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31.
Crack coalescence in rock masses was studied by performing a series of biaxial compresion tests on specimens made of rock-like
material. Specimens of size 63.5 × 27.9 × 20.3 cm, made of 72% silica sand, 16% cement (Type I) and 12% water by weight were
tested. The joint inclination angle was maintained at 45°, while the offset angle i.e. angle between the plane of the joint
and the line that connects the two inner tips of the joints, was changed from 0° to 90° with an increment of 15°. Three levels
of lateral stress were used; 0.35 MPa, 0.7 MPa and 1.5 MPa on each sample. HP data acquisition system was used to record the
data for each sample. In each sample, four LVDTs were fixed to measure the axial and lateral displacement along the sample.
The failure mechanisms were monitored by eye inspection and a magnifier to detect crack initiation and propagation. For each
test, the failure surfaces were investigated to determine the characteristics of each surface. Wing cracks initiated at the
tip of the joint for the low confining stress applied, while at higher confining stresses wing cracks also initiated at the
middle of the joint. Secondary cracks initiated at the tip of the joint due to shear stress. Three modes of failure took place
due to coalescence of the secondary and wing cracks. The bridge inclination was the main variable that controlled the mode
of failure. For bridge inclination of 0°, the coalescence occured due to shear failure and for bridge inclination of 90° the
coalescence occurred due to tensile failure while for the other bridge inclinations coalescence occured due to mixed tensile
and shear failure. 相似文献
32.
Anthropogenic Pb accumulation in forest soils from Lake Clair watershed: Duchesnay experimental forest (Québec, Canada) 总被引：1，自引：0，他引：1
Mineral soil horizons (Ae, Bhf1, Bhf2, Bf, BC and C) were carefully collected from two podzolic soil profiles in the Lake Clair watershed (Québec) in order to assess anthropogenic trace metal accumulation. Petrographic and selective analyses were performed to establish the soil mineralogy and properties. Furthermore, a complete sequential extraction procedure has been applied to help understanding the complex chemical speciation of Pb in forest soils. Chemical speciation of Pb showed a strong vertical gradient: 85% of this metal is mainly partitioned in refractory minerals in the C-horizon whereas in the upper Bhf1 and Ae-horizons, less than 50% of Pb is associated with this fraction. In the Ae-horizon, for example, 35%, 30% and 12% of total Pb, respectively, is associated with the exchangeable, labile organic matter and amorphous Fe-Mn oxides fractions. The distribution of Pb and Cr in the studied forest soils mainly reflects progressive contamination of the watershed by anthropogenic atmospheric sources. The anthropogenic source is indicated by elevated Cr and Pb concentrations in the topsoil (Bhf and Ae) horizons and by strong negative correlation between 206Pb/207Pb ratios and total Pb concentrations. According to these isotopic values, penetration of anthropogenic Pb does not exceed 10 cm in both soil profiles. Below this depth, both Pb concentrations and isotopic ratios remain nearly constant and similar to values observed in pre-anthropogenic sediments from Lake Clair. These values are interpreted as the natural geochemical backgrounds of the watershed. Based on that behaviour, calculated anthropogenic Pb net inputs amounted to between 1.24 and 1.8 g/m2. 相似文献
33.
Ground motion amplifications in the Dinar basin, and contributions of the surface waves generated from basin edges are investigated in frequency and time domains. Amplification functions are computed from the aftershock data of the October 1, 1995 Dinar earthquake (MW=6.4) using the Standard Spectral Ratio method which requires a pair of instruments; one located at the site under investigation (generally on alluvium) and the other on a reference site, preferably a nearby rock site. First, a time window covering the whole signal is used to compute the amplification function, and, successively, the noise, P wave, S wave and the surface wave time windows are used in computation to observe their contributions to the amplification function. It is seen that the maximum amplifications observed at about 2.0 Hz on the amplification functions of the stations located in the basin are largely due to basin edge induced surface waves. These waves have significantly increased the duration of signals recorded within the basin. Particularly, on the vertical component records, the amplitudes of surface waves are larger than the S-wave amplitudes. The periods of waves amplified maximally due to the basin structure coincide with the natural periods of 4–6-story buildings which were heavily damaged in Dinar. This indicates that the site effects may have been important regarding the damage which occurred during the Dinar earthquake of October 1995. 相似文献
34.
