Plaxis

Geosynthetic-reinforced soil segmental retaining walls are now an economical solution. The design of these structures is carried out according to the Association of State Highway and Transportation Officials or the Federal Highway Administration design guidelines, which are based on the limit equilibrium approach. Many experimental, analytical, and numerical studies have identified several sources of conservatism in these design guidelines. This article focuses on a numerical study undertaken using the finite difference code Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D), to investigate the influence of facing batter angle, soil/facing interface friction angle, and backslope angle on the behavior of geosynthetic-reinforced soil segmental retaining walls. The numerical results show that the design guidelines lead to overly conservative design where the soil/facing interface is rough and/or the backslope is present.

It has been known that a group pile lateral capacity is smaller than the sum of each pile capacity composing the group. A reduction factor, also known as efficiency factor, is required to determine the effective lateral capacity of group piles. To the authors knowledge, in most geotechnical text books, only the spacing of piles is considered in evaluating the pile group lateral capacity. No consideration on the effects of soil stiffness modulus and the total number of piles forming the group are taken into account. The availability of a geotechnical 3D finite element software, namely Plaxis 3D foundation, made it possible to evaluate those factors. It is found that the bigger the number of piles in a group the lower the efficiency factor, the higher the soil stiffness modulus the greater the efficiency.

Les parois moulées offrent un large champ d'application dans le domaine de réalisation de fouilles en déblai, pour les fouilles de grande profondeur et en site urbain. Le présent travail s’intéresse à l’étude de l’effet des paramètres géotechniques (modèle de comportement, les interfaces et les écoulements) et de modélisation (géométrie du problème, maillage et tolérance) sur le comportement d’une paroi moulée. Le modèle de référence c’est une paroi moulée périphérique rectangulaire, et qui a été réalisé pour le soutènement de trois niveaux en sous-sols surmontant par une tour, l’ensemble constitue le nouvel immeuble d’Algérie Poste. La modélisation numérique est réalisée à l’aide du code d’éléments finis Plaxis. Les résultats obtenus montrent l’influence importante de variation de certains paramètres sur le calcul.

Identifikacija mehanizma sloma i općenito, istraživanje ponašanja zidova od armiranog tla pri velikim pomacima, privlači pažnju velikog broja istraživača u novije vrijeme. Ipak, ograničene su studije utjecaja interakcije između pojedinih elemenata zidova na način njihovog otkazivanja. Utvrđivanje nosivosti različitih geometrijskih konfiguracija zidova, obuhvaćajući pri tome interakciju pojedinih elemenata, provodi se u ovom radu primjenom numeričkih i fizičkih modela. U radu se detaljno istražuje interakcija armature i nekoherentnog zasipa u uvjetima pokusa izvlačenja i u zidovima armiranim mrežama.
Numeričkim 2D i 3D simulacijama pokusa izvlačenja u radu se istražuju utjecaji rubnih uvjeta na rezultat pokusa. U prvoj fazi istraživanja provodi se niz parametarskih analiza i usporedbi s eksperimentalnim istraživanjima. Model, koji uspješno simulira mehanizme interakcije u pokusu, iskorišten je za istraživanje utjecaja rubnih uvjeta na rezultate. Rezultati istraživanja uspostavljaju vezu između dimenzija sanduka, zbijenosti zasipa i granične otpornosti na izvlačenje. Radom se daju preporuke za oblikovanje i pripremu sanduka i armature koji se koriste pri provođenju pokusa izvlačenja.
Numeričkim 2D i 3D simulacijama zidova u radu se istražuje utjecaj interakcije armature i nekoherentnog zasipa na proračun stabilnosti zidova. U prvoj fazi istraživanja provodi se niz parametarskih analiza i usporedbi s eksperimentalnim istraživanjima. Model, koji uspješno simulira mehanizme interakcije u zidu, primijenjen je za istraživanje utjecaja geometrije armature, čvrstoće spoja zasipa i armature i čvrstoće temeljnog tla na mehanizam otkazivanja i faktor sigurnosti zidova. Rezultati analiza iskorišteni su za definiranje preporuka o načinu modeliranja pojedinih komponenti zidova i njihove interakcije.
Pored niza numeričkih simulacija u radu su objavljeni rezultati nekoliko umanjenih fizičkih modela zidova uz opažanje pomaka kompletnog zasipa digitalnom kamerom kroz prozirnu staklenu bočnu stijenku. Obrada digitalnih fotografija provodi se metodom korelacije digitalnih fotografija što rezultira pomacima kompletnog zasipa uz prednju bočnu stijenku. Rezultati mjerenja pokazuju vezu između čvrstoće i geometrije armature na jednoj i mehanizma sloma zida na drugoj strani. Pored toga, navedeni rezultati mjerenja predstavljaju bazu za verificiranje numeričkih modela jedne grupe geometrijskih konfiguracija zidova.

