| Based on relevant theoretical results such as mine engineering mechanics,rock mechanics,mine roadway engineering,and soft rock roadway support,systematic research on the time-space evolution feature of stress shell and mechanism of surrounding rock control is conducted by comprehensively using field research,laboratory tests,theoretical analysis,numerical simulation,and field measurement methods.Field test research about the stress field,displacement field and destruction field of surrounding rock in deep tunnels with soft rock is conducted,the rules of surrounding rock deformation affected by the evolutionary features of stress field are revealed,and an elasto-plastic mechanical model of the deep soft rock tunnel is constructed.The stress distribution regularity of the surrounding rock of the roadway is obtained,and the mechanical nature of the stress shell around the roadway rock is revealed.Based on the mechanical shape and space-time evolution of surrounding rock stress shell,the 3D stress field,displacement field and failure field of roadway surrounding rock are taken as objects to study the mechanical properties of stress shell of surrounding rock during excavation and its relation with displacement field and destruction field,and the space-time evolution mechanism of three-dimensional stress field in deep soft rock roadway is revealed.Based on theoretical analysis and numerical simulation,the theory of minimum deformation of roadway surrounding rock is proposed,the mechanics mechanism is analyzed,and the engineering application is carried out.The aim is to provide theoretical support and reference for the scientific soft rock roadway support and stability control.Main research results are as follows:1.The features of dynamic redistribution of stress field of surrounding rock after deep excavation of soft rock are studied,and it is revealed that the evolution of stress field is the source of deformation and destruction of roadway surrounding rock.In view of the serious deformation and destruction of surrounding rock in deep soft rock tunnel,field test and indoor rock physical and mechanical performance tests are conducted,and the evolution regularities of stress field,displacement field and destruction field of surrounding rock in deep soft rock tunnel are obtained.After analyzing the interaction between stress field,displacement field and failure field,the main conclusions are as follows:(1)The time effect of surrounding rock main stress in deep roadway is:as time increases,maximum main stress of roadway surrounding rock within 1m from the surface gradually decrease,maximum main stress in the range of 2-7m increase to the peak and then decrease gradually while maximum main stress beyond the range of 7m gradually increase.The space effect is that the peak of main stress in roadway surrounding rock gradually shifts deeply into the roadway as the distance of excavation increases,the main stress near the surface of tunnel gradually decreases.(2)During the process of peak stress of tunnel gradually shifting deeply into the tunnel,there are three stages for the displacement of surrounding rock on the surface of tunnel:rapid deformation,slow deformation and rheological deformation.Influenced by the excavation,the tunnel surrounding rock turns from three-dimensional stress state to two-dimensional stress state in the stage of rapid deformation.The redistribution of stress in the surrounding rock occurs at the stage when the stress and deformation of the surrounding rock of tunnel are severe.(3)The closer to the heading,the more severe for the destruction of deep surrounding rock of tunnel,and the destruction span of deep surrounding rock tends to gradually decrease towards the rear of the roadway.(4)Based on the indoor test of physical and mechanical properties of rock,it is known that the lithology of surrounding rock in the deep soft rock roadway is generally soft and the uniaxial compressive strength is lower than 25 MPa,suggesting that the rock is geologically soft category.The triaxial compression test shows that with the unloading of the stress on one side of the confining pressure,the specimen rapidly enters the yielding stage,the deformation increases sharply,and finally the instability failure occurs.2.The mechanical mechanism of stress shell formation in roadway surrounding rock is revealedThe theoretical analysis method is used to obtain the stress expressions of surrounding rock in different deformation and failure stages of roadway surrounding rock.The variation regularities of stress field of the surrounding rock under excavation of surrounding rock of the roadway and different supporting forces are analyzed,and the mechanical mechanism of stress shell formation in roadway surrounding rock is revealed.