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181.
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184.
Statistical and geostatistical features of streambed hydraulic conductivities in the Platte River, Nebraska 总被引:1,自引:0,他引:1
Xunhong Chen 《Environmental Geology》2005,48(6):693-701
This paper presents streambed hydraulic conductivities of the Platte River from south-central to eastern Nebraska. The hydraulic
conductivities were determined from river channels using permeameter tests. The vertical hydraulic conductivities (K
v
) from seven test sites along this river in south-central Nebraska belong to one statistical population. Its mean value is
40.2 m/d. However, the vertical hydraulic conductivities along four transects of the Ashland test site in eastern Nebraska
have lower mean values, are statistically different from the K
v
values in south-central Nebraska, and belong to two different populations with mean values of 20.7 and 9.1 m/d, respectively.
Finer sediments carried from the Loup River and Elkhorn River watersheds to the eastern reach of the Platte River lowers the
vertical hydraulic conductivity of the streambed. Correlation coefficients between water depth and K
v
values along a test transect indicates a positive correlation – a larger K
v
usually occurs in the part of channel with deeper water. Experimental variograms derived from the vertical hydraulic conductivities
for several transects across the channels of the Platte River show periodicity of spatial correlation, which likely result
from periodic variation of water depth across the channels. The sandy to gravelly streambed contains very local silt and clay
layers; spatially continuous low-permeability streambed was not observed in the river channels. The horizontal hydraulic conductivities
were larger than the vertical hydraulic conductivities for the same test locations. 相似文献
185.
A multi-layered aquifer, typical of riverbank alluvial deposits in Korea, was studied to determine the hydrologic properties.
The geologic logging showed that the subsurface of the study site was comprised of four distinctive hydrogeologic units: silt,
sand, highly weathered and fresh bedrock layers. The electrical resistivity survey supplied information on lateral extension
of hydrogeologic strata only partially identified by a limited number of the geologic loggings. The laboratory column tracer
test for the recovered core of the sand layer resulted in a hydraulic conductivity of 5.00×10−2 cm/s. The slug tests performed in the weathered rock layer yielded hydraulic conductivities of 4.32–7.72×10−4 cm/s. Hydraulic conductivities for the sand layer calculated from the breakthrough curves of bromide ranged between 2.08×10−3 and 2.44×10−2 cm/s with a geometric mean of 6.89×10−3 cm/s, which is 7 times smaller than that from the laboratory column experiment. The trend of increasing hydraulic conductivity
with an increase in tracer travel length is likely a result of the increased likelihood of encountering a high conductivity
zone as more of the aquifer is tested. The combined hydrogeologic site characterization using hydraulic tests, tracer tests,
and column test with geologic loggings and geophysical survey greatly enhanced the understanding of the hydrologic properties
of the multi-layered alluvial aquifer. 相似文献
186.
Plastic Deformation and Recrystallization of Garnet: A Mechanism to Facilitate Diffusion Creep 总被引:5,自引:0,他引:5
Elongate and deformed garnets from Glenelg, NW Scotland, occurwithin a thin shear zone transecting an eclogite body that hasundergone partial retrogression to amphibolite facies at circa700°C. Optical microscopy, back-scattered electron imaging,electron probe microanalysis and electron back-scatter diffractionreveal garnet sub-structures that are developed as a functionof strain. Subgrains with low-angle misorientation boundariesoccur at low strain and garnet orientations are dispersed, aroundrational crystallographic axes, across these boundaries. Towardshigh-strain areas, boundary misorientations increase and thereis a loss of crystallographic control on misorientations, whichtend towards random. In high-strain areas, a polygonal garnetmicrostructure is developed. The garnet orientations are randomlydispersed around the original single-crystal orientation. Somegarnet grains are elongate and Ca-rich garnet occurs on thefaces of elongate grains oriented normal to the foliation. Commonly,the garnet grains are admixed with matrix minerals, and, wherein contact with other phases, garnet is well faceted. We suggestthat individual garnet porphyroclasts record an evolution fromlow-strain conditions, where dislocation creep and recoveryaccommodated deformation, through increasing strain, where dynamicrecrystallization occurred by subgrain rotation, to higheststrains, where recrystallized grains were able to deform bydiffusion creep assisted grain boundary sliding with associatedrotations. KEY WORDS: diffusion creep; EBSD; garnet; plastic deformation; recrystallization 相似文献
187.
