Ultimate Pullout Resistance Research Articles

Modelling the ultimate pullout resistance of geogrids

This paper provides a review of the modelling of geogrid ultimate pullout resistance. Several analytical models were found to disregard the effect of the geogrid stiffness as well as the particle size distribution of the soil. A sensitivity analysis was done on 289 pullout tests to evaluate the significance of these omitted variables as well as other key variables contributing to pullout resistance. It was found that ultimate pullout resistance was the most sensitive to normal stress followed by geogrid length, geogrid stiffness and the friction angle of the soil. By considering geogrid geometry, stiffness and soil grading descriptors, in addition to the standard variables of length, stress and friction angle, regression models of ultimate pullout capacity improved by 15%. In addition, an alternative model to the simplified linear models of FHWA and EBGEO which maintains dimensional consistency while incorporating geogrid stiffness and non-linearity in the model, was proposed. This alternative model performed 32% better than the simplified linear models.

Effects of cyclic loading on soil-geogrid interaction characteristics

The benefits of geosynthetic-reinforced soil systems over conventional earth-retaining structures are now well established. These reinforced systems are often subjected not only to static loads, but also to seismic and/or traffic loads, in which case the effects of repeated loading on soil-geosynthetic interaction characteristics should be properly considered. This study investigates the behaviour of a geogrid typically used for soil reinforcement under cyclic pullout loading through load-controlled laboratory pullout tests. To examine the influence of cyclic loading amplitude, number of cycles and static pullout force acting on the geogrid at the onset of cyclic loading, distinct loading patterns are considered. A well-graded residual soil from granite is used as backfill material. A comparison between the cyclic and monotonic pullout response of the reinforcement is then established in order to identify any potential strength loss attributed to cyclic loading. The experimental results show that the ultimate pullout resistance of the geogrid embedded in medium dense residual soil from granite may be adversely affected by cyclic loading. The cumulative cyclic displacements of the reinforcement are more pronounced during the initial loading cycles, but tend to stabilize with the increasing number of cycles when the soil is densely compacted. In the presence of dense soil, the cyclic strains of the geogrid specimen are particularly significant at the front section and almost negligible towards the back end.

Influence of Strengthened Nodes on the Mechanical Performance of Aeolian Sand–Geogrid Interface

Node thickening is a way to strengthen the nodes of a geogrid. Increasing the node thickness in conventional biaxial geogrids enhances the interface frictional strength parameters and improves its three-dimensional reinforcement effect. Based on the triaxial tests of aeolian sand, single-rib strip tests of geogrids, and pull-out tests of geogrid in aeolian sand, a three-dimensional discrete element pull-out model for geogrids with strengthened nodes was developed to investigate the mechanical performance of an aeolian sand–geogrid interface. The influences of increasing node thickness, the number of strengthened nodes, and the spacing between adjacent nodes on the mechanical performance of the geogrid–soil interface were extensively studied used the proposed model. The results demonstrated that strengthened nodes effectively optimize the reinforcing performance of the geogrid. Among the three node-thickening methods, that in which both the upper and lower sides of nodes are thickened showed the most significant improvement in ultimate pull-out resistance and interface friction angle. Moreover, when using the same node-thickening method, the ultimate pull-out resistance increase shows a linear relationship with the node thickness increase and the strengthened node quantity. In comparison with the conventional geogrid, the strengthened nodes in a geogrid lead to a wider shear band and a stronger ability to restrain soil displacement. When multiple strengthened nodes are simultaneously applied, there is a collective effect that is primarily influenced by the spacing between adjacent nodes. The results provide a valuable reference for optimizing the performance of geogrids and determining the spacing for geogrid installation.

Comparative analysis of anchor cables in pullout tests using distributed fiber optic sensors

The interaction mechanism between grouted anchor cables and the surrounding rock mass or soil are complicated and difficult to investigate using conventional monitoring technologies. This study focuses on the in-situ pullout behavior of grouted anchor cables using Brillouin Optical Time-Domain Analysis technique. A series of pullout tests were conducted on anchor cables with five different anchor lengths and three grouting methods. Distributed fiber optic sensors were used to measure the strain distribution of cable bolts from tip to top. The in-situ pullout test results show that both ultimate pullout resistance and ultimate displacement at the ultimate pullout resistance increase with anchor length. The bond strength suffers a slight variation with an increase in anchor length. Both ultimate pullout resistance and the ultimate displacement for Type-B grouting (grouting with reaming) and Type-C grouting (secondary grouting) are larger than those for Type-A grouting (one-time grouting). The shear bond strength of Type-C grouting is greater than that of Type-A grouting. Results from Gaussian functions analysis show that it is feasible to use the function to characterize the axial stress of anchor cables. Furthermore, the overall mobilized percentage η was evaluated. The anchor cables with smaller anchor lengths will result in greater η. The η for the anchor cables of 6 m reaches 92% at the last load, whereas the anchor cables of 18 m were mobilized by only 29% at the last load. The grouting method has a negligible effect on the η, increasing from 22% to 29% in process of the pullout test.

