土工织物充灌袋简易设计计算方法研究

土工织物充灌袋广泛应用于围堤结构、挡水结构以及橡胶坝中。其理论分析方法国内外许多学者进行了较深入的研究,但研究成果多为解析解,在工程设计应用中具有一定的局限性。为了提出一种能够方便设计使用的简易而准确的设计计算方法,建立了能够根据泵送压力计算充灌袋拉力、截面形状的解析方程。为了能够方便研究不同泵送压力与充灌袋周长、充灌袋拉力以及截面尺寸之间的关系,对泵送压力、充灌袋拉力、充灌袋高度和宽度进行无量纲化处理。根据提出的解析方程编制计算程序,计算标准化泵送压力与标准化高度、标准化截面面积以及标准化拉力之间的关系曲线。采用Chapman-Richard成长曲线模型对标准化的曲线进行拟合,进而提出土工织物充灌袋简易的设计计算方法。通过与其他计算方法和模型试验结果对比,验证了该方法的正确性。因此该方法可以用于土工织物充灌袋的工程设计。     

Analysis of geosynthetic tubes inflated by liquid and consolidated soil

When permeable geosynthetic tubes are used for dewatering of waste sludge or construction of dikes or embankments, the tubes have to be inflated using sludge or soil slurry several times. After each inflation, the soil slurry is consolidated into solid. Hence from the second inflation onwards, the geosynthetic tube is filled by both slurry and consolidated soil. In this paper, a new analytical method is proposed to provide a solution to the above specific case. Friction between geosynthetic sheet and soil, and friction between geosynthetic tube and subgrade, are considered. Parametric studies are also carried out to compare the design between geosynthetic tubes inflated using pure slurry and that using slurry and consolidated soil to study the key factors affecting the design. The study shows that tensile forces vary along the cross-section of the geosynthetic tube with the minimum value occurring at the center of the base. The effect of friction and lateral earth pressure on the geometry and tensile forces of the geosynthetic tube is insignificant when the height of the consolidated soil in the tube is small, but increases considerably with an increase in the height.     

A simplified method for assessing the serviceability performance of geosynthetic reinforced and pile-supported embankment

A simplified method for assessing the serviceability performance of geosynthetic reinforced and pile-supported embankment is presented, where the subsoil consolidation is introduced remaining compatible with the development of soil arching and the reinforcement sag. A piecewise function of the ground reaction curve is developed and used to quantify the arching efficiency. The link between the arching evolution and the subsoil consolidation is then established through the load-carrying equilibrium in the area between piles together with the tensile membrane theory. The reaction of the subsoil is described using the 1-D consolidation theory where the stress history is considered. A parametric study is performed to demonstrate the serviceability performance of a geosynthetic reinforced and pile-supported embankment. The serviceability design of the geosynthetic reinforced and pile-supported embankment is achieved with the proposed method which offers an approach to estimate the time consumed and the subsoil settlement required to achieve a service state.     

Analysis of geosynthetic tubes filled with several liquids with different densities

A two dimensional model of a geosynthetic tube sitting on a rigid horizontal foundation and filled with several separated liquids with different densities is proposed. The material from which the tube is made is a special synthetic fabric which is inextensible, perfectly flexible, and leakproof. Such a model is useful for modeling a consolidations process in the tube filled with a slurry. The equilibrium equations of the model are formulated. Unknown values like the pressure on the top and bottom of the tube, the tension in the geosynthetic fabric, the length of the contact zone between the tube and the rigid foundation are searched with respect to the given perimeter, the volumes and densities of liquids. Such a problem is solved by the Newton’s method. The initial approximation is obtained by solving a simplified problem with one liquid with the average density. The problem is implemented in a MATLAB code for geosynthetic tubes filled with two, three, and four liquids with different densities. The tubes filled with two different liquids are studied in more detail. The graphs of the relations are compared with the graphs for the tube filled with the single liquid whose density is the average of the densities of the liquids. The comparison enables to discuss the influence of the consolidation process on the height, the contact zone, the pressures and the tension of the tube. The results of the proposed model for a tube filled with a single liquid are compared with another model.     

