Ground Anchors Research Articles

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.

Study on safety assessment methods of gravity anchors based on a simplified mechanical model

Gravity anchor blocks are a common type of ground anchor used for suspension bridges, whose bearing depends on its large body and gravity. As there is no stratum requirement, the safety of the anchor block is important for bridge stability. This study summarizes all available estimation indexes, calculating methods, and evaluation criteria for gravity anchor block safety for the Ruili bank of the Banjin Dam grand suspension bridge. The anti-overturning, anti-sliding, base stress, and deformation safeties were comprehensively evaluated using methods including the suggested specification method (SM), simplified mechanical method (SMM), and finite element method (FEM), the results of which were compared and analyzed. The reasons for errors and improved formulas and working conditions were presented. The main conclusions were as follows. 1) The methods for calculating different evaluation indexes according to specifications lack consistency. Moreover, FEM requires that designers have good computer skills and has low feasibility in practice. 2) The SMM for gravity anchor block safety estimation as described in this study, whose indexes cover systematic and overall, the computational formula is simple and speedy, with relatively conservative results and good practicability. 3) SM, SMM, and FEM were all used for the safety estimation of gravity anchor blocks in Ruili bank. The anti-overturning and anti-sliding stability coefficients must all meet the specification requirements of 2.0. SM cannot be used to estimate the base tensile stress under limited conditions. SMM denoted tensile stress at 2.5 times the main cable design force, compared to 3.2 P for FEM. Deformation calculation methods are not given by SM, but can be suggested by SMM based on the elastic mechanics. The horizontal displacements under design load conditions were 122 mm (SMM), 108 mm (FEM), and 44 mm (composite foundation treated by root piles), with a safety standard of <80 mm. The vertical displacements were 338 mm (SMM), 110 mm (FEM), and 123 mm (composite foundation treated by root piles), with a safety standard of <160 mm. These findings proved the feasibility of SMM for the safety design of gravity anchor blocks in cases lacking regional experience.

Comparative Analysis of Riverbanks Retrofitting Planning Using Strauss Pile and Ground Anchor

This research was conducted to reinforce the sheet pile located on the embankment of the Ciliwung Lama river – Inspection Road (RSCM) in Central Jakarta. The road is beside the riverbanks of the collapsed river for 40 m and the position of the sheet pile that slopes towards the river. Based on field observations and analysis of the stability of the slopes carried out, the road’s collapse was not due to the unstableness of the embankment but due to the inability of the sheet pile to receive lateral soil pressure. The research method used Plaxis 2D Software to analyze the reinforcement applied to the sheet pile in withstanding lateral soil pressure. The planned reinforcement of the sheet pile uses a Strauss pile with a sling and ground anchor. In retrofitting, using a Strauss pile, a diameter of 0.4 meters, a length of 9 meters, and a sling with a diameter of D32 with a distance between slings of 2.5 meters. Ground Anchor retrofitting is planned to be 27 m long, 159 mm in diameter, and 88 mm in body grout. Compared to the Safety Factor that occurs between the Strauss pile with the sling and the ground anchor, the safety factor of the Strauss pile with the sling is greater. The Strauss pile’s safety factor was obtained by 1.75, while the ground anchor safety factor was 1.55 without considering the earthquake load.

Contact tensions under the sole of rigid deep laying foundations and ground anchors

