Cavernous Weathering in the Taylor Dry Valley, Victoria Land, Antarctica
TAYLOR VALLEY (77° 33′ S., 163° 25′ E.) is part of a deglaciated valley complex called the McMurdo Oasis, which is located about 80 km to the west of Ross Island across McMurdo Sound. Since the IGY many New Zealand and American geological parties have worked in this area1–3, which is easily accessible by helicopter from Scott Base and McMurdo Station at the southern end of Ross Island. Now that the topographical and geological reconnaissance stage has been completed and adequate maps cover the 2,500 km2 of the McMurdo Oasis, more attention is being devoted to the study of various anomalies and problems.
Salt weathering in the coastal environment : the deterioration of wall paintings at Delos, Greece
Salt weathering, apart from being an important geomorphologic agent, comprises a major hazard for both modern and heritage structures. Although its action is witnessed globally, it is particularly aggressive in coastal environments. The coastline attracted in antiquity a considerable part of human activity that has left valuable built traces. Conservation research is frequently called upon to define sustainability in this aggressive context. Wall paintings comprise an integral part of the built heritage. The particular importance of wall paintings and finishing layers derives from their unique aesthetic function in the building's integrity as well as the plethora of information that they carry. Whereas wall paintings are more susceptible than masonry materials, the tolerance against loss is much smaller due to their descriptive nature and scale. It is not until recently that international heritage organisations recognised the technical particularities of wall paintings suggesting that they must be investigated independently and treated in situ. This project aims to identify the particularities of wall paintings' susceptibility to salt weathering in the coastal environment. The methodology is composed of both in situ and ex situ experiments. The in situ investigation follows a comparative approach, guided by specific variables, in a number of monuments at the archaeological site of Delos island. The goal of the in situ investigation is to determine the optimal conditions for preservation, by modeling the salts interactions, in an effort to define sustainability against salt weathering in this aggressive environment. The ex situ approach comprises laboratory simulation of the weathering mechanism and aims to describe the particularities of the substrate that lead to the distinct loss of the external finishing layer, which carries the principal information. The results of the project underline the importance of kinetic deviations deriving from the solution and the substrate properties. Despite the limitations of determining the optimal conditions for preservation, the variables that directed the comparative approach permitted the generation of a periodic model in agreement with the phenomenological observations. The model suggests that the potential of salt damage in real conditions of various contamination pathways and sources cannot be restricted to a single resultant. Although the model follows a certain periodicity in response to the annual climatic cycle, random events and fractionated accumulation lead to the production of mixtures with variable composition. Additionally the results stress the role of solar radiation and air movement as evaporation accelerators. Consequently environmental control against salt weathering should be directed towards multiple components which in the case of coastal environments, mainly due to the presence of marine aerosols, cannot be achieved simply by hygrothermal management. On the other hand we traced specific deviations from the theoretical model of salts interactions, concerning mixtures commonly found in coastal regions that should also be taken into account. Besides we tested the hypothesis of salts accumulation at the interface of rendering layers, caused by hydraulic discontinuity, with a weathering simulation. The aim of this investigation was to provide evidence descriptive of damage. It has been shown that the external layer of wall paintings is particularly susceptible to marine aerosols and it can be damaged independently and in advance of the bulk mortar. The salts crystallise selectively under the lime wash layer causing gradually its detachment from the mortar. The results of the weathering simulation raise serious implications for remedial and preventive conservation practice and suggest that research must focus as well on the kinetics of particular cases.
Analysis of the stress wave effect during coal breakage by a high-pressure abrasive air jet
In view of the defects of borehole collapse, inhibition of gas desorption and migration of gas existing in hydraulic fracturing and other hydraulic permeability–increasing measures for soft coal seams with low-permeability technology is proposed for coal breakage by a high-pressure abrasive gas jet for relieving pressure and increasing permeability. The comparative analysis of gas jet flow field structure between convergent nozzle and Laval nozzle has been given by numerical simulation. For Laval nozzle, the expansion wave and compression wave alternate and move forward steadily in gas jet and vanish when potential core length reaches maximum. So, the Laval nozzle can form more stable flow filed structure of gas jet and avoid shock wave in gas jet. Furthermore, a high-speed camera is adopted to analyze the jet structure and verify the conclusion of numerical simulation. Based on thermodynamic theory, this article calculates and analyzes the critical local sound velocity and pressure generated from the stress wave during the process of coal breakage by the gas jet. Furthermore, experimental coal breakage by a high-pressure abrasive gas jet is carried out. The high-pressure abrasive gas jet impacts the coal body as a quasi-static load and a dynamic load and forms corrosion pits on the surface of the coal body. Penetrating cracks are formed within the coal in the pattern of the loaded stress wave which leads to coal breakage. The effects of porosity and permeability on the propagation of the stress wave in coal are analyzed by establishing the dispersion equation for the spread of the stress wave in coal. The results show that porosity has a significant effect on wave velocity and that the attenuation of the stress wave is intensified with an increase in porosity. Moreover, the stress wave attenuation is more obvious at high frequency. The effect of permeability on the wave velocity is not significant at low frequencies. In contrast, at high frequency and relatively low permeability, the wave velocity increases with the permeability, and the attenuation of the wave velocity initially increases and then decreases. When the permeability is greater than 10−11 m2, the wave velocity is not affected by the permeability. However, the stress wave is not attenuated.