Anchor Body Research Articles

Introduction of an optimised dynamic installation anchor via model test and numerical analysis: Freefall in the water column

This paper introduces a novel shaped dynamically installed anchor (called ‘maverick anchor’) with optimised geometric components (tip, shaft, and fins). The performance of the maverick anchor in terms of hydrodynamic characteristics (terminal velocity, hydrodynamic drag, and directional stability) obtained through freefall drop tests in water and Computational Fluid Dynamics (CFD) analyse was compared with that of existing dynamically installed anchors used in offshore Brazil and in the Gulf of Mexico. Freefall drop tests on model anchors were performed in a 1.56 m depth water tank at UWA. Freefall motions of the anchors were filmed mounting two cameras, and subsequently quantified using Python code. In testings, geometric similarity was ensured between the model and prototype. CFD analyses were then carried out on the corresponding field scale anchors using Ansys/Fluent, fixing the anchor at a particular location, and flowing the water column with a velocity. Numerical analyses ensured similarity in Reynolds number. Results have confirmed that compared to the commercially used dynamically installed anchors, the maverick anchor can attain a higher terminal velocity, and the corresponding drag coefficient is lower due to smooth fluid flow along the anchor body. The verticality or lateral stability during the freefall was also promising.

Grouting sleeve/bird’s nest anchor cable anchoring capacity characteristics and numerical simulation study

With the deepening of coal mining resources, the safety issues of broken soft coal seams become increasingly prominent, severely affecting the safety of deep mining operations and workers. Traditional anchoring methods alone are ineffective in achieving secure anchorage. Therefore, the grouting anchor cable composite structure is explored to address the safety of roadway excavation in deep broken soft coal seams. Indoor grouting anchorage tests and pull-out tests for grouted anchorages are conducted to study their bearing characteristics and failure mechanisms. Discrete element numerical simulation methods are employed to verify the findings from indoor tests. Research indicates that the ultimate pull-out forces at grouting pressures of 0.5, 1.0, 1.5, and 2.0 MPa are 87, 104, 118, and 131 kN, respectively. The pull-out force of the grouted anchorage is positively correlated with the grouting pressure. At the loading end, shear stress and axial force reach their maximum values of 1.8 MPa and 106 kN, respectively, under 2.0 MPa grouting pressure. The distribution patterns of shear stress and axial force decrease gradually with increasing anchoring depth. Microscopic analysis reveals that the failure of the anchor body model is primarily due to the tensile cracks formed by the particle flow code in two dimensions. This finding is consistent with the failure mode observed in indoor tests, which involves the slip and debonding failure of the anchor cable. Crack evolution is categorized into three stages: initiation, continuous propagation, and anchor failure. As the inter-particle contact forces within the anchor body model decrease, the region of chain fracture expands. These results provide technical support for understanding the bearing characteristics of grouting anchor cable composite structures.

Study of the static response and zoning of the existing tunnel adjacent to the suspension bridge's tunnel-type anchorage

Due to the ability to utilize the strength of the surrounding rock to enhance bearing capacity, tunnel-type anchorages have been consistently utilized in suspension bridges. Nevertheless, a close interaction occurs between the tunnel and the tunnel-type anchor when a highway tunnel is connected to a suspension bridge. This study employed numerical simulation and theoretical analysis based on the G317 Line Huangjiayuan tunnel and Zipingpu Bridge tunnel-type anchorage project, focusing on this specific type of adjacent engineering. Firstly, the discriminant degree of adjacent influence suitable for the interaction between the tunnel-type anchorage and the tunnel structure is established. The calculation conditions are distinguished by the influencing factors determined in the discriminant. The interaction law between tunnel-type anchorage and pre-built tunnel structure is further obtained. Using the method of curve regression, based on the criterion of proximity influence degree, the partition of mutual influence degree between the tunnel-type anchorage and the tunnel structure is obtained. At the same time, it is concluded that under the original design condition, the displacement degree of the tunnel structure will be greatly affected, and the tunnel structure is located in the strong influence area. According to the partition result, under the benchmark engineering geological condition, it is suggested that the angle of intersection between tunnel anchorage and tunnel structure should be increased to 3.3° and the anchor body inclination should be increased to 44°.

