Stress regime in compacted fills during wetting and drying cycles under laterally restrained conditions

Healthy and resilient infrastructure (for example retaining walls and buried utilities) provides the basic ingredients for economic success in developed and developing nations. This infrastructure is under severe strain due to a rapidly changing environment with hot summers and wet winters in many part of the world including the UK. Clay rich soils (which are the most common deposits in the UK) respond to these climate changes and the consequences on the infrastructure are severe, particularly in terms of financial implications. The aim of the project is to explore a specific aspect of the problem in relation to the performance of retaining structures or rigid walls backfilled with clay rich soils. The specific objectives of the projects are:
1) Collection of at least three different soils commonly found in the UK and characterization of them in terms of soil water characteristics, mineralogy together with the routine classification tests such as index properties, particle size distributions and compaction characteristics.
2) Construction of a model testing chamber with dimensions of 1mX1mX1m combined with instrumentation to measure suction, volumetric water content, small strain stiffness, lateral pressure and deformation.
3) Evaluation of the performance of the retaining structure (the rigid wall of the model chamber represents a retaining wall) back filled with clay rich soils (three different types) and subjected to several cycles of wet (i.e. creating a typical rainfall event on the soil surface) and dry (exposing the soil surface to elevated temperature i.e. the maximum recorded in the UK) conditions.
4) Rectification of potential issues such as build-up of lateral pressure (as observed in Objective 3) by modifying the top surface of the clay bed in such a way to limit or prevent ingress of water during backfill in wet periods and to limit the shrinkage of the soil bed during dry periods.
5) Assessment of soil performance at micro level by performing element testing using a state of the art stress path cell developed at Queen University Belfast for investigation soils undergoing wetting and drying cycles.
6) Extending the model study as outlined in Objectives 3 and 4 to more realistic in-situ conditions by performing investigations using centrifuge testing available at the University of Dundee.
7) Dissemination of the findings at international conferences and in journals.
The postgraduate student associated with this project will ensure (with guidance from the supervisor) that all of the objectives are achieved in a timely manner and to a good standard. Retaining structures or rigid walls are normally designed by assuming the soils surrounding them are saturated. It is a very simplified assumption as the soil may have been compacted in the first instance or it may undergo drying and wetting. Existing information on the topic under investigation is limited due to complexity of the soil being unsaturated and the required scientific knowledge in interpreting the observations. The supervisor has 25 years of experience in carrying of investigations on unsaturated and saturated soils and a well-developed laboratory to conduct the investigations. It is hoped that the outcome from the research will have an impact on the current methods adopted for designing retaining structures and rigid walls.