Pull-out Model Research Articles

Experimental and theoretical study of mechanical properties of root-soil interface for slope protection

Plant roots mechanically enhance the strength of soil and improve slope stability through anchoring. Given the popularization of ecological slope-protection technology, a quantitative study of how roots help to anchor soil is highly pertinent. The object of the present study is thus to investigate how roots and soil combine to affect the mechanical properties of the root-soil interface. Toward this end, pullout experiments of cedar roots of different diameters in soils of different density were conducted. The experimental results show that the maximum pullout force increases significantly with increasing root diameter, but only slightly increases with increasing soil density, which indicates that the root diameter has a greater impact on the maximum pullout force than soil density. Next, based on studies of fiber-reinforced composites, a root-soil pull-out model was proposed to study the evolution of shear stress on root-soil interface. This approach ensures that the model accurately reflects the dynamic stress distribution evolution at the root-soil interface and can calculate the pullout process of embedded root from soil. The accuracy of the model is verified by comparing the calculated results with experimental results. Finally, how soil density and root diameter affect the anchoring force was analyzed. The results indicate that the maximum anchoring force increases linearly with increasing root diameter, but nonlinearly with increasing soil density until reaching a fixed value. These results show that the root soil pull-out model has significant practical value in slope protection.

Experimental study of an innovative driven and grouted soil nail (x-Nail)

This paper describes an experimental investigation of a newly developed driven and grouted soil nail (x-Nail), which combines the capabilities of a purely frictional driven nail and a compaction-grouted nail. The innovative design allows the x-Nail to be driven into the ground with a latex balloon attached that is subsequently used for compaction grouting. A grout bulb is thus formed at the driven end of the nail to improve its pull-out resistance. For compaction grouting, a special type of additive−mixed cement grout was used in this investigation because of its zero bleeding and high bond strength. A series of pullout model tests was conducted to examine the performance of the x-Nail compared to a purely frictional soil nail. It was found that more than 90% of the pullout force of the x-Nail was resisted by the expanded grout bulb and the end bearing resistance of the grout bulb increased with the increment of the injected grout volumes. The experimental results revealed that the pullout force of the x-Nail increased approximately 1800%, 1550%, 1200%, and 900% compared to the purely frictional soil nail for the injected grout volumes of about 350, 270, 220, and 170 mL, respectively.

Reliability-based design and analysis for internal limit states of steel grid–reinforced mechanically stabilized earth walls

This paper demonstrates reliability-based design (RBD) and analysis for tensile strength (rupture) and pullout limit states for mechanically stabilized earth (MSE) walls constructed with steel grid reinforcement in combination with frictional soils. Five different reinforcement tensile load models for walls under operational conditions are considered in combination with six different pullout models and one tensile strength model. The general approach considers the accuracy of the load and resistance models that appear in each limit state equation plus uncertainty in the choice of nominal values at the time of design that is linked to the concept of “level of understanding” used in Canadian load and resistance factor design (LRFD) foundation engineering practice. The effect of potential steel corrosion on reliability index for the tensile strength limit state is considered in calculations. A well-documented MSE wall case study is used to demonstrate the general approach. The relationship between nominal factor of safety and reliability index is used to demonstrate how to optimize steel grid member diameters and arrangement to achieve a target reliability index of β = 2.33. The approach described in this paper is an important contribution to next-generation analysis and design using modern concepts of RBD for MSE walls.

Prediction of tensile response of UHPC with aligned and ZnPh treated steel fibers based on a spatial stochastic process

This paper proposed a new method for predicting tensile response of UHPC based on a spatial stochastic strength distribution model. The steel fibers in UHPC were aligned by a developed device and chemically treated by ZnPh. A direct tension test was conducted to obtain the tensile response of UHPC with treated fibers. Image analysis was used to obtain the frequency of overall fiber orientation distribution. The spatial stochastic distribution model was proposed for cross sectional strength of UHPC based on the Ornstein-Uhlenbeck stochastic process. The model introduced some assumptions such as the correlation coefficient between the cracking strength and fiber bridging strength. Parametric analysis was conducted to obtain the crucial stochastic parameters in the model. Combining with the single fiber pullout model, tensile behavior of a single crack, and minimum crack spacing, the model predicted the strain hardening and multiple cracking behaviors with precise accuracy, as compared to experimental results.