Mechanical properties of partially bonded rock anchors in squeezing large-deformation soft rock tunnels

Partially bonded rock anchors are crucial structural tunnel support elements whose effectiveness depends on their interactions with the surrounding rock. This study combined laboratory experiments and numerical simulations to examine the mechanical behavior of partially bonded rock anchors under pull-out tests, focusing on the influence of bonded lengths. The axial strain of the anchor body and the vertical strain of the concrete block along the anchor axis were tested using distributed optical fibers. The results indicated that the anchor body stress remained relatively constant in the unbonded sections but gradually decreased as the depth into the bonded section increased. Simultaneously, the significant compressive stress range induced by the rock anchor in the concrete block decreased rapidly as the bonded length increased. Subsequently, the effects of different bonded lengths, unbonded section positions, and bonding combinations on the mechanical behavior and support effectiveness of partially bonded rock anchors in highly stressed soft rock tunnels undergoing substantial deformation were investigated using numerical simulations in ABAQUS. These findings suggest that rock anchors with longer bonded lengths have better control of the rock between the anchors. Simultaneously, the maximum axial stress of rock anchors tended to increase with longer bonded lengths. The rock displacement tended to be obviously larger when the unbonded section was set at the end of the rock anchors compared with when the unbonded section was set in the middle. The rock displacement was larger when the unbonded section was set at the outer end of the rock anchors, indicating that setting unbonded sections near the tunnel wall was detrimental to controlling rock deformation while improving structural safety. Setting one unbonded section near the tunnel wall and another unbonded section in the middle of the rock anchors resulted in excellent structural safety and rock deformation control. Furthermore, fully bonded rock anchors were compared with partially bonded rock anchors based on suitable bonding combinations in the deformation section of Muzhailing Tunnel. The results indicated that the fully bonded rock anchors experienced axial forces exceeding the yielding load in the early stages of support, with noticeable early yielding of the anchor plate. In contrast, the unbonded sections in the partially bonded rock anchors did not yield in either the bonded anchor body or the anchor plate. Partially bonded rock anchors exhibited better overall stability and reliability under high-deformation tunnel conditions.

In-Situ Test and Numerical Simulation of Anchoring Performance of Embedded Rock GFRP Anchor

Compared to traditional steel reinforcement, GFRP anchors demonstrate outstanding mechanical performance and corrosion resistance, and so they are an ideal substitute for steel reinforcement in anti-floating projects. Based on finite element software, a 3D axisymmetric calculation model of GFRP anti-floating anchors in medium-weathered granite was established in this paper. Combined with the in-situ ultimate pull-out tests, the bonding anchoring performance and bearing characteristics between the anchor body, anchoring mortar, and rock–soil mass were analyzed. The research findings indicated that the cohesive bonding elements exhibited a high degree of conformity in defining the interface contact relationship of the GFRP anti-floating anchor anchoring system. The axial force of the GFRP anti-floating anchor body is “attenuated” along the depth direction, and there was a critical value of anchoring length; under the same conditions, the reasonable anchoring length should be 3.5~5.0 m. All the anchors in the in-situ tests exhibited interfacial shear slip failure between the anchor body and the anchor mortar, with an average maximum load of 450 kN, which is consistent with the maximum failure load of the simulated anchors. Compared to a load of 50 kN, the maximum stress of the anchor mortar increased by 50% under a load of 450 kN. The displacement variation of the surrounding rock–soil mass showed a decreasing trend from the inside to the outside and from the top to the bottom. The research results provided valuable references for the optimization design of GFRP anti-floating anchors.

