Study of pore pressure variation during liquefaction using two constitutive models for sand   总被引：1，自引：0，他引：1  

Mahdi Taiebat  Hadi Shahir  Ali Pak 《Soil Dynamics and Earthquake Engineering》2007,27(1):60-72

Numerical analyses of liquefiable sand are presented in this paper. Liquefaction phenomenon is an undrained response of saturated sandy soils when they are subjected to static or dynamic loads. A fully coupled dynamic computer code is developed to predict the liquefaction potential of a saturated sandy layer. Coupled dynamic field equations of extended Biot's theory with u–P formulation are used to determine the responses of pore fluid and soil skeleton. Generalized Newmark method is employed for integration in time. The soil behavior is modelled by two constitutive models; a critical state two-surface plasticity model, and a densification model. A class ‘B’ analysis of a centrifuge experiment is performed to simulate the dynamic response of level ground sites. The results of the numerical analyses demonstrate the capability of the critical sate two-surface plasticity model in producing pore pressures that are consistent with observations of the behavior of liquefiable sand in the centrifuge test.  相似文献   

Numerical study of the coupled hydro-mechanical effects in dynamic compaction of saturated granular soils     

Ali Ghassemi  Ali Pak  Hadi Shahir 《Computers and Geotechnics》2010,37(1-2):10-24

Dynamic compaction is a widely used method for improvement of loose granular deposits. Its applicability in saturated layers generally considered to be less effective because of the fact that part of the applied energy is absorbed by pore water. Up to now the majority of numerical simulations have focused on the analysis of dynamic compaction in dry/moist soils. In this paper, a fully coupled hydro-mechanical finite element code has been developed and employed to evaluate the dynamic compaction effects on saturated granular soils. After verification of the results by comparing the numerical results with those measured in a real field case of DC treatment in a highway, some sensitivity analyses have been performed to evaluate the effect of water phase on the dimensions of the zone of improvement in the soil beneath the tamper. The results indicate that in the DC process the soil demonstrate two different behaviors. At the very early stage after impact, the soil behaves in an undrained manner and high oscillation of pore pressure occurs. After this phase, consolidation begins during which the pore-water-flow out of the soil mass takes place. The numerical analysis reveals that most of the DC improvement occurs during the undrained phase. The main mechanism responsible for the densification of soil during the undrained phase seems to be the compressibility of pore water. The simulation results indicate that the improvement zone diminishes when the degree of saturation increases.  相似文献   

Zircon U–Pb ages and Sr–Nd isotope ratios for the Sirstan granitoid body,NE Iraq: Evidence of magmatic activity in the Middle Cretaceous Period     

Imad Kadhim Abdulzahra  Ayten Hadi  Hossein Azizi  Yoshihiro Asahara  Koshi Yamamoto 《Comptes Rendus Geoscience》2017,349(2):53-62

The Sirstan granitoid (SG), comprising diorite and granodiorite, is located in the Shalair Valley area, in the northeastern part of Iraq within the Sanandaj–Sirjan Zone (SSZ) of the Zagros Orogenic Belt. The U–Pb zircon dating of the SG rocks has revealed a concordia age of 110 Ma, which is interpreted as the age of crystallization of this granitoid body during the Middle Cretaceous. The whole-rock Rb–Sr isochron data shows an age of 52.4 ± 9.4 Ma (MSWD = 1.7), which implies the reactivation of the granitoid body in the Early Eocene due to the collision between the Arabian and Iranian plates. These rocks show metaluminous affinity with low values of Nb, Ta and Ti compared to chondrite, suggesting the generation of these rocks over the subduction zone in an active continental margin regime. The SG rocks are hornblende-bearing I-type granitoids with microgranular mafic enclaves. The positive values of ?_Nd (t = 110 Ma) (+0.1 to +2.7) and the low (⁸⁷Sr/⁸⁶Sr)_i ratios (0.7044 to 0.7057) indicate that the magma source of the SG granitoids is a depleted subcontinental mantle. The chemical and isotope compositions show that the SG body originated from the metasomatic mantle without a major role for continental contamination. Our findings show that the granitoid bodies distributed in the SSZ were derived from the continuous Neo-Tethys subduction beneath the SSZ in Mesozoic times and that the SSZ was an active margin in the Middle Cretaceous.  相似文献   

