Rapid Prototyping of High Strength Geosynthetic Interfaces

Construction using geosynthetics offer savings both in terms of cost and embodied carbon. However, their application is limited by poor understanding of geosynthetic soil interaction, resulting in at best over conservative designs and at worst failures resulting in uncontrolled contamination and loss of life. This fifteen month project will use digital imaging and rapid prototyping to create higher strength interaction between geosynthetics and adjacent materials, allowing steeper, higher and safer slopes to be constructed, thus facilitating sustainable construction using these materials.

In barrier systems, geomembranes are typically placed, as part of multilayer systems, over low permeability clay to create a composite barrier benefiting from the low permeability of the geomembrane and attenuation properties of the clay. The geomembrane is then overlain by a geotextile or sand to project it from puncture and damage from the overlying material. This project will allow design of geomembrane surfaces for interaction with these adjacent materials. The designed interfaces will have greater peak strength and allow designers to understand and specify the characteristics of interface shear strength beyond simply the height of the surface texturing (asperity height). In practical terms it will allow higher and steeper slopes when using geomembrane barrier systems, offering improved project profitability and safer use across all applications.

The upper bound interface shear strength is controlled by the material adjacent to it. For a geosynthetic-soil interface this is the strength of the soil. For a geomembrane-geotextile interface the maximum strength will be controlled by the internal bond and fibre strength of the geotextile. The role of the texturing is to transfer the stresses into the adjacent material. The "one size fits all" approach of 0.25mm asperity results in the same texturing being used for interactions with fine grained soils, coarse grained soils and geotextiles and also at low and high confining stresses.

The main gaps in knowledge to be addressed are as follows:
1. What are the physical mechanisms that develop peak strength in geomembrane-soil and geomembrane-geosynthetic interfaces?
2. How do these mechanisms differ for interactions with geotextile, coarse grained soil and fine grained soils?
3. Can the nature of the geomembrane surface be designed to better transfer and distribute load, to produce an interface with higher strength?

The project will use scanning electron and optical microscopes to study material interaction to determine how peak strength is mobilised and from these studies produce CAD models of high strength interfaces. The CAD models shall be converted into physical models through 3D printing allowing their interaction with soils and geotextiles to be observed and quantified.
The work will allow design of geomembrane surfaces for interaction with typically used materials. The designed interfaces will have greater peak strength and allow designers to understand and specify the characteristics of interface shear strength beyond simply asperity height. In practical terms it will allow higher and steeper slopes when using geomembrane barrier systems offering improved project profitability.

The proposed research project will benefit the geosynthetics manufacturing industry and clients of geo-environmental protection systems. The project will fundamentally change how geomembranes are specified, allowing surfaces to be specified for specific interactions. This improved knowledge and understanding of geosynthetic interface behaviour will facilitate safer structures, more efficient design and improved product manufacturing practice. Providing a better understanding of the mechanisms of geosynthetic interface shear strength development will allow better understanding of geosynthetic systems and their behaviour. In detail the beneficiaries of the research are:

1. Geosynthetic manufacturers, as this will allow them to optimise texturing techniques to suit applications without the need for significant change to the manufacturing process. These organisations will be researched through an IGS dissemination events and media.
2. UK designers and specifiers as they will be able to specify beyond simple asperity height as the only function of interface behaviour. These organisations will be contacted directly through CPD events.
3. Regulatory bodies (e.g. the Environment Agency, SEPA), public (e.g. local authorities) and private clients (UK based mining companies and waste operators) will have greater confidence in the reliability of strength characteristics of geosynthetic materials, allowing steeper yet safer slopes to be constructed.
4. Clients will benefit from greater design confidence allowing a better balance between cost effectiveness, sustainability and safety of a design solution.
5. The global geosynthetics research community will have a greater understanding of the fundamental aspects of shear strength development thus allowing a platform for future modelling and predictive tools. These will be reached though academic publications and conference presentation.

The greatest benefits of the project will be through changing the way geomembranes are specified to facilitate performance gains available through surface design. Specifiers for the first time will be able to understand the nature of the interface requirement variations dependant of the interaction medium.

The UK geotechnical consulting sector operates widely within the global mining and containment industries which rely heavily on geosynthetic interfaces for stability of their assets. An improved depth of understanding of these interfaces gained through the contents of this work and dissemination events gives the UK a commercial advantage in global knowledge markets. In particular it will allow improved specification of texturing and allow manufacturer's to better understand client requirements, resulting in steeper and higher slopes, with improved economies for clients, whilst reducing the occurrence of stability failures.

The EA in their role of UK regulators of containment activities will benefit from an improved knowledge of geosynthetic interface specification. This will also benefit clients, as improved material and understanding will allow lining and capping of steeper slopes, with fewer slope failures, avoiding the need for regrading, additional soil import or land acquisition.

Industry engagement will be facilitated through three main routes:
1. Through liaisons with the project collaborators. Meetings are proposed at project commencement then at quarterly intervals through the project.
2. A dissemination seminar. The IGS (UK) has allocated a sum of £1000 to facilitate a half day dissemination event for this project.
3. CPD industry engagement events. The project will target eight consulting engineering companies within the UK and deliver, free to participants, a 2 hour training course of geosynthetic interfaces, introducing the importance of specification of texturing and demonstrating the findings of this project.