Mechanism Of Surface Subsidence Of The Bei Bate Coal Mined-out Area Along Qing-lan Highway And Its Numerical Simulation

In this paper, which took the Bei Bate coal mined-out area along Qing-lan highway from Handan to Shexian as the object of study, through field investigation and indoor tests, we studied the characteristics , affecting factors and collapse mechanism of the ground subsidence in the mined-out area, calculated the deformation of surface subsidence using probability-integral method and its numerical simulation. Then, using GIS technology ,by the mothed of superimpose of a layer of the right ,we judged the level of risk of ground subsidence in the mined-out area. Mainly obtained following research and the understanding:⑴In the study area of this paper, minings are mostly in the small coal mines. Types of surface subsidence is mainly cracks and collapse pits, which inclode a few sink basin around a few small well. The collapse pits in the area were mostly developed from the ground cracks .⑵The causing factor of the surface subsidence in the study area is mainly due to the followings: mining depth is shallower, caving zone and fracture zone can reach the surface, overlying a loose layer of loess has some structural strength, which resulting the lag phenomenon of the surface subsidence, after the crack from vertical joints was formed in the loose layer of loess, it would be enlarged ang extended by the submarine erosion and corrosion under the action of surface water occurred in cracks, and thus it would form the collapse pit. The characteristics of micro-structure of the loose layer soil in the area is loose, high porosity, and weakly cementation, direct contact and less contact between grains, the dissolution of carbonate minerals-prone with water, which can result in the loss of the loess structural strength , followed by loess collapse caused by subsidence. These are the main innovation of this paper.⑶According to the calculation of the surface subsidence deformation by the method of the probability integration method and numerical simulation,it shows that the largest volume of the surface subsidence in the Bei Bate region can add up to 6353.42mm, and the largest amount of residual subsidence up to 953.01mm. The Subsidence deformation and residual volume is expected to total more than the value of highway embankment allowed in China. The calculation results from the two methods were similar, which can show that the method of numerical simulation by FLAG3D is feasible to indicate the surface subsidence of the mined-out areas.⑷According to the risk evaluation results of the surface subsidence in the the study area along the highway and both sides of the section, it can show that, in addition to the scope of the fall columns, there will be at risk and the more dangerous areas and should be taken appropriate measures to deal with mined-out area .⑸The achievement of this study can be further spreaded to the same or similar engineering geological conditions of the mined-out area and the whole loess region underlying coal mining area to predict the amount of the surface subsidence deformation , which can contribute theoretical guidance and tremendous economic benefits in the field of ground stability evaluation ,design and treatment for the construction of high-grade highways which across the mined-out area, and for the underlying coal mining under the highway.