Research On The Characteristics And Regulation Strategies Of The Hygrothermal Environment In The Maijishan Grottoes

Grottoes has high value in the field of art,culture and history.Different from movable cultural relics,immovable cultural relics such as grottoes are protected in their original location in principle.And the physical environment in that is often complex.The hygrothermal environment has a great influence on the deterioration of the grottoes’ relics.The drastic change of temperature and relative humidity is easy to cause cultural relics to experience flaking,hollowing and efflorescence.Therefore,it is of great significance to research the relationship between the hygrothermal environment and the grottoes protection.The Maijishan Grottoes are situated in the transition zone of semihumid regions and humid regions.Compared with the grottoes in the arid regions of northwest China,the climate of Maijishan grottoes is humid,so the murals fall off more obviously.Moreover,Maijishan grottoes have various types,which are different in the hygrothermal environment.However,there is not a reasonable hygrothermal simulation model to predict the variation of hygrothermal environment in the present research.Therefore,the research on the characteristics and simulation model of the hygrothermal environment in the Maijishan grottoes can provide verification methods for the regulation of the hygrothermal environment in grottoes,and promote the development of protection technology of cultural relics in semihumid regions and humid regions.In this paper,the hygrothermal environment of Maijishan grottoes was measured,the hygrothermal simulation model is established,and then the regulation strategies were proposed.The main research contents and conclusions of this paper are as follows:Firstly,the change characteristics of hygrothermal environment in the Maijishan grottoes were revealed by field measurements.The large caves and small caves which are relatively closed were in an annual cycle from low temperature and relative humidity to high temperature and relative humidity.The hygrothermal environment of shallow caves with big vents is affected dramatically by the climate outside the cave,and the variation trend of temperature and relative humidity inside the cave is close to that outside.The relative humidity inside the cave is high in summer,which in the large caves easily reached 100%.At the same time,the influence of the weight ratio of soil to sand on the hygrothermal properties was analyzed by experimental test.The ratio of soil to sand has less effect on the thermal properties than the wet properties.Secondly,the hygrothermal simulation model of Maijishan Grottoes was established for the first time via the coupled heat and moisture transfer method.The cliff was set as wet porous medium,which was considered the influence of fissure water.According to the characteristics that only one side of the caves is adjacent to the air,the calculation range and boundary conditions are proposed which are suitable for the analysis of the annual hygrothermal environment inside the cave.Then,the heat-moisture-flow coupling model was established which combining with the theory of fluid mechanics,which can analyze the distribution of temperature and relative humidity in the cave.The effectiveness of the two models is verified by comparing the measured results with the simulated results in Cave 101。Thirdly,the hygrothermal simulation model is used to quantitatively analyze the hygrothermal environment in the cave,revealing the influence of different factors on the hygrothermal environment of Maijishan grottoes.The tunnel and the door of caves have positive effects on the stability of the hygrothermal environment in the cave.With increasing size and decreasing air change per hour,the annual amplitude and diurnal change in temperature and RH in the cave decrease.The greater the diurnal fluctuation of temperature and relative humidity in the cave,the more obvious the monthly cumulative change of temperature and moisture content.The wight ratio of soil to sand has little effect on the change of temperature,but great effect on the change of moisture content.Therefore,the relative humidity in summer should be taken seriously in the cave.Finally,according to the principle of preventive protection,the "FAMI" regulation system of hygrothermal environment is put forward combined with the characteristics of Maijishan grottoes.The hygrothermal simulation model which is adopted by the regulation system reflects the mechanism of the hygrothermal environment of Maijishan Grottoes,and can predict the variation trend of the hygrothermal environment more accurately.The regulation system includes four aspects,namely forecast,assessment,monitoring and intervention.That takes into account the management level and the interaction of each stage,so the regulation system has good applicability.In the end,the regulation strategies of different types are summarized according to the characteristics and the target of the hygrothermal environment in Maijishan grottoes.