面形式进行系统的边坡稳定性分析,结果表明：石灰掺土稳定砖料是一种很好的路基填料,上下路床均采用建筑垃圾填筑时,在非浸水条件和浸水条件下,路基高度为3 m的边坡稳定安全系数均能够满足规范要求。强度折减法和双强度折减法分析发现：边坡高度为3 m时,稳定安全系数均1.07左右。     

铁路湿陷性黄土路基水泥改良分析

在铁路工程施工中,对于路基填筑土,应尽量选择强度大且水稳定性较高的土。对于湿陷性黄土路基,可采用水泥改良土进行填筑,以提升路基强度。对此,本文首先对湿陷性黄土路基进行了介绍,然后对水泥改良土的作用机理进行了分析,并结合工程实例,对铁路湿陷性黄土路基水泥改良方法以及效果进行详细探究,以为类似工程提供借鉴。     

膨胀岩地区公路工程边坡人工坡率及变形破坏分析

结合张石高速实际情况,根据现场调查和有关图件,统计了不同坡高情况下的自然坡率,结合规范推荐路堑坡率值,提出了膨胀岩地区人工边坡坡率的确定方法,同时分析了裂隙对边坡稳定性的影响,指出裂隙位于边坡后部时对稳定性的影响最大。     

土工格栅加筋边坡坡顶条基极限荷载的预测

通过土工合成材料加固的边坡,承载能力显著提高,因而获得广泛应用。为了合理的评价加筋边坡的坡顶条形基础的极限荷载,制作了足尺寸模型并进行了试验,采用延性较好但强度较低的聚丙烯(PP)土工格栅对边坡进行了加固,在坡顶通过条形基础(钢梁)施加荷载直至边坡破坏,获得了极限荷载以及边坡的变形和破坏规律,通过细致的测试手段,详细地捕捉到模型的力学响应。在此基础上,通过校验的FLAC数值模型,对土工格栅加筋边坡的承载能力进行了预测,得到了满意的结果。     

汶川地震中道路边坡工程震害分析

 发生在山区的地震对边坡工程所造成的危害,在致灾机制和破坏形式方面具有鲜明的特征。结合汶川地震灾区道路边坡工程震害实例,分析路堑、路堤以及与桥隧相连的各类边坡及相应支挡结构的震害机制和破坏形式。锚索(杆)地梁或预应力锚索抗滑桩加固的边坡具有较好的抗震性能,其原因是这些结构已与坡体联接在一起而形成一个整体,在地震波作用下结构与坡体的位移和变形能够很好地协调一致。铺设土工格栅或施加加筋材料的路堤边坡工程具有较好的抗震性能,一般填筑路堤特别是高路堤,其抗震性能较差。根据沙土液化和软弱黏性土层震陷造成的震害实例,提出含水沙质地层路堤边坡应注意坡脚沙土液化造成的震害,应采取措施防止软弱黏性土层地基震陷造成路面破坏以及坡脚震陷造成的边坡失稳。山区隧道洞口边、仰坡的抗震设计应重视支挡结构的耐震性。建于坡体上的桥台、桥基和桥路过渡段的安全性与坡体稳定性直接相关,应切实加强这些结构所在边坡的抗震设计。对于依山傍水而建的顺河桥,相关边坡的失稳危害桥梁时,应对其采取抗震措施。目前公路、铁路工程抗震规范涉及边坡工程及支挡结构的内容极少,研究成果可为规范的修改和补充提供有益的参考。     

Model Test and Consolidation Analysis of Failure of a Loose Sandy Embankment Dam During Seepage

Failures of earth dam embankments and river dikes, which are constructed of sandy soils with low dry densities, have been observed to occur during rising of water levels. In this paper, a large-scale physical model test was conducted in order to investigate the behavior of a small dam embankment as water levels rose. The test results were simulated by use of a consolidation analysis method coupled with an elastoplastic model for unsaturated soils. All parameters used in the simulation were obtained from element tests; oedometer, triaxial compression, soil water retention, and permeability tests. First, in order to verify the parameters identified, direct shear tests were simulated using the consolidation analysis method; results of the simulation and the tests were consistent. From the embankment model test it was found that the crest of the embankment moved upstream at the first stage of impounding and then moved back. After a seepage surface appeared on the downstream slope, tension cracks occurred on the downstream slope, and sliding occurred through the crack and the downstream toe. The results of the simulation were consistent with those of the model test. This consolidation analysis method could be used to simulate the complex deformations induced by saturation collapse and shear strains and even failure behavior. Old embankments constructed with loose densities might have histories in which cracks occurred on the downstream slopes when the reservoir water level rose, and their stabilities might have decreased.     

