Installation Of Anchors Research Articles

A Study on Offshore Anchor Selection with a Focus on Torpedo Anchor Stability and Performance

The global pursuit of renewable energy has significantly accelerated offshore wind energy development. Floating offshore wind turbines (FOWTs) are increasingly in the spotlight as they offer superior capabilities for harnessing abundant wind resources in deep-water areas, outperforming traditional fixed-bottom turbines. The deployment and station-keeping of these floating structures are critically dependent on robust mooring systems and the precise selection of anchoring solutions. This paper provides an overview of various anchors, including driven and suction caissons, torpedo, and drag anchors, and their applications in real-world projects. These commonly used anchors were discussed in relation to mooring types, soil conditions, and expected bearing capacities. Torpedo anchor installation failures have been reported in cases where excessive tilt angles occur during deployment. This motivates us to present an in-depth study on the importance of directional stability during installation of torpedo anchors. The study will utilize computational fluid dynamics Star-CCM+ 2402 to analyze and assess the impact of the center of gravity configuration on stabilization. Additionally, theoretical formulas will be used to estimate the holding capacity that the torpedo anchor can provide. These insights are designed to assist wind energy developers in making informed and effective anchoring decisions for floating wind turbine projects.

Simulation Study on the Installation of Helical Anchors in Sandy Soil Using SPH-FEM

Simulation Study on the Installation of Helical Anchors in Sandy Soil Using SPH-FEM

The installation behavior and capacity of piggy-backed anchors for offshore wind turbine

Piggy-backed anchors present a promising solution to address the limitations of single Drag Embedment Anchors (DEAs). A series of centrifugal model tests were performed on the installation of piggy-backed anchors with varying spacings and attachment points in saturated sand using a magnetometer system. The experimental results validated the proposed theoretical prediction model, which can identify the trajectory, capacity, orientation, and soil failure wedge slip surface. Key findings include: (1). the embedment depth of the second anchor in piggy-backed anchors is significantly greater than that of a single anchor, resulting in the total capacity of piggy-backed anchors exceeding twice that of a single anchor at appropriate spacing; (2). investigating spacing effects shows that capacities are less than twice that of the single anchors when spacing is less than 1Lf due to overlapping failure soil wedges; optimal spacing was found to be 2Lf to 3Lf; (3). piggy-backed anchors with attachment points at the back of fluke exhibit better embedment performance and capacity stability compared to those with attachment points at the padeye. Finally, the prediction model explored the capacity performance of piggy-backed anchors at different loading angles at the final embedment depth, revealing a two-stage failure process compared to single drag anchors.

The pull-out capacity of torpedo anchor in clay considering the full opening cavity

Torpedo anchors are increasingly being considered for mooring floating facilities in deep waters owing to their efficient and economical installation. The anchor was released from a specified height above the seabed to allow it to gain velocity as it fell freely into the water before penetrating the seabed. A cavity was formed above the anchor shaft after the anchor installation. The formation of this post-installation cavity is largely dependent on the soil strength conditions and affects the anchor capacity after installation. However, there is a lack of understanding regarding the formation mechanisms of the cavity and its effect on the bearing capacity of a torpedo anchor. Thus, this study focuses on the effects of the post-installation cavity on the bearing capacity of the torpedo anchor. The impact of a fully open post-penetration cavity on both the vertical and inclined bearing capacity of a torpedo anchor without fins was investigated using the Coupled Eulerian–Lagrangian (CEL) method in ABAQUS with three-dimensional large deformation finite element (LDFE) analysis. A method for evaluating the vertical bearing capacity of a torpedo anchor, considering the effect of a post-installation cavity, was proposed. This study provides insight into the installation effect on the bearing capacity of torpedo anchors.