Numerical study on the pull-out behaviour of planar reinforcements with consideration of residual interfacial shear strength

Interface mechanics has always been a hot issue in geotechnical engineering, particularly in reinforced soil structures, but most existing numerical evaluations still used ideal elastoplastic models to predict the interaction of the reinforced soil surface, resulting in imprecise results. In this paper, based on a sophisticated analytical solution, a finite element analysis method was proposed for analysing the pull-out behaviour of embedded planar reinforcements considering the residual interfacial shear strength. In the numerical model, an improved cohesive element, which can precisely characterize realistic tri-linear shear slip models basing on a tabular function, was employed to simulate full-range progressive pull-out behaviour. Meanwhile, the parameters of the tri-linear shear slip model can be simply calibrated from pull-out tests using the proposed analytical solution, and the calibrated shear slip model can subsequently be used for modelling more complex problems. The finite element model was verified by two pull-out tests, and a parametric study was carried out for providing insights into the pull-out behaviour of embedded planar reinforcements. The results show that increasing the reinforcement length, the residual shear strength factor and the overburden pressure can improve the interface ductility and the ultimate pull-out capacity; Increasing the reinforcement stiffness improves the ultimate pull-out resistance increases but decrease the ductility.

Finite Element Analysis on Behavior of Single Battered Pile in Sandy Soil Under Pullout Loading

Batter piles are the piles driven in the soil at an inclination with the vertical to withstand oblique loads or large horizontal loads and have been widely used to support high buildings, offshore buildings, and bridges. These constructions are risky because of the exposure to moments and overturning resulting from winds, waves, and ship impact. A 3D FEA using PLAXIS 3D software was used to investigate the effect of several variables that affect the behavior of single batter piles under pull-out loads. The study is achieved on a steel pipe pile model embedded in a dry sandy soil with three relative densities (loose, medium, and dense) at different inclination angles and three embedment ratios, L/D of 25, 37.5, and 50, respectively. The numerical results showed that the ultimate pull-out resistance of the battered pile raise as the battered angle increases reaches a maximum value, then decreases. The ultimate pull-out load capacity of a single battered pile is directly proportional to the slenderness ratio and relative density; the ultimate pull-out load increases with the increase in the ratio of slenderness and relative density. The ultimate uplift load of the battered pile was less affected by the free-standing length. Vertical and battered piles at a battered angle of (10ᵒ and 20ᵒ) and free-standing lengths equal to zero have higher ultimate pull-out capacity; by increasing the free-standing length, the ultimate pull-out capacity decreased.

Experimental study on grouting mortar GFRP anchor rod pulling test

Owing to that the anchor rod is easy to be cut through and maintains good mechanical properties, it is widely used in reinforcement engineering. In this paper, the performance of grouted mortar GFRP anchor rod was studied through laboratory experiments in terms of the ultimate pull-out resistance, stress change, bolt deformation, and surrounding soil deformation. The results showed that the pull-out force suddenly decreased when it reached the ultimate pull-out load, the displacement of the anchor head increased sharply, and the axial force on the anchor rod body decreased exponentially with the distance from the pulling point. Through these regulars, it can provide a theoretical basis for the application of anchor rods in the actual foundation pit engineering.

Ultimate pullout capacity of single vertical plate anchors in sand

This paper presents a limit equilibrium solution for calculating the ultimate pullout resistance of shallow vertical plate anchors in sand, considering the combined effects of anchor embedment ratio, sand shear strength, sand-anchor interface strength and anchor aspect ratio. The geometry of the failure mechanism in the solution reflects observations from model tests. The ultimate failure load of a strip plate anchor was then determined by global equilibrium analysis of the passive and active failure soil wedge. The two-dimensional limit equilibrium solution is extended for rectangular plate anchors by introducing the shape factors of Ovesen and Strømann. The solution is compared with a database of 102 pullout model tests of vertical plate anchors in sand assembled from the literature and some limit analysis results. The comparison results suggest that the proposed solution can provide a reliable analytical tool for the ultimate pullout capacity prediction of shallow vertical plate anchors buried in sand.

