Study of the mechanical behavior of marls: Case from Fes - Meknes region (Morocco)

In relationship with urban expansion at the level of cities located in the Sais basin, several projects have been carried out and others still in progress. Therefore, the recognition of the mechanical characteristics of soils and subsoil remains essential before any construction project, in order to avoid the shrinkage-swelling phenomenon associated with marls soil. In order to minimize the risk of instability, the present work consists of the characterization and study of the mechanical behavior of marly soils in some locations of Sais basin. In-situ tests have been performed in the field and samples submitted to other geotechnical tests in the laboratory such as the odometer compressibility and direct shear tests. The obtained results show that the studied marly soils exhibit strongly consolidated behaviors with the depth according to Menard test, and to the ratio of the pressiometric modulus (EM) and the corrected limit pressure (PL*)

Geochemical and isotopical analyzes of groundwater in a karst system - the case study of Fez-Meknès basin (Morocco).

Plenary Flash Oral Presentation and poster.International audienceThe karst Middle Atlas Causses reservoir mainly composed of Liasic dolomitic limestone, overlyingTriassic clays, evaporates and basalts, is the main drinking water supply in Fez-Meknès region (SaïsBasin). Because of the increase in population, the number of drilling for irrigation of agricultural landand some longer drought periods in recent years, the issue of sustainable groundwater managementarises. Recent analyzes have shown a decline in its chemical quality and punctually some turbidityproblems. In order to enhance understanding of this hydrosystem and the interactions between thedifferent main springs of Liasic and Triassic origin, and their connections to the major spring (Bittit), anintegrated hydrogeochemical study was conducted coupled to isotopic analyzes of delta O-18, deltaDand Radon-222. Four surveys were performed in fall and spring seasons (2009 -2011). Watergeochemistry shows two kinds of water- a major Liasic origin along the transition between theCausses and the Saïs basin, and a major Triassic origin for El Mir, Sbaa, and Maarouf springs locatedat the southern border of Saïs basin extremities. Deuterium excess highlights a local recharge whiledelta O-18 versus delta D characterize two aqui fers with different evaporations. Radon -222,underlined the existence of areas of rapid exchange between waters of Liasic aquifer characterized bylow Radon activity (3500 Bq m3) and waters in contact with Triassic aquitard characterized by a highRadon activity (> 15000 Bq m3). The transit time is less than two weeks to surface. The watersrenewal is only conducted by major rainfalls. Four recharge zones of different altitudes have beenfound and two main mixing zones (limits of Saïs Basin)

Implication of Guigo and L'Hajeb Causses in the renewal and circulations of Saïs basin groundwaters (Middle-Atlas Causses, Morocco).

International audienceIn a context of overexploitation of the karst system of the Middle Atlas Causses feeding the Saïs basin and the current climatic variations, the study of circulations and of renewal of waters of this system in the Fes-Meknes area becomes essential for the population, in order to maintain a sufficient quality of waters with a good management.By coupling hydrochemical and isotopic analysis methods (delta-D, delta O-18, Radon-222), saturation indices obtained from PHREEQC code and principal component analysis (PCA) of ten springs and three wells, a first conceptual model of groundwater flows of this karst system was obtained . These waters are mainly renewed by the rainfall of L'Hajeb Causse and secondarly by the rainfall of Guigo Causse containing several springs. Hydrochemistry and saturation indexes allowed us to highlight two types of waters: a main contribution of Liasic origin and two low contributions of Triassic origin at the southern extremities (SE, SW) of the basin. We pointed out the existence of five local recharge zones of different altitudes (900 to 1500 m asl.) including the two main mixing zones to the south (SE, SW). Radon-222 showed areas of rapid exchange (upwelling time less than two weeks) between waters of Liasic aquifer and the ones of Triassic origin with high radon activity.The use of PCA on hydrochemical data, allowed us to refine the kind of waters, their transit times and highlighted the existence of several mixing zones between the Triassic aquitard and the Liasic aquifers in more or less faulted structures for the two causses. Our results allow us to obtain a first conceptual model of groundwater circulations between the two causses and the Saïs basin.Previous campaigns of electrical resistivity tomography coupled with electromagnetic measurements (EM34) revealed lateral and vertical variations of electrical conductivity changing with the depth along the North-South axis, and a preferential drain perpendicularly to the causses (EGU 2009). We can note that groundwater flows are conditioned by two major fracture networks, NE-SW and NW-SE directions (Bentayeb & Leclerc 1977, Amraoui 2005). A karstic complex water circulation is especially developed locally at the border of the two hydrogeological units (Qarqori 2015)

Implication of Guigo and L'Hajeb Causses in the renewal and circulations of Saïs basin groundwaters (Middle-Atlas Causses, Morocco).

