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The purpose of this paper is to describe the variability of soil rheological properties based on research carried out using load tests of ground anchors under complex geotechnical conditions. The heterogeneity of soil should always be considered when designing geotechnical constructions. In the present case, the earthwork created at the Warsaw Slope revealed an embankment of anthropogenic origin, located in a geologically and geomorphologically complex area of the Vistula valley slope. Excavation protection was anchored mainly in soils of anthropogenic origin. When the acceptance tests of the ground anchor were completed, the subsoil randomness was confirmed using nondirect, geostatistical methods. A standard solid rheological model with nonlinear fitting to the data was used. This model was established to describe the creeping activity of the ground anchor more accurately. The characteristics of man-made embankments were described using the parameters obtained with the rheological model of the subsoil.

This study evaluates load variations in instrumented prestressed ground anchors installed in a bored pile retaining wall system in sandy soil. Data were collected from instrumentation assembled in the bonded length of three anchors, which were monitored during pullout tests and during different construction phases of the retaining wall system. Instrumentation consisted of electrical resistance strain gauges positioned in five different sections along the bonded length. Skin friction distributions were obtained from the field load measurements. Results showed that the skin friction followed a non-uniform distribution along the anchor bonded length. The mobilized skin friction concentrated more intensely on the bonded length half closest to the unbonded length, while the other half of the bonded length developed very small skin friction. The contribution of the unbonded length skin friction to the overall anchor capacity was significant and this should be accounted for in the interpretation of routine anchor testing results. Displacements applied to the anchor head were sufficient to mobilize the ultimate skin friction on the unbonded length, but not on the bonded length. Performance of loading-unloading stages on the ground anchor intensified the transfer of load from the unbonded length to the bonded length. Long-term monitoring of the anchor after lock-off revealed that the load at the anchor bonded length followed a tendency to reduce with time and was not significantly influenced by the retaining wall construction phases. resumo: O presente estudo avalia as variações de carga em ancoragens protendidas instrumentadas, instaladas em uma estrutura de contenção composta por estacas escavadas em solo arenoso. Os dados foram coletados a partir de instrumentação disposta no trecho ancorado de três ancoragens, monitoradas durante ensaios de arrancamento e durante diferentes etapas construtivas da contenção. As ancoragens foram instrumentadas com extensômetros elétricos de resistência em cinco seções distintas posicionadas ao longo do trecho ancorado. Distribuições de atrito lateral foram obtidas a partir das medições de carga em campo. Os resultados revelaram uma distribuição não uniforme do atrito lateral ao longo do trecho ancorado. O atrito lateral mobilizado concentrou-se mais intensamente na metade do trecho ancorado mais próxima ao trecho livre, ao passo que uma parcela muito pequena de atrito lateral foi mobilizada na outra metade do trecho ancorado. A contribuição do atrito lateral no trecho livre para a capacidade de carga da ancoragem foi significativa, o que deve ser levado em consideração na interpretação dos resultados de ensaios de rotina em tirantes. Os deslocamentos aplicados na cabeça da ancoragem foram suficientes para mobilizar o atrito lateral último no trecho livre, porém não no trecho ancorado. A execução de estágios de carga-descarga na ancoragem contribuiu para intensificar a transferência de carga do trecho livre ao trecho ancorado. O monitoramento de longo-prazo da ancoragem após incorporação do carregamento revelou que a carga no trecho ancorado seguiu uma tendência de redução ao longo do tempo, não tendo sido significativamente influenciada pelas etapas construtivas da contenção.

With increasing level of urbanization, new buildings are erected in close proximity to existing buildings or quite close to site boundaries. Such practice affects the complexity of retaining wall installation technology. When a retaining wall is installed close to an existing building, a street or a steep slope, the stability of the wall has to be ensured first. There are cases when a retaining wall has to be strengthened by creating a permanent or temporary support, i.e. by installing ground anchors. According to literature analysis, the major problem is that a profile stops without reaching its designed depth (Van Baars). Merifield et al. distinguish three major types of anchors: circular, square and rectangular. They emphasise that anchor surface unevenness does not impact anchor resistance. According to Nagar, most frequently anchors disintegrate due to excessive tensile strength of the anchor. The increase of this force is related to tensile strength measured in anchor testing. In this paper, three types of retaining walls with ground anchors are considered: pile wall, Berlin Wall, and sheet piling with excavation depth of 6 m. The conditions are selected as follow: when walls are installed in clay soils, sandy soils, sandy soils at high groundwater levels, and when the wall is installed next to the building. Mechanical resistance and stability of construction incline are calculated by means of GEO5 software. A survey was designed basing on the calculation results and the selected evaluation criteria. In the survey geotechnical engineers rated 18 different cases. The relevance of criteria is determined by employing the entropy method after the primary results of the survey are summarised; afterwards a multiple criteria decision analysis carried out using the utility function. The multi-criteria assessment results indicate the most rational type of a retaining wall for the chosen conditions. This article is based on master thesis topic “Research on Installation Technologies of Retaining Walls with Ground Anchors”.

