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.     

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。     

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.     

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.     

Three-dimensional behavior of geosynthetic tubes

Geosynthetic tubes filled with pressurized slurry are used for various purposes (e.g., as dikes or breakwaters). The three-dimensional behavior of such structures is investigated. The tubes are assumed to be comprised of two rectangular sheets connected at their edges, and to rest on a tensionless elastic foundation. As the slurry is pumped in, the top surface rises and the outer portion of the bottom surface lifts off the foundation. For tubes with aspect ratios of 2:1 and 5:1, the deflected shapes, mid-surface stresses, and contact regions with the foundation are determined with the use of the finite element method and thin shell elements. Wrinkling occurs close to the long edges of the tubes.     

Two-dimensional analysis of stacked geosynthetic tubes on deformable foundations

Stacked geosynthetic tubes resting on a deformable foundation such as soil are analyzed. The tubes contain a slurry which applies hydrostatic pressure. The material of the tubes is assumed to act like an inextensible membrane and to have negligible weight, and the foundation is assumed to exert a normal upward pressure which is proportional to the downward deflection. Friction is neglected between tubes and at the foundation interface. Two configurations are considered: (a) one tube on top of another and (b) one tube straddling two tubes underneath it. For the latter formation, the case of external fluid acting on one side is analyzed, to simulate an application as a dike, and rigid blocks are utilized to prevent sliding of the tubes. Equilibrium shapes of the tubes are obtained numerically from a closed-form integral formulation, and the tension in each tube is computed.     

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.     

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.     

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.     

Shear strength of geosynthetic composite systems for design of landfill liner and cover slopes

Torsional ring shear tests were performed on composite specimens that simulate the field alignment of municipal solid waste (MSW) landfill liner and cover system components. Simultaneous shearing was provided to each test specimen without forcing failure to occur through a pre-determined plane. Composite liner specimens consisted of a textured geomembrane (GM) underlain by a needle-punched geosynthetic clay liner (GCL) which in turn underlain by a compacted silty clay. Hydrated specimens were sheared at eleven different normal stress levels. Test results revealed that shear strength of the composite liner system can be controlled by different failure modes depending on the magnitude of normal stress and the comparative values of the GCL interface and internal shear strength. Failure following these modes may result in a bilinear or trilinear peak strength envelope and a corresponding stepped residual strength envelope. Composite cover specimens that comprised textured GM placed on unreinforced smooth GM-backed GCL resting on compacted sand were sheared at five different GCL hydration conditions and a normal stress that is usually imposed on MSW landfill cover geosynthetic components. Test results showed that increasing the GCL hydration moves the shearing plane from the GCL smooth GM backing/sand interface to that of the textured GM/hydrated bentonite. Effects of these interactive shear strength behaviors of composite liner and cover system components on the possibility of developing progressive failure in landfill slopes were discussed. Recommendations for designing landfill geosynthetic-lined slopes were subsequently given. Three-dimensional stability analysis of well-documented case history of failed composite system slope was presented to support the introduced results and recommendations.     

A large-scale shaking table model test for acceleration and deformation response of geosynthetic encased stone column composite ground

Effective mitigation of seismic-induced ground hazards requires an improved understanding of ground response in terms of earthquake wave propagation and ground deformation. Here, this paper examines the effects of geosynthetic-encased stone columns (ESCs) and ordinary stone columns (SCs) on the acceleration amplitude and frequency content responses of sand profiles, and the deformation of the ground using a large-scale shaking table model test. The model was excited by 15 shaking events including El Centro motion, Wenchuan Qingping motion and Kobe motion with peaks ranging from 0.1 to 0.9 g. The results indicate that the ESCs more significantly amplify surface accelerations compared to the SCs in the frequencies ranging from 10 to 17 Hz and from 2.5 to 9 Hz. The horizontal peak acceleration values in the ESCs composite ground are approximately twice those of the SCs composite ground. The acceleration response of the ground is influenced by the applied acceleration peak and frequency content, reinforced type, and structure. After the seismic excitation, the ESCs composite ground develops much narrower surface cracks distributed in a larger area compared to the SCs.     

Effect of geosynthetic component characteristics on the potential for GCL internal erosion

Experiments quantifying GCL permittivity and the ultimate water head the GCLs can sustain before the initiation of internal erosion when underlain by a 50 mm angular to subangular gravel subgrade are conducted. The influence of different geotextiles over the subgrade, water heads, hydration periods before testing, masses per unit area of bentonite within the GCL, and ionic strengths of the solution (cation exchange) are considered. Test results show that GCL with the scrim-reinforced nonwoven geotextile over the subgrade has the best hydraulic performance against internal erosion, followed by the woven geotextile coated with a 110 g/m² polypropylene film. A woven or nonwoven is the least useful for preventing internal erosion, with the corresponding threshold water head initiating internal erosion >39 m for scrim-reinforced nonwoven, 21 m for lightly coated woven, 4–5 m for woven and nonwoven alone, respectively. Cation exchange, length of hydration, and mass per unit area of bentonite do not notably affect the threshold water head for the subgrade examined. Once internal erosion occurs, there is a 3-order of magnitude increase in permittivity. The practical implications are discussed.     

