Experimental Evaluation of Geocell Reinforcement Behavior using Transparent Soil Techniques

Christopher Nelsen, The University of Texas at Austin & Hayward Baker, Inc.

Dr. Jorge G. Zornberg, The University of Texas at Austin

Geocells are a growing type of geosynthetic product used in many applications, including the reinforcement of unbound granular materials for the construction of flexible pavements. Much of the growth in the geocell market share is expected to be driven by extensive infrastructure construction in emerging economies throughout Asia Pacific, the Middle East, and South America. Geocells are used in many applications such as erosion control, channel lining, and retaining wall construction, but a large portion of the projected market growth is expected to be in the construction of low volume roads with a majority of that construction focused in the traditional and renewable energy production industries.

Despite the burgeoning presence of geocells in the civil engineering industry, their acceptance and further implementation by design engineers is limited by the lack of a clear design methodology. Although significant research has been conducted to quantify the performance of geocell-reinforced soil masses, there is no accepted design method for these structures. The Mechanistic-Empirical Pavement Design Guide (MEPDG) is a solid framework on which to base a geocell design method. The resilient modulus of a material is constitutive relationship between the imposed stress state and resilient strain. It is the relevant design parameter that should be modified in the MEPDG for the design of pavement structures using geocells. However, a better understanding of the behavior and mechanisms that contribute to the performance of geocell-reinforced materials is necessary to develop theoretically-sound model.

As such, the materials and equipment necessary to conduct a thorough analysis of geocells were conceived and developed as part of this study. This equipment is based on the transparent soil concept – transparent soils are two-part media consisting of solid particles and a saturating fluid with matching refractive indices. Fused quartz and mineral oil were selected as appropriate materials to use as a granular soil surrogate. The large-scale equipment consists of a steel-framed tank with cast acrylic sides. Many lessons were learned with regard to the use of transparent soil techniques in large-scale experiments. Preliminary results indicate the equipment is adequate to validate the results of prior geocell experiments and provide novel insights into geocell behaviors and reinforcement mechanisms. Additional improvements will allow for the full utilization of transparent soil capabilities and the direct observation of geocell reinforcement behavior and mechanisms in-situ. Generalized results of this study, primarily the experience with transparent soils, can also be used for research into virtually any type of geosynthetic product.