Ground anchors represent an important structural element in the area of geotechnical engineering. Despite their extensive usage, a design process of these elements is usually performed using simple empirical and semi-empirical methods, neglecting several important influencing factors. This paper gives an analysis of the factor of non-uniform distribution of skin friction resulting in a progressive failure of ground anchors. First, the finite element method in combination with a material model involving regularized strain softening is utilized. Next, an experimental program, including several investigation anchor load tests, was carried out. The goal of this program was to confirm preliminary conclusions drawn from numerical studies and to obtain relevant data for further back analysis. After, there is then described a newly developed application based on the load transfer method, in which all the findings from numerical computations and experimental measurements are incorporated.

The article describes the features of modeling monolithic trench “diaphragm wall” with ground anchors without the use of distribution beams on the progressive collapse caused by the failure of one of the anchors. In the simulation of the above calculation case, in the flat formulation commonly used in practice, it is assumed that the “diaphragm wall” is a continuous structure in the longitudinal direction, without taking into account the presence of vertical joints formed between the grippers when concreting the fence and the lack of connection between the longitudinal reinforcement of adjacent reinforcement spatial frameworks. The performed calculations show that the failure to take into account these circumstances leads to a significant reassessment of the ability of the “diaphragm wall” to redistribute the load from the broken anchor to the neighboring anchor and can lead to an incorrect assessment of the results of the calculation for a progressive collapse. The need to take into account the reduction of structural rigidity of the “diaphragm wall” due to the formation of cracks in two directions is also shown.

To improve the capacity of ground anchors, scholars and engineers worldwide have developed various types of underreamed anchors with expanded anchor parts. Underreamed anchors have a completely different mechanism from traditional shaft anchors. The expanded section of an underreamed anchor induces an end bearing force to endure the uplift force similar to a reversed pile. Therefore, the total resistance of an underreamed anchor includes friction and end bearing force. To clarify the bearing mechanism of underreamed anchors, a series of model tests were performed using fiber Bragg grating (FBG) sensors and the photogrammetry measuring method. Based on the tests, the distribution and development of the friction and end bearing force of the underreamed anchor model were acquired by the FBG sensors when being pulled out. Moreover, the deformation state of the soil around the anchor model was observed by the digital photogrammetry measuring method. Finally, the interaction mechanism between an underreamed anchor and surrounding sand was obtained, which was identified as the inherent reason for the distribution and development law of the resistance of the underreamed anchor in sand.

The paper presents an application of statistical and numerical methods for the determination of the forcedisplacement curves and that of pullout capacity of prestressed grouted ground anchors installed in Miocene clay. A regression analysis of data from a database of acceptance test records for ground anchors to create has been performed, the force-displacement curve of the tested anchor corresponding to the range of loads applied for acceptance tests has been created. A linear regression model, employing the weighted least squares method and robust standard errors techniques were concluded to serve as a reliable statistical method suitable for achieving this goal. The discovered linear regression dependence then served as a lower control limit for the displacement values calculated at the anchor head applying the numerical model. A finite element model has been created to predict the behaviour of ground anchors being installed in fine-grained soils. The developed numerical model that employs Mohr-Coulomb strength criterion constitutive model evaluates the influence of high-pressure grouting by development additional radial stresses and that of an increment of fixed length diameter.

The research campaign aimed on the better understanding of behavior of prestressed soil anchors in neogene clay, including conduction of variety of in-situ (CPT, PMT) and laboratory (Triaxial test, Simple shear test an Oedometric test) ground investigation methods, has been done during 2012 – 2015 in Czech Republic. The stress – strain diagrams and distribution of axial force along the anchor free length and anchor bond length was determined, based on the data obtained from variety types of sensors placed onto the tendon and into the gravity and post-grouted part of the grout body. On the basis of this information the software application for prediction of the anchor pull-out force and stress-strain diagram was developed, calibrated and verified. The application for purposes of conduction of prestressing tests and test reports elaboration was programmed also. Research activities leading to development of the pair of forenamed software are described in paper.