A Peer-Delivered Intervention for High School Students With Impairing ADHD Symptoms

This study evaluates a peer-delivered intervention for high school students with impairing attention deficit hyperactivity disorder (ADHD) symptoms targeting organization, time management, and planning (OTP) and motivation (Students Taking Responsibility and Initiative through Peer Enhanced Support; STRIPES). A mixed methods open trial (Study 1; N = 18) and parallel group randomized controlled trial (Study 2; N = 72) were conducted to examine acceptability, target mechanisms, student outcomes, population fit, and feasibility. Study 1 established acceptability for STRIPES delivered after school but identified forgetfulness and competing social activities as population-specific implementation barriers. In Study 2, three schools employed unique implementation strategies and results varied. An elective pullout model engaging 12th grade peer interventionists under teacher supervision demonstrated good fidelity, attendance, and population fit and significant between-group differences in book bag organization (d = 1.11), academic motivation (d = 0.85 to 2.05), and class attendance (d = 1.47) over time compared to control. When implementation strategy demonstrates population fit, STRIPES shows promise for preventing declining school engagement across ninth grade.

Constitutive model for fibre reinforced concrete by coupling the fibre and aggregate interlock resisting mechanisms

This paper describes the development of a constitutive model for Fibre Reinforced Concrete (FRC) by combining the fibre and aggregate interlock resisting mechanisms. The proposed model predicts the normal and shear stresses in function of the crack opening and sliding displacements. For this purpose, two well established aggregate interlock models and three fibre pull-out models reported in the literature are used, and their predictive performance is assessed in the context of the present study. In order to understand the impact of the variables involved in the model, a parametric study, targeting different maximum aggregate diameters, concrete compressive strengths and fibre volume ratios, is conducted. The results show that higher concrete compressive strengths and fibre volume ratios lead to higher normal and shear stresses. Finally, the predictive performance of the model is assessed by comparing the numerical predictions with experimental results collected from the literature. Results show that the model is capable of predicting the shear peak-stress with good accuracy, however the post-peak response is generally overestimated. A modification to the aggregate interlock models is proposed in order to adapt the original formulations for FRC. The results of the modified version show an overall much better agreement between the numerical and experimental results.

Co-teaching: Equity for English Learners?

This study adds to the current understanding of co-teaching in rural school systems, specifically its use to equitably serve the needs of English learners (ELs). The authors investigated one western U.S. rural district’s implementation of a co-teaching model where general classroom teachers shared teaching responsibilities with an English as a second language (ESL) teacher in a secondary school setting. Research has long shown traditional pull-out models for teaching ELs are not the most effective because there is often a disconnect between what is happening in the mainstream classroom and what is happening in the pull-out placement. This quantitative study included observations of 20 co-taught classes during 400 minutes of classroom instruction to measure fidelity to the district’s co-teaching model. This article details the extent to which teachers utilized specific co-teaching strategies. It also reports on the quantity of teacher-student interactions in general and relative to ELs and non-ELs. Observations revealed that EL students worked primarily with the language specialist, and most of those interactions took place in the context of individualized support. Implications regarding equity and opportunity to learn academic content for both EL and non-EL students are discussed.

Single-fiber pull-out analysis comparing the intensities of singular stress fields (ISSFs) at fiber end/entry points

This paper deals with a partially-embedded single-fiber under pull-out force in comparison with a single fiber embedded in matrix focusing on two distinct singular stress fields. Then, the intensities of the singular stress fields (ISSFs) are compared at the fiber end named Point A and the fiber/surface intersection named Point E. The results show that if the embedded length lin is shorter, interface debonding may occur at Point A. Instead, if lin is longer, the interface debonding may occur at Point E. To analyze the ISSFs accurately, a mesh-independent technique coupled with the finite element method (FEM) is indicated by applying the same FEM mesh pattern to the pull-out model and the reference model. As the reference solution, a single fiber embedded in matrix is also calculated under arbitrary material combinations by using the body force method (BFM). Stress distributions along the fiber/matrix interfaces are also calculated for carbon and glass fibers.

