Subsidence | EPFL Graph Search

Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope movement. Processes that lead to subsidence include dissolution of underlying carbonate rock by groundwater; gradual compaction of sediments; withdrawal of fluid lava from beneath a solidified crust of rock; mining; pumping of subsurface fluids, such as groundwater or petroleum; or warping of the Earth's crust by tectonic forces. Subsidence resulting from tectonic deformation of the crust is known as tectonic subsidence and can create accommodation for sediments to accumulate and eventually lithify into sedimentary rock. Ground subsidence is of global concern to geologists, geotechnical engineers, surveyors, engineers, urban planners, landowners, and the public in general. Pumping of groundwater or pe

Morphological analysis of the upper reaches of the Kukuy Canyon derived from shallow bathymetry

Yosef Akhtman, Nicolas Le Dantec

We present preliminary results on the morphology of the upper reaches of the Kukuy Canyon and Selenga shelf in front of Proval Bay (Lake Baikal), derived from newly acquired, high-resolution bathymetry. Numerous and varied erosional and transport features provide an interpretation framework for source to sink transfer and gravity flow processes in this shallow and active tectonic environment, suggesting on-going gravity instabilities and sediment-laden flows. Scarps in the canyon head are likely signatures of retrogressive incision of the western tributary and eastward lateral migration of the western tributary, the latter coming within about 1 km of the shoreline. Immature gullies incising the upper-slope feedings of the Kukuy Canyon indicate gravity flows with low erosional power. Large arcuate scarps on the break of the narrow shelf east of Proval Bay reveal gravity instabilities. The morphological connection between the Selenga Delta and the Kukuy Canyon suggests a direct pathway for fluvial sediment focused through breaches in the Sakhalin sand shoal, with likely occurrence of hyperpycnal flows into canyons heads during high sediment discharges. The neotectonic activity affects both the accommodation space around the prograding delta via earthquake-induced subsidence of coastal areas, and the location of incisions through slope instability triggering. Subsequent surveys allowing diachronic analysis would help determining the influence of tectonic and climatic factors controlling sediment transfer across the land-lake continuum and interpreting the morphological signature of the associated gravity processes shaping the delta and surrounding shelf and canyons.

2014

Analysis of the compaction phenomena due to the water injection in reservoirs with a three-phase geomechanical model

Lyesse Laloui, Mathieu Nuth

In the coastal regions, the land subsidence due to the industrial pumping of underground fluids such as methane is documented by the means of in situ surveys. The laboratory characterization of the gas bearing formations has also been published, which complements the knowledge of the reservoir compaction due to the variation of fluid pressures. The withdrawal of gas is reproduced in the laboratory by injecting water under a constant uniaxial or hydrostatic load simulating the overburden. The water injection experiments provoke a plastic compaction of the samples. The paper proposes a new attempt to model the observed compaction of samples, as well as the changes in compressibility and size of the domain of elasticity during the process of water injection. The conceptual framework essentially relies on the mechanics of unsaturated weak rocks, provided that the subsidence phenomenon concerns a three-phase material with solid grains, liquid water and gas. The proposed constitutive model provides a description of the water retention capability of the studied soils that is coupled with the mechanical behaviour. Consequently, the elasto-plastic volumetric changes within the porous medium incorporate the effects of the water saturation and the capillary pressure, also called suction. The formulation of the yield locus is such that the shape of the yield limit depends on suction in order to model the apparent added stiffness brought by low water saturation. The modelling framework, based on the generalization of the effective stress principle to three-phase media, also provides an elasto-plastic comprehension of the well-known “wetting pore collapse” phenomenon. The ACMEG-s model shows consistent understanding of changes of compressibility with the quantity of retained water. The successive phases of isotropic compression and uniaxial mechanical compaction are used for the model calibration. Interestingly, the phases of plastic compression during the water injection are captured with accuracy, which evidence the applicability of such a model to the reservoir-related subsidence studies.

Elsevier2010

A boundary element solution to land subsidence above 3-D gas/ oil reservoirs

Andrea Rinaldo

A linear boundary element (BE) model is proposed for the uncoupled simulation of land subsidence due to gas, oil and hot water production over 3-D arbitrarily shaped reservoirs. The present model is based on the theory of the linear poroelasticity and is implemented for a mechanically homogeneous and isotropic half- space. It allows for any arbitrary geometry of the reservoir and for a non-uniform distribution of the pore pressure decline. It may easily be extended to other physical settings for which a vertical surface point load solution is available.-from Authors

1987

Analysis of the compaction phenomena due to the water injection in reservoirs with a three-phase geomechanical model

Lyesse Laloui, Mathieu Nuth

Elsevier2010