Quantifying the penetration depth of a dragging anchor on a horizontal layer of rockfill provides the possibility to optimize the layer thickness of rockfill layers with a protective function. Current research on this subject is limited and is often aimed at anchor capacities in sand and clay. Penetration behaviour in rockfill is mainly investigated for protections with a limited width. Anchor dragging tests carried out for a canal expansion project show that as the rock size increases, the penetration depth and the holding capacity of the anchor decrease. A semi-empirical prediction formula is derived. An additional series of scaled down tests shows that the process of anchor drag in rockfill is scalable, as long as all aspects of the trial design are taken into account. This provides possibilities for accessible further research, expanding on the prediction of penetration depth and further anchor behaviour in different types of rockfill.

The poor performance and durability of traditional steel tendon and cement grout have become serious constraints to the development of ground anchor systems, especially when these systems are permanent features in large-scale projects such as ground anchors with capacities of more than 4,000 kN in Aizhai Bridge, China. This paper presents a large-scale ground anchor system with carbon fiber-reinforced polymer (CFRP) tendon and reactive powder concrete (RPC) grout as the bonding media in both above-ground and below-ground parts. Two full-scale ground anchor specimens named GA12-20 and GA12-9 were designed and installed at the construction site, and their behavior was systematically studied through monotonic and cyclic load testing. The two systems displayed acceptable displacements under both monotonic load testing with maximum tension twice the design lock-off load and in cyclic load testing under about 90% of its bearing capacity, with residual displacements all less than 5 mm. Furthermore, the bond stress distributions in the grouted portions of the rods in tendon showed both systems have reliable bonding capacities under tension. This innovative ground anchor system with CFRP tendon and RPC grout showed a good behavior and successfully served as the ground anchor of the Aizhai Bridge.

The design of the bond length of an postgrouted presstressed anchor is based on presumption of bond shear stress on contact of the bond skin and surrounding soil. Statistical analysis of measured test data was performed, including Latin Hypercube Sampling technique, to specify shear stress parameter for geotechnical conditions of Neogene fluvial clays stiff to very stiff consistency. Information about anchors installed into clays was abstracted from acceptance tests records provided by TOPGEO – Czech special foundations contractor. All tested anchors were used as supports of temporary retaining structures on construction site in Olomouc, Czech Republic. Results of conducted analysis are expressed as confidence interval estimation of mean of bond shear stress parameter. This parameter is usable for future design of anchors installed into analogical geotechnical conditions. Influencing of results by technological aspects of the construction process is partially discussed too.

In bridge design, economically addressing large, lateral earth pressures on bridge abutments is a major challenge. Traditional approaches employ enlargement of the abutment components to resist these pressures. This approach results in higher construction costs. As an alternative, a formal approach using ground anchors to resist lateral soil pressure on bridge abutments is proposed herein. The ground anchors are designed to minimise lateral forces at the pile cap base. Design examples for high stem abutments (heights 6–8 m) are conducted for a simple 33 m long concrete bridge span, with two to three traffic lanes. The abutments are supported by driven, reinforced concrete piles. As lateral forces at the pile cap are significantly reduced, only one row of piles is needed. When compared with common abutment design, the proposed approach halved the number of piles required and decreased the required abutment volume by 37%. Deposited by bulk import

In a ground anchor system, cables or tendons connected to a bearing plate are used for stabilization of slopes. Then, the stability of a slope is dependent on maintaining the tension levels in the cables. So far, no research on a strain-based field sensing system for ground anchors has been reported. Therefore, in this study, a practical monitoring system for long-term sensing of tension levels in tendons for anchor-reinforced slopes is proposed. The system for anchor-reinforced slopes is composed of: (1) load cells based on vibrating wire strain gauges (VWSGs), (2) wireless sensor nodes which receive and process the signals from load cells and then transmit the result to a master node through local area communication, (3) master nodes which transmit the data sent from sensor nodes to the server through mobile communication, and (4) a server located at the base station. The system was applied to field sensing of ground anchors in the 62 m-long and 26 m-high slope at the side of the highway. Based on the long-term monitoring, the safety of the anchor-reinforced slope can be secured by the timely applications of re-tensioning processes in tendons.