International audienceIn a context of overexploitation of the karst system of the Middle Atlas Causses feeding the Saïs basin and the current climatic variations, the study of circulations and of renewal of waters of this system in the Fes-Meknes area becomes essential for the population, in order to maintain a sufficient quality of waters with a good management.By coupling hydrochemical and isotopic analysis methods (delta-D, delta O-18, Radon-222), saturation indices obtained from PHREEQC code and principal component analysis (PCA) of ten springs and three wells, a first conceptual model of groundwater flows of this karst system was obtained . These waters are mainly renewed by the rainfall of L'Hajeb Causse and secondarly by the rainfall of Guigo Causse containing several springs. Hydrochemistry and saturation indexes allowed us to highlight two types of waters: a main contribution of Liasic origin and two low contributions of Triassic origin at the southern extremities (SE, SW) of the basin. We pointed out the existence of five local recharge zones of different altitudes (900 to 1500 m asl.) including the two main mixing zones to the south (SE, SW). Radon-222 showed areas of rapid exchange (upwelling time less than two weeks) between waters of Liasic aquifer and the ones of Triassic origin with high radon activity.The use of PCA on hydrochemical data, allowed us to refine the kind of waters, their transit times and highlighted the existence of several mixing zones between the Triassic aquitard and the Liasic aquifers in more or less faulted structures for the two causses. Our results allow us to obtain a first conceptual model of groundwater circulations between the two causses and the Saïs basin.Previous campaigns of electrical resistivity tomography coupled with electromagnetic measurements (EM34) revealed lateral and vertical variations of electrical conductivity changing with the depth along the North-South axis, and a preferential drain perpendicularly to the causses (EGU 2009). We can note that groundwater flows are conditioned by two major fracture networks, NE-SW and NW-SE directions (Bentayeb & Leclerc 1977, Amraoui 2005). A karstic complex water circulation is especially developed locally at the border of the two hydrogeological units (Qarqori 2015)

Geophysical constraints on the groundwater circulation and its renewal at the main Bittit spring, supplying Meknes and its region (Sais Basin): Characterization & conceptual model.

International audiencePrevious hydrochemical and isotopic studies of the tabular Middle-Atlas karst showed that the Sais basin is mainly fed at its northern border by the carbonated Causses of the fractured Lias, in particular by El Hajeb causse to the east and the Guigo causse west (Miche et al, 2018).In a context of over-exploitation of the water karst system accentuated by the current climatic variations, with recurrent droughts and sparse strong thunderstorms, the karstic spring of Bittit, main water source of Meknes and its region, is strongly solicited. Since we have obtained a conceptual model using hydrochemical and isotopic data, Bittit is mainly involved by the causse of El Hajeb (1500m) and partially by the causse of Imouzzer (1340m). It is necessary to localize the depth of mixing zones and the direction of preferential flows around Bittit spring, for a better understanding of aquifers renewal. The coupling of electromagnetic sounding (EM34) and electrical resistivity tomography (ERT) show a tightening of conductivity zones according to the SE-NW direction. It means preferential flows at depth quasi-perpendicularly to the causses, contrary to what was supposed.This was confirmed by depth estimates of potential sources (drainage area in the porous structure) by using electrical multi-scale wavelet tomography of spontaneous potential (SP) around Bittit. A global conceptual model based on hydrochemical, isotopic and geophysical data is proposed

Geochemical and isotopical analyzes of groundwater in a karst system - the case study of Fez-Meknès basin (Morocco).

Plenary Flash Oral Presentation and poster.International audienceThe karst Middle Atlas Causses reservoir mainly composed of Liasic dolomitic limestone, overlyingTriassic clays, evaporates and basalts, is the main drinking water supply in Fez-Meknès region (SaïsBasin). Because of the increase in population, the number of drilling for irrigation of agricultural landand some longer drought periods in recent years, the issue of sustainable groundwater managementarises. Recent analyzes have shown a decline in its chemical quality and punctually some turbidityproblems. In order to enhance understanding of this hydrosystem and the interactions between thedifferent main springs of Liasic and Triassic origin, and their connections to the major spring (Bittit), anintegrated hydrogeochemical study was conducted coupled to isotopic analyzes of delta O-18, deltaDand Radon-222. Four surveys were performed in fall and spring seasons (2009 -2011). Watergeochemistry shows two kinds of water- a major Liasic origin along the transition between theCausses and the Saïs basin, and a major Triassic origin for El Mir, Sbaa, and Maarouf springs locatedat the southern border of Saïs basin extremities. Deuterium excess highlights a local recharge whiledelta O-18 versus delta D characterize two aqui fers with different evaporations. Radon -222,underlined the existence of areas of rapid exchange between waters of Liasic aquifer characterized bylow Radon activity (3500 Bq m3) and waters in contact with Triassic aquitard characterized by a highRadon activity (> 15000 Bq m3). The transit time is less than two weeks to surface. The watersrenewal is only conducted by major rainfalls. Four recharge zones of different altitudes have beenfound and two main mixing zones (limits of Saïs Basin)

Geophysical constraints on the groundwater circulation and its renewal at the main Bittit spring, supplying Meknes and its region (Sais Basin): Characterization & conceptual model.