Geometrical and material optimisation of deformed steel fibres: Spirally deformed fibres

This paper presents an optimisation procedure of geometrical and material properties of steel fibres using the validated three-dimensional nonlinear Finite Element (FE) pullout model previously proposed by the authors. The FE model is employed as a virtual laboratory unit to investigate the pullout performance of steel fibres with various shapes such as hooked-end and spirally deformed steel fibres. The preliminary FE pullout analyses imply that the optimisation of the fibre with spiral configuration (adjustment of geometrical and material properties of the fibre) could result in an efficient high-performing steel fibre; hence such a fibre is selected for the optimisation procedure. In order to re-validate the numerical pullout model and further adjust its nonlinear parameters for enhancing the simulations prediction, a set of experimental pullout tests are conducted on four spirally deformed steel fibres with different geometrical properties. Extensive parametric studies are performed on the material and geometrical properties of the fibre to examine their effects on the fibre pullout performance. Moreover, an empirical equation is proposed for the estimation of fibre efficiency and optimum design of spirally deformed steel fibres in which geometrical and material properties are taken into account.

Investigation into the differences of pull-out resistance between normal and osteoporotic cancellous bone

Pedicle screw loosening or pullout has occurred from time to time in patients with poor bone quality. However, there have been no rigorous mechanical analysis of the pullout process, and the resistance region to pullout force remains under-investigated. The objective of the current study was to investigate the stress state of cancellous resistance to pullout in normal and osteoporotic conditions using plane finite element method. The pull-out model was simplified to a simpler two dimensional axisymmetric model by symmetry. A prescribed axial displacement of 2 mm was imposed on the screw head and a fixed boundary condition was set on edge nodes of the bone to simulate the pullout process. The results of numerical simulation showed that the high-stress area of normal bone was clearly larger than that of osteoporotic bone, and the normal bone provided the higher pullout force of 86.09 N, which was about 3 times than that for osteoporotic bone. From the study it was found that osteoporosis would diminish the active region of resistance to pullout around the screw and decrease the pullout strength about threefold. The results of the current study can be used for screw augmentation techniques.

Analysing of the Yarn Pull-out Process for the Characterization of Reinforcing Woven Fabrics

Our goal was to test the theoretical yarn pull-out model we developed. We examined eight glass woven fabrics from the same manufacturer. We compared the values provided by the theoretical model with the measurement results, and based on these, we determined the relationship between the length of the yarn embedded in the woven fabric and the tensile force acting on the yarn. All in all, we concluded that the model described the yarn pull-out process well; hence it can be applied to more complex woven fabric models and simulations.

A critical evaluation of predictive models for rooted soil strength with application to predicting the seismic deformation of rooted slopes

This paper presents a comparative study of three different classes of model for estimating the reinforcing effect of plant roots in soil, namely (i) fibre pull-out model, (ii) fibre break models (including Wu and Waldron’s Model (WWM) and the Fibre Bundle Model (FBM)) and (iii) beam bending or p-y models (specifically Beam on a Non-linear Winkler-Foundation (BNWF) models). Firstly, the prediction model of root reinforcement based on pull-out being the dominant mechanism for different potential slip plane depths was proposed. The resulting root reinforcement calculated were then compared with those derived from the other two types of models. The estimated rooted soil strength distributions were then incorporated within a fully dynamic, plane-strain continuum finite element model to assess the consequences of the selection of rooted soil strength model on the global seismic stability of a vegetated slope (assessed via accumulated slip during earthquake shaking). For the particular case considered in this paper (no roots were observed to have broken after shearing), root cohesion predicted by the pull-out model is much closer to that the BNWF model, but is largely over-predicted by the family of fibre break models. In terms of the effects on the stability of vegetated slopes, there exists a threshold value beyond which the position of the critical slip plane would bypass the rooted zones, rather than passing through them. Further increase of root cohesion beyond this value has minimal effect on the global slope behaviour. This implies that significantly over-predicted root cohesion from fibre break models when used to model roots with non-negligible bending stiffness may still provide a reasonable prediction of overall behaviour, so long as the critical failure mechanism is already bypassing the root-reinforced zones.

