Experimental Technique of Rock Multi-Strain Rates Dynamic and Static Load Superposition and its Application

Exploring the physical and mechanical properties of rocks under dynamic and static load superposition is crucial for preventing and controlling underground engineering dynamic disasters. Therefore, a rock experimental technology based on a gas‒liquid composite dynamic and static load superposition cylinder is proposed. This experimental technology overcomes four technical difficulties: (1) simulating a preimposed static load with superimposed dynamic load and strain energy accumulation; (2) progressive automatic constant loading of creep load; (3) medium strain rate cyclic impact loading; and (4) integrated control and multiple information coupling collection. Through this technology, multiple strain rate dynamic and static loads, such as creep loads (< 10^–4 s⁻¹), hydraulic loads (10^–4 ~ 10⁰ s⁻¹), and cyclic impact dynamic loads (10⁰ ~ 10² s⁻¹), can be superimposed on the rock. It can quickly compensate for the static load during rock collapse and instability to simulate the strain energy of the rapid release process of the surrounding rock. The experimental results verify that the peak strength and failure duration of rock are negatively correlated with the preimposed static load and positively correlated with the impact frequency. The cumulative damage and ultimate strain are positively correlated with the static load and negatively correlated with the impact frequency. With increasing static load or decreasing impact frequency, the rock failure mode transitions from “slope shear failure to vertical tensile failure to overall burst failure”. The energy generated by the preimposed static load mainly accumulates at the rock fracture tip, and the dynamic load can increase the brittleness of the rock.