Experimental Study On Dynamic Mechanical Properties Of Coral Reef Limestone

The coral reef limestone,with its biologic origin,has relatively complex rock mass structure and mechanical properties that are different from the ordinary continental brittle rocks.In order to provide reliable dynamic mechanical parameters of coral reef limestone for the countries with engineering construction on reefs,it is necessary to study the dynamic mechanical properties of the coral reef limestone.The testing samples of this paper are saturated coral reef limestone.Its physical and mechanical properties in static state are tested by the multi-function rock test system and the dynamic uniaxial compression test,dynamic Brazil disc splitting test and dynamic uniaxial cyclic impact test are carried out by the Hopkinson pressure bar system(SHPB).The main research results of this paper are as follows:1.Study on the physical and mechanical properties of coral reef limestone in static state.The coral reef limestone tested in this paper,compared with the general coral reef limestone,has higher density,smaller porosity,and faster elastic longitudinal wave velocity,and its static uniaxial compression strength and splitting tensile strength are both higher.The compression stage and the elastic stage of the static uniaxial compression stress-strain curve are hard to distinguish and the static compression and tensile strength decrease with the increase of porosity.2.Study on the conventional SHPB dynamic test of coral reef limestone.The dynamic stress-strain curves of coral reef limestone are different from the ordinary continental brittle rocks with its relatively obvious compaction stage.The sensibility of coral reef limestone's dynamic uniaxial compressive strength to the strain rate is stronger than the ordinary continental brittle rocks.In the dynamic uniaxial compression test,the energy density of the sample has a linear function relationship with the incident energy,a energy power function relationship with the strain rate,and a linear function relationship with its dynamic uniaxial compressive strength.In the dynamic Brazil disc splitting test,the energy density has a good linear relationship with incident energy,strain rate and dynamic splitting tensile strength.3.Study on the uniaxial cyclic impact test of coral reef limestone.In the uniaxial cyclic impact test,with the increase of the times of cyclic impact,the reflected wave gradually increases and the transmission wave decreases gradually.The peak strain and energy density of the specimen increases with the increase of the times of cyclic impact yet the peak strength and the deformation modulus decrease with the increase of the increase of the times of cyclic impact.The damage variable solved by the mean method which synthesizes the energy absorption method,elastic modulus method and maximum stress method could well reflect the damage condition of the specimen.The dynamic statistical damage constitutive model based on Weibull distribution has a good agreement with the experimental data,yet the model curve of the stress rise section is a little higher than that of the test curve which is mainly due to the conflict between the basic assumptions of the model and the mechanical properties of coral reef limestone.The acquisition of dynamic mechanical property parameters of coral reef limestone can provide important technical support for the design of excavation and protection section of coral reef underground engineering.