Obras geotécnicas necessitam de elevado grau de acurácia na previsão do comportamento mecânico. A partir dessa correta antecipação de cenários de comportamentos, especialmente em obras subterrâneas, decisões corretas frente a situações adversas podem ser tomadas, com a escolha de melhorias das condições de maciços. Para isso, o estudo prévio aprofundado das características geomecânicas do maciço de túneis se faz necessário complementarmente à previsão de deslocamentos. Combinados, torna-se possível simulações numéricas com acurácia suficiente e com resultados realistas das condições de campo. Neste artigo a análise do comportamento de um túnel já executado será realizada por meio do software PLAXIS, com modelo constitutivo de Mohr-Coulomb. Nestas simulações bidimensionais, além de se comparar os deslocamentos observados após a construção do túnel com os obtidos pelo software, idealizou-se soluções hipotéticas de forma a entender como cada uma afetaria o comportamento do túnel analisado, com a posterior comparação entre as soluções hipotéticas e as reais, tanto em esforços como em deslocamentos.

Our world is in the path of development. Several activities are ongoing which contributes to the development. But some
of these activities interfere the nature and climate very badly.Sudden and unexpected climate change is a result of such man
made activities. For the recent two years Kerala state has faced severe flood during rainy season. But the fact is that our state
doesnot received much rainfall during monsoon. These are result of unsustainable human activities. On August 2019 ,
Kavalappara (Malappuram) and Puthumala (Wayanad), located on either side of ecologically sensitive Western Ghats , faced
severe landslide which cause loss of several lives and damage to property. Kavalappara is the area considered for this study. The
slope lost its naturality due to human interference for plantations activities. Along with that continous rain also triggered the
disaster ; hence it is a rain triggered landslide. Rain is an external factor that triggers landslide, which is threat to entire
humanity. There arise the need of adopting some measures to slope modification. There is no sure that landslide can be avoided
completely, but to some extent we can mitigate the risk and reduce impact of landslide. Here PLAXIS software is used for the
stability analysis .It is a FEM (Finite Element Method) modelling.

Sachant que la plupart des ouvrages de génie civil sont réalisés en contact avec le sol/la roche. Cependant, des problèmes d’interaction interviennent entre le sol/la roche et les structures implantées sur ce dernier. La présente étude a pour objet la modélisation en éléments finis à l’aide du code PLAXIS de trois ouvrages différents tels que : un tunnel, un bâtiment et une excavation et ce dans le but d’illustrer l’effet des paramètres géotechniques et celui des paramètres de calcul sur le phénomène d’interaction sol-structure. En fonction de la zone d’interaction sol-structure choisie, les résultats obtenus montrent clairement l’influence importante de certains paramètres tels que : l’angle de frottement interne, le module de Young et le modèle de comportement, sur les calculs. Ce qui nécessite une attention particulaire pour le choix des paramètres de calcul ainsi que pour l’estimation des paramètres géotechniques.

Nowadays, Geosynthetics have been used as routine reinforcement in earth structures such as reinforced soil retaining walls. Over the last few years new technology which is combination of reinforced concrete lofts and cantilever retaining wall has been used for construction of retaining wall also called as Graviloft. This Paper presents the study carried out to analyse the behavior of retaining wall and backfill soil for various approaches. Analysis is performed on cantilever retaining wall, Reinforced soil retaining wall and Graviloft wall and the comparison of behavior is based on parameters ,displacements (vertical and horizontal displacement), Stresses (shear stresses and normal stresses) using PLAXIS V8.6.The comparison shows that displacements and stresses occurred in reinforced wall and graviloft wall are much less as compared to conventional cantilever retaining wall, thereby reducing lateral thrust and improving stability.

