Numerical parametric study of geosynthetic reinforced soil integrated bridge system (GRS-IBS)

A 2-D finite flement model was developed in this study to conduct a FE parametric study on the effects of some variables in the performance of geosynthetic reinforced soil integrated bridge system (GRS-IBS). The variables investigated in this study include the effect of internal friction angle of backfill material, width of reinforced soil foundation (RSF), secondary reinforcement within bearing bed, setback distance, bearing width and length of reinforcement. Other important parameters such as reinforcement stiffness and spacing were previously investgated by the authors. The performance of GRS-IBS were investgated in terms of lateral facing displacement, strain distribution along reinforcement, and location of potential failure zone. The results showed that the internal friction angle of backfill material has a significant impact on the performance of GRS-IBS. The secondary reinforcement, setback distance, and bearing width have low impact on the performance of GRS-IBS. However, it was found that the width of RSF and length of reinforcement have negligible effect on the performance of GRS-IBS. Finally, the potential failure envelope of the GRS-IBS abutment was found to be a combination of punching shear failure envelope (top) that starts under the inner edge of strip footing and extends vertically downward to intersect with Rankine active failure envelope (bottom).     

Performance monitoring of Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) in Louisiana

The Geosynthetic Reinforced Soil (GRS) Integrated Bridge System (IBS) is an alternative design method to the conventional bridge support technology. Closely spaced layers of geosynthetic reinforcement and compacted granular fill material can provide direct bearing support for structural bridge members if designed and constructed properly. This new technology has a number of advantages including reduced construction time and cost, generally fewer construction difficulties, and easier maintenance over the life cycle of the structure. These advantages have led to a significant increase in the rate of construction of GRS-IBS structures in recent years. This paper presents details on the instrumentation plan, short-term behavior monitoring, and experiences gained from the implementation of the first GRS-IBS project in Louisiana. The monitoring program consisted of measuring bridge deformations, settlements, strains along the reinforcement, vertical and horizontal stresses within the abutment, and pore water pressures. In this paper, the performance of instrumentation sensors was evaluated to improve future instrumentation programs. Measurements from the instrumentations also provide valuable information to evaluate the design procedure and the performance of GRS-IBS bridges. The instrumentation readings showed that the magnitude and distribution of strains along the reinforcements vary with depth. The locus of maximum strains in the abutment varied by the surcharge load and time that did not corresponds to the (45+?/2) line, especially after the placement of steel girders. A comparison was made between the measured and theoretical value of thrust forces on the facing wall. The results indicated that the predicted loads by the bin pressure theory were close to the measured loads in the lower level of abutment. However, the bin pressure theory under predicted the thrust loads in the upper layers with reduced reinforcement spacing. In general, the overall performance of the GRS-IBS was within acceptable tolerance in terms of measured strains, stresses, settlements and deformations.     

Experimental study on the load bearing behavior of geosynthetic reinforced soil bridge abutments with different facing conditions

This paper presents an experimental study on reduced-scale model tests of geosynthetic reinforced soil (GRS) bridge abutments with modular block facing, full-height panel facing, and geosynthetic wrapped facing to investigate the influence of facing conditions on the load bearing behavior. The GRS abutment models were constructed using sand backfill and geogrid reinforcement. Test results indicate that footing settlements and facing displacements under the same applied vertical stress generally increase from full-height panel facing abutment, to modular block facing abutment, to geosynthetic wrapped facing abutment. Measured incremental vertical and lateral soil stresses for the two GRS abutments with flexible facing are generally similar, while the GRS abutment with rigid facing has larger stresses. For the GRS abutments with flexible facing, maximum reinforcement tensile strain in each layer typically occurs under the footing for the upper reinforcement layers and near the facing connections for the lower layers. For the full-height panel facing abutment, maximum reinforcement tensile strains generally occur near the facing connections.     

Experimental study on the load bearing behavior of geosynthetic reinforced soil bridge abutments on yielding foundation

This paper presents an experimental study of the load bearing behavior of geosynthetic reinforced soil (GRS) bridge abutments constructed on yielding clay foundation. The effects of two different ground improvement methods for the yielding clay foundation, including reinforced soil foundation and stone column foundation, were evaluated. The clay foundation was prepared using kaolin and consolidated to reach desired shear strength. The 1/5-scale GRS abutment models with a height of 0.8 m were constructed using sand backfill, geogrid reinforcement, and modular block facing. For the GRS abutments on three different yielding foundations, the reinforced soil zone had relatively uniform settlement and behaved like a composite due to the higher stiffness than the foundation layers. The wall facing moved outward with significant movements near the bottom of facing, and the foundation soil in front of facing showed obvious uplifting movements. The vertical stresses transferred from the footing load within the GRS abutment and on the foundation soil are higher for stiffer foundation. The improvement of foundation soil using geosynthetic reinforced soil and stone columns could reduce the deformations of GRS abutments on yielding foundation. Results from this study provide insights on the practical applications of GRS abutments on yielding foundation.     