(1)The deformation mechanics model for deep tunnel under uneven stress field is established.Based on rock damage theory,the stress-strain constitutive equation of surrounding rock is constructed.The deformation and destruction range of surrounding rock in deep tunnel is divided into four zones such as destruction zone,plastic softening zone,plastic hardening zone and elastic zone.Also by considering the expansion mechanism,the analytical solutions to the surrounding rock stress of the four zones are obtained.(?)(2)The shell-forming ratio of surrounding rock stress shell is defined.(?)The surrounding rock stress shell exists in the stress concentration area where the tangential stress of surrounding rock exceeds 20% of the original rock stress.This area mainly exists in the plastic hardening zone and is the main bearing body of roadway surrounding rock.The outer boundary of the surrounding rock stress shell is an elastic stress zone where its stress is close to the original rock stress,and the inner boundary is a plastic softening zone.The stress shell loads the most weight of the outer overlying strata and its existence is the key to realize the self-stabilization of roadway surrounding rock.3.The spatial distribution pattern and spatial-temporal evolution of three-dimensional stress field of roadway surrounding rock is revealed.Based on the mechanical shape and spatial-temporal evolution regularities of stress shell of roadway surrounding rock,the characteristic parameters such as three-dimensional stress field,displacement field and failure field of roadway surrounding rock are taken as objects.The mechanical features and their interactions of stress shell of roadway surrounding rock in deep high-stress soft rock is studied which further reveals the evolution of stress shell of roadway surrounding rock in deep high-stress soft rock.(1)During the excavation of deep soft roadway,there is stress shell consisting of high stress bundles in the roadway surrounding rock with the feature that the main stress is highest in the stress shell of the surrounding rock while the main stress value of the rock inside and outside the shell is relatively low.And the roadway under construction lies in the stress shell of roadway surrounding rock which is the low stress area with stress shell protection.(2)With the increase of excavation distance,the maximum main stress of tunnel surrounding rock increases gradually to a peak point,and then gradually reduces to the original stress.The greater the excavation distance,the greater the distance from the peak of the maximum main stress of surrounding rock to the surface of the roadway.As the distance of roadway excavation increases,the high stress concentration area of roadway surrounding rock gradually shifts to the outside of the roadway.(3)As the burial depth increases,the transfer degree of the stress shell around the roadway to the deep roadway gradually increases.On the one hand,the main stress concentration range of surrounding rock expand gradually.On the other hand,the peak of maximum main stress gradually appears in the two shoulders of the roof and in the floor.(4)Affected by uneven stress field,especially as the increase of horizontal stress,the stress shell of tunnel surrounding rock gradually transfers from horizontal ellipses to vertical ellipses,and in the mean time,it put great influence on deformation and destruction of roadway roof and floor.4.Based on the evolutionary regularities of stress shell and displacements of surrounding rock in deep soft rock roadway,it is found that there is a sudden change in the deformation rate and this mutation point is the key to control the minimum deformation of roadway surrounding rock which further enriches the concept of controlling the minimum deformation of roadway surrounding rock.The mechanics essence is to control the mutation of rock deformation rate in tunnel and field application is applied successfully.(1)The concept of controlling the minimum deformation of roadway surrounding rock is enriched,that is to say,in the range of stress shell of surrounding rock of roadway,proper deformation of roadway surrounding rock is allowed.Before the sudden change of deformation rate of roadway surrounding rock,there should be timely reinforcement and support of the easy-to-destruction parts of the roadway to control the spread of deformation failure,and the strengthened support to the roadway surrounding rock and floor at the right time is needed to realize the long-term safety and stability support for roadway.(2)It can be obtained through the comparative analysis of evolution of stress field,displacement field and destruction field with different support plans that roadway surrounding rock can be kept in low stress area protected by stress shell through improving roadway rock support strength,which can make stress shell shift to the surface of roadway.With the protection of stress shell,the deformation and plastic failure of surrounding rock of the roadway are obviously reduced,realizing the stability control of surrounding rock in deep soft rock roadway. |
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