Piled raft foundations have been more and more widely applied, especially for tall buildings. In piled raft foundations, piles are not designed to take the full load but only to reduce the settlement to an allowable level. Basing on the experimental results performed by the Author, a simplified method, which can be easily used for the design practice, was suggested. This method can be used in combination with FEM method for a conceptual design of a piled raft foundation, with a desired settlement. Using this approach, in this paper a foundation for a large high-rise complex is studied. The foundation is currently designed as a conventional piled foundation. Piled raft foundation is studied as an alternative option. At a chosen settlement of 20mm, a considerable number of piles can be saved. 3D FE analyses are performed to verify the settlement of the foundation system.

ÖZET: Doğal afetlerin en önemlisi sayılan depremler dünyanın her kesiminde etkili olmakta ve bunun sonucunda da can ve mal kayıplarına neden olmaktadır. Deprem kuşağında bulunan ülkemizde de inşa edilen yapıların zemin özelliklerine göre uygun temel sistemlerinin belirlenmesi zorunludur. Zemin özellikleri, sismik etkiler altında, normal olmayan yüklemenin üzerinde zorlanması sonucu, yapının tasarım aşamasında hatalarını ortaya çıkarmaktadır. Bu çalışmada, c=5kPa, Ø=35 o ve c=40kPa, Ø=5 o olan zemin üzerinde, yeraltı su seviyeleri 0m ve 2m göz önüne alınarak, 1., 2., ve 3. deprem bölgelerinde yapılacak olan 5 katlı bir binada depremin etkisi Geo5 bilgisayar programı kullanılarak hesap yapılmıştır. Sonuçta, farklı değerler kullanılarak yapılan analizler sonucunda, temel tasarımı üzerine; zemin sınıfının etkisi, yeraltı suyunun etkisi ve deprem büyüklüğünün etkisi incelenmiştir. ABSTRACT: Earthquakes that are considered as one of the most destructive natural disasters, effect every part of the world and as a result they cause loss of life and property. In accordance with the soil properties, it is necessary to determine the most appropriate foundation systems of the structures that are built in our country which is also located on the seismic belt. As a matter of fact, the soil properties show the imperfections of the structure in the process of its design as a result of an extreme loading force under seismic influences. Therefore, in this work, considering the underground water level as 0m and 2m, the earthquake affects on a five-storey building that was built on the grounds c=5kPa, Ø=35 o and c=40kPa, Ø=5 o in the 1 st , 2 nd and 3 rd earthquake zones have been calculated. Eventually, the effect of the soil class, underground water and earthquake magnitude on the foundation design were examined at the end of the analysis by theme and of combinations made by using different values.

L’utilisation de la méthode des éléments finis dans le domaine géotechnique est très courante, pour des grands projets. On peut réaliser des analyses par éléments finis afin de vérifier la stabilité d’un ouvrage en interaction avec son environnement, de contrôler les valeurs de déplacements admissibles et d’aider au dimensionnement des structures.
L’étude consiste à mettre un modèle numérique pour notre projet, qui concerne l’interaction sol avec différents ouvrages placés dans un site urbain. Les ouvrages concernés sont : un tunnel, un bâtiment et une excavation. L’étude paramétrique montre l’effet des paramètres de calcul et des paramètres géotechniques sur les résultats. Pour atteindre l’objectif visé, le travail sera divisé en quatre chapitres. Après une étude bibliographique sur l’interaction sol-structures, ce travail se compose de trois autres chapitres :
Tout d'abord, un bref aperçu de la méthode des éléments finis concerne l’historique, les concepts de base et l’utilisation de cette méthode dans le domaine géotechnique. On a choisi le code éléments finis PLAXIS, qui nous permet le passage d’un projet réel complexe au modèle numérique, et de faire l’étude paramétrique facilement et rapidement. PLAXIS utilise plusieurs modèles de comportement qui dépendent de la nature du sol et de type d’ouvrage.
Deuxièmement, on détermine un modèle géotechnique de référence pour notre projet. Après la mise des hypothèses est la définition de la géométrie du modèle et des caractéristiques des matériaux ; on passe au calcul par PLAXIS. D’abord, dessiner le modèle, faire le maillage et mettre les conditions initiales, ceci se fait à l’aide du programme d’entrée des données (Input) ; ensuite, faire les calculs par le programme de calcul (Calculations) ; les résultats sont donnés par le programme de résultats (Output).
Finalement, l’étude paramétrique, qui montre l’effet des paramètres de calcul et des paramètres géotechniques sur les résultats, on utilise la même coupe du projet, avec les mêmes données et on change chaque fois le paramètre à comparer ; on a deux types de paramètres, paramètres de calcul et paramètres géotechniques. La comparaison est présentée sur des diagrammes pour chaque paramètre.
En conclusion, L’étude a mis en évidence l’influence importante non seulement des paramètres géotechniques, mais également des paramètres de modélisation sur les résultats de calcul. On peut donc expliquer les résultats très différents qui peuvent être obtenus pour un même projet par plusieurs utilisateurs, même d’un seul logiciel.

