Reliability-based analysis of embankment on soft Bangkok clay

Six slope failures occurred at random locations along a 10 km embankment adjacent to an irrigation canal. The slope failures occurred when the embankment was raised to 2.05 m above MSL from an average elevation of 1.7 m above MSL coinciding with the lowering of the canal water level at the end of the dry season. Slope stability analysis was carried out using both conventional and reliability-based procedures. The spatial variability of undrained strength, the actual variation in embankment geometry, and the varying water level in the canal were considered in the analysis. Both idealized and empirical autocorrelation functions (ACF) of the undrained shear strengths were used in the analyses. An analysis using a factor of safety based on the deterministic soil profile defined by the mean undrained strength resulted in a prediction favoring a reverse failure pattern along the embankment. Using the probability of failure which incorporates spatial variation of undrained strength and uncertainties associated with stability prediction yielded a result conforming to the actual failure pattern along the embankment. The use of empirical autocorrelation function (ACF) seems to confirm and explain better the occurrence of the failure zones than utilizing the idealized ACF.     

软土地基路堤施工监控

软土地基上高速公路路堤施工中的监测是保证工程质量和安全的重要手段。文中结合具体工程监测数据,讨论了软土地基路堤施工监测方法、控制标准和注意事项等问题,可以为同类工程提供借鉴。     

高原斜坡软土路基施工试验研究

高原斜坡软土是一种罕见的地质现象 ,是在特定的地质条件和气候条件下形成的具有特殊性质的软土 ,在高原斜坡软土地基上修筑公路、铁路都将面临路基稳定这一课题。通过内昆铁路老锅厂-李子沟区间斜坡路基施工试验研究 ,提出了“强基固本”、“治软抗滑”确保斜坡路基稳定性的技术措施 ,所得出的研究结论对类似工程具有一定的参考价值。     

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.     

桩–网复合地基与桩承式路堤的对比数值模拟

刚性桩加固软土地基常采用桩体+格栅以及桩+桩帽两种不同的处理形式,前一种处理方式是一种桩–网复合地基的处理形式,后一种一般称为桩承式路堤。两种形式在变形特性以及桩体受力特性上有其不同的特点。由于缺乏有效的对比研究,在处理方式的选取上存在一定的困难。鉴于现场试验手段的局限性,在现场对比试验的基础上对两种处理方式进行了三维流固耦合模拟和对比分析工作,揭示了不同处理方式桩顶平面沉降变形的特性,同时对桩体的应力进行了对比研究。     

Design of reinforced embankments on soft clay deposits considering the viscosity of both foundation and reinforcement

The combined effects of the viscoplastic nature of foundation soil and viscoelastic behaviour of geosynthetic reinforcement (polyester, polypropylene and polyethylene) are investigated. A new method for defining the critical stage, with respect to embankment stability, and the operational field strain rate for use in assessing the undrained shear strength of rate-sensitive foundation soils similar to those examined is proposed. The effect of construction rate on the reinforcement stiffness at the critical stage is examined. The study shows that the selection of a design stiffness using the data obtained from a creep test provided reasonable and conservative results. The effects of the undrained shear strength profile, reinforcement stiffness and soil viscosity on embankment performance under working stress conditions are explored and a new limit equilibrium based design procedure is proposed. Finite Element analyses are used to examine the potential effectiveness of the proposed simplified design procedure.     

Performance monitoring and numerical assessment of a test embankment with preloading and vertical drains on Texcoco lacustrine soft clays

This paper presents the performance monitoring results and long-term numerical analyses of a 2.8-m-high test embankment with vertical drains on soft highly compressible clays during a four years and two months observation period (1525 days). The peculiar study site is characterized by thick layers of lacustrine soft clay with water contents up to 300%, void ratios between 7 and 9 and ratios C_α/C_c range from 0.06 to 0.03. The loading applied by the test embankment was 43.4 kPa. The vertical drains installed were of two types: sand and prefabricated. The settlements that only take into account the effect of the preloading embankment at the end of the observation period were 2.62 m and 2.71 m, in the zones with sand and prefabricated vertical drains, respectively. The settlement measured by regional subsidence was 0.47 m. The ultimate primary settlement was approximately 2.0 m and was estimated by two observational methods based on field settlement records. The settlement developed by secondary consolidation in the embankment ranged from 0.62 m to 0.71 m at the end of the observation period. The test embankment behavior was simulated by 2D and 3D numerical analyses. The 2D analyses used a theory to convert the axisymmetric drainage into plane drainage. The long-term numerical results and the field measurements were compared and discussed.     