Omer L. Sen Deniz Bozkurt John B. Vogler Jefferson Fox Thomas W. Giambelluca Alan D. Ziegler 《Climatic change》2013,118(2):213-226
Regional climate model simulations with RegCM3 were performed to investigate how future land-cover/land-use (LCLU) change in Montane Mainland Southeast Asia (MMSEA) could affect regional climate. Simulation land-surface parameterizations included present day and plausible 2050 land-covers, as well as two extreme deforestation simulations. In the simulations, the original land cover map of RegCM3, based on AVHRR 1992–93 observations, was replaced with one obtained from MODIS 2001 observations; and the model was set to work at two different spatial resolutions using the sub-grid feature of the land surface model: 27.79 km for the atmosphere and 9.26 km for the land surface. During validation, modeled precipitation closely matched observed precipitation over southern China, but underestimated precipitation in the Indochina Peninsula. The plausible 2050 LCLU simulation predicted little change in regional climate. However, an extreme irrigated crop parameterization caused precipitation to increase slightly in the Indochina Peninsula, decrease substantially in southeastern China, and increase significantly in the South China Sea. The extreme short-grass parameterization caused substantial precipitation decreases in MMSEA, but few changes elsewhere. These simulations indicate in order for significant climatological changes to occur, substantially more LCLU conversion is required than the 16 % change we incorporated into the plausible 2050 land-cover scenario. 相似文献
35.
36.
Low‐temperature thermochronology provides information on the timing of rifting and denudation of passive margins, and the Red Sea with its well‐exposed, young rift margins is a suitable setting for its application. Here we present new apatite fission‐track (AFT) data from Sudan northern hinterland and Red Sea coastal areas. From the former region we obtained ages between 270 ± 2 Ma ad 253 ± 53 Ma, and from the coastal belt between 83 ± 8 Ma and 39 ± 7 Ma. These data prompted a review and comparison with low‐temperature thermochronological data from the whole Nubian Red Sea Margin, and a discussion on their implication in assessing the margin evolutionary style. AFT data are available for Egypt and Eritrea as well as apatite (U‐Th)/He (AHe) ages for two transects transversal to the margin in Eritrea. Both in Egypt and Eritrea AFT data record a cooling event at about 20–25 Ma (Early Miocene) and an earlier, more local, cooling event in Egypt at about 34 Ma (Early Oligocene). The thermal modeling of the Sudan samples provides an indication of a rapid cooling in Miocene times, but does not support nor rules out an Early Oligocene cooling phase. The re‐assessment of new and existing thermochronological data within the known geological framework of the Nubian and conjugate Arabian margins favours the hypothesis that early rifting stages were affecting the whole Gulf of Suez–Red Sea–Gulf of Aden system since the Oligocene. These precocious, more attenuated, phases were followed by major extension in Miocene times. As to the mode of margin evolution, AFT age patterns both in Egypt and Eritrea are incompatible with a downwarp model. The distribution of AHe ages across the Eritrean coastal plain suggests that there the escarpment was evolving predominantly by plateau degradation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
37.
Omer Nawaf Maaitah 《Geotechnical and Geological Engineering》2012,30(6):1345-1356
Soil treatment is commonly resorted in order to improve the strength, stiffness properties of road foundations, and reduce the swelling potential of expansive soils. In Jordan, considerable amount of construction activity is carried out at relatively shallow depths where soil is likely to be unsaturated and subjected to low stresses level. Road damage is frequently observed when it is founded on weak sub-grade in Karak. Therefore, chemical stabilization of the base course, sub base course and sub-grade is essential. The soil will be treated by using sodium silicate and lime with different percentages. An experimental program was designed to study the behavior of soil as the percent of additive agent changes. The results showed that; the geotechnical properties have been improved when soil is treated by mixing lime and sodium silicate. The initial consumption of lime is of 4 and 2?% for sodium silicate. The reaction time is a significant parameter where strength improves as time increases. 相似文献
38.
