Ground Anchors Research Articles

Экспериментальные исследования комбинированных анкеров и варианты их практического применения

In the article, the authors for the first time proposed combined anchor structures that can work effectively as wire anchors working on a pulling load, as well as pile anchors working on a pressing force. Such structures can be effectively used as anti-landslide structures, support and anchor foundations, which are also patented by the authors and their designs are given in the article. In practice, such structures are necessary as foundations, for poles of power lines, high towers exposed to high wind loads and other structures. The support can work both on a pressing load and on pulling out, depending on the specific conditions. The research methodology is described and the results of experimental studies are presented. During the research, the following factors were taken as the main factors: the diameter of the pile and the conical tip, the length of the pile part of the combined anchor, the distance from the end of the pile to the conical tip. The pulling force was adopted as an optimization parameter.

Experimental and numerical investigation on the impact of MS2AF on local scour protection performance

Suction anchor foundations are widely used in the offshore wind power industry. The installation of suction caissons alters the near-bed flow field and leads to local scour. This study proposes a novel integrated design for the scour protection of suction anchor foundations, known as the multihole sector suction anchor foundation (MS2AF). Through indoor flume experiments and numerical flume simulations, the local scour protection performances of MS2AFs with different design parameters under the action of steady flow were investigated. The results showed that the scour evolution of MS2AFs can be divided into three stages: slow scour, rapid scour, and scour equilibrium. The MS2AF reduced the flow shear stress on the sediment bed, thereby decreasing the depth and range of the local scour. The maximum scour depth, width, and length of the scour hole exhibited negative linear relationships with the width and thickness of the sector and decreasing-then-increasing relationships with the diameter and area ratio of the holes. Among these factors, the sector's thickness had the most significant impact. There existed an optimal diameter and area ratio that maximized the stratification effect and deceleration effect of the multihole sector.

About effect of dynamic loading caused by concrete pump on bending moments, anchor forces and deformations in single level anchored retaining wall

This paper explore effect of dynamic loading caused by concrete pump on bending moments, anchor forces and deformations in single level anchored retaining wall. Dynamic loading is obtained by using a special developed dynamic mathematical model of truck-mounted concrete pump, by means of which are calculated the maximal dynamic loadings (acceleration and forces), which are transferred from concrete pump to the soil, and from there accordingly – from soil to the retaining wall under consideration. After that is performed a detailed finite element analysis of the retaining wall, by using software product Plaxis 3D, during which are analyzed the variation of bending moments, anchor forces and deformations in single level anchored retaining wall and after dynamic loading applying. There is also a numerical example considered, for which are calculated the maximal dynamic loadings, which are transferred from concrete pump to the soil, and from ground supports to the retaining wall. An amplification factor (dynamic factor) due to dynamic effects is calculated, by which is necessary to be multiplied the static loadings caused by concrete pump on soil. In the conclusion is made a qualitative assessment of the dynamic influence of concrete pump on the soil and the retaining wall section and ground anchor.

Twinning of the Egongyan Bridge

The First Egongyan Bridge in Chongqing, China was opened to traffic on December 27, 2000. It carries six-lanes of city traffic and two pedestrian paths, one on each side. It is a 600 m span suspension bridge. It was planned that the two pedestrian paths might eventually be converted to transit tracks in the future. However, with the rapid increase in urban traffic, the deck was transformed into an 8-lane bridge instead. Therefore, a new bridge parallel and adjacent to the old bridge was built for the rail transit. For aesthetic reasons, the city decided that the new bridge should also be a suspension bridge, with the same span length and tower height as the first bridge. The First Egongyan Bridge was a true suspension bridge with main cables anchored to ground anchors. However, the new bridge bridge’s proximity to the first bridge necessitated the construction of a self-anchored suspension bridge that did away with a second set of ground anchors. This 600 m span happened to be the world’s longest span for a self-anchored suspension bridge.