A case study: cantilever retaining wall founded on concrete blocks (counterforts)

A large number of relatively high cantilever retaining structures in BiH were built in last 10 years. These walls were part of motorway route “Vc” project, regional road remediation project and in private sector as well. Many were constructed like cantilever walls founded on concrete block (so called counterforts). The construction phases for this type of retaining structures were defined in special chapter of this manual. Since these walls are found as cost effective solution that is adopted to local construction companies for more than 40 years, it is not surprising that it was involved in mentioned project as well. One of the walls is selected as case study for this manual. The details like construction sequence, geotechnical investigations, numerical analysis and practical construction details are presented in order to promote this type of structures. On the other side, the shortcomings of these structures are highlighted to draw the attention to practical engineers that will built these walls in the future.

Soil is a complex multiphase material its stress, strain and strength are represented by pressure dependency with coupling between shear and volumetric behavior. With these complexities it is not possible to think in terms of developing a completely generalized model for all soils. It is fundamental to tailor the modeling of material behavior to the particular problem of interest and the required accuracy of solution. Perhaps this explains why the finite element method has been used in many fields of engineering practice for over thirty years, however it is only relatively recently that it has begun to be widely used for analyzing geotechnical problems.
The main objective of this course is to provide the undergraduate student with an insight into the  use of the finite element method in simulation of geotechnical engineering problems. The methodology that will be followed in this research to achieve its objectives are directed towards the following points:
-Presentation of the theory, assumptions and approximations involved in finite element analysis;
- Description of several constitutive models that commonly used, and explore their strengths and weaknesses.
- Provide sufficient field case studies and solved examples so that students can make judgement as to the credibility of numerical results that they may obtain, or review, in the future. These practical examples are also used to demonstrate the restrictions, advantages and disadvantages of numerical analysis.

Este documento muestra el análisis de estabilidad de una presa para almacenamiento de agua bajo condiciones de desembalse rápido. Una rápida reducción del nivel del reservorio puede llevar a la inestabilidad de la presa debido a la alta poro presión que permanece dentro de la presa, la cual tiene 30 m de altura, con un ancho de corona de 5 m y un ancho de base de 172.5 m. La presa está constituida por un núcleo de arcilla con un relleno bien gradado en ambos lados. El nivel normal de agua es 25 m, la situación considerada como desembalse lleva este nivel a los 5 m de altura. El nivel freático normal en el lado derecho de la presa se encuentra a 10 m debajo del terreno natural. El subsuelo consiste en una arena limosa sobreconsolidada.

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Este ejercicio muestra el efecto en la frecuencia natural de un edificio de cinco pisos cuando se somete a vibración libre y carga sísmica. Los dos cálculos emplean diferentes condiciones dinámicas de contorno: En la vibración libre, las condiciones de contorno viscosas son consideradas. Esta opción está disponible para problemas donde la fuente dinámica está dentro de la malla. En la carga sísmica, se consideran las condiciones de contorno Free-field y Compliant base. Estas opciones se prefieren para el análisis sísmico, donde la entrada dinámica se aplica a lo largo del límite del modelo.