Centrifuge Modeling of the Monotonic Capacity of Offshore Ring Anchors in Sand

The development of offshore wind technology has become a feasible solution to meet the increasing demands for clean and renewable energy. The United States has a total of 4250GW offshore wind energy potential; however, 65% of it is in deep water zones (Lopez et al., 2022) where wind turbines with fixed foundations typically are economically and technically unfeasible. In those situations, floating turbines supported by subsea anchors are a more competitive solution. Based on previous studies, ring anchors can be more material-efficient than piles and caissons because they require less material. Ring anchors also perform better than drag anchors due to their greater embedment depth. To further understand the behavior of ring anchors in saturated sand, a series of centrifuge load tests were performed at the University of California Davis Center for Geotechnical Modeling (CGM) at an acceleration of 70g. This test series investigated the effect of the anchor embedment depth and loading angle on the monotonic loading behavior. The ring anchor models were embedded in dense saturated sand, and then connected to an actuator using taut steel wire ropes. Sensors were used to measure the line tension, displacement, and inclination. The results indicate that the ring anchors mobilize greater capacities as their embedment depth is increased and when they are loaded at angles close to the horizontal direction, while vertical loading leads to the smallest capacity. The anchor displacement during the tests deviated slightly from the loading direction, showing a horizontal deviation at the earlier stages of the tests and a vertical one after the peak load. Furthermore, soil disturbance induced by the anchor installation was found to have a strong effect on the vertical capacity of the ring anchors. Overall, this study provides valuable information regarding the monotonic loading behavior of ring anchors which can aid in their future field deployment.

An undrained dynamic strain-pore pressure model for deep-water soft clays from the South China Sea

With the increasing use of oceans for engineering purposes, such as the installation of suction anchors and pipelines, the stability of seabed structures has become a pivotal concern and is intricately linked to the characteristics of seabed soils. This study focuses specifically on deep-sea soft clay, a predominant seabed soil type distinguished by its high water content, thixotropy, and low permeability. These clays are vulnerable to destabilization and damage when disturbed, thereby posing threats to seabed installations. While the existing literature extensively examines the cyclic behavior of clay, considering factors such as the pore pressure response and strain and deformation characteristics, there is a notable gap in research addressing the behavior of deep-sea soft clay under comprehensive stress levels and prolonged cyclic loading. In this study, cyclic shear tests of the natural marine clay of the South China Sea were conducted, and the cyclic stress ratio (CSR), overpressure consolidation ratio (OCR), consolidation ratio (Kc), and loading frequency were varied. It was found that the CSR, OCR, and Kc significantly impact the cumulative dynamic strain in deep-sea soft clay during undrained cyclic dynamic tests. Higher CSR values lead to increased dynamic strain and structural failure risk. Subsequently, a dynamic strain-dynamic pore pressure development model was proposed. This model effectively captures the cumulative plastic deformation and dynamic pore pressure development, showing correlations with the CSR, OCR, and Kc, thus providing insights into the deformation and pore pressure trends in deep-sea clay under high cyclic dynamic loading conditions. This research not only furnishes essential background information but also addresses a critical gap in understanding the behavior of deep-sea soft clay under cyclic loading, thereby enhancing the safety and stability of seabed structures.

Experimental Development and Field Validation of Rock Anchors for Sustainable Onshore Foundations

The development of an innovative rock anchor prototype manufactured using high strength steel sheets produced locally in Sweden is the core of the PROWIND concept. Steel sheets provide a design freedom to easily manufacture complex geometries, which can be advantageous to enhance the shear force transmission in the bond-length segment of the anchor. The underlying challenge of this concept has been to design a solution which meets the design requirements of today and future technological advancements, all while keeping conventional installation practices in mind. The project followed a 4-step development process: (1) concept analysis and modelling, (2) small-scale prototypes testing and (3) large scale lab-validation and lastly (4) field validation. The performance of the developed rock anchor prototype and grouting material was experimentally quantified on both small and large-scale test specimens and also validated in full scale in the field concerning installation process, proof-loading and maintaining the prestress over time. The PROWIND anchors with the end feature with ribbed design have 4-5 times higher load bearing capacity. The experience from the anchor installation proved that the developed grout and anchors are faster and easier to install. The field test in two different geological conditions has proven that the news design is reducing the required anchorage length to just 1 meter. The restressing of anchors is fully possible with the proposed lock-off solution with a nut. All of those contribute to lower costs of installations and possibly longer service-life.

An innovative interface friction algorithm for simulating dynamic installation of anchors using CEL approach

Dynamic installation of anchors is now commonly simulated using the coupled Eulerian-Lagrangian (CEL) approach in ABAQUS/Explicit. However, capturing anchor (Lagrange)-soil (Eulerian) interface frictional resistance during continuous penetration remains a challenge. This paper introduces an advanced frictional resistance algorithm called the Integrated Nodal Friction Algorithm (INFA) to improve the accuracy of capturing frictional resistance, and to increase computational efficiency. The innovative features of the method include automatic capturing of the anchor nodes in contact with the adjacent soil, estimating local shear strength of the contacted soil nodes, and calculating frictional resistance for the identified contacted areas based on the estimated local shear strengths. The algorithm was validated against centrifuge test data for a free-fall piezocone penetrometer, with good agreement obtained in terms of measured frictional resistance and end bearing profiles with penetration depth, and final tip embedment depth. Parametric analyses were then conducted for optimising mesh sizes and output frequency. Performance of the INFA method was compared with the existing two methods, demonstrating that the proposed algorithm is capable of improving the accuracy of capturing anchor-soil interface frictional resistance profile along the penetration depth.