Numerical simulation of mechanical characteristics and tension-torsion coupling effect of tension-type anchor cable

PurposeThe purpose of this paper is to simulate the tension process of tension-type anchor cable and to explore the mechanical characteristics and tension-torsion coupling effect of anchor cable subjected to tension.Design/methodology/approachABAQUS numerical software is applied to construct the numerical models of tension-type anchor cables with different diameters. Through explicit contact, the characteristics of contact between grouting body-anchor cable and grouting body-rock mass are determined. Confining pressure is applied to the model through surface pressure, and drawing force is applied to the model by displacement loading so as to simulate the tension process of the anchor cable.FindingsThe results show that the stress is transmitted in both axial and radial directions in the anchorage section and distributed in a cone. The shear stress in the grouting body is unevenly distributed, and its peak value increases with the rise in confining pressure and anchor cable diameter. The stress characteristics of torque and axial force are basically consistent and evenly distributed in the free section; they gradually decrease in the anchorage section. Due to the tension-torsion coupling effect, the internal stress characteristics of the anchor cable structure vary. On average, the anchorage performance of each anchor cable model is improved by 6.19%.Originality/valueThe proposed method of numerical modelling is effective in addressing the interface contact between the anchor cable and the grouting body and in solving the problem with convergence of calculation. Compared with the indoor test, this method is more suited to collecting the internal mechanical data of the anchor body.

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.

Numerical study on the performance of a novel gravity installed anchor with ring fins in clay

A novel gravity installed anchor with ring fins (RGIA) is proposed in the present work, which combines features of the conventional gravity installed anchor (GIA) and the drag embedment plate anchor, with two soft shanks attached to the anchor body. A systematic study on the performance of the RGIA in clay is performed by large deformation finite element analyses using the coupled Eulerian-Lagrangian technique (CEL), with emphasis on the initial penetration, the behaviors of keying, diving and pulling out, the optimization of the shackle point, and the effect of loading rates on the maximum embedment loss (MEL). The initial penetration of the anchor is simulated under various impact velocities, from which the maximum initial embedment depth in the seabed is acquired. Two factors of the shackle point, en and eh, are defined and the detailed criteria for optimizing the shackle point are put forward. A series of analytical cases are designed to thoroughly explore the effects of the shackle point on the performance of the RGIA in clay, focusing on the keying and diving behaviors and the pullout capacity. The formulas for calculating the diving angle and the MEL are then constructed with high precision, by taking into account the effect of the shackle point, and can be utilized to optimize the position of the shackle point. Comprehensive drag effects under multiple factors, especially the high loading rate, on the performance of the RGIA in clay are quantitatively investigated by performing six groups of cases, from which the effects of drag velocity, initial embedment depth, gradient of shear strength of clay, and cable parameters can be known. The formula for calculating the MEL of the RGIA in clay is also constructed with high precision by taking into account comprehensive drag effects. The numerical study demonstrates that, compared with the OMNI-Max anchor, the RGIA achieves deeper initial penetration depth during installation, requires shallower initial penetration depth that ensures subsequent keying and diving, and possesses stronger ability of resisting dynamic loading with high loading rates.

Field study on behavior of load distributive compression anchor installed in weathered rock and soft rock

As a load distributive compression anchor (LDCA) consists of multiple anchor bodies and unbonded tendons, the load applied to the tendon is transmitted to grout and ground by the movement of each anchor body installed along the anchor length. Therefore, the load transfer behavior of LDCA is affected by the interference between adjacent anchor body, and the effect of multiple anchor bodies should be considered in the LDCA design. This study performed a series of pull-out field tests on LDCAs installed in soft rock. LDCAs were designed to have various number and spacing of anchor bodies to investigate the effect of multiple anchor bodies. Furthermore, the test results were compared with the results of pull-out field tests conducted on weathered rock to examine the effect of ground conditions. The load-displacement relationship showed that the grout failure occurred in the LDCA installed in soft rock, and thus the ultimate bearing capacity was smaller than that of the LDCA installed in weathered rock. Additionally, the grout axial load distribution indicated that the LDCA installed in soft rock expressed tensile stress in the grout due to the effect of multiple anchor bodies leading to the tensile failure on the grout.

