We report on the crystallization behavior and the salt weathering potential of Na2SO4, MgSO4 and an equimolar mixture of these salts in natural rock and porous stone. Geochemical modeling of the phase diagram of the ternary Na2SO4–MgSO4–H2O system was used to determine the equilibrium pathways during wetting (or deliquescence) of incongruently soluble minerals and evaporation of mixed electrolyte solutions. Model calculations include stable and metastable solubilities of the various hydrated states of the single salts and the double salts Na2Mg(SO4)2·4H2O (bloedite), Na2Mg(SO4)2·5H2O (konyaite), Na12Mg7(SO4)13·15H2O (loeweite) and Na6Mg(SO4)4 (vanthoffite). In situ Raman spectroscopy was used to study the phase transformations during wetting of pure MgSO4·H2O (kieserite) and of the incongruently soluble salts bloedite and konyaite. Dissolution of kieserite leads to high supersaturation resulting in crystallization of higher hydrated phases, i.e. MgSO4·7H2O (epsomite) and MgSO4·6H2O (hexahydrite). This confirms the high damage potential of magnesium sulfate in salt damage of building materials. The dissolution of the incongruently soluble double salts leads to supersaturation with respect to Na2SO4·10H2O (mirabilite). However, the supersaturation was insufficient for mirabilite nucleation. The damage potential of the two single salts and an equimolar salt mixture was tested in wetting–drying experiments with porous sandstone. While the high damage potential of the single salts is confirmed, it appears that the supersaturation achieved during wetting of the double salts at room temperature is not sufficient to generate high crystallization pressures. In contrast, very high damage potentials of the double salts were found in experiments at low temperature under high salt load.1 相似文献
The aim of the paper was to document the use of 3D subsurface geological-geotechnical modelling to optimise the planning and development of subsurface structures in city areas. The proposed procedure was applied to the analysis of the subsoil of the City of Turin (Northern Italy). The results of more than 300 boreholes were analysed to develop a model of the geological setting up to a depth of 60 m from the surface. The cementation variability of the alluvial sediments was also spatially described and the influence of this aspect on the soil excavation resistance was highlighted. In order to face the need of archiving, correlating and analysing a large amount of data, a 3D GIS (Geographical Information System) was used to better manage the model and to achieve a useful methodological reference that would be available for the planning and construction of future underground works.
A portion of the geological model, related to the centre of the city of Turin (Italy), was chosen to set up a more detailed geotechnical model, based on laboratory tests and back-analysis procedures, as data input for some engineering applications.
Two case studies were performed concerning:
– analyses used to forecast the subsidence induced on the ground surface by the excavation of the metro line;
– the influence of the works of the metro line on the new Underground Railway Link (interference between two important underground works).
A comparison between the forecasts of the degree of cementation, supplied by the 3D model along a metro tunnel tract, and the excavation specific energy effectively absorbed by the head of the boring machine is reported to testify the reliability of the model of the subsoil of Turin centre. This comparison shows the good reliability of the model and its potential to choose of the optimal boring machines for the future development of the Underground Metro System in Turin. 相似文献
In Europe the process of agricultural engagement or disengagement is attributed to the economic factor and mainly on the level
of alternative employment source development. It is the relational quality of economic, social and environmental factors that
determine sustainability of agricultural holdings and, hence, households. In regions of poor agricultural structures and of
many employment opportunities as well as in regions suffering from agricultural depression, households exhibit stronger tendencies
towards agricultural disengagement. Remarkably in southern Europe a stable agricultural engagement and not disengagement is
observed, even though in recent years there are limited possibilities of alternative income sources and prevailing agricultural
depression. This article highlights the factors which lead households to stable engagement with agriculture in a region of
southern Europe, the island of Lesvos. The island is characterised by traditional olive grove mono-culture, poor agricultural
structures and limited employment opportunities. The investigation of the economic, social and environmental farm household
characteristics concluded that in regions where poor agricultural infrastructure and lack of employment prevail, all three
factors of sustainability contribute to stability and/or low agricultural disengagement. Among these, the economic factor
is the most sensitive and hence highly influential. The social factor is highlighted as a quality and consistent factor due
to the respect for tradition. The environmental factor, finally, is characterised by mild cultivation practices, contributing
to environment conservation. 相似文献
Evaporites, including rock salt (halite) and gypsum (or anhydrite), are the most soluble among common rocks; they dissolve
readily to form the same types of karst features that commonly are found in limestones and dolomites. Evaporites are present
in 32 of the 48 contiguous states in USA, and they underlie about 40% of the land area. Typical evaporite-karst features observed
in outcrops include sinkholes, caves, disappearing streams, and springs, whereas other evidence of active evaporite karst
includes surface-collapse structures and saline springs or saline plumes that result from salt dissolution. Many evaporites
also contain evidence of paleokarst, such as dissolution breccias, breccia pipes, slumped beds, and collapse structures. All
these natural karst phenomena can be sources of engineering or environmental problems. Dangerous sinkholes and caves can form
rapidly in evaporite rocks, or pre-existing karst features can be reactivated and open up (collapse) under certain hydrologic
conditions or when the land is put to new uses. Many karst features also propagate upward through overlying surficial deposits.
Human activities also have caused development of evaporite karst, primarily in salt deposits. Boreholes (petroleum tests or
solution-mining operations) or underground mines may enable unsaturated water to flow through or against salt deposits, either
intentionally or accidentally, thus allowing development of small to large dissolution cavities. If the dissolution cavity
is large enough and shallow enough, successive roof failures can cause land subsidence and/or catastrophic collapse. Evaporite
karst, natural and human-induced, is far more prevalent than is commonly believed. 相似文献
The Astrakhan Arch region contains one of the largest sub-salt structures of the Pricaspian basin, where perspectives for
hydrocarbon generation and accumulation in the Devonian to Carboniferous deposits are considered to be high. The paper addresses
the problem of structural and geothermal evolution of the region deformed by salt movements. Initially, we developed a model
of the regional structural evolution along a geological profile using the volume-balancing and back-stripping methods and
geological constraints on the sedimentation, erosion, and paleo-water depths. Then we developed geothermal models (along the
study profile) associated with the regional structural evolution. The models were constrained by the temperatures measured
in four deep boreholes along the profile. We show that the present temperatures and heat flux are influenced by the presence
of salt diapirs. Since the Early Carboniferous and till Middle Permian times, the temperatures predicted by the models vary
significantly due to the regional transgression and the presence of seawater. The temperature of Devonian–Carboniferous carbonates
increases since the Late Permian (time of post-salt deposition) and attains its maximum values in the SW-part of the profile.
If the model assumptions concerning the constant vertical and zero lateral heat fluxes are valid, we can conclude that hydrocarbons
are most likely to be generated in the SW-part of the region for the post-Early Permian time. 相似文献