scholarly journals Till Fabric and Deformational Structures in Drumlins Near Waukesha, Wisconsin, U.S.A.

1985 ◽  
Vol 31 (109) ◽  
pp. 220-228 ◽  
Author(s):  
Scott D. Stanford ◽  
David M. Mickelson
Keyword(s):  
Ground Water ◽  
Pore Pressure ◽  
Effective Stress ◽  
Ice Flow ◽  
The Core ◽  
Minimum Drag ◽  
Melt Water ◽  
Sediment Flow ◽  
Till Fabric ◽  
Sand And Gravel

AbstractDeep gravel-pit exposures reveal the distribution and structure of till and underlying sand and gravel in drumlins near Waukesha, Wisconsin. The subglacial sediment is interpreted to have moved laterally into the drumlin sites because the till thickens from the margin to the core of the drumlins, the stone orientation in the till is perpendicular and oblique to ice flow on the drumlin margins, and recumbent isoclinal folds occur in sand on the drumlin margins with axes parallel to the drumlin axes. The resulting accumulations of sediment presented obstacles to ice flow and were streamlined into the minimum-drag drumlin shape by erosion on the margins and by remolding of material in the core of the drumlins. These drumlin nuclei may have formed at spots where there was low effective stress on the bed. The subglacial sediment became mobile as a result of high pore pressure that may have developed as ground water and subglacial melt water were trapped behind a frozen bed at the ice margin. Under certain conditions, however, lateral sediment flow might also have occurred when the sediment was frozen.

scholarly journals Till Fabric and Deformational Structures in Drumlins Near Waukesha, Wisconsin, U.S.A.

1985 ◽  
Vol 31 (109) ◽  
pp. 220-228 ◽  
Author(s):  
Scott D. Stanford ◽  
David M. Mickelson
Keyword(s):  
Ground Water ◽  
Pore Pressure ◽  
Effective Stress ◽  
Ice Flow ◽  
The Core ◽  
Minimum Drag ◽  
Melt Water ◽  
Sediment Flow ◽  
Till Fabric ◽  
Sand And Gravel

AbstractDeep gravel-pit exposures reveal the distribution and structure of till and underlying sand and gravel in drumlins near Waukesha, Wisconsin. The subglacial sediment is interpreted to have moved laterally into the drumlin sites because the till thickens from the margin to the core of the drumlins, the stone orientation in the till is perpendicular and oblique to ice flow on the drumlin margins, and recumbent isoclinal folds occur in sand on the drumlin margins with axes parallel to the drumlin axes. The resulting accumulations of sediment presented obstacles to ice flow and were streamlined into the minimum-drag drumlin shape by erosion on the margins and by remolding of material in the core of the drumlins. These drumlin nuclei may have formed at spots where there was low effective stress on the bed. The subglacial sediment became mobile as a result of high pore pressure that may have developed as ground water and subglacial melt water were trapped behind a frozen bed at the ice margin. Under certain conditions, however, lateral sediment flow might also have occurred when the sediment was frozen.

scholarly journals Morphology, Stratigraphy, and Genesis of Small Drumlins in Front of the Glacier Mýrdalsjökull, South Iceland

1984 ◽  
Vol 30 (104) ◽  
pp. 94-105 ◽  
Author(s):  
Johannes Krüger ◽  
Henrik Højmark Thomsen
Keyword(s):  
Internal Structure ◽  
Flow Direction ◽  
Characteristic Pattern ◽  
Essential Factor ◽  
Ice Flow ◽  
Axis Orientation ◽  
Fluvial Deposits ◽  
The Core ◽  
Melt Water ◽  
Till Fabric