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 Study on the Effect and Mechanism of Supporting Pile Equivalent Calculation Methods in Pile–Anchor Support System

In numerical analysis, the pile equivalent calculation method plays a key role in foundation pit calculation results. However, the effect and mechanism of different pile equivalent calculation methods in the foundation pit has remained unclear. To solve this question, based on FLAC3D, four pile equivalent calculation methods were introduced into a typical pile–anchor pit. This research was carried out from the perspective of soil displacement and stress, special points’ stress paths, and the plastic zone. The results revealed that there was a remarkable influence on the calculation results for different pile equivalent calculation methods. Specifically, compared with structural pile elements, displacements near the pile were smaller in solid pile element mode. Moreover, with the increase in excavation depth, stress concentration appeared in the solid pile element mode. The solid support pile with the interface, compared to that without the interface, had less displacement but more stress concentration around the pile, which led the special points’ stress paths around the solid pile to become irregular. Regarding the structural pile elements, it is suggested that both modeling approaches had a similar effect. These findings could help to provide a deeper insight into pile–anchor foundation pit numerical analysis.

The Effect of Incorporating Vertical Spatial Variability on the Probabilistic Analysis of a Deep Excavation: A Case Study

This study explores the impact of including the vertical spatial variability in effective stress friction angle of clay on the probabilistic analysis of deep excavations. The proposed methodology is demonstrated and verified by conducting random finite element modeling (RFEM) of an instrumented deep excavation project situated in Ankara, Turkey. The excavation has a depth of 20 meters and is supported by six levels of pre-stressed ground anchors. To simulate the vertical spatial variability of effective stress friction angle in the clay, Monte Carlo simulation method and the random field theory are employed. The simulated parameters are then inserted into the finite element model via Python programming language to analyze the probabilistic distribution of lateral deflections and bending moments in the drilled shaft wall. The results obtained from the Monte Carlo simulations reveal that the incorporation and selected value of spatial variability significantly impacts the resulting lateral movements, bending moments, and the probability of failure of the system.

Experimental and Theoretical Study on the Self-Weight Penetration Velocity of Suction Anchor Foundations in Sand

Experimental and Theoretical Study on the Self-Weight Penetration Velocity of Suction Anchor Foundations in Sand

Selection of Foundation Types for Mechanized Construction of 220 kV Overhead Transmission Lines in Mountainous Areas Suitable for Fujian Province

The construction of overhead transmission lines in mountainous areas poses a significant challenge when it comes to foundation construction. The type of foundation selected in these areas has a direct impact on equipment selection and access road planning. Fujian Province, located on the southeastern coast of China, is predominantly hilly and mountainous. Therefore, selecting an appropriate foundation for overhead transmission lines is crucial for successful mechanized construction of transmission lines in this region. In this study, we aimed to enhance the economy of mechanized construction of the foundation of the 220 kV overhead transmission lines in Fujian Province. We analyzed the typical geological conditions and foundation reactions in the area and compared the construction costs of mechanical pile foundations, mechanical digging foundations, and rock anchor foundations. The results show that the mechanical pile foundation requires the least amount of concrete when the foundation reaction of the 220 kV suspension tower is less than 1700 kN and the foundation reaction of the 220 kV tension tower is less than 1300 kN. Additionally, the quantity of the rock anchor foundation is less than that of the digging foundation. In terms of cost, the rock anchor foundation is the most economical, followed by the mechanical pile foundation and then the digging foundation.

Field experimental study on the pull-out characteristics of a new type of expanding shell bolt