Bayesian model checking, comparison and selection with emphasis on outlier detection for geotechnical reliability-based design

Model checking, evaluation and comparison are critical steps in Bayesian data analysis but not routinely considered in statistical analysis of geotechnical data. This paper presents an overview of model checking and comparison concepts and techniques employed in modern Bayesian data analysis that are useful for analysis of geotechnical engineering data. These methods are applied to statistical analysis of load and pullout model bias data for steel strip mechanically stabilized earth walls. It is shown how model checking can result in statistical models with better fits. The practical implications of using improved statistical models are discussed in the context of reliability-based design and load and resistance factor design calibration of the internal stability pullout limit state. Finally, statistical model uncertainty and Bayesian model averaging are discussed and explored using an example of reliability-based design for the same limit state.

Implementation and Perceptions of Classroom-Based Service Delivery: A Survey of Public School Clinicians.

Purpose The choice of service delivery model is important for public school clinicians. Despite a theoretical emphasis on inclusive classroom-based services, data from a recent American Speech-Language-Hearing Association Schools Survey indicated that the pullout model is still the more frequently used approach (American Speech-Language-Hearing Association, 2016). In the current study, public school clinicians' use and perceptions of inclusion were examined to better understand potential influences on its implementation. Method Three hundred forty-four school-based clinicians completed an online survey about their training in and implementation of inclusion services, along with their perceptions of positive and potentially challenging aspects of this model. Descriptive data were examined, and the relationships of use and perceptions to issues such as caseload size, training, school setting, teacher factors, and administrative support were analyzed. Additionally, qualitative analysis was used to examine responses to 3 open-ended questions. Results Over half of the respondents served 1%-25% of their caseload through an inclusion model, and it was most frequently utilized to address language and social skills. Teacher collaboration and planning time were the 2 most frequently reported keys to inclusion success and were also 2 of the most frequently reported challenges to implementation. Conclusions The majority of the respondents reported many positive aspects of inclusion, yet they also reported many of the same challenging perceptions and roadblocks that existed when speech-language pathologists were surveyed over 20 years ago. Based on the results of this study, training in the inclusion model, teacher "buy-in," planning time, and administrative support are relevant to successful use of classroom-based intervention.

Analytical Modeling of the Bond Behavior between ‎Textile ‎and Mortar Based on Pull-Out ‎Tests

It is clear that the fiber-to-mortar bond behavior plays a major role on the performance of Textile Reinforced Mortars (TRMs) used for strengthening of existing structures. This aspect, however, has been only the subject of few studies and require further attention.This paper presents an analytical model for extraction of the textile-to-‎mortar bond-slip laws from pull-out tests. The ‎objective is to ‎characterize the parameters that ‎influence the ‎pull-out behavior of TRM ‎systems. ‎In the formulation of the ‎pull-out model, a ‎modified approach ‎based ‎on a mathematical model by Naaman ‎is applied. Firstly, based on ‎the ‎experimental ‎results, a relationship between the bond shear stress and the ‎relative slip ‎along the fiber-mortar ‎interface is obtained. Then, based on the ‎shear stress-slip law, the ‎boundary conditions, equations ‎of equilibrium, and ‎the equation of ‎compatibility and hooke’s ‎law, the bond response ‎between ‎textile and mortar is predicted and modeled.

First Results of a 3D Pull-Out Model of Steel Anchors in Fired-Clay Bricks

The paper reports the results of a numerical simulation performed to study the experimental pull-out behavior of twisted steel connectors inserted in fired-clay brick units. The experimental results obtained in a previous campaign are used to calibrate a 3D refined numerical model developed by means of the finite element program Abaqus. The numerical model is tuned to accurately reproduce the experimental results in terms of loads and bar displacements.

