ICE - Institution of Civil Engineers - Virtual Library

This paper presents state-of-the-art examples to show that, in a wide variety of cases, the behavior of geosynthetics can be quantified using theoretical analyses. Seven examples are reviewed: geotextile filter retention, geotextile filter clogging, geomembrane stress–strain behavior, geomembrane strain concentrations, geomembrane stress cracking pattern, geomembrane wrinkles, and geosynthetic resistance to differential settlement. The selected examples are such that the important behavioral aspect is not the behavior of the structure in which the geosynthetic is incorporated, but the behavior of the geosynthetic itself. In each case, the phenomenon or problem is described, the theoretical analysis is presented, and the results are discussed. An important message conveyed by this paper is that the solution of engineering problems can only result from rational analyses, not from common sense. Note: This paper is an updated version of a paper initially published as a Special Lecture in the proceedings of the Fifth International Conference on Geotextiles Geomembranes and Related Products, held in Singapore in 1994.

In the numerical analysis of geosynthetic-reinforced soil structures subjected to earthquake loadings, the constitutive model for the geosynthetic reinforcement is important, because it affects the accuracy of numerical simulations. Two different approaches for modeling the monotonic and cyclic behavior of geosynthetic reinforcements are discussed in this paper: a nonlinear mathematical function combined with the modified Masing rule, and bounding surface plasticity. The Masing rule was modified so that it can simulate the hysteretic behavior of geosynthetics under cyclic loading, including the decrease in the residual strain rate with the number of loading cycles (cyclic strain-hardening). For the bounding surface model, different bounding lines were defined for primary loading, unloading, and reloading. An exponential function was used as the bounding line for primary loading in order to capture the stiffening behavior of some geosynthetics. Constitutive models were proposed based on the two approaches for different types of geosynthetic. Experimental results for six geogrids were used to verify the proposed models, and it was shown that they were able to capture the nonlinear and hysteretic behavior of the corresponding geosynthetics. It was shown that the approach utilizing a mathematical function combined with the modified Masing rule is simple and straightforward. Bounding surface plasticity provides an approach that is more rational for simulating the cyclic behavior of geosynthetics, especially for the case of irregular earthquake loading.

ABSTRACT: A series of uniaxial and triaxial compression tests was carried out in order to study micro- and macro-mechanical compressive behavior as well as some other mechanical properties of expanded polystyrene. Micromechanical behavior was analyzed by performing uniaxial compression tests on small cubic specimens. These tests were carried out using a load frame designed to be placed inside a scanning electron microscope. Using an automatic camera, micrographic sequences were taken during the loading process. These photographic sequences allowed the identification of the internal structure changes that occurred at different strain levels. Macro-mechanical behavior of expanded polystyrene (EPS) under compressive loading was investigated by means of triaxial tests on 10 cm-diameter specimens. Triaxial test results showed that the behavior was strongly influenced by EPS density, confining stress and displacement rate. Finally, based on the triaxial test results, a set of equations was proposed to estimate the compressive behavior of EPS and the accuracy of the equations was assessed by comparisons with experimental results.

• 3.1 Introduction

• 3.2 Joint Venture

• 3.3 National Culture

• 3.4 Workplace Behavior

• 3.5 Hypothesis

• 3.6 Data Collection

• 3.7 Data Analysis

• 3.8 Statistical Result

• 3.9 Discussion

• 3.10 Conclusion

• References

Four half-scale arches have been constructed in the laboratory and tested to simulate the response of masonry arch bridges to moving loads. The arches were built using lime mortar with 17 voussoirs and span length of 1.22 m. The loads varied from 115 kg to 910 kg and were obtained by hanging steel weights from the center-of-gravity of the voussoirs. A data acquisition system was used to record the displacements normal to the voussoirs at 16 points around the extrados. Results from the experiments show that the lime mortar affects the system behavior of a masonry arch. The mortar joints exhibit significant plastic behavior with the first few cycles of loading, then behave in a more elastic fashion when the magnitude of load and load cycles increase. When applying moving loads across the arch ring, two distinct types of deformation are noticed; elastic deflections of the voussoirs along the extrados and plastic deformations that accumulate in the mortar joints.

