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INTRODUCTION Sea ice is characterized by strength anisotropy as a function of load application mode which may be normal (┴) or parallel (||) to the freezing plane. This problem was addressed in a number of papers (Frederking and Timco, 1984). Anisotropy coefficient, kR introduced by the Moscow Construction Engineering Institute (MISI) is obtained as: where R= is the mean value of ultimate uniaxial compressive strength of ice when load direction is normal to the freezing plane and R': is that when load direction is parallel to the freezing plane (MISI Report, 1992). Note that the introduction of anisotropy coefficient involves a number of issues opened to argument. It is known from the law of probability that the ratio of mean values is not the mean value in itself (as opposed to the production of mean values), i.e. kR may be a measure of the mean value but the error of the measure will be unknown. Furthermore, the mean value depends substantially on the number of tests, which is not taken into account in the expression (I). However, anisotropy coefficient was used by MISI and estimated based on a number of data used by some authors involved in anisotropy studies. It varied from 1.04–2.0 (MISI Report, 1992). Anisotropy coefficient was estimated as kR =1.39 during the expedition on the icebreaker "Yermak" in the sea of Okhotsk in 1982 (Report on Expedition... 1982). Institute "SakhalinNIPImorneft" performed ice studies in the Chayvo Bay also using anisotropy coefficient (Polomoshnov, 1990; Polomoshnov et al, 1992). However, no reliable results were obtained: anisotropy coefficient was either over or below 1. Note that the majority of ice strength tests were performed on samples cut out normal to the freezing plane, therefore, knowledge of ice strength anisotropy is required adequate evaluation of the results obtained and substantiation
- North America > United States (0.50)
- Europe > Russia > Central Federal District > Moscow Oblast > Moscow (0.26)
- Asia > Russia > Far Eastern Federal District (0.15)
ABSTRACT: In this study, the solid rock is represented by an assembly of particles joined together by breakable bonds using PFC3D. The contact bonding model supported in PFC3D can transmit a force which acts only at the contact points and it consists of shear and normal strength components. No slip is possible when the contact bond remains intact, but it offers no resistance to rolling. While determining the micro parameters of the model, the effect of stiffness of the particles on Young's modulus and Poisson's ratio are studied. The effect of confining pressure is studied by considering the values corresponding to typical overburden pressures. Along with the stress strain plots at various confining pressures, the extracted micromechanical data are also presented to analyze the strain softening behaviour with special emphasis on the breakage of the bonds. The variation in the strength and mechanical behaviour of the rock masses with respect to the bond strength is thoroughly studied by conducting axisymmetric triaxial tests. The effect of varying bond strengths on the uniaxial compressive strength is also studied at various confining pressures. It can be clearly seen that as the bond strength increases, the compressive strength also increases. Further as the confining pressure increases, there is an increase in compressive strength for the same contact bond strength. Similarly the variation of the values of cohesion and angle of internal friction are also studied for various values of bond strengths. The parametric studies indicate that as the bond strength increases, there is a linear increase in the value of cohesion at various confining pressures, but the angle of internal friction remains almost the same with minor fluctuations. INTRODUCTION Majority of the earth"s crust is covered by sedimentary rocks which are formed by the sedimentation of materials. In due course of time, they will be deposited in layers forming rocks and their strength will depend on various factors including the matrix which bind these particles together. Usually the damage of rock masses occur when the entire bond breaks and the material changes from solid to granular material. Sandstone is a type of sedimentary rock which is comprised of rock fragments or minerals held together by natural cementing materials. Depending upon the strength of the cementation, the behaviour of the rocks also changes. Numerical simulations adopting discrete element method generally represents rock mass as an assembly of particles joined together by breakable bonds. The Bonded Particle Model (BPM) suggested by Potyondy & Cundall [1] states that particles can be bonded together at contacts forming a cemented granular material and the macro-scale mechanical behaviour of this cemented material can be related to the rock mass behaviour. But the suitable selection of the particle-contact parameters for the modeling is very challenging. Unless suitable particle-contact parameters are used, the macro-scale response of the modeled block will not be reliable. Experimental studies have showed that the behavior of intact rock in compression is complex, resulting in a nonlinear failure envelope with high frictional resistance [2].
