Niels Nielsen Foged

Face logging in Copenhagen Limestone, Denmark

The nature-inspired concept of self-healing materials in construction is relatively new and has recently attracted significant attention as this could bring about substantial savings in maintenance costs as well as enhance the durability and serviceability and improve the safety of our structures and infrastructure. Much of the research and applications to date has focused on concrete, for structural applications, and on asphalt, with significant advances being made. However, to date no attention has been given to the incorporation of self-healing concepts in geotechnical and geo-environmental applications. This includes the use of concrete and other stabilising agents in foundations and other geotechnical structures, grouts, grouted soil systems, soil-cement systems and slurry walls for ground improvement and land remediation applications. The recently established Materials for Life (M4L) project funded by EPSRC has initiated research activities in the UK focussing on those applications. The project involves the development and integration of the use of microcapsules, biological agents, shape memory polymers and vascular networks as healing systems. The authors are exploring development of self-healing systems using mineral admixtures, microencapsulation and bio-cementation applications. The paper presents an overview of those initiatives to date and potential applications and presents some relevant preliminary results.By contrast to studies in petroleum geology and, despite their world-wide occurrence, geotechnical studies of ancient fluvial sediments are rare. This paper introduces the main characteristics of these sediments by reference to a classic UK example. Attention is then drawn to a number of major overseas examples where, although the principal features can be recognised, large differences arise as a result of factors such as the tectonic setting, the volume and mineralogy of the source material and the climate at the time the sediments were deposited. The first, over-riding problem for their engineering evaluation comes during the site investigation phase with the difficulty of deducing the geological structure and distribution of the widely varying lithologies.Strain accumulation in granular soils due to dynamic loading is investigated through long term cyclic triaxial tests and cyclic triaxial tests according to ASTM D 3999-91. Soil parameters, test equipment and loading conditions have a significant influence on strain accumulation, therefore a parameterization of the silica sand and a description of the cyclic triaxial test device are explained. Cyclic triaxial tests are performed and test results are presented illustrating the evolution of Young’s modulus during long term cyclic loading. The influence of the width of the stress-strain loop and the initial void ratio on strain accumulation is investigated and validated with existing accumulation models. The usefulness of Miner’s rule on sand subjected to cyclic loading is demonstrated by two tests with different packages of loading cycles.

Elastic Deformation Behaviour of Palaeogene Clay

In this study, naturally water saturated Palaeogene clay samples were obtained from Fehmarn Belt area and used to study the elasticity of this highly plastic smectite rich clay. We used geotechnical and elastic wave velocity data to model the elasticity and then related it to clay mineralogy and BET surface area. Smectite content is the main controlling factor for the elasticity of the studied Palaeogene clay. Our results could have implications for engineering practice, including structural design and slope stability analysis. The obtained results may also aid in the estimation of elastic parameters for use in AVO analysis. Additionally, the mineral modulus can be obtained from velocity data.

Recovery of Porosity and Permeability for High Plasticity Clays

Stress history is normally evaluated based on an evaluation of geological history and if possible combined with oedometer tests where preconsolidation stress σp and compaction properties are measured. Often the constrained modulus M is used to define the stiffness, and the value will typically depend on the stress state of the sample. The stress state of a sample is typically defined by overconsolidation ratio OCR defined as the ratio between vertical preconsolidation stress and actual vertical stress (OCR = σp/σ0). Janbu (1963), Maine & Kulhawy (1982) and others have published typical relations that describe stress state and constrained modulus as functions of OCR, plasticity index and other quantities. They are all based on the assumption that the soil sample “remembers” previous load levels, and that stiffness of the sample is consequently increased due to the preloading. Definition and applicability of the reconsolidation stress is now questioned when high plasticity calys are considered. Even if it is known, that a clay layer has been exposed to a high stress level, for instance due to the weight of an ice shield, the actual stress level according to that preloading might not be the relevant parameter when estimating stiffness properties for use in basin modeling or other models.

Creep of Highly Porous Chalk and Biot Critical Frequency

Chalk behaves with time dependent deformation when subjected to a load. We review a previously published data set from high pressure oedometer tests and apply a friction factor corresponding to the friction between solid and pore fluid. The friction factor is the Biot critical frequency used in acoustic theory to discriminate between the high and low frequency domains. By doing this we show how test results from dry, oil, and water saturated chalk can be combined in one simple expression.