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1.
The hydro-mechanical behaviour of a reconstituted unsaturated soil under different suctions and strain rates was studied through various rate-controlled unsaturated/undrained triaxial tests. The fully saturated reconstituted specimens were desaturated to four different initial suctions (s0?=?0, 100 kPa, 200 kPa and 300 kPa) and then triaxially sheared (conventional triaxial compression) at three different strain rates in undrained conditions (\(\dot{\varepsilon }_{1} = 0.001\) h?1, 0.01 h?1, and 0.1 h?1). The observed hydro-mechanical behaviour during shearing including the volumetric strain, deviatoric stress, degree of saturation and suction is presented and discussed in this paper. The results indicate that when the strain rate rises at the given initial suctions (or pore water pressures), the maximum deviatoric stress (qmax), critical net stress ratio (M) and critical state suction (sc) increase but the degree of saturation (Src) and volumetric strain at the critical state (εcv
) reduce. The critical effective stress ratio (M′) is not dependent on the strain rate for saturated and unsaturated samples. The critical state lines for unsaturated soils with the constant strain rates are parallel with each other in the e???lnp′ space. 相似文献
2.
In this study, magnetic techniques were used to characterize the surface soil from different geomorphologies (i.e., sand desert,
oasis, Gobi, and dry lake) in Central Asia. Results demonstrate that the main magnetic minerals in the surface soil are magnetite,
maghaemite and haematite with some paramagnetic materials. Cross plots of M
rs/ M
s versus B
cr/ B
c and χ fd% versus χ arm/saturation isothermal remanent magnetization (SIRM) indicate that the main magnetic grain sizes in surface soil are pseudo
single domain (PSD) and multidomain (MD). The samples from West China (i.e., Tarim basin and Junggar basin) are dominated
by magnetic minerals with larger grain size, while those from North China (i.e., Alxa plateau, Erdos plateau, and Mongolia
plateau) are dominated by fine magnetic minerals. The similarity in magnetic mineral constitutions between the Chinese loess
and the surface soils from Central Asia implies that the loess originated from a vast area of arid, semi-arid regions of Central
Asia. The low value of concentration-dependent magnetic parameters indicates that the low concentration of magnetic minerals
in the surface soils from Central Asia and the magnetic enhancement from the pedogenic take place in both the loess and the
paleosols, although the progress is stronger in the latter.
Translated from Quaternary Sciences, 2006, 26(6): 937–946 [译自: 第四纪研究] 相似文献
3.
A 28-m-long section situated on the coast of the Arctic Ocean, Russia (74°N, 113°E) was extensively sampled primarily for the purpose of magnetostratigraphic investigations across the Jurassic/Cretaceous boundary. The section consists predominantly of marine black shales with abundant siderite concretions and several distinct siderite cemented layers. Low-field magnetic susceptibility ( k) ranges from 8 × 10 − 5 to 2 × 10 − 3 SI and is predominantly controlled by the paramagnetic minerals, i.e. iron-bearing chlorites, micas, and siderite. The siderite-bearing samples possess the highest magnetic susceptibility, usually one order of magnitude higher than the neighboring rock. The intensity of the natural remanent magnetization ( M0) varies between 1 × 10 − 5 and 6 × 10 − 3 A/m. Several samples possessing extremely high values of M0 were found. There is no apparent correlation between the high k and high M0 values; on the contrary, the samples with relatively high M0 values possess average magnetic susceptibility and vice versa. According to the low-field anisotropy of magnetic susceptibility (AMS), three different groups of samples can be distinguished. In the siderite-bearing samples (i), an inverse magnetic fabric is observed, i.e., the maximum and minimum principal susceptibility directions are interchanged and the magnetic fabric has a distinctly prolate shape. Triaxial-fabric samples (ii), showing an intermediate magnetic fabric, are always characterized by high M0 values. It seems probable that the magnetic fabric is controlled by the preferred orientation of paramagnetic phyllosilicates, e.g., chlorite and mica, and by some ferromagnetic mineral with anomalous orientation in relation to the bedding plane. Oblate-fabric samples (iii) are characterized by a bedding-controlled magnetic fabric, and by moderate magnetic susceptibility and M0 values. The magnetic fabric is controlled by the preferred orientation of phyllosilicate minerals and, to a minor extent, by a ferrimagnetic fraction, most probably detrital magnetite. Considering the magnetic fabric together with paleomagnetic component analyses, the siderite-bearing, and the high-NRM samples (about 15% of samples) were excluded from further magnetostratigraphic research. 相似文献
4.