Numerical study of geosynthetic reinforced soil bridge abutment performance under static and seismic loading considering effects of bridge deck

Although the use of Geosynthetic Reinforced Soil (GRS) bridge abutments has been increasing, the seismic performance of such structures has remained a significant concern due to their unknown behavior in load-bearing and stress distribution under bridge load and seismic conditions simultaneously. This paper investigates the static and dynamic response of GRS bridge abutment. A series of numerical models representing the realistic field conditions of these structures, including two reinforced soil walls and a single span deck that restrains the top of walls, rather than equivalent surcharge load, was developed. The calibrated numerical model in FLAC program was used to evaluate the effects of horizontal restraint from the deck on the GRS wall displacements and reinforcement loads at the end of construction and under harmonic base acceleration up to 0.5 g. Results indicated that the restraint mobilized from the bridge deck presence, considerably affected the results at both the end of construction and after the dynamic load was applied. Moreover, a series of the parametric studies were performed to investigate the influences of backfill soil relative compaction, reinforcement stiffness, reinforcement length, and reinforcement vertical spacing on the response of GRS abutments at the end of construction and post dynamic state.     

Numerical evaluation of a granular column reinforced by geosynthetics using encasement and laminated disks

Structures built on soft strata may experience substantial settlement, large lateral deformation of the soft layer and global or local instability. Granular columns reinforced by geosynthetic materials reduce settlement and increase the bearing capacity of the composite ground. Reinforcement is more common in the form of geosynthetic encasement, but laminated disks can also be used. This paper compares these two forms of reinforcement by means of unit cell finite element analyses. Numerical results were initially validated using field and experimental data, and parametric studies were subsequently performed. The parametric studies varied the geosynthetic interval and the geosynthetic tensile stiffness of the laminated disks as well as the length of the reinforced column. The analyses showed that in both modes; encasement and laminated disks; the geosynthetic increases the vertical stress mobilized on the reinforced column and reduces settlement on soft soil. It was also observed that in order to achieve the same performance as with encased column, the optimum interval between laminated disks is dependent on the stiffness of the geosynthetics and the column reinforced length.     

Numerical simulation of compaction-induced stress for the analysis of RS walls under working conditions

This paper aimed to verify numerical modelling of compaction-induced stress (CIS) for the analysis of geosynthetic-reinforced soil (GRS) walls under working stress conditions. Data from a full-scale well-instrumented GRS wall was used for a numerical analysis. The results from the wall used in this study have already been used for validation in several other numerical modelling studies. Nevertheless, in none of these studies was the real value of CIS specified for the vibrating plate compactor used in the wall employed. In the present study, the real value of CIS is employed. The CIS is modelled using a new procedure presented in this paper in addition to two other procedures found in the literature. The results indicate that when the real value of CIS was simulated using a strip load applied to the top of each backfill layer, the numerical model accurately represented the measurements. The accuracy of the results, however, depends on the width of the strip load used to model the CIS. Nevertheless, as this type of compaction modelling procedure is time consuming, modelling of CIS by applying a distribution load at the top and bottom of each soil layer is suggested as an alternative procedure.     

Improving the reliability of a Bridge Management System (BMS) using an ANN-based Backward Prediction Model (BPM)

The slow adoption of Bridge Management Systems (BMSs) and its impractical future prediction of the condition rating of bridges are attributed to the inconsistency between BMS inputs and bridge agencies' existing data for a BMS in terms of compatibility and the enormous number of bridge datasets that include historical structural information. Among these, historical bridge element condition ratings are some of the key pieces of information required for bridge asset prioritisation but in most cases only limited data is available.