AbstractInvestigations have been made of the geomorphology, internal structure, and till fabric of small drumlins in a drumlin field exposed in front of the retreating northern part of Mýrdalsjökull, Iceland. The drumlins either comprise irregular drumlin complexes or they show clearly the shape of typical drumlins with their highest points at the up-glacier ends of streamlined hills.The core of each drumlin consists either of undisturbed glacio-fluvial deposits or glacio-dynamically deformed drift. The distribution of the first type often has a characteristic en échelon arrangement, similar to the interstream areas in the upper reaches of outwash fans. The second type forms a pattern with a predominant trend conforming to the glacier margin; this type is superimposed on overridden ice-margin push-moraine ridges. It is shown that the material in the drumlin cores is only slightly eroded by the glacier that formed the drumlins. The core is mantled by subglacial lodgement till about 0.1–1.5 m in thickness.Seventeen fabric analyses of 25 clasts each were performed on material from within the till mantle. These analyses show a preferred long-axis orientation but indicate a considerable between-site variability ranging up to 45° even between samples taken a few metres apart. The preferred clast orientation for samples taken along the drumlin crests only deviates 0–10° from the regional ice-flow direction indicated by fluted moraines, whereas the deviation for samples from the flanks and the stoss-sides is up to 35°. However, the fabrics show a characteristic pattern relative to the shape of the drumlin; on their tops, the clast fabric parallels the ice-flow direction, whereas it tends to follow the contour direction on the flanks and stoss-sides.It is concluded that the cores of the drumlins consist of pre-existing deposits, whereas the mantles are composed of subglacial till. Regarding the processes involved, the material contained in the core is mainly eroded by pro-glacial melt-water streams and not by ice. During the subsequent flow of ice across the area, the most prominent terrain elements have acted as subglacial obstacles, leading to localized till deposition and drumlin formation. Thus, the drumlins were formed mainly by subglacial deposition of till but the obstacles acted as an essential factor favouring their initiation.

scholarly journals Morphology, Stratigraphy, and Genesis of Small Drumlins in Front of the Glacier Mýrdalsjökull, South Iceland

1984 ◽  
Vol 30 (104) ◽  
pp. 94-105 ◽  
Author(s):  
Johannes Krüger ◽  
Henrik Højmark Thomsen
Keyword(s):  
Internal Structure ◽  
Flow Direction ◽  
Characteristic Pattern ◽  
Essential Factor ◽  
Ice Flow ◽  
Axis Orientation ◽  
Fluvial Deposits ◽  
The Core ◽  
Melt Water ◽  
Till Fabric

AbstractInvestigations have been made of the geomorphology, internal structure, and till fabric of small drumlins in a drumlin field exposed in front of the retreating northern part of Mýrdalsjökull, Iceland. The drumlins either comprise irregular drumlin complexes or they show clearly the shape of typical drumlins with their highest points at the up-glacier ends of streamlined hills.The core of each drumlin consists either of undisturbed glacio-fluvial deposits or glacio-dynamically deformed drift. The distribution of the first type often has a characteristicen échelonarrangement, similar to the interstream areas in the upper reaches of outwash fans. The second type forms a pattern with a predominant trend conforming to the glacier margin; this type is superimposed on overridden ice-margin push-moraine ridges. It is shown that the material in the drumlin cores is only slightly eroded by the glacier that formed the drumlins. The core is mantled by subglacial lodgement till about 0.1–1.5 m in thickness.Seventeen fabric analyses of 25 clasts each were performed on material from within the till mantle. These analyses show a preferred long-axis orientation but indicate a considerable between-site variability ranging up to 45° even between samples taken a few metres apart. The preferred clast orientation for samples taken along the drumlin crests only deviates 0–10° from the regional ice-flow direction indicated by fluted moraines, whereas the deviation for samples from the flanks and the stoss-sides is up to 35°. However, the fabrics show a characteristic pattern relative to the shape of the drumlin; on their tops, the clast fabric parallels the ice-flow direction, whereas it tends to follow the contour direction on the flanks and stoss-sides.It is concluded that the cores of the drumlins consist of pre-existing deposits, whereas the mantles are composed of subglacial till. Regarding the processes involved, the material contained in the core is mainly eroded by pro-glacial melt-water streams and not by ice. During the subsequent flow of ice across the area, the most prominent terrain elements have acted as subglacial obstacles, leading to localized till deposition and drumlin formation. Thus, the drumlins were formed mainly by subglacial deposition of till but the obstacles acted as an essential factor favouring their initiation.

scholarly journals PENGARUH MUKA AIR TANAH TERHADAP TEGANGAN EFEKTIF TANAH DASAR CANDI PRAMBANAN BERDASAR METODE ELEMEN HINGGA

2019 ◽  
Vol 18 (1) ◽  
Author(s):  
Tri Wahyu Kuningsih ◽  
Dwi Novi Wulansari
Keyword(s):  
Ground Water ◽  
Water Level ◽  
Pore Pressure ◽  
Effective Stress ◽  
Ground Water Level ◽  
Excess Pore Pressure ◽  
Physical Damage ◽  
World Cultural Heritage ◽  
Excess Pore

