A nanoscopic hydro-thermo-mechanical model for nuclear waste shale/clay repositories

Shales or highly compacted engineered clay layers are being used as buffers in deep surface nuclear waste repositories. Due to the complex natural structure and fabric of clay and non-clay minerals associated with high in situ stresses, high temperatures, and the practical difficulties in the replication of the field stress and temperature conditions in the lab testing facilities, swell potential from the macro and micro investigations does not provide reliable and universally applicable results. In this study, a comprehensive molecular-level simulation-based volume change constitutive model has been developed for clay minerals incorporating the effects of cation exchange capacity, density, water content, in situ stress state, temperature, exchangeable-cations type and proportion, pore fluids, and the dissolved salts. The molecular simulations were performed using molecular mechanics, molecular dynamics, and Monte Carlo simulation techniques. Comparing the model predictions with the results of the lab tests, the model has been proven to be quite precise in the prediction of the swell potential of these strata under various overburden pressures and temperatures. There is several fold increase in swelling of clay samples at 80 °C as compared to the equivalent specimen tested at 25 °C. The effect of higher temperature is lesser at lower initial water content (higher density) while at higher water content (lower density) the structure has been found to be more vulnerable at higher temperatures. About 100 times higher confining pressure results in the same swell at 80 °C as in its counterpart specimen at 25 °C, the corresponding swell increase factor in case of 50 °C specimens is about 45. A sharp increase in swelling with a drop in in situ pressure emphasizes the probability of higher swell as a result of an accidental reduction in in situ pressure such as the higher concentration of nuclear reactions. In this study, the cohesive energy density (CED) was found to be highly sensitive to various volume change variables, such as water content, density, CEC, type, and percentage of exchangeable and non-exchangeable cations. Contrary to all the previous models, CED-based model developed in this study is universal in nature and can be adopted for any case with minimal basic material input parameters. The good agreement found between the predicted and real values for the swell potential of the undisturbed samples suggests that the model presented here can effectively be used for the assessment of the swelling potential of shale/clay deposits to be used as buffers to the nuclear waste storage.     

Development of design storm hyetographs in hyper-arid and arid regions: case study of Sultanate of Oman

The temporal distribution of the design storm is an important input in hydrological models. This research aims to develop design storm profiles representative of arid and hyper-arid areas based on actual storm recordings. Two hundred thirty-six rainfall storms were collected from seventeen rainfall gauges that cover the coastal zone of Oman for the period from 1993 to 2007. Storms were classified into four categories according to their total durations. Design storm hyetographs were derived from raw rainfall records for all four categories using the Alternating Block Method (ABM) and were also computed by ABM applied on the Intensity-Duration-Frequency (IDF) curves. Both design storm profiles were compared and it was found that the ABM_IDF storm profiles were equivalent to the four ABM_Storms profiles from a practical point of view as they produce similar peak discharges. The storm profiles developed in the current research were also compared to the commonly used Soil Conservation Service (SCS) dimensionless distributions and the UK50 storm profiles. The results showed that the most conservative commonly used SCS type II and the UK50 summer profiles are not safe to be used in design purposes in arid and hyper arid regions, despite their wide utilization in many codes of practice in these regions. The study recommends using the newly developed dimensionless storm profiles derived from the actual records.     

Geomorphic and lithologic characteristics of Wadi Feiran basin,southern Sinai,Egypt, using remote sensing and field investigations

Wadi Feiran is an important drainage basin in southern Sinai Peninsula covering an area of about 1785 \(\hbox {km}^{2}\), its streams drain into the Gulf of Suez crossing variety of rocks and sedimentary units varied in age from Precambrian to Quaternary. Field investigations, geographic information systems (GIS) and remote sensing studies including Landsat-7 ETM+, Radarsat-1, and SRTM DEM were integrated to reveal its lithologic, geologic and geomorphic features. Besides the field investigations, rock units including basement and pre- and syn-rift sedimentary units were discriminated using band ratios and principal component analysis techniques (PCA). Such techniques revealed that the crystalline rocks covering W. Feiran are unaltered rocks lacking OH-bearing minerals. Radar data successfully displayed the structures and geomorphic features related to topography. Moreover, the techniques allowed the extraction of the dyke-like structures along faults and shear zones. This also characterized the topographic variations through analysis of the shaded terrain and the altitudinal profiles. The results of data integration, lineament analysis and lineament density maps revealed that the structural grain in the present study has four different trends: N20–45E, N30–45W, N–S and E–W. Based on analysis of radar data and geomorphic indices, W. Feiran is an asymmetrical basin, its left side occupies \(\sim \)34% of the total area that leads to a supposedly massive tilt towards the south which caused the southwestward slope.     