In the underground waste isolation projects such as the ANDRA'one in the site of Bure, the transport properties of the surrounding rock mass is of fundamental importance. To measure very low permeability, we use the modified version of the pulse test proposed by Hsieh et al. [Hsieh, P.A., Tracy, J.V., Neuzil, C.E., Bredehoeft, J.D., Silliman, S.E., 1981. A transient laboratory method for determining the hydraulic properties of ‘tight’ rocks — I. Theory. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. Vol. 18, pp. 245-252] which enables the intrinsic permeability, k, and the specific storage coefficient, Ss, of rocks such as mudstone to be characterized. In this paper, the special effort performed on the laboratory apparatus design, to ensure a good sensitivity of the rock response with respect to both parameters, k and Ss, is presented. In addition, two parameters identification procedures are proposed: the graphical method given by Hsieh et al. [Hsieh, P.A., Tracy, J.V., Neuzil, C.E., Bredehoeft, J.D., Silliman, S.E., 1981. A transient laboratory method for determining the hydraulic properties of ‘tight’ rocks — I. Theory. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. Vol. 18, pp. 245-252] and a parameter identification based on the solution of an inverse problem. The efficiency of the apparatus design and the parameters identification procedures is then demonstrated though some pulse tests performed on the Meuse/Haute-Marne mudstone. 相似文献
188.
The present work proposes an approach to adapt existing isotropic models to transversely isotropic materials. The main idea is to introduce equivalence relations between the real material and a fictitious isotropic one on which one can take all the advantages of the well‐established isotropic theory. Two applications of this approach are presented here: a failure criterion and a damage model that takes into account the load‐induced anisotropy. In both cases, theoretical predictions are in agreement with the experimental data. In the present paper, the developed approach is applied to sedimentary rock materials; nevertheless, it can be generalized to any material that exhibits transverse isotropy. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
189.
A cavity expansion–based solution is proposed in this paper for the interpretation of CPTu data under a partially drained condition. Variations of the normalized cone tip resistance, cone factor, and undrained-drained resistance ratio are examined with different initial specific volume and overconsolidation ratio, based on the exact solutions of both undrained and drained cavity expansion in CASM, which is a unified state parameter model for clay and sand. A drainage index is proposed to represent the partially drained condition, and the critical state after expansion and stress paths of cavity expansion are therefore predicted by estimating a virtual plastic region and assuming a drainage-index–based mapping technique. The stress paths and distributions of stresses and specific volume are investigated for different values of drainage index, which are also related to the penetration velocity with comparisons of experimental data and numerical results. The subsequent consolidation after penetration is thus predicted with the assumption of constant deviatoric stress during dissipation of the excess pore pressure. Both spherical and cylindrical consolidations are compared for dissipation around the cone tip and the probe shaft, respectively. The effects of overconsolidation ratio on the stress paths and the distributions of excess pore pressure and specific volume are then thoroughly investigated. The proposed solution and the findings would contribute to the interpretation of CPTu tests under a random drained condition, as well as the analysis of pile installation and the subsequent consolidation. 相似文献
190.
Actual pumping tests may involve continuously decreasing rates over a certain period of time, and the hydraulic conductivity (K) and specific storage (Ss) of the tested confined aquifer cannot be interpreted from the classical constant‐rate test model. In this study, we revisit the aquifer drawdown characteristics of a pumping test with an exponentially decreasing rate using the dimensionless analytical solution for such a variable‐rate model. The drawdown may decrease with time for a short period of time at intermediate pumping times for such pumping tests. A larger ratio of initial to final pumping rate and a smaller radial distance of the observation well will enhance the decreasing feature. A larger decay constant results in an earlier decrease, but it weakens the extent of such a decrease. Based on the proposed dimensionless transformation, we have proposed two graphical methods for estimating K and Ss of the tested aquifer. The first is a new type curve method that does not employ the well function as commonly done in standard type curve analysis. Another is a new analytic method that takes advantage of the decreasing features of aquifer drawdown during the intermediate pumping stage. We have demonstrated the applicability and robustness of the two new graphical methods for aquifer characterization through a synthetic pumping test. 相似文献