Risk assessment and prediction of safety factor for circular failure slope using rock engineering systems     

Hadi Fattahi 《Environmental Earth Sciences》2017,76(5):224

Circular failure is generally observed in the slope of soil, highly jointed rock mass, mine dump and weak rock. Accurate estimation of the safety factor (SF) of slopes and their performance is not an easy task. In this research, based on rock engineering systems (RES), a new approach for the estimation of the SF is presented. The introduced model involves six effective parameters on SF [unit weight (γ), pore pressure ratio (r _u), height (H), angle of internal friction (φ), cohesion (C) and slope angle (\(\beta\))], while retaining simplicity as well. In the case of SF prediction, all the datasets were divided randomly to training and testing datasets for proposing the RES model. For comparison purposes, nonlinear multiple regression models were also employed for estimating SF. The performances of the proposed predictive models were examined according to two performance indices, i.e., coefficient of determination (R ²) and mean square error. The obtained results of this study indicated that the RES is a reliable method to predict SF with a higher degree of accuracy in comparison with nonlinear multiple regression models.  相似文献   

Generic hierarchy of sandstone facies quality and static connectivity: an example from the Middle-Late Miocene Miri Formation,Sarawak Basin,Borneo     

Numair A. Siddiqui  Abdul Hadi A. Rahman  Chow W. Sum  Manoj J. Mathew  Muhammad Hassaan  David Menier 《Arabian Journal of Geosciences》2017,10(11):237

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Assessing the effects of the climate change on land cover changes in different time periods     

Hassan Khosravi  Ali Azareh  Hadi Eskandari Dameneh  Elham Rafiei Sardoii  Hamed Eskandari Dameneh 《Arabian Journal of Geosciences》2017,10(4):93

The present research evaluated the relation between the normalized difference vegetation index (NDVI) changes and the climate change during 2000–2014 in Qazvin Plain, Iran. Daily precipitation and mean temperature values during 2015–2040 and 2040–2065 were predicted using the statistical downscaling model (SDSM), and these values were compared with the values of the base period (2000–2014). The MODIS images (MOD13A2) were used for NDVI monitoring. In order to investigate the effects of climate changes on vegetation, the relationship between the NDVI and climatic parameters was assessed in monthly, seasonal, and annual time periods. According to the obtained results under the B2 scenario, the mean annual precipitation at Qazvin Station during 2015–2040 and 2040–2065 was 6.7 mm (9.3%) and 8.2 mm (11.36%) lower than the values in the base period, respectively. Moreover, the mean annual temperature in the mentioned periods was 0.7 and 0.92 °C higher than that in the base period, respectively. Analysis of the correlations between the NDVI and climatic parameters in different periods showed that there is a significant correlation between the seasonal temperature and NDVI (P < 0.01). Moreover, the NDVI will increase 0.009 and 0.011 during 2015–2040 and 2040–2065, respectively.  相似文献   

Applying Optimized Support Vector Regression Models for Prediction of Tunnel Boring Machine Performance     

Hadi Fattahi  Nima Babanouri 《Geotechnical and Geological Engineering》2017,35(5):2205-2217

One of the main factors in the effective application of a tunnel boring machine (TBM) is the ability to accurately estimate the machine performance in order to determine the project costs and schedule. Predicting the TBM performance is a nonlinear and multivariable complex problem. The aim of this study is to predict the performance of TBM using the hybrid of support vector regression (SVR) and the differential evolution algorithm (DE), artificial bee colony algorithm (ABC), and gravitational search algorithm (GSA). The DE, ABC and GSA are combined with the SVR for determining the optimal value of its user defined parameters. The optimization implementation by the DE, ABC and GSA significantly improves the generalization ability of the SVR. The uniaxial compressive strength (UCS), average distance between planes of weakness (DPW), the angle between tunnel axis and the planes of weakness (α), and intact rock brittleness (BI) were considered as the input parameters, while the rate of penetration was the output parameter. The prediction models were applied to the available data given in the literature, and their performance was assessed based on statistical criteria. The results clearly show the superiority of DE when integrated with SVR for optimizing values of its parameters. In addition, the suggested model was compared with the methods previously presented for predicting the TBM penetration rate. The comparative results revealed that the hybrid of DE and SVR yields a robust model which outperforms other models in terms of the higher correlation coefficient and lower mean squared error.  相似文献   