A single crystal X-ray diffraction study on lithium tetraborate Li 2B 4O 7 (diomignite, space group I4 1
cd) has been performed under pressure up to 8.3 GPa. No phase transitions were found in the pressure range investigated, and
hence the pressure evolution of the unit-cell volume of the I4 1
cd structure has been described using a third-order Birch–Murnaghan equation of state (BM-EoS) with the following parameters:
V
0
= 923.21(6) Å 3, K
0
= 45.6(6) GPa, and K′ = 7.3(3). A linearized BM-EoS was fitted to the axial compressibilities resulting in the following parameters a
0
= 9.4747(3) Å, K
0a
= 73.3(9) GPa, K′
a
= 5.1(3) and c
0
= 10.2838(4) Å, K
0c
= 24.6(3) GPa, K′
c
= 7.5(2) for the a and c axes, respectively. The elastic anisotropy of Li 2B 4O 7 is very large with the zero-pressure compressibility ratio β
0c
/β
0a
= 3.0(1). The large elastic anisotropy is consistent with the crystal structure: A three-dimensional arrangement of relatively
rigid tetraborate groups [B 4O 7] 2− forms channels occupied by lithium along the polar c–axis, and hence compression along the c axis requires the shrinkage of the lithium channels, whereas compression in the a direction depends mainly on the contraction of the most rigid [B 4O 7] 2− units. Finally, the isothermal bulk modulus obtained in this work is in general agreement with that derived from ultrasonic
(Adachi et al. in Proceedings-IEEE Ultrasonic Symposium, 228–232, 1985; Shorrocks et al. in Proceedings-IEEE Ultrasonic Symposium, 337–340, 1981) and Brillouin scattering measurements (Takagi et al. in Ferroelectrics, 137:337–342, 1992). 相似文献
5.
This paper presents the distribution of magnetic susceptibility, χ 0, in fragments of the Chelyabinsk ordinary chondrite (LL5, S4, W0, fall of February 15, 2013) from the collection of the Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, and results obtained by standard magnetic techniques for the meteorite material, including thermomagnetic analysis, measurements of natural remanent magnetization (NRM) and saturation isothermal remanent magnetization (SIRM), as well as the spectra of their alternating field demagnetization at amplitudes up to 170 mT, measurements of hysteresis loops and back-field remanence demagnetization curves at temperatures from 10 K to 700°C etc. The mean logχ 0 values for the light-colored (main) lithology of the meteorite material and impact-melt breccia from our collection are 4.54 ± 0.10 ( n = 66) and 4.65 ± 0.09 ( n = 38) (×10 ?9 m 3/kg), respectively. According to international magnetic classification of meteorites, Chelyabinsk falls within the range of LL5 chondrites. The mean metal content was estimated from the saturation magnetization, M s, of the light- and dark-colored lithologies as 3.7 and 4.1 wt %, respectively. Hence, the dark lithology is richer in metal. The metal grains are multidomain at room temperature and show low coercive force, B c (<2 mT) and remanent coercive force, B cr (15–23 mT). The thermomagnetic analyses of the samples showed that the magnetic properties of the Chelyabinsk meteorite are controlled mainly by taenite and kamacite at temperatures >75 K. In the temperature range below 75 K, magnetic properties are controlled by chromite; the magnetic hardness of the samples is maximal at 10 K and equals to 606 and 157 mT for the light- and dark-colored lithologies, respectively. 相似文献
6.
The ratios M
R = E/ σ
c for 11 heterogeneous carbonate (dolomites, limestones and chalks) rock formations collected from different regions of Israel
were examined. Sixty-eight uniaxial compressive tests were conducted on weak-to-strong (5 MPa < σ
c < 100 MPa) and very strong ( σ
c > 100 MPa) rock samples exhibiting wide ranges of elastic modulus ( E = 6100–82300 MPa), uniaxial compressive strength ( σ
c = 14–273.9 MPa), Poisson's ratio ( ν = 0.13–0.49), and dry bulk density ( ρ = 1.7–2.7 g/cm 3). The observed range of M
R = 60.9–1011.4 and mean value of M
R = 380.5 are compared with the results obtained by Deere (Rock mechanics in engineering practice, Wiley, London, pp 1–20,
1968) for limestones and dolomites, and the statistical analysis of M
R distribution is performed. Mutual relations between E, σ
c, ρ, M
R for all studied rocks, and separately for concrete rock formations are revealed. Linear multiple correlations between E on the one hand and σ
c and ρ on the other for Nekorot and Bina limestone and Aminadav dolomite are obtained. It is established that the elastic modulus
and M
R in very strong carbonate samples are more correlated with ρ− σ
c combination and ε
a max, respectively, than in weak to strong samples. The relation between M
R and maximum axial strain ( ε
a max) for all studied rock samples (weak-to-strong and very strong) is discussed. 相似文献
7.