International audiencePrevious hydrochemical and isotopic studies of the tabular Middle-Atlas karst showed that the Sais basin is mainly fed at its northern border by the carbonated Causses of the fractured Lias, in particular by El Hajeb causse to the east and the Guigo causse west (Miche et al, 2018).In a context of over-exploitation of the water karst system accentuated by the current climatic variations, with recurrent droughts and sparse strong thunderstorms, the karstic spring of Bittit, main water source of Meknes and its region, is strongly solicited. Since we have obtained a conceptual model using hydrochemical and isotopic data, Bittit is mainly involved by the causse of El Hajeb (1500m) and partially by the causse of Imouzzer (1340m). It is necessary to localize the depth of mixing zones and the direction of preferential flows around Bittit spring, for a better understanding of aquifers renewal. The coupling of electromagnetic sounding (EM34) and electrical resistivity tomography (ERT) show a tightening of conductivity zones according to the SE-NW direction. It means preferential flows at depth quasi-perpendicularly to the causses, contrary to what was supposed.This was confirmed by depth estimates of potential sources (drainage area in the porous structure) by using electrical multi-scale wavelet tomography of spontaneous potential (SP) around Bittit. A global conceptual model based on hydrochemical, isotopic and geophysical data is proposed

Geophysical constraints on the groundwater circulation and its renewal at the main Bittit spring, supplying Meknes and its region (Sais Basin): Characterization & conceptual model.

International audiencePrevious hydrochemical and isotopic studies of the tabular Middle-Atlas karst showed that the Sais basin is mainly fed at its northern border by the carbonated Causses of the fractured Lias, in particular by El Hajeb causse to the east and the Guigo causse west (Miche et al, 2018).In a context of over-exploitation of the water karst system accentuated by the current climatic variations, with recurrent droughts and sparse strong thunderstorms, the karstic spring of Bittit, main water source of Meknes and its region, is strongly solicited. Since we have obtained a conceptual model using hydrochemical and isotopic data, Bittit is mainly involved by the causse of El Hajeb (1500m) and partially by the causse of Imouzzer (1340m). It is necessary to localize the depth of mixing zones and the direction of preferential flows around Bittit spring, for a better understanding of aquifers renewal. The coupling of electromagnetic sounding (EM34) and electrical resistivity tomography (ERT) show a tightening of conductivity zones according to the SE-NW direction. It means preferential flows at depth quasi-perpendicularly to the causses, contrary to what was supposed.This was confirmed by depth estimates of potential sources (drainage area in the porous structure) by using electrical multi-scale wavelet tomography of spontaneous potential (SP) around Bittit. A global conceptual model based on hydrochemical, isotopic and geophysical data is proposed

Electrical signature of modern and ancient tectonic processes in the crust of the Atlas mountains of Morocco.

The Atlas Mountains in Morocco are considered as type examples of intracontinental chains, with high topography that contrasts with moderate crustal shortening and thickening. Whereas recent geological studies and geodynamic modeling have suggested the existence of dynamic topography to explain this apparent contradiction, there is a lack of modern geophysical data at the crustal scale to corroborate this hypothesis. Newly-acquired magnetotelluric data image the electrical resistivity distribution of the crust from the Middle Atlas to the Anti-Atlas, crossing the tabular Moulouya Plain and the High Atlas. All the units show different and unique electrical signatures throughout the crust reflecting the tectonic history of development of each one. In the upper crust electrical resistivity values may be associated to sediment sequences in the Moulouya and Anti-Atlas and to crustal scale fault systems in the High Atlas developed during the Cenozoic times. In the lower crust the low resistivity anomaly found below the Mouluya plain, together with other geophysical (low velocity anomaly, lack of earthquakes and minimum Bouguer anomaly) and geochemical (Neogene-Quaternary intraplate alkaline volcanic fields) evidence, infer the existence of a small degree of partial melt at the base of the lower crust. The low resistivity anomaly found below the Anti-Atlas may be associated with a relict subduction of Precambrian oceanic sediments, or to precipitated minerals during the release of fluids from the mantle during the accretion of the Anti-Atlas to the West African Supercontinent during the Panafrican orogeny ca. 685 Ma)