A case study of geotextile-reinforced embankment on soft ground

Full-scale test embankments, with and without geotextile reinforcement, were constructed on soft Bangkok clay. The performances of these embankments are evaluated and compared with each other on the basis of field measurements and FEM analysis. The analyses of failure mechanisms and the investigations on the embankment stability using undrained conditions were also done to determine the critical embankment height and the corresponding geotextile strain. The high-strength geotextile can reduce the plastic deformation in the underlying foundation soil, increase the collapse height of the embankment on soft ground, and produce a two-step failure mechanism. In this case study, the critical strain in the geotextile corresponding to the primary failure of foundation soils may be taken as 2.5–3% irrespective of the geotextile reinforcement stiffness.     

中膨胀土路堤包边方案及其试验验证

中膨胀土具有较强的吸水膨胀软化特性，其CBR值低于3％，不能满足路基对填料的强度要求，若用作路基填料必须进行处理。对中膨胀土路堤包边方案进行深入论证，对中膨胀土包边路堤边坡稳定性、路基强度与变形及石灰包边层的保湿作用进行分析。分析结果表明：中膨胀土包边路堤具有较好的浅层稳定性和整体稳定性；包边条件下，填土具有较高的强度和较低的变形，满足路用要求；包边层具有良好的防风化和保湿作用。在此基础上，提出中膨胀土路堤包边方案，并通过现场试验进行验证，试验验证表明，石灰包边方案能经受当地自然条件和气候条件的影响，能保证路基的稳定和安全营运。     

膨胀土用作路基填料的分类指标体系研究

交通部西部"膨胀土路基设计、加固与施工技术研究"项目课题组在不同地区用不同胀缩等级膨胀土直接修筑了多段路堤实体工程已取得成功经验,为促进这种处治新技术的推广并保证路基的强度和稳定性,必须建立与之配套的填料分类指标体系。为此,依据室内大量的膨胀土路用性能试验结果,归纳总结已有的实体工程修筑经验,遵循继承与创新相结合的原则,探讨采用改进的CBR试验强度、CBR膨胀量以及稠度三项指标建立膨胀土路堤填料分类指标体系,并对三种典型膨胀土开展了相关指标的试验验证。结果表明:该体系真正反映了膨胀土的本质特征及作为填料的工程特性,且指标参数的获取测试简便、快捷,能大大拓宽膨胀土用作填料的使用范围,可供编制路基新规范和工程师们进行膨胀土路堤设计与施工时参考。     

A comprehensive method for analyzing the effect of geotextile layers on embankment stability

Commercial software is used widely in slope stability analyses of reinforced embankments. Almost all of these programs consider the tensile strength of geotextiles and soil–geotextile interface friction. However, currently available commercial software generally does not consider the drainage function of nonwoven geotextile reinforcement. In this paper, a reinforced channel embankment reinforced by a nonwoven geotextile is analyzed using two methods. The first method only considers the tensile strength and soil–geotextile interface friction. The second method also considers the drainage function. In both cases, the reinforced embankment is modeled in rapid drawdown condition since this is one of the most important conditions with regard to stability of channel embankments. It is shown that for this type of application, modeling a nonwoven geotextile reinforced embankment using commercial software which neglects the drainage function of the geotextile may be unrealistic.     