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En este ejercicio estudiamos la influencia de la vibración de una fuente sobre un suelo. Para reducir el tiempo de cálculo, solo un cuarto de toda la geometría es modelado, usando la condición de contorno simétrico a lo largo de las líneas de simetría. El amortiguamiento (damping) debido al efecto viscoso es tomado en cuenta mediante el amortiguamiento Rayleigh. También, debido a la propagación radial de ondas, el "amortiguamiento geométrico" puede ser significativo en la atenuación de la vibración. El modelamiento de los contornos es una de los puntos clave en el cálculo dinámico. Para evitar falsas reflexiones de onda en los contornos del modelo (que no existen en realidad), condiciones especiales tienen que ser aplicadas para absorber ondas que alcancen los límites o contornos.

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A serious problem has been discovered in the interface formulation in one of the most popular finite element software programs used in geotechnical practice. This paper analyses the problem of interface formulation which is not in agreement with the definition given in program manuals. Problem explained appears to have been solved in the most recent version, but the author finds it important to discuss the implications of this problem, because there are so many investigation conclusions given in the recent past without being aware of this problem. A simple example of sliding block on elastic soil is used for this investigation and the results with discussions are presented, with intimate details of the computational model.

The most often remediation measure for landslide stabilisation is the construction of drainage system that controls the underground water as most often trigger for soil failure. Deep gravity drains are usually designed to reduce hydrostatic water pressure. Since the named pressure influence the soil strength by reducing the effective stress, the concept of preventing high water levels along the slope is for a long time recognized as remediation measure in practical geotechnical engineering. The construction phases for this kind of remediation measures are well known in local practice. It consists of excavation of trench that is usually performed in segments. After the excavation, the lean concrete is poured, drainage pipe is installed and covered first by filter material wrapped around by geotextile and later by granular material. Finally, near the top of the excavation, natural fine grained soil is used as trench cover for preventing the infiltration of surface water into the drainage system. This remediation measure is found as relatively cost effective and practical solution that is known to local construction companies for a long time. One of the practical examples is selected as case study for this manual. The details like construction sequence, geotechnical investigations, numerical analysis and practical construction details are presented in order to share experiences with this concept of landslide remediation. On the other hand, the shortcomings of this remediation approach are highlighted to draw the attention to practical engineers that will design it and construct it in the future.

The construction of a relatively shallow mining tunnel in Brasilia was done under challenging ground conditions. After the end of the construction phase, numerical simulations were performed to compare the real settlements occurred on the tunnel portals with the predicted settlements of the numerical analysis. These analyses were three-dimensional. The adjustment of the on-site instrumentation and the software output was good for engineering purposes. The proximity of the results was possible by the author’s knowledge of the parameters used in the primary design and because of some modelling techniques, specifically a simplified way to model pre-support interventions adapted from Hoek (2003), described in the article.

Observation and numerical modeling of MSE test wall is presented here. The 6m wide and 3.2m high wall with 10cm thick precast concrete face elements and reinforcement length of 2.15m was built on construction site of Motorway 5C in Bosnia and Herzegovina. Welded wire mash Q335 was used as reinforcement. Compared to other MSE test walls, the presented work is unique due to the choice of backfill material consisting of course crushed stone aggregate ranging from ~0-100mm in size whereas most of other published studies used sandy backfill. Two weeks after the construction, the top of the wall was loaded with additional overburden weight 1,5m in height (~30 kPa). The forces in reinforcement were measured with a series of embedded sensors and deformation with an inclinometer installed in the middle of the wall length, including geodetic survey of wall face. Experimentally observed results are compared to the analysis results obtained from numerical model created using Plaxis software.

Piled raft system proves to be more effective on such problematic soft soil conditions. It takes the high vertical load and used to bring the settlement, differential settlement and tilting of structure within the permissible limit. Piled raft system proves to be cost effective than the conventional pile foundation system. Piled raft foundation accounts for complex soil-structure interaction, which needs interaction between structural engineer and geotechnical engineer. Geo-foam application is introduced below the footing to enhance floating resistance. The performance behavior of piled raft foundation in clayey soil and layered soil is carried out using laboratory experimental and then verified by 2D PLAXIS. There is a significant relationship between the decrease in settlement of the piled raft due to hydrostatic uplift.