Optimization of inclined coal seam tunnel section angle and anchor angle based on response surface method

The mining of inclined coal seams is often accompanied by problems such as difficult to control deformation of the tunnel roof and failure of anchor bolts. Taking the transportation channel of Jinping Coal Industry 1071-1 in Shanxi Xiangkuang Mine as the background, FLAC3D numerical simulation software was used, and the method of response surface experimental design and data analysis was used to systematically study the effects of the anchor installation angle and the roof inclination angle of the tunnel section on different inclination angles. Influence of the surrounding rock stability of coal seam roadways. On this basis, a multi-index tunnel support design evaluation method based on the response surface method was proposed, and the actual support plan was optimized and industrial tests were carried out based on the actual on-site support plan. The research results show that: in terms of inclined coal seam support, the degree of influence on the tunnel stability is in the following order: anchor installation angle > tunnel section roof inclination angle > coal seam inclination angle; the optimized support design obtained through the proposed technology The method has good application effect and can improve the stability of the roadway during the mining of the working face. It also proves the effectiveness of this technology and provides new ideas for the design of anchor support of inclined coal seam roadways and the optimization of roadway sections.

Mechanical performance of CRTS II slab tracks in reinforced-unreinforced transition zone in extreme heat events

Anchors have been widely utilized to reinforce the CRTS II slab tracks. The mechanical performance of the tracks in the reinforced-unreinforced transition zone exposed to extreme heat waves can be very complex due to the difference in mechanical properties between the two kinds of track segments. This paper investigates the damage behavior of the tracks in the reinforced-unreinforced transition zone in extreme heat events. A finite element model of the CRTS II slab track in the transition zone has been established and validated, in which the nonlinear mechanical properties of track materials and interfaces are considered by applying the Concrete Damaged Plasticity model and the Cohesive Zone Model respectively. The nonlinear temperature field in the track structure in extreme heat events is applied to the model. Structural damage of the track, including slab-end arching and interfacial failure, in the transition zone under extreme heat is thoroughly investigated. In particular, the effects of joint use of post-installed reinforcement anchors and other track maintenance measures like interface adhesives and concrete joint restoration are studied. The following conclusions are drawn: (1) The more reinforced track-slabs in the transition zone, the milder the track diseases including slab-end arching and interfacial gapping. (2) Joint use of anchor installation and other maintenance measures such as interface adhesives and concrete joint restoration shows a better effect on mitigating track damage than using post-installed reinforcement anchors solely. (3) Concrete joint restoration overweighs interface adhesives in terms of reducing slab-end arching and interfacial damage when they are jointly used with post-installed reinforcement anchors. (4) In the transition zone, track damage surges when the air temperature increases from 42 ℃ to 47 ℃, which is the temperature range for an extreme heat wave. Monitoring of track state in the transition zones is necessary during extreme heat waves. The novel findings are expected to provide some insights into the mechanical performance of slab tracks and help to prevent potential damage to the tracks in the transition zone, which is a common and practical issue in railway engineering.

Installation performance of torpedo anchor at different installation heights under the action of currents: The example of T98 torpedo anchor

The deep-sea torpedo anchor is an innovative and cost-effective anchorage foundation. However, marine environmental loads such as currents have a significant impact on the free-fall installation of torpedo anchors in water, often leading to the failure of installation due to excessive inclination or large deviations from the installation location. Therefore, taking the T98 torpedo anchor commonly used in practical engineering as an example, this paper systematically investigates its installation characteristics under the action of currents. First, based on OpenFOAM®, a 3D numerical model is established to simulate the underwater falling process of torpedo anchors via dynamic model analysis method. Using the validated model, the influence of currents on the installation performance of torpedo anchors is then explored. Based on the findings, the installation conditions of T98 anchors at different installation heights are recommended. Finally, a semi-empirical method for estimating the anchor inclination and deviation of torpedo anchors under current action is proposed, which may facilitate the assessment of installation inclination and determine the installation release point of torpedo anchors.

