Water is one of the fundamental causes of deterioration in cave temples and most immovable cultural relics. Sensors based on dielectric constants to measure the water content of rock and soil objects are capable of capturing changes in water content in the surrounding rock masses of cave temples in real time，and thereby provides an extremely convenient method for studying water damage in cave temples. However，there is a chance that the temperature and soluble salts of the test materials could cause errors in the monitoring results；in addition，the correction of the collected data is likely to be affected by certain sensor test principles，features of the monitored objects，and environmental factors. While monitoring the water in the rock masses of the Yulin Grottoes，research has found that the monitored amount of water is obviously higher than the actually measured water

content. This study used indoor temperature compensation tests to obtain the values of the monitored water content and actually measured water content at different temperatures，respectively，which can be used to calibrate the errors in the 5TE sensor by combining this data with the Gaussian process regression model. The calibrated monitoring data is more consistent with the actual measured results，and this in turn helps to improve the monitoring accuracy of the 5TE sensor. The calibrated sensor can provide valuable support for the analysis of on-site water content at the Yulin Grottoes in Gansu Province，and is thus of great significance for understanding and preventing water damage in cave temples.

Under the long-term effect of geological forces，serious geological deterioration has appeared at Fengxian Temple （Fengxiansi Cave） in the Longmen Grottoes. Due to the development of several cracks and karsts，the deterioration caused by water seepage at the site has gradually intensified，eventually leading to the direct erosion of the statues in the temple and seriously threatening the safety of the stone carvings. This study has identified the sources of water seepage by utilizing geological radar detection，infrared thermal imaging detection and water drilling pressure tests，to understand the characteristics of the wall seepage and the seepage mode of atmospheric precipitation. Based on the results，this study proposes a complete water prevention and drainage system that utilizes the original drainage system of the Shenxian Cave site under the guidance of an irrigation philosophy that combines the various measures of cutting，blocking，and discharging，and by filling in cracks，building drainage ditches，and constructing eaves and diversion channels. This study will play a guiding role in the future control and prevention of waterdamage at the Longmen Grottoes.

Calculating the air changesperhour （ACH） in caves under natural ventilation conditions is of practical significance for evaluating and controlling the air quality in caves. The tracergas method based on the CO2 exhaled by tourists is a convenient，economical and dynamic method for ACH calculation. In this study，the ACH in the Mogao Caves was calculated by using this method to measure metabolically generated CO2，as well as artificially released CO2，and to determine the spatial uniformity of CO2 distribution in the caves. In addition，a discussion ofthe reliability and applicability of the tracer gas method based onexhaled gases is provided. The results show that the spatial distribution of CO2 exhaled during the tourist season was relatively uniform，and that the ACH in the southwest and northeast corners of the main chamber were roughly equivalent with only small differences between them. This final observation is a good representative result for the overall ACH calculation of the cave. As for the methodology，this study finds that the tracer gas method is highly reliable for the conditions of these caves，but that understanding the initial concentration and spatial distribution uniformity of CO2，and ensuring measurements over a reasonable period of time，are all critical factors for the accuracy of ACH calculation. For this reason, importance should be attached to selecting an appropriate time period when exhaled CO2 is abundant in the caves. Theresults of this study are meant toprovide updated ideas and methods for evaluating and researching the natural ventilation mechanisms in cave temples.

The methods of monitoring trend extraction and possible anomaly alerts are important techniques in data analysis that can help researchers to find patterns and anomalies hidden within sets of data. Based on periodic monitoring of the environmental risk factors that geotechnical cultural relics are exposed to，as well as regular feedback regarding the conditions of these relics，potential problems that might endanger the safety of cultural relics can be detected in time to implement appropriate conservation measures as early as possible，and with the minimum amount of resources. In this study, the intrinsic change in trend for cultural relics was extracted by multi-dimensionally analyzing the long-term monitoring data of two sites，the Maijishan Grottoes and ancient Suoyang City. Based on this case study，researchers have obtained a method of extracting the intrinsic change trend for cultural relics that eliminates the influence of environmental factors such as temperature and humidity in order to more clearly extrapolate early warning thresholds. This method is meant to provide a feasible solution for the scientific conservation of cultural relics，and to guide the preventative protection and management of these relics.

