Academic literature on the topic 'Reinforced Soil Foundation - Numerical Simulations'

In this research, a reinforcement mechanism for shallow foundations is determined through laboratory model tests and numerical analyses. The numerical analyses are performed with the finite element program FEMtij-2D using the elastoplastic subloading tij model. The frictional behavior between the reinforcement and the ground is simulated using an elastoplastic joint element. Several tests were performed whereby the installation depth, length, roughness, and fixity conditions at the edges of the reinforcement were varied. Results show that the effectiveness of the reinforcement and the bearing capacity of the reinforced ground depend on the position, length, roughness, and fixity condition of the reinforcement. A significant increase in the bearing capacity can be achieved if the geosynthetics are properly placed at an optimum length with the boundary fixed to the ground. The effect of the loading position is also investigated because in reality the load on a foundation does not always act at the center of the foundation. The numerical results accurately describe the experimental results; the simulations accurately account for the mechanical behaviors of both the soil and reinforcement and the frictional behavior between them. Therefore, the simulation technique can be used to predict the bearing capacity of reinforced ground.

The water filling preloading method is the common ground treatment method adopted to reinforce soft tank foundation. The influence laws of load speed, soil parameters on the reinforced effect of soft tank foundation were analyzed by the three-dimension finite element numerical analysis procedure. The research shows that the fovea deformation of single tank bottom under preload is similar to the pan bottom shape; the influence of soil constrained modulus on settlement is remarkable and it also affects the settlement time curve shape; when the constrained modulus is constant, with the permeability coefficient decreasing, the surface doming phenomenon around the tank foundation increases, and the range of upheaval is related to constrained modulus; the influence of loading function on the final settlement is very small, but the influence on pore water pressure is remarkable.

Introduction. The overwhelming majority of construction areas are characterized by difficult engineering and geological conditions, represented by the presence of weak soils at the base. There are construction sites on which a large thickness of fill soil is observed. In these conditions, designers apply: soil consolidation, soil reinforcement, significant deepening of the underground part of buildings, etc. This article presents the formulation and solution of the problems of interaction of reinforced concrete piles with weak soils, as well as the interaction of soil piles with bulk soils as part of a pile-slab foundation, which allow one to determine the reduced deformation modulus and the bedding value. Materials and methods. To describe the change in shear stresses depending on depth, a law was adopted in the form τ(z)=τ0е–αz. The solution is presented by analytical and numerical methods. The results obtained were compared by the analytical solution of the problem with the results obtained in the PLAXIS 3D software package. Results. Regularities of the distribution of the total load on the pile-slab foundation between the pile field and the grillage have been obtained. The analytical solutions in the article are supported by the graphical part, performed using the Mathcad program. Numerical simulation of the problem was carried out in the PLAXIS 3D software package. The dependence of the settlement on the load, calculated by analytical and numerical methods, is shown. An expression is obtained for defining the stresses in different sections of the pile shaft and under the grillage slab. The theoretical and practical aspects of the construction of crushed stone piles are considered. The theoretical substantiation of compaction of bulk soils with crushed stone piles using a special technology is given. A dependence is obtained for determining the reduced modulus of deformation for bulk soil mass reinforced with soil piles. Conclusions. Comparative evaluation of the results of solutions obtained by analytical and numerical methods showed good convergence. The solutions obtained can be used to preliminary determination of the settlement of piles as part of a pile-slab foundation. Selection of the optimal ratio of the pile length and its diameter allows the most effective use of the bearing capacity of the pile. For bulk soils, reinforced with soil piles, it is possible to select the optimal reduced modulus of deformation by varying the pitch of the soil piles.

With the increasing in freezing shaft sinking depth of the mine，Mine permanent derrick was located into the frozen wall. The internal force distribution of the shaft-tower foundation was obtained by field measurement shaft-tower foundation basal pressure, foundation reinforced strain and the strain of concrete and foundation deformation of mechanical quantity. The numerical simulation of the interaction between coal derrick and foundation in freezing and thawing process shows that: the field measurement and numerical simulation laws were consistent and the values were in good agreement. It has very important theoretical and practical significance for the safe production of derrick and future derrick foundation design in freezing method construction.

In order to study the bearing characteristic of the geosynthetic-encased stone column (GESC) on the composite foundation, a series of field tests and numerical simulation were carried out on the composite foundations reinforced by the traditional stone column and the GESC. The pile–soil stress ratio, excess pore water pressure and lateral displacement of two kinds of composite foundations were monitored. The effects of geotextile stiffness, geotextile wrapping length and gravel internal friction angle on the composite foundation with the GESC were analyzed by establishing different numerical models. The results show that the GESC can bear larger loading compared with the traditional stone column. The pile–soil stress ratio of the composite foundation with the traditional stone column gradually increases from 1.1 to 1.5 with the increasing of the embankment height. However, the pile–soil stress ratio of the composite foundation with the GESC reaches 1.5 at the initial filling stage and increases to 1.7 with the filling construction. The drainage effect of the GESC is better than that of the traditional stone column, and the GESC can effectively improve the overall stiffness of stone column, so as to reduce the lateral displacement of soil mass. The increases of geotextile stiffness, geotextile wrapping length and gravel internal friction angle can improve the bearing performance of the composite foundation with the GESC. However, after geotextile stiffness and wrapping length reach a certain value, the influence of its lifting amount on the composite foundation will be reduced.