Effect of subgrade soil stiffness on the design of geosynthetic tube

Water or soil filled geotextile or geosynthetic tubes have been used for coastal or river protection projects in recent years. How to design and analyze geosynthetic tube is still an important research topic. Although a number of solutions for geosynthetic tube have been proposed in the past, most of these solutions assume that the geosynthetic tube is resting on a rigid foundation. In this paper, a two-dimensional analysis of geosynthetic tube resting on deformable foundation soil is presented. The deformable foundation is assumed to be an elastic Winkler type represented by the modulus of subgrade reaction, K_f. The study shows that the smaller the modulus, the smaller the height of the geosynthetic tube above the ground surface and the higher the tensile force in the geotextile or geosynthetic given the other conditions the same. When the foundation soil has a modulus higher than 1000 kPa/m which is representative of soft clay, the foundation soil can be assumed to be rigid in the analysis. The results obtained from the method proposed in this paper are compared with those from the solutions of Leshchinsky et al. and Plaut and Suherman for verification. The differences between the solutions are also discussed.     

A simplified model for the analysis of piled embankments considering arching and subsoil consolidation

An analytical model is presented for the design of geosynthetic-reinforced and pile-supported (GRPS) embankments in this paper. The originality of the proposed solution lies in the fact that it allows considering the influence of the subsoil consolidation on the soil arching and geosynthetic strain. A nonlinear function is implemented to describe the subsoil behavior with the consolidation process in a closed-form solution. A simplified approach is then presented to link the arching development with the subsoil consolidation. The arching theory is combined with the tensioned membrane theory and the soil-structure interaction mechanisms to provide a simple and suitable design approach that enables a realistic approximation for designing soil–geosynthetic systems. The analytical model is capable of performing an ultimate and serviceability limit state design of GRPS embankments. While current methods cannot fully address the important effects of the subsoil consolidation, the analytical results suggested that arching and differential settlements increase with an increase of the subsoil consolidation degree. The analytical model is compared to field measurements and five other design standards for several full-scale field tests to study its validity. The results showed a satisfactory agreement between the proposed model and measured data, and generally better results are obtained as compared with other design methods.     

An analytical method for predicting load acting on geosynthetic overlying voids

Soil arching often occurs in geosynthetic-reinforced structures, where the underlying soil has voids, resulting in load transmission from the subsided area to surrounding less deformed area. A new method is proposed to predict load acting on gensynthetic overlying voids. The shape of soil arch and stress states of all the points at the soil arch can be obtained by combining nonlinear M-C yielding criterion, non-associated flow rule with static equilibrium of segmental arch through a dilatancy coefficient. The load applied to the geosynthetic can be determined by load transmission from the overlying soil, to the soil arch, and onto the collapsed soil. The model is verified using a model test conducted by Zhu et al. (2012), the soil pressure acting on the deflected geosynthetic is reasonably predicted. Due to the inherent nonlinear behaviour of soil, nonlinear failure criterion can better describe the stresses and deformations of the soil and geosynthetic. Soil nonlinearity has significant influence on the evaluation of arching effect. Ignoring the nonlinear behaviour of soil tends to underestimate the soil pressure acting on the geosynthetic. There exists an optimal subsidence width for which the soil pressure acting on the geosynthetic is minimal. The method used in this study is more appropriate where a large deflection occurs in the geosynthetic and provides a novel approach to evaluating soil arching under these conditions.     

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.     