Field test and numerical simulation of initial support effect of negative Poisson's ratio anchor cable under strong impact and vibration

Bolt/cable support technology is widely used in the rock engineering protection field to limit large deformations of surrounding rocks, improve the anti-explosion and anti-impact mechanical properties of engineering rock mass, and increase stability and safety. The underground protective cavern suffers significant damage due to the powerful impact produced by the explosion. This paper studies the macro static and dynamic mechanical properties of the negative Poisson's ratio (NPR) constant resistance and large deformation anchor cable. In addition, an in-situ blasting test scheme is proposed to simulate the approximate plane wave generated by a nuclear explosion in the field. Hence, the anti-explosion and anti-impact properties of the NPR anchor cable support system and failure mode of ternary structure (rod body, anchor body, and rock mass) under explosion influence can be obtained. Finally, numerical modeling is utilized to validate the NPR anchor cable support and PR anchor bolt support under the high vibration condition with the same blasting equivalent. The findings showed that the cavern supported by the NPR anchor cable revealed better overall stability under strong impact and vibration than the PR anchor bolt.

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.

Development of a Novel Hybrid Suture Anchor for Osteoporosis by Integrating Titanium 3D Printing and Traditional Machining.

The aim of this study is to develop a titanium three-dimensional (3D) printing novel hybrid suture anchor (HSA) with wing structure mechanism which can be opened to provide better holding power for surrounding osteoporotic bone. A screw-type anchor (5.5-mm diameter and 16-mm length) was designed with wing mechanism as well as micro dual-thread in the outer cortex bone contact area and macro single-thread in the anchor body. Both side wings can be opened by an internal screw to provide better bone holding power. The suture anchor and internal screw were manufactured using Ti6Al4V 3D printing and traditional machining, respectively. Static pullout and after dynamic 300-cyclic load (150 N) pullout tests for HSA with or without the wing open and commercial solid anchor (CSA) were performed (n = 5) in severely osteoporotic bone and osteoporotic bone to evaluate failure strengths. Comparison of histomorphometrical evaluation was performed through in vivo pig implantation of HSAs with the wing open and CSAs. The failure strengths of HSA with or without the wing open were 2.50/1.95- and 2.46/2.17-fold higher than those of CSA for static and after dynamic load pullout tests in severely osteoporotic bone, respectively. Corresponding values for static and after dynamic load pullout tests were 1.81/1.54- and 1.77/1.62-fold in osteoporotic bone, respectively. Histomorphometrical evaluation revealed that the effects of new bone ingrowth along the anchor contour for CSA and HSA were both approximately 20% with no significant difference. A novel HSA with wing mechanism was developed using 3D printing and the opened wing mechanism can be used to increase bone holding power for osteoporosis when necessary. Better failure strength of HSA than CSA under static and after dynamic load pullout tests and equivalence of bone ingrowth along the anchor contours confirmed the feasibility of the novel HSA.

Investigation of the Bearing Characteristics of Bolts on a Coal–Rock Combined Anchor Body under Different Pull-Out Rates

In order to reveal the influence of the pull-out rate on the load-bearing properties of the coal–rock combined anchor body, the mechanical properties and failure characteristics of a coal–rock combined anchor body under different pull-out rates (10, 20, 30, 40, 50 mm/min) were studied using the pull-out test and theoretical analysis. The results show that the bearing capacity of the bolt on the coal–rock combined anchor body improves under a dynamic load, but the load-bearing properties of the coal–rock combined anchor body are different from those of the full rock (coal) anchor body. With the increase in the pull-out rate, the maximum pull-out load of the bolt on the coal–rock combined anchor body increases first, then decreases, and finally tends to be stable. Under the condition of a low drawing rate, the bearing capacity of the coal–rock combined anchor system can be greatly improved, but when the pull-out rate exceeds 20 mm/min, the bearing capacity of the anchor system is reduced. The debonding process of the anchoring section of the coal–rock combined anchor body gradually expands from the beginning section of the anchor to the bottom of the borehole. The coal–rock combined anchor body undergoes time differential development of cracks, and the failure of the coal and rock mass occurs at different times. Its failure process can be divided into three stages: (1) the coal anchor and rock anchor act together; (2) the rock anchor acts alone; and (3) the coal anchor and rock anchor have residual action.