Evolution of Pleistocene travertine depositional system from terraced slope to fissure-ridge in a mixed travertine-alluvial succession (Jebel El Mida,Gafsa, southern Tunisia)

The Quaternary stratigraphic record of Jebel El Mida, composed of continental deposits, is a useful example of concomitant travertines and alluvial deposition in an extensional setting. Travertine deposition occurred in a faulted Pleistocene alluvial fan giving rise to seven (recognised) facies interfingering with five other alluvial ones. The travertine depositional events indicate a tectonically driven evolution from terraced slope (facies group FC1–FC6) to a travertine fissure ridge-type depositing phase (facies group of FC1–FC7). Interfingering between travertine and alluvial facies indicates the co-existence of adjacent and time-equivalent depositional environments. The travertine deposition resulted from deep origin hydrothermal fluids channelled along damaged rocks volumes associated to a regional fault system, named as the Gafsa Fault (GF). The travertine–terrigenous succession in Jebel El Mida highlights the major role played by the GF in controlling: (i) the hydrothermal fluid flow, still active as also indicated by the numerous thermal springs aligned along the fault zone; (ii) paleoflow directions, discharge locations, volume, rate and fluctuations of the water supply. The paleoclimatic correlation with adjacent localities reveals that, at that time, humid episodes could have contributed to the recharge of the hydrothermal system and to the deposition of alluvial sediments.     

Review of the Integrated Groundwater and Surface-Water Model (IGSM)

Development of the finite-element-based Integrated Groundwater and Surface-Water Model (IGSM) began in the 1970s. Its popularity grew in the early 1990s with its application to California's Central Valley Groundwater Surface-Water Model in support of the Central Valley Project Improvement Act. Since that time, IGSM has been applied by federal, state, and local agencies to model a number of major basins in California. Our review of the recently released version 5.0 of IGSM reveals a solution methodology that deviates from established solution techniques, potentially compromising its reliability under many circumstances. One difficulty occurs because of the semi-explicit time discretization used. Combined with the fixed monthly time step of IGSM, this approach can prevent applications from accurately converging when using parameter values typically found in nature. Additionally, IGSM fails to properly couple and simultaneously solve ground water and surface water models with appropriate mass balance and head convergence under the reasonable conditions considered herein. As a result, IGSM-predicted streamflow is error prone, and errors could exceed 100%. IGSM does not inform the user that there may be a convergence problem with the solution, but instead generally reports good mass balance. Although our review touches on only a few aspects of the code, which exceeds 17,000 lines, our experience is that similar problems arise in other parts of IGSM. Review and examples demonstrate the potential consequences of using the solution methods in IGSM for the prediction, planning, and management of water resources, and provide perspective on the roles of standards and code validation in ground water modeling.     

Source process of the southeast Beni-Suef, northern Egypt earthquake Using Empirical Green's Function Technique