Abstract In this paper it is presented how the influence of soil-structure interaction (SSI) interferes on reinforced concrete structures in small buildings with deep foundations, with the objective of analyzing the influence of SSI on the loads and repressions, global stability and costs of materials. The analysis were based on numerical-computational simulations of a commercial building using CAD/TQS commercial software. The building was simulated with 4, 6 and 8 floors with 3 different profiles of soils, generating 8 case studies. When considering SSI, the loads and repressions did not present significant variations and the parameters of global instability were within the normative recommendations. Among the variables analyzed, the material cost of the structure was the least affected item with the SSI consideration.

The paper presents results of numerical simulations of the stress distribution and deformations within of foundations of huge monument of Christ The King erected in Świebodzin (Poland) in 2010. It is 3 meters taller than the better known statue of Christ the Redeemer in Rio de Janeiro, standing at 30.1 meters tall without its pedestal. Foundations were built as a system of reinforced concrete columns and slabs which can be classified as a spatial column-slab system. Actual mechanical parameters of the substrate and of the artificial mound made of field stones, sand, gravel and clay were adopted in calculations. The numerical simulations of structural members of foundation and determination of the stress distribution are presented in the article. Monument itself was not included into the model. Instead of it the rigid cantilever was introduced to which resultant forces were applied. Three different stages were distinguished: the initial state after foundation and mound accomplishment, the initial state plus the dead load and the initial state plus the dead load and the wind load. It was assumed that the wind load was taken into account in a quasi-static formulation by applying the equivalent horizontal force and the torque. Stresses and displacements for these three stages were determined by Finite Element Method using Simulia ABAQUS system. It was disclosed what was a contribution of particular parts of foundations in sustaining loads in considered load cases. The state of exertion of structural members of foundations and the soil itself was assessed. It was showed that the column-slab foundations and soils of the mound play important role in taking loads of the statue, spreading them and safe transferring to the undisturbed level of natural soils. According to the numerical simulations results the columns of foundation take as much as 64% of the vertical load (in the most unfavourable load conditions). At the same time soils of the mound take through the side surface of piles about 20 % of the vertical load.

Dynamic compaction and geogrid reinforcement are two of the well-known methods used in improving the mechanical properties of fill foundations. In order to investigate their mutual restriction when used simultaneously and optimize the design parameters, model experiments and numerical simulations were conducted. First, three factors (embedded ratio of reinforced geogrid, number of reinforced layers and interval of reinforced layers) that are related to performance of reinforced geogrid were analyzed by model experiments with dynamic compaction. Then, orthogonal analysis was performed by numerical simulation (dynamic analysis in FLAC3D) to take into account five different elastic moduli and internal angle of friction along with the aforementioned three factors. Last, range analysis and variance analysis were performed on the orthogonal results to optimize the five factors by the calculated indicators. Additionally, linear regression analysis reflecting the relationships between five factors and four indicators was presented. The displacement field, compaction effect, earth pressure, and geogrid deformation of the reinforced soil under different combinations of the five factors were explored. Experiment and simulation results provide practical guides to the design of reinforced methods and a reference for the stability and deformation of other earth reinforcement projects under dynamic loads.

Mechanism of composite pre-reinforced micro pile soil-nail and pure soil-nail retaining structure in foundation-pit engineering are analyzed in this paper through general three dimension nonlinear numerical simulation software. Research contents include whole construction process simulation of construction such as excavation by steps, piles and soil-nail installation and panel manufacture etc. By the comparison of mechanical characteristics between the pure soil-nail and composite soil-nail retaining structures in the same slope engineering example, differences of tension distribution range of soil layer, deformation features, mechanical characteristics of support and axial force distribution along nails etc. are analyzed. Research results are verified by in-site projects and measured data. The action mechanism and working performance of composite soil-nail retaining support are also systematically studied and theoretical basis can be provided in the similar application.

The new CFG pile-board structure composite foundation is a ground treatment technique based on CFG pile foundation and pile-board structure composite foundation. It can make full use of the load distributing function of board, the bearing capacity and the deformation compatibility of soil between piles, by taking advantage of the pile-platform-soil interaction. A part of soft ground in a high-speed railway was taken as the engineering background and study object. The settlement controlling effect of common CFG pile ground and new CFG pile-board structure composite foundation were analyzed by finite element numerical method, and various factors to the effect on settlement-controlling were discussed. Pile-soil stress ratio of CFG pile and reinforced concrete pile were studied. Some useful conclusions of the numerical simulation of the new CFG pile-board structure composite foundation were obtained.

