Experimental and 3D Numerical Simulation of Reinforced Shear Joints   总被引：1，自引：0，他引：1  

Hossein Jalalifar  N. Aziz 《Rock Mechanics and Rock Engineering》2010,43(1):95-103

The load transfer capacity and failure mechanism of a fully grouted bolt installed across a joint in shear is investigated, both experimentally and numerically, in five types of bolt. The double-shearing testing of bolts were studied in concrete blocks of 20, 40 and 100 MPa strengths, subjected to different pretension loads of 0, 5, 10, 20, 50 and 80 KN, respectively. The parameters examined include: shear resistance, shear displacement, induced strains and stresses during the bolt-bending process, and its ultimate failure across the sheared joint planes. The conclusions drawn from the study were that the strength of the concrete, bolt profile configuration and bolt pretension load played a significant influence on the shear resistance, shear displacement and failure mechanism of the reinforced medium. Experimental and numerical simulations showed that the failure occurs as a result of the induced axial and shear stresses acting between the hinge point distances in the vicinity of the shear joint plane.  相似文献   

Integrated stratigraphy and ⁴⁰Ar/³⁹Ar chronology of the early to middle Miocene Upper Freshwater Molasse in western Bavaria (Germany)     

Hayfaa Abdul Aziz  Madelaine B?hme  Alexander Rocholl  Jerome Prieto  Jan R. Wijbrans  Valerian Bachtadse  Albert Ulbig 《International Journal of Earth Sciences》2010,99(8):1859-1886

A detailed integrated stratigraphic study (biostratigraphy and magnetostratigraphy) was carried out on five sections from the western part of the Bavarian Upper Freshwater Molasse of the North Alpine Foreland Basin (NAFB), greatly improving the chronostratigraphy of these sediments. The sections belong to the lithostratigraphic units Limnische Untere Serie (UL) and Fluviatile Untere Serie (UF) and contain 19 (mostly new) small-mammal bearing levels, significantly refining the local biostratigraphy. Radiometric ages obtained from glass shards from tuff horizons are used together with the biostratigraphic information for constructing and confirming the magnetostratigraphic correlation of the studied sections to the Astronomical Tuned Time Scale (ANTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). This correlation implies that the UL lithostratigraphic unit corresponds to the latest Ottnangian and the Early Karpatian, whereas the UF corresponds to the Karpatian and the Early Badenian. This indicates that the Brackish- to Freshwater Molasse transition already occurred during the late Ottnangian. The pre-Riesian hiatus occurred in the latest Karpatian and lower Early Badenian in Eastern Bavaria and Bohemia and in the Late Karpatian and earliest Badenian in Western Bavaria. The geochemical and Ar–Ar data of volcanic ashes suggest that highly evolved silicic magmas from a single volcano or volcanic center, characterized by a uniform Nd isotopic composition, erupted repetitively over the course of at least 1.6 Myr. Three phases of eruptive activity were identified at 16.1 ± 0.2 Ma (Zahling-2), 15.6 ± 0.4 Ma (Krumbad), and 14.5 ± 0.2 Ma (Heilsberg, Hegau). The correlation of the local biostratigraphic zonation to the ANTS04 enables further the characterization of both the Ottnangian–Karpatian and Karpatian–Badenian boundaries in the NAFB by small-mammal biostratigraphy. According to these results the Ottnangian–Karpatian boundary is contemporaneous with the first appearance datum of Megacricetodon bavaricus (in the size of the type population) and the first common occurrence of Keramidomys thaleri, whereas Ligerimys florancei, Melissiodon dominans and Prodeinotherium aff. bavaricum have been already disappeared during the late Ottnangian. The Karpatian–Badenian boundary is characterized by a significant size increase of the large Megacricetodon lineage and possibly a (re-)immigration of Prodeinotherium bavaricum.  相似文献   

Copula based analysis of rainfall severity and duration: a case study   总被引：4，自引：0，他引：4  

Ummul Fahri Abdul Rauf  Panlop Zeephongsekul 《Theoretical and Applied Climatology》2014,115(1-2):153-166

