Study On The Deformation And Failure Law Of Rock Beam

Coal seam roof and overburden rock are layered sedimentary rocks , so in the research of underground pressure and strata control, they are usually simplified as beam which is called rock beam. Rock beam model is generally accepted and used because it's convenient for analysis. At present, The calculation formula used on the analysis of rock beam is often form material mechanics and structural mechanics, which ignore the characteristics of medium, the geometric properties and the environment of rock beam. In fact,under many conditions rock beam for mining engineering is not completely agrees with the slender rod model and hypothesis (1. plane assumption; 2. vertical fiber no should force assumption; 3.linearly elastic hypothesis; 4. the same tension and conpression constitutive hypothesis.) in engineering mechanics, so in some conditions some errors that should not be not neglected will be caused when directly using the calculation formula of engineering mechanics.To realize the differences between rock beam and beam in engineering mechanics, to analysis the errors that caused when directly using the formula of engineering mechanics, to obtain the condition in which the formula of engineering mechanics can be used, and to establish the formula that competely suitable for rock beam, special research on rock beam should be done, which is an important subject in the research of underground pressure and strata control and it's important to the development the theory and technology of mine safety, mine resources and environment protection.As an exploration on the research of rock beam, bending experiment is done to granite rock beams with different span to depth ratio, strain values of each rock beam are tested under different loads, the tensile modulus ( E+ ) and tensile strength of granite are analysised, the deformation and failure law of rock beam is studied; The beam specimens are analysised respectively by the method of material mechanics, classical elastic mechanics and different modulus elastic theory, and the analysis results are compared with with experimental results; The errors of formula of material mechanics are analysised and the applicable conditions are given.The research results show: The tensile modulus ( E+ ) and compressive modulus ( E~- ) of granite are different; Tensile strength which is tested with the method of bending beam should be used when analysising the tensile failure of rock beam; The deformation and failure law of rock beam is relative with it's span to depth ratio and the tensile modulus and compressive modulus; Different elastic modulus elastic theory should be used for more accurate analysis; The error between results calculated base on material mechanics and experiment results is directly affected by the span to depth ratio (l/h) of granite, when span to depth ratio is over 2.2, error is less than 10%, under this condition the influence on project is not significant.Engineering application: Research should be done on rock beam that under the condition of different stratum and different projects, and formula according with the precision of project should be choosen. Under some conditions using the material mechanics calculation formula meets requirement, but under some conditions big errors can be caused, now different modulus elastic theory can be used, and tensile modulus and compressive modulus of material should be studied.