Soil liquefaction may induce buoyancy of underground structures such as tanks, tunnels and pipelines. Several cases of uplift of underground tanks and pipelines have been observed in the past. Although such an evidence has not been registered yet for tunnels, centrifuge testing has shown that the high mobility of liquefied soil near surface would encourage floatation of very shallow or immersed tunnels. Starting from the back-analysis of the results of a published centrifuge test on a model tunnel in a dry layer of Leighton Buzzard sand that undergoes ground shaking, this work explores numerically the behaviour of the same tunnel after that the sand has been saturated. An effective stress constitutive model, available in a finite element code, was calibrated on the results of laboratory tests on the sand used in centrifuge along monotonic and cyclic stress paths. The ability of the model to predict the dynamic response of the sand layer both in dry and saturated conditions and a reasonable pore pressure build-up in undrained conditions is showed and discussed in the paper. Later, the behaviour of the model tunnel is deeply analysed in terms of displacements and internal forces arising in the tunnel lining during the seismic event.

The paper presents the effect of addition of phosphogypsum and coir fibre on the compaction, unconfined compressive strength and swelling characteristics of bentonite-lime mix. The content of lime, phosphogypsum and coir fibre was varied from 0 to 10 %, 0 to 10 % and 0 to 2 % respectively. The curing period was varied from 3 to 28 days. The results of this study reveal that the dry unit weight and optimum moisture content of bentonite + 8 % lime increased with the addition of 8 % phosphogypsum whereas the dry unit weight decrease and optimum moisture content increases with the addition of 1.0 % coir fibres. The strength ratio of bentonite increases with the addition of lime-phosphogypsum-coir fibres. The swelling characteristics of bentonite were markedly reduced with the addition of 8 % lime, 8 % phosphogypsum and 1.0 % coir fibres. The end-time of primary swelling of bentonite + 8 % lime + 8 % phosphogypsum + 1.0 % coir fibres in duration of 40 days was 80 % less than that reached by bentonite. This accelerated reduction in swelling of bentonite brings new hope for the construction activities on such problematic areas. The microstructural development of bentonite modified with 8 % lime and 8 % phosphogypsum were studied through techniques like the scanning electron microscope and the electron dispersive absorption x-ray diffraction to account for the changes in the structure of bentonite with the addition of lime and phosphogypsum. Scanning electron micrographs of the bentonite specimens modified with lime showed the formation of cementing compounds in forms of compact matrix which increases with the increase in curing period. Further, this development led to the improvement in strength ratio which was also observed in strength test results. Scanning Electron Micrograph (SEM) and Electron dispersive absorption x-ray diffraction (EDAX) study shows the emissions of Ca, Si and hydrates and Ca, Al and S with the addition of lime and phosphogypsum in bentonite respectively. The improved strength characteristics and reduction in swelling of bentonite with the addition of lime-phosphogypsum-coir fibre can be used for the construction activities on such problematic areas.

L’utilisation de la methode des elements finis dans le domaine geotechnique est tres courante, pour des grands projets. On peut realiser des analyses par elements finis afin de verifier la stabilite d’un ouvrage en interaction avec son environnement, de controler les valeurs de deplacements admissibles et d’aider au dimensionnement des structures. L’etude consiste a mettre un modele numerique pour notre projet, qui concerne l’interaction sol avec differents ouvrages places dans un site urbain. Les ouvrages concernes sont : un tunnel, un bâtiment et une excavation. L’etude parametrique montre l’effet des parametres de calcul et des parametres geotechniques sur les resultats. Pour atteindre l’objectif vise, le travail sera divise en quatre chapitres. Apres une etude bibliographique sur l’interaction sol-structures, ce travail se compose de trois autres chapitres : Tout d'abord, un bref apercu de la methode des elements finis concerne l’historique, les concepts de base et l’utilisa...

Various innovative foundation techniques have been in practice to counteract the swell–
shrink problems posed by expansive soils. Apart from techniques such as belled piers and
under-reamed piles, chemical stabilization of expansive soils has also met with considerable
success. Lime, cement and fly ash are the various additives used in chemical stabilization.
This paper presents an innovative foundation technique in the form of fly ash columns (FAC)
for expansive clay beds.
Results from a laboratory experimental study on expansive clay beds reinforced with fly ash
columns (FAC) are presented. Heave tests and compressive load tests were performed on
expansive clay beds into which fly ash were introduced as compacted columns. Heave
decreased significantly on reinforcing the clay beds with FACs. Stress-settlement
characteristics of expansive clay beds also improved when reinforced by FACs. Curing of
FAC-reinforced expansive clay beds improved stress-settlement characteristics.

