CREEP - Creep of Geomaterials
CREEP is a Industry-Academia Partnerships and Pathways (IAPP) project funded from the 7th Framework Programme (FP7/2007-2013) of the EC under grant agreement PIAG-GA-2011-286397.
Creep is a time dependent process in which materials accumulate strains (deformations) under the influence of constant (effective) stresses. Creep of geomaterials can be often observed in slopes where creep manifests as slow mass wasting, that is slow downhill movement of soil and rock mass - see picture below.
Creep considerations in Geotechnical Engineering are not limited to slopes: All infrastructure that introduces load in the subsoil is subject to creep, too. For economic and functional design the magnitude of creep is to be known. The CREEP project aims at developping new design tools for creep in soft soils, frozen soils and also hard soils. Further information on the aims and objectives of the CREEP project is given below.
Web Content Article
Slow time-dependent movements caused by creep of natural geomaterials affect the performance of infrastructure and cause high maintenance and repair costs, and the partial closures of infrastructure networks during the repair work have significant economic and social impact. Although the phenomenon of creep is well-known for being a major design issue, there is currently no accepted consensus on the best way to model creep. Reliable calculation tools are either missing or - due to their scientific nature - out of reach for the engineer in charge. If as a consequence creep is underestimated in design, structures will possibly be damaged so that they will not reach their design life. On the other hand, if creep is overestimated, unnecessary countermeasures such as soil improvement, deep foundations, or additional structural reinforcement will take up additional resources. For sustainable building processes it is therefore imperative to adequately incorporate creep behaviour in analyses and design.
The research topic of this Marie Curie action is creep behaviour of geomaterials and its incorporation in geotechnical design; the project aims at establishing a consensus in creep modelling. The project shall supply tools and knowledge needed in creep analysis. Past research in the field of creep behaviour of soils has concentrated mainly on soft silts and clays. Different theoretical frameworks and numerical models were proposed. Yet, creep is likewise observed in geomaterials such as peat, sand, and warm permafrost. Key questions formulated by industry and academia are therefore: Can existing creep concepts be adopted equally for those materials? Can different creep concepts be unified? Of the alternatives proposed, which work best at both element level and real geotechnical problem level? This project intends to answer these questions by combining the practical experience gathered by industry with the theoretical concepts worked out by academia.
Keywords: Geotechnical Engineering, Material Model, Finite Element Method, Creep, Soft Soil, Organic Soil, Permafrost, Sand, Structure, Anisotropy
Research topic aim and implementation
The research topic of this collaboration project is creep behaviour of geomaterials and its embedment in geotechnical design; the project aims at establishing a consensus in creep modelling. The project shall supply tools and knowledge needed in creep analysis of geomaterials through build up of new knowledge and transfer of knowledge between industry and academia. The project will be implemented via secondments and recruitment of 156 researcher months in total (114 months of secondment and 42 months of recruitment).
Overall S&T objectives
The project's overall S&T objectives is to formulate, implement, and validate a set of novel time dependent material (creep) models for clay, peat, sand, and frozen soil, which allow for enhanced creep predictions. As model formulation prerequisites experimental quantification of creep behaviour in the respective materials, the latter is an overall S&T objective as well.
State-of-the-art and innovation
Previous research on creep of geomaterials was mostly conducted on soft soils. Various concepts for modelling creep of soft soils therefore exist. A wide range of constitutive models, each one with its formulation and theoretical basis, is proposed by academia. This generates somewhat confusion in the community of geotechnical engineers. The lack of general understanding of the basic principle of each formulation is hindering the use of advanced constitutive models in production although comparison of different soft soil creep concepts in benchmark exercises showed that there can be reasonable agreement. However, different soft soil creep concepts are sensitive to various material parameters, for example the geologic stress history of the material often quantified by the apparent over consolidation ratio (OCR). If this parameter is varied, the creep concepts vary significantly in their predictions. As this poses a serious problem to industry application, the CREEP project strives for an innovative creep model for clays that unifies existing creep concepts in their response. Fundamental features of natural soft soils, such as anisotropy and destructuration, shall be incorporated in the soft soil creep model as well. Several papers have documented creep behaviour of other geomaterials than clay and constitutive models for modelling their time dependent behaviour have been put forward based on classical Isotach theory or the so-called Evanescent Viscosity. Even more than in clay, however, constitutive models for viscous behaviour of peat, frozen soil, and sand are confined to research. The CREEP project aims to create innovative industry-ready frameworks for modelling creep in these materials and the knowledge required so that they can be fruitfully employed in day-to-day engineering practice.
The 2nd CREEP newsletter of September 2015 is now out.
3rd CREEP Workshop was held at NGI, Oslo, at the 8th of January 2015. Dowload presentations.
2nd CREEP Course was held in the Fall 2014. Download HANDOUTS of 2nd course.
The 1st CREEP newsletter of January 2014 is now out.