Purpose. To solve the problem of the allocation of contact vertical normal tensions along the sole of a rigid round stamp, located in an elastic isotropic half-space at a certain depth h  0. To compare the obtained solution with the well-known classical result for h = 0, to check the obtained results for adequacy. Methodology. Based on the analysis of the decision on the stress-strain state of the base, inside which there is a vertical arbitrary load distributed over the area of the circle, the necessary formulas are obtained to solve the problem. An algorithm for constructing an approximate solution has been developed, the essence of which is to use a combination of the boundary element method and the iteration process by S.N.Klepikov. For a number of depths, approximate solutions of the considered problem are obtained. Findings. The proposed algorithm for the approximate solution of the problem of indenting a round rigid stamp into the upper boundary of an elastic isotropic half-space has good agreement with the exact solution and can be used to solve contact problems. The outlines of the contact stress diagrams depend on the depth at which they are determined – the greater the depth, the flatter the outlines of the diagrams are, while starting from a certain depth, the diagrams of contact stresses practically coincide. The greater the depth is at which the stamp is located, the more force must be applied to obtain equal displacements of the stamp. Originality. The obtained research results significantly expand the possibilities of solving various problems of soil mechanics and foundation engineering, make it possible to obtain absolutely new results. In particular, a clear dependence of the contact stresses along the sole of a rigid round stamp on the depth at which it is located was identified. In addition, the presented data allow us to designate an absolutely new direction in the calculation of the foundations of ground anchors, namely, the calculation of their deformations. Practical value. For engineering practice, it is important that the greater the value of Poisson’s ratio of the base is, the greater the contact stresses are, other things being equal.

Influence of ground anchors corrosion and uncertainty strength parameters: A case study slope failure in northern Taiwan

A significant fatal scale dip slope failure incident occurred at The Freeway No.3, located in Northern Taiwan, on April 25, 2010. From the post-failure investigations, it is found that the deteriorating anchor systems and uncertainties in strength parameters as the most likely the primary reasons for this slope failure. This study main conducted a numerical modeling work using Universal Distinct Element Code (UDEC), a two-dimensional numerical program based on the distinct element method for discontinuum modeling. First, the numerical modeling was generated to check the original design of this dip slope failure. Then a series of parametric studies were introduced to investigate the influences of the triggering design factors that affected this slope-failure event. The ground anchor failure order in this slope is also assessed by bracketing approach and strength-reduction method using a new term called “Adjusted Factor”. Furthermore, this study will focus on an anchors’ failure order from the perspective of the random field to assess whether the anchors’ failure mechanism considering the random field will match or be closely similar to the anchor failure order in the field.

Stability analysis of gravity anchor foundation of layered argillaceous sandstone under dry-wet cycles

Stability analysis of gravity anchor foundation of layered argillaceous sandstone under dry-wet cycles

Load-bearing performance of caisson-bored pile composite anchorage foundation for long-span suspension bridge: 1-g model tests

Load-bearing performance of caisson-bored pile composite anchorage foundation for long-span suspension bridge: 1-g model tests

Inclinometer and Improved SBAS Methods with a Random Forest for Monitoring Landslides and Anchor Degradation in Otoyo Town, Japan

Kochi Prefecture is located in an active zone of Japan that is frequently subjected to landslides due to heavy precipitation in typhoon seasons. Slow-moving landslides have been reported by both the local prefectural authorities and the National Government of Japan. We observed landslide movements in Otoyo Town by using ground- and satellite-based tools. Despite the high cost of establishing a borehole inclinometer survey to obtain accurate ground-based measurements, no previous InSAR study has been conducted in Otoyo Town, and the capacity for regional discrimination between active and inactive slow-moving landslides when using these tools remains unclear. We found that the horizontal velocity component was dominant at a rate of 21.4 mm/year across the whole of Otoyo Town. Satellite-based monitoring of ground-anchor efficiency may be possible in combination with ground-based inclinometer surveys. Three types of land cover are present in the study area—urban, field, and forests—and we selected a random forest (RF) model to extract low-coherence pixels by using optical and radar satellite sensors to identify important features and precisely remove pixels causing decorrelation. Long-term monitoring results from ground-based surveys, including inclinometer (boreholes) and anchor tension distribution data, were compared with the results of synthetic radar by using coherence-based small baseline subset (CB-SBAS) measurements. Generally, landslide occurrence was investigated across the whole of Otoyo Town, and we specifically evaluated the reliability of InSAR measurements in the Kawai landslide as a study site scale. The activity of the Kawai landslide channel was evaluated with borehole inclinometer displacement measurements (15.46 mm) and an anchor pressure survey (736 kN) from 2016 to 2019, as well as the steady state of the area (1.7 mm for the borehole inclinometer and 175 kN for the anchor pressure measurements), although a high cumulative precipitation of 3520 mm was reached during 2020 due to the ground anchor efficiency, which showed a consistent tendency with respect to the InSAR displacement measurements (14 mm during 2018 and 2019 and 0.7 mm during 2020). This comparison showed a consistent time-series displacement correlation, which was strengthened after introducing the RF mask into the analysis procedure, as the RF model correction reduced the standard deviation from the line-of-sight (LoS) average velocity estimation by 1.9 mm/year. Our research will help mitigate landslide impacts in Otoyo Town and its surroundings.