Strip footing built over expansive soils may be subject to considerable upward movement, which can lead to undesirable structural cracks. The aim of this study is to investigate the efficiency of the use of micropiles surrounded by compacted sand as a strategy may be used with strip footing to increase resistance to upward movement caused by expansive soils. Series of numerical models have been developed using PLAXIS 3D and the necessary material properties and boundary conditions have been defined. The influence of micropiles surrounded by compacted sand, the active zone, and the expansion degree of expansive soils were evaluated and discussed. Findings show that the use of micropiles enclosed by compacted sand with a strip footing enhances the resistance against swelling pressure.

The use of the finite element method (FEM) in analyzing the behavior of clay deposits reinforced with sand columns is not new. In previous studies conventional constitutive models were used to represent the sand. These models do not account for the post-peak strain softening that generally occurs in compacted sands. The main objective of this paper is to investigate the use of the recently developed hypoplastic model which provides the ability to account for the post-peak strain softening in applications involving soft clays that are reinforced with sand columns. This objective was achieved in two stages. In the first stage, the hypoplastic model for both materials (sand and clay) was derived and built from the results of laboratory tests that were carried out on Ottawa sand and Kaolin clay. The numerical analyses of triaxial tests on these sand and clay materials, using Plaxis 2D and the hypoplastic models, closely matched the observed laboratory behavior. In the second stage, laboratory tests that were conducted on sand-reinforced clay specimens were analyzed numerically using the calibrated hypoplastic models. The numerical analyses were based on the same geometries and testing conditions as those used in the actual laboratory tests with sand columns having diameters of 3 cm and 4 cm, penetrating 10.65 cm into a 7.1 cm diameter clay specimen with a height of 14.2 cm. The consolidated drained triaxial tests were carried out at confining pressures of 100 kPa, 150 kPa and 200 kPa. The FEM results using the hypoplastic models closely matched the laboratory results, indicating that the hypoplastic model could be used in FEM analyses to accurately predict the behavior of floating sand columns in soft clays under drained loading conditions. The hypoplastic model presents an interesting and promising alternative to conventional models, which fail to capture the full range of response of the complex clay-sand system.

— Skirted foundations are the shallow foundations in which the footing is reinforced by the addition of vertical plates or skirts. Skirted foundation is one of the new approaches for improving the performance of shallow raft foundation by using skirts to it. The improvement in performance of skirted foundation depends on the geometrical and structural properties of the skirt and footing such as shape, depth of the footing and skirt, skirt geometry etc; soil characteristics namely index properties of soil and the interface conditions of the soil-skirt-foundation systems such as roughness and material of the skirt etc. In the present work an attempt has been made to determine the behaviour of surface raft with and without skirts under two different soil model-Hardening soil model and Mohr-Coulomb model using a finite element software PLAXIS 2D. The analytical results show that with the increase in skirt depth, the bearing capacity increases and settlement decreases for both the model.

This paper presents the results of the design of shallow foundations for 14 wind turbines using 3D finite element modelling with Plaxis 3D. The site investigation consisted of deep boreholes at each turbine location and geophysical tests: electro-resistivity and MASW (Multichannel Analysis of Surface Waves) tests. The data were interpreted and soil parameters obtained for each soil/rock layer. This work involves an initial assessment of the foundations by standard plasticity theory method, followed by Plaxis 3D analysis using the Hardening soil small strain model (HS-small).

Shallow foundations are usually used for structures with light to moderate loads where the soil underneath can carry them. In some cases, soil strength and/or other properties are not adequate and require improvement using one of the ground improvement techniques. Stone column is one of the common improvement techniques in which a column of stone is installed vertically in clayey soils. Stone columns are usually used to increase soil strength and to accelerate soil consolidation by acting as vertical drains. Many researches have been done to estimate the behavior of the improved soil. However, none of them considered the effect of stone column geometry on the behavior of the circular footing. In this research, finite element models have been conducted to evaluate the behavior of a circular footing with different stone column configurations. Moreover, an Artificial Neural Network (ANN) model has been generated for predicting these effects. The results showed a reduction in the bending moment, the settlement, and the vertical stresses with the increment of the stone column length, while both the horizontal stress and the shear force were increased. ANN model showed a good relationship between the predicted and the calculated results.