The main objective of this study is to investigate the joint distribution of rainfall severity and rainfall duration in the state of Victoria, Australia, based on monthly rainfall data from selected rain-gauge stations which are located in the north-eastern and south-western parts of the state, during the period from 1950 to 2010. Traditional approach for considering the joint distribution of rainfall characteristics using standard bivariate modeling presents some limitations that can be circumvented by using Copula models. Archimedean and extreme-value copulas will be used to obtain the bivariate distribution of rainfall severity and duration. The Standard Precipitation Index (SPI), which is employed extensively to quantify rainfall severity, will be discussed in detail. Several goodness of fit tests will be performed to find the best fitting copulas and the results will be summarized. The final fitted copulas will then be applied to obtain the joint and conditional return periods from a minimum of two years to one hundred years of rainfall events in Victoria.  相似文献   

Adjoint formulation and constraint handling for gradient-based optimization of compositional reservoir flow     

Drosos Kourounis  Louis J. Durlofsky  Jan Dirk Jansen  Khalid Aziz 《Computational Geosciences》2014,18(2):117-137

An adjoint formulation for the gradient-based optimization of oil–gas compositional reservoir simulation problems is presented. The method is implemented within an automatic differentiation-based compositional flow simulator (Stanford’s Automatic Differentiation-based General Purpose Research Simulator, AD-GPRS). The development of adjoint procedures for general compositional problems is much more challenging than for oil–water problems due to the increased complexity of the code and the underlying physics. The treatment of nonlinear constraints, an example of which is a maximum gas rate specification in injection or production wells, when the control variables are well bottom-hole pressures, poses a particular challenge. Two approaches for handling these constraints are presented—a formal treatment within the optimizer and a simpler heuristic treatment in the forward model. The relationship between discrete and continuous adjoint formulations is also elucidated. Results for four example cases of increasing complexity are presented. Improvements in the objective function (cumulative oil produced) relative to reference solutions range from 4.2 to 11.6 %. The heuristic treatment of nonlinear constraints is shown to offer a cost-effective means for obtaining feasible solutions, which are, in some cases, better than those obtained using the formal constraint handling procedure.  相似文献   

Effects of Shear Rate on Cyclic Loading Shear Behaviour of Rock Joints Under Constant Normal Stiffness Conditions     

Ali Mirzaghorbanali  Jan Nemcik  Naj Aziz 《Rock Mechanics and Rock Engineering》2014,47(5):1931-1938

  相似文献   

Pile Head Cyclic Lateral Loading of Single Pile     

N. M. Sa’don  M. J. Pender  A. R. Abdul Karim  R. Orense 《Geotechnical and Geological Engineering》2014,32(4):1053-1064

This paper presents an elastic continuum model using an extended nonlinear Davies and Budhu equations, which enables the nonlinear behavior of the soil around the long elastic pile to be modeled using a simple expression of pile-head stiffness method. The calculated results were validated with the measured full-scale dynamic field tests data conducted in Auckland residual clay. An idealized soil profile and soil stiffness under small strain (i.e. shear modulus, G _s and shear wave velocity, V _s of the soil) determined from in situ testing was used to model the single pile tests results. The predictions of these extended equations are also confirmed by using the three-dimensional finite-element OpenSeesPL (Lu et al. in OpenSeesPL 3D lateral pile-ground interaction: user manual, University of California, San Diego, 2010). A soil stiffness reduction factor, G _s /G _s,max of 0.36 was introduced to the proposed method and model. It was found to give a reasonable prediction for a single pile subjected to dynamic lateral loading. The reduction in soil stiffness found from the experiment arises from the cumulative effects of pile–soil separation as well as a change in the soil properties subjected to cyclic load. In summary, if the proposed method and model are accurately verified and properly used, then they are capable of producing realistic predictions. Both models provide good modelling tools to replicate the full-scale dynamic test results.  相似文献   

An Elasto-Plastic Constitutive Model for Rock Joints Under Cyclic Loading and Constant Normal Stiffness Conditions   总被引：1，自引：1，他引：0  

Jan Nemcik  Ali Mirzaghorbanali  Naj Aziz 《Geotechnical and Geological Engineering》2014,32(2):321-335

An elasto-plastic constitutive model is introduced for rock joints under cyclic loading, considering the additional shear resistance generated by the asperity damage in the first forward shear cycle and sliding mechanism for further shearing. A series of cyclic loading direct shear tests was conducted on artificial joints with triangular asperities and replicas of a real rock asperity surface under constant normal stiffness (CNS) conditions. The model was calibrated and then validated using selected data sets from the experimental results. Model simulations were found to be in good agreement with the rock joints behaviour under cyclic loading and CNS conditions both in stress prediction and dilation behaviour. In addition, dynamic stability analysis of an underground structure was carried out, using Universal Distinct Element Code and the proposed constitutive model.  相似文献   