- Asia > India (0.48)
- North America > United States (0.47)
- Research Report > New Finding (0.69)
- Research Report > Experimental Study (0.48)
- Reservoir Description and Dynamics > Reservoir Simulation (0.75)
- Data Science & Engineering Analytics > Information Management and Systems (0.67)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.55)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.36)
SUMMARY: Strength indices for a wide variety of rocks in dry as well as in water-saturated condition have been measured by the point load test. The general trend is that rocks suffer from a strength reduction when saturated with water. However, a few very fine grained rocks show a significant increase in strength. The results are discussed. A grouping of the rocks based on petrography and water induced changes of strength is presented. RESUMÉ: Dans cet article plusieurs mesures de tension par pression pointue ont ete conduites sur une variete de roches dans des conditions sèches ainsi que saturee d'eau. La tendence generale indique que la resistance dec rout avec la saturation d'eau, avec l'exception de quelque roche de granulometric tres fine qui montre une augmentation du resistance. On discute les resultats et on montre que les roches peuvent etre divisees en sous-groupes selon leur petrographie ainsi que les variation du resistance provoquee par la saturation d'eau. ZUSAMMENFASSUNG: Festigkeitsindexen fuer ein breites Auswahl von Felsen in trocken als auch in wassergesattigten Zustand sind mit dem Punktlastapparat gemesst. Die Felsen wollen in Gewöhnlichkeit wenn mit Wasser gesattigt einen Festigkeitsreduktion aufzeigen. Einige wenige, sehr feinkörnige Felsen zelgen doch elne signifikante Vergrösserung der Festigkeit. Die Resultaten sind diskutiert. Eine Gruppierung der Felsen die auf Petrographie und wasserindusierte Anderungen in Felsfestigkeiten basiert ist, ist presentiert. INTRODUCTION In an earlier paper on the influence water may have on some rock properties, strength reduction as a function of water content was demonstrated for six different rocks, figure 1, BROCH [1974]. For these rocks the reduction in point load strength, from oven dry to fully saturated specimens, varies between 20 and 45% with 34% as an average value. Strength reductions were also observed for rocks tested in uniaxial and triaxial compression. In fact, the reductions in these tests were generally greater than in the point load test. A study of the influence of water saturation on the internal friction, showed that for isotropic, magmatic rocks no change in internal friction was observed. The drop in strength for these rocks must therefore be due to other effects as for instance the reduction in surface energy when the rock Specimens are covered with water. For anisotropic, mica-containing gneisses there was a significant difference in the coefficient of friction from dry to water saturated condition for higher confining pressures. Thus there was no doubt that water reduced the internal friction of such rocks. With a mica content of approximately 15% and with micas being minerals with extreme physical and mechanical properties, it was concluded that the presence of this mineral might explain the great reduction in strength as well as in internal friction for the gneisses. In the present paper the results from a large number of point load strength tests on a wide variety of rocks in dry and water saturated conditions will be reported. This will be followed by a discussion of the petrographical factors that may have an influence on the change of strength from dry to water saturated rocks. THE TESTING AND THE RESULTS The strength test used was the so-called point load strength test which is described in detail by BROCH & FRANKLIN [1972]. The testing was carried out in accordance with suggestions from the COMMISSION ON STANDARDIZATION OF LABORATORY AND FIELD TESTS OF THE I.S.R.M. [1972] as diametral tests on cores. The core diameter used was 32 mm as this is more convenient for harder rocks. The cores were drilled from blocks brought in to the laboratory. Coring was done both parallel and normal to the bedding or foliation of the rocks. All rocks were Norwegian and of Precambrian or Paleozoic age. Porosities of such rocks are normally in the range of 0,25 - 1,25%, seldomly greater than 1,5%. Dry specimens were obtained by storing the cores in an electrical oven with a temperature of 105°C for two days. Wet specimens, or more pricesely fully water saturated specimens, were obtained by first evacuating the air from dry cores and then carefully adding water to the cores while they were still under low pressure. After that the pressure was raised to normal and the cores kept submerged for 15 to 24 hours. (More detailed test description in BROCH [1974 and 1977]). The results from the testing of 27 different rocks are plotted in figure 2, dots indicating results from tests performed on cores drilled parallel and crosses from cores drilled normal to the bedding or foliation. The inclined lines give the varying relation of point load strengths for saturated rocks in percent of strengths for dry rocks. As the figure shows rocks will in general suffer a strength reduction when saturated with water. The point load strength may for some rocks even be reduced to approximately half of their "dry strength".