L'objectif de ce travail est d'analyser l'influence du renforcement du sol par la method Soil Mixing sur le comportement des fondations superficielles et profondes. Une étude numérique a été effectuée – avec des analyses éléments finis dans ABAQUS - dans le but d'acquérir une compréhension du fonctionnement et une estimation de la performance des fondations améliorées. Pour être en mesure d'utiliser des colonnes SM pour l'amélioration de la fondation, il est nécessaire de bien comprendre leur performance sous charge axiale statique. Par conséquent, une série de simulations reproduisant des essais de chargement d'une seule colonne, et d’un groupe de colonnes ont été réalisées. Les essais à pleine et petite échelle ont été modélisés et leurs résultats comparés avec les observations expérimentales. Un bon accord entre les prédictions numériques et les mesures confirme une bonne calibration des lois constitutives des sols, des colonnes et de l’interface sol/colonne en SM. En outre, cette étude a révélé que la colonne SM agit d'une manière similaire à un pieu en béton, son comportement est régi principalement par l'interface. Ensuite, la modélisation numérique d’une fondation superficielle à petite échelle a été menée. Deux types de renforcement ont été étudiés. Le premier consiste en une seule colonne, située au centre sous la semelle analysée. Le second cas correspond à un groupe de quatre colonnes SM. Deux densités de sol ont été analysés. L'objectif de la modélisation est d'identifier l'efficacité du renforcement en termes de capacité portante de la fondation et de la réduction de son déplacement vertical. Il a été trouvé que la densité du sable a un impact significatif sur le comportement de la semelle. La variation de densité a entraîné une différence significative entre les forces totales portées par les fondations. Mais, il a été constaté que le pourcentage de la force reprise par le sol par rapport à la force total, est indépendant de la densité. L'influence du renforcement obtenu par un groupe de colonnes SM sur une fondation profonde, a été étudiée. La modélisation numérique d'un seul pieu théorique installé dans le sol homogène, a été réalisée. L'objectif de l'étude est de détecter l'impact de divers paramètres, tels que la distance horizontale entre les colonnes de SM, la distance verticale entre les têtes de colonnes et la pointe de pieu, le diamètre et la longueur des éléments SM, sur la capacité portante de la fondation. On a montré que la distance entre les colonnes et leur diamètre ont la plus grande influence sur la force de charge, la longueur de renforcement conduit à une moindre influence
The aim of this work is to analyse the influence of soil reinforcement executed by the Soil Mixing method on the behaviour of shallow and deep foundations. Numerical investigation has been carried out - with the use of Finite Element (FE) analyses in ABAQUS - in an attempt to identify the mechanisms guiding the performance of supported foundations. To be able to use SM columns as the foundation’s improvement, it is necessary to fully understand their performance under applied static, axial load. Therefore, a set of simulations reproducing loading tests of single and group of columns have been carried out. Full and small scale tests have been modelled and their results compared with experimental observations. Good agreement between numerical predictions and measurements, confirms proper calibration of the chosen constitutive laws of: soils, columns and interactions between them. Moreover, this study has revealed that the SM column acts in a similar way to concrete pile, hence its behaviour is governed mainly by the interface. Afterwards, numerical modelling of small scale shallow foundation has been accomplished. Two kinds of reinforcement have been investigated. The first one consists of a single column situated centrally under the analysed footing. The second kind of improvement involves group of four SM columns. Two densities of soil have been analysed. The goal of the modelling is to identify the efficiency of the reinforcement in terms of: bearing capacity of the foundation and reduction of its vertical displacement. Despite significant difference between total forces borne by the foundation tested on soil with different densities, it has been found that the percentage of the total force that was taken by the soil is density independent. The influence of reinforcement executed by group of SM columns on a deep foundation has been studied. Numerical modelling of a theoretical, single pile, installed in homogeneous soil, has been carried out. The aim of the investigation is to detect the impact of parameters such as: pattern of reinforcing elements, horizontal distance between SM columns, vertical distance between columns’ heads and tip of the pile, diameter and length of SM elements, on the bearing capacity of the foundation. It has been found that the distance between columns and their diameter has the biggest influence on the borne force. However, the length of the reinforcement has shown the least significant influence

Use of geosynthetics for reinforcing soil beds supporting shallow foundations has gained tremendous popularity in recent times. In this thesis, to study and understand the behaviour of geosynthetics reinforced soil foundations, model load tests are carried out on square footings resting on sand beds reinforced with geosynthetics. The effects of various parameters like type and tensile strength of geosynthetic material, depth of reinforced zone, spacing of reinforcement layers, width of reinforcement and form of reinforcement on the performance of square footings on reinforced sand beds are studied. Results from these tests are analyzed to understand the effect of various parameters in improving the bearing capacity and reducing the settlement of footings. An equation is developed to estimate the ultimate bearing capacity of square footings resting on geosynthetic reinforced sand beds by multiple regression analysis of the experimental data. The model loading tests on reinforced soil foundations are simulated in the numerical model using the computer program FLAC3D (Fast Lagrangian Analysis of Continua in 3D). Finally parametric studies on a full scale reinforced soil foundation are conducted. From the experimental, analytical and numerical investigations carried out in this thesis, some important conclusions are drawn regarding the effective depth of reinforced zone, optimum spacing and quantity of reinforcement layers. Relative efficiency of various forms of reinforcement is discussed. Validity of the regression and numerical models developed is verified through experimental data from present study and also for data from other researchers.

Use of geosynthetics for reinforcing soil beds supporting shallow foundations has gained tremendous popularity in recent times. In this thesis, to study and understand the behaviour of geosynthetics reinforced soil foundations, model load tests are carried out on square footings resting on sand beds reinforced with geosynthetics. The effects of various parameters like type and tensile strength of geosynthetic material, depth of reinforced zone, spacing of reinforcement layers, width of reinforcement and form of reinforcement on the performance of square footings on reinforced sand beds are studied. Results from these tests are analyzed to understand the effect of various parameters in improving the bearing capacity and reducing the settlement of footings. An equation is developed to estimate the ultimate bearing capacity of square footings resting on geosynthetic reinforced sand beds by multiple regression analysis of the experimental data. The model loading tests on reinforced soil foundations are simulated in the numerical model using the computer program FLAC3D (Fast Lagrangian Analysis of Continua in 3D). Finally parametric studies on a full scale reinforced soil foundation are conducted. From the experimental, analytical and numerical investigations carried out in this thesis, some important conclusions are drawn regarding the effective depth of reinforced zone, optimum spacing and quantity of reinforcement layers. Relative efficiency of various forms of reinforcement is discussed. Validity of the regression and numerical models developed is verified through experimental data from present study and also for data from other researchers.