基于不完全土拱效应的土工格栅加固机制与设计方法

 假设理想条件下的倾斜滑移面,根据路堤底部产生的相对位移?下的土工格栅膜效应,利用莫尔圆推导出在土工格栅不同挠曲变形时土体中剪应力的计算公式,根据应力平衡条件得到路堤土的应力–应变状态。这种剪应力没有达到屈服状态时路堤土中应力调整即应力重分布现象称为“不完全土拱效应”。同时,设计以水袋泄水模拟路堤底部产生差异沉降的大型模型试验,分别监测路堤特定位置处的沉降、静止土压力以及铺设的土工格栅的轴向拉应变,代入模型计算并且与现有的几种设计理论比较。结果显示：Terzaghi方法与Handy方法的应力计算都不考虑差异沉降的过程,由于对侧向应力系数的定义不同,前者的竖向应力结果偏小而后者偏大;对于土工格栅的轴向拉应变,Giroud方法计算值偏向于保守,虽然Esponiza方法与实测结果比较接近,但是考虑到长期安全性以及土工材料的耐久性,采用本文的计算方法是比较合理的。     

Analysis of installation damage tests for LRFD calibration of reinforced soil structures

North American design codes are now committed to the development of load and resistance factor design (LRFD) for reinforced soil structures including internal stability limit states. Reliability-based analysis is required to carry out these calibrations. A framework for LRFD calibration has been proposed by the writers that requires bias statistics for load and resistance terms for each limit state function. In this paper the formulation of the limit state for reinforcement tensile rupture is developed and the component strength-reduction bias statistics identified. The paper describes how to compute bias statistics from project-specific installation damage trials for use in reliability-based design for the reinforcement rupture limit state or using data from multiple sources for LRFD calibration. A database of results from field installation damage trials on 103 different geosynthetic products was collected from 20 different sources. A total of 799 and 2248 in-air tensile test results were reviewed for undamaged and damaged geosynthetic specimens, respectively. This database is used to compute installation damage bias statistics for six different categories of geosynthetic and four categories of backfill soils classified according to the D₅₀ particle size. A practical outcome is that for analysis purposes, bias statistics can be grouped into two ranges for each geosynthetic type based on D₅₀ of the soil greater than or less than 19 mm. The paper shows how bias statistics together with load and resistance factors for the geosynthetic rupture limit state function recommended by AASHTO (2010) can be used to calculate probability of failure using Monte Carlo simulation and demonstrates the sensitivity of probability of failure to magnitude of installation damage bias statistics. The installation damage data is valuable for future LRFD calibration to select resistance factors for use in design codes for the geosynthetic rupture limit state in reinforced soil structures.     

A simplified method for analysis of a piled embankment reinforced with geosynthetics

Piled embankments provide an economic solution to the problem of constructing embankments over soft soils. The piles and geosynthetic combination can alleviate the uneven surface settlements that sometimes occur in embankments supported by piles without reinforcement. The main focus of this paper is to present a new method for analysis of an embankment of granular fill on soft ground supported by a rectangular grid of piles and geosynthetic. This method is based on consideration of the arching effect in granular soil and similar to the method proposed by Low, B.K., Tang, S.K., Choa, V. [1994. Arching in piled embankments. Journal of Geotechnical Engineering 120 (11), 1917–1938]. The main refinements are: inclusion of a uniform surcharge load on the embankment fill, individual square caps were used, and taking into account the skin friction mechanism, which contributes to soil–geosynthetic interface resistance. Using this method, the influence of embankment height, soft ground depth, soft ground elastic modulus, and geosynthetic tensile stiffness on efficiency, stress concentration ratio, settlement ratio, tension of geosynthetic, and axial strain of geosynthetic are investigated. The results show that inclusion of a geosynthetic membrane can increase the fill load carried by piles. As a result, both the total and differential settlements of the embankment can be reduced. The new design method was verified against several current design methods. Theoretical solution showed that BS8006 [1995. Code of Practice for Strengthened/Reinforced Soils and other Fills. British Standards Institution, London, p. 162] and Guido, V.A., Kneuppel, J.D., Sweeny, M.A. [1987. Plate loading tests on geogrid-reinforced earth slabs. In: Proceedings of the Geosynthetics '87, New Orleans, USA, IFAI, pp. 216–225] methods overpredict the vertical stress acting on the geosynthetic due to that the reaction of the soft ground on the geosynthetic is not considered in their methods. It also showed that the present method is in good agreement with Low, B.K., Tang, S.K., Choa, V. [1994. Arching in piled embankments. Journal of Geotechnical Engineering 120 (11), 1917–1938] method.     