Ore microscopic investigation of the Fe?CTi oxide minerals was carried out on samples from three Oligo-Miocene basaltic occurrences from Sinai, Egypt. These occurrences are Gebel Maghara (north Sinai), Rageibet Naama (central Sinai), and Wadi Matulla (west Sinai). The results and correlations of magnetic parameters such as NRM intensity and susceptibility, coercive force H c, and the ratio M r/ M s, H c and Q value, the ratio M r/ M s, saturation magnetization M s, and K are discussed in light of opaque mineralogical studies. It has been found that the variations in the magnetic properties of the basaltic occurrences are strongly dependent on the crystallite size and nature and style of exsolution textures and fabrics. The latter are controlled by the cooling conditions, being most sensitive to the partial pressure of oxygen in the melt. 相似文献
8.
Chemically-zoned amphibole porphyroblast grains in an eclogite (sample ws24-7) from the western Tianshan (NW-China) have been
analyzed by electron microprobe (EMP), micro Fourier-transform infrared (micro-FTIR) and micro-Raman spectroscopy in the OH-stretching
region. The EMP data reveal zoned amphibole compositions clustering around two predominant compositions: a glaucophane end-member
(
B
Na 2
C
M 2+
3 M 3+
2
T
Si 8(OH) 2) in the cores, whereas the mantle to rim of the samples has an intermediate amphibole composition (
A
0.5
B
Ca 1.5Na 0.5
C
M
2+
4.5 M
0.53+
T
Si 7.5Al 0.5(OH) 2) ( A = Na and/or K; M
2+ = Mg and Fe 2+; M
3+ = Fe 3+ and/or Al) between winchite (and ferro-winchite) and katophorite (and Mg-katophorite). Furthermore, we observed complicated
FTIR and Raman spectra with OH-stretching absorption bands varying systematically from core to rim. The FTIR/Raman spectra
of the core amphibole show three lower-frequency components (at 3,633, 3,649–3,651 and 3,660–3,663 cm −1) which can be attributed to a local O(3)-H dipole surrounded by
M(1) M(3)Mg 3,
M(1) M(3)Mg 2Fe 2+ and
M(1) M(3) Fe 2+
3, respectively, an empty A site and
T
Si 8 environments. On the other hand, bands at higher frequencies (3,672–3,673, 3,691–3,697 and 3,708 cm −1) are observable in the rims of the amphiboles, and they indicate the presence of an occupied A site. The FTIR and Raman data from the OH-stretching region allow us to calculate the site occupancy of the A, M(1)– M(3), T sites with confidence when combined with EPM data. By contrast M(2)- and M(4) site occupancies are more difficult to evaluate. We use these samples to highlight on the opportunities and limitations
of FTIR OH-stretching spectroscopy applied to natural high pressure amphibole phases. The much more detailed cation site occupancy
of the zoned amphibole from the western Tianshan have been obtained by comparing data from micro-chemical and FTIR and/or
Raman in the OH-stretching data. We find the following characteristic substitutions Si( T-site) (Mg, Fe)[ M(1)– M(3)-site] → Al( T-site) Al[ M(1)– M(3)-site] (tschermakite), Ca( M4-site)□ ( A-site) → Na( M4-site) Na + K( A-site) (richterite), and Ca( M4-site) (Mg, Fe) [ M(1)– M(3)-site] → Na( M4-site) Al[ M(1)– M(3)-site] (glaucophane) from the configurations observed during metamorphism. 相似文献
9.
