Studying the effect of partial drainage on the response of soft clays reinforced with sand column groups

Acta Geotechnica - The drained and undrained response of soft clays reinforced with granular columns has been the subject of numerous geotechnical research efforts to date. Although these studies...     

Delineation of potential recharge area using a hybrid model,case of Djelfa Hadjia watershed

Groundwater potential map is important for environmental assessment and water resources management. In this work, a groundwater recharge potential map was established for the watershed of Oued Djelfa Hadjia in Algeria, based on new multiparameters hybrid model. The model has hydroclimatic parameters, geological settings, slope factor, and stream network density factor as inputs. The groundwater recharge estimated by the model range from 0.71 to 14 mm. The model allows delineation of potential area of recharge. The total water abstraction in Djelfa city is about of 14 hm³; however, the calculated groundwater recharge is about 3 mm/year (min 0.71 mm and max 14 mm), which correspond to an average recharge volume of 3.9 hm³ which mean that the aquifer is under over exploitation.     

Identification and Simultaneous Optimisation of Tunisian Clay Properties: Preliminary Study for the Ceramic Products

The relationship between composition and physical parameters such as specific surface area, cationic exchange capacity and plasticity is studied with the aim of developing regression models that would permit the prediction of clay properties. These models could be useful for mineralogists and industrial applications. Nineteen representative clay samples were collected from Jebel Ressas in north-eastern Tunisia. Mineralogical data show that clay samples cover a very large variety of minerals. The main clay mineral is illite (50–60 wt%), secondary minerals including quartz, calcite and minor amounts of Na-feldspar. This study reveals that the average amount of silica (SiO₂) and alumina (Al₂O₃) are 51.9 and 19.6 wt%, respectively. The contents of lime (CaO) and iron (Fe₂O₃) vary between 4 and 8 wt% whereas the amount of alkalis (Na₂O + K₂O) is on average 4.1 wt%. The grain size data indicates a significant amount of silt fraction, and the fraction <2 µm varies between 23 and 35 wt%. Values for plasticity index range from 16 to 28 wt%. The cation exchange capacity and the specific surface values are 34.1–45.7 meq/100 g of air-dried clay and 302–374 m²/g, respectively. Lastly, regression models are used to correlate the properties with the mineralogical and chemical compositions. The significance and the validity of models were confirmed by statistical analysis and verification experiments. The regression models can be used to select the clay properties (plasticity index, cation exchange capacity and specific surface) in relation with clay minerals proportions and the finer fraction amounts.     

The Condition of Hydrostatic Equilibrium of Stellar Models Using Optimal Control

The condition of hydrostatic equilibrium of relativistic stellar models is formulated as an optimal control problem. Application of Pontryagin's maximum principle leads directly to the Tolman-Oppenheimer-Volkoff equation. This revised version was published online in July 2006 with corrections to the Cover Date.     

http://www.sciencedirect.com/science/article/pii/S1674987112001247

The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift, the Dead Sea Transform fault, and the Red Sea rift. The upper and lower crustal structures of this tectonically active, rapidly developing region are yet poorly understood because of many limitations. For this reason, a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian National Seismographic Network (ENSN) from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai. Because the velocity model used for routine earthquake location by ENSN is one-dimensional, the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures. Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west. The crustal V_p/V_s ratio is 1.74 from shallow (depth ≤ 10 km) earthquakes and 1.76 from deeper (depth > 10 km) crustal events. The majority of the regional and local travel-time residuals are positive relative to the Preliminary Reference Earth Model (PREM), implying that the seismic stations are located above widely distributed, tectonically-induced low-velocity zones. These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures. The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities, which should be excluded from major future development projects and large constructions in central and southern Sinai.     

