Sandstone from the Longshan Grottoes in Taiyuan, China, was the research object of this paper. The sandstone samples were soaked in distilled water, Na₂SO₄ solution, and NaCl solution and subjected to freeze–thaw testing. Sandstone specimens were treated with 0, 5, 10, 15, 20, 25, and 30 freeze–thaw cycles. The mass ratio, P-wave velocity, surface hardness, uniaxial compressive strength, and other physical-mechanical features of rock samples were measured after different numbers of cycles. The results of mercury injection, scanning electron microscopy, and X-ray diffraction were combined to explore the damage mechanisms and characteristics of the rock samples under the combined action of chemicals and freeze–thaw cycles. It was found that the damage degree of sandstone increased logarithmically with the number of cycles, with Na₂SO₄ solution causing the most damage. Damage variables D of the samples soaked in distilled water, Na₂SO₄ solution, and NaCl solution after 30 freeze–thaw cycles were 3.89%, 6.51%, and 4.74%, respectively. The difference in damage between the solutions is caused by the combination of frost heave, dissolution, and salt crystallization, and the damage process generally occurs from the inside and the outside and is manifested as an increase in the number of macropores and the appearance of new pores. Freezing–thawing and salt action are important causes of the powdering and detachment of sandstone in the Longshan Grottoes.

Water seepage is one of the main factors leading to the damage of grottoes. The sources and pathways of water seepage need to be identified to relieve it. Although the sources and pathways are investigated using geophysical exploration methods commonly, the results are unsatisfactory due to the limitation of resolution. The tracer method has been widely used to examine water seepage in the natural sciences and engineering. However, most tracers have an impact on grottoes, making this method inapplicable. This study was the first to use the carbon quantum dots as a tracer of water seepage in grottoes. The characteristics of the carbon quantum dots, which was synthesized by various biomass precursors through large-scale synthesis in the field, were analyzed to determine the optimal precursor. The structure, fluorescence intensity, and water solubility of the carbon quantum dots were evaluated. Laboratory tests were designed to examine the transport properties of the carbon quantum dots in rocks and cracks. The results showed that the carbon quantum dots synthesized by Ginkgo biloba were small and had uniform size, excellent fluorescence, good water solubility and transport ability. Furthermore, the carbon quantum dots were successfully used to tracing the source of water seepage at the chest of the Leshan Giant Buddha. The low cost of synthesis, wide precursors, easy and convenient synthesis methods, friendliness to grottoes, and excellent performance of the carbon quantum dots as a tracer suggest the efficacy of this method. These findings could lead to the widespread use of tracer method in studies of water seepage in grottoes.

Soil microbial communities play a key role in the functioning of terrestrial ecosystems, in particular through their interaction with above-ground plants and weathering of rocks. In this study, the chemical properties and microbial diversity of soils covered by different organisms on Leshan Giant Buddha body were analyzed. The results showed that the concentration of soil total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) increased significantly with the change of above-ground organisms from lichens to bryophytes and vascular plants. TOC, TN, TP, C:N, and C:P were significantly correlated with the composition of microbial community. Bacterial and fungal diversity responded differently to the change of organisms, and the diversity of bacterial communities changed significantly among different sites. The settlement of Embryogenic plants increased the α-diversity indices including Sobs, Shannon, Ace and Chao indices, which were highest in sites covered with Ferns. The relative abundances of Chloroflexi, Acidobacteria, Nitrospirae and Planctomycetes increased with the order of Bryophyte, Fern, Grass and Shrub, and Cyanobacteria was opposite, with the highest in samples covered with lichens. These results improve understanding of plant–fungi–bacteria interactions during the early stages of soil development, and provide a scientific basis for protection of Leshan Giant Buddha.

Burial stone relics remain in a humid, semi-enclosed environment for long periods, and temperature and humidity variations can cause deterioration acceleration. Yang Can’s tomb was selected as the research object, and field monitoring and simulations were performed to investigate the characteristics of temperature and humidity variations, after which the simulation results were evaluated. The monitoring results showed that solar radiation, rainfall, wind speed, and depth of entry are important factors affecting the variation in the temperature and humidity of burial stone relics. The temperature outside the chamber is greatly affected by seasonal variations, while the humidity inside the chamber is influenced by seasonal variations, so appropriate measures should be implemented inside and outside the chamber during different seasons to alleviate deterioration. On the basis of the above analysis, a temperature and humidity model for the interior chamber of burial stone relics was established in COMSOL software 5.6, combined with a porous medium heat transfer model and computational fluid dynamics (CFD) model. The temperature and humidity inside the chamber can be calculated by the temperature and humidity outside the chamber. This study provides data support for hydrothermal, condensation and other related studies of burial stone relics.

We report a new self-powered Kelvin waterdrop generator driven fog harvesting system with increased fog harvesting efficiency especially under low concentration fog conditions.

Water seepage can accelerate the deterioration of stone, but previous experimental studies often only focused on a single solution, ignoring the complexity of the natural water environment. In this study, sandstone samples from two strata of Leshan Giant Buddha were collected. Then the wet-dry cycle experiment was carried out using the prepared water seepage solution with a concentration equivalent to the on-site solution. The severity of sandstone deterioration followed the order of Na₂SO₄ > CaSO₄ > water seepage solution > H₂O. The water seepage solution caused less deterioration than did the salt solutions (Na₂SO₄ and CaSO₄) at the same concentration. Sandstones with strong cementation deteriorated slower, which was attributed to the variations in the mineral cementation balance index (MCBI). Furthermore, the uniaxial compressive strength of sandstones was predicted based on nondestructive indices combined with random forest (R² ≥ 0.97), providing a nondestructive assessment method for the preservation of stone heritage.