Cement-Stabilization of Sabkha Soils from Al-Auzayba,Sultanate of Oman

Sabkha soils are salt-bearing formations that are formed in arid regions. In their in situ states the sabkha soils have high compressibility and low shear strength. These soils are also heterogeneous and their properties depend on the type and amount of salt present. Thus, these soils are not suitable for support of infrastructures without the risk of high settlement and/or bearing capacity failure. This paper investigates the possibility of using cement to improve the shear strength of sabkha soils for possible use as a foundation-bearing soil. The sabkha soil used in this study is a sandy sabkha obtained from the coastal plains at Al-Auzayba, Sultanate of Oman. Cement was added in percentages of 2.5, 5, 7.5 and 10%, by dry weight of soil. The soil-stabilizer mixers were allowed to cure for 7, 14 and 28 days. Laboratory tests such as compaction, unconfined compression, consolidated undrained triaxial and durability tests were performed to measure the engineering characteristics of the stabilized material. The results showed substantial improvements in the shear strength of the sabkha–cement mixtures and the mixtures are also durable with small weight loss after 12 wetting/drying cycles. Thus, cement can be used to improve the shear strength of sabkha soils. Furthermore, the effective stress path and the tress-strain relation of the sabkha–cement mixtures follow trends similar to those of cemented calcareous soils.     

Comprehensive laboratory study on stress–strain of granular soils at constant global void ratio: combined effects of fabrics and silt content

The published literature has revealed conflicting results regarding the effect of low plastic fines fraction (I_p?≤?5.0%) on the mechanical behavior of sandy soils. For this reason, the use of different sample initial structures as (initial relative density approach, global void ratio index approach, etc.) could explain these different mechanical responses of granular materials. Thus, it is necessary to evaluate the quantitative aspect of the low plastic fines effects on the undrained monotonic response of sand-silt mixtures using the global void ratio approach. To achieve this goal, an experimental testing program through controlled monotonic triaxial tests was carried out on reconstituted saturated Chlef sand containing from 0 to 50% silt with an interval of 10% at three global void ratios (e?=?0.64, 0.66 and 0.68) and subjected to constant confining pressure (σ'₃?=?100 kPa). The different samples were reconstituted using two different preparation techniques: DFP and MT. The obtained results show that the low plastic fines content appears as a very relevant parameter in the characterization of the mechanical response of sand-silt mixture samples reconstituted at constant global void ratios, where the steady state shear strength and instability shear strength decreased with the increase in low plastic fines content up to the limiting fines contents (F_c?=?40% and F_c?=?10%) considering both studied initial structures (Dry funnel pluviation and Moist tamping), respectively. Beyond these thresholds fines contents, a reverse trend was observed for all parameters under study. Moreover, the test results indicate that the brittleness index, flow potential (V_f), friction index, equivalent void ratio (e*) and equivalent relative density (Dr*) could be considered as reliable parameters in the prediction of the mechanical behavior of the silty sand soils under study.

     

Geochemistry and quality assessment of groundwater using graphical and multivariate statistical methods. A case study: Grombalia phreatic aquifer (Northeastern Tunisia)

The Grombalia coastal aquifer, situated in Northeastern Tunisia, is a water source for public, agricultural, and industrial supplies in the region. The overexploitation of this aquifer, since 1959, and the agriculture activities led to the degradation, by places, of the water quality. The present study implemented graphical, modeling, and multivariate statistical tools to investigate natural and anthropogenic processes controlling Grombalia groundwater mineralization and water quality for promoting sustainable development. To attempt this goal, groundwater was collected from 33 observation wells in January 2004, and samples were analyzed for 10 physicochemical parameters (temperature, pH, salinity, Na⁺, Ca²⁺, K⁺, Mg²⁺, Cl^?, HCO^3?, and SO ₄ ^2? ). Hydrochemical facies using Piper diagram indicates a predominance of a mixed facies, of the Na-Cl-HCO₃ type, or Na-Ca-Cl-SO₄ type, and, with less expansion, Na Cl type. The main factors controlling Grombalia groundwater mineralization seem to be mineral dissolution of highly soluble salts especially, the halite dissolution existing in the surface salty deposits and, with less importance, the ion exchange and reverse ion exchange process with clay minerals existing in the aquifer. The comparison of the major ions of the Grombalia groundwater, with the World Health Organization norms of potability (WHO 2004), reveals that these waters cannot be used for human consumption without any treatment. Most waters of the Grombalia aquifer, with a relatively high salinity, are not suitable for irrigation, in ordinary conditions. Nevertheless, they can be used for permeable soils, with an adequate drainage and applying an excess of leaching water.     