Variations in groundwater levels and quality due to agricultural over-exploitation in an arid environment: the phreatic aquifer of the Souf oasis (Algerian Sahara)

Groundwater is a major source of supply for domestic and agricultural purposes, especially in arid and semi-arid regions. In this study, we followed the variations in water levels in the Souf oasis in the Algerian Sahara by measuring depths to groundwater across 65 points during the period from 2010 to 2015. Additionally, electrical conductivity (EC) was measured for assessing variations in groundwater salinity in the same groundwater monitoring network over the same time interval. The results from these investigations indicated that there are significant and continuous declines in the groundwater level across all study areas throughout the period of investigation. This is especially the case in the northern part of the study area where the water table declined by up to 18.2 m in Ghamra in 2015. Additionally, this study has indicated that the rate of decline of groundwater levels has increased from 0.29 m/year as an average in 2011 to 2.37 m/year in 2015, where the situation has become alarming. As a consequence of this, the depth to groundwater now exceeds 2 m over more than 77% of the study area, and only about 17% of the study area now has a water table depth that lies within the optimal depth interval for extractive uses (between 1 and 2 m). This decline in groundwater levels has been accompanied by a significant increase in the electrical conductivity values (salinity) of this water, and there is a strong correlation between these variables (R > 0.99). This alarming situation has been caused by the continuous over-exploitation and unsustainable management of this limited resource, especially by the agricultural sector. For a long time, this critical situation led to the demise of the agricultural world heritage cultivation system (Ghout) due to the increasing salinity of groundwater. Two solutions are proposed to manage the effects of groundwater depletion in the area: firstly, rationalizing groundwater use through effective groundwater allocation management measures, and secondly by implementing the reuse of treated wastewater as an alternative water source for agricultural use. This latter measure could be in two ways: either by direct use in irrigation to relieve pressure on the phreatic aquifer, or by artificial recharge of the phreatic aquifer.     

http://www.sciencedirect.com/science/article/pii/S1674987112000084

Seismic anisotropy and its main features along the convergent boundary between Africa and Iberia are detected through the analysis of teleseismic shear-wave splitting.Waveform data generated by 95 teleseismic events recorded at 17 broadband stations deployed in the western Mediterranean region are used in the present study.Although the station coverage is not uniform in the Iberian Peninsula and northwest Africa,significant variations in the fast polarization directions and delay times are observed at stations located at different tectonic domains.Fast polarization directions are oriented predominantly NW-SE at most stations which are close to the plate boundary and in central Iberia;being consistent with the absolute plate motion in the region.In the northern part of the Iberian Peninsula,fast velocity directions are oriented nearly E—W;coincident with previous results.Few stations located slightly north of the plate boundary and to the southeast of Iberia show E—W to NE-SW fast velocity directions,which may be related to the Alpine Orogeny and the extension direction in Iberia.Delay times vary significantly between 0.2 and 1.9 s for individual measurements,reflecting a highly anisotropic structure beneath the recording stations.The relative motion between Africa and Iberia represents the main reason for the observed NW-SE orientations of the fast velocity directions.However,different causes of anisotropy have also to be considered to explain the wide range of the splitting pattern observed in the western Mediterranean region.Many geophysical observations such as the low Pn velocity,lower lithospheric Q values,higher heat flow and the presence of high conductive features support the mantle How in the western Mediterranean,which may contribute and even modify the splitting pattern beneath the studied region.     

Lithospheric structure of Southeast Anatolia from joint inversion of local and teleseismic data

A joint tomographic inversion of local and teleseismic arrival times recorded at 41 seismic stations in southeast Anatolia is conducted to study the 3-D lithospheric velocity structure and its relation to the prevailing tectonic processes. A total of 21300 arrivals from local and teleseismic events are used in the final inversion. The tomographic model reveals prominent lower crustal/uppermost mantle low-velocity anomalies. High-velocity zones are imaged in the western part of the study area. The background seismic activity occurs mainly at the low-velocity areas and to a lesser extent in some high-velocity zones. Large crustal earthquakes occur in average velocity zones, but not in high-velocity areas that can resist stress. Results of the checkerboard resolution test indicate the reliability of the obtained images; while the large hit counts at most depth slices denote reasonable ray-path coverage for most parts of the study area. The obtained velocity anomalies are generally consistent with many previous geophysical measurements and give much deeper understanding of the current seismotectonic processes occurring in the region.