| Mogao Grottoes, also called the "Thousand-Buddha Cave", is a grottoes with rich content and grand scale. Mogao Grottoes is famous for its exquisite murals and statues. The amounts of preserved caves, murals, painted sculptures, flying apsaras, lotus pillar and floor tiles are so great that it has become the world’s existing largest and best preserved intact Buddhist art treasure house. However, during the long geological history period, due to the rock loose from excavation of dense hole group and the long-term unloading of the vertical cliff body, the rock mass at the exposed rock surface and cliff top of the slope occurred severe weathering by temperature difference, sunshine, wind erosion, humidity variety and other factors. In some weak tectonic locations, there are severe weathering damage or even collapse, which poses great threat to the preservation of cave murals and other artifacts. If preventive measures can’t be taken in time, This outstanding world cultural heritage will eventually disappear.Based on the previous studies, firstly, the engineering geology survey to the Mogao Grottoes is carried and the main meteorological and the hydrology data are collected. Secondly, The rock mass in the test area was stripped off by layer and layer, the characteristic is analyzed by the field description, sound wave test, rebound test and size distribution test, X-diffraction test and soluble salt test. Through the indoor simulation test(accelerated salt weathering test and freeze-thaw cycle test), the effects of different salts to Yumen glutenite are analyzed. At the same time, we also discuss rock mass quality variation under freezing and thawing cycle test. Finally, by combining the main affecting factors and the weathering characteristics of the rock mass, the mechanism of the surrounding rock weathering are discussed.The following conclusions are obtained from the above experiments:1. The main factors that influence the weathering of surrounding rock are determined, which include wind and sand wind, temperature and temperature difference, water and soluble salts.2. The weathering characteristics of JiuQuan sandy conglomerate include:(1) The main rock cements are quartz, calcite, feldspar and dolomite, and clay mineral is chlorite. The content of Quartz is the highest, and in most strata, the content of calcite shows a rising trend with the increase of the depth.(2)The soluble salts in rock mass are mainly Na2SO4 and NaCl. And along the vertical direction, the salinity shows the trend of decrease from top to bottom, while along the horizontal direction, the salt concentration from the inside to the outside showed a rising trend.(3) Wave velocity of rock mass decreases gradually with the increase of depth, then it begins to fluctuate and the overall trend is rising. At the same time, the results indicate that the wave velocity of rock mass and the content of fine grained soil have a good positive correlation.3. The weathering characteristics of YuMen sandy conglomerate include:(1) The main rock cements are quartz, calcite, feldspar, dolomite and gypsum, and clay mineral is chlorite. The content of calcite shows a rising trend with the increase of the depth.(2) Soluble salts include Na2SO4, NaCl and Ca SO4, and along the horizontal direction, the salt concentration from the inside to the outside showed a decreasing trend.(3) With the increase of the depth, wave velocity and strength of rock mass increase.4. The rock particles gradually fall off and the rock quality decrease with the increase of the cycle times in the freezing and thawing cycles test. In the process of salt weathering test, the failure of the rock is mainly perform as fine particles separated from the matrix. The surface of the rock gradually becomes powdering, the quality decreases with the increase of the cycle times. High concentration of NaCl and Na2SO4 solutions has more significant damage to the rock. At the same time, the destruction of the saturated Na2SO4 solution is the strongest. |
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