Rock joint modeling using a visco-plastic multilaminate model at constant normal load condition

Rock joints play an important role in the behavior of rock masses under normal and shear loading conditions. Numerical simulation of the behavior of jointed rock masses is not an easy task due to complexities involved in the problem such as joint roughness, joint shear strength, hardening and softening phenomenon and mesh dependency. In this study for modeling purposes, a visco-plastic multilaminate model considering hardening and softening effects has been employed. For providing the necessary data for numerical simulation, a series of laboratory experiments have been carried out on regular tooth-shape asperities made by gypsum, under constant normal load conditions. Shear stress–shear displacement and normal displacement–shear displacement of artificial joint specimens are simulated using the proposed numerical model at constant normal load condition (CNL). The results indicate the capability of the model for simulating rock joints behavior in both strength and deformation field. Although the numerical model has been developed for simulating the behavior of artificial joints, the concept of the method can also be used for natural rock joints.     

T-phases from Atlantic earthquakes

Summary Underwater sound waves from earthquakes or so-calledT-waves are investigated for the Atlantic-Arctic area for the years 1953–1968, mainly from Swedish seismograph records, and for comparison also from an earthquake in the equatorial Atlantic withT-waves recorded on both sides of the ocean. The waves travel as sound waves through water, and asPg, Sg andRg over the land path. The North Atlantic source area of theT-waves, recorded at Scandinavian stations, is very well limited in extent with a strong concentration northeast of Jan Mayen, probably due to favourable bottom topography. The calculated sound velocities in water are 1.43 km/sec for the Arctic case and 1.52 km/sec for the equatorial one. TheT-waves exhibit a clear inverse dispersion. The dispersion explains their long duration. The duration of theT-phase increases logarithmically with the maximum amplitudes within theT-wave group and decreases linearly with distance over the land path, corresponding to a quality factor of about 700. Propagation across the ocean by multiple reflections between surface and bottom appears as the most probable mechanism. The particle motion ofT Sg is dominantly transverse horizontal, which is explained by refraction when the waves are transmitted to land. TheT-wave spectra at two different localities show clear relations, depending upon the ocean depths.     

Deep echo state network: a novel machine learning approach to model dew point temperature using meteorological variables

ABSTRACT

The potential of different models – deep echo state network (DeepESN), extreme learning machine (ELM), extra tree (ET), and regression tree (RT) – in estimating dew point temperature by using meteorological variables is investigated. The variables consist of daily records of average air temperature, atmospheric pressure, relative humidity, wind speed, solar radiation, and dew point temperature (T_dew) from Seoul and Incheon stations, Republic of Korea. Evaluation of the model performance shows that the models with five and three-input variables yielded better accuracy than the other models in these two stations, respectively. In terms of root-mean-square error, there was significant increase in accuracy when using the DeepESN model compared to the ELM (18%), ET (58%), and RT (64%) models at Seoul station and the ELM (12%), ET (23%), and RT (49%) models at Incheon. The results show that the proposed DeepESN model performed better than the other models in forecasting T_dew values.     

Teleconnections between oceanic–atmospheric indices and drought over Iran using quantile regressions

ABSTRACT

In this research, the Bayesian quantile regression model is applied to investigate the teleconnections between large oceanic–atmospheric indices and drought standardized precipitation index (SPI) in Iran. The 12-month SPI time series from 138 synoptic stations for 1952–2014 were selected as the drought index. Three oceanic–atmospheric indices, the North Atlantic Oscillation (NAO), the Southern Oscillation Index (SOI) and the Multivariate El Niño/Southern Oscillation Index (MEI), were selected as covariates. The results show that NAO has the weakest impact on drought in different quantiles and different regions in Iran. La Niña conditions amplified droughts through all SPI quantiles in western, Caspian Sea coastal regions and southern regions. The positive phase of MEI significantly modulates low SPI quantiles (i.e. drought conditions) throughout the Zagros region, Caspian Sea coastal regions and southern regions. The study shows that the effect of large oceanic–atmospheric indices have heterogeneous impacts on extreme dry and wet conditions.     

Stochastic Modeling of Groundwater Fluoride Contamination: Introducing Lazy Learners

While it remains the primary source of safe drinking and irrigation water in northwest Iran's Maku Plain, the region's groundwater is prone to fluoride contamination. Accordingly, modeling techniques to accurately predict groundwater fluoride concentration are required. The current paper advances several novel data mining algorithms including Lazy learners [instance-based K-nearest neighbors (IBK); locally weighted learning (LWL); and KStar], a tree-based algorithm (M5P), and a meta classifier algorithm [regression by discretization (RBD)] to predict groundwater fluoride concentration. Drawing on several groundwater quality variables (e.g., concentrations), measured in each of 143 samples collected between 2004 and 2008, several models predicting groundwater fluoride concentrations were developed. The full dataset was divided into two subsets: 70% for model training (calibration) and 30% for model evaluation (validation). Models were validated using several statistical evaluation criteria and three visual evaluation approaches (i.e., scatter plots, Taylor and Violin diagrams). Although Na⁺ and Ca²⁺ showed the greatest positive and negative correlations with fluoride (r = 0.59 and −0.39, respectively), they were insufficient to reliably predict fluoride levels; therefore, other water quality variables, including those weakly correlated with fluoride, should be considered as inputs for fluoride prediction. The IBK model outperformed other models in fluoride contamination prediction, followed by KStar, RBD, M5P, and LWL. The RBD and M5P models were the least accurate in terms of predicting peaks in fluoride concentration values. Results of the current study can be used to support practical and sustainable management of water and groundwater resources.     