This study addresses the abovementioned difficulties faced by bridge management agencies by using limited historical bridge inspection records to model time-series element-level data. This paper presents an Artificial Neural Network (ANN) based prediction model, called the Backward Prediction Model (BPM), for generating historical bridge condition ratings using limited bridge inspection records. The BPM employs historical non-bridge datasets such as traffic volumes, populations and climates, to establish correlations with existing bridge condition ratings from very limited bridge inspection records. The resulting model predicts the missing historical condition ratings of individual bridge elements. The outcome of this study can contribute to reducing the uncertainty in predicting future bridge condition ratings and so improve the reliability of various BMS analysis outcomes.     

桩锚（撑）与加筋联合支护结构的数值模拟与设计理论研究

本文采用岩土工程数值模拟方法建立桩锚（撑）与加筋联合支护结构的计算模型，对不同土层和桩锚（撑）刚度的联合支护结构的作用机理和变形性状进行数值模拟，得到了一些有意义的研究成果。同时，总结规律并对已有的设计方法进行改进，提出一套行之有效的设计理论和方法，并成功地应用于多个工程的实践中。     

Analyses and design of steep slope with GeoBarrier system (GBS) under heavy rainfall

A GeoBarrier system (GBS) is a combination system of reinforced soil walls to stabilize near-vertical cut slopes and capillary barrier principles to protect the wall from the effect of rainfall infiltration. Singapore requires construction materials that are cost-effective to support sustainable urban development. Therefore, recycled materials are utilized as GBS materials to avoid the use of high-cost materials, such as steel or concrete. GBS consists of planting geobags with unique geosynthetic pockets for sustainable plant growth as a facing layer of GBS. The negative pore-water pressure (suction) within the reinforced soil behind GBS was assured to be constant during rainfall since GBS is designed specially to minimize the rainfall infiltration into the reinforced soil. This paper presents the practical design and stability analysis of the GBS, considering the presence of suction within the reinforced soil body. The monitoring of GBS performance in the field was carried out via field instrumentation. Finite element analyses of the GBS under extreme rainfalls were also performed for evaluation of the GBS performance. The field instrumentations and numerical analysis results showed that GBS was able to protect the slope from rainfall infiltration; therefore, the stability of the slope retained by GBS was not affected by the rainfall. Results from the analytical calculation showed that the most critical mode of failure is sliding along the base, followed by the global and local slope stability. The GBS is not susceptible to local instability.     

Finite element parametric study of the performance of a deep excavation

Deep excavations are widely used for the development of underground space. The structural performance of any deep excavation is influenced by details of the soil behaviour, the form of the retaining and support structures that are employed and also the sequence of construction. Finite element analysis is potentially an effective tool for considering both the geotechnical and structural aspects of the design of deep excavations. To capture the main features of the excavation behaviour, a finite element model is required that is able to represent the principal deformation and structural mechanisms at an appropriate level of detail. The current paper explores the various modelling assumptions that need to be considered when developing detailed 3D finite element models for the design of deep excavations. A parametric study is described, based on an idealised square excavation, to investigate the influence that certain key features of the model can have on the quality of the computed results. The study includes the choice of element type to model the structural components, the selection of appropriate material parameters, the choice of procedures to model post-cure shrinkage of the concrete elements and the choice of procedure to model the soil/structure interfaces. The results of this parametric study provide guidance for the development of finite element models for practical design purposes.     

组合桁架节点的试验及有限元分析

采用模拟试验及有限元方法,对某桁架斜拉桥中组合节点的力学性能进行分析。试验研究了此节点的安全裕度及适用性,模型缩尺比例为1:2.5。分析了应力分布、裂缝抵抗能力、锚栓剪切抵抗力,研究了节点的力学性能及传力途径。在荷载达到设计荷载的1.7倍前,钢板和混凝土弦杆的最大应变均在弹性范围内,说明这种结构有很好的安全裕度。基于试验结果,建立三维有限元模型,有限元分析的承载力和刚度计算结果与试验吻合较好。本分析为后续研究及组合桁架桥、组合节点的设计,提供了有价值的参考。     

Testing and numerical simulation of a medium strength rock material under unconfined compression loading

