Arthur E. Lord

Long-term durability and aging of geotextiles

Abstract The potentially adverse effects of long-term phenomena on the performance of geotextiles and related materials is addressed in this paper. The subject is subdivided into the various topics felt to be most significant. They are the effects of clogging, creep, chemicals, micro-organisms, light, burial and cumulative aspects. Each topic is reviewed separately by way of available literature and then extended into currently ongoing efforts primarily in the USA. The paper concludes with a summary chart of each topic area versus its (a) perceived severity, (b) current state of knowledge, (c) past or present activity and (d) likelihood of definitive guidelines. Admittedly, the chart is subjective, but it gives our assessment of this important subject at this point in time. Clearly, if the currently existing wide variety of questions on long-term durability and aging are to be answered, a major thrust into the area must be made.

EFFECT OF HIGH-ALKALINITY LEVELS ON GEOTEXTILES. PART 2: NAOH SOLUTION

Abstract Alkaline water has been known to affect polymeric materials, such as geotextiles, and this on-going study is aimed at providing a data base to see the extent, nature and incidence of the effects. An earlier study used calcium hydroxide to provide the alkalinity, whereas this study uses sodium hydroxide. Solutions of pH 10 and pH 12 (with pH 7 as control) were prepared and various geotextiles were incubated up to 120 days. Flow tests and strength tests were conducted on all test specimens on a weekly basis for the entire duration. Results of the two phases (i.e. calcium and sodium) essentially parallel one another in that the alkalinity increases the flow time for a given volume of solution to pass through the geotextile. The effect is more pronounced for pH 12 than for pH 10. A precipitate is formed which rests either upon or within the fabric structure causing the major portion of the increased flow time. In addition to this blinding and/or clogging phenomenon is a strength reduction in some of the fabrics. Certain polyester fabrics show measurable strength losses, while others do not. The type of polyester (there are over 200 types) is felt to play a major (but unknown) role in this selection process. Considerable research into both surface and internal morphologies seems to be warranted. Future efforts will be targeted in these directions.

The identification and location of buried containers via non-destructive testing methods

Abstract The problem of identifying and locating containers of hazardous materials located beneath the ground surface or under water can be solved by either som The conclusions section gives recommendations as to where each method is most applicable, as well as a comparison of each method on the basis of cost,

The anomalous behavior of the viscosity in molten Au55Pb22.5Sb22.5—an easy glass former—from 400 to 600 °C

The kinematic viscosity of the molten alloy Au55Pb22.5Sb22.5 was found to be extremely high, ranging from 0.32 S (stokes) at 400 °C to 0.25 S at 475 °C. At 475 °C a very sharp decrease begins, ending with a value of 0.53 cS (centistokes) at 500 °C. An anomaly in the electrical conductivity mimics the viscosity behavior but is broader in temperature. Differential scanning calorimetry reveals a small peak in specific heat in the vicinity of these anomalies.

Use of acoustic emission to detect regions of structural change in metallic glass tape

A method is demonstrated for the rapid detection of localized structural variation in ferromagnetic metallic glass tapes. The method employs the acoustic Barkhausen effect.

Ultrasonic Wave Propagation in Metal-Matrix Composites

With the more widespread use of composite materials in structures, more attention is being paid to the non-destructive testing of these materials for assessing reliability. This study of conventional pulse-echo techniques applied to metal/metal composite specimens permits some qualitative generalizations to be made. The results have some bearing on the possible application of conventional ultrasonic (and, to a lesser extent, of acoustic emission) flaw detection techniques to composite materials. The sytems investigated were:

Stress Cracking Morphology of Polyethylene (PE) Geomembrane Seams

The high crystallinity of polyethylene (PE) geomembranes offers an excellent chemical resistance to harsh chemical leachates, but can be problematic with regard to stress cracking. Particularly vulnerable are field seams due to their overlapping geometry, necessity for surface grinding for removal of oxide layers, and possibility of poor quality. Using laboratory test specimens under constant load (ASTM D 2552 [modified]) it was shown that field seams can be subjected to such stress cracking. This paper presents a fracture surface morphological study of the cracked specimens from those particular tests. Five different seam types were evaluated, compared, and contrasted under different applied stress levels. Qualitatively, the morphology patterns were grouped into five categories: long fibrous, short fibrous, flake, hackle, and lamellar. These morphologies appear to be related to the magnitude of the applied global stress. The short fibers occurred at low stress, the long fibers at moderate stress, and the flake at high stress. Hackle often appears before the plastic failure as the cross-sectional area of the specimen decreases. Lamellar, the least common structure, may be caused by a combination of a low stress cracking with local plastic failure. What remains now is to see if this tentative classification applies to stress-cracked specimens from large laboratory tests and for field situations. If the nature of the field failure can be ascertained by comparison with the laboratory-generated categories (small and large sizes), implications to optimal seam types and/or polymer compound type may become apparent.

A REVIEW OF THE DEGRADATION OF GEOSYNTHETIC REINFORCING MATERIALS AND VARIOUS POLYMER STABILIZATION METHODS

The paper describes the two major degradation mechanisms of geosynthetics: oxidation of polyolefins (polyethylene and polypropylene), and hydrolysis of polyester (polyethylene terephthalate). These are the polymers which comprise the vast majority of geotextiles and geogrids used for soil reinforcement. Details of the degradation mechanisms of each material and their consequences are described based on the presently available literature. The influence of material structure, in particular the orientation, and ambient environmental conditions on the degradation are also discussed. The mechanisms and methods of stabilization which are currently used to minimize degradation are also presented. Finally, the paper concentrates on various possible test methods which can be used for monitoring the degradation of geosynthetic materials. (A) For the covering abstract see IRRD 860243.

GEOSYNTHETIC/SOIL STUDIES USING A GEOTECHNICAL CENTRIFUGE

Abstract Presented herein is a brief introduction to the centrifuge as used in geotechnical engineering studies. The rationale for centrifuge studies and the basic background are discussed in the Introduction. More scientific detail about centrifuge studies is presented in the ‘Physics of the centrifuge’ section, including derivation of the radial stress distribution in the model. Some history and mention of previous uses is given in the section entitled ‘History and uses of the geotechnical centrifuge’. Another section deals completely with scaling considerations. This is an important and difficult area and discussions of geotextile and geotextile/soil interactions are given. Previous centrifuge studies of reinforced slopes are detailed. The Drexel Geotechnical Centrifuge is described and a conclusion ends the body of the report and mention is made of future work planned for the Drexel system. The article casts a critical eye at certain aspects of the centrifuge problem. There appear to be some possible fundamental problems concerning the basics of centrifuge modeling that have not been adequately addressed theoretically or experimentally to date.

Diffusion of water from soils encapsulated by impregnated geotextiles (MESLs)

Abstract An analytical model for moisture flow in the composite system of soil-impregnated geotextile-air is presented. It is directed towards the membrane encapsulated soil layer (MESL) problem, although the approach is applicable to a wide range of geomembrane situations. General results are obtained as a function of membrane diffusion coefficients for the change in water content of an encapsulated soil mass over a given time. As an example, by using a criterion of allowing no more than a 1% change in water content of the encapsulated soil (100 cm thick) over one year, it is found that a diffusion coefficient of 10 −7 cm 2 /s or lower is needed for a 0·1 cm thick membrane. Similarly, other situations of practical interest can be formulated.