Plaxis 2D Modelling of an Anchor Sheet Pile for Soil Slope Strengthening at Segamat, Johor

In soil engineering, the soil slope is one of the important issues in geotechnical and environmental engineering that can fail due to settlement behaviour. Due to soil slope instability, roads near the Segamat River’s slopes have seen severe settlement. Therefore, this study was carried out to determine how the geometry of the soil slope and the properties of the soil affect soil stability and deformation. Because of the varying slope geometries along the river, this study used two alternative slope geometries in its modelling. A comparison was made between the existing slope and the slope stabilised with sheet piling by using Plaxis 2D. Other parameters that affect slope stability are also being investigated, such as anchor length and anchor installation angle. The anchor sheet pile's presence is intended to improve the slope's stability. As a result of this analysis using PLAXIS 2D software, the optimal anchor length depends on the passive pressure of the soil behind the sheet pile. According to the results, installing an anchor with a 60° angle is more stable because the safety factor obtained is 3.26 which is greater than that of a 45° angle which is 1.33. It shows the anchor is the best support of the sheet pile for the soil slope stability.

An efficient approach to tackle the challenges of LDFE modelling of plate anchor-chain system during installation process

This technical note presents an efficient approach to tackle the challenges in large deformation finite element (LDFE) modelling of plate anchor-chain system during installation process. This is realised by using a local coordinate system based on the displacement-control technique, where the chain loading direction is updated compatibly with the anchor behaviour at each calculation increment. The effectiveness of the approach is demonstrated through two analysis examples that model the anchor installation (keying) process. The results agree well with established analytical solution based on plasticity analysis, which was developed based on deeply embedded anchor. The LDFE results numerically testify that plate anchors with well-designed padeye position are able to dive into deeper seabed under chain loading, where this concept was only suggested in previous analytical and plasticity analysis.

A study on the coupling mechanism of hydrate dissociation-seepage-heat transfer induced by suction anchor installation in marine sediments

The suction anchor base has been widely used in marine engineering as an innovative and efficient foundation for marine structures. However, prior research endeavors have neglected to account for the influence of hydrate dissociation within the seabed sediments on suction anchors' negative pressure installation process. This paper elucidates the intricate coupling mechanism of hydrate dissociation, seepage, and heat transfer within marine sedimentary layers, all of which are induced by installing suction anchors. Employing a multi-physical field coupling methodology, numerical simulations were conducted to analyze the influencing factors and spatiotemporal evolution of hydrate dissociation and the impact of hydrate dissociation on seepage and pressure fields. The results indicate that the increases in negative installation pressure, penetration depth, and stratigraphic sensible heat promote hydrate dissociation. The hydrate dissociation enhances seepage, reduces the pressure gradient in the anchor, and decreases the suction anchor sinking force. Consequently, this research holds practical implications for guiding suction anchor installation within seabed characterized by buried hydrate.

Soil–Structure Interactions in a Capped CBP Wall System Triggered by Localized Hydrogeological Drawdown in a Complex Geological Setting

Retaining walls are often used to construct basements and underground station boxes. This unique case study compares the field-measured contiguous bored pile (CBP) wall, surrounding geology, and hydrogeology or groundwater responses against the results using 2D and 3D numerical back analyses of a deep excavation project that experienced localized groundwater drawdown through the leaking ground anchor points. Site observations indicated that the ground anchor installation works had caused larger than expected through-the-wall leakages that subsequently triggered nearby ground and building settlements. In order to study the complex soil–structure interaction behavior, back analyses using a hybrid modeling technique of through-the-wall transient hydrogeological seepage and geomaterial stress-strain analyses was implemented. Through these soil-structure interaction back analyses, it was evidently revealed that the presence of the continuous capping beam was key in providing pile head restraints against the active earth pressures when the groundwater was depressed, as well as efficiently distributing the beneficial wall corner effects towards the middle CBP wall, leading to smaller bending moment magnitudes, characterized by their ‘S-shaped’ profiles. This behavior had been correctly diagnosed, as opposed to the ‘D-shaped’ bending moment profile usually only seen in a typical free-head cantilever wall in similar geology. The eventual results show that the wall and ground responses, i.e., deflection, bending moment, and settlement, were reasonably well predicted when compared against the instrumented field data, thus validating the reliability of the geotechnical modeling technique, key geological parameters, and hydrogeological fluctuations adopted in the 2D and 3D numerical models, as well as the beneficial contributions of the continuous capping beam, which tend to be overlooked during routine retaining wall design.