This study aims to numerically and experimentally investigate the response of a medium strength rock material under unconfined compression loading up to failure. The unconfined compressive strength (UCS) is one of the most important parameters in characterising rock material behaviour. Hence the UCS is crucial in understanding the failure mechanism of fractured rocks. An effective approach to determine the UCS and to investigate the behaviours of rock materials under unconfined compression is essential in the majority of research fields of rock mechanics. The experimental configuration for the unconfined compression test, suggested by the protocols of the ASTM standard, has some limitations which affect the accuracy in determination of the real UCS. Among several alternative configurations proposed, the Mogi's configuration seems to be the most appropriate one. Therefore, the ASTM and Mogi's configurations were used to perform the tests on a medium strength rock material, i.e. Pietra Serena sandstone. The results using two configurations were discussed in terms of the differences. The tests were also replicated in LS-DYNA using a finite element method (FEM) coupled smooth particle hydrodynamics (SPH) technique. This technique is employed in this study due to its capabilities to cope with large deformation issues related to the rocks. An advanced material model, called the Karagozian and Case Concrete (KCC) model, is implemented in the numerical simulations. The KCC model consists of three independent fixed failure surfaces and it can consider the damage accumulation based on the current state of stress among these failure surfaces. An equation-of-state (EOS) is used in conjunction with KCC material model for decoupling the volumetric and deviatoric responses. The numerical and experimental results were finally compared with the focus on the stress–strain diagram and the failure patterns. The comparison shows that the numerical results are in good agreement with the experimental results.     

On the dynamic response of sandwich panels with different core set-ups subject to global and local blast loads

The recent increase in blast and impact threats has led to an emerging interest in sandwich structures due to their superior performance in such loading environments. The optimised architecture of this class in conjunction with additional benefits of high strength-to-weight and stiffness-to-weight ratios vital to weight-sensitive military applications has led to numerous research works on the topic. In this study, the dynamic response of four circular sandwich panel constructions with different core designs under global and local blast loading conditions has been investigated. Numerical finite element (FE) models have been set up to study the effect of additional core interlayers on blast resistance enhancement of these sandwich panels. The objectives are (1) to assess the existing blast resistance capacity, (2) to increase the dynamic energy absorption, (3) to improve the stress distribution through plastic deformation, and (4) to ensure sacrificial damage to the additional core layers; hence, to avoid the main part of the core being damaged by excessive shear deformation, the dominant failure mode in conventional sandwich panels. A ductile elastomeric layer of polyurea, and a fairly compressible Divinycell-H200 foam layer have been selected as the additional core interlayers, and they have been placed in different arrangements to improve the overall blast resistance of the standard sandwich panel with glass-fibre-reinforced plastic (GFRP) face-sheets, and balsawood core. Dynamic explicit FE analyses were carried out using the commercial package ABAQUS 6.9-1. Comparison of specific kinetic and strain energies shows the effect of additional core layers on the blast energy absorption of a sandwich system. The study shows the improvement in shear failure prevention of the core as a result of the use of additional core layers and a reduction in the level of kinetic and strain energies in the protected core in both absolute and relative terms. The stress contours show a smoother stress distribution in enhanced cases. These conclusions are confirmed and explained by using a qualitative two-degree-of-freedom system with an elastic-viscoplastic spring element representing the integral effects of sacrificial additional core interlayers and a nonlinear spring representing the stiffness of the conventional sandwich system and comparing the results of dynamic analysis with a similar qualitative single-degree-of-freedom model of a conventional sandwich panel.     

Behaviour of concrete filled steel tubular (CFST) stub columns under eccentric partial compression

This paper investigates the behaviour of concrete filled steel tubular (CFST) stub columns subjected to eccentric partial compression. Twenty-eight specimens were tested and presented. The main parameters in test program include: (1) section type: circular, square and rectangular; (2) load eccentricity ratio (including uniaxial and biaxial loading): from 0 to 0.4; and (3) shape of the loading bearing plate (BP): circular, square, strip and rectangular. The test results indicated that, similar to the corresponding fully loaded CFST stub columns under eccentric loading, CFST stub columns under eccentric partial compression have generally reasonable bearing capacity and favorable ductility. A finite element analysis (FEA) model for CFST stub columns under eccentric partial compression is developed and the predicted performances are validated through measured results. The FEA model is then used to investigate the mechanisms of such composite columns further.     

考虑不同边界约束条件下的风电机塔架固有频率分析

为了准确分析地基土刚度和基础本身刚度对风力发电机塔架动力特性的影响,利用大型通用有限元软件ANSYS对某风力发电机塔架分别建立塔筒有限元模型和塔筒及基础的整体有限元模型,对塔架进行模态分析：考虑不同的边界约束条件,包括塔筒底部刚接、混凝土基础底部刚接、基础底部和侧面均刚接、基础底部刚接侧面约束两个水平方向、基础底部加扭转和竖向弹簧、基础底部加扭转和竖向弹簧并且侧面加水平向弹簧几种模型,确定其固有频率和振型。有限元模型中,机舱质量和叶轮质量以质量单元方式加于塔筒顶部。不同约束条件下的固有频率计算结果显示,地基和基础的弹性对整体结构固有频率有一定影响,是否考虑地基土刚度和基础本身刚度的计算结果的差别为11.6%。这表明在设计中,宜考虑基础本身刚度和地基土刚度对风电机塔架动力性能的影响。最后将塔架固有频率与叶片转动频率1p（1个叶片）、3p（3个叶片）进行比较,结果显示塔架固有频率与1p上限值非常接近,对塔架系统动力特性较为不利。     