ABSTRACTIndonesia which geographically has an area located at 6º LU up to 11º LS and 97º BT up to 141º BT is an area prone to earthquakes. Determination of the temple as a world cultural heritage has implications for the responsibilities and obligations of the Indonesian people in an effort to protect and maintain the building in accordance with the conventions set by UNESCO. The convention, among others, is maintaining the preservation of buildings from the dangers of war, physical damage due to age, and natural disasters. This research was conducted with the aim to determine the effect of groundwater depth and earthquake acceleration on the strength of Prambanan Temple subgrade based on finite element method. Simplification of Siwa Temple as a modeling in software input. The results of the study are the shallower depth of the ground water level, the effective stress of the soil will also be reduced. When effective stress decreases, the strength of the soil will also decrease. The deeper the depth of the water table, the effective stress of the soil increases. The depth of the ground water level affects the amount of excess pore pressure. The more shallow the depth of the ground water level, the amount of excess pore pressure will also increase even the value is positive. The deeper the depth of the ground water level, the greater the amount of excess pore pressure decreases even the value is negative.Key words : Prambanan Temple, effective stresses, excess pore pressureABSTRAKIndonesia yang secara geografis mempunyai wilayah yang terletak pada 6º LU sampai dengan 11 º LS serta 97º BT sampai dengan 141º BT merupakan daerah yang rawan terhadap gempa bumi. Penetapan candi sebagai warisan budaya dunia berimplikasi pada tanggung jawab dan kewajiban bangsa Indonesia dalam upaya melakukan pelindungan dan pemeliharaan bangunan tersebut sesuai dengan konvensi yang telah ditetapkan oleh UNESCO. Konvensi tersebut antara lain menjaga pelestarian bangunan dari bahaya perang, kerusakan fisik karena termakan usia, dan bencana alam. Penelitian ini dilakukan dengan tujuan untuk mengetahui pengaruh kedalaman muka air tanah dan percepatan gempa terhadap kekuatan tanah dasar Candi Prambanan berdasar metode elemen hingga. Ilustrasi penyederhanaan Candi Siwa sebagai pemodelan dalam input perangkat lunak. Hasil penelitian adalah semakin dangkal kedalaman muka air tanah, maka tegangan efektif tanah juga akan berkurang. Pada saat tegangan efektif berkurang maka kekuatan tanah juga akan berkurang. Semakin dalam kedalaman muka air tanah, tegangan efektif tanah semakin meningkat. Kedalaman muka air tanah mempengaruhi besarnya excess pore pressure. Semakin dangkal kedalaman muka air tanah, besarnya excess pore pressure juga akan meningkat bahkan nilainya positif. Semakin dalam kedalaman muka air tanah, besarnya excess pore pressure semakin menurun bahkan nilainya negatif.Kata kunci : candi prambanan, tegangan efektif, excess pore pressure.

A comparative study on methods for determining the hydraulic properties of a clay shale

2020 ◽  
Vol 224 (3) ◽  
pp. 1523-1539
Author(s):  
Lisa Winhausen ◽  
Alexandra Amann-Hildenbrand ◽  
Reinhard Fink ◽  
Mohammadreza Jalali ◽  
Kavan Khaledi ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Ion Beam ◽  
Applied Pressure ◽  
Pressure Oscillation ◽  
Stress Conditions ◽  
Data Set ◽  
Clay Shale ◽  
Permeability Coefficients ◽  
Effective Stresses