Bumping against a Gas Ceiling   总被引：1，自引：0，他引：1  

Hadi Dowlatabadi 《Climatic change》2000,46(3):391-407

The adoption of physical thresholds as a ceiling for permitted climate change sidesteps contentious issues such as: policy cost, impact valuation, discounting and equity. In this paper I offer some reflections on the concept of tolerable climate change. I also use an integrated climate assessment model (ICAM-3) to demonstrate how uncertainties in our understanding of socioeconomic and earth systems reduce the probability of success in keeping climate change within a pre-defined tolerable range. Finally, I explore the implications of socioeconomic thresholds for welfare loss in pursuit of a climate policy (e.g., tax rebellions). Crossing such regional socioeconomic thresholds will lead to local failures to pursue climate change mitigation policies — increasing the probability of straying beyond the tolerable window of global climate change. Given various uncertainties and the dynamics of the socioeconomic and the earth systems, the odds of success in staying within a climate change window of T 2°C, and T/yr 0.015°C are estimated to be no higher than 25% over the next century. A risk-risk tradeoff approach appears to hold promise, but while adoption of a larger window of tolerance increases the probability of success, it also opens the window specification criteria to contention.  相似文献   

The effect of surface profile, rock strength and pretension load on bending behaviour of fully grouted bolts     

Hossein Jalalifar  Naj Aziz  Muhammad Hadi 《Geotechnical and Geological Engineering》2006,24(5):1203-1227

Fully encapsulated rock bolting has, in recent years, become a universally accepted system of ground reinforcement in mining and tunnel construction. The application of bolting systems extends both to rebar as well as cable bolting. The effectiveness of the bolt application has been studied in shear, both by laboratory tests as well as by numerical modeling. A specially constructed double shearing apparatus (DSA) was used to examine the shearing behaviour of a bolt installed perpendicularly across two joints. The experimental study was complemented with three-dimensional numerical analysis. Parameters examined include, the effect of reinforced material on tension/compression zones along the sheared bolt, shear resistance, shear displacement and induced strains and stresses during bolt bending process. The study was undertaken at both free load and pretension conditions. The conclusions drawn from the study were the level of bolt resistance to shear was influenced by bolt profile configuration, the strength of the rock or medium influenced the level of load generated on the bolt and the increased bolt pretension contributed to increased shearing load of the bolted medium. The numerical simulation of the bolt/medium interaction and deformational behaviour were found to be in close agreement with the experimental test results.  相似文献   

Challenges in financing public sector low-carbon initiatives: lessons from private finance for a school district in British Columbia,Canada     

Thor Jensen  Hadi Dowlatabadi 《Climate Policy》2018,18(7):878-888

Governments are major investors in climate change mitigation, but aversion to public indebtedness has led to reliance on private finance to deliver public assets. Compounding this challenge, financing through Energy Service Contracts is ruled out by accounting rules. With public and traditional private funding avenues closed, government departments have sought contracts that do not disclose the full cost of borrowing, such as the Public–Private Partnership (PPP) described in this case study. We unpack the utility contract filed with the provincial regulator to show that circumventing budgetary constraints cost the Delta School Board (DSB) 8.75% per annum on borrowed private funds while public finance would have cost 4%pa. All levels of the public sector are keen to play their role in climate mitigation. Climate policy is about not passing our burden of unbridled fossil fuel use and greenhouse gas emissions to future generations. If we do not exempt public sector capital investments for decarbonization from deficit regulations, we risk passing an unnecessary economic burden to future generations.

Key policy insights

• Transition to a low-carbon economy requires public sector investments that exceed budget deficit regulations and political aversion in many jurisdictions;

• Private–Public Partnerships are currently viewed as the solution to this self-imposed fiscal constraint;

• PPPs without clear performance targets or contractual templates will expose less experienced public sector investors to high costs and emissions above expectations.

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