Anchor Embedment Research Articles

The kinematic behaviour of drag anchors in sand

The kinematic behaviour of drag achors during embedment in sand is examined in this paper. A series of centrifuge model anchor tests has been performed in silica and calcareous sands in which both force and kinematic data were obtained during the course of anchor embedment. In this paper, the kinematic data have been examined to determine general rules for the kinematic behaviour of a drag anchor during embedment. These rules provide an essential step towards a theoretical simulation of a complete anchor embedment history and hence a predictive tool for the ultimate holding capacity of a drag anchor. Key words: drag anchor, kinematics, sand, limit equilibrium, ultimate holding capacity.

The kinematic behaviour of drag anchors in sand

The kinematic behaviour of drag achors during embedment in sand is examined in this paper. A series of centrifuge model anchor tests has been performed in silica and calcareous sands in which both force and kinematic data were obtained during the course of anchor embedment. In this paper, the kinematic data have been examined to determine general rules for the kinematic behaviour of a drag anchor during embedment. These rules provide an essential step towards a theoretical simulation of a complete anchor embedment history and hence a predictive tool for the ultimate holding capacity of a drag anchor. Key words: drag anchor, kinematics, sand, limit equilibrium, ultimate holding capacity.

Uplift Behavior of Horizontal Anchor Plates in Sand

The influence of anchor geometry, embedment, and soil density on the uplift capacity of one‐meter prototype anchors is investigated by subjecting 25‐mm models to an acceleration of 40 g in the Liverpool centrifuge. Uplift resistances expressed as dimensionless breakout facctors increase significantly with anchor embedment and soil density but reduce with increased aspect ratio. Failure displacements also increase with embedment but reduce with increased soil density and aspect ratio. The influence of anchor geometry is relatively insensitive to anchor size but increases with both embedment ratio and soil density. In general, the design approaches considered underestimate the observed capacity of one‐meter strip anchors in dense sand, although predictions using the Meyerhof and Adams and Rowe and Davis theories are acceptable. However, both these approaches appear overoptimistic for anchors in looser sand. In this case, Vesic's theory gives the closest agreement, while the formula of Majer yields overly co...

Uplift capacity of circular plate anchors in layered soil

For anchors embedded in cohesive soil, the uplift capacity remains almost constant when the ratio of anchor embedment depth to anchor diameter (D/B) increases above about 4.5. The uplift capacity of anchors in cohesionless soil increases as D/B increases and the increase is greater with increased density of the cohesionless soil. Then, given that an anchor is embedded in cohesive soil, it may be possible to increase the uplift capacity of the anchor by placing a cohesionless overlay on the clay layer.The purpose of the model tests reported in this note was to investigate the effectiveness of placement of a cohesionless layer over a clay seabed in increasing the uplift capacity of a shallow anchor buried in the clay (D/B < 2.0). The sand overburden did increase the uplift capacity, but to obtain a substantial increase in capacity, a very large anchor displacement is required. In fact, the anchor had to displace through almost the entire clay layer before it mobilized the frictional resistance of the sand overlay. Key words: circular anchor, uplift, layered system.

