DOI: 10.5194/tc-9-2183-2015
Scopus记录号: 2-s2.0-84948391714
论文题名: A new methodology to simulate subglacial deformation of water-saturated granular material
作者: Damsgaard A ; , Egholm D ; L ; , Piotrowski J ; A ; , Tulaczyk S ; , Larsen N ; K ; , Brædstrup C ; F
刊名: Cryosphere
ISSN: 19940416
出版年: 2015
卷: 9, 期: 6 起始页码: 2183
结束页码: 2200
语种: 英语
英文关键词: 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
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). Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/75222
Appears in Collections: 影响、适应和脆弱性 气候变化与战略
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作者单位: Department of Geoscience, Aarhus University, Aarhus C, Denmark; Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA, United States; Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Copenhagen K, Denmark
Recommended Citation:
Damsgaard A,, Egholm D,L,et al. A new methodology to simulate subglacial deformation of water-saturated granular material[J]. Cryosphere,2015-01-01,9(6)