Numerical investigation on hydrodynamic characteristics of a novel gravity installed anchor with ring fins

A novel gravity installed anchor (GIA) is proposed in the present work, which combines features of the GIA and the drag embedment plate anchor, with a ring fin attached to the anchor tail during free fall to enhance the directional stability and separated from the anchor body when penetrating the seabed. A systematic numerical investigation on hydrodynamic characteristics of the novel GIA is performed by the computational fluid dynamics (CFD) approach to clarify the effects of the ring fin. First, different anchor shapes for the novel GIA are compared to acquire the optimum anchor body, focusing on the drag coefficient, terminal velocity and directional stability. Second, a set of orthogonal tests and three groups of cases are designed and performed to thoroughly investigate the effects of ring fin on the hydrodynamic characteristics, from which the effects of the radius, height and thickness of the ring fin can be known on the terminal velocity and the directional stability of the anchor. Finally, empirical formulas for calculating the restoration moment coefficient and the terminal velocity of the novel GIA are constructed with high precision and efficiency, by taking into account the effects of the ring fin, which can be used to determine the optimum dimensions of the ring fin. The numerical investigation confirms that the novel GIA possesses better directional stability and higher terminal velocity compared to the OMNI-Max anchor.

Arthroscopic Suture Anchor Design Finite Element Study

AIM: This in-vitro study investigated arthroscopic suture anchors’ main design parameters effect on surrounding bone. METHODS: Thirty-dimensional arthroscopic suture anchor designs’ models were created on engineering CAD software by changing thread profile, pitch, and anchor tip profile as design parameters. These models were imported into ANSYS Workbench for finite element analysis. Bone was simplified and modeled as two coaxial cylinders. Tensile vertical load of 300 N, and oblique at 45º to the vertical axis, were applied to each model as two loading conditions while the simplified bone base was fixed in place as a boundary condition. RESULTS: The finite element analyses on all models under both loading conditions showed stresses within physiological limits on bone. Trapezoidal teeth and inclined cut teeth designs showed the lowest values of stresses and deformations respectively on the bone under oblique loads, while curved tooth and square tooth designs showed the lowest values of stresses and deformations respectively on the bone under vertical loads. General ascending or descending trend was recorded by increasing pitch from 1.2 to 1.5 to 1.8 mm on the total deformation and maximum Von Mises stress on bone and anchor body. Tapered tip slightly increased bone and anchor stresses. CONCLUSION: Arthroscopic anchors thread profile has minor affect on cortical bone behavior. Trapezoidal teeth, square tooth, and inclined cut teeth profiles showed the lowest values of stresses and deformations on cortical bone. Increasing thread pitch of arthroscopic suture anchors increases or decreases stress on the bone, and anchor body according to thread profile edges. Anchor tip profile negligibly affects both deformations and stresses on bone and anchor body.

Load transfer mechanism of a load distributive compression anchor installed in weathered rock layer

The demand for a load distributive compression anchor (LDCA) in construction sites has been increasing, owing to its high bearing capacity and removable steel strands. As an LDCA comprises multiple anchor bodies and unbonded steel strands, the load applied to the strands generates a distributive compressive stress in the grout, preventing high concentration of grout–ground shear stress. Unlike in the conventional anchors, in an LDCA, independent load transfer of each anchor body induces interference effect between adjacent anchor bodies. Therefore, for an efficient design of an LDCA, it is necessary to investigate the load transfer mechanism considering the effect of multiple anchor bodies. In this study, a series of anchor pull-out field tests was conducted for LDCAs consisting of a single anchor body, and double and triple anchor bodies spaced by 1, 2, and 3 m. According to the test results, the LDCA showed a stiffer load–displacement behavior with an increase in the number and spacing of the anchor bodies. The multiple anchor bodies of the LDCA generated an overlapping of the grout axial load and induced its rapid dissipation, increasing the grout–ground shear stress. This interference effect was more clearly observed with a decrease in the anchor body spacing.

