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DOI	10.5194/tc-9-2183-2015
	A new methodology to simulate subglacial deformation of water-saturated granular material
	Damsgaard A.; Egholm D.L.; Piotrowski J.A.; Tulaczyk S.; Larsen N.K.; Brædstrup C.F.
发表日期	2015
ISSN	19940416
卷号	9 期号:6
英文摘要	The dynamics of glaciers are to a large degree governed by processes operating at the ice-bed interface, and one of the primary mechanisms of glacier flow over soft unconsolidated sediments is subglacial deformation. However, it has proven difficult to constrain the mechanical response of subglacial sediment to the shear stress of an overriding glacier. In this study, we present a new methodology designed to simulate subglacial deformation using a coupled numerical model for computational experiments on grain-fluid mixtures. The granular phase is simulated on a per-grain basis by the discrete element method. The pore water is modeled as a compressible Newtonian fluid without inertia. The numerical approach allows close monitoring of the internal behavior under a range of conditions. Our computational experiments support the findings of previous studies where the rheology of a slowly deforming water-saturated granular bed in the steady state generally conforms to the rate-independent plastic rheology. Before this so-called critical state, deformation is in many cases accompanied by volumetric changes as grain rearrangement in active shear zones changes the local porosity. For previously consolidated beds porosity increases can cause local pore-pressure decline, dependent on till permeability and shear rate. We observe that the pore-water pressure reduction strengthens inter-granular contacts, which results in increased shear strength of the granular material. In contrast, weakening takes place when shear deformation causes consolidation of dilated sediments or during rapid fabric development. Both processes of strengthening and weakening depend inversely on the sediment permeability and are transient phenomena tied to the porosity changes during the early stages of shear. We find that the transient strengthening and weakening in turn influences the distribution of shear strain in the granular bed. Dilatant strengthening has the ability to distribute strain during early deformation to large depths, if sediment dilatancy causes the water pressure at the ice-bed interface to decline. Oppositely, if the ice-bed interface is hydrologically stable the strengthening process is minimal and instead causes shallow deformation. The depth of deformation in subglacial beds thus seems to be governed by not only local grain and pore-water feedbacks but also larger-scale hydrological properties at the ice base. © 2015 Author(s).
学科领域	deformation mechanism; experimental study; glacier flow; granular medium; Newtonian fluid; numerical model; porewater; porosity; rheology; saturation; shear flow; shear strength; shear stress; subglacial environment; unconsolidated medium
语种	英语
scopus关键词	deformation mechanism; experimental study; glacier flow; granular medium; Newtonian fluid; numerical model; porewater; porosity; rheology; saturation; shear flow; shear strength; shear stress; subglacial environment; unconsolidated medium
来源期刊	Cryosphere
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/119780
作者单位	Department of Geoscience, Aarhus University, Aarhus C, 8000, Denmark; Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, United States; Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Copenhagen K, 1350, Denmark
推荐引用方式 GB/T 7714	Damsgaard A.,Egholm D.L.,Piotrowski J.A.,et al. A new methodology to simulate subglacial deformation of water-saturated granular material[J],2015,9(6).
APA	Damsgaard A.,Egholm D.L.,Piotrowski J.A.,Tulaczyk S.,Larsen N.K.,&Brædstrup C.F..(2015).A new methodology to simulate subglacial deformation of water-saturated granular material.Cryosphere,9(6).
MLA	Damsgaard A.,et al."A new methodology to simulate subglacial deformation of water-saturated granular material".Cryosphere 9.6(2015).