碩士
國立暨南國際大學
土木工程學系
101
This goal of this research is to study the effect of geosynthetic material on reinforcing foundation soil. This research is implemented by conducting finite element analyses of soils layers. First, numerical models of foundation soil layers are built to simulate published cases. The numerical approach is validated by the promising comparison with the loads and deformations both concerning the trends and the magnitudes as reported on literatures. A series of parametric study of varying design parameters of the baseline numerical model are performed to identify that the thickness of base layer, CBR of Subgrade layer, elastic stiffness of geosynthetic material, and the placing depth of geosynthetic material, are important parameters for performing numerical analysis of geosynthetic reinforced foundation soil layers. More serious of parametric study are conducted to understanding how the ground settlement of reinforced foundation soil responds to the mesh size, loading pattern, material properties and placement location of reinforcement, and the coefficient between soil/geosyntheitc interface.

The various aspects of the 3D cellular confinement systems (geocells) subjected to static loading are comprehensively studied with the help of experimental and numerical studies. The performances of the geocells were separately studied in both sand and clay beds. Laboratory tests were performed on single as well as multiple cells. The behavior of 3D-cells made of different materials such as Novel polymeric alloy, geogrids and bamboo were compared. Moreover, the performances of the geocells were compared with other forms of geosynthetic reinforcements namely, geogrids and the combination of geocells and geogrids. In addition to comprehensive experimental study, 2-dimensional and 3-dimensional numerical modelling efforts are also presented. A Realistic approach of modelling the geocells in 3D framework has been proposed; which considers the actual curvature of the geocell pockets. An Analytical equation has been proposed to estimate the increase in the bearing capacity of the geocell reinforced soft clay beds. Similarly, a set of equations to estimate the stress and strains on the surface of the geocells subjected to compressive loading were also proposed. A case study highlighting the innovative use of the geocell foundation to support the embankment on soft settled red mud has been documented in the thesis. A new and emerging application of geocell to protect underground utilities and the buried pipelines has been proposed. At the end, behavior of the geocell under cyclic loading has also been discussed. Firstly, laboratory model tests were performed to understand the behavior of the geocells in sand and clay beds. Test results of unreinforced, geogrid reinforced, geocell reinforced, and geocell reinforced with additional planar geogrid at the base of the geocell cases were compared separately for sand and clay beds. Results revealed that the use of geocells increases the ultimate bearing capacity of the sand bed by 2.9 times and clay bed by 3.6 times. Provision of the basal geogrid increases the ultimate load carrying capacity of the sand and clay bed by about 3.6 times and 4.9 times, respectively. Besides increasing the load carrying capacity, provision of the planar geogrid at the base of the cellular mattress arrests the surface heaving and prevents the rotational failure of the footing. Geocells contribute to the load carrying capacity of the foundation bed, even at very low settlements. In addition, the effect of infill materials on the performance of the geocell was also studied. Three different infill materials, namely aggregate, sand and local red soil were used in the study. Results suggest that the performance of the geocell was not heavily influenced by the infill materials. Out of which aggregate found to be slightly better than other two infill materials. Further, 2-dimensional numerical studies using FLAC2D (Fast Lagrangian Analysis of Continua in 2D) were carried out to validate the experimental findings. The equivalent composite approach was used to model the geocells in 2-dimensional framework. The results obtained from the FLAC2D were in good agreement with the experimental results. However, in the sand bed, FLAC2D overestimated the bearing pressure by 15% to 20% at higher settlements. In addition, the joint strength and the wall deformation characteristics of the geocells were studied at the single cell level. The study helps to understand the causes for the failure of the single cell in a cellular confinement system. Experimental studies were conducted on single cells with cell pockets filled up with three different infill materials, namely, silty clay, sand and the aggregates. The results of the experimental study revealed that the deformation of the geocell wall decreases with the increase in the friction angle of the infill material. Measured strain values were found to be in the range of 0.64% to 1.34% for different infill materials corresponding to the maximum applied bearing pressure of 290 kPa. Experimental results were also validated using FLAC3D. Findings from the numerical studies were in accordance with the experimental results. A simple analytical model based on the theory of thin cylinders was also proposed to calculate the accumulated strain of the geocell wall. This model operates under a simple elastic solution framework. The proposed model slightly overestimates the strains as compared to experimental and numerical values. A realistic approach of modelling the geocells in 3-dimensional (3D) framework has been proposed. Numerical simulations have been carried out by forming the actual 3D honeycomb shape of the geocells using the finite difference package FLAC3D. Geocells were modeled using the geogrid structural element available in the FLAC 3D with the inclusion of the interface element. Geocells, foundation soil and the infill soil were modeled with the different material model to match the real case scenario. The Mohr Colombo model was used to simulate the behavior of the sand bed while modified Cam clay was used to simulate the behavior of the clay bed. It was found that the geocells distribute the load in lateral direction to a relatively shallow depth as compared to unreinforced case. More than 50% reduction in the stress in the presence of geocells and more than 70% reduction in the stress in the presence geocells with basal geogrid were observed in sand and clay beds. The numerical model was also validated with the experimental studies and the results were found to be in good agreement with each other. The validated numerical