This paper evaluates performance of anchored geosynthetic systems (AGS) on stability of slopes under seepage condition using a centrifuge modeling technique. A series of centrifuge tests were carried out at 50 g on unreinforced and AGS slope models, using a centrifuge container equipped with seepage flow simulator. AGS slope models were tested by varying slope inclination, number of anchors and keeping inclination of anchors as constant. The water was allowed to seep through the model slopes during flight at 50g. Ground anchors were modeled as drilled pre-tensioned anchors using sand epoxy mixture, polyester strand and a plastic tube. An anchor inclination of 15 degrees with the horizontal was adopted for AGS slopes. A layer of geocomposite was used for modeling geosynthetic component of anchored geosynthetic systems. All models were instrumented to measure surface settlements and pore water pressure within the slope at onset of seepage during centrifuge test. A digital image analysis technique was adopted to trace displacement vectors of plastic markers embedded toward the front elevation of the model and plastic markers glued to facing during model construction. Analysis and interpretation of centrifuge model test results indicate that the stability and deformation behavior of slopes, under seepage conditions, can be substantially improved using anchored geosynthetic systems. With an increase in slope inclination and reduction in number of anchors, surface settlements and face movements were observed to increase substantially. Further, stability analysis results on the unreinforced and AGS slope models were found to be in good agreement with those of physically observed centrifuge test results. (C) 2012 Elsevier Ltd. All rights reserved.

Application of pre-stress on strand wires inside a structure is a way to reinforce the low tensile strength of concrete and soil materials. After years in service, the strands may lose the pre-stress due to corrosion or other reasons endangering the whole structure. Since there is no accessibility to the strands inside the structure, any inspection should be conducted on the anchor head. In this study, elastic waves on the anchor head are numerically simulated. Parameters like the wave amplitude and propagation time are influenced by the stress of the strand wires which affects the contact between the threaded steel rod, and the surrounding anchor head influencing the acoustic impedance mis-match on the interfaces. The change of contact pressure between the strands and anchor head is simulated by modifying the rigidity of a model interphase material. Results are compared with experimental under different levels of pre-stress. Therefore, an easy and fast procedure for non-destructive inspection of the pre-stress load on the strands is discussed.

With the purpose to develop a fast procedure of intervention for stabilising earth slopes, a new retaining structure system taking advantage of prefabrication, post-tensioning technique, high-performance concrete and steel fibres was designed. The retaining structures is constituted of four framed precast panels and ten slabs used as external contrast for ground anchors. The paper describes the design, the on site placement phases and the GPRS monitoring of the structure during the first twenty four months. The on site behaviour of the whole retaining structure has been monitored by means of fourteen loading cells used to measure the strand forces, forty-two vibrating wire transducers for the surface strains and several optical measures used to control the rigid movement of the structure. The experience is part of a larger research project aimed at investigating the soil-structure interaction and improving the current techniques employed to stabilize ground slopes.

The research work reported in this paper involves investigation of the tensile behavior of fiber-reinforced polymer (FRP) ground anchors. Variables of the tests on the anchor models were anchor fixed length, tendon type, and tendon constituent. Sixteen monorod and four multirod grouted aramid FRP (AFRP) (Arapree and Technora) and carbon FRP (CFRP) (CFCC and Leadline) anchors were tested according to standard methods of tensile tests and sustained load tests under different load levels. Test results indicated that AFRP Arapree and Technora monorod anchors showed higher displacement and slip in comparison with CFRP CFCC and Leadline anchors. Technora anchors failed because of the detaching of winding fibers from the core of the rod. CFRP anchors had a higher tensile capacity and lower creep displacement than AFRP anchors. All the tested CFRP monorod and FRP multirod anchors with a 1,000-mm fixed length appeared to have an acceptable tensile behavior according to existing codes. Creep behavior appeared to co...

The ultimate pull-out tensile load of ground anchors is strongly dependent onsoil nature,grout injection and effective stress state around the bulb. In this paper, the comparison between the results of conventional pull-out testson instrumented anchors built in a flysch formation and those of small scale pull-out tests performed in the laboratory,on undisturbed soil samples recovered at the depth of the anchor bulb,allowed to closely examine the skin friction that can be mobilizedin undrained conditionsat the soil-structure interface. The experiments highlight a strong scale effect, probably depending on the real size androughness ofthe lateral surface of the bulb. In fact, theirregular bulb profiledue to flysch features strongly contributes to the pull-outstrength.

The results of a full scale investigation on instrumented anchors, bored through a typical pliocenic stiff clay formation, are reported and analyzed. The variation with depth of the normal stress in the reinforcement bars, found to be non-linear up to failure load, is predicted by a non-linear numerical analysis of the interaction among the reinforcement, the grout mortar and the surrounding soil taking into account the cracking of the mortar. The best correlation with experimental results, however, is obtained with values of soil and mortar properties somewhat different from laboratory values.A similar correlation of load-upheaval curves has been obtained, by the same analysis and with the same values of parameters, only for the first stage of the curves and not for the final stage, near to failure load.This inconsistency is discussed, pointing out the need for further theoretical and experimental investigations.