The efficiency of granular pile anchor foundation system in reducing heave of Irbid expansive clayey soil: An experimental investigation

This study is devoted to investigate the efficiency of granular pile anchor (GPA) in controlling heave of shallow foundations constructing over expansive soils. In this study heave measurements were made on laboratory model footings reinforced with GPAs having different diameter (3 cm, 4 cm and 5 cm) and embedded length (20 cm, 30 cm and 40 cm). The GPAs foundation system was constructed on expansive clay compacted in a steel box 60 cm in diameter and 70 cm in height. The measured percent reduction in heave was found to increase with increasing embedded length and diameter of GPA. The experiments conducted in this study showed that the percent reduction in heave when using GPAs may reach as high as 93 %. A theoretical formulation for the prediction of the percent reduction in heave was developed in this study. A comparison of the predicted percent reduction in heave using the developed formulation with the measured values in this study indicated good agreement and suggested that the proposed formulation in this study can be used to estimate the percent reduction in heave of shallow foundations constructing over expansive soils reinforced with GPAs.

Application of infrared thermography for estimating residual stress in ground anchors for maintenance

Characterizing the integrity of ground anchors is essential for examining their usability in the maintenance of soil structure. However, the lift-off test, which is generally used for this purpose, has limitations when applied to covering all installed ground anchors. The objective of this study is to assess the possibility of using infrared thermography to measure the residual stress in ground anchors as a noncontact technique that bypasses the disadvantages associated with existing techniques. A preliminary experiment is performed to determine the exact emissivity of the tested materials. Both passive and active methods, as representative techniques in infrared thermography, are applied. In the large-scale experiment, infrared images of four installed strands with growing stress in the range of 0–400 kPa at 100 kPa intervals are used in the passive method of measurement. For the active method, these same stress ranges are applied to a heated anchor head using a UTM machine. The results of the passive method show that the temperature increased and decreased according to load and unload steps. Values for the cooling rate index are deduced through the active method results, and reliable behavior are observed at 10 and 15 min. The number of pixels with huge temperature changes also changed with the loading step in both passive and active methods. This study demonstrates that infrared thermography is a suitable alternative method for assessing the residual stress in ground anchors as a type of noncontact technique.

Improvement of inclined anchors pullout capacity in geogrid-reinforced sand

A three-dimensional numerical analysis of inclined anchors embedded in unreinforced and geogrid-reinforced sand is presented in this paper. The pullout forces and breakout factors are compared for the unreinforced and reinforced cases. The pullout capacity increased when placed below a layer of geogrid reinforcement. The influence of several other parameters, such as geogrid stiffness, inclination angle, soil friction angle, and embedment ratio, are investigated and reported in this study. Finally, a comparison between pile and anchor foundation is shown for a transmission tower subjected to lateral wind force.

Influence of Water on Anchor Plate Behavior in Sandy Soil with and Without Improvement

Plate anchors are one of the most common types of ground anchors used in foundation systems, as they transfer loads from the foundation to the soil to prevent overturning the foundation and overcome the forces that could threaten the integrity of the structure. The present work concerns the study of the combined effects among the behavior of the anchor plate in sandy soil with and without water presence as a static state at a different head level (h=15, 30, and 40 cm) above the base of the anchor plate and for two states of the soil with improvement by geogrid at various location and without improvement. The soil sample was brought from AL-Nidaa district in the city of AL-Najaf (Iraq). The highest value of the ultimate uplift capacity is observed when the geogrid layer is adjacent to the anchor plate for dry and submerged cases of the soil. The negative effect of the presence of the geogrid layer appears when the water table level rises above the ground surface level.

