Query: geogrid pull out

title: Discrete Element Analysis of the Load Transfer Mechanism of Geogrid Ballast Interface under Pull Out Load
abstract: Geogrids have been extensively used in subgrade construction for stabilization purposes of unconfined ballast. Based on well calibrated microparameters, a series of geogrid reinforced ballast models with different geogrid sizes and particular structures were developed to reproduce the mechanical behavior of the geogrid under pull out load in this paper. And the rationality of the DEM model is verified by comparing the evolution law pull out force measured by laboratory tests and numerical simulations under comparable conditions. Moreover, the macro pull out force and the internal force distribution of the geogrid were analyzed, and the contact force statistical zones of the particle system were divided accurately according to the results. Meanwhile, both the force transfer mechanism in the geogrid ballast interface and the sectionalized strain of the geogrid were discussed. And results unveil that the pull out load is transmitted along the longitudinal ribs to the transverse ribs, and nearly 90% of the load is transmitted to the contact network (in statistical zone 1) in front of the first transverse rib, resulting in strong interlocking between the particles occurs in statistical zone 1. And the second transverse rib is the strength dividing line between strong and weak contact forces. Then, additional pull out tests on the control groups were conducted, and the sectionalized strain of the geogrid and the peak pull out force, as well as the energy dissipation were systematically analyzed. In addition, the proposed method used in simulation holds much promise for better understanding of the reinforcement mechanism and further optimizing the performance of geogrid reinforced structures.

title: DEM simulation of the pullout behavior of geogrid stabilized ballast with the optimization of the coordination between aperture size and particle diameter
abstract: Based on the well established constitutive models and particular configurations used in the discrete element method (DEM) simulation of the geogrid stabilized ballast system, this paper presents the pull out behavior of a triangular geogrid embedded in ballast under special consideration of the particle size. A representative particle size that equals to the diameter of the inscribed circle of the triangular aperture was selected to visualize the axial force distribution and the interface responses regarding the contact force. Meanwhile, fabric anisotropy on the normal component of contact force was introduced to explain the development of macroscopic strength. Results show that the first transverse rib makes the most contribution to the pull out force. The V shaped strong contact force chains were mainly grown in the geogrid ballast substantial interaction region R1, and this interaction mode is not affected by particle size. Moreover, the maximum number of particles trapped in an aperture, Nmax, is used as the quantized indicator for numerical pull out tests on 6 controlled conditions, and results unveil that the optimal reinforcement can be achieved when Nmax 2, by evaluating the pull out resistance, the interlocking effect, the energy dissipation, and the volumetric response.

title: Numerical study of large scale pull out test of horizontal corrugated strips
abstract: The interaction between soil and geosynthetic plays an important role in the design and analysis of reinforced soil structures. Pullout tests are commonly used to simulate the soil reinforcement interaction mechanism along the interface. Thus, different types of reinforcements are used in these structures and present different behaviours. In this paper, we propose a new kind of reinforcement based on horizontal corrugated strips in order to improve the parameters interfaces between the soil and the reinforcement. To simulate the pullout interaction process of horizontal corrugated strips, we carry out a numerical study using the software package FLAC3D. We have modelled the soil as an elastic perfectly plastic Mohr Coulomb and the reinforcement as linear elastic geogrid elements. In fact, the most important aim is to explain the horizontal corrugated reinforcement's behaviour and to investigate the factors that affect the mechanical response (Confining pressure, friction angle, amplitude and number of the waves of the strip) A comparative study is also presented between the horizontal corrugated and planar strips. In our study, the numerical results showed that the confining pressure has significant influence on the interface properties of the horizontal strips corrugated. It also showed that the pullout shear stress on the head of horizontal corrugated strips is higher than the planar reinforcements.

title: Variation of Pull out Resistance of Geogrid with Degree of Saturation of Soil
abstract: This paper presents the results of experimental investigation on the effect of degree of saturation of soil on the pullout behavior of a geogrid. Different test variables were taken into account while performing the experiment including the soil physical conditions based on water content and external loading applied. The soil used was locally available weathered granite soil. The tests included variations in saturation of about 90% 80% 70% and 45% (optimum moisture content) The pullout tests were performed according to ASTM standard D 6706 01. The results indicate that increasing the degree of saturation in the soil decreases the pull out capacity, which in turn decreases the interface friction angle and interaction coefficient. The decrease in the pullout interface coefficient was observed to be around 12.50% to 33.33% depending on the normal load and degree of saturation of the soil. The test results demonstrated the detrimental effect of increasing the degree of saturation within the reinforce soil on the pullout behavior of reinforcement, thus on the internal stability. The practical inferences of the outcomes are analyzed in detail.