The Joint Board Cable Foundation Ultimate Pullout Resistance Formula Derivation and Aided Program Design

As a new type of transmission line foundation developed by the author, joint board cable foundation has obtained an invention patent and has a good application in the transmission tower foundation of thick collapsible loess regions. The research on the ultimate tensile strength of the base plate will be the key to carry on this design. In order to do a better job in the general design of the base plate, the author starts with the research on the uplift resistance theory of joint board cable foundation, who has put forward uplift resistance theory of joint board cable foundation formula, simplified the formula, and derived the calculation formula of the uplift stability of joint board cable foundation. The author has calculated dimensionless coefficient by self-compiled program and has studied on the rationality of the simplified calculation formula. The results from the study indicate that the calculation formula of the uplift stability of joint board cable foundation is easy to use, dimensionless coefficient can be derived through using chinese procedure, the formula reduces the computational difficulty of lower plate uplift resistance, the rationality and accuracy of the formula are proved through the research on the rationality of the simplified formula.

Developing hybrid artificial neural network model for predicting uplift resistance of screw piles

The pull-out capacity of screw piles is affected by the complex underground and geological conditions, the helical pile’s configuration, and the penetration depth. Several experimental, theoretical, and neural network methods are available to predict the pull-out capacity of these piles. However, the weaknesses of ANN with regard to slow rates of convergence as well as in finding reliable testing outputs with reasonable errors are known to be major drawbacks of implementing ANN-based techniques. The present study aimed to develop an ICA-ANN-based model to estimate the pull-out capacity of screw piles in a simple way. A total of 36 experimental observations were collected and used to train, test, and optimize the ANN using an imperialist competitive algorithm (ICA). The developed ICA-ANN model can be considered an effective method for predicting the ultimate pull-out resistance of the helical screw piles since excellent agreement is obtained with respect to the reliability of the proposed model. The overall (training and testing) errors obtained for the proposed ICA-ANN model in comparison with the experimental data are 0.706, 0.17, and 0.996 for the mean absolute error (MAE), root-mean-square error (RMSE), and correlation factor (CF) respectively.

Investigations on pullout behavior of geogrid-granular trench using CANAsand constitutive model

Experimental and numerical investigations have been carried out on behavior of pullout resistance of embedded circular plate with and without geogrid reinforcement layers in stabilized loose and dense sands using a granular trench. Different parameters have been considered, such as the number of geogrid layers, embedment depth ratio, relative density of soil and height ratio of granular trench. Results showed that, without granular trench, the single layer of geogrid was more effective in enhancing the pullout capacity compared to the multilayer of geogrid reinforcement. Also, increasing the soil density and embedment depth ratio led to an increase in the uplift capacity. When soil was improved with the granular trench, the uplift force significantly increased. The granular trench improved the uplift load in dense sand more, as compared to the same symmetrical plate embedded in loose sand. Although it was observed that, in geogrid-reinforced granular trench condition, the ultimate pullout resistance at failure increased as the number of geogrid layers increased up to the third layer, and the fifth layer had a negligible effect in comparison with the third layer of reinforcement. Finite element analyses with hardening soil model for sand and CANAsand constitutive model for granular trench were conducted to investigate the failure mechanism and the associated rupture surfaces utilized. The response of granular material in the proposed model is an elastoplastic constitutive model derived from the CANAsand model, which uses a non-associated flow rule along with the concept of the state boundary surface possessing a critical and a compact state. It was observed that the granular trench might change the failure mechanism from deep plate to shallow plate as the failure surface can extend to the ground surface. The ultimate uplift capacity of anchor and the variation of surface deformation indicated a close agreement between the experiment and numerical model.

A state boundary surface model for improving the dilatancy simulation of granular material in reinforced anchors

It is acknowledged that for extending the experimental results to real scale design, it is necessary to use an appropriate numerical analysis. The good analysis in geotechnical problems needs to adopt a suitable constitutive model for the materials. This paper presents a modeling approach to investigate the complex behavior of granular trench and reinforcement system. For this purpose, an experimental and numerical investigation has been carried out on the behavior of pullout resistance of an embedded anchor (circular plate) with and without geogrid reinforcement layers in stabilized loose and dense sand using a granular trench. Different parameters have been considered, such as number of geogrid layers, embedment ratios, relative density of soil, and height ratios of granular trench. Finite element analysis with Hardening Soil Model was utilized for sand and CANAsand constitutive model was used for granular trench to investigate failure mechanism and the associated rupture surfaces. Results showed that, when soil was improved with the granular-geogrid trench, the uplift force significantly increased, but in geogrid-reinforced granular trench condition, the ultimate pullout resistance at failure increased as the number of geogrid layers increased up to the third layer, the fifth layer had a negligible effect in comparison with the third layer of reinforcement. The ultimate uplift capacity of anchor plate and the variation of surface deformation for all the tests indicated a close agreement between the experimental and numerical models.