The deterioration caused by water seepage in the rock mass underlying the engraved Sleeping Buddha（Nirvana Buddha） statue at Dafowan in Dazu is characterized by narrow seepage channels and a complex seepage mechanism，both of which are typical in the sandstone cave temples in southern China. In this study，an analysis method for the detailed zoning of relatively independent hydrogeological conditions has been proposed based on a series of research tests. The methodology used to conduct this research includes in-depth study of the micro-geomorphology of the rock masses and sources of secondary water recharge，detailed analysis of the seepage characteristics in structural fissures, precise evaluation of the rock surface’s horizontal bedding properties，and analysis of the hydraulic properties of the weak intercalated layers. The refined hydrogeological model of water seepage deterioration for this site has been designed based on the results of the above analyses and is meant to take into account the sources of water recharge, the characteristics and effects of the seepage channels，the relationship between seepage deterioration and the seepage channels，the overall characteristics of the fissures in the underlying rock mass，and the characteristics of water drainage. The proposed model is meant to be specific to the Sleeping Buddha site at Dazu，but also applicable in many of its key features to understanding the water seepage and deterioration that occurs in other similar cave temples in China.

There are a large number of cement-based materials currently in use at the Mogao Grottoes. Considering the precious cultural properties and environmental constraints of the site，study of these materials using conventional sampling methods is quite impossible. Because the macro-mechanics and durability of the cement-based materials are determined by their micro-scale mechanisms，this study decided to utilize nanoindentation technology，scanning electron microscopes and XRD to test the floor cement in Mogao cave 335 and characterize its micro-structure characteristics and mechanical properties，so as to provide data support for the future removal of cement floors. The results of these analyses have found that the micro-mechanical properties of the cement floor in Mogao cave 335 are relatively low，that the cement materials have been completely carbonized，and that they generally tend to be neutral. Finally，the success of the study has proven that this combination of test methodology is not only accurate and easy to implement，but also safe and feasible even in the complex environment of the grottoes.

A systematic investigative study of the bird life at the Binglingsi Grottoes，a world cultural heritage site in Yongjing，Gansu Province，was conducted from January 2019 to December 2021 in order to ascertain the diversity richness of bird species living there，to measure the damage caused by bird activity to the cultural relics at the site，and to provide a basis for establishing effective damage prevention and control measures. The results show that there are birds belonging to 10 orders，26 families and 44 species within the study area，including 17 species of resident birds，13 species of summer migratory birds，4 species of winter migratory birds，

and 10 species of migratory birds. Among these species，3 are under national protection. The fauna at the site is consistent with the Palearctic region，with a distribution type of Palearctic（U）. The birds that have caused damage at the caves have been identified as belonging to 2 orders，6 families and 6 species，the most notable of which is the species Columba rupestris. The main types of bird damage in the caves are physical damage and excrement pollution，areas affected by bird damage account for about 18% of the total area of the cultural relicsin the caves. Birds responsible for the damage to the cultural relics reach a peak in both population and number of species in the summer，and gradually reduce through autumn，spring and winter. The interannual species diversity index at the site has been calculated as：1.192（2020）>1.152（2019）>0.821（2021）. This research recommends utilizing intervention measures such as artificial attraction and “acoustic-optical” technology in order to control the damage caused by birds at the Binglingsi Grottoes.

This paper presents an investigation and analysis of the modern repainting applied to the sculptures in the cave temples of Sichuan and presents several revealing case studies. The following conclusions can be drawn based on this research： （1）Painting activities have never ceased in the cave temples of Sichuan，while most of the modern painting activities in the region occurred in the 1980s and 1990s. These activities have greatly affected the artistic value of the sculptures，and deterioration of the paint layer has caused damage to the body of many of the pieces.（2）Most of the sculptures have been painted several times；one of the sampled artworks is covered in five layers of pigment，each of which varies between 0.04—0.4 mm in thickness. （3）The binding agent used in most of the paints is alkyd resin and most of the pigments are modern chemical compounds. The blue paint is phthalocyanine blue（also known as Prussian blue），while the yellow is lead-chrome yellow（PbCrO4），the white is made with white lead，lead carbonate or lithopone，the green contains lavendulan，the gold is aluminum or brass foil，and the black is made with carbon.