Ready-made garments exports earning and its contribution to economic growth in Bangladesh

GeoJournal - This study attempts to explore the cointegration among economic growth rate, ready-made garments (RMG) exports earning and foreign direct investment (FDI) inflow in Bangladesh. It uses...     

Slope stability analysis of the Rangamati District using geotechnical and geochemical parameters

Natural Hazards - Landslide and human mortality have been a common phenomenon in the Rangamati district over the past several years. This study examined the geotechnical properties (e.g., grain...     

Pseudo-static Seismic Bearing Capacity of Shallow Foundations in Unsaturated Soils Employing Limit Equilibrium Method

There exist many structures founded on unsaturated soil deposits. Shear strength augmentation due to the evolution of the matric suction within the unsaturated porous media enhances the bearing capacity of the overlying foundation. This paper presents the evaluation of the pseudo-static seismic bearing capacity of the shallow foundations resting on unsaturated soil deposits using limit equilibrium method. Adopting the Coulomb failure mechanism and Bishop effective stress concept, the bearing capacity equations are solved. The distribution of the matric suction beneath the footing is assumed to be linear. The results of the bearing capacity evaluation are validated against some experimental data found in literature for the static condition. For the seismic loading consideration, the pseudo-static method is utilized. The dual effect of the earthquake acceleration vertical component is thoroughly discussed and a suction transition point is introduced in which the minimum bearing capacity is observed to bear the same value for both upward and downward directions. The increase in the matric suction throughout the soil deposit leads to the increase in the soil shear strength, thus posing more resisting forces as well as higher ultimate bearing capacity. The offered solution is deemed a consistent and useful tool for the accurate prediction of the seismic bearing capacity of shallow footings resting on unsaturated soil deposits.

     

基于变分技术的天气雷达速度退模糊算法的改进研究

为有效地识别和提取多普勒天气雷达风场信息,对Gao和Droegemeier提出的基于变分技术的多普勒雷达径向速度数据退模糊方法进行了改进。原方法中将背景风场、方位和径向速度距离梯度信息同时作为约束条件,对Nyquist数进行校正。但是该方法在迭代过程中使用了大量的数值分析和偏微分方程计算,造成径向速度场过度平滑和数据失真。针对这个问题,改进算法在得到径向速度分析场后,结合原始径向速度观测场,通过图像变化检测法,自动识别存在速度模糊的区域及计算需要校正的Nyquist数,对观测场的模糊区域进行校正。利用强对流天气和台风过程的雷达体扫数据验证了改进算法的可行性,并与原始算法及业务应用的WSR-88D算法对比。结果表明:改进算法有效地解决了原始算法中的不足,恢复真实的风场结构和分布特征,改善了退速度模糊的质量,从而得到更为合理的径向速度观测场;并且该算法退模糊效果优于WSR-88D算法,有助于为科研和业务应用服务。     

An Experimental Characterization of Shear Wave Velocity (V<Subscript>s</Subscript>) in Clean and Hydrocarbon-Contaminated Sand

The characteristics of hydrocarbon-contaminated soils have been among major concerns of geotechnical engineers due to its significant frequency of event and also its influential consequences on our surroundings from various environmental and engineering viewpoints. Heretofore, the effects of diverse kinds of hydrocarbon contaminants on majority of geotechnical properties of fine- and coarse-grained soils such as grain size, hydraulic conductivity, plasticity, compressibility, internal friction, cohesion, and shear strength have been investigated. However, there has not been a concentrated research study examining shear wave velocity (\({\text{V}}_{\text{s}}\)) of hydrocarbon-contaminated soils as an important geotechnical property of soil due to this fact that, in small/very small strain levels, the maximum shear modulus of soils (\({\text{G}}_{ \hbox{max} }\)) can be determined using shear wave velocity (\({\text{G}}_{ \hbox{max} } =\uprho{\text{V}}_{\text{s}}^{2}\)). This paper aims to investigate effects of hydrocarbon contamination on shear wave velocity of sandy soils by comparing shear wave velocities in identically prepared clean and contaminated samples. To this aim, an Iranian light crude oil, a standard type of silica sand (Ottawa sand), and a bender element apparatus were used to minutely measure shear wave velocity of clean and crude oil contaminated sand samples. Moreover, dry and quasi-moist tamping methods were employed in order to provide comparable clean and contaminated specimens (containing 4, 6, 8, 10, and 12 wt% of crude oil), respectively. Firstly, a comprehensive bender element (BE) and resonant column tests were conducted on the identically prepared clean sand samples at various amounts of frequency (2–20 kHz) and under various confining pressure (50–500 kPa) to find the best methods of accurately determining shear wave travel time in BE tests. Thereafter, BE tests were conducted to examine shear wave velocity in contaminated specimens. Based on the results, it was found that there was a critical value for crude oil content with the maximum shear wave velocity so that shear wave velocity of 4 wt% contaminated sand (V_s-4 wt%) was about 1.2 times higher than clean one (V_s-clean), and contrastingly adding further crude oil up to 6 wt% made a significant reduction in value of shear wave velocity to some extent that V_s-6 wt% was slightly lower than V_s-clean (V_s-6 wt% = 0.95–0.97V_s-clean). Moreover, adding more contaminant (8–12 wt%) into sand had negligible influences on shear wave velocity. In this paper, the effects of crude oil contamination on sand microstructure were also evaluated using scanning electron microscopy.