Combined effect of PVDs and reinforcement on embankments over rate-sensitive soils

A numerical study of the behavior of geosynthetic-reinforced embankments constructed on soft rate-sensitive soil with and without prefabricated vertical drains (PVDs) is described. The time-dependent stress–strain-strength characteristic of rate-sensitive soil is taken into account using an elasto-viscoplastic constitutive model. The effects of reinforcement stiffness, construction rate, soil viscosity as well as PVD spacing are examined both during and following construction. A sensitivity analysis shows the effect of construction rate and PVD spacing on the short-term and long-term stability of reinforced embankments and the mobilized reinforcement strain. For rate-sensitive soils, the critical period with respect to the stability of the embankment occurs after the end of the construction due to a delayed, creep-induced, build-up of excess pore pressure in the viscous foundation soil. PVDs substantially reduce the effect of creep-induced excess pore pressure, and hence not only allow a faster rate of consolidation but also improve the long-term stability of the reinforced embankment. Furthermore, PVDs work together with geosynthetic reinforcement to minimize the differential settlement and lateral deformation of the foundation. The combined use of the geosynthetic reinforcement and PVDs enhances embankment performance substantially more than the use of either method of soil improvement alone.     

Investigating the effect of geogrid on stabilization of high railway embankments

This paper investigates the effect of geogrid on controlling the stability and settlement of high railway embankments using laboratory testing and finite element modeling. To do this, five series of embankments with 50?cm height were constructed, at a scale of 1:20 and then were uniformly loaded on the crest in a loading chamber in dimensions of 240?×?235?×?220?cm. In this regard, the embankments of the first series were constructed without geogrid reinforcing layers. Following to preliminary numerical simulations for determining the appropriate level of geogrid layers installation, the second to fifth series of embankments were constructed. These embankments were reinforced with one to four layers of geogrid respectively and finally, the results of their load in terms of settlements were compared. In these studies, the reinforced embankments with a single geogrid layer had 7.14% raise in bearing capacity and 11.24% reduction in settlement respectively, in comparison with the unreinforced embankment. The obtained results for the third to fifth series of embankments were respectively in order of (19, 36.14), (26.3, 52.8) and (28.9, 53.42)%. In the next stage, by modeling the embankments in the PLAXIS 2D software, the results were validated by the values obtained through laboratory models. In continuation of the study, real embankments with heights of 5, 10, 15, and 20?m were simulated and placed under LM71 loading pattern (Eurocode, 2003). In this respect, the impact of important effective parameters such as number of geogrid layer, soil characteristics, embankment dimensions, interface coefficient between soil and geogrid and tensile strength of geogrid on bearing capacity and settlement have been studied. The numerical results like the experimental ones, confirmed the increase in bearing capacity and settlement diminishing with definite increase in the geogrid layers, so that more geogrid layers do not affect these parameters. With respect to improving the soil characteristics and reducing the height of embankments, the FEM models showed decreasing effect of geogrid tensile strength on embankment crest settlement. On the other side, the value of geogrid-soil interface coefficient has minor effect on both settlement and sliding safety factor.     

External Stability of Group Column Type Deep Mixing Improved Ground Under Embankment Loading

The Deep Mixing Method (DMM), a deep in-situ soil stabilization technique using cement and/or lime as a binder has been often applied to improve soft soils. Group column type improvement has been extensively applied to foundations of embankment or lightweight structures. A design procedure for the group column type DM ground has been established in Japan mainly for application of embankment, in which two failure patterns are assumed: sliding failure in the external stability and rupture breaking failure in the internal stability. The internal stability of the improved ground has been investigated experimentally, and it was found that the DM columns show various failure modes: shear, bending and tensile failure, depending not only on the ground and loading conditions but also on the location of each column. However, the current design does not incorporate the effects of these failure modes, but only that of shear failure mode. For the external stability, it is known that a collapse failure pattern, in which the DM columns tilt like dominos, could take place instead of sliding failure. The current design method, which does not take into account this failure pattern, might overestimate the external stability. In this study, a series of centrifuge model tests and elasto-plastic FEM analyses were performed to investigate the external stability of group column type DM improved ground under embankment loading. The centrifuge model study has revealed that the improved ground does not fail with a sliding failure pattern but with a collapse failure pattern in the model test condition. The FEM analyses confirmed the model test results and showed that the improved ground could fail with sliding failure in a certain type of ground conditions such as a floating type improved ground. A simple calculation incorporating the collapse failure pattern gave reasonable estimation of the embankment pressure at ground failure. This paper demonstrates the importance of simulating appropriate failure pattern for evaluating the external stability accurately.