The thermoelastic behaviour of anthophyllite has been determined for a natural crystal with crystal-chemical formula ANa 0.01
B(Mg 1.30Mn 0.57Ca 0.09Na 0.04) C(Mg 4.95Fe 0.02Al 0.03) T(Si 8.00)O 22
W(OH) 2 using single-crystal X-ray diffraction to 973 K. The best model for fitting the thermal expansion data is that of Berman
(J Petrol 29:445–522, 1988) in which the coefficient of volume thermal expansion varies linearly with T as α
V,T
= a
1 + 2 a
2 ( T − T
0): α 298 = a
1 = 3.40(6) × 10 −5 K −1, a
2 = 5.1(1.0) × 10 −9 K −2. The corresponding axial thermal expansion coefficients for this linear model are: α
a
, 298 = 1.21(2) × 10 −5 K −1, a
2,a
= 5.2(4) × 10 −9 K −2; α
b
, 298 = 9.2(1) × 10 −6 K −1, a
2,b
= 7(2) × 10 −10 K −2. α
c
, 298 = 1.26(3) × 10 −5 K −1, a
2,c
= 1.3(6) × 10 −9 K −2. The thermoelastic behaviour of anthophyllite differs from that of most monoclinic ( C2/ m) amphiboles: (a) the ε
1 − ε
2 plane of the unit-strain ellipsoid, which is normal to b in anthophyllite but usually at a high angle to c in monoclinic amphiboles; (b) the strain components are ε
1 ≫ ε
2 > ε
3 in anthophyllite, but ε
1 ~ ε
2 ≫ ε
3 in monoclinic amphiboles. The strain behaviour of anthophyllite is similar to that of synthetic C2/ m
ANa B(LiMg) CMg 5
TSi 8 O 22
W(OH) 2, suggesting that high contents of small cations at the B-site may be primarily responsible for the much higher thermal expansion
⊥(100). Refined values for site-scattering at M4 decrease from 31.64 epfu at 298 K to 30.81 epfu at 973 K, which couples with similar increases of those of M1 and M2 sites. These changes in site scattering are interpreted in terms of Mn ↔ Mg exchange involving M1,2 ↔ M4, which was first detected at 673 K. 相似文献
10.
In order to investigate the strength and deformation anisotropy of compacted decomposed granite soils, a series of drained
triaxial compression tests was performed on unsaturated and saturated decomposed granite soils. The specimens were subjected
to compression tests such that the angle δ of the direction of the major principal stress, σ
1, during triaxial compression relative to the compaction plane (bedding plane) varies, with δ = 0°, 45° and 90°. Test results indicated that the compressive strain of the specimens subjected to isotropic consolidation
was influenced strongly by the angle δ. In addition, the effect of the angle δ on the triaxial compressive strength and deformation was more evident in unsaturated specimens than in saturated specimens.
Based on the test results, a procedure which can be used to estimate the shear strength of unsaturated soils taking into account
various angles δ was proposed. 相似文献
11.
Phengite samples (2 M
1 and 3 T politypes) and a synthetic end-member muscovite specimen were studied by in situ high-temperature synchrotron radiation X-ray
diffraction. The measured volume thermal expansion of 2 M
1 phengite (< α
V> ≈ 36.6 × 10 −6 K −1) was systematically greater than < α
V> of the 3 T polytype (≈33.3 × 10 −6 K −1). A positive linear correlation between the average thermal expansion on (001) plane and the mean tetrahedral rotation angle
at ambient condition is proposed on the ground of new measurements and literature data. Dehydroxylation processes were observed
in 2 M
1, starting at 1,000 K in 3 T at 800 and 945 K in synthetic muscovite. Rietveld refinements allowed a determination of structural variations upon heating
of phengite samples and their dehydroxylate phases. The phengite structure expands by regularizing the tetrahedral sheet and
by reducing the bond length differences between the outer and inner coordination shell of the interlayer site. The dehydroxylate
phase derived from 2 M
1 is characterized by fivefold polyhedra in the low temperature form as a consequence of two OH groups reacting to form H 2O + O (residual). The dehydroxylate exhibits an increase of the cation–cation distances along the M–Or–M bonds with respect
to low-temperature phengite structures. For the 3 T phase, we were unable to achieve completion of dehydroxylation. The refined structural model of the dehydroxylate phase shows
two hydroxyl sites, but at a short distance from one another. This result suggests that the dehydroxylation reaction did not
proceed to completion.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
12.