The site response at 15 stations in the Adana-Ceyhan region (Southern Turkey) is calculated from the recordings of aftershocks of June 27, 1998 Adana-Ceyhan earthquake (MS=6.2) by using the Standard Spectral Ratio (SSR) and the Horizontal-to-Vertical Spectral Ratio (HVSR) methods. While the two methods are in good harmony at a few stations in determining the site effects, they show differences on the estimated amplifications or on the site resonance frequencies at most stations. It was not clear which one of the two methods underestimates or overestimates the amplification values. We observe that at some stations, where the local site conditions are rather complex, the vertical component records are strongly influenced from the local soil conditions. Thus, the HVSR method fails at these stations. The SSR method underestimates the amplifications at some stations since the rock site, selected as reference site, has its own site response and/or the path correction we applied, considering the geometrical spreading factor only, is insufficient. At the sites where high intensity values were observed, we found high amplifications. The fundamental soil frequencies characterize the damage properties observed in the Adana-Ceyhan earthquake. The fundamental soil frequency is nearly at 1.1 Hz at the Ceyhan site, where severe damage was observed in the 5–6 story buildings, while the fundamental soil frequency is between 3–6 Hz at the Adana site, where damage was in the low-story buildings. Therefore, in addition to inefficient construction practices, it is clear that the resonance effects have also contributed to the observed damage. 相似文献
39.
Two-dimensional finite element model was created in this work to investigate the stress distribution within rock-like samples
with offset open non-persistent joints under uniaxial loading. The results of this study have explained the fracture mechanisms
observed in tests on rock-like material with open non-persistent offset joints (Mughieda and Alzo’ubi, Geotech Geol Eng J
22:545–562, 2004). Finite element code SAP2000 was used to study the stresses distribution within the specimens. Four-noded
isoperimetric plain strain element with two degrees of freedom per node, and the three-noded constant strain triangular element
with two degree of freedom per node were used in the present study. The results of the present study showed that the tensile
stress in the bridge area caused coalescence for specimens with overlapped preexisting cracks (joints) while the coalescence
of the secondary cracks, due to shear stress, caused the failure of specimens with non-overlapping cracks. 相似文献
40.
Large-scale pile tests in Mercia mudstone: Data analysis and evaluation of current design methods 总被引：3，自引：0，他引：3
J. R. Omer R. B. Robinson R. Delpak J. K. C. Shih 《Geotechnical and Geological Engineering》2003,21(3):167-200
Full-scale load tests were carried out on six instrumented large diameter bored, cast in-situ piles formed in Mercia mudstone, as part of the design of a new Viaduct in Cardiff, UK. In this paper, the results from six
test piles and extensive data from 218 ground investigation boreholes are systematically processed in order to study the load
transfer and resistance mechanisms in Mercia mudstone. Data from strain gauges embedded in each pile are first analysed to
calibrate the load-deformation relationship of each pile as-built, taking into account (i) the non-linearity of concrete and
(ii) the effect of partial steel encasement on pile stiffness at various levels. The shaft and base capacity of the piles
are each predicted using 10 calculation methods belonging to the four basic categories: (i) Undrained analysis, (ii) Drained
analysis, (iii) Mixed approach and (iv) Empirical correlation. It is found that the shaft capacity prediction methods are
moderately consistent. The standard deviations of the ratio Q
sp/Q
sm of predicted to observed shaft capacity lies in the range 0.06–0.24. However, 8 of these methods are over-conservative, giving
Q
sp/Q
sm values in the range 0.29–0.67. The remaining two methods yield Q
sp/Q
sm = 1.01 and 1.49. In contrast, the prediction methods for base capacity are found to be much less consistent. The ratio Q
bp/Q
bm of predicted to measured base capacity falls in the interval 0.52–1.93, with corresponding standard deviations of 0.16–0.82.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献