Abstract: Based on the construction project of a subgrade section in the Mihe coal mining area of the ZLGSTJ-2 bid section
of the Zhengzhou-Luoyang expressway,aiming at the potential major safety hazards of the goaf overlying strata structure in
the hilly fracture zone,such as underground cavities,cracks and collapses,which pose a potential major safety hazard to the
construction and operation of adjacent expressways,the critical depth of goaf under highway load was calculated by mechanical
balance analysis method,and then the structural stability of overlying strata in goaf was evaluated. and the influence of different
factors on the structural stability of the overlying strata was analyzed by numerical simulation. Based on these findings,the appropriate
grouting reinforcement measures for the goaf were proposed. The results show that under the influence of the new surface
load,the critical depth of the goaf at the maximum mining width amounts to 111. 07 m,which exceeds the depth of the goaf
in this section,thus the overlying strata are in an unstable state. The burial depth and mining width of the goaf are positively
correlated with the vertical displacement of the overlying strata,while the dip angle of the coal seam is negatively correlated;
The additional surface loading will aggravate the stress change of the overlying strata,increase the deformation degree of the
strata,and lead to the cracking and collapse of the roof;After the treatment with full filling grouting method,the uniaxial compressive
strength of the slurry stone body obtained from the core sample test is greater than 0. 6 MPa,and the grouting effect
detection indexes meet the requirements.

Key words: hilly fracture zone,goaf,expressway,overlying strata,structural stability,additional surface loading,grouting
reinforcement