Study On Damage Evolution Law Of Water Soaked Gypsum Rock And Stability Of Goaf

There are abundant gypsum resources in China,due to the unreasonable exploitation and lack of reasonable maintenance and supervision in recent years,gypsum mine accidents continue to happen in recent years.The most serious accidents are the casualties caused by large area collapse in goaf.This paper aims at the problems of ultra wide,ultra high mining and goaf water in gypsum mine in North Jiangsu.The research methods of field investigation,laboratory test,theoretical analysis and numerical calculation are used to make a systematic study on the stability of the goaf in gypsum mine.The main research results are as follows:(1)Testing the water content of gypsum rock with different soaking days,and analyzing the development law of microcosmic fissure of gypsum rock by SEM.The compressive and tensile strength of gypsum rock with different soaking days were tested by laboratory tests.According to the test results,the elastic modulus,Poisson's ratio and other mechanical parameters of gypsum rock are obtained through fitting analysis,which provides basic parameters for numerical simulation of the stability of mined out area and calculation of safety factor of pillar.The test results show that the mechanical properties of gypsum rock after water soaking are decreasing,thus the strength of the pillar and roof of the goaf is reduced and the accident occurs.(2)The damage factor is defined based on the number of microelement body destruction,and the uniaxial compression constitutive model of gypsum rock with different water soaking time is established and the damage constitutive model is derived.The change law of the brittleness coefficient of gypsum rock after water soaking is studied.The acoustic emission characteristics of gypsum rock with different soaking time were tested and analyzed by acoustic emission equipment,and the energy evolution characteristics of gypsum rock in different compression time were analyzed combined with stress-strain curves.And then based on the acoustic emission characteristics and evolution of the energy feature definition damage factor,establish the gypsum rock triaxial damage constitutive model,damage constitutive equation.The models can describe damage evolution law of the soaking gypsum rock from different aspects.(3)Combined with address characteristics,actual mining status and test data of gypsum mine in North Jiangsu,FLAC3 D is used to simulate the stability of goaf in gypsum mine under natural and soaking respectively.The simulation results show that the stability of the goaf which meet the design requirements in natural unsoaked area is in a better condition,the development of the plastic zone is less.Under the condition of satiety,the development of the plastic zone in the goaf is very active.All the pillars are unstable,which endanger the safety of the goaf.(4)According to the relationship between the pillar load and the strength of the pillar,the safety factor of the pillar in two states of natural and soaking in the selected area is calculated.The calculation results show that only a few pillars in natural which do not meet the design requirements is lower than the prescribed safety factor,the failure rate is about 4.1%.While in the saturated state before,most of the pillar is lower than the prescribed safety factor,the unqualified rate reached 79.59%.The results of the above researchs provide reference and basis for judging the stability of gypsum mine mined out area under soaking condition.