A Penetrating-Anchoring Mathematical Model for the Soft Asteroid Anchoring System

The asteroid landing mechanism is necessary to be anchored to avoid flowing away. At present, the study on the anchoring system is mainly focused on the mechanical design, but there are few researches on the penetrating or anchoring mathematical model, and the researches on combining two models with each other are even more lacking. In the paper, based on the characteristics of Mohr-Coulomb material, a penetrating mathematical model of the anchoring system is established. This penetrating mathematical model can be used to calculate the penetrating depth of the anchor body according to the penetrating speed and the medium properties. Secondly, an anchoring mathematical model is established, which shows the relationships among the anchoring force, medium properties, and penetrating depth. Finally, a penetrating-anchoring mathematical model is built with the penetrating depth as the link. The model establishes a relationship between the anchoring force and the initial penetrating conditions.

Experimental Study of the Failure Mechanism of the Anchorage Interface under Different Surrounding Rock Strengths and Ambient Temperatures

In order to study the anchoring instability mechanism of surrounding rock in deep roadway, the failure mechanism of the bolt‐anchoring agent interface was studied by simulating different strength rock mass and ground temperature environment, using C20, C40, and C60 strength concrete and steel pipe to simulate different surrounding rock strength environments. Indoor pull‐out tests were carried out to study the pull‐out load displacement relationship, ultimate pull‐out force, residual anchoring force, the distribution law of axial stress and tangential stress along the bar, and the energy consumption value of drawing failure at 20, 50, and 70°C. The test results show that, with the decrease of surrounding rock strength or the increase of ambient temperature, the pull‐out force, residual anchoring force, and energy consumption value of anchorage interface gradually decrease; under different axial forces, the axial force distribution of the rod body decreases exponentially from the anchoring end to the opposite end; and the shear stress transfers to the deep part of the anchor body with the increase of the load. According to the failure phenomenon of the specimen, the failure modes of the bolt bolt‐anchorage agent interface can be divided into shear slip mode and shear expansion slip mode. The shear expansion slip formula of anchorage interface is derived. Using high‐strength and temperature‐resistant resin anchoring agent for comparative test, the rationality of the mechanism analysis is proved, which provides more clear guidance for the construction of anchor support.

Laboratory Model Test Research on Mechanical Characteristics of Anchor in Loess Tunnel under the Action of Pull‐Out Load

The deformation mode of loess surrounding rock of anchor under the action of pull‐out load and the shear stress distribution law of loess anchor and loess interface under the condition of different lengths anchor are studied by using the laboratory self‐made model test chamber and micro anchor pullout instrument. A total of three tests are carried out for the selected test anchor. Three deformation modes of loess surrounding rock under the action of pull‐out load are obtained according to the test results. It is proposed that the maximum shear stress of loess anchor under the action of pull‐out load appears in the section 25 times the anchor diameter from the anchor head, and the shear stress in the middle and rear part of the anchor body can only be brought into full play when the length‐to‐diameter ratio of the anchor body is 110 or more. Based on the displacement solution of Mindlin problem, the drawn conclusion is compared with the theoretical solution of shear stress and axial force of loess anchor under the action of pull‐out load. The results compared are basically consistent, indicating that the conclusion has strong engineering practice, which can provide technical basis for the design and optimization of the system anchor in the sidewall of loess tunnel.

Strain Response of Tunnel Anchor Using Rayleigh Scattering-based Optical Fiber Sensing Technology in the Field Test

Tunnel anchor is a relatively new type of anchor for suspension bridges. Loading tests on a scale model in site are generally considered to be the most direct way to evaluate the bearing capacity of the tunnel anchor system. The response of the anchor body has received minimal attention and involves only a few or no measuring points, because the anchor plug does not undergo elastoplastic failure in a model test. This article intends to explore the relationship between the strain response of the anchor and the state of the surrounding rock. Optical fiber strain sensing technology based on adjustable wavelength optical time domain reflectometry (i.e., TW–COTDR) was applied to the scale model test of Baotaping Bridge tunnel anchor. The strain distribution and evolution of the entire anchor body were determined by optical measurements during overload. In the elastic and plastic stages of the anchor system, the strain around the anchor body linearly decreased from back to front, except for the top arch and the bottom plate at the end. The anchor strain–load curve was nonlinear, similar to the displacement–load curve, but unrelated to concrete damage, which signaled that plasticity began to appear in the anchor system. Therefore, the strain response of the anchor body can be used as an alternative to determine bearing capacity of the anchor system, especially when the displacement is too small to observe.