• Introduction

• Experimental Program

• Results

• Conclusions

• References

ABSTRACT: Earth structures constructed of fine-grained soils have a tendency to crack. One possible solution to this problem is the inclusion of discrete and randomly distributed geofibers. The purpose of the research presented herein was to assess the feasibility of using commercially available geofibers to improve the tensile strength–strain characteristics of soils. An experimental investigation consisting primarily of flexural tensile tests was conducted to examine the influence of geofibers on the flexural behavior of three different types of soil molded at three different water contents. Polypropylene tape fibers were used in this study as reinforcing elements. The test results showed that the geofibers were effective in improving the tensile strength–strain characteristics of the moist-compacted fine-grained soils used in the present study. The inclusion of geofibers increased tensile strain at crack initiation of a soil moist-compacted at different molding water contents. With an increase in plasticity index of the soil, fiber content and molding water content, a trend of increasing tensile strain at crack initiation was observed. Among several fiber contents and aspect ratios, it appears that 0.5% polypropylene tape fibers and an aspect ratio (length to breadth) in the range 30–45 provided the best combination to increase tensile strain at crack initiation and effectiveness to restrain the cracking of soils. Further, the flexural rigidity at crack initiation was found to increase with an increase in the fiber content for soils having a low plasticity index and moist-compacted at low molding water contents.

• Introduction

• Structural Loads

• Forces and Displacements on the Edge

• The First Few Rings

• Assembly Progress

• Dead Load Effects

• Towers

• Conclusions

The short- and long-term compressive behaviors of a high-density polyethylene (HDPE) geonet at five inclined conditions—horizontal (0°), 1(V)-to-9(H) (6.3°), 1-to-5 (11.3°), 1-to-4 (14.0°), and 1-to-3 (18.4°)—were evaluated. The results of the short-term tests indicate that the compressive strength decreases linearly with inclined angle, whereas the compressive strain increases. The long-term compressive behavior (i.e. creep) was evaluated using the stepped isothermal method (SIM) at applied stresses of 10%, 20% and 30% of the normal compressive strength. The creep strain increases with inclined angle at all applied stresses. At 10% applied stress the primary creep deformation is obtained, while the secondary and tertiary creep stages are detected at the two higher stresses. The relationship between compressive behavior and the rollover of upper ribs of the geonet is established. The geometry of the geonet, particularly the inclined angle of the ribs, is found to be critical to the short- and long-term behavior of the geonet. In addition, the short- and long-term compressive behavior of the geocomposite was evaluated at horizontal (0°) and 1-to-4 (14.0°) to investigate the effects of thermally bonded geotextiles. The results are different from those of the geonet alone owing to the localized interface friction between the needle-punched nonwoven geotextile and ribs.

ABSTRACT: The short- and the long-term compressive behavior of an expanded polystyrene (EPS) geofoam were both evaluated to assess the effects of temperature and stress. The short-term compressive strength decreased bi-linearly as temperature increased with a transition point at the temperature of 43^oC. For the long-term compressive creep behavior, three accelerated creep test methods were used in the evaluation: stepped isothermal method (SIM), time–temperature superposition (TTS), and time–temperature–stress superposition (TTSS). The results from these three tests were compared with that of the conventional creep test at room temperature. Due to the 43°C transition in the short-term compressive strength, the predicted creep strains from SIM and TTS, employing a higher temperatures than 43°C, were found to be much higher than those from the conventional test. Furthermore, the activation energies were significantly different at temperatures above and below 43°C. On the other hand, the creep strains predicted from the TTSS tests were similar to those from the conventional method. The TTSS tests employed test temperatures below 44°C. Instead of using elevated temperatures, higher stress levels were used to accelerate the creep. A modified four-parameter Weibull model was developed to predict the linear and non-linear creep behavior, and a good agreement was found with test data from TTSS and the conventional method.