The behaviour of anchor plates in sand

This Paper describes a theoretical investigation into the behaviour of anchor plates in sand. Consideration is given to the effects of anchor embedment, friction angle, dilatancy, initial stress state K0 and anchor roughness for anchor plates with either a vertical or a horizontal axis. Collapse loads are observed to increase sensibly with embedment. Deep anchors exhibited high collapse loads. However, because of local yield, the deformations of deep anchors before collapse may be sufficiently large to necessitate the adoption of a practical definition of failure at loads below the actual collapse load. Soil dilatancy and anchor roughness significantly affect anchor capacity for certain cases, but the effect of K0 on collapse load is small for typical cases. The theoretical results are compared with the results of the Authors' model tests as well as other model and field test data. There is encouraging agreement and, for the cases considered, the theoretical results provide a reasonable prediction of anchor capacity. The theoretical results for sand are extended to the case of cohesive–frictional soils. The theoretical results are presented in influence charts which may be used in hand calculations to obtain an estimate of anchor capacity for a wide range of geometries and soil types. The use of these charts is illustrated by a worked example. L'article décrit une recherche théorique sur le comportement des plaques d'ancrage dans le sable, en fonction de l'encastrement de l'ancrage, de l'angle de frittement, de la dilatance, de l'état de contrainte initiale K0 et de la rugosité des plaques d'ancrage à axe vertical ou horizontal. On a constaté que la charge de rupture s'accroît sensiblement avec l'encastrement de l'ancrage et que des ancrages profonds fournissent de grandes charges de rupture. Cependant à cause de fluage local les déformations des ancrages profonds avant rupture peuvent être assez grandes pour nécessiter l'adoption d'une definition pratique de la rupture à des charges audessous de la charge de rupture réelle. La dilatance du sol et la rugosité de l'ancrage affectent la charge utile de l'ancrage d'une façon significative dans de certains cas, mais l'effet de la valeur K0 sur la charge de rupture est faible dans les cas typiques. Les résultats théoriques sont comparés aux résultats des tests-modèles de l'auteur aussi bien qu'avec d'autres données modéles et pratiques. On trouve une correspondance encourageante et les résultats théoriques fournissent une prévision raisonnable de la charge utile dans les cas considerérés. Les résultats théoriques obtenus pour le sable sont étendus au cas des sols cohérents. Les résultats théoriques sont présentés sous la forme d'abaques d'influence qui peuvent être employés dans des calculs manuels pour obtenir une évaluation approximative de la charge utile pour une large gamme de géométries et de types de sol. L'emploi de ces abaques est illustré a l'aide d'un exemple.

The behaviour of anchor plates in clay

The undrained behaviour of anchor plates with a vertical or horizontal axis, resting in a saturated clay, is examined. Theoretical consideration is given to the effects of anchor embedment, layer depth, overburden pressure and breakaway condition as well as anchor roughness, thickness and shape. The influence of these parameters on the failure mechanism and the anchor capacity is discussed. It is shown that in many cases ultimate collapse is preceded by significant anchor displacement and a definition of failure which allows reasonable displacement predictions to be made at working loads is proposed. Model tests for anchors with a vertical axis are reported. A comparison of these results and other published data with the theoretical solutions indicates encouraging agreement. The results of this study are presented in the form of charts which may be used directly in hand calculations for estimating the undrained failure load for anchor plates. L'article décrit le comportement non-drainé des plaques d'ancrage à axe vertical ou horizontal qui reposent dans l'argile saturée et décrit du point de vue théorique les effets de l'encastrement de l'ancrage, de la profondeur des couches, de la pression du terrain de couverture de la rugosité de l'épaisseur et de la forme de l'ancrage. L'influence exercée par ces paramètres sur le mécanisme de rupture et la charge utile de l'ancrage sont aussi discutées. On démontre que dans beaucoup de cas la rupture finale est précédée d'un déplacement significatif de l'ancrage et on propose une définition de la rupture qui facilitera la prévision raisonnable des déplacements sous charges de service. Un compte-rendu est donné de tests-modèles pour les ancrages à axe vertical. Une comparaison de ces résultats et d'autres données déjà publiées avec les solutions théoriques indique une correspondance encourageante. Les résultats de cette étude sont présentés sous la forme d'abaques qui peuvent être employés de façon directe dans des calculs manuels pour évaluer la charge de rupture des plaques d'ancragé dans des conditions.