Issues and verification of the effect calculation formula of ground anchor with the simplified Janbu method and the simplified Bishop method

Issues and verification of the effect calculation formula of ground anchor with the simplified Janbu method and the simplified Bishop method

Mechanical Behavior Analysis of Fully Grouted Ground Anchor in Soft-Hard Alternating Stratum

Assuming that the ground anchor is connected with the rock–soil of the sidewall by a tangential linear spring, the load transfer model of the fully grouted ground anchor is established by using the spring element method, and the analytical solutions of the displacement, axial force, and shear stress distribution of the ground anchor in the upper and lower parallel strata foundation and sandwich foundation are given, respectively. Corresponding to the above two kinds of alternating strata, the mechanical behavior of the vertical fully grouted ground anchor in the soft–hard alternating stratum is analyzed using the four conditions in Case 1 and the six conditions in Case 2, respectively. Through the case analysis, it can be concluded that the mechanical behavior of the round anchor is greatly affected by the shear modulus of the shallow stratum, and is less affected by the shear modulus of the deep stratum. The depth of the stratum interface and the thickness of the interlayer have some influence on the mechanical behavior of the whole ground anchor but have little influence on the displacement and axial force distribution of the ground anchor. This paper has certain guidance and reference significance for the design of vertical fully grouted ground anchors in the alternating strata.

One-Dimension Finite Element Modeling of Grouted Ground Anchor

In the present research work, a one-dimension finite element model has been developed to simulate both compression and tension types of grouted ground anchors. The steel tendon-grout interface has been modeled by using the local bond-slip model, while the soil-grout interface has been modeled with a series of perfectly elastic plastic springs. The verification of the proposed one-dimension finite element model has been made by comparison of the model results with a three-dimension finite element model developed by commercial finite element software PLAXIS, and with the results of field tests of tension-type grouted ground anchor. A parametric study has been made to study the load-transfer mechanism for both types of anchors, compression, and tension. The compression-type anchor exhibits less displacement than the tension one under the same applied load. The developed strain in the grouted body of the compression-type anchor is much smaller than the tension-type one, regardless of the type of strain.

Field tests of grouted ground anchors in the sandy soil of Najaf, Iraq

Abstract This article presents test results documentation for four grouted ground anchors embedded in sandy soil. Three anchors were trial, while one was a working anchor. One trial anchor is instrumented with eight resistance-type strain gauges glued on the corrugated pipe and embedded within the grouted body. An acceptance test was made for all anchors to determine the working load. Acceptance criteria suggested by the Post-Tensioning Institute were applied, and the working anchor did not pass the creep criterion, so it was taken out of service. The strain measurements indicated that the compression stresses were generated along the free length, while the tension stresses were generated along the bonded length. The transition point, which is the point with zero axial stress within the grouted body, was located at a distance of 10–12% of the bonded length, measured from the proximal end of the bonded length. The skin friction distribution along the grouted body was nonuniform, and it had a peak at the transition point. The maximum measured value of the skin friction is almost compatible with the estimated one by Fujita’s formula. The skin friction developed along the free length indicates a significant contribution of the free length to the pullout capacity.

Ultimate Uplift Capacity Relation of Plate Anchor Using Model Testing

Friction anchors are gaining popularity in civil structures. However, the bond length can be increased to use the friction between the ground and friction anchor body. They are often bonded deep in the ground and fixed to the bedrock; this causes problems, including the anchor overlapping the underground structure or invading the lower part of another structure when anchors are installed in downtown sites. Herefore, combination anchors that combine the advantages of plate anchors that resist uplift because of the ground's bearing capacity with a friction-type anchor have gained attention. However, the ground failure mechanism of plate anchors applied to combination-type anchors has not been accurately analyzed; therefore, various theoretical anchor uplift capacity formulas have been proposed. A model test was performed in this study by forming a sandy ground in a state of plane strain to verify the uplift capacity of the plate anchor installed at a shallow depth and ground failure mechanismPhotos obtained from experiment were evaluated to analyze the shape of the ground failure of the plate anchor. Furthermore, by classifying the depth of the installed anchor, an equation for calculating the ultimate uplift capacity of the plate anchor was proposed according to the classified depth. A model test was performed in this study based on the formation of a sandy ground in a state of plane strain to verify the uplift capacity of the plate anchor installed at a shallow depth and ground failure mechanism. Photos obtained from experimental tests were evaluated to analyze the shape of the ground failure of the plate anchor. Furthermore, by classifying the depth of the installed anchor, an equation for calculating the ultimate uplift capacity of the plate anchor was also proposed according to the classified depth.

