Abstract: This study focuses on the calcareous cemented conglomerate on the side wall of the Zhoukoudian Ape Man Cave site in Beijing. We analyzed the change patterns of cracks in grotto rock under natural conditions using statistical analysis of continuous monitoring data from 12 rock fracture measurement points for 7 years and environmental monitoring data. The results indicated that: (1) Under natural conditions, rock fracture width exhibited seasonal and periodic variations, which can be predicted using autoregressive integrated moving average (ARIMA) model. The ARIMA (2, 1, 1) model has the highest fitting accuracy. (2) The width of rock fractures showed a negative correlation with ambient temperature and relative humidity, with a stronger correlation with temperature. Changes in fracture width lagged behind changes in temperature and relative humidity, with a higher lag correlation and shorter lag time for temperature compared to relative humidity. (3) The degree of correlation and lag correlation between rock fracture width and ambient temperature followed the trend of room-temperature＞ high-temperature＞low-temperature＞extremely-low-temperature. The lag time followed the trend of extremely-low-temperature＞low-temperature＞high-temperature. Additionally, more stable relative humidity of the surroundings indicated a higher correlation. (4) At a constant, the width of rock fractures increased gradually over time, following an approximate exponential growth or asymptotic distribution. (5) At the same temperature, more stable relative humidity corresponded to a slower increase in rock fracture width over time. Under natural conditions, lower ambient temperatures led to a rapid increase in rock fracture width over time. These findings enhance our understanding of the expansion patterns of cracks in grotto rock under natural conditions. Moreover, they provide a reference framework for predicting crack changes in the preventive conservation of ancient rock sites, caves, and stone carvings in temperate monsoon climate regions.

Key words: rock cracks, temperature, relative humidity, correlation, Ape Man Cave