风电中空夹层钢管混凝土结构塔筒在往复扭矩作用下的破坏机理研究

本文基于ABAQUS有限元软件,建立了风电中空夹层钢管混凝土结构塔筒在纯扭往复荷载作用下的“壳-实体”精细有限元模型,并进行了数值模拟计算。有限元模型计算结果与试验结果吻合较好。在此基础上,对风电中空夹层钢管混凝土结构塔筒在纯扭往复荷载作用下的变形过程、破坏形态和机理进行了分析。研究表明,风电中空夹层钢管混凝土结构塔筒在达到极限承载力之前,具有较好的组合工作性能,风电中空夹层钢管混凝土结构塔筒在往复扭矩作用下的破坏过程为钢管的鼓曲变形进一步发展为鼓曲区域钢材低周疲劳开裂破坏,同时提出了风电中空夹层钢管混凝土结构塔筒受扭承载力简化计算方法,计算结果与试验结果吻合较好,可用于工程设计参考。     

Design method for geotextile tubes considering strain - Formulation and verification by laboratory tests using photogrammetry

Geotextile tubes are usually made of at least one layer of high-strength woven geotextiles. However, if only highly elastic materials are used, experience shows -comprehensibly - that the designed geometry and stresses, derived from standard formulations or special computer software, both using small strain membrane theory, essentially differ from reality. Therefore, an extended formulation, considering large strains, was developed within the scope of a study on the structural and hydraulic design of geosynthetic dewatering tubes at the University of Rostock. The solution was evaluated using a sensitivity analysis and verified in laboratory experiments, where small-scale tubes were surveyed using a low-budget, high-precision photogrammetric measurement technique. The new design method proved to produce good results. It should be used if the construction is indeed a long tube and if the limit strain of the geotextile tubes exceeds 10% strain. Finally, the results were compared with the existing methods for the structural design of geosynthetic applications, adding to the discussion about attenuation factors in geotextile tube dewatering projects. For short-term applications without refilling of the partly dewatered tubes, the product of attenuation and safety factors will usually not exceed a value of two.     

Performance issues of barrier systems for landfills: A review

The objective of the paper is to give an update in key topics related to performance issues of barrier systems for landfills. The objective of using barrier systems is to minimize the impact of contaminants on the surrounding environment. To achieve this goal puncture protection of the geomembrane must be ensured. An update is first given with respect to this matter. The question of the stability on slope of geosynthetic barrier systems is then discussed and an insight is given in modeling and laboratory measurement of parameters required to perform reliable modeling, especially as regards the case of piggy-back landfills. Geotechnical centrifuge modelling tests are very important for simulation of landfill stability induced by the failure of geosynthetic interfaces and validation of complicated numerical models, especially for the high food waste content landfills. The seismic design or assessment of landfill stability with respect to geosyntheics needs to be investigated. Finally, the question of transfers through bottom barrier systems is addressed, giving an update especially in the analytical solutions developed in the past 10 years in China in this matter. The breakthrough time based design method for landfill liner system was then summarized. The behaviour of double-liner system and its simplified performance-based design method should be further investigated in the high food waste landfills with high leachate level.     