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.48)
- Geology > Rock Type > Metamorphic Rock > Gneiss (0.48)
ABSTRACT This paper discusses the derivation of soil strength from the vane shear test, examining factors such as rotation rate and waiting time that may influence the observed result. In addition, several different vane geometries (differing height/diameter ratios) have been tested to examine the effect of aspect ratio on the observed vane shear strength. Results from vane shear tests are compared with those obtained from other in situ tests, in particular T-bar penetration tests. A new form of "helical" vane test Is discussed, In which the standard vane apparatus is continuously rotated during penetration into the soil sample, resulting in a complete profile of soil strength. In the discussion, profiles of soil strength determined with varying penetration and rotation rate are compared with strength measurements obtained from more traditional in situ test methods. INTRODUCTION Accurate determination of soil strength is a fundamental aspect of foundation design for offshore structures. At present, in situ assessment of soil strength is comprised primarily of cone penetrometer and vane shear testing, combined with core sampling to retrieve material for laboratory testing. More recently, the T-bar penetrometer has been used to estimate in situ soil strength. As part of a centrifuge modelling study of the performance of skirted foundations for offshore structures (Watson, 1999), a number of in situ strength measurement techniques were examined. Tests were conducted in a range of material types, with varied stress histories ranging from normally consolidated to heavily overconsolidated. Testing included different penetrometers including the cone (CPT) and T-bar, as well as a range of rotational devices including the vane shear test (VST). To complement the in situ tests, a suite of laboratory tests (including simple shear, triaxial compression and triaxial extension tests) was also conducted.
- Oceania > Australia (0.29)
- North America > United States (0.28)
Strength Properties of Deformed Ice in the Kara, Laptev and East Siberian Seas
Efimov, Yaroslav O. (Arctic Research Centre) | Kornishin, Konstantin A. (Arctic Research Centre) | Tarasov, Petr A. (Arctic Research Centre) | Bekker, Alexander T. (Engineering School, Far Eastern State University) | Pomnikov, Evgeniy E. (Engineering School, Far Eastern State University) | Anokhin, Pavel V. (Engineering School, Far Eastern State University) | Guzenko, Roman B. (Arctic and Antarctic Research Institute) | Kovalev, Sergey M. (Arctic and Antarctic Research Institute)
ABSTRACT The article describes correlations between the strength and physical (salinity, temperature) properties of deformed sea ice, determined during ice research in 2013-2017 in the Kara, Laptev and East Siberian Seas. It also provides results of special polygon studies of the ice hummock strength conducted in 2019-2020 in the Khatanga Bay of the Laptev Sea. It is shown that there is no significant difference between level ice and deformed ice (consolidated layer of ice hummocks) in terms of the strength/temperature dependence. Furthermore one-year level ice and two-year level ice, as well as one-year ice hummocks formed on drifting sea ice, can be combined into one group in terms of strength properties (in dependence on the ice temperature). Near mouths of large rivers fast ice and ice hummocks formed on it are characterized by lower salinity and have another characteristic. Correlations between temperature/salinity and the following strength characteristics of level and deformed ice are proposed and refined: local strength, uniaxial compression strength, central bending strength. The coefficients of variation of ice strength have been specified for research sites of 50x50 meters on ice of various types. Regardless of the ice type, these coefficients take typical values in the range of 5-15%. Ratio of local strength to uniaxial compressive strength for the entire set of studied ice has been also determined. A new method is proposed for calculating the level ice strength averaged on its thickness and for calculating the strength of consolidated layer in ice hummocks. The ice strength is defined as a function of the ice temperature in upper horizon (45 cm from the ice surface). The biggest one-year ice hummock of the East Siberian Sea was comprehensively studied: the strength of its consolidated layer (330 cm) was measured with a bore hole-indenter and its cross-section was reconstructed. The obtained data can be used to assess the typical and extreme strength properties of ice hummocks and for calculation of the ice loads on offshore structures in the Arctic.
- North America > United States (1.00)
- Europe (1.00)
- Asia (1.00)
- Asia > Russia > Siberian Federal District > East Siberian Basin (0.89)
- Asia > Russia > Kara Sea > West Siberian Basin > South Kara/Yamal Basin > Leningrad Field (0.89)