Rock bolt foundation is becoming increasingly popular for transmission line engineering in mountainous areas due to the ability to maximize rock foundation bearing performance, reduce foundation size and burial depth, and save investment. However, failure modes such as pull-out of bolt can lead to insufficient utilization of bearing capacity of rock bolt. To overcome this problem, a new form of expanding shell bolt is proposed and the effect of several variables including grouting materials, bolt diameter, site weathering degree, and anchoring depth are investigated in this study. The results indicate that the new expanding shell bolt may significantly increase the pull-out bearing capacity compared to common rock bolts, due to the built-in effect between the bottom part of bolt and the rock on the hole wall. The effect of grouting material and anchoring length on the shell anchor's uplift bearing capacity is minimal. Considering that the ultimate tensile strength when the anchor bar breaks depends on the diameter of the steel bar, increasing the diameter of the anchor bar will effectively improve the pull-out characteristics of the bolt. The failure mode of anchor rods is also influenced by the rock layers. Rock layers with lower weathering levels have stronger embedding force, and the expansion head can effectively play a role. Due to the group anchor effect, the ultimate uplift bearing capacity of group anchor foundation in rocks is not simply the sum of the bearing capacity of each one, but must be multiplied by the group anchor coefficient. This coefficient is close to 0.9 in moderately weathered and strong-medium weathering sites. Finally, the calculation method for ultimate pullout force of expanding shell bolt is established. The feasibility of this method is verified by comparing on-site test values and calculated values.Author keywords: Rock bolt; Expanding shell bolt; Pull-out bearing capacity; Failure mode; Group anchor effect.

Laboratory Investigations on the Mode of Failure in Frictional and Low-Cohesive Materials Under the Load of a Ground Anchor

Ground anchors are widely used in many types of construction works, such as stabilization of rock slopes, wind turbines, concrete dams and bridge towers. Some of the modes of failure for these anchors still have an insufficient scientific basis, and that applies especially to what happens in the ground when overloaded. This paper presents investigations on the failure development in frictional and low-cohesive materials which are subjected to loading by an embedded anchor with a free length towards the surface. The failure development is demonstrated through a series of small-scale physical model tests performed in the laboratory. The physical model setup consists of a transparent PVC test chamber, a rigid «anchor block», and a hydraulic jack. The model is instrumented with a camera, an extensometer and a load cell to continuously record the failure development and resistance from the material as the anchor block is pushed through the sample material. The main question investigated is how the failure appears, as a failure along the whole pull-out body at once or as an advancing fracture along the plane, where in the first case the shear capacity of the material will be the main input in calculations, and for the second case, one also needs to take failure propagation into account.

A comparison of countermeasures against landslide on the road No.152, Sapa Town, Lao Cai Province, Vietnam

Landslide hazards are one of the most common geological disasters due to the impacts of natural factors, mainly rainfall, and human activities, such as the construction of transport infrastructure and mining projects. In Vietnam, most of the landslides and slippage frequently occur in mountainous areas, especially in Lao Cai province during the rainy season. In 2021, a slope failure happened near the Mong Hoa valley, on Road No. 152, sections Km 2+728.26–Km 2+827.04 in Cau May ward, Sapa town, Lao Cai province. In this study, topographical features, geomorphological features, hydrological features, geological investigation, and laboratory tests were performed to analyse the slope stability. This study used the Limit Equilibrium Method (LEM) and the Finite Element Method (FEM) to analyse the slope stability, and several countermeasures were proposed for this slope such as the retaining wall, ground anchors, and soil nails. This numerical result showed that the ground anchors and soil nails are the suitable method to prevent the instability of the slope. This study shows that compared with the traditional LEM method and advanced FEM method is that it can capture more results not only safety factor but also horizontal displacement and load anchor result. As a result, this analysis showed that the safety factor value in the finite element method was greater than that in the limit equilibrium method.

ITUAVs: Intermittently Tethered UAVs for Future Wireless Networks

We propose the intermittently tethered unmanned aerial vehicle (iTUAV) as a tradeoff between the power availability of a tethered UAV (TUAV) and the flexibility of an untethered UAV. An iTUAV can provide cellular connectivity while being temporarily tethered to the most adequate ground anchor. Also, it can flexibly detach from one anchor, travel, then attach to another one to maintain/improve the coverage quality for mobile users. Hence, we discuss here the existing UAV-based cellular networking technologies, followed by a detailed description of the iTUAV system, its components, and mode of operation. Subsequently, we present a comparative study of the existing and proposed systems highlighting the differences in key features such as mobility and energy. To emphasize the potential of iTUAV systems, we conduct a case study, evaluate the iTUAV performance, and compare it to benchmarks. Obtained results show that with only 10 anchors in the area, the iTUAV system can serve up to 90% of the users covered by the untethered UAV swapping system. Moreover, results from a small case study prove that the iTUAV allows to balance performance/cost and can be implemented realistically. For instance, when user locations are clustered, with only 2 active iTUAVs and 4 anchors, achieved performance is superior to that of the system with 3 TUAVs, while when considering a single UAV on a 100 minutes event, a system with only 6 anchors outperforms the untethered UAV as it combines location flexibility with increased mission time.