The rupture process of a moderateearthquake (ML4.9) occurred southeastBeni-Suef, northern Egypt was analyzed. Thecharacterization of the rupture process andsource properties were extracted fromstudying the relative moment rate function(RMRF). RMRFs were retrieved bydeconvolution of small aftershock recordsusing an inversion procedure for onlyP-wave part of the records.Although, this event is a moderateearthquake, its RMRFs exhibitedcomplexity and directivity of the rupturebehavior. The deconvolution pulses reflectthree subevents or more. The detailedanalysis of the distinct subevents revealedgross temporal and spatial characteristicsof the rupture propagation. The azimuthalvariation in the time delay of thesubevents with respect to the initiationrupture indicates that the subevents arelocated at 0.85 ± 0.17 and3.5 ± 0.07 km in directions of320^° ± 45^° and330^° ± 15^° with rupturevelocities 3.4 ± 0.45 and4.0 ± 0.7 km/sec, respectively. Thismeans that the rupture is predominatelypropagated toward the North. Estimation ofthe rupture direction was combined withP-wave focal mechanism to identify thefault plane for the initial rupture ofmainshock.Source parameters were calculated for eachdistinct subevent, including seismicmoments 8.53E14 to 6.80E15 Nm, fault radii713 to 1800 m and stress drops 0.725 to2.932 MPa. The large estimated stress dropfor the main subevent reflects failureasperity.     

Dependency of unit shaft resistance on in-situ stress: Observations derived from collected field data

In this study, a database comprised of 30 pullout pile load tests was collected from geotechnical literature and analyzed to investigate the dependency of unit shaft resistance on effective vertical stress. The collected database consists of steel pipe, timber, and concrete piles, with varying normalized penetration depth with respect to pile diameter, driven into loose to very dense sand. Different correlations for the uplift lateral earth pressure coefficient K, Bjerrum-Burland ratio , and the average unit shaft resistance f _ave were derived using different assumptions. A comparison between measured and predicted capacities of the collected piles using the developed correlations indicated that the assumption of values of K and that were constant with depth did not provide a reasonable fit for the measured capacities of the collected piles and thus this assumption is inappropriate. The best correlations for K and that yield a reasonable fit to the measured capacities of the collected piles were found to be functions of sand relative density, pile diameter, and level of effective vertical stress. This indicates that average unit shaft resistance does not reach a limiting value, but rather continues to increase with depth. Moreover, the correlations for K and in terms of effective stress revealed that average unit shaft resistance increases as pile diameter decreases and this increase depends on initial sand relative density. Comparisons of measured and predicted pullout capacities of the collected piles using the best-obtained correlations for K and were made and compared to predictionsobtained from other methods. On the basis of these comparisons, it is concluded that the correlations for K and in terms of effective stress give results comparable to those obtained from other methods, without stipulating limiting values for the average unit shaft resistance.     

Microcracks and Overpressure-Induced Fractures

1　ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｔｈｅｐａｓｔｄｅｃａｄｅｓｎｕｍｂｅｒｏｆｓｔｕｄｉｅｓｉｎｖｅｓｔｉｇａｔｅｄｍｉｃｒｏｃｒａｃｋｓｉｎｒｏｃｋｓｈａｓｒａｐｉｄｌｙｉｎｃｒｅａｓｅｄ .ＭｉｃｒｏｃｒａｃｋｈａｓｂｅｅｎｄｅｆｉｎｅｄｂｙＲｉｃｈｔｅｒ     

East-west stationkeeping requirements of nearly synchronous satellites due to Earth's triaxiality and luni-solar effects

A closed form solution, for longitude and semimajor axis deviations in the neighborhood of a prespecified station, is obtained for nearly synchronous satellites. The model use includes the important terms in Earth's zonal and tesseral harmonics as well as the luni-solar perturbations. The initial semimajor axis for two-maneuver east-west stationkeeping is then deduced. Due to the luni-solar effects, it is found that the initial semimajor axis deviation from synchronous orbit value is highly dependent on the initial position of the satellite relative to the Moon and the Sun. Verifications of the results by means of numerical integrations are also included.     

Description of the trajectory functions of TOPEX/POSEIDON navigation

TOPEX/POSEIDON is a joint American/French ocean topography experiment. It was launched by an Ariane launch vehicle on August 10, 1992 to study and map ocean circulation. The primary functions of the navigation subsystem of the TOPEX/POSEIDON project are to establish and maintain a pre-designed reference orbit, and to measure, monitor, and predict the satellite ground track continuously. To fulfill these functions, trajectory analysis is required to design and generate all trajectory related products. This paper is concerned with the trajectory functions of TOPEX/POSEIDON navigation. It describes various activities of this support function.