Evaluation of the uplift behavior of plate anchor in structured marine clay

ABSTRACTThe uplift behavior of a plate anchor in a structured clay (soft Ariake clay) is investigated through a series of laboratory tests and method of finite element analysis. The tests are adopted to identify the factors influencing the behavior of the anchor, including the thixotropic nature of Ariake clay, consolidation time, and embedment ratio of the anchor. A finite element method (FEM) is used to analyze and predict the uplift behavior of the anchor plate well in the elastic region and the yield load. The results from both the laboratory tests and the FEM analysis suggest that the embedment ratio for a deep anchor in Ariake clay is close to 4. Further increase in embedment ratio improves the capacity to a lesser extent. FEM overestimates the failure load of the uplift anchor in soft Ariake clay by about 20%. This may be ascribed to the hypothesis in the FEM analysis that there is continuous contact between the clay and the anchor until failure. Vesic’s theory for deep anchors, which may be used to predict the ultimate pullout resistance of the plate anchor in reconstituted Ariake clay, is verified to be applicable. In this paper, the plastic flow zone around the anchor is discussed using FEM which makes the behavior of anchor more understandable during the design stage.

Novel strip-anchor for pull-out resistance in cohesionless soils

In this research, a novel reinforcing element is introduced. It includes a series of extra elements (anchors) that are attached to conventional steel strips. The new elements increase the pull-out resistance of the reinforcements and reduce the anchorage length. A total of 55 pull-out tests were performed to evaluate the pull-out resistance and optimum geometry of the new system. The effect of the anchor’s angle, length and spacing, as well as the influence of the dimensions of the cubic anchors on the coefficient of interaction ratio (CIRp) were investigated. The coefficient of interaction ratio directly affects the pull-out capacity – the number of anchors on the anchorage length. As a result, the pull-out resistance increased significantly with the addition of new anchors to the conventional reinforced strip. Test results indicated that the use of strip anchors increased the ultimate pull-out resistance under surcharge pressures of 50, 100, 120 and 150 kPa by factors of 7.4, 4.95, 4.3 and 4.3, respectively, in comparison with conventional strips. The finite element method (FEM) was also used to compare and verify the results of the experimental pull-out. It was observed that the results of the FEM were in good agreement with the laboratory test results.

A Comparison of Pull-Out Capacity of Suction Anchors in Clay and Sand

With the oil and gas exploitation develop to the deep sea; offshore platform under extreme environment load needs more stable anchorage foundation. Based on the slender suction anchor of SPAR, three-dimensional numerical analysis method was presented to study the ultimate pull-out capacity. Based on the geological conditions from South China Sea, clay and sand was selected as soil conditions to make a comparison analysis. The effects of soil type, load positions, load angles and aspect ratio on the ultimate bearing pull-out resistance of the suction foundation were studied. The comparison analysis results indicated that the ultimate pull-out resistance of suction anchors in sand has a greater rise rate and achieve ultimate pull-out capacity need smaller displacement than in clay; load point and load angles have a great impact on the resistance and there is a critical aspect ratio under inclined loading in sand.

Experimental, numerical and analytical study on conventional and innovative Grid-Anchor system in the pull-out test

With increasing use of geosynthetic applications in earth structures the need to develop more efficient reinforcement elements becomes evident. In this paper a conventional and an innovative geogrid system (named Grid-Anchor) are tested. The Grid-Anchor system consists of a conventional geogrid with anchors attached to it. The pull-out test has been used to highlight the capabilities of the product. Experimental investigation along with numerical studies using a finite element computer code was carried out. It was found that the ultimate pull-out resistance of a Grid-Anchor is more than that for an ordinary geogrid. Analytical study has been performed and the effect of an anchor group on the ultimate resistance of a geogrid was investigated.