Calibration of PET strap pullout models using a statistical approach

Polyester (PET) straps are being used more frequently in mechanically stabilized earth (MSE) walls. At present, there is no consensus on a model or models that are suitable for design codes to calculate the pullout capacity of these materials. A database of 296 pullout tests from 81 test series with single and closely-spaced parallel double PET strap configurations was collected by the writers. The data were taken from laboratory and in situ pullout tests. Existing linear and bi-linear pullout models for geosynthetic and steel strip reinforcement were investigated as candidate models and then empirically modified to improve pullout capacity predictions for both single and double PET strap arrangements. A non-linear exponential model with the same number of empirical coefficients was also investigated. The accuracy of each model was assessed quantitatively using bias analysis where bias is the ratio of measured to predicted capacity. The paper shows that non-linear models performed best based on mean and coefficient of variation (COV) of bias values and bias dependency with predicted pullout capacity and magnitude of vertical stress acting on the pullout length. The models investigated in this study are useful for pullout limit state calculations using both deterministic and reliability-based analysis and design approaches.

Pullout Strength Predictor: A Machine Learning Approach.

Study DesignA biomechanical study.PurposeTo develop a predictive model for pullout strength.Overview of LiteratureSpine fusion surgeries are performed to correct joint deformities by restricting motion between two or more unstable vertebrae. The pedicle screw provides a corrective force to the unstable spinal segment and arrests motions at the unit that are being fused. To determine the hold of a screw, surgeons depend on a subjective perioperative feeling of insertion torque. The objective of the paper was to develop a machine learning based model using density of foam, insertion angle, insertion depth, and reinsertion to predict the pullout strength of pedicle screw.MethodsTo predict the pullout strength of pedicle screw, an experimental dataset of 48 data points was used as training data to construct a model based on different machine learning algorithms. A total of five algorithms were tested in the Weka environment and the performance was evaluated based on correlation coefficient and error matrix. A sensitive study of various parameters for obtaining the best combination of parameters for predicting the pullout strength was also preformed using the L9 orthogonal array of Taguchi Design of Experiments.ResultsRandom forest performed the best with a correlation coefficient of 0.96, relative absolute error of 0.28, and root relative squared error of 0.29. The difference between the experimental and predicted value for the six test cases was not significant (p >0.05).ConclusionsThis model can be used clinically for understanding the failure of pedicle screw pullout and pre-surgical planning for spine surgeon.

Peridynamic simulation of two-dimensional axisymmetric pull-out tests

In this study, a systematic pull-out simulation scheme in the formwork of two dimensional (2D) axisymmetric domain using peridynamics (PD) is presented. An axisymmetric ordinary state-based peridynamic model is used to model the pull-out deformation just like the axisymmetric stress element in the finite element method (FEM). A failure criterion based on the bond energy density is adopted to predict the interfacial debonding, while a new PD contact model in the 2D axisymmetric domain is proposed to simulate the friction sliding during the pull-out process. The PD pull-out simulation scheme based on the respective 2D axisymmetric model, interfacial failure criterion and contact model is quantitatively validated in comparisons with either the FEM or analytical solutions. The whole process of the pull-out test is simulated using the proposed PD scheme, and the influences of both the interfacial fracture toughness and friction coefficient on the bond-slip behavior are investigated. The developed PD pull-out modeling scheme is capable of effectively simulating the pull-out tests and predicting the bond-slip behavior.

Numerical approach of the steel-concrete bond behavior using pull-out models

This paper deals with the analysis of monotonic loading behavior in pull-out tests. The main objective is to obtain a reliable numerical model to represent the steel-concrete bond behavior using previously obtained experimental results. The tests were performed in RILEM pull-out specimen using 10 mm steel bar and concrete with compressive strength of 30 MPa. The numerical study used Ansys® software, based on FEM (Finite Elements Method). The numerical simulation adopted non-linear constitutive relationships to represent the behavior of both concrete and steel. A contact surface composed of special finite elements modeled the interface between the concrete and the steel bar, allowing a steel–concrete slip. The numerical analysis performed with variation of the main parameters of the software permitted determining the best ones, and choosing them to obtain a good representation of the bond phenomena. The numerical results had a good agreement with the experimental results. Both linear and non-linear approaches represented the pre-peak behavior, however only the non-linear model gave the best approach for the pull-out force. In addition, the numerical results had shown the simplified model can be used to represent the steel-concrete bond behavior reducing the processing time for current structures analysis. Keywords: bond strength, pull-out tests, numerical approach, contact surface, finite element method.