Numerical investigation of the penetration of torpedo anchors in sand-overlying-nonhomogeneous clay deposit

This study presents a comprehensive investigation of torpedo anchors penetrating into sand-overlying-nonhomogeneous clay deposit, with the main objective of predicting the anchor embeddment depth after it penetrates through the top sand layer. The behavior of the torpedo anchor and soil failure mechanisms during the installation process are analyzed using large deformation finite element (LDFE) methods. To validate the numerical models, comparisons are made with data from existing centrifuge and field tests. An extensive parametric study is then conducted, exploring a wide range of soil properties, soil layer thickness, anchor velocities, and parameters related to torpedo anchor geometry. Two intriguing findings emerge from the analysis. Firstly, there is an evolving soil failure, with the strain-softening region expanding in the clay near the boundary between the two soil layers. Secondly, the velocity profile during both the acceleration and deceleration stages varies with different sand layer thicknesses, displaying a nonlinear relationship with the anchor's final embedment depth. Based on the findings, a simple design procedure is developed to account for the influencing factors on the anchor installation depth. This procedure is expected to be valuable for engineers seeking to estimate the behavior of torpedo anchor installations in sand-overlying-nonhomogeneous clay soil deposits.

Discrepancies between element tests and large-scale LDFE simulations: A case study on anchor kinematics during installation in clay

Harsh offshore conditions impose significant challenges to the design of floating offshore wind turbines (FOWTs). In particular anchoring systems face many uncertainties due to the unknown soil response and post-installation soil state. This study investigates the drag embedment anchor (DEA) installation in fine-grained soil through numerical simulations, employing large-deformation finite element (LDFE) analyses using the CEL method and visco-hypoplastic constitutive equations. Three parameter sets for kaolin clay were determined, which show excellent agreement to experimental data (MPE <6%). The study analyses the variation of the viscosity index Iv, determined by three acknowledged methods (oedometer test, triaxial test, and liquid limit). Despite element tests revealing minimal differences, large-scale LDFE simulations of DEA installation with varying Iv values significantly diverge. However, the viscosity index does not impact the relationship between anchor rotation and penetration. These findings emphasise the necessity for a comprehensive understanding of anchor-soil interaction and the limitations of numerical simulations lacking physical validation. This study contributes to the reliable design and installation of FOWTs by spreading awareness on the complex DEA kinematics in fine-grained soils and showcasing the importance of careful parameter calibration for numerical frameworks.

Dynamic installation of torpedo anchors in slightly overconsolidated clay-overlaying-sand deposit

Torpedo anchor installation involves uncertain design and construction parameters, especially in layered soil deposits. Large deformation finite element and coupled Eulerian–Lagrangian (LDFE/CEL) analyses are performed in this study to elucidate the dynamic installation of torpedo anchors in an over consolidated clay-overlaying-sand deposit. The parametric analysis is conducted after model verification to explore the effect of upper clay layer thickness, anchor impact velocity, anchor submerged weight, soil properties and anchor geometric dimensions. The soil failure patterns and dynamic installation behaviour in the clay-overlaying-sand soil deposit are found to differ substantially from those in single-layer clay and sand deposits, which exhibit a squeezing flow pattern at the clay-sand soil layer interface. As the demarcation of the two velocity phases during the anchor penetration process (acceleration and deceleration phases) falls below the interface of two soil layers, the contribution of the internal friction angle of sand to the anchor final penetration depth exceeds that of the clay undrained shear strength. Based on intensive modelling data, an empirical method for predicting the anchor penetration depth in single and layered soil deposits is derived for engineering applications.

Dynamic installation of offshore torpedo anchors in spatially variable clay

Dynamic installation of offshore torpedo anchors in spatially variable clay

Investigation of the installation process of drag-in plate anchors from LDFE modelling

The installation of drag-in plate anchors is investigated using advanced large-deformation finite-element (LDFE) analysis. A new modelling technique that can realise the continuously evolving loading angle on the anchor line is described. The entire anchor trajectory is simulated until the anchor reaches an ultimate state after dragging for a very large distance, typically in the range of 40–70 times the anchor width. An installation in simple uniform and non-sensitive soil is first presented with agreement against well-established plasticity analysis and an analytical solution offering verification of the techniques developed. The effects of anchor padeye position, seabed soil conditions, anchor line properties and the anchor–soil interface on the installation response are then discussed. The findings highlight that plasticity and analytical approaches are not necessarily conservative when the yield surface derived from deep embedded anchors is applied in shallow conditions. The LDFE results also demonstrate the importance of accounting for soil remoulding around both the anchor and anchor installation line. The results of this study provide insights for offshore engineers to consider and incorporate when estimating a drag anchor installation trajectory and holding capacity.