Investigation of mechanical behaviour of a quasi-brittle material using Karagozian and Case concrete (KCC) model

The mechanical behaviour of a quasi-brittle material,i.e.Pietra Serena sandstone,was investigated both numerically and experimentally in order to build a reliable numerical modelling system applicable to more complex cases.The Karagozian and Case concrete(KCC) model was exploited as the material constitutive law and a new method to utilise this model for efficient and accurate simulation of quasibrittle materials is discussed.The capability of this model is evaluated by comparing the results of the numerical simulations with the corresponding experimental results,and the method itself is critically assessed.     

节理岩体表征单元体尺寸确定的数值模拟

从节理岩体表征单元体的力学意义出发,在通过对某物理试验结果进行模拟以验证RFPA程序模拟节理岩体强度及破裂模式具有适用性的基础上,提出一种基于RFPA数值模拟确定节理岩体表征单元体的方法。该方法基于蒙特卡洛法生成二维节理裂隙网格,实现节理裂隙的表征,将其导入岩石破裂过程分析软件中,分析节理岩体弹性模量和单轴抗压、抗拉强度的尺寸效应和各向异性,并据此确定了节理岩体的表征单元体尺寸。最后,针对某采场围岩节理面统计参数,分析讨论节理岩体的尺寸效应和各向异性,通过综合分析确定了节理岩体的弹性模量、抗压强度和抗拉强度等参数,并得出其表征单元体的尺度为6 m×6 m,这为后续的岩石力学研究奠定基础。     

Repertory grid technique in the development of Tacit-based Decision Support System (TDSS) for sustainable site layout planning

Site layout planning is a significant but relatively ignored work on construction site, which has been treated improperly as somewhat routine. It is known that the complex interrelationship of material, equipment, laborers, space, environment, assess road, surrounding buildings, and building types affect the productivity and efficiency of a construction process. This complexity was inhibiting the smooth flow of resources especially when many trade contractors were working simultaneously on site. The study aimed to extract a set of core factors in site planning focusing on the tacit knowledge acquisition process to develop a Tacit-based Decision Support System (TDSS). A combination of the repertory grid technique and open-structured interviews was conducted for the tacit knowledge acquisition process. Cluster analysis and repertory grid analysis on the extensive responses from a structured interview were conducted. A computer program entitled “TDSS” was developed as a flexible tool to assist both senior and junior site layout planning engineers.     

Photodegradation of phenol red in the presence of oxyhydroxide of Fe(III) (Goethite) under artificial and a natural light

The (α‐FeOOH) Goethite composite is a stable and an efficient catalyst in aqueous suspension under irradiation at 365 nm and by solar light. The photocatalytic activities of this composite were evaluated using Phenol Red (PR) dye (phenolsulfonphthalein class). In the dark, controlling factors, such as the pH and the adsorption of PR on Goethite surface were evaluated (before starting the photochemical experiments). It was found that the system PR‐Goethite present a small decrease in the main band of the dye (435 nm) which was explained by the low rate of adsorption of this dye on the Goethite. Also, we note that 40% of PR decolourisation was obtained after 200 min by the system PR‐Goethite‐hydrogen peroxide (H₂O₂) in dark due to the formation of ^?OH by thermal decomposition of H₂O₂ on the surface of Goethite. The effects of various experimental parameters, such as initial dye concentration, pH, photocatalyst amount, tert‐Butyl alcohol effect and H₂O₂ addition were investigated in the study of photodegradation of the dye. The results showed that the photodegradation of PR under UV‐A (365 nm) irradiation could be enhanced greatly in the presence of H₂O₂. Natural radiation tests (under sunlight) showed that degradation was faster comparing with that obtained using the artificial one at 365 nm. Studies of the mineralization using total organic carbon method under naturel light certify that this method, compatible with the environment, may be considered in the treatment of wastewater and generally in the process of removal of this kind of pollutant.