A homogenous earthquake catalog is a basic input for seismic hazard estimation, and other seismicity studies. The preparation
of a homogenous earthquake catalog for a seismic region needs regressed relations for conversion of different magnitudes types,
e.g. m
b
, M
s
, to the unified moment magnitude M
w. In case of small data sets for any seismic region, it is not possible to have reliable region specific conversion relations
and alternatively appropriate global regression relations for the required magnitude ranges and focal depths can be utilized.
In this study, we collected global events magnitude data from ISC, NEIC and GCMT databases for the period 1976 to May, 2007.
Data for m b magnitudes for 3,48,423 events for ISC and 2,38,525 events for NEIC, M
s
magnitudes for 81,974 events from ISC and 16,019 events for NEIC along with 27,229 M
w
events data from GCMT has been considered. An epicentral plot for M
w
events considered in this study is also shown. M
s
determinations by ISC and NEIC, have been verified to be equivalent. Orthogonal Standard Regression (OSR) relations have
been obtained between M
s
and M
w
for focal depths ( h < 70 km) in the magnitude ranges 3.0 ≤ M
s
≤ 6.1 and 6.2 ≤ M
s
≤ 8.4, and for focal depths 70 km ≤ h ≤ 643 km in the magnitude range 3.3 ≤ M
s
≤ 7.2. Standard and Inverted Standard Regression plots are also shown along with OSR to ascertain the validation of orthogonal
regression for M
s
magnitudes. The OSR relations have smaller uncertainty compared to SR and ISR relations for M
s
conversions. ISR relations between m
b
and M
w
have been obtained for magnitude ranges 2.9 ≤ m
b
≤ 6.5, for ISC events and 3.8 ≤ m
b
≤ 6.5 for NEIC events. The regression relations derived in this study based on global data are useful empirical relations
to develop homogenous earthquake catalogs in the absence of regional regression relations, as the events catalog for most
seismic regions are heterogeneous in magnitude types. 相似文献
13.
The magnetic behavior of the Jahn-Teller structure braunite, (Mn 2+
1−yM
y
)(Mn 3+
6−
x
M x)SiO 12, is strongly influenced by the incorporation of elements substituting manganese. Magnetic properties of well-defined synthetic
samples were investigated in dependence on the composition. The final results are presented in magnetic phase diagrams. To
derive the necessary data, ac susceptibility and magnetization of braunites with the substitutional elements M = Mg, Fe, (Cu+Ti)
and Cu were measured. Whereas the antiferromagnetic ordering temperature, T
N
, of pure braunite is hardly affected by the substitution of nonmagnetic Mg, it is rapidly suppressed by the substitution
of magnetic atoms at the Mn positions. Typically for a concentration ( x, y) ≥ 0.7 of the substituted elements, a spin glass phase occurs in the magnetic phase diagrams. Additionally, for the braunite
system with Fe 3+ substitutions, we observe in the concentration range 0.2 < x< 0.7 a double transition from the paramagnetic state, first to the antiferromagnetic state, followed by a transition to a
spin glass state at lower temperatures. The unusual change of the magnetic properties with magnetic substitution at the Mn
positions is attributed to the peculiar antiferromagnetic structure of braunite, which has been resolved recently.
Received: 19 April 2001 / Accepted: 6 September 2001 相似文献
14.
Magnetite-bearing mylonitic garnet–micaschists close to the major suture between the Baltica and Iapetus terranes (Seve Nappe
Complex, Scandinavian Caledonides) show very high anisotropy of magnetic susceptibility (AMS) with corrected degree of anisotropy
( P′) up to 4.8. Three different magnetic fabric types can be distinguished. They correspond to protomylonite (type I, P′ < 2), mylonite (type II, 2 < P′ < 3), and ultramylonite (type III, P′ > 3), respectively. The orientation of the ellipsoid axes from all applied magnetic fabric methods in this study is similar
with shallow dips of the metamorphic foliation toward WSW and subhorizontal, mostly NW–SE trending mineral lineation. Differences
between subfabrics were minimized under high shear strain as all markers tend to align parallel with the shear plane. The
very high anisotropies and mostly oblate ellipsoid shapes of type III correlate with high magnetic susceptibility ( k
mean up to 55 × 10 −3 SI units) and are related to the concentration of magnetite aggregates with shape-preferred orientation. They show a distinct
field dependence of magnetic susceptibility of up to 10% in the k
max-direction. We attribute this field dependence to a “memory” of high strains in the domain walls of the crystals acquired
during synkinematic magnetite growth during shear zone fabric development at temperatures of 550–570°C. 相似文献
15.
