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The conglomerate reservoir is rich in oil and gas reserves; however, the gravel's mechanical properties and laws are difficult to gain through laboratory experiments, which furthermore constrain the hydraulic fracturing design. To analyse the failure law of conglomerate, we simulated the uniaxial compression test based on discrete element software PFC2D and analysed the effect of different cementation strength, gravel content and gravel geometry on the rock deformation and failure characteristics. Results show that (i) as the cementation strength decreases, the compressive strength and elasticity modulus both reduce clearly, while the crack shapes get more complex and the critical value is 0.3; (ii) as the gravel content increases, the conglomerate strength first decreases then increases under the influences of cracks bypassing gravels; cementation strength and gravel content of the conglomerate both contribute to the increase in local additional stress, which leads to a series of changes in crack shapes and mechanical properties of the conglomerate. Based on the above research, the conglomerate strength and crack shapes after failure are relatively complex due to the common influence of cementation strength and gravel content. The gravel edge crack caused by stress concentration is the micro-mechanism that affects the conglomerate mechanical properties.

The grotto rock mass is a type of cave structure, formed under the complex forces of environment, geology, and human interventions. Many scholars have carried out a lot of work in the protection of cultural relics. However, the research on detection and monitoring methods based on the parametric evolution system remains incomplete. In recent years, with the intersection and integration of disciplines, IoT (IoT: Internet of Things) systems and sensor technologies have developed rapidly. Under this background, a new monitoring system suitable for the protection of cultural relics was independently developed and applied to the protection and research work of Yuanjue rock cave, and the system was corrected and improved in practice. In this paper, according to the complex force characteristics of the sandstone roof of the Yuanjue rock cave at Dazu Rock Carvings and the geological conditions. Initially, a detailed survey of the geological conditions of the Yuanjue rock cave area was conducted; furthermore, according to the unique structural and load characteristics of the outer and inner surfaces of the roof, the monitoring methods and principles of each main control factor were explored, while the layout of monitoring points was optimized; finally, based on the microsensing technology, intelligent high-precision sensing hardware was installed and debugged for each main control factor, while the network was formed to form a multisource monitoring IoT system for the roof stability of the circular sense hole. After nearly half a year of continuous monitoring, the deformation and denudation rules of the roof of Yuanjue Cave were revealed, and a new approach of evaluating roof stability was proposed. This research provided technical support and research ideas for monitoring the stability of similar cultural relics.

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