Assessment of ground-anchored slope stability based on variation in residual tensile forces

The current maintenance process for ground-anchored slopes in Japan involves conducting lift-off tests to measure the residual tensile forces acting on the ground anchors of the slopes of interest. On highway slopes, at least 5% of the total number of anchors on a particular slope is measured once every five years. If a sufficient number of anchors is found to be under excessive tensile forces, additional lift-off tests are conducted to confirm the distribution of the residual tensile forces. Furthermore, if the collapse risk of the slope is estimated to be significant in these lift-off tests, additional surveys, which take measurements of the slope movement, borings, and so on, are carried out and necessary countermeasures are planned by technical committees. As the number of ground-anchored slopes in Japan is tremendous, however, the maintenance process could be time-consuming and costly. Therefore, the aim of this study is to develop a simple approach for identifying the dangerous ground-anchored slopes (that is, those requiring countermeasures) based only on the results of lift-off tests. This would allow maintenance engineers to significantly reduce the number of slopes that they submit to technical committees for further evaluation.This paper discusses comprehensive ground-anchored slope stability based on the variation in residual tensile forces. Firstly, the most significant parameter for judging dangerous slopes is identified through lift-off tests based on an examination of 45 ground-anchored slopes that had previously undergone maintenance, including additional surveys, slope stability evaluations, and countermeasure planning, as was necessary. Secondly, a probabilistic approach, using a simple circular slip analysis, is employed to confirm the relationship between the probability of slope failure and the parameter identified in the first step.

Relative Localization Estimation for Multiple Robots via the Rotating Ultra-Wideband Tag

Most distributed algorithms for robot coordination require relative location information, but how to obtain relative locations in a distributed manner is still a primary problem to address in multi-robot applications. In order to obtain the relative locations between robots, no matter whether they are in relative motion or stationary situation, we design a rotating ultra-wideband tag to provide the persistency of excitation condition and two estimation algorithms to estimate the relative locations in a distributed manner. Moreover, our approach relies only on on-board sensors and requires only one ultra-wideband tag per robot, eliminating the need for any ground anchors, thus allowing deployment in GNSS-denied environments without range restrictions. The proposed approach in this letter is also tested in simulations and experiments to verify the theoretical findings and effectiveness in practice.

Bored Injection Piles ERT (RIT, FORST, ERST) - Structures for Ensuring Slope Stability

The problem of increasing the bearing capacity of foundations is always an urgent task in modern geotechnical construction. It is of particular importance when building on slopes cut by ravines. As a rule, construction on slope surfaces due to the discharge of filtration flows in the form of springs is always a problematic measure. Hydrogeological processes often bring rugged surfaces intended for the construction of objects into an unstable state, leading them to landslides. Thus, the safe erection of buildings and structures in such areas is always accompanied by the simultaneous erection of retaining buried building structures. The most competitive retaining structures are monolithic reinforced concrete corner retaining walls erected on bored piles and fixed with ground anchors. The article gives examples of the use of ERT bored piles (RIT, FORST, ERST) and ERT ground anchors.