SUMMARY A comprehensive characterization of clay shale behavior requires quantifying both geomechanical and hydromechanical characteristics. This paper presents a comparative laboratory study of different methods to determine the water permeability of saturated Opalinus Clay: (i) pore pressure oscillation, (ii) pressure pulse decay and (iii) pore pressure equilibration. Based on a comprehensive data set obtained on one sample under well-defined temperature and isostatic effective stress conditions, we discuss the sensitivity of permeability and storativity on the experimental boundary conditions (oscillation frequency, pore pressure amplitudes and effective stress). The results show that permeability coefficients obtained by all three methods differ less than 15 per cent at a constant effective stress of 24 MPa (kmean = 6.6E-21 to 7.5E-21 m2). The pore pressure transmission technique tends towards lower permeability coefficients, whereas the pulse decay and pressure oscillation techniques result in slightly higher values. The discrepancies are considered minor and experimental times of the techniques are similar in the range of 1–2 d for this sample. We found that permeability coefficients determined by the pore pressure oscillation technique increase with higher frequencies, that is oscillation periods shorter than 2 hr. No dependence is found for the applied pressure amplitudes (5, 10 and 25 per cent of the mean pore pressure). By means of experimental handling and data density, the pore pressure oscillation technique appears to be the most efficient. Data can be recorded continuously over a user-defined period of time and yield information on both, permeability and storativity. Furthermore, effective stress conditions can be held constant during the test and pressure equilibration prior to testing is not necessary. Electron microscopic imaging of ion-beam polished surfaces before and after testing suggests that testing at effective stresses higher than in situ did not lead to pore significant collapse or other irreversible damage in the samples. The study also shows that unloading during the experiment did not result in a permeability increase, which is associated to the persistent closure of microcracks at effective stresses between 24 and 6 MPa.

Experimental Investigation of Depletion- and Injection-Induced Changes in Poromechanical, Transport, and Strength Properties of High-Porosity Sandstone

SPE Journal ◽  
2021 ◽  
pp. 1-21
Author(s):  
Saeed Rafieepour ◽  
Stefan Z. Miska ◽  
Evren M. Ozbayoglu ◽  
Nicholas E. Takach ◽  
Mengjiao Yu ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Microstructural Analysis ◽  
Optical Microscope ◽  
Strength Properties ◽  
Rock Properties ◽  
Absolute Permeability ◽  
High Porosity ◽  
Confining Stress ◽  
Stress Changes

Summary In this paper, an extensive series of experiments was performed to investigate the evolution of poromechanical (dry, drained, undrained, and unjacketed moduli), transport (permeability), and strength properties during reservoir depletion and injection in a high-porosity sandstone (Castlegate). An overdetermined set of eight poroelastic moduli was measured as a function of confining pressure (Pc) and pore pressure (Pp). The results showed larger effect on pore pressure at low Terzaghi’s effective stress (nonlinear trend) during depletion and injection. Moreover, the rock sample is stiffer during injection than depletion. At the same Pc and Pp, Biot’s coefficient and Skempton’s coefficient are larger in depletion than injection. Under deviatoric loading, absolute permeability decreased by 35% with increasing effective confining stress up to 20.68 MPa. Given these variations in rock properties, modeling of in-situ-stress changes using constant properties could attain erroneous predictions. Moreover, constant deviatoric stress-depletion/injection failure tests showed no changes or infinitesimal variations of strength properties with depletion and injection. It was found that failure of Castlegate sandstone is controlled by simple effective stress, as postulated by Terzaghi. Effective-stress coefficients at failure (effective-stress coefficient for strength) were found to be close to unity (actual numbers, however, were 1.03 for Samples CS-5 and CS-9 and 1.04 for Sample CS-10). Microstructural analysis of Castlegate sandstone using both scanning electron microscope (SEM) and optical microscope revealed that the changes in poroelastic and transport properties as well as the significant hysteresis between depletion and injection are attributed to the existence and distribution of compliant components such as pores, microcracks, and clay minerals.

scholarly journals The stability of a viscous till sheet coupled with ice flow, considered at wavelengths less than the ice thickness

1998 ◽  
Vol 44 (147) ◽  
pp. 285-292 ◽  
Author(s):  
Richard C. A. Hindmarsh
Keyword(s):  
Large Scale ◽  
Flow Instability ◽  
Ice Thickness ◽  
Ice Flow ◽  
Perturbation Amplitude ◽  
Sediment Flow ◽  
Viscous Models ◽  
The Stability ◽  
Parameter Ranges ◽  
Ice Sheet Modelling

AbstractA perturbation method is used to analyse the stability of a thin till layer overlain by a deep ice layer. Ice is modelled as a linearly viscous fluid, while the till viscosity has power-law dependence on stress and effective pressure. A linearized set of equations yields descriptions of the coupling of the ice flow with the sediment flow and reveals parameter ranges where the till-perturbation amplitude can grow. This sheet-flow instability is an essential part of any theory of drumlin formation and shows that viscous models of till have the ability to explain typical deforming-bed features. This is of great significance for large-scale ice-sheet modelling.

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