title: Determination of Pullout Strength of Geogrid in Sandy Soil
abstract: Geogrid reinforcement of soil has been successfully used for many years in a wide variety of applications. This paper presents data obtained from a series of laboratory tests performed on the geogrid. The tests were conducted to determine the mechanical property including the tensile strength of the geogrid and its corresponding pullout test. Tests were performed to find out the effect of width of geogrid on the pullout resistance. It was found that the pull out resistance of geogrid is a function of the relative density of the soil, the length and the width of geogrid specimen. A mechanism of soil geogrid interaction is described and used to explain the results of' the pull out tests. A significant finding is that the selection of geogrid specimen dimensions for laboratory pullout tests must take into account the strain to failure of the soil and the stiffness of the geogrid in order to properly represent the maximum pull out stress that will be available in field applications.

title: Reliability Analysis of Reinforced Slopes Using Monte Carlo Simulation
abstract: 1 Reliability Analysis of Reinforced Slopes Using Monte Carlo Simulation H. Rahmati* Seyed Morteza Marandi PhD Student of Civil Engineering Department, Shahid Bahonar University of Kerman, Kerman, Iran H.rahmati@eng.uk.ac.ir Professor of Civil Engineering Department, Shahid Bahonar University of Kerman, Kerman, Iran marandi@uk.ac.ir * Reliability analysis has gained special importance in geotechnical engineering in the past decades. One of the most important fields of geotechnical issues is the slopes stability. Slope stability analysis and their reliability analysis against slip and loading are important. Geotechnical engineers are also interested in improving and reinforcing weak slopes and increasing their factor of safety and reliability index. In this study, the uncertainties in soil strength parameters such as cohesion, internal friction angle and unit weight and force created in geogrid layers due to pull out and bonding between soil and geogrid are considered. Then using Monte Carlo simulation Depending on the height of the slope, the reliability index is obtained in both of unreinforced and reinforced states. The critical slip surface of slope failure is also determined using PSO. The results of this analysis indicate the important role of reinforcements in increasing the reliability of soil slopes.

title: PARAMETRIC STUDY ON GEOGRID REINFORCED RETAINING WALL SYSTEM
abstract: The use of geogrids as reinforcement to improve the pull out strength of retaining structures has gained attention in field of Geotechnical Engineering. Reinforced retaining walls play important role in development of various retaining structures due to less cost, durability, strength, safety and its availability. Several researches have demonstrated that various parameters like length, layers ,spacing and aperature of geogrid in reinforced retaining structures can be varied to improve the strength and bearing capacity of the structures. This paper presents the summary of varies research papers currently worked on geogrid reinforced structures inclusive of its strength durability and economic value.

title: Influence the rib length of geogrid exerts on the pull out property

title: Geogrid pull out modelling using DEM
abstract: With the advancement of the use of synthetic reinforcements in geotechnics, a greater understanding of the mechanisms involved in soil reinforcement interaction is the focus of major research centres on the subject. The topic of this study is the shearing behaviour at interfaces between granular materials and geogrids. The main objective is to provide a more fundamental understanding of some micromechanisms present in this type of interface, which in turn are important to optimize the design of such reinforcement. The numerical modelling of these reinforced structures must deal with the complexity of the material reinforcement interaction problem; therefore, it requires specific numerical models whose formulations admit localized behaviours in the contacts as well as the granular nature of the material (e.g. soil, gravel, ballast) A robust and flexible way of modelling this problem is through the Discrete Element Method (DEM) The DEM proposes to model this granular nature by representing the soil as interacting constituent particles, whose behaviour is ruled by physical laws defined at the contact points. The numerical approach is desirable since it allows, in an articulated and relatively fast way, studying closely different regions of the interface, in order to identify factors and variables that are important for the problem. The purpose involves the DEM for a 3D modelling of a geogrid pull out test to calculate the magnitude of forces in different elements of the geogrid (i.e. nodes, longitudinal and transverse members) Preparation of numerical samples has a particular importance in the final results of simulations. Thus, the numerical techniques used to obtain better geometry for the geogrid and a granular assembly with a representative grain rolling effect are also presented in this paper.

title: A laboratory study on pull out resistance of geogrid in clay soil
abstract: Geosynthetics such as geotextiles, geogrids and geocells are outstanding materials for reinforcement of soils. Recently, reinforcing the clay soils with geosynthetics, by increasing the bearing capacity and decreasing over consolidation, was used increasingly in geotechnical applications. The behavior of soil with reinforced material is crucial on design of reinforced soil. In this study the interaction between geogrid and clay soil was investigated by pulling out the geogrid experimentally with the help of direct shear tests machine. In experiments the geogrid was placed on shear surface that was the midpoint of test mold. The soil samples were prepared with different water content that was including optimum water content (OWC) A special cap was designed to pull out the reinforcing material through the soil sample. According to experimental results, the variation of pullout load against displacement seems to be similar to classical load displacement behavior of soil and it increases when the normal stress increases. Under the same normal stresses, pull out load observed to be greater when the soil sample has OWC. At stress level s 27,2 kPa, when water contents of soil samples increase 60% the pull out loads increase approximately 30% These observations can be interpreted the interlocking between soil and geogrid is stronger if the water content of soil samples are equal to OWC. It is also showed from the tests results that pull out load values are generally greater than interfacial strength of soil samples.