앵커기초의 균열을 고려한 모형 전기 캐비닛의 지진거동특성 분석을 위한 진동대실험

앵커기초의 균열을 고려한 모형 전기 캐비닛의 지진거동특성 분석을 위한 진동대실험

Numerical investigation of pull-out capacity and failure mechanism of suction anchors with mooring line in sand

Suction anchor is a widely used anchorage foundation in taut or catenary mooring systems to fix floating structures. This paper aims to investigate the pull-out capacity and failure mechanism of suction anchors in sand using the finite element method which models the attached mooring line on the anchor padeye. The advanced critical state elastoplastic constitutive model SIMSAND is utilized which can well simulate the state-dependent peak strength and stress-dilatancy behavior of sand, and its accuracy and effectiveness are validated with centrifuge test results. A series of systematical parametric studies are then carried out to explore the effects of the mooring line, aspect ratio, padeye position and loading angle on the pull-out capacity and failure mechanism of the suction anchor. Based on the numerical results and those obtained in other researchers’ work, the optimal padeye position and the normalized V–H envelopes are explicitly discussed. Finally, a calculation framework is put forward for predicting the inclined pull-out capacity of suction anchor in sand considering the mooring line effect.

Design bond stress parameters for rock anchors in Brisbane

Little published information is available on bond stress parameters at the grout-ground interface for the design of ground anchors within Brisbane rocks. In the absence of data, a designer will typically fall back to ‘universal’ correlations with measurable parameters such as Uniaxial Compressive Strength (UCS) or descriptions of rock type to nominate design bond stress values. In doing so, there is often little understanding of the limitations of such correlations or how applicable those correlations are for the rocks encountered within the local region. A study of Proof Test data from testing of sacrificial ground anchors constructed within materials from the Brisbane Tuff and Neranleigh Fernvale Beds Stratigraphic Units for an infrastructure project in Brisbane has been carried out to consider bond stress values at the grout-ground interface. Materials within the bond zone of ground anchors constructed in Brisbane Tuff and Neranleigh Fernvale Beds units have been classified into different rock units based on rock substance strength and Geological Strength Index. Details of anchor construction and testing procedures are presented, together with the adopted approach to test interpretation. Data from Proof Testing of ground anchors bonded into these materials is then interpreted and evaluated for each unit, with relationships developed for each rock type for ultimate and yield bond stress values at the grout-ground interface as a function of rock substance strength (UCS) and rock mass strength (based on Hoek and Brown,2018). For both rock types, grout-ground interface bond stresses increase with rock strength and quality, with better correlations evident based on rock mass strength than for UCS data. Comparisons of the interpreted bond stress relationships based on UCS are made for both rock types to published information for ground anchors and shaft adhesion parameters for cast-in-situ piles. Suggestions are made for amendments to the Proof Anchor test method to reduce the potential for premature termination of the test and consequent underestimation of the bond stress, and to obtain consistency between Proof and Production test methods.

Key Techniques for Construction of East Anchorage of the Lingdingyang Bridge on Shenzhen-Zhongshan Link

The Lingdingyang Bridge is a (580+1666+580m) two-tower three-span sea steel box girder suspension bridge. The east anchorage adopts a figure eight-shaped ground connecting wall foundation. The ground connecting wall has a diameter of 107.1m and a width of 65m. The wall thickness is 1.5m. the maximum depth of the wall is 63m, the embedded medium weathered granite depth is 5m. The overburden thickness is nearly 50m, the bedrock depth above 80Mpa is 10m, and the excavation depth of the foundation pit is 42m. The anchor body is a diamond shaped anisotropic anchor body, with a total volume of 93000 m3. The anchorage foundation adopts “locking steel pipe piles + I-shaped sheet piles + parallel wire ropes” combined island-building cofferdam, and the diameter of the island is 150m. There are 79 groove sections in the ground wall. Three-axis mixing piles are used to reinforce the joints and both sides of the groove wall before grooving. The technique of alternately forming grooves by “rotary drilling + groove milling machine” is adopted. The deep foundation pit is unearthed together with the excavation portal frame and the telescopic boom excavator, and the lining is constructed with the hanging form. After the excavation, the waterproof effect of the ground connecting wall is obvious, and the foundation pit is safe and reliable. The anchor body is constructed with a layer of 2m with a large amount of limestone powder concrete, and a 2m post pouring section is set at the same time. The maximum temperature is 65 °C, and the crack control effect is obvious.