model was used to study the influence of various properties of the geocells on the performance of the reinforced foundation beds. The performance of the foundation bed was directly influenced by the modulus and the height of the geocells. Similarly, the pocket size of the geocell inversely affected the performance of the reinforced beds. The geocell with textured surface yielded better performance than the geocell with smooth surface. A case history of the construction of a 3 m high embankment on the geocell foundation over the soft settled red mud has been documented. Red mud is a waste product from the Bayer process of Aluminium industry. The reported embankment is located in Lanjigharh (Orissa) in India. The geotechnical problems of the site, the design of the geocell foundation based on experimental investigation and the construction sequences of the geocell foundations in the field are discussed. Based on the experimental studies, an analytical model was also developed to estimate the load carrying capacity of the soft clay bed reinforced with geocell and the combination of geocell and geogrid. The solution was established by superimposing the three mechanisms viz. lateral resistance effect, vertical stress dispersion effect and the membrane effect. By knowing the pressure applied on the geocell, tensile strength of the geogrid and the limiting settlement, the increment in the load carrying capacity can be calculated. The analytical model was validated with the experimental results and the results were found to be in good agreement with each other. The results of the experimental and analytical studies revealed that the use of the combination of geocell and the geogrid is always beneficial than using the geocell alone. Hence, the combination of geocell and geogrid was recommended to stabilize the embankment base in Lanjigharh. Over 15,000 mof embankment base was stabilized using geocell foundation. The foundation work was completed within 15 days using locally available labors and the equipment. Construction of the embankment on the geocell foundation has already been completed. The constructed embankment has already sustained two monsoon rains without any cracks and seepage. Like Aluminum tailings (redmud), geocell foundations can also be used in various other mine tailings like zinc, copper etc. Geocell foundation can offer potential solutions to storage problems faced by various mining industries. The thesis also proposes a potential alternative to the geocells in the form of bamboocells in order to suit the Indian scenario. Indian has the 2nd largest source of bamboo in the world. The areas particularly rich in bamboo are the North Eastern States, the Western Ghats, Chattisgarh and Andaman Nicobar Islands. The tensile strength and surface roughness of the bamboo was found to be 9 times and 3 times higher than geocell materials. In order to use the bamboo effectively, 3D cells (similar to geocells) and 2D grids (similar to geogrids) are formed using bamboo known as bamboocells and bamboogrids respectively. The idea behind forming bamboocells is to extract the additional confining effect on the encapsulated soil by virtue of its 3-dimensional shape. The laboratory investigations were performed on a clay bed reinforced with natural (bamboo) and commercial (geosynthetics) reinforcement materials. The performance of bamboocells and bamboogrids reinforced clay beds were compared with the clay bed reinforced with geocells and geogrids. The ultimate bearing capacity of the bamboocell and bamboogrid reinforced clay bed was found to be 1.3 times that of reinforced with geocell and geogrid. The settlement of the clay bed was reduced by 97% due to the insertion of the combination of the bamboocell and bamboogrid as compared to the unreinforced clay bed. The bamboo was treated chemically to increase the durability. The performance of the bamboo was reduced by 15-20% after the chemical treatment; still the performance was better than its geosynthetic counterparts. Analytical studies revealed that the 3% of the ultimate tensile strength of the bamboogrid was mobilized while resisting the footing load. The study also explored the new and innovative applications of the geocells to protect underground utilities and buried pipelines. The laboratory model tests and the numerical studies were performed on small diameter PVC pipes, buried in geocell reinforced sand beds. In addition to geocells, the efficacy of only geogrid and geocell with additional basal geogrid cases were also studied. A PVC (Poly Vinyl Chloride) pipe with external diameter 75 mm and thickness 1.4 mm was used in the experiments. The vehicle tire contact pressure was simulated by applying the pressure on the top of the bed with the help of a steel plate. Results suggest that the use of geocells with additional basal geogrid considerably reduces the deformation of the pipe as compared to other types of reinforcements. Further, the depth of placement of pipe was also varied between 1B to 2B (B is the width of loading plate) below the plate in the presence of geocell with additional basal geogrid. More than 50% reduction in the pressure and more than 40% reduction in the strain values were observed in the presence of reinforcements at different depths as compared to the unreinforced beds. Further, experimental results were validated with 3-dimensional numerical studies using 3D FLAC. Good agreement in the measured pipe stain values were observed between the experimental and numerical studies. In addition, the results of the 1-g model tests were scaled up to the prototype case of the shallow buried pipeline below the pavement using the appropriate scaling laws. The efficacy of the geocells was also studied under the action of cyclic loading. The laboratory cyclic plate load tests were performed in soft clay bed by considering the three different cases, namely, unreinforced, geocell reinforced and geocell with additional basal geogrid reinforced. The coefficient of elastic uniform compression (Cu) was evaluated from the cyclic plate load tests for the different cases. The Cu value was found to increase in the presence of geocell reinforcement. The maximum increase in the Cu value was obtained for the case of the clay bed reinforced with the combination of geocell and the geogrid. The results of the laboratory model tests were extrapolated to prototype foundation supporting the low frequency reciprocating machine. The results revealed that, in the presence of the combination of geocell and the geogrid the natural frequency of the foundation-soil system increases by 4 times and the amplitude of the vibration reduces by 92%.