The arched roof and left wall of the south cave of Leigutai in the Longmen Grottoes were rebuilt with grey bricks sometime following their original construction. However，after prolonged natural weathering，rainfall infiltration and human interference，many protrusions have appeared on the south side of top of the masonry，accompanied by cracks that are spreading at an alarming rate and causing serious stability issues. Emergency support and protection measures are now necessary to protect the integrity of the cave. Based on field investigation of the site，it was been confirmed that water damage and subsequent destruction of masonry were

the two primary sources of deterioration. In light of both the imminent and potential risks，emergency support structures were constructed in order to preserve the cave，and a monitoring system was established to observe the effectiveness of the emergency support measures. Both field tests and monitoring results show that emergency bolstering has been effective.

Rock stability，water damage, and surface deterioration of the rock structures of cave templesare critical issues for the conservation of cave temples in China. Critical to the long term security and protection of these structures are the form of the caves，the environment of the caves，clarifying the extent and volume of unstable rock surrounding the caves, the complexity of the destabilization mode for these structures （which is usually characterized by sudden occurrence），and the difficulty of accurately predicting rock stability. This paper summarizes the basic characteristics of the rock masses of China’s cave temples，notes difficulties in reinforcing the rock masses，and proposes key technical issues that require urgent attention. The latter issue includes determining the coupling loosening and instability mechanisms of rock masses, establishing a set of monitoring technology for detecting instability in rock structures，refining the use of grouting and repair materials and technology，and choosing a reinforcement technology for flat-roofed caves. The ideas listed above have been proposed with a large set of goals in mind and are intended to be carried out through multidisciplinary cooperation.These goals include：understanding the destabilization modes of cave rock masses，revealing the principles of instantaneous，progressive destabilization，the development of a multi-scale grouting and reinforcement technology，the establishment of comprehensive measures for reinforcing the rock structures of caves with flat rooves，and finally to provide technological support for the long-term conservation of the cave temples of China.

Gansu is well-known for the Buddhist cave temples，therefore often named as the “hometown of grotto art” in China. Underpinned by the dedicated investigation of the cave temples in Gansu，this paper summarizes the relationship of their geographical distribution，value，preservation environment and various diseases. We also explain the current situation of the cave temples in Gansu from the following three perspectives：management，security system and conservation measures. In this paper，the analytic hierarchy process （AHP） is applied to quantitative assessment of the current situation of conservation and utilization. According to the assessment result，the overall cave temples in Gansu can be divided into three levels and different improvement measures are given accordingly. The overarching layout of the cave temples in Gansu is proposed， led by one conservation model and research highland，supported by three world cultural heritages，co-developed by four different regions，and facilicated by the policy support of one corridor and one road. An illustration of important tasks and future directions are centred on five aspects of conservation，research，management，utilization and talent training，which provide crucial basis for the decision-making of the development and layout of the cave temples in Gansu in the next stage.

Salt weathering is a common process affecting the surface morphology and grains of rock-hewn cave temples that are significant built-heritage sites in China. It can consequently result in serious damage to these sites，but with few solutions for the problem. This study aims to evaluate and predict the type，distribution and phase transition process of the soluble salts on the faade of rock-hewn cave temple through the combined approach of the non-destructive in situ salt extraction and salt behaviour modelling named ECOS-RUNSALT. The study site is North Grottoes Temple （NGT） which is the largest cave temple in the Longdong area，Gansu Province，China. The results imply a higher concentration of salt in the upper area of the NGT facade than that in the lower area. ECOS-RUNSALT also predicted complex salt mixtures，including 9 single salts and 4 double salts. Crystallization of salts was predicted to occur at relative humidities of around 81.4%. Based on ambient temperature and humidity data from NGT it is likely that salts start to crystallize out during the morning.

Cave temples are an important type of immovable cultural relic in China and thus are of significant value for cultural heritage. Conservation of the rock structures of cave temples is a prerequisite for the security of all kinds of cultural relics in cave temples，but is also a particularly difficult issue for research on cave temple conservation to address. Firstly，this paper discusses past research conducted on the topic with particular attention paid to the four aspects of conservation principles，mechanisms of deterioration, survey technologies，and conservation techniques. Secondly，a summary of the research progress and current problems faced by this body of research is provided，following with several proposals for future studies. These proposals include recommendations for principles of conservation，detailed engineering surveys and quantitative deterioration evaluation, monitoring of the chemical and physical mechanisms that damage rock masses，and preventative conservation measures.