얕은 지압형 앵커의 인발거동특성에 관한 실험적 연구

앵커는 지중에서 힘을 받는 형태에 따라 마찰형 앵커, 지압형 앵커, 마찰지압병용형 앵커로 나눌 수 있으며 최근에는 두 가지 형태가 복합적으로 사용되어지는 앵커가 개발되고 있다. 지압형 앵커에 관하여도 많은 연구가 진행 되었지만, 파괴면을 직접 관찰한 예는 적었다. 그리고 지반재료도 주로 실제 모래가 아닌 탄소봉등을 이용하여 실험을 한 것이 대부분이다. 본 연구에서는 토조에 모래지반을 형성하고, 지압형 앵커를 토피비(H/h)에 따라 1~6까지 나누어 설치하고 각 토피비에 따른 인발력과 지반의 거동을 관찰하였다. 또한 지반변형해석 프로그램을 통해 지반 변위, 무신축 방향, 최대전단변형률 등고선에 대해서 분석하였다. 분석결과 극한 인발력의 발현시점인 변위 5mm에서는 파괴면의 폭이 기존의 이론보다 좁은 영역에서 진행되는 것을 관찰 할 수 있었고, 10, 15mm까지 변위가 증가할수록 파괴면의 폭이 넓어지고 지표면까지 확장하는 것을 확인할 수 있었다. Depending on the underground load support mechanism, anchors are classified as friction anchors, bearing plate anchors and the recently developed combined friction-bearing plate anchors which combine the characteristics of both the friction and bearing plate type anchors. Even though numerous studies have been performed on bearing plate anchors, there were only few studies performed to observe the failure surface of bearing plate anchors. Furthermore most of the soil materials used on these tests were not real sand but carbon rods. In this study, sand was placed in the soil tank and laboratory tests were performed with bearing plate anchors installed with an embedment depth (H/h) ranging from 1~6. The variation in the pullout capacity and the behaviour of soil with the embedment depth (H/h) were observed. Ground deformation analysis program was also used to analyze soil displacement, zero extension direction, maximum shear strain contours. It was determined from the analysis of the results that at ultimate pullout resistance the deformation was 5 mm and the failure surface occurred in a narrower area when compared with results of the previous researches. It was also observed that the width of the fracture surface gradually becomes wider and expands up to the surface as the deformation increases from 10 mm to 15 mm.

Comparative Study on Ultimate Pullout Resistance Test and Theoretical Derivation of Flexible Pressurized Anchor with Numerical Simulation Result

The study on anchorage characteristics of flexible pressurized anchor should be along with theoretical analysis, numerical simulation and test study. Through comparing three calculation results, it is concluded that the theoretical analysis and numerical simulation can authenticate the correctness of calculation process each other; After considering the situation that friction coefficient changed with different contact pressure stress, the deviation of calculation of theory derivation and numerical simulation with experimental results significantly reduced; Anchor was simplified for anisotropic composite material body, which should be able to better reduce deviation among test, theoretical derivation and numerical simulation calculation.

Pullout behavior of cell-type tires in reinforced soil structures

A series of field-scaled pullout tests were carried out to investigate the pullout behavior of cell-type tires in reinforced soil structures. It is difficult to perform laboratory-scale pullout tests due to the size and geometry of the cell-type tires. Therefore it was necessary to perform field tests. The purpose of the field tests carried out in this study was to investigate the effects of surcharge height, effective anchorage length, tires connection materials, and the number of tires on the pullout behavior of cell-type tires. The ultimate tensile strength of cell-type tires was determined for the design and construction of reinforced soil structures. For comparison, pullout testing of the commercially available geocell was also conducted. The pullout resistance of cell-type tire increased with increasing surcharge height, effective anchorage length, and the number of tires. The ultimate pullout resistance of cell-type tires was approximately 1.25 times that of the geocell reinforcement. This difference was mainly due to the high-strength steel wires inside the tires. The pullout resistance normalized by the number of tires and the surcharge height was 4 kN.

Comparison of Pullout Behaviour on Sand between Planer Grid Forms and Grid with Rib of Reinforcement

In conventional reinforced soil structures, the reinforcements are often laid horizontally in the soil. In this paper, a new concept of grid reinforcement with ribbed inclusions is proposed. In the proposed of soil reinforcement, besides conventional grid reinforcements, some vertical and 3D reinforcing rib are also placed in the soil. Pullout tests are necessary in order to study the interaction behavior between soil and geosynthetics in the anchorage zone. Then, a series of pullout tests are conducted and the various parameters studied in this testing program include rib height and grid size of reinforcement. The result shows that the ultimate pullout force of plexiglass with rib is significantly larger than ordinary ones in the same normal stress. Ultimate pullout resistance increased as the increase of the height of tooth, and also is significantly impacted by grid size.