The compressibility at room temperature and the thermal expansion at room pressure of two disordered crystals (space group
C2/ c) obtained by annealing a natural omphacite sample (space group P2/ n) of composition close to Jd 56Di 44 and Jd 55Di 45, respectively, have been studied by single-crystal X-ray diffraction. Using a Birch–Murnaghan equation of state truncated
at the third order [BM3-EoS], we have obtained the following coefficients: V
0 = 421.04(7) Å 3, K
T0 = 119(2) GPa, K′ = 5.7(6). A parameterized form of the BM3 EoS was used to determine the axial moduli of a, b and c. The anisotropy scheme is β
c
≤ β
a
≤ β
b
, with an anisotropy ratio 1.05:1.00:1.07. A fitting of the lattice variation as a function of temperature, allowing for linear
dependency of the thermal expansion coefficient on the temperature, yielded α V(1bar,303K) = 2.64(2) × 10 −5 K −1 and an axial thermal expansion anisotropy of α
b
≫ α
a
> α
c
. Comparison of our results with available data on compressibility and thermal expansion shows that while a reasonable ideal
behaviour can be proposed for the compressibility of clinopyroxenes in the jadeite–diopside binary join [ K
T0 as a function of Jd molar %: K
T0 = 106(1) GPa + 0.28(2) × Jd (mol%)], the available data have not sufficient quality to extract the behaviour of thermal expansion for the same binary join in
terms of composition. 相似文献
16.
Magnetic measurement of Fe 3−
x
Si
x
O 4 spinel solid solutions indicates that their Curie temperatures decrease gradually, but not linearly, from 851 to 12 K with
increasing content of nonmagnetic ions Si 4+. Magnetic hysteresis becomes more noticeable in solid solutions having a larger content of Fe 2SiO 4. Saturation magnetizations of Fe 3−
x
Si
x
O 4 samples increase up to x=0.357 and they are easily saturated in the field of H=0.1 T. However, magnetization of the sample of x=0.794 does not approach saturation even at high field of H=7.0 T and has a large coercive force. The Si 4+ disordered distribution is confirmed to be tetr[Fe 3+
1−
x
+
x
t
Si 4+
x
(1−
t
)] octa[Fe 2+
1+
x
Fe 3+
1−
x
−
x
t
Si 4+
x
t
] O 4 by the spin moment, which is consistent with site occupancy obtained from X-ray crystal structure refinement. Their molecular
magnetizations would be expressed as M
B={4(1+ x)+10 xt}μ B as functions of composition parameter x and Si 4+ ordering parameter t of the solid solution. The sample of x=0.794 is antiferromagnetic below the Néel temperature, mainly due to the octahedral cation interaction M
O– M
O, while both M
T– M
O and M
O– M
O interactions induce a ferrimagnetic property. Concerning magnetic spin configuration, in the case of x>0.42, the lowest dɛ level becomes a singlet, resulting in no orbital angular momentum.
Received: 20 April 2000 / Accepted: 11 September 2000 相似文献
17.
Creep strength of oriented orthopyroxene single crystals was investigated via shear deformation experiments under lithospheric
conditions [ P (pressure) = 1.3 GPa and T (temperature) = 973–1,373 K]. For the A-orientation (shear direction [001] on (100) plane), the samples have transformed
completely to clinoenstatite and much of the deformation occurred after transformation. In contrast, for the B-orientation
(shear direction [001] on (010) plane), samples remained orthoenstatite and deformation occurred through dislocation motion
in orthoenstatite. The strength of orthopyroxene with these orientations is smaller than for olivine aggregates under all
experimental conditions. Flow of the B-orientation samples is described by a power-law, and the pre-exponential constant,
the apparent activation energy, and the stress exponent are determined to be A = 10 −9.5 s −1·MPa −4.2, Q = 114 kJ/mol and n = 4.2. However, for the A-orientation, the results cannot be fit by a single flow law and we obtained the following: A = 10 8.9 s −1·MPa −3.0, Q = 459 kJ/mol and n = 3.0 at high temperatures (≥1,173 K), and A = 10 −27.4 s −1·MPa −14.3, Q = 296 kJ/mol and n = 14.3 at low temperatures (<1,173 K). The stress exponent for the low-temperature regime is high, suggesting that deformation
involves some processes where the activation energy decreases with stress such as the Peierls mechanism. Our study shows that
orthopyroxene with these orientations is significantly weaker than olivine under the lithospheric conditions suggesting that
orthopyroxene may reduce the strength of the lithosphere, although the extent to which orthopyroxene weakens the lithosphere
depends on its orientation and connectivity. 相似文献
18.