The various aspects of the 3D cellular confinement systems (geocells) subjected to static loading are comprehensively studied with the help of experimental and numerical studies. The performances of the geocells were separately studied in both sand and clay beds. Laboratory tests were performed on single as well as multiple cells. The behavior of 3D-cells made of different materials such as Novel polymeric alloy, geogrids and bamboo were compared. Moreover, the performances of the geocells were compared with other forms of geosynthetic reinforcements namely, geogrids and the combination of geocells and geogrids. In addition to comprehensive experimental study, 2-dimensional and 3-dimensional numerical modelling efforts are also presented. A Realistic approach of modelling the geocells in 3D framework has been proposed; which considers the actual curvature of the geocell pockets. An Analytical equation has been proposed to estimate the increase in the bearing capacity of the geocell reinforced soft clay beds. Similarly, a set of equations to estimate the stress and strains on the surface of the geocells subjected to compressive loading were also proposed. A case study highlighting the innovative use of the geocell foundation to support the embankment on soft settled red mud has been documented in the thesis. A new and emerging application of geocell to protect underground utilities and the buried pipelines has been proposed. At the end, behavior of the geocell under cyclic loading has also been discussed. Firstly, laboratory model tests were performed to understand the behavior of the geocells in sand and clay beds. Test results of unreinforced, geogrid reinforced, geocell reinforced, and geocell reinforced with additional planar geogrid at the base of the geocell cases were compared separately for sand and clay beds. Results revealed that the use of geocells increases the ultimate bearing capacity of the sand bed by 2.9 times and clay bed by 3.6 times. Provision of the basal geogrid increases the ultimate load carrying capacity of the sand and clay bed by about 3.6 times and 4.9 times, respectively. Besides increasing the load carrying capacity, provision of the planar geogrid at the base of the cellular mattress arrests the surface heaving and prevents the rotational failure of the footing. Geocells contribute to the load carrying capacity of the foundation bed, even at very low settlements. In addition, the effect of infill materials on the performance of the geocell was also studied. Three different infill materials, namely aggregate, sand and local red soil were used in the study. Results suggest that the performance of the geocell was not heavily influenced by the infill materials. Out of which aggregate found to be slightly better than other two infill materials. Further, 2-dimensional numerical studies using FLAC2D (Fast Lagrangian Analysis of Continua in 2D) were carried out to validate the experimental findings. The equivalent composite approach was used to model the geocells in 2-dimensional framework. The results obtained from the FLAC2D were in good agreement with the experimental results. However, in the sand bed, FLAC2D overestimated the bearing pressure by 15% to 20% at higher settlements. In addition, the joint strength and the wall deformation characteristics of the geocells were studied at the single cell level. The study helps to understand the causes for the failure of the single cell in a cellular confinement system. Experimental studies were conducted on single cells with cell pockets filled up with three different infill materials, namely, silty clay, sand and the aggregates. The results of the experimental study revealed that the deformation of the geocell wall decreases with the increase in the friction angle of the infill material. Measured strain values were found to be in the range of 0.64% to 1.34% for different infill materials corresponding to the maximum applied bearing pressure of 290 kPa. Experimental results were also validated using FLAC3D. Findings from the numerical studies were in accordance with the experimental results. A simple analytical model based on the theory of thin cylinders was also proposed to calculate the accumulated strain of the geocell wall. This model operates under a simple elastic solution framework. The proposed model slightly overestimates the strains as compared to experimental and numerical values. A realistic approach of modelling the geocells in 3-dimensional (3D) framework has been proposed. Numerical simulations have been carried out by forming the actual 3D honeycomb shape of the geocells using the finite difference package FLAC3D. Geocells were modeled using the geogrid structural element available in the FLAC 3D with the inclusion of the interface element. Geocells, foundation soil and the infill soil were modeled with the different material model to match the real case scenario. The Mohr Colombo model was used to simulate the behavior of the sand bed while modified Cam clay was used to simulate the behavior of the clay bed. It was found that the geocells distribute the load in lateral direction to a relatively shallow depth as compared to unreinforced case. More than 50% reduction in the stress in the presence of geocells and more than 70% reduction in the stress in the presence geocells with basal geogrid were observed in sand and clay beds. The numerical model was also validated with the experimental studies and the results were found to be in good agreement with each other. The validated numerical model was used to study the influence of various properties of the geocells on the performance of the reinforced foundation beds. The performance of the foundation bed was directly influenced by the modulus and the height of the geocells. Similarly, the pocket size of the geocell inversely affected the performance of the reinforced beds. The geocell with textured surface yielded better performance than the geocell with smooth surface. A case history of the construction of a 3 m high embankment on the geocell foundation over the soft settled red mud has been documented. Red mud is a waste product from the Bayer process of Aluminium industry. The reported embankment is located in Lanjigharh (Orissa) in India. The geotechnical problems of the site, the design of the geocell foundation based on experimental investigation and the construction sequences of the geocell foundations in the field are discussed. Based on the experimental studies, an analytical model was also developed to estimate the load carrying capacity of the soft clay bed reinforced with geocell and the combination of geocell and geogrid. The solution was established by superimposing the three mechanisms viz. lateral resistance effect, vertical stress dispersion effect and the membrane effect. By knowing the pressure applied on the geocell, tensile strength of the geogrid and the limiting settlement, the increment in the load carrying capacity can be calculated. The analytical model was validated with the experimental results and the results were found to be in good agreement with each other. The results of the experimental and analytical studies revealed that the use of the combination of geocell and the geogrid is always beneficial than using the geocell alone. Hence, the combination of geocell and geogrid was recommended to stabilize the embankment base in Lanjigharh. Over 15,000 mof embankment base was stabilized using geocell foundation. The foundation work was completed within 15 days using locally available labors and the equipment. Construction of the embankment on the geocell foundation has already been completed. The constructed embankment has already sustained two monsoon rains without any cracks and seepage. Like Aluminum tailings (redmud), geocell foundations can also be used in various other mine tailings like zinc, copper etc. Geocell foundation can offer potential solutions to storage problems faced by various mining industries. The thesis also proposes a potential alternative to the geocells in the form of bamboocells in order to suit the Indian scenario. Indian has the 2nd largest source of bamboo in the world. The areas particularly rich in bamboo are the North Eastern States, the Western Ghats, Chattisgarh and Andaman Nicobar Islands. The tensile strength and surface roughness of the bamboo was found to be 9 times and 3 times higher than geocell materials. In order to use the bamboo effectively, 3D cells (similar to geocells) and 2D grids (similar to geogrids) are formed using bamboo known as bamboocells and bamboogrids respectively. The idea behind forming bamboocells is to extract the additional confining effect on the encapsulated soil by virtue of its 3-dimensional shape. The laboratory investigations were performed on a clay bed reinforced with natural (bamboo) and commercial (geosynthetics) reinforcement materials. The performance of bamboocells and bamboogrids reinforced clay beds were compared with the clay bed reinforced with geocells and geogrids. The ultimate bearing capacity of the bamboocell and bamboogrid reinforced clay bed was found to be 1.3 times that of reinforced with geocell and geogrid. The settlement of the clay bed was reduced by 97% due to the insertion of the combination of the bamboocell and bamboogrid as compared to the unreinforced clay bed. The bamboo was treated chemically to increase the durability. The performance of the bamboo was reduced by 15-20% after the chemical treatment; still the performance was better than its geosynthetic counterparts. Analytical studies revealed that the 3% of the ultimate tensile strength of the bamboogrid was mobilized while resisting the footing load. The study also explored the new and innovative applications of the geocells to protect underground utilities and buried pipelines. The laboratory model tests and the numerical studies were performed on small diameter PVC pipes, buried in geocell reinforced sand beds. In addition to geocells, the efficacy of only geogrid and geocell with additional basal geogrid cases were also studied. A PVC (Poly Vinyl Chloride) pipe with external diameter 75 mm and thickness 1.4 mm was used in the experiments. The vehicle tire contact pressure was simulated by applying the pressure on the top of the bed with the help of a steel plate. Results suggest that the use of geocells with additional basal geogrid considerably reduces the deformation of the pipe as compared to other types of reinforcements. Further, the depth of placement of pipe was also varied between 1B to 2B (B is the width of loading plate) below the plate in the presence of geocell with additional basal geogrid. More than 50% reduction in the pressure and more than 40% reduction in the strain values were observed in the presence of reinforcements at different depths as compared to the unreinforced beds. Further, experimental results were validated with 3-dimensional numerical studies using 3D FLAC. Good agreement in the measured pipe stain values were observed between the experimental and numerical studies. In addition, the results of the 1-g model tests were scaled up to the prototype case of the shallow buried pipeline below the pavement using the appropriate scaling laws. The efficacy of the geocells was also studied under the action of cyclic loading. The laboratory cyclic plate load tests were performed in soft clay bed by considering the three different cases, namely, unreinforced, geocell reinforced and geocell with additional basal geogrid reinforced. The coefficient of elastic uniform compression (Cu) was evaluated from the cyclic plate load tests for the different cases. The Cu value was found to increase in the presence of geocell reinforcement. The maximum increase in the Cu value was obtained for the case of the clay bed reinforced with the combination of geocell and the geogrid. The results of the laboratory model tests were extrapolated to prototype foundation supporting the low frequency reciprocating machine. The results revealed that, in the presence of the combination of geocell and the geogrid the natural frequency of the foundation-soil system increases by 4 times and the amplitude of the vibration reduces by 92%.