Retrieval and Validation of Chlorophyll-a Concentrations in the Coastal Waters Off Yanam and Kakinada (Godavari) Basin Along East Coast of India     

T. Preethi Latha  P. V. Nagamani  K. H. Rao  S. K. Dash  S. B. Choudhury  Aziz Rehman  V. V. S. S. Sarma  M. Naveen Babu  P. Amarendra  B. Srinivasa Rao  T. D. V. Prasad 《Journal of the Indian Society of Remote Sensing》2014,42(1):129-138

In this study chlorophyll measurements were made during March 2012 in the estuarine waters of Off Kakinada and Yanam coast, Bay of Bengal onboard a coastal vessel. In-situ water samples and optical data was collected at 21 stations (surface to 150 m depth) using Underwater radiometer (Hyperpro-II). In-vivo chlorophyll profiles were collected using wet labs fluorometer integrated with underwater Hyperspectral radiometer. Chlorophyll-a concentrations were estimated using HPLC by collecting the water samples at each sampling location. And also chlorophyll-a concentrations were retrieved from the OCM-2 data of OCEANSAT-2 satellite, processed using SeaDAS v.6.2 with the available global ocean colour algorithms namely, OC2 and OC4V4. A total of 33 samples used covering all the stations for chlorophyll-a estimation, and surface water samples of all the stations only being used for direct comparison among chlorophyll concentrations of HPLC, in-situ (fluorometrically integrated to Hyperpro-II) and retrieved from OCM-2. A good correlation found between the Fluorometer derived and HPLC measured chlorophyll-a concentration with an R² value of 0.78. The relation between Chlorophyll-a concentration measured from HPLC and retrieved from OCM-2 (OC2 and OC4V4 algorithms) using SeaDASv.6.2 for 10 samples has been compared for validation and obtained an R² value of 0.6. Also comparisons done with the in-situ measured (fluorometer) Chlorophyll-a concentration with OCM-2 chlorophyll data (OC4-V4 and OC2 algorithms) and validation with 10 concurrent in-situ surface measurements showed a significant overestimation by OCM-2 at low chlorophyll-a concentrations and underestimation at high chlorophyll-a concentrations.  相似文献   

Impact of rangeland enclosure and seasonal grazing on protected and unprotected rangelands in Chakwal region,Pakistan     

ISLAM Muhammad  RAZZAQ Abdul  ZUBAIR Muhammad  HASSAN Sawsan  AHMAD Sarfraz  GUL Shamim  RISCHKOWSKY Barbara  LOUHAICHI Mounir 《山地科学学报》2022,(1):46-57

Scrub rangelands support livestock grazing and provide ecosystem services to their inhabitants.The present study was conducted in Chakwal,an important tract of ...  相似文献   

Cultural characteristics of chromium resistant unicellular cyanobacteria isolated from local environment in Pakistan     

Abdul Hameed Shahida Hasnain 《中国海洋湖沼学报》2005,23(4):433-441

Many unicellular cyanobacteria were isolated from different places： fields, ponds, polluted water, and soils from Muredkey and Kasur tannery areas, near Lahore, Pakistan. Different media like BG 11 medium, Bold Basal medium, Chu＇s # 10 medium and Gotham＇s medium, in standard forms and with slight variations of ingredients, and different pH, temperature and light regimes were checked for the optimum growth of the isolates. The isolation pro- cedure was repeated with different concentrations of chromium to select the resistant strains. These selected strains grew on chromium of the range 100-200 μg/ml in BG 11 medium. Cyanobacteria were maintained in solid and liquid media with/without shaking. Cyanobacterial strains were collected from natural habitats that were accompanied by a diversified group of organisms including bacteria, protozoan, and rotifers etc. In order to eliminate these agents termed as contaminants, we used several methods including phenol treatment, use of antibiotic and careful manual picking of unicellular cyanobacteria. Resistance of these strains against different heavy metals （ZnSO4, MnSO4, NiSO4, COCl2, Pb（NO3）3, CuSO4, HgCl2, AgNO3 and CdCl2） and antibiotics （erythromycin, streptomycin, kanamycin, chloramphenicol, neomycin） was evaluated. Optimum temperature was 30℃ with variable pH for the reduction of Cr^6＋ in to Cr^3＋ in majority of strains.  相似文献