CoGeO 3 was synthesized at 1,273 and 1,448 K using ceramic sintering techniques in the monoclinic and orthorhombic modification,
respectively. The two compounds were analysed by magnetic susceptibility measurements and neutron diffraction in order to
study magnetic ordering and spin structures at low temperature. The monoclinic form of CoGeO 3 has C2/ c symmetry and orders magnetically below 36 K with a small negative paramagnetic Curie temperature θ
P = −4.6 (2) K. The magnetic structure can be described with k = (1, 0, 0) in the magnetic space group C2′/ c′ having a ferromagnetic spin arrangement within the chains of M1 sites, but a dominating antiferromagnetic coupling between
the chains. At the M1 sites the magnetic spins are aligned within the a–c plane forming an angle of 120° with the + a-axis and they are not parallel to the spins at M2. Here spins are also ferromagnetically coupled within, but antiferromagnetically
coupled between the M1/M2 site bands. The orthorhombic phase of CoGeO 3 displays Pbca symmetry and transforms to an antiferromagnetically ordered state [ θ
P = −18.6(2) K] below 33 K. The magnetic spin structure can be described with k = (0, 0, 0) in space group Pbca′ and it is similar to the one of the C2/ c phase except that it is non-collinear in nature, i.e. there are components of the magnetic moment along all three crystallographic
axes. Small magneto-elastic coupling is observed in the orthorhombic phase. 相似文献
19.
The variation and anisotropy in hydraulic conductivity and the coefficient of consolidation was investigated for two Swedish
sulphide clays. A series of constant rate of strain oedometer tests was performed on samples trimmed in the vertical and horizontal
direction. A methodology to evaluate the horizontal coefficients of consolidation c
h
via the horizontal hydraulic conductivity k
h
and the vertical compression modulus M
v
is proposed. Laboratory evaluations of c
h
are also compared with determinations of c
h
from in situ piezometer measurements in vertically drained sulphide clay. Furthermore, the validity of the empirical correlation
between hydraulic conductivity change index C
k
and initial void ratio e
0, C
k
= 0.5 e
0 (Tavenas et al. in Can Geotech J 20(4):645–660, 1983b), was investigated for the sulphide clays. The results from the investigation show large ranges in measured hydraulic conductivities
and coefficients of consolidation. However, the results indicate that the correlation C
k
= 0.5 e
0 is valid. The anisotropy in hydraulic conductivity and the coefficient of consolidation of the sulphide clays tested seems
to be small. For design purposes, multiple tests for assessment of hydraulic conductivity and the coefficient of consolidation
should be made, and a partial factor of safety, depending on the requisite level of safety and the spatial variability of
the parameters, should be introduced. For design purposes in this type of clay, k
h
= k
v
and c
h
= c
v
are suggested. 相似文献
20.
Marine clay supporting high-temperature offshore structure susceptible to random movements (such as a buckling high-temperature pipeline) experiences variable shearing rates at an elevated temperature that is higher than the marine environment (typically 4 °C). This practically implies that the undrained shear strength (su) of the marine clay being routinely characterized in situ by penetrometers at a constant rate under an isothermal condition (4 °C) should be carefully corrected, by taking into account the temperature and rate dependency. To date, the combined effects of rate and temperature on the undrained shear behaviour of marine clay are merely investigated experimentally and theoretically. This study presents the development of an anisotropic thermo-elastic–viscoplastic model and a series of temperature- and rate-controlled triaxial tests for validation purpose. Compared to the modified Cam-Clay model, the proposed model only introduces three new parameters to characterize the temperature dependency, rate dependency and the inherent anisotropy of K0-consolidated marine clay. The predictive capability of the model has been validated by the triaxial test results. Based on the new model, an explicit equation is formulated for quantifying the temperature- and rate-dependent su of marine clay. Calculation charts are also developed to quantify su of marine clay with different plasticity indexes under various strain rates and temperatures. 相似文献
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