Numerical simulation of the nonlinear bending response of fibre-reinforced cementitious matrix beams and comparison with experimental results

The aim of this work is the efficient numerical simulation of the bending behaviour of fibre reinforced cementitious matrix (FRCM) beams. For the production of the FRCM specimens, a high-strength cementitious matrix with hooked-end steel fibres is used. Two types of FRCM beams are considered. The first type has no conventional steel reinforcement, while the second one includes longitudinal and transverse reinforcement steel bars. For comparison reasons, conventional reinforced concrete (RC) beams are also studied. The beams are tested under static and cyclic loading. The response of the tested beams is simulated by means of effective two-dimensional finite element models, in which the contribution of the FRCM is taken into account by means of two different layers of finite elements. The first one represents the cementitious matrix while the second one accounts for the contribution of the steel fibres in a homogenized manner. The presented models are able to follow the nonlinearities that appear in the corresponding physical models. The validity of the proposed methodology is established by comparing the numerical results with the corresponding experimental results.     

Wind-driven rain on the facade of a monumental tower: Numerical simulation,full-scale validation and sensitivity analysis

Wind-driven rain (WDR) is one of the most important moisture sources that affect the hygrothermal performance and the durability of building facades. The facades of the Dutch monumental building St. Hubertus show severe deterioration caused by WDR. Assessment of the amount and intensity of WDR falling onto the facades is necessary as input for numerical heat-air-moisture (HAM) transfer models to analyse the causes of the moisture problems and the impact of remedial measures. In this study, a numerical simulation method based on Computational Fluid Dynamics (CFD) is used to predict the amount of WDR impinging on the south-west facade of the tower of the building. The paper focuses on the numerical simulation results, the validation of these results and their sensitivity to two parameters: the level of geometrical detailing of the computational building model and the upstream terrain aerodynamic roughness length. Validation is performed by comparison of the numerical results with a dataset obtained from on-site WDR measurements. It is shown that the CFD simulations provide fairly good predictions of the amount of WDR impinging on the south-west facade of the tower, except for the lower part. It is also shown that the local effects of geometrical facade details are significant and can yield differences in WDR exposure up to 40%, while their effect at other positions is negligible. Finally, the sensitivity of WDR simulations to the upstream aerodynamic roughness length is discussed.     

软基台后路基填土对桥台桩基侧向影响的试验研究

基于现场测试试验,获得了台后路基填筑前后桥台桩基应力变化的第一手资料;根据测试结果求出了基桩在台后填土前后基桩的弯矩。结果表明,在过渡段填筑之前,远处路基填土已在桩身产生了弯矩;在过渡段填筑期间,基桩弯矩随填土高度的增加而增加;过渡段路基填筑完毕,基桩弯矩也停止了增长。所得结论有助于进一步认识台后填土对桥台桩基侧向影响规律。     

基于ANSYS加筋路堤沉降的有限元分析

利用通用软件ANSYS对加筋路堤结构进行了数值模拟,在相同荷载下对不同高度、不同边坡坡度、不同加筋间距、不同加筋位置均加筋路堤进行了沉降的对比分析,得出有益的结论.     

透壁式通风管–块石复合路基降温效果模型试验及数值模拟

为研究透壁式通风管–块石复合气冷路基的降温效果,针对年均气温-3.5℃,平均风速2.5 m/s,主导风向为西北方向的高原环境条件开展了室内模型试验,对比分析了单一块石路基和透壁式通风管–块石复合路基的孔隙空气对流速度、特征点地温及模型整体温度场变化过程。试验结果表明:在透壁式通风管的疏导作用下,通风管与块石层复合结构能够起到强化路基体对流的效果,复合路基块石孔隙中的空气流速比单一块石路基提高约20%,使得复合路基模型底部的降温幅度是单一块石路基模型的2.2倍。建立了透壁式通风管–块石复合路基数值计算模型,对通风管内空气流速分布、路基温度场变化进行了预测分析。结果表明:空气流速在通风管中心达到最大值4.06 m/s,在管壁处流速出现跃变陡降,在块石介质区域里速度的数量级为10-1,与室内试验的结果较为一致。模型试验和数值计算结果均表明复合路基能够起到储存冷量、降低下伏多年冻土地温的作用。     