Model Test of the Pull-up Capacity of Folding Type Ground Anchors in Cohesive Soil

The purpose of this research is to develop a folding anchor model, which is a modification of the star-shaped plate anchor, and to investigate the pull-up capability operating in cohesive soils. Physical testing is performed in the laboratory and on a full scale in the field, with the findings of the pull-up capacity achieved compared. The anchor model is made up of four leaves with varying widths and depths. It is flexible and may be closed and opened like an inverted umbrella. The effective area of each anchor was determined in laboratory experiments to be A1=30.00, A2=57.60, and A3=147.20 cm2, evaluated in a test column bath and filled with statically compressed, cohesive soil in four layers to a height of 30 cm. Each model was evaluated at three different depths: 30, 60, and 90 cm. The effective area of each anchor in field testing is B1=57.60, B2=147.20, and B3=600 cm2. The qualities of the soils chosen in the laboratory and in the field are identical. Each model was tested at three different depths: 100, 200, and 300 cm. The most resemblance to pull-up test results was found in laboratory and outdoor testing. The findings indicated that the area of each anchor model increased at each depth, resulting in a considerable rise in pull-up load. The change in depth of each anchor variation, however, did not result in a substantial increase in pull-up load. This implies that the folding type model anchors do not need extensive design. Each area change has a fundamental constraint in that adding depth will no longer result in a higher maximum pull-up capability. It also shows that these anchors are relatively simple to install in the field using basic tools without excavating or drilling the soil. Doi: 10.28991/CEJ-2022-08-09-07 Full Text: PDF

Self-inspection system for ground anchors monitoring on long-term load change

This study proposes a newly method for inspecting the load changes of ground anchors (or call smart anchor assembly). The smart anchor operates in a similar fashion to that of the tell-tale load cell in principle. It only requires the components used in a typical anchor assembly and consists of only one extra strand as the reference strand, which is not engaged on the anchorage. For this method, when the anchor load changes, the anchorage moves and a relative displacement between the reference strand and anchorage is generated. Based on the measured relative displacement and the characteristics of ground anchor, the change in anchor load can be approximately calculated. At the same time, by the use of linear potentiometer, data logger, power supply, and data transmitter, automating the self-inspection function of load monitoring can also be achieved. The reliability of automatic load monitoring capabilities of the smart anchor was confirmed by sensing tests performed on field anchors. It would reduce maintenance costs and the engineers can contribute their expertise to value tasks. Lastly, when there’s need to increase anchor loading, reference strands can also serve as restressing component. This can extend the service life of ground anchors and achieve the goal of sustainable development.

Calculation of the Overall Coordination Internal Force of the Grille Beam-Column under the Impact of Debris Flow

At present, the research on the new ground anchor counterfort grille dam is not perfect. In order to analyze and design the new grille dam accurately and reasonably, it is necessary to carry out theoretical research on the internal force calculation of the overall coordination of the grille beam-column under the impact of debris flow. Under the condition of full reservoir of debris flow, the grille beam-column meets the working principle of elastic foundation beam; therefore, the equation of the overall cooperative work of the grille beam-column is derived based upon Winkler’s theory of elastic foundation beam. Finally, combined with the engineering example, this calculation method is used for analysis; the results show that the bending moment of the grille beam-column increases compared with that regardless of considering the overall coordination, and the increased value of the bending moment at the bottom of the grille column and the middle of the grille beam is the largest. Therefore, from the perspective of safety, the overall coordination cannot be ignored when designing a blocking dam.