As well known, foundation pit excavation influences the stress and deformation of adjacent soil, and thus existing tunnel. However, the behavior on the deformation of a twin-track tunnel subjected to adjacent excavation is not clear. In order to investigate this behavior, a series of numerical simulations using PLAXIS are conducted in this study. The result shows that the displacement and internal forces near the foundation pit is almost double those far away. Moreover, as the depth of excavation reaches the burial depth of tunnel, the value of displacement of tunnel begins to increase markedly.

Abstract Offshore wind is increasingly utilised as a renewable energy source. A growing number of bottom fixed wind turbines installed offshore are supported by suction caisson foundations. The suction-assisted installation remains a source of uncertainty towards the in-service performance due to the unknown post-installation soil plug state. Cone penetration tests within the suction caisson can help to improve the reliability. Therefore, cone penetration tests were employed in centrifuge tests to investigate the plug state in a previously installed suction caisson. However, the performance of a cone penetration test in a small-scale experiment is connected to uncertainties: A relatively large diameter device is required to conduct the cone penetration test — especially in a centrifuge test. Different finite element models are developed in order to visualise and investigate a cone penetration test inside a suction caisson. The numerical analysis results are validated through the back-calculation of centrifuge cone penetration tests. The results of the simulated cone penetration tests inside a suction caisson are evaluated and compared to the centrifuge experiments. This investigation reinforces the scope of the centrifuge experiments and emphasises a considerable effect of the pressure transferral through the caisson lid in the soil plug state. Hence, the results of this study reduce existing uncertainties regarding possible suction installation effects on the in-service performance of caisson foundations.

Abstract. Metros are one of the important transportation systems in urban areas. Due to rapid development in urban areas, there is huge commercial demand resulting in the development of underground spaces are rapid. Some of the developments may have deep excavations for basements in close proximity to existing tunnels. If the induced tunnel deformation and internal forces exceed the capacity of the tunnel structures then damages such as segmental cracking, leakage and longitudinal distortion of the tracks occur and it threatens the safety of the passengers and hence is a major concern. A parametric study on the effect of basement excavation on the underground metro in soil gives an idea about the influence of various factors like lining material and lining thickness. The crown and right spring line undergo more displacements in both the excavation and loading stage. From the study it was observed that, providing FRC as tunnel lining material has significant effect on reducing foundation settlement.