换填法处理软基的迎水面加固堤防稳定性分析

针对某迎水面剖面加固堤防工程,采用极限平衡法,分析了软基处理前后临水坡在施工期及运行期的稳定性,结果表明该断面稳定性满足规范要求,软基处理加固方法可行。     

土工格室对路堤沉降影响的有限元分析

通过研究土工格室如何对软土路堤进行加筋,并且应用ANSYS有限元软件来数值模拟土工格室增强土体的强度。通过添加土工格室前后情况对比,改变土工格室的添加层数进行分析,研究了铺设土工格室对软土路堤的沉降影响以及最优的铺设层数。结果表明,添加土工格室能限制路堤的沉降,使土体稳定性整体提高。     

新型轻质条板填充墙对RC框架抗震性能的数值模拟

为研究轻质条板对填充墙RC框架抗震行为的影响,基于ABAQUS构建有限元计算模型并结合前人的实测数据对所建模型进行对比验证.在已验证模型的基础上,通过构建自主研制的新型轻质材料的抗压本构模型,改变条板布置方式、条板厚度和柱轴压比等关键参数,分析这些参数对填充墙RC框架的滞回曲线、刚度退化曲线及耗能能力的影响.结果表明:...     

福州地区软土的修正剑桥模型试验及其数值模拟验证

本文通过室内试验获取了修正剑桥模型的参数,利用ABAQUS有限元分析软件进行了数值模拟,并对比了试验结果和计算结果,结果表明,有限元计算值与试验值吻合较好,说明试验得到的修正剑桥模型参数是合理和可靠的。     

Numerical evaluation of the effect of foundation on the behaviour of reinforced soil walls

This study numerically investigates the influence of foundation conditions, in combination with other factors such as wall height and reinforcement and facing stiffness, on the behaviour of reinforced soil walls (RSWs) under working stress conditions. The foundation was simulated using different stiffnesses and geometries (with and without slope). The results highlight the importance of the combined effect of foundation conditions and the abovementioned factors on the performance of RSWs. The results of these analyses indicate that the shape of the distribution of the maximum reinforcement loads (T_max) with respect to wall height depends on the combined effect of the foundation condition, facing and reinforcement stiffness, and wall height, and varies from trapezoidal to triangular. Additionally, the results indicate that the effect of variations in foundation stiffness on reinforcement tension mobilisation decreases with wall height. Furthermore, the T_max prediction accuracy of three design methods were evaluated and some limitations of each method are presented and discussed.     

Numerical simulation of compaction parameters for sand-filled embankment using large thickness sand filling technique in Jianghan Plain district

The study uses the finite element method to simulate a new technique of highway sand embankment filling in Jianghan Plain district, which can raise the thickness of sand-filled layer from 30 cm to 70 cm and can significantly shorten the construction period based on the guarantee of sand embankment construction quality. After simulating the three compacting proposals carried out on the field test, the study uses COMSOL software to research on the compacting effects of sand-filled layers in larger thicknesses by 22 ton vibratory roller alone, and then to investigate the steady compacting effect of 12 ton vibratory roller. The simulation results indicate that the sand-filled layer thickness of 70 cm is suitable for the new sand filling technique, and the sand-filled embankment project with tight construction period is suggested to choose the 12 ton vibration roller for steady compaction.     

Effectiveness of CFG pile-slab structure on soft soil for supporting high-speed railway embankment

The use of cement-fly ash-gravel (CFG) pile-slab structures is a new effective technique for reducing the settlements of soft foundations in China. A comprehensive research was conducted to investigate the effectiveness of a CFG pile-slab structure-supported embankment of the Beijing-Shanghai high-speed railway in China. Firstly, an analytical method was formulated to calculate the settlements of the CFG pile-slab structure-supported embankment. Secondly, mechanical scaling laws were derived for the proposed testing plan at model scale. Model tests were conducted to quantify and to interpret the settlement distributions. Thirdly, the influence of three key factors (pile length, pile diameter, and slab thickness) for the structural form of the CFG pile-slab structure-supported embankment on the settlement distribution were studied using numerical simulations. The maximum settlements of the CFG pile-slab structure-supported embankment in optimizing the structural form were obtained using the above three research methods and then they were compared with each other. The results show that (1) the settlements obtained by the analytical method, the physical model tests, and the numerical simulations showed good concordance with each other; (2) the settlement-controlling effect of the CFG pile-slab structure was able to meet the requirements of high-speed railway construction; (3) the piles and the soil-bearing capacities of the CFG pile-slab structure-supporting embankment could be fully mobilized because of the “load re-distribution” function of the slab; and (4) the affected area of the engineering load had a depth of more than 18.75?m and a horizontal length of 7.5?m near the toe of the embankment slope.