Use of geographical information system and water quality index to assess groundwater quality in El Khairat deep aquifer (Enfidha, Central East Tunisia)

Groundwater is the most important natural resource used for drinking by many people around the world, especially in rural areas. In Tunisia, since the quantity and the quality of water available for different uses is variable from one place to another, groundwater quality in El Khairat deep aquifer was evaluated for its suitability for drinking purposes. To this end, an attempt has been made for the first time in order to determine spatial distribution of groundwater quality parameters and to identify places with the best quality for drinking within the study area based on: (1) an integrated analysis of physical?Cchemical parameters, (2) use of Geographical Information System, and (3) Water Quality Index (WQI) calculation. The physical?Cchemical results were compared with the World Health Organization (WHO) standards for drinking and public health, in order to have an overview of the present groundwater quality. According to the overall assessment of the basin, almost all the parameters analyzed are above the desirable limits of WHO. Using GIS contouring methods with Arcview 3.2a, spatial distribution maps of pH, TDS, EC, TH, Cl, HCO₃, SO₄, NO₃, Ca, Mg, Na, and K have been created. The spatial analysis of groundwater quality patterns of the study area shows that the TDS value increases from north-west to south-east following the general trend of the Khairat aquifer flow direction. The spatial distribution map of TH shows that a majority of the groundwater samples falls in the very hard category. WQI was used to assess the suitability of groundwater from the study area for human consumption. From the WQI assessment, over 82% of the water samples fall within the ??Poor?? and ??Very poor?? categories, suggesting that groundwater from the south-eastern of the El Khairat deep aquifer is unsuitable for drinking purposes.     

Intraplate uplift: new constraints on the Hoggar dome from the Illizi basin (Algeria)

Zones of anomalously high topography within continental interiors, distant from active plate boundaries, are interpreted as being either dynamically supported by viscous flow in the underlying mantle or influenced by plate tectonics. Constraining the models of their genesis requires accurate data on the timing and dimensions of such features. New apatite fission‐track and thermal maturity data from the Illizi Basin in Algeria quantify the magnitude and timing of kilometre–scale uplift and exhumation of the northern flank of the Hoggar swell in North Africa. The findings of this study, integrated with previously published thermochronological data, confirm that long‐wavelength regional uplift occurred during the Cenozoic extending over a distance in excess of 1500 km from north to south. The uplift, centred on the Hoggar Massif, significantly impacted the flanking Illizi and Tim Mersoï basins. The combination of thermal history modelling and regional stratigraphic observations indicates that the onset of exhumation of the Illizi Basin likely occurred during the Eocene, broadly coincident with magmatism on the Hoggar Massif to the south and the onset of tectonic shortening in the Atlasic belt to the north.     

Stabilization of desert sands using municipal solid waste incinerator ash

This paper presents experimental results on the use of incinerator ash in stabilizing desert sands for possible use in geotechnical engineering applications. The incinerator ash was added in percentages of 2, 4, 8, 10 and 12%, by dry weight of sand. Laboratory tests such as compaction, unconfined compression, shear box and hydraulic conductivity were performed to measure the engineering characteristics of the stabilized material. The results showed substantial improvements in unconfined compressive strength and shear strength parameters (c and φ). Thus, incinerator ash can be used to improve the shear strength characteristics of desert sands. The permeability of the sand–incinerator ash mixture was relatively low.     

基于Ecopath模型的孟加拉国孟加拉湾海域营养结构和能量流动分析

依据现有研究提供的信息,在孟加拉国孟加拉湾（BoB）新划定的超过90 000 km²的海域基于Ecopath方法利用2016年7月至2017年6月的数据构建了该生态系统的营养通道模型。对食物网中营养级从1（主要生产者和碎屑）到3.45（鲨鱼）的各功能群之间的营养相互作用进行评估,所研究的共19个功能群被认为代表了其中所有的营养级。大多数消费者的生态营养转换效率（EE）超过0.80;表明这是一个被高度利用的生态系统,并且从低营养级到高营养级有较高的能量转换效率。此外,整个生态系统的净效率（0.0018）和能量转换效率（11.12%）标志着当前这一"正在发展中的生态系统"已趋向成熟。生态系统的冗余度（64.6）和聚合度（35.4）也表明了这一生态系统的稳定性。因此,本研究认为这一海域具有显著的后备力量面对压力情况并有能力快速恢复到初始状态。     

Diversity and distribution of gelatinous zooplankton in the Southwestern Mediterranean Sea

Gelatinous zooplankton species composition, distribution and abundance were investigated in the bay and the lagoon of Bizerte (North Tunisian coast) from January 2004 to December 2005. In total, 48 species were identified in the study area: 24 medusae, 11 siphonophores, four appendicularians, six chaetognaths, two pteropods and one doliolid. The hydromedusa Eutima mira was recorded for the first time in the Western Mediterranean Sea. The diversity in the Bay of Bizerte was greater than the diversity in the Bizerte lagoon. There was a loss of species diversity. Siphonophores were the most sensitive group to anthropogenic discharge. Only two species of siphonophores were recorded in the lagoon. Four species of gelatinous zooplankton, Muggiaea kochi, Lensia conoidea, Oikopleura longicauda and Podocorynoides minima were the most frequent species in the lagoon and may benefit from eutrophication. Appendicularians were numerically the most dominant group in the bay and the lagoon of Bizerte. Mesozooplankton density declined significantly in autumn and winter of 2004 and 2005 in relation to the dense aggregations of the scyphomedusae Pelagia noctiluca. Statistical analysis divided the study area into three zones: lagoon zone, bay zone and channel zone.