Shallow foundation structures offer ecological benefits compared to pile foundations as less noise is emitted at sea floor level during construction process. On the other hand, shallow offshore foundations can rarely be placed on top of the sea floor. Weak soils usually need to be excavated to place the foundation structure on more stable ground and thus, anthropogenic submarine pits result. Steep but stable slopes of the pit meet both economic and ecologic aims as they minimise material movement and sediment disturbance. According to Terzaghi [1] the angle β between slope and the horizontal of the ground surface of cohesionless soil is at most equal to the critical state friction angle φc. However, it can be observed that natural submarine slopes of sandy soils are always much more shallow. Artificial (temporary) slopes do not appear and behave as natural submarine slopes, since the latter are already shaped by perpetual loads of waves, tide and mass movements. Physical simulations of different scales were presented at the OMAE 2011 [2] to analyse the stability of artificial submarine slopes of sandy soil in the North Sea. The laboratory tests focused on gravitational forces and impacts from the excavation processes. This paper presents additional numerical simulations of wave-induced bottom pressure on the suggested submarine foundation pits. Furthermore, in-situ tests will be performed in 2012 and 2013. Both dredging process and resulted foundation pits will be considerably surveyed.

In this paper the design robustness of Tension Leg Platform (TLP) tendon and tendon foundation systems of a TLP that is located in offshore Western Australia is investigated. A case study of a TLP that is self-stable (without tendons) has been considered. The study involves the numerical simulation of progressive failure of tendons in cyclonic events. The TLP response during the transition from a restrained TLP with all tendons to the free-floating condition has been numerically simulated. The numerical results from this simulation have been verified against physical model test measurements. The numerical simulation is repeated for a TLP with an optimized hull design that does not maintain stability when all tendons fail. Cost versus benefit in these two cases is quantified and compared. The progressive failure of the TLP Gravity Base Foundation (GBF) system has also been investigated in this paper. One of the potential failure modes for this type of foundation is the loss of suction underneath the foundation. Increasing the amount of solid ballast in the GBF increases the net downward load on the soil and reduces the reliance on the soil suction. Numerical simulations of the progressive loss of suction are performed for two cases; 1) slightly over designed foundation to include extra ballast and 2) optimized foundation design that is highly rely on the soil suction. Again, cost versus benefit in these two cases is presented. The paper provides clear insights supported by calculations and model tests for proposed design robustness that could be built in a TLP design at a relatively small additional cost to address uncertainties associated with designing TLP in offshore Western Australian harsh environment region.

The use of geosynthetic materials to improve soil bearing capacity below shallow foundation is relatively novel area of study of geotechnical engineering. A large number of studies have been carried out analysing impact of geosynthetic materials on the bearing capacity of the soil, and these are based mostly on experimental analysis and numerical simulations. This work gives an overview of studies about the application of reinforcement of soil with geogrids and their influences on the soil failure mechanisms. The work represents a basis for future investigations analysing the sensitivity of influence of the relevant parameters of geosynthetics on failure mechanisms.

The design of buried pipes, in terms of the allowable minimum and maximum cover heights, requires the use of both geotechnical and structural design procedures. The geotechnical procedure focuses on estimating the load on the pipe and the compressibility of the foundation soil. The focus of the structural design is choosing the correct cross-section details of the pipe under consideration. The uncertainties of the input parameters and installation procedures are significant. Because of that, the Load Resistance Factor Design (LRFD) method is considered to be suitable for the design of buried pipes. Furthermore, the interaction between the pipe structure and surrounding soil is better captured by implementing soil-structure interaction in a finite element numerical solution technique. The minimum cover height is highly dependent on the anticipated traffic load, whereas the maximum cover height is controlled by the section properties of the pipe and the installation type. The project focuses on the determination of the maximum cover heights for lock-seam CSP, HDPE, PVC, polypropylene, spiral bound steel, aluminum alloy, steel pipe lock seam and riveted, steel pipe and aluminum arch lock seam and riveted, non-reinforced concrete, ribbed and smooth wall polyethylene, smooth wall PVC, vitrified clay, structural plate steel or aluminum alloy pipe, and structural plate pipe arch steel, or aluminum alloy pipes. The calculations are done with the software CANDE, a 2D plane strain FEM code that is well-accepted for designing and analyzing buried pipes, that employs the LRFD method. Plane strain and beam elements are used for the soil and pipe, respectively, while interface elements are placed at the contact between the pipe and the surrounding soil. The Duncan-Selig model is employed for the soil, while the pipe is assumed to be elastic. Results of the numerical simulations for the maximum fill for each type and size of pipe are included in the form of tables and figures.

This technical report documents the research and development (R&D) study in support of the development of a combined Load and Resistance Factor Design (LRFD) methodology that accommodates both geotechnical and structural design limit states for design of the US Army Corps of Engineers (USACE) batter pile-founded, reinforced concrete flood walls. Development of the required reliability and corresponding LRFD procedures has been progressing slowly in the geotechnical topic area as compared to those for structural limit state considerations, and therefore this has been the focus of this first-phase R&D effort. This R&D effort extends reliability procedures developed for other non-USACE structural systems, primarily bridges and buildings, for use in the design of batter pile-founded USACE flood walls. Because the foundation system includes batter piles under flood loading, the design procedure involves frame analysis with significant soil structure interaction. Three example batter pile-founded T-Wall flood structures on three different rivers have been examined considering 10 geotechnical and structural limit states. Numerical procedures have been extended to develop precise multiple limit state Reliability calculations and for complete LRFD analysis of the example batter pile-founded, T-Wall reinforced concrete, flood walls.