Modified Broms’ method for formation of working platform on very soft soil

Construction over soft soil is a challenge as the ground can be too soft to work on it. To overcome this, a working platform has to be formed before any soil improvement work can be carried out. One of such methods was proposed by Broms (1987) which uses geotextile and sand berms. In this paper, a modified Broms' method is proposed to use geotextile tubes to confine the sand berms. A new analytical solution is also proposed to calculate the tensile strain and the profile of geotextile under the sand berms/tubes. Design charts for different design conditions are also developed. Parametric studies were conducted to identify the key parameters affecting the design. Finite element analyses (FEA) and a field trial were also carried out to verify the modified Broms' method and the proposed solution. The monitoring data agree reasonably well with the results obtained from proposed solution and FEA. A design procedure for modified Broms' method and Broms’ method is proposed using the analytical solution.     

土工合成材料约束碎石桩承载特性研究

土工合成材料约束碎石桩作为一种新型软土地基处理技术在工程中广泛应用,其单桩承载力取决于土工合成材料抗拉强度和土的工程性质。通过对土工合成材料、碎石桩及地基土的相互作用机理进行分析,提出了考虑土工合成材料约束拉力与土体围压的桩身强度计算方法,进而推导出考虑上部荷载作用的,由桩身强度控制的单桩极限承载力计算方法,并采用MATLAB编写了计算程序,根据得出的单桩极限承载力计算了土工合成材料拉力沿深度的分布,结合一算例说明了计算所需要的参数及计算过程,成果可为土工合成材料碎石桩的设计提供计算依据。     

基于蒙特卡罗法的加筋路堤稳定可靠性分析

软土路基上加筋路堤的稳定性可以采用圆弧滑动极限平衡法进行分析,加筋路堤的破坏可以归纳为圆弧内加筋的破坏、圆弧外加筋的破坏以及加筋路堤的整体破坏,建立了计算加筋路堤稳定系数K的3个不同的稳定系数表达式,运用蒙特卡罗法对设计参数随机变量与加筋土路堤稳定可靠指标的关系进行分析,通过数值计算发现密度越小,黏聚力、内摩擦角、筋材抗拉强度和筋土摩擦角越大,加筋土路堤稳定性越好,因此,在加筋土路堤可靠性设计中建议采用密度小、黏聚力和内摩擦角大的填料以及高强度筋材,并且重点考虑内摩擦角的变异水平。     

耗能减震结构基于能量和位移的抗震设计方法研究

在现有研究成果基础上提出一种新的基于能量和位移的耗能减震结构抗震设计方法,该法综合考虑了能量和位移指标,无需将结构进行简化,能准确地计算出耗能器的数量和布置位置,减少了迭代计算过程。采用ABAQUS有限元软件对安装位移相关型耗能器的某14层钢框架结构进行基于重要性能目标的抗震设计,结果表明本文方法能较好地满足预期的性能...     

筒中筒结构弯扭耦联简化分析

本文在文献[1]、[2]的基础上,讨论了筒中筒结构的弯扭耦联问题,得到了结构弯扭耦联问题的闭合解,并给出三种典型荷载下的位移、内力计算公式。文中提出的求解内外简之间相互作用力的方法,避免了复杂的解耦困难,有广泛的适用性,无论对于较精确的空间有限元法、有限条法或其他简化计算,只要符合楼板平面内刚度无穷大,出平面刚度忽略不计的基本假定,都是有效的。只要求出各自的柔度矩阵,按本法求得内外筒之间的相互作用力后,即可利用现有程序对内外筒分别进行计算。     

Controlling strain in geosynthetic liner systems used in vertically expanded landfills

According to relevant new regulations in China,a composite liner system involving geosynthetic materials must be installed at the bottom of an expanded landfill.The deformation and integrity of the composite liner under a variety of factors are important issue to be considered in the design of a landfill expansion.In this paper,we investigate the strain distribution in geosynthetic materials within the composite liner system of expanded landfills,including strains in geosynthetic materials resulting from overall settlement and lateral movement of landfills,localized subsidence in landfills,and differential settlement around gas venting wells.The allowable strains of geosynthetic materials are discussed based on the results of tensile tests,and the corresponding design criteria for composite liner systems are proposed.Meanwhile,practical measures allowing strain control in geosynthetic materials used in landfill engineering are proposed.