Effects Of Weak Rock Stratum On Stability Of Deep Shaft

With coal mining gradually converting into the deep area,shaft stability becomes one of the key problems that restrict coal mine construction.This problem will be more pronounced,especially when the shaft passes through a deep weak rock formation.Therefore,in the process of deep shaft construction,how to prevent deep weak rock from damaging the shaft lining has become a key technical issue waiting to be investigated and solved urgently.After a systematic investigation and analysis,the results show that: the properties,occurrence depth and thickness of the weak rock strata are the essential factors affecting shaft stability when the shaft crosses the weak rock strata.Accordingly,a basic mechanical model of shaft has been established.The thickness of plastic zone,elastic modulus and Poisson's ratio of surrounding rock are sorted as indexes to quantitively characterize the properties of weak rock strata and then investigate the effects of these properties on shaft stability.The results demonstrate that the elastic module is the most important factor impacting the shaft stability in the model.FLAC3D software is used to construct a three-dimensional geological model of a shaft.The deformation vector,deformation,plastic zone distribution and stress of surrounding rock are selected as indicators to analyze the influence of occurrence depth and thickness on shaft stability.The results illustrate that: 1)with the increasing of the occurrence depth and thickness of weak rock,the deformation value and range of the shaft increase,resulting in great difficulty in stabilizing the shaft.2)horizontal stress is the main factor affecting shaft stability,while vertical stress aggravates the instability of shaft.Besides,the horizontal strain and failure forms of plastic zone of surrounding rock are the most considerable indicators to measure shaft instability.3)The stress of the shaft has an inverse proportional relationship with deformation of the shaft.The shear stress is not the main reason for shaft instability;4)The shaft is prone to instability at the junction of soft and hard strata,and thus the support for the shaft at the junction should be enhanced.Referring to the analyses on the influences of the properties,occurrence depth and thickness of the weak rock strata on the shaft stability,the control countermeasures are proposed,i.e.,increasing the thickness of the shaft wall,raising the height of the new shaft wall and grouting the surrounding rock.The research sheds a new sight into the design of shaft lining and safe construction.