| Similar material simulation, numerical simulation, mechanical analysis, mutation bifurcation theory, chaos theory, etc. are applied to study systematically on the relationships among surrounding rock, roadway-inside support and roadside support, to determine stability criterion of surrounding rock of the secondary gob-side entry retaining in different stage, and to reveal the failure mechanism of surrounding rock deformation.Through similar material simulation and numerical simulation, rock stress, displacement and failure characteristics of the secondary gob-side entry retaining in different stage have been analyzed, and the influence of bolting parameters on surrounding rock of the secondary gob-side entry retaining in different stage have been studied.The stability of key block in working face end directly affects the stability of supports and surrounding rock under the key block, keeping the key block stable is conducive to reducing surrounding rock deformation of the secondary gob-side entry retaining and to keeping backfilling body stable. Based on thw activity laws of overlying strata,"S-R" structural mechanical models of key block in working face end have been established in different stage, and the stability criterion of key block has been determined. Based upon the stability of key block, backfilling body in different stage has been made force analysis, the formula of roadside supporter resistance has been derived, and reasonable backfilling width which keeps key block stable is determined.Due to the secondary gob-side entry retaining must service for two working face in the upper section and next section, service time of roadway is very long, and backfilling body suffers from the influence of lateral abutment pressure of the goaf chronically. As time elapses, backfilling body may be in the rheological state, the rheology of backfilling body will directly affect the stability of surrounding rock of the secondary gob-side entry retaining. Mutation bifurcation theory has been applied to study on mechanical characteristics of nonlinear creep of backfilling body, least square method is adopted to fit model parameters, chaotic criterion of nonlinear creep has been determined, and the failure mechanism of nonlinear creep has been revealed. Backfilling body in the process of deformation and failure are of both the rheological properties and damage characteristics, the former reflects the time effect, and the latter reflects the development of defects inside the material. Based upon Lemaitre's strain equivalence hypothesis, damage constitutive of backfilling body has been derived, and damage instability criterion has been determined.Many factors affect the stability of backfilling body, these factors have a great deal of variability, and service time of the roadway is very long, thus backfilling body must be of sufficient reliability. Reliability theory of engineering structure is applied to calculate the reliability of backfilling body in different stage.The key to the success of the secondary gob-side entry retaining is whether backfilling body can adapt to the activity law of overlying strata and control effectively immediate roof. Based on energy conservation principle, mechanical models of immediate roof in different stage have been established, the stability criterion of immediate roof has been derived. Displacement variational method is applied to study on the relationships of immediate roof subsidence and backfilling width, plastic zone of coal rib, support resistance of coal rib, roadway width, roadway-inside support resistance, roadside support resistance, etc.Coal rib of the first gob-side entry retaining suffers from tunneling influence and twice mining influence during the whole process of the secondary gob-side entry retaining; keeping coal rib stable is conducive to reducing immediate roof subsidence and to keeping key block stable. Based on energy conservation principle, stability criterion of coal rib has been determined, support resistance of coal rib and bolting interval which keep coal rib stable have been obtained, which provides theoretical foundation for determining bolting interval. Based upon Lemaitre's strain equivalence hypothesis, yield criterion of Drucker-Prager and limit equilibrium theory, the width of rib spalling has been predicted, which provides theoretical foundation for determining bolting length of coal rib.Surrounding rocks of the secondary gob-side entry retaining belongs to the surrounding rock of large deformation and has a strong sensitivity to changes in initial conditions, so it is difficult to be judged through traditional direct observation method. Power spectrum analysis has been applied to study on chaotic dynamical characteristics of rock stress of the secondary gob-side entry retaining in different stage. Studies suggest that rock stress is of a strong volatility when backfilling body is narrower. With the increase of backfilling width, the peak of power spectrum increases, and the proportion of irregular movement gradually reduces. Lyapunov exponential method has been applied to study on the influence of backfilling width, pretightening force of bolting, and support strength of bolting on chaos degree of surrounding rock of the secondary gob-side entry retaining in different stage, backfilling width, pretightening force of bolting, support strength of bolting and bolt ing diameter, etc. are determined reasonably.Based upon activity law of overlying strata and the characteristics of rock deformation and failure of the secondary gob-side entry retaining in different stage, surrounding rock contol of the secondary gob-side entry retaning is regarded as an extremely complex systems engineering."Making full use of stable structure of the key block of basic roof, dynamic control, keeping roadside backfilling stable all along, matching coordination, active reinforcement, weakening the disturbance, whole strengthening and whole process control" are put forward,"support technology system of supporting optimization, roadway-inside bolting enhanced, roadside backfilling body enhanced, assistant enhanced of strong self-moving type active control top support and rock structure enhanced" have been formered.The parts of above results are applied successfully to haulage roadway in working face512(5) of Xieyi coal mine, Huainan, and provide a theoretical basis for the secondary gob-side entry retaining which is adopted to establish Y-type ventilation system for working face with high gas and difficult extraction.
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