金属拱型波纹屋盖结构的简化设计方法

金属拱型波纹屋盖结构在力学性能上具有很强的几何非线性,结构设计必须考虑几何非线性的影响。本文通过对这种结构进行线性和几何非线性对比分析,找到了两种计算结果之间的对应规律,从而提出了一套基于线性分析的简化设计方法。本文运用这套方法对若干实际工程进行了试设计,试设计结果证明了简化设计方法的合理性和可操作性。     

A simplified method for determining sway in reinforced concrete dual buildings and design applications

Sway analyses of reinforced concrete buildings generally are carried out with computer programs. However, as the number of iterative solutions increase, the process may become tedious. This paper proposes a simple analytical method to evaluate sway of dual buildings subject to various types of lateral loads. The proposed method is based on the continuum model. Story drift limited by building codes can be controlled by the proposed method. Likewise, design engineers can use the simple analytical expressions to calculate the stability index, which includes sway terms at each story level. Stability index equation without sway terms is obtained by using the developed analytical expressions. Use of the equation, which is free of sway terms, is quite simple. Additionally, by using the proposed method, shear wall–frame interaction can be modeled simply. Thus, moment at the base of shear walls can be determined by using this model. Copyright © 2012 John Wiley & Sons, Ltd.     

Numerical modelling and validation of geosynthetic encased columns in soft soils with installation effect

If the bearing capacity of the soil is not sufficient an improvement method has to be considered. In case of soft and cohesive soils the vibroreplacement technique can be used. This paper describes the numerical simulation of a group of encased granular columns under an embankment based on a real life project situated to the north of Hamburg, Germany. The soft soil creep model and the hardening soil model were used to model the behaviour of the soft clay and granular material respectively. The material parameters were determined based on laboratory tests conducted on test samples from the field. The installation effect of columns in numerically modelled based on the cavity expansion method in a 2D axis symmetric model. The results of the installation effect in terms of stress state changes in the soft soil after complete consolidation are then imported to the 3D model involving group of columns. The results of the numerical simulations are validated against field measurement data in form of vertical settlement of the ground at various locations with respect to time and horizontal deformations in the encased columns with depth.     

耗能减振结构基于性能简化抗震设计方法研究

介绍位移相关型耗能器的性能特性及其分析模型,针对安装位移相关型耗能器结构的特点,在现有耗能减振结构性能设计研究成果的基础上,提出耗能减振结构基于性能的简化抗震设计方法;采用SAP2000软件对某7层钢框架进行性能设计和基于不同性能目标的多种方案的对比分析.分析结果表明:采用等效单自由度(SDOF)耗能减振结构性能点对应的周期和阻尼比来预估加入耗能减振装置后原结构的实际周期和阻尼比是可行的;提出基于性能简化抗震设计方法是合理的,并且该种方法可判断耗能支撑应给结构提供附加刚度及初始屈服位移的较优的性能参数.     

A new simplified analytical design method for steel and composite sway frames

Eurocode 4 is the European design code for composite construction; in its so-called EN 1994-1-1 version, the design of “non-sway buildings” is mainly covered. As a result, EC4 focuses on the checking of structural elements like beams, columns, slabs and joints. However, in the last years, the construction of taller buildings and larger industrial halls without wind bracing systems tends to make global instability a relevant failure mode, which is not well covered by Eurocode 4. Recently, intensive experimental, numerical and theoretical investigations have been carried out at Liège University. The latter aimed at improving the knowledge in the field of sway composite building frames and at developing appropriate design rules. The rotational behavior of the beam-to-column composite joints is one of the key aspects of the problem to which a special attention has been paid. This paper reflects investigations carried out at Liège University on this topic. In particular, an innovative simplified analytical method to predict the ultimate loading factor and the associated collapse mode of both steel and composite frames subjected to static loadings is presented.     

桩承式加筋路堤的改进设计方法研究

具有深厚软土层的路堤若采用桩承加筋式复合地基,可提高地基承载力,减少路堤不均匀沉降,也可布置成疏桩,降低工程成本,在国内外得到越来越广泛的应用,但还没有可靠实用的设计计算方法,且现有的设计均忽略了桩间土的承载作用,这与工程实际有很大差别。基于三维土拱效应,改进Hewlett土拱效应算法,得到桩承式路堤的桩土荷载分担比,进而考虑加筋体影响以及桩间土承载作用,推导桩土应力比计算式,并将此式应用于路堤的设计。     

连续矩形楼板设计的近似简化方法

针对连续矩形楼板要想得到精确解比较困难的问题,论述了采用简化方法的可能性并予以计算,得出计算结果与精确解之间差别不大,能满足工程精度要求的结论,以推广该近似简化方法的应用。     

接触爆炸荷载下钢—混凝土组合梁简化设计方法研究

接触爆炸荷载作用下可引起结构的破坏.为研究钢-混凝土组合梁的抗爆性能,基于等效单自由度方法和能量方法,推导了接触爆炸荷载作用下钢-混凝土组合梁最大弹塑性变形的简化计算方法,并同数值分析结果进行了对比.结果表明,此方法有较高的计算精度,可用于评估钢-混凝土组合梁的抗爆能力,并可供实际工程参考使用.