Behaviour of single and multiple underream anchors in a gibson soil : Rowe, R K; Booker, J R University of Sydney, School of Civil Engineering, research report R373, Sept 1980, 54P

An accurate and economical technique for the analysis of buried footings and multiple underream anchors in a non- homogeneous elastic soil is outlined. The method of analysis may be used for quite general non-homogeneous, anisotropic elastic soil profiles although in this paper, attention is restricted to anchors in a soil whose modulus increased linearly with depth. The behaviour of both isolated underreams and multiple underream systems is examined. Consideration is given to the effect on anchor response of non-homogeneity, anchor embedment, layer depth and Poisson's ratio as well as the number and spacing of underreams. The influence of anisotropy and anchor inclination are also discussed. The results from this study are presented in the form of influence charts which may be used as a hand method for estimating the elastic load- displacement behaviour for quite general anchor systems to sufficient accuracy for most practical purposes. The use of the charts is illustrated by two examples (A). (TRRL)

The elastic displacements of single and multiple underream anchors in a Gibson soil

An accurate and economical technique for the analysis of buried footings and multiple underream anchors in a non-homogeneous elastic soil is outlined. The method of analysis may be used for general non-homogeneous, anisotropic elastic soil profiles although, in this Paper, attention is restricted to anchors in a soil whose modulus increased linearly with depth. The behaviour of both isolated underreams and multiple underream systems is examined. Consideration is given to the effect on anchor response of non-homogeneity, anchor embedment, layer depth and Poisson's ratio as well as the number and spacing of underreams. The influence of anisotropy and anchor inclination are also discussed. The results from this study are presented in the form of influence charts which may be used as a hand method for estimating the elastic load-displacement behaviour for general anchor systems to sufficient accuracy for most practical purposes. The use of the charts is illustrated by two examples. Une technique précise et économique pour l'analyse de semelles enterrées et d'ancrages à bases élargies multiples dans un sol élastique non homogèn est esquissée. Il est possible d'utiliser cette méthode d'analyse pour toutes sortes de profils de sols élastiques anisotropiques, non homogènes, bien que cet article se limite aux ancrages dans un sol dont le module augmente linéairement avec la profondeur. Le comportement de bases élargies isolées et de systèmes à bases élargies multiples est examiné. Il est tenu compte de l'effet que produisent la non-homogénéité, l'encastrement de l'ancrage, la profondeur de la couche et le coefficient de Poisson, ainsi que le nombre et l'espacement des bases élargies sur les réactions de l'ancrage. L'influence de l'anisotropie et de l'inclinaison de l'ancrage est également étudiée. Les résultats de cette étude sont présentés sous la forme de diagrammes d'influence pouvant servir de méthode manuelle pour l'estimation du comportement charge-déplacement élastique de systèmes d'ancrage généraux, le degré de précision étant suffisant pour la plupart des applications pratiques. Deux exemples illustrent l'emploi des diagrammes.

Embedment Anchors Subjected to Repeated Loading

In order to provide a reliable method of estimating the effects of repeated loading on the holding capacity of an anchorage for the purpose of designing embedment anchor systems for long-term use, tests were performed on circular plate anchors connected to a rigid tie shaft which were placed in a medium, uniform saturated sand. The loading device consisted of a hydraulic loading system capable of applying a variety of static and cyclic load patterns to the anchor. It was found that the deterioration in the cyclic loading-relative movement properties of an embedment anchor appears due to the accumulated amount of cyclic relative movement, whether developed by a few strong or many small stress pulses. However, care must be taken when using simple cyclic loading tests to predict the behavior of anchor systems subjected to long-term sustained-repeated loading conditons. Tests performed at different stress levels for deep anchors suggest that, when the cyclic relative movement of the anchor is kept below about half the relative movmeent to failure in a static pull-out test, there is essentially no reduction in strength due to cyclic loading. If this criteria is adopted, cyclic loading failure could be defined as a cyclic strain of 50 percent of the static strain to failure. Although this investigation is at an early stage, it is clear that cyclic failure of embedment anchors can be